1. Distribution and Migration of cod, the impact of climate Geir Ottersen Institute of Marine Research, Bergen, Norway and Douglas P. Swain Department of Fisheries and Oceans, Gulf Fisheries Centre, Moncton, N.B., Canada
IMR

2. I will present examples from different stocks on Habitat associations
Highlights from the Distribution and migration chapter of a book on ICES/GLOBEC Cod and Climate Change WG science: ”Cod in a changing climate – effects of physical variability on a key predator in North Atlantic marine ecosystems” edited by K. Drinkwater and K. Brander
I will present examples from different stocks on
Habitat associations
Seasonal migrations
Geographic range and its variation
IMR

3. Distribution of Atlantic cod and sea temperatures at 100m depth
Russia
Greenland
Norway
Canada UK
Spain
Sundby (2000)

4. Habitat associations Temperature preferences Depth preferences
Ontogenetic variation
Interannual variation
Seasonal variation
IMR

5. Seasonal variations in temperature distribution of cod Georges Bank, W and E Scotian Shelf, S. Gulf St. Lawrence
On Georges and Scotian Shelf Banks seasonal var in cod ambient temperature variability reflects seasonal cycle of warming and cooling.
S. Gulf cod occupy warmer water during winter than cooling due to migration patterns (as do N. Gulf and Barents Sea cod).
Not that data for all four seasons only were available fro Georges Bank.

6. Seasonal variations in depth distribution of cod Georges Bank, W and E Scotian Shelf, S. Gulf of St. Lawrence
While Georges and Scotian Shelf Banks cod show little seasonal var in depth distribution, S. Gulf cod occupy much deeper water during winter than summer.

7. Interannual and ontogenetic variability in temperature distribution of cod Mean ambient winter temperature Arcto-norwegian cod age 1-7 1 2 3 4 5 6
1988
1989
1990
1991
1992
1993
1994
1995
Ambient temperature 7 K
Older cod in warmer water
Larger interannual var in ambient temp. than at a fixed location,
In particular for younger cod.

8. Seasonal variation in ambient temperature of Arcto-norwegian cod
K. Michalsen, IMR

9. Seasonal migrations between spawning grounds, nursery areas and adult feeding grounds
Seasonal migration patterns of two large, highly migratory northern stocks:
- Southern Gulf of St. Lawrence Arcto-norwegian (Barents Sea)
Cod populations may typically be divided into migratory and non-migratory. The large, migratory variety tend to dominate in the northerly areas.
IMR

10. Southern Gulf of St. Lawrence cod: Seasonal migrations and spawning grounds
The southern Gulf stock migrates distances up to 650 km between spawning and feeding grounds in the southern Gulf and overwintering grounds along the southern slope of the Laurentian Channel in the Cabot Strait area. Southern Gulf cod migrate into the Gulf in late April and May. Spawning occurs throughout the southern Gulf, but the main spawning ground is believed to be in the Miscou area in the western Gulf. Most spawning occurs between late May and early July. After spawning, cod disperse throughout the southern Gulf to feed throughout summer and early autumn. In October, the cod aggregate before migrating out of the Gulf between late October and early December. Larger, older individuals migrate farther out of the Gulf in autumn than do small, young individuals

11. Arcto-norwegian cod: Seasonal migrations and spawning grounds

12. Geographic range and its variation
- Interannual and ontogenetic changes in geographic range
- Density-dependent changes in geographic range
DDHS
IMR

13. Modified from Keith Brander, ICES
Spread of Cod at West Greenland
Late 1930’s Upernavik
1900 Cape Farewell & Fiskenes Bank
Fredrikshaab
Umanak
1919 Godhaab
1922 Sukkertoppen
Christianshaab
Distribution shifted North by about 1000 km in 20 years and then retreated again. Cod have still not recovered at Greenland although temperatures now have started to become more favourable and some reasonably abundant year-classes have spawned at Iceland.
Late 1960 decline and retreat
Modified from Keith Brander, ICES

14. Density-dependent changes in geographic distribution for Southern Gulf of St. Lawrence cod20 30 40 50
1970
1975
1980
1985
1990
1995
2000
Year
Geographic Range 20 30 40 50 60 80
100
Abundance (millions)
3-yr moving average for 6-year old cod. Geographic distribution of this population on its summer and early autumn feeding grounds in the southern Gulf has been monitored by a bottom-trawl survey conducted each September since 1971.
Abundance follows same development as Georange – shown: Low abundance in the mid-1970s and then increased rapidly to very high abundance in the mid-1980s, reaching a peak in abundance nearly twice the previous high levels in the early 1950s. Abundance declined equally rapidly from this peak in the late 1980s and early 1990s, and has remained at a low level since then.
Cod density did not increase uniformly over all areas as population size increased in the late 1970s and early 1980s Instead, density increased slowly in regions where cod were concentrated at low population sizes and more rapidly in surrounding areas. This resulted in an expansion in geographic range on the feeding grounds as abundance increased and a subsequent contraction in range as abundance decreased in the early 1990s.

15. Geographic distribution in September of 5-yr old Southern Gulf of St
Geographic distribution in September of 5-yr old Southern Gulf of St. Lawrence cod during periods of low abundance ( , ), high abundance ( ) and recent (2001).
Instead of expanding and contracting around the same regions of “optimal” habitat as abundance increased and decreased, shifts in distribution accompanied the changes in abundance, with cod densities highest in different regions at different levels of abundance. This density-dependent shift in distribution may be due to a trade-off between the density-dependent benefits of greater food resources in warm shallow waters and the density-independent benefits of lower metabolic costs in the colder waters at intermediate depths.
An alternative hypothesis to explain these changes in the distribution of southern Gulf cod is that they reflect a response to environmental change, with cod avoiding areas of extreme (cold) bottom conditions.

16. Example of change in geographic range
Relative distribution and abundance of cod in NW Atlantic derived from NEFSC Spring bottom trawl surveys.
Short animation
Yellow circles: Cod present Larger circles: More cod +: Stations without cod
Thanks to Mike Fogarty for use of the maps
NEFSC=NorthEastern Fisheries Science Centre (Woods Hole)

25. Thanks for your attention!
Geir Ottersen
IMR