On the life history and autecology of North Atlantic rorquals

Abstract

Background and methods: this paper briefly reviews in qualitative terms available information on exploitation, stock development, life history and autecology of North Atlantic rorquals (mainly blue, fin, sei, minke and humpback whales) with special reference to interspecific variations in abundance. Historical catches and information on growth, reproductive rate and food preferences are examined in relation to present stock sizes. Results and conclusions: recent sighting surveys show that the North Atlantic rorquals cannot be regarded as threatened or endangered by exploitation, although some species are depleted locally in some areas. The minke and fin whales are both euryphagic seasonal feeders that prior to exploitation and still today number in the 50,000–100,000 and 100,000–200,000 range, respectively. Their opportunistic feeding habits and choice for vast open ocean breeding areas seem to give rise to relatively large stocks and to their apparent sustenance for high catches. The near stenophagic crustacean feeding blue and sei whales seem on the other hand to have had smaller historical stock levels of well within 20,000 animals. While the sei whale is probably at present in the 10,000–15,000 range, the blue whale is still at a low level, although increasing in some areas, such as off Iceland. The humpback whale seems to be the species that historically occurs in smallest numbers, although the northwestern stock seems to be in a healthy state (increasing by ∼10% per year). The strong recovery of the species in recent decades may be linked with its euryphagous lifestyle. However, the relatively small population size may also be correlated with its dependence on the rather limited coastal zones for breeding.