Norwegian spring spawning herring extending into the Svalbard fjords
Top image: Jørgen Berge, Tove Gabrielsen and Ole Jørgen Lønne with recently fished herring aboard R/V Helmer Hansen on 29 April 2012. Photo: UNIS.
UNIS researchers have recorded large amounts of Norwegian spring spawning herring in Adventfjorden and Isfjorden. This represents the northernmost mass-occurrence of herring, and a significant extension of its northern distribution limits.
UNIS has several teaching and research cruises around Svalbard each year, and although environmental monitoring is not a primary concern, these cruises offer a unique chance to monitor changes in the fauna and flora of our region.
Previous courses have for instance examined the first occurrence and re-establishment of blue mussels in Svalbard since the Viking age and compared the decapod faunae (shrimps and crabs) of today with that of 100 years ago. Both studies have revealed important insights into the biological and ecosystem effects on the current warming of the Arctic.
Recently, during our April student course AB-330, UNIS researchers could for the first time document a large amount of Norwegian spring spawning herring in Isfjorden. In the two bottom trawls taken in Adventfjorden, herring was by far the most dominating fish species with more than 50% of the total weight in both catches.
The Institute of Marine Research, Norway has long time series of fish recordings in the Barents Sea and the waters around Svalbard from cruises in late summer/early autumn, obtained by acoustic recordings and bottom- or pelagic trawl sampling. In recent years the abundance of the gadoid species like North East Arctic cod and haddock have been increasing, and these species have had a clear north – north eastward shift in their distribution (see figure below).
Young of the year, or 0 – group herring, have been recorded on both UNIS and IMR cruises near Svalbard in recent years (see figure below), but not larger herring. Thus the recent UNIS recordings of large, mature herring in Adventfjorden is surprising.
Nevertheless, mature Norwegian spring spawning herring has a high migratory capacity with the potential to distribute from the coast of North Western Norway in the east, the coast of South Western Norway in the south, Iceland in the west, and now all the way up to the fjords of Svalbard in the north!
No accidental influx event
At present, there seem to be several age classes of herring in Isfjorden. In both January and April 2012, we observed relatively high numbers of one-year-old (0+ age class) juveniles. Now in April, these were still present, but the large and mature herring were now the most dominating. These most likely include both 2+ and 3+ age classes, and the largest had well developed gonads.
The current distribution of herring in the fjord must therefor be regarded as something more than just one accidental influx event. Rather, there must have been a number of repeated events allowing the herring to migrate into the fjord throughout the winter.
This pattern of repeated influx is similar to what has previously been observed for cod; over the last ten years, the amount of cod in Isfjorden has increased, and we now regularly catch both small pelagic juveniles and large (>10kg) adults in the fjord. If we can expect the same situation at a more regular basis also for herring remains to be seen, but if so, the potential effect on the ecosystem structure and functioning might be significant.