Age, growth, longevity, and mortality of blackcheek tonguefish, Symphurus plagiusa (Cynoglossidae: Pleuronectiformes), in Chesapeake Bay, Virginia


Terwilliger, Mark. R. , and Thomas A. Munroe
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Age structure, longevity, and mortality were determined for a population of blackcheek tonguefish, Symphurus plagiusa, in Chesapeake Bay. Blackcheek tonguefish (36–202 mm TL) were randomly collected by means of otter trawl in lower Chesapeake Bay and major Virginia tributaries (James, York, and Rappahannock rivers) from April 1994 through August 1995. Ages were determined by interpreting growth increments on thin transverse sections of sagittal otoliths. Marginal increment analysis showed that a single annulus was formed in June of each year. Blackcheek tonguefish caught during this study reached a maximum age of 5+ years. Growth was rapid during the first year, then slowed rapidly at a time coincident with maturation. We used the following von Bertalanffy growth equations: for males—Lt = 196.5(1 – e–0.285(t + 0.92)); and for females—Lt = 190.6(1 – e–0. 320(t + 0.78)). Von Bertalanffy parameters were not significantly different between sexes. Extrapolated instantaneous mortality rates for a possible seventh year class were 0.73 (Hoenig’s equation) and 0.77 (Royce’s equation). High estimates of instantaneous total mortality may reflect either loss due to emigration of adults from Chesapeake Bay onto the continental shelf or high natural mortality occurring in this northernmost population. Compared with sympatric pleuronectiforms, blackcheek tonguefish have a relatively high mortality rate, small asymptotic length, and high growth parameter K. Species, such as blackcheek tonguefish, that feature this combination of growth parameters are hypothesized to be better adapted at exploiting seasonally dynamic and highly unpredictable environments, such as those estuarine habitats within Chesapeake Bay.