By DAVID RAINER, Alabama Department of Conservation and Natural Resources
With the exception of those essential workers like healthcare, first responders and transportation, to whom we owe a great debt of gratitude, the COVID-19 outbreak has most of the world at a standstill.
Schedules had to be adjusted when Alabama Governor Kay Ivey issued the directives to minimize the spread of the virus.
One of those schedules involved the release of the southern flounder fingerlings that had been spawned at the Alabama Marine Resources Division’s (MRD) Claude Peteet Mariculture Center in Gulf Shores.
The flounder spawn was a first for MRD’s saltwater hatchery, and Max Westendorf, hatchery manager, said the release was executed about a week earlier than originally planned, but this didn’t pose a risk to the fingerlings.
“It really wasn’t detrimental,” Westendorf said. “We just had to throw it into gear and get it done.”
Another change of plans involved where the flounder were released. Hatchery staff had to find the best suitable salinity to maximize the survival of the fingerlings. The staff boated to the west but came back with reports that the salinity was too low.
“Initially, we had planned to release them in the Bon Secour and Oyster Bay areas and around Dauphin Island,” Westendorf said. “But with all the floodwater that had been coming down from the northern part of the state, from basically the mouth of the Intracoastal Waterway at Bon Secour all the way to Fort Morgan, the salinity levels were below two parts per thousand. We were looking for salinity levels of 10-15 parts per thousand.
“We had to go east to the Wolf Bay and Josephine areas. We were able to find water that was from 9 to 11 parts per thousand. “
The salinity in the tanks at the hatchery was reduced to match the conditions in the wild, and the fingerlings were released the following day.
“We released an estimated 12,236 fingerlings,” Westendorf said.
The method the hatchery used to determine the number of fish released is common to aquaculture facilities. The fish are removed from the holding tanks and a total weight is obtained. A random 50 fish are weighed and the total weight of this sample is divided by the number of fish counted to determine an average weight per fish. The total weight of all fish is divided by the average weight to determine the total number of fish released.
Westendorf said the density of fish in the tanks correlated with the size of the fingerlings. The tanks with fewer fish had larger individuals. Some fish in high density tanks could have been moved to a tank of low density to improve overall growth, but the extra handling could have stressed the fish and led to increased mortality.
MRD Chief Marine Biologist Kevin Anson said releasing the fish in the Perdido Bay system was not ideal but the best option under the circumstances.
“Releasing the fish in Mobile Bay would have been more productive than the Perdido system because it is more productive and typically has more juvenile shrimp than the Perdido system,” Anson said. “Small shrimp are entering the estuaries this time of year and serve as their primary food source.”
Anson said he hopes funding for a tagging program is available in the future to determine how many of the hatchery-raised fish enter the adult population (recruitment).
“We have an estimate of how many wild flounder enter the population, but we don’t know if the hatchery-raised fish will have the same survival rate as the wild fish,” he said.
Anson agrees that the early release date likely was not detrimental to the fish. He said the feed and brine shrimp fed to the fish in the hatchery is not as nutritionally beneficial as food sources in the wild.
Westendorf said the MRD team learned significant lessons during the hatchery’s inaugural flounder spawn.
“We had a lot of trouble getting potential broodstock flounder to eat consistently after bringing them into the hatchery,” Westendorf said. “We finally figured out a way to get them to eat consistently a month or two before spawning was scheduled to occur. If the fish were eating all year long, we would have had brood fish in better condition for spawning.
“Most of the mortality occurred right after hatch, which I attributed to poor egg quality. The fingerlings we were able to release came from the brood fish that looked significantly healthier than other spawned fish. They had better gonad development and their eggs looked healthier when placed under a microscope. We now know what we have to do to ensure that the appetite of the adult fish is maintained throughout the year.”