Age-dependent habitat identification of Mediterranean swordfish: application on commercial fishery data and potential use in fisheries management

Based on fisheries data from the 90's and 00's in the eastern Mediterranean Sea, we applied generalized additive models to investigate the relative influence of environmental factors on swordfish catch rates. We separately modeled: (1) young-of-the-year swordfish and (2) the remaining 'adult' swordfish. Results suggested that the two sub-populations differentiated significantly: adults were more abundant to the south-east (Levantine basin), at the open seas, preferring 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. There were strong indications that the Ionian and Levantine may actually constitute favorable spawning grounds. Based on the models suggested associations, we obtained an indirect identification of the swordfish potential habitats. 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.

DAMALAS Dimitrios;  MEGALOFONOU Persefoni; 

2014-11-03

Taylor & Francis

JRC91261

2330-8249,   

http://www.tandfonline.com/doi/full/10.1080/23308249.2014.951987#.VEZ6r_mSyVM,    https://publications.jrc.ec.europa.eu/repository/handle/JRC91261,   

10.1080/23308249.2014.951987,