Observations on the spatio-temporal patterns of the fuegian sprat Sprattus fuegensis in the Beagle Channel

MARIANO J. DIEZ; ARIEL G. CABREIRA; ADRIAN MADIROLAS; GUSTAVO A. LOVRICH

Rio de Janeiro

Simposio; Rio Acoustics 2017; 2017

OES

Fuegian sprat Sprattus fuegensisis the clupeiform fish distributed further south and the only sprattusinhabiting South Western Atlantic Ocean (SWAO). The distribution area coversthe sub-Antarctic waters of the SWAO, including the fuegian archipelago and theBeagle Channel.  This species is the mostabundant pelagic resource in the region and until today it is not exploitedcommercially. Many aspects of this ecosystem are still under-studied. The firstscientific observations about the acoustics recordings of this species weredocumented by INIDEP (Instituto Nacional de Investigación y DesarrolloPesquero) during 1995-1996. Since 2012, several seasonal acoustic studies werecarried out at a more local scale, covering different zones of the Beaglechannel by means small vessels operated by the Centro Austral deInvestigaciones Científicas (CADIC-CONICET). During those cruises a SIMRADES-70 portable echosounder operating a Combi-D 38/200 kHz was used.  Sprat aggregations were identified by visualappraisement of the echograms, evaluating patterns in the school morphometryand in the frequency response of the volume backscattering strength. Morerecently, concurrent underwater video images were taken to validate the acousticinterpretation of the echo-recordings. In this work, we compiled acousticobservations realized over a period of 5 years which allowed us to prove thatsprat is a year resident resource of the internal area of the channel.Different schooling patterns were recorded during day time, typicallyrepresented by small mid water pelagic schools. However, other uncommonschooling pattern is reported here for the first time. This is characterized bylarge and dense schools that located deeper (>130 m depth) and very near thebottom. Both, size and fish density within these schools were also notablyhigh.