Photo-identification Monitoring of the Eastern Taiwan Strait Population of Indo-Pacific Humpback Dolphins

Principal Investigator: John Wang, FormosaCetus Research and Conservation Group

Funding year: 2012-2013

Main objectives:

• To continue a long-term, photo-identification monitoring project on this critically endangered population (initiated in 2007).
• To investigate whether a suspected population decline is real given the myriad of serious threats it faces.
• To try to examine ranging patterns, finer-scale distribution and some aspects of social structure.

Main outcomes:

• Extensive small boat survey effort (296 h, 4,420 km) conducted from May to July  in 2012 and 2013, covering almost the entire known range of this population, yielded 99 sightings of humpback dolphins. When added to the existing 2011 date this results in a total of almost 400 hours and 5,800 km of effort with a grand total of 144 sightings  (mean group size = 5.7, SD 4.91).
• A total of 57,000 images were collected from 2011-2013, of which almost 12,500 were useful for photo-identification; 66 individuals were identified and importantly none of them were new to the existing catalogue.
• Corrected estimates of abundance for each survey year are consistently under 80 individuals with high degrees of precision (CVs of 3-6%). However, there is indication of a possible subtle decline since 2010, consistent with results of a population viability analysis that indicated a high probability (>76%) of decline. This requires further investigation.
• Photographic evidence indicates that bycatch is a major threat to this population, and the incidence of new injuries and entangled animals appears to be increasing (since 2007). However more long-term monitoring data are needed to determine if this is the case.

Reports/Papers:

Wang, JY. 2014. Photo-identification Monitoring of the Eastern Taiwan Strait Population of Indo-Pacific Humpback Dolphins (Sousa chinensis). Final Progress Report – 12 June 2014, 13 pp. (for more details about this report, please contact the author)

Dares et al. 2014. Short Note: Habitat Characteristics of the Critically Endangered Taiwanese Humpback Dolphins (Sousa chinensis) of the Eastern Taiwan Strait. Aquatic Mammals 40(4):368-374.

Click here to read.