CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS 



the early and mid-1960's and noted that while the 

 decrease had obviously been greater in the case of 

 species for which there were directed fisheries, 

 declines had nevertheless been general. Gross- 

 lein 8 examined autumn research vessel survey 

 data (stratified mean catch per tow, pounds) for 

 the 1963-71 period for southern New England and 

 Georges Bank (strata 1-12, 13-23, and 25, Figure 

 1) and observed reductions in abundance of over 

 90% for haddock and ocean pout, Macrozoarces 

 americanus, and more moderate reductions in 

 other components of the groundfish community. 

 Overall, Grosslein's data indicated declines in 

 finfish biomass of 62% and 74% for southern New 

 England and Georges Bank strata, respectively. 

 Brown et al. (see footnote 4) presented additional 

 analyses of Grosslein's data and documented 

 pronounced declines for nearly all groundfish 

 species or species groups, skates (Raja spp.), and 

 sea herring; the decline for all species combined 

 (with individual species weighted by cumulative 

 landings for the 1962-71 period) was 64%. Brown 

 et al. (in press) updated these analyses by includ- 

 ing 1972 data and found an overall decline of 56%. 



Since 1950, fishery management in the 

 northwest Atlantic region has been conducted 

 under the auspices of ICNAF, an international 

 body currently consisting of 18 member nations 

 pledged to cooperate in research and management 

 of marine fishery resources in the northwest 

 Atlantic area. This Commission, after considering 

 the advice of various standing committees and 

 subcommittees, formulates regulations, estab- 

 lishes quotas or "total allowable catches" (TAC's), 

 and handles other matters necessary for the 

 conservation of fish stocks in the seven regions 

 composing the ICNAF Convention Area. The 

 present study is concerned with the southernmost 

 regions within this area adjoining the U.S. coast 

 (ICNAF Subarea 5 and Statistical Area 6, Figure 

 1, hereafter referred to as SA 5 and 6). 



In response to accumulating evidence indicat- 

 ing biomass declines in SA 5 and 6, STACRES in 

 1973 recommended an overall TAC for this area 

 for 1974 (International Commission for the 

 Northwest Atlantic Fisheries 1974d). Accord- 



8 Grosslein, M. D. 1972. A preliminary investigation of the 

 effects of fishing on the total fish biomass, and first approxi- 

 mations of maximum sustainable yield for finfishes in ICNAF 

 Division 5Z and Subarea 6. Part I. Changes in the relative 

 biomass of groundfish in Division 5Z as indicated by research 

 vessel surveys, and probable maximum yield of the total 

 groundfish resource. Int. Comm. Northwest Atl. Fish. Annu. 

 Meet. 1972, Res. Doc. No. 119, Serial No. 2835 (mimeo.), 20 p. 



ingly, a TAC of 923.9 x 10 3 tons was adopted by 

 the Commission for 1974 to stabilize biomass 

 levels (International Commission for the 

 Northwest Atlantic Fisheries 1974a); for 1975, 

 this figure was reduced to 850 x 10 3 tons (In- 

 ternational Commission for the Northwest At- 

 lantic Fisheries 1974b). In addition, STACRES 

 further recommended that biomass levels, as 

 measured by bottom trawl surveys, be used to 

 monitor the effect of this regulation (International 

 Commission for the Northwest Atlantic Fisheries 

 1974d). 



The validity of such an approach is well 

 documented. Grosslein (1971) has presented 

 evidence that abundance indices derived from 

 bottom trawl surveys are of sufficient accuracy to 

 monitor major changes in stock size; for selected 

 groundfish species, current levels of sampling 

 appear adequate to detect changes on the order of 

 50%. Similarly, Schumaker and Anthony (see 

 footnote 7) and Anderson 9 have found that trends 

 in bottom trawl survey data accurately reflect 

 major changes in stock abundance for pelagic 

 species (herring and Atlantic mackerel, Scomber 

 scombrus, respectively). 



The objective of the present study was to further 

 investigate changes in biomass of finfishes and 

 squids in SA 5 and 6 as evidenced by trends in U.S. 

 research vessel survey data. In this study, we have 

 expanded on previous analyses of untransformed 

 data (Grosslein see footnote 8; Brown et al. see 

 footnote 4; Brown et al. in press) so as to include all 

 available data from SA 5 and 6 for the 1963-74 

 period. In addition, we have attempted to com- 

 pensate for anomalies in survey catch data and 

 bias resulting from catchability differences by 

 transforming and weighting data by species and 

 summarizing resulting values to provide com- 

 bined biomass estimates by year. We believe that 

 the resulting trends obtained are more realistic 

 than those derived from unadjusted survey data. 



In this paper, we define biomass as consisting of 

 weight of all species of finfishes and squids re- 

 ported to ICNAF, excluding other invertebrates 

 and large pelagic species such as swordfish, 

 Xiphias gladius; sharks other than dogfish 

 (Squalus acanthias and Mustelus canis); and 

 tunas, Thunnus spp. We have also chosen to 

 exclude inshore species such as American eel, 



9 Anderson, E. D. 1973. Assessment of Atlantic mackerel in 

 ICNAF Subarea 5 and Statistical Area 6. Int. Comm. Northwest 

 Atl. Fish. Annu. Meet. 1973, Res. Doc. No. 14, Serial No. 2916 

 (mimeo.), 37 p. 



