Smith and Morse Larval distribution patterns of Oupea harengus or\ the Georges Bank 



343 



<2 weeks 



5 to 8 weeks 



■€■ 



2 to 5 weeks 



■<?"- 



<r- 



if < 



>8 weeks 



Figure 5 



Composite representation of the distribution of Atlantic herring Clupea harengus larvae by age in the Georges Bank area, 1985-87. 



larval distribution patterns through the 1990 spawn- 

 ing season that the historically prominent spawning 

 beds on eastern Georges Bank had been reoccupied. 



Discussion 



The literature contains conflicting descriptions of the 

 herring population structure in the western North At- 

 lantic, lies & Sinclair (1982) hypothesized that the 

 number of Atlantic herring spawning stocks in the Gulf 

 of Maine region is determined by the number of 

 geographically-stable larval retention areas. They rec- 

 ognized four stocks: southwest Nova Scotia, Grand 

 Manan, Georges Bank, and Nantucket Shoals. Sinclair 

 & lies (1985) revised the stock structure to include 

 Jeffreys Ledge, coastal Gulf of Maine, and Scots Bay 

 Both lies & Sinclair (1982) and Sinclair & lies (1985) 

 further hypothesized that (1) stocks are segregated only 

 during autumn when herring return to their respec- 

 tive spawning grounds, (2) larvae of different stocks 

 do not intermix for several months after hatching, the 

 period when imprinting occurs, and (3) hydrographic 



conditions create retention areas by isolating larvae in 

 vertically-mixed areas surrounded by stratified waters. 

 Their retention hypothesis recognized that the geo- 

 graphic extent of the retention areas could vary annu- 

 ally and that some horizontal displacement could oc- 

 cur during larval development. 



Grosslein ( 1987) reviewed the stock structure of her- 

 ring in the Gulf of Maine region using the collective 

 evidence from prior studies. He concluded that the 

 population was composed of three major stocks: Georges 

 Bank, western Nova Scotia, and the Gulf of Maine, 

 with lesser spawning occurring elsewhere around the 

 gulf. Grosslein indicated, however, that this breakdown 

 was speculative and that direct attempts to differenti- 

 ate between stocks through larval surveys, tagging 

 studies, meristic and morphometric characters, bio- 

 chemical methods, and parasitology produced incon- 

 clusive results. 



Smith & Jamieson (1986) argued that no scientific 

 basis existed for the stock concepts of Atlantic herring 

 in either the eastern or western North Atlantic. They 

 viewed the breakdown of herring stocks as transient 

 subdivisions having no taxonomic or evolutionary 



