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

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.

Download Full-text

Fishing catch shares in the face of global change: a framework for integrating cumulative impacts and single species management

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f10-118 ◽

2010 ◽

Vol 67 (12) ◽

pp. 1968-1982 ◽

Cited By ~ 57

Author(s):

Isaac C. Kaplan ◽

Phillip S. Levin ◽

Merrick Burden ◽

Elizabeth A. Fulton

Keyword(s):

Global Change ◽

Ocean Acidification ◽

Fishery Management ◽

Single Species ◽

Ecosystem Model ◽

Careful Consideration ◽

Reference Points ◽

Cumulative Impacts ◽

English Sole ◽

Modeling Tools

Any fishery management scheme, such as individual fishing quotas (IFQs) or marine protected areas, should be designed to be robust to potential shifts in the biophysical system. Here we couple possible catch scenarios under an IFQ scheme with ocean acidification impacts on shelled benthos and plankton, using an Atlantis ecosystem model for the US West Coast. IFQ harvest scenarios alone, in most cases, did not have strong impacts on the food web, beyond the direct effects on harvested species. However, when we added the impacts of ocean acidification, the abundance of commercially important groundfish such as English sole ( Pleuronectes vetulus ), arrowtooth flounder ( Atheresthes stomias ), and yellowtail rockfish ( Sebastes flavidus ) declined up to 20%–80%, owing to the loss of shelled prey items from their diet. English sole exhibited a 10-fold decline in potential catch and economic yield when confronted with strong acidification impacts on shelled benthos. Therefore, it seems prudent to complement IFQs with careful consideration of potential global change effects such as acidification. Our analysis provides an example of how new ecosystem modeling tools that evaluate cumulative impacts can be integrated with established management reference points and decision mechanisms.

Download Full-text

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

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu081 ◽

2014 ◽

Vol 71 (9) ◽

pp. 2457-2468 ◽

Cited By ~ 12

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.

Download Full-text

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

ICES Journal of Marine Science ◽

10.1093/icesjms/fsv270 ◽

2016 ◽

Vol 73 (4) ◽

pp. 1074-1090 ◽

Cited By ~ 6

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 .

Download Full-text

Harvesting at the Cohort and Population Levels

Fishery Ecosystem Dynamics ◽

10.1093/oso/9780198768937.003.0011 ◽

2020 ◽

pp. 185-204

Author(s):

Michael J. Fogarty ◽

Jeremy S. Collie

Keyword(s):

Multiple Equilibria ◽

Yield Curve ◽

Size Structure ◽

Single Species ◽

Reference Points ◽

Stable States ◽

Equilibrium Yield ◽

Stock Recruitment ◽

Age Structured ◽

Dynamics Models

This chapter explores dynamical behaviors that go beyond globally stable outcomes to include alternate stable states, and non-equilibrium behaviors. The possibility of multiple equilibria emerges quite readily in models with non-linear harvesting functions. In practice, most fisheries management protocols at least implicitly assume that harvested populations have well-behaved stable equilibrium properties. If this is not the case, then sudden changes (including collapse) can occur and be totally unanticipated. This chapter describes the spectrum of single-species harvesting models from biomass dynamics models that do not include age or size structure, to delay–difference models with a simple demographic structure, to full age-structured models. Dynamic-pool models combine yield per recruit and egg-per-recruit with a stock-recruitment model to obtain an equilibrium yield curve. These single-species models are used to estimate biological reference points with which to assess stock status.

Download Full-text

A perspective on the use of spatialized indicators for ecosystem-based fishery management through spatial zoning

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.01.010 ◽

2005 ◽

Vol 62 (3) ◽

pp. 469-476 ◽

Cited By ~ 80

Author(s):

Elizabeth A. Babcock ◽

Ellen K. Pikitch ◽

Murdoch K. McAllister ◽

Panayiota Apostolaki ◽

Christine Santora

Keyword(s):

Fishery Management ◽

Single Species ◽

Reference Points ◽

System Level ◽

Management Tool ◽

Clear Understanding ◽

Potential Bias ◽

Spatial Management ◽

Developing System ◽

Destructive Fishing

Abstract Although much work has been done developing system-level indicators for ecosystem-based fishery management (EBFM), few of those proposed include a spatial component. Even in single-species management, time and area closures have been applied without a clear understanding of what their effect might be on identifying overfishing thresholds and other reference points. For EBFM, spatial zoning of the marine environment, including no-take marine reserves and areas where destructive fishing gears are prohibited, may become a prime management tool. Therefore, indicators of the effectiveness of spatial management will be required, along with an understanding of how indicators related to other objectives will be influenced. We review single-species models that have been used to model spatial zoning, including potential bias in assessment and current work on effort reallocation after area closure, as well as available ecosystem-based models and metrics and how they might account for spatial management. Metrics that can be derived from explicitly spatial approaches such as GIS-based ecosystem and fishery evaluations are also discussed.

Download Full-text

Analytical models for fishery reference points

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f97-212 ◽

1998 ◽

Vol 55 (2) ◽

pp. 515-528 ◽

Cited By ~ 14

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.

Download Full-text

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

ICES Journal of Marine Science ◽

10.1093/icesjms/fsn217 ◽

2009 ◽

Vol 66 (3) ◽

pp. 445-454 ◽

Cited By ~ 30

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.

Download Full-text

Mitigating unwanted catches in the southern Iberian hake stock fisheries: Improving fishing technology vs market control policies

Scientia Marina ◽

10.3989/scimar.04739.25a ◽

2018 ◽

Vol 82 (S1) ◽

pp. 63

Author(s):

José María Da-Rocha ◽

Javier García-Cutrín ◽

María José Gutiérrez

Keyword(s):

Fold Increase ◽

Steady State Solution ◽

Reference Points ◽

Human Consumption ◽

Management Problem ◽

Optimal Management ◽

The European Union ◽

Market Control ◽

Percentage Points ◽

Two Measures

Unwanted catches can be reduced by improving fishing effectiveness in targeting species and sizes and by banning their sale for human consumption. The landing obligation introduced by the European Union can be seen as a combination of these two measures, and the aim of this paper is to analyse its effects on the Southern Iberian Hake Stock fishery. To this end, reference points for a mixed fishery are computed under the two measures as the steady-state solution of a dynamic optimal management problem. Our results show that measures that improve selectivity obtain better results than sales ban strategies in terms of increasing yields and stocks and reducing discards. In particular, we find that reducing the selectivity parameters by 90% for the three early ages leads to an almost six-fold increase in the hake yield and lowers the discard rate by more than 20 percentage points. Banning the sale of the two youngest ages also increases hake yield by 21% and the discard rate by 7 percentage points.

Download Full-text

Using AMOEBAs to display multispecies, multifleet fisheries advice

ICES Journal of Marine Science ◽

10.1016/s1054-3139(03)00042-0 ◽

2003 ◽

Vol 60 (4) ◽

pp. 709-720 ◽

Cited By ~ 21

Author(s):

Jeremy S. Collie ◽

Henrik Gislason ◽

Morten Vinther

Keyword(s):

Response Surface ◽

Single Species ◽

Fishing Effort ◽

Response Surface Model ◽

Reference Points ◽

Surface Model ◽

Interacting Species ◽

The North ◽

Age Structured ◽

Fishing Fleets

Abstract In multispecies fish communities, predation levels change dynamically in response to changes in the abundance of predator and prey species, as influenced by the fisheries that exploit them. In addition to community-level metrics, it remains necessary to track the abundance of each species relative to its biological reference point. In situations with many interacting species, exploited by multiple fishing fleets, it can be complicated to illustrate how the effort of each fleet will affect the abundance of each species. We have adapted the AMOEBA approach to graph the reference levels of multiple interacting species exploited by multiple fleets. This method is illustrated with 10 species and eight fishing fleets in the North Sea. We fit a relatively simple response-surface model to the predictions of a fully age-structured multispecies model. The response-surface model links the AMOEBA for fishing effort to separate AMOEBAs for spawning stock biomass, fishing mortality, and yield. Ordination is used to give the shape of the AMOEBAs functional meaning by relating fish species to the fleets that catch them. The aim is to present the results of dynamic multispecies models in a format that can be readily understood by decision makers. Interactive versions of the AMOEBAs can be used to identify desirable combinations of effort levels and to test the compatibility of the set of single-species biological reference points.

Download Full-text

A perspective on steepness, reference points, and stock assessment

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2012-0372 ◽

2013 ◽

Vol 70 (6) ◽

pp. 930-940 ◽

Cited By ~ 67

Author(s):

Marc Mangel ◽

Alec D. MacCall ◽

Jon Brodziak ◽

E.J. Dick ◽

Robyn E. Forrest ◽

...

Keyword(s):

Life History ◽

Fishery Management ◽

Stock Assessment ◽

Reference Points ◽

Production Model ◽

Published Data ◽

Difficult Situation ◽

Life History Parameters ◽

Stock Recruitment ◽

Age Structured

We provide a perspective on steepness, reference points for fishery management, and stock assessment. We first review published data and give new results showing that key reference points are fixed when steepness and other life history parameters are fixed in stock assessments using a Beverton–Holt stock–recruitment relationship. We use both production and age-structured models to explore these patterns. For the production model, we derive explicit relationships for steepness and life history parameters and then for steepness and major reference points. For the age-structured model, we are required to generally use numerical computation, and so we provide an example that complements the analytical results of the production model. We discuss what it means to set steepness equal to 1 and how to construct a prior for steepness. Ways out of the difficult situation raised by fixing steepness and life history parameters include not fixing them, using a more complicated stock–recruitment relationship, and being more explicit about the information content of the data and what that means for policy makers. We discuss the strengths and limitations of each approach.

Download Full-text