CHANGES IN BIOMASS OF FINFISHES AND SQUIDS FROM THE GULF OF MAINE TO CAPE HATTERAS, 1963-74, AS DETERMINED FROM RESEARCH VESSEL SURVEY DATA

Trends in finfish and squid biomaBB for the 1963·74 period in the International Commission for the Northwest Atlantic Fisheries (lCNAF) 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 le~er 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, Melanogrammusaeglefinus; 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 ofchanges in species composition were also observed, in that white hake, Urophycis tenuis; Atlantic mackerel, Scomber scombrus; and squids, Loligo pealei and Illex 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 GulfofMaine areas) reveal unacijusted 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 acijusting 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 108 tons, one·fourth ofthe estimated virgin biomaBBlevel and one·halfofthe level corresponding to maximum sustainable yield.