Growth rates in pāua vary considerably around New Zealand and are influenced by a range of factors such as water temperature, wave exposure, habitat type and food availability. Growth rate data across the fishery is crucial for pāua fisheries management as it is a key input for stock assessment models and a central consideration in guiding decisions on appropriate minimum legal size (MLS) and minimum harvest size (MHS). The Pāua Industry Council, in conjunction with regional PauaMACs, have an ongoing project to collect growth data across all paua Quota Management Areas (QMA). The general aim is to collect growth data from one new site per year in each QMA. Growth data is collected using ‘tag-recapture’ methods. This involves tagging up to 800 pāua in an area of interest with cable tie tags that fit through the front respiratory pore of the pāua. Tags are coloured and have a unique code against which initial length are recorded. Tagged pāua are carefully placed back to where they were taken from and left for approximately one year to grow. After this, recapture surveys are undertaken to find tagged pāua to retrieve length data and calculate annual growth. Generally, a recapture rate of 20 percent of initially tagged pāua is considered good, which is why it takes tagging such a high number initially to recapture enough individuals to get reliable data. This process allows for site specific growth rates of pāua in this area to be calculated and used for future management of the QMA. All work to collect growth data is undertaken under a Special Permit for investigative research from Fisheries New Zealand.

A useful way of monitoring the status of pāua fisheries is to measure and monitor the size of the pāua that are commercially landed. If, over time, shell lengths of pāua landed from a QMA (or statistical area) are decreasing, it is not a good sign and management measures need to be implemented. However, if shell lengths are staying the same or increasing, it is generally an indicator that the fishery is in good shape. Commercially landed shell length data is also an important input for the pāua stock assessment model and is useful in guiding decision making around appropriate MHS within and across QMAs. The Pāua Industry Council (PIC) has run a Fisheries New Zealand Catch Sampling project since 2006, monitor the shells lengths of commercial pāua catches around New Zealand. Until recently, the main way this data has been collected is by requiring harvesters to haphazardly select a bin of pāua (30kg, or approximately 100 pāua) from the day’s catch for measuring. When this bin reaches the processing facility – Licensed Fish Receiver (LFR) – shells are kept aside to be measured by a trained technician. The general goal is to have approximately one bin of pāua measured for every tonne of pāua landed. This process works well when pāua are landed at an LFR for shucking and processing; however, an increasing proportion of pāua are now being landed to be sold live, or whole in the shell. This means significant quantities of catches are not able to be sampled as they have been historically. The solution that has been recently implemented is to use an electronic measuring board on the vessel where every pāua is measured before it is packed into landing bins. This allows thousands of individual pāua to be measured per day. The electronic measuring boards also log the exact Global Positioning System (GPS) location for spatial management and can be programmed to notify harvesters as to whether pāua reach the regionally variable MHS. On board measuring boards are now being used in most QMAs which has seen a substantial increase in the quantity and quality of data available.

Length at maturity is the length at which pāua reach sexual maturity and is described in terms of L50 or L95 – the length at which 50 percent or 95 percent of the pāua population in an area is sexually mature. Like growth, length at maturity can vary considerably around New Zealand. It is also an important stock assessment input and factor in Minimum Harvest Size (MHS) considerations. Length at maturity data is collected from different sites within QMAs, often at the same time as growth data is collected. To determine length at maturity, approximately 120 pāua, ranging in sizes of 60mm to 120mm, are collected from one locality. The meat is removed from the pāua and the gonad is left intact in the shell. All individuals are measured and a corresponding maturity score of ‘mature’ (easily identifiable male or female), ‘just mature’ (a few gametes visible), or ‘immature’ (no visible gametes) is given. This data is then modelled to produce L50 and L95 for each site. Meat from the pāua sampled for length at maturity is donated to local Iwi and work is authorised by Special Permit from Fisheries New Zealand.

The most relied upon source of data to assess the status of pāua stocks is catch per unit effort (CPUE). Measured in kg hr-1, CPUE trends are one of the strongest drivers in estimating stock status during stock assessment. Since the implementation of the Quota Management System (QMS), catch and effort data for commercial pāua catches are a mandatory legal requirement for every day spent fishing. Until recently, harvesters manually reported the amount of catch for each diver, the number of hours spent in the water, the QMA and statistical area fished, presence of a boat boy and sea conditions (swell and visibility) for each day commercial harvesting takes place. Across all crews within a QMA, this information is able to be standardised to give a general indication of CPUE trends for the QMA. Pāua is a unique fisheries species as they are sedentary and separate populations can display very different biological and demographic characteristics requiring different fisheries management approaches. Effective fisheries management at biologically relevant scales requires data to be collected at finer scales. This logic underpinned the industry-implemented data-logger programme that ran from 2012 to 2020. The programme employed the use of a ‘boat logger’ and a ‘diver logger’, or ‘turtle unit’, to collect fine scale catch and effort data with GPS location accuracy and detailed dive information. At the time, this data collection system was ground-breaking and allowed for detailed catch and effort data to be collected at the reef scale. The data it generated has also been critical for determining fine scale catch histories in areas that underpin current projects. The data logger programme enabled the undertaking of a landmark study by Abraham et al., (year) which showed that CPUE correlates strongly to pāua abundance (link). The data logger programme also catalysed the development of the pāua ‘dashboards’ which allowed for real time visualisation of where commercial catch was landed for the purpose of implementing catch spreading and fine-scale management. Today, catch reporting and the data logger programme have been superseded by mandatory electronic reporting (ER) and global positioning reporting (GPR) for all commercial fishing vessels that is managed by Fisheries New Zealand . This system incorporates many of the same principles and utilities of the data logger programme, but is now mandatory across all harvesters and will ultimately lead to a higher quality of data at a more appropriate spatial resolution for fisheries management.