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Blue Morwong (2020)

Nemadactylus valenciennesi

  • Jeffrey Norriss (Department of Primary Industries and Regional Development, Western Australia)
  • Steph Blake (Australian Bureau of Agricultural and Resource Economics and Sciences)
  • Fred Bailleul (South Australian Research and Development Institute)
  • Amy Smoothey (Department of Primary Industries, New South Wales)
  • Nils Krueck (Institute for Marine and Antarctic Studies, University of Tasmania)

Date Published: June 2021

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Summary

The biological stock structure of Blue Morwong is unknown, although the its lengthy pelagic larval phase suggests considerable potential for individuals from geographically separated areas to mix. Assessments are presented here at the jurisdictional level. Stocks are classified as sustainable in WA, negligible in NSW and SA, and undefined with limited data in TAS and by the Commonwealth.

Photo credit: Chris Dowling.

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Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
Commonwealth Commonwealth Undefined
New South Wales New South Wales Negligible
South Australia South Australia Negligible
Tasmania Tasmania Undefined
Western Australia Western Australia Sustainable

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

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Stock Structure

Blue Morwong's natural distribution is throughout the southern coastal waters of Australia's mainland. The stock structure is largely unknown. Its family, the Cheilodactylidae, typically have a pelagic larval phase lasting several months, facilitating transport over substantial distances. For Western Australia Coulson et al. [2010] suggested that as juveniles grow, substantial numbers move from the south coast to the lower west coast where they soon mature and spawn. Larvae are then transported south and then eastwards to the south coast, which is a juvenile nursery. Here assessment of stock status is presented at the jurisdictional level—Commonwealth, New South Wales, South Australia, Tasmania and Western Australia. 

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Stock Status

Commonwealth

In Commonwealth Waters, Blue Morwong are largely taken in the area of the Great Australian Bight by sectors of the Southern and Eastern Scalefish and Shark Fishery (SESSF). An average of around 27 tonnes (t) of Blue Morwong has been caught annually over the last ten years. In 2018–19, 21.4 t were caught. No formal stock assessment has been conducted for this species in Commonwealth waters, however risk assessments undertaken indicate that the species is at low risk from fishing. The stock status for this species is consequently undefined.

New South Wales

Stock status of Blue Morwong in New South Wales is reported as Negligible due to historically low catches in this jurisdiction and the stock has not been subject to targeted commercial fishing and the species is not a major component of recreational landings. Fishing is unlikely to be having a negative impact on the stock.

South Australia

Stock status of Blue Morwong in South Australia is reported as Negligible due to historically low catches in this jurisdiction and the stock has not been subject to targeted fishing. South Australia’s commercial catch of Blue Morwong over the past 20 years has averaged 1.2 t per annum, and the species is not a major component of recreational landings. Fishing is unlikely to be having a negative impact on the stock.

Tasmania

In Tasmanian waters, catches of Blue Morwong are recorded by state authorities and the Commonwealth. Total catches average only about 0.1 t per year, primarily representing records for the Tasmanian Scalefish Fishery and indicating that the species is not actively targeted but largely a by-product of gillnet fishing operations on the northern end of the east coast. The maximum recorded total commercial catch was below 0.4 t in the 1999–00 season. The species is unlikely to be targeted by recreational fishers and species-specific estimates of recreational catches are not available. Overall minor catches suggest that the species is at low risk from fishing, but no formal stock assessment has yet been conducted. The status of the Tasmanian stock of Blue Morwong is consequently undefined.

Western Australia

In Western Australia, Blue Morwong are taken mainly by the commercial demersal gillnet sector off the lower west and south coasts. The size selectivity of the net, coupled with the larger size reached by males, results in a higher level of fishing mortality for males. Catch-at-age sampling of 2,621 south coast Blue Morwong from the demersal gillnet and recreational sectors from 2012 to 2014 suggested regular and consistent recruitment for the previous two decades [Norriss et al. 2016]. The demersal gillnet sample (n = 1,234) from the eastern sub-region of the south coast was considered the most representative for an age based stock assessment. Two alternative methods were used to generate median estimates of female spawning potential ratio (SPR, the reproductive potential of the stock at the current level of fishing mortality compared to that at an unfished level, ± 95 per cent CI): SPR1 = 0.58 (0.46–0.71) and SPR2 = 0.54 (0.41–0.68), with an almost zero chance of breaching the threshold reference point (SPR=0.30) for either method. There was a 7 per cent and 25 per cent chance, respectively, of breaching the threshold reference point (SPR=0.30). For males, SPR1 = 0.36 (0.25–0.51) and SPR2 = 0.34 (0.23–0.50) with a 19% and 31% chance of breaching the threshold reference point, respectively. There was an almost zero chance of males beaching the limit reference point (SPR=0.20). Estimates of natural mortality M (i.e. all sources of mortality other than fishing) were 0.22 (0.18–0.26) and fishing mortality F year-1 were Ffemales = 0.106 (0.072–0.137) and Fmales = 0.180 (0.123–0.231)giving a point estimates of F/M of 0.49 and 0.84 for females and males respectively. The probability of F breaching the threshold level (F/M = 1) was almost zero for females and 25% for males, and almost zero for either sex breaching the limit (F/M = 1.5).

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 Australian jurisdictional stock is classified as a sustainable stock

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Biology

Blue Morwong from the south of Western Australia reach a maximum age of 24 years, are gonochorists (do not functionally change sex) with onset of sexual maturity at age 3 to 8 years at about 40 to 60 cm FL for females and 50 to 65 cm FL for males, with moderately fast growth (at age 5 years average total length was 55 cm for females and 58 cm for males) [Coulson et al. 2010, Norriss et al. 2016].

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

24 years, 98 cm total length

Females: 3–8 years, 400–600 mm FL. Males 3–7 years, 500–650 mm FL.

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Distributions

Distribution of reported commercial catch of Blue Morwong.

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Tables

Fishing methods
Commonwealth Western Australia New South Wales Tasmania South Australia
Commercial
Demersal Longline
Demersal Gillnet
Otter Trawl
Hand Line, Hand Reel or Powered Reels
Line
Dropline
Gillnet
Fish Trap
Longline (Unspecified)
Various
Unspecified
Recreational
Spearfishing
Rod and reel
Charter
Hook and Line
Rod and reel
Management methods
Method Commonwealth Western Australia New South Wales Tasmania South Australia
Charter
Bag limits
License
Limited entry
Marine park closures
Spatial closures
Temporal closures
Commercial
Effort limits
Effort limits (individual transferable effort)
Gear restrictions
Licence
License
Limited entry
Marine park closures
Size limit
Spatial closures
Spatial zoning
Recreational
Bag and possession limits
Fishing gear and method restrictions
Licence (Recreational Fishing from Boat License)
Marine park closures
Size limit
Spatial closures
Temporal closures
Catch
Commonwealth Western Australia New South Wales Tasmania South Australia
Commercial 21.38t 44.59t 856.55kg
Charter 2 t
Recreational 14 t (2017/18)

New South Wales – Indigenous (Management Methods) https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing

New South Wales – Recreational (Catch) Murphy et al. [2020].

 

Tasmania – Commercial (catch) Catches reported for the Tasmanian Scalefish Fishery are for the period 1 July to 30 June the following year. The most recent assessment available is for 2018/19.

Tasmania – Recreational (management methods) A recreational licence is required for fishers using dropline or longline gear, along with nets, such as gillnet or beach seine. A minimum size limit of 250 mm is in place for all Morwong species other than Banded Morwong in Tasmanian waters. A bag limit of 10 fish and a possession limit of 20 fish (all Morwong species other than Banded Morwong) are also in place.

Tasmania – Indigenous (management methods) In Tasmania, Indigenous persons engaged in traditional fishing activities in marine waters are exempt from holding recreational fishing licences, but must comply with all other fisheries rules as if they were licensed. For details, see the policy document "Recognition of Aboriginal Fishing Activities” (https://dpipwe.tas.gov.au/Documents/Policy%20for%20Aboriginal%20tags%20and%20alloting%20an%20UIC.pdf).

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Catch Chart

Commercial catch of Blue Morwong - note confidential catch not shown.

Downloadable reports

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