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| Trenkel, Verena; Cotter, John. |
| Ecosystem assessments of fisheries based only on survey data will often have to use surveys that were designed historically for special purposes, e. g. for assessing abundances of two or three target species, or for tuning VPAs. An important question then is whether the previously collected data can provide informative time series of abundance indices and other state indicators for a wider range of target and non-target species. Some potential shortcomings of existing data series are treated in this paper leading to four questions which can guide the user to determine the suitability of an existing time series: did the survey cover the stock of each species adequately? Did survey catchability vary significantly between length or age classes? Did survey... |
| Tipo: Text |
Palavras-chave: Bias; Survey based methods; Indicators. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6900.pdf |
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| Cotter, John; Mesnil, Benoit; Witthames, Peter; Parker-humphreys, Matt. |
| This paper reviews a selection of nine indicators for assessing the biological state of a fish population monitored only by using trawl surveys in which catchability is assumed constant from time to time and place to place. The intention is to inform or remind of the range of possibilities and of associated practical and statistical issues. The indicators, grouped according to relationships with abundance, length, age, weight, and reproduction, are documented in a standard format covering estimation, interpretability, sensitivity, considerations for reference points where possible, and an example of their application. Lastly, selected indicators together with year-class curves fitted to abundance indices-at-age are applied to the North Sea cod to... |
| Tipo: Text |
Palavras-chave: Ecosystem approach to fisheries management; Year class curves; Weight index; Maturity stage; Age composition; Length based indicators; Biological indicators. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6901.pdf |
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| Cotter, John; Petitgas, Pierre; Abella, Alvaro; Apostolaki, Panayiota; Mesnil, Benoit; Politou, Chrissi-yianna; Rivoirard, Jacques; Rochet, Marie-joelle; Spedicato, Maria Teresa; Trenkel, Verena; Woillez, Mathieu. |
| Ideas and considerations are put forward for managing fisheries and marine populations using primarily trawl surveys to supply biological and spatial indicators of the state of stocks, and to permit catch per unit effort (CPUE)-based assessments. Trawl surveys seldom allow absolute estimates of fish population sizes but, if appropriately located, timed, and designed, can provide a broad range of information about catchable fish species and the ecosystem that supports them. This information may be more conducive to sustainable management of fisheries than the traditional focus on the abundances of selected stocks. The paper first briefly proposes how survey-based methods might supplement existing fishery-dependent stock assessments, as would be necessary... |
| Tipo: Text |
Palavras-chave: Fishing effort indicator; Fisheries independent assessment; Survey based stock assessment; Spatial indicator; State indicator; Trawl survey; Fisheries management. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6691.pdf |
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