Abstract. -The relationship be- 

 tween latitude and birth timing was 

 assessed for captive-born California 

 sea lions (Zalophus californianus), 

 northern (Steller) sea lions 

 (Eumetopias jubatus), northern fur 

 seals (Callorhinus ursinus), and Pa- 

 cific harbor seals iPhoca vitulina 

 richardsi) from zoos and aquaria in 

 the United States, Canada, South 

 Korea, and New Zealand. The births 

 of 466 viable California sea lion pups 

 demonstrated highly significant, 

 negative and curvilinear latitudinal 

 variation in birth timing. Over the 

 latitudinal range of captive births, 

 this variation accounted for a change 

 of approximately -0.6 days/°latitude. 

 Furthermore, the variances of the 

 mean dates of birth for the largest 

 18 captive populations were signifi- 

 cantly dependent upon latitude; 

 shorter birthing periods occurred at 

 higher latitudes. Northern sea lions 

 (n=9) had a similar, but non-signifi- 

 cant latitudinal relationship in 

 which birthing dates occurred ap- 

 proximately 30 days later. No sig- 

 nificant relationship between lati- 

 tude and birthing date was found 

 for northern fur seals (rc=13). The 

 birth dates of 110 viable Pacific har- 

 bor seal pups had highly significant, 

 positive and curvilinear latitudinal 

 variation, similar to that previously 

 described for this subspecies in the 

 wild between 30° and 47°N. Pupping 

 dates for each species in captivity 

 were comparable to those found for 

 wild populations of North Pacific pin- 

 nipeds. The described latitudinal 

 variation and the temporal consis- 

 tency between captive and wild 

 populations of California sea lions 

 and Pacific harbor seals support the 

 hypothesis that photoperiod re- 

 sponse maintains specific birth tim- 

 ing in these species. 



Latitudinal variation in the birth 

 timing of captive California sea lions 

 and other captive North Pacific 

 pinnipeds 



Jonathan L. Temte 



Department of Zoology, 42 1 Birge Hall. University of Wisconsin 

 Madison, Wisconsin, 53706 



Present address: Department of Family Medicine. University of Wisconsin 

 777 South Mills, Madison, Wl 537 I 5 



Manuscript accepted 4 June 1993. 

 Fishery Bulletin 9 1 : 7 10-7 1 7 ( 1993 1. 



710 



Captive pinnipeds are not only of 

 educational and entertainment value 

 to zoo and aquarium visitors, but also 

 offer an exceptional opportunity to 

 examine temporal aspects of their re- 

 productive biology. Zoo records usu- 

 ally document birth dates, outcomes, 

 and parental histories which are dif- 

 ficult, if not impossible, to obtain 

 in field studies. Moreover, captive 

 animals live in environments where 

 availability of food is relatively con- 

 stant and any movements (i.e., trans- 

 fers between facilities) are well 

 documented. 



A recent census (Asper et al., 1988) 

 identified 924 pinnipeds in captivity 

 in North America. Of these, four 

 North Pacific species — the California 

 sea lion (Zalophus californianus), the 

 northern or Steller sea lion (Eumeto- 

 pias jubatus), the northern fur seal 

 (Callorhinus ursinus), and the har- 

 bor seal (Phoca vitulina) — repre- 

 sented 91 percent («=837). These spe- 

 cies breed successfully in captivity 

 over wide latitudinal ranges. 



Standard reviews of the pinnipedia 

 (Mate, 1979; Mate and Gentry, 1979; 

 Udell, 1981; Schusterman, 1981; 

 King, 1983) identify fixed seasons of 

 birth for each of the North Pacific 

 sea lions. Moreover, Bigg (1973) 

 found that captive California sea li- 

 ons at the London Zoo (5 IN) breed 

 at the same time as the parent popu- 

 lation in California (33°N). In con- 

 trast, Schusterman et al. (1982) noted 



that births of California sea lion pups 

 at Sea Life Park, Hawaii (21°N), oc- 

 curred significantly later than births 

 in California at Marineland (34°N) 

 and Marine World (38°N). 



Regional or latitudinal variation in 

 birth timing, or both, has been re- 

 ported for the harbor seal (Bigg, 

 1969a; Temte et al, 1991) and the 

 grey seal (Halichoerus grypus: 

 Coulson, 1981). Likewise, Temte 

 (1985) demonstrated a 14-day shift 

 in the mean date of pupping for 

 northern fur seals between colonies 

 on St. George Island, Alaska (57N), 

 and San Miguel Island, California 

 (34°N). These variations in birth tim- 

 ing have been interpreted as 1 ) se- 

 lection acting on discrete populations 

 to match reproductive efforts with 

 seasonal constraints (Bigg, 1973). 

 2) responses to latitudinally chang- 

 ing temporal cues, such as tempera- 

 ture or photoperiod (Coulson, 1981; 

 Temte, 1985), or 3) a combination of 

 the above (Temte et al., 1991; Boyd, 

 1991). 



This study identifies and defines 

 the extent of latitudinal variation in 

 birth timing of captive California sea 

 lions, northern sea lions, northern fur 

 seals and Pacific harbor seals from 

 birthing records available from zoos 

 and aquaria scattered across a wide 

 latitudinal range. Comparisons of 

 birthing periods were made, where 

 applicable, between captive and wild 

 populations. 



