Distribution and spatial structure of pelagic fish schools in relation to the nature of the seabed in the Sicily Straits (Central Mediterranean)

Hydroacoustic data collected during two echosurveys carried out in the Sicily Channel in 1998 and 2002 were analysed to investigate the distribution and spatial structure of small pelagic fish species in relation to the sedimentological nature of the sea bottom. The study was carried out on two contiguous areas (labelled ZONE 1 and ZONE 2) of the continental shelf off the southern coast of Sicily, characterised by different dominant texture, ‘sand’ for ZONE 1 and ‘clayey-silt’ for ZONE 2. Simultaneous information on small pelagic fish schools and the seabed was obtained using a quantitative echo-sounder (SIMRAD EK500) that measures echoes due to the scattering from both fish schools and the bottom surface. Acoustically determined fish school and seabed data were integrated, respectively, with information on species composition obtained by experimental fishing hauls, and with granulometric information obtained from the analysis of in situ sediment samples. The results indicate a general preference of small pelagic fish schools for seabeds of finer granulometry. First, the occurrence of fish schools was higher over the acoustically classified ‘soft’ seabeds of ZONE 2. Secondly, although ZONE 2 represents 60%) was concentrated over ‘soft’ seabed substrates of ZONE 2. Different species composition and/or behaviour of fish schools in the two areas investigated were postulated in relation to seabed conditions. Specifically, over the hard and soft bottoms of ZONE 2, fish schools were found at lower depths and at shallower bottom depths compared to ZONE 1. Furthermore, over the softer bottoms of ZONE 2, fish schools exhibiting a more ‘pelagic’ behaviour (i.e. detected at a greater distance from the bottom) showed a preference for softer (and finer) seabed substrate conditions. Conversely, fish schools exhibiting a more ‘demersal’ behaviour (i.e. at a smaller distance from the bottom) were mostly found on relatively harder substrates.

[1]  Jacques Masse,et al.  The structure and spatial distribution of pelagic fish schools in multispecies clusters: an acoustic study , 1996 .

[2]  Francis P. Shepard,et al.  Nomenclature Based on Sand-silt-clay Ratios , 1954 .

[3]  Pierre Fréon,et al.  Dynamics of pelagic fish distribution and behaviour : effects on fisheries and stock assessment , 1999 .

[4]  T. Bahri,et al.  Spatial structure of coastal pelagic schools descriptors in the Mediterranean Sea , 2000 .

[5]  Ole Arve Misund,et al.  Dynamics of moving masses: variability in packing density, shape, and size among herring, sprat, and saithe schools , 1993 .

[6]  J. Blaxter,et al.  The Biology of the Clupeoid Fishes , 1982 .

[7]  George W. Boehlert,et al.  Dynamics of temperature and chlorophyll structures above a seamount: an oceanic experiment , 1985 .

[8]  C. Maravelias.  Habitat selection and clustering of a pelagic fish : effects of topography and bathymetry on species dynamics , 1999 .

[9]  S. Kim Juniper,et al.  Relationship between phytoplankton production and the physical structure of the water column near Cobb Seamount, northeast Pacific , 1995 .

[10]  G. Swartzman,et al.  Relating spatial distributions of acoustically determined patches of fish and plankton: data viewing, image analysis, and spatial proximity , 1999 .

[11]  Paul G. Fernandes,et al.  Diel variation in the vertical distribution and schooling behaviour of sardine (Sardina pilchardus) off Portugal , 2007 .

[12]  G. Swartzman,et al.  Seabed substrate, water depth and zooplankton as determinants of the prespawning spatial aggregation of North Atlantic herring , 2000 .

[13]  J. Blaxter,et al.  Herring (Clupea harengus) filter-feeding in the dark , 1986 .

[14]  Henry M. Manik,et al.  Quantifying Sea Bottom Surface Backscattering Strength and Identifying Bottom Fish Habitat by Quantitative Echo Sounder , 2006 .

[15]  E. Hamilton,et al.  Sound velocity and related properties of marine sediments , 1982 .

[16]  W. R. Runyan,et al.  Acoustical Properties of Water-Filled Sands , 1963 .

[17]  Kazuo Amakasu,et al.  Measurement of sea bottom surface backscattering strength by quantitative echo sounder , 2006, Fisheries Science.

[18]  M. Giannoulaki,et al.  Ambient luminance and vertical migration of the sardine Sardina pilchardus , 1999 .

[19]  Howard Freeland,et al.  A strong biological response to oceanic flow past Cobb Seamount , 1992 .

[20]  K. Furuya,et al.  Well-developed subsurface chlorophyll maximum near Komahashi No. 2 Seamount in the summer of 1991 , 1998 .

[21]  Linda G. Shapiro,et al.  Computer and Robot Vision , 1991 .

[22]  M. Iglesias,et al.  The characterization of sardine (Sardina pilchardus Walbaum) schools off the Spanish-Atlantic coast , 2003 .

[23]  J. Blaxter,et al.  The Behaviour and Physiology of Herring and Other Clupeids , 1963 .

[24]  Seiji Ohshimo,et al.  Acoustic Estimation of Biomass and School Character of Anchovy Engraulis japonicus in the East China Sea and the Yellow Sea , 1996 .

[25]  Marc Soria,et al.  Effect of external factors (environment and survey vessel) on fish school characteristics observed by echosounder and multibeam sonar in the Mediterranean Sea , 2003 .

[26]  M. Cardinale,et al.  Diel spatial distribution and feeding activity of herring ( Clupea harengus) and sprat (Sprattus sprattus) in the Baltic Sea , 2003 .

[27]  S. Andréfouët,et al.  Enhanced seamount location database for the western and central Pacific Ocean : Screening and cross-checking of 20 existing datasets , 2008 .

[28]  W. Stuetzle,et al.  MODELING THE DISTRIBUTION OF FISH SCHOOLS IN THE BERING SEA: MORPHOLOGICAL SCHOOL IDENTIFICATION , 1994 .

[29]  Constantin Koutsikopoulos,et al.  The effect of coastal topography on the spatial structure of anchovy and sardine , 2006 .

[30]  Jacques Masse,et al.  Acoustic detection of the spatial and temporal distribution of fish shoals in the Bay of Biscay , 1993 .