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Mortality rates of 0-group plaice (Platessa platessa L.), dab (Limanda limanda L.) and turbot (Scophthalmus maximus L.) in European waters: III. Density-dependence of mortality rates of 0-group plaice and some demographic implications
Beverton, R.J.H.; Iles, T.C. (1992). Mortality rates of 0-group plaice (Platessa platessa L.), dab (Limanda limanda L.) and turbot (Scophthalmus maximus L.) in European waters: III. Density-dependence of mortality rates of 0-group plaice and some demographic implications. Neth. J. Sea Res. 29(1-3): 61-79
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Beverton, R.J.H.
  • Iles, T.C.

Abstract
    This last of our three linked contributions on the dynamics of North Sea plaice is concerned with the detection and measurement from demographic data of the density-dependence of mortality rate during the early demersal phase of the life history. A mathematical expression is developed for the survival trajectory of a cohort subject to an instantaneous relative mortality rate which is a linear function of the logarithm of its density. This is used to analyse three independent data sets; a. pairs of densities at or soon after settlement in the Wadden Sea, b. estimates of seasonal mortality rates and initial density of 0-group plaice cohorts derived by linear regression and c. autumn estimates 0- and 1-group fish from the ICES Young Fish Surveys. After correcting for various sources of bias, these each gave statistically significant estimates of the density-dependent mortality coefficient µ2 of 0.015, 0.0044 and 0.0010 per day, respectively. The same theoretical treatment of density-dependent mortality is used to develop an equation predicting the progressive 'damping' of the extremes of inter-year-class variation with age. The above three estimates of the density-dependent mortality coefficient µ2 applied in sequence provide more than sufficient 'damping' to explain the very low variability of recruitment and long-term stability which is characteristic of the North Sea plaice stock.

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