scholarly journals Simulation testing the robustness of stock assessment models to error: some results from the ICES strategic initiative on stock assessment methods

2014 ◽  
Vol 72 (1) ◽  
pp. 19-30 ◽  
Author(s):  
J.J. Deroba ◽  
D.S. Butterworth ◽  
R.D. Methot ◽  
J.A.A. De Oliveira ◽  
C. Fernandez ◽  
...  
Keyword(s):  
Large Scale ◽  
Stock Assessment ◽  
Assessment Methods ◽  
Fish Stocks ◽  
Production Models ◽  
Self Testing ◽  
Stock Assessments ◽  
The World ◽  
Simulation Testing ◽  
Pseudo Data

Abstract The World Conference on Stock Assessment Methods (July 2013) included a workshop on testing assessment methods through simulations. The exercise was made up of two steps applied to datasets from 14 representative fish stocks from around the world. Step 1 involved applying stock assessments to datasets with varying degrees of effort dedicated to optimizing fit. Step 2 was applied to a subset of the stocks and involved characteristics of given model fits being used to generate pseudo-data with error. These pseudo-data were then provided to assessment modellers and fits to the pseudo-data provided consistency checks within (self-tests) and among (cross-tests) assessment models. Although trends in biomass were often similar across models, the scaling of absolute biomass was not consistent across models. Similar types of models tended to perform similarly (e.g. age based or production models). Self-testing and cross-testing of models are a useful diagnostic approach, and suggested that estimates in the most recent years of time-series were the least robust. Results from the simulation exercise provide a basis for guidance on future large-scale simulation experiments and demonstrate the need for strategic investments in the evaluation and development of stock assessment methods.

scholarly journals Reflections on the success of traditional fisheries management

2014 ◽  
Vol 71 (5) ◽  
pp. 1040-1046 ◽  
Author(s):  
Ray Hilborn ◽  
Daniel Ovando
Keyword(s):  
Fisheries Management ◽  
Statistical Models ◽  
Management Systems ◽  
Marine Resources ◽  
Fish Stocks ◽  
Stock Assessments ◽  
The World ◽  
The Status ◽  
Management Approaches ◽  
Precautionary Management

Abstract The argument persists that the continued overexploitation by many fisheries around the world is evidence that current approaches to fisheries management are failing, and that more precautionary management approaches are needed. We review the available estimates of the status of fish stocks from three sources: the FAO's “State of Marine Resources”, a database on scientific stock assessments, and recent estimates from statistical models designed to determine the status of unassessed fish stocks. The two key results are (i) that stocks that are scientifically assessed are in better shape and indeed are not typically declining but rebuilding, and (ii) that large stocks appear to be in better shape than small stocks. These results support the view that stocks that are managed are improving, while stocks that are not managed are not. Large stocks receive far more management attention than small stocks in jurisdictions that have active fisheries management systems, and most unassessed stocks are simply not managed. We assert that fisheries management as currently practised can (and often does) lead to sustainable fisheries, and what is needed is to actively manage the unassessed fisheries of the world. More precautionary management is not necessarily needed to ensure the sustainability of managed fisheries.

scholarly journals Review of integrated size-structured models for stock assessment of hard-to-age crustacean and mollusc species

2013 ◽  
Vol 70 (1) ◽  
pp. 16-33 ◽  
Author(s):  
Andre E. Punt ◽  
TzuChuan Huang ◽  
Mark N. Maunder
Keyword(s):  
Stock Assessment ◽  
Age Distribution ◽  
Size Composition ◽  
Data Sources ◽  
Multiple Sources ◽  
Surplus Production ◽  
Production Models ◽  
Stock Assessments ◽  
Mollusc Species ◽  
Size At Age

Abstract Punt, A. E., Huang, T., and Maunder, M. N. 2013. Review of integrated size-structured models for stock assessment of hard-to-age crustacean and mollusc species. – ICES Journal of Marine Science, 70:16–33. Crustaceans and molluscs such as crabs, rock lobsters, prawns, abalone, and oysters constitute large and valuable fisheries. However, assessments of these species are hampered because they cannot be production aged, in contrast to many teleosts. The major data sources for these species, in addition to catch and abundance index data, are the size compositions of the catches and of any fishery-independent indices. Assessments of such species have been conducted using age-based methods of stock assessment, as well as surplus production models. However, size-structured methods are now preferred because they can make full use of size-composition data, are able to integrate multiple sources of data, and produce the types of outputs which are needed for management purposes. An advantage of size-based models over age-based models is that all processes can be size-based, and these processes can modify the (unmodelled) size-at-age distribution. We review these methods, highlighting the choices that need to be made when developing integrated size-structured stock assessments, the data sources which are typically available and how they are used for parameter estimation, and contrast a number of such assessments worldwide.

scholarly journals Scientific Methods to Understand Fish Population Dynamics and Support Sustainable Fisheries Management

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 574
Author(s):  
Shewit Gebremedhin ◽  
Stijn Bruneel ◽  
Abebe Getahun ◽  
Wassie Anteneh ◽  
Peter Goethals
Keyword(s):  
Developing Countries ◽  
Population Dynamics ◽  
Life History ◽  
Freshwater Fish ◽  
Life History Traits ◽  
Stock Assessment ◽  
Freshwater Ecosystems ◽  
Sustainable Fisheries ◽  
Fish Stocks ◽  
The World

Fisheries play a significant role in the livelihoods of the world population, while the dependence on fisheries is acute in developing countries. Fisheries are consequently a critical element for meeting the sustainable development (SDG) and FAO goals to reduce poverty, hunger and improve health and well-being. However, 90% of global marine fish stocks are fully or over-exploited. The amount of biologically unsustainable stocks increased from 10% in 1975 to 33% in 2015. Freshwater ecosystems are the most endangered ecosystems and freshwater fish stocks are worldwide in a state of crisis. The continuous fish stock decline indicates that the world is still far from achieving SDG 14 (Life Below Water), FAO’s Blue Growth Initiative goal and SDG 15 (Life on Land, including freshwater systems). Failure to effectively manage world fish stocks can have disastrous effects on biodiversity and the livelihoods and socio-economic conditions of millions of people. Therefore, management strategies that successfully conserve the stocks and provide optimal sustainable yields are urgently needed. However, successful management is only possible when the necessary data are obtained and decision-makers are well informed. The main problem for the management of fisheries, particularly in developing countries, is the lack of information on the past and current status of the fish stocks. Sound data collection and validation methods are, therefore, important. Stock assessment models, which support sustainable fisheries, require life history traits as input parameters. In order to provide accurate estimates of these life history traits, standardized methods for otolith preparation and validation of the rate of growth zone deposition are essential. This review aims to assist researchers and fisheries managers, working on marine and freshwater fish species, in understanding concepts and processes related to stock assessment and population dynamics. Although most examples and case studies originate from developing countries in the African continent, the review remains of great value to many other countries.

Overcoming long Bayesian run times in integrated fisheries stock assessments

2019 ◽  
Vol 76 (6) ◽  
pp. 1477-1488 ◽  
Author(s):  
Cole C Monnahan ◽  
Trevor A Branch ◽  
James T Thorson ◽  
Ian J Stewart ◽  
Cody S Szuwalski
Keyword(s):  
Parallel Computation ◽  
Stock Assessment ◽  
Likelihood Estimation ◽  
R Package ◽  
Complex Model ◽  
Bayesian Algorithm ◽  
Fish Stocks ◽  
Model Builder ◽  
Long Run ◽  
Stock Assessments

Abstract Bayesian inference is an appealing alternative to maximum likelihood estimation, but estimation can be prohibitively long for integrated fisheries stock assessments. Here, we investigated potential causes of long run times including high dimensionality, complex model structure, and inefficient Bayesian algorithms for four US assessments written in AD Model Builder (ADMB), both custom built and Stock Synthesis models. The biggest culprit for long run times was overparameterization and they were reduced from months to days by adding priors and turning off estimation for poorly-informed parameters (i.e. regularization), especially for selectivity parameters. Thus, regularization is a necessary step in converting assessments from frequentist to Bayesian frameworks. We also tested the usefulness of the no-U-turn sampler (NUTS), a Bayesian algorithm recently added to ADMB, and the R package adnuts that allows for easy implementation of NUTS and parallel computation. These additions further reduced run times and better sampled posterior distributions than existing Bayesian algorithms in ADMB, and for both of these reasons we recommend using NUTS for inference. Between regularization, a faster algorithm, and parallel computation, we expect models to run 50–50 000 times faster for most current stock assessment models, opening the door to routine usage of Bayesian methods for management of fish stocks.

Comparative performance of data-poor CMSY and data-moderate SPiCT stock assessment methods when applied to data-rich, real-world stocks

2020 ◽  
Author(s):  
Paul Bouch ◽  
Cóilín Minto ◽  
Dave G Reid
Keyword(s):  
Stock Assessment ◽  
Assessment Methods ◽  
Production Model ◽  
Fishing Mortality ◽  
Comparative Performance ◽  
Fish Stocks ◽  
Surplus Production ◽  
Stock Biomass ◽  
Surplus Production Model ◽  
The Status

Abstract All fish stocks should be managed sustainably, yet for the majority of stocks, data are often limited and different stock assessment methods are required. Two popular and widely used methods are Catch-MSY (CMSY) and Surplus Production Model in Continuous Time (SPiCT). We apply these methods to 17 data-rich stocks and compare the status estimates to the accepted International Council for the Exploration of the Sea (ICES) age-based assessments. Comparison statistics and receiver operator analysis showed that both methods often differed considerably from the ICES assessment, with CMSY showing a tendency to overestimate relative fishing mortality and underestimate relative stock biomass, whilst SPiCT showed the opposite. CMSY assessments were poor when the default depletion prior ranges differed from the ICES assessments, particularly towards the end of the time series, where some stocks showed signs of recovery. SPiCT assessments showed better correlation with the ICES assessment but often failed to correctly estimate the scale of either F/FMSY of B/BMSY, with the indices lacking the contrast to be informative about catchability and either the intrinsic growth rate or carrying capacity. Results highlight the importance of understanding model tendencies relative to data-rich approaches and warrant caution when adopting these models.

scholarly journals The use and performance of survey-based pre-recruit abundance indices for possible inclusion in stock assessments of coastal-dependent species

2020 ◽  
Vol 77 (5) ◽  
pp. 1953-1965
Author(s):  
Olivier Le Pape ◽  
Youen Vermard ◽  
Jérome Guitton ◽  
Elliot J Brown ◽  
Karen E van de Wolfshaar ◽  
...  
Keyword(s):  
Large Scale ◽  
Stock Assessment ◽  
Geographical Area ◽  
Short Term ◽  
Spatial And Temporal Scales ◽  
Stock Assessments ◽  
Abundance Indices ◽  
Assessment Survey ◽  
And Performance ◽  
The Relationship

Abstract We reviewed the use of survey-based pre-recruit abundance indices in short-term recruitment forecasts for fish species relying on coastal habitats at the juvenile stage and that are assessed by ICES. We collated information from stock assessment reports and from a questionnaire filled out by the stock assessors. Among the 78 stocks with juvenile coastal dependence, 49 use short-term forecasts in stock assessment. Survey-based pre-recruit abundance indices were available for 35 of these stocks, but only 14 were used to forecast recruitment. The questionnaire indicated that the limited use of survey-based pre-recruit abundance indices was primarily due to sampling inefficiency, which may preclude reliable recruitment estimates. The sampling is inefficient because the juvenile coastal distribution is outside the geographical area covered by large-scale surveys or targeted coastal surveys are conducted on limited spatial and temporal scales. However, our analysis of the relationship between survey-based pre-recruit indices and assessment-generated recruitment indices revealed that survey-based pre-recruit abundance indices were sufficiently accurate to provide useful information for predicting future recruitment. We recommend expansion of the use of survey-based indices of pre-recruit abundance in stock assessment and recruitment forecasting, and consideration of how to include juveniles in ongoing and future surveys.

scholarly journals Stock assessment methods for sustainable fisheries

2014 ◽  
Vol 72 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Steven X. Cadrin ◽  
Mark Dickey-Collas
Keyword(s):  
Fishery Management ◽  
Stock Assessment ◽  
Management Strategies ◽  
Assessment Methods ◽  
Reference Points ◽  
Fish Stock ◽  
Mortality Trends ◽  
Sustainable Fisheries ◽  
Management Procedures ◽  
Pseudo Data

Abstract This special volume of the ICES Journal compiles contributions from the World Conference on Stock Assessment Methods for Sustainable Fisheries (July 2013, Boston, USA). The conference was the product of a strategic initiative on stock assessment methods that engaged many national and regional fishery management organizations to assure that scientists can apply the most appropriate methods when developing management advice. An inclusive workshop was designed to evaluate the performance of a variety of model categories by applying multiple models to selected case study data as well as simulated pseudo-data that had realistic measurement error. All model applications had difficulties in recovering the simulated stock and fishing mortality trends, particularly at the end of the assessment time series, when they are most important for informing fishery management. This general result suggests that the next steps in evaluating the performance of stock assessment methods should include stock status relative to sustainable reference points, catch advice, multi-model consideration, and alternative management procedures. Recognition of the limitations of conventional stock assessment methods should promote further development of data-limited approaches, methods with time-varying parameters, or spatial complexity, and a more revolutionary shift towards the application of multispecies and ecosystem models. The contributions in this volume address methodological themes that are expected to improve the scientific basis of fishery management. Furthermore, the limitations of stock assessment methods and associated uncertainty should be more extensively considered in fishery management strategies and tactical decisions. Recommendations developed during the conference called for the establishment of a global initiative to synthesize regional advances, form guidance on best practices, promote strategic investments, and highlight research needs for fish stock assessments.

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

2020 ◽  
Vol 77 (5) ◽  
pp. 857-868
Author(s):  
Lisha Guan ◽  
Yong Chen ◽  
Robert Boenish ◽  
Xianshi Jin ◽  
Xiujuan Shan
Keyword(s):  
Time Series ◽  
Life History ◽  
Stock Assessment ◽  
Assessment Methods ◽  
Stock Index ◽  
Fish Stocks ◽  
Stock Status ◽  
Index Development ◽  
Data Requirements

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.

scholarly journals Complex assessments or simple management procedures for efficient fisheries management: a comparative study

2014 ◽  
Vol 72 (1) ◽  
pp. 262-274 ◽  
Author(s):  
H. F. Geromont ◽  
D. S. Butterworth
Keyword(s):  
Fishery Management ◽  
Stock Assessment ◽  
Assessment Methods ◽  
Essential Requirement ◽  
Fish Stocks ◽  
Control Rules ◽  
Management Procedures ◽  
Simple Rules ◽  
Sound Management

Abstract Complex stock assessment methods are data- and expertise-hungry, with the annual updates of catch-at-age data and models typically seen as an essential requirement for sound management. But are the heavy commitments of resources required for this level of annual intervention really necessary to achieve efficient long-term fishery management? This question is addressed through a retrospective analysis of management performance over the last 20 years for four North Atlantic fish stocks. The assessments for two of these stocks have exhibited fairly strong retrospective patterns. The actual assessment advice for these stocks was provided based on complex assessment methods making use of age data. The outcomes are compared with what could have been achieved with much simpler catch control rules based upon age-aggregated survey indices alone. Even for the stocks whose assessments exhibit retrospective patterns, these simple rules can achieve virtually equivalent catch and risk performance, with much less interannual TAC variability, compared with what actually occurred over the past 20 years.

scholarly journals Data-poor stock assessment of fish stocks co-exploited by commercial and recreational fisheries: applications to pike (Esox lucius) in the western Baltic Sea

2021 ◽  
Author(s):  
Rob van Gemert ◽  
Dieter Koemle ◽  
Helmut Winkler ◽  
Robert Arlinghaus
Keyword(s):  
Stock Assessment ◽  
Recreational Fishing ◽  
Recreational Fisheries ◽  
Fish Stocks ◽  
Explanatory Variables ◽  
Recreational Angling ◽  
Mixed Use ◽  
Stock Assessments ◽  
The Status

AbstractInformation on catch and effort of recreational angling in mixed-use fisheries (co-exploited by commercial and recreational fishers) is often scarce, preventing the application of data-rich stock assessments typically performed for industrialized commercial fisheries. Here, we show how data-poor stock assessment methods developed for marine fisheries, particularly a class of models labelled as “catch-only” models (COMs), offer a possible solution. As a case study, we use COMs to assess a northern pike stock around the German Baltic island of Rügen. We fit multiple COMs to a time-series of total pike removals, and use their outputs as explanatory variables in superensemble models. We conclude that the stock is fully exploited and currently declining. Our study highlights the potential for using COMs to determine status of previously-unassessed coastal and freshwater stocks facing recreational fishing pressure, and demonstrates how incorporating recreational removals is crucial for achieving reliable insights into the status of mixed-use stocks.

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