To open the third day of ICES Capelin Symposium 2022 in Bergen, Mariano Koen-Alonso, Fisheries and Oceans Canada, gave his keynote "Capelin-cod dynamics: A comparison between the Newfoundland-Labrador and Barents Sea ecosystems, and what it may tell us about ecosystem regulation". Read an overview of his talk here.
Capelin is a key forage species in many northern hemisphere high-latitude marine ecosystems. Fluctuations in capelin stocks have often been associated with the performance of top predators in these systems: Atlantic cod is frequently used as an example of this connection between capelin and top predators.
Looking beyond Atlantic cod's important role as predator, it is useful to consider the contrast provided by the exploitation histories and stock trajectories from different cod populations. For example, cod stocks in the Barents Sea and the Newfoundland-Labrador Shelves ecosystems have shown divergent trajectories over the past 40 years. Cod experienced a significant decline in the Barents Sea and a collapse in the Newfoundland-Labrador Shelves in the mid-1980s and early-1990s respectively. Barents Sea cod quickly rebounded and has reached record high levels in recent years, while Newfoundland-Labrador cod is yet to recover and has only started to show some improvements since the mid-2000s.
In addition to fishing impacts, these contrasting cod trajectories occurred against a backdrop of broader ecosystem changes, including several capelin declines and recoveries in the Barents Sea and a collapse with only marginal improvement in the Newfoundland-Labrador Shelves.
How these differences (capelin and fishing history) impacted the cod trajectories in the Barents Sea and the Newfoundland-Labrador Shelves ecosystems was evaluated using a series of modelling exercises, including an integrated model architecture which allowed estimating common parameters for the two cod stocks.
The results indicated that despite their contrasting trajectories, the dynamics of both cod stocks could be explained by the combined impacts of fishing and capelin availability. Furthermore, model parameters that encapsulate intrinsic vital rates for cod were not significantly different between stocks, indicating that Barents Sea and the Newfoundland-Labrador cod are biologically similar.
This implies that the differences in cod trajectories were driven by the ecosystem context in which these stocks were embedded, more than intrinsic differences in their biological traits. This finding not only highlights the relevance of considering capelin within the management of cod stocks but also emphasizes the role of food availability and bottom-up control in regulating cod dynamics in particular, and top predators more broadly.
A better understanding of these mechanisms can be of particular importance given the expectation of future reductions in ocean productivity due to climate change.
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.