Objectif The proposed research work will improve estimates of the spawning stock biomass of the western mackerel and horse mackerel stocks and provide new information on the characteristics of the spawning stock. Since the spawning areas of the 2 species overlap, the work on the 2 species is being combined in order to achieve a substantial saving in costs. During 1992 a major survey of mackerel and horse mackerel off western Europe was accomplished. Trawlers from 3 countries sampled the stock at peak spawning time. It was discovered that there are significant differences in spawning pattern of mackerel and horse mackerel. Mackerel are asynchronous spawners with spawning throughout the 24 hour cycle whereas horse mackerel show synchrony with a peak of egg production between 15.00 and 20.00 hours local time. Mackerel typically produce 30 batches of eggs spawning every 2 days on average whereas horse mackerel produce about 7 batches spawning every 10-15 days approximately. A typical batch in mackerel is 50 eggs per gram female body weight compared with over 200 per gram for horse mackerel. These differences affect the application of egg production methods for estimation of spawning stock biomass. In mackerel there seems to have been a decline in batch fecundity in the centre of the main spawning area since 1989. Batch fecundity tends to be higher in the centre of the spawning area so the apparent change in batch fecundity over the years could reflect a change in location of the spawning area. An unexpected finding in 1992 was spawning further west in deeper water than ever previously recorded. Spawning fish of both species were found near the surface in water 3200 m deep west of Ireland. Spawning was previously thought to be confined to the continental shelf and shelf edge areas. This project has achieved a comprehensive reappraisal of reproductive biology and distribution of mackerel and horse mackerel in the European sector of the northeast Atlantic. The change in spawning distribution has precluded the immediate the recommendation of the new daily egg production method (DEPM) for use in future estimates of spawning stock biomass.Mackerel, Scomber scombrus, and horse mackerel, Trachurus trachurus of the wide ranging western stocks account for a total annual catch of 500 000 tonnes and 100 000 tonnes respectively. In mackerel, the average catch has consistently exceeded the total allowable catch (TAC) and the spawning stock biomass has declined from an estimated 3.6E6 tonnes in 1975 to less than 2E6 tonnes in 1988. Recently the biomass has stabilised but there is concern that spawning has become dependent on younger age classes. In horse mackerel only approximate estimates of spawning stock biomass are available. Improved absolute precision of spawning stock biomass measurement is necessary together with detailed knowledge of population age structure and spawning characteristics in order to define appropriate TACs. The spawning area of mackerel and horse mackerel is so large that, even with the combined resources of all the EC countries concerned, a biomass estimate is only conducted once every 3 years. The biomass in intervening years is interpolated by virtual population analysis. Recent studies by the partners in this proposal have shown that it is possible to measure the spawning stock biomass using a new batch fecundity egg production method. This method is cheaper and potentially more accurate than the existing total fecundity method and it may be possible to measure spawning stock biomass more frequently than once every 3 years. Further important information on spawning biology of these fish must be obtained before the new method can be applied with full potential precision. Data on batch fecundity is required for more than the one year so far available. Data on spatial variation in batch fecundity is necessary. Data on duration of oocyte maturation stages and postovulatory follicles is necessary. Currently ad hoc approximations are used to estimate daily spawning fraction. Finally, information on diel patterns of spawning is necessary. This data will be obtained by trawl sampling of fish in the spawning season. Detailed information of the fish population structure, spawning characteristics and variation throughout the spawning area will be compared with a comprehensive survey of 1989. Oocyte stage durations will be determined in laboratory spawning experiments on captive fish. Champ scientifique agricultural sciencesagricultural biotechnologybiomassnatural sciencesbiological sciencesreproductive biology Programme(s) FP2-FAR - Community research and coordination programmes (EEC) in the fisheries sector, 1988-1992 Thème(s) Data not available Appel à propositions Data not available Régime de financement Data not available Coordinateur University of Aberdeen Contribution de l’UE Aucune donnée Adresse 2 Tillydrone Avenue AB9 2TN Aberdeen Royaume-Uni Voir sur la carte Coût total Aucune donnée Participants (5) Trier par ordre alphabétique Trier par contribution de l’UE Tout développer Tout réduire AZTI-SIO Espagne Contribution de l’UE Aucune donnée Adresse Donostia-San Sebastian Voir sur la carte Coût total Aucune donnée FISHERIES RESEARCH CENTRE-ABBOTSTOWN Irlande Contribution de l’UE Aucune donnée Adresse Dublin 15 Voir sur la carte Coût total Aucune donnée Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER) France Contribution de l’UE Aucune donnée Adresse Station de Nantes Rue de l'Ile d'Yeu 44037 Nantes Voir sur la carte Coût total Aucune donnée RIVO-RIJKSINSTITUUT VOOR VISSERIJONDERZOEK Pays-Bas Contribution de l’UE Aucune donnée Adresse Ijmuiden Voir sur la carte Coût total Aucune donnée Scottish Office Agriculture, Environment and Fisheries Department Royaume-Uni Contribution de l’UE Aucune donnée Adresse Victoria Road AB11 9DB Aberdeen Voir sur la carte Coût total Aucune donnée
