Catch Limits Research Articles

Forensic species identification of elasmobranchs landed in Costa Rican artisanal fisheries

Elasmobranchs represent one of the most imperiled taxa, yet few nations have developed catch limits and no international or bilateral catch limits exist. One barrier to establishing catch limits is a lack of accurate species-specific extraction rates due to many species looking similar, distinguishing characteristics (fins and head) being removed, or grouping of all elasmobranchs together in fisheries data. To better understand the species-specific impacts fisheries are having on elasmobranchs we used forensic genetic techniques to identify the types and quantities of shark species landed in Costa Rican artisanal small-scale and mid-scale fisheries. We collected elasmobranch tissue samples from fishermen in three locations along Costa Rica’s Pacific Coast: Coyote, Bejuco, and Ojochal, from April 2013 to September 2014. We used DNA barcoding techniques, utilizing a 1044 base pair region of the NADH dehydrogenase subunit 2 gene, to identify to species 275 of the 416 samples collected. Within these fisheries, seven species of shark and one ray were identified, with the scalloped hammerhead shark (Sphyrna lewini) accounting for ∼75−80% of all sharks landed. Observed total lengths (TL) for the scalloped hammerhead shark (10.9–99 cm) in these fisheries suggests the sharks sampled were all either juveniles or neonates. Based on these data it is likely that the areas from which these samples were collected represent nursery grounds for the scalloped hammerhead shark. The quantity of young scalloped hammerhead sharks removed from these areas, and ones similar to them, by these artisanal fisheries could be of great importance when determining future conservation measures for this species. Our findings also indicate that sharks caught in these artisanal fisheries do not appear to represent those sold in markets around San Jose.

Optimal fishing mortality assignment for southern hake Merluccius australis in Chile

Since 1979, southern hake (Merluccius australis) has been exploited in Chile from the Bio Bio to the Magallanes regions, between the parallels 41°28.6'S and 57°S. There is evidence of a constant fishing effort and a sustained reduction of the fish population, consistent with a progressive decrease in total annual catches. Management strategies based on the maximum sustainable yield (MSY) and quota assignment/ distribution criteria have not been able to sustain acceptable biomass levels. A non-linear optimization model with two objective functions was proposed to determine an optimal total catch quota for more sustainable exploitation of this fishery. The first function maximizes the total catch over time in response to an optimal assignment of fishing mortality rates per fleet; the second function maximizes the total economic benefit associated with the total catch. The dynamics of the fish population were represented with the equations of a predictive age-structured model. Decision variables were fishing mortality rates and annual catch quotas per fleet, subject to constraints that guarantee a minimum level of biomass escape over a long-term period. The input parameters were obtained from the last stock evaluation report carried out by the Instituto de Fomento Pesquero (IFOP) of Chile. The historical background data of the fishery and the regulatory framework were relevant aspects of the methodology. Five scenarios were evaluated with the two objective functions, including a base scenario, which considered the referential mortality rate as input data as the average mortality rate per fleet from 2007 to 2012. Total economic benefits fluctuate between 102 and USD 442 million for total catches in the range of 108 to 421 thousand tons, which were obtained from maximizing the economic and biological objective functions. Economic benefit/catch ratios were reduced for scenarios with higher constraints on catch limits, and they were more efficient from a biological point of view. Situations with lighter constraints showed in general higher economic benefits and better performance ratios than those with stronger restrictions. The use of optimization models may provide a useful tool to evaluate the effect of regulations for adequate conservation and economical utilization of a limited resource.

Estimation of fisheries reference points of the Largehead hairtail, Trichiurus lepturus (Teleostei: Trichiuridae) in Iranian waters of Persian Gulf and Oman Sea

The purpose of this study was to develop a framework to investigate the catch trend and estimation of the optimized catch limit of the Largehead hairtail, Trichiurus lepturus , stock by collecting catch data in the Iranian part of Persian Gulf and Oman Sea. In this research, catch data was collected for 20 years (1997-2018) and the optimized catch limit was estimated using data-limited approach and R Software. The average catch (Ct) for this period was 11550 tonnes (95% confidence interval 11500-11599 tonnes) and it has significantly increased over the past two decades (R=0.68, P <0.05). The intrinsic growth rate (r), carrying capacity (K), maximum sustainable yield (MSY), biomass of maximum sustainable yield (Bmsy), current biomass (B), fishing mortality of maximum sustainable yield (Fmsy) and present fishing mortality (F) were obtained by Catch-maximum sustainable yield (CMSY) models. The results showed that stock of the Largehead hairtail is suffering from over fishing and thereby, reduction of the fishing mortality and exploitation rate and bring back them to the MSY level are essential to save the stock.

Global status and conservation potential of reef sharks.

Decades of overexploitation have devastated shark populations, leaving considerable doubt as to their ecological status1,2. Yet much of what is known about sharks has been inferred from catch records in industrial fisheries, whereas far less information is available about sharks that live in coastal habitats3. Here we address this knowledge gap using data from more than 15,000standardized baited remote underwater video stations that were deployed on 371reefs in 58nations to estimate the conservation status of reef sharks globally. Our results reveal the profound impact that fishing has had on reef shark populations: we observed no sharks on almost 20% of the surveyed reefs. Reef sharks were almost completely absent from reefs in several nations, and shark depletion was strongly related to socio-economic conditions such as the size and proximity of the nearest market, poor governance and the density of the human population. However, opportunities for the conservation of reef sharks remain: shark sanctuaries, closed areas, catch limits and an absence of gillnets and longlines were associated with a substantially higher relative abundance of reef sharks. These results reveal several policy pathways for the restoration and management of reef shark populations, from direct top-down management of fishing to indirect improvement of governance conditions. Reef shark populations will only have a high chance of recovery by engaging key socio-economic aspects of tropical fisheries.

Can multi‐species shark longline fisheries be managed sustainably using size limits? Theoretically, yes. Realistically, no

Abstract Size limits are a common fisheries management strategy that are applied to many fisheries and species. Most size limits use a minimum legal size to protect adult fish as per the ‘reproduce at least once’ paradigm, where stock collapse becomes impossible if every adult can produce one spawner prior to harvest. These approaches can be useful in fisheries where determining catch is difficult and therefore catch limits can be ineffective and potentially cause stock decline. Shark longline fisheries can be complicated to manage due to a deficiency of species‐level reporting. Catch limits are therefore difficult to determine, creating a need for other management measures. Here, three different size‐based management approaches were tested using the shark longline fishery from Papua New Guinea as a case study. These approaches included minimum size, maximum size and harvest slot approaches. Age‐structured Leslie matrix models revealed a broad range of productivities for 12 commonly caught species, ranging from low population growth rates of 1% per year for pelagic thresher sharks Alopias pelagicus to &gt;33% per year for blue sharks Prionace glauca. Therefore, different harvest strategies were required for each species to be fished sustainably. However, management could be applied by grouping similar and easily distinguishable groups of species together. Synthesis and applications. The most pragmatic harvest strategy for all shark species included in this study was to limit harvest to mature individuals using minimum legal sizes. This provided sufficient resilience for all species to tolerate higher levels of fishing mortality than the Papua New Guinea (PNG) longline fishery could impose. Legal minimum lengths were derived from the largest length‐at‐maturity within each species group. However, while this produced a sustainable harvest strategy, issues with selectivity, post‐release mortality, interactions with other fisheries, economic viability and illegal, underreported and unregulated fishing were challenges to restricting fishing to the correct size classes and overall management efficacy. Therefore, while theoretically viable harvest strategies were outlined, it is apparent that size limits would not ensure that these shark species are fished sustainably. Therefore, the PNG longline fishery cannot operate sustainably if it were to reopen using size limits as its sole management strategy.

Are fish sensitive to trawling recovering in the Northeast Atlantic?

Abstract The protection of sensitive species from overfishing is a key aspect of the ecosystem approach to fisheries management. We use life‐history parameters and knowledge of fish shape and habitat to estimate the sensitivity of 270 species in the Northeast Atlantic to demersal trawling and compare sensitivity to the most recent IUCN categorization. Species classified as threatened were on average significantly more sensitive to trawling than other species. Using trawl surveys in European Atlantic waters from 36°N to 62°N, we estimated indicators of abundance of 31 highly sensitive species and compared changes in abundance to sensitivity, management measures, and value of landings. The abundance of 23 of the 31 sensitive species increased after year 2000 with 14 of the species showing increases significant at the 5% level. The increases were not due to specific management measures, as less than half of the species were covered by catch limits. Furthermore, sensitivity or value of landings was not related to trends in abundance. Three species (Atlantic wolf‐fish, tusk and starry ray) declined significantly. These species are all at their southern distributional limit in the North Sea. Synthesis and applications. We recommend monitoring the development of sensitive species to identify species under pressure and allow rapid management actions before species enter the IUCN threatened category. Furthermore, we recommend taking precautions where species are under combined pressure from climate change and fishing.

Achieving sustainable exploitation through co-management in three Chilean small-scale fisheries

Small-scale fisheries account for most of the worldwide landings and employment. However, they are difficult to manage scientifically because the program of research and management applied to the relatively few large-scale fisheries is too onerous to be expanded to the myriad small-scale fisheries. Does this mean that SSF have a higher risk of overfishing so it would be necessary to implement more aggressively conservative measures to preemptively avoid collapse? Implementation of a stock assessment methodology developed for data-poor fisheries reveals that this may not be the case. We show that in the absence of formal stock assessment and enforcement of catch limits, Chilean small-scale fishers first apply excessive exploitation causing depletion then they eventually re-build their stocks supported by a process of co-management. We analyze three small-scale fisheries in central-south Chile: the striped clam Ameghinomya antiqua fishery in the Bay of Ancud, the razor clam Ensis macha fishery in the Gulf of Arauco, and the red octopus Enteroctopus megalocyathus fishery in the inner sea of Chiloé. We find that in the oldest fishery, for the striped clam, fishers are slowly re-building the stock from a very depressed condition, in the younger fishery for the razor clam they are recovering the stock and are close to re-building to the BMSY, and in the youngest fishery, for the red octopus, they have just shrank biomass to below BMSY. We observe that the best managed case, the fishery for the razor clam, is connected to a more mature co-management process, with fishers collaborating with government through committees of participatory management, which have provided a framework to co-manage for sustainability.

A spatially explicit individual-based model to support management of commercial and recreational fisheries for European sea bass Dicentrarchus labrax

The European sea bass (Dicentrarchus labrax) is a slow growing and late maturing high value fish that is exploited by both commercial and recreational fisheries. In recent years, scientific assessments have shown a rapid decline in spawning stock biomass around the UK attributed to poor recruitment (driven by environmental factors) and high fishing mortality. This resulted in significant reductions in the harvest of sea bass following technical measures implemented by the European Commission to conserve stocks. Individual-based models (IBMs) are simulations of individual ‘agents’ of organisms that interact with each other and their environment locally and have been shown to be effective management tools in many systems. Here, an IBM that simulates the population dynamics and spatial distribution of sea bass was developed to assess how technical management measures applied to subsets of the population impact the overall stock. Conventional stock assessment techniques were used to model the processes affecting population dynamics, while the spatial distribution was simulated using a combination of temperature preferences and information from tagging studies. The IBM was parameterised using existing knowledge from the literature and can mimic key assessment outputs used to inform management and advice on fishing opportunities. Utility of the IBM is demonstrated by simulating the population consequences of several key management scenarios based on those implemented by the European Commission, including short-term bans on pelagic trawling in spawning areas, commercial and recreational catch limits and increasing the minimum conservation reference size. The IBM has potential to complement the annual stock assessment in managing European sea bass because it models individual movement, environmental drivers and emergent spatial distribution, thereby providing enhanced predictions of management strategy outcomes that could inform spatial advice on fishing opportunities and policy.

Fishery management and spatial variation of giant clam stocks: lessons from New Caledonia

Giant clams have been over-exploited throughout their wide geographical range in the Indo-Pacific. Marine reserves could be one tool to potentially safeguard broodstock, but their effect on giant clam abundance and the differential benefits of lagoon reserves compared to barrier reef reserves is still unclear. We assessed abundances of four species of giant clams across 20 barrier reef and 30 lagoon reef sites across 600 km of coastline in New Caledonia using stratified underwater visual censuses. Tridacna maxima was the most common species. T. derasa was significantly more abundant in marine reserves than at sites open to fishing, but there was no effect of marine reserves on total abundance pooled across the four species. T. squamosa was significantly more abundant on barrier reefs, while Hippopus hippopus was found solely on lagoon reefs. National data from fisher logbooks shows a marked reduction in commercial catches of giant clam following implementation of daily catch limits of 5 giant clams per vessel per trip. Despite small daily bag limits of 2 giant clams per recreational fisher per trip, the recreational catch appears to be significant and much greater than the commercial catch. The utility of marine reserves on giant clams appears to be species specific, and might be diminished for the group as a whole by the concomitant protection of their natural predators. Both lagoon and barrier reef sites should be included in reserve networks. Our data suggest that daily boat/trip limits are an effective output control, at least for commercial fishers, but might not safeguard giant clams if recreational fishers are numerous. Further fishery restrictions on the less common species might be needed to ensure their persistence in the Indo-Pacific.

Changes in Shrimping Effort in the Gulf of Mexico and the Impacts to Red Snapper.

Despite a complex management landscape and decades of overfishing, Red Snapper (Lutjanus campechanus) stocks have grown substantially in the Gulf of Mexico and restrictions on the fisheries that catch them are being loosened. This year, annual shrimping effort was allowed to increase by 21% after National Marine Fisheries Service scientists concluded that the resulting bycatch of Red Snapper would only reduce the annual allowable catch in other fisheries by ∼1% and have no impact on population growth. Nonetheless, the recreational fishing sector intensely campaigned against this rule, fueled by wild mischaracterization of shrimp trawl bycatch in media outlets targeting anglers. Here, we aim to elevate the debates surrounding Red Snapper management by presenting scientific and historical context for the potential impacts from shrimping. We discuss our views of the current problems facing Red Snapper and key ecological questions to address for more effective management of this resource.

Sixty-five years of northern anchovy population studies in the southern California Current: a review and suggestion for sensible management

Abstract The central stock of northern anchovy (CSNA; Engraulis mordax), the most abundant small pelagic fish in the southern California Current, is key to ecosystem functions. We review drivers of its population dynamics in relation to management. Springtime upwelling intensity lagged by 2 years co-varied positively with CSNA biomass, as did the abundance of Pacific sardine (Sardinops sagax; weakly negative). CSNA population dynamics indicate the need for a multi-species stock assessment, but given serious challenges with modelling population collapse and recovery dynamics, and its moderate fisheries, we suggest that sensible management could be a simple 2-tier harvest control rule designed to emphasize the key trophic role of CSNA in the ecosystem while maintaining moderate socio-economic services. We recommend a monitoring fishery of no more than 5 KMT year−1 split between central and southern California when the stock falls below the long-term median abundance estimate of 380 KMT across the California portion of its range, and a catch limit of 25 KMT year−1 when the stock is above this reference point. This rule would be precautionary, serving to maintain the most important small pelagic forage in the ecosystem, various fisheries interests, and information streams when the population is in a collapsed state.

Long-term observations from Antarctica demonstrate that mismatched scales of fisheries management and predator-prey interaction lead to erroneous conclusions about precaution

Low catch limits for forage species are often considered to be precautionary measures that can help conserve marine predators. Difficulties measuring the impacts of fisheries removals on dependent predators maintain this perspective, but consideration of the spatio-temporal scales over which forage species, their predators, and fisheries interact can aid assessment of whether low catch limits are as precautionary as presumed. Antarctic krill are targeted by the largest fishery in the Southern Ocean and are key forage for numerous predators. Current krill removals are considered precautionary and have not been previously observed to affect krill-dependent predators, like penguins. Using a hierarchical model and 30+ years of monitoring data, we show that expected penguin performance was reduced when local harvest rates of krill were ≥0.1, and this effect was similar in magnitude to that of poor environmental conditions. With continued climate warming and high local harvest rates, future observations of penguin performance are predicted to be below the long-term mean with a probability of 0.77. Catch limits that are considered precautionary for forage species simply because the limit is a small proportion of the species’ standing biomass may not be precautionary for their predators.

A review of approaches to quantifying uncertainty in fisheries stock assessments

Scientific uncertainty affects all parts of the fisheries management process. This study reviews methods for quantifying scientific uncertainty for presentation as part of the scientific advice to fisheries managers. We surveyed stock assessment scientists to a) identify the methods commonly used to quantify uncertainty, b) describe how method use has changed over time, c) investigate the factors that influence which methods are used, and d) characterize how scientific uncertainty is presented to fisheries managers. We found that scientific uncertainty is being quantified and included in scientific advice across multiple fishery management systems. Frequentist approaches for quantifying uncertainty are used more broadly than Bayesian approaches, and the survey did not detect this changing over time. Time restrictions and methodology requests during the scientific review process were commonly reported as factors influencing the use of uncertainty methods. Uncertainty in estimates of management targets (e.g., fishing mortality or biomass), projections, and catch limits were the quantities most frequently included in the scientific advice presented to fisheries managers. Methods for quantifying uncertainty and their incorporation into management advice are quickly advancing, and our approaches for reviewing progress towards clearly and explicitly communicating the sources, treatment, and impacts of uncertainty in management processes must keep pace.

The Concept of the Right to Management of Coastal Communities in the Regional Autonomy Era: Experience from Community Assistance to Obtain the Right to Manage Sea Cucumbers in Sunsak Bay, East Lombok.

The purpose of this research is having experience from around the world shows that fisheries management that produces lasting economic and ecological performance requires the use of fishing rights (rights-based fisheries management/RBFM) integrated as part of a well-designed management system that includes sustainable catch limits and effective monitoring and enforcement. The concept of fishing rights is not a new thing in Indonesia – in fact, many adat (traditional) customs such as sasi, awig-awig, and penglima laut are consistent with fishing rights and have been recognized for centuries. Such customary systems can provide a foundation for a new and effective system of fishing rights specially tailored to the culture, customs and needs of Indonesia. This research is using a qualitative method to identify what exactly happened in a coastal zone area. In reality, the concept of the Right to Management of Coastal Communities in the Regional Autonomy era has never been implemented in regional regulations that explicitly consider the rights needs of local communities. From the case of processing sea cucumber management permits in Sunsak Bay, East Lombok, it shows that local communities have never been a priority in the regional regulations to obtain the right to manage sea cucumbers.

Fish distributions reveal discrepancies between zonal attachment and quota allocations

AbstractThe oceans’ fisheries contribute to human wellbeing by providing essential nutrients, employment, and income. Changes in fish distribution, due to climate change or stock expansion, jeopardize conservation objectives because fishers catch more than is allocated as quota. Quotas, or catch shares, should, therefore, correspond to the share of the fish stock biomass present within a country's Exclusive Economic Zone, a concept known as Zonal Attachment. Here, we assess the Zonal Attachment of transboundary fish stocks present in northern Europe, in the waters of the United Kingdom, the European Union (without the United Kingdom), and Norway. In 12 of 14 important fish stocks, estimates of Zonal Attachment to the United Kingdom were significantly higher than current quota allocations, explaining the country's substantial discard problem. With environmental change, and stock recovery under improved fisheries conservation, scientific evidence should be used not only to set catch limits, but also to re‐examine catch shares.

Improving data-limited stock assessment with sporadic stock index information in stock reduction analysis

As most exploited fisheries lack a coherent time series of biomass index, development of data-limited stock assessment methods such as stock reduction analysis (SRA), is critical for fishery stock assessment due to their modest data requirements for estimating stock status and overfishing catch limits. In this study, we propose that sporadic time series of biomass indices, if available, may be fully utilized to inform priors of recent relative biomass (BT/B1) for data-limited stocks. We evaluated the performance of SRA incorporating this index-based prior by comparing two other common SRA priors (a deterministic prior set at 40% of the unfished biomass and a catch-based prior) with estimates from the likelihood-based assessments of 91 fish stocks from the RAM Legacy database. We extended our analysis by evaluating performance based on life history attributes and two depletion levels with BT/BMSY equaling 1 as the breakpoint. Results suggest index-based priors enhance accuracy for fish stocks at both depletion levels. We demonstrate that performance of SRA can be affected by three factors: the reliability of priors for BT/B1, recent depletion level, and life history.

Leveraging scientific uncertainty in fisheries management for estimating among-assessment variation in overfishing limits

AbstractFisheries management systems can utilize probability-based harvest control rules to incorporate scientific uncertainty and manager risk tolerance when setting catch limits. A precautionary buffer that scales with scientific uncertainty is used to calculate the acceptable biological catch from the overfishing limit (OFL) for US West Coast groundfish and coastal pelagic species. A previous analysis formed the basis for estimating scientific uncertainty as the among-assessment variation in estimates of historical spawning biomass time-series. This “historical biomass” approach may underestimate scientific uncertainty, because the OFL is a function of estimated exploitable biomass and fishing mortality. We developed a new approach that bases the calculation of scientific uncertainty on projected spawning biomass (SSB) and OFLs, accounting for uncertainty in recruitment and among-assessment variation. OFL projections yielded a higher estimate of uncertainty than SSB (0.502 vs. 0.413 for 25-year projections and 0.562 vs. 0.384 for a 1-year projection, assuming a deterministic stock-recruitment relationship). Assuming a stochastic stock-recruitment relationship produced smaller estimates of uncertainty (0.436, 25-year OFL projections; 0.452, 1-year OFL projections; 0.360, 25-year SSB projections; 0.318, 1-year SSB projections). The projection-based approach presented herein is applicable across stocks and regions that conduct assessments with sufficient and consistent outputs for calculating an OFL.

Retrospective Analyses of Commercial Trip Limit Efficacy in the Southeastern USA

AbstractTrip limits are frequently used as a management measure to control or reduce harvest by restricting harvest to a maximum amount. The goal of trip limits is often to lengthen the fishing season relative to the annual catch limit by slowing the landings rate or incentivizing fishers to target another species. Two recent commercial trip limits implemented in the southeastern USA were examined to determine the accuracy of the predicted changes in harvest. For South Atlantic Snowy Grouper Hyporthodus niveatus, analysts accurately predicted the change in landings (weight) that could be expected per trip in response to a trip limit increase but did not account for an increased number of trips early in the fishing season. An increased number of trips resulted in higher landings causing Snowy Grouper to reach the quota and close earlier than desired. For Gulf of Mexico Gray Triggerfish Balistes capriscus, analysts underestimated the predicted change in landings per trip that could be realized from implementing a trip limit (numbers of fish). The Gray Triggerfish analysis failed to account for fishers retaining larger individual fish on average after the trip limit was implemented, resulting in higher landings than predicted. When examining per‐fish trip limits, it is recommended that other potential changes in fishing behavior, such as changes in the mean weight of fish being retained or increased effort, be considered. The results of this study could be used to improve the effectiveness of trip limits as a management tool.

Using censored regression when estimating abundance with CPUE data to account for daily catch limits

In fisheries where there is a limit on total catch in a given period, catch-per-unit-effort (CPUE) data may not be proportional to abundance because catches may be censored at the limit. Commonly used depletion estimators (e.g., Leslie method) could be biased when ordinary least squares (OLS) regression is used to estimate abundance with censored CPUE data. We used simulations to examine the performance of OLS regression and a censored regression approach when estimating abundance and exploitation using censored CPUE data over a range of known exploitation rates. We also applied the censored regression approach to data from a commercial fishery for the eastern oyster (Crassostrea virginica). The censored regression approach always performed better than the OLS regression when estimating abundance and exploitation in our simulations. Harvest and abundance of oysters in Fishing Bay, Maryland, increased during 2009 to 2013 and then decreased through 2016, while exploitation rates had no substantial trend over time. The censored regression approach is useful for estimating abundance and exploitation when the distribution of CPUE is affected by daily catch limits.

Management strategies for spasmodic stocks: a Canadian Atlantic redfish fishery case study

There exist few recommendations for managing stocks with spasmodic recruitment, despite such stocks being not uncommon. Management procedures (MPs), developed for two species of redfish (Sebastes mentella and Sebastes fasciatus) in eastern Canada, are recommended for setting catch limits during periods of high and low abundance. A well-designed fishery-independent trawl survey is essential to provide advance warning of strong recruitment events and project future recruitment. Under an “inventory management” strategy, a more appropriate aim in spasmodic stocks may be to maximize the number of years with “good catches,” instead of maximizing total catches, as is traditionally considered in management strategy evaluation (MSE). Following a spasmodic recruitment event, an empirical harvest control rule based on larger fish delays the harvest of large cohorts by a few years, targets more commercially valuable fish sizes, and reduces the risk of growth overfishing. Capped MPs produced longer periods of large catches than uncapped MPs. MPs allowed for low harvests during periods of low abundance, thus avoiding unnecessary hardship in the industry. MPs evaluated here could be good candidates for other stocks with similar or less extreme recruitment variability.