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The stock structure of Hapuku in Australian waters is unknown. Hapuku stock status at the jurisdictional level is sustainable in WA, negligible in QLD and SA, and undefined in NSW and Commonwealth waters.

The stock structure of Hapuku throughout Australian waters is unknown. Life history characteristics similar to Bass Groper (Polyprion americanus) suggest mixing across broad geographic areas [Ball et al. 2000]. However, Beentjes and Francis [1999] inferred the likelihood of separate stocks within New Zealand based on tagging studies of Hapuku, despite recorded movements of up to about 1 400 km. Paul [2002] reported on the stock structure of Hapuku (and Bass Groper) in New Zealand, concluding that stock structure could not be described, and that there was insufficient data describing the life history characteristics to distinguish different stocks. Wakefield et al. [2010] described differences in aged-based demography and reproduction of Hapuku among regions of Western Australia, and likely pan-oceanic mixing of the broader Hapuku population (including Indian Ocean). No such investigations have been done on Hapuku throughout eastern and south eastern Australian waters to develop our understanding of stock structure. It is likely Hapuku in eastern and south eastern Australian waters constitute one or more stocks of a greater population and fisheries within this region access this stock or subset of stocks in support of their annual catches. Panmixia could be expected throughout the region, owing to the extended larval/juvenile phase (years) and large-scale genetic homogeneity of congener P. americanus which has similar life-history traits [Ball et al. 2000, Roberts 1996, Sedberry et al. 1996, Wakefield et al. 2010]. Evidence in support of a single biological stock, or stock structuring within broader Australian waters is limited.

Here, assessment of stock status is presented at the jurisdictional level—Commonwealth, Western Australia, Queensland, New South Wales and South Australia.

Commonwealth

Hapuku are captured in multiple sectors of the Southern and Eastern Scalefish and Shark Fishery (SESSF), within Australia's exclusive economic zone (EEZ), and by Australian-flagged vessels operating outside Australia's EEZ in the South Pacific Regional Fisheries Management Organisation (SPRFMO) area and the Southern Indian Ocean Fisheries Agreement (SIOFA) area. Most of the catch in Commonwealth fisheries within Australia's EEZ is taken by demersal longlines in the Gillnet Hook and Trap (GHAT) Sector and by trawling in the Commonwealth Trawl Sector (CTS) and Great Australian Bight (GAB) Sector. Total annual catches across all sectors declined from over 110 tonnes (t) in 2008 to around 26 t in 2013. Since then, catches have increased to approximately 42 t in 2019, with around 20 t of this being taken in the SIOFA area, 14 t in the GHAT, 6 t in the CTS, 1 t in the GAB and <1 t in the SPRFMO area. The increase in the proportion of overall Commonwealth catches being taken in SIOFA and the decrease in the proportion of overall Commonwealth catches being taken within Australia's EEZ has important implications for status determination, as catches taken from the SIOFA area are unlikely to be from the same biological stock (or sub-stock) as that in eastern Australia.  

In 2012, a Sustainability Assessment for Fishing Effects (SAFE) analysis assessed Hapuku as precautionary extreme high risk in the SESSF due to the cumulative impacts of fishing from the CTS and demersal longline fishing in the GHAT Sector [Zhou et al. 2012]. A residual risk analysis that considered additional scientific information did not reduce the overall risk rating for Hapuku [AFMA 2014]. The SAFE analysis was based on catch data from 2007 to 2010, when the average catch was about 82 t, and indicated that it was plausible that Hapuku could have been subject to overfishing during those years.

Due to the risk rating from the 2012 SAFE assessment, Hapuku is currently a priority species in the application of an Ecological Risk Management strategy for the SESSF [AFMA 2015]. Specific management measures adopted by AFMA to reduce the impact of demersal longline fishing on Hapuku include a limit on the number of hooks deployed, spatial and temporal closures, and the mandatory installation of electronic monitoring on all auto longline vessels.

In 2018, a model-assisted catch-only assessment (Catch-MSY method) [Martell and Froese 2013] was fitted to catches of Hapuku across all sectors of the SESSF from 1986 to 2017 [Penney et al. 2018]. The Catch-MSY method uses population productivity (r) and carrying capacity (K) parameters of an underlying Schaefer production model to estimate the ranges in biomass and harvest rate that could have resulted in the annual catches. The assessment estimated biomass to have been above B_MSY from 1986 to 2006 and between B_MSY and 20 per cent of unfished biomass (0.2B₀) since 2007. The mean estimate of biomass in 2017 was approximately 33 per cent of B₀ (95 per cent CI of 11–55 per cent). Reported catch, mostly from the CTS, increased in 2017, but remained below the mean estimated MSY of 51 t. However, the harvest rate in 2017 was estimated to be 0.15, above the F_MSY level of 0.11, as a result of the 2017 increase in reported trawl catch. Five year projections at the 2017 catch level of 48 t predicted that biomass would decline slowly at this catch level. Catches from the eastern Australian component of this management unit are likely to have been around 22 t in 2019.

The estimated harvest rates from this assessment are consistent with estimates of fishing mortality derived from the SAFE assessment by Zhou et al. [2012]. However, there is high uncertainty in the estimates of biomass depletion, harvest rate and MSY that have been derived using the Catch-MSY method due to the deterministic nature and uncertainty about the stock structure of Hapuku. Given the broad distribution of Hapuku within Australian waters, it is plausible that there are a number of separate biological stocks with limited connectivity across the extent of the SESSF and more broadly across other Australian jurisdictions and internationally. These may have been subject to different exploitation patterns. Resolving the stock structure of Hapuku would help reduce the uncertainty in the status of the species. 

On the weight of available evidence, it is plausible that maintaining the levels of fishing pressure estimated in 2017 would cause the Commonwealth Hapuku stock to decline below its current level and lead to it being recruitment impaired. However, catches in 2019 from the relevant components of the Commonwealth management unit appear to have fallen to around half of the levels estimated in 2017 and on which projections for future stock status were done. The available evidence indicates that the biomass of the stock is uncertain and that it is unclear whether recruitment has been impaired.

On the basis of the evidence provided above, Hapuku in the Commonwealth is classified as an undefined stock.

Hapuku biology [Ball et al. 2000, Paxton et al. 1989, Wakefield et al. 2010]

Distribution of reported commercial catch of Hapuku

Western Australia – Recreational (management methods) Recreational Fishing from Boat Licence is required for use of a powered boat to fish or to transport catch or fishing gear to or from a land-based fishing location.

Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

New South Wales – Indigenous (Management Methods) - https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing

Commercial catch of Hapuku - note confidential catch not shown

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