TPWD’s Marine Sportfish Enhancement Program - Stocking Allocation and Site Selection

The Texas Parks and Wildlife Department’s (TPWD) Coastal Fisheries Sportfish Enhancement Program is now in its fourth decade of operation and has stocked over 900 million Red Drum and Spotted Seatrout in Texas’ public waters.  If you spend any amount of time on the Texas coast, there is a good chance you’ve seen our flatbed trailers with white fiberglass boxes emblazoned with the Texas Parks and Wildlife logo. These hauling units are used to transport and stock millions of fingerlings into Texas’ bays and estuaries each year. But not every location is suitable for juvenile fish growth and survival. So how and why are some sites selected? And, how many fingerlings should be released? To answer these questions, we rely on the cooperation between two different Coastal Fisheries programs: the resource management teams, which monitor our marine fisheries resources, and the hatcheries, which produce and stock the fingerlings. It is this cooperation that has made stock enhancement an effective tool in our state’s resource management.

The primary goal of the Fisheries Enhancement Program is to supplement the recruitment of juvenile Red Drum into the fishery because the success of natural reproduction varies from year to year. For a variety of reasons (like red tide and freezes), some years are better than others for newly hatched Red Drum. To ensure fingerlings are being stocked where they are needed most, the distribution of hatchery produced fingerlings also varies. This “allocation” is a percentage of the 15 million fingerlings that are produced every year by TPWD’s saltwater fish hatcheries.

To determine the allocation, Coastal Fisheries biologists sample shoreline habitat with a bag seine and count the number of juvenile Red Drum observed from November to March. This gives us an idea of how successful the year was for Red Drum reproduction. From these samples, we calculate the catch rate, which we call “catch per unit effort” (CPUE). If the CPUE is increasing from previous years, we know that natural reproduction of Red Drum was more successful. If CPUE is decreasing, we can plan to stock more hatchery-raised fingerlings in those areas. So, based on average catch rates and the amount (hectares) of suitable shallow water habitat in each bay system, a percentage of the overall hatchery-produced Red Drum is assigned (Table 1). The 2019-2020 coastwide CPUE was the third highest on record, and six of the nine major-bay systems exhibited above average catch rates, indicating a healthy and increasing population of Red Drum on the Texas coast. (Figure 1).

Once we know how many fingerlings will be distributed to each major bay system, we can start thinking about exactly where to stock the fingerlings.

When choosing a stocking site, a primary concern must be: does this location contain the correct habitat for these juvenile sportfish? The location should not just be somewhere they can survive but somewhere they thrive! Juvenile Red Drum and Spotted Seatrout can grow upwards of a millimeter a day. This means energy demands are substantial and require lots of prey items to fuel their growth. Good habitat also provides shelter that protects them from wading birds, larger fish, and crustaceans that prey on juvenile fish. Cordgrass, oyster shell, and seagrass beds can all provide suitable places for the fingerlings to hide, feed, and grow.

A secondary concern is identifying sites with adequate water quality. Dissolved oxygen levels, salinity, and water temperature can all influence fingerling survival. Ideally, the water quality of a site should be the same as the water in the hauling unit. This is not always possible as conditions vary along the Texas coast. Therefore, in most cases, the fish are stocked after acclimation, the process of slowly replacing the water in a hauling unit with water from the site. This allows the fish to adapt to the local water conditions before being released.

Site accessibility must also be taken into consideration. Hauling units can safely transport and stock upwards of 300,000 fingerlings per trip. The sheer logistics of stocking millions of Red Drum annually make these trailerable life support systems the most common method we use. These hauling units can weigh over 8,500 pounds when loaded, so a site must be able to accommodate these heavy trailers close to the water. We prefer sites with good habitat, adjacent to a paved or gravel road or parking lot. In some areas, a boat is utilized to access areas unreachable by vehicle. Although logistically more challenging, using a boat can greatly increase our ability to stock fingerlings into the best habitats available. It is desirable to spread the allotment of Red Drum to as much suitable habitat as possible, so no more than 300,000 fingerlings are released into a one square mile area.

Over time, some stocking sites begin to feel like an old friend you see year after year, while others get eliminated due to land use, construction, or changing environmental conditions. Hatchery staff use tools such as Google Earth to identify new sites and expand the range of the stock enhancement program. After all, choosing excellent stocking sites is vital to ensure successful stocking and a healthy fishery. Your TPWD fisheries enhancement program helps to ensure there are angling opportunities for both present and future generations.