Springer Nature is making SARS-CoV-2 and COVID-19 research free. View research | View latest news | Sign up for updates

Relationships between water mass characteristics and estimates of fish population abundance from trawl surveys


The Canadian Department of Fisheries and Oceans conducts annual bottom trawl surveys to monitor changes in the abundance of the major commercially important groundfish populations. Some of these surveys have been in operation for almost 20 yr. The estimates from these surveys often indicate rapid changes in abundance over time beyond that expected from the population dynamics of the fish. Much of this interannual change has been interpreted as variation, the magnitude of which has often made it difficult to measure anything but the most severe effects of fishing, pollution or any other intervention on the population. Recent studies have shown that some of this variation may be attributed to changes in catchability of fish due to the effects of environmental variables on fish distribution. Annual changes in abundance as estimated from such field surveys may be confounded by changes in catchability due to annual changes in environmental conditions. In this study, trawl catches of age 4 Atlantic cod (Gadus morhua) from surveys conducted during March 1979–1988 were compared with concurrent measurements of bottom salinity, temperature and depth. Large catches of age 4 cod are more likely to occur in water characterized as the intermediate cold layer defined by salinities of 32–33.5 and temperatures<5°C. This relationship also appears to be modified by depth. We further show that internnual changes in the estimated abundance from the surveys were, in a number of cases, coincident with changes in the proportion of the bottom water composed of the intermediate cold water layer. The implications that these patterns may have on interpreting trends in the estimates of abundance from trawl surveys are discussed.

This is a preview of subscription content, log in to check access.


  1. ChapmanD. C. and BeardsleyR. C.: 1989, ‘On the Origin of Shelfwater in the Middle Atlantic Bight’, Journal of Physical Oceanography 19, 384–391.

  2. CochranW. G.: 1977, Sampling Techniques, Wiley, New York, 428 p.

  3. Doubleday, W. G. (ed.): 1981, Manual on Groundfish Surveys in the Northwest Atlantic, Nafo Scientific Council Studies. No. 2. 55p.

  4. Doubleday, W. G. and Rivard, D. (eds.): 1981, ‘Bottom Trawl Surveys’, Canadian Special Publication of Fisheries and Aquatic Science 58, 273 p.

  5. Etter, M. L. and Mohn, R. K.: 1989, ‘Scotia-Fundy Shrimp Stock Status-1988’, Cafsac Research Document. 89/4. 25p.

  6. Fanning, L. P. and MacEachern, W. J.: 1989, ‘Stock Status of 4VsW cod in 1988’, Cafsac Research Document. 89/57. 71p.

  7. FrancisR. I. C. C.: 1984, ‘An Adaptive Strategy for Stratified Random Trawl Surveys’, New Zealand Journal of Marine and Freshwater Research 18, 59–71.

  8. GavarisS. and SmithS. J.: 1987, ‘Effects of Allocation and Stratification Strategies on Precision of Survey Abundance Estimates for Atlantic Cod (Gadus morhua) on the Eastern Scotian Shelf’, Journal of the Northwest Atlantic Fishery Science 7, 137–144.

  9. HacheyH. B.: 1942, ‘The Waters of the Scotian Shelf’, Journal of the Fisheries Research Board of Canada 5, 377–397.

  10. HoughtonR. W., SmithP. C. and FournierR. O.: 1978, ‘A Simple Model for Cross-Shelf Mixing on the Scotian Shelf’, Journal of the Fisheries Research Board of Canada, 35, 414–421.

  11. JollyG. M. and SmithS. J.: 1989, ‘A Note on the Analysis of Marine Survey Data’, Proceedings of the Institute of Acoustics 11, (3), 195–201.

  12. Mahon, R., Smith, R. W., Bernstein, B. B. and Scott, J. S., 1984, ‘Spatial and Temporal Patterns of Groundfish Distributions on the Scotian Shelf and in the Bay of Fundy, 1970–1981’. Canadian Technical Report Series of Fisheries and Aquatic Sciences. 1300: ix+ 164 p.

  13. McCullaghP. and NelderJ. A.: 1983, Generalized Linear Models, Chapman and Hall. New York. 580 pp.

  14. McLellanH. J.: 1954a, ‘Temperature-Salinity Relations and Mixing on the Scotian Shelf’, Journal of the Fisheries Research Board of Canada 11, 419–430.

  15. McLellanH. J.: 1954b, ‘bottom Temperatures on the Scotian Shelf’, Journal of the Fisheries Research Board of Canada 11, 404–418.

  16. McLellan, H. J. and Trites, R. W.: 1951, ‘The Waters on the Scotian Shelf, June 1950–May 1951’, Manuscript Report of the Atlantic Oceanographic Group, St. Andrews, N. B.

  17. Parsons, D. G.: 1988, ‘Two-Phased Survey Design for Shrimp off Labrador’, Cafsac Research Document. 88/18:10p.

  18. PayneC. D. (ed.): 1986, ‘The Glim (Generalized Linear Interactive Modelling) System’, Numerical Algorithms Group, Oxford, U.K.

  19. PenningtonM.: 1985, ‘Estimating the Relative Abundance of Fish from a Series of Trawl surveys’, Biometrics 41, 197–202.

  20. PenningtonM.: 1986, ‘Some Statistical Techniques for Estimating Abundance Indices from Trawl Surveys’, Fishery Bulletin 84, 519–525.

  21. Perry, R. I., Scott, J. S. and Losier, R. J.: 1988. ‘Water Mass Analysis and Groundfish Distributions on the Scotian Shelf, 1979–84’, Nafo SCR Doc. 88/81. 14p.

  22. PetrieB. D.: 1983, ‘Current Response at The Shelf Break to Transient wind Forcing’, Journal of Geophysical Research 88C: 9567–9578.

  23. PinhornA. T. and HallidayR. G.: 1985, ‘A Framework for Identifying Fisheries Management Problems Associated with the Influence of Environmental FActors on Distribution and Migration of Marine Species’, Nafo Scientific Council Studies. 8: 83–92.

  24. ScottJ. S.: 1982, ‘Depth, Temperature and Salinity Preferences of Common Fishes of the Scotian Shelf’, Journal of Northwest Atlantic Fishery Science 3, 29–39.

  25. Smith, S. J.: 1988, ‘Abundance Indices from Research Survey Data’, in Rivard, D. (ed.), Collected Papers on Stock Assessment Methods, Cafsac Res. Doc. 88/61:16–43.

  26. SmithS. J.: 1990, ‘Use of Statistical Models for the Estimation of Abundance from Groundfish Trawl Survey’, Canadian Journal of Fisheries and Aquatic Science 47, 894–903.

  27. Tremblay, M. J. and Sinclair, M.: 1985, ‘Gulf of St. Lawrence Cod: Age-specific Geographic Distributions and Environmental Occurrences from 1971 to 1981’, Canadian Technical Report of Fisheries and Aquatic Science. 1387: iv + 43p.

Download references

Author information

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Smith, S.J., Perry, R.I. & Fanning, L.P. Relationships between water mass characteristics and estimates of fish population abundance from trawl surveys. Environ Monit Assess 17, 227–245 (1991). https://doi.org/10.1007/BF00399305

Download citation


  • Annual Change
  • Bottom Trawl
  • Fish Distribution
  • Trawl Survey
  • Interannual Change