Flounder Stock Research Articles

Predator–prey size relationship between Pseudopleuronectes americanus and Carcinus maenas

Young-of-year flatfish grow through a series of critical periods in which they are vulnerable to different predators, including decapod crustaceans. The purpose of this study was to determine if winter flounder, Pseudopleuronectes americanus, were vulnerable to one such decapod, the green crab, Carcinus maenas, and to determine if vulnerability differed between wild and cultured fish. To examine the predator–prey size relationship, an experiment was conducted in which six cultured and three wild winter flounder size class treatments were tested against six crab size class treatments. Flounder of all size classes were preyed on by all size classes of green crabs; however, mortality was highest when the largest crabs were matched with the smallest flounder. The number of flounder killed per day was significantly higher (31%) in winter flounder <20 mm compared to all other larger fish size classes (4–8%). Additionally, these fish were attacked at a faster rate than any other fish size class. For the 31–60 mm fish size classes tested, more wild fish (11%) were killed per day by crabs than cultured fish (6.3%). These results suggest that in a winter flounder stock enhancement program, only fish >20 mm should be released to promote post-release survival.

Application of a population dynamics model to the probabilistic assessment of cooling water intake effects of Millstone Nuclear Power Station (Waterford, CT) on a nearby winter flounder spawning stock

A major concern of the Connecticut Department of Environmental Protection at Millstone Station has been the long-term effects of the station’s Cooling Water Intakes System (CWIS) on a small stock of winter flounder spawning in the Niantic River. Following the selection of a population modeling approach for long-term impact assessment in 1983, sampling programs were directed to collect data specifically for this purpose. These data were used to estimate the size of the local flounder stock and the fraction of its annual production lost to CWIS effects, and also evaluate a possible relationship between late-winter water temperatures and recruitment success of flounder. Since the mid 1980s, the main assessment tool at Millstone has been an age-structured population model that incorporated uncertainty in selected model parameters and provided output suitable for probabilistic analyses of simulation results. This model projected annual population sizes resulting from different fishing rates, larval entrainment losses, and impingement of juvenile and adult fish. Compensation was introduced via a Ricker stock-recruit function with an additional term to describe the effect of water temperature on recruitment success. Ricker’s α parameter, which describes the species inherent capacity to increase in numbers, was derived by four indirect methods based on life history parameters. In the basic simulation strategy, an unfished flounder stock was simulated first, and then fishing effects and mortality of the young attributed to CWIS effects were added. Combinations of different fishing rates and CWIS effects, either estimated or hypothesized, could be simulated for comparing the effectiveness of different mitigation alternatives. This approach helped identify fishing mortality as the driving force shaping the future size and viability of the local flounder population at Millstone and suggested that larval entrainment mitigation measures, costing hundreds of millions of dollars, would be ineffective in reversing currently declining trends of that population.

On optimum size limit for the Gulf of Gdańsk flounder stock

The protective size limit of flounder Platichthys flesus L. at the present exploitation level (F = 0.40) was estimated by means of two methods: the Beverton and Holt on the one hand and the Goh on the other. Regardless of the procedure used, it was found advisable to increase the present protective size limit (21.0 cm). In the author&prime;s opinion, the Goh method assuming a limited fishing season yields more reliable results. The author proposes to increase the flounder protective size limit from 21.0 to 24.0 cm.