Researcher examines spawning of mackerel in the North Atlantic

Brazilian marine researcher Thassya Christina dos Santos Schmidt based at the Icelandic Marine Institute has delivered a talk on mackerel spawning in the Northeast Atlantic

Thassya Christina dos Santos Schmidt, an expert in pelagic fish science at the Icelandic Marine and Fresh Water Institute has delivered a talk on mackerel spawning.

Her talk entitled, ‘New findings on Northeast Atlantic mackerel (Scomber scombrus) reproductive strategy and extension of spawning area into Nordic Seas’ is now available on YouTube in English.

In her research Thassya Christina dos Santos Schmidt writes:

Mackerel spawning season is long (from January – July). Its spawning has been the subject of scientific discussion for more than a decade, and there has been debate about whether it spawns all eggs at once (e. determinate) or spawns more often during the spawning period (e. indeterminate). This uncertainty can affect the correct way to determine mackerel fecundity and is important to determine when calculating the size of the spawning stock from an estimate of the number of spawned eggs.

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This study used state-of-the-art methods to determine the reproductive biology of mackerel. The results indicate that egg development is ongoing and therefore it is important for marlin to spawn frequently during the spawning season.

Following the warming of the sea and large spawning cohorts several years in a row after 2000, the population size of mackerel after 2010 was larger than previously seen. At the same time, the mackerel spawning area expanded both north and west without being able to assess how far the spread reached. Therefore, it was also assessed whether mackerel spawning even reached its feeding area in the North Seas, north of 60°N. The data used were obtained from different scientific expeditions together with catch samples from the pelagic fleet during the feeding period (May-July) between the years 2004-2021. During these months, mackerel were regularly found in the southern North Atlantic since 2009, with the proportion of mature and spawning fish increasing over time. A clear change occurred after 2011, with spawning fish, albeit in small numbers, being found as far north as 75°N in July.

Microscopic analysis showed that up to 90% of the spawn were ready for spawning in May, and about 10% in June and July. Furthermore, approximately 38% of the samples taken in the later months indicated that spawning was complete, and the remains of immature eggs were detectable (atresia). The results indicate that mackerel ended spawning to use the energy for foraging to accumulate energy to be able to spawn again later.

Thassya C. dos Santos Schmidt did her undergraduate studies in biology and master’s degree in oceanography both in Brazil. Thassya got her a PhD in biology at the University of Bergen in 2017. Her doctoral thesis was on reproductive traits across the Atlantic herring stocks complex. She did her postdoc at the Institute of Marine Research, Norway, where she worked with reproductive biology on Northeast Atlantic mackerel. Thassya’s research interests are mainly on fish reproduction and recruitment and the effect of environmental parameters on long-term changes on life history traits. She joined the pelagic group at HAFRO in mid-February 2022.

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