712 



Fishery Bulletin 91(4). 1993 



1978) was utilized to control for differences in latitudi- 

 nal distributions. 



Results 



California sea lion 



The captive births of 610 California sea lions were 

 evaluated (Table 1). Stillborn and non-viable pups ac- 

 counted for 122 births (20.0%). Stillbirths occurred as 

 early as 1 January and as late as 1 August. Whereas 

 no significant difference was found between the tim- 

 ing of stillbirths and non-viable births (Kruskal- 

 Wallace: df=l; #=0.371; NS), stillborn and non-viable 

 pups were born an average of 28.0 days earlier than 

 viable pups, this difference being highly significant 

 (Kruskal-Wallace: df=l; H=70.49; P<0.001>. Hence, only 

 viable births (n=466; 22 pups with estimated birth 

 dates were excluded) were examined for latitudinal 

 variation. 



Viable births occurred over a 21°46' latitudinal range, 

 between 2P20'N and 43°06'N. These were normally 

 distributed over the birthing period (Fig. 2), occurring 

 as early as 30 April and as late as 1 September. Mean 

 dates of pupping for individual colonies occurred from 

 27 May to 25 June. The mean date of birth for all 

 viable pups was 12 June ± 13.5 days (± SD). 



The variances of the mean birth dates were calcu- 

 lated for the 18 largest captive colonies (each with at 

 least 6 viable births). A significant latitudinal gradient 

 existed for this variance (Fig. 3), with a decrease of 5.6 

 days 2 for each degree of northward displacement. 



A plot of pupping date versus latitude indicated that 

 latitude variation occurred within captive California 

 sea lions (Fig. 4). A second order orthogonal polyno- 

 mial model (Table 2) was highly significant (r-'=0.206; 

 F ; , „ =60.23; P<0.0001 ) and estimated a negative lati- 

 tudinal slope of approximately -0.6 days/°latitude over 



W 140- 



f20 



CD 

 XI 



E 



3 



California Sea Lion 



466 



100 110 120 130 140 150 160 170 160 190 200 210 220 230 240 250 



Pupping Date 



Figure 2 



Frequency of viable California sea lion births at all facilities 

 during 10-day periods from 31 March (day 1001 to 6 Septem- 

 ber (day 259). Dates are numbered sequentially from 21 De- 

 cember. 



c 

 o 



*i_ 

 o '00 



> 



.E 50 

 Q. 

 Q_ 



3 



Q- o-l — , — , — , — i — i — i — i — i — , — i — i — i — , — i — i — .— . — —r 



20 25 30 35 40 45 



Latitude of Captive Colony (°N) 

 Figure 3 



Intra-colony variance of the mean pupping date from the 18 

 largest California sea lion colonies as a function of latitude. 

 Each colony had at least six viable births. Linear regression 

 model: Variance (days 2 ) = 219 - 5. 58( latitude); r- = 0.405; 

 ',!„„. = -3.30; P < 0.005. 



