A Comparative Analysis Approach to Reducing Vessel Strikes on the
Florida Manatee
By Leela Rao
Dr. Andrew Read, Advisor
May 2011
Masters project submitted in partial fulfillment of the
requirements for the Master of Environmental Management degree in
the Nicholas School of the Environment of
Duke University
2011
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ABSTRACT
The Florida manatee (Trichecheus manatus latirostris) is an endangered species, having been
listed in the first U.S. federal endangered species legislation in 1967. However, forty years later, they
have not been removed from endangered status.
Watercraft collisions with manatees have been estimated to have the greatest impact on
their population sustainability. These accidents account for about a quarter of manatee deaths
every year. The Florida registered boater population has now reached almost one million registered
boaters, and the manatee population is growing as well. Consequently, the frequency of manatee-vessel
collisions is likely to become even more frequent.
A comparison of terrestrial wildlife collision management measures, primarily of ungulates, to
the mitigation management schemes for the Florida manatee was undertaken. A unique approach to
viewing the problem after decades of management may provide new insights and approaches to reduce
occurrence of manatee-boat collisions.
Based on the findings from this research, the application of many terrestrial wildlife collision
mitigation measures are inappropriate to reduce manatee-boat strikes. However, some of the terrestrial
strategies may be appropriate if the manatee population becomes more imperiled. Aggressive
management techniques such as marine fencing, seagrass management, and measures to encourage or
force boaters to reduce speed may become necessary. Lessons from effective signage from the
terrestrial environment can be successfully applied to signage in the marine environment indicating that
further work in this area should be a priority for marine wildlife managers.
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TABLE OF CONTENTS
INTRODUCTION........................................................................................................................ 4
I.
II.
III.
IV.
Objective
Manatee Anatomy, Physiology, and Behavior
Human Impacts
Federal and State Protection
THE TERRESTRIAL SCENE………………………………………………………………………………………………………. 11
I.
II.
Overview of Wildlife Vehicle Collisions
Mitigation Measures and their effectiveness
THE COASTAL SCENE……………………………………………………………………………………………………………… 21
I.
Mitigation Measures and their effectiveness
APPLYING TERRESTRIAL STRATEGIES TO THE COASTAL ARENA……………………………………………… 30
CONCLUSIONS……………………………………………………………………………………………………………………….. 36
ACKNOWLEDGEMENTS………………………………………………………………………………………………………….. 37
LITERATURE CITED…………………………………………………………………………………………………………………. 38
APPENDICES…………………………………………………………………………………………………………………………… 40
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INTRODUCTION
The Endangered Florida manatee (Trichecheus manatus latirostris) is the only species of Sirenian
that inhabits U.S. waters. The species has an evolutionary history spanning 50 million years. The Steller’s
sea cow, the only other Sirenian to inhabit U.S. waters, once thrived in the waters around Alaska.
However, they were hunted to extinction in the 18th century. There are now only a handful of extant
members of the order Sirenia, and Florida is home to one of the remaining species, a subspecies of the
West Indian Manatee. Moreover, the Florida manatee is unique among marine mammals as the only
strict herbivore. The species is highly valued, an icon of Florida’s wildlife, and honored as the state
marine mammal. Having been listed as endangered for over forty years, it is now considered one of the
most researched and well studied of all marine mammals.
OBJECTIVE
The objective of this study is to provide new insights for manatee managers by examining the
effectiveness of various mitigation measures to reduce terrestrial wildlife vehicle collisions, and whether
they could be applied in some form to mitigating manatee and boat collisions. This project analyzed 11
wildlife-vehicle collision studies and 10 manatee-boater studies. After over 40 years of research and
conservation, a formal comparison has not yet been conducted between mitigation strategies in
terrestrial wildlife vehicle collisions and reduction strategies in marine wildlife vessel strikes. There must
have been some caution in applying terrestrial strategies to marine environments, and this is probably
the reason why research has not been conducted in this area until now. Shackeroff (author in
Ecosystem-based Management for the Oceans, 2009) stated, “While it is not necessary to reinvent the
wheel - many human-wildlife relationships may indeed be relevant to the oceans – we suggest
terrestrial approaches be applied with caution.” Shackeroff provided three major critiques. First, data
limitations are more of an issue in marine environments than in terrestrial environments. Second, ocean
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ecosystems exhibit fundamental ecological and evolutionary differences from terrestrial systems. And
third, the human-environmental interactions are fundamentally different on land and in the sea
(McLeod and Leslie 2009).
Based on the findings from this research, these three critiques hold true for many mitigation
efforts. However, the foundational problem in both environments is the same: increasing vehicle traffic
on highways and increasing boater traffic on coastal waterways is being associated with the increased
likelihood of human-wildlife conflicts. Therefore, it seems likely that some new understanding can be
realized from viewing the marine problem through a terrestrial lens.
MANATEE ANATOMY, PHYSIOLOGY, AND BEHAVIOR
The biology and behavior of the manatees is critical to understanding how the species will react,
at an individual and population level, to vessel strikes, and what mitigation measures may be
appropriate to reduce collisions with watercrafts.
The manatee is a large, slow moving species. Adults average in weight from 880-1200 lbs and in
length from 8.8- 9.8 ft. Females are usually larger and heavier than males. They typically swim between
two and seven km/hr, although they can travel up to 18-25 km/hr in short bursts (Hartman 1979).
Manatees are long-lived creatures with slow reproductive capacity. They mature at two to five
years, and can live well over the age of 50. There is a long gestation time of 12-14 months, and a single
offspring is often produced. The mother-calf bond is the main social unit, lasting 1.5 to 2.5 years.
Mothers have a 2.5 to 3 year calving interval.
Manatees have reduced visual, olfactory, and taste systems, but have an expanded sensory hair
system. Their bodies are covered in sparse hairs that act as sensory organs to detect vibrations in the
water. Manatees hear best at a range between 10-18 kHz, but vocalize infrequently; Chirps and squeaks
are most commonly made between mothers and calves (Reep and Bonde 2006).
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Like their terrestrial cousins the elephant, manatees have unusually thick skin, sometimes over
one inch thick. Having such a thick skin layer provides protection from rough objects in the water like
branches and limestone outcroppings. The skin also has an extraordinary potential to heal itself,
allowing manatees to survive lesions that penetrate deep into the underlying dermis, exposing muscle
and other deep structures (Reep and Bonde 2006).
The skin has other properties to help regulate body temperature. Blood vessels near the surface
of the skin allow the animals to release heat and cool off in the warm summer months. Conversely, in
the winter months manatees are often seen with their backs above the surface of the water, basking in
the sun’s rays. Physiologically, manatees are a tropical species, not suited for some of the cold
temperatures that often occur in Florida during the winter months. Their larger body size relative to
other Sirenian species may help them survive the temperature extremes that occur annually in this
geographic area. Manatees begin to show signs of cold stress with prolonged exposure to water less
than 68oF (O’Shea 1988). The lower end of their thermal neutral zone is 68-74oF (Gallivan, Best et al.
1983; Irvine 1983; Bossart, Meisner et al. 2003). This low tolerance for cold water is seen when
manatees actively seek out warm water locales in the winter months.
Manatees’ bones are very dense and solid, allowing them to descend and rest on the ocean,
river, or spring floor with little energy expended. Dense bones and other adaptations related to the
lungs give manatees the ability to maintain neutral buoyancy in the water column, facilitating swimming
and foraging.
The manatee is a shallow water species, living in waters 1-4 meters deep, foraging on seagrass.
Abundance of aquatic vegetation and lack of predation have probably been major determinants in the
evolution of the rather sedentary lifestyle observed in Florida manatees (Reep and Bonde 2006).
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Manatees spend four to eight hours feeding every day, consuming a volume of plants that is five to ten
percent of their body weight.
Manatee’s niche in the ecosystem is as an herbivorous forager, selectively grazing on
underwater plants, and promoting a high level of productivity in sea grass communities. Manatee
foraging may also affect succession, or the change over time in the type and abundance of aquatic
vegetation (Packard 1984). Their grazing can also influence nutrient content and digestibility by altering
the proportion of new growth and changing the patterns of use by other primary consumers (Thayer,
Bjorndal et al. 1984; Lefebvre, Reid et al. 2000). Manatees appear to maximize the efficiency with which
they extract nutrients by utilizing an extremely slow gut transit time for ingested food.
HUMAN IMPACTS
Recent published analysis indicates that the two most prominent current and future threats to
the manatee are from water-craft caused deaths and loss of warm water refuges (Runge, Sanders-Reed
et al. 2007). Vessel strikes account for 23-30% of manatee deaths every year (Ackerman, Wright et al.
1995), and pose the most significant human threat to manatees. Deaths from watercraft collisions have
increased disproportionately to the total increase in all manatee mortality since 1976 (Ackerman, Wright
et al. 1995). As of 2010, Florida has reached almost 1 million registered boaters (Florida Department of
Highway Safety and Motor Vehicles 2011), and the number is expected to increase. Unfortunately,
manatees inhabit the same coastal waterways that many boats do, increasing the likelihood of their
collisions. Moreover, manatees are slow swimmers, and must surface often to breathe, making them
particularly vulnerable to being struck by a boat. Manatees have unusually thick skin that allows them to
survive some boat strikes. Many display one or more scar relics of collisions with boat propellers,
suggesting survival from numerous boat strike events (O’Shea, Ackerman et al. 1995). Intuitively, a
lethal strike is much more likely to occur at high speeds. Thus, it has been a priority of the US Fish and
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Wildlife Service (FWS) and the Florida Fish and Wildlife Conservation Commission (FWC) to have
designated areas of manatee-slow zones and protection areas where manatees frequently aggregate.
Areas where the manatees can rest, eat, and travel undisturbed are critical to their health and overall
population recovery.
FEDERAL AND STATE PROTECTION
The history of Florida is intertwined with that of the manatee. In the 1600s, a papal decree was
issued declaring manatees fish, and therefore, they could be eaten on Fridays. More than two hundred
years later, in 1893, Florida enacted the first manatee protection law. In 1907, Florida took protection
efforts a step further, strengthening the law to level fines for harassment and killings.
The institutional framework that protects the Florida manatee is an example of strong federal
and state management. The Florida manatee has been protected for over forty years by federal law. It
was one of the first 78 species to be protected under the Endangered Species Preservation Act of 1966,
and continued to be protected under the Endangered Species Act (ESA) of 1973. The current federal
legislation that protects the Florida manatee, in addition to the ESA, is as follows: the National
Environmental Protection Act (NEPA), the Administrative Procedures Act (APA),the Marine Mammal
Protection Act (MMPA) of 1972, and the Clean Water Act (CWA) of 1977. Section 3 of the MMPA states
that it is illegal, and considered a “take,” to“ harass, hunt, capture, or kill any marine mammal”
(Congress 1972). The ESA’s Section 7 maintains that it is not enough just to protect the species, but
protection of critical habitat for the species must occur as well (Congress 1973). In the case of the
Florida manatee, there are numerous manatee sanctuary areas where entry is prohibited. Section 4 of
the ESA mandates that states have a Recovery Team that is responsible for the creation of a Recovery
Plan (Congress 1973). The CWA reined in point-source pollution. This led to improved water quality, and
the return of some of the lost seagrass beds that serve as a food source for the manatee. On the other
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hand, this Act prevented power plants from discharging warm water, a feature which has been
benefitting manatees because many of these discharge sites have replaced the loss of natural warm
spring flows or access to these flows.
The federal Florida Manatee Recovery Team (disbanded two years ago, but expected to
reconvene to focus on re-listing efforts) addressed regulatory issues, manatee protection,
entanglement, water control structures, interagency management, and developed a Recovery Plan for
the Florida Manatee. The goals of the federal Recovery Plan were to 1) minimize causes of manatee
disturbance, harassment, injury, and mortality, 2) determine and monitor the status of the manatee
population, 3) protect, identify, evaluate, and monitor manatee habitats, and 4) facilitate manatee
recovery through public education and awareness (U.S. Fish and Wildlife Service 2001).
Florida has developed its own state Manatee Management Plan, as mandated by the ESA.
Furthermore, many localities have similarly decided to become involved, establishing Manatee
Management Plans in thirteen counties. This was a proactive and crucial move by the state of Florida
and its localities. Many aspects of the management of Florida manatees can only effectively be
addressed at local levels. For example, the state has established four management units of the Florida
manatee, each inhabiting separate geographic regions and facing different threats. The Atlantic Coast
management unit accounts for an estimated 46% of the overall population and is thought to be stable.
The Southwest Florida management unit represents an estimated 38% of the population. However, little
information is available on their status, although research is currently underway. The Northwest and
Upper St. John River management units account for about 12% and 4% of the total population,
respectively, and both populations are growing rapidly and doing well (U.S. Fish and Wildlife Service
2010). The state also enacted the Florida Manatee Sanctuary Act of 1978 that states “it is unlawful for
9
any person, at any time, intentionally or negligently, to annoy, molest, harass, or disturb any manatee”
(Florida Department of State 2010).
The FWS (Southeast region), which is part of the U.S. Department of the Interior, is the federal
agency responsible for the protection and recovery of the West Indian Manatee, and receives guidance
from the Marine Mammal Commission. In addition, the U.S. Coast Guard helps with the enforcement
and permitting of manatee protection areas, and the U.S. Army Corp of Engineers regulates watercraft
access facilities and permits manatee protection areas.
Overall, the state of Florida accepts much of the responsibility in protecting the Florida
manatee. The FWC is the state agency primarily responsible for manatee protection, performing
Manatee Protection Plan review and development, rule-making, developing manatee speed zone sign
plans, marking and maintaining manatee speed zones, enforcing regulations, evaluating manatee
habitat and protection measures, and monitoring activities. Monitoring activities include assessing the
effectiveness of management techniques, genetics research, carcass salvage, and manatee rescues. The
FWC’s Division of Habitat and Species Conservation aids in the protection of manatees and their habitat
through the Imperiled Species Management Section (ISM) and the Aquatic Habitat Conservation and
Restoration Section. FWC’s Fish and Wildlife Research Institute and the Division of Law Enforcement are
also charged with manatee conservation and protection. The ISM staff conducts reviews of Manatee
Protection Plans, environmental resource permits, and other types of planning documents, such as
comprehensive plans. The ISM staff also oversees the process of publicizing manatee protection boat
speed and access rules. In addition, they administer activities related to slow speed zones, including
permit and variance reviews, and evaluating data and development rules for consideration by the FWC
(Florida Fish and Wildlife Conservation Commision 2011).
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Numerous non-profit organizations also play a significant role in manatee protection and
education awareness; for example, the World Conservation Union, World Wildlife Fund, Wildlife
Conservation Society, Sirenian International, and Save the Manatee Club. These organizations take very
seriously the job of ensuring that the FWS is fulfilling its responsibilities. In January 2000, the Save the
Manatee Club and several other groups filed a lawsuit against the FWS and the Army Corp of Engineers
alleging violations of the MMPA, ESA, NEPA, and the APA (2000). As a result, the FWS now must develop
incidental take regulations for the incidental take of manatees, and more recently, designate critical
habitat.
THE TERRESTRIAL SCENE
America's highways allow people and products to travel to every corner of the country. These
roads cross through the habitat of many native wildlife species, and when the paths of vehicles and
wildlife intersect, collisions can occur, in greater numbers than most people realize. There is an
estimated one to two million collisions between cars and large animals every year in the United States
(U.S. Department of Transportation 2008). This presents a serious danger to human safety as well as
wildlife survival.
According to the U.S. Department of Transportation (DOT), wildlife vehicle collisions (WVCs) on
two-lane roads from 2001-2005 accounted for 89% of collisions. These two-lane roads are critical travel
corridors for many people commuting to and from work. Thus, WVCs are a challenge in every state and
for almost all drivers across the country. The number of all reported motor vehicle crashes has been
holding relatively steady at slightly above six million per year. By comparison, the number of reported
animal-vehicle collisions (AVCs), including wildlife and domestic animals, has increased by approximately
50 percent over the same period, from less than 200,000 per year in 1990 to a high of approximately
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300,000 per year in 2004. AVCs now represent approximately 5 percent (or 1 in 20) of all reported motor
vehicle collisions (U.S. Department of Transportation 2008).
Human injuries and fatalities resulting from WVCs are relatively rare, but can be devastating
when they do occur. A more common result is vehicle damage. The U.S. DOT stated that more than 90%
of collisions with deer result in damage to the driver’s vehicle. Nearly 100% of collisions with larger
animals such as elk or moose result in substantial vehicle damage. The average cost of repairing a
vehicle after a deer collision was estimated at $1,840 and $3,000 to $4,000 for elk or moose strikes. The
best estimate for the total annual loss associated with WVCs is almost $8.4 million. Collisions with deer
constitute the single largest collision category involving human and vehicle costs (U.S. Department of
Transportation 2008).
WVCs present an immediate danger to some species individual survival, and certain threatened
and endangered species are faced with a further reduction in their population survival probability. Road
mortality is considered one of the major threats to survival for 21 federally listed threatened or
endangered animal species in the United States (U.S. Department of Transportation 2008). For other
species, the long-term survival of a local or regional population may be threatened, especially in
combination with other threats such as habitat loss.
Another concern is that WVCs may also be biased towards a certain section of the population,
altering population structure, and potentially population sustainability. One study explored the age and
condition of deer killed by predators and automobiles (O'Gara and Harris 1988). They found that
predators, such as mountain lions and coyotes, killed prime-age animals, and that automobiles killed
more fawns and old animals. 90% of the deer killed by vehicles were also in poor health. It was
suggested that the less healthy deer went down the slopes to travel on the snow-free highway.
Interestingly, males were more often killed by predators, either due to habitat selection that made them
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more vulnerable or because they are larger, and thus, more noticeable. In another study, it was
discovered that males were more often killed by vehicles as well, despite the fact that the population
ratio was heavily female-biased (Putmam 1997). These collisions were found to occur most often in late
autumn, coinciding with the fallow rut in the area. Males may be actively searching for females during
this time, making them more likely to encounter roads, and thus, be more vulnerable to vehicle strikes.
Different techniques to address WVCs are grouped into three categories: efforts to change or
influence the behavior of wildlife, efforts to reduce wildlife population size, and efforts to change or
influence driver’s behavior.
Methods used to Influence Wildlife Behavior
Deterring animals from approaching roadways or directing animals toward a safer location to
cross the road are two ways in which to alter wildlife behavior. Wildlife fences have a successful record
for reducing WVCs and are now used extensively. Numerous studies in the last 20 years have shown that
wildlife fencing, with or without crossing structures, can reduce collisions with deer and other large
animals by 87% on average (U.S. Department of Transportation 2008). In a study investigating the
effectiveness of highway fencing, it was found that fence ends had the highest accident rate (Clevenger,
Chruszcz et al. 2001). Therefore, the importance of funneling deer into safe areas to cross is extremely
important, otherwise the benefits of fenced areas can be negated. Possible displacement of collision
areas should be considered as well.
On the other side of the argument, fencing disrupts the natural movement patterns, and may
isolate and fragment previously continuous populations (Putmam 1997). Many other factors soon come
into play with using fencing. Fencing should be designed to withstand the largest animal of concern in
the areas, and should provide some means of exit so wildlife that does get onto the road can escape
readily. Fencing is expensive to construct and maintain, and the fencing area must be long enough to
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discourage “end-runs,” or areas where the deer cross and may be struck by a vehicle. These “end-runs”
should be located in areas where the driver’s line of sight is maximized to provide motorists adequate
time to react if an animal does cross (Reuer, Transportation et al. 2007). To be most effective, fencing
should be considered in conjunction with over and under passes for wildlife.
The effectiveness of wildlife over and under passes is controversial because of the difficulty in
designing them appropriately. The location, type, and dimensions of wildlife crossing structures must be
carefully planned with regard to the species and the landscape. A study conducted in Arizona that
explored the effects of traffic volume and type during underpass use found that ungulate passage rates
were the lowest during intermittent traffic volumes (Gagnon, Theimer et al. 2007). The researchers
suggested that the reason for this behavior could be explained by the deer being shocked by the sudden
sound and the visual stimuli of a single passing vehicle during periods of relative quiet compared to a
relatively continuous stream of traffic. Thus, it was recommended that managers consider measures to
reduce noise and visual stimuli, especially those caused by semi-trailer trucks, when constructing
underpasses. A WVCs management report stated underpasses should have a minimum of 3-4 m in
height and width, be the shortest practicable length, and have secluded entrance areas to the
underpasses (Putmam 1997). Effective overpasses were described as extremely demanding to create;
they should be grassed and planted with trees to provide a suitable corridor for animals.
Cattle guards are an extremely effective way to reduce livestock and vehicle collisions. Cattle
guards are s a type of obstacle used to prevent livestock, such as sheep, cattle, hogs, horses, or mules
from passing along a road or railway which penetrates the fencing surrounding an enclosed piece of
land. It consists of a depression in the road covered by a transverse grid of bars or tubes, normally made
of metal and firmly fixed to the ground on either side of the depression, such that the gaps between
them are wide enough for animals' legs to fall through, but sufficiently narrow not to impede a wheeled
14
vehicle. They rely for their effect on barring passage to animals but not to wheeled vehicles. Animals do
not cross these structures because livestock lack depth perception, and will not cross open-slatted
construction. Painting white stripes on black pavement has also worked for cattle crossing, and even for
deer crossings which were reduced by 95% using this approach (Reuer, Transportation et al. 2007).
However, under snow conditions, the effectiveness of this method disappears.
Roadside reflectors have also been used to create a temporary visual “barrier” to wildlife. They
do not prevent the movement of wildlife, but rather simply delays road crossing until the road is free of
traffic. These devices reflect (or mirror) the light from oncoming vehicle headlights into adjacent
roadside areas. Their primary objective is to reduce nighttime DVCs by using reflected/mirrored light to
frighten, distract, freeze, and/or alarm animals enough that they will not cross the roadway. This
technique allows minimal disruption to natural movement patterns within an animal’s home range or to
dispersal movements. However, habituation to the reflectors is a concern, and the reflectors will not
provide an effective barrier where the animal is determined to cross (Putmam 1997)). Evidence of
habituation was seen in a study evaluating the effectiveness of wildlife warning reflectors in reducing
WVCs (Ujvári, Baagøe et al. 1998). Increasing indifference to reflectors was observed, so it was
concluded that roadside reflectors are not reliable to reduce collisions with vehicles in the long term.
Moreover, the cost of installation and maintenance would be high.
The use of chemical repellents and whistles are another technique used to reduce humanwildlife collisions. High frequency whistles are claimed to be a deterrent to deer and other roadside
wildlife. However, there is no scientifically documented behavioral response to suggest animal
acknowledgement or avoidance of vehicles equipped with such devices (Putmam 1997). In Germany,
“scent fences” as an olfactory deterrent have been promoted by the country’s motoring organizations. It
is not thought to be an effective barrier in itself, but rather, it is claimed that deer may pause, become
15
more alert, and consequently more responsive to additional dangers, such as approaching cars (Putmam
1997). The evidence is controversial surrounding chemical repellents on deer, and impacts on other
species would need to be studied as well. Providing this method is proven to work, it would only be
practicable in high crash locations, and the cost of installing and maintaining the repellents would have
to be explored to ascertain its feasibility.
Management of roadside vegetation, or habitat management, is a common practice across the
country for addressing wildlife movement. Vegetation removal in certain areas of the highway deters
deer from getting to close to the road. Habitat management, such as providing cover with trees and
planting grass to increase the use of over and under pass entrances and exits could be a beneficial
technique. The current practice of planting trees near motorway cutting and verges, while desirable
from a landscaping perspective, may actually encourage deer to frequent roadside edges, and increase
the likelihood of an accident (Putmam 1997).
Wildlife is also attracted to roads for many other reasons. For example, grasses growing within
close proximity can encourage feeding close to the roadside, removal of snow on roads can provide ease
of movements for animals, more wind on the road can provide animals relief from biting insects, and
product spillage (such as grain) from vehicles can create temporary food sources, and the intentional
placement of road salt for de-icing purposes can attract animals (Reuer, Transportation et al. 2007).
Intercept feeding is a less common practice where people strategically place food to lure
animals into desired areas or to stop animals with food before they cross a roadway. The cost of such a
program would be much too high to justify, and long-term feeding could attract more even more deer to
the area (Authority and Systematics 2005).
Deer flagging models are another lesser-known technique to scare deer away. Erected wooden
silhouettes of deer with their tail raised to expose their white undersurface, a common alert pose for
16
white-tailed deer, were used to see whether real deer avoid those areas. The results suggested this was
an ineffective method (Authority and Systematics 2005).
Reducing Wildlife Population
Wildlife culling, usually of deer, involves a substantial reduction in the population size of a
particular species in a certain area. Culling is frequently carried out by recreational hunters through
increased deer quotas, and is sometimes accomplished by hiring professionals (U.S. Department of
Transportation 2008). The elimination of females is more effective than the killing of males because
there is a greater impact of the reproductive capacity of a population. Data on the effect of DVCs is
scarce. The effort would have to be repeated periodically as the deer population would return to the
same levels if the habitat conditions remained similar; culling is not a one-time-only measure.
Furthermore, culling efforts can meet with strong public opposition.
Techniques Used to Influence Human Behavior
The last approach to mitigating WVCs is to influence human behavior. Animal detection systems
use sensors (radio frequencies, thermal, or infrared) to detect large animals that approach the road.
Once an animal is detected, warning signals are activated to inform drivers a large animal may be on or
near the road. These alerting systems are applied over long stretches of road and do not restrict natural
animal movement. The systems may be applied at gaps in wildlife fencing or at fence ends; however,
limited data exists on the effectiveness of these animal detection systems. A study conducted in
Wyoming on Highway 30, a highway associated with hundreds of DVCs every year, determined that a
deer-sensing warning system may be effective in preventing collisions in areas where a lower speed limit
and more local traffic exists, but the system was not suitable for application in places of high speed
traffic (more than 100km/hr) with a higher proportion of interstate traffic (Gordon, McKinstry et al.
2004). The largest differences in speed occurred at night for both automobiles and semis with speed
17
reductions of 5-6 km/hr. These researchers did not think speed reductions of 6-7 km/hr were sufficient
to justify the cost of the installation and maintenance of this system, because they were not convinced
this degree of speed reduction would have a significant impact on mitigating DVCs. A Swiss study
demonstrated that collisions with large hoofed animals were reduced by 82% on average for seven
different locations that used warning systems (U.S. Department of Transportation 2008). However,
while this Swiss data is encouraging, animal detection devices should still be regarded as experimental
and more investigations are needed to ascertain their effectiveness.
Speed limit reduction is the most common measure to reduce wildlife strikes. A study was
conducted that investigated the effectiveness of reduced speed zones on the Yellowhead Highway in
Jasper National Park, one of the most biologically productive and diverse areas in the entire park, and is
the main transportation corridor through the Rockies (second only to the Trans-Canada Highway). Three
“Slow Down for Wildlife” zones were installed on the highway, reducing speed limits from 90 km/hr to
70 km/hr. It was found that reduced speed had a significant effect on reducing elk collisions, but big
horn sheep collisions actually increased slightly in the 70 km/hr zones and decreased in the 90 km/hr
zones (Bertwistle 1999). This is most likely due to big horn sheep behavior; they tend to remain in traffic
lanes regardless of traffic volume. Overall, speed restrictions are considered an effective way to reduce
WVCs, though research is ongoing to firmly establish this (Reuer, Transportation et al. 2007). Night time
speed reduction in areas of high wildlife activity is another research area being investigated. It is
important to note that a speed limit not considered reasonable by the driving public will generally be
ignored (Authority and Systematics 2005).
Radio and television public service announcements, color brochures, videos, and signs are all
mechanisms by which to increase public education and awareness for WVCs. It is estimated that 60% of
drivers will not notice wildlife crossing signage (Reuer, Transportation et al. 2007). Combining wildlife
18
signs along with speed limit signs seems to increase their effectiveness (Reuer, Transportation et al.
2007). Flashing lights are also thought be effective in combination with these signs. It has also been
found that novel signs placed in high risk areas only during high risk times might provide the most
effective means of altering motorist behavior and reducing DVCs (Sullivan and Messmer 2003). Some
experimental trials of animated signs have been carried out in the U.S., but only limited effectiveness
was observed (Putmam 1997).
Integration of transportation planning and wildlife management on a regional and statewide
scale can play a significant role in reducing WVCs. By working together, planners from the transportation
sector, natural resources departments, state and local parks, and other government agencies can
successfully find opportunities to share information and make planning decisions that help prevent or
reduce WVCs. One example of this is relates to the issue of avoidance of key habitat. Some states have
chosen to avoid road construction in the most biologically or ecologically sensitive areas after identifying
and prioritizing WVC problem areas. Some transportation agencies use roadkill data, animal movement
data, aerial photos, and mapping tools to identify habitat linkage zones (areas of high animal
movement) and WVC locations(U.S. Department of Transportation 2008). This information helps
agencies focus limited resources on mitigating high priority areas. Consistent and standardized data
collection across state and local agencies is necessary for efforts at integration and planning. Such data
can also help in evaluating the effectiveness of potential mitigation measures. Some states have
established data standards; others are developing methods to make it easier to collect detailed and
accurate information.
Consideration of the geometric roadside design can also potentially mitigate WVCs. Steeper
slopes may prohibit drivers from seeing a deer approach the roadway until the animal leaps over the
guardrail. If a steeper slope is unavoidable, a landing area may allow drivers to see animals before they
19
jump over the guardrail. At locations where the road crosses drainages, known migration corridors, or
known animal habitat, the road design should not have curves, steep side slopes, or narrow clear zones
to aid in driver visibility of wildlife. Drainage features can be designed to minimize wildlife attraction and
influence wildlife movement. Pooled water increases vegetation and attracts wildlife. When considering
seeding mixes for the roadside, unpalatable species and species that do not grow tall enough to obscure
approaching wildlife should be favored (U.S. Department of Transportation 2008). Roadway lighting,
though expensive, could be established on certain problem stretches of road to aid in the driver’s visual
acuity.
Based on the previous information, it appears that there is no single, low cost solution for WVCs
that can or should be applied everywhere. A successful mitigation strategy requires a detailed, locationspecific analysis of the problem and often involves a combination of different types of mitigation
measures (U.S. Department of Transportation 2008). However, wildlife fencing, with or without wildlife
crossing structures, animal detection systems, and long tunnels or bridges may reduce WVCs
significantly (greater than 80%). Another major recommendation from a study by Sullivan and Messmer
that examined the perceptions of Division of Transportation managers and state wildlife managers
stated that both agencies “must break out of a single discipline approach to mitigating DVCs and
recognize the existence of a multi-value system by seeking common ground, taking an ecosystem
perspective, and integrating management, research, and education” (Sullivan and Messmer 2003).
THE COASTAL SCENE
It is estimated that Florida spends between 9 and 11 million dollars annually on manatee
conservation (Florida Fish and Wildlife Conservation Commision 2007). The amount spent by the USFWS
has varied substantially over time. Over the past 10 years, it is estimated that the agency has spent
about $976,000 on manatee conservation every year (Florida Fish and Wildlife Conservation Commision
20
2007). Consistently penalizing wildlife violations, establishing speed reduction zones and protected
areas, posting signs to increase boater awareness, conducting educational programs for the general
public and boaters, and funding research to investigate avoidance technology are just some of the
efforts undertaken by federal, state, and local agencies to date. Based on the previous information, it
appears that the predominant strategies have focused on altering wildlife behavior to reduce collisions.
Avoidance technology is currently the only proposed measure to alter manatee behavior.
Strategies Used to Influence Human Behavior
There are governance structures in place, at the county, state, and federal level, to discourage
speeding in designated slow zone areas by imposing a monetary penalty on boaters that strike a
manatee. A graduated sanctions approach based on a sliding schedule starts at $125 for the first
offense, $250 for the second, and $350, or a mandatory court appearance in front of the U.S. Magistrate
Judge, or in the case of a trial, potentially the U.S. District Court Judge. Previous violations issued by the
Florida Fish and Wildlife Conservation Commission also count, and those violators who have received a
previous written warning are usually cited with a violation notice the next time they are stopped.
Service officer's cases have resulted in fines of up to $3,800, and some repeat violators have been
barred from operating in a manatee zone permanently. Repeat violators also run the risk of jail time
(Andrew Aloise 2010).
The fines for “intentionally or negligently, annoying, harassing, or disturbing any manatee” can
reach up to $500 and/or imprisonment for up to 60 days. If convicted at the federal level, fines can
increase to $100,000 and/or one year in prison (Florida Fish and Wildlife Conservation Commision 2011).
The MMPA defines harassment as any act of pursuit, torment, or annoyance which (Level A Harassment)
has the potential to injure a marine mammal or marine mammal stock in the wild, which is how a
manatee-watercraft collision would be classified (Congress 1972).
21
Florida has also established a regulatory structure in place to encourage observers to report
other boaters that are violating the law. If an observer reports a boating violation to the FWC hotline
number, and the information results in an arrest, then the observer is eligible for a reward. Those who
report someone molesting threatened and endangered species, considered a category III offense, may
earn a reward of $250. The taking or killing of an endangered species, a category IV offense, may result
in a reward of $1,000 for the person who reports the incident (Florida Fish and Wildlife Conservation
Commision 2011).
Regardless of this regulatory and incentive framework, no one has ever been fined for a
manatee boat strike in the history of their decades-long protection, until this year (Dr. Tom Reinert,
researcher at the Florida Fish and Wildlife Research Institute, personal communication, 2010). Thus,
addressing boat strike reduction and reporting through the use of the current regulatory schemes has
not been effective. However, regulatory action is not the only avenue manatee managers have
considered.
The Florida state government also attempts to educate the public about boating and manatees.
The FWC’s Division of Law Enforcement makes hundreds of annual “educational stops” to inform
boaters about laws, regulations, and safety requirements on the water, not issuing any citations during
this process. Both staff and the public view this as being a positive experience (Dr. Tom Reinert,
researcher at the Florida Fish and Wildlife Research Institute, personal communication, 2010).
Nevertheless, only about 30 boat strikes in the last 30 yrs have been reported by the operator (Dr.
Richard Flamm, researcher at the FWC, personal communication, 2010).
The first step in order to appropriately educate and influence the public is to learn what the
deficiencies in knowledge or understanding are, and how best to motivate people to comply with
protection strategies (Aipanjiguly, Jacobson et al. 2003). Aipanjiguly explored the knowledge and
22
perceptions boaters have about manatee conservation. Greater knowledge about manatees was
positively correlated with support for manatee conservation. Not surprisingly, boaters indicated more
support for public education rather than for more stringent regulations, such as speed and wake limits in
sea grass areas, no entry areas, or increased marine patrols. Yet respondents were more highly
motivated to comply with law enforcement. Aipanjiguly recommended the use of normative messages
to strengthen boaters’ intentions to follow regulations and the use of targeted media to address
boaters’ gap in knowledge about manatees and conservation. The clarification of speed zone regulations
and harassment behaviors, and publicity about the negative consequences on signs were also
mentioned. Exploring alternative sources of getting information out to the public such as in newspaper
and magazine articles were also suggested, as well as different communication channels such as visual
displays and at ramps and marinas.
The next logical step is to determine if the educational programs in place are effective. Morris
investigated the effectiveness of a boater outreach program in the Tampa Bay area that had been in ongoing for three years (Morris, Jacobson et al. 2007). The researchers compared the attitudes,
knowledge, and behavioral intentions of boaters who were exposed to the educational program and to
those that were not. The educational program, called the Manatee Watch program, targeted boaters by
directly approaching them on the water from a pontoon boat and on boat ramps near manatee slow
areas. Three trained volunteers gave boaters a brief, informal talk on manatees and provided them with
a boaters’ kit. The kit included waterproof maps of the local area that showed manatee habitat and
suggested voluntary speed zones, in addition to explaining the meaning of different regulatory signs and
speed zones. Also included were polarized sunglasses, fish measuring stickers, and floating key chains
illustrated with recommendations about boating safety with manatees and the FWC hotline number to
report injured or dead manatees. The catchphrases “Go Slow Manatee Below” and “Go Slow Manatee
Below where Seagrass Grows” were written on the contents as well. Unfortunately, the findings from
23
the study were not encouraging. There were few measurable effects on boaters’ knowledge, attitude,
and behavioral intentions because most boaters were fairly knowledgeable in general, making it difficult
to discern the program’s impacts. The boats that were exposed to the program were less likely to agree
that there were adequate speed limit signs on the waterways, although this could be because they were
more aware of manatee designations. And lastly, few boaters remembered how to finish the slogan
when they were questioned.
It is important to determine whether signs can have a positive impact on boaters’ decisions
because it is a common and cost-effective way to educate boaters. Sorice examined the factors
influencing behavior in a boating speed zone (Sorice, Flamm et al. 2007). One purpose of the study was
to evaluate the effectiveness of an on-site sign to enhance boater compliance in a boating speed zone.
The second objective was to determine the boat types that were the least compliant in following the
regulatory signs. The results revealed that the sign was not related to compliance levels. The rectangular
sign read, in big block capital lettering, “Watch your speed” across the top. A cartoon of a manatee with
gray waves in the background was illustrated in the middle, and the “max fine $500” was written in the
same block writing on the bottom. Personal watercrafts were the least compliant vessels. Compliance
tended to be positively correlated with boat length: larger boats, greater than 35 feet, tend to go slower
in such areas because they are less maneuverable and have a bigger draft.
Compliance with signage is necessary in order to determine the effectiveness of this
management method. Gorzelany evaluated boater compliance with manatee speed zones along the Gulf
Coast of Florida (Gorzelany 2004) . The study took place in two counties in Florida, Sarasota and Lee.
Speed regulations were represented to boaters in a variety of ways. Regulatory signs were placed at
intervals along the boundary of a speed restriction area. Each survey site was established closely to one
or more of the posted regulatory signs. Boater education and awareness took the form of boaters’
24
guides and other informational material about the location of speed restriction zones. Informational
kiosks were placed at public docks, marinas, and boat ramps. Overall boater compliance in Sarasota
County was 63% and 58% in Lee County. Again, it was found that smaller powered vessels, usually
personal watercrafts, consistently had the lowest levels of compliance, while larger yachts and cabin
cruisers were among the most compliant vessel types. This study highlighted the idea that higher traffic
areas with moderate levels of compliance may be of greater concern than areas that have very low
levels of compliance and lower traffic. Prioritizing areas where enforcement officials should concentrate
their energy is one method to reduce speed infractions. From a management perspective, Gorzelany
recommended that speed zones for the protection of manatees be evaluated on a site-by-site basis to
identify specific areas of concern. Thus, sign placement should be unique for each site depending on its
characteristics.
The rationale behind reduced speed zones as a mitigation measure for manatee-boat collisions
is that it allows the boat driver more time to both see and react to a manatee in the water, and the
manatee more time to detect and avoid to an approaching vessel. Moreover, it is reasonable to assume
that a reduction in the severity of an injury would occur if the boat was traveling at a slower speed. A
study conducted in 2006 found preliminary evidence that reduced boat speeds reduce deaths of Florida
Manatees (Laist and Shaw 2006). The study mentioned that in 1997, FWS supported a study that
revealed 9.2% of all vessel traffic was blatantly noncompliant and an additional 22.6% was in technical
noncompliance. Steps to post the new zone and advise local boaters of the new restrictions took
several months. Since enforcement of the new rules began, watercraft-manatee related deaths in the
two refuges decreased sharply. Regardless of this one example, the absence of a clear decline in strikes
overall could be due to many factors. Four such factors are: 1.) the assumption that manatees are able
to avoid slow moving boats is false and boat speed restrictions offer little protection, 2.) compliance
rates with established zones have been too low to reduce collision risk, 3.) the type or extent of speed
25
zones have been too weak to protect the manatee (slow or idle speed restrictions are not covering the
right areas or enough area), and 4.) the new zones have been partially effective, but increasing numbers
of boats and manatees have increased the number of collisions at a pace faster than new speed zones
have reduced them (Laist and Shaw 2006).
A study conducted in 2007 supported the idea that slower speeds reduce risks to manatees as
well (Calleson and Frolich 2007). Even though more than 1400 boat-related manatee deaths have been
recorded, little definitive data is available on boat size, boat type, or the circumstances of the strike. The
purpose of this paper was to discuss the conceptual basis for reducing boat speed as a means of
reducing risks to manatees. It was found the manatees first responded to approaching vessels 165 to
190 ft away. The most common behavior was slow submergence, and the second most common
behavior was movement into deeper water. The researchers concluded that manatees can hear boats at
a distance of 330 ft. The severity of injury is in part determined by the size of the propeller. Fast spinning
prop blades cut through skin more readily, but slower moving blades may cause more impact trauma.
The severity of blunt force trauma is directly related to the mass/weight of the boat and its
speed(Calleson and Frolich 2007).
Calleson and Frolich also mentioned in their 2007 study three primary arguments against
requiring slower speeds. The first claim was that manatees have a limited ability to hear boats traveling
at slower speeds, and therefore, requiring slower speeds may actually increase risks to manatees. The
second argument was that requiring smaller boats to travel at slower speeds is unnecessary because it is
predominately larger boats that injure or kill manatees. The third contention was that requiring planing
hull boats to operate at slower speeds creates more risk because more of the boat is below the surface
of the water when the boat is offplane, providing more surface area that could strike a manatee and
also make it necessary for the manatee to dive deeper to avoid a collision (Calleson and Frolich 2007).
26
Calleson and Frolich explained the fallacy of each of the three arguments, and supported the use of
reduced speed zones.
Gerstein explored the hearing ability of manatees in relation to boat noise in attempting to
explain why collisions between manatees and boats occur (Gerstein 2002). He found that the hearing of
two captive manatees had a functional hearing range of 400-46, 000 Hz, and peak sensitivity in the
16,000 to 18,000 Hz range (Gerstein 2002). He found that manatees would be able to hear a boat when
it was 650 ft away, or 16s away if the boat was traveling at 24 mph, whereas it would not be able to hear
a boat until it was less than 12 ft, or 2s away if the boat was traveling at 3 mph. Thus, he concluded
boats traveling faster would be “easier” to hear and slower moving boats would be “more difficult” for
manatees to hear.
A study in 1999 examined the relationship among manatees’ use of particular areas including
sanctuaries with respect to temperature and the level of boating activity. Kings Bay is the largest natural
thermal refuge for manatees (Buckingham, Lefebvre et al. 1999). Three general responses of the
manatees were measured: attraction, habituation, and avoidance. The findings suggest manatees are
not deterred by boating intensity. They continued to use Kings Bay and Crystal River regardless of the
number of boats present, although the manatees did alter their distribution. They were also more likely
to exhibit avoidance as the number of boats increased. The researchers’ recommendations for
management schemes included designating additional sanctuaries, spatially and temporally limiting the
number of boaters allowed, and prohibiting recreational activity during morning hours to reduce the
length of time manatees are exposed to people. This study also provided managers criteria to use in
determining whether and when to increase the size of the sanctuary area: If there was an observed
increase in manatee injuries or deaths from boat collisions, and the disappearance of all vegetation in
the sanctuary before the end of winter. Additional criteria that could be used in the Sanctuary area
27
would be an observed increase in the number of boaters using Kings Bay in the winter, and a decline in
the survival rate of Crystal River region’s manatee population.
Methods Used to Alter Manatee Behavior
Gerstein took his research a step further, and investigated the use of a pinger device to deter
manatees from approaching boats. Avoidance technology is an emerging field of interest for manatee
conservation managers because focusing solely on altering the behavior of boaters has proven
extremely problematic. The rationale behind Gerstein’s work is that manatees are capable of exhibiting
bursts of speed. They have good hearing abilities at higher frequencies, but relatively poor sensitivity in
the low frequency range. Most boats and ships emit at frequencies below 1,000 Hz, and these lower
frequencies fall outside or overlap the lower range of manatees’ hearing. Even in quiet conditions,
manatees would have difficulty detecting these sounds at acoustic levels less than 90 to 100 decibels.
The ambient noise in manatee habitat typically ranges from 60-90 decibels over a frequency range of 1
to 20,000 Hz. In addition to simply detecting sounds, manatees must be able to locate them as well.
Unfortunately, the low frequency sounds of many boats are omnidirectional, and are therefore difficult
to locate. Localization of sounds was significantly greater at higher frequencies, and when the signal
lasted longer than 200 milliseconds, localization improved because the manatee had the opportunity to
make a slight head movement to scan the sound field. Gerstein determined that manatees can readily
locate the sounds of prop cavitation, but have difficulty detecting low frequency sounds such as idling
boats. He therefore recommended an acoustic alerting device that emits at 20,000 Hz, audible to both
manatees and dolphins. He claimed that manatees would only hear the signal when they are in the
direct line of an approaching boat at a distance of up to 200 m. Even though Gerstein’s work seems to
provide an optimistic view of the success of an acoustic alerting device, many other researchers are
28
skeptical of the approach and the science behind his work (Dr. Doug Nowacek, Professor of
Conservation Technology, personal communication, 2010).
A very important manatee behavior was observed by Nowacek that can contribute to the
understanding of manatee management (Nowacek, Wells et al. 2004). The study determined that
manatees do actively avoid boats. The apparent generalized response involved turning toward or
moving toward or into deeper water, occurred without specific regard to boat type, boat speed,
distance from the manatee, the kind of habitat the boat was in, or the kind of habitat the manatee was
in. Manatees began to respond when vessels were at a distance of 25-50 m away. Manatee habitat and
the boat habitat may significantly affect the behavior of the manatee because of the way sound
propagates in different environments. Sound propagation is poor in shallow water, and thus, manatees
may have no clear way of localizing the direction from which the vessel is approaching. Nowacek
provided two main reasons why manatees continue to be struck by boats. Firstly, manatees detect
vessels but do not respond appropriately or in sufficient time to avoid being struck (they may habituate
or may not be able to discriminate between approaching boats), and are unable to localize the position
of the boat accurately to avoid collision. Secondly, manatees are unable to detect approaching boats
due to some individual problem or environmental factor. However, this study demonstrated that
manatees are capable of detecting and responding to boats at a relatively long distance. Vessel speed
was not a significant factor in eliciting response, i.e. fast boats elicited no more or less response than
slower boats, and collisions at high speeds could obviously cause more trauma. Thus, their research
supported the concept of slower speeds to reduce collisions with manatees by allowing boat operators
and manatees time to react appropriately.
APPLYING TERRESTRIAL STRATEGIES TO THE COASTAL ARENA
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The most effective mitigation measures on land appear to be managing the behavior of the
animals with exclusionary fencing. However, in the marine realm, the most effective measures have
been to manage the behavior of people; protected areas for manatees limit or restrict human access.
This difference in management approach may derive from the fact that marine environments are
inherently more difficult to manage than terrestrial environments, and people have more experience in
managing terrestrial wildlife. Moreover, the terrestrial landscape has been more vastly altered for
human use than the ocean, which may explain why there are many more strategies for addressing WVCs
than manatee-boat collisions.
The difference in the successes of both the terrestrial and marine realm could also depend on
the underlying difference in biology between the species. Understanding the biology of the animals is
vital in developing methods to influence certain behaviors. Deer are prey animals, with highly developed
senses of hearing and vision. They share an environment with numerous competing and predatory
species. Deer have evolved to react and flee quickly to escape threatening situations. Manatees,
however, have evolved with no natural predators because of their ability to reach a large size. They are
slow moving, with limited olfaction and visual abilities because their formerly peaceful and shallow
water environment did not require such abilities. Sirenians are the only marine mammal to be strictly
herbivorous so there is little competition for seagrass. Thus, deer and ungulates are more likely to be
sensitive to deterrence techniques than manatees.
The damage to personal property and the threat of human injury or death are the main driving
forces to reduce WVCs. However, boat damage or human injury from manatee strikes is non-existent.
This fact probably plays a significant role in the perception of the animals, and the amount of funding
and attention Congress and state legislatures dedicate to research and implementation strategies.
Management Schemes to Influence Manatee Behavior
30
If the manatee population exhibits increased effects from human involvement, and managers
are more willing to consider more aggressive approaches to management, then the application of some
terrestrial mitigation measures may become appropriate. One of these more aggressive approaches
might be the application of fencing to the marine environment. In theory, the Army Corp of Engineers
could build a fence that encompasses one large area in a bay (a hot spot area for boat strikes) with a
narrow corridor to provide access to another bay. The fence is built from the bottom of the coastal floor
to three feet above the water in order to exclude boaters. The fence is made out of waterresistant/weather resistant material, very costly to buy and to place in the water. The cost of
maintenance would be expensive as well. The first biological concern is that the fencing would affect the
behavior and movement of other species, potentially altering other species’ health. Trash or detritus
could accumulate on the fences, impeding the flow of water, altering currents and affecting water
quality. A second concern is that boaters would be excluded from these areas, regardless of the season
and time of day; this would face some serious opposition from recreational and commercial boaters.
Perhaps the fencing could be removed at certain times of the year, on a seasonal basis. Thirdly, the
aesthetic factor is a major issue. People do not want to see fencing when they gaze out at the ocean.
The detrimental effect on tourism, beach-goers, and the local community could be devastating to
Florida’s economy. Therefore, there may be many negative affects to fencing in the marine
environment. However, if extreme measures are needed to protect the manatee from extinction, this
strategy could be explored further. Technological innovations and research into this method may find
ways to mitigate the impact on other species and the environment.
Would it be possible to manage the plant life manatees feed upon in order to indirectly alter
their behavior? In the terrestrial environment, it is common practice to remove vegetation around
roadways and keep the grass cut short. Protection of seagrass communities is a major aspect of
manatee conservation, and so far, seagrass abundance and nutritional quality has not been a problem
31
for the manatee. Managers may at some point wish to consider managing the growth of seagrass, the
manatees’ principal food source as a strategy. However, if managers designate specific areas of sea
grass beds for feeding, eradicating seagrass in locations deemed unsafe for manatees to frequent, they
may inadvertently affect the abundance and quality of the food source. The areas chosen to be
managed may be in environments that yields inferior quality seagrass. Manatees are a species that
consume a food resource already low in nutritional quality, and consequently, spend the majority of
their day foraging in order to maintain their body size and meet nutritional requirements. Other
potential effects from managing sea grass beds could be the loss of refuge for small fish and larvae, and
altering the foraging behavior of sea turtles that also feed on seagrasses. Thus, there appears to be
numerous potential problems in managing seagrass in this manner. However, if the manatee population
becomes further threatened from human watercraft collisions, more research and experimentation with
seagrass management should be undertaken to protect the population.
One method that has been introduced to alter manatee behavior is a pinger device. Gerstein’s
pinger is similar in theory to how deer whistles operate – the sound alerts the animal to danger and it
reacts to avoid the sound (Gerstein 2002). Unlike the findings on the effectiveness of deer whistles,
however, Gerstein claims to have found evidence of manatees actively responding to and avoiding boats
equipped with these pinger devices. The theory behind the pinger device is that manatees are not
avoiding the sound of the pinger itself because it scares them, but rather, they learn to associate the
noise with an approaching vessel and a danger. This response requires a much more sophisticated level
of cognition, and also requires a learning curve for individual manatees.
There are many concerns with the pinger technology; the theory behind Gerstein’s shallow
water sound propagation is controversial among researchers (Dr. Doug Nowacek, Professor of
conservation technology, personal communication, December 2010). Gerstein also claims that
32
habituation to the pinger would not occur, and that manatees would be able to successfully associate
the pinger noise with being struck by a boat. Nevertheless, habituation is an issue that cannot be easily
dismissed. Habituation has been documented in mitigation strategies in the terrestrial environment,
such as with reflective mirrors (Ujvári, Baagøe et al. 1998). The pinger strategy has been considered a
short-term management approach, but not a method that would work in the long run because of
potential habituation. The money and time spent investing in a possible short –term strategy to reduce
vessel strikes should be weighed against the effort spent in long-term reduction strategies.
Another drawback of the pinger is that it may have unintentional affects on other species. The
pinger emits at a frequency audible to not only manatees, but dolphin species as well. This could
interfere with dolphin communication or their ability to echolocate successfully. Despite the
uncertainties and difficulties associated with avoidance technology, the Florida Manatee Management
Plan (FWS 2007) listed an avoidance technology grant program as one of their research areas in
managing manatee-boat interactions over the next five years.
Management Strategies Influencing Human Behavior
Passive acoustic monitoring, similar in idea to deer-sensing warning systems in the terrestrial
environment, maybe a potential method to alert boaters to manatees in the area. The sensing system
would be designed to flash to alert boaters when manatees are in the vicinity. These devices could be
located throughout areas manatees frequent. Unfortunately, manatees do not vocalize often unlike
most other marine mammals, so passive acoustic monitoring would not be a reasonable method.
Perhaps infrared or radio waves could be used to detect manatees. However, large fish, sea turtles, or
dolphins may trigger the device. Thus, unlike deer-sensing systems, technology to alert boaters of
manatee presence in the water appears to be challenging, and would require more research to identify
a more appropriate means of detecting manatees.
33
Mechanisms to force drivers to slow down such as speed bumps, curving roads, and the use of
illusions to give the impression to the driver that he is traveling faster than he thinks, are commonly
used in the terrestrial environment. In areas of high concern for boat strikes, buoys could demarcate
areas boaters must stay within. The buoys could be placed in a curving aquatic roadway design in order
to force boaters to slow down. The benefit of this strategy is that it could be used as-needed. It would
be relatively simply to place and remove buoys in the water, and alter the path design itself. Moreover,
it would be an inexpensive approach to encourage speed reductions. This technology could be readily
implemented to test its effectiveness.
It is important to remember that slow speed zones on the water often do not state a specific
speed because different boats types can be in compliance at different speeds. Boaters, therefore, must
understand that slow speed means the vessel should not be raised out of the water nor creating an
excessive wake, relatively subjective measurements. It is not as easy as glancing down at the
speedometer and reading your speed as people do in cars on the highway. This also means that signs
and radar used on land that tell drivers “your speed is being monitored” and displaying the driver’s
speed will not work in the marine setting. However, signs in general may be the key to influencing
boater behavior.
The most commonly used tool to reduce collisions with wildlife in both the terrestrial and
marine environments is signage. Signs are a simple and relatively inexpensive method to increase driver
awareness and promote reduced speeds zones. However, most people ignore signs. On land, combining
wildlife signs with speed limit signs seems to increase their effectiveness (Reuer, Transportation et al.
2007). Flashing lights are also thought be effective in combination with signs. It has also been found that
novel signs placed in high risk areas only during high risk times might provide the most effective means
34
of altering motorist behavior and reducing DVCs (Sullivan and Messmer 2003). Thus, experimentation
and research into this field should be a priority.
Some Modest Proposals to Consider for Signage Improvements
Using statistic as an anchor, (statistics are easy to frame –e.g., 30% of manatee deaths are
attributed to boat strikes vs. 70% of manatee deaths are not related to boat strikes) it is possible to relay
to the public the importance of avoiding boat strike events. One proposal for a sign could be, “Did you
know: boat hits account for 80% of all human-related deaths for the manatee? Do you follow manatee
speed restrictions?” or “Of the x amount of revenue from tourism, y percent comes from manatee
tourism. Protecting the manatee means protecting Florida’s economy.”
The use of framing, which is how to cogently phrase a question or statement, can also be a
powerful tool. A sign could say, “Of the x number of manatees born every year, y amount will be struck
by boats,” and include a colored photograph of a cute baby manatee on the sign. The term availability
bias describes the phenomenon where easily remembered events may inflate people’s probability
judgments, and if no such event comes to mind, their judgment of likelihoods may be distorted
downward (Thaler 2008). Therefore, a digital electronic sign could depict the latest update of where a
manatee was found, dead or injured, their location (ideally, in the nearby area), time found, and a
picture of the individual manatee. For example, “Bubbles was found struck by a boat in northern Tampa
Bay yesterday at 4pm. Please be aware of the manatees in the area.” The sign should be periodically
changed and/or updated in order to avoid habituation. This electronic signage could be a powerful
method to grab boaters’ attention and make the threat to manatees more real and immediate. The
signs could be a located where people congregate, or at least slow down, and where people are about
to access the water. Places such as above water fountains in marina areas may be effective for example.
35
The FWC might consider contracting with a professional advertisement agency to create signs
and slogans that would be more appealing than those currently in use. Attractive signs, some electronic
and some static, with the FWC hotline number could be placed on docks or by recreational areas so
people would know the number to call. There could be free maps of the manatee zones by heavily used
boating docks, all having the number to call in case of finding an injured or dead manatee. The FWC
and/or nonprofit groups and agencies might consider running ads promoting the protection of manatees
in fishing and wildlife magazines, in order to better reach recreational and commercial fishermen. Public
service announcements on television, while expensive, may be effective as well.
Conclusions
Although there have been decades of conservation management for the Florida manatee, a
comprehensive and systematic comparison of prevention strategies implemented for terrestrial wildlife
vehicle collisions and those used to prevent manatee vessel strikes has never been conducted. Concepts
learned from terrestrial strategies may provide useful insights as to what might work or fail for manatee
conservation. Currently, many of the terrestrial mitigation measures do not to appear to be applicable
to the marine setting. Some of the terrestrial strategies may become a necessary last resort if the
manatee population becomes severely threatened with extinction and more aggressive measures
ecessary. However, effective signage is one area where both terrestrial and marine environments can
learn from each other. In addition to manatee protected areas, research into innovative sign design and
placement appears to be the most promising strategy for addressing manatee-vessel collisions.
The incidence of human-wildlife conflicts is likely to increase due to increasing human
population levels; this is especially true in the state of Florida, home to manatees. Thus, increasing
responsibility falls on people to alter their own behavior to reduce the frequency of such occurrences.
Finding an effective means to encourage people to accept this responsibility may be the key to success.
36
ACKNOWLEDGEMENTS
I would like to thank those individuals who have guided and motivated me in completing this
project. Dr. Richard Flamm, a manatee conservation researcher from the Florida Fish and Wildlife
Conservation Commission, aided me in developing a project that sought to address reducing manatee
water-craft collisions. He also took the time to read over my work and clarify any misunderstandings I
had. I also want to thank Dr. Tom Reinert, a research administrator at the Florida Fish and Wildlife
Conservation Commission, for taking the time to answer my questions and update me on manatee
news. I want to thank my advisor, Dr. Andy Read, for helping focus my masters project, and providing
constructive advice. Dr. Doug Nowacek also provided me with useful insights into the realm of
bioacoustics. Janil Miller helped me with my endless questions concerning Endnotes and citing sources.
I also need to acknowledge my family and friends for providing me with encouragement. I
specifically want to thank my mother, who has unflagging confidence in my abilities, and my father, who
has always supported my educational pursuits. I also want to thank Amy Bishop for taking the time to
edit my paper and provide me with valuable advice.
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Table 1: Terrestrial Management Schemes
Influence Wildlife
Behavior
Influence Human Behavior
METHOD
Exclusionary Wildlife Fencing
SUCCESS
Yes
Over and Underpasses
Roadside Reflectors
Deer Whistles / Chemical Repellents
Difficult, but yes
No, habituation
No
Roadside Vegetation Management
Yes
Signs
Maybe
39
Table 2: Current Marine Management Schemes
Influence Human Behavior
Influence Manatee Behavior
METHOD
Fines for injuring a manatee or
violating speed restrictions
Education
Signs
Sanctuaries
Avoidance Technology
SUCCESS
No
Maybe
Maybe, if improvements made
Yes
Maybe
Table 3: Recommendations
Influence Manatee
Behavior
Influence Human
Behavior
METHOD
Marine Fencing
RELATIVE FEASIBILITY
Difficult; does not
currently exist
Seagrass Bed
Management
Avoidance Technology
Passive Acoustic
Monitoring
Buoy Paths
Difficult; grants needed
to research and develop
Difficult; grants needed
to research and develop
Difficult; grants needed
to research and develop
Easy
Signs
Easy
APPLICATION
When manatee
population severely
threatened with
extinction
Currently
appropriate
40
Figure 1: Florida manatee distribution within the four designated regional management units.
USFWS (2001).
41
Figure 2: 13 Counties with Manatee Management Plans
Table 4: Florida Counties having the highest
watercraft-related manatee mortality from
1985 - 2005. Data from Florida Fish and
Wildlife Research Institute (2006).
42
Figure 3: Major causes of documented manatee mortality in Florida from 1985-200 (data from
Florida Fish and Wildlife Research Institute (2006).
43
Figure 4. Total manatee mortality in Florida by year from 1985 - 2005. Data from
Florida Fish and Wildlife Research Institute (2006).
Figure 5. Watercraft collisions from 1985 - 2005. Data from Florida Fish and
Wildlife Research Institute (2006).
44