Successful Enhancement of the Texas Red Drum (Sciaenops ocellatus) Population

Lawrence W. McEachron, C.E. McCarty, and Robert R. Vega

Texas Parks and Wildlife Department
702 Navigation Circle, Rockport, Texas 78382

ABSTRACT

Red drum (Sciaenops ocellatus) is an estuarine-dependent sciaenid that inhabits estuaries, bays, and coastal regions from New York to Mexico. In Texas, the red drum population began a dramatic decline in the 1970s, prompting the Texas Parks and Wildlife Department (TPWD) to set up a three-pronged recovery plan. Management approaches were: 1) Initiate an independent monitoring program to assess relative abundance; 2) Implement restrictive regulations to reduce fishing pressure, including license restrictions, size, bag, and possession limits, a commercial quota, restrictions on netting, and a ban on commercial sale of red drum; and 3) Develop and start a marine enhancement program based on the release of hatchery-reared fingerlings and assessment of subsequent survival.

Recently, the red drum population in Texas coastal water rebounded because of several factors that had a positive effect on the recovery. TPWDs long-term management plan utilizing hatcheries and stocking to supplement natural spawning played a role in reversing the decline of the red drum population. The strategy used by the TPWD can serve as a blueprint for other marine enhancement programs.

INTRODUCTION

The objective of this paper is to provide a synopsis of Texas 20-year red drum enhancement program. The red drum population consists of two distinct groups: adults in the inner shelf habitat, and young less than 6 years old in estuaries and nearshore habitats (Pearson 1929, Matlock 1984). Red drum spawn in late summer and fall in the nearshore habitat; larvae migrate through passes into estuarine nursery grounds (Pearson 1929). Historically, red drum supported recreational and commercial fisheries throughout its range.

Texas recreational fishery, with about 1.6 million fishermen, is worth $2.3 billion (U.S. dollars); red drum is a major targeted species. In the 1970s, the red drum population in Texas began a dramatic decline because of growth (Matlock 1984) and possibly recruitment overfishing. In response to this decline, Texas Parks and Wildlife Department (TPWD) fishery managers formulated the following recovery plan in 1975:

1) Establish a long-term monitoring program to assess red drum relative abundance. Experimental gill nets are used to assess estuarine sub-adult relative abundance; bag seines are used to assess juvenile recruitment to theestuary population (Dailey et al. 1992).

2) Implement increasingly more strict regulations on both sport and commercial fishermen. Ultimately, no nets were allowed in Texas waters, the sale of red drum was banned, and sport anglers were restricted to three fish per day, 51-71 cm long.

3) Set up a stock enhancement program using hatcheries. For the purpose of the present paper, the focus will be on stock enhancement.

Red drum is an excellent candidate for enhancement through stocking because larval recruitment into estuaries from nearshore spawning areas is probably a limiting factor of year class abundance. Matlock (1987) presented results showing that in 1967, recruitment of red drum in upper Laguna Madre (Fig. 1) was higher than in any of the previous 8 years. This was a result of three passes created by a hurricane storm surge, thus providing excellent conditions for ingress of larvae into the bay. If managers could bypass mortality associated with larval recruitment from the nearshore spawning areas into the bays, then stocking "enough" red drum directly into estuaries could possibly supplement the natural stock. Capture of tagged stocked red drum up to 284 days following release in Matagorda Bay (Fig. 1) in 1976 documented that stocked red drum can survive in the wild (Matlock et al. 1984).

Matlocks limited recruitment theory and possible use of hatchery-produced fish for enhancement were tested in St. Charles Bay from 1979 through 1981 (Matlock et al. 1986). This 566 ha bay was stocked with two million fingerling red drum (25-30 mm total length) in summer 1979, fall 1980, and spring 1981. Since red drum spawn in late summer and fall, the 1 million fish stocked in spring and early summer were smaller than all natural fish spawned during the previous falls. These out-of-phase fish were tracked by length frequency up to 9 months after stocking in both bag seine and gill net samples. Some fish were micro-tagged before stocking, a few of which were later recaptured. Therefore, double confirmation of survival of stocked fish was documented. Based on the success of this study (Matlock et al. 1986), the TPWD, in partnership with the Gulf Coast Conservation Association and the Central Power and Light Company, constructed its first production-scale marine fish hatchery in 1982.

THE RED DRUM HATCHERY SYSTEM

The present hatchery system consists of spawning/incubation facilities with 30 ha of production ponds. Red drum broodfish are maintained in 13,000-L circular tanks in environmentally controlled rooms. Each spawning tank contains five to six broodfish (three females) ranging from 8-18 kg; they are fed shrimp (Penaeidae), squid (Loliginidae), and mackerel (Scombridae). Twenty-five percent of the broodfish are exchanged annually with wild fish to maintain genetic diversity. Broodfish are subjected to a 150-day photoperiod-temperature maturation cycle (McCarty 1990). Spawning occurs at a water temperature of 24o to 26o C, salinity of 30-38 ppt with 11 hours of light. Buoyant fertilized eggs float to the top of the circular tanks where they are skimmed off the surface, flow into an egg collector, then are collected by dip-net. Eggs are volumetrically measured and counted. On average, two million eggs are collected each night from March through November. Eggs are transferred to 945-L incubators where they hatch within 24 hours. Within 36 to 40 hours post hatch, larvae have developed mouthparts, distinct eye pigmentation, and a complete digestive tract. These first-feeding larvae average 2.7 mm total length.

Rearing ponds, filled five to 10 days earlier with filtered water and fertilized, are stocked with larvae when zooplankton densities reach 250 organisms/L. A combination of inorganic and organic fertilizers applied to rearing ponds produce a rapid phytoplankton bloom that stimulates a copepod population, a primary food for larval red drum. Dissolved oxygen, salinity, temperature, zooplankton densities, and fish growth rates are routinely monitored. Larvae remain in the ponds for 30 days or until they reach a target size of 30 mm total length. Once they reach target size, ponds are drained, fish are harvested, and they are transferred to distribution tanks for stocking into coastal waters. Between 1983 and 1989, 5 to 10 million fingerlings were stocked each year. In 1990 the primary facility was enlarged, and additional grow-out ponds went into production. Each year between 1990 and 1992, 15 to 20 million fingerlings were stocked. Through 1992, more than 115 million fingerlings were stocked into Texas coastal waters.

ASSESSING THE RESULTS OF STOCK ENHANCEMENT

The key question is: Does stocking work? Evaluations of the success of enhancing the red drum population using hatchery-reared fingerlings have been ongoing since 1983. Three different methods are used in assessment: 1) bag seines chronicle year class strength of young-of-the-year red drum (Dailey et al. 1992); 2) gill nets estimate relative abundance of sub-adults (Dailey et al. 1992); and 3) sport anglers catches are measured by surveying harvest and fishing success (Weixelman et al. 1992). Length distribution of wild fish each month is relatively tight; all naturally spawned fish follow this normal seasonal pattern (Figs. 2, 3). Fish stocked in upper Laguna Madre during late spring and early summer in 1991 and 1992 were caught in bag seines up to 8 months following stocking (TPWD unpublished data), after which they were not vulnerable to bag seine collection. These "out-of-phase" fish were collected during routine TPWD sampling. Each month, 18.3-m bag seines (19 mm stretched mesh in wings; 13 mm stretched mesh in bag) are pulled along the bay shoreline at 20 randomly selected sites. [For a detailed description of bag seine sampling methodology, see Dailey et al. (1992).] At least 20% of all red drum caught in upper Laguna Madre bag seine samples in both 1991 and 1992 were positively identified as stocked fish (TPWD unpublished data).

During 1983 to 1985, TPWD gill net catches in a stocked (Corpus Christi Bay) and unstocked (upper Laguna Madre) bay were compared (Matlock 1990). Gill nets used were 182.9 m long, 1.2 m deep, with 45.7 m sections of 7.6-cm, 10.2-cm, 12.7-cm, and 15.2-cm stretched monofilament mesh tied end to end with smallest mesh on shore. [For a detailed description of gill net sampling methodology, see Dailey et al. (1992).] Fish were stocked in 1983 in Corpus Christi Bay. Matlock (1990) reported that these fish began to be caught in fall 1984 in the 7.6 cm mesh; increased catches 1 year after stocking were primarily in this mesh. This pattern was not apparent in the unstocked bay. Stocked fish were also caught 6 months later in the 10.2 cm mesh and 1 year later in the 12.7 cm mesh. Again, this trend was not observed in the unstocked bay. Also, in fall 1985 the 7.6 cm mesh began to catch fish from the second stocking. These fish wre caught in the 10.2 cm mesh 6 months later, thus following the same pattern observed after the first stocking.

In these same two bays, sport-boat fishermen catches were estimated. The TPWD has conducted a continuous survey of sport-boat fishermen since 1975 (Weixelman et al. 1992). The number of red drum landed annually and catch-per-unit-effort (No./hour) were estimated before stocking and after stocked fish reached the minimum size limit. Matlock (1990) reported that the number of red drum harvested from the stocked bay increased 100% over the historic mean (1979-1984). There was a 27% increase in the number of fish landed in the unstocked bay but sport fishermen fished 45% more man-hours than in the stocked bay. This pattern is also reflected in the catch rate, which is a measure of success. In the stocked bay, the catch rate increased 150% over the historic mean, whereas in the unstocked bay the catch rate only increased 50% over the historic mean.

Gill nets, described previously, have been used since fall 1975 to estimate sub-adult relative abundance (Dailey et al. 1992). Fall catch rates were highly variable through 1984 (Dailey et al. 1992; Fig. 4). In 1983, Texas hatchery went on-line and large-scale stocking began. Regulations implemented in the mid- to late-1980s were also starting to affect the red drum population. Since 1985 the coastwide gill net relative abundance index has stabilized and increased (Fig. 4). Stocking probably stabilized recruitment from the typical marine scenario of high recruitment in a few years and low recruitment in most years by supplementing the natural spawn. Improved regulations allowed more fish to survive and, as a result, stocked fish helped enhance the population.

Four studies are currently underway to further assess the success of enhancement through stocking. First, selectively bred fingerlings will be stocked in East Matagorda Bay. TPWD geneticists found a gene marker (King et al. 1993) that can be used in estimating the magnitude of enhancement. For the first time, researchers can follow stocked fish throughout their 4- to 6-year life in the bay. Second, the Optical Pattern Recognition System (Biosonics 1987) is being used to distinguish differences in scale annuli patterns between hatchery and wild fish caught in TPWD samples. Third, oxytetracycline (OTC) marked fish will be stocked to distinguish stocked fish from wild fish during fall and winter. OTC lays down a mark on otoliths and other calcified structures that will fluoresce under UV illumination (Thomas 1993). Fourth, TPWD fishery managers are in the initial stage of conducting a detailed multivariate analysis partitioning biological, environmental, sampling, and stocking components, so the parameters affecting success of stocking can be identified. All four of these studies should allow a more precise, quantifiable assessment of the role hatcheries played in the increase in red drum abundance.

CONCLUSIONS

TPWD fishery managers have used several different techniques to address the success of hatcheries in enhancing populations. This was planned at the very beginning of the program because multiple approaches increase the chance of detecting and quantifying the influence of hatchery production. The answer to the question of hatchery success is very complex with many components to address.

It has taken the TPWD 20 years to reach the present stage in development of its stocking and recovery prgram. To date, over 115 million fingerlings have been stocked. Fishery managers in Texas have taken the often controversial technique of hatcheries and used it to benefit the red drum resource and fishery. The innovative use of stocking, combined with traditional management practices, has proven to be a powerful combination in managing Texas natural resources wisely. We encourage fishery managers in other overexploited fisheries to assess the feasibility of using hatcheries to supplement marine populations. All evidence in Texas at this stage weighs heavily in favor of the fact that stocking hatchery fish has enhanced Texas red drum. This enhancement program serves as a model for managers developing future recovery programs.

ACKNOWLEDGMENTS

Thanks go to Kyle Spiller for creating the figures depicting red drum bag seine and gill net catch rates.

LITERATURE CITED

Biosonics, Inc., 1987. Optical Pattern Recognition System. Data acquisition program manual, version 1.08. Seattle.

Dailey, J.A., J.C. Kana, and L.W. McEachron, 1992. Trends in relative abundance and size of selected finfishes and shellfishes along the Texas coast: November 1975-December 1990. Management Data Series Number 74. Texas Parks and Wildlife Department, Fisheries and Wildlife Division, Austin, Texas.

King, T.L., R. Ward, and I.R. Blandon, 1993. Gene Marking: A viable assessment method. Fisheries XVIII(2):4-5.

Matlock, G.C., 1984. A basis for the development of a management plan for red drum in Texas. Doctoral dissertation, Texas A&M University, College Station, Texas.

Matlock, G.C., 1987. The role of hurricanes in determining year-class strength of red drum. Contributions in Marine Science 30:39-47.

Matlock, G.C., 1990. Preliminary results of red drum stocking in Texas. In: A. Sparks (ed.), Marine Farming and Enhancement: Proceedings of the 15th U.S.-Japan Meeting on Aquaculture, October 22-23, 1986, Kyoto, Japan, pp. 11-15. NOAA Technical Report NMFS 85. U. S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Washington, D.C.

Matlock, G., B.T. Hysmith, and R.L. Colura, 1984. Return of tagged red drum stocked into Matagorda Bay, Texas. Management Data Series Number 63. Texas Parks and Wildlife Department, Coastal Fisheries Branch, Austin, Texas.

Matlock, G.C., R.J. Kemp, Jr., and T.L. Heffernan, 1986. Stocking as a management tool for a red drum fishery, a preliminary evaluation. Management Data Series Number 75. Texas Parks and Wildlife Department, Coastal Fisheries Branch, Austin, Texas.

McCarty, C.E., 1990. Design and operation of a photoperiod/temperature spawning system for red drum. In: G.W. Chamberlain, R.J. Miget, and G. Haby (eds.), Red Drum Aquaculture, pp. 44-45. Texas A&M University Sea Grant College Program Number TAMU-SG-90-603, College Station, Texas.

Pearson, J.C., 1929. Natural history and conservation of redfish and other commercial sciaenids of the Texas coast. Bulletin of the United States Bureau of Fisheries 44:129-214.

Thomas, L.M. 1993.Chemical mark application in red drum (Sciaenops ocellatus). M.S. Thesis. Texas A&M University, College Station, Texas.

Weixelman, M., K.W. Spiller, and P. Campbell, 1992. Trends in finfish landings of sport-boat anglers in Texas waters, May 1974-May 1991. Management Data Series Number 85. Texas Parks and Wildlife Department, Fisheries and Wildlife Division, Austin, Texas.


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