On the West Greenland sea-life area of the Atlantic salmon

摘要

It is the contention of this present note that the West Greenland salmon fishery at least, and probably the other two as well, have come into existence because the salmon themselves have quite recently shifted their sea-life feeding area in response to marine climatic change. The salmon which now appear in west Greenland waters swim very close to the surface and are taken in surface drift nets. The West Greenland waters have been fished and hunted for some four centuries. ... It is entirely unreasonable to believe that, had the salmon been in these waters during such a period of time, they could have escaped detection and exploitation long since. ... Marine (hydrospheric) climates differ from atmospheric climates in that the response of the living populations associated with marine climate changes is immediate, at least as regards planktonic and nektonic communities: there is clearly a lag in the response of benthonic attached and in-faunal communities. We have abundant evidence of drastic changes in the marine climate of the North Atlantic and Subarctic area, particularly in West Greenland waters, during the past century. The increase in temperature since about 1915, which lasted into the 1940s, and brought the Atlantic cod fishery into existence in that region, is especially well documented .... It may be assumed that one selective advantage in the evolution of salmon migration is the attainment of marine regions of high food production; such regions are not stationary in the long term, or even in the comparatively short term, but are dependent on patterns of nutrient production and advection, which are in turn dependent on the changing pattern of wind and current. ... The patterns of migration, and of breeding area, of many marine animals have changed most significantly in recent decades in association with, but not necessarily directly caused by, change in marine climate .... It is therefore reasonable to search for means of navigation, in terms of information used by the migrants, which have also changed during the same period. Of the means so far considered, only two, those of the electric field and of olfactory information, change rapidly enough to be relevant in the present context. If ocean currents carry their own identifying smells and tastes ... then olfactory information may well be involved, but it is the possibility of the relevance of the electric field that is put forward here. It has been suggested by several workers ... that oceanic electrical information may be used by migrating animals .... The potentials developed by the passage of ocean currents through the earth's magnetic field are proportional to the velocity and transport of the current, and therefore the pattern must change as current velocities change; and changes in transport and velocity are clearly involved in changes in hydrospheric climate .... If electric fields are used in migration of fish, therefore, we should expect the migrational routes and termini to change with the climatic cycle. ... Shifts in the distribution and migration of marine exploitable species are of immense economic and international importance, and underline the urgent necessity for far better understanding of entire processes controlling changes in marine climate.