NEVES: OFFSHORE DISTRIBUTION OF ALEWIFE AND BLUEBACK HERRING 



Table l. — Summary of seasonal bottom trawl surveys con- 

 ducted by U.S. research vessels between Cape Hatteras, N.C., 

 and Nova Scotia, 1963-78. 



Pertinent survey station and catch data in- 

 cluded date, location, time, depth, bottom and sur- 

 face water temperatures, and number and length 

 frequencies of river herring captured. Only 

 catches of 10 or more alewives or blueback 

 herring/trawl tow were used in this study. I plotted 

 catch locations from all surveys (Table 1) by 10' 

 rectangles of latitude and longitude on depth con- 

 tour maps according to month or season. Locations 

 of catches during spring ( March-May) and autumn 

 (September- November) were plotted by month, al- 

 though cruise direction and time schedules influ- 

 enced date of sampling within the survey area. 

 Surveys in summer (June-August) and winter 

 (December- February) were grouped by season be- 

 cause sampling effort and catch frequency were 

 lower during these seasons. Commercial catches 

 reported to the International Commission for the 

 Northwest Atlantic Fisheries (ICNAF^) by 

 member nations from 1970 to 1978 were provided 

 by Hodder.^ These catch data were used to locate 

 U.S. and foreign catches of river herring within 

 each ICNAF division and were correlated with 

 distribution patterns based on survey data. Sur- 



''ICNAF was replaced by the Northwest Atlantic Fisheries 

 Organization (NAFO) in January 1980, 



^V. M. Hodder, ICNAF Office, Dartmouth, N.S., Canada B2Y 

 3Y9, pers. commun. July 1977, June 1980. 



face and bottom temperatures (to the nearest 1° C) 

 and depths were plotted for each trawl tow that 

 collected 10 or more alewives or blueback herring. 



RESULTS 



Bottom trawling at 9,194 stations during the 36 

 survey cruises yielded 37,313 alewives at 512 sta- 

 tions and 3,058 blueback herring at 96 stations 

 within the survey area. The fish ranged from 6 to 

 35 cm fork length. Water temperatures recorded at 

 approximately 95% of these collecting stations 

 were used to plot catch frequency at 1° C intervals. 

 Water temperatures at stations where alewives 

 were collected ranged from 2° to 23° C at the sur- 

 face (Figure 2) and from 3° to 17° C at the bottom 

 (Figure 3). Surface temperatures at stations with 

 blueback herring ranged from 2° to 20° C and 



80 



60 



o 

 §30 



z 



20 



J 



I BLUEBACKS 

 *Q| ALEWIVES 



8 9 10 11 12 13 14 15 16 17 

 BOTTOM TEMPERATURE °C 



FIGURE 3. — Bottom temperatures at stations where alewives 

 and blueback herring were collected during bottom trawl sur- 

 veys, 1963-78, Cape Hatteras, N.C., to Nova Scotia. 



Figure 2. — Surface temperatures at stations 

 where alewives and blueback herring were 

 collected during bottom trawl surveys, 1963-78, 

 Cape Hatteras, N.C., to Nova Scotia. 



100 

 90 

 80 

 70 



I 60| 



30 

 20 

 10 



I 



I BLUEBACKS 

 Q( ALEWIVES 



llLdUiJfc- 



M « 



10 11 12 13 14 15 16 17 18 19 20 21 22 23 



SURFACE TEMPERATURE °C 



475 



