Annual estimates of the unobserved incidental kill of pantropical spotted dolphin (Stenella attenuata attenuata) calves in the tuna purse-seine fishery of the eastern tropical Pacific

Archer, F.; Gerrodette, T.; Chivers, S.

Fishery Bulletin 102(2): 3-44


ISSN/ISBN: 0090-0656
Accession: 009769668

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We estimated the total number of pantropical spotted dolphin (Stenella attenuata) mothers killed without their calves ("calf deficit") in all tuna purse-seine sets from 1973-90 and 1996-2000 in the eastern tropical Pacific. Estimates were based on a tally of the mothers killed as reported by color pattern and gender, several color-pattern-based frequency tables, and a weaning model. Over the time series, there was a decrease in the calf deficit from approximately 2800 for the western-southern stock and 5000 in the northeastern stock to about 60 missing calves per year. The mean deficit per set decreased from approximately 1.5 missing calves per set in the mid-1970s to 0.01 per set in the late-1990s. Over the time series examined, from 75% to 95% of the lactating females killed were killed without a calf. Under the assumption that these orphaned calves did not survive without their mothers, this calf deficit represents an approximately 14% increase in the reported kill of calves, which is relatively constant across the years examined. Because the calf deficit as we have defined it is based on the kill of mothers, the total number of missing calves that we estimate is potentially an underestimate of the actual number killed. Further research on the mechanism by which separation of mother and calf occurs is required to obtain better estimates of the unobserved kill of dolphin calves in this fishery. Reprinted by permission of the publisher.