Observations on the spatio-temporal patterns of the Fuegian Sprat (Sprattus fuegensis) in the Beagle Channel

DIEZ, MARIANO J.; CABREIRA, A.; MADIROLAS, A.; LOVRICH, G.

Rio de Janeiro

Congreso; RIO Acoustics 2017; 2017

Fuegian sprat Sprattus fuegensis is the clupeiform fish distributed further south and the only sprattus inhabiting South Western Atlantic Ocean (SWAO). The distribution area covers the sub-Antarctic waters of the SWAO, including the fuegian archipelago and the Beagle Channel. This species is the most abundant pelagic resource in the region and until today it is not exploited commercially. Many aspects of this ecosystem are still under-studied. The first scientific observations about the acoustics recordings of this species were documented by INIDEP (Instituto Nacional de Investigación y Desarrollo Pesquero) during 1995-1996. Since 2012, several seasonal acoustic studies were carried out at a more local scale, covering different zones of the Beagle channel by means small vessels operated by the Centro Austral de Investigaciones Científicas (CADIC-CONICET). During those cruises a SIMRAD ES-70 portable echosounder operating a Combi-D 38/200 kHz was used. Sprat aggregations were identified by visual appraisement of the echograms, evaluating patterns in the school morphometry and in the frequency response of the volume backscattering strength. More recently, concurrent underwater video images were taken to validate the acoustic interpretation of the echo-recordings. In this work, we compiled acoustic observations realized over a period of 5 years which allowed us to prove that sprat is a year resident resource of the internal area of the channel. Different schooling patterns were recorded during day time, typically represented by small mid water pelagic schools. However, other uncommon schooling pattern is reported here for the first time. This is characterized by large and dense schools that located deeper (>130 m depth) and very near the bottom. Both, size and fish density within these schools were also notably high.