Target Species

Target species were chosen to represent key elements of the holoplanktonic and icthyoplanktonic assemblages on Georges Bank (Figure 7). The suggested target species include pelagic life stages of cod and haddock, and the holoplanktonic copepods of the genera Calanus finmarchicus and Pseudocalanus (both moultoni and newmanii). These copepods are major prey of the larval fish (Kane, 1984). The population dynamics of these target species will be studied in depth, focussing on those processes discussed earlier (Figure 3).

Other species which are thought to be important in the life cycle of the target species, but are not designated for in depth population dynamics study, include: copepods, (Centropages, Paracalanus, Oithona), chaetognaths (Sagitta elegans), amphipods (Monoculodes edwardsi, Gammaraus annulatus, Themisto gaudichaudi), mysids (Neomysis americana), and euphausiids (Thysanoessa inermis, Meganyctiphanes norvegica). Gelatinous predators of copepods and fish larvae also are suggested for study; these include medusae (Staurophora mertensii, Aglantha digitale, Cyanea capillata) and the ctenophore Pleurobrachia pileus. Non-target species should be studied in relation to their impact on the target species, focussing on such factors as distribution, abundance, and predation rates. Information on these species should be collected collaterally with data on the target species.

Criteria for selecting target species are outlined in the U.S. GLOBEC Initial Science Plan (1991b; pp. 38-39) and in the U.S. GLOBEC Northwest Atlantic Program report (1991c; pp. 12-20). In short, cod and haddock are commercially important species whose population dynamics are known to be sensitive to physical variability including temperature, mixing, and advection (e.g., Buckley and Lough, 1987). In addition, a long historical data record exists for these species and, in the case of cod, there is a current international ICES program (Cod and Climate Change) to study the potential effects of climate change on their population dynamics. The target holoplanktonic species, Calanus and Pseudocalanus, are dominant members of the zooplankton community on Georges Bank during the late winter, spring, and summer when the planktonic stages of cod and haddock are in the water column. Study of the physical and biological factors affecting their population dynamics will provide information on mechanisms of dispersal and recruitment of marine planktonic populations in general as well as on processes controlling food availability to and predation on the target fish species.