detour into cleaner water, and there is some evidence that this may be the reason for humpbacks avoiding central Foveaux Strait, but there is no evidence that it accounts for changes in course along any other part of the New Zealand coast. The presence of whalefeed is greatest in New Zealand waters during the summer months, and at that time south-bound humpbacks appear to deviate into such cul-de-sacs as Hauraki Gulf providing feed is present. They sometimes linger in an area for days at a time in these circumstances and there is some evidence that a small number of humpbacks remain in New Zealand waters possibly feeding on Munida or other shoaling organisms instead of completing the southward migration to Antarctic waters. In spite of this there is no evidence that the main southward pathway is determined by the presence or absence of whalefeed.

The main factor modifying the coastal migration route appears to be the orientation of the New Zealand land mass across the humpbacks' migration route, which shows some tendency to be in a north-westerly or south-westerly direction rather than due north and south in New Zealand waters. If these are the true directions followed, then the northward route along the east coast of New Zealand is explicable, including the tendency to follow the coast between East Cape and North Cape, while large sectors of western New Zealand are avoided. Similarly a return approach from the north-west towards the south-east would be modified by the orientation of the land to produce a course similar to that actually found along most of northern and western New Zealand.

The orientation of New Zealand in relation to the humpback migration routes may also be the main factor in producing the apparent increase in numbers as a cumulative effect near shore from south to north along the east coast of New Zealand during the northward migration and from north to south along the west coast during the southward migration. Some groups of humpbacks from the north-bound stocks which move up the east coast, depart from this stock to go through Cook Strait, and others probably depart from the vicinity of East Cape, so the cumulative effect is partially masked along northern New Zealand. South-bound whales encountering any part of the west coast of New Zealand are deflected to the south-west by the trend of the coastline down as far as Puysegur Point. As very few leave this group to pass through Cook Strait or from any other point until the south-west corner of New Zealand is reached, the aggregations in the latter area probably represent nearly all the humpbacks which encounter any portion of the west coast of New Zealand. These possibly include many of the humpbacks which travelled along the east coast of New Zealand when north-bound, and the great relative size of the aggregation at the south-west corner of New Zealand suggests that it may also include humpbacks which travelled north by some route other than close to the New Zealand coast.