Behaviour of mackerel schools during summer feeding migration in the Norwegian Sea, as observed from fishing vessel sonars

Abstract

In July 2002, two commercial vessels were used to study the distribution of Northeast Atlantic mackerel (Scomber scombrus L.) during their feeding migration in the eastern part of the Norwegian Sea between 62°N and 70°N. Pelagic trawling and school tracking with SIMRAD 24–36 kHz sonar demonstrated that the stock was distributed throughout the study area. Information about time, geographic position, size, depth, speed, and direction was stored for each school during tracking. This study reports analyses of data from 63 schools that were tracked for 30 s or longer. All schools were recorded at depths of less than 100 m, and the majority (65%) were found between the surface and 40 m. The direction of migration (north 0° ± 22.5°, northeast 45° ± 22.5°, etc.) was non-random, with east and west as dominant swimming directions. School size and migration speed varied from 1 to 7000 tonnes and 0 to 6 m s−1, respectively. Methodological improvements are discussed.

Prey selection of offshore killer whales Orcinus orca in the Northeast Atlantic in late summer: spatial associations with mackerel

“…The densities of NEA mackerel and Atlan tic blue whiting are stable in the area, feeding in July and August , while NSS herring have already passed their peak feeding period at that time (Langøy et al 2012). Mackerel are associated to a greater extent with warmer water than herring are (Utne et al , 280 2006 (Iversen 2002, Godø et al 2004), whereas we found herring and blue whiting mostly in Arctic water in the present study. Generally, all 3 fish species were abundant and available as prey for killer whales during our study period.…”

“…Based on the observed spatial associations, killer whales showed a clear preference for NEA mackerel over NSS herring and blue whiting within the same ecosystem. This may be caused by one or more interacting factors: NEA mackerel are typically distributed in smaller schools in the upper water column, both day and night (Godø et al 2004, Prokopchuk & Sentyabov 2006, whereas NSS herring perform diurnal vertical migrations to deeper waters (Langøy et al 2012), and blue whiting have a more pronounced mesopelagic distribution down to 300− 500 m with occasional migrations to shallow waters, and only at night (Monstad 2004, Prokopchuk & Sentyabov 2006. Killer whales are mainly visual predators (White et al 1971) and seem to depend on daylight when hunting (Similä & Ugarte 1993, Similä 1997b, Nøttestad & Axelsen 1999, Nøttestad et al 2002.…”

Feeding strategy of mackerel in the Norwegian Sea relative to currents, temperature, and prey

“…The energetic costs of migration in mackerel can be offset by swimming with the tidal currents (Nøttestad et al, 1999;Godø et al, 2004) or by taking advantage of mesoscale eddies (Simons et al, 2015) in the Norwegian Sea and along the Norwegian coast (Orvik and Niiler, 2002;Godø et al, 2012). The Norwegian North Atlantic Current (Nw NAC) transports warm water in offshore waters and up along the coast of Norway, whereas cold Arctic water is brought south at the western border of the Norwegian Sea (Blindheim, 2004;Skjoldal et al, 2004), but it is not known whether mackerel utilize these currents for long-distance transportation.…”

“…Mackerel lack a swimbladder and are difficult to detect with acoustic methods, and small loosely aggregated mackerel schools close to the surface are in the echosounder acoustic blind zone (Tenningen et al, 2003;Simmonds and MacLennan, 2005). However, omnidirectional sonar has been successfully used to record migratory behaviour of schooling fish (Nøttestad et al, 1996(Nøttestad et al, , 2004Brehmer et al, 2006), and high-frequency omnidirectional sonars have even better spatial resolution, permitting studies of mackerel behaviour (Godø et al, 2004).…”

Fish Behavior on Fisheries Boat Lift Net (Bagan Petepete) by Using Led Lights

“…Ikan-ikan yang berada di sekitar waring bagan dan kolom perairan diindikasikan adalah ikan kembung, tembang dan layang. Hal ini sesuai dengan apa yang dikemukakan oleh Godø et al (2004) bahwa sekitar 65 % ikan mackerel berada diantara permukaan sampai kedalaman 40 m, sedangkan ikan yang berada di sekitar permukaan adalah ikan teri yang merupakan ikan berfototaksis positif.…”