Effects of No-Take Zones on Reef Fish Populations after Five
Years of Protection in the Florida Keys National Marine Sanctuary.
James A. Bohnsack, David B. McClellan, and Douglas E. Harper
Southeast Fisheries Science Center, NOAA Fisheries, Miami, FL
Jerald S. Ault, Steven G. Smith
Rosenstiel School of Marine and Atmospheric Science, University
of Miami, Miami, FL
Billy Causey
Florida Keys National Marine Sanctuary, Marathon, FL
On July 1, 1997, the Florida Keys National Marine Sanctuary
(FKNMS) Management Plan became effective which prohibited all
fishing and other extractive uses in 23 sites:, four research only
zones,18 Sanctuary Protected Areas (SPAs) dispersed along the
Florida Keys, and in a 30 km2 Ecological Reserve near Key West.
In order to assess impacts of no-take protection of reef fish
populations inside and outside of protected zones, the Southeast
Fisheries Science Center (SEFSC, NOAA Fisheries) and the
University of Miami in cooperation with the FKNMS has conducted
extensive monitoring of reef fish populations before and after new
regulations became effective.
A possibility existed that no-take
protection would have minimal or no impact on reef fishes due to
any of the following factors: lack of compliance and inability to
enforce regulations, high emigration rates of reef fishes moving out
of small zones, or the existence of fishing regulations that
potentially provided adequate protection for exploited populations.
Non-destructive visual sampling was used to assess reef fish
composition, abundance (density), and size structure in randomly
selected circular 15m diameter plots.
After listing all species
observed during the first five minutes, individuals were then
counted and their size estimated.
were recorded.
Habitat features and depth
During analyses, the reef habitat was classified as
one of 5 categories and all individuals of exploited species were
classified as either as exploitable-sized
(i.e. at or above minimum
legal size or reproductive adults for species not covered by
fishing regulations) or juveniles (below minimum legal size; below
the size of reproduction).
Sample points were selected using a two-stage stratified random
sampling design in which the Florida Keys were first divided into a
grid of 200 x 200 m cells.
The first stage randomly selected cells
to be sampled based on the known presence of reef habitat
according to maps.
The second stage randomly selected two
sample units with reef habitat within a cell.
Each sample unit
consisted of two (or more) circular 15 m diameter plots sampled
by individuals of a buddy team which were combined to make one
sample for analyses.
Stratification was based on habitat type and
protection level.
Changes in no-take and fished zones were assessed system-wide
and compared to a four-year baseline (1994-1997) monitored
before new regulations were established.
Results indicate that
although no-take zones comprise only 0.5% of the FKNMS, they
include ~5.5% of the reef habitat because no-take zones were
preferentially selected to include reefs.
Also, density of exploitable
sized fishes was higher in no-take zones than in fished strata from
the outset in1997 because no-take zones were preferentially
selected to include good reef habitat.
Preliminary analyses
showed a significant and dramatic increase in mean density of
exploitable-sized individuals but no significant changes for two
species not targeted by fishing.
In no-take zones within 5 years
(1998-2002), abundance of economically important exploitable
phased yellowtail snapper (Ocyurus chrysurus) and combined
grouper (Serranidae) increased 36 times over the baseline, gray
snapper (Lutjanus griseus) increased over 10 times, and black
grouper (Mycteroperca bonaci) increased over 20 times!
In
comparison, average abundances of species not exploited, striped
parrotfish (Scarus croicensis) and stoplight parrotfish (Sparisoma
viride), were within historical performance bounds.
Although the average observed density of exploitable species was
significantly higher in no-take zones than in similar fished areas,
mean density tended to increase in both strata apparently in
response to a systemwide recruitment increase during the 5-yr
period.
In one case, combined grouper, average
density also
increased significantly in fished areas in 2001 and 2002 compared
to the baseline period.
This response may also reflect influences
in increased minimum size limits for grouper and the prohibition of
fish traps in 1990.
Overall, the increased mean density in no-take
zones was much greater than in fished zones.
whole are performing as expected.
Reserves as a
Further analyses will examine
relative performance of individual reserves.
This study shows the impact of fishing on reef fish populations
targeted by fishing.
The presence of no-take zones provide
valuable reference areas with minimal extractive influence from
which to assess impacts of changing hydrology in Florida Bay
associated with the Everglades Restoration.
The magnitude of
the population response to relaxed fishing pressure suggests that
human extractive activities have much more pronounced impacts
on abundances of exploited species than ambient differences in
water quality.
James Bohnsack, NOAA Fisheries, Southeast Fisheries Science
Center, 75 Virginia Beach Dr., Miami, FL, 33149, Phone: 305-3614252, Fax: 305-361-4499, Jim.Bohnsack@noaa.gov, Question 5