Abundance and survival estimates of the southeastern pacific humpback whale stock from 1991-2006 photo-identification surveys in Ecuador

Abstract

Southeastern Pacific humpback whales (Breeding Stock G) breed along the northwestern coast of South America and farther north up to Costa Rica. Photo-identification surveys conducted aboard whalewatching vessels during the migration/breeding season from June to September between 1991 and 2006 off the coast of Ecuador (2 °S, 81 °W) have produced a database of 1,511 individual whales. Comparisons of photographs produced 190 between-year re-sightings of 155 individual whales. Closed and open capture-recapture models were used to estimate abundance and survival. The best estimate of abundance in 2006 with the Chapman modified-Petersen was 6,504 (95% CI: 4,270-9,907; CV = 0.21). Abundance estimates from open population models were considerably lower due to heterogeneity in capture probability which produced a 'transient' effect. Our best estimate of true survival was 0.919 (95% CI: 0.850-0.958). Heterogeneity most likely occurred from inter-annual variation in sampling and unknown structure and variation in the migration timing and corridor. A more extensive collaborative effort including other wintering areas further north as well as integrating breeding-feeding data will help to reduce heterogeneity and increase precision in abundance and survival estimates.