Western King Prawn (2020)
Date Published: June 2021
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Western King Prawn is harvested in WA, SA and QLD. Stocks in all states are sustainable, except for the South Australian West Coast Prawn Fishery, which is depleting.
Stock Status Overview
|Western Australia||South West Trawl Managed Fishery||Sustainable||Catch|
|Western Australia||Exmouth Gulf Prawn Managed Fishery||Sustainable||
Survey catch rates, size composition, catch, catch rates
|Western Australia||North Coast Prawn Managed Fisheries||Sustainable||
|Western Australia||Shark Bay Prawn Managed Fishery||Sustainable||
Survey catch rates, size composition, catch, catch rates
Western King Prawn is distributed throughout the Indo–West Pacific [Grey et al. 1983]. No research has been conducted into Western King Prawn biological stock structure in Western Australia or Queensland, and status in those states is therefore reported at the management unit level. In South Australia, one study of the genetic structure of Western King Prawn found no differences between the three fisheries [Carrick 2003], however, each fishery functions as an independent population at time scales relevant to management, with distinct adult and juvenile habitats and independent variations in recruitment and abundance. Each fishery in South Australia is therefore assessed and managed as a separate management unit.
Here, assessment of stock status is presented at the management unit level—Exmouth Gulf Prawn Managed Fishery, North Coast Prawn Managed Fisheries, Shark Bay Prawn Managed Fishery, South West Trawl Managed Fishery (Western Australia); East Coast Otter Trawl Fishery (Queensland); Gulf St. Vincent Prawn Fishery, Spencer Gulf Prawn Fishery, and West Coast Prawn Fishery (South Australia).
Exmouth Gulf Prawn Managed Fishery
As with the Shark Bay management unit, the status of stocks is assessed annually using a weight-of-evidence approach that considers all available information about the stocks [Wise et al. 2007]. The assessment is based on a combination of fishery-independent and fishery-dependent catch rates where fishery-independent surveys provide the recruitment indices and fishery-dependent data provide the spawning stock indices. Fishery-independent sampling of the spawning stock has been undertaken since 2016 and will be utilised in combination with the fishery dependent data when a sufficient time series is available. Analysis of these two indices from the 1970s to 1990s provide no evidence of a stock-recruitment relationship for Western King Prawn [Caputi et al. 1998], with no indication of reduced recruitment in relation to spawning stock sizes over this period. Elevated temperatures since 2011 in this region appears to be contributing to lower than average recruitment levels [Caputi et al. 2014a], in response to which conservative harvesting strategies have been introduced, resulting in reduced annual landings.
Fishery-independent recruitment surveys have been undertaken in March and April each year since 1985 to assess prawn abundance and size structure and are used for a catch prediction [Caputi et al. 2014b] and management decisions such as spatial-temporal opening of fishing areas [Kangas et al. 2015a, DoF 2014]. In 2019, the Western King Prawn fishery-independent survey mean recruitment index was 47.6 kg per hour, well above the target [DoF 2018] (30 kg per hour). The spawning stock commercial catch rate index in August–September in key Western King Prawn fishing grounds provides a long-term dataset of spawning stock abundance. For 2019, the mean commercial catch rate was 30.4 kg per hour, above the target (25 kg per hour) [DoF 2014]. The fishery-independent survey in 2019 indicated a mean catch rate of 40.3 kg per hour in August and 29.2 kg per hour in September with an average over that period of 34.8 kg per hour, well above the target reference level [25 kg/hr, DOF 2014].
Historical commercial catch and catch rates from 1989–98, when it was known that recruitment was not affected by fishing effort, were used as the basis for calculating target total catch ranges for this stock [Gaughan and Santoro 2020] (350–500 tonnes (t)) and a mean commercial catch rate target (12 kg per hour; range 8–14 kg per hour). However, due to the apparent negative impacts of increased water temperature on Western King Prawn recruitment and with the level of effort having declined for the fishery as a result of fleet reductions and targeting larger prawns, a catch range based on more recent years (2007–16) of production, sets a revised catch range of 100-450 t and a mean catch rate target (11 kg per hour; range 5–19 kg per hour). The commercial catch for 2019 of 194 t was within the target range as was the mean commercial catch rate (7.9 kg per hour).
The above evidence indicates that the biomass of the management unit is unlikely to be depleted and that recruitment is unlikely to be impaired. Furthermore, the evidence indicates that the current level of fishing pressure is unlikely to cause the management unit to become recruitment impaired.
On the basis of the evidence provided above, the Exmouth Gulf Prawn Managed Fishery (Western Australia) management unit is classified as a sustainable stock.
North Coast Prawn Managed Fisheries
The North Coast Prawn Managed Fisheries (Western Australia) management unit is made up of four separate multispecies prawn fisheries but is reported as one unit due to minimal catches. Western King Prawn forms a very minor part of total prawn landings in these fisheries and in some years no Western King Prawns are landed in at least one of these four fisheries [Gaughan and Santoro 2020]. Total commercial catch for 2019 was 5.5 tonnes with the Nickol Bay prawn fishery landing the majority of the total catch. Only in the Broome Prawn Managed Fishery is Western King Prawn historically the key target species, but costs and logistics of fishing in this fairly remote fishery has meant that since 2008 only one or two out of five licensed boats have briefly fished in this fishery and then only when transiting through the area to other more productive fisheries. No prawn landings were recorded in the Broome fishery in 2019. Elevated water temperatures since 2011 in these North Coast Prawn Managed Fisheries may be contributing to lower than average recruitment levels [Caputi et al. 2014a] hence low catches.
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 North Coast Prawn Managed Fisheries (Western Australia) management unit is classified as a sustainable stock.
Shark Bay Prawn Managed Fishery
The status of the stocks of Western King Prawns in Shark Bay is assessed annually using a weight-of-evidence approach that considers all available information about the stocks [Wise et al. 2007]. The assessment approach is primarily based on monitoring of fishery-independent survey indices of recruitment (March–April) and spawning stock levels (June–August) relative to reference points specified in terms of survey catch rates for these two periods [DoF 2014]. Although these abundance indices are the key indicators for the stocks, other information collected throughout the season (such as commercial catch, effort, grade categories and environmental data) is also evaluated to provide insight on, for example, operational factors that might affect fishery performance, or environmental factors affecting prawn recruitment.
Western King Prawns are comparatively more resilient to fishing than the Brown Tiger Prawn (the other key target species) because they are less catchable (strongly nocturnal and readily bury themselves when disturbed) and have a protracted spawning period [Penn 1984, Penn and Caputi 1986]. The two species overlap in their spatial distribution within Shark Bay, and the rates of fishing that maintain the spawning biomass of Brown Tiger Prawn near target levels are considered to be below those that could result in Western King Prawn becoming recruitment overfished [Caputi et al. 1998].
Spatial and temporal analysis of historical commercial catch and effort data complemented by research sampling to identify key recruitment and spawning grounds provided no evidence of reduced recruitment for Western King Prawns across the range of spawning biomass levels in the 1970s–90s [Caputi et al. 1998], indicating that the spawning stock was never reduced to levels that affected recruitment. During this period, recruitment remained relatively stable despite substantial environmental changes, including variations in the Leeuwin Current, La Niña, and El Niño. There was also no significant correlation between spawning stock and recruitment indices derived from fishery-independent surveys for the Western King Prawn since 2000 [Kangas et al. 2015b] and examination of water temperature effects indicate a positive relationship with recruitment. This relationship is the opposite to what has been experienced in Exmouth Gulf which is probably due to the average water temperatures in Shark Bay being 2–3oC cooler than Exmouth. The fishery-independent recruitment surveys undertaken each year since 2000 assess size structure and are used for catch prediction [Kangas et al. 2015b, Caputi et al. 2014b] and to inform management decisions regarding spatial-temporal opening of fishing areas. These surveys however, have indicated that the mean size of recruiting prawns declined between 2012 and 2018 for both Western King and Brown Tiger prawns and the cause of this is being investigated given the environmental changes occurring in Shark Bay resulting from the heatwave event (2010–11) and the long-term winter cooling trend. In 2019 the size composition for recruiting Western King Prawn had increased but not to sizes observed prior to 2012.
There is no evidence of a declining trend in recruitment in fishery-independent survey indices since 2000 with the annual recruitment indices remaining well above the target reference level each year (25 kg per hour) [DoF 2014]. The fishery-independent recruitment survey in 2019 indicated a mean catch rate (92.1 kg per hour) which was well above the target level, with a catch prediction between 800 and 1200 t [Gaughan and Santoro 2020]. The introduction of seasonal, moon and area-closures since the early 1990s limits the overall fishing effort, providing protection for the breeding stock of Western King Prawn [Kangas et al. 2015b]. Although the spawning stock surveys conducted in Shark Bay target key Brown Tiger Prawn areas, they also cover some of the Western King Prawn spawning areas and are considered to be indicative of overall spawning stock abundance for this species [Kangas et al. 2015b] and a target survey catch rate level of 25 kg per hour is set for this area. In 2019, the mean spawning stock survey catch rate was 61.2 kg per hour.
Historical catch from 1989–98, when it was known that recruitment was not affected by fishing effort, were used as the basis for calculating target total catch ranges for this stock [Gaughan and Santoro 2020] (950–1350 t). Total commercial catch for 2019 of 878 t was in the predicted range but below the target catch range [Gaughan and Santoro 2020, Kangas et al. 2015b]. Due to the lower recruitment level and reduced size of individual recruiting prawns which in combination with changes in the environmental conditions in Shark Bay precautionary management through reduction in overall effort was iimplemented for 2020.
The above evidence indicates that the biomass of the management unit is unlikely to be depleted and that recruitment is unlikely to be impaired. Furthermore, the current level of fishing pressure is unlikely to cause the management unit to become recruitment impaired.
On the basis of the evidence provided above, the Shark Bay Prawn Managed Fishery (Western Australia) management unit is classified as a sustainable stock.
South West Trawl Managed Fishery
The South West Trawl Managed Fishery (Western Australia) (SWTMF) management unit is a comparatively small, low-activity fishery, in which effort has been related to either the abundance of Western King Prawn or Ballot’s Saucer Scallop (Ylistrum balloti) in any given year, which can be highly variable due to sporadic scallop recruitment. Only 2–4 vessels have operated in the fishery since 2005, and they have only covered approximately 1–3 per cent of the allowable fishery area [Gaughan and Santoro 2020]. Since 2005, until the last few years, an average of 168 boat days was recorded annually, with a catch range of Western King Prawn of 3–14 t, compared to 490 boat days on average over the previous 10 years (1995–2004), with a catch range of 9–37 t. Only one boat fished in the SWTMF in 2019, for 32 days. The level of fishing pressure is unlikely to adversely impact the spawning biomass of Western King Prawn. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Furthermore, 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 South West Trawl Managed Fishery (Western Australia) management unit is classified as a sustainable stock.
Western King Prawn biology [Kangas et al. 2015 a,b, Penn 1980, Noell and Hooper 2019]
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|Western King Prawn||2–3 years, maximum 4 years South Australia: males 46 mm CL, females 57 mm CL Western Australia: males 45 mm CL, females 60 mm CL||6–7 months, 25 mm CL|
|Recreational fishing licence|
Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing
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