Hunt et al.: Movement of Gadus morhua in the Gulf of Maine area 



843 



results from experiments conducted between 1923 

 and 1960. An earlier summary of cod tagging stud- 

 ies is given in Wise ( 1963 ). Templeman ( 1962 ) pro- 

 vided a comprehensive summary of the basis for 

 separating cod stocks in the northwest Atlantic 

 using meristic and results of tagging experiments 

 and concluded "there are Browns Bank and east- 

 ern Georges Bank stocks, probably essentially 

 separate as spawning stocks but with some inter- 

 migration in both directions across the Fundian 

 Channel and some intermingling of both these 

 stocks with those of southwestern Nova Scotia." 

 In general, results of these early experiments in- 

 dicate substantial movement of cod within the 4X 

 area and to a lesser extent to and from the adja- 

 cent 5Y and 5Ze areas. The pattern of recapture 

 locations shows a general dispersal from the area 

 of release and some increase in the number of cod 

 moving with elapsed time. However, it is difficult to 

 interpret these studies as proportional movements 

 because landings and effort are generally not avail- 

 able for weighting probability of recapture by area. 

 Canada has conducted a number of tagging 

 studies on cod in the Browns Bank, Georges Bank, 

 and Bay of Fundy areas since the 1970s. Studies 

 conducted between 1994 and 1996 were part of a 

 co-operative research study involving Canada and 

 the United States. This report provides an inter- 

 pretation of cod movements in the Gulf of Maine 

 area based on results of recaptures of cod tagged 

 in the 1979-97 time period. 



Methods 



Canada has conducted stratified random bottom 

 trawl surveys in the Gulf of Maine since 1970 and 

 on Georges Bank since 1986. The United States 

 has also conducted similar surveys in the spring 

 (1968) and fall (1963) of each year. Indices of abun- 

 dance derived from these surveys are routinely 

 used in stock assessment models to estimate popu- 

 lation abundance (Hunt and Buzeta, 1996), and 

 they provide a synoptic view of cod distributions 

 in the Gulf of Maine area during both spawning 

 and postspawning seasons. The mean catch per 

 tow, aggregated by ten-min latitude and longitude 

 squares, was calculated for the U.S. spring and fall 

 research-vessel time series. These surveys cover most 

 of the Gulf of Maine area, compared with the Cana- 

 dian summer survey (4X only) and Canadian winter 

 survey (5Ze only), and therefore provide a distribu- 

 tion pattern for cod in the entire study area. 



Tagging locations were determined from areas of 

 high catch rates in research vessel surveys, as well 



TD 68 66 64 



-46 



5Zo 



5Zn 



70 



69 



— 1 — 

 68 



67 



66 



65 



63 



Figure 1 



North Atlantic Fislieries Organization (NAFO) division (4X, 5Y. 

 5Z) and unit areas (eg. 5Zj) boundaries in the Gulf of Maine area 

 and cod tag release locations. The dashed lines indicates the In- 

 ternational Maritime Boundary line between Canada and the 

 United States. 



as the location and timing of historical cod spawn- 

 ing activity. Additional tagging was completed dur- 

 ing other times in areas of fishing activity or special 

 interest locations. Fishing trials were used to iden- 

 tify sites with high catch rates and at least BOVe cod 

 composition, and new sites were selected when catch 

 rates or cod composition declined. Typically, once an 

 aggregation of cod was located, fishing and tagging 

 continued at that site for 1-2 days. Areas with high 



