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Age-Dependent Habitat Identification of Mediterranean Swordfish: Application on Commercial Fishery Data and Potential Use in Fisheries Management

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Version 2 2014-10-31, 20:05
Version 1 2014-10-02, 00:00
journal contribution
posted on 2014-10-31, 20:05 authored by Dimitrios Damalas, Persefoni Megalofonou

Based on fisheries data from the 1990s and 2000s in the eastern Mediterranean Sea, generalized additive models were applied to investigate the relative influence of environmental factors on swordfish catch rates. (1) Young-of-the-year swordfish and (2) the remaining “adult” swordfish were modeled separately. Results suggested that the two stock components differentiated significantly: adults were more abundant to the south-east (Levantine basin), at the open seas, showing a clear relationship to cooler water masses. In contrast, juveniles were more frequently observed to the north-west (Ionian Sea), close to the coast, in warmer waters. Seasonally, juvenile swordfish were more abundant during the start and end of the fishing period, and during years of elevated water temperature. Lunar disc illumination affected positively all year classes; maximum catches observed around full-moon. The proportion of large swordfish decreased significantly throughout the study period, indicating a change in size-structure of the population or availability to the fishing gear. There were strong indications that the Ionian and Levantine may actually constitute favorable spawning grounds. Based on the models suggested associations, an indirect identification of the swordfish potential habitats was obtained. It was further considered how size-dependent habitat delineation could form the basis for a more realistic management approach, through the introduction of spatio-temporal closures of fishing activities.

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