A prohibition on seabed mining out to 12 nautical miles from the western North Island coastline is among proposed options in public consultation on ways to protect Maui and Hector’s dolphins.

Submissions close on 4 August on a draft threat management plan, updated on Monday, with little or no robust evidence presented on the impacts of seabed mining on the dolphins.

With an estimated 63 Maui dolphins remaining, this Hector’s dolphin subspecies is “classified as nationally critical and face a real threat of extinction”, Fisheries Minister Stuart Nash and Conservation Minister Eugenie Sage said.

Affected ironsands interests would be Trans-Tasman Resources in South Taranaki, with minerals exploration permit 54068, and Ironsands Offshore Mining off North Taranaki, with MEP 55709.

Alleged seabed mining threats

Non-fishing related threats, including seabed mining, are listed in the draft TMP as “injury, disease, disturbance, noise, habitat modification, impacts on prey distribution and abundance, reduced foraging success, displacement, and habitat fragmentation”.

The threat risk assessment also considers the cumulative impacts of multiple threats, including from fishing, and toxoplasmosis, a disease affecting cats and other animals that can kill dolphins.

Seabed mining is characterised as using mechanical/suction dredges on the seafloor to scoop up sediment, and then discharge waste material “into the sea, either at surface, or at depth”.

“The three main components of seabed mining with the potential to affect dolphins are underwater noise, direct seabed disturbance, and the discharge of sediments.”

The draft TMP says underwater noise could affect dolphins’ ability to communicate, sense predators and forage.

Noise, sediment plumes, and altered habitat could cause the dolphin’s prey to change their distribution, affecting the ability of dolphins to find food, according to the draft TMP.

“Collectively these effects, if sufficiently large, may result in the affected area becoming sub-optimal as Hector’s or Māui dolphin habitat, or in extreme cases, lead to partial or full displacement.”

Lack of evidence for government assertions

The Department of Conservation and Fisheries New Zealand concede that, “Apart from theoretical or modelled assessments for individual consent applications (for example, noise production and attenuation), no studies have been undertaken to assess the effects of seabed mining on Hector’s or Māui dolphins.

“No seabed mining has been undertaken in an area where Hector’s or Māui dolphins occur, meaning there has been no opportunity to monitor effects.

“Thus, there is no direct experimental or similar evidence that shows seabed mining adversely affects Hector’s or Māui dolphins.”

Agencies note the difficulty of studying long-lived, slowly-reproducing animals, which may be exposed during their lives to a wide range of impacts, making it challenging to attribute cause.

The above throws into doubt the agencies’ claims with regard to potential detrimental effects of mining upon the dolphins.

That said, the 2015 decision on Chatham Rock Phosphate’s marine consent application to mine phosphorite on the Chatham Rise discussed the potential for seabed mining to adversely affect marine mammals.

Southward extension to the marine mammal sanctuary

An extension of the West Coast North Island Marine Mammal Sanctuary south to Wellington is among proposals for consideration.

The justification for proposing the southward extension of the WCNIMMS as far as Wellington’s south coast relies on anecdotal evidence.

“While there is no evidence of a resident population south of Cape Egmont, public sightings and acoustic detections confirm Hector’s and/or Māui dolphins are infrequently present there, and historical evidence suggests they were likely to have been more abundant in this area in the past.

The risk assessment identified this southern area as a potential transitional area between Hector’s and Māui dolphins and an area of suitable habitat for the dolphins.

Therefore, risk reduction in this southern area may reduce barriers to population connectivity or facilitate recolonisation of previously occupied areas.

-Bernie Napp

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