Date of Award

Summer 1989

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

John R. McConaugha

Committee Member

Patricia Tester

Committee Member

Michael Prager

Call Number for Print

Special Collections LD4331.O35V37

Abstract

Recruitment processes are important information for the management of commercially and recreationally exploited marine species. Recruitment processes of the Chesapeake Bay's most important commercial and recreational species, the blue crab, are unknown, due in part to the lack of knowledge of the processes directly preceeding recruitment.

The present study was undertaken to investigate and explain the movement and developmental patterns of blue crab larvae while offshore. Interannual and intraseasonal variations of these patterns were also examined.

Sampling occurred from May to November during 1982 and 1983. Larvae were collected at three depths (neuston layer (upper 10 cm), one meter and three meters) from eighteen stations covering the bay mouth and the mid-Atlantic bight adjacent to the Chesapeake Bay.

A total of 494 samples containing 4,936,543 larvae were collected during the study. Sixty eight percent of the total larvae were collected in 1982. Stage I larvae dominated the collections in both years.

Peak abundances of all larval stages combined occurred in mid-July in 1982 and mid-August in 1983. Wild developmental rates, determined by calculating mean dates, were not significantly different between 1982 and 1983 for stage I, II and III larvae (P=0.2254) and were consistent with laboratory developmental rates.

Mean distances from bay mouth increased from stage I to stage VI each year. Postlarvae mean distances were less than mean distances from stages V-VIII each year, but were never less than 30 miles from the bay mouth. Center of mass calculations, defining two dimensional movement patterns, are presented for total larvae and for each larval stage. Center of mass for total larvae was influenced greatly by the large proportion of stage I larvae in the total sample and was within approximately 20 miles of the bay mouth at all sampled dates. Center of mass for each larval stage varied with stage and/or year. Second order center of mass was calculated to define the average seasonal location patterns of blue crab larvae. Center of mass locations between stage I larvae and postlarvae were dissimilar each year; however, postlarvae second order center of mass was approximately the same each year (about 30 miles east-southeast of the bay mouth).

All larval stages displayed tendencies toward the neuston layer. Significant differences in depth distribution were apparent only for postlarvae in 1983, and for all larval stages except stage III and stage VIII larvae in 1982. These differences are most likely attributable to sea state and may partially explain the differences in movement patterns from 1982 to 1983.

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DOI

10.25777/5ss4-zx33

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