Where’s that dolphin?
Using sightings of bottlenose
dolphins to study spatial patterns
Objectives
• Learn about the ecology of bottlenose dolphins and
the research methods used to study dolphins
• Plot points on a coordinate scale using latitude and
longitude
• Learn about utilization areas
• Calculate area of geometric shape and convert
measurements using a map scale
• Think spatially: look at patterns in data related to
location
Dolphin surveys
• Each group of dolphins is called a “sighting”
• During each sighting, the scientists:
– Use a GPS device to record position (latitude and
longitude)
– Record the number and
behavior of dolphins
– Record environmental
conditions
– Take photos of each dolphin’s
dorsal fin to identify individual
dolphins
Photo by C. Kovacs
Latitude and longitude
The coordinate system
Where are you located?
Common bottlenose dolphins
• Scientific name name is Tursiops truncatus
• Are marine mammals; therefore, they need to go
to the surface to breathe air
• Live in tropical and temperate waters worldwide
• Primarily eat fish and squid
02Aug10 photo by R. Perrtree under permit #14219
Photo-identification
• Scientists use nicks and notches to identify dorsal fins
• Dolphins receive a number based on the location of
their nicks
• Some dolphins receive names as well, for example
dolphin 80068 is also known as Fingers
12Jul09 photos by R. Perrtree under permit #14219
80068 – “Fingers”
1Aug09 photo by R. Perrtree under permit #14219
70025
Strand feeding
• Behavior observed only in South Carolina and Georgia (Petricig 1995,
Hoese 1997)
• Dolphins rush towards the shore of a mudbank, and their wave
causes fish to wash up on the bank
• The dolphins temporarily strand themselves on the bank to eat
the fish, and then slide back into the water
• This behavior occurs mostly in shallow creeks at low tide (Bowen
2011), when mud banks are exposed
01Aug10 photo by R. Perrtree under permit #14219
For another activity in which students explore strand feeding, see Bowen-Stevens et al. 2011
Tides in Savannah, Georgia
• Tides in Savannah are very large (ranging from 2 to 3 m)
• Tides in Savannah are semidiurnal, meaning there are two high
tides and two low tides each day.
• Fish can hide in the marsh plants at high tide, but at low tide
the fish move into the creeks and rivers
• Mud banks are exposed at low tide, as seen in the photos below
Photo by C. Kovacs
High tide
Photo by C. Kovacs
Low tide
Shrimp fishery
• In Georgia, fishermen trawl for shrimp in the Atlantic Ocean just
outside of sounds and the mouths of rivers
• The fishermen sometimes anchor in Wassaw Sound overnight
• There are 3 major shrimp docks in Savannah, referenced here
by the stars
Atlantic Ocean
Shrimp docks
Shrimp docks
Atlantic Ocean
Wassaw Sound
Dolphins feed in association
with shrimp trawlers
• Dolphins near Savannah, Georgia feed in association with shrimp
trawlers, either by swimming behind moving vessels and eating
fish that are stirred up by the nets or by consuming bycatch that
the fishermen push off the boat (Kovacs 2012)
• Bycatch is any species of animal that is caught by accident. Trawl
nets catch many types of fish, jellyfish, and crustaceans
8Jun10 Photo by C. Kovacs under permit #14219
Dolphins following a shrimp trawl net
Begging
• Some dolphins in Savannah also beg for food from humans in
recreational or fishing boats (Perrtree 2012)
• Begging usually occurs when boats are traveling slowly or
stopped
12Jun10 photo by K. Doyle under permit #14219
27Aug09 photo by R. Perrtree under permit #14219
Begging
• Begging is not a natural behavior
• It is illegal to feed wild dolphins under the Marine Mammal
Protection Act
• Feeding dolphins is potentially harmful to the animals and
dangerous to humans
– Dolphins that become conditioned
to boats are more likely to get
struck by a boat or propeller
(Donaldson et al. 2010)
– Mother dolphins may not teach
their calves to catch fish (Perrtree 2012)
– Dolphins have sharp teeth and
sometimes bite people
(Cunningham-Smith et al. 2006)
08Jul10 Photo by R. Perrtree under permit #14219
Calf with scars from a boat propeller
Other behaviors
• In addition to foraging, dolphins spend time
traveling, resting, and socializing
11Jun09 photo by P. Perrtree under permit #14219
08Jun10 Photos by C.Kovacs under permit #14219
Utilization area
• The area that a dolphin spends most of its time in is
called a utilization area
• Some dolphins have a small utilization area and
remain there, and other dolphins travel more and
have a large utilization area
Utilization area:
Minimum convex polygon (MCP)
• Connects the outside points of a group of points
Each of you has:
• A Sighting Summary Sheet with sighting
information for two dolphins
• A Study Area Map
• A Student Report Sheet
You will:
• Plot the locations of the sightings for each of
your dolphins using the coordinates provided
• Find the utilization area using a simplified
minimum convex polygon
• Look for spatial relationships in the data
Real MCP vs a simplified MCP
• In this activity, you will draw a simplified MCP around
the sightings you plot. The simplified MCP should be in
a shape such that you can easily find the area of it.
• On the left is an example of a real MCP, on the right is a
simplified MCP for the same sightings. There is more
than 1 possible simplified MCP for each set of sightings.
Conclusions
• Where were your dolphins found?
• Based on what you learned about dolphin behavior,
why do you think your dolphins were found in those
areas?
• These data only cover one summer. If we had
sighting information for the entire year, do you think
it would look the same? Why or why not?
References
•
Bowen, S.R. 2011. Diet of Bottlenose Dolphins Tursiops truncatus in the Northwest Panhandle and Foraging
Behavior Near Savannah, Georgia. Masters thesis, Savannah State University, Savannah, Georgia, 162 pp.
•
Bowen-Stevens, S.R., T.M. Cox, and M.C. Curran. 2011. What are bottlenose dolphins doing on land? An activity
teaching the scientific method through the unique behaviors of strand feeding. The American Biology Teacher
73 (7): 407-411.
•
Cunningham-Smith, P., D.E. Colbert, R.S. Wells, and T. Speakman. 2006. Evaluation of human interactions with a
provisioned wild bottlenose dolphin (Tursiops truncatus) near Sarasota Bay, Florida, and efforts to curtail the
interactions. Aquatic Mammals 32:346-356.
•
Hoese, H.D. 1971. Dolphin feeding out of water in a salt marsh. Journal of Mammalogy 52 (1): 222-223.
•
Kovacs, C.J. 2012. Interactions between common bottlenose dolphins (Tursiops truncatus) and shrimp trawlers
in Savannah, Georgia. Masters thesis. Savannah State University, Savannah, Georgia, 155 pp.
•
Donaldson, R., H. Finn, and M. Calver. 2010. Illegal feeding increases risk of boat-strike and entanglement in
bottlenose dolphins in Perth, Western Australia. Pacific Conservation Biology 16:157-161.
•
Perrtree, R.M. 2011. Begging behavior by the common bottlenose dolphin (Tursiops truncatus) near Savannah,
Georgia: Prevalence, spatial distribution, and social structure. M.Sc. thesis, Savannah State University, 203 pp.
•
Petricig, R.O. 1995. Bottlenose dolphins (Tursiops truncatus) in Bull Creek, South Carolina. Ph.D. dissertation,
University of Rhode Island, Kingston, Rhode Island. 298 pp.