North Atlantic Sperm Whale, Physeter macrocephalus, strandings on the coastlines of the British Isles and Eastern Canada

Abstract

Sperm Whale stranding records for the British Isles and Eastern Canada were analysed to investigate short and long term stranding trends on either side of the North Atlantic Ocean. Annual stranding events across a ten year period from 1988 to 1997 showed no significant trend with time in either the British Isles or eastern Canada, although stranding events were nearly three times as numerous on the Scottish coast during this period than in any other region. Strandings during this period occurred throughout the year in Scotland, Ireland and eastern Canada, but peaked in the autumn and winter periods. Strandings on the English coast were the least numerous and occurred only in the autumn and winter. Decadal analysis of stranding events for the 20th Century as a whole showed significant exponential increases in Sperm Whale strandings in all regions of the British Isles (except England due to small sample size). Decadal stranding events were fitted to an exponential model which revealed a rate of increase of 14%/yr for the British Isles as a whole, beginning at about 1970. The stranding rate on the Scottish coast, 18%/yr, was twice that for Ireland, 9%/yr, with most of the strandings increase occurring in the offshore Scottish Islands. The time series data for eastern Canada was of insufficient extent to conduct a rigorous decadal analysis. Almost all stranded Sperm Whales on the British and East Canadian coasts have been males. Sperm Whale strandings have been most dense, and have increased fastest, in the offshore Scottish islands of Hebrides, Orkney and Shetland. The data support no firm conclusions but valid hypotheses include increased reporting and anthropogenic effects, which may be acting synergistically. The increase in the British data is too dramatic to have been caused solely by a simple increase in Sperm Whale population size.