by Jason Lemus
Maintenance of the genetic structure of a wild fishery is a key component for responsible marine stock enhancement. The historic model of spawning for stock enhancement of red drum in Florida’s Central Gulf coast required five 12-feet-diameter (12-ft) tanks with three female and three male adult red drum in each to achieve a satisfactory effective spawning population size. A single 20-feet-diameter (20-ft) tank, five times the volume of a 12-ft tank, for spawning 30 adult red drum presents opportunities to improve efficiency through reduced logistical complexities, labor, and footprint, while maintaining or improving genetic diversity of hatchery offspring in Florida Stock Enhancement Hatcheries. A study is in progress at SERF to determine the effective population size of spawning red drum in a 20-ft tank to determine if this strategy is a more efficient alternative than the historic model.
A key consideration before implementing the study was to design and construct a prototype filtration and egg collection system that could be used with the 20-ft tank. Traditional filtration systems for spawning tank are not efficient for large tanks. The new spawning system designed and tested by SER team members reduced water use and labor, and improved water chemistry from the traditional design. These improvements were keys to effectively operate a large spawning tank. SER staff then adapted the prototype design for a 20-ft-tank. Construction and assembly of the spawning system was accomplished by SER staff and key functions tested and refined before stocking fish.
Adult red drum were stocked into the 20-ft tank and a 12-ft tank on November 4 and 6, 2014 to evaluate husbandry and maintenance of the 20-ft tank. Although not expected necessarily, spawning commenced soon afterward in both tanks as fish were stocked at the end of the natural spawning season. Beginning in late January, the red drum captive maturation cycle (a compressed seasonal cycle of 150 days) was initiated. Spawns began in July and are being collected for through October 2015. The spawning contribution of the individuals in the 12-ft and 20-ft tanks will be determined using genetic markers over the course of the four-month spawning period and replicated with new populations of red drum in subsequent years. This data is a key to the design and operation of stock enhancement facilities in Florida and other states that subscribe to approaches for maintaining the genetic structure of wild red drum populations.