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Fishery Bulletin 88(2), 1990 



that Loligo is a principal prey item of pilot whales in 

 the shelf waters of the mid-Atlantic during late winter 

 and early spring. It also seems apparent that Atlantic 

 mackerel could be considered an important prey of pilot 

 whales in the mid-Atlantic. This conclusion is based on 

 the observations of pilot whales feeding around and in 

 the opening of the mackerel trawls, the occurrence of 

 mackerel in the stomachs of two pilot whales taken in 

 the Atlantic mackerel fishery, and the high incidence 

 of mortality in the Atlantic mackerel fishery. It is possi- 

 ble, however, that feeding on Atlantic mackerel is an 

 opportimistic phenomenon related to fisheries only, and 

 that pilot whales do not otherwise prey significantly 

 on mackerel. 



Sex and maturity of common dolphins and 

 pilot whales taken in foreign fishing operations 



It is likely that most of the common dolphins killed in 

 the Loligo and Atlantic mackerel fisheries were sex- 

 ually immature. Estimates of total length at sexual 

 maturity for male common dolphins are extremely 

 variable between populations (Hui 1979, Perrin and 

 Reilly 1984, Collett and Saint-Girons 1984). Collett and 

 Saint-Girons (1984) found that, in the northeast Atlan- 

 tic, sexual maturity in male common dolphins is reached 

 at 200 cm, with animals <190 cm prepubescent. Sev- 

 eral species of dolphins, including common dolphins, 

 are known to travel in herds segregated by age and 

 sex. In the northwest Atlantic, segregation by age and 

 sex has been found in bottlenose dolphins (Irvine et al. 

 1981, Shane et al. 1986) and the harbor porpoise 

 (Gaskin 1982). Irvine et al. (1981) found that subadult 

 males formed bachelor groups, and sexually mature 

 adult males rarely mixed with subadult males. Also, 

 male and subadult female dolphins may follow fishing 

 nets more often than females with calves. The dolphins 

 reported in Table 6 were not captured simultaneously 

 (i.e., having come from one group or pod) but rather 

 were captured on several separate occasions. Although 

 female common dolphins with calves have been ob- 

 served in the areas of foreign fishing activity, none 

 have been captured during trawling operations. 



The size/sex composition of pilot whales killed in the 

 Atlantic mackerel fishery indicates that most of the 

 animals were sexually mature females. The size and sex 

 ratios of pilot whales killed in the Atlantic mackerel 

 fishery are similar to those ratios observed from pilot 

 whale mass strandings in New England waters (Greg 

 Early, New England Aquarium, Boston, MA, pers. 

 commun.. May 1988). Pilot whales are gregarious and 

 social groupings are believed to be comprised of several 

 sexually mature females and a few mature males (Mar- 

 tin et al. 1987). 



Incidental take of common 

 dolphins and pilot whales relative to 

 available abundance estimates for each species 



Estimates of the total number of common dolphins and 

 pilot whales are available both for the shelf-edge alone 

 and the combined all-shelf and shelf-edge waters of the 

 northeastern United States (an area which is contained 

 within the EEZ) by season (CETAP 1982). These esti- 

 mates are based on standardized aerial surveys con- 

 ducted during November 1978-January 1982, using 

 line-transect methodology. Althf)ugh these estimates 

 are not for the same time period as the majority of the 

 incidental take described in this paper, and these esti- 

 mates have very high degrees of uncertainty (e.g., stan- 

 dard deviations of the estimates equal to the estimates 

 themselves), they are the only population estimates 

 available which can provide an indication of the relative 

 magnitude of these incidental takes. 



The shelf-edge abundance estimate for common 

 dolphins during winter (most incidental takes for this 

 species occurred during Deceml)er and February) is 

 15,703 (CV 0.78) (CETAP 1982, table 17, p. 261).'The 

 average take per year for 1977-88 was 17 and 39 in 

 1984-88. These takes represent 0.11% and 0.25% of 

 the winter abundance estimate. The maximum annual 

 rate of take based on this winter abundance estimate 

 was 0.48 (« = 76) in 1986 and was nearly twice the 

 1984-88 average. 



Similar CETAP shelf-edge estimates for pilot whales 

 during spring and summer are 6823 (C V 0.52) (spring) 

 and 5251 (CV 079) (summer) (CETAP 1982, table 15, 

 p. 233). The average take per year for 1977-88 was 

 25 and 46 in 1984-88. These takes represent 0.37% and 

 0.67% (spring) and 0.48% and 0.88% (summer) of the 

 average seasonal abundance estimates for this species. 

 The maximum annual rate of take based on the spring 

 and summer abundance estimates, respectively, were 

 2.01% and 2.70% (n = 142) in 1988 and were three 

 times the 1984-88 spring and summer rates of take. 

 The shelf-wide abundance estimates for common 

 dolphins 31,124 (CV 0.59) (winter), and pilot whales 

 1 1 ,4 17 (C V 0.37) (spring) and 9808 (C V 0.66) (summer) 

 are nearly twice the shelf-edge estimates, which re- 

 duces the above estimated rates of incidental take by 

 nearly 50% if animals from the shelf-edge and shelf are 

 considered as a single population. 



To place pilot whale takes within the EEZ in perspec- 

 tive, present pilot whale incidental kill levels are com- 

 parable with recent mass strandings in New England 

 waters (Greg Early, New England Aquarium, Boston, 

 MA, pers. commun., May 1988). They do not approach 

 the mortalities reported by Mercer (1975) for the 

 historical Newfoundland drive fisheries (1948-71: Total 

 54,248; average 2260/yr). The impact of trophic 



