Acoustic telemetry is used to measure impacts of catch-and-release
fishing on goliath grouper and to determine behavior patterns of
this federally protected species.
Background
Goliath grouper (Serranidae: Epinephelus itajara) occur
in tropical and subtropical waters from the west coast of Africa to
the east coast of Florida, south to Brazil, and throughout the Gulf
of Mexico and the Caribbean Sea. One of the world's largest
groupers, this species can grow to over 7 feet long, exceed 750
pounds, and live at least 37 years. Goliath grouper grow slowly,
mature relatively late (4-6 years old), and aggregate to spawn--all
factors that increase their vulnerability to overfishing.
Harvest of goliath grouper was banned in U.S. waters in 1990
after a noted dramatic decline in population numbers, and in 1994
they were listed as critically endangered on the IUCN World
Conservation Union's Red List of Threatened Species (www.iucnredlist.org). Fisheries for
goliath grouper persist in some countries, and the status of the
species throughout its entire geographic range is unclear. Goliath
grouper remain protected from harvest in U.S. waters due to
uncertainty regarding the population, as well as concerns regarding
the species' resilience to fishing pressure. For more information
regarding goliath grouper biology and regulations, please visit the
Goliath Grouper Web section.
Protection from harvest does not ensure that fishing mortality
is negligible. Recreational fishing charters throughout Florida
advertise goliath grouper as a prime target species for
catch-and-release fishing. A fish of this size produces a
challenging and exciting fight on rod and reel. Goliath grouper are
also often caught unintentionally during angling efforts for other
reef species. They are opportunistic predators that will readily
feed upon a struggling fish being reeled in by anglers.
To date, the effects of catch-and-release angling on goliath
grouper have not been established. As with many reef fish, angling
at deeper depths may result in gas expansion and extensive
boat-side handling that can cause injury or mortality.
Additionally, goliath grouper often remain at the same sites for
extended periods, so repeated capture events may affect their
survival at heavily fished sites.
Goals
The primary goals of the goliath grouper telemetry program are
twofold:
- To describe the effects of catch-and-release angling on the
survival of goliath grouper across a range of depths.
- To quantify the long-term behavioral patterns and residence
times of goliath grouper within the study area.
Acoustic telemetry and conventional tagging will be used to
assess both immediate and long-term effects of catch-and-release
angling and to provide data regarding residency and behavior of
this protected species. Goliath grouper are known to remain in the
same area for extended periods, and they have a tendency to
aggregate around habitat such as shipwrecks. The monitored
shipwrecks in this study (Figure 1) have been chosen based on
ongoing research that indicates consistent goliath grouper
presence. Quantitatively assessing the effects of catch-and-release
angling for goliath grouper, in addition to continued investigation
into population dynamics, movement patterns, and stock structure,
will provide valuable information for future management or
regulation.
Methods
Goliath grouper are caught using typical recreational fishing
gear. Once at the surface, goliath grouper are left in the water
and positioned at the side of the boat so that they can be
measured, photographed, and fitted with tags. Two external tags are
inserted just beneath the dorsal fin. The first is a conventional
ID tag (Figure 2), and the second is an acoustic transmitter, or
"pinger" (Figure 3). Each pinger has its own unique code that will
allow for the identification of individual fish. Goliath
grouper are tracked manually immediately after release, which
provides information regarding short-term survival and behavior
after a catch-and-release event.
Two to four acoustic receivers (hydrophones) are permanently
deployed at each monitored shipwreck. Each receiver has a listening
area of approximately 500,000 square meters, or 124 acres. Whenever
a tagged fish swims within listening range (Figure 4), a hydrophone
will record the fish's individual ID as well as the time, date, and
depth of the fish within the water column. These data will yield
information regarding long-term movements and behavioral patterns
of goliath grouper at the study sites.
Conventional external ID tags are attached to each goliath
grouper to provide recapture/resighting data through diver surveys
and angler recapture reports. Any tagged fish that are observed
should be reported to the Florida Fish and Wildlife Conservation
Commission's (FWC)
Angler Tag Return Hotline,
800-367-4461. Researchers need to know the date and location of the
sighting and the relative condition of the fish.
Movement and behavioral data will indicate the effects of
catch-and-release fishing on this reef species. Minimum estimates
of survival immediately after a catch-and-release event can be
assessed. Long-term acoustic telemetry data will allow for
estimates of residence time for individuals at specific sites.
Continued underwater surveys will provide further information
regarding abundance, size distribution, and seasonal patterns for
goliath grouper within the study area. It is the goal of this
project to synthesize these data for a better understanding of
goliath grouper biology and ecology that can support the
development of responsible and effective management.
To learn more about our telemetry studies, visit the Acoustic Telemetry
Research section.
Figure 1. Map of the study
area. Acoustic receivers were placed at designated shipwrecks shown
in previous research to be frequented year-round by goliath
grouper.
Depths ranged from 40 to 105 feet.
Figure 2.
Sightings of fish with conventional ID tags can be reported to the
FWC's Angler Tag Return Hotline, 800-367-4461, with details
including the date, location, and condition of the fish.
Figure 3. Each
acoustic transmitter has a unique code that allows goliath grouper
to be
identified individually. Transmitter darts are inserted into the
flesh below the dorsal fin.
Figure 4. Example
of an underwater acoustic array. Receivers positioned strategically
around the shipwreck maximize the monitored area and ensure
adequate detection of tagged fish. The rings on this map represent
a listening radius of 100 meters (109 yards), although receivers
may have a much greater listening range (up to 800 m, or half a
mile) under ideal conditions.
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