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Open Access research with a European policy impact...

The Strathprints institutional repository is a digital archive of University of Strathclyde's Open Access research outputs. Strathprints provides access to thousands of Open Access research papers by Strathclyde researchers, including by researchers from the European Policies Research Centre (EPRC).

EPRC is a leading institute in Europe for comparative research on public policy, with a particular focus on regional development policies. Spanning 30 European countries, EPRC research programmes have a strong emphasis on applied research and knowledge exchange, including the provision of policy advice to EU institutions and national and sub-national government authorities throughout Europe.

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Estimating natural interstage egg mortality of Atlantic mackerel (Scomber scombrus) and horse mackerel (Trachurus trachurus) in the Northeast Atlantic using a stochastic model

Portilla, E. and McKenzie, E. and Beare, D. and Reid, D.G. (2007) Estimating natural interstage egg mortality of Atlantic mackerel (Scomber scombrus) and horse mackerel (Trachurus trachurus) in the Northeast Atlantic using a stochastic model. Canadian Journal of Fisheries and Aquatic Sciences, 64 (12). pp. 1656-1668. ISSN 1205-7533

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Abstract

Egg mortality is a key parameter for understanding early life histories of fish. Small variations in estimated mortality cause large differences on adult fish biomass estimates. Therefore, the assumption of a constant egg mortality rate may be misleading. Here, we show how to estimate mortality rates for the individual egg stages of Atlantic mackerel (Scomber scombrus) and horse mackerel (Trachurus trachurus) from triennial surveys conducted since 1977. We use a standard, continuous-time Markov process model that combines the numbers of eggs sampled in each stage with experimental data on egg stage duration (dependent on water temperature). This is the first attempt to study mortality among egg stages in such detail and the first comprehensive effort to estimate horse mackerel egg mortality in the Northeast Atlantic. The results include detailed descriptions of spatial-temporal dependencies in mortality. The daily egg mortality rates estimated are ˜0.56·day[sup-1] for Atlantic mackerel (far higher than suggested in the literature) and 0.54-day[sup-1] for horse mackerel. Although it was not possible to estimate stage 1 egg mortality directly, the results suggest high mortality in the first stage. This might lead to underestimation of fish biomass when assessed traditionally by egg survey data alone.