Browsing by Issue Date, starting with "1998-06"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- Potential fecundity of twaite shad Alosa fallax fallax (Pisces: Clupeidae) from the upper estuary of the river Mira (SW Portugal): preliminary resultsPublication . Pina, Teresa; Esteves, Eduardo; Coelho, M.L.; Andrade, José Pedro AndradeThe great majority of European anadromous fishes are threatened species (Leleck, 1980). Despite the existing legal protection for migration fishes, these are vulnerable and particulary threatened by antropogenic impact, by physical obstacles for migrating fish and by physical impacts on spawning and nursery areas.
- Relevance of cod (Gadus morhua L.) predation for inter-cohort variability in mortality of juvenile Norwegian spring-spawning herring (Clupea harengus L.)Publication . de Barros, P; Tirasin, EM; Toresen, RMortality of juvenile Norwegian spring-spanning herring growing up in the Barents Sea is characterized by a high inter-cohort variability. Variable predation pressure from the north-east Arctic cod stock has been proposed as an explanation, but it has been difficult to test this hypothesis with actual field data. Data on the abundance of the main fish stocks in the Barents Sea ecosystem. collected by the Institute of Marine Research in Bergen during the period 1983-1993, were analysed to test this hypothesis. Since capelin has been the major prey of cod during the period investigated, the relationship between herring juvenile mortality and the abundance of cod, capelin and herring was investigated,More than 90% of the inter-cohort variation in mortality of juvenile herring observed during this period was explained by a simple model using the ratio of capelin abundance to the abundance of juvenile cod as the explanatory variable, The relationship is strong enough to warrant using the simple model for improving the short-term forecasts of recruitment to the spawning stock of Norwegian spring-spawning herring. (C) 1998 International Council for the Exploration of the Sea.
- Diel variation of fish eggs and larvae in two Portuguese estuaries (rivers Mira and Guadiana)Publication . Esteves, Eduardo; Coelho, M.L.; Pina, Teresa; Andrade, José Pedro AndradeThe importance of estuaries as fish nurseries areas has been well documented. Several studies have indicated that a variety of factors, both abiotic and biotic, influence the distribution of fish species in a estuary (Robinson & Bain, 1989).
- Variable natural mortality rate of juvenile Norwegian spring-spawning herring (Clupea harengus L.) in the Barents SeaPublication . de Barros, P; Toresen, RUnderstanding the patterns of mortality rate in the juvenile stages of exploited fish populations is essential for improving current stock assessment procedures. Most of the research on "the recruitment problem" has focused on the larval stages, but recent work. indicates that a large part of the variability in year-class strength may be associated to variable mortality rates during the juvenile stages. The data on abundance of juvenile Norwegian spring-spawning herring in the Barents Sea collected by the Bergen Institute of Marine Rest-arch between 1983 and 1993 was analysed iv test this hypothesis. The results give strong support to the hypothesis. Survival from the start of the 0-group stage to age 3 years may have varied from 0 to 30% for the cohorts investigated. Mortality rate is shown to be strongly age-dependent. and between 75% and 99% of the total juvenile mortality occurs during the first year of life. (C), 1998 International Council for the Exploration of the Sea.