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

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

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

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

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.

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.

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.

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

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

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

Arcto-norwegian cod: Seasonal migrations and spawning grounds

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

Modified from Keith Brander, ICES Spread of Cod at West Greenland Late 1930’s Upernavik 1900 Cape Farewell & Fiskenes Bank 1917-18 Fredrikshaab 1931-36 Umanak 1919 Godhaab 1922 Sukkertoppen 1927-30 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

Density-dependent changes in geographic distribution for Southern Gulf of St. Lawrence cod 20 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.

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 (1973-1975, 1993-1995), high abundance (1980-1982) 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.

Example of change in geographic range Relative distribution and abundance of cod in NW Atlantic 1979-2002 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)

Thanks for your attention! Geir Ottersen IMR