MEPS 562:193-209 (2016)  -  DOI: https://doi.org/10.3354/meps11951

ABSTRACT: Humpback whales breeding in the southwest Indian Ocean are thought to exhibit population substructure between Madagascar and east Africa. To investigate regional movements, breeding behavior and habitat utilization, 23 whales were satellite-tagged off Madagascar during peak breeding season off the northeast and southwest coasts. Mean tag duration was 24.2 d (3 to 58 d), during which time no individual remained near the immediate tagging sites and several displayed extensive long-range movements. We applied a switching state-space model to estimate behavioral modes of ‘transiting’ (b-mode approaching 1.0) vs. ‘localized’ (b-mode approaching 2.0) movement. A general linear mixed-effects model indicated females were more likely to display transiting behavior than males (mean b-mode females = 1.27, males = 1.65; p = 0.031). Whales tagged in the northeast displayed localized movements off the central east coast, whereas whales tagged in the southwest did so on the southern coasts, with little overlap. Long-distance movements included north-westerly trajectories to eastern Africa and southerly transits to Walters Shoals and the Crozet Islands. Despite these long-range movements in short periods, no whale travelled to the northwest coast of Madagascar, nor to Mozambique or the Mascarene Islands. These results suggest there may be more interchange between Madagascar and central-east Africa than previously thought, and whales off east and west Madagascar may not use the same habitat within breeding seasons; important findings for defining sub-population structure and conservation management strategy. Furthermore, male mating strategy may involve more localized searching or displaying, whereas females travel more extensively during the breeding season, observations that are consistent with a large-scale lek mating system.

KEY WORDS: Humpback whales · Satellite telemetry · Madagascar · Breeding behavior · Movement patterns · Population structure