Fisheries Stock Research Articles

Impact of unequal distances among acoustic sensors on cross-correlation based fisheries stock assessment technique

Cross-correlation based fisheries stock assessment technique utilized array of multiple acoustic sensors which were equidistant pair. However, at practical implementation of this technique, equal distances among acoustic sensors is sometimes challenging due to different practical phenomenon. Therefore, in this study, we work on this issue and investigated the impact of unequal distances among the acoustic sensors. We found that cross-correlation based technique proved its effectiveness even for the unequal spacing among acoustic sensors. We considered chirp generating species of fish and mammals, i.e., damselfish (Dascyllus aruanus), humpback whales (Megaptera novaeangliae), dugongs (Dugong dugong), etc., species, and three acoustic sensors array for simulation purposes. Some limitations including negligence of multipath interference, assuming the delays to be integer were compromised during simulations.

A risk table to address concerns external to stock assessments when developing fisheries harvest recommendations

ABSTRACT This paper develops a risk table to facilitate incorporation of additional information into the fisheries stock assessment and management process. The risk table is designed to evaluate unanticipated ecosystem and environmental impacts on marine resources that may require a rapid management response. The risk table is a standardized framework to document concerns about the assessment model, population dynamics, and the ecosystem/environment that are not explicitly addressed within the stock assessment model. A scoring procedure is used to evaluate the severity of the concern. These concerns can then be evaluated in support for or against a reduction from the maximum Acceptable Biological Catch while providing reviewers and stakeholders transparent documentation of the concerns. The risk table was applied successfully to several stocks on a trial basis during the 2018 groundfish assessment cycle for the North Pacific Fishery Management Council, and will be used for all full groundfish assessments in 2019. Rapid changes in climate are likely for Alaska marine ecosystems in coming decades, and these changes are not entirely predicable. Therefore, we avocate that the risk table approach should be included in the suite of management tools used to address the effects of climate change on Alaska marine resources.

Azorean demersal longline survey abundance estimates: Procedures and variability

Survey data from the Azores is used for fisheries stock assessments under the ICES Working Group on the Biology and Assessment of Deep-sea Fisheries Resources (WGDEEP) covering deep open ocean areas. The Azores research cruise using bottom longlines for abundance estimation is probably unique in the Northeast Atlantic Ocean. This study analyzed data from annual Azorean bottom longline surveys (ICES subdivision 10a2) from 1996 to 2018 to calculate abundance indices of commercial demersal species, to estimate the statistical significance of the annual changes in the abundance estimates, and to examine the possible factors that cause this variability. The catch rates of these surveys appear to provide accurate indices of abundance for most of the commercially important demersal species. The observed inter-annual variability of the survey abundance estimates can be explained by survey effort distribution, fishery dynamics, aggregation patterns of some species, habitat preferences, fish movements, and environmental effects. However, other factors can affect these estimates (soak time, gear saturation and competition for hooks) and we recommend that additional studies be undertaken to understand these effects.

STATUS PEMANFAATAN PERIKANAN KEPITING MERAH (Scylla olivacea) DI PERAIRAN MIMIKA DAN SEKITARNYA, PAPUA

Red mud crab (Scylla olivacea) is an economic commodity that is traded into foreign countries such as China, Malaysia, and Singapore so that fishing activities are carried out intensively. Therefore, we need scientific information about the status of red mud crab fishery stock. Information about the natural mortality, fishing mortality, and the exploitation level of crabs can be used as the basis for crab fisheries management. The study was conducted for 2 (two) years, February to October 2017, and March to December 2018 using the survey method. The results showed that 36% of the crabs were caught below the 120 mm size as regulated in Regulation of the Minister of Marine Affairs and Fisheries No. 12 Year 2020. The carapace width of the first capture (CWc) is smaller than the size of the carapace width of the first gonad maturity (CWm). This shows that the crab has been captured before the first gonad maturity (CWc < CWm). The growth rate (K) is 0.65 per year with fishing mortality (F) higher than natural mortality (M). Exploitation level (E) 0.70 which indicates that the status fisheries of red mud crab in Mimika have been overexploited. Efforts need to be done by the Regional Government in collaboration with local community leaders in providing counseling and information about the size of red mud crabs that can be caught and reduce efforts to use crabs by as much as 40% of what is currently done. 
 Keywords: status explotation, red mud crabs, Mimika, FMA 718

Genetic population structure and tools for the management of European sprat (Sprattus sprattus)

AbstractThis study used RAD-seq-derived SNPs to explore population connectivity, local adaptation, and individual assignment in European sprat (Sprattus sprattus) and inform the alignment of management units with biological processes. FST, clustering, and outlier analyses support a genetically cohesive population spanning the Celtic Sea-English Channel-North Sea-Kattegat (NE Atlantic) region. The lack of structure among the NE Atlantic samples indicates connectivity across current management boundaries. However, the assumption of demographic panmixia is cautioned against unless verified by a multidisciplinary approach. The data confirm high genetic divergence of a Baltic population (average FST vs. NE Atlantic samples = 0.051) with signatures compatible with local adaptation in the form of outlier loci, some of which are shown to occur within exonic regions. The outliers permit diagnostic assignment of individuals between the NE Atlantic and Baltic populations and thus represent a “reduced panel” of markers for monitoring a potential mixed stock fishery within the western Baltic. Overall, this study provides information that may help refine spatial management boundaries of sprat and resources for genetic-assisted management.

A new way to visualize and report structural and data uncertainty in stock assessments

We present a visual and tabular representation of fisheries stock assessment model outputs to rapidly examine and effectively communicate sensitivity analysis results from numerous alternative model comparisons. This approach uses multiple output metrics to identify which alternative stock assessment model configurations relative to the reference model deserve further attention when quantifying intermodel uncertainty. An accompanying table of likelihood components, parameters, and model-derived quantities highlights where major changes exist compared with the reference model. The general method is applicable to any stock assessment and should aid in model behavior diagnosis and communicating uncertainty to managers. Specific examples and code are provided for the Stock Synthesis modelling framework.

Increasing marine ecosystems conservation linking marine protected areas and integrated coastal management in southern Cuba

The southern archipelagos of Cuba comprise important ecosystems of mangrove, seagrass beds, and coral reefs of regional significance. Biodiversity and fisheries stocks in this area experienced a severe decline due to a combination of factors (overfishing, habitat degradation, climate change). This work presents the main impacts of the project “Southern Archipelagos”, led by the National Center of Protected Areas of Cuba and funded by GEF, between 2009 and 2015 and the trends of the indicators of success. The project contributed to the conservation of marine biodiversity in Cuba through the creation of 12 new marine protected areas (MPAs). “Southern Archipelagos” facilitated the inclusion of the new and existing MPAs in Integrated Coastal Management Zones (ICMZs), thus contributing to buffering the impacts of productive activities and strengthening the integration between the conservation and productive sectors. Studies were conducted to characterize the MPAs and monitoring programs for priority species and ecosystems were implemented, increasing the knowledge available for decision-making about marine species and ecosystems in the region. To guarantee the financial sustainability of MPAs, a strategy for sustainable tourism was developed and a series of studies on the economic value of the goods and services offered by ecosystems were conducted. Different training programs for local leaders, MPAs workers and workers of productive sectors were organized. Sustainable productive alternatives were implemented in several communities diversifying the economic activities of local people. As a result, revenues from a representative sample of 12 MPAs of the project increased in the two currencies that are managed in Cuba.

Fishery Stock Assessments in the Min River Estuary and Its Adjacent Waters in Southern China Using the Length-Based Bayesian Estimation (LBB) Method

The Min River Estuary and its adjacent waters, connecting to the East China Sea, is one of the most important fishing grounds in Fujian Province, southern China; however, the stock assessments have not yet been conducted. In the present study, the length-based Bayesian estimation (LBB) method was applied for the first time to assess 20 fishery single-species stocks in the region. Catches of 8 fishes from the Class Actinopterygii and 12 shrimps from the Class Malacostraca were obtained from two commercial demersal trawlers, operated in the Min River Estuary and its adjacent waters in February, May, August and November of 2017 and 2018, covering all four seasons. The results showed that 8 species were overexploited with the estimated B/BMSY (i.e., the current exploited biomass relative to the biomass producing the maximum sustainable yield) 1.2). The results revealed that some commercially important food fishes are overexploited in the region, and small-sized, non-commercial food species can also be overexploited. There is an urgent need for local and national fisheries authorities to focus on coastal fishery management.

Assessing Northwest Pacific Fishery Stocks Using Two New Methods: The Monte Carlo Catch-MSY (CMSY) and the Bayesian Schaefer Model (BSM)

The CMSY and Bayesian Schaefer model (BSM) methods were applied to assess data-limited fishery stocks in the Japan Sea and surrounding areas of the Northwest Pacific. Ten stocks including 4 fish species and 5 cephalopod species were assessed; the CMSY method was used in 3 stocks with catch data only, and the BSM method in 7 stocks with both catch time series and catch per unit effort (CPUE) data available. The two methods estimated the maximum intrinsic rate of population increase (r) and carrying capacity of each stock, which allowed the computation of maximum sustainable yield (MSY), and exploited biomass relative to the biomass at maximum sustainable yield (B/BMSY). All 10 stocks were overfished, if to a different extent, and one, the spear squid (Heterololigo bleekeri) has collapsed. The reference points estimated here may be used as indicator for fishery management in this ecoregion.

Effect of diet during larval development of Menippe nodifrons Stimpson, 1859 and Callinectes danae Smith, 1869

The worldwide decrease in fishery stocks in recent years is related to the degradation of coastal environments and to the increases in capture effort and extreme natural events. Restocking dilapidated populations with artificial hatchery-reared larvae has arisen in recent years as a viable technique for the reparation and maintenance of stocks of commercially exploited species. One of the first steps in larvae cultivation is the evaluation of an appropriate diet for rearing. We aimed to test viable diets for feeding zoea larvae of the crab Menippe nodifrons and the swimming crab Callinectes danae. We tested five live food treatments, three microalgae (Tetraselmis gracilis, Chaetoceros calcitrans, and Thalassiosira weissflogii), the rotifer Brachionus plicatilis, and Artemia sp. nauplii. The most suitable feeding protocol for rearing M. nodifrons larvae was a combined diet of enriched B. plicatilis up to the zoea III instar with the introduction of hatched Artemia sp. nauplii onwards to the megalopa stage. Larvae of C. danae showed high mortality rates and none achieved the zoea III phase on any of the diets tested. Although our results for C. danae rearing were not conclusive, the data provide additional information on improper rearing diets for this species for future research. Future studies testing other food sources are necessary to improve larvae production.

Redefining spatial population structure of winter flounder (Pseudopleuronectes americanus): implications for stock assessment and management

The southern New England – mid-Atlantic (SNE–MA) stock of winter flounder (Pseudopleuronectes americanus) collapsed in the 1990s without discernable recovery to date. Owing to the lack of recovery, consideration of population subcomponents, which are currently ignored in fisheries stock structure definitions, may be necessary for rebuilding. We used the otolith chemistry tracer manganese–calcium ratios (Mn/Ca) to estimate inshore- versus ocean-nursery contributions of 77.3%/22.7% in SNE–MA, 15.7%/84.3% in the Gulf of Maine (GOM), and 60.0%/40.0% in Georges Bank (GB). In addition, we used strontium–calcium ratios (Sr/Ca) to estimate migratory- and resident-contingent membership of nursery-classified fish. Across all stocks, 30.2% of fish were classified as bay residents, 25.2% as bay migrants, 25.8% as ocean residents, and 18.8% as ocean migrants. Finally, model selection indicated that both nursery-specific and contingent-specific growth models were more appropriate than a common model. Nursery-specific models exhibited increasing deviations in length with age. Contingent-specific model reflected moderate differences at the youngest ages but convergence at older ages. These findings are informative for the population structure and migration ecology of winter flounder; however, simulation is required to determine whether partial migration and substock structure are necessary inputs for sustainable fisheries management.

Genetic connectivity of black drum (Pogonias courbina) stocks in the southwestern Atlantic Ocean

The delimitation of fishery stocks is an important aspect for the development and implementation of fishery stock management and sustainable use programs. Genetic analyses can provide useful information for the definition of population units, migration rates and changes in effective population sizes over long time frames. The black drum Pogonias courbina (Lacepede, 1803) is a marine fish that inhabits estuaries, bays and coastal waters of both hemispheres of the Western Atlantic, including Brazil, Uruguay and Northern Argentina. Intensely exploited at the Lagoa dos Patos Estuary in South Brazil, it is considered locally collapsed and since 2014 it is included in the National List of Endangered Fauna. Here we studied the population genetics of Pogonias courbina from South Brazil and the Argentinean and Uruguayan margins of the Rio de la Plata Estuary, using the mitochondrial DNA control region. We showed that along the study area Pogonias courbina groups present high genetic diversity, no genetic structure, and are undergoing slight expansion. These characteristics favor resilience of the population, decreasing the extinction risk of local stocks. However, the slow recovery after the black drum fisheries collapse at Lagoa dos Patos indicates that the recolonization process is slow; this is corroborated by migration estimates, in which we observe a low number of migrants between Argentina/Uruguay and South Brazil. Therefore, we suggest that the South Brazil reproductive stock, impacted by regional fisheries, can be considered a unique stock in terms of management, independent of Uruguayan and Argentinean management strategies. However, an integrated management plan should ideally be considered for these groups, since impacts and conservation efforts are likely shared between areas.

A review on insect meals in aquaculture: the immunomodulatory and physiological effects

The depletion of global fishery stock has posted significant effects to the world capture fishery industry. Constant environmental issues and fluctuation of fish meal (FM) costs have pushed the aquafeed industry to seek for alternative protein sources to sustain the huge demand of feed in aquaculture production. Insect meal (IM) has already started to gain global attention as an alternative for FM replacement. Substantial feeding trials have revealed its promising application not only beneficial as in protein replacement but also playing a vital role as a functional ingredient that boosting immunostimulatory effects in a wide range of aquatic animals. Here, we compiled and categorized several major groups of insects, for example black soldier fly, yellow mealworm, housefly, silkworm, alongside a minor group of insect species widely used as the alternative diet in aquaculture. Critically, we discuss the functional properties of the IMs, their immunomodulatory, and physiological effects in aquatic species. Biological parameters include oxidative stress, serum biochemical, hematological parameters, and immune-related genes are also further discussed in this review. In short, we suggest that low levels of IM supplementation could improve survival, immunity, and feed conversion efficiency of targeted aquaculture species. Chitin and its derivatives alongside active substances in insect exoskeleton, such as antimicrobial peptides (AMPs) play an essential role in the immunomodulation of aquatic organisms. Knowledge of this area is still in infancy. Therefore, it is a critical need to further address the mechanism of immunomodulation focusing on the isolated components from IMs.

Improving the robustness of fisheries stock assessment models to outliers in input data

Outliers caused by atypical observation error often occur in fishery data. These outliers have an adverse effect on the parameter estimation for fishery stock assessment models. We tested a robust distribution for identifying and removing outliers from fishery data. We conducted a simulation study in which a surplus production model was used to mimic fishery population dynamics and outliers caused by atypical observation error were imposed in the biomass index data. The method performed well by effectively identifying the real outliers and avoiding defining other data points as outliers. By removing the detected outliers and fitting the model with the remaining data points, the accuracy of the parameter estimation was improved. We discussed the precautions of applying this method and its potential applicability in other fishery stock assessment models.

Understanding Gender and Factors Affecting Fishing in an Artisanal Shellfish Fishery

Fishing strategies, effort and harvests of small-scale fishers are important to understand for effective planning of regulatory measures and development programs. Gender differences in fishing can highlight inequities deserving transformative solutions, but might mask other important factors. We examined fishing modes, fishing frequency, catch-per-unit effort (CPUE), resource preferences and perceptions of fishery stock among artisanal gastropod (trochus) fishers in Samoa using structured questionnaires and mixed effects models. The fishery has an extremely modest carbon footprint of 20.4 tonnes of CO2 p.a., as few fishers used motorised boats. Trochus (Rochia nilotica), an introduced gastropod, was the second-most harvested resource, after fish, despite populations only being established in the past decade. Daily catch volume varied according to gender and villages (n = 34), and was also affected by fishing effort, experience, assets (boat), and fishing costs of fishers. Boat users had much higher CPUE than fishers without a boat. Fishers who practiced both gleaning and diving caught a greater diversity of marine resources; effects that explained otherwise seeming gender disparities. Trochus tended to be ranked more important (by catch volume) by women than men, and rank importance varied greatly among villages. Local ecological knowledge of fishers informed the historical colonisation of trochus around Samoa and current trends in population abundance. Fishing efficiency, catch diversity and perspectives about stocks were similar between fishermen and fisherwomen, when accounting for other explanatory variables. Greater importance of these shellfish to women, and gender similarities in many of the fishing responses, underscore the need to ensure equal representation of women in the decision making in small-scale fisheries.

Essential features of the next-generation integrated fisheries stock assessment package: A perspective

Integrated analysis (or integrated population modelling) methods have become the preferred approach for conducting stock assessments, and providing the basis for management advice for fish and invertebrate stocks since the publication of a seminal paper by Fournier and Archibald in 1982. Methods to assess fish stocks based on single-species, single-area, age-structured models are now standard, with the major debates associated with these models related to data choice, model configuration assumptions, and data weighting. However, the current generation of stock assessment packages is not addressing all of the needs of stock assessment analysts and managers. A major challenge for any next-generation stock assessment package is the set of extensions needed to assess stocks that do not satisfy the ‘well-mixed single-stock’ paradigm. In addition, the next-generation stock assessment package needs to: (a) be able to capture age and size/stage dynamics simultaneously yet computationally efficiently, (b) scale from data-rich to data-poor, (c) include some multi-species capability, and (d) more appropriately deal with temporal variation (e.g., random effects and state-space models). In relation to data, there is a need to ensure that the next-generation stock assessment package better handles tagging data (age-size/stage models may help in this regard), in particular, to be able to use close-kin mark-recapture data. Efficient methods are needed to share parameter priors among stocks (satisfying the promise of the ‘Robin Hood’ paradigm). The next-generation stock assessment package needs to have associated appropriate training programs and documentation. Adoption of such a package will be facilitated by a data entry system that is well-documented, does not require specification of inputs that will not be used in an application, has an expert system to configure default settings based on best practices, and has associated code to automatically produce diagnostic statistics. Some technical challenges that have plagued stock assessment for decades warrant continued attention (at the theoretical and applied level) such as automatic data weighting and tuning, how to handle spatial and stock structure, improved coding to facilitate application of state-of-the-art methods for quantifying uncertainty, and adoption of true state-space formulations to allow more parameters to be treated as random effects. Future needs for features cannot be anticipated, so the key design consideration for the next-generation stock assessment package is to be flexible and modifiable to meet the requirements of analysts and users.

The Nash-Cournot approach to shared fish Stocks: An empirical investigation

The Nash-Cournot equilibrium in a competitive fisheries game leads to severe depletion of fish stocks compared with a cooperative solution. We review the Nash-equilibrium solution and how it depends (i) on the number of identical players and (ii) the share of the dominant player in a two player game. We then investigate what has happened in two shared stock fisheries in the Northeast Atlantic where stock sharing agreements have broken down recently. Have these fisheries moved closer to a Nash-Cournot equilibrium as a result? Contrary to expectations, we find that the rate of exploitation in these fisheries has not increased as a result of a breakdown of sharing agreements. In conclusion, we offer some thoughts on why the Nash-Cournot approach may not be appropriate for shared fish stocks.

Examining the relationship between morphological variation and modeled broadband scattering responses of reef-associated fishes from the Southeast United States

Non-lethal methods are sought to provide indices or measure of absolute abundance to fit fishery stock assessment models, including those computed for reef fishes. Calibrated scientific echosounders provide the foundation for stock assessments in low-diversity ecosystems but are hampered by complicated target strength responses in high diversity systems like coral and rocky reefs. Newly available broadband echosounders present advantages over narrowband predecessors including increased spatial resolution, increased signal to noise and spectral resolution; however, a better understanding of the sound scattering properties is necessary for operational use in surveys of diverse reef fish assemblages. To gain insight into the feasibility of implementing broadband techniques, we first model the frequency dependent backscatter of ecologically and commercially important species; results will aid our understanding of the backscattering as well as provide a supporting dataset to develop algorithms for classification of species/functional groups. Computed-tomography (CT) scans were performed on 149 individuals across reef fish species from the northeastern Gulf of Mexico to generate three-dimensional swim bladder models for estimation of morphometrics to input into numerical scattering models. Principal component analysis of the swim bladder morphology indicated significant variation among species; however, closely related species (confamilials) were not different. We employed boundary element method modeling to examine the frequency-dependent backscatter responses across a range of fish orientations (+/- 45°). Comparisons of frequency-dependent backscatter revealed strongest similarities between closely related species and greatest differences between more distantly related species or species groups. Patterns in the spectra have the potential to be used to classify targets toward species (or species group) for estimates of density from marine ecosystem acoustic surveys. Given that broadband echosounders are not yet commonplace, and many surveys in the region utilize narrowband echosounders, we also developed narrowband target strength – length relationships for six of the reef fish species with model fits ranging widely (r2 = 0.05 to 0.93). The potential utility of broadband echosounders to enhance ecosystem studies, or to develop fisheries-independent indices of abundance for use in stock assessment is discussed.

Why are catches in mixed fisheries well below TAC?

In major mixed stock fisheries of the United States, the actual catch is well below the total allowable catch (TAC). In recent years, only 20–30% of the TAC is caught in the US West Coast non-whiting fishery, whereas 60–80% of the TAC is caught in the Gulf of Alaska groundfish trawl fishery. Possible explanations for the underutilization are (1) lack of infrastructure, (2) lack of market demand, and (3) low quota limits on some species restricting the ability to harvest other species. Using species by species data on catch, TAC and lease price for species under Individual Transferable Quotas, we evaluate the support for these hypotheses. The results suggest that rebuilding plans, under a strict timeline, ultimately created many of the choke species on the West Coast and reduced processing infrastructure, such that the fishery still struggles with low quota utilization even after stocks have been rebuilt. In comparison, the Gulf of Alaska has not had a history of rebuilding plans and generally has higher utilization. The results suggest that rebuilding plans intended to increase sustainable harvest have been successful at increasing abundance but have been unsuccessful at rebuilding the fishery.

Genetic Assessment of a Black Rockfish, Sebastes schlegelii, Stock Enhancement Program in Lidao Bay, China Based on Mitochondrial and Nuclear DNA Analysis

The black rockfish Sebastes schlegelii is a commercially important fish species for marine fishery stock enhancement in Asia. This work aimed to evaluate the potential genetic impacts of releasing hatchery-reared juvenile black rockfish on wild stock in Lidao Bay, China. A partial sequence of the mitochondrial DNA (mtDNA) control region and 38 microsatellite DNA loci were used to assess the genetic impact. The haplotype diversity parameter (h) and nucleotide diversity parameter (π) in hatchery-released stock were 0.902 and 0.00483, respectively. The h values in wild stock before stock enhancement and the mixed stock after enhancement were 0.970 and 0.939, respectively, and the π values were 0.00581 and 0.00526, respectively. The mean effective numbers of alleles (Ne) in hatchery-released stock was 4.76, the mean polymorphism information content (PIC) was 0.674, the observed heterozygosity (Ho) was 0.668, and the expected heterozygosity (He) was 0.697. In wild stocks before stock enhancement and the mixed stock after enhancement, the Ne, PIC, Ho, and He values were 6.01 and 5.82, 0.698 and 0.716, 0.709 and 0.741, and 0.735 and 0.754, respectively. These results showed that there was no marked decrease in the hatchery-released stock, although it displayed slightly lower levels of genetic diversity and heterozygosity than the wild stock. The mixed stocks after S. schlegelii release exhibited similar genetic diversity to that of the wild stock before release, and the genetic variation in the natural stock did not decrease after stock enhancement. Moreover, both the fixation index (FST) and AMOVA analysis clearly showed minimal population structure differences between the hatchery-released and wild stocks, and the wild stock before enhancement and the mixed stock after enhancement. These results showed that stock enhancement may not cause any negative genetic effects on wild S. schlegelii stock in Lidao Bay over the short term. Accordingly, we propose that the current breeding and release methods are appropriate for conserving the genetic diversity of S. schlegelii. However, our results also showed a slight reduction in some genetic parameters, such as allelic diversity, heterozygosity, and effective population size, in the mixed stock after restoration. Consequently, long-term genetic evaluation might be required.