The spatial and temporal patterns of distribution in Hector’s dolphins off Kaikōura, South Island New Zealand, over a time period spanning a catastrophic natural event

Coastal cetaceans are often discontinuously distributed through their range and face threats from anthropogenic activities in the nearshore environment. Long-term studies of coastal dolphin distribution and habitat use at local scales, in addition to the effects of natural catastrophes, have important implications for species management and marine spatial planning. The Hector’s dolphin (Cephalorhynchus hectori hectori) is a small delphinid endemic to the coastal waters of South Island New Zealand and exhibits high levels of geographic and genetic population structure. In November 2016, a 7.8 Mw earthquake struck the Kaikōura district, causing major disruption to the coastal environment. Sightings of Hector’s dolphins from boat-based surveys conducted over an eight-year period (2013 - 2020) spanning the 2016 Kaikōura earthquake, were used to analyse spatio-temporal variations in patterns of distribution during the austral summer using Generalized Linear Models. Species distribution models were then fitted using Generalised Additive Models to analyse environmental covariates of distribution over the same time period. This study demonstrates that Hector’s dolphins along the Kaikōura coastline have a patchy distribution with distinct areas of high occurrence at Haumuri Bluffs and the Hapuku River mouth, situated between areas of relatively low use. Recent patterns of distribution were similar to those observed before the Kaikōura earthquake, indicating long-term consistency in habitat use over an 8-year period. Important environmental predictors of Hector’s dolphin distribution were water depth, sea surface temperature, percentage sand in bottom substrate, and distance to river mouth. The quantification of local distribution patterns and environmental characteristics of important areas of habitat are pertinent for the management of Hector’s dolphins along the Kaikōura coastline and provide important insights into the resilience of local populations to habitat disturbance events.