We document the presence of a large highly migratory fish species, bluefin tuna Thunnus thynnus, in east Greenland (Denmark Strait) waters during August 2012. This location is much farther north of their usual summer feeding areas and their presence there is a very unusual event.
The tuna were caught in the Denmark Strait (between east Greenland and Iceland), where temperatures are usually several degrees too cold for them, but reached suitable temperatures in summer of 2012. The tuna (only 3 individuals!!, but likely many more were present because they are a schooling species) were caught as bycatch during an exploratory fishery for mackerel, which is one of their main prey. In fact, the tuna were all caught in the same haul together with 6 tonnes of mackerel. Each of the tuna weighed about 100 kg.
We estimated the temperatures using satellite imagery and some historical data, and detected a warming trend in the last 10-15 years. This has made the area thermally more suitable both for mackerel, which is a key prey of bluefin tuna, and the bluefin tuna themselves.
The findings raise many new scientific questions about the migration behaviour and spatial distribution of bluefin tuna, how they are influenced by ecosystem conditions, and where the tuna came from.
Changes in environmental conditions like these have big impacts on spatial distributions of species and how they interact with each. Also, the changes will affect fishery management because the distributions of the fish move across boundaries of different national and international jurisdictions. This means that the vulnerability of the fish to fishing fleets of different countries changes.
The study is described in the August 2014 issue of Global Change Biology:
Reference:
MacKenzie, B. R., Payne, M. R., Boje, J., Høyer, J. L. and Siegstad, H. (2014), A cascade of warming impacts brings bluefin tuna to Greenland waters. Global Change Biology, 20: 2484–2491. doi: 10.1111/gcb.12597