Using Telemetry to Monitor Goliath Grouper

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 8 feet long, exceed 800 pounds, and live on average 30-50 years. Goliath grouper grow slowly, mature relatively late (4-6 years old), and aggregate to spawn.

Harvest of goliath grouper was prohibited in U.S. waters in 1990, after a noted decline in population numbers. Scientists have attempted to quantify rebuilding progress since the closure through the federal stock assessment process three times (2004, 2010, 2016).  These assessments were rejected by independent expert reviewers due to unknowns about life history, absence of long-term datasets (e.g., landings), uncertainty regarding historical landings, and lack of information about the stock outside of the southeastern U.S.  The status of the species throughout its entire geographic range is unclear. Because goliath are not suited to traditional stock assessments, in 2018, FWC developed alternative management goals and metrics to monitor goliath population status.  In 2022, FWC approved a limited, highly regulated recreational harvest for goliath grouper that requires a special permit. For more information regarding goliath grouper biology and regulations, please visit MyFWC.com/Recreational/Goliath.

Though most goliath group are protected from harvest, this 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. However, when improper fish handling techniques are used, such as removing large fish from the water or delaying release, fish can still perish from injuries sustained from being handled.

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:

1. To describe the effects of catch-and-release angling on the survival of goliath grouper across a range of depths.
2. 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.