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Western Blue Groper (2020)

Achoerodus gouldii

  • Jeff Norriss (Department of Primary Industries and Regional Development, Western Australia)
  • Fred Bailleul (South Australian Research and Development Institute)

Date Published: June 2021

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Summary

Western Blue Groper occur along the coasts of SA and southern WA. In SA, small annual catches of Western Blue Groper are mostly taken as incidental bycatch. The average annual catch of the species in SA state-managed waters between 1999–00 and 2018–19 was <500 kg. Catch data for most seasons are confidential. In WA, the species is taken primarily in demersal gillnets. Stock structure is uncertain, but may be complex. In the absence of more detailed knowledge, this assessment is presented at the jurisdictional level. Western Blue Groper are classified as sustainable in WA, and negligible in SA.

Photo: Simon Bryars, Paul Rogers, South Australia Research and Development Institute

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Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
Western Australia Western Australia Sustainable

Catch, catch distribution, biology, length and age composition, fishing mortality, index of spawning stock biomass.

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Stock Structure

Western Blue Groper's distribution spans the coastal waters of South Australia and southern Western Australia. Stock structure has not been studied extensively, but acoustic telemetry of tagged adults in South Australia showed a high site fidelity along a narrow strip of fringing coastal reef (~1 km by ~40 m width) throughout a 12-month period [Bryars et al. 2012]. There is some ontogenetic movement towards deeper reefs as they grow [Shepherd and Brook 2007]. This suggests a complex population structure among adults. Here assessments are provided at the jurisdictional stock level. 

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Stock Status

Western Australia

In Western Australia, Western Blue Groper are taken predominantly by the commercial demersal gillnet fishery off the lower west and south coasts. Catch-at-age sampling of 682 south coast Western Blue Groper from this sector in 2013 and 2014 found good numbers of older fish (>35 yrs) [Norriss et al. 2016]. Two alternative methods were used to generate median estimates of female spawning potential ratio (SPR ± 95 per cent CI): SPR1 = 0.74 (0.52–0.97) and SPR2 = 0.71 (0.48–0.97), with an almost zero chance of breaching the threshold reference point (SPR=0.30) for either method [Norriss et al. 2016]. For males, SPR1 = 0.49 (0.23–0.94) and SPR2 = 0.48 (0.21–0.93) with a 14 per cent and 18 per cent chance of breaching the threshold reference point (SPR=0.30), respectively, and an almost zero chance of males breaching the limit reference point (SPR=0.20) for either method. Estimates of natural mortality M and fishing mortality F year-1 were 0.077 (0.059–0.097) and 0.023 (0.002–0.047), respectively, giving a point estimate of F/M of 0.30. The probability of F breaching the threshold level (F/M = 1) was almost zero.

The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. The above evidence also 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 Western Australia jurisdictional stock is classified as a sustainable stock.

 

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Biology

The Western Blue Groper is a protogynous hermaphrodite (some change sex from female to male) that can reach ~40 kg, with exceptional longevity (71 years), slow growth rate, late onset of sexual maturity (~17 years) at a large total length (~65 cm), very late sex change (age ~35 years) at a very large total length (~82 cm), and highly variable inter-annual recruitment [Coulson et al. 2009, Norriss et al. 2016]. During sub-adulthood there is a migration from inshore protected habitats to deeper (up to 20 m) waters with increasing bottom relief, but they otherwise maintain small home ranges [Shepherd and Brook 2007, Bryars et al. 2012], making them vulnerable to localised depletion from overfishing.

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Western Blue Groper

71 years, 116 cm total length

~17 years, 623-693 mm TL

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Distributions

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Tables

Fishing methods
Western Australia
Commercial
Hand Line, Hand Reel or Powered Reels
Gillnet
Longline (Unspecified)
Recreational
Spearfishing
Hook and Line
Rod and reel
Charter
Hook and Line
Rod and reel
Management methods
Method Western Australia
Charter
Bag limits
Gear restrictions
License
Limited entry
Seasonal closures
Spatial closures
Commercial
Effort limits
Effort limits (individual transferable effort)
Gear restrictions
License
Limited entry
Marine park closures
Size limit
Spatial closures
Spatial zoning
Recreational
Bag limits
Gear restrictions
Licence (Recreational Fishing from Boat License)
Possession limit
Size limit
Spatial closures
Temporal closures
Catch
Western Australia
Commercial 31.41t
Charter < 0.5 t
Recreational 2 t (2017/18)
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Catch Chart

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Downloadable reports

Click the links below to view reports from other years for this fish.