Climate and the ecosystem of the Arctic cod (Boreogadus saida)

在气候变化和工业化的双重压力下，北极正在迅速发生变化。北极鳕鱼（Boreogadus saida）在北极海域的近海生态系统中占主导地位，占公海鱼类总数的95%。一些海鸟和海洋哺乳动物，如环海豹（北极熊的主要猎物）、白鲸和独角鲸，主要以小型北极鳕鱼为食。因此，这一关键物种对气候变化的反应将直接影响海洋生态系统为因纽特人社区提供的服务，如传统食物、健康和服装、代际纽带、艺术、狩猎收入、旅游业等。

The Arctic is transforming rapidly under the double pressure of climate change and industrialization. The Arctic cod (Boreogadus saida) dominates the offshore ecosystem of Arctic seas, making up to 95% of the fish assemblage in the open sea. Several seabirds and marine mammals such as the ring seal (the main prey of polar bear), the beluga and the narwhal, feed primarily on the small Arctic cod. Hence, the response of this pivotal species to climate change will directly impact the services provided by the marine ecosystem to Inuit communities, such as traditional food, health, and clothing, inter-generation bonding, art, hunting revenues, tourism, etc. My team study the ecology of Arctic cod and its response to variations in climate. Each year since 2003, the annual expedition of the Canadian research icebreaker Amundsen has provided access to Baffin Bay, the central Canadian Archipelago, and the Beaufort Sea. The sophisticated sonars of the ship measure continuously the distribution and abundance of juvenile and adult fish in these seas. Plankton nets and trawls are deployed to identify the fish detected by the sonars. The number and size of juvenile arctic cod at the end of the summer season are of particular interest as they dictate the future size of the population. We discovered that the biomass (number multiplied by size) of juvenile Arctic cod is large in years when the sea-ice break-up is early. An early break-up allows the surface layer of the ocean to warm up during summer. An early break-up and warmer temperatures could enable the young fish to grow faster. Alternatively, an early break-up could allow the larvae hatched early in March and April to survive with a longer time to achieve a large size by the end of summer. We propose to test these hypotheses in the coming years. We also discovered that the otoliths or ear-stones, small concretions in the orientation system of Arctic cod, is preserved in the bottom sediments of some areas of the Canadian Archipelago. The otolith records the daily growth of the young fish and the annual growth of the adults. We propose to correlate the reconstructed abundance and growth of Arctic cod over the last millennium to corresponding variations in climate and the timing of the ice break-up. Finally, we will test the idea that fast growth and a relatively large size allow young Arctic cod to avoid predation by seabirds by comparing the otoliths retained in the gizzard of different seabirds (an index of the size and growth of fish captured by seabirds) to the otoliths of the fish captured with nets and trawls. The Inuit communities of Canada, the oil exploration sector active in the Arctic, and policy makers in government agencies (e.g. Energy Board Canada; Fisheries and Oceans Canada; Indigenous and Northern Affairs, Canada) are the end users of the improved understanding of the response of arctic marine ecosystems to climate change and development generated by this research.