Ecosystem changes and the effects on capelin (Mallotus villosus), a major forage species

Capelin (Mallotus villosus), an important forage and commercial fish in the Northwest Atlantic, has exhibited dramatic changes in its biology during t he 1990s, coincident with extreme oceanographic conditions and the collapse of major groundfish stocks. Commercial exploitation has not been a serious factor influencing the population biology of capelin in the area. The over all consumption of capelin has declined as predator stock abundances have c hanged. Data on plankton are sparse, but there appears to have been a decli ne in zooplankton abundance during the 1990s, and at the same time, a phyto plankton index increased. The impact of the changes in the physical environ ment has been the subject of previous studies and these are reviewed. The r elative impacts of four factors, commercial exploitation, predation, food a vailability, and the physical environment, on the changes in capelin biolog y are discussed in the context of capelin as a single species and in the co ntext of the ecosystem. The overall patterns suggest the existence of a "tr ophic cascade" within the distributional range of capelin in the Northwest Atlantic during the 1990s primarily driven by declines in major finfish pre dators.