Effect of Assumptions about the Stock–Recruitment Relationship on a Lobster (Homarus gammarus) Stock Assessment

1986 ◽  
Vol 43 (11) ◽  
pp. 2353-2359 ◽  
Author(s):  
R. C. A. Bannister ◽  
J. T. Addison
Keyword(s):  
Carapace Length ◽  
Stock Assessment ◽  
Fishing Effort ◽  
Yield Curves ◽  
Recruitment Curve ◽  
Homarus Gammarus ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Yield Per Recruit ◽  
Marked Tendency

Stock assessment of the European lobster (Homarus gammarus) has involved yield per recruit analysis based on the established length cohort methodology of Jones (1974. ICES C.M. 1974/F:33; 1981. FAO Fish. Circ. 734) which assumes that recruitment to the fishery is independent of spawning stock. The Shepherd (1982. J. Cons. Int. Explor. Mer 40: 67–75) model has been used to simulate a range of assumed stock–recruitment relationships, and the resulting sensitivity analysis describes how these affect the relation between yield or biomass and four management variables, namely fishing mortality, minimum carapace length, maximum carapace length, and the capture or noncapture of egg-bearing females. Yield curves show a clear maximum with a marked tendency to stock collapse when fishing effort is high. For the range of simulations considered, the probability of an early recruit failure is greatest for asymptotic stock–recruitment curves, which generate yield curves with maxima at an effort substantially lower than the present level. Only with a highly overcompensatory stock–recruitment curve is there a case for increasing effort to maximise yield, but such a relationship tends to reduce the benefit of increasing minimum carapace length or of setting a maximum carapace length. The model predicts that the assumption made about the stock–recruitment relationship also has a marked effect on the results expected from a ban on the landing of egg-bearing females. Overall the results confirm the unsatisfactory prognosis of the yield per recruit model and emphasise the need to gain an understanding of the biological factors determining the shape of the lobster stock–recruitment curve.

Population Dynamics of the Arcto-Norwegian Cod

1967 ◽  
Vol 24 (1) ◽  
pp. 145-190 ◽  
Author(s):  
D. J. Garrod
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Fishing Effort ◽  
Catch Per Unit Effort ◽  
Group Iii ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Post War ◽  
The One ◽  
Definition Of

By reason of its geographical distribution, the Arcto-Norwegian cod (Gadus morhua) supports three distinct fisheries, two feeding fisheries in the Barents Sea and at Bear Island–Spitsbergen, and a spawning fishery off the Norway coast. In the past this diversity of fishing on the one stock has made it difficult to unify all the data to give an overall description of post-war changes in the stock. In this contribution three modifications of conventional procedures are introduced which enable this to be done. These are: (i) a system of weighting the catch per unit effort data from each fishery to a level of comparability; (ii) a more rigorous definition of the effective fishing effort on each age-group; (iii) a method of estimation of the effective fishing effort on partially recruited age-groups.Using these methods the analysis presents the effects of fishing on each fishery in the context of its effect on the total stock, and at the same time it indicates ways in which factors other than fishing may have influenced the apparent abundance of the stock. The treatment of the data is also used to derive estimates of spawning stock and recruitment of 3-year-old cod for subsequent analysis of stock–recruitment relationships.

Problems and Perspectives Regarding Recruitment of Spiny Lobsters, Panulirus argus, to the South Florida Fishery

1986 ◽  
Vol 43 (11) ◽  
pp. 2099-2106 ◽  
Author(s):  
William G. Lyons
Keyword(s):  
Carapace Length ◽  
Spiny Lobster ◽  
Fishing Effort ◽  
International Management ◽  
South Florida ◽  
Panulirus Argus ◽  
Minimum Size ◽  
Juvenile Growth ◽  
Larval Recruitment ◽  
Yield Per Recruit

Inappropriate minimum size, illegal harvest, fishery-induced juvenile growth retardation and mortality, and excessive effort have reduced reproductive contributions and depressed yield-per-recruit in the overcapitalized south Florida spiny lobster (Panulirus argus) fishery. Measures recommended to improve yield-per-recruit are as follows: increase minimum legal size to 85–90 mm carapace length; require escape gaps in traps; eliminate possession of sublegal lobsters aboard vessels; prohibit harvest in nurseries; reduce fishing effort; improve enforcement of fishery regulations; and initiate programs to educate fishermen regarding impacts of fishery practices. International management is recommended to assure larval recruitment among Pan-Caribbean stocks.

Recruitment variation in abalone: Its importance to fisheries management

1995 ◽  
Vol 46 (3) ◽  
pp. 555 ◽  
Author(s):  
PE McShane
Keyword(s):  
Egg Production ◽  
Field Experiments ◽  
Stock Assessment ◽  
Reference Points ◽  
High Fecundity ◽  
Spatial And Temporal Scales ◽  
Recruitment Failure ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Many Sources

Recruitment failure has been implicated in the decline of several abalone fisheries. Traditionally, fisheries scientists invoke theoretical stock-recruitment relationships to predict trends in abundance of an exploited stock under various harvest regimes. The empirical evidence in support of a positive relationship between spawning stock and recruits is not strong. A further problem in interpretation of such relationships is that both 'stock' and 'recruitment' have various definitions in fisheries and ecological literature. The definition of a stock for abalone is not clear. As emphasized in this review, which considers each stage in the life history of abalone, the abundance of spawners is one of many sources of variation in recruitment. The evidence for invertebrates, particularly those with high fecundity, is that recruitment varies independently of the abundance of spawners. This is also the case for abalone, where recruits have been measured as the density of immediate post-settlement individuals, juveniles, or as adults entering the exploitable stock. A problem with stock-recruitment hypotheses is that they have intuitive appeal. It is considered 'dangerous' to manage fisheries under the assumption that a reduction in the number of spawners by fishing will not affect recruitment. Such danger to abalone stocks has been more recently assessed by egg-per-recruit analyses, whereby various harvest strategies are examined relative to reference points for egg production. These studies are reviewed and assessed relative to the often conflicting aims of managers and scientists. This review of studies of recruitment variation in abalone emphasizes the need for a more rigorous, autecological approach to stock assessment in which field experiments are conducted over realistic spatial and temporal scales, permitting robust testing of hypotheses.

An Assessment of the Stocks of the Banana Prawn Penaeus merguiensis in the Gulf of Carpentaria

1979 ◽  
Vol 30 (5) ◽  
pp. 639 ◽  
Author(s):  
C Lucas ◽  
G Kirkwood ◽  
I Somers
Keyword(s):  
Carapace Length ◽  
Growth Parameters ◽  
Stock Assessment ◽  
Total Mortality ◽  
Mortality Data ◽  
Optimal Size ◽  
Natural Mortality ◽  
Commercial Fishery ◽  
Significant Movement ◽  
Yield Per Recruit

A stock assessment of P. merguiensis in the Gulf of Carpentaria was made by means of a yield per recruit analysis based on studies of migration, growth and mortality. Data were collected both from the commercial fishery and tag recapture experiments. No significant movement of tagged prawns out of the fishing grounds occurred during the fishing season. Estimates of the von Bertalanffy growth parameters (L∞ = 38.0 mm carapace length, K = 0.08 week-1) were obtained from the change in monthly size distribution of commercial catches. The natural mortality coefficient (M) was 0.05 week-1 while the total mortality coefficient (Z) estimates for fishing seasons during 1974-1976, ranged from 0.22 week-1 to 0.35 week-1. The corresponding estimates of the optimal size at first capture ranged from 30.6 to 32.6 mm carapace length. Despite the high rates of exploitation (E = 0.78-0.86), there was no evidence to suggest that recruitment had been adversely affected.

Simplified Calculation of Optimum Spawning Stock Size from Ricker's Stock Recruitment Curve

1985 ◽  
Vol 42 (11) ◽  
pp. 1833-1834 ◽  
Author(s):  
Ray Hilborn
Keyword(s):  
Stochastic Variation ◽  
Simple Modification ◽  
Recruitment Curve ◽  
Stock Size ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Simplified Calculation

The optimum spawning stock size for a Ricker stock recruitment curve was shown to be accurately approximated by the equation Ps = Pr(0.5–0.07a) when 0 < a < 3. A simple modification was also shown to incorporate stochastic variation about the stock recruitment curve into calculations of optimum stock size.

scholarly journals Extending process and understanding for the development of complex ecosystem models, with application to the Chatham Rise Atlantis model

2021 ◽  
Author(s):  
◽  
Vidette McGregor
Keyword(s):  
Population Dynamics ◽  
New Zealand ◽  
Species Interactions ◽  
Initial Conditions ◽  
Ecosystem Models ◽  
Recruitment Curve ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Species Groups ◽  
Oceanographic Variables

<p>The Chatham Rise is a highly productive deep-sea ecosystem that supports numerous substantial commercial fisheries, and is therefore a likely candidate for an ecosystem based approach to fisheries management in New Zealand. This thesis describes model construction, calibration and validation, for the first end-to-end ecosystem model of the Chatham Rise, New Zealand. The work extends beyond what has previously been done for validating such models, and explores uncertainty analyses through bootstrapping the oceanographic variables, perturbing the model's initial conditions, and analysing species interaction effects, with the results further analysed with respect to known data gaps. This enables the inclusion of uncertainty in simulated scenarios using the Chatham Rise Atlantis model, thus providing an envelope of results with which to analyse and understand the likely responses of the Chatham Rise ecosystem. The model was designed with 24 dynamic polygons, 5 water column depth bins, 55 species functional groups, and used 12-hour timesteps. The transfer of energy was tracked throughout the system using nitrogen as the model's main currency. The model simulated the system from 1900–2015, preceded by a 35 year burn-in period. The model produced very similar biomass trajectories in response to historical fishing to corresponding fisheries stock assessment models for key fisheries species. Population dynamics and system interactions were considered realistic with respect to growth rates, mortality rates, diets and species group interactions. The model was found to be generally stable under perturbations to the initial conditions, with lower trophic level species groups having the most variability. The specification of the Spawning Stock Recruitment curve was explored, as it relates to the multi-species and ecosystem models within which it is now applied. Close attention needs to be given to population dynamics specific to multi-species interactions such as predation-release, in particular the Spawning Stock Recruitment curve. Potentially misleading dynamics under predation-release were identified, and the simple solution of applying a cap to recruitment when biomass exceeds virgin levels was explored. The population dynamics of myctophids under fishing induced predation release were analysed with and without limiting recruitment to virgin levels. The effects were evident in several ecosystem indicators, suggesting unintentional mis-specification could lead to erroneous model results. It raises several questions around the specification of the Spawning Stock Recruitment relationship for multispecies models, and more generally, whether the concept of ‘virgin’ (or ‘unfished’) biomass should be reconsidered to reflect dynamic natural mortality and potentially changing unfished states. The model components that had knowledge gaps and were found to most likely to influence model results were the initial conditions, oceanographic variables, and the aggregate species groups ‘seabird’ and ‘cetacean other’. It is recommended that applications of the model, such as forecasting biomasses under various fishing regimes, should include alternatives that vary these components, and present appropriate levels of uncertainty in results. Initial conditions should be perturbed, with greater variability applied to species groups modelled as biomass-pools, and age-structured species groups that have little data available from the literature.</p>

Extending process and understanding for the development of complex ecosystem models, with application to the Chatham Rise Atlantis model

2021 ◽  
Author(s):  
◽  
Vidette McGregor
Keyword(s):  
Population Dynamics ◽  
New Zealand ◽  
Species Interactions ◽  
Initial Conditions ◽  
Ecosystem Models ◽  
Recruitment Curve ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Species Groups ◽  
Oceanographic Variables

<p>The Chatham Rise is a highly productive deep-sea ecosystem that supports numerous substantial commercial fisheries, and is therefore a likely candidate for an ecosystem based approach to fisheries management in New Zealand. This thesis describes model construction, calibration and validation, for the first end-to-end ecosystem model of the Chatham Rise, New Zealand. The work extends beyond what has previously been done for validating such models, and explores uncertainty analyses through bootstrapping the oceanographic variables, perturbing the model's initial conditions, and analysing species interaction effects, with the results further analysed with respect to known data gaps. This enables the inclusion of uncertainty in simulated scenarios using the Chatham Rise Atlantis model, thus providing an envelope of results with which to analyse and understand the likely responses of the Chatham Rise ecosystem. The model was designed with 24 dynamic polygons, 5 water column depth bins, 55 species functional groups, and used 12-hour timesteps. The transfer of energy was tracked throughout the system using nitrogen as the model's main currency. The model simulated the system from 1900–2015, preceded by a 35 year burn-in period. The model produced very similar biomass trajectories in response to historical fishing to corresponding fisheries stock assessment models for key fisheries species. Population dynamics and system interactions were considered realistic with respect to growth rates, mortality rates, diets and species group interactions. The model was found to be generally stable under perturbations to the initial conditions, with lower trophic level species groups having the most variability. The specification of the Spawning Stock Recruitment curve was explored, as it relates to the multi-species and ecosystem models within which it is now applied. Close attention needs to be given to population dynamics specific to multi-species interactions such as predation-release, in particular the Spawning Stock Recruitment curve. Potentially misleading dynamics under predation-release were identified, and the simple solution of applying a cap to recruitment when biomass exceeds virgin levels was explored. The population dynamics of myctophids under fishing induced predation release were analysed with and without limiting recruitment to virgin levels. The effects were evident in several ecosystem indicators, suggesting unintentional mis-specification could lead to erroneous model results. It raises several questions around the specification of the Spawning Stock Recruitment relationship for multispecies models, and more generally, whether the concept of ‘virgin’ (or ‘unfished’) biomass should be reconsidered to reflect dynamic natural mortality and potentially changing unfished states. The model components that had knowledge gaps and were found to most likely to influence model results were the initial conditions, oceanographic variables, and the aggregate species groups ‘seabird’ and ‘cetacean other’. It is recommended that applications of the model, such as forecasting biomasses under various fishing regimes, should include alternatives that vary these components, and present appropriate levels of uncertainty in results. Initial conditions should be perturbed, with greater variability applied to species groups modelled as biomass-pools, and age-structured species groups that have little data available from the literature.</p>

scholarly journals Biased stock assessment when using multiple, hardly overlapping, tuning series if fishing trends vary spatially

2009 ◽  
Vol 66 (10) ◽  
pp. 2272-2277 ◽  
Author(s):  
Sarah B. M. Kraak ◽  
Niels Daan ◽  
Martin A. Pastoors
Keyword(s):  
Stock Assessment ◽  
Fishing Effort ◽  
Assessment Procedure ◽  
Moderate Degree ◽  
Fishing Mortality ◽  
Stock Biomass ◽  
Spatial Coverage ◽  
Spawning Stock ◽  
Age Model ◽  
Biased Perception

Abstract Kraak, S. B. M., Daan, N., and Pastoors, M. A. 2009. Biased stock assessment when using multiple, hardly overlapping, tuning series if fishing trends vary spatially. – ICES Journal of Marine Science, 66: 2272–2277. Fishing-effort distributions are subject to change, for autonomous reasons and in response to management regulations. Ignoring such changes in a stock-assessment procedure may lead to a biased perception. We simulated a stock distributed over two regions with inter-regional migration and different trends in exploitation and tested the performance of extended survivors analysis (XSA) and a statistical catch-at-age model in terms of bias, when spatially restricted tuning series were applied. If we used a single tuning index that covered only the more heavily fished region, estimates of fishing mortality and spawning-stock biomass were seriously biased. If two tuning series each exclusively covering one region were used (without overlap but together covering the whole area), estimates were also biased. Surprisingly, a moderate degree of overlap of spatial coverage of the two tuning indices was sufficient to reduce bias of the XSA assessment substantially. However, performance was best when one tuning series covered the entire stock area.

Stock assessment and management of cephalopods: advances and challenges for short-lived fishery resources

2020 ◽  
Author(s):  
Alexander I Arkhipkin ◽  
Lisa C Hendrickson ◽  
Ignacio Payá ◽  
Graham J Pierce ◽  
Ruben H Roa-Ureta ◽  
...  
Keyword(s):  
Alternative Assessment ◽  
Stock Assessment ◽  
High Volume ◽  
Fishing Effort ◽  
Age Validation ◽  
Stock Biomass ◽  
Assessment Approach ◽  
Complex Population ◽  
Population Structures ◽  
Stock Recruitment

Abstract Cephalopods have become an important global food source, but their sustainable management is challenged by unique life history characteristics associated with short lifespans and semelparous reproduction, high natural mortality rates, rapid and often nonasymptotic growth, and complex population structures. Weak stock-recruitment relationships together with the time-consuming work required for age validation and high-volume annual age determinations make traditional age-based modelling impractical. We propose that the best method for cephalopod assessment involves innovative depletion models, fitted with in-season data on catch numbers and fishing effort, to produce realistic estimates of stock biomass. A “fast lane” assessment approach is suggested that includes high-frequency data collection for separate, in-season stock assessments of each cohort to ensure sustainable exploitation of these short-lived resources. However, most cephalopod fisheries are data-poor and/or lack the infrastructure and resources needed to apply depletion methods; therefore, we also present alternative assessment methods that have been recently applied worldwide. We also offer suggestions for further research on the remaining challenges of cephalopod stock assessment and management.

Stock-recruitment relationships of the tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in the Australian northern prawn fishery

1996 ◽  
Vol 47 (1) ◽  
pp. 87 ◽  
Author(s):  
YG Wang ◽  
D Die
Keyword(s):  
Population Model ◽  
Fishing Effort ◽  
Maximum Sustainable Yield ◽  
Production Model ◽  
Commercial Catch ◽  
Penaeus Semisulcatus ◽  
Spawning Stock ◽  
Tiger Prawn ◽  
Stock Recruitment ◽  
Northern Prawn Fishery

This paper investigates the stock-recruitment and equilibrium yield dynamics for the two species of tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in Australia's most productive prawn fishery: the Northern Prawn Fishery. Commercial trawl logbooks for 1970-93 and research surveys are used to develop population models for these prawns. A population model that incorporates continuous recruitment is developed. Annual spawning stock and recruitment indices are then estimated from the population model. Spawning stock indices represent the abundance of female prawns that are likely to spawn; recruitment indices represent the abundance of all prawns less than a certain size. The relationships between spawning stock and subsequent recruitment (SRR), between recruitment and subsequent spawning stock (RSR), and between recruitment and commercial catch were estimated through maximum-likelihood models that incorporated autoregressive terms. Yield as a function of fishing effort was estimated by constraining to equilibrium the SRR and RSR. The resulting production model was then used to determine maximum sustainable yield (MSY) and its corresponding fishing effort (fMSY). Long-term yield estimates for the two tiger prawn species range between 3700 and 5300 t. The fishing effort at present is close to the level that should produce MSY for both species of tiger prawns. However, current landings, recruitment and spawning stock are below the equilibrium values predicted by the models. This may be because of uncertainty in the spawning stock-recruitment relationships, a change in carrying capacity, biased estimates of fishing effort, unreliable catch statistics, or simplistic assumptions about stock structure. Although our predictions of tiger prawn yields are uncertain, management will soon have to consider new measures to counteract the effects of future increases in fishing effort.

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