An energy budget for northern sand lance, Ammodytes dubius , on Georges Bank, 1977-1986

The northern sand lance, Ammodytes dubius, is a small planktivorous fish, classified as a "ubiquitous shelf species" (Sherman et aI., 1983) and is found offthe northwest Atlantic coast from North Carolina to Greenland (Nizinski et aI., 1990). Sand lance are consumed by many piscivorous marine vertebrates. They have been found in the stomachs of dogfish, Squalus spp. , skates, Raja spp. , Atlantic cod, Gadus morhua, haddock, Melanogrammus aegle/inus, pollock, Pollachius virens, sculpin, Myoxocephalus spp. , Atlantic salmon, Salmo salar, various flatfishes, Paralichthys, Limanda, and Pseudopleuronectes, and other fishes (Scott, 1968; Reay, 1970; Meyer et aI., 1979; Bowman and Michaels, 1981; Winters, 1981), as well as seabirds (Backus and Bourne, 1987). Humpback whales, Megaptera novaeangliae, have also been observed feeding on sand lance (Payne et aI., 1986). Negative correlations have been shown between the abundance of sand lance and right whales, Eubalaena glacialis, and it has been suggested that in the northwestAtlantic these two animals may actually compete for their primary food source, the copepod Calanus finmarchicus (Kenney et aI., 1986; Payne et aI., 1990). Therefore, although the sand lance is not commercially important, as a plankton feeder and an important prey species, it may exert significant influence over the efficiency of energy transfer from primary to higher trophic levels. Georges Bank was chosen as a study area in which dramatic changes in the northern sand lance population might be examined in terms of the consumption and production of fish relative to the production of the region as a whole. This 41,809 km2, 50-m deep plateau (Sherman et aI., 1984) is located off the northeast coast of the United States and is a highly productive fishing ground with high annual primary production (350 g carbon'm-2'y-l) owing to the retention of nutrients (Sherman et aI., 1984; Backus and Bourne, 1987). Because of its commercial significance, Georges Bank has been well studied. Energy budgets have been developed for the entire Bank (Cohen et aI., 1982; Jones, 1984; Sissenwine et aI., 1984) and offer a convenient way to examine the significance of the consumption and production of an individual species within an important area of the Northeast Shelf ecosystem. Individual energy budgets offish have been developed for many species <Edwards et aI. , 1972; Adams, 1976; Kitchell et aI. , 1977; Kitchell and Breck, 1980; Cho et aI. , 1982; Kerr, 1982; Diana, 1983; Durbin and Durbin, 1983; Rice and Cochran, 1984; Kerr and Dickie, 1985; Cui and Wooton, 1989). In this study, the energy budget of the northern sand lance was developed from experiments that measured the following parameters: growth, metabolism, feeding and assimilation efficiency (Larimer, 1992), and reproductive production. These parameters were assembled into an annual energy budget based on the daily activity ofthe fish in the field associated with temperature and food availability. Monthly growth was used to estimate annual ration and the budget was extrapolated to northern sand lance population abundance levels measured on Georges Bank from 1977 to 1986.1 The potential predatory impact of the northern sand lance population on seasonal and annual zooplankton productivity on the bank2 (Sherman et aI., 1987) was examined. Finally, the annual production and consumption by these populations were compared with energy budget model values for Georges Bank.