The status of the primary target species of estuarine and nearshore resource fish in south-west WA is periodically assessed using a weight-of-evidence risk-based approach of all available data. Based on the evidence provided above, the mullet stock in south-west WA is classified as stable.
South-West Estuarine and Nearshore Finfish Resource
The main influence of the clear, warm, nutrient-poor water of the Leeuwin Current is the growth and spread of temperate seagrass. These form extensive meadows in protected coastal waters of the WCB, generally at depths of 20 m (but down to 30 m), and act as important nursery grounds for many fish species.
Selection of Indicator Species for Resource
In line with the current harvest strategy for the resource (see section 7.2), this resource assessment report is currently focused on one of the primary target species for which biomass-based stock assessments are regularly undertaken - mullet. Although not considered a primary species in the context of the harvest strategy for this resource, the report also includes a recent stock assessment for yellowfin.
Sea mullet (Mugil cephalus)
- Taxonomy and Distribution
- Stock Structure
- Life History
- Inherent Vulnerability
Summary of biological parameters for WCB & SCB sea urchins (n/a=not available). et al. 2006) Reproduction gonochoristic; isochronally. Due to the tolerance of this species to a wide range of salinities, sea mullets may occur in the upper reaches of estuaries (Chubb et al. 1981).
Yellowfin whiting (Sillago schomburgkii)
- Taxonomy and Distribution
- Stock Structure
- Life History
- Inherent Vulnerability
Yellowfin whiting (YFW) is endemic to southwestern Australia and ranges from WA (Exmouth) to South Australia (Gulf St Vincent). Monthly proportions of adult yellowfin whiting (fish only >=200 mm TL) at each macroscopic gonad stage, sampled from the Metro Zone of the WCB, largely sampled in but monthly trends the same in previous years, so all years are included).
Fisheries / Sectors Capturing Resource
Susceptibility to commercial and recreational fishing
What is the area overlap (i.e. spatial distribution of fishing effort compared to the distribution of the exploited stock). What is the stock's detectability within the water column in relation to the fishing gear (generally high for target species).
West Coast Estuarine Managed Fishery
History of Development
In addition to this major reduction in vessels, commercial efforts and finfish landings in this estuary have also been affected by several other major events: i) major environmental changes (eutrophication leading to algal blooms in the 1980s and 1990s, then implementation of the Dawesville Cut in 1994 leading to increased marine impact), which affected catchability and species composition; ii) change from gill nets to seines to target crabs during the period 1996-1999, which .. eliminated the by-product of fish previously taken while targeting crabs; iii) implementation of the first formal harvest strategy for finfish in 2015. Annual total retained fish catches (tonnes) and fishing effort (number of active boats) in each area of the commercial West Coast Estuarine Managed Fishery between 1912 and 2015, the year of the first formal harvest strategy.
Current Fishing Activities
Fishing Methods and Gear
Shark Bay Beach Seine and Mesh Net Managed Fishery
History of Development
Current Fishing Activities
Shark Bay Shark Net and Shark Bay Marine Park Managed Fishery Boundaries in Shark Bay Inner Shark Bay.
Fishing Methods and Gear
The catch is usually transported by truck to the processing plant within 24 hours of capture. After this period, the mullet begins to spawn in deeper water (and becomes inaccessible to fishermen) or has finished spawning and is in poor condition (low market value). The processing plant effectively determines the fishing season for sea mullet by refusing to accept catches during the spawning and post-spawning periods.
Recreational Fishery
History of Development
Whiting catches occur mainly from April to September, when tides are high, and fishermen have the easiest access to shallow banks (Lenanton 1970). Catch levels are strongly influenced by the processing factory, which sets catch quotas for tailoring to maintain prices within the limited market demand for this species. Western yellowfin bream catches occur mainly in August, when fish form dense spawning aggregations and are therefore highly accessible to anglers.
Current Fishing Activities
Fishing Methods and Gear
Customary Fishing
Illegal, Unreported or Unregulated Fishing
Management System
The West Coast Estuarine Managed Fishery
The majority of the commercial catch of estuarine and coastal finfish in the West Coast Bioregion is taken by the Peel-Harvey Estuary Fishery (Area 2 of the . WCEMF), which has been certified as sustainable against the highly respected MSC Standard for Sustainable Fishing since 2016. Fishermen in the Peel-Harvey Estuary primarily target mullet and yellowfin whiting to supply local markets.
Shark Bay Beach Seine and Mesh Net Managed Fishery
Recreational / Charter Fishery
These limits applied to both commercial and recreational fishermen until 1991 when the LML for recreationally caught herring was removed. In February 2013, a statewide daily catch limit of 30 'other fin whales' (including herring) was introduced in all bioregions. In March 2015, the specific bag limit for herring was reduced to 12 while still remaining within the state-wide mixed species limit of 30 "other fin whales."
Harvest Strategy
Fishing impacts are considered an undesirable level of risk to any conserved species' populations, i.e. high risk. Fishing impacts are considered an undesirable level of risk to any bycatch species' populations, i.e. high risk. Fishing impacts are considered an undesirable level of risk for any ETP species.
External Influences
- Environmental Factors
- Introduced Pest Species
- Market Influences
- Non-WA Managed Fisheries
- Other Activities
A smaller portion of the catch is used as bait by the fishermen in WCEMF Area 2 who are also licensed to catch blue swimmer crabs in the estuary. This market shift and change in demand has significantly impacted red mullet catches in WCEMF Area 2, which are below historical levels. Whiting species, whitebait and southern garfish are sold for human consumption, with a relatively strong and consistent market demand for these species.
Range of Information
During the 1970s and early 1980s, large quantities of sea mullet were sold as bait, mainly for the Western Rock Lobster Managed Fishery. Summary of information available for the assessment of southern nearshore fin whale species, specifically the mullet (Mugil cephalus) and yellowfin whiting (Sillago schomburgkii). Dependent Monitoring of commercial catch and effort trends, calculation of catch rates and the area fished.
Monitoring
- Commercial Catch and Effort
- Recreational / Charter Catch and Effort
- Fishery-Dependent Monitoring
- Fishery-Independent Monitoring
- Environmental Monitoring
- Other Information
This data is collected and collated by DPIRD and stored in a Catch and Effort Statistics (CAES) database. Since 2011, a biennial state-wide recreational survey has been conducted to collect information on private (non-charter) recreational boat-based catch and effort in WA (Ryan et al. Since 2001, it has been a statutory requirement for boat-based charter fishing operators to submit monthly statements detailing information on catches and efforts.
Assessment Principles
Regardless of the types of assessment methodologies used, all inventory assessments performed by the department follow a risk-based, weight-of-evidence approach (Fletcher 2015). For each species, all lines of evidence are then combined within the department's ISO 31000-based risk assessment framework (see Fletcher 2015) to determine the most appropriate combinations of impacts. The strength of the weight-of-evidence risk-based approach is that it explicitly shows which lines of evidence are consistent or inconsistent with a specific level of consequence and thus where there are uncertainties that help determine the overall level of risk.
Assessment Overview
Peer Review of Assessment
A weight-of-evidence approach involving an age-based Level 3 assessment has been used by the Department for a number of fish stocks (e.g. Wise et al. The most recent Level 3 assessment for King George mole was subject to external peer review prior to publication (Fisher et al. 2014).All coastal and estuarine bonyfish fisheries were previously assessed against the Marine Stewardship Council (MSC) Standard for Sustainable Fisheries in 2013–2014 using a bioregional assessment approach (Bellchambers et al. 2016).
Analyses and Assessments
Data Used in Assessment
Catch and Effort Trends
Yellowfin whiting is caught with gill nets and trawl nets in the Peel-Harvey Estuary. Landings take place in the summer (December-February) in the SWBBF and the WCBBMF (and also the WCB recreational fisheries). Anecdotal evidence suggests that yellowfin whiting is a popular species caught in the summer by recreational fishermen ashore in the WCB and GCB.
Catch Distribution Trends
Yellow barb The limits of any commercial fishery are fixed so there is little room for intra-fishery variation in catch or effort, but inter-fishery variation can occur.
Fishery-Dependent Catch Rate Analyses
Commercial fisheries catch figures indicate a sudden, large increase in abundance in each bioregion after the 2011 heat wave, peaking first in the Gascoyne, then in the West Coast bioregion, and finally in the South Coast bioregion (Figure 1). 9.12). In the SCB, catch rates suggest a gradual increase in abundance during followed by a rapid increase, peaking in 2016. Yellowfin Tuna Whiting Catch rates from commercial fisheries indicate a sudden, large increase in abundance in each bioregion following the heat wave of 2011, peaking first in the Gascoyne, then West Coast Bioregion, and finally in the South Coast Bioregion.
Trends in Age/Length Structures
Length composition data for male (blue) and female (red) red mullet sampled from commercial catches in the Shark Bay. Yellowfin whiting In the West Coast Bioregion, the maximum age of fish sampled in 2015 and 2016 was 9 years in the Metro Zone and 11 years in the Southwest Zone. Given the maximum observed age for species is 12 years, the age structure in the West Coast Bioregion suggests a.
Productivity Susceptibility Analysis
PSA sensitivity results for each fishery/sector affecting yellowfin whiting (Sillago schomburgkii) in south-west WA. Sea mullet Sea mullet have low to moderate longevity (maximum age recorded in WA is 12 years), mature at around 3 to 4 years, and have high fecundity. Based on a productivity score of 1.29 and a key fisheries sensitivity score of 1.65, the overall PSA score of 2.09 indicates a low risk of overexploitation of the stock under current management arrangements and fishing effort.
Catch Curve Analysis
Age-based fishing mortality and selectivity estimates (±95% confidence intervals) derived from catch-curve analysis of age-composition data for yellowbelly sampled from commercial and recreational fisheries in the West Coast Bioregion in 2015 and 2016. Perennial, variable Model of recruitment-catch curve (blue line) fitted to age-composition data for yellowfin sampled from. Assuming a natural mortality (M) value for yellow perch of 0.35 yr-1, estimates of fishing mortality (F) are derived from a catch curve model fitted to the age composition sample.
Per-Recruit Analysis and Extended Equilibrium Age-Structured Model
The SPR analyzes were based on catch curve estimates of F and selectivity for the commercial sector, in addition to available biological information for this species (DPIRD unpublished data). As these estimates are all above the SPR target of 0.4 and well above the SPR threshold of 0.3 considered to be equivalent to BMSY, current fishing levels are considered acceptable. The dashed lines indicate the current SPR estimates based on the commercial F estimate of 0.6 yr−1 for 2015–16.
Biomass Dynamics Modelling
Total sea mullet catch (tons, t) in WA and (Bottom plot) unadjusted (black line) and adjusted (blue line) catch per unit effort (CPUE; kg/day) in the Shark Bay commercial fishery. Fit of Schaefer ADMB model to nominal, adjusted (for changes in fishing efficiency) catch rate data for sea marten in Shark Bay. Results from a Schaefer biomass dynamic model adjusted to commercial catches and catch rates indicate that the sea mullet stock has been largely maintained above the level of BMSY.
Catch-MSY Modelling
The model shows that biomass stocks gradually declined from 1941 to the early 1980s due to increases in catch and exploitation to levels expected to reach and briefly exceed MSY. Model-derived estimates (±95% CL) of K, r, MSY, and current (2020) levels of biomass and fishing mortality relative to levels expected to reach MSY (ie, B/BMSY and F/FMSY) catch-only (CMSY; Froese et al. 2017) adjusted for sea mullet catch data in south-west WA. Assuming a moderate level of productivity for sea mullet (r results from the catch-only model (CMSY; Froese et al. 2017) adjusted to the time series of commercial catches show that the annual catch mostly remained below the estimated maximum sustainable catch of 642 t throughout history of fishing.
Stock Status Summary
Sea mullet
Sea mullet catches in the Gascoyne Coastal Bioregion were primarily caught by the Shark Bay Beach Seine and Mesh Net Managed Fishery. Over the past five years, less than 10% of the total annual catch has been caught in the South Coast bioregion. C4 (Major depletion): Remote L1 – Annual commercial catch rates of young sea mullet in the Peel-Harvey estuary since 1975 show no evidence of recruitment loss of the stock to date.
Yellowfin whiting
Biology of two shoefish species (Mugilidae) in five estuaries on the south coast of Western Australia. Western Australian Fisheries and Aquatic Resources Status Reports 2014/15: The State of Fisheries. Stock status of key indicator species for demersal crustacean fisheries in the West Coast Bioregion.
