Predators are attracted to acclimation cages used for winter flounder stock enhancement

Acclimation cages are used for juvenile, cultured winter flounder Pseudopleuronectes americanus so that the fish can adjust to their new environment, hone their burial skills, begin pigment change, and recover from the stress of transport to the release site, all in the absence of predation. However, there have been indications that the cages attract the predatory green crab, Carcinus maenas. Studies conducted at the release site in the Hampton-Seabrook Estuary, New Hampshire, USA, determined that green crab abundance was significantly higher (ANOVA, p < 0.01) on cages containing fish than on empty cages, proving that acclimation cages containing flounder do attract green crabs. In addition, when empty acclimation cages were deployed, crab densities significantly increased (ANOVA, p < 0.01) in the vicinity of the acclimation cages and continued to increase each day, indicating that green crabs are also attracted to empty cages. Thus, although acclimation cages are a necessary tool that allows the stocked fish to adjust to their new environment, they also may be a detriment if they attract predators to the site. Using active adaptive management, release strategies must be reevaluated to reduce such predator-prey encounters, thereby improving fish survival.