Chesapeake Bight Research Articles

Nearshore surface currents in the Chesapeake Bight during summer

In this study, several different approaches are used to study coastal surface currents in an application to the dispersion of blue crab larvae from Chesapeake Bay onto the Middle Atlantic Bight. Observations from the deployment of a newly developed surface current meter (RBCM—Rapid Boundary Current Meter) are presented and compared to calculated surface currents from a simple model. In addition, using currents calculated with actual winds in this model, traces are constructed from point of encounter of larvae on the shelf back to the bay entrance. This has provided a unique Lagrangian tag for evaluating model parameters and forcing terms. Comparisons to Lagrangian traces and to RBCM measurements led to the inclusion of “wall” layer boundary conditions in the model. Without this layer, modeled currents seriously underestimated measured currents. Vector correlations between wind stress and measured currents were high with average veering suggestive of Ekman dynamics at a site offshore of the entrance to Chesapeake Bay. At a shallower site, correlations were relatively high, but topography or coastline guidance was strong.

87:6043 Nearshore surface currents in the Chesapeake Bight during summer: Johnson, D.R., 1987. Continent. Shelf Res., 7(4):367–378

87:6043 Nearshore surface currents in the Chesapeake Bight during summer: Johnson, D.R., 1987. Continent. Shelf Res., 7(4):367–378

Wind-forced dispersion of blue crab larvae in the Middle Atlantic Bight

Blue crab larvae are advected out of Middle Atlantic Bight estuaries immediately after spawning occurs in the estuary entrance. For the next 30 to 50 days the larvae are found offshore and mainly at the surface where they are influenced by wind-driven currents. Using a previously derived circulation model and winds from Norfolk (VA) airport, a backward trace is made from where relatively dense concentrations of megalopae were found in the Chesapeake Bight during 1983 to a point of origin (spawning). During 1983, the megalopae encountered on the shelf had their origin in Chesapeake Bay and took, at minimum, 31 to 36 days to grow to the megalopae stage. Wind forcing dominated the inner shelf region in the summer of 1983 and the resulting dispersion of Chesapeake Bay megalopae occurred briefly in the southern sector early in the season, but toward the northern sector over most of the season. Although no firm conclusions could be drawn regarding the mechanism for return, it did not seem likely that wind advection back to the point of origin would be effective.

Seasonal Distribution of Black Sea Bass, Centropristis striata, in the Mid-Atlantic Bight with Comments on the Ecology and Fisheries of the Species

Abstract Black sea bass in the Middle Atlantic Bight spawn in the summer, at depths of 18 to 45 m, primarily from Virginia to Montauk, Long Island. Young of the year become demersal at 13–24 mm total length and enter estuarine nursery grounds. In fall black sea bass migrate south and offshore to the Chesapeake Bight where the entire population spends the winter. Larger and older fish move offshore sooner than do young of the year and winter in deeper water (73–165 m). Black sea bass may tolerate temperatures as low as 6 C but are captured in larger numbers and more frequently in waters 9 C and above. In the spring sea bass migrate inshore and to the north; adults to their coastal spawning areas, juveniles to estuarine nursery areas (including lower Chesapeake Bay). In recent years, the commercial catch per effort of sea bass has dropped and the fishery lands fewer large and medium size fish. Concurrently domestic trawling effort has decreased somewhat whereas effort by the recreational, foreign trawl, and...

Eggs and larvae of the ophichthid eel,Pisodonophis cruentifer, from the Chesapeake Bight, Western North Atlantic

Eggs and larvae of the ophichthid eel,Pisodonophis cruentifer, from the Chesapeake Bight, Western North Atlantic

Eggs and Larvae of the Ophichthid Eel, Pisodonophis cruentifer, from the Chesapeake Bight, Western North Atlantic

Eggs and early larvae (5.8–34.2 mm SL) of the snake eel,Pisodonophis cruentifer (Ophichthidae) are illustrated and described for the first time. The eggs are distinguished by their large size (>2 mm), large perivitelline space, segmented yolk, one to many oil globules, and pigmentation on late stage embryos. The larvae are distinguished most readily by myomere counts (145–153) and the number (8–9) and location of gut pigment patches.Leptocephalus mucronatus Eigenmann and Kennedy (1902) is synonymized withP. cruentifer.

Development of Young Bluefish (Pomatomus saltatrix) and Distribution of Eggs and Young in Virginian Coastal Waters

Cruises were made off Chesapeake Bight from December 1959 through April 1963 to determine species composition and distribution of fishes spawned on the Continental Shelf. Illustrations of young fish, herein provided, now complete figures from newly hatched larvae to juveniles. Verbal descriptions provide prominent features of young bluefish to aid in identification and osteological development and to compare similar appearing larvae. Bluefish larvae can be distinguished from similar appearing species (Peprilus triacanthus and Urophycis chuss) with which they were taken in Chesapeake Bight by myomere numbers and pigment patterns. Bluefish larvae closely resemble the larval scombrids, Scomber scombrus and S. japonicus, and larval carangids. They may be separated by myomere numbers or relative lengths of the preopercular spine. Continental Shelf waters off the Virginia-North Carolina coast are major spawning grounds of bluefish. Major spawning sites in the Chesapeake Bight were located over the outer half of the shelf between 55 km (30 nautical mi) and 148 km (80 nautical mi) offshore and where water temperatures were 22 C or greater and surface salinities were 31‰ or greater. Minimum temperature at the onset of spawning was 18 C and minimum salinity was 26.6%. Our data show that bluefish spawning commences in June, peaks in July, and continues into August. Peak spawning activity occurred in early evening near sundown (1900-2100 hr). Eggs are thought to be transported south and offshore by prevailing surface currents. Larval bluefish inhabit surface waters and greatest numbers were found near the edge of the Continental Shelf. Juvenile bluefish move inshore during their first growing season. Despite intensive sampling, none were captured in offshore waters. We speculate that with growth young bluefish move to depths above the thermocline. We suspect that the most important single factor in determining the fate of every year class is the circulation of Continental Shelf waters.

Autumn and Winter Occurrence of Decapod Crustaceans in Chesapeake Bight, U.S.a

Autumn and winter collections of decapod crustaceans in Chesapeake Bight suggest that the region may be divided into three zoogeographical zones: The Gulf Stream with its attendant tropical and southern fauna; the environmentally stable outer continental shelf and upper slope where C. irroratus, H. americanus, and M. iris are abundant; and the seasonally variable inner shelf which may support tropical or boreal species at certain seasons, but where the fauna is dominated by Virginian species such as C. irroratus and 0. ocellatus.

Larvae of the Fourspot Flounder, Hippoglossina oblonga (Pisces: Bothidae), from the Chesapeake Bight, Western North Atlantic

Larvae from 4 mm SL to metamorphosis (11-12 mm SL) are illustrated and described. Identification of these larvae is easily made before fin ray and vertebral counts are possible because of their distinctive pigmentation. Pigment differences and possible osteological differences between young of the closely related genera Hippoglossina (H. oblonga) and Paralichthys (P. dentatus, P. lethostigma, and P. albigutta) are discussed.

Age and Growth of the Striped Searobin

Abstract Age, rate of growth, spawning, and weight-length relationship of the striped searobin, Prionotus evolans, were studied. The fish were collected from Chesapeake Bight and Chesapeake Bay during 1966 and 1967. Age was determined from otoliths which had been cross-sectioned, polished, and heated. Age groups 0 to VII were represented in the sample of 803 specimens. Males and females had the same growth rate and weight-length relationship. Growth in length was rapid until the fish reached maturity at age II. Age group II averaged 221 mm fork length. The fish accomplished most annual growth between May and September. Spawning occurred from May through the first part of July.