Research Document - 2004/077

Aspects of the Epidemiology of Bitter Crab Disease (Hematodinium sp.) in Snow Crabs, Chionoecetes opilio from Newfoundland, Canada

By Shields, J.D., Taylor, D.M., Sutton, S.G.,
O'Keefe, P.G., Ings, D.W., Pardy, A.L.

Abstract

The parasitic dinoflagellate Hematodinium sp. causes a condition known as bitter crab disease (BCD) in snow crabs, Chionoecetes opilio, and Tanner crabs, C. bairdi. As the name of the condition implies, crabs infected with BCD are unmarketable due to their bitter flavor. We surveyed the distribution of BCD in three regions within the snow crab fishery of Newfoundland from 1997 to 2003. Over time, the disease has become firmly established in Conception and Bonavista bays and persists at low levels in the Avalon fishing grounds. An epizootic occurred within Bonavista and Conception bays in 1999 and persisted in Conception Bay in 2000 reaching prevalences of over 2% to 9% in trapped and trawled male crabs and from 19% to 26% in trawled and trapped female crabs, respectively. The hydrography of this bay may have contributed to the epizootic as infections were centered within the deeper confines or near the inshore terminus of the bay. Infections were highest in females and small males, i.e., the unfished and pre-recruit portions of the fishery. In a mortality study, all of the overtly infected crabs died and 50% of the experimentally inoculated crabs died. Patterns in the molting cycle and prevalence of infection indicate that transmission occurs during the post-molt condition, and that overt infections probably develop two to four months after infection, lasting three to four months thereafter. Analysis of various abiotic factors uncovered a significant positive association between prevalence, depth and mud/sand substrates; the nature of this relationship was not apparent but may be related to diet or alternate hosts. Lastly, given the startling rise in BCD in snow crabs in Newfoundland, we recommend that fishery management programs employ non-selective gear to monitor for Hematodinium infections in female and juvenile crabs because these under-sampled members of the population may forewarn of impending recruitment declines that might otherwise remain unexplained.

Complete document (PDF, 326 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.