Harvesting at the Cohort and Population Levels

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.

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.

Equilibrium Yields and Yield Isopleths from a General Age-Structured Model of Harvested Populations

1985 ◽  
Vol 42 (11) ◽  
pp. 1766-1771 ◽  
Author(s):  
Timothy A. Lawson ◽  
Ray Hilborn
Keyword(s):  
Structured Model ◽  
Surplus Production ◽  
Pacific Halibut ◽  
Production Models ◽  
The Pacific ◽  
Hippoglossus Stenolepis ◽  
Equilibrium Yield ◽  
Stock Recruitment ◽  
Age Structured ◽  
Age Structured Model

The equilibrium properties of an age-structured model that includes any arbitrary age-specific weights, vulnerabilities, fecundities, and natural mortality rates, combined with stock–recruitment relationships, are derived. The numbers, biomass, and catch at each age can be calculated quite simply. These relationships can be used to construct yield-isopleth diagrams, or to plot equilibrium yield and biomass against harvest intensity. We used the results to compute yield isopleths for the Pacific halibut (Hippoglossus stenolepis) fishery. The analysis can also include a fishing season of any specified length. Relationships are given to translate the aggregate properties of the age-structured models into several alternative surplus production models.

The estimation and robustness of FMSY and alternative fishing mortality reference points associated with high long-term yield

2012 ◽  
Vol 69 (9) ◽  
pp. 1468-1480 ◽  
Author(s):  
Jan Horbowy ◽  
Anna Luzeńczyk
Keyword(s):  
Total Yield ◽  
Reference Points ◽  
Superior Performance ◽  
Equilibrium Yield ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Yield Per Recruit ◽  
Different Sources ◽  
Recruitment Model

Equations for equilibrium yield and biomass are presented and used to derive FMSY and alternative reference points (ARPs). ARPs are analogues of the traditional points based on yield-per-recruit (YPR) or spawning stock-per-recruit (SPR) (F0.1, F40%, F50%), but refer to the equilibrium total yield or biomass. The method combines YPR and SPR analysis with stock–recruitment relationships. The sensitivity of FMSY and ARPs to the range of available stock–recruitment data, recruitment variance, various steepness levels in the stock–recruitment models, assessment variance, and bias are tested. The analysis showed that in most cases, F40%B and F50%B, defined by the equilibrium biomass (B), were the most robust relative to the different sources of uncertainty. However, in the case of the misspecification of the stock–recruitment relationship, FMSY showed superior performance. F40%B for the Beverton and Holt stock–recruitment model and F50%B for the Ricker recruitment model can be recommended as conservative fishing mortalities associated with high long-term yield. For the considered steepness, they produced yield up to 5%–10% lower than yield at FMSY.

An age-structured model with leading management parameters, incorporating age-specific selectivity and maturity

2008 ◽  
Vol 65 (2) ◽  
pp. 286-296 ◽  
Author(s):  
Robyn E Forrest ◽  
Steven J.D. Martell ◽  
Michael C Melnychuk ◽  
Carl J Walters
Keyword(s):  
Life History Traits ◽  
Stock Assessment ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Fish Stock ◽  
Structured Model ◽  
Specific Selectivity ◽  
Stock Recruitment ◽  
Age Structured ◽  
Age Structured Model

Previous authors have shown analytically that the optimal equilibrium harvest rate (UMSY) for an iteroparous fish stock is a function of the slope of the stock-recruitment curve at low stock size (α) and that UMSY can therefore be considered a direct measure of stock productivity. As such, it can be used as a leading parameter in stock assessment models and directly estimated using Bayesian or similar techniques. Here we present an alternative method for deriving α from UMSY that incorporates age-specific selectivity and fecundity, avoiding assumptions of knife-edged recruitment and maturity. We present an age-structured model with two fisheries reference points (UMSY and maximum sustainable yield, MSY) as its leading parameters. We show equilibrium properties of the model, chiefly in terms of its ability to show relationships between life history traits, density dependence, and UMSY. We also demonstrate a simple Bayesian estimation routine to illustrate estimation of UMSY and MSY directly from data. We compare our results to those from a structurally identical model with leading biological parameters. Using models with leading management parameters can improve communicability of results to managers.

scholarly journals Indicators of the health of the North Sea fish community: identifying reference levels for an ecosystem approach to management

2006 ◽  
Vol 63 (4) ◽  
pp. 573-593 ◽  
Author(s):  
Simon P.R. Greenstreet ◽  
Stuart I. Rogers
Keyword(s):  
North Sea ◽  
Time Series Data ◽  
Size Structure ◽  
Single Species ◽  
Ecosystem Approach ◽  
Reference Points ◽  
Series Data ◽  
Anthropogenic Activity ◽  
Data Sets ◽  
The North

Abstract The shift in emphasis away from the single-species focus of traditional fisheries management towards an ecosystem approach to management requires application of indicators of ecosystem state. Further, an ecosystem approach to management requires the identification of ecological reference points against which management objectives might be set. In applying indicators, identifying reference points, and setting objectives, an obvious requirement is that the indicators respond primarily to the anthropogenic activity being managed and are sufficiently sensitive that impacts of the activity and the responses to management action are clearly demonstrable. Here we apply a suite of 12 indicators to Scottish August groundfish survey data collected in the northern North Sea over the period 1925–1997. These include indicators of size structure, life-history character composition, species diversity, and trophic structure within the community. Our choice of analytical design has two purposes; first to show that fishing has unequivocally affected these various aspects of the structure of the groundfish community, and second to illustrate an approach by which long time-series data sets might be used to identify possible management reference points. The results are discussed in the context of selecting ecological indicators in support of an ecosystem approach to management and determining appropriate reference points for objective-setting.

scholarly journals Using AMOEBAs to display multispecies, multifleet fisheries advice

2003 ◽  
Vol 60 (4) ◽  
pp. 709-720 ◽  
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.

A perspective on steepness, reference points, and stock assessment

2013 ◽  
Vol 70 (6) ◽  
pp. 930-940 ◽  
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.

The Equilibrium Yield Curve for Government Securities

1979 ◽  
Vol 35 (3) ◽  
pp. 31-39 ◽  
Author(s):  
Herbert F. Ayres ◽  
John Y. Barry
Keyword(s):  
Yield Curve ◽  
Equilibrium Yield

POTENTIAL YIELD OF A ROCK SHRIMP STOCK, SICYONIA PENICILLATA IN THE NORTHERN GULF OF CALIFORNIA

Crustaceana ◽  
1999 ◽  
Vol 72 (6) ◽  
pp. 581-590 ◽  
Author(s):  
Juana Lopez-Martinez ◽  
Edgar Alcantara-Razo ◽  
Sergio Hernandez-Vazquez ◽  
Ernesto Chavez
Keyword(s):  
Gulf Of California ◽  
Age Groups ◽  
Potential Yield ◽  
Natural Oscillations ◽  
Recruitment Pattern ◽  
Stock Recruitment ◽  
Age Structured ◽  
Stochastic Recruitment ◽  
Age Structured Model ◽  
Compensatory Effect

AbstractA stock of rock shrimp Sicyonia penicillata was assessed in a fishery recently opened at Bahoa Kino, Sonora, Mexico. An age-structured model with stochastic recruitment was developed, which considers growth rate, natural mortality, and fishing mortality by age. Age groups were followed year by year with a stock-recruitment Ricker function where the seasonal recruitment pattern was defined as well. Simulations might be interpreted as showing a stable population with four year cycles, reflecting a density-dependent process. In 1996, fishing intensity had an apparent compensatory effect on the stock, decreasing the amplitude of natural oscillations and maintaining the stock at a biomass level similar to the size observed in a condition of no exploitation. The stock was found currently underexploited. As a result of the seasonal accessibility and the age of first-catch fishing (adult shrimp), the stock might be capable to withstand high fishing pressure without being overexploited. Se evaluo una poblacion de camaron de roca Sicyonia penicillata, de una pesqueroa recientemente abierta en Bahoa Kino, Sonora, Mexico. Se desarrollo un modelo basado en la estructura por edades que considera reclutamiento estocastico, tasa de crecimiento, mortalidad natural y mortalidad por pesca por grupo de edad. Estos grupos de edad fueron determinados ano tras ano mediante la funcion de reclutamiento de Ricker, en los que tambien se definio el patron estacional de reclutamiento. Las simulaciones muestran una poblacion estable con ciclos de cuatro anos, que indican un proceso de densodependencia. En 1996, la intensidad de pesca tuvo un efecto compensatorio sobre la poblacion, reduciendo la amplitud de las oscilaciones naturales y manteniendo al stock en un nivel de biomasa similar al observado en la condicion sin explotacion. Se encontro que el recurso esta subexplotado. Como resultado de la accesibilidad estacional y de que la edad de primera captura corresponde a camaron adulto, el recurso soporta alta presion de pesca sin dar evidencias de sobreexplotacion.

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