#Capelin2022 Small but mighty: Capelin symposium kicks off in Bergen

A four-day capelin symposium hopes to expand our knowledge base on the biology, ecology, and role of this key forage fish in Arctic and Sub-Arctic ecosystems.
Published: 10 October 2022
​Capelin has been described as having the bad luck of being one of the most important forage fish in the Northwest Atlantic and is preyed upon ​​by Atlantic cod, mackerel, haddock, seals, whales, puffins, and more. ​‘‘Capelin – What Are They Good For? Biology, Management, and the Ecological Role of Capelin​” was the first ICES symposium on capelin – taking place in Reykjavik, Iceland in 2001. In the two decades since, capelin populations have fluctuated considerably and large-scale shifts in the spatial distribution at all life stages have been observed in all Sub-Arctic systems. ​

Capelin experts gather this week in Bergen, Norway as the Institute of Marine Research hosts the second-ever ICES Capelin symposium​. The event runs from 10​–13 October. ​Capelin's responsiveness to changes in the marine environment, has led Rose to suggest (2005) that it could be a “canary in the coalmine" to detect signals of changes in the Arctic Ocean. ​This 4-day ICES symposium on capelin will seek to revise and expand our knowledge base on capelin biology, ecology, and roles in Arctic and Sub-Arctic ecosystems, with focus 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. 

Climate and fisheries

F​​rédéric Cyr​, Fisheries and Oceans Canada,​ opened the symposium with his talk "Climate and fisheries: Decadal-scale bottom-up control of the Newfoundland and Labrador ecosystem​". Here, Cyr provides an overview of his plenary.

In marine sciences, a bottom-up trophic control refers to an ecosystem that is resource-driven and limited by biotic or non-biotic parameters, such as the physical environment and secondary production, whereas its counterpart, a top-down trophic control, refers to a consumer-driven cascade where the dominant control is exerted by predators such as fish and marine mammals. In my keynote at the Capelin Symposium Bergen, I presented evidence of climate variability exerting a bottom-up control on the fish community of the Canadian Newfoundland and Labrador (NL) shelf, a region known as an iconic fishing ground for centuries and also prone to large climate variability.

Circulation changes​

Located at the confluence of Arctic, Subarctic, and subtropical currents, the NL shelf is especially affected by large-scale ocean circulation changes. Such circulation changes impact not only the regional ocean climate but also the overall composition of water masses and the immediate habitat of numerous commercial and non-commercial fish species. 

Canada and other countries carried out ocean observations over the last seven decades. Using these observations, the time period was separated into different phases (or regimes) based on the trends in the region's mean climate. For example, the period 1948–1971 was found to be the warmest period in recent history, while the decade between the mid-1980s and mid-1990s was the coldest - a period that also witnessed a near-complete collapse of most fisheries in the region.

Climate regimes​

Our findings show that these different climate regimes are well explained by changes in atmospheric pressure at sea level. These changes, accompanied by modifications in the mean wind fields, also affect large-scale ocean circulation such as the strength of the subpolar gyre, and thus the interactions between the Labrador and the North Atlantic currents, two major contributors to the NL shelf climate variability. Furthermore, the different climate regimes on the NL shelf are linked to changes in the productivity of the ecosystem and the natural variability in fish biomass, including groundfish species, but also capelin, the keystone forage species in the region.

The following hypotheses explain these findings and are well supported by observations: during warmer climatic phases, the spring phytoplankton bloom occurs earlier and may better match the emergence of key zooplankton species (e.g. Calanus finmarchicus) from overwintering. This further translates into increased food availability for capelin, and thus more efficient energy transfer from primary and secondary producers to higher trophic levels. In turn, this explains the observed natural fluctuations (non-fishery related) of capelin and other fish biomasses. 

During colder phases of the NL climate, the phytoplankton bloom is later, which may result in a mismatch with Calanus emergence from overwintering and, consequently, less food availability for capelin and other fish species. Since these climate changes occur at a relatively low frequency (decadal timescales), the recognition of the current ecosystem phase (or regime) offers a potential forecasting capability of ecosystem productivity that could be integrated into fish stock assessments.​

The Capelin Symposium Bergen continues all this week. Follow the news coming from Bergen @CSB_2022

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#Capelin2022 Small but mighty: Capelin symposium kicks off in Bergen

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