FISHERY BULLETIN: VOL. 75, NO. 1 



Anguilla rostrata; white perch, Morone ameri- 

 cana; and Atlantic menhaden, Brevoortia 

 tyrannus. The latter species is an important 

 component of the biomass, but is taken primarily 

 inshore in the southern portion of SA 6 and is, 

 therefore, not of direct interest in the present 

 study. 



The term species, for convenience, refers to both 

 species and species groups. Terms such as other 

 pelagics, other fish, and groundfish refer to species 

 so designated in ICNAF statistical bulletins 

 (International Commission for the Northwest 

 Atlantic Fisheries 1965-1973, 1974c, 1975a). 



BOTTOM TRAWL SURVEY 

 PROCEDURES 



Autumn bottom trawl survey data have been 

 collected by the U.S. National Marine Fisheries 

 Service RV ALBATROSS IV since 1963; the RV 

 DELAWARE II has also participated infre- 

 quently. In all of these surveys, both vessels have 

 used the standard "36 Yankee" trawl with a 1.25- 

 cm stretched mesh cod end liner. This trawl 

 measures 10-12 m along the footrope and 2 m in 

 height at the center of the headrope, and is 

 equipped with rollers to make it suitable for use on 

 rough bottom (Edwards 1968). 



The area sampled extends from Nova Scotia to 

 Cape Hatteras. A stratified random sampling 

 design has been used in this survey (Cochran 

 1953); thus, the survey area has been stratified 

 into geographical zones (Figure 1) primarily on 

 the basis of depth (Grosslein 1969). During 1963- 

 66, only strata from the New Jersey coast 

 northward (1-42, Figure 1) were sampled; addi- 

 tional strata (61-76, Figure 1) were added in 

 autumn 1967 to cover the mid- Atlantic region 

 (Grosslein 10 ). An additional section covering part 

 of the Scotian Shelf was also added in 1968 but is 

 not considered in this study. 



In each cruise, sampling stations were allocated 

 to strata roughly in proportion to the area of each 

 stratum and were assigned to specific locations 

 within strata at random. A 30-min tow was taken 

 at each station at an average speed of 3.5 knots. 

 After each tow, weight and numbers captured, 

 fork length, and other pertinent data were re- 

 corded for each species. Data were summarized, 



'"Grosslein, M. D. 1968. Results of the joint USA-USSR 

 groundfish studies. Part II. Groundfish survey from Cape 

 Hatteras to Cape Cod. Int. Comm. Northwest Atl. Fish. Annu. 

 Meet. 1968, Res. Doc. No. 87, Serial No. 2075 (mimeo.), 28 p. 



audited, and transferred to magnetic tape follow- 

 ing the completion of each survey. The reader is 

 referred to Grosslein (1969, footnote 11) for 

 further details concerning survey procedures. 



Following procedures given by Cochran 

 (1953:66) we calculated stratified mean catch per 

 tow values in terms of weight by 



y, = VN 2 [au] (1) 



h = V 



where y st = stratified mean catch per tow, 

 N h = area of the hth stratum, 

 N = total area of all strata in the set, 

 ft, — mean catch per tow in the hth 



stratum, and 

 k = number of strata in the strata set. 



We calculated the estimated population variance 

 as 



S 2 = 1/A7 



k 



I 



h = l 



N h y h '- 



Ny st 2 +1^ 



/! = ! 



(N h 



1) + 



(N h - N) (N h - n h ) 



N 



m 



(2) 



where S 2 = estimated population variance, 



n h = number of tows in the hth stratum, 

 s/, 2 = variance within the hth stratum, and 

 y st , N, N h , y h , and k are defined as before. 



We used stratified mean weight per tow 

 (kilograms) in preference to numbers as an index 

 of biomass change due to its convenience when 

 working with different species groups and the 

 high degree of variability in numbers associated 

 with fluctuations in recruitment. Obviously, 

 numbers would also tend to overemphasize the 

 importance of small organisms in the community 

 under study, as pointed out by Odum and Smalley 

 (1959). 



RECENT TRENDS IN LANDINGS 



Commercial landings as reported to ICNAF 

 (International Commission for the Northwest 

 Atlantic Fisheries 1965-1973, 1974c, 1975a, 



"Grosslein, M. D. 1969. Groundfish survey methods. NMFS, 

 Woods Hole, Mass., Lab. Ref. No. 69-2, 34 p. 



