FISHERY BULLETIN: VOL. 83, NO. 4 



69° 



68° 67' 



66' 



42' 



41" 



GEORGES BANK SPRING ASSEMBLAGES 



42° - 



41° 



NORTHEAST PEAK, 



''d^ 



«^ 



INTERMEDIATE 



69° 68° 67° 66° 



GEORGES BANK FALL ASSEMBLAGES 



Figure 5.— Composite maps showing seasonal changes in the 

 Georges Bank assemblages and their approximate areas. NPI = 

 Northeast Peak Interior; NP-GM Deep = Northeast Peak-Gulf of 

 Maine Deep; GM Deep = Gulf of Maine Deep. 



mining the distribution of fish. The Northeast Peak 

 assemblage, for instance, spans several depth zones 

 and encroaches on the Shallow assemblage, reducing 

 its area during this part of the year. 



The assemblage maps presented in Figure 5 were 

 useful for organizing the 36 species of Ikble 1 into 

 their corresponding demersal subunits (Tkble 2). 

 Four basic species categories were defined in the 

 various assemblages. These included ubiquitous 

 species, resident species, periodics, and those resi- 

 dent species present in several assemblages during 

 different parts of their life history. Ubiquitous 

 species, such as ocean pout, goosefish, sea raven, and 

 Atlantic cod, were found with regularity in almost 

 all of the assemblages. Resident species, such as lit- 

 tle skate, winter skate, longhorn sculpin, yellow tail 

 flounder, winter flounder, American plaice, and 

 witch founder, were present in only one or two 



assemblages in abundance Periodic or seasonal 

 migrants include bluefish, butterfish, and mackerel, 

 as well as short-finned squid and long-finned squid. 

 These species moved in and out of the various assem- 

 blages on a seasonal basis with temperature being 

 a likely dominant force, and were often highly 

 variable in terms of their abundance and were there- 

 fore not included in Ikble 2. 



A number of species, including silver hake, red 

 hake, white hake, and haddock, were present in more 

 than one assemblage as different life history stages. 

 Silver hake, for example, are found in the Slope and 

 Canyon and Shallow assemblages, with adults on the 

 average, occurring more frequently in the Slope and 

 Canyon and Gulf of Maine Deep assemblage, while 

 juveniles are more abundant in the Shallow assem- 

 blage. It appears that for many of the abundant fish 

 species on Georges Bank, adults occupy the deeper 

 peripheral assemblages while juveniles of these same 

 species occupy the shallower zones during much of 

 the year. 



ASSEMBLAGE TRAJECTORIES 



Assemblage CPUE indices were calculated for 

 several of the spring and fall assemblages and used 

 for evaluating temporal trends in total catch and 

 catch by species. Assemblage CPUE declined drama- 

 tically in the mid-1960's to early 1970's in four of 

 five Georges Bank assemblages in fall (Fig. 6). In par- 

 ticular, research catches in the Shallow, Northeast 

 Peak, and Gulf of Maine Deep assemblages reached 

 all-time lows in the early 1970's, coincident with 

 large increases in international effort and landings 

 at that time (Figs. 6, 7). International effort, mea- 

 sured in thousands of days fished, increased three- 

 fold over the period 1960-69 (Fig. 7). Assemblage 

 biomass showed some signs of recovery in the late 

 1970's when good year classes of Atlantic cod, had- 

 dock, and other species occurred and international 

 effort declined due to the Magnuson Fishery Con- 

 servation and Management Act of 1976 (Figs. 6, 7). 



Research catch of silver hake, fourspot flounder, 

 red hake, white hake, and black belly rosefish re- 

 mained nearly stable over the spring period 

 (1968-75), then increased abruptly after 1976 due to 

 increases in the silver hake (Fig. 8A). 



Total catch for the fall time series was also stable 

 for most years, until 1972 when silver hake and red 

 hake abundance fluctuated (Fig. SB). 



Figure 8C shows the trends in percent by weight 

 for the five species during fall indicating a change 

 in biomass dominance for silver hake and red haka 

 Blackbelly rosefish and fourspot flounder showed the 



512 



