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Auckland University science student Wednesday Davis has been looking into gatherings of creatures in the Hauraki Gulf to figure out how they can be best protected.
When out on the water, we often see groups of whales, dolphins, seabirds, and predatory fish foraging together in gatherings known as workups or bust-ups, usually at pretty good fishing spots. Over the last three years, researchers from the University of Auckland have been going out into the Hauraki Gulf searching for these workups to determine who is there, what they are doing and how we can best monitor them to track future ecosystem changes.
Many species rely on others for prey detection, access, and capture. By foraging within workups, predators often gain better access to their prey where it is herded together by underwater predators. For example, white-fronted terns forage with the fish kahawai. The kahawai herd zooplankton up to the surface, making it easier for terns to feed on the zooplankton. These workups are dynamic, patchily distributed, and short-lived. Some predators, like Bryde’s whales, act as terminators, ending the workup by eating almost all of the prey patch in just one lunge.
Dolphins, however, are facilitators. They herd fish into a tight ball at the surface, making an easy meal for seabirds, sharks, manta rays and whales.
Animals that share prey have distinct social networks, allowing us to use their attendance at workups to determine the prey present and the quality of a prey patch. The diet of the species present tells us what prey is present. For example, storm petrels and Bryde’s whales both eat plankton, so the prey is likely to be plankton when they are seen together.
However, when fish eaters and plankton eaters are foraging together, there is prey across various food-chain levels, allowing many species to feed together. These variations in workup attendance can help us understand changes in ecosystem health over time, with attendance reflecting various challenges in finding quality meals.
Recent research by the Marine Mammal Ecology Group at the University of Auckland has found that over the last ten years, Bryde’s whales have shifted their diet from fish to plankton and are now foraging more frequently in plankton-based workups. However, not much is known about workup attendance patterns for other species. Our research is a baseline, allowing us to detect changes over time for other species within the Hauraki Gulf, allowing us to better understand associations and foraging patterns.
To enhance this research, drones (with DOC permits) are being flown above the workups, capturing a birds-eye view, enabling us to understand better the role of subsurface predators such as sharks, manta rays and cetaceans (dolphins and whales) in these workups. Alongside this, we are training artificial intelligence tools to automatically detect predators and their behaviours, enhancing our ability to process footage and extend survey efforts. These novel research approaches can help us better understand these workups and how we can best protect marine megafauna and taonga species in the Hauraki Gulf.
