a1 Department of Biology and Ocean Sciences Centre, Memorial University, St. John's, Newfoundland, Canada, A1B 3X9
Studies conducted in the 1980s suggested that parasites were useful in distinguishing adjacent populations of Atlantic cod Gadus morhua in the north-western Atlantic. During the mid-1980s, cod populations began to decline, culminating in closure of the fishery in 1992. A marked decrease of cod off the coast of Labrador was coincident with climatic shifts, including a decline of bottom sea temperature, and virtual absence of capelin Mallotus villosus, its main food prey. These changes in some components of the ecosystem were independent of anthropogenic influences. An initial survey of cod parasites in 2000 from coastal Labrador revealed a dramatic decline in abundance of metazoans and also a change in dominance of species of digenetic trematodes compared to 1980–1981. Comparison of metazoan parasites in three other populations of cod inhabiting the Grand (northern and southern) and St. Pierre Banks, where there was no apparent evidence of environmental changes but only commercial over-exploitation, revealed no major alterations in abundance or dominance between 1980–1981 and 2003. The results of this current study suggest that environmental changes in the food web affected the abundance of metazoan parasites only off coastal Labrador but did not influence the use of the parasites to distinguish between cod populations inhabiting the Grand or St. Pierre Banks.
(Accepted March 12 2007)