Workpackages

Biological information on horse mackerel related to production aspects, will be analysed along its entire area of distribution. Growth and reproduction together with the mortality are the main parameters in population dynamics theory. Distribution and abundance are the resultant in space and time of these dynamic characteristics. The analysis of these factors will allow to identify production units that can be related to stocks in a operational and evolutionary sense.

6.1- Growth
Growth is as a production parameter that characterizes populations rather than species. Consequently we can use it as a tool for identification of production units or stocks (in a operational sense). To achieve this objective a representative sampling for age structure will be carried out in each target area. Specimen otoliths will be removed (Partners 01, 02, 03, 04, 05, 07, 08 and 10) and been sent for subsequent reading (Partner 01). Additional samples can be required by Participant 01 to obtain representative age/length keys from each area (see diagram page ). The von Bertalanffy growth curve will be fitted to the data obtained. To identify diferences in growth parameters (t0, K and L4) among areas, likelihood ratio tests will be applied. We will complete the information with a general revision of the bibliography and of the data already produced by some of us for selected areas, but not analysed yet.

6.2.- Reproduction
Reproduction can be used as Growth, to identify production units. The sampling will be representative from each locality to estimate the maturity ogive by length and by age as well as the fecundity. To achieve this, samples will be taken during the spawning season. The information related to age, weight, length, sex and maturity stage, which are collected by Participants 01, 02, 03, 04, 05, 07,08 and 10 will be sent to Participant 09. Additional samples can be required by Participant 09 to estimate other reproductive aspects, e.g.: fecundity, and gonadosomatic index (see diagram page ). Logistic models will be fitted to estimate maturity ogives. The confidence intervals by each length or age class will be analysed to identify significative differences between areas or sampling localities. The information will be completed with a general bibloiographic revision and retrospective analysis of historic data produced by some of the Partners.

6.3.- Distribution
Every organism lives in a matrix of space and time that can be considered as a unit. Consequently, the distribucion and the abundance are closely related. The determination of the range of distribution and the correlation in the abundance indices among areas could be very useful to identify production units / or stocks. To achieve this knowledge it is necessary to analyse the information from the references and the data available at ICES and FAO. Some data could be requested to ICES taking into account that Partners 01, 02, 03, 08 and 10 are members of ICES and participate actively in the assessment of the horse mackerel. Partner 08 will carry out this analysis exploring the concordance among areas in cohorts strengths and CPUE indices.

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