Abstract
There is limited information on the post-whaling spatiotemporal distribution and habitat preferences of humpback whales (Megaptera novaeangliae) migrating through the Fiordland Marine Area in southwest New Zealand. Data on humpback whale encounters (n=637) were collated from dedicated boat-based surveys for marine mammals in Fiordland between 2008-2022, from tourism trips between 2012-2022 and from a public sightings database between 2005-2022. There were few encounters prior to 2008. Ninety-five percent of visual encounters occurred during the southward migration in the austral spring (September to December). There were significantly higher sighting rates during spring compared to summer for boat-based surveys (p = 0.01) and tourism trips (p = 5.45×10-05). Annual encounter rates were variable between databases. Photo-identification revealed short-term residency and migration route fidelity in a small proportion of individuals. Apparent foraging behaviour was documented in 8.3% of photographed encounters and in 9.3% of encounters recorded during tourism trips. Spatial analyses showed that 61.2% of encounters were on the outer coast, with the remainder occurring within fjord boundaries. Kernel density estimation showed that the probability of encountering a humpback whale was highest off the entrance to Doubtful Sound/Patea, around the northwestern coastline of Taumoana/Five Fingers Peninsula and in the outer part of Tamatea/Dusky Sound. Analysis of passive acoustic data from a hydrophone deployed in Tamatea/Dusky Sound between 20th February – 31st December 2022 showed that humpback whale acoustic signals were detectable in all months bar February, indicating that hydrophones deployed inside a fjord entrance are likely able to detect humpback whales on the outer coast. Detection rates were highest during June (p = 3.59×10-4), coinciding with the northward migration period. Overall, acoustic detections were bimodal, with peaks in detections reflective of the north- and southward migration periods. Binomial generalised additive models were used to describe associations with abiotic habitat variables for humpback whales on the outer coast and inside the fjords; the models described 10-12.6% and 27.3-34.6% of deviance respectively. Humpback whale presence was significantly correlated with depth and mixed layer depth inside the fjords, and with slow tidal current on the outer coast. All of the significant habitat associations may be indicators of productivity, and thus of foraging, but may also be linked to resting. Future research should investigate the importance of the Fiordland Marine Area as a migratory stopover for humpback whales during the southbound migration period.