The humpback whale off The Coast of Ecuador, population parameters and behavior

Abstract

Between 1991 and 1997 the southeastern Pacific humpback whale (Megaptera novaeangliae) stock was studied off the central part of Ecuador (0124.S, 8055.W) during the breeding season (June-September). For this purpose, surveys were carried out onboard whale-watching boats at two different sites: Puerto López and Puerto Cayo. Some population parameters such as distribution, group structure, population size, calving rate and behavior were evaluated. The first whales arrived by the end of May, they peaked in July and most of them had left the area by the end of September. Along the Puerto López route, groups were significantly larger (P<0.01) but whales were significantly less abundant (P<0.01) than Puerto Cayo.s. GPS-positioned sightings showed that whales presented a clumped distribution with concentrations at specific sites along both surveyed routes. Analyses of group composition suggest a type of age/sex-class segregation inside the study area. Around sites such as La Plata Island and the Bajo de Cantagallo groups were composed mainly of adult and subadult animals. In contrast, nearby Puerto Cayo groups were composed mainly of mothers with calves and solitary individuals. Groups changed at least one member every 257 minutes on the average, but no change in membership was noticed when a mother-calf pair was present. Most calves were recorded from the second half of August onward and showed a preference for shallow waters with 20m or less in depth. The crude birth rate average obtained (0.039) is considered underestimated. A low resighting rate of photo-identified individuals indicates both a low residence level and a poor degree of fidelity to the study site. The size of the stock was estimated in 1996 to be 1,922 whales (95% C.I. 77-3,367).