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.

Effects of an erroneous natural mortality rate on a simple age-structured stock assessment

1999 ◽  
Vol 56 (10) ◽  
pp. 1721-1731 ◽  
Author(s):  
William G Clark
Keyword(s):  
Mortality Rate ◽  
Stock Assessment ◽  
Natural Mortality ◽  
Structured Model ◽  
Harvest Rate ◽  
Specific Selectivity ◽  
Age Structured ◽  
Age Structured Model ◽  
Size Estimates

The abundance of many stocks is estimated by fitting an age-structured model to catch-at-age and relative abundance data from the commercial fishery and scientific surveys. The natural mortality rate used in the model is usually estimated externally and its value is uncertain. An erroneous natural mortality rate will bias the stock size estimates obtained by fitting the model and will also bias the yield calculations that are done to choose a harvest rate and recommend quotas. This paper describes the general features of both effects by analyzing a simple age-structured model fitted to artificial data. It is shown that an erroneous natural mortality rate mainly affects the estimates of fishing mortality and hence abundance but not the estimates of age-specific selectivity. Errors in estimated abundance and target harvest rate are always in the same direction, with the result that, in the short term, extremely high exploitation rates can be recommended (unintentionally) in cases where the natural mortality rate is overestimated and historical exploitation rates in the catch-at-age data are low. A conservative (low) estimate of natural mortality can avoid that danger. Long-term yield under either an FMSY or F35% strategy is not very sensitive to error in natural mortality rate unless it is grossly underestimated.

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.

An Analysis of the Hecate Strait Pacific Cod Fishery Using an Age-structured Model Incorporating Density-dependent Effects

1983 ◽  
Vol 40 (8) ◽  
pp. 1233-1243 ◽  
Author(s):  
D. A. Fournier
Keyword(s):  
Fishing Effort ◽  
Natural Mortality ◽  
Pacific Cod ◽  
Structured Model ◽  
Density Dependent ◽  
Gadus Macrocephalus ◽  
Stock Recruitment ◽  
Age Structured ◽  
Age Structured Model ◽  
Relationship Of

An age-structured model was used to analyze the Hecate Strait Pacific cod (Gadus macrocephalus) fishery for the years 1960–80. The data consisted of estimates of fishing effort, together with estimates of numbers of fish at age caught in each year. The latter estimates were derived from length–frequency analysis. A stock–recruitment relationship of the Ricker type with an additional environmental factor was estimated. The data is also analyzed for evidence of the existence of age-dependent trends in natural mortality, density-dependent trends in natural mortality and catchability, and for time-dependent trends in catchability. Evidence of a density-dependent trend in natural mortality was discovered. The average level of natural mortality was also estimated to be 0.65.

scholarly journals MULTIFAN-CL: a length-based, age-structured model for fisheries stock assessment, with application to South Pacific albacore, Thunnus alalunga

1998 ◽  
Vol 55 (9) ◽  
pp. 2105-2116 ◽  
Author(s):  
Daid A Fournier ◽  
John Hampton ◽  
John R Sibert
Keyword(s):  
Time Series ◽  
Growth Parameters ◽  
Stock Assessment ◽  
South Pacific ◽  
Environmental Data ◽  
Model Parameters ◽  
Structured Model ◽  
Thunnus Alalunga ◽  
Age Structured ◽  
Age Structured Model

We introduce a length-based, age-structured model, MULTIFAN-CL, that provides an integrated method of estimating catch age composition, growth parameters, mortality rates, recruitment, and other parameters from time series of fishery catch, effort, and length frequency data. The method incorporates Bayesian parameter estimation, estimation of confidence intervals for model parameters, and procedures for hypothesis testing to assist model development. We apply the method to South Pacific albacore, Thunnus alalunga, fishery data and demonstrate the incorporation of model structure such as spatial heterogeneity, age-dependent natural mortality and movement rates, time series trends and seasonal variation in catchability, and density-dependent growth. Consistency of the results of the albacore analysis with various exogenous sets of biological and environmental data gives credence to the model results.

scholarly journals Life history changes and fisheries assessment performance: a case study for small yellow croaker

2019 ◽  
Vol 77 (2) ◽  
pp. 645-654
Author(s):  
Qi Lee ◽  
Alice Lee ◽  
Zunlei Liu ◽  
Cody S Szuwalski
Keyword(s):  
Life History ◽  
Reference Points ◽  
Structured Populations ◽  
Production Model ◽  
Life History Variation ◽  
Structured Model ◽  
Small Yellow Croaker ◽  
Age Structured ◽  
Age Structured Model

Abstract Many intensely exploited fish stocks have experienced changes in trophic structure and environmental conditions, resulting in non-stationary population processes. We evaluate the ability of assessment methods to estimate quantities used in management (like target biomasses and fishing mortalities) when life history processes are non-stationary and comprehensive data are not available. We use the small yellow croaker (Larimichthys polyactis) fishery in the East China and Yellow Seas as a case study. We simulate age-structured populations with time-varying fishery and life history characteristics similar to that of the small yellow croaker in China based on historical studies that demonstrate changes in life history. We then fit surplus production and statistical catch-at-age models to simulated catch and index data from these populations. Given our assumptions, both estimation models yielded biased quantities important to management. The production model estimated reference points associated with target biomass with less bias than the age-structured model, while the latter outperformed the former when estimating reference points associated with target fishing mortality. The age-structured model also better captured relative population trends and provided flexibility to consider impacts of life history changes over time. We suggest that assessments of similar stocks consider the potential of life history variation impact management quantities.

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.

scholarly journals A continuous hockey stick stock–recruit model for estimating MSY reference points

2010 ◽  
Vol 67 (8) ◽  
pp. 1780-1784 ◽  
Author(s):  
Benoit Mesnil ◽  
Marie-Joëlle Rochet
Keyword(s):  
Stock Assessment ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Sustainable Yield ◽  
Political Commitment ◽  
Hockey Stick ◽  
Differentiable Functions ◽  
Piecewise Function ◽  
Management Plans ◽  
Stock Recruitment

Abstract Mesnil, B., and Rochet, M-J. 2010. A continuous hockey stick stock–recruit model for estimating MSY reference points. – ICES Journal of Marine Science, 67: 1780–1784. With political commitment to restore stocks to levels where they can produce maximum sustainable yield (MSY), fisheries managers request evaluation of management plans that include options for an FMSY policy. The procedure to estimate FMSY with dynamic-pool, stock assessment models is well established for common stock–recruitment relationships (S–RR), and this capacity is extended to another S–RR, a piecewise function known as the hockey stick (HS), which is frequently assumed when the data do not support more elaborate functions. However, the HS is not continuous, which makes it problematic for this application, where differentiable functions are required. The bent-hyperbola model proves to be an adequate continuous equivalent to the HS for estimating FMSY.

Sign in / Sign up

Export Citation Format

Share Document