Abstract

The migration route of humpback whales in New Zealand waters as indicated by approximately 9,000 sightings is described. North-bound humpbacks pass mainly along the eastern coastlines of New Zealand, plus one group passing through Cook Strait to the western side of the North Island and another passing the western side of Stewart Island and round the south-west corner of the South Island before leaving the coast. South-bound humpbacks pass mainly along the western coast of New Zealand, forming a large aggregation near the south-west corner of the South Island, while others follow the east coast of the North Island as far as East Cape, but few occur elsewhere along the eastern coastlines or pass through Cook Strait. Seasonal variation in commencing dates, duration of migration, tune of peak and the periods taken by equivalent proportions of the humpback groups are described for 36 seasons in Cook Strait, three at Whangamumu and four at Centre Island. The rate of migration, times of arrival, peak concentration and latitudinal spread of the migrating stock, at phases of the passage from Antarctic to tropical waters and return, are calculated and discussed.

Of a number of environmental factors discussed as possible modifiers of the route followed by humpbacks in New Zealand coastal waters, the most important appears to be the orientation of coastline in relation to the migration route, which shows some evidence of trends towards the north-west and south-east during the northward and southward migration past New Zealand. While small and localised effects are produced by turbidity, tidal streams, and the presence of whalefeed, no consistent modification of the migration route in relation to bottom topography, direction of ocean currents or the hydrological conditions of differing water masses could be demonstrated. The routes followed by migrating humpbacks in all oceanic waters are consistent with the hypothesis that the main requirement of this species is to reach some area of coastal waters in sub-tropical or tropical regions for normal breeding behaviour, whether near continental shores or small islands. Because of the geographical position of continental land masses and islands in relation to all the oceanic areas, the fulfilling of the above requirement should result in migration routes and segregated populations distributed in almost exactly the oceanic areas in which humpbacks are known to occur.