Morning Glory

Most coastal anglers in Texas know that the Texas Parks & Wildlife Department (TPWD) stocks millions of fingerlings representing a “Texas Slam” (Red Drum, Spotted Seatrout, and Southern Flounder) into Texas’ bay systems. TPWD uses stock enhancement as a fisheries management tool by operating three saltwater hatcheries: Sea Center Texas (SCT) in Lake Jackson, Perry R Bass Marine Fisheries Research Center (PRB) in Palacios, and the CCA Marine Development Center (MDC) in Corpus Christi.  Annually, the hatcheries release around 15 million Red Drum, 10 million Spotted Seatrout, and 50,000 Southern Flounder into Texas bays.  Sea Center Texas focus their stocking efforts on the upper and middle coast from Sabine Lake to San Antonio Bay, while MDC stocks the lower coast bay systems from Aransas Bay to the Lower Laguna Madre.  PRB stocks fish from both the upper and lower coast fish primarily focused on Matagorda Bay to Aransas Bay.

The hatchery production of fish for stock enhancement is a three-phase process, beginning with collecting and spawning wild adult fish (broodfish).  Sea Center Texas maintains the broodfish for the upper Texas coast, and MDC has the lower coast fish. A responsible approach to stock enhancement always includes taking broodfish genetics into consideration. Therefore, 25% of hatchery spawning broodstock are “cycled out” and replaced with new wild-caught fish each year to help support genetic diversity. Upon entry to their hatchery homes, new broodfish go through a quarantine period before they become part of the spawning stock.  All hatchery brood fish are conditioned to spawn using a 150-day maturation cycle (Figure 1).  The temperature and photoperiod (daylight hours per day) are adjusted to simulate an entire seasonal year in six months.  After undergoing this 150-day maturation cycle, they are ready to spawn.

The next phase of this process begins with collecting and incubating eggs for stocking outdoor ponds. Red Drum and Spotted Seatrout eggs are collected by staff and placed in 100-gallon incubator tanks, where they will hatch within 24 hours of spawning. When larvae are approximately three days old, they are harvested from incubators and transported to outdoor grow-out ponds. Fish from MDC and SCT are stocked in the ponds at their respective facilities, while PRB ponds are stocked with fish from both facilities. These grow-out ponds are filled with filtered seawater and fertilized to promote the primary productivity of phytoplankton and, subsequently, zooplankton, a natural food source for larval fish.  Once a pond has enough zooplankton, they are ready for a new batch of larvae.

The final phase of fingerling production is pond grow-out and, ultimately, the pond harvest.  Red Drum and Spotted Seatrout fingerlings are grown to a target size of about 1.5 inches.  Fingerling growth is monitored weekly by measuring a subsample of fish from each stocked pond.  Depending on how fast they grow, fingerlings can reach the target size in 35-40 days and are ready to be harvested from the ponds and stocked into Texas coastal waters.  Personally, I think pond harvest is the best part of the job because it is the fruits of our labor! It is fun, yes, but easy; I’ll leave that up to interpretation. A harvester’s (TPWD staff assigned to a harvest) circadian rhythm is interrupted once it’s time to start harvesting grow-out ponds. After months of a “standard daytime routine,” harvesters are charged with pulling an “all nighter” to harvest the fingerlings from their ponds.  Hatchery team members tasked with harvest responsibilities leave work at 3 pm only to return at midnight to harvest all fingerlings before sunrise the next morning.  What’s the story? Morning glory is right! Loading 150 pounds or more of healthy fingerlings into a trailer destined for one of Texas’ bays is nothing less than glorious! 

Fingerling harvest begins with the opening of the drain valve of the pond. Depending on the size and number of ponds being harvested, it can take up to three days from the opening of the drain until the last fingerling is loaded into a trailer. Each pond consists of a harvest kettle which is a concrete basin where the drain is located with adjacent concrete steps leading down into the pond. As fingerlings reach the kettle, they are dipped out using nets, weighed (around 3-5 pounds per net), and placed in the buckets. Once in the bucket, they are re-weighed, and the displacement is the recorded weight.  A transport trailer can haul 150 pounds of fingerlings, and during harvest, there can be more than 100 pounds of fingerlings in the kettle, which is exciting and nerve-racking at the same time!  However, screens are in place to prevent fingerlings from exiting the pond via the drain, and oxygen is added to the water throughout the harvest to keep the fingerlings alive.   

So, let’s do the math.  If a pond produces 150 pounds of fish, and there are an average of 1,200 fish per pound, then 180,000 fingerlings are loaded in the transport trailer. A harvester can walk up and down the steps of a pond around 30 times when they are “running buckets.” This can become quite a workout. The harvester takes five random sub-samples of 100 fingerlings during each harvest. These fish are counted and weighed as a group of 100. The average weight of the five samples is used to determine the number of fingerlings produced (per pound) during a harvest.  From these 500 fingerlings, 20 are measured individually from each sample group, and the total length and weight are recorded.  This data calculates the number of fingerlings produced and the percent return of fingerlings from the original number of larvae stocked in the pond.

The final step in a successful harvest is transporting and releasing the fingerlings into their new home, one of Texas’ bays. Hatchery biologists work closely with the Ecosystem Management team biologists to select stocking sites to release hatchery fish. These sites can be accessed by both land and boat, with excellent habitat being the driving factor.  Some research has suggested that about 6% of the fishable Red Drum stock in Texas are of hatchery origin, with a range of 3.8% - 17.4%, which varies by bay and year. So, the next time you see a TPWD truck and trailer loaded with fingerlings along some bay shoreline on the Texas coast, you can rest assured we are doing our part to ensure great fishing for future generations of Texans.