IngentaConnect Ecology and Population Estimates of Indo-Pacific Humpback Dolphin...

Authors: Guissamulo A.; Cockcroft V.G.

Source: Aquatic Mammals, Volume 30, Number 1, 1 January 2004 , pp. 94-102(9)

Publisher: European Association for Aquatic Mammals

Abstract:

The ecology and abundance of humpback dolphins inhabiting Maputo Bay were studied between December 1995 and December 1997 through boat-based surveys and photo-identification mark-recapture analysis. The sighting rate was low, corresponding to 21% of 146 surveys conducted. Estimated group size (mean=14.9 ± SD 7.32 individuals) was the largest reported for the eastern Africa region and did not change significantly with month, season, daylight, or tidal state. The proportion of individually marked adults was high among adults (0.52) and in a dolphin group (0.26). There is evidence for summer influxes of humpback dolphins into eastern Maputo Bay, and there are considerable numbers of apparently transient individuals. Nevertheless, a substantial proportion of humpback dolphins (13.5%) display high site fidelity to eastern Maputo Bay and could be long-term residents. Mark-recapture analysis (Jolly-Seber model) suggests a population size of approximately 105 dolphins, but the precision of the estimate is low (30.5-150.9). Births seem to occur throughout the year, and the birth rate is relatively high (0.11); however, the recruitment rate to six months in eastern Maputo Bay is low (0.05) and the calf mortality (or mortality and emigration) rate is high (0.47). Current conservation issues include primarily fishery interactions and habitat alteration, but the levels of impact on the dolphin population require further assessments.

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Ecology and Population Estimates of Indo-Pacific Humpback Dolphins (Sousachinensis) in Maputo Bay, Mozambique