Hawaiʻi Island spinner surveys - Phase 1

Written by Claire Lacey

To anyone who has spent as much time reading papers about Hawaiian spinner dolphins as I have, the leeward (west) side of Hawaiʻi Island is almost legendary. It's where a very large amount of what we know about these animals was researched and discovered - and it's somewhere I've been itching to visit since I first started this project. Now our Oʻahu fieldwork is completed, my opportunity to visit the fabled Hawaiʻi Island resting bays is finally here.

Fieldwork days start early - 0530 sunrise over Mauna Loa

From a weather and conditions perspective, this is a dream place to work. Mauna Loa - the worlds largest active volcano - comprises over half of the island and provides a fantastic wind break from the prevailing trade winds. This means that west coast sea conditions are very often incredibly calm. This is invaluable for a project such as ours, which relies on conducting surveys in good, calm sea conditions, so that we maximize our chances of seeing animals. In addition, the water gets very deep very quickly, which in turn means that species which prefer deeper water - like short finned pilot whales, sperm whales, beaked whales and others, can be found much closer to the coast than is the case in other places - even other Hawaiian islands.

For spinner dolphins, which like sheltered water to rest in during the day, the coastline provides numerous bays with very calm conditions

Short-finned pilot whale surfacing in beautiful sea conditions - taken under NOAA research permit number 21476

The Hawaiʻi Island boat fieldwork will be split into two main phases, the first took place in June 2022, and the second will take place later in the summer. The work follows a similar pattern to that carried out on Oʻahu (see blog posts here), with the survey area being split into inshore (coast to 1.5km) and offshore (1.5 to 5km) survey strata, and surveyed using pre-designed zig-zag survey lines which ensure we cover the whole area equally. Although we are only doing the west coast of Hawaiʻi island, the coastline is long, with the total distance being almost as much as the full circumference of Oʻahu.

The first phase of the work brought us encounters with seven different species of cetacean - spinner dolphins, spotted dolphins, bottlenose dolphins, rough-toothed dolphins (see photo below), short-finned pilot whales, a sperm whale and two dwarf sperm whales. Whilst some of these (spinner, spotted and bottlenose dolphins) have been regularly recorded during our Oʻahu work, the others are primarily deep water species which we haven't recorded prior to coming here.

Rough toothed dolphins are a deeper water species, and have a very distinctive head shape, which allows them to be pretty easy to identify at sea. Image taken under NOAA research permit 21476.

The great conditions meant a very productive few weeks - we covered a lot of ground (almost 4000km) and had 23 encounters with spinner dolphins, each resulting in a trove of images which we can use for photo identification, as well as data for the line transect surveys (see Counting dolphins for more info on these techniques).

This map shows where the different species were seen, along with some example tracklines so showing the type of survey coverage we are able to achieve

Phase 2 of the project kicks off mid August - keep an eye on our spinner dolphin Facebook page nearer the time for daily field updates.