Why Hector's Dolphins Are Endangered

One of the world’s smallest and most endangered marine dolphins, the Hector's Dolphin is found only around the coast of New Zealand in isolated subpopulations. The New Zealand Department of Conservation estimates only about 15,000 Hector’s dolphins older than one year are alive today. There is also a subspecies known as the Māui dolphin that is critically endangered with a population of only 54.

On the international level, Hector’s dolphins have been listed as endangered with decreasing numbers since 2000, when a population viability analysis estimated the species would decline by 74% over just three generations. Discover why these dolphins are rapidly disappearing.  

Threats

Hector’s dolphins live only in the shallow coastal waters along the western shores of New Zealand’s North Island. Living so close to land makes the species more susceptible to bycatch, becoming tangled in recreational and commercial gill and trawl nets.

While there is little evidence for large-scale changes in prey abundance thanks to the dolphin’s broad diet—studies have identified at least 29 different taxa in Hector’s dolphin stomachs—other threats include boat strikes, pollution, and disease.

Bycatch

Bycatch in set gillnets is considered to be the most serious threat to Hector's dolphins. Gillnets are especially problematic as they’re made of a thin mesh that dolphins can’t detect underwater.

The number of dolphins killed each year was most recently assessed in 2000 using data from an observer program in a commercial gillnet fishery off Canterbury, New Zealand. Between 2000 and 2006, an average of 110 to 150 dolphins were caught each year nationwide. Likewise, out of all reported Hector’s and Māui dolphin deaths caused by entanglement between 1998 and 2018, 58% had set nets as the gear type involved.

Pollution

Pesticides can reach dolphin habitats through coastal runoff, and metals such as mercury, lead, and cadmium can enter the environment through human activities. These materials don’t break down and can accumulate in dolphins and whales over time.

Crude oil extraction and transportation can also pose a threat to Hector’s dolphins since they’ve been linked to cancers in some marine mammal species. Pollutants found in Hector's dolphin tissues include DDT, PCBs, and dioxin, which have been shown to reduce reproductive output in other marine mammals. However, there isn't much research on the impacts of these pollutants on Hector’s dolphins specifically to determine their threat level.

Like other ocean creatures, Hector’s dolphins can become entangled or otherwise jeopardized by plastic debris, which can impair their ability to catch prey or avoid predation. 

Disease

Hector’s dolphins may also be exposed to a range of diseases through ocean-bound runoff or through contact with other species. Toxoplasmosis, a disease caused by parasites, is a particular threat to both Hector's dolphins and the critically endangered Māui dolphin subspecies.

In one study, over half of the dead Māui and Hector's dolphins examined were infected with the parasite causing toxoplasmosis, while at least two out of the ten Māui dolphins found dead between 2006 and 2013 had died of the disease specifically. Since Cephalorhynchus dolphins are long-lived and slow reproducing compared to other marine mammals, populations have trouble rebounding from any widespread losses.

What We Can Do

Seeing as Hector’s dolphins only occur within a single country’s jurisdictions, much of their conservation outcomes have depended on politics. Currently, the most effective management methods known for Hector’s dolphins are

• removing gillnet and trawl fisheries from their habitat, and
• changing to more sustainable fishing methods that do not interfere with dolphins.

Since the late 1980s, the New Zealand Government has created two protected areas to promote the conservation and sustainable management of these important marine mammals. In 1988, the 1,170 km² Banks Peninsula Marine Mammal Sanctuary was established under the Marine Mammals Protection Act to protect Hector’s dolphins, extending 70 nautical miles alongshore and out to 4 nautical miles offshore. However, its effectiveness has been criticized due to the fact that the dolphins’ offshore habitat extends beyond the protected area, and up to 65% of the dolphins in the area are found outside the protected sanctuary boundaries in the winter months.

In 2003, a second protected area was created off the North Island’s west coast, where gillnets were banned from the shoreline to 4 nautical miles offshore. The country’s department of conservation extended protection in 2008, 2012, and again in 2020 when bycatch numbers remained unsustainable.