*

Bluespotted Emperor (2018)

Lethrinus punctulatus

  • Stephen Newman (Department of Primary Industries and Regional Development, Western Australia)
  • Corey Wakefield (Department of Primary Industries and Regional Development, Western Australia)
  • Thor Saunders (Department of Primary Industry and Resources, Northern Territory)
  • Fabian Trinnie (Department of Primary Industries and Regional Development, Western Australia)
Toggle content

Summary

The 2 WA stocks of Bluespotted Emperor, in the Pilbara and Kimberley, are sustainable. The NT stock is classified as negligible.

Toggle content

Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Western Australia Kimberley NDSMF Sustainable Spawning stock biomass, fishing mortality rate, age structure, catch, CPUE
Northern Territory Northern Territory Negligible Catch
Western Australia Pilbara PFTIMF, PLF, PTMF Sustainable Spawning stock biomass, age structure, fishing mortality rate, catch, CPUE
NDSMF
Northern Demersal Scalefish Managed Fishery (WA)
PFTIMF
Pilbara Fish Trawl (Interim) Managed Fishery (WA)
PLF
Pilbara Line Fishery (WA)
PTMF
Pilbara Trap Managed Fishery (WA)
Toggle content

Stock Structure

The distribution of Bluespotted Emperor is restricted primarily to Western Australian waters and extends from around Geraldton in the south to Darwin in the Northern Territory with its greatest relative abundances in the western Pilbara region [Carpenter and Niem 2001, Newman et al. 2018a]. Bluespotted Emperor are exploited primarily in the North Coast Bioregion of Western Australia [Newman et al. 2018a]. Very small catches are landed in the Northern Territory. Bluespotted Emperor 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. 2018b].

Johnson et al. [1993] examined allozymes (allelic variants of enzymes encoded by structural genes) from samples of Bluespotted Emperor from the Lacepede Islands, Bedout Island, Lowendal Islands, Ningaloo, Shark Bay and the Abrolhos Islands in Western Australia (spread over a distance of approx. 2 000 km). Bluespotted Emperor displayed little genetic variation over the geographic distance of sampling. While adult populations were not totally intermixed, the low level of genetic variation indicates extensive connectivity among populations of Bluespotted Emperor over large distances.

The lack of genetic differentiation among populations of Bluespotted Emperor across the northwest region of Western Australia indicates that there is gene flow among populations [Johnson et al. 1993, Moran et al. 1993] and there is one biological stock. Moran et al. [1993] examined the elemental composition in sagittal otolith carbonates of Bluespotted Emperor from Maud Anchorage (Point Maud, Ningaloo), North-West Alison Point (Ningaloo) and Bedout Island (Pilbara). Significant differences were demonstrated between all three locations. The Maud Anchorage and North-West Alison Point locations are only separated by a distance of approximately 40 km. The results of the Moran et al. [1993] study indicate that there is limited mixing of adult Bluespotted Emperor assemblages. This indicates that in Western Australia, Bluespotted Emperor may comprise separate management units, if management arrangements are mediated in a way that harmonises with the spatial patterns of exploitation.

Here, assessment of stock status is presented at the management unit level—Pilbara and Kimberley (Western Australia); and at the jurisdictional level—Northern Territory.

Toggle content

Stock Status

Kimberley

Bluespotted Emperor are landed in the Northern Demersal Scalefish Managed Fishery (NDSMF) in the Kimberley management region of the North Coast Bioregion of Western Australia [Newman et al. 2018a]. Bluespotted Emperor in this management unit are assessed on the basis of the status of two indicator species (Red Emperor and Goldband Snapper) that are considered to represent the entire inshore demersal suite of species occurring at depths of 30–250 m [Newman et al. 2018b]. The major performance measures for these indicator species are estimates of relative spawning stock levels derived using an integrated age-structured model. The target level of spawning biomass is 40 per cent of the unfished level. The limit level is 30 per cent of the estimate of initial spawning biomass [DPIRD 2017]. The spawning biomass levels of these two indicator species were either greater than the target level or between the target level and the threshold level in the NDSMF in 2014 [Newman et al. 2018a]. The above evidence indicates that the biomass of Bluespotted Emperor is unlikely to be depleted and that recruitment is unlikely to be impaired.

The catch of Bluespotted Emperor in the NDSMF has been low and stable for the past five years (2013–17), ranging from 42–63 tonnes (t), with a mean annual catch of 53 t. 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 Kimberley management unit is classified as a sustainable stock.

Northern Territory

Stock status for the Northern Territory jurisdiction is reported as Negligible due to extremely low or zero catches from this region, and because the stock is not subject to targeted fishing. There has been no recent catch reported for this species although there is probably a small annual catch (< 1 t) that is misreported as ‘Emperor general’ in recreational fishing surveys.

Pilbara

Bluespotted Emperor are landed primarily in the Pilbara Trap Managed Fishery and Pilbara Fish Trawl Interim Managed Fishery in the Pilbara management region of the North Coast Bioregion of Western Australia [Newman et al. 2018a]. The major performance measures for the Pilbara management unit are based on estimates of current relative spawning stock levels of Bluespotted Emperor in the Pilbara Demersal Scalefish Fisheries derived using an integrated age-structured model. The target level of spawning biomass is 40 per cent of unfished (1972) biomass. The limit level is 30 per cent of the unfished spawning biomass [DPIRD 2017]. The spawning biomass level of Bluespotted Emperor overall (across all management areas was greater than 40 per cent in the Pilbara Demersal Scalefish Fisheries in 2015 (the year the last integrated assessment was undertaken). The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

An assessment of fishing mortality derived from representative samples of the age structure of Bluespotted Emperor has also been undertaken for separate management areas in the Pilbara subregion in 2015. These fishing mortality (F) based assessments utilise the following reference levels based on ratios of natural mortality (M) that are applicable to each species, i.e. Ftarget = 2/3M, Fthreshold = M and Flimit = 3/2M [DPIRD 2017]. The fishing mortality based assessments and associated uncertainty ranges indicated that the fishing levels on Bluespotted Emperor in 2015 were mainly between the target and threshold levels in all management areas. The estimates of F indicate that the overall management unit is unlikely to have been heavily exploited during the time series for which data are available. The low estimates of F in the west, in its main area of abundance, further indicate that the exploitation on the overall management unit is currently low. 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 Pilbara management unit is classified as a sustainable stock.

Toggle content

Biology

Bluespotted Emperor biology [Wakefield et al. unpublished data]

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Bluespotted Emperor 16 years, 384 mm FL 1.6 years, 206 mm FL
Toggle content

Distributions

Distribution of reported commercial catch of Bluespotted Emperor

Toggle content

Tables

Fishing methods
Western Australia Northern Territory
Commercial
Hand Line, Hand Reel or Powered Reels
Otter Trawl
Unspecified
Fish Trap
Recreational
Spearfishing
Handline
Charter
Handline
Management methods
Method Western Australia Northern Territory
Charter
Bag limits
Limited entry
Passenger restrictions
Size limit
Spatial closures
Spatial zoning
Commercial
Effort limits
Gear restrictions
Limited entry
Size limit
Spatial closures
Spatial zoning
Total allowable catch
Total allowable effort
Vessel restrictions
Indigenous
Laws of general application
Recreational
Bag limits
Licence (Recreational Fishing from Boat License)
Possession limit
Size limit
Spatial closures
Active vessels
Western Australia Northern Territory
<3 in Charter, 5 in NDSF, <3 in PFTIMF, <3 in PLF, <3 in PTMF
Charter
Tour Operator (WA)
NDSF
Northern Demersal Scalefish Fishery (WA)
PFTIMF
Pilbara Fish Trawl (Interim) Managed Fishery (WA)
PLF
Pilbara Line Fishery (WA)
PTMF
Pilbara Trap Managed Fishery (WA)
Catch
Western Australia Northern Territory
Commercial 41.85t in NDSMF, 358.57t in PFTIMF, PLF, PTMF
Charter 0.25 t
Indigenous Unknown
Recreational 0.52 t ± 0.173 t se
NDSMF
Northern Demersal Scalefish Managed Fishery (WA)
PFTIMF
Pilbara Fish Trawl (Interim) Managed Fishery (WA)
PLF
Pilbara Line Fishery (WA)
PTMF
Pilbara Trap Managed Fishery (WA)

Western Australia Active Vessels data is confidential as there were fewer than three vessels in the Pilbara Fish Trawl Interim Managed Fishery, the Pilbara Trap Managed Fishery and the West Coast Demersal Gillnet and Demersal Longline (Interim) Managed Fishery.

Western Australia – Recreational (Catch) Boat-based recreational catch is from 1 September 2015–31 August 2016. These data are derived from those reported in Ryan et al. 2017.

Western Australia – Recreational (management methods) A Recreational Fishing from Boat Licence 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 Subject to the defence that applies under 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 “…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”.

Toggle content

Catch Chart

Commercial catch of Bluespotted Emperor - note confidential catch not shown

Toggle content

References

  1. Carpenter, KE and Niem, VH (eds.) 2001, FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Volume 5. Bony fishes part 3 (Menidae to Pomacentridae). Rome, FAO, pp. 2791–3380.
  2. 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.
  3. 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.
  4. Moran M, Edmonds J, Jenke J, Cassells G and Burton C 1993, Fisheries biology of emperors (Lethrinidae) in north-west Australian coastal waters. Final Report to the Fisheries Research and Development Corporation (FRDC) on Project No. 89/20. Fisheries Department, Perth, Western Australia. 58p.
  5. 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: 1122.
  6. Newman, SJ, Wakefield, C, Skepper, C, Boddington, D, Jones, R and Smith, E 2018, North Coast Demersal Resource Status Report 2017. pp. 127–133. In: Gaughan, DJ and Santoro, K (eds.). Status Reports of the Fisheries and Aquatic Resources of Western Australia 2016/17: The State of the Fisheries. Department of Primary Industries and Regional Development, Western Australia, Perth, Australia. 237p.
  7. Ryan, KL, Hall, NG, Lai, EK, Smallwood, CB, Taylor, SM, Wise, BS 2017, Statewide survey of boat-based recreational fishing in Western Australia 2015/16. Fisheries research Report No. 287. Department of Primary Industries and Regional Development, Government of Western Australia, Perth.