Association between bluefin tuna schools and oceanic features in the western Mediterranean

Type Article
Date 2004
Language English
Author(s) Royer Francois, Fromentin Jean-Marc, Gaspar P
Affiliation(s) Collecte Localisat Satellites, Div Oceanog Spatiale, F-31526 Ramonville St Agne, France.
IFREMER, Ctr Rech Halieut Mediterraneen & Trop, F-34203 Sete, France.
Source Marine Ecology Progress Series (0171-8630) (Inter-research), 2004 , Vol. 269 , P. 249-263
DOI 10.3354/meps269249
WOS© Times Cited 67
Keyword(s) Thunnus thynnus, Gulf of Lions, point process analysis, front detection, sea surface temperature, ocean colour, aggregation
Abstract We present an analysis of the distribution of bluefin tuna Thunnus thynnus schools spotted during aerial surveys in the Gulf of Lions, in relation to oceanographic features. Bio-optical and thermal properties of the sea surface derived from high-resolution sensors (AVHRR and SeaWiFS) were studied on a daily basis, and an edge-detection technique was applied to detect frontal zones. Geostatistics and point-process analyses were used to evaluate the role of the environment in structuring the spatial pattern of bluefin tuna (BFT). The distribution of schools spotted was strongly non-stationary both in space and time; this is believed to be an effect of the survey design (transect sampling) and the influence of transient oceanographic structures (surface fronts and eddies). The empirical variograms indicated a spatial range of the BFT schools at around 40 km, with substantial daily variability. Ripley's K statistic, as well as autocorrelation plots, revealed that the fish schools were clustered over a wider range of scales (from 10 to 80 km), indicating more spatial structure than would be expected from a random process. Finally, BFT school distributions appeared well determined by the oceanic features, except at very small scales (<10 km), where over-aggregation occurred, and at the largest scales of our study (>40 km), where over-spreading was detected. Dynamical ecological processes, such as foraging, are likely to induce this complex spatial pattern. Possible reasons for the association of tuna with fronts are presented.
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