The biological characteristics and population dynamics of a sedentary species such as abalone require a much finer scale of spatial management than most other fish species. New Zealand's pāua industry increasingly uses s.11A Fisheries Plans as the vehicle to deliver fine scale management and to ensure the support of harvesters.
The following includes some key management tools and initiatives industry implement in pāua fisheries:
Pāua spawning and recruitment of juveniles into the fishery can be intermittent with most pāua spawning only once or twice in a year. Sometimes, the spawning event can be weak. This is often due to a number of environmental reasons such as marine heatwaves or storm events that destroy juvenile pāua habitat. These events can lead to a gap in a “cohort” or year class of pāua growing through into a fishery and leads to short term overfishing due to the loss of numbers growing through any particular year. Although these effects are short term, the Government's management response of a long term TACC reduction is typically not agile enough for pāua fisheries. Instead, pāua quota owners collectively and voluntarily reduce their catch, by way of “shelving” some of their annual catch entitlement (ACE). This is also a response the pāua industry use when the government close areas of the coast to fishing , in order to mitigate the impact of displaced catch on the wider fishery. Shelving of ACE is also used to increase biomass for a number of non-sustainability reasons.
HARVEST CONTROL RULES
A Harvest Control Rule (HCR) is a way of varying catch on an annual basis in response to data collected from the fishery. The use of HCRs is well established in the rock lobster fishery here in New Zealand and in some Australian abalone fisheries. HCRs are regarded as best practice management internationally, and are used widely used in a number of fisheries, for example in Iceland. The HCR is developed by using a fisheries population model which takes available research and data and compares it to a series of agreed trigger points. The trigger points initiate a tiered management response. For example, if the model pointed to a reduction in biomass to a certain level over a period of time at current catch levels, then a shelving of catch would be triggered for the following year. PIC is interested in such an approach being agreed to by Fisheries New Zealand as a way of managing all pāua fisheries on an annual basis as an improvement on the current regime.
CATCH SPREAD & CAP
Pāua fisheries populations are not homogenous. They are made up of large numbers of sub populations. The health of the fishery is dependent on the health of these smaller populations which do not interact much. There is a well-recognised problem with abalone populations called serial depletion which is a feature of this type of population structure. Serial depletion occurs when a sub population, for example a group of pāua on a particular reef system, is overfished to the point that recruitment failures occur. Fishers then move on to the next available subpopulation and overfish that, and so on. The domino effect of subpopulation failures eventually leads to the weakening of the whole fishery. To avoid this phenomenon, professional pāua harvesters use a catch spread and catch capping arrangement in some Quota Management Areas (QMA). This means that estimates are made of the amount of catch a subpopulation can support and the catch is capped at that. Once harvesters have caught the agreed catch cap for an area it is closed to commercial harvesting until the following fishing year. To help harvesters observe the catch limits each PauaMAC runs an electronic “dashboard" system which displays total catch to date from an area and an alert when the cap is reached.
VARIABLE HARVEST SIZE
In New Zealand, the Minimum Legal Size (MLS) for taking pāua is 125mm across the country. Research indicates that this "one size fits all" measure does not work well for all pāua fisheries. For example, some pāua fisheries are in areas where environmental conditions cause pāua to grow more slowly - a lack of seaweed and kelp for example. Pāua in much of the North Island are one such example of a population that seldom reach 125mm due to environmental factors. By contrast, there are also areas of fast pāua growth where pāua grow so quickly that they only have a year or two of spawning before they reach 125mm. Fiordland, Cook Strait, Kaikoura and Stewart Island are notable faster growth areas. The Pāua Industry Council encourage divers to adopt a "best practice" policy for harvesting. That is: adult pāua should not be available to harvest until they have had at least three spawning seasons to contribute to the population. While larger fish may produce more eggs per recruit, the key feature of pāua fisheries is that it is the available numbers of adults living in aggregations which determine recruitment success. So, it is better to have many aggregations of medium sized pāua than a few larger ones. To implement this, the industry has agreed Minimum Harvest Sizes (MHS) which are observed voluntarily by divers, but differ from the MLS which is a legal requirement . On Stewart Island, the industry MHS is now 140mm, and in other areas it varies from 125mm upwards depending on local conditions.
Sometimes there is the need to help increase local populations of pāua. They may be areas which have been overfished, or have been come under stress from other environmental factors such as warming oceans. A recent example us the loss of pāua population after a magnitude 7.8 earthquake hit the coast of Kaikoura in 2016 earthquake. Enhancement techniques were required to rebuild the population. Enhancement techniques include: • Reseeding by out-planting hatchery-reared juvenile (10mm – 20mm) pāua to the wild • Reseeding by release of pre-settlement larvae into the wild • Translocation of “stunted“ pāua from slow growth/limited adult size areas to fast growth, big fish areas • Translocation of groups of adults to re-establish spawning bank aggregations. Each of these techniques is used depending on the particular issues for the area requiring enhancement and habitat suitability. All such work is covered by a special permit granted by Fisheries New Zealand. This permit is also required to meet strict biosecurity protocols and includes close consultation with iwi. The cost is met by quota owners, there is normally no government funding provided.
MAINTAINING HIGH BIOMASS
Fisheries New Zealand's default management target for a pāua population is 40 percent B0 (biomass), this means a fish stock should be not fished below a level of 40 percent of the fish stock which would exist if there was no fishing. The pāua industry favours a higher target level. PIC believes that a higher biomass than the default target provides a better buffer against the unexpected to ensure long term sustainability. As an example, in 2018 the National Institute of Water and Atmospheric science (NIWA) estimated the pāua biomass on Stewart Island to be 48 percent B0 and likely to increase.
Normally headlands and high energy reef systems provide the water movement, aeration and food availability which allow pāua to grow at a faster rate. The fastest growing areas will allow pāua to grow to the minimum legal size within four to five years, but in slow growing areas the pāua may never reach this size. Translocation involves the moving of pāua from slow growing areas to areas that have a faster growth rate. This operation involves the removal of pāua from the reef, transportation to the new site and hand placement of the pāua onto a reef. Translocated pāua are then left alone in aggregations to not only increase in size in the better growing conditions at the new site, but more importantly to act as spawning banks which contribute to increasing local abundance over time. This has not been done on a large commercial scale in any of the pāua fisheries but it is a management tool that has been employed overseas and is being researched for use in New Zealand.
Catch and effort data (CPUE) is recorded by each commercial pāua harvester. This data (along with other data sets) are utilised in the stock modelling process where a highly sophisticated computer programme models the fishery and predicts what will happen to it in the future. There is a problem however, in that the fishing is happening on a very fine scale (i.e. in one breath you can cover approximately 10 square meters), the data is being recorded on a larger scale (i.e. the total time a diver was in the water during the day and the total number of kilograms the diver caught during the day) and the model is operating on an even larger scale (i.e. it looks at the entire Quota Management Area). The model then produces assumptions / reports and fisheries managers make decisions based on a QMA scale. Pāua fisheries are extremely variable and pāua populations can change in very short distances along the coast. As such, data needs to be recorded at a very fine scale and the computer modelling system must operate on a similar scale so that fisheries management decisions can be made on an equivalent scale. Ultimately, this could result in each pāua bed being managed individually but more realistically, each QMA would be broken down into similar stratum and managed at this level. The pāua industry embarked on a project that saw harvesting crews equipped with GPS data loggers that record CPUE (catch per unit effort) data plus the exact location harvesters are working at. This is the first step in having data at the same scale as the fishing effort and the ability to manage pāua fisheries at a scale appropriate to the fishing effort. If pāua fisheries are managed on a finer scale, there will be far greater chance of maximising productivity and utilisation while ensuring sustainability.