Minimum Legal Length Research Articles

Stock Enhancement in Greenlip Abalone Part I: Long-Term Growth and Survival

A cohort of Haliotis laevigata, spawned from wild broodstock, was monitored from settlement at a hatchery until age 8. Animals were released into the wild at 31 mm (± 4 SD), targeting an enhancement size-class of 135–145-mm shell length. Release densities were tailored to match wild-stock densities using a size-dependent mortality model. A total of 7,500 animals were released into 24 sites, and each site was precisely mapped to control release densities. Environmental and husbandry factors were also quantified. Initial survival rates (six months post-release) differed significantly among sites (range: 11–67%) but not beyond this time period. Legal minimum length (140 mm) was achieved, on average, at 5 years of age or 3.5 years post-release, and the cohort entered the fishery over 3 years (age 5–8). Cumulative survival at age 5 varied between 20% at the better sites and 6% at the worst sites, with an average of 13%. Water depth was significantly positively correlated with growth (r = 0.47; p < 0.05), but no other ecological variables influenced growth or survival. Husbandry factors were implicated in sites with poor survival, but this was not confirmed statistically. The cohort successfully entered the fishery and was harvested at an overall fishing mortality (F) of 0.27, but site differences in F were significant and highly correlated with growth.

Legal Minimum Lengths and the Management of Abalone Fisheries

A management strategy evaluation framework was used to simulate multiple populations making up a management or quota zone for Australian blacklip abalone (Haliotis rubra). The simulation was conditioned on the properties of blacklip abalone and its fishery on the east coast of Tasmania. Abalone are well known for exhibiting spatial heterogeneity in their biological properties. Each population in the simulation was represented by a size-based population dynamics model and had biological properties of growth, maturation, emergence from crypsis, and mortality specific to each population; the range of these properties varies to different degrees in the different quota zones around Tasmania. The simulation was used to compare the effects of applying different legal minimum length (LML) regulations on the fishery. Because of spatial heterogeneity in growth, a single LML within a zone has always been a compromise between underprotecting some populations and overprotecting others. The simulation was used to determine the protection afforded the overall mature biomass and the variation likely among different populations, and how these populations then responded to exploitation. In addition, when setting an LML within a zone, an analysis was made, using the simulation, of the potential trade-offs between the total allowable catch (TAC), the number of abalone needed to take that TAC, the proportion of the mature biomass protected by the LML, and the stock depletion level after fishing with different LMLs but the same TAG.

Reproductive characteristics of the ocean leatherjacket, Nelusetta ayraudi

The ocean leatherjacket (Nelusetta ayrau- di) is one of the largest members of the family Monacanthidae. Distributed throughout inshore waters around the southern half of Australia, this schooling species supports substantial commercial and recrea- tional fisheries. N. ayraudi do not conform to either of the general reproductive modes reported within the family, but exhibit characteristics of both strong social reproductive behaviour and of being promiscuous and polygynous. Sexual dimorphism, with males and females exhibiting differing colouration and body shapes, and ripe ovaries being an order of magnitude larger than ripe testes, are characteristic of social reproductive behaviour and pair spawning. In contrast, high batch fecundity (mean of 320 oocytes per gram of body weight), similar sizes and ages at sexual maturity (350 mm and 2.5 years respectively) and the forma- tion of large spawning aggregations in offshore waters are characteristic of being promiscuous and polygy- nous. Similar to many other coastal marine species off the east and west coasts of Australia, N. ayraudi are partial spawners during the austral winter months with spawning restricted to the part of their distribution that is towards the upper area of the prevailing currents. It is hypothesized that N. ayraudi off eastern Australia have evolved a life-history strategy whereby fish move northwards through time, spawning occurs in these more northern waters and the southerly flowing Eastern Australian Current facilitates dispersal of eggs and larvae southwards. The reproductive characteris- tics described provide various options to fishery managers who wish to enhance the sustainability of the fishery through increased egg production. These include spatial and temporal fishing closures to protect breeding fish during the spawning period, the protec- tion of juveniles through either inshore area closures, improving the selectivity of fishing gears and/or regulated minimum legal lengths.

A software tool for monitoring legal minimum length of landings: Case study of a fishery in southern Spain

Abstract The regulation of minimum legal size (MLS) of catches is a tool widely applied in the management of fisheries resources, although the MLS does not always coincide with the length at first maturity (LFM). The optimization of this management tool requires a series of quality control in fish markets and transportation. A software application has been developed to make the control of the landings of several target species easier and faster. In order to test and make this tool operational, six species of commercial interest were selected: four species of fish and two species of bivalves. It is proposed to estimate the proportion of illegal specimens in the studied lot from the proportion of illegal individuals found in the samples taken from this lot. The input data for the application are the minimum legal size (MLS) of the species and the total length (TL) of each specimen sampled. The output data is a statistical summary of the percentage of specimens of size less than the legal minimum (TL≤MLS) within different confidence intervals (90%, 95% and 99%). The software developed will serve as a fast, efficient and easy to manage tool that allows inspectors to determine the degree of compliance on MLS control and to make a decision supported by statistical proof on fishing goods.

Linking biology to fishing regulations: Australia’s Murray Crayfish (Euastacus armatus)

Summary Murray Crayfish (Euastacus armatus) can be legally fished by recreational fishers in two states of Australia; however, there is limited published biological information on which recreational fishing regulations can be based. Murray Crayfish populations were surveyed in a 230‐km river reach of the River Murray, New South Wales, Australia. Only 39% of the female Murray Crayfish were sexually matured at the minimum legal length (90‐mm occipital carapace length) set by current fishing regulations. Females first came into berry 16 days after the commencement of the open fishing season. During handling of berried females, an average of 1.3 eggs dropped off when the tail was left closed and 3.9 when the tail was opened. Results of this study suggest that fishing regulations relating to minimum legal length and timing of the open fishing season may need to be re‐evaluated.

Evaluation of population decline and fishing sustainability of the endangered Australian freshwater fish Macquaria australasica

Abstract Macquarie perch, Macquaria australasica Cuvier, is an endangered Australian freshwater fish that has historically supported popular recreational fisheries, but since the 1980s, it has experienced a decline in both distribution and abundance. This study investigated whether a marked decline in the population size of Macquarie perch has occurred at Lake Dartmouth between the mid‐1980s and 2000 and the likelihood of the current legal minimum length (LML) of 350 mm TL protecting the population from recruitment overfishing. Recreational angler survey data showed strong evidence for a temporal population decline. Sampling of the population and construction of a simulation model indicated that the current LML would protect the population from recruitment overfishing. This study highlights the value of specifically investigating suspected threats to endangered fish populations to allow the instigation of effective fisheries management.

Undersized Acanthopagrus butcheri Caught and Released from Commercial Gill Nets Show High Survival Rates in the Gippsland Lakes, Southeastern Australia

AbstractA substantial decline in the commercial catches and catch rates of black bream Acanthopagrus butcheri in the Gippsland Lakes, Australia, signified a depletion of the stock and prompted management to increase the legal minimum length (LML) from 26 cm to 28 cm (total length) in December 2003. The effectiveness of this increase depends on the postrelease survival rate of undersized fish. The present study estimates the rates of release and initial survival (1 h after capture) of undersized A. butcheri during commercial fishing by gill nets in the Gippsland Lakes. Field capture and holding trials were also used to estimate initial and delayed survival (72 h after capture). Almost 6,000 A. butcheri from 347 gill net shots were caught during 2005–2006. The average total length increased by 1 cm from 2005 to 2006, increasing the proportion of the catch that was retained in 2006 (75%) compared with 2005 (50%). The best estimates of initial and delayed survival were 97.2% (SE, 0.3%) and 94.4% (SE, 3.8%), respectively. The total survival rate, which combines the initial survival rate from observer work with the delayed survival rates from the trials, was estimated as 90.8% (SE, 3.8%). The increase in the LML from 26 to 28 cm afforded significant protection to fish between these size limits, but the level of protection will be short term (1 or at most 2 years) for each year‐class because of the growth rate of the species. Released, retained, and postrelease survival rates are discussed for various LMLs and with regard to their implications for fishery management.

Population dynamics and stock status of cobia, Rachycentron canadum, caught in Australian recreational and commercial coastal fisheries

Abstract Age and growth of Rachycentron canadum (L.) was studied in northern and eastern Australia to provide data for a preliminary assessment of the stock and to explore possible fisheries management strategies using minimum legal lengths. Fish collected from commercial and recreational fisheries ranged in size and weight from 125 to 1633 mm fork length (FL) and 0.031 to 55 kg respectively. Annual growth increments in sectioned otoliths formed by November–December. Estimated ages ranged from 0 to 7 yr for both genders. Longevity was estimated to be at least 13 yr. Von Bertalanffy growth function parameters were L = 1160 mm FL, K = 0.63 yr−1 and t0 = −0.21 yr−1. Rachycentron canadum reach 600 mm FL in their first year and over 1000 mm FL in 3 years. Natural and total mortalities were estimated at 0.35 yr−1 and 0.85 yr−1, respectively. Populations of R. canadum may be vulnerable to growth overfishing under the current minimum legal length of 750 mm total length (TL) in Queensland waters. An increase in minimum legal length to 850 mm TL is recommended.

Stock assessment and efficacy of size limits on longtail tuna ( Thunnus tonggol) caught in Australian waters

A stock assessment of longtail tuna ( Thunnus tonggol) in Australian waters was undertaken using per-recruit analyses to assess: (i) the current stock status, and (ii) the effect of Minimum Legal Lengths (MLL) as a management tool. Exploited age compositions differed between the commercial (age classes 3–4 years) and sport fishery (4–6 years). The fishing mortality ( F current) from these fisheries for 2004–2006 was estimated as 0.167–0.320 year −1. Yield-per-recruit analyses revealed that size limits and improving post-release survival had no significant effect on the population. This was due to fish becoming vulnerable to both fisheries at age 2–3 years, after fish presumably had the opportunity to spawn. Under all MLL scenarios, the current fishing mortality rate did not exceed biological reference points. However, any significant increase in fishing mortality may result in recruitment overfishing due to longtail tuna being slow-growing and the stock currently in the vicinity of the F 40% reference point. Since longtail tuna are now a “recreational-only” species in Australia with minimal commercial bycatch, investigation of daily catch limits for the sport fishery requires exploration using more sophisticated age-structured stock assessment models.

Amount and Disposition of Striped Bass Discarded in Delaware's Spring Striped Bass Gill‐Net Fishery during 2002 and 2003: Effects of Regulations and Fishing Strategies

AbstractThe Delaware Division of Fish and Wildlife allocated 95% of the 87,748‐kg annual commercial quota for striped bass Morone saxatilis to the spring gill‐net fishery. Many striped bass were discarded during the fishery for regulatory and market reasons. The Delaware Division of Fish and Wildlife conducted 45 onboard samples with 10 cooperating netters during the 2002 and 2003 spring gill‐net seasons to determine the discard rate and discard mortality rate in this fishery to compare with the 1988 discard and discard mortality rates. Discarded striped bass constituted 29% of the cooperators' total striped bass catch in 2002 and 31% in 2003. Dead discards were 55% of the total discarded striped bass in 2002 and 36% in 2003. Striped bass catch per unit effort, adjusted for the gill‐net meters fished, was significantly higher in 2002–2003 than in 1988, but the discard mortality rate was lower than the earlier figure (47% versus 41%). Females comprised almost 60% of dead discards, and many of the discarded females were mature. Eighty‐four percent of the discards were above the minimum legal length. The number of sublegal striped bass caught increased as net mesh size decreased. Most discards and all dead discards came from anchor nets. As derived from the discard catch per unit effort of the onboard samples, the estimated number of striped bass discarded dead by Delaware Bay anchor gillnetters was 3,577 during the 2002 season and 4,120 during the 2003 season. The management response by the Delaware Division of Fish and Wildlife to discarding in the spring striped bass gill‐net fishery included attempts to curtail anchor netting and encourage drift netting.

Bioaccumulation and trophic transfer of mercury in striped bass ( Morone saxatilis) and tautog ( Tautoga onitis) from the Narragansett Bay (Rhode Island, USA)

We examined the bioaccumulation and trophic transfer of mercury in two marine finfish species, striped bass ( Morone saxatilis) and tautog ( Tautoga onitis), collected from the Narragansett Bay (Rhode Island, USA). For each of these target fish, white muscle tissue was analyzed for total mercury (Hg) and results were evaluated relative to fish age, body size, and Hg content of preferred prey. Dietary and stable isotope analysis was also used to elucidate the effect of trophic processes on Hg concentrations in fish. The Hg content of muscle tissue was positively correlated with fish age and length for both species, although striped bass accumulated Hg faster than tautog. Accelerated Hg bioaccumulation in striped bass is consistent with its high trophic level (trophic level = 4.07) and Hg-enriched prey (forage fish and macrocrustaceans; mean Hg content = 0.03 mg Hg kg wet wt −1). In contrast, tautog maintain a lower trophic status (trophic level = 3.51) and consume prey with lower Hg levels (mussels and crabs; mean Hg content = 0.02 mg Hg kg wet wt −1). Despite differences in Hg bioaccumulation between target fish, the mean Hg concentration of tautog exceeded levels in striped bass (0.24 and 0.16 mg Hg kg wet wt −1, respectively) due to a disparity in age-at-catch between sampled groups (mean age of tautog and bass = 11.3 and 4.3 yr, respectively). Taking into account legal minimum catch lengths further revealed that 75.0% of legal-size striped bass (>70.2 cm TL; n = 4) and 44.8% of tautog (>40.6 cm TL; n = 29) had Hg levels beyond the US EPA regulatory threshold of 0.3 mg Hg kg wet wt −1. Moreover, Hg-length relationships suggest that each target fish meets this threshold near their minimum legal catch length. Our findings reiterate the value of species ecology to improve predictions of fish Hg and permit better management of human contamination by this important dietary source.

The novel use of harvest policies and rapid visual assessment to manage spatially complex abalone resources (Genus Haliotis)

To date, the development of fisheries harvest policies has typically focused on the use of indices estimated from quantitative stock assessment models. Where does this leave the small-scale and spatially complex resources for which costs and logistics prevent adequate data collection for the construction of quantitative assessment models at scales appropriate for the component populations being fished? This paper presents a novel harvest policy framework developed in Australia by the Victorian Western Zone Abalone Diver’s Association (WADA) to assess and manage their resource at the scale of component abalone reefs (100s–1000s m). This novel harvest policy framework uses a rapid visual evaluation of population fecundity based on shell shape and appearance. Codified and applied using a decision tree, it is being used in Australia by an increasing number of zonal abalone industry associations. Abalone populations on reef complexes are being assessed and managed with voluntary catch caps and voluntary minimum lengths larger than legal minimum lengths. It will probably be decades before a satisfactory quantitative analysis on the efficacy of the approach will be possible, but positive anecdotal accounts and the relatively rapid spread of the approach suggest industry members believe they are seeing benefits.

A decision support system for setting legal minimum lengths of fish

Abstract The use of legal minimum lengths is one of the oldest forms of regulation in fisheries management. Management objectives using minimum legal lengths are varied, often conflicting and generally poorly communicated. This paper introduces a decision support system that will assist fisheries managers in determining optimal legal minimum lengths. The system uses multi‐criteria decision analysis to enable the integration of objective scientific and biological information into a system that assesses the success of any potential length limit in achieving each of the management objectives. The system can also document trade‐offs between options that achieve management objectives and short‐term socio‐economic impacts. The decision support system is demonstrated using 13 commercially and recreationally important coastal species from New South Wales, Australia.

Migrations and Biological Characteristics of Adfluvial Coaster Brook Trout in a South Shore Lake Superior Tributary

AbstractWe used fish traps and electrofishing surveys to characterize the biology, life history traits, and potential biotic interactors important to the rehabilitation of native, adfluvial coaster brook trout Salvelinus fontinalis in Lake Superior. This study focused on the Salmon Trout River, Michigan, which is the site of the last known remnant population of adfluvial brook trout on the south shore of Lake Superior. The brook trout captured in passive traps (weirs) in the river ranged from 56 to 554 mm in total length (TL) and from 0 (young of the year) to 6 years of age. This population displayed a protracted 5‐month migration into the river but one that included relatively few fish. Coaster brook trout in this population appear to initiate adfluvial migrations near age 3 and 300 mm TL. Relative weight values increased with fish length and therefore reproductive life stage, possibly indicating the shift from river to lake habitats. This population of coaster brook trout is small and subject to potential biotic interactions with exotic species and population limitation because of an active fishery in the lake and river. Migratory runs of brook trout coincided with large runs of coho salmon Oncorhynchus kisutch, and the instream juvenile salmonid composition included proportionately high densities of coho salmon and rainbow trout O. mykiss. In addition, Floy tag return data indicated that exploitation of reproductive‐age Salmon Trout River coaster brook trout was at least 12% and may have been as high as 50% in the open waters of Lake Superior. A recent increase in the legal minimum length limit and reduction of the daily bag limit for recreational harvest may slow or reverse this trend.

Estimating post-release survival and the influential factors for recreationally caught Black bream ( Acanthopagrus butcheri) in the Glenelg River, south eastern Australia

Black bream ( Acanthopagrus butcheri) is the main target species amongst the estuarine recreational fisheries of Victoria, Australia. The A. butcheri fishery is managed through legal-minimum length and daily bag limits. The success of this management strategy requires that the survival rate for released fish is high. This study used the most common angling practices to estimate post-release survival and identify influential factors for undersized A. butcheri in Victoria. In total 1557 and 923 A. butcheri were caught and monitored for initial (≤1 h) and delayed (72 h) survival, respectively. Fish were caught across 3 years, with each year separated into cold and warm water periods with 8 fishing trial days in total. Only 1 of the 266 controls used to assess confinement effects died. Total survival was 95% (S.E. ± 0.8%) for shallow- and 74% (S.E. ± 3%) for deep-hooked fish and decreased as fish length increased. A post-mortem (PM) procedure was developed and showed that throat and gill injuries were the most frequent cause of deep-hooking death. It revealed that 97% of hooks left in fish remained there after 72 h and identified hooking location inaccuracies recorded at the time of capture. Total survival for deep-hooked fish was 20% higher when hooks were left in the fish. Deep-hooked fish were more likely to bleed when hooks were removed and total survival was lower for fish that bleed (58%) than fish that did not bleed (80%). Shallow-hooking rates decreased as fish length increased and were higher during warm water compared to cold water trials. The high shallow-hooking and survival rates observed suggest that A. butcheri survival in the fishery would be high, but deep-hooking has the potential to undermine the management strategy. Determining the shallow-hooking rate in the fishery would help clarify the impact of these findings at the fishery level.

Growth and reproductive biology of tarwhine Rhabdosargus sarba (Sparidae) in eastern Australia

The growth and reproductive biology of the commercially and recreationally important sparid fish, tarwhine (Rhabdosargus sarba), was examined from the coastal waters of New South Wales (NSW), south-eastern Australia. Previous research on this species in other parts of the world has yielded conflicting results concerning its growth and reproductive biology. Age estimates were made by counting opaque zones in otolith sections. The method was validated by marking the otoliths of captive fish with alizarin complexone, and also by marginal increment analyses using otoliths from wild-caught fish. Both sexes grew at a similar rate. Von Bertalanffy growth function parameters were: L∞ = 26.40 ± 0.40 cm fork length (FL), k = 0.39 ± 0.02 year–1 and to = –0.56 ± 0.09 years. The maximum estimated age was 16.5 years. Spawning occurred from May to August with a peak in July. Both sexes matured at a similar size (L50 = 19.44 ± 0.15 cm FL), which was larger than the current minimum legal length in NSW. Ovotestes were identified in adult tarwhine and were confirmed by histological analyses. Results of this study provided evidence that tarwhine are likely to be rudimentary hermaphrodites in eastern Australia and are more similar in growth rate, maximum size/age, and reproductive biology to tarwhine from Western Australia than those from other parts of the world.

The effect of hook/bait size and angling technique on the hooking location and the catch of recreationally caught black bream Acanthopagrus butcheri

The black bream Acanthopagrus butcheri recreational fishery is the largest estuarine fishery in Victoria. This fishery is managed through legal-minimum length and daily bag limits. The success of this management strategy requires a high survival rate for released fish. Deep-hooking is known to reduce the chance of fish survival after recreational capture and release. This study investigated the potential to reduce deep-hooking and the number of under-size A. butcheri caught by varying angling gear and techniques. Three sizes of long shank hook (small [size 8], medium [size 4] and large [size 1/0]) and two angling techniques (slack line and tight line) were tested for their deep-hooking rates and selectivity characteristics. Increasing the hook size from small to large decreased the likelihood of deep-hooking by 6.6 times (95% CI 2.3–16.3 times). Fishing with a tight line instead of a slack line decreased the chance of deep-hooking by almost 100% (95% CI 0.8–3.6). Fishing with a large hook instead of a small hook significantly ( F = 6.71, df = 2, P = <0.001) increased the mean A. butcheri length , although this mean size increase was less than 1 cm. This study was able to identify angling gear and angling technique manipulations that reduced the rate of deep-hooking when targeting A. butcheri in Victorian estuaries.

Population dynamics and fishery benefits of a large legal size of a pelagic sportfish, the Talang queenfish, Scomberoides commersonnianus, in northern Australia

The life history of an increasingly important pelagic commercial and sport fish, the Talang queenfish, Scomberoides commersonnianus, was studied in northern Australia to investigate the stock status and assess current management of the species using minimum legal lengths (MLL). Estimated von Bertalanffy growth parameters were L ∞ = 1404 mm FL, K = 0.10 year −1 and t 0 = −1.21 year −1. There was no significant difference in growth between sexes. Ages ranged from 1 to 11 years with age composition differing between the commercial (mainly 6–7 years) and sport fishery (mainly 2–4 years). Females matured ( L 50) at 635 mm FL and 4–5 years. Spawning occurred between August and March when mature females were estimated to produce 259,488–2,859,935 eggs per spawning. Natural mortality ( M) was estimated as 0.16–0.26 year −1, while the combined fishing mortality ( F current) from commercial and sport fisheries was 0.38–0.48 year −1. Yield-per-recruit analyses revealed that under current MLL limits (no MLL or 45 cm TL) and natural mortality ( M = 0.16, 0.2 and 0.26 year −1), F current exceeded the reference points F max (0.15–0.22 year −1) and F 0.1 (0.10–0.15 year −1), suggesting the stock may be growth overfished if the current situation remains unchanged. Although a stock–recruitment relationship is unknown, spawning stock biomass-per-recruit analysis indicates the stock may also be recruitment overfished since F current exceeded the reference points F 25% (0.19–0.24 year −1) and F 40% (0.11–0.15 year −1). Increasing the MLL corresponding to L 50 of females (70 cm TL) will greatly improve the yield and long-term sustainability of the stock, and also enhance the sport fishery by increasing the number of larger trophy fish.

Seasonal, spatial and gear-related influences on relationships between retained and discarded catches in a multi-species gillnet fishery

A scientific observer program was used to quantify relationships among the compositions and rates of retained and discarded catches taken in a temperate estuarine commercial gillnet fishery in southeastern Australia. Sampling was stratified across six estuaries and three fishing seasons that corresponded to different permitted setting practices (set and immediate retrieve versus overnight set). A total of 265 fishing trips was sampled throughout 2001, yielding 57 species (52 finfish, 3 invertebrate, 1 bird and 1 tortoise), of which 42 and 45 species were retained and discarded, respectively. More species and a greater mean number and weight of total individuals were retained than discarded during each fishing season. Throughout the entire survey, 6.2% by number and 3.3% by weight of catches were discarded. Average retained catches ranged from 37 to 609 kg fisher-day −1 and discarded catches from 1 to 10 kg fisher-day −1. Mugil cephalus and Girella tricuspidata accounted for 85% by number of total observed catches, with a further 10% being contributed by Acanthopagrus australis, Platycephalus fuscus and Portunus pelagicus. G. tricuspidata, A. australis and P. pelagicus below the minimum legal length collectively accounted for 69% by number and 49% by weight of all discards observed. Discarding was greatest in the smallest mesh sizes and during winter when nets can be set overnight. Increasing the minimum permitted mesh size as well as decreasing the maximum soak time of nets set in winter will further reduce the low levels of discarding in this fishery.

Discards from the commercial gillnet fishery for dusky flathead, Platycephalus fuscus, in New South Wales, Australia: spatial variability and initial effects of change in minimum legal length of target species

AbstractA scientific observer programme was used to quantify the composition and magnitude of discards in the gillnet fishery for dusky flathead, Platycephalus fuscus (Cuvier), in three barrier estuaries in New South Wales, Australia, during the 2001 fishing season. Regulations only permit the retention of legal‐sized dusky flathead and legal‐sized blue swimmer crab, Portunus pelagicus L., and mud crab, Scylla serrata (Forskål); all other organisms were discarded. Sampling was stratified into two time periods; before and after 1 July 2001 which coincided with the increase in the minimum legal length (MLL) of dusky flathead from 33 to 36 cm total length (TL). Eighty one catches were sampled, yielding 38 finfish species and two portunid crab species. Legal‐sized dusky flathead were the most abundant organism captured, accounting for 23–47% by number and 34–54% by weight of the mean observed catch depending on the estuary and survey period, with a mean catch of 25–59 flathead weighing 13–25 kg per fishing‐night. Species composition and relative abundance of catches differed among estuaries, but not between sampling periods. Predominant bycatch species included legal and undersize blue swimmer crab, sea mullet, Mugil cephalus L., luderick, Girella tricuspidata (Quoy &amp; Gaimard), bream, Acanthopagrus australis (Günther) and yellowfin leatherjacket, Meuschenia trachylepis (Günther). These five species accounted for 82% of total bycatch by number and 71% by weight, pooled across the three estuaries. More crabs were retained than discarded, with retained legal‐size crabs (byproduct) accounting for 16% of total bycatch by number and 13% by weight, with an average of 5–22 crabs weighing 1–6 kg being caught per fishing‐night, depending on the estuary. Overall, 7% of dusky flathead captured (number) were below the MLL of 36 cm and discarded, suggesting the nets as currently configured may be relatively selective in catching legal‐size flathead. However, 41% of dusky flathead were &lt;40 cm TL, indicating that if the MLL for this species is increased to this length as proposed, new nets must be introduced into the fishery. The findings are discussed in terms of making the flathead fishery more sustainable, including alternative management strategies for the fishery.