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The Hammer Octopus occurs along the east coast of Australia from central Queensland to southern NSW. While stock structure is unknown, the species has biological traits that suggest a single biological stock is unlikely. Additionally, no joint stock assessment covering both Queensland and NSW is available. Consequently, stock status is assessed here at the jurisdictional level. Hammer Octopus is classified as undefined in Queensland and sustainable in NSW. 

The Hammer Octopus is distributed along the east coast of Australia from central Queensland to southern New South Wales [Reid 2016]. The stock structure of Hammer Octopus is currently unknown. However, on the basis of the relatively large size of mature eggs (8–12 mm, equating to 13.7–21.4% of dorsal mantle length), the species is likely to be holobenthic [Boletzky 1974; Stranks and Norman 1992]. Holobenthic octopuses typically have large benthic rather than pelagic hatchlings, with limited dispersal capacity, and show finer scale population structuring across their distributions [e.g., Pale Octopus, Doubleday et al. 2008; Higgins et al. 2013]. Therefore, it is unlikely that Hammer Octopus forms a single biological stock across its geographic distribution. Furthermore, there is no joint stock assessment for this species, so stock status is reported here at the jurisdictional level - Queensland and New South Wales.

New South Wales

The Hammer Octopus is a small, short-lived species that is found in coastal waters and bays on sand and mud substrates in depths between 3 and 140 m [Stranks and Norman 1992]. In NSW, combined octopus are an important by-product species group, with most of the commercial catch taken by the prawn trawl sector of the Ocean Trawl Fishery in northern NSW, and smaller amounts reported from the fish trawl sector along the central coast [Hall 2020]. 

In NSW, total annual commercial catches of combined octopus are available from 1979–80 to 2008–09 and for separate species from 2009–10 to 2021–22 [Hall 2020]. Commercial catches of combined octopus steadily increased from around 200 tonnes (t) in the late 1970s to a peak of 783 t in 1997–98. Catches then rapidly declined over 2 years to 277 t in 1999–2000, briefly returned to over 500 t in 2000–01 and have since fluctuated at lower levels (76–256 t since 2004–05). Separate species catch data since 2009–10 suggest that Hammer Octopus typically dominates commercial catches, accounting for 84.2–94.6% of total catches [Hall 2018]. The total commercial catch of Hammer Octopus in 2021–22 was 61 t. 

The most recent estimate of the recreational harvest of combined octopus species in New South Wales was approximately 1,634 octopus during 2019–20, with an additional 2,241 octopus caught and released [Murphy et al. 2022]. The proportion of Hammer Octopus in this estimate is unknown. The estimate was based on a survey of Recreational Fishing Licence (RFL) households, comprised of at least one fisher possessing a long-term (1 or 3 years duration) fishing licence and any other fishers resident within their household. The equivalent estimates from previous surveys in 2017–18 and 2013–14 were approximately 1,145 and 1,877 octopus harvested, with an additional 2,700 and 5,227 octopus caught and released, respectively [Murphy et al. 2020]. Relative to the total commercial catch, these recreational catches are very small (< 1% of the total state harvest). A survey of Aboriginal cultural fishing in the Tweed River catchment identified octopus as a common component of the marine invertebrate catches [Schnierer and Egan 2016]; however, statewide estimates of the annual Aboriginal harvest of octopus in New South Wales are unknown.

Evidence suggests that the bulk of the historical combined octopus catches taken by the Ocean Trawl Fishery are likely to have comprised Hammer Octopus [Hall 2018]. Historical combined octopus catch rates from monthly records (standardised catch per unit effort, CPUE, in kg per day) for the prawn and fish trawl sectors indicate widely fluctuating trends (between 14.6–50 kg per day), with gradual increases over several years, followed by a sudden rapid decrease over one or a few years (e.g., from 42.4 kg per day in 1998 to 17.2 kg per day in 1999 and back up to 40.0 kg per day in 2004) [Hall 2020]. This pattern of abundance corresponds to anecdotal evidence from fishers indicating that after several good years, combined octopus catches suddenly decrease in trawl landings. 

Recent standardised CPUE (in kg per hour trawled) for Hammer Octopus from daily records for both the fish trawl and prawn trawl sectors, which have been recorded since 2009, indicate that over the preceding three years catch rates had been steadily increasing to well above-average levels, but in 2021–22 suddenly decreased to near the long-term average (of 3.2 kg per hour trawled) [Hall 2023]. These recent trends in CPUE, combined with historical levels for combined species dominated by Hammer Octopus, suggest that although the biomass of this stock fluctuates considerably, it is unlikely to be depleted and that recruitment is unlikely to be impaired. However, this assessment involves considerable uncertainty given the monthly and combined species reporting prior to 2009 and reliance on catch-rate analyses for a non-target species.

Current levels of fishing effort in the prawn trawl and fish trawl sectors of the Ocean Trawl Fishery (3,916 and less than 800 days fished, respectively) are much lower than historical levels (18,000 and 3,054 days fished in the early 2000s) due to a reduced number of operators [Hall 2023]. While no current fishing mortality estimates are available for the species, the current level of fishing mortality is considered unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, Hammer Octopus in New South Wales is classified as a sustainable stock.

[Nuttall 2009]

Distribution of reported commercial catch for Hammer Octopus.

New South Wales – Recreational (Catch). Estimate from Murphy et al. [2022], based on a survey of Recreational Fishing Licence households. Note, estimates for octopus are highly uncertain, with a relative standard error of greater than 30% and based on survey data from fewer than 20 households.

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

Queensland – Indigenous (Management Methods). For more information see: https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

Queensland – Recreational Fishing (Catch). Data with high uncertainty (Residual Error >50 %) has been excluded and listed as unknown. More information available at: https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/monitoring-reporting/statewide-recreational-fishing-surveys  

Queensland – Commercial (Catch). Queensland commercial and charter data has been sourced from the commercial fisheries logbook program. Further information available through the Queensland Fisheries Summary Report https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/data/queensland-fisheries-summary-report 

Queensland – Commercial (Management Methods). Harvest strategies available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy

Commercial catch data for Hammer Octopus, provided in financial years and aligned according to end year.

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