Status of the Major Oyster Diseases in Virginia 1996 A Summary of the Annual Monitoring Program

L.M. Ragone Calvo
EXECUTIVE SUMMARY ·weather. The winter of 1996 was unusually cold and water temperature was consistently below the long-term average. Water temperatures remained below 5°C for a period of ten weeks, two weeks longer than normal. The spring was also relatively cold while summer temperatures were fairly typical. With the exception of a few weeks in early October and early December, temperatures during October through December were generally above average. Above average rainfalls and atypical
more » ... s and atypical climatic events during 1996, including several winter storms and a hurricane in early September, resulted in record high strearnflows in many of the Chesapeake Bay tributaries. Record high James River strearnflows were recorded in January, September and December. High strearnflows decreased salinities in upper river areas and subsequently had a significant impact on oyster diseases. Haplosporidium nelsoni (MSX). For the first time in four years some abatement of H. nelsoni occurred in the James River Wreck Shoal seed area. Infections acquired in the summer of 1995 were present at a prevalence of 24% in January 1996, however prevalence declined to 0% by May. Infections were absent or rare the remainder of the year. Fall abundances of H. nelsoni in other Virginia tributaries were generally lower than in 1995. Low prevalences of H. nelsoni were observed in the Piankatank River at Burton's Point (4%) and in the Rappahannock River at Parrot Rock (8% ). Prevalences and intensities of H. nelsoni were higher in bayside and seaside eastern shore oysters than in western shore oysters. On the bayside, Haplosporidium nelsoni was present at Byrd Rock (30%) in Pocomoke Sound and in Nasawadox Creek (16%). On the seaside H. nelsoni was present at relatively high prevalences in Bradford Bay (56%), Fishermans Island (36-64%), and in Quinby Channel (20-76%). Moderate and heavy infections were observed in some of these eastern shore areas and it is likely that disease associated oyster mortality occurred. Haplosporidium nelsoni was also abundant in the lower York River. VIMS tray oysters. which were transplanted from Ross Rock to the lower York River site on 1 May 1995, had a high prevalence (52%) of H. nelsoni by 11 July 1995. Prevalence increased to 84% in August and remained between 60-70% for the remainder of the year. Haplosporidium nelsoni contributed to disease-associated mortality in the trays which was nearly 70% by 11 September. Once again, for the fifth consecutive year, H. nelsoni prevalence at VIMS was at a record high level. Perkinsus marinus (Dermo). Our fall survey of Virginia oyster bars indicated that P. marinus was present at all western shore oyster bars. However, the unusually cold winter and
doi:10.21220/v5x438 fatcat:4mbu3etaw5bthnsicwugtm5n4y