CHANGES IN BIOMASS OF FINFISHES AND SQUIDS FROM 



THE GULF OF MAINE TO CAPE HATTERAS, 1963-74, 

 AS DETERMINED FROM RESEARCH VESSEL SURVEY DATA 



Stephen H. Clark and Bradford E. Brown 1 



ABSTRACT 



Trends in finfish and squid biomass for the 1963-74 period in the International Commission for the 

 Northwest Atlantic Fisheries (ICNAF) Subarea 5 and Statistical Area 6, as evidenced by autumn 

 bottom trawl survey data, were reviewed. Commercial statistics reported to ICNAF reveal that 

 landings for groundfish species of major commercial importance peaked in 1965 and subsequently 

 declined with shifts in directed effort to major pelagic species (for which landings peaked in 1971). 

 Trends in landings for species of lesser commercial importance primarily reflect increasing effort 

 throughout this period. 



Relative abundance indices (stratified mean catch in kilograms per tow) from the autumn bottom 

 trawl survey revealed drastic declines in abundance of haddock, Melanogrammus aeglefinus; silver 

 hake, Merluccius bilinearis; red hake, Urophycis chuss; and herring, Clupea harengus, during this 

 period although decreases were observed for nearly all finfish species of commercial importance. 

 Possible evidence of changes in species composition were also observed, in that white hake, Urophycis 

 tenuis; Atlantic mackerel, Scomber scombrus; and squids, Loligo pealei and lllex illecebrosus , have 

 shown pronounced increases in relative abundance in recent years coincident with declines in other 

 species occupying similar ecological niches. Analysis for four strata sets (Middle Atlantic, southern 

 New England, Georges Bank, and Gulf of Maine areas) reveal unadjusted declines in biomass ranging 

 from 37% on Georges Bank to 74% in the Middle Atlantic area; by combining data for all strata, a 

 decline of 32% was obtained for the 1967-74 period (including the Middle Atlantic section, added in 

 1967), while for all remaining strata (1963-74) the corresponding figure is 43%. By adjusting biomass 

 components according to catchability and computing stock size estimates for the entire biomass, a 65% 

 decline was obtained for all strata (including the Middle Atlantic) using untransformed abundance 

 indices, and a 66% decline was computed from retransformed abundance indices. For the remaining 

 strata (Middle Atlantic strata excluded) declines of 47% and 46% were obtained, respectively. By 

 combining these data sets, the corresponding figures were 51% and 47%. Stock size estimates for 1975 

 approximated 2.0 x 10 e tons, one-fourth of the estimated virgin biomass level and one-half of the level 

 corresponding to maximum sustainable yield. 



The continental shelf waters of the northwest 

 Atlantic adjacent to the U.S. coast support a 

 valuable and productive fishery resource. Prior to 

 1960, this area was exploited almost exclusively 

 by a coastal fleet of U.S. vessels of under 300 gross 

 registered tons. Landings averaged less than 500 

 x 10 3 tons 2 annually (International Commission 

 for the Northwest Atlantic Fisheries 1953-1961), a 

 level substantially lower than the estimated 

 maximum sustainable yield (MSY) of approx- 

 imately 950 x 10 3 tons obtained for this area by 

 various investigators (Au 3 ; Brown et al. 4 ; Brown 



•Northeast Fisheries Center, National Marine Fisheries 

 Service, NOAA, Woods Hole, MA 02543. 



2 Landings and estimated stock levels in this paper are given in 

 terms of metric tons. 



3 Au, D. W. K. 1973. Total sustainable finfish yield from 

 Subareas 5 and 6 based on yield per recruit and primary pro- 

 duction consideration. Int. Comm. Northwest Atl. Fish. Annu. 

 Meet. 1973, Res. Doc. No. 10, Serial No. 2912 (mimeo.), 7 p. 



4 Brown, B. E., J. A. Brennan, E. G. Heyerdahl, M. D. Gross- 



et al. in press). In the early 1960's, however, 

 distant-water fleets of the U.S.S.R., Poland, and 

 other nations entered the fishery and as that dec- 

 ade progressed these fleets underwent continual 

 modernization and expansion. As a result, fishing 

 effort and landings have increased greatly in this 

 area in recent years. Brown et al. (in press) es- 

 timated that during the 1961-72 period stan- 

 dardized effort increased sixfold, while landings 

 more than tripled. Assessments now indicate that 

 all major stocks in this area are fully exploited and 

 some, notably haddock, Melanogrammus 

 aeglefinus, and herring, Clupea harengus, on 

 Georges Bank and yellowtail flounder, Limanda 

 ferruginea, off southern New England have been 



lein, and R. C. Hennemuth. 1973. An evaluation of the effect of 

 fishing on the total finfish biomass in ICNAF Subarea 5 and 

 Statistical Area 6. Int. Comm. Northwest Atl. Fish. Annu. Meet. 

 1973, Res. Doc. No. 8, Serial No. 2910 (mimeo.), 30 p. 



Manuscript accepted September 1976. 

 FISHERY BULLETIN: VOL. 75, NO. 1, 1977. 



