The History of New Zealand/ Aotearoa Dolphins Cephalorhynchus hectori: Abundance and Distribution

Abstract

Hector’s and Māui dolphins (Cephalorhynchus hectori) are endemic dolphins of Aotearoa New Zealand. This thesis documents how C. hectori have changed from being the most common dolphin species seen in New Zealand waters to one of the rarest. The decline of C. hectori has been almost entirely due to bycatch in inshore net fisheries. This collection and analysis of historical information documents and examines observations and the earliest scientific information of C. hectori from the 1800s onwards. Peer reviewed publications, old books and historical media have been accessed, providing general descriptions, information about distribution, habitat use, sightings, strandings, bycatch and pod sizes. Creative components produced as part fulfilment of the MSciComm and documented in this thesis include a music CD, a public awareness campaign and a museum exhibition. Convincing evidence is presented that C. hectori were previously abundant in many places around New Zealand including the wider Cook Strait, Tasman Bay and much of the North Island. Many small subpopulations (hapū) have been removed or reduced to very small population fragments from the Hauraki Gulf, Bay of Islands, Hawkes Bay, Wairarapa, Palliser Bay, Kapiti, Whanganui and Taranaki. Some of these hapū began to be impacted in large numbers from the 1960s onwards. Estuaries, lagoons and rivers were historically much more important foraging areas than they are now. Group sizes used to range in the hundreds and have reduced over time. This important, historical information is critical to a comprehensive analysis of the conservation status of these dolphins. By understanding the patterns of decline, we can know what to expect to see when Hector’s and Māui dolphin hapū are on the path to true recovery. This will require adequate protection from the fishing impacts responsible for their demise.