By Otago Marine Science 05/06/2019

Professor Steve Dawson, Professor Liz Slooten, Associate Professor Bruce Robertson

The Department of Conservation (DOC) has downgraded the threat status of the New Zealand sea lion and New Zealand (Hector’s) dolphin. NZ sea lion has changed from “Nationally Critical” (the same category as the kākāpō) to “Nationally Vulnerable” based on “actual improvement”.

The problem is, the available data do not support any actual improvement in sea lion numbers. Indeed, the graph in DOC’s publication (Baker et al. 2019) shows the decline is ongoing. Plus, across all breeding locations in 2019, there was a decline in the number of sea lion pups born, which is not what one would expect for a species showing “actual improvement”. The question must be asked then, how a species’ threat classification can improve when the data shows the opposite.

New Zealand sea lions, Liz Slooten, Zoology Department, Otago University.

The answer lies in the selective use of the precious available data on sea lion pup numbers. This has the effect of reducing the sea lion decline from 40% to 29%. DOC have ignored the sea lion pups born in 1998, stating that this number is “negatively biased” (because there was no pup count for Campbell Island). Importantly, the pup count for the Auckland Islands, where the vast majority of sea lions were born back in 1998, has been used in sea lion management for two decades. Removing the 1998 pup count has the effect of reducing the decline in sea lion numbers, thereby supporting the NZ government’s narrative that the sea lion population is now stable.

It’s worth noting that under the rules of the NZ Threat Classification Scheme, a 29% decline places the NZ sea lion in the even lower threat category of “At Risk – Declining”. Despite this, DOC invokes a “precautionary approach” to round the decline up to 30%, thereby giving the species it new threat category of “Nationally Vulnerable”.

It is very concerning that NZ species can be bumped between threat categories by what effectively appears to be selective use of the available information (Collins et al. 2016, Meyer et al. 2015, 2017, Robertson 2015). The NZ sea lion still has a declining trend that has not been stopped via government management. While genetic data suggest that NZ sea lions historically numbered up to 68,000 individuals, DOC appears to be satisfied with a sea lion population numbering around a tenth its original size.

Hector’s dolphin, Steve Dawson, Marine Science Department, Otago University.

The proposed downlisting of NZ (Hector’s) dolphin from “Nationally Endangered” to “Nationally Vulnerable” is similarly flawed. The most recent abundance estimates indicate declines everywhere except the east coast of the South Island. For example, we have lost almost a thousand Hector’s dolphins from the west coast of the South Island since 2001. This is exactly the decline predicted by published risk analyses, which indicated that the west coast population would continue to decline due to continued overlap with gillnet and trawl fisheries (Slooten 2013, Slooten and Dawson 2010, 2016).

The population trend for the North Island subspecies, Maui dolphin, indicates continued decline. The only area where the most recent population estimate is higher than the previous one is the east coast of the South Island, where the latest estimate is a surprising five times higher than the previous one. This is partly explained by the fact that the most recent survey went much further offshore, but much of the apparent increase appears to be the result of unresolved problems with the field methods and data analysis. These problems have been pointed out in several peer reviews since 2014 (e.g. IWC 2016) and brushed under the carpet by MPI, who funded the last survey.

More importantly, the new surveys show that the overlap between NZ dolphins and fishing is much greater than previously thought, increasing entanglement risk. NIWA’s 2008 estimate of dolphin deaths in fishing gear was 110-150 NZ dolphins per year. In 2008, the NIWA and fishing industry team assumed that 50% of gillnet fishing overlaps with NZ dolphins. We now know that 50% was far too low. As the DOC report proposing to downlist NZ dolphins points out (Baker et al. 2019), the higher population estimate does not indicate an actual improvement in their conservation status. The report mentions that published estimates of population decline are different from unpublished calculations by NIWA (under contract to MPI) but fails to mention that peer reviews of the NIWA work have been highly critical of it (e.g. Taylor et al. 2018).

The assessment process does not consider whether a species is found only in NZ, leading to some bizarre outcomes. The “Nationally Critical” list consists of Maui dolphin, Bryde’s whale, southern elephant seal and orca. Maui dolphin, at 57 individuals (1 year and older; Cooke et al. 2019) is the only one that belongs on this list. The IUCN also list Maui dolphin as Critically Endangered, the second most endangered small cetacean after the Mexican vaquita porpoise which is down to 10-20 individuals. Vaquita and Maui dolphin are literally teetering on the brink of extinction, as are several small populations of Hector’s dolphins.

Bryde’s Whale/istock.

By contrast, the NZ populations of Bryde’s whale, southern elephant seal and orca are part of much larger, worldwide populations. None of these species are listed as Vulnerable or Endangered, let alone Critically Endangered, by the IUCN. Bryde’s whale and southern elephant seal are listed by IUCN as “Least Concern” and orca as “Data Deficient”. Bryde’s whale is found right around the world, at latitudes from New York in the north to Dunedin in the south. Their worldwide population is thought to number around 80,000 and Japan are planning to start whaling this species when they officially leave the International Whaling Commission in July. Southern elephant seal is distributed right around Antarctica, has a population of more than half a million and listed as “stable” by the IUCN. Orca are the most widely distributed of all whales and dolphins, found in every ocean in the world.

We should certainly make every effort to reduce impacts on all marine mammal species in NZ waters. But to suggest that protecting southern elephant seal is a higher priority than reducing impacts on our two endemic marine mammal species is absurd. To put Maui dolphin in the same category as Bryde’s whale, orca and southern elephant seal obscures the very real conservation emergency for Maui dolphins.

The DOC process has a national focus, but to be credible it must reflect the fact that if we lose Maui dolphin, it would be lost globally. In contrast if we lose NZ’s elephant seals, the species would still be (very) safe elsewhere.

The downlisting of NZ sea lion and NZ dolphin says more about the listing criteria used by DOC than it says about the conservation status of our two only endemic marine mammals. Both are seriously threatened by fisheries and urgently need better protection. The fishing industry has been lobbying for many years for both species to be downlisted. To give into that pressure right now shows a lack of commitment to a science-based, precautionary approach to protecting NZ’s own dolphins and sea lions.

Professor Steve Dawson (Marine Science), Professor Liz Slooten (Zoology) and Associate Professor Bruce Robertson (Zoology) are researchers at the University of Otago.