A step in the right direction – new minimum legal size for Kaikōura pāua

In late September the Minister of Fisheries announced new management settings for PAU3A – the Kaikoura pāua fisheries.

Alongside increased catch allowances for all sectors, Minister Jones announced that there would be a new minimum legal size (MLS) of 130mm for pāua for the fishery affected by the November 2016 earthquake related emergency fisheries closure. This is the coastal area from Marfell’s Beach (PAU7) in the north to the Conway River (PAU3A) in the south. This is the first time there has ever been a regulated increase in MLS for a significant part of a fishery and it is something we strongly advocated for.

Minimum legal size is one of the most widely used tools in fisheries management in NZ and internationally. The primary purpose of setting a MLS is to allow for the protection of immature animals and a minimum proportion of spawning biomass. In other words, MLS enables animals to reach maturity and spawn for a number of years to sustain the fishery before they can be harvested and removed from the population. The higher the MLS, the bigger the proportion of the spawning biomass is protected.

Appropriate MLS setting is highly dependent on the biological characteristics of the specific population, in particular growth rates and length at maturity. It is widely documented that our pāua demonstrate demographic variability in these traits around different regions – very generally, they grow faster and to larger maximum sizes in the cooler waters of the south and they grow slower and to smaller maximum sizes in the north. It has been recognised in the scientific literature for more than 40 years that “regionally specific minimum legal size limits determined on the basis of local growth parameters, would be necessary to obtain the best yield per recruit from the nationwide fishery” (Sainsbury, 1982). What this means in practice is that having one MLS of 125mm for the whole country (with the one exception in Taranaki) is much too simplistic. It has also meant that a number of our pāua fisheries have been caught at too small a size for a long time.

In the commercial pāua fisheries the need for harvesting at more biologically appropriate harvest sizes has been recognised for a long time. Commercial divers harvest at variable sizes larger than the MLS across different regions. For example the commercial size is 145mm on the East Coast of Marlborough (PAU7) and has been set to range between 130mm and 135mm along the Kaikōura coast (PAU3A). We have recently commissioned independent analyses (using a Spawning Potential Ratio approach) from extensive survey data along this part of the coast that confirm the recommended MLS for this part of the fishery should be at least 130mm to sustain the fishery long term.

It is therefore very encouraging to see that Fisheries New Zealand has taken a step in the right direction in setting the MLS in this region at a size that is more biologically appropriate. This is particularly important in this region which underwent catastrophic pāua population mortality as a result of the Kaikōura earthquake. Increasing the MLS means that a higher proportion of the spawning biomass is protected to spawn and sustain future populations. It also provides extra insurance against serial depletion of localised populations which has already been shown to be occurring in locations that are very easily accessible to recreational divers.

One of the main arguments presented against increasing the MLS was that it would increase incidental mortality as more undersized pāua would be returned to the water and potentially die, as divers adjust to the larger size. While a relatively minor cut can be potentially lethal to pāua, the reality is that incidental mortality is reasonably constant in pāua fisheries, regardless of the MLS. That has been our long experience in commercial fisheries. You get a consistent “size band” of return to sea fish. The band just shifts up or down depending on harvest size. Post harvest mortality of returned undersized pāua is, for example, almost certainly still an issue in the Taranaki pāua fishery with its reduced MLS of 85mm. In fact, as smaller pāua are more likely to be susceptible to incidental mortality, increasing the MLS is actually likely to reduce it because larger pāua are stronger and more physically resilient. A more helpful argument is simply to focus effort and persuasion into educating harvesters in responsible harvesting technique and how to return undersized to the reef so they will survive.

Another primary issue with changing the MLS (as is the case with any change to management settings) is the challenge it presents to fisheries enforcement. This is a real consideration, but there are examples of how this has been successfully managed with different species around the country without major difficulty. In Kaikōura there is already a different size being enforced successfully in the Oaro-Hamuri Taiāpure of 135mm. Whatever the arguments are against we strongly believe that the size should be set on what is biologically appropriate for the fishery as the overall sustainability of the fishery should always outweigh other considerations.

While the details of the recreational pāua season have not been determined yet for PAU3A, divers should prepare themselves to have the right tools and measuring devices for when it opens. A simple way to do this is to just cut a 5mm notch out of the end of your 125mm Fisheries New Zealand pāua tool. Another great option is the pāua and measuring tool designed by Ocean Hunter which has increments of 130 to 145mm (https://www.oceanhunter. co.nz/shop/products/knives-measures-tools/ultimate-tool.html).

Finally, taking pāua at this larger size means that you will get a pretty useful increase in the meat-weight you get for the barbeque for the numbers taken. Which has to be a plus!