Consumption of marine resources by seabirds and seals in Crozet and Kerguelen waters: changes in relation to consumer biomass 1962–85

Abstract

The total annual food consumption of the seabird and seal community breeding at lles Kerguelen was estimated to be 1.8×10⁶ t in 1985. This biomass included c. 0.99×10⁶ t (55%) of crustaceans, 0.46×10⁶ t (26%) of myctophid fish, 0.07×10⁶ t (4%) of other fish species, and 0.26×10⁶ t (15%) of squid. During the same year, the mass of prey consumed in Crozet waters was previouly estimated to be 3.1×10⁶ t, the total food consumption in the Indian Ocean area including the two archipelagos thus totalling c. 5×10⁶ t in 1985. Four species of top predators, the king penguin, macaroni penguin, elephant seal, and fur seal, consumed 59% and 56% of the amount of prey eaten in 1985 by the whole community at Kerguelen and Crozet islands, respectively. Between 1962 and 1985, population changes of these four species induced 18 and 41% increases in their food consumption at Kerguelen and Crozet islands. Population changes included a moderate increase in the number of macaroni penguins and a marked rise of king penguin populations. Assuming that the diet of king penguin was similar in 1962 and 1985, its population increase will have required a concomitant increase of 0.6×10⁶ t in the consumption of myctophid fish in Crozet and Kerguelen waters.