Starting off the second day of the Capelin Symposium, Hannah Murphy, Fisheries and Oceans Canada and Mayumi Arimitsu, USGS Alaska Science Center gave their keynote "Marine heatwaves and cold-spells: Persistent collapse of capelin in two oceans at opposite ends of the thermal optima" as part of Theme session 2: Capelin ecology and Response to Climate Variation. Murphy and Arimitsu provided an overview of their talk.
Beyond thermal optima
Capelin are subject to population collapses that appear to be regulated by environmental conditions when temperatures exceed the boundaries of their thermal optima. For example, in Newfoundland, Canada, the Northwest Atlantic Fisheries Organization (NAFO) Divisions 2J3KL capelin stock collapsed in 1991 during an anomalous cold spell (1991–1993). This stock has not recovered in the 30 years since then, despite a warming period from 1996–2013, suggesting a change in ecosystem structure (i.e. regime shift).
A regime shift was also associated with an abrupt decline of capelin in the North Pacific when ocean temperatures warmed (1977–1978). Although capelin stocks recovered in the Gulf of Alaska, particularly during a cool period (2008–2013), an abrupt collapse was again observed following a prolonged marine heatwave (2014–2016).
We compared and contrasted ecosystem responses to marine heatwaves and cold spells in the Gulf of Alaska and Newfoundland to identify similarities between capelin population collapses at opposite ends of their thermal optima. Presenting analyses that identify the responses in capelin biology and demography in relation to extreme sea surface temperature anomalies in both oceans, we find broad similarities between the Gulf of Alaska and Newfoundland regions suggesting that thermal optima is a common mechanism driving population variability.
Following a population collapse, capelin exhibit faster growth, earlier maturation at a smaller size, and late spawn timing, which can all drive low recruitment over extended periods. We anticipate that in the near term, the lack of a directed fishery in the Gulf of Alaska could promote faster local recovery when ocean cooling occurs; however, future climate change will be a primary driver of population dynamics in the future. For Newfoundland capelin, the prolonged collapsed state of the stock suggests that the low ecosystem productivity conditions after the regime shift in 1991 and warming environmental conditions are not conducive to stock rebuilding.
Because the Gulf of Alaska and Newfoundland populations are both near the southern edge of the species' range, capelin in both regions will likely move northward to find optimum temperature conditions in the future.
Capelin Symposium Bergen
Capelin experts have gathered this week in Bergen, Norway as the Institute of Marine Research hosts the second-ever ICES Capelin symposium.
Capelin's responsiveness to changes in the marine environment led Rose to suggest in 2005 that it could be the sea “canary” for the northern boreal marine ecosystem.
This four-day ICES symposium on capelin will seek to revise and expand our knowledge base on capelin biology, ecology, and its role in Arctic and Sub-Arctic ecosystems, focussing specifically on capelin stocks in the Barents Sea, waters around Iceland–East Greenland–Jan Mayen, the Newfoundland–Labrador Shelf, and the Gulf of Alaska and the Bering Sea.
The Capelin Symposium Bergen continues from 10–13 October 2022. Follow the news coming from Bergen @CSB_2022.
