scholarly journals Interactions between ageing error and selectivity in statistical catch-at-age models: simulations and implications for assessment of the Chilean Patagonian toothfish fishery

2016 ◽  
Vol 73 (4) ◽  
pp. 1074-1090 ◽  
Author(s):  
Vania Henríquez ◽  
Roberto Licandeo ◽  
Luis A. Cubillos ◽  
Sean P. Cox
Keyword(s):  
Reference Points ◽  
Parameter Estimates ◽  
Model Parameters ◽  
Time Varying ◽  
Age Composition ◽  
Composition Data ◽  
Spawning Stock ◽  
Patagonian Toothfish ◽  
Stock Depletion ◽  
Age Structured

Abstract In age-structured fisheries stock assessments, ageing errors within age composition data can lead to biased mortality rate and year-class strength estimates. These errors may be further compounded where fishery-dependent age composition data are influenced by temporal changes in fishery selectivity and selectivity misspecification. In this study, we investigated how ageing error within age composition data interacts with time-varying fishery selectivity and selectivity misspecification to affect estimates derived from a statistical catch-at-age (SCA) model that used fishery-dependent data. We tested three key model parameters: average unfished recruitment (R0), spawning stock depletion (Dfinal), and fishing mortality in the terminal year (Fterminal). The Patagonian toothfish (Dissostichus eleginoides) fishery in southern Chile was used as a case study. Age composition data used to assess this fishery were split into two sets based on scale (1989–2006) and otolith (2007–2012) readings, where the scale readings show clear age-truncation effects. We used a simulation-estimation approach to examine the bias and precision of parameter estimates under various combinations of ageing error, selectivity type (asymptotic or dome-shaped), selectivity misspecification, and variation in selectivity over time. Generally, ageing error led to overly optimistic perceptions of current fishery status relative to historical reference points. Ageing error generated imprecise and positively biased estimates of R0 (range 10 to >200%), Dfinal (range −20 to >100%), and Fterminal (range −15 to >150%). The bias in Dfinal and R0 was more severe when selectivity was dome-shaped. Time-varying selectivity (both asymptotic and dome-shaped) increased the bias in Dfinal and Fterminal, but decreased the bias in R0. The effect of ageing error was more severe, or was masked, with selectivity misspecification. Correcting the ageing error inside the SCA reduced bias and improved precision of estimated parameters .

scholarly journals The importance of length and age composition data in statistical age-structured models for marine species

2014 ◽  
Vol 72 (1) ◽  
pp. 31-43 ◽  
Author(s):  
Kotaro Ono ◽  
Roberto Licandeo ◽  
Melissa L. Muradian ◽  
Curry J. Cunningham ◽  
Sean C. Anderson ◽  
...  
Keyword(s):  
Life History ◽  
Life Histories ◽  
Stock Assessment ◽  
Marine Species ◽  
Reference Points ◽  
Assessment Model ◽  
Sources Of Information ◽  
Age Composition ◽  
Composition Data ◽  
Age Structured

Abstract Management of marine resources depends on the assessment of stock status in relation to established reference points. However, many factors contribute to uncertainty in stock assessment outcomes, including data type and availability, life history, and exploitation history. A simulation–estimation framework was used to examine the level of bias and accuracy in assessment model estimates related to the quality and quantity of length and age composition data across three life-history types (cod-, flatfish-, and sardine-like species) and three fishing scenarios. All models were implemented in Stock Synthesis, a statistical age-structured stock assessment framework. In general, the value of age composition data in informing estimates of virgin recruitment (R0), relative spawning-stock biomass (SSB100/SSB0), and terminal year fishing mortality rate (F100), decreased as the coefficient of variation of the relationship between length and age became greater. For this reason, length data were more informative than age data for the cod and sardine life histories in this study, whereas both sources of information were important for the flatfish life history. Historical composition data were more important for short-lived, fast-growing species such as sardine. Infrequent survey sampling covering a longer period was more informative than frequent surveys covering a shorter period.

scholarly journals A two-stage biomass model to assess the English Channel cuttlefish (Sepia officinalis L.) stock

2014 ◽  
Vol 71 (9) ◽  
pp. 2457-2468 ◽  
Author(s):  
Michaël Gras ◽  
Beatriz A. Roel ◽  
Franck Coppin ◽  
Eric Foucher ◽  
Jean-Paul Robin
Keyword(s):  
Reference Points ◽  
Sea Surface ◽  
Sepia Officinalis ◽  
Sustainable Utilization ◽  
English Channel ◽  
Two Stage ◽  
Stock Biomass ◽  
Exploitation Rate ◽  
Spawning Stock ◽  
Age Structured

Abstract The English Channel cuttlefish (Sepia officinalis) is the most abundant cephalopod resource in the Northeast Atlantic and one of the three most valuable resources for English Channel fishers. Depletion methods and age-structured models have been used to assess the stock, though they have shown limitations related to the model assumptions and data demand. A two-stage biomass model is, therefore, proposed here using, as input data, four abundance indices derived from survey and commercial trawl data collected by Ifremer and Cefas. The model suggests great interannual variability in abundance during the 17 years of the period considered and a decreasing trend in recent years. Model results suggest that recruitment strength is independent of spawning–stock biomass, but appears to be influenced by environmental conditions such as sea surface temperature at the start of the life cycle. Trends in exploitation rate do not reveal evidence of overexploitation. Reference points are proposed and suggestions for management of the sustainable utilization of cuttlefish in the English Channel are advanced.

Performance of a fisheries catch-at-age model (Stock Synthesis) in data-limited situations

2011 ◽  
Vol 62 (8) ◽  
pp. 927 ◽  
Author(s):  
Chantell R. Wetzel ◽  
André E. Punt
Keyword(s):  
Stock Assessment ◽  
Estimation Method ◽  
Assessment Method ◽  
Assessment Model ◽  
Limited Data ◽  
Composition Data ◽  
Spawning Stock ◽  
Age Model ◽  
Age Structured ◽  
The Impact

Limited data are a common challenge posed to fisheries stock assessment. A simulation framework was applied to examine the impact of limited data and data type on the performance of a widely used catch-at-age stock-assessment method (Stock Synthesis). The estimation method provided negatively biased estimates of current spawning-stock biomass (SSB) relative to the unfished level (final depletion) when only recent survey indices were available. Estimation of quantities of management interest (unfished SSB, virgin recruitment, target fishing mortality and final depletion) improved substantially even when only minimal-length-composition data from the survey were available. However, the estimates of some quantities (final depletion and unfished SSB) remained biased (either positively or negatively) even in the scenarios with the most data (length compositions, age compositions and survey indices). The probability of overestimating yield at the target SSB relative to the true such yield was ~50%, a risk-neutral result, for all the scenarios that included length-composition data. Our results highlight the importance of length-composition data for the performance of an age-structured assessment model, and are encouraging for the assessment of data-limited stocks.

scholarly journals Bayesian survey-based assessment of North Sea plaice (Pleuronectes platessa): extracting integrated signals from multiple surveys

2009 ◽  
Vol 66 (4) ◽  
pp. 665-679 ◽  
Author(s):  
Johannes A. Bogaards ◽  
Sarah B. M. Kraak ◽  
Adriaan D. Rijnsdorp
Keyword(s):  
North Sea ◽  
Small Sample Size ◽  
Small Sample ◽  
Distribution Area ◽  
Parameter Estimates ◽  
Model Parameters ◽  
Fishing Mortality ◽  
Pleuronectes Platessa ◽  
The North ◽  
Spawning Stock

Abstract Bogaards, J. A., Kraak, S. B. M., and Rijnsdorp, A. D. 2009. Bayesian survey-based assessment of North Sea plaice (Pleuronectes platessa): extracting integrated signals from multiple surveys. – ICES Journal of Marine Science, 66: 665–679. Dependence on a relatively small sample size is generally viewed as a big disadvantage for survey-based assessments. We propose an integrated catch-at-age model for research vessel data derived from multiple surveys, and illustrate its utility in estimating trends in North Sea plaice abundance and fishing mortality. Parameter estimates were obtained by Bayesian analysis, which allows for estimation of uncertainty in model parameters attributable to measurement error. Model results indicated constant fishing selectivity over the distribution area of the North Sea plaice stock, with decreased selectivity at older age. Whereas separate analyses of survey datasets suggested different biomass trends in the southeast than in the western and central North Sea, a combined analysis demonstrated that the observations in both subareas were compatible and that spawning-stock biomass has been increasing over the period 1996–2005. The annual proportion of fish that dispersed in a northwesterly direction was estimated to increase from about 10% at age 2 to 33% at age 5 and older. We also found higher fishing mortality rates than reported in ICES assessments, which could be the consequence of inadequate specification of catchability-at-age in this study or underestimated fishing mortality by the conventional ICES assessment, which relies on official landings figures.

scholarly journals Time-varying parameter models for catchments with land use change: the importance of model structure

2018 ◽  
Vol 22 (5) ◽  
pp. 2903-2919 ◽  
Author(s):  
Sahani Pathiraja ◽  
Daniela Anghileri ◽  
Paolo Burlando ◽  
Ashish Sharma ◽  
Lucy Marshall ◽  
...  
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Land Cover ◽  
Parameter Estimates ◽  
Parameter Method ◽  
Model Parameters ◽  
Model Structure ◽  
Time Varying ◽  
Time Varying Parameter ◽  
Invariant Parameter

Abstract. Rapid population and economic growth in Southeast Asia has been accompanied by extensive land use change with consequent impacts on catchment hydrology. Modeling methodologies capable of handling changing land use conditions are therefore becoming ever more important and are receiving increasing attention from hydrologists. A recently developed data-assimilation-based framework that allows model parameters to vary through time in response to signals of change in observations is considered for a medium-sized catchment (2880 km2) in northern Vietnam experiencing substantial but gradual land cover change. We investigate the efficacy of the method as well as the importance of the chosen model structure in ensuring the success of a time-varying parameter method. The method was used with two lumped daily conceptual models (HBV and HyMOD) that gave good-quality streamflow predictions during pre-change conditions. Although both time-varying parameter models gave improved streamflow predictions under changed conditions compared to the time-invariant parameter model, persistent biases for low flows were apparent in the HyMOD case. It was found that HyMOD was not suited to representing the modified baseflow conditions, resulting in extreme and unrealistic time-varying parameter estimates. This work shows that the chosen model can be critical for ensuring the time-varying parameter framework successfully models streamflow under changing land cover conditions. It can also be used to determine whether land cover changes (and not just meteorological factors) contribute to the observed hydrologic changes in retrospective studies where the lack of a paired control catchment precludes such an assessment.

Comparing the performance of three data-weighting methods when allowing for time-varying selectivity

2020 ◽  
Vol 77 (2) ◽  
pp. 247-263 ◽  
Author(s):  
Haikun Xu ◽  
James T. Thorson ◽  
Richard D. Methot
Keyword(s):  
Simulation Experiment ◽  
Time Varying ◽  
Simulation Experiments ◽  
Age Composition ◽  
Ongoing Research ◽  
Composition Data ◽  
The Third ◽  
Stock Assessments ◽  
Data Weighting ◽  
Weighting Methods

How to properly weight composition data is an important ongoing research topic for fisheries stock assessments, and multiple methods for weighting composition data have been developed. Although several studies indicated that properly accounting for time-varying selectivity can reduce estimation biases in population biomass and management-related quantities, no study to date has compared the performance of widely used data-weighting methods when allowing for time-varying selectivity. Here, we conducted four simulation experiments on this topic, aiming to provide guidance on weighting age-composition data given time-varying selectivity. The first simulation experiment showed that over-weighting should be avoided in general and even when estimating time-varying selectivity. The second simulation experiment compared three data-weighting methods (McAllister–Ianelli, Francis, and Dirichlet-multinomial), within which the Dirichlet-multinomial method outperformed the other two methods when selectivity is time-varying. The third and fourth simulation experiments further showed that given time-varying selectivity, the Dirichlet-multinomial method still performed well when age-composition data were over-dispersed and when the level of selectivity variation needed to be simultaneously estimated. Our simulation results support using the Dirichlet-multinomial method when estimating time-varying fishery selectivity. Also, the simulations suggest that improving stock assessments by accounting for time-varying selectivity requires simultaneously addressing data weighting and time-varying selectivity.

scholarly journals Reference points based on dynamic optimization: a versatile algorithm for mixed-fishery management with bioeconomic age-structured models

2012 ◽  
Vol 69 (4) ◽  
pp. 660-669 ◽  
Author(s):  
José-María Da Rocha ◽  
María-José Gutiérrez ◽  
Santiago Cerviño
Keyword(s):  
Dynamic Optimization ◽  
Fishery Management ◽  
Single Species ◽  
Steady State Solution ◽  
Reference Points ◽  
Management Problem ◽  
Species Management ◽  
Intertemporal Discounting ◽  
Spawning Stock ◽  
Age Structured

Abstract Da Rocha, J-M., Gutiérrez, M-J., and Cerviño, S. 2012. Reference points based on dynamic optimization: a versatile algorithm for mixed-fishery management with bioeconomic age-structured models. – ICES Journal of Marine Science, 69: 660–669. Single-species management objectives may not be consistent within mixed fisheries. They may lead species to unsafe situations, promote discarding of over-quota, and/or misreporting of catches. We provide an algorithm for characterizing bioeconomic reference points for a mixed fishery as the steady-state solution of a dynamic optimal management problem. The optimization problem takes into account that: (i) species are caught simultaneously in unselective fishing operations, and (ii) intertemporal discounting and fleet costs relate to reference points to discounted economic profits along optimal trajectories. We illustrate how the algorithm can be implemented by applying it to the European northern hake stock (Merluccius merluccius), where fleets also capture northern megrim (Lepidorhombus whiffiagonis) and northern anglerfish (Lophius piscatorius and Lophius budegassa). We find that optimal mixed management leads to a target reference point that is quite similar to two-thirds of the Fmsy single-species (hake) target. Mixed management is superior to single-species management because it leads the fishery to higher discounted profits, with higher long-term spawning-stock biomass for all species. We calculate that the losses due to the use of the Fmsy single-species (hake) target in this mixed fishery account for 11.4% of total discounted profits.

scholarly journals Time varying parameter models for catchments with land use change: the importance of model structure

2017 ◽  
Author(s):  
Sahani Pathiraja ◽  
Daniela Anghileri ◽  
Paolo Burlando ◽  
Ashish Sharma ◽  
Lucy Marshall ◽  
...  
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Land Cover ◽  
Parameter Estimates ◽  
Model Parameters ◽  
Model Structure ◽  
Time Varying ◽  
Time Varying Parameter ◽  
Paired Control ◽  
Invariant Parameter

Abstract. Rapid population and economic growth in South-East-Asia has been accompanied by extensive land use change with consequent impacts on catchment hydrology. Modelling methodologies capable of handling changing land use conditions are therefore becoming ever more important, and are receiving increasing attention from hydrologists. A recently developed Data Assimilation based framework that allows model parameters to vary through time in response to signals of change in observations is considered for a medium sized catchment (2880 km2) in Northern Vietnam experiencing substantial but gradual land cover change. We investigate the efficacy of the method as well as the importance of the chosen model structure in ensuring the success of time varying parameter methods. The framework was utilized with two conceptual models (HBV and HyMOD) that gave good quality streamflow predictions during pre-change conditions. Although both time varying parameter models gave improved streamflow predictions under changed conditions compared to the time invariant parameter model, persistent biases for low flows were apparent in the HyMOD case. It was found that HyMOD was not suited to representing the modified baseflow conditions, resulting in extreme and unrealistic time varying parameter estimates. This work shows that the chosen model can be critical for ensuring the time varying parameter framework successfully models streamflow under changed land cover conditions. It also serves as an effective tool for separating the influence of climatic and land use change in retrospective studies where the lack of a paired control catchment precludes such an assessment.

Analytical models for fishery reference points

1998 ◽  
Vol 55 (2) ◽  
pp. 515-528 ◽  
Author(s):  
Jon T Schnute ◽  
Laura J Richards
Keyword(s):  
Fishery Management ◽  
Reference Points ◽  
Analytical Models ◽  
Model Parameters ◽  
Harvest Management ◽  
Structured Population Models ◽  
General Utility ◽  
Special Cases ◽  
Age Structured ◽  
Mathematical Definitions

Fishery reference points are widely applied in formulating harvest management policies. We supply precise mathematical definitions for several reference points in common use. We then derive analytical expressions for these quantities from age-structured population models. In particular, we explain how the maximum sustainable harvest rate and catch (h*, C*), two quantities of management importance, can replace the classical recruitment parameters ( alpha , beta ) in the Beverton-Holt and Ricker recruitment curves. We also demonstrate dependencies of various reference points on subsets of model parameters. Although our analysis is restricted to special cases, our models still have general utility. For example, simple calculations from analytical formulas enable checks on the output from more complex models and guide the choice of reference points for fishery management.

scholarly journals The advantage of explicitly incorporating predation mortality into age-structured stock assessment models: an application for Atlantic mackerel

2009 ◽  
Vol 66 (3) ◽  
pp. 445-454 ◽  
Author(s):  
H. Moustahfid ◽  
J. S. Link ◽  
W. J. Overholtz ◽  
M. C. Tyrrell
Keyword(s):  
Stock Assessment ◽  
Fish Predation ◽  
Reference Points ◽  
Assessment Model ◽  
Fishing Mortality ◽  
Atlantic Mackerel ◽  
Predation Mortality ◽  
Spawning Stock ◽  
Age Structured ◽  
The Impact

AbstractMoustahfid, H., Link, J. S., Overholtz, W. J., and Tyrrell, M. C. 2009. The advantage of explicitly incorporating predation mortality into age-structured stock assessment models: an application for Atlantic mackerel. – ICES Journal of Marine Science, 66: 445–454. An age-structured assessment programme (ASAP) that explicitly incorporates predation mortality was applied to Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic. Predatory removals were modelled in the same manner as fishing mortality, with a comparable set of time-series, to produce estimates of predation mortality at age and for each year. Results from the analysis showed that incorporating predation into a mackerel stock assessment model notably altered model outputs. When excluding explicitly modelled rates of predation, the model underestimated the magnitude and uncertainty in spawning-stock biomass (SSB) and recruitment. Further, the rates of predation mortality varied across time and were higher for younger fish. Predation mortality was higher than fishing mortality for fish aged 1 year, approximately equal for 2-year-olds, and lower for older fish (3 years and older). Biological reference points for Atlantic mackerel differed considerably when predation mortality was included. For example, SSBMSY was more than twice as high in the model where predation was incorporated than in the fisheries-only model. Although there are several caveats to the predation model outputs, chief of which is that the estimates are conservative because some mackerel predators were excluded, the results demonstrate the feasibility of executing such an approach with an extant tool. The approach presented here ultimately has the advantage of detecting, and upon detection parsing out, the impact of predators relative to fisheries and has the potential to provide useful information to those interested in small pelagic fish and their associated fisheries.

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