. Bulletin. Science; Natural history; Natural history. PINNIPEDS AT SAN NICOLAS ISLAND 123. :«) illy (JO 231 / (") 232 (3B) "3, (3C) "1 „., "'2« 243 I I "") ..AN 261 «fll (4B)(4C) 262 , m I 2S8 Nouticol Miles Fig. 1. San Nicolas Island showing census areas and numerical codes. may therefore not be detected unless the carcasses initially appear well above the high tide line. Pups that die at sea are also unlikely to be detected. Therefore, without specific mark-recapture studies of pups or of parous females, the rela- tionship (and its variability) of observed dead
. Bulletin. Science; Natural history; Natural history. PINNIPEDS AT SAN NICOLAS ISLAND 123. :«) illy (JO 231 / (") 232 (3B) "3, (3C) "1 „., "'2« 243 I I "") ..AN 261 «fll (4B)(4C) 262 , m I 2S8 Nouticol Miles Fig. 1. San Nicolas Island showing census areas and numerical codes. may therefore not be detected unless the carcasses initially appear well above the high tide line. Pups that die at sea are also unlikely to be detected. Therefore, without specific mark-recapture studies of pups or of parous females, the rela- tionship (and its variability) of observed dead pups to estimates of pup production is unknown. We estimated sea lion pup mortality by recording the number of new pup carcasses observed on each biweekly census during the whelping season (25 May through 4 July each year). Dead pups found before 25 May were considered to be premature and were not considered as part of the whelping season mortality. Because most dead sea lion pups could not be marked without major disturbance to rookeries, we simply tallied the number of fresh pup carcasses from observation points above rookeries during biweekly censuses between 25 May and 4 July each year. Sea lion pups are smaller than elephant seal pups and faster rates of decay (both passive and by gull scavenging) and burial in the sand prevented detailed monitoring of the fate of sea lion pup carcasses during the biweekly censuses. We summed counts of dead pups from all censuses during the whelping season to determine a minimal estimate of whelping season mortality. This estimate was derived by dividing the cumulative total of dead pups by an estimate of natality (pup production plus dead pup total). During the course of other studies, we placed numbered plastic tags (Dalton Jumbo Roto) in the interdigit webbing of the rear flippers of harbor seals and elephant seals at San Nicolas and San Miguel Islands. During the breeding season we also marked adult and subadult male, adult femal
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