The effect of season and sex on trophic levels of marine fishes
The diet of 76 species from Greek waters (north Aegean Sea) was examined for the determination of trophic level by species, season and sex. Trophic level estimates were derived from TrophLab software based on collected stomach content data. Such estimates are important for the implementation of marine management indicators, such as the marine trophic index. The mean ±s.e. difference between minimum and maximum trophic levels among seasons within species was 0·45 ± 0·04 and for 28·8% of the species this difference was larger than the correspondings.e. of the trophic level of the pairs of seasons examined. Depending on which seasonal trophic level (i.e. autumn, winter, spring or summer) was used for assigning a species into a functional trophic group 33·9 and 8·5% of the species changed one and more than one group, respectively. Finally, the mean ±s.e. absolute difference of male and female trophic level was 0·18 ± 0·02, and only for 6·6% of the species this difference was larger than thes.e. of trophic level for each sex separately. Depending on the trophic level used for assigning the species into a functional group (i.e. male v. female), only 6·6 and 3·2% of the species changed one and more than one groups, respectively. It is therefore clear that all measures used in this study indicated that the effect of season on trophic level estimates was higher, compared to that of sex, the latter being of minor importance to feeding studies. Hence, future effort on stomach content analysis should focus on the examination of seasonal, small to moderate sample sizes.
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Document Type: Regular Paper
Affiliations: Aristotle University of Thessaloniki, School of Biology, Department of Zoology, Laboratory of Ichthyology, BOX 134, Thessaloniki, GR-54124, Greece
Publication date: 2008-04-01