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bioRxiv · 10.1101/2020.05.15.098889

Critique of the scientific basis for currently proposed protection options for Hectors and Maui dolphins

Slooten, E.·Dawson, S. M.
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Abstract

New Zealands Ministry for Primary Industries (MPI) developed a risk analysis for Hectors and Maui dolphins, in order to inform protection options being considered by the Ministers of Fisheries and Conservation. Unfortunately, MPIs risk analysis combines several estimates that are biased, and the biases consistently act together to underestimate the level of bycatch and overestimate the species ability to sustain impacts. In essence, the approach uses abundance estimates that are likely biased high, multiplies them by a reproductive rate that has been arbitrarily raised, multiplied by an assumed figure for calf survival, to reach a number of dolphins that would be added each year if the population were to remain stable. From this number, they subtract their estimates of bycatch, which are almost certainly biased low. The remaining number of dolphins is apportioned a cause of death according to autopsy data from 55 Hectors and Maui dolphins found dead on beaches. This is then compared to estimates of what level of takes would be sustainable, calculated using a formula that is not well understood and less conservative than the international standard (PBR, developed by the US National Marine Fisheries Service). This is a poor basis for rational management of an endangered, endemic marine mammal. A key problem with the MPI approach is that its definition of "risk" does not relate to the risk of population decline or extinction, and is inconsistent with the modern understanding of the behaviour of meta-populations. The approach defines risk as the likelihood of capture, which is apportioned to different areas according to fishing effort and the habitat models outputs for dolphin distribution. The protection options are therefore targeted where high densities of dolphins and high fishing effort coincide. Large populations are allocated the highest level of protection, while small populations remain poorly protected. This approach is likely to increase the risk of local extinctions, contractions of dolphin distribution, population fragmentation, loss of genetic variability and result in increased risk to the species as a whole. Many of these points were made by an International Expert Panel in 2018. MPI have failed to provide a list of recommendations from the Expert Panel Report with their responses (if any) to those recommendations. This standard step in scientific practice, following peer review (e.g. response to reviewers comments) has not been followed.

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Slooten, E., Dawson, S. M.. 2020-05-17. Critique of the scientific basis for currently proposed protection options for Hectors and Maui dolphins. https://doi.org/10.1101/2020.05.15.098889

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