Patterns in Seasonal Abundance, Growth and Biomass of the Atlantic Silverside, Menidia menidia, in a New England Estuary

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Abstract
Patterns in seasonal abundance (numbers per m2 surface area), growth and biomass (grams per m2 surface area) of an annual fish, the Atlantic silverside, M. menidia (L.) were investigated in a marsh and more seaward bay region of Essex Bay, Massachusetts from Aug. 1976-May, 1978 using a quantitative beach seining technique. Silverside abundance varied greatly by season and year class during the study period. Abundance was high in 1976 but winter mortality (99%) left an adult density of only .01/m2 surface area in the marsh during spring 1977. Resultant 1977 year class density in the marsh was 1.88/m2 by late fall 1977 but winter mortality again produced an adult density of .01/m2 in spring 1978. Abundance was generally higher in the marsh than in the bay region especially during spring and late fall when catches in the bay were negligible. Based on catch rate comparisons, the summer and fall juvenile abundance of the 1976 year class was much higher than the juvenile abundance of the 1977 year class. Mean lengths and condition of the abundant 1976 year class in the late fall were significantly lower than those of the 1977 year class, suggesting density dependent population regulation. In both years, juveniles grew rapidly and reached full adult size by Nov. when an offshore movement to deeper waters outside Essex Bay occurred. Biomass peaked in the marsh region in late fall 1977 at 7.8 g/m2 wet weight. Winter mortality was size selective, favoring larger individuals. The annual life history design of M. menidia including an offshore winter movement and high winter mortality suggests that silversides represent an important pathway of energy flow from marsh to offshore trophic systems.

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