912 



Fishery Bulletin 97(4), 1999 



and were linked into progressively larger groups until 

 they formed a single large group. This analysis ex- 

 amines the relationships between individuals in the 

 entire population. 



We postulate that the significant long-term asso- 

 ciations observed were based on genealogical rela- 

 tionships. Judged from known relationships (moth- 

 ers and offspring born during the study), the strength 

 of bonds among individuals within pods appeared 

 directly correlated with their degree of relatedness. 



20 

 30 

 40 

 50 

 60 

 70 

 80 

 90 

 100 



D3 



27 

 Ills 



•17 



944 



AIO39 



ns 



-35 



1054 



102 101 



•25 



1005 



AI01 d AI02C5 



-29 



-36 



835 



AlOSd 



AI06 



d 



A1049 



AID? cse) 



Figure 8 



Top: dendro^am illustrating intrapod groups and relationships among 

 individuals with CAI values calculated at the population level. (Rela- 

 tionships among intrapod groups' shown in Figure 2.1 Middle: matrix 

 showing CAI values between pairs of individuals calculated at the pod 

 level for AI pod. Numbers at the base of each column in the matrix are 

 the numbers of valid photo sequences in which that individual appears. 

 Bottom: inferred genealogical trees. 



Our findings that resident killer whales in Prince 

 William Sound are organized in statistically identi- 

 fiable pods and intrapod groups are similar to re- 

 sults from studies of resident killer whales in Brit- 

 ish Columbia and Washington State (Heimlich- 

 Boran, 1986; Bigg et al., 1990). Bigg et al. (1990) 

 defined a pod as a group of individuals that traveled 

 together at least 50% of the time. All the resident 

 pods described in Prince William Sound fit that defi- 

 nition. Pod membership is also supported by pod- 

 specific vocal dialects in both areas (Bigg 

 et al., 1990; Ford, 1991; Fordi). 



Pod delineations based on direct obser- 

 vation were supported by association 

 analysis in all but two cases. Both dis- 

 crepancies appeared in the final stages 

 of the agglomerative linking procedure. 

 Although each pod was a distinct clus- 

 ter, AD 16 pod was found to be linked to 

 AK pod with a PCC value of eight, at 

 somewhat higher than the level of link- 

 age between other pods. This was not 

 supported by direct observation and was 

 apparently an artifact of small sample 

 size. AD 16 pod was infrequently photo- 

 graphed and was often part of multipod 

 groups that included AK pod. 



The ABIO subpod was linked with AI 

 pod (PCC=4) before being linked with 

 other members of AB pod. AI pod fre- 

 quently traveled with AB pod early in the 

 study, and we suspect that AI pod (7 

 whales in 1996 ) was in the final stages of 

 a gi-adual split from the then 35-member 

 AB pod when the study began in 1984. 

 AI pod traveled more independently of AB 

 pod in later years. The pod-specific dia- 

 lects for AI and AB pods are very similar 

 (Ford^), supporting this hypothesis. The 

 preponderance of adult males in AI pod (4 

 out of 7 whales in 1996) may have contrib- 

 uted to the independence of this matrilin- 

 eal group. Bigg et al. (1990) found that 

 matrilineal groups with a high percentage 

 of males tend to travel more independently. 

 This was also evident for the ABIO subpod, 

 in which 3 out of 4 members were adult 

 males. ABIO subpod often traveled a dis- 

 tance away fi-om the remainder of AB pod. 

 Direct observation and photographic 

 analysis also indicated that some males 



108 

 04 



D6 



05 



loe 



01 



Ford, J. K. B. 1997. Vancouver Public Aquarium, 

 P.O. Box 3232, Vancouver, B.B., Canada. Personal 

 commun. 



