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MEPS 265:243-253 (2003)
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Abstract
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Effect of coastal topography on the spatial structure of the populations of small pelagic fish
M. Giannoulaki1,*, A. Machias1, C. Koutsikopoulos2, J. Haralabous1, S. Somarakis1,2, N. Tsimenides1
1Institute of Marine Biology of Crete, PO Box 2214, 71003 Iraklion, Crete, Greece
2University of Patras, Department of Biology, 26500 Patra, Greece
*Email: marianna@imbc.gr
ABSTRACT: Acoustic data from 6 research surveys (4 in summer and 2 in winter) in the Aegean and Ionian Seas (eastern Mediterranean Sea) were analyzed to examine the effect of coastal topography on the spatial structure of populations of small pelagic fish
using geostatistical techniques (omnidirectional and exhaustive variograms). The effect of topographic characteristics related to depth and the degree of land enclosure on the spatial structure of fish populations (as expressed by several parameters
calculated from omnidirectional and exhaustive variograms) was studied by multiple regression analysis. The estimated autocorrelation range of omnidirectional variograms indicated that fish formed meso-scale to large-scale patches, but it was not
significantly related to any of the area characteristics examined. The nugget effect was negatively correlated with mean bottom depth. Parameters related to anisotropy, calculated from the exhaustive variograms, did not show any consistent pattern related
to the geographical characteristics of the area studied. Geometric descriptors of the exhaustive variograms provided a more detailed picture of the underlying spatial continuity, indicating the effect of the enclosure index (stronger in summer) and the
size of the area (stronger in winter) on the spatial structure of fish populations. The organization of fish into clusters of schools was heterogeneous in closed sub-areas during both seasons and, for a given degree of enclosure, they were more
homogeneous in small-sized sub-areas than in large sub-areas. These results suggest that the environmental spatial heterogeneity mainly affected the way schools were organized into aggregations rather than the maximum size of the area occupied by these
aggregations.
KEY WORDS: Small pelagic fish · Spatial structure · Degree of enclosure · Exhaustive variograms
Full text in pdf format
Published in MEPS Vol.
265
(2003) on December 31
Print ISSN: 0171-8630; Online ISSN: 1616-1599.
Copyright © Inter-Research, Oldendorf/Luhe, 2003
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