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  • 1
    ISSN: 1573-5117
    Keywords: fish ; assemblage ; artificial reefs ; substrate ; colonization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Migjorn artificial reef (MAR) was deployed in the summer of 1990 and is made by 48 concrete blocks set 30 m deep on a sea bed of sand with a small proportion of Posidonia oceanica (L.) Delile meadow. Visual censuses of blocks on both substrata were carried out during the months of February, May and September in 1992 and 1993. The MAR fish assemblages were influenced by the surronding substrate. Thus, a group of ubiquitous species, frequent on both substrata and typical of natural rocky habitats (mostly Sparidae) and a group associated with the samples recorded on the Posidonia meadow (mostly Labridae) could be distinguished. Season had only a secondary and slight effect on fish assemblages. The MAR was colonized by 74% of the species in the first two years after deployment. Positive and lineal relationships between species richness, diversity, abundance of necto-benthic species and time since deployment on sandy substrata were found. On Posidonia oceanica deployment time has only increased very sedentary and cryptic species. Although some ways in which the MAR would have a productive function are not rejected, the most obvious MAR working pattern is that of fish aggregation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5117
    Keywords: fish ; assemblage ; artificial reefs ; substrate ; colonization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Migjorn artificial reef (MAR) was deployed in the summer of 1990 and is made by 48 concrete blocks set 30 m deep on a sea bed of sand with a small proportion of Posidonia oceanica (L.) Delile meadow. Visual censuses of blocks on both substrata were carried out during the months of February, May and September in 1992 and 1993. The MAR fish assemblages were influenced by the surronding substrate. Thus, a group of ubiquitous species, frequent on both substrata and typical of natural rocky habitats (mostly Sparidae) and a group associated with the samples recorded on the Posidonia meadow (mostly Labridae) could be distinguished. Season had only a secondary and slight effect on fish assemblages. The MAR was colonized by 74% of the species in the first two years after deployment. Positive and lineal relationships between species richness, diversity, abundance of necto-benthic species and time since deployment on sandy substrata were found. On Posidonia oceanica deployment time has only increased very sedentary and cryptic species. Although some ways in which the MAR would have a productive function are not rejected, the most obvious MAR working pattern is that of fish aggregation.
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  • 3
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The red mullet Mullus surmuletus is one of the main target species of the trawling fishery along the continental shelf off the Island of Majorca. The size distribution of the catches, and the reproduction, age and growth of this species have been studied based on sampling carried out from 1990 to 1992. The length range of the catches was between 10 and 32 cm, with a main distribution between 15 and 20 cm, but this included small specimens (recruits of 10 to 11 cm) from August. In the 〉19 cm length-class, females clearly dominated. Monthly variations in the gonadosomatic index (GSI) and in the percentage of mature specimens showed that males spawn from December to June, whereas the reproductive activity of the females centres around spring. Fifty percent of males and females mature at 15 and 16.8 cm, respectively, corresponding to 1 yr of age. Otolith age-readings indicate that the population exploited in the trawl fishery consists of six age-groups, including a very high proportion of individuals between 0 and 4 yr old. Population growth curves revealed that females grow comparatively slowly over a longer period of time and attain greater asymptotic sizes than males. The growth parameters for the whole population are: asymptotic length, L ∞=31.28 cm; growth coefficient, K=0.211 yr-1; theoretical age when length is zero, t 0=-2.348 yr.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The diet of the dusky grouper Epinephelus marginatus, from the Balearic Islands, western Mediterranean, consisted primarily of crustaceans, molluscs and fishes, but diet composition varied with body size. The smaller dusky groupers (〈300 mm LT) fed primarily on crustaceans, and particularly on brachyurans, which accounted for 46% of the prey identified. As dusky groupers grew, cephalopods became increasingly important and constituted 10 to 40% of the prey identified in subadult and adult specimens. The largest dusky groupers fed primarily on fishes that represented 40·9% of prey identified. These shifts in diet were accompanied by a positive selection of increasingly large prey and by an expansion of trophic niche. δ15N values of dusky grouper white muscle ranged from 8·8 to 13·1% and 71% of the variation in δ15N was explained by differences in dusky grouper size. δ13C values ranged from – 17·9 to – 15·9%, and no significant body size effect on δ13C was detected. Stomach content and 13C values indicated that from 1 year old, the diet of E. marginatus was based on the benthic food web. The enrichment in δ15N registered from juvenile to large males was c. 3·8%. Overall, there was good agreement between gut content and stable isotope data indicating that the latter may be useful as a tool in trophic studies in marine protected areas where sampling for fishes is not allowed.
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