Study on the acoustic stimulus impact on density of marine organisms aggregation around squid fishing vessel and on jigger catches of squids
Density of aggregations within the surface layer around squid fishing vessel formed by squids and other marine organisms attracted by light was estimated comparatively using an echointegration acoustic complex and jigging both in natural conditions and under action of the pneumatic acoustic system which radiates the sounds imitating the signals of small physostomous fish (japanese anchovy, smelts, sardines) - objects of the japanese common squid feeding. Efficiency of the squid jigging was valued simultaneously. The sound action allowed to intensify the attracting effect of light and to raise search-feeding activity of the squid in zone of action. Besides, distribution and density of marine organisms under and near the vessel was surveyed in passing with the echosounders Simrad EY-60 and ES-60 in mode of vertical (70 kHz) and horizontal (120 kHz) scanning; the density was valued on mean of the back scattering strength both in natural conditions and under the action of the pneumatic acoustic system. The effect of aggregations concentration and the squid catches increasing under the sound action was statistically significant: the density became in 1.1-3.5 times higher, the total echo intensity was 2.56 times higher for the frequency 120 kHz and 1.78 times higher for the frequency 70 kHz, the catch of jiggers increased in 47 % under the acoustic stimulation. The effect was the highest for vertical scanning (frequency 70 kHz) the layer with initially observed echotracks of squid. The squid catches did not depend on acoustic density of the aggregations under and near the vessel but were determined by its feeding behavior; moreover, the density of aggregations and the catches had opposite trends during a night because of daily rhythm of feeding that limited the use of jigging for estimation of the squid aggregations density. Possibilities are considered of the squid echosignals identifications in certain water layers by their target strengths and typical form of echo tracks.