Age and Growth, Movements and Distribution of the Cownose Ray, Rhinoptera bonasus, in Chesapeake Bay

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Abstract
Ages were estimated for 115 of 899 cownose rays,Rhinoptera bonasus, collected primarily from commercial fishing gear, in lower Chesapeake Bay and vicinity from May through October, 1976–78. Age determinations were made using sectioned vertebral centra and estimates of von Bertalanffy parameters were for males DW∞=119.2, K=0.126, and t0=−3.699, and for females DW∞=125.0, K=0.119, and t0=−3.764. Females attained a larger adult size and the oldest specimen aged was a female 13 years old and 107 cm disc width. Both sexes mature after reaching about 70% of their maximum size and ages at maturity were estimated at 5 to 6 years for males and 7 to 8 years for females. In spring migrating rays schooled by size; they arrived along the North Carolina coast by April and entered Chesapeake Bay by early May. Rays were abundant in the major Virginia tributaries of Chesapeake Bay throughout summer and occurred in salinities as low as 8‰ and at water temperatures between 15–29 °C. Size segregation continued during summer and adults schooled by sex. Most rays left Chesapeake Bay by early October.

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