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Distribution and abundance of the cownose ray,Rhinoptera bonasus, in lower Chesapeake Bay

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Abstract

Aerial surveys were conducted in the lower Chesapeake Bay during 1986–1989 to estimate abundance and examine the distribution of the cownose ray,Rhinoptera bonasus, during its seasonal residence, May–October. Most of the survey effort was concentrated in the lower and mid-bay regions. Cownose rays appeared uniformly distributed across the bay during mid-summer, but were more abundant in the eastern portion of the bay during migration. North-south distribution varied and reflected the general seasonal migration pattern. Mean abundance increased stepwise monthly from June through September and declined dramatically in October with their emigration from the bay. Abundance estimates from individual surveys varied. The greatest range of individual survey abundance estimates occurred in September (0–3.7×107 cownose rays0 due to high variation in school size and abundance between surveys. Monthly mean cownose ray abundance ranged from 0 in May and November to an estimated maximum of 9.3×106 individuals in September. The magnitude of the population suggests that the cownose ray plays an important role in the trophic dynamics of the Chesapeake Bay ecosystem. The historical data were insufficient to determine whether the population has increased, but these surveys provided the baseline data which would allow future investigation of cownose ray population dynamics in lower Chesapeake Bay.

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Author notes

  1. Robert A. Blaylock

    Present address: Marine Mammal Research Program, Oceanic Pelagic Resources Division, Southeast Fisheries Science Center, Miami Laboratory, 75 Virginia Beach Drive, 33149, Miami, Florida

Authors and Affiliations

  1. Virginia Institute of Marine Science School of Marine Science, College of William and Mary, 23062, Gloucester Point, Virginia

    Robert A. Blaylock

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Virginia Institute of Marine Science Contribution No. 1741.

This paper represents part of a Ph.D. dissertation presented to the faculty of the School of Marine Science of the College of William and Mary.

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Blaylock, R.A. Distribution and abundance of the cownose ray,Rhinoptera bonasus, in lower Chesapeake Bay. Estuaries 16, 255–263 (1993). https://doi.org/10.2307/1352498

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