Fish Stock Assessment Research Articles

Dome-shaped selectivity in LB-SPR: Length-Based assessment of data-limited inland fish stocks sampled with gillnets

Inland fisheries can support complex social-ecological systems and contribute to food security. However, many target stocks lack monitoring and quantitative assessment. There may be scope to apply current data-limited assessment models in these fisheries. The Length-Based Spawning Potential Ratio (LB-SPR) model requires only fish length data and input estimates of key life history parameters. LB-SPR has been seldom applied in inland systems, partly due to the current model assumption of asymptotic fishing gear selection, characteristic of trawls. In contrast, most inland fisheries operate gillnets or hooks, having dome-shaped selection curves. This is problematic because the largest size classes of fish are not fully retained by the gear, but their absence in the catch will be assumed by the LB-SPR model to reflect fishing mortality. LB-SPR was extended to include dome-shaped selection. Case study assessments were undertaken using survey gillnet catches of brown trout Salmo trutta from four Irish lakes. Bayesian Monte Carlo methods were used to quantify uncertainty around estimates of life history parameters for each stock. Despite small sample sizes, the model produced estimates of SPR that corresponded to expert knowledge of stock status. The extended LB-SPR can be applied to assess data-limited inland fish stocks, and other stocks for which selection is dome-shaped.

Fish Larvae Counting System Using Image Processing Techniques

This paper presents the use of computer technology based on image processing techniques to count the number of fish larvae with less time processing. Computer technology used is as an alternative solution to the manual counting approach method in term of determination fish larvae survival rate, stock assessment and monitoring fish growth population. Generally, the fish larvae counting is performed with sequential process with laborintensive task which difficult to be used for counting large sample dataset. Traditional counting method has been used for many years, however many researchers highlighted several drawbacks of the manual counting process such as time consuming, laborious, required human skills-eyes, less-accurate, less consistent, difficult to estimate with many large sample and too many involve with human intervention. Since the problems is addressed, many researchers are interested to develop many techniques to facilitate the process of fish counting with fast assessment. In this study, we present combination of image processing techniques that consists of image enhancement, edge detection, and thresholding process. Meanwhile, the blob analysis is used as the statistical information to measure the objects properties in the image automatically. Total number of 150 samples dataset of Nile Tilapia (Oreochromis niloticus) were used in the experiment. All the samples are divided into three part which are small dataset (50 samples), medium dataset (50 samples) and large dataset (50 samples). The performance of the proposed method and the manual approach method are compared based on the number of fish that was successfully estimated and processing time taken through the experiment. All 150 samples of fish larvae were collected from the Freshwater Hatchery of University Malaysia Terengganu. The experimental results shows that the proposed method based on computer technology is outperformed compared to the manual counting approach in the experiment. This is because, the number of fish larvae measurement by using the proposed method is almost similar and some of samples present accurate result compared to the traditional approach. Moreover, the proposed method is promising on the processing time for measuring all samples with less time processing and more reliable.

Assessment of fish stocks and economic value in accordance with fishway renovation: Case study of Samcheokoshipcheon0010 Weir

Assessment of fish stocks and economic value in accordance with fishway renovation: Case study of Samcheokoshipcheon0010 Weir

Patterns and practices in fisheries assessment peer review systems

With wild-capture fisheries, important globally as a source of food and livelihood, and facing chronic overfishing, development of the best available science can reduce scientific uncertainty and improve the quality of science-based advice and the credibility to stakeholders of the management decisions based on that science. Fish stock assessments are complex scientific analyses used to provide critical, science-based advice for decision-making, such as quota setting. Building on findings from a 2017 American Fisheries Society (AFS) symposium, this paper describes and compares different national, multilateral, and private peer review systems to assess peer review characteristics and the role of peer review in the development of best available science and science-based advice. There is considerable diversity in how peer review systems are organized in terms of how reviewers are selected, use of internal or external expertise, the level of independence required of reviewers, and the steps in the assessment process at which peer review is conducted. Peer review systems face a number of challenges, including limited funding, a small pool of available expertise and the often highly technical nature of reviews, and trade-offs related to competing demands such as thoroughness versus timeliness, independent technical expertise versus local knowledge, and efficiency versus transparency, among others. The prevalence of peer review systems underscores the importance of objective, peer-reviewed, scientific-based advice across fishery management systems. The diversity of approaches to peer review demonstrates that there is no one ideal way to implement peer review, and there are tradeoffs inherent in designing a peer-review system.

Maximum Sustainable Yield, Maximum Economic Yield and Sustainability in Fisheries

A brief review of the concept of Maximum Sustainable Yield (MSY) used in fisheries management is discussed. The convenience of assessing the exploited stocks with the aid of simulation is advised, because implies the possibility to analyze the age structure of the fishery in more detail, as compared to the traditional methods of fish stock assessment. Emphasis is given to the use of the MSY as limit reference point because as long as the Fishing Mortality or fishing effort required for that point is kept at lower values, the fishery will have a good chance to be sustainable. A mention of the Maximum Economic Yield is made, proposing its use a target for the management, because it is reached in general with lower F values that for the MSY, and this way keeping the fishery in a healthy condition.

Stock assessment of pelagic fish in the eastern part of Java Sea: A case study in offshore Regency of Rembang and Tuban, Indonesia

Total annual landing of pelagic fish resources from the eastern part of Java Sea tend to be increased, but the stock status is not known well. This study was aimed to analyse optimal exploitation and stock status of pelagic fish in the eastern part of Java Sea and enlighten overfishing issues. Monthly catch of pelagic fish and effort data (trips) based on fishing gear during the period 2010 to 2016 were collected from four representative fish landing base or fishing port (i.e. Tasik Agung, Sarang, and Karang Anyer of Rembang Regency, and Bulu of Tuban Regency). Analyses were carried out using a surplus production model, and the best fit estimation was the Schaefer Model with Fox algorithm approach. Estimated bio-technique parameter of pelagic fish stock such as intrinsic growth rate (r) was 0.27 ton per year, catchability coefficient (q) was 0.000017 ton per unit, and environmental carrying capacity (K) was 622,614.72 ton per year. Result also showed that optimal production (h), effort (E) and profit (π) at Maximum Sustainable Yield (MSY) level 42,553.58 ton per year, 8,138 trips per year, and 263,783 billion rupiah (IDR), respectively. Meanwhile, those three variables at Maximum Economic Yield (MEY) were 41.670,87 ton per year, 6,966 trips per year, and 271,468 billion rupiah. However, the average of actual production, effort, and profit were 40,409.83 ton per year, 6,972 trips per year, and 260,408 billion rupiah. Moreover, total production and effort in 2016 were 42,009 ton and 10,114 trips. The status of pelagic fish stock in this area tends to be economic overfishing due to increased effort and less effective of fishing cost. Reducing fishing effort must be applied in fisheries management.

Maximum sustainable yield, maximum economic yield and sustainability in fisheries

A brief review of the concept of Maximum Sustainable Yield (MSY) used in fisheries management is discussed. The convenience of assessing the exploited stocks with the aid of simulation is advised, because implies the possibility to analyze the age structure of the fishery in more detail, as compared to the traditional methods of fish stock assessment. Emphasis is given to the use of the MSY as limit reference point because as long as the Fishing Mortality or fishing effort required for that point is kept at lower values, the fishery will have a good chance to be sustainable. A mention of the Maximum Economic Yield is made, proposing its use a target for the management, because it is reached in general with lower F values then that for the MSY, and this way keeping the fishery in a healthy condition.

Population structure, reproduction and exploitation of the greater forkbeardPhycis blennoides(Brünnich, 1768) from the Algerian basin

The objective of this study was to determine the population distribution and some biological aspects for fish stock assessment of the greater forkbeardPhycis blennoidesalong the Algerian basin. The distribution ofP. blennoides(3418 individuals) was studied using data collected between 170–779 m depth during two bottom trawl surveys developed on 2003 and 2004. Additionally, some biological parameters were obtained from 1050 individuals sampled from commercial fisheries in Algerian ports (i.e. Annaba, Azeffoun, Dellys, Cap Djinet, Zemmouri, Bouharoun, Algiers, La Madrague, Cherchell, Tenes and Mostaganem) during the period 2013–2017.P. blennoidessampled from bottom trawl surveys showed a depth related distribution with the largest individuals being found at 600–800 m depth and the smallest at shallower depths. Density and biomass varied with depth and density also with longitude, while biomass showed no pattern with longitude. Recruitment was recorded in the eastern sector of Algeria during winter, for individuals sampled by bottom trawl surveys. YoungP. blennoidesentered commercial fisheries in summer, with an overall sex ratio skewed towards males (1F:2.18M). The size at first maturity (L50) was 24.30 cm and 30.39 cm for males and females, respectively. The age at 50% maturity was 2–3 years for specimens collected by a bottom trawl survey in 2003 and commercial fisheries, but 3–4 years for the bottom trawl survey in 2004.

Some consequences of unreported fishing on the results of simple fish stock assessment

Unreported fishing received less attention than illegal fishing but the later contributed the problem of data availability. Among various data needed for fish stock assessment, catch and fishing effort are popular for some preliminary analysis to describe annual trends of catch, fishing effort and catch per unit effort. Surplus production models can be used to determine the status of fish stock, maximum sustainable yield (MSY) and optimum annual fishing effort. Fisheries authorities then can determine some management measure promoting sustainability of the fisheries, such as total allowable catch. This study exercised some consequences of unreported fishing effort and catch data on the outputs of the assessment by a simulation with different levels of data using the model. The estimates of both MSY and optimum fishing effort were lower when catch and fishing effort were not fully reported. When the authority should firmly use the best available but limited data, their decision on the maximum annual catch and fishing effort will be more conservative. In contrast, their decision can be risky if over-estimated catch and fishing effort were used. If fishers expected fair levels of catch and fishing effort, the authorities can firmly ask them to provide data completely.

Impact of time-varying productivity on estimated stock–recruitment parameters and biological reference points

Models with time-varying parameters are increasingly being considered in the assessment of fish stocks, but their reliability when used to derive biological reference points or benchmarks has not been thoroughly evaluated. Here, we evaluated stock–recruitment models with and without time-varying productivity in a simulation framework for sockeye salmon (Oncorhynchus nerka) under different scenarios of productivity and exploitation. Ignoring trends in productivity led to overestimates of productivity and underestimates of capacity when both exploitation rates and productivity declined over time, resulting in an underestimation on average of benchmarks of biological status. Despite being less biased, time-varying models had relatively poor fit based on AICc and BIC model selection criteria. Our simulation results were compared with empirical analyses of 12 Fraser River sockeye salmon stocks in British Columbia, Canada. Although benchmarks were less biased when based on time-varying models, underlying true benchmarks based on spawner abundances at maximum sustainable yield, SMSY, trend downwards when productivity declines, which may not be aligned with conservation objectives. We conclude with best practices when adapting biological benchmarks to time-varying productivity.

THE CO-OPERATIVE STUDY OF KUROSHIO (CSK): IS IT BENEFICIAL FOR INDONESIA?

The Cooperative Study of Kuroshio and its marginal seas (CSK) is one of the international joint research project conducted in the Western Pacific region. Many Asian countries had been involved in this project from 1965 to1979. Data and information from the CSK are enormous and cover wide-ranging aspects of marine science from the Kuroshio and adjacent regions (e.g. physical aspects, biological aspects and biogeochemical aspects). Indonesia had committed to participate actively in several marine research programs in the area linked to the CSK program by conducting marine research in its internal waters. This essay explained the CSK from biological aspects and Indonesia perspective. During the CSK, biological aspects (e.g. primary productivity, zooplankton biomass, and fisheries) were studied intensively. Indonesia conducted research in internal waters (Natuna Sea and the Java Sea) for oceanography monitoring and fish stock assessment. Participation in the CSK program allowed Indonesia to pursue the establishment of the National Center for Ocean Research (NCOR), develop human capacity building, research properties and standardized all techniques and procedures related to oceanography aspects. After the CSK, Indonesia has continued to conduct marine research linked to the previous study. We learn a lot from the past CSK that a key to succeeding in running this program depending on co-operative spirit, enthusiastic in understanding marine science from the region and enhancing human capacity for doing better marine research.

Population Dynamics of Five Important Commercial Fish Species in the Sundarbans Ecosystem of Bangladesh

Aims: To determine the population dynamics and assess the exploitation level of Mystus gulio, Acanthopagrus latus, Chelon parsia, Otolithoides pama and Lates calcarifer in the Sundarbans ecosystem of Bangladesh.
 Study Design: Monthly length-frequency data of five fish species were collected from the Sundarbans ecosystem. The lengths of five fish species were recorded to the nearest one cm intervals in each month.
 Place and Duration of Study: The study was conducted from January to December 2011 in the Sundarbans ecosystem in Bangladesh.
 Methodology: The FAO-ICLARM Fish Stock Assessment Tools (FiSAT II) software was used to estimate the von Bertalanffy growth parameters (L∝ and K), mortality coefficients (Z, M and F), probability of capture, recruitment pattern and Yield/Biomass-per-recruit for five commercially important fish species caught by fishers in the Sundarbans ecosystem of Bangladesh.
 Results: In the Sundarbans ecosystem of Bangladesh area the values of asymptotic length (L∝) for Mystus gulio, Acanthopagrus latus, Chelon parsia, Otolithoides pama and Lates calcarifer were found to be 23.0 cm, 33.6 cm, 30.0 cm, 32.5 cm and 55.0 cm respectively while the growth co-efficient (K) were 0.75, 0.85, 1.1, 0.8 and 0.5 respectively. The estimates for L∝ (23.00 – 55.0 cm) and K (0.5-1.1 year-1) obtained were consistent with those available in the literature. Relatively high K and low L∝ values, typical of short-lived tropical fishes, were obtained for Mystus gulio, Acanthopagrus latus, Chelon parsia and Otolithoides pama. The length growth performance index (ϕ’) of the Pauly and Munro’s function was in the range of 2.599 – 3.180. Natural mortality, fishing mortality and total mortality were in the range of 0.956-1.89, 0.55-1.58 and 1.52-3.3 respectively. Estimates for total mortality (Z) and natural mortality (M) imply low annual rates of survival and high turnover rates. The recruitment pattern suggested one main pulse of annual recruitment. The exploitation rate was estimated to be between 27% and 47% and the length at first capture was estimated to be approximately 19-54% of L∝. The exploitation rate obtained for five fish species are relatively lower compared to other available studies in the coastal areas of Bangladesh. The growth and exploitation rates obtained were compared with available estimates to evaluate the consistency of the results with current knowledge about the species in the region.
 Conclusion: The study indicated that the length-at-first-capture/L∝ seem to be a simple parameter, which could be used to make a rapid assessment of the status of the stocks. All together, the present study reveals that the population of these five studied species attains acceptable sustainability levels in the Sundarbans ecosystem and scope for a slight increase in catch efforts.

Development Learning Models of Fish Stock Assessment Technique Subjects based E-Learning at Aquatic Resources Technology Management Program Study at the Jakarta Fisheries High School

The aim of the study in general is to develop a learning model fish stock assessment techniques based e-learning to meet competencies for program Students study of Aquatic Resources Management Technology in the Jakarta Fisheries University. This research uses research and development methods. Result of study: In the field trial, the value obtained from the results of the post-test is higher than the value of the Pre-test, the average value of the results of the pre-test 62 and the post-test average value of 86.79, so there is an increase of 24 , 79 points, the rate of increase is very significant, meaning that this figure shows that the model developed can improve student learning achievement in the Study Program of Aquatic Resources Management Technology. While the average percentage value obtained from field trials is 88.88%, this number is higher than the learning objectives specified in the specific instructional objectives of 80%..

Valuing changes in frequency of fish stock assessments

Updating stock assessments frequently and ensuring that the most recent fishery-dependent and -independent data are included is a costly endeavor. We use a management strategy evaluation for the mid-Atlantic summer flounder (Paralichthys dentatus) fishery to determine the economic returns to increasing update frequencies and decreasing the data management lag. We simulate the annual acceptable biological catch for the period 2015–2040 under a range of update frequencies and data lags. We calculate present value net economic benefits for the commercial and recreational fisheries for each scenario. Discounting, the timing of harvest quotas, species-specific price flexibilities, and fishing cost response to biomass and quota differences suggest that the benefits gained from frequent updating and reduction in data lags will vary by fishery. For summer flounder, we find the cost of more frequent updating (1 versus 5 years) and reducing the data management lag (1 versus 2 years) are more than compensated for by societal benefits generated by the fishery.

Non-linearity in stock–recruitment relationships of Atlantic cod: insights from a multi-model approach

Abstract The stock–recruitment relationship is the basis of any stock prediction and thus fundamental for fishery management. Traditional parametric stock–recruitment models often poorly fit empirical data, nevertheless they are still the rule in fish stock assessment procedures. We here apply a multi-model approach to predict recruitment of 20 Atlantic cod (Gadus morhua) stocks as a function of adult biomass and environmental variables. We compare the traditional Ricker model with two non-parametric approaches: (i) the stochastic cusp model from catastrophe theory and (ii) multivariate simplex projections, based on attractor state-space reconstruction. We show that the performance of each model is contingent on the historical dynamics of individual stocks, and that stocks which experienced abrupt and state-dependent dynamics are best modelled using non-parametric approaches. These dynamics are pervasive in Western stocks highlighting a geographical distinction between cod stocks, which have implications for their recovery potential. Furthermore, the addition of environmental variables always improved the models’ predictive power indicating that they should be considered in stock assessment and management routines. Using our multi-model approach, we demonstrate that we should be more flexible when modelling recruitment and tailor our approaches to the dynamical properties of each individual stock.

Assessing the exploitation status of main fisheries resources in Ghana’s reservoirs based on reconstructed catches and a length-based bootstrapping stock assessment method

Abobi SM, Mildenberger TK, Kolding J, Wolff M. 2019. Assessing the exploitation status of main fisheries resources in Ghana’s reservoirs based on reconstructed catches and a length-based bootstrapping stock assessment method. Lake Reserv Manage. 35:415–434.The cichlid species Oreochromis niloticus, Sarotherondon galilaeus, and Coptodon zillii, which are among the most exploited resources in the small-scale fisheries of the Tono, Bontanga, and Golinga reservoirs in northern Ghana, were assessed based on length frequency samples. Growth, mortality, exploitation status, stock size, and relative yield per recruit reference points were determined using bootstrapping fish stock assessment (BFSA), a novel framework that allows for the estimation of uncertainties around the life-history parameters and reference levels (e.g., L∞, K, and F0.1). The results suggest that the 3 species studied are heavily exploited in all 3 reservoirs, but with no alarming signs of overexploitation. The fishing effort at Golinga is comparatively low as a result of insignificant fishing during the agriculture season, which relates to low exploitation rates. Sarotherondon galilaeus and C. zillii have the highest and lowest biomass (t/km2) respectively in all the 3 reservoirs. The small shallow reservoir (Golinga) has the highest biomass of the target resources per unit area. According to a second assessment approach, based on length-based indicators, all species at Bontanga and O. niloticus and S. galilaeus populations at Golinga have spawning stock biomasses below 40% of the unfished biomass. This points to a situation of a possible ongoing recruitment overfishing of those species in the 2 reservoirs and suggests that a further increase in fishing effort should be prevented. Further monitoring of these fisheries will be needed for the improvement of assessments and thus management advice.

Data for Fish Stock Assessment Obtained from the CMSY Algorithm for all Global FAO Datasets

Assessing the state of fish stocks requires the determination of descriptors. They correspond to the absolute and relative (to the carrying capacity of the habitat) fish biomasses in the ecosystem, and the absolute and relative (to the intrinsic growth rate of the population) fishing mortality resulting from catches. This allows, among other things, to compare the catch with the maximum sustainability yield. Some fish stocks are well described and monitored, but for many data-limited stocks, catch time series are remaining the only source of data. Recently, an algorithm (CMSY) has been proposed, allowing an estimation of stock assessment variables from catch and resilience. In this paper, we provide stock reference points for all global fisheries reported by Food and Agriculture Organization (FAO) major fishing area for almost 5000 fish stocks. These data come from the CMSY algorithm for 42% of the stock (75% of the global reported fish catch) and are estimated by aggregated values for the remaining 58%.

Evidence of deep-sea interactions between toothed whales and longlines.

Toothed whales (odontocetes) feeding on fish caught on hooks in longline fisheries is a growing issue worldwide. The substantial impacts that this behaviour, called depredation, can have on the fishing economy, fish stocks and odontocetes populations, raise a critical need for mitigation solutions to be developed. However, information on when, where and how odontocete depredation occurs underwater is still limited, especially in demersal longline fisheries (fishing gear set on the seafloor). In the present study, we investigated depredation by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) on demersal longlines in the French Patagonian toothfish fishery (Southern Ocean). Using a combination of animal-borne behavioural and longline-attached data loggers, we demonstrated that both species are able to depredate longlines on the seafloor. This study, therefore, suggests that odontocetes whales-longline interaction events at depth may be unrecorded when assessing depredation rates from surface observations during hauling phases only. This result has implications for the management of fisheries facing similar depredation issues as underestimated depredation rates may result in unaccounted fish mortality in fish-stock assessments. Therefore, while further research should be conducted to assess the extent of deep-sea whale-longline interaction events during soaking, the evidence that depredation can occur at any time during the whole fishing process as brought out by this study should be considered in future developments of mitigation solutions to the issue.

The Importance of Involving Stakeholders and Scientists in the Management of Marine Fisheries

In recent years there has been increasing concern over the state of fish stocks, especially those that support key fisheries and supply food to many consumers. There is also concern over the state of aquatic environments, and the effects of climate change. Fisheries management is controlled by government agencies, often cooperating with similar agencies from other nations. This paper deals with the need for expert advice on fisheries, involving fishers as well as scientists. Mention is made of a Fisheries Partnership set up in Europe, bringing fishers and scientists together with other stakeholders to discuss the problems of managing fish stocks. The partnership was especially successful in improving relationships between fishers and scientists, and made significant improvements to some fish stock assessments. European Regional Advisory Councils were later established to play a similar role. They are providing significant advice on fisheries, but they do not yet play a key role in actual management. It is important to consider how stakeholders and scientists can become more actively involved in fisheries management. There is a crucial need to develop new, more participatory ways of managing fisheries.

The Importance of Involving Stakeholders and Scientists in the Management of Marine Fisheries

In recent years there has been increasing concern over the state of fish stocks, especially those that support key fisheries and supply food to many consumers. There is also concern over the state of aquatic environments, and the effects of climate change. Fisheries management is controlled by government agencies, often cooperating with similar agencies from other nations. This paper deals with the need for expert advice on fisheries, involving fishers as well as scientists. Mention is made of a Fisheries Partnership set up in Europe, bringing fishers and scientists together with other stakeholders to discuss the problems of managing fish stocks. The partnership was especially successful in improving relationships between fishers and scientists, and made significant improvements to some fish stock assessments. European Regional Advisory Councils were later established to play a similar role. They are providing significant advice on fisheries, but they do not yet play a key role in actual management. It is important to consider how stakeholders and scientists can become more actively involved in fisheries management. There is a crucial need to develop new, more participatory ways of managing fisheries.