At the top of the South Island, scientists are learning more about the diets and groupings of the little-studied Hector’s dolphins.
For the first time, scientists have discovered that groups of Hector’s dolphins at the top of the South Island have distinct diets, indicating that there are distinct subpopulations.
This information, which was discovered by scientists working with the Department of Conservation at the University of Auckland, may aid in the monitoring and protection of the endangered dolphins, of which there are probably only a few hundred in the area.
At Queen Charlotte Sound and Cloudy Bay in the Marlborough Sounds, the Hector’s dolphins in Golden Bay do not appear to interact with those on the opposite coast.
“We knew almost nothing about the Hector’s dolphins at the top of the South Island. Small and isolated subpopulations can be more vulnerable to environmental threats, so this is very useful information to have.”
Professor Rochelle Constantine, a co-author of a study.
“We’ve known practically nothing about the Hector’s dolphins at the highest point of the South Island,” says Teacher Rochelle Constantine, a co-creator of a review distributed in the Marine Biology Progress Series. “Little and segregated sub-populations can be more defenseless against ecological dangers, so this is exceptionally valuable data to be aware of.”
Hector’s dolphins, one of the world’s littlest marine dolphins, are found exclusively in Aotearoa, New Zealand. They have markings in gray, white, and black, and their black dorsal fin resembles one of Mickey Mouse’s ears.
Courtney Ogilvy, a Ph.D. student, and her colleagues were able to determine where and what the dolphins were eating by analyzing chemical markers in tissue samples. Based on their distinct diets, it appeared that the groups were staying apart and pursuing distinct prey.
Clear or deep water may be preventing movement between Golden Bay on the west coast and Queen Charlotte Sound and Cloudy Bay on the east coast. Hector’s dolphins prefer clear, deep water to turbid, shallow coastal water.
“There is absolutely, by all accounts, a natural limit that forestalls the development of Hector’s dolphins between the two districts,” says Ogilvy, who is in the School of Organic Sciences.
As part of a genetic monitoring program, she examined 111 skin samples that were collected by the Department of Conservation—Te Papa Atawhai (DOC) and Waipapa Taumata Rau—University of Auckland over the course of 11 years.
Constantine asserts, “We are using genetics to better understand the connections among dolphins across the top of the South Island.” We will be able to better inform actions to support the flourishing of these dolphin populations by combining this with the diet study.”
In the case of Hector’s dolphins, the prey that is represented by carbon and nitrogen isotopes in their tissues is small fish and squid. The synthetic examination doesn’t uncover which definite species a dolphin is eating.
Over 15,000 Hector’s dolphins are thought to make up the entire population.
More information: C Ogilvy et al, Spatial variation in isotope values of Hector’s dolphins from the north coast of the South Island, New Zealand, Marine Ecology Progress Series (2023). DOI: 10.3354/meps14301
