Research Document - 2000/083
Spatial association between cod and capelin: a perspective on the inshore-offshore dichotomy.
By R.L. O'Driscoll, G.A. Rose, J.T. Anderson, and F. Mowbray
Abstract
Northern cod (Gadus morhua) and capelin (Mallotus villosus), their major prey, have both exhibited major changes in spatial distribution during the 1990s. To study the influence of these changes on the predator-prey interaction between cod and capelin, we computed numbers of potential capelin prey surrounding cod predators (potential contact) from spring acoustic survey data. Between 1989 and 1994 the distribution of cod NAFO 2J3KL shifted to the south and east. This distribution shift occurred at the same time as similar changes in capelin spatial distribution, and potential contact between cod and capelin did not decrease in spring surveys from 1991-1994. Since the mid-1990s cod have been concentrated inshore with low densities offshore. Potential contact of remaining cod with capelin is high. High acoustic densities of capelin were observed inshore in spring 1998 and 1999 in Placentia Bay and Trinity Bay close to aggregations of cod. Offshore, acoustic estimates of capelin density and biomass in 1998 and 1999 were low compared to the 1980s. We suggest that cod are unlikely to re-establish offshore areas in 2J3KL unless capelin abundance offshore increases. There have been encouraging signs of a return to a more northerly distribution of capelin off southern Labrador in 1998 and 1999, and we are currently monitoring the response of northern cod to this change
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