Research Document - 2001/086
Trends in prevalence of Bitter Crab Disease (Hematodinium spp.) in snow crab (Chionecetes opilio) at Newfoundland and Labrado
By E. G. Dawe, H. J. Drew, and R. T. Warren
Abstract
This paper describes the spatial distribution and prevalence of Bitter Crab Disease (BCD) in snow crab throughout the Newfoundland and southern Labrador Continental Shelf (NAFO Divisions 2J3KLNO) during 1996-2000. The disease, caused by hemo-parasitic infection by a dinoflagellate of the genus Hematodinium, occurs predominately in recently-molted (new-shelled) crabs of both sexes and is fatal to the snow crab host. Estimation of prevalence of this parasitism was based on macroscopic identification of chronic cases during annual fall bottom trawl surveys. BCD was overall most prevalent within the center of the broad snow crab distribution (Div. 3K) and was rare in southern-most areas of the Grand Bank (Div. 3NO). Spatial and annual changes in both distribution and prevalence of BCD were considerable. Prevalence was highest in mature females and in intermediate-sized males, but there was annual and spatial variation in size ranges most affected. Inverse relationships were apparent between catch rates and prevalence of BCD, suggesting that this parasitism may represent a substantial source of natural mortality. There is considerable uncertainty regarding the extent to which observations from the trawl-caught samples represent true prevalence in the wild.
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