Gear Selectivity Research Articles

Length at first maturity and length at first capture for bullet tuna (Auxis rochei Risso, 1810) in the southern waters of Bali

Bullet tuna (Auxis rochei Risso, 1810) is one of the neritic tuna species which has the second largest number of catches after small pelagic fish. The high potential for neritic tuna has a risk of continuous fishing pressure. This study presents mainly two biological indicators, the length at first capture (Lc=L50%) and the length at first maturity (Lm50) of bullet tuna, based on the biological data collected from the southern waters of Bali from June to November 2021. Parameters and characteristics of biological aspects are expected to be useful in policies in determining the optimum catch size, restrictions on fishing effort and determining the optimum of mesh size to be used in commercial fishing. Biological sampling was conducted at Fish Landing Base Kedonganan Bali from the catches of the neritic gillnet. A total of 151 female fish and 95 male fish were studied. Fresh gonad samples were fixed and analyzed histologically by a paraffin method and Harris-Haematoxylin and Eosin staining. The results showed that the length at first capture (Lc=L50% = 20,1 cm) was significantly lower than the length at first maturity (Lm50 = 22,76 cm); this was indicating that the young fish (the immature and never spawn) were dominant in the catch and would lead to an overfishing status. It is recommended that the fishing efforts and gear selectivity of bullet tuna with neritic gillnets must better manage for the sustainability of the fish resources.

Effect of the Nordmøre grid bar spacing on size selectivity, catch efficiency and bycatch of the Barents Sea Northern shrimp fishery.

The introduction of the Nordmøre grid in shrimp trawls has reduced the bycatch of non-target species. In the Norwegian Northern shrimp (Pandalus borealis) fishery, the mandatory selective gear consists of a Nordmøre grid with 19 mm bar spacing combined with a 35 mm mesh size diamond mesh codend. However, fish bycatch in shrimp trawls remains a challenge and further modifications of the gear that can improve selectivity are still sought. Therefore, this study estimated and compared the size selectivity of Nordmøre grids with bar spacings of 17 and 21 mm. Further, the effect of applying these two grids on trawl size selectivity was predicted and compared to the legislated gear configuration. Experimental fishing trials were conducted in the Barents Sea where the bottom trawl fleet targets Northern shrimp. Results were obtained for the target species and two by-catch species: cod (Gadus morhua) and American plaice (Hippoglossoides platessoides). This study demonstrated that reducing bar spacing can significantly reduce fish bycatch while only marginally affecting catch efficiency of Northern shrimp. This is a potentially important finding from a management perspective that could be applicable to other shrimp fisheries where flexibility in the use of different grid bar spacings may be beneficial to maximize the reduction of unwanted bycatch while minimizing the loss of target species.

Effects of fishery and environmental factors on a novel multispecies pot targeting European lobster (Homarus gammarus), Atlantic cod (Gadus morhua) and edible crab (Cancer pagurus)

Small-scale fisheries along the Swedish west coast are often operated by using small vessels, targeting multiple species by means of pots and gillnets. Fisheries using pots targeting shellfish such as European lobster (Homarus gammarus), and edible crab (Cancer pagurus) along the Swedish west coast have a relatively high economic value. However, gillnet fisheries targeting demersal fish are currently diminishing primarily due to depleted fish stocks and increased seal depredation. Small-scale fisheries are considered sustainable fisheries due to the use of selective gears and low energy consumption. To be able to retain and promote a sustainable small-scale fishery, there is a need to develop an economically viable fishery, where selective, seal-safe and sustainable gear is utilized. One potential way forward could be to develop a pot to be used for multiple target species traditionally caught in pots and gillnets. Since both shellfish and cod (Gadus morhua) can be caught in pots, the objective of this work was to develop a multispecies pot targeting lobster, edible crab and cod. Seven multi-species pots were developed and tested off the west coast of Sweden between 2015 and 2017. The catch rate, defined as catch per pot per day (CPUE) of lobster, edible crab and cod, was evaluated taking into regard fisheries-related variables such as pot type, bait, soak time, seal damage and abundance of species in the pot. The relative CPUE of lobster and cod was highest in larger pots with two chambers and three open entrances. The highest CPUE for lobster was 0.24 individuals per pot and the highest CPUE for cod was 0.17 individuals per pot. Pots with entrances equipped with funnels, preventing cod from escaping, also had a high cod CPUE (0.23 individuals per). The CPUE of crabs was not affected by pot type. For cod, lobster and crab, the CPUE significantly decreased with increasing soak time. Seal damage only occurred when cod were trapped in the pots and the CPUE of cod was higher in pots subjected to seal damage, indicating that seals raid pots specifically when cods are trapped inside.

Economic and social impacts of the landing obligation of the European Common Fisheries Policy: A review

The European Union landing obligation (LO) entered fully into force in 2019, with the aim of reducing discards by inducing fishing gear selectivity improvements and fleets’ behaviour changes. However, to date there has been no synthesis review of the economic and social impacts of the LO. To cover this gap, the objective of this paper is to provide a summary of what the scientific literature concludes on the economic and social impact of the LO considering also the exemptions and management adaptations in force. Resultswe show that while the number of scientific studies related to the economic impact of the LO is high, almost all of them are related to the forecasted consequences of the LO rather than actual consequences. Only a few studies used quantitative social indicators to measure the impacts of the LO. Findings from the synthesis review also indicate that the scientific literature generally concludes that the short-term economic and social impacts of the LO are likely to be negative, because choke effects will occur and mitigation measures require time to deliver results, while long term effects are variable and will depend on the mitigation measure in place. However, these results assume there is full compliance by fishers with the LO, while the literature suggests this is not the case. The review concludes that analysis of the economic and social impacts of the LO based on actual and not on forecasted results are scarce, which ultimately drives the policy recommendation of producing actual results and contrasting them with the forecasted results.The results serve as a decision-making framework to determine how critical factors of the LO may have the most economic and social effects, which are relevant in the context of the evaluation of the EU Common Fisheries Policy.

Assessing the economic effects of the European landing obligation on the Spanish fishery in the Celtic Sea

European Union has agreed to implement the landing obligation for all species subject to quota in order to ensure long term harvest in a healthy marine environment, implying a prohibition on discarding species subject to quota that can legally be caught and landed under Community fisheries legislation. Landing obligation has been progressively implemented since 2014 and entered fully into force in January 2019. This work analyses the potential economic effects of the landing obligation on the Spanish fleet fishing in the Celtic Sea. The profitability of the fleet is evaluated in the years preceding the entry into force of the European regulation and compared with the profitability obtained since its implementation. The results show a significant economic impact of the landing obligation on small and micro-enterprises. The first years of partial application of the regulations coincide with a drop in diesel prices that helps smaller companies maintain a high profitability. However, once diesel prices recover, the profitability of micro-enterprises falls to negative values when the application of the discards ban is complete, leading to the closure of many companies. This scenario of effort reduction and control of overexploitation of the fishing grounds, positive from an environmental point of view, nevertheless suggests the need for some kind of institutional support to mitigate the socio-economic damage generated by the landing obligation and to improve the gear selectivity of the fleets concerned, allowing them to adapt to the new management scenario.

Characterization of discards along a wide bathymetric range from a trawl fishery in the NW Mediterranean

Discards represent a loss of natural resources and negatively affect the sustainability of fisheries. Information on discards, such as diversity and size of the species discarded is essential to better manage trawl fisheries. Thus, this study aims to gain knowledge on discards from the Catalan bottom trawl fisheries in the NW Mediterranean Sea to offer information needed for fisheries management. Discard ratios, species composition of discards and lengths of the discards were analyzed from data collected on board commercial trawlers, from November 2018 to December 2020 and analyzed by depth, zone, and season. Discard ratio varied among depths from 30.5% in the shallowest depth (20 – 70 m) to 14.3% in the deepest (400–700 m), with depth being the main factor determining the species composition of discards. This study also focused on the discards of six main commercial species, i.e. European hake (Merluccius merluccius), red mullet (Mullus barbatus), black-bellied angler (Lophius budegassa), poor cod (Trisopterus capelanus), deep-water pink shrimp (Parapenaeus longirostris) and Norway lobster (Nephrops norvegicus). The length at which 50% of individuals were discarded (L50d) was lower than the Length at First Maturity (LFM) and the Minimum Conservation Reference Size (MCRS) for the six species. These findings provide relevant information to comply with the Marine Strategy Framework Directive’s (EU Directive 2008/56/EC) ecosystem approach to fisheries and to evaluate the implementation of measures for fisheries’ best management practices, such as gear selectivity and spatial planning.

Fishers can optimize gear design if the management system allows for enough flexibility: A modified SELTRA codend can reduce fish catch in the Danish trawl fishery for Norway lobster

Through an industry-science collaboration, a modified SELTRA codend consisting of a grid with scaring floats (GSF) was successfully developed by the fishing industry, and tested in a scientific trial on board a twin-rig demersal trawler. The selectivity of the gears used in the fishery needs to be tailored to each vessel and season, as quota availability differs across vessels and seasons. The modified gear aims at avoiding catching unwanted fish when targeting Norway lobster. The use of the modified codend showed good potential for effectively reducing catches of unwanted fish without affecting the catch of the target species Norway lobster. With respect to a standard SELTRA codend, the GSF design led to a significantly lower retention of unwanted fish, with 71 (61–79) % less cod, 94 (73–100) % less saithe and 22 (14–37) % less plaice being retained. The results show that fishers have the knowlegde to develop more selective gears. The authors argue that fisheries management should support such industry driven innovation through more flexible management approaches.

Assessing Sustainability Aspects of Mud Crab (Scylla sp.) Fishery and Its Link to Social-Ecological Traps in the Bangladesh Sundarbans

Small-scale fisheries are affected by both local and external pressures, despite the contribution to poverty alleviation, employment, and food and nutritional security. Diverse social and ecological pressures make small-scale fishing communities trapped in persistent cycles of a particular fisheries resource dependence. Consequently, the overall sustainability of that particular species, especially biological, economic and social aspects, becomes vulnerable. This study investigates the biological, economic, and social aspects of a commercially important fish species, i.e., mud crab (Scylla sp.) and explores its link to social-ecological traps. The findings show how the social-ecological traps are forming based on mud crab resource utilization, poverty, overcapitalization and seasonality of crab availability, coupled with weak institutions and governance. Apart from ongoing environmental risks (e.g., extreme climate events), negative feedback comes from poor enforcement of rules and regulations, illegal and destructive fishing, inadequate income, social conflicts, and declining stock. In response to crises, fishers are increasingly dependent on middlemen, leading to the unfair price of their products compared to the market. To escape from the social-ecological traps, strong local institutions, alternative income opportunities, compliance of fishing laws (e.g., gear selectivity, harvest, and trade prohibition of undersize crabs), strong collaboration between management authority and local stakeholders are important toward ensuring the sustainability of the mud crab fishery in the Bangladesh Sundarbans.

Being able is not necessarily being willing: governance implications of social, policy, and science-related factors influencing uptake of selective gear

AbstractImproving the selectivity of fishing gear and practices has been a challenge for fishers, scientists, and policy-makers for decades. In Europe, urgency increased with the introduction of the landing obligation. Voluntary uptake of proven selective gears has been poor across the globe. To increase uptake levels, a move from science-led to industry-led development of selective gears has been advocated. In the Netherlands, gear innovation has, since the mid-2000s, been fisher-led. Nevertheless, this did not result in the assumed increase in uptake. Our qualitative study amongst Dutch demersal fishers shows that decisions to voluntarily adopt proven fishing gear are driven by a complex interplay of social, policy, and science-related factors. These can be attributed to two behavioural components: Willingness and Ability. Willingness, our study showed, is closely linked to: (i) intrinsic motivations and beliefs about sustainable fishing as well as perceptions about the motivations and behaviour of other fishers; (ii) the extent to which fishers consider policy goals and regulations as legitimate; and (iii) strong normative beliefs amongst fishers about the presence (or absence) of a level playing field, in terms of both the same rules applying to all and trust in compliance and enforcement. Ability is associated with knowledge, skills, economic, and legal possibilities to enable voluntary uptake, and tends to be the focus of science and policy. We conclude that a narrow focus on Ability as a driver for encouraging selective fishing is unlikely to result in real changes, and recommend a stronger emphasis on addressing social, policy- and science-related factors associated with Willingness in encouraging more selective fisheries.

Assessing the size selectivity of capture gears for reef fishes using paired stereo-baited remote underwater video

All methods used to sample fish populations exhibit some degree of size selectivity, whether due to the physical properties of the gear, behavioral responses to the gear, or the spatial distribution of the targeted population. In most stock assessments, selectivity functions are assumed and their parameters estimated due to a paucity of empirical data necessary to estimate selectivity. However, incorrect assumptions about selectivity functions can impart significant bias, ultimately affecting assessment outcomes. In 2016, a study was conducted to assess the size selectivity of three fishery-independent survey methods for reef fish in the U.S. South Atlantic: (1) a chevron trap survey, (2) a standardized repetitive timed drop hooked-gear survey, and (3) an unstandardized hooked-gear survey designed to mimic industry fishing practices. Each survey method was paired with a stereo-baited remote underwater video (S-BRUV) camera, which was treated as a comparative reference, considering that it is the least selective of the four gears used. A total of 93 stations were sampled with all gear types, and size data were analyzed for three managed reef fishes: red snapper, Lutjanus campechanus (all gears), black sea bass, Centropristis striata (all gears), and vermilion snapper, Rhomboplites aurorubens (all gears except chevron traps). For red snapper, all three capture gears showed dome-shaped selectivity, the degree of doming being more pronounced for chevron traps as evidenced by a decreasing capture probability for individuals over ~500 mm FL. Despite the largest red snapper (> 800 mm FL) being observed more often on S-BRUV, mean size of red snapper was generally smaller on S-BRUV than for either hooked-gear survey, indicating that hooked-gears capture proportionally fewer smaller red snapper. For black sea bass, there was evidence of flat-topped selectivity for all gear types, but chevron traps captured smaller individuals on average than did hooked gears. For vermilion snapper, both hooked gears exhibited dome-shaped selectivity. Given these results it’s clear that improper assessment of selectivity can lead to poor assumptions about the sampled population. Therefore, when the selectivity function of a particular gear type is not explicitly known, studies that directly estimate selectivity should be conducted to reduce assumptions applied to assessments. This study demonstrates the utility of non-destructive video surveys to complement and evaluate the selectivity functions of standard fisheries assessment methods. Furthermore, efforts to broaden the spatial scale of this study’s survey methods, expand the species to be examined, validate collected life history data, and determine the potential influence of interannual recruitment variability on observed selectivity patterns are necessary to better understand selectivity processes for all reef fishes assessed in the region.

Introducing selfisher: open source software for statistical analyses of fishing gear selectivity

There is a need to improve fishing methods to select for certain sizes and species while excluding others. Experiments are conducted to quantify selectivity of fishing gears and how variables such as gear design (e.g., mesh size, mesh shape), environmental parameters (e.g., light, turbidity, substrate) or biological parameters (e.g., fish condition) alter selectivity; the resulting data need to be analyzed using specialized statistical methods in many cases. Here, we present a new tool for analyzing this type of data: an R package named “selfisher”. It allows estimating multiple fixed effects (e.g., fish length, total catch weight, environmental variables) and random effects (e.g., haul). A bootstrapping procedure is also provided. We demonstrate its use via four case studies, including (A) covered codend analyses of four gears, (B) a paired gear study with numerous covariates, (C) a catch comparison study of unpaired hauls of gillnets and (D) a catch comparison study of paired hauls using polynomials and splines. This software will make it easier to model selectivity, teach statistical methods, and make analyses more repeatable.

Correction to: Gear selectivity of functional traits in coral reef fisheries in Brazil

Correction to: Gear selectivity of functional traits in coral reef fisheries in Brazil

Length-girth relationships of 24 marine fishes in the northern Aegean Sea (eastern Mediterranean Sea)

The knowledge of morphological relationships and particularly of those concerning fish body girth (G) with total length (TL) is necessary in gear selectivity and specifically the technical measures to avoid capture of undersized individuals. This study concerns 24 marine species exploited by the small-scale coastal fleet in the Aegean Sea (eastern Mediterranean Sea), for 6 of which, the TL-G relationships are mentioned for the first time in the Mediterranean Sea and the adjacent seas. Samples were collected seasonally, from April 2016 to February 2017. The coefficients of the linear regression of body girth in three body positions, (Geye, posterior to the eye; Ghead at the posterior end of the operculum; Gmax at the maximum body depth), with the total length were estimated for each species and for the groups formatted when Geye, Ghead and Gmax were plotted against total length for all the species combined. Statistically significant differences among the three groups were detected (ANCOVA, P<0.001). Comparison of the total length-body girth relationships for 18 species previously studied in different geographic areas of the Mediterranean and the adjacent seas, showed differences mainly with the results from Portuguese waters for certain species populations. Based on the resulted equations, the maximum girth (G max) corresponding to the Minimum Conservation Reference Size (MCRS) and to the total length at maturity (L m) were calculated for each species. Identified mesh sizes respective to G max values were quite larger than the minimum legal mesh size for gillnets and the inner sheet of trammel nets, indicating that the relevant current fisheries regulations cannot meet the requirements for sustainable exploitation of fish resources.

Exploring the mechanics of fish escape attempts through mesh

Predictive selectivity modelling is used to study fishing gear selectivity. These models rely on fish morphology parameters and fall-through experiments. Here, we developed a model of the mechanical interaction between a fish and a netting mesh during an escape attempt. In this model, the fish is described with three parameters: the first parameter measures its mechanical ability to penetrate a mesh and the others are body stiffness coefficients accounting for fish body deformation under mesh twine pressure. These parameters were identified from the results of a bench test simulating a fall-through experiment through a single 60-mm Polyethylene (PE) mesh. A rigid circular cone, a rigid elliptical cone and a small number of horse mackerel and haddock, offering a limited length range, were tested. Results were generalised and compared with those obtained on a piece of netting. Within the model's assumptions, it is possible to predict the success of an escape attempt if one knows the three fish parameters and the mesh load in normal and transverse directions. The study showed that escape potential is greater through an actual deformable mesh than through a non-deformable mesh. The potential size of this difference depends on the mesh load and orientation.

Effects of sample gear on estuarine nekton assemblage assessments and food web model simulations

Long-term fisheries-independent sampling data inform population status and trends of species-specific biomass and are often used to drive biomass-based food web models such as the Comprehensive Aquatic Systems Model (CASM). Indicators such as total biomass and mean trophic level derived from these data and from CASM outputs inform management and facilitate assessments of on-going and predicted coastal change and restoration activities on fisheries, but rely on consistent sampling to enable comparisons across space and time. Changes in coastal estuarine gradients, combined with the availability of new sampling technologies, highlight a need to assess the potential consequences of changing sampling technologies on fisheries data and the cascading impact on model outputs. In Louisiana, USA, CASM models are used to inform coastal restoration projects, relying on 40 years of fisheries-independent data derived from 50′ seine sampling. However, alternative use of electrofishers as a sampling method has been proposed to replace the seine sampling. In this study, we examine data from concurrent seine and electrofisher sampling in Barataria Basin, Louisiana, and compare biomass, assemblage data and CASM outputs related to species biomass, food web structure and energy cycling. In a paired comparison of data in 2018–2019, the electrofisher captured higher total catch and diversity compared to the seine. The electrofisher samples were dominated by shrimp (grass, white, brown) and larger bodied fish, while seine samples were dominated by smaller-bodied fish (i.e., anchovy, menhaden). Ecosystem indicators derived from running the CASM using biomass data from seine and electrofisher sampling separately in two different simulation exercises provide contrasting results. In Simulation Exercise 1, the use of different datasets (long-term CASM calibration, 2018–2019 seine, 2018–2019 electrofisher) to initialize the CASM biomasses did not result in large or long-running changes in the simulated biomasses over time. In contrast, in Simulation Exercise 2, CASM model outputs using adjusted gear ratios indicated changes in biomass structure when using electrofisher data, with a doubling of total food web biomass due to the increased shrimp count, and a 13% increase in total energy flow through the food web. Conversions based on area and gear efficiency for overall catch may be useful in maintaining the continuity of historical data. However, differences in species-specific catch due to gear selectivity could have large consequences for constructing and calibrating fish and ecosystem models and remain difficult to reconcile. These differences in assemblages, and estimated biomasses for key food web species, suggest careful consideration in changing gears.

Gear selectivity of functional traits in coral reef fisheries in Brazil

Gear selectivity of functional traits in coral reef fisheries in Brazil

Boat-electrofishing transect location and flow levels: influence on riverine fish monitoring in non-wadeable habitats

Fisheries monitoring can be improved by studying the influence of gear selectivity, sampling design, and habitat conditions. We used boat-electrofishing data to investigate how sample unit placement (shoreline and channel transects) and sampling conditions (low and high flow years) affect detection of fishes in a highly regulated Ontario (Canada) river system. Species detection histories associated with a spatially replicated sampling design was fit to a Bayesian hierarchical site occupancy model for 14 fishes. Habitat (transect location) had a significant effect on detection probabilities (p) for all species, with shoreline sampling more likely to detect species than channel. Sampling year had a significant effect on detectability of six species. The relative influence of habitat and sampling year varied among species. Detection probabilities based on combined shoreline and channel transect data across both years ranged from 0.09 to 0.48 and were positively correlated to species abundance. High detection probabilities and precise occupancy estimates were associated with sunfish and bass abundant in shoreline habitats. Small-bodied species closely associated with the riverbed or exhibiting schooling behavior tended to be poorly detected. Power to detect future changes in species distribution is expected to differ based on habitat sampled, with greater power associated with shoreline boat-electrofishing. Detecting small to moderate changes is not likely for most species. The addition of channel transects did not improve the effectiveness of shoreline sampling. Improvements to the current design could be realized by reallocating sampling effort from channel to shoreline and testing different gear in deep (> 3m) habitats.

Catch Pattern for Antarctic krill (Euphausia superba) of Different Commercial Trawls in Similar Times and Overlapping Fishing Grounds

Antarctic krill (Euphausia superba) is harvested using different design midwater trawls. Knowing the selective properties between trawls is crucial information for the management of the krill resources. This study compared the catch patterns between different commercial krill trawls at similar times and overlapping fishing grounds based on scientific data collected by scientific observers onboard commercial trawlers Long Teng (LT) and Fu Rong Hai (FRH). The results showed significant differences in the length-dependent catch densities and cumulative catch densities of krill between the two trawls. The krill length range in catches from LT's trawl was wider than that of FRH's trawl. Furthermore, the catch would consist of a larger proportion of smaller krill in the LT's trawl. The LT's trawl caught significantly higher proportions of krill below 38 mm than FRH's trawl. Even, the LT's trawl caught substantial numbers of krill <30 mm, whereas the FRH's trawl caught very few of them. The main factors causing the difference between trawls in catch pattern were inferred to be related to gear design including differences in mesh sizes used. The results of this study enhance the quality of comparative analysis of scientific data from commercial trawls and the understanding of gear selectivity of different configuration trawls used for harvesting krill.

MULTIDISCIPLINARY APPROACH TO ASSESS COMMERCIALLY IMPORTANT MARINE STOCKS IN THE COASTAL WATERS OF THE YUCATAN PENINSULA – CONTRIBUTION BY CCBA-UADY

<p><strong>Background. </strong>Since the formation of the research group in marine biology at the CCBA, different aspects of this discipline have been developed. One of them is the identification of populations and possible stocks of fish of commercial importance, using different techniques.<strong> </strong>The stock delineation (or population structure) are central considerations for fishery assessment and strategic management of marine natural resources and have to be addressed from a meta-population perspective where complementary technical approaches meet to enable the best picture to delineate complex stock structures. <strong>Objective.</strong> To review the current knowledge on the stock concept and the use of a multidisciplinary approach to properly assess commercially important marine stocks in the coastal waters of the Yucatan peninsula. <strong>Methodology. </strong>We present the research explored so far by the marine biology laboratory (LABIOMA by its acronym in Spanish) of the Autonomous University of Yucatán regarding the marine resources off the coast of the Yucatan peninsula, and the future lines of investigation pursued by our personnel, from fishing gear selectivity, abundances and catchability estimates, traditional morphometrics, parasitological and life history traits as biological tags, to more precise analyses such as fish otolith shape or even stable isotope analysis, genotypic markers, and marine natural products chemistry. <strong>Main findings. </strong>Single technical approaches are insufficient to delineate complex stock structures, especially in wide marine open access ecosystems, and there is a need to harness the full power of complementary and synergistic multidisciplinary approaches to improve fishery assessment and management efficiency in marine natural resources from the coastal areas of the Yucatan peninsula. <strong>Implications. </strong>Most stock assessment models are based on a single unit stock assumption, however the full impact of management actions, including identifying the complexity of the stock of any marine species subject to fishing, could affect the perpetuity of its abundances if the population subunits are not properly located. <strong>Conclusion. </strong>Identification of stocks is necessary for several reasons including allocation of catches, recognition and protection of nursery and spawning areas, and for development of optimal harvest and monitoring strategies. To this end, the LABIOMA are strengthening the assessments of commercially important marine stocks by using multidisciplinary approaches, whose lines of research represent basic aspects to be known and would be of great help to decision makers at the time of establishing more precisely, catch quotas, fishing areas, closed seasons, and therefore make more efficient the management strategies.</p>

A Bayesian approach to estimating mortality rates using hazard functions: Application to an Australian halfbeak, Hyporhamphus australis fishery

Stock assessments are a key requirement supporting the sustainable harvest of fisheries resources globally. In this study, the population of an important south-eastern Australian halfbeak, Hyporhamphus australis targeted by a lampara-net fishery was assessed via hazard functions within a Bayesian framework (that was also compared to maximum likelihood). Fifteen-years of yield, effort and size-at-age data were used to generate the required population parameters (natural and fishing mortalities, selectivity and catchability) within competing models to derive biomass, recruitment and maximum sustainable yield (MSY). The suitable model included a parameter capturing a legislated change in gear selectivity mid-way through the time series, and with parameter estimates remaining synonymous between Bayesian and maximum likelihood approaches. Notwithstanding likely variable environmental influences, the legislated mesh-size change along with some effort reduction appears to have increased spawning stock biomass (SSB) to ∼112 t larger than that required for MSY (∼78 t per annum), and considerably greater than the current level of exploitation (∼50 t per annum). There was also a close relationship between catch-per-unit-of-effort and SSB, implying that fewer size-at-age data (and associated costs) could be realised without affecting future stock estimates. The results underscore the utility of simple input controls for regulating the exploitation of H. australis, and the chosen analytical approach for quantifying the consequences.