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Rankin Cod (2023)

Epinephelus multinotatus

  • Corey Wakefield (Department of Primary Industries and Regional Development, Western Australia)
  • Jo Randall (Department of Industry, Tourism and Trade, Northern Territory)
  • Fabian Trinnie (Department of Primary Industries and Regional Development, Western Australia)
  • Stephen Newman (Department of Primary Industries and Regional Development, Western Australia)

Date Published: June 2023

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Summary

Rankin Cod is assessed as sustainable in the Pilbara and North Western Australia (which includes the Kimberley and Timor Reef Fishery of the NT) management units.

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Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
Northern Territory North Western Australia Sustainable

Catch, indicator species status

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Stock Structure

Rankin Cod are widely distributed throughout the Indian Ocean. Within Australia, Rankin Cod are distributed from the Houtman Abrolhos Islands in Western  Australia, north to the waters offshore from Darwin in the Northern Territory. Rankin Cod is exploited primarily in the North Coast Bioregion of Western Australia [Newman et al. 2020]. Catches of Rankin Cod taken in the Northern Territory are low. Rankin Cod is one of the indicator species used to assess the status of the demersal resources in the Pilbara subregion of the North Coast Bioregion [Newman et al. 2018].

Johnson et al. [1993] examined allozymes (allelic variants of enzymes encoded by structural genes) from samples of Rankin Cod from the Lacepede Islands, Bedout Island, Lowendal Islands, Ningaloo and Shark Bay. There was evidence of a low level of genetic variation, indicating extensive connectivity among populations over large distances (at least 1,400 km). It was noted that no adjacent samples differed significantly, suggesting a latitudinal clinal change [Johnson et al. 1993], and a high degree of connection across populations throughout the sampled range (1,400 km) in Western Australia. Stephenson et al. [2001] examined stable isotopes in sagittal otolith carbonates of Rankin Cod from four locations: Shark Bay (Gascoyne), Ningaloo (Gascoyne), Pilbara, and Broome (Kimberley). The results of Stephenson et al. [2001] indicated that adult Rankin Cod do not mix extensively.

There is no evidence of discrete breeding populations of Rankin Cod in Western Australia, indicating that there is one biological stock. Although adults do not mix extensively, they all contribute to the total adult spawning biomass and larval dispersal. However, the limited mixing of adults among locations indicates some potential for localised depletion and supports the use of regional fishery management boundaries in Western Australia (e.g. Pilbara and Kimberley). Given the large distances involved and uncertainty over actual mixing rates of juveniles and adults, the regionally separate stock assessments are appropriate for managing potentially different levels of fishing pressure and stock status of this resource in the Kimberley (and Northern Territory combined) and Pilbara regions.

Here, assessment of stock status is presented at the management unit level—Pilbara and North-western Australia.

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Stock Status

North Western Australia

Rankin Cod in the Kimberley are landed commercially in the Northern Demersal Scalefish Managed Fishery (NDSMF). Rankin Cod is assessed on the basis of the status of several indicator species (for example, Red Emperor and Goldband Snapper in the Kimberley region) within the North Coast Demersal Resource (NCDR) that represent the entire inshore demersal suite of species occurring at depths of 30–250 m [Newman et al. 2018]. The indicator species in the Kimberley have been classified as sustainable [Wakefield et al. 2023]. The level of risk associated with the sustainability of Rankin Cod in the Kimberley is assessed as low. This assessment of Rankin Cod is also supported by predictions for biomass and harvest rates from a data-limited Catch-MSY assessment model compared periodically to a model prediction for maximum sustainable yield (MSY). 

Total catch of Rankin Cod in the Kimberley over the last 10 years (2013–22) have ranged from 46–100 t, with a mean annual catch of 70 t. This is an increase on the averages catches across the previous 10 years of 43 t. Recreational and charter catch are relatively low compared to the commercial catch, in the past 10 years where reliable catches estimates are available, the proportion of the total catch has averaged less than 3%. The Catch-MSY model applied to data on annual catches for this species (1990–22), indicate that the annual catches have generally been below the median model estimate for maximum sustainable yield (MSY), but catches have been increasing and were above the MSY estimate in 2016–17 and 2020–22. This is consistent with the predicted biomass estimates remaining above BMSY for the entire time series, with biomass declining as catches have been increasing. This is also consistent with fishing mortality remaining below FMSY. However, it is important to recognise that Catch-MSY is a data-limited technique with relatively strong assumptions, dependent on user inputs. For this assessment, these included specified ranges for initial depletion (0.4–0.8), based on likely but unknown catches from foreign fleets prior to the start of the time series, final depletion (0.15–0.7), based on recent catches relative to maximum recorded annual catch and the non-targeted nature, and low resilience (r=0.1–0.6, consistent with species longevity, of approximately24 years in WA). Given the recent catches of this species are within the confidence of the predicted MSY, and status of the indicator species for the Kimberley, it is considered unlikely that the biomass of Rankin Cod in the Kimberley is depleted and recruitment is unlikely to be impaired.

For the Northern Territory part of the management unit, only relatively small catches are recorded in the Timor Reef and Demersal fisheries. Targeting of Rankin Cod by these fisheries is constrained by the fact that this species distribution largely resides outside of these fisheries boundaries. As a result, during the period 2013–22 the average annual catch by these fisheries was less than 4.0 t. Additionally, the generally offshore distribution of Rankin Cod in NT waters means that the recreational and Fishing Tour Operator landings are likely to be negligible. Consequently, the Northern Territory component is considered to only contribute a negligible catch to this stock. The above evidence indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, the North Western Australia management unit is classified as a sustainable stock.

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Biology

Rankin Cod biology [Wakefield et al. unpublished data]

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Rankin Cod

24 years, 776 mm FL

2 years, 391 mm FL  

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Distributions

Distribution of reported commercial catch of Rankin Cod

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Tables

Fishing methods
Northern Territory
Commercial
Unspecified
Fish Trap
Charter
Hook and Line
Indigenous
Hook and Line
Recreational
Hook and Line
Management methods
Method Northern Territory
Charter
Gear restrictions
Limited entry
Vessel limits
Commercial
Gear restrictions
Limited entry
Spatial closures
Spatial zoning
Total allowable catch
Indigenous
Laws of general application
Recreational
Gear restrictions
Possession limit
Catch
Northern Territory
Commercial 2.95t
Charter Unknown
Indigenous Unknown
Recreational Unknown

Western Australia – Commercial (Management Methods). Rankin Cod forms part of the combined Total Allowable Commercial Catch for other mixed demersal species in the Gascoyne Demersal Scalefish Managed Fishery.

Western Australia – Active Vessels. Data are confidential as there were fewer than three vessels in Pilbara Fish Trawl Interim Managed Fishery (Western Australia) and Pilbara Trap Managed Fishery (Western Australia).

Western Australia – Recreational (Catch). Boat-based recreational catch is from 1 September 2020–31 August 2021. These data are derived from those reported in Ryan et al. [2022].

Western Australia – Recreational (Management Methods). A Recreational Fishing from Boat License is required for the use of a powered boat to fish or to transport catch or fishing gear to or from a land-based fishing location.

Western Australia – Indigenous (Management Methods). Subject to application of Section 211 of the Native Title Act 1993 (Cth), and the exemption from a requirement to hold a recreational fishing licence, the non-commercial take by Indigenous fishers is covered by the same arrangements as that for recreational fishing.

Northern Territory – Charter (Management Methods). In the Northern Territory, charter operators are regulated through the same management methods as the recreational sector but are subject to additional limits on license and passenger numbers.

Northern Territory - Indigenous (Management Methods). The Fisheries Act 1988 (NT), specifies that: “Unless expressly provided otherwise, nothing in this Act derogates or limits the right of Aboriginal people who have traditionally used the resources of an area of land or water in a traditional manner to continue to use those resources in that area in that manner.”

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Catch Chart

Commercial catch of Rankin Cod - note confidential catch not shown

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References

  1. DPIRD 2017, North Coast demersal scalefish resource harvest strategy 2017 – 2021. Version 1.0. Fisheries Management Paper No. 285. Department of Primary Industries and Regional Development, Government of Western Australia, Perth, Australia. 35p.
  2. Johnson, MS, Hebbert, DR and Moran, MJ 1993, Genetic analysis of populations of north-western Australian fish species. Australian Journal of Marine and Freshwater Research, 44: 673–685.
  3. Newman, SJ, Brown, JI, Fairclough, DV, Wise, BS, Bellchambers, LM, Molony, BW, Lenanton, RCJ, Jackson, G, Smith, KA, Gaughan, DJ, Fletcher, WJ, McAuley, RB and Wakefield, CB 2018, A risk assessment and prioritisation approach to the selection of indicator species for the assessment of multi-species, multi-gear, multi-sector fishery resources. Marine Policy, 88: 11–22.
  4. Ryan, KL, Lai, EKM and Smallwood, CB 2022, Boat-based recreational fishing in Western Australia 2020/21. Fisheries Research Report No. 327 Department of Primary Industries and Regional Development, Western Australia. 221pp.
  5. Stephenson, PC, Edmonds, JS, Moran, MJ and Caputi, N 2001, Analysis of stable isotopes to investigate stock structure of red emperor and Rankin cod in northern Western Australia. Journal of Fish Biology, 58: 126–144.
  6. Wakefield, C, Trinnie, F, Skepper, C, Boddington, Newman, SJ, and Steele, A 2023, North Coast Demersal Resource Status Report 2022. pp. 167–176. In: Gaughan, D.J. and Santoro, K. (eds.). 2023. Status Reports of the Fisheries and Aquatic Resources of Western Australia 2021/22: The State of the Fisheries. Department of Primary Industries and Regional Development, Western Australia, Perth, Australia.

Downloadable reports

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