Hake catchability by the French trawler fleet in the Bay of Biscay: estimating technical and biological components

Mahévas, Stéphanie; Trenkel, Verena M.; Doray, Mathieu; Peyronnet, A.

doi:10.1093/icesjms/fsq140

Cited by 8 publications

(3 citation statements)

References 27 publications

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“…To disentangle these two effects, real-time observations on the species population are required; unfortunately these were not available for this study. Promising results from a recent study combining the use of acoustic and cpue data from a small fleet operating in a limited spatial area during a short period (Doray et al, 2010;Mahévas et al, 2010) have provided insight into our greater understanding into the magnitude of the two effects (that is the technological-human component and the biological component). Table 1. Fleet characteristics and average summary information from this study.…”

Section: Discussionmentioning

confidence: 99%

An investigation of human vs. technology-induced variation in catchability for a selection of European fishing fleets

Mahévas

Vermard

Hutton

et al. 2011

ICES Journal of Marine Science

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Mahévas, S., Vermard, Y., Hutton, T., Iriondo, A., Jadaud, A., Maravelias, C. D., Punzón, A., Sacchi, J., Tidd, A., Tsitsika, E., Marchal, P., Goascoz, N., Mortreux, S., and Roos, D. 2011. An investigation of human vs. technology-induced variation in catchability for a selection of European fishing fleets. – ICES Journal of Marine Science, 68: 2252–2263. The impact of the fishing effort exerted by a vessel on a population depends on catchability, which depends on population accessibility and fishing power. The work investigated whether the variation in fishing power could be the result of the technical characteristics of a vessel and/or its gear or whether it is a reflection of inter-vessel differences not accounted for by the technical attributes. These inter-vessel differences could be indicative of a skipper/crew experience effect. To improve understanding of the relationships, landings per unit effort (lpue) from logbooks and technical information on vessels and gears (collected during interviews) were used to identify variables that explained variations in fishing power. The analysis was undertaken by applying a combination of generalized additive models and generalized linear models to data from several European fleets. The study highlights the fact that taking into account information that is not routinely collected, e.g. length of headline, weight of otter boards, or type of groundrope, will significantly improve the modelled relationships between lpue and the variables that measure relative fishing power. The magnitude of the skipper/crew experience effect was weaker than the technical effect of the vessel and/or its gear.

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Section: Discussionmentioning

confidence: 99%

An investigation of human vs. technology-induced variation in catchability for a selection of European fishing fleets

Mahévas

Vermard

Hutton

et al. 2011

ICES Journal of Marine Science

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“…This means that escapement capabilities and aggregation behaviour of juvenile hakes around 20 cm are not the same as those of larger individuals of the same age class, i.e. close to 30 cm (Mahévas et al 2011): this decrease in catchability with size could partially affect the juvenile stage. In addition, the lack of information of cohorts (intra-annual recruitment events) recruiting to the nursery grounds after the survey (late summer or autumn) could also affect survival estimates.…”

Section: Discussionmentioning

confidence: 99%

Size-dependent survival of European hake juveniles in the Mediterranean Sea

et al. 2020

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Most studies on European hake focus on the recruitment process and nursery areas, whereas the information is comparatively limited on the ecology of the juvenile stage (ca. second year of life)—the one most exploited by the Mediterranean trawl fisheries. Using information of the MEDITS programme, we provide a spatial and temporal assessment of the influence of body size and growth on hake survival from recruits (age 0) to juveniles (age 1), along with the impact of surface temperature and chlorophyll variability. At a biogeographic scale, size-dependent survival is supported, with areas with higher mean length of recruits and juveniles yielding higher survival. A similar pattern was observed at interannual level in some western Mediterranean areas, also mediated by a density-dependent effect on growth. However, the most recurrent inter-annual pattern was a negative effect of size on survival, which could be attributed to potential ontogenetic changes in catchability and underrepresentation of intra-annual recruitment pulses that are seasonally inaccessible to the MEDITS survey. Results also evidence that survival in the Alboran and Adriatic seas is dependent on the primary production variability, and that Corsica and Sardinia could be potential feeding grounds receiving juveniles from neighbouring areas. The present study reveals the importance of size- and growth-dependent survival in the juvenile stage of European hake in the Mediterranean Sea.

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“…Accessibility in ISIS-Fish is the biological component of catchability and quantifies changes in the probability of a fish to be caught due to the biology or the ecology of the stock (ex. behaviour: burying, schooling)(accessibility and vulnerability sensu Mahevas et al 2011). It is a key parameter of the model as it is one of the parameters which convert effort into fishing mortality.…”

Section: Calibration Of Category (V) Parametersmentioning

confidence: 99%

Selection and validation of a complex fishery model using an uncertainty hierarchy

Lehuta¹,

Petitgas²,

Mahévas³

et al. 2013

Fisheries Research

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Assessing the validity of a model is essential for its credibility especially when the model is used as decision making tool. Complex dynamic fishery models are recommended to investigate the functioning of fisheries and to assess the impact of management strategies, particularly spatial fishing regulations. However, their use is limited due to the difficulty and computational cost of parameterizing and gaining confidence, particularly for parameter rich models. These difficulties are compounded by uncertainty regarding parameter values, many of which are often taken from literature or estimated indirectly. Here we propose a methodology to improve confidence and understanding in the model, easily transferable to any complex model. The approach combines sensitivity analysis, scalability of parameters, optimization procedures, and model skill assessment in order to parameterize, validate and achieve the most plausible formulation of a model given the available knowledge while reducing the computational load. The methodology relies on five steps: (1) sensitivity analysis, (2) classification of parameters into a hierarchy according to their sensitivity and the nature of their uncertainty, (3) building of alternative formulations, (4) calibration and (5) skill evaluation. The approach is illustrated here by reviewing the parameterization of the ISIS-Fish model of the anchovy fishery in the Bay of Biscay. By using this approach, it is possible to make a thorough assessment of lacking information (e.g. accessibility to fishing and adult mortality) and to identify the strengths and weaknesses of the model in the context of different hypotheses. When applied to the ISIS-Fish model, the results suggest higher egg and adult mortality than formerly estimated, as well as new estimates for the migration towards spawning areas. They show the reliability of the model in terms of correlations with observations and the need for further efforts to model purse seiner catches. The methodology proved to be a cost-efficient tool for objectively assessing applied model validity in cases where parameter values are a mix of literature, expert opinion and calibration. Highlights ► A five-step methodology is proposed to parameterize and validate a complex fishery model. ► It combines scalability of parameters, optimization procedure and model skill assessment. ► It is used to review the ISIS-Fish model of the anchovy fishery in the Bay of Biscay. ► It modifies our understanding of anchovy dynamics and evidences model strengths and weaknesses.

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Hake catchability by the French trawler fleet in the Bay of Biscay: estimating technical and biological components

Cited by 8 publications

References 27 publications

An investigation of human vs. technology-induced variation in catchability for a selection of European fishing fleets

An investigation of human vs. technology-induced variation in catchability for a selection of European fishing fleets

Size-dependent survival of European hake juveniles in the Mediterranean Sea

Selection and validation of a complex fishery model using an uncertainty hierarchy

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