Winter mortality, growth, and behavior of young-of-the-year of four coastal fishes in New Jersey (USA) waters

Winter mortality has been hypothesized to select for large body size in you ng-of-the-year (YOY) fishes, yet substantiation of winter mortality and its cause(s) are available for few estuarine or marine species. We examined se asonal length distributions of wild populations of four common marine speci es, black sea bass (Centropristis striata), tautog (Tautoga onitis), cunner (Tautogolabrus adspersus), and smallmouth flounder (Etropus microstomus), and mortality (i.e., frequency of death), growth, and behavior of their YOY in the laboratory at ambient winter temperatures (mean 7 degreesC, range 2 -13 degreesC) during a 135-day period (December 1992 through mid-April 1993 ) to establish potential causes of their mortality in the field. Young-of-t he-year black sea bass experienced 100% mortality when water temperatures d ecreased to 2-3 degreesC in February, emphasizing the importance of winter emigration from estuaries in this southern species. The low mortality of tw o labrid species, YOY tautog (14%) and YOY cunner (3%), was consistent with their northern distribution and year-round occurrence in estuarine and nea rshore coastal waters. Laboratory mortality of YOY smallmouth flounder (33% ) was higher for small (<35 mm total length) fish, suggesting that this sma ll species may experience high winter mortality in estuaries and nearshore coastal waters. Seasonal differences in fish length result potentially from several mechanisms (e.g., mortality and/or migration) that are difficult t o assess, but our laboratory experiments suggest that seasonal temperature changes cause size-specific mortality of YOY smallmouth flounder and offsho re migration of YOY black sea bass.