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Some of our iconic marine mammals are threatened with extinction

New Zealanders’ relationship with our marine mammals has changed profoundly during our human history. For example, Europeans and Māori hunted seals and whales around New Zealand in massive numbers until the late 1800s. The last harpooning of a whale by a New Zealand vessel in our waters was in 1964. This was along the Kaikoura coast – now the location of a well-established whale-watching industry. All whales, and other marine mammals, are now totally protected (Hutching & Walrond, 2015).

Today, the main pressures on marine mammals are entanglement in fishing lines and nets, ship strike (when whales are hit by ships or boats), marine pollution, and habitat degradation (eg, from dredging and blasting) (Department of Conservation, nd; Whitehead et al, 2000).

Bycatch from commercial and recreational fishing is the main identified cause of death of Hector’s and Māui dolphins

Data on bycatch of Hector’s and Māui dolphins come from members of the public, fisheries’ observers, and fishers. Along with reports on dolphins washed up dead on beaches or found floating dead at sea, there are reports on dolphins caught during commercial or recreational fishing.

Between 1921 and 2015, entanglement in fishing gear accounted for 71 percent of the 301 Hector’s and Māui dolphin deaths for which a cause of death was determined. Of the 174 deaths where the type of fishing gear was recorded, 86 percent were caused by commercial and recreational set nets.

Bycatch of Hector’s and Māui dolphins has decreased over the last decade. However, limitations to the data mean we cannot estimate the size of this decrease. In addition, numbers of Māui dolphins are now so low that the probability of a dolphin being caught has also diminished.

Hector’s dolphins caught in a recreational set net. Hector’s dolphins are small coastal dolphins at risk of dying from being caught in fishing gear. Their conservation status is nationally endangered. (Photo: Department of Conservation)

For more detail see Environmental indicators Te taiao Aotearoa: Bycatch of protected species: sea lion and fur seal and Bycatch of protected species: Hector’s and Māui dolphins.

Bycatch of New Zealand sea lions and fur seals is decreasing but still a major cause of death

The estimated number of New Zealand sea lions and fur seals injured or killed as commercial bycatch has decreased since the late 1990s. However, we cannot confidently estimate the size of the decrease as there is a large probability of error for estimates for some years.

Our data on New Zealand sea lion bycatch goes back to 1996, when the estimated bycatch was 143 individual sea lions. This decreased to 43 individuals in 2014 (see figure 7). The New Zealand sea lion is classified as nationally critical with a declining population (see Twenty-eight percent of our marine mammal species are threatened with extinction).

Figure 7

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Note: The vertical line that sits on a column is an error bar – the longer the line, the greater the margin of error of the mean (average) number of individuals. Where error lines overlap in any two years, then the data between those years is unlikely to be significantly different.

This graph shows estimated sea lion bycatch between 1996 and 2014. Visit the MfE data service for the full breakdown of the data.

Our data on estimated fur seal bycatch goes back to 1999, when the average estimated bycatch was 1,729 individual fur seals. This decreased to 490 individuals in 2014.

As with seabirds, these decreases are thought to be partly due to increased use of mitigation measures (Ministry for Primary Industries, 2016a). Reliable data on the bycatch of New Zealand sea lions and fur seals from recreational fishing are not available.

Twenty-eight percent of our marine mammal species are threatened with extinction

New Zealand has 29 species and subspecies of resident indigenous marine mammals – species and subspecies that established naturally and breed in New Zealand. Of these, eight (28 percent) are classified as threatened with extinction and nine (31 percent) are not threatened (see Appendix 2: Conservation status of New Zealand’s resident indigenous seabirds, shorebirds, and marine mammals). The status of the remaining 12 species or subspecies (41 percent) cannot be assessed because of lack of information about their distribution and abundance – these are reported as data deficient (see figure 8).

Figure 8

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Note: No marine mammals were classified as at risk – which is a lower threat assessment than threatened.

This graph shows the conservation status of indigenous marine mammals in 2013. Classes graphed include, threatened, at risk, not threatened and data deficient. Visit the MfE data service for the full breakdown of the data.

Of the eight species and subspecies classified as threatened with extinction, five (17 percent) are classified as nationally critical, facing an extremely high risk of extinction in the wild, including the New Zealand sea lion and Māui dolphin, which are endemic to New Zealand.

Before human settlement, the New Zealand sea lion was often found around the coast of New Zealand’s main islands, but is now only rarely seen in Otago, Southland, and Stewart Island. It has a stronghold population of about 12,000 in the subantarctic Auckland Islands (Breen et al, 2010). Since 1996, the population in the Auckland Islands is estimated to have declined by about 25 percent – although the latest population size estimate is for 2009 (Breen et al, 2010; Ministry for Primary Industries, 2016a). Along with bycatch, competition for food from commercial fishing and disease may also play a role in this decline (Robertson & Chilvers, 2011).

The latest survey in 2010/11 estimated that 55 individual Māui dolphin over a year old were left in the wild, making it one of the rarest marine mammals in the world (Ministry for Primary Industries, 2016a).

The conservation status of one marine mammal species, southern right whale, improved between the 2008–11 and 2012–14 assessment periods. This was due to a population increase associated with the slow reestablishment of former wintering grounds around New Zealand. However, southern right whale is still classified as nationally vulnerable (Carroll et al, 2014) and its distribution may be pushed further south as sea temperatures increase over the next century (Torres et al, 2013).

For more detail see Environmental indicators Te taiao Aotearoa: Conservation status of marine mammals and Changes in the conservation status of indigenous marine species.