Preliminary Mark-Recapture Abundance Estimates of Humpback Whales on a Breeding Area in the Mariana Archipelago

The Pacific Islands Fisheries Science Center conducted small-boat surveys for endangered Western North Pacific humpback whales off Saipan and neighboring islands in the Mariana Archipelago during the winter months of 2015 to 2019. A total of 42 non-calf whales and 14 calves were observed, and individual resight durations ranged from 1 to 10 d during the 10-18 d survey periods. Preliminary annual mark-recapture abundance estimates of humpback whales within the study area were obtained using photo-identification data collected during the surveys and were adjusted to account for calves. Yearly abundance estimates ranged from 34 (SE, 19; 95% CI, 12 to 92) whales in 2019 to 126 (SE, 44; 95% CI, 65 to 246) whales in 2017, with an

average of 61 (SE, 13; 95% CI, 41 to 91) whales across all years. Density estimates were calculated by year for the full study area where surveys were conducted, as well as a truncated area where most of the survey effort and all of the humpback whale sightings occurred. Yearly density estimates for the truncated survey area ranged from 0.09 to 0.33 whales/km2, and the average density estimate across years was 0.16 whales/km2. Care should be taken in the interpretation of the density estimates as they may be biased given they were derived from mark-recapture abundance estimates that are likely associated with sampling biases and that are not spatially-explicit. They cannot be used to estimate humpback whale density throughout the

Mariana Archipelago or beyond. Regardless, the study area off Saipan represents an important area for an endangered population of humpback whales that should be considered in protection and conservation efforts.

Hill MC, Bradford AL, Oleson EM. 2020. Preliminary mark-recapture abundance estimates of humpback whales on a breeding area in the Mariana Archipelago. Pacific Islands Fisheries Science Center, PIFSC Administrative Report. H-20-07, 18 p. doi:10.25923/v3fd-yf59

Requestor will be asked to submit a request by email to Erin Oleson {erin.oleson@noaa.gov) or Marie Hill (marie.hill@noaa.gov)

Requestor will be asked to submit a request by email to Erin Oleson {erin.oleson@noaa.gov) or Marie Hill (marie.hill@noaa.gov)

Requestor will be asked to submit a request by email to Erin Oleson {erin.oleson@noaa.gov) or Marie Hill (marie.hill@noaa.gov)

Requestor will be asked to submit a request by email to Erin Oleson {erin.oleson@noaa.gov) or Marie Hill (marie.hill@noaa.gov)

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