Spangled Emperor (2020)
Date Published: June 2021
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Spangled Emperor has a wide distribution around Australia. There are eight stocks—defined at either the management unit or jurisdictional level—across WA, the NT, QLD and NSW. In WA three management units are sustainable and one is recovering. The NT jurisdictional stock is sustainable. In QLD one management unit is sustainable and one is undefined. The NSW management unit is negligible.
Stock Status Overview
|Queensland||Gulf of Carpentaria||Undefined||Catch, effort|
|Queensland||East Coast Queensland||Sustainable||
Catch, effort, standardised CPUE
Spangled Emperor have a widespread Indo-West Pacific distribution, ranging from the Red Sea, Persian Gulf, and East Africa east to southern Japan in the north, around northern Australia and extending east to Samoa [Carpenter and Allen 1989]. In Australia, Spangled Emperor are found from around Rottnest Island on the lower west coast, across northern Australia to south of Sydney on the east coast [Carpenter and Allen 1989, Carpenter and Niem 2001].
The population structure of Spangled Emperor in Western Australia has been studied by assessing spatial variation in allozymes [Johnson et al. 1993], otolith microchemistry [Moran et al. 1993], tagging and recapture [Moran et al. 1993], DNA micro-satellite markers [Berry et al. 2012], and acoustic telemetry [Pillans et al. 2014]. Individuals generally demonstrate a limited home range of less than three nautical miles [Moran et al. 1993]. Relatively high site fidelity has been shown for at least some individuals in Western Australia and elsewhere [Chateau and Wantiez 2008, Pillans et al. 2014]. Limited mixing of post-settlement individuals is also indicated from an analysis of otolith microchemistry of Spangled Emperor sampled from different sites [Moran et al. 1993].
Genetic studies have demonstrated homogeneous genetic characteristics across broad spatial scales (10–1 500 km) throughout the distribution of Spangled Emperor in Western Australian [Johnson et al. 1993]. Analysis of fine-scale patterns using high resolution micro-satellite markers, however, has found that juveniles exhibit fine-scale genetic autocorrelation, which declines with age [Berry et al. 2012]. This implies both larval cohesion and limited juvenile dispersal prior to maturity, primarily in the vicinity of the Ningaloo Marine Park [Berry et al. 2012]. Hydrodynamic modelling indicated that Spangled Emperor larvae were likely to be transported hundreds of kilometres, easily accounting for the observed gene flow, despite relatively restricted adult dispersal [Berry et al. 2012]. As such, Spangled Emperor are considered to comprise a single biological stock in at least Western Australia. However, there is limited mixing of adult Spangled Emperor. Further, management arrangements are mediated in a way that harmonises with the spatial patterns of exploitation. This indicates that in Western Australia, Spangled Emperor comprise separate management units.
There is a high likelihood that these population characteristics (extensive gene flow, limited adult movement) are shared across each of the jurisdictions. Low genetic subdivision between northwest Western Australia and the Great Barrier Reef suggests gene flow is likely to be high between these regions [Berry et al. 2012]. There is possibly one genetic stock in Australia, however, improved stock delineation work is required in jurisdictions outside Western Australia.
Here, assessment of stock status is presented at the management unit level—West Coast, Gascoyne, Pilbara, Kimberley (Western Australia); Gulf of Carpentaria, East Coast (Queensland); and New South Wales; and at the jurisdictional level—Northern Territory.
East Coast Queensland
There has been no formal stock assessment of the species across this management unit. Estimated recreational harvest of Spangled Emperor on the east coast of Queensland has declined from 50 tonnes (t) to 27 t over successive state-wide surveys between 2000–01 and 2019–20 respectively [Webley et al. 2015, Teixeira et al. 2021]. An increase in minimum legal size in 2003 (from 400 to 450 mm TL) and decrease in the possession limit (from 10 to 5) would likely have contributed to this decline. Recreational catches was 32 per cent of the total recreational and commercial landings for the species by weight based on 2019–20 recreational catch numbers.
In 2004, decreased commercial catch coincided with expansion of no-take marine reserves within the Great Barrier Reef Marine Park and the introduction of a quota management system for coral reef finfish species. The numbers of commercial fishing days where Spangled Emperor were reported since 2010–11 have been stable [QFISH 2020]. The annual reported commercial line harvest has been relatively stable with an average of 56 t for the last nine years and 58 t in 2018–19. Catch rates (kg per dory day and kg per primary vessel day) have also been stable since 2008–09.
Spangled Emperor is a secondary target and by-product species in the Reef Line Fishery (RLF). While commercial harvest is only constrained by a multi-species total allowable commercial catch (TACC) and a minimum legal size, species-specific harvest control rules and catch reference points introduced in early 2020 for secondary target species including Spangled Emperor through the RLF Harvest Strategy [QDAF 2020] provide additional harvest constraints. Harvest of Spangled Emperor that exceeds the harvest reference points and control rules will trigger a stock assessment and the implementation of an interim species-specific TACC. Recreational harvest is also controlled through the minimum legal size and a possession limit. The Indigenous harvest of Spangled Emperor is unknown but is considered to be minor. It is likely that a portion of the biomass would be afforded some protection from fishing through zoning (restricting or prohibiting fishing) in the Great Barrier Reef Marine Park system, although this has not been quantified. The above evidence indicates that the biomass of this stock is unlikely to be depleted, recruitment is unlikely to be impaired, and the current level of fishing pressure is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, the East Coast of Queensland management unit is classified as a sustainable stock.
Gulf of Carpentaria
There has been no stock assessment of the species across this management unit. Spangled Emperor are a byproduct species group in the Gulf of Carpentaria Line Fishery and Gulf of Carpentaria Demersal Fin Fish Trawl Fishery with low annual harvest (~1 t average since 2011–12). There are no reliable estimates of catch of Spangled Emperor for Indigenous or recreational fishers in the GOC. There is insufficient information available to confidently classify the status of this stock.
On the basis of the evidence provided above, the Gulf of Carpentaria (Queensland) management unit is classified as an undefined stock.
Spangled Emperor biology [Currey et al. 2013, DAF unpublished data, Marriott et al. 2010, 2011]
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|Spangled Emperor||31 years: 707 mm FL (WA) 24 year:, 810 mm FL and 8.9kg (east coast Queensland/GBR)||3.6 years: 350 mm FL|
Distribution of reported commercial catch of Spangled Emperor
|Hook and Line|
|Hook and Line|
|Individual transferable quota|
|Total allowable catch|
|Recreational||27 t (2019–20)|
Western Australia – Recreational (Catch) Boat-based recreational catch is from 1 September 2017–31 August 2018. These data are derived from those reported in Ryan et al. (2019).
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.
Western Australia – Commercial (catch) Catch is unavailable as there were fewer than three vessels in the Pilbara Fish Trawl Interim Managed Fishery, Pilbara Trap Managed Fishery and West Coast Demersal Gillnet and Demersal Longline (Interim) Managed Fishery.
Western Australia – Active Vessels Data is confidential as there were fewer than three vessels in the Pilbara Fish Trawl Interim Managed Fishery, Pilbara Trap Managed Fishery and West Coast Demersal Gillnet and Demersal Longline (Interim) Managed Fishery.
Western Australia – Commercial (management methods) Spangled Emperor forms part of the combined Total Allowable Commercial Catch for other mixed demersal species in the GDSMF.
Queensland – Commercial (fishing methods) Spangled Emperor is trawled in only one of the Queensland fisheries in which it is caught commercially - the Gulf of Carpentaria Developmental Fin Fish Trawl Fishery
Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-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 “…without derogating from any other law in force in the Territory, nothing in a provision of this Act or an instrument of a judicial or administrative character made under it limits the right of Aboriginals who have traditionally used the resources of an area of land or water in a traditional manner from continuing to use those resources in that area in that manner”.
Commercial catch of Spangled Emperor - note confidential catch not shown
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