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  • 1
    Online Resource
    Online Resource
    Redundancy in metrics describing the composition, structure, and functioning of the North Sea demersal fish community
    Oxford University Press (OUP) ; 2012
    In:  ICES Journal of Marine Science Vol. 69, No. 1 ( 2012-01-01), p. 8-22
    Details
    In: ICES Journal of Marine Science, Oxford University Press (OUP), Vol. 69, No. 1 ( 2012-01-01), p. 8-22
    Abstract: Greenstreet, S. P. R., Fraser, H. M., Rogers, S. I., Trenkel, V. M., Simpson, S. D., and Pinnegar, J. K. 2012. Redundancy in metrics describing the composition, structure, and functioning of the North Sea demersal fish community. – ICES Journal of Marine Science, 69: 8–22. Broader ecosystem management objectives for North Sea demersal fish currently focus on restoring community size structure. However, most policy drivers explicitly concentrate on restoring and conserving biodiversity, and it has not yet been established that simply restoring demersal fish size composition will be sufficient to reverse declines in biodiversity and ensure a generally healthy community. If different aspects of community composition, structure, and function vary independently, then to monitor all aspects of community general health will require application of a suite of metrics. This assumes low redundancy among the metrics used in any such suite and implies that addressing biodiversity issues specifically will require explicit management objectives for particular biodiversity metrics. This issue of metric redundancy is addressed, and 15 metrics covering five main attributes of community composition, structure, and function are applied to groundfish survey data. Factor analysis suggested a new interpretation of the metric information and indicated that a minimum suite of seven metrics was necessary to ensure that all changes in the general health of the North Sea demersal fish community were monitored properly. Covariance among size-based and species-diversity metrics was low, implying that restoration of community size structure would not necessarily reverse declines in species diversity.
    Type of Medium: Online Resource
    ISSN: 1095-9289 , 1054-3139
    URL: Article
    DOI: 10.1093/icesjms/fsr188
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2012
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  • 2
    Online Resource
    Online Resource
    A random effects population dynamics model based on proportions-at-age and removal data for estimating total mortality
    Canadian Science Publishing ; 2012
    In:  Canadian Journal of Fisheries and Aquatic Sciences Vol. 69, No. 11 ( 2012-11), p. 1881-1893
    Details
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 69, No. 11 ( 2012-11), p. 1881-1893
    Abstract: Catch curves are widely used to estimate total mortality for exploited marine populations. The usual population dynamics model assumes constant recruitment across years and constant total mortality. We extend this to include annual recruitment and annual total mortality. Recruitment is treated as an uncorrelated random effect, while total mortality is modelled by a random walk. Data requirements are minimal as only proportions-at-age and total catches are needed. We obtain the effective sample size for aggregated proportion-at-age data based on fitting Dirichlet-multinomial distributions to the raw sampling data. Parameter estimation is carried out by approximate likelihood. We use simulations to study parameter estimability and estimation bias of four model versions, including models treating mortality as fixed effects and misspecified models. All model versions were, in general, estimable, though for certain parameter values or replicate runs they were not. Relative estimation bias of final year total mortalities and depletion rates were lower for the proposed random effects model compared with the fixed effects version for total mortality. The model is demonstrated for the case of blue ling (Molva dypterygia) to the west of the British Isles for the period 1988 to 2011.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    URL: Article
    DOI: 10.1139/f2012-103
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 2012
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    SSG: 21,3
    SSG: 12
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  • 3
    Online Resource
    Online Resource
    Capacity management, not stock status or economics, drives fleet dynamics in the Bay of Biscay ecosystem on a decadal time scale
    Canadian Science Publishing ; 2012
    In:  Canadian Journal of Fisheries and Aquatic Sciences Vol. 69, No. 4 ( 2012-04), p. 695-710
    Details
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 69, No. 4 ( 2012-04), p. 695-710
    Abstract: This paper introduces a semiqualitative approach to analyse the joint dynamics of fleets and stocks in a multispecies, multifleet fishery. We ask whether changes in fleets affect resource dynamics and whether trends in resource influence fleet dynamics more than external drivers do. External drivers include vessel buyback, fuel price, and fish prices, as well as environmental fluctuations. Resource status is measured by abundance and length metrics; fleet capacity is measured by total horse power, and economic metrics such as profitability and earnings are examined as well. A maximum likelihood approach is used to identify the combined metric trends with the largest support in the data. The approach is applied to the French Bay of Biscay fisheries in 2000–2007. Combined-metric time trends suggest that decreases in fleet capacity did not result in decreasing fishing impacts; trends in stocks and fish prices were not the major drivers of changes in fleets either. Rather, the vessel buyback program might have been the main factor determining fleet dynamics over that period.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    URL: Article
    DOI: 10.1139/f2012-002
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 2012
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    detail.hit.zdb_id: 1473089-3
    SSG: 21,3
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
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