Humpback whale (Megaptera novaeangliae) occurrence near the Cape Verde Islands, based on American 19th century whaling records

Résumé

American 19th century whalers often passed through the Cape Verde Islands (CVI) during the boreal winter and some of them spent a few weeks or months hunting humpback whales (Megaptera novaeangliae) in the bays and near-shore waters of the archipelago. Logbooks were examined from 26 voyages that involved some humpback whaling at the CVI, and information was obtained from various sources on approximately 77 additional voyages that definitely or probably humpbacked there. Twenty of the logbooks contained 396 records of an estimated 1,105 humpback whale encounters (catches, strikes and sightings). The largest estimated numbers of encounters and most of the whaling activity were around the islands of Sal, São Vicente and São Nicolau (272, 269 and 229 encounters, respectively). The peak month for humpback whale occurrence in the region appears to have been March (160 records of an estimated 465 whale encounters), with many records from February (110 records of 282 encounters) and April (86 records of 258 encounters). Catch data from the logbooks were combined with commercial data on landings of oil and reported vessel positions to estimate numbers of humpback whales taken in the CVI by the American fleet. Results suggest that American whaling for humpback whales was most intensive in the Cape Verdes during the 1850s and 1860s when at least a few hundred and perhaps more than 500 whales were killed in at least 45 and perhaps more than 80 vessel-seasons. In many respects, the Cape Verdes fishery was similar to that in the West Indies, with cows and calves frequently taken and a similar seasonal peak in whale occurrence. A crude analysis of encounter rates suggests that humpback whale density in the CVI was comparable to that in the major West Indies grounds, a situation that is clearly not the case today.