Nature 366, 458 - 461 (02 December 1993); doi:10.1038/366458a0

Cod spawning on a migration highway in the north-west Atlantic

George A. Rose

Science Branch, Department of Fisheries and Oceans, PO Box 5667, St John's, Newfoundland, Canada A1C 5X1

FIVE hundred years of fishing and fifty years of research have produced only vague accounts of the spawning and migrations of Atlantic cod (Gadus morhua) off Newfoundland in the north-west Atlantic¹. Here I report the discovery of 'spawning columns' and a 'highway' used by cod to traverse the northeastern Newfoundland Shelf during annual springtime feeding migrations. Sea research using echosounders^2,3 showed that cod spawned in dense shoals (to one fish per m³) that featured midwater spawning columns comprised of pairs of fish. Immature joined mature post-spawning cod to migrate in large (scales of tens of kilometres and hundreds of millions of fish) size-structured aggregations led by larger 'scouts'. Cod traversed the cold waters of the shelf along a deep highway of warm oceanic water (2–2.5 °C). During migration, fish spacing appeared to maximize search volumes while maintaining visual contact. Aggregations fragmented when prey (capelin Mallotus villosus; shrimp, Pandalus spp.) were encountered.

References

1.	Harris, L. Independent Review of the Northern Cod Stock (Comm. Dir. Dept Fish. Oceans, Ottawa, 1990).
2.	Sund, O. Nature 135, 953 (1935).
3.	MacLennan, D. N. & Simmonds, E. J. Fisheries Acoustics (Chapman & Hall, London, 1992).
4.	Cushing, D. H. & Harden-Jones, F. R. Nature 218, 918−920 (1968).
5.	Baird, J. W., Bishop, C. A., Brodie, W. B. & Murphy, E. F. CAFSAC Res. Doc. 92/75 (1992).
6.	Blaxter, J. H. S. in Marine Ecology (ed. Kinne, O.) 213−320 (Wiley, New York, 1970).
7.	Clarke, G. L. & Denton, E. J. in The Sea (ed. Hill, M. N.) 456−468 (Wiley, New York, 1962).
8.	Clarke, G. L. in Proceedings of the International Symposium on Biological Sound Scattering in the Ocean, 1970 (ed. Farquhar, G. B.) 41−50 (Dept of the Navy, Washington DC, 1971).
9.	Blaxter, J. H. S. in Fish Behavior and its Use in the Capture and Culture of Fishes (eds Bardach, J. E., Magnuson, J. J., May, R. C. & Reinhart, J. M.) 33−55 (ICLARM Conf. Proc. 5) (Manila, Phillipines, 1980).
10.	Duntley, S. Q. in The Sea (ed. Hill, M. N.) 452−455 (Wiley, New York, 1962).
11.	Griffin, D. R. in Recent Studies in Avian Biology (ed. Wolfson, A.) 154−197 (Univ. Illinois Press, Urbana, 1955).
12.	de Young, B. & Rose, G. A. Can. J. Fish aquat. Sci. (in the press).
13.	Brawn, V. M. Behaviour XVIII, 177−198 (1961).
14.	Pitcher, T. J. in The Behaviour of Teleost Fishes (ed. Pitcher, T. J.) 294−337 (Johns Hopkins, Baltimore, 1986).
15.	Kieffer, J. D. & Colgan, P. W. Rev. Fish Biol. Fisheries 2, 125−143 (1992).
16.	Dodson, J. J. Env. Biol. Fishes 23, 161−182 (1988).
17.	Trout, G. C. Fish. Invest. London II, XXI (6) 51 (1957).
18.	Woodhead, A. D. J. mar. Bio. Ass. U.K. 38, 417−422 (1959).
19.	Harden-Jones, F. R. Fish Migration (Arnold, London, 1968).
20.	Dragesund, O., Hamre, J. & Ulltang, O. Rapp P.-V. Reun. Cons. Int. Explor. Mer. 177, 43−71 (1980)