Pāua population monitoring in areas affected by the 2016 Kaikōura earthquake, April 2024 update

The November 2016 Kaikōura earthquake caused coastal uplift resulting in high pāua (Haliotis iris) mortality and extensive loss of critical pāua habitats. The uplift affected approximately 120 km of coastline that supports significant customary, recreational, and commercial pāua fisheries. There has been a closure of the pāua fishery from the Conway River in the south to Marfells Beach in the north (the ‘closed area’) since November 2016 to allow for recovery of affected pāua populations. The fishery was initially re-opened on the 1st of December 2021 and is now in its third successive annual fishing season since re-opening.

The objective of this project was to continue annual monitoring of pāua abundance and length frequency at the scale of the fishery closure at sites established initially in 2017. These surveys have employed a modified timed-swim methodology to estimate site and area-wide (Quota Management Area) trends in pāua abundance and length frequency. Results from these surveys had initially shown an overall increase in adult biomass, and widespread juvenile recruitment, which supported the decision to re-open the fishery.

Data analysis followed methods reported in previous updates, namely using generalised linear mixed models. Additional diagnostics to those presented for previous surveys were inspected to ensure that the model adequately captured variation in survey data across various strata (e.g., survey strata, quota management areas, survey periods, and covariates). These efforts suggested that multi-modality in the response within survey sites is a key driver of high variability (CVs) in survey estimates, a feature that arises from patchiness of pāua distribution and is largely irreducible with limited survey effort.

Analyses show that abundance of pāua increased from initial baseline surveys until the 2021–22 survey period, after which the fishery was re-opened. Since re-opening, abundance has declined in both PAU 3A and PAU 7 QMAs in the earthquake-affected areas, although there are some subtle differences in trends between QMAs. This decline is as expected and shows that the surveys have value in detecting changes in fishery wide pāua abundance in response to fishing effort. Analyses of abundance at the fine spatial scales (i.e., within ‘management zones’) can help to illustrate what specific areas may be driving overall fishery wide trends, although site bias in relation to where recent harvesting has taken place could influence this.

In PAU 3A, length frequency analyses showed that pāua are smaller in the latest surveys, which could be influenced by harvesting at sites over the last season. There were fewer pāua in smaller size classes in the last survey which is most likely reflective of general variability in recruitment. In PAU 7, pāua were overall larger in the last survey period, but this may be influenced by site bias. The current Fisheries New Zealand project SEA2023-06 is testing the utility of the relative abundance trends from these surveys in estimating stock status and developing management procedures for determining future catch levels.