Fisheries-Independent Monitoring Red Drum Hatchery Release Program

Read about an experimental approach to using stock enhancement to support Tampa Bay's red drum population.

Have you caught a red drum lately?

Juvenile red drumWhat is stock enhancement? It's a practice that involves the use of fish hatchery technology to spawn and raise fish in a controlled hatchery environment. Spawning and raising fish under controlled hatchery conditions dramatically reduces the level of natural mortality on eggs and larvae, thus increasing the number of young that survive.

These fish are allowed to grow to a certain size in the hatchery, and then they are introduced, or stocked, into the natural environment to enhance existing populations. The technology to spawn and raise fish in captivity has existed in the U.S. for more than 100 years (e.g. Grimes, 1995). However, saltwater fish like the red drum have only recently been raised on a scale large enough to make stock enhancement feasible.

Many of Florida's economically important marine species have declined in abundance due to over-fishing, habitat loss, and environmental disturbances such as chemical spills, cold kills, and red tide. Hatchery production is frequently suggested as a remedy for such declines (Travis et al., 1998).

Rearing, or raising, fish in captivity is expensive, so it is difficult for state agencies and other organizations to justify the cost unless they can measure success. Despite the expansive efforts focused on the production and release of hatchery-reared red drum into the wild, there is still very little scientific information that addresses the effect of these fish on the natural population and the fishery.

For marine stock enhancement to be validated, the proper experimental designs, assessments, and subsequent analyses must be conducted. This scientific process requires an in-depth understanding of complimentary fishery management strategies, population genetics, ecosystem dynamics, habitat structure and carrying capacity, disease management, economics (cost/benefit ratio), and an accurate assessment of enhancement efforts.

The Florida Fish and Wildlife Conservation Commission's (FWC) Fish and Wildlife Research Institute (FWRI), in collaboration with the Mote Marine Laboratory (MML) have designed and implemented Project Tampa Bay, a study to develop cost effective and environmentally sound stock enhancement of red drum (Sciaenops ocellatus).

Red drum were chosen for this study for several reasons. They are a highly popular recreational fish with a fishery that is currently perceived to be very restrictive with a recreational bag limit of one fish between 18 and 27 inches. Also, the technology to spawn red drum in captivity is well known and has been successfully conducted in several other states, including Texas and South Carolina. Much of this technology was perfected at the   FWC Stock Enhancement Research Facility (SERF) located at Port Manatee (Colura, et al., 1976; Arnold, et al., 1977; Roberts, et al., 1978; Willis, et al., 1995).

The main objectives of this study are to:

  1. determine the optimal size at release, the location/habitat for release and season of release;
  2. assess the survival, growth, and movement of wild and hatchery-reared red drum; and,
  3. determine the most cost effective rearing and release strategy that will increase the population size and build the fishery.

Once the most effective release strategies (e.g. fish size, release location, and season) are known, we will then use those strategies to determine how many red drum must be produced and stocked into Tampa Bay to reflect the desired impact on the natural population and fishery.

Once the most effective release strategies (e.g. fish size, release location, and season) are known, we will then use those strategies to determine how many red drum must be produced and stocked into Tampa Bay to reflect the desired impact on the natural population and fishery.

The area selected for this study was the Alafia River.Alafia River study area

The Alafia River feeds into the northeast portion of Tampa Bay and has been documented by FWRI scientists as a highly productive nursery area for natural red drum stocks (Peters and McMichael 1987).

Since March 2000, over 1.6 million hatchery-reared red drum have been released into the Alafia River as part of this study. The size of the fish released varied depending on the time of year, in order to be in sync (In-Syncrony with the natural spawning population) with the size of naturally occurring red drum in the river. During the spring releases, fish averaged three-inches in standard length (SL), six-inches in summer, and one-inch in the winter.

Fish larger than three inches were all marked with a very small (< 1/16 inch-long) coded wire tag (CWT), which was placed into the cheek muscle prior to release of the fish. These tags cannot be seen, but may be detected by scientists who have specially designed metal detectors. The detectors are used to check for CWT marked red drum in scientific collections and in the fishery.

The Little Manatee River was the site of an experiment testing the effect of releasing hatchery-reared red drum out-of-sync with the wild red drum population.  Four in -sync (August - October 2000, 2001, 2002, 2003) and two out-of-sync (May - June 2002 and 2003) releases were conducted totaling over 2.5 million fish.  Red drum released into the Little Manatee River were all Phase 1 fish (30-45 mm).  These small fish can only be identified by genetic analysis of fin clips.
In Tampa Bay, research has shown that red drum normally spawn between August and November with a peak in larval abundance in October.

Fish released into the Alafia River were of three sizes and can be identified genetically by fin clips (all sizes) or by scanning the larger fish (Phase 2, Phase 3) for a magnetic coded wire tag which hatchery fish have implanted into their cheek muscle.

Combined, Project Tampa Bay has been involved in the release of about 4.2 million fish tagged with genetic markers and/or coded wire tags into the Alafia and Little Manatee rivers. This included two important juvenile red drum habitats in the Tampa Bay estuarine system.

Fish were transported from SERF to the Alafia and Little Manatee rivers using trucks with live wells. The fish were then carefully transferred onto boats where the fish were held in a live well system. Scientists distributed the fish evenly along the entire study area, releasing fish into suitable shoreline habitats (i.e. marsh grasses and mangroves).

Once the fish were released, the work had just begun for the FWC Fisheries Independent Monitoring program. In order to answer many of the questions that we are asking, it is important to properly monitor the survival, growth, abundance, and movement of both hatchery-reared and wild red drum in the study area.

The abundance of both wild and hatchery-reared red drum is monitored each month using a standardized sampling design. Specially designed seine nets are used to collect red drum and other native fish species along the shoreline habitats of the Alafia and Little Manatee rivers. The number and sizes of all red drum collected are recorded and a subset are kept for health and genetic evaluation.

Red drum are also checked for CWTs. Fish found with tags are kept so that the tags may be extracted and read to identify the origin of the fish (hatchery parents, spawn date, grow-out pond, harvest date, age, size at release, date released, coordinates of the release site). This process provides valuable data on fish survival, movement, and habitat preference.  Although hatchery releases stopped in 2004 the monitoring for hatchery fish continues.

As red drum grow, generally over 12 inches (> 12 inches), they typically leave their nursery areas in the river and spend more of their time in the bay. Monitoring these fish is somewhat difficult and requires a cooperative effort between scientists and the fishing public.

One way that we monitor these fish is by sonic tagging. Sonic tags are typically used for larger fish over 10 inches (> 10 inches) and are surgically placed into the abdominal cavity. Once the tag is in place, it is activated and the tag begins emitting a sonic signal that scientists can track and identify with special hydrophonic equipment.

Scientists hope that these fish will lead them to other red drum, both wild and hatchery-reared, and help them better understand how red drum move and what types of habitats these fish prefer. All of the sonic tagged fish are also marked with at least one external tag (dart or internal anchor).

If a red drum is collected with an external tag, please record the tag number, total length of the fish, capture date, location, time, and call the REDFISH HOTLINE number 1-800-367-4461. If the fish is to be released, please record the proper information and leave the tag in the fish. For more information anglers are encouraged to e-mail or

Multiple recaptures are fairly common and useful to scientists. If you plan on keeping your catch, keep the tag and the head of the fish (frozen) and contact the REDFISH HOTLINE for instructions.  A reward t-shirt will be mailed to anglers reporting catches of tagged red drum.

Scientists also sight-search for red drum in Tampa Bay and capture them with a large trammel net (300-yards long). This net is designed to collect larger fish and instead of gilling the fish, which is often harmful, the fish are collected in a pocket of mesh. All red drum collected are measured, counted, checked for tags (CWT and external), fin clipped, and released alive. Fin clips from the fish will be used (via genetic analysis) to identify whether the fish is wild or hatchery-reared, and where and when the fish was released.

To estimate the number of hatchery-reared red drum that are surviving and thriving into the fishery, scientists have interviewed thousands of fishermen in Tampa Bay, solicited volunteer anglers and fishing guides to collect fin clips from the red drum that they catch, and asked fishermen to donate their red drum carcasses. This portion of the study is very important to the success of the experiment and is highly dependent upon the help and cooperation of the fishing public.

Fishers and guides wanting to participate in the Angler Fin Clip Reward Program are encouraged to e-mail for an information package and a fin clip kit. Through these collaborations, scientists will be able to learn more about red drum in Tampa Bay, and how stock enhancement can be used to ensure a healthy and bountiful population for future generations.

Visit the Stock Enhancement Section for more information.

Literature Cited:

Arnold, C.R., W.H. Bailey, T.D. Williams, A. Johnson and J.L. Lasswell. 1977, Laboratory spawning and larval rearing of red drum and southern flounder. Proc. Annu. Conf. Southeast Assoc. Game Fish Comm., 31: 4377-440.

Colura, R.L., B.T. Hysmith and R.E. Stevens. 1976, Fingerling production of striped bass (Morone saxatilis), spotted seatrout (Cynoscion nebulosus), and red drum (Sciaenops ocellata) in saltwater ponds. Proc. World Maricult. Soc., 7: 122-134.

Grimes, C.B. 1995. Perspective of the AFS marine fish section on uses and effects of cultured fishes in aquatic ecosystems. American Fisheries Society Symposium 15:593-594.

Roberts, D.E. Jr., B.V. Harpster and G.E. Henderson. 1978, Conditioning and induced spawning of the red drum (Sciaenops ocallata) under varied conditions of photoperiod and temperature. Proc. World Maricult. Soc., 9: 311-332.

Travis, J., F. C. Coleman, C. B. Grimes, D. Conover, T.M. Bert and M.Tringali. 1998. Critically assessing stock enhancement: an introduction to the mote symposium. Bulletin of Marine Science 62 (2):305-311.

Willis, S.A., W.W. Falls, C.W. Dennis, D.E. Roberts and P.G. Whitchurch. 1995, Assessment of season of release on recapture rates of hatchery-reared red drum. American Fisheries Society Symposium 15:354-365.

FWC Facts:
A harmful algal bloom, or HAB, is a high concentration of toxic or nuisance algal species that negatively affects natural resources or people.

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