Climate change no threat to cod

Research published online in a paper today suggests that climate change has had little influence on adult cod movements in the North Sea. Scientists David Righton from the Centre for Environment, Fisheries & Aquaculture Science (Cefas) and Francis Neat from Fisheries Research Services (FRS) jointly investigated the thermal ecology of cod throughout the North Sea.

The recent warming of the North Sea has been accompanied by the decline of Atlantic cod (Gadus morhua L.) over the past 20 years. Whereas over-fishing has been a factor, cod distribution has been shown to be moving north. Other potential reasons for the shift could be changes in prey distribution or the fact that the southern component of this commercially important stock is more depleted than the northern.

Cod are highly mobile fish. Scientists conjecture that they might be expected to move to cooler habitats if global warming has created unfavourable habitats in the south. To test this theory, Neat and Righton compared the temperature experience of cod with independently measured sea-bottom temperature data.

Using “data loggers”, tiny electronic data storage tags (DSTs), the scientists tagged individual fish between 1999 and 2005. From 129 returned tags, it was found that most cod occupied a warmer fraction of the sea than was potentially available to them, despite cooler waters being within reach. Thus adult cod do not avoid warm water, suggesting that climate change is just one of many factors that influence cod distribution.

Cefas scientist, David Righton, said; “We've got some amazing individual-based data that provide us with information on how adult cod respond to thermal habitat changes. Probably for a number of complex reasons, cod don’t seem to avoid high temperatures. Our study shows that understanding the processes that drive the interaction between species and their environment is crucial to making predictions about how marine ecosystems will change in the future as climate changes.”

Notes for editors

1. “Warm Water occupancy by North Sea Cod”, by Francis Neat and David Righton is published online in the Proceedings of the Royal Society London Series B (doi:10.1098/rspb.2006.0212). The series is one of seven journals published by the Royal Society containing high-quality submitted research articles across the full spectrum of the biological sciences. See http://www.pubs.royalsoc.ac.uk/index.cfm?page=1087.
2. Cefas is an internationally renowned scientific research and advisory establishment undertaking work on fisheries management, environmental protection and aquaculture. It offers a wide range of research, advisory, consultancy, monitoring and training activities to government departments (UK and foreign, central and local), international agencies, commercial companies and aid organisations. For more about Cefas’ work, visit www.cefas.co.uk.
3. Fisheries Research Services (FRS) is an agency of the Scottish Executive Environment and Rural Affairs Department (SEERAD). FRS provides expert scientific and technical advice to government on marine and freshwater fisheries, aquaculture and the protection of the aquatic environment. For more about FRS’ work visit www.marlab.ac.uk.
4. For information about cod stocks in the North Sea or to interrogate data held by Cefas go to www.cefas.co.uk/data.aspx
5. The Atlantic cod (Gadus morhua L.) is a very adaptable species. It can tolerate temperatures between -2°C and 19°C. Cod migrate huge distances (>1000km) in an annual cycle, but can also remain virtually in the same place all year round. Cod live in a huge variety of environments, from water as shallow as a few metres to water more than 500m deep. As a result, some cod only move a few centimetres or metres above the seabed, while some swim more than 200m away from the seabed before going back again. For more about the ecology of cod, see www.cefas.co.uk/projects/cod-spatial-dynamics-and-implications-for-fisheries-management-(codyssey).aspx.

Press contacts:
Anne McClarnon, Cefas:  01502 52 4370 / anne.mcclarnon@cefas.co.uk
Hilda Stewart, FRS:  01224 295 340 / stewarthm@marlab.ac.uk