Redthroat Emperor (2023)
Lethrinus miniatus
Date Published: June 2023
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Summary
Redthroat Emperor is fished in WA and the east coast of QLD. The stock in both states is classified as sustainable.
Stock Status Overview
Jurisdiction | Stock | Stock status | Indicators |
---|---|---|---|
Western Australia | Western Australia | Sustainable | Catch, effort, mean lengths, fishing mortality, relative spawning biomass |
Stock Structure
While records of occurrence are known from the Torres Strait, Gulf of Carpentaria and the Northern Territory [Atlas of living Australia], the distribution of Redthroat Emperor in Australia appears to be discontinuous [Van Herwerden et al. 2009], ranging from south of Perth to the Montebello Islands on the west coast, and between approximately 17.5º S (Innisfail) to at least 31°S (Lord Howe Island) on the Australian east coast. Genetic analysis using mitochondrial genome hypervariable region 1, indicates that the biological stocks from Western Australia are different compared to eastern Australian populations [Van Herwerden et al. 2009]. Here, assessment of stock status is presented at the biological stock level—Western Australia and East Coast Queensland.
Stock Status
Western Australia
Redthroat Emperor are primarily caught by commercial line fishers in Western Australia, with this sector landing around 80% of the annual retained catches over the past decade. While early catch information for Redthroat Emperor is uncertain due to inconsistent reporting at the species level, available data suggest that total annual catches of the commercial and recreational sectors peaked above 200 t in the mid-2000s. Retained catches of this species in Western Australia have fluctuated around 40–80 t since 2010, after significant management action was taken to reduce fishing effort and catch of demersal scalefish in the West Coast Bioregion (WCB), where the majority of Redthroat Emperor are landed. A 20-year recovery plan is in place to monitor the recovery of the West Coast Demersal Scalefish Resource (WCDSR). In addition to periodic assessments of indicator species [Newman et al. 2018], annual reviews of retained catches and estimates of post-release mortality (PRM) for key species are also undertaken against recovery benchmarks for each sector to inform management of the resource [DPIRD 2021].
In the WCB, retained catches of Redthroat Emperor by the commercial and recreational fishing sectors in 2020–21 were 27 t and 4 t, respectively, with the latter (which includes all Emperor spp.) comprising 2 t landed by charter fishers and 2 t landed by private boat-based fishers [Ryan et al. 2022]. The combined retained catch and estimated PRM (referred to here as total fishing mortality) of Emperor spp. by the commercial sector has been below the original recovery benchmark of 102 t since 2009 (27 t in 2021–22). Total fishing mortality of Emperor spp. by the recreational sector has been below the original recovery benchmark of 11 t in all years that the Statewide Boat-Based Recreational Fishing Survey has been undertaken (2011–12, 2013–14, 2015–16, 2017–18, 2020–21). This suggests that management has been effective at maintaining catches of Redthroat Emperor at acceptable levels.
A 2021 assessment of the WCDSR, to which Redthroat Emperor belongs, showed that declines in the spawning biomass of key indicator species (West Australian Dhufish and Snapper) at the bioregion level have been halted, but remain below the threshold reference level corresponding to BMSY [Fairclough et al. 2021]. In the case of Snapper, the estimated relative spawning biomass in the West Coast Bioregion in 2020 was still below the limit reference level of 0.2, with model projections indicating that fishing pressure has remained too high to allow stocks to recover above the threshold level by 2030. In response, new management measures for the WCDSR were implemented in early 2023, designed to further reduce retained catches and PRM of key demersal scalefish species in the WCB, to below 50% of the original recovery benchmarks specified in the WCDSR Harvest Strategy [DPIRD 2021]. The indicator species approach used is based on management being focused on species at highest risk of further depletion, to ensure the overall WCDSR is sustainably fished [Newman et al. 2018].
A data-limited Catch-MSY analysis of the Western Australian stock of Redthroat Emperor, based on available catch data from 1975 to 2022, predicts a Maximum Sustainable Yield (MSY) of 87 t (95% CLs: 63–107 t). Although annual catches between 2001 and 2008 substantially exceeded this range, recent management measures to recover the WCDSR resulted in catches of Redthroat Emperor below the predicted MSY since 2009. While uncertain and based on assumptions about the initial and final levels of depletion of the stock (0.4–0.8 and 0.15–0.7, respectively), the analysis indicates that the recent low catches have resulted in reduced fishing mortality (F) being experienced by the stock (now below the predicted level of FMSY of 0.12 per year). The predicted relative stock biomass (i.e., the depletion level) in 2022 was 0.47 of the estimated unfished level (95% CLs: 0.19–0.68), just below the threshold reference level corresponding to BMSY (0.5).
Outputs from the Catch-MSY analysis are broadly consistent with available catch curve estimates of F for Redthroat Emperor, based on age composition data collected periodically from commercial catches in the Mid-west area of the WCB since the mid-2000s. The estimated long-term, average F of fully-selected fish in the population, derived from a catch curve model that accounts for variable recruitment between years [Fisher 2013], has reduced over time. While the most recent F estimate based on data from 2016–17 remains above the estimated value of natural mortality for Redthroat Emperor, the data indicate that individuals may not be fully selected by the fishery by the time they attain the minimum legal length of 280 mm. The mean lengths of Redthroat Emperor in charter catches since 2002 have remained well above the length at 50% female maturity [Crisafulli et al. in review], providing an indication of lower fishing pressure on the female component of the breeding stock. The estimated relative spawning biomass for both sexes combined in 2016–17, generated by a per-recruit model that incorporates a stock-recruitment relationship and accounts for age-based selectivity and female-to-male sex change, was around 0.5, i.e., above the proxy for BMSY of 0.3.
On the basis of the evidence provided above, the Western Australia biological stock of Redthroat Emperor is classified as a sustainable stock.
Biology
Redthroat Emperor biology [Williams 2003; Williams et al. 2003; Van Herwerden et al. 2009]
Species | Longevity / Maximum Size | Maturity (50 per cent) |
---|---|---|
Redthroat Emperor | 20 years, 650 mm TL |
Protogynous-variant sequential hermaphrodite with large overlap in size and ages Females mature: 1.2 years, 310 mm TL (east coast) |
Tables
Western Australia | |
---|---|
Commercial | |
Hand Line, Hand Reel or Powered Reels | |
Line | |
Dropline | |
Gillnet | |
Fish Trap | |
Charter | |
Spearfishing | |
Hook and Line | |
Indigenous | |
Spearfishing | |
Hook and Line | |
Unspecified | |
Recreational | |
Spearfishing | |
Hook and Line |
Method | Western Australia |
---|---|
Charter | |
Bag/possession limits | |
Gear restrictions | |
Licence | |
Limited entry | |
Marine park closures | |
Passenger restrictions | |
Size limits | |
Spatial zoning | |
Commercial | |
Effort limits | |
Gear restrictions | |
Limited entry | |
Marine park closures | |
Seasonal or spatial closures | |
Size limits | |
Spatial zoning | |
Total allowable effort | |
Vessel restrictions | |
Indigenous | |
Gear restrictions | |
Size limits | |
Spatial zoning | |
Temporal closures | |
Recreational | |
Bag/possession limits | |
Gear restrictions | |
Licence (boat-based sector) | |
Marine park closures | |
Size limits | |
Spatial zoning | |
Temporal closures |
Western Australia | |
---|---|
Commercial | 29.79t |
Charter | 5 t (2021–22) |
Indigenous | Unknown |
Recreational | 10 t (2020–21) |
Western Australia – Commercial/Charter. Catches reported by calendar year.
Western Australia – Recreational. Boat-based catch from 1 September 2020 to 31 August 2021.
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.
Queensland – Indigenous (Management Methods). For more information see: https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing
References
- Crisafulli BM, Hesp SA, Denham A, Fairclough DV, Fisher EA, Wakefield CB, Newman SJ and Lewis, P (in review), Exploring the reliability of data-limited, length-based assessments using recreational charter fishing information, Fisheries Research Report No. 331, DPIRD WA.
- DPIRD 2021, West Coast Demersal Scalefish Resource Harvest Strategy 2021-2025, Fisheries Management Paper No. 305, Department of Primary Industries and Regional Development, Western Australia.
- Fairclough, DV, Hall, NG and Potter, IC 2023, Length and age compositions, hermaphroditic traits and reproductive characteristics vary among five congeneric species of labrid in a large embayment, Estuarine, Coastal and Shelf Science, 291: 108429.
- Fairclough, DV, Molony, BW, Crisafulli, BM, Keay, IS, Hesp, SA and Marriott, RJ 2014, Status of demersal finfish stocks on the west coast of Australia, Fisheries Research Report No. 253, Department of Fisheries, Western Australia.
- Fisher, E 2013, Tools for assessing data-limited fisheries and communicating stock status information, PhD thesis, Murdoch University, Perth.
- 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.
- Northrop, A and Campbell, A B 2020, Stock assessment of the Queensland east coast redthroat emperor (Lethrinus miniatus), Technical Report, State of Queensland, Brisbane.
- 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.
- Statewide recreational fishing surveys. Recreational fishing catch estimates dashboard. Accessed September 2023.
- Teixeira, D, Janes, R, and Webley, J 2021, 2019–20 Statewide Recreational Fishing Survey Key Results. Project Report. State of Queensland, Brisbane.
- Van Herwerden, L, Aspden, WJ, Newman, SJ, Pegg, GG, Briskey, L and Sinclair, W 2009, A comparison of the population genetics of Lethrinus miniatus and Lutjanus sebae from the east and west coasts of Australia: evidence for panmixia and isolation, Fisheries Research, 100: 148–155.
- Williams, AJ 2003, Spatial patterns in population biology of a large coral reef fish: what role can movement play? James Cook University, Townsville.
- Williams, AJ, Davies, CR, Mapstone, BD and Russ, GR 2003, Scales of spatial variation in demography of a large coral-reef fish: an exception to the typical model? Fishery Bulletin, 101: 673–683.