Stone and Jessop: Seasonal distribution of Alosa pseudoharengus and A. aestivalis 



383 



spring 



summer 



Season 



Figure 6 



Mean catch-per-set of river herring in day and night collec- 

 tions from spring, summer, and fall groundfish surveys, 

 1979-84, conducted off the Atlantic coeist of Nova Scotia. Ver- 

 ticaJ bars represent + 1 SE. Number of tows is indicated above 

 error bars. 



Survey catch indices and NAFO landings 



Seasonal catch indices (annual mean number and 

 weight of river herring per set) from research vessel 

 surveys were uncorrelated with NAFO bycatch data 

 for the Scotian Shelf-Bay of Fundy area (4VWX) 

 (Table 3). However, landings from the central and 

 eastern shelf (4 VW) were significantly correlated with 

 spring (1979-89) survey indices. The relationship be- 

 tween mean weight index and 4VW NAFO landings 

 (Fig. 7) gave the highest Spearman rank correlation 

 coefficient (r^ 0.74). 



Seasonal length-composition 

 and distribution 



River herring from bottom-trawl collections 

 measured 5-33cmFL (x 23.7cm; Table 4). 

 Mean fork length in spring catches was less 

 than in summer or fall. Fork lengths of river 

 herring from foreign and domestic fisheries 

 were 22-33cm (i 29.6cm) and were of 

 comparable size in spring and summer sam- 

 ple collections. The larger size of bycatch 

 fish compared with those from bottom-trawl 

 surveys is probably due to the larger cod end 

 mesh size (6 cm stretched) of commercial 

 gear permitting escapement of smaller fish. 

 In all seasons, large river herring (>19 

 cmFL) were more abundant than small 

 «19cm) fish (Fig. 8). Polymodal length- 

 frequency distributions indicated the 



Table 3 



Spearman rank correlation coefficients for river herring (Alosa 

 spp.) catch indices from spring (1979-89), summer (1970-89), 

 and fall (1978-84) groundfish surveys vs. NAFO landings from 

 the Scotian Shelf-Bay of Fundy (4VWX) and the central and 

 eastern Scotian Shelf (4VW). (n = number of years; * signif- 

 icant at P<0.05; "significant at P<0.01). 



NAFO areas 



Spring 

 (nil) 



Summer 

 (n20) 



Fall 

 (n7) 



Mean catch/set ■ yr ' 



4VWX -0.23 -0.15 -0.07 



4VW 0.60* -0.01 -0.18 



Mean weight/set • yr"' 



4VWX -0.19 -0.17 -0.29 



4VW 0.74*' -0.05 -0.09 



Table 4 



River herring (Alosa spp.) fork-length statistics by season from ground- 

 fish surveys conducted by the Canadian Department of Fisheries and Oceans 

 and from foreign and domestic bycatches recorded by Canadian Interna- 

 tional Observers. All fork lengths were truncated at 33cm (see 'Materials 

 and methods' for explanation). SD = sample standard deviation. 



Fork length (cm) 



Season 



Years 



SD 



range 



Groundfish survey data 



Spring (Feb-Apr) 1979-89 7543 22.7 5.08 5.0-33.0 



Summer (June-July) 1970-89 3167 25.4 3.77 9.0-33.0 



Fall (Sept-Dec) 1978-84 1512 24.8 4.92 5.0-33.0 



Combined 1970-89 12213 23.7 4.91 5.0-33.0 

 Bycatch data 



Spring (Feb-May) 1980-89 1754 29.4 2.14 20.0-33.0 



Summer (June- Aug) 1980-89 249 30.4 1.45 26.0-33.0 



Combined 1980-89 2032 29.6 2.13 20.0-33.0 



