Perspectives provided by bottom trawl transect surveys conducted in the 1950s and 1960s on the dynamics of commercially exploited groundfish species on southern Grand Bank and St. Pierre Bank

Abstract

Biomass estimates for Atlantic cod, haddock, American plaice and yellowtail flounder in NAFO divisions 3NO and Subdivision 3Ps were calculated from research vessel bottom trawl (RV) surveys conducted in the 1950s and 1960s using a transect survey design. Although these data are not currently included in resource assessment, they represent some of the earliest available data for these stocks and provide a means to examine population dynamics prior to the start of the stratified random surveys. Analyses of the survey data demonstrates that there was a deepening in the distribution of cod, haddock and American plaice, in 3Ps in response to changes in water temperatures during the late 1980s and early 1990s, and that this accounted for much of the reduction in biomass in shallow waters. Comparisons of RV estimates of population parameters with those from Sequential Population Analyses for cod in 3NO and 3Ps concluded that the latter provided valid measures of changes in population during the 1960s and 1970s.