An abundance estimate for humpback whales Megaptera novaeangliae breeding around Boa Vista, Cape Verde Islands

Abstract

The abundance of humpback whales occurring around Boa Vista, Cape Verde Islands, was estimated by mark-recapture modelling. Photographs of markings on tail flukes of individual whales were collected during the breeding season. Sighting histories were constructed for each individual and an abundance of 171 animals was estimated using a Jolly-Seber mark-recapture model. Correcting for known biases arising due to sex-specific behaviour and temporary emigration insofar as possible, an estimate of 260 whales was obtained. This is significantly higher than the previous estimate of 99 humpback whales from this region. Due to limited survey effort it is not known how representative the study area is of the entire Cape Verde archipelago and this estimate may be considered to be biased low and serves as a minimum estimate. The high recapture probability (0.37) coupled with the low abundance is consistent with a small local population. The low survival rate (0.86) suggests possible emigration and further studies are needed to assess connectivity between humpback whales breeding in Cape Verde and other breeding locations. The amount of exchange between groups of whales breeding in Cape Verde and adjacent areas remains unknown. It is unclear whether the abundance estimate herein applies to part of an isolated population or part of a larger and continuous one.