Anchovy Schools Research Articles

The structure and spatial distribution of pelagic fish schools in multispecies clusters: an acoustic study

Two acoustic surveys were carried out in the Bay of Biscay, in 1993 and 1994, to study the distribution and abundance of pelagic stocks. Acoustic data were systematically stored using the INES/MOVIES acquisition and processing system along isobath perpendicular transects, from 25 m to 200 m bottom depth. Species identifications were obtained from midwater trawl catches. From the acoustic data, sections of cruise track in the vicinity of the trawl catches were selected for analysis. Three species, anchovy (Engraulis encrasicolusL.), sprat (Sprattus sprattusL.), and horse mackerel (Trachurussp.) were investigated. The objectives of this study were to analyse the echo traces for estimation of species-specific preferences and to examine the influence of species assemblages on the vertical position and shape of the schools. Using MOVIES-B software, 4789 fish schools were detected and isolated. Characteristics investigated were size (height, vertical cross-sectional area), elongation (length/height), back-scattered energy (density), and vertical distribution (bottom depth, school altitude). Comparative analysis of the vertical distribution of echo traces and catch compositions revealed some species-specific preferences. Horse mackerel were found close to the bottom and anchovy at a mean of 16 m above the bottom. No variation in vertical distribution was detected where sprats were mixed with anchovies. In the presence of horse mackerel in the bottom layer, anchovy appeared to be displaced upwards. A modification of the shape of schools was also detected when sprats were mixed with anchovies. In anchovy-horse mackerel mixtures, a suggested modification of behaviour could explain the observed decrease in the density of anchovy schools.

Acoustic Estimation of Biomass and School Character of Anchovy <i>Engraulis japonicus</i> in the East China Sea and the Yellow Sea

The biomass of anchovy Engraulis japonicus in the East China Sea and the Yellow Sea was estimated by using a quantitative echo sounder (Furuno FQ-70) combined with the analysis of midwater trawling catches. The shape of anchovy schools were calculated from echograms. The acoustic survey, conducted in May and June 1992, was executed along 7 east-west transect lines ranging from latitude 30° 00' to 35° 45' N. Trawling was made at 5 areas. Over the 5 trawling areas, 97.8% of caught fish were anchovy in the daytime, but the percentage of anchovy decreased to 67.4% at night. Anchovy behaviour differed between day and night. In the daytime anchovy compactly shoaled inmidwater or nearbottom layers with the mean packing density of 53.6g/m3. The mean vertical height and the mean horizontal width of anchovy schools in the daytime were 3.3 (±3.4, S. D.)m and 16.3 (±7.7)m, respectively. At night, they were scattered at midwater or surface water layers. The total biomass of anchovy over the survey area was estimated to be 1, 960, 000 tons using TS kg=-31.4 dB/kg (204, 289km2). Some problems inherent with acoustic method for the estimation of the biomass are discussed.

Tidal transport of the bay anchovy, Anchoa mithchilli, in darkness

Transport of the adult bay anchovy, Anchoa mitchilli, in darkness was studied in laboratory and field experiments. In a hydraulic flume, anchovy schooling ceased in darkness and, at a current speed of 30cms−1, 99% of all fish were transported to the end of the flume. In field experiments, fish marked with neutral red dye and released in a creek at flood tide were recaptured 5–1 km upstream 4 h after release at night, and were recaptured within 200m of the release site 3 h after release in daylight. It is concluded that in the neutral environment, bay anchovy schools break up at night and individual fish are transported by currents, whereas in daylight, bay anchovy schools maintain a relatively fixed location. This nocturnal transport phenomena may also exist in other marine and estuarine pelagic fishes, and may help in understanding behaviour and distribution of peiagic estuarine fishes.

定置網漁場における魚群の移動行動

The migrating behaviour of fish schools such as jack mackerel Trachurus japonicus, spotted mackerel Scomber australasicus, and Japanese anchovy Engraulis japonicus was investigated in set-net fishing grounds by means of sonar image records. The spotted mackerel and Japanese anchovy schools moved at an average speed of 18-19cm/s, while the jack mackerel schools moved at 29cm/s. Schools of all species changed their direction of movement at an average veering angle of 19 ?? 36°. However, the veering angle of Japanese anchovy schools showed a tendency to be larger than that of the other two species. The average duration of straight movement of the spotted mackerel and Japanese anchovy schools was 2 ?? 2.4min, while that of the jack mackerel schools was 2.9min. This confirms a frequent veering of fish schools in the set-net fishing grounds. The jack mackerel and Japanese anchovy schools tend to move along the isobathic route with a depth change ratio of 0.6 ?? 0.8m/min between the first and final image. In case of the spotted mackerel schools the larger depth change was observed up to 6m/min.

Relation between Engraulis anchoita concentrations and presence of Merluccius hubbsi on the patagonian continental shelf

During the second cruise of the R.V. “Professor Siedlecki” in spring and summer, 1973, concentrations of anchovy and hake were reported in the area off Golfo Nuevo and the Bay of San Mathias, Argentina. Observations were mainly made with the help of acoustic equipment. The echo recordings revealed an interrelationship between the presence of anchovy schools and the appearance of hake concentrations. This paper demonstrates that this relation is trophic in character.