A research paper has shown that the migration pattern of Northeast Atlantic mackerel changes as the fish grows older

A research paper has shown that the migration pattern of Northeast Atlantic mackerel changes as the fish grows older

A research paper has shown that the migration pattern of Northeast Atlantic mackerel changes as the fish grows older.

The Space-time recapture dynamics of PIT-tagged Northeast Atlantic mackerel (Scomber scombrus) reveal size-dependent migratory behaviour

The scientific paper used RFID data to study the migration patterns of mackerel. A total of 430 thousand fish were tagged on the west coast of Ireland and Scotland, and at Snæfellsnes in the years 2011 – 2021.

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The study relied on recoveries 1-3 years after marking or a total of 7522 recoveries. Results show that as mackerel ages and grows (length increases), it moves further north into the Norwegian Sea and west into Iceland’s territorial waters and some years into Greenlandic waters. It is common for 3-4 year old (32-34 cm) mackerel to be restricted to the southern part of the Norwegian Sea, 4-5 year old (34-35 cm) fish go further north into the northern part of the Norwegian Sea, and 5+ year old (>35 cm) fish to the west into Icelandic territory and even further north towards Svalbard.

The size of the mackerel is not the only factor that controls the migration path, as there are large differences between years in migration patterns by size. It suggests that environmental conditions, such as ocean currents and food conditions, and population size also affect migration patterns. The results of the distances from the marking point on the spawning route to the destination point and the swimming speed of the mackerel that would be needed to get between indicate that there is a high probability that mackerel will enter the Icelandic EEZ from the north-west of Ireland, south of the Faroe Islands, without leaving first into the Norwegian Sea.

The paper says, “Based on GIS-mapping and semi-parametric modelling of recaptures from PIT-tag experiments in the North Sea nursery area (September 2011), the Celtic Seas spawning area (May-June 2014-2021) and the Icelandic Waters feeding area (August 2015-2019), we argue that the distribution of Northeast Atlantic (NEA) mackerel is influenced by a size-dependent migratory behaviour. The time-space recapture dynamics revealed that larger mackerel tended to migrate a longer distance between spawning and feeding areas, either through a western route from the Celtic Seas into the Icelandic Waters and the Greenland Sea or by following the main route northwards through the Faroe-Shetland Channel into the Norwegian Sea. This long-distance travel resulted in turn in delayed arrival in the North Sea wintering area. During the return spawning migration into the Celtic Seas, larger individuals remained in the front, likely heading to spawning grounds farther south than smaller conspecifics. Migration patterns also evolved with time at liberty as the mackerel grew older and larger, while possibly covering a progressively wider area over its annual migration cycle as suggested from the tagging data. However, the study also showed large inter-annual variability in the recapture patterns which likely reflect changes in environmental condition (prey availability and ocean current), NEA mackerel population demographics, and the spatial fishery dynamics.”

mackerel migration pattern changes

FIGURE 1 (A) ICES ecoregions used as basis for GAM modelling of recapture probabilities from PIT-tag experiments of NEA mackerel in Celtic Seas and Icelandic Waters 2014-2020. (B) The main features of the near-surface circulation in the eastern North Atlantic and the Nordic Seas (modified from Stefánsson and Ólafsson, 1991; Turrell et al., 1996; Hansen and Østerhus, 2000; Orvik, 2004). (C) Abundance at ages 3-12+ compared with recruitment at age 2 (ICES, 2021) to demonstrate stock decline and aging over the study period.

mackerel migration pattern changes

FIGURE 2 Illustration of the size dependent migration hypothesis for NEA mackerel with the wintering area in the Greater North Sea as the starting point. Maps show a hypothetical development of the migration cycles over three years (A–C), from spawning at age 3 (~32 cm in body length) until spawning at age 6 (~36 cm in body length). According to this hypothesis, mackerel may potentially migrate farther south to spawn (Bay of Biscay, Spain) and farther north (Spitsbergen) and west (Greenland) to feed when tagged at larger sizes or as they grow larger, thereby periodically being outside the fishing areas scanned for PIT-tags.

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