Flounder fishery gets a needed push
Texas’ struggling flounder fishery received a modest but welcomed boost a little more than a week ago when state coastal fisheries staff released about 5,000 fingerling flatfish into the winter-cooled waters of Aransas Bay.
Those 2- to 3-inch fingerlings, which can reach 14 inches and adulthood in about two years, are the most recent manifestation of hard-won progress Texas fisheries scientists have made in a program to use hatchery-produced southern flounder to enhance populations of one of the state’s most popular inshore marine fish. It’s an effort Texas Parks and Wildlife Department coastal fisheries staff hope to accelerate over the coming years by expanding the agency’s currently limited infrastructure devoted to flounder research and propagation.
Flounder need the help. Between 1982 and 2008, the relative abundance of flounder in Texas bays, as gauged by TPWDgill net surveys (which track adult fish) and bag seines (which track abundance of juvenile flounder), declined by half. Angler catches of flounder also plummeted. And the decline came as other popular inshore fish such as speckled trout and redfish were stable or improving. Opening a can of worms
The problem was low recruitment of young flounder; few juvenile flounder were being produced and fewer surviving to become adults. Part of the problem was loss of crucial estuarine habitat and high mortality of juvenile flounder to by-catch in shrimp trawls. But a huge factor, fisheries managers found, was climate change.
Southern flounder spawn in the open Gulf of Mexico each winter, and the success of that spawn is directly tied to water temperature. Flounder need cold winters. When water temperatures are higher than about 60 degrees, survival of flounder eggs and larvae is limited. Adecade or more of winters in which water temperatures were higher than normal had resulted in a series of years when flounder recruitment was extremely low.
As part of a multi-part plan to help stabilize and rebuild the flounder population, TPWDin the early 2000s initiated efforts to produce flounder in its marine hatcheries for stocking in Texas bays. After all, that had worked with redfish and speckled trout. Since the late 1980s, TPWDhas had spectacular success with hatchery production of redfish and speckled trout, producing and stocking tens of millions of the fish each year. Those stocked reds and trout have enhanced those fisheries; TPWDgill net surveys have documented as many as 7 percent to 10 percent of redfish in some bays are hatcheryproduced fish.
But scientists quickly discovered producing the large numbers of flounder fingerlings required to make an impact on the population was not a simple task.
“Working with flounder is challenging,” Shane Bonnot, hatchery manager of TPWD’s Sea CenterTexas, a marine research and hatchery complex in Lake Jackson, told the Texas Parks and Wildlife Commission this past Thursday during a briefing on the agency’s flounder initiatives. Behind the count
For one thing, flounder don’t produce nearly as many eggs as redfish or trout. Asingle adult redfish can provide 2 million eggs per spawning cycle, Bonnot said. An adult female flounder produces 60,000-150,000.
Also, flounder eggs and larvae require much different environmental conditions than redfish or trout and develop at much different rates.
Aredfish or trout larvae grows to 2 inches or so in 20-30 days.
Aflounder takes 60-90 days to reach that length. And getting there isn’t easy on the fish.
Flounder larvae and fry are extremely sensitive to water quality, temperature and salinity, Bonnot said. Over its first two to three weeks of life, the tiny flounder require high salinity (mimicking open-ocean salinity) and a narrow temperature range.
“Water temperature has to be within 2 degrees of 62 degrees Fahrenheit for those first 30 days or so,” he said. Those conditions can be maintained only in indoor tanks and require constant monitoring.
About two to three weeks after hatching, the larval flounder, which begin life looking like most other fish, begin their metamorphosis into flatfish.
“This metamorphosis is very stressful on the fish,” Bonnot said. Unless the larval/fry flounder are maintained in near-perfect environments through their metamorphosis — water at 62 degrees, right salinity level, plenty of rotifers and brine shrimp to eat — survival is low.
But once the young flounder complete their metamorphosis, they are much more hardy and can survive in a wider range of water temperatures and salinities.
“It’s almost as if you’re raising two different fish — pre-metamorphosis and post-metamorphosis,” Bonnot said.
Post-metamorphosis flounder placed in outside “grow-out” ponds, where they are held until growing large enough for stocking, have about a 70 percent survival rate.
The differences between flounder and redfish or speckled trout in hatchery settings has forced hatchery staff up a steep learning curve.
“We’ve had to do a lot of developing new culturing techniques,” Bonnot said.
Also, flounder culturing in the TPWDmarine hatcheries has been limited to winter, the only time of the year when needed hatchery tanks, grow-out ponds and staff aren’t being used for production of redfish or speckled trout. Growth on the horizon
The combination of having to develop the most efficient culturing techniques, limited time to focus on flounder production and limited hatchery facilities devoted to flounder production has meant relatively low numbers of flounder have been stocked into Texas bays.
The first hatcheryproduced flounder stocked in Galveston Bay were about 2,000 fingerlings placed in West Galveston Bay in 2010. Since TPWD’s marine hatcheries began producing flounder in 2006, the agency has stocked about 184,000 juvenile southern flounder in Texas bays, Bonnot said. The agency has a goal of stocking 25,000 flounder fingerlings this year.
But those numbers could significantly increase over coming years as TPWDlooks to expand its focus on flounder. The agency has plans, pending obtaining funding, to develop, build and equip a 3,000-square-foot building at Sea Center-Texas that will be devoted exclusively to research and year-round production of flounder, Bonnot said.
The project, which already has drawn some funding from Texas-based marine conservation groups such as Coastal Conservation Association and Saltwater-fisheries Enhancement Association, is tentatively planned to be built by spring of 2017, Bonnot told the TPW Commission.
shannon.tompkins@chron.com