Genetic identity and ecology of Bryde's whales in the Hauraki Gulf, New Zealand

Abstract

Little long-term research has been conducted in the Hauraki Gulf on Bryde’s whales; the least studied baleen whale. This thesis investigates this population using photoidentification and sighting records obtained from boat-based opportunistic surveys and genetic analyses of samples from living and `stranded’ whales. Samples from `stranded’ Bryde’s whales have been collected since 1994 from the North Island of New Zealand. In addition, biopsy samples were collected from whales in the Hauraki Gulf. Fifty-two samples from `stranded’ and biopsied Bryde’s whales identified 49 unique individuals using 12 polymorphic microsatellites. The sex ratio for both sample collection types were equal with 22 males : 23 females (the sex of four could not be determined). MtDNA D-loop analysis (~800 bp) identified the samples as being consistent with Balaenoptera brydei with 11 haplotypes defined by 16 variable sites. Comparisons with published sequences (373 bp) revealed three shared haplotypes between the North Pacific and Indian Oceans. However, an AMOVA (FST and ΦST) showed high levels of differentiation between these oceans, likely resulting from ancestral gene flow. Between March 2001 and February 2006, 1,102 boat-based surveys were conducted during which there were 1,059 sightings over 521 days of Bryde’s whales (including two birth-length calves) in the Gulf. Since whales with calves, were observed during all months this suggests that the Hauraki Gulf is an important area for breeding whales. The seasonal change in `trip encounter rate’ indicated that some whales leave the Gulf for part of the year. Whales in the Gulf were observed in shallower (12.1 to 59.8 m) and cooler (12 to 24.5oC) water than has generally been reported elsewhere. Balaenoptera brydei corresponds to the form described in the offshore waters of the western North Pacific. In contrast, their habitat use in the Hauraki Gulf was more consistent with the `inshore’ form from the coasts off South Africa.