Abundance estimates of three cetacean species in the coastal waters of Matang, Perak, Peninsular Malaysia

Abstract

1. The paucity of baseline data on coastal cetaceans due to a lack of research in developing countries frequently precludes assessment of their status and informed management actions for conservation.2. This study provides the first abundance estimates of Indo-Pacific humpback dolphins, Irrawaddy dolphins, and Indo-Pacific finless porpoises in the coastal waters of Matang, Peninsular Malaysia. 3. Boat-based surveys covering 1,152 km 2 of coastal waters with 4,108 km of survey effort were conducted between 2013 and 2016 to collect data for line transect analysis of Irrawaddy dolphins and finless porpoises. Photo-identification data of humpback dolphins were concurrently collected for mark-recapture analysis. 4. Estimates of abundance from four sampling strata totalled 763 Irrawaddy dolphins (CV = 13%, 95% confidence interval (CI) [588, 990]) and 600 Indo-Pacific finless porpoises (CV = 27%, 95% CI [354, 1,016]). 5. The annual abundance estimates of humpback dolphins ranged between 171 (95% CI [148, 208]) in 2014-2015 and 81 (95% CI [67, 98]) in 2015-2016, likely due to the presence of offshore individuals that moved in and out of the study area. The estuarine strata were inhabited by 68 (95% CI [63, 73]) inshore humpback dolphins in 2013-2014 to 87 (95% CI [78, 97]) dolphins in 2014-2015. 6. As an International Union for Conservation of Nature important marine mammal area, the productive coastal waters of Matang are shown to support a high density of small coastal cetaceans, and the results serve as an important baseline for future studies to identify population trends for conservation management plans.

Estimating the Abundance of Marine Mammal Populations

“…Abundance has been estimated and compared using these two methods for humpback and blue whales off the west coast of the United States and Mexico (Calambokidis and Barlow, 2004), and for killer whales in British Columbia (Williams and Thomas, 2009). Two studies that consider some of these issues for small cetaceans are Minton et al (2013) and Kuit et al (2021). The first study used small boat line transect surveys to estimate the abundance of Irrawaddy dolphin (Orcaella brevirostris) and Indo-Pacific finless porpoise (Neophocaena phocaenoides) in coastal waters of Sarawak, Borneo, and also used markrecapture analysis of photo-id data to estimate the number of Irrawaddy dolphins using the study area.…”

“…The second study used small boat line transect surveys to estimate the abundance of Irrawaddy dolphin and Indo-Pacific finless porpoise in coastal waters of Matang, Malaysia, and mark-recapture analysis of photo-id data to estimate the number of Indo-Pacific humpback dolphins (Sousa chinensis) using the study area. Kuit et al (2021) did not use markrecapture for Irrawaddy dolphins because the animals' behavior led to poor-quality photographs and adversely affected individual identification. Minton et al (2013) also noted that obtaining photo-id pictures of Irrawaddy dolphins was challenging.…”

Abundance, spatial distribution and threats to Indo-Pacific bottlenose dolphins (Tursiops aduncus) in an Important Marine Mammal Area in Tanzania

“…Photographs of left (LDFs) and right (RDFs) dorsal fins were treated as two separate datasets when creating the catalogues and during analysis. This was due to the inability in most cases, to definitively link the LDFs and RDFs of individual dolphins; this approach is commonly used in the studies of cetaceans (Minton et al, 2013, Kuit et al, 2021.…”

“…A lack of information on whales and dolphins due to limited research in many developing countries frequently prevents assessment of their status, and for informed management actions to aid in their conservation (Kuit et al, 2021). Cetaceans typically occur at low densities, in hard to access habitats, and because they spend much of their lives underwater are also challenging to detect, with the result that gathering baseline data requires several years of study; requiring funds and time that are often unavailable.…”

“…Obtaining an abundance estimate is an essential component of a baseline survey, and this is especially important for coastal species that are under threat from anthropogenic activities in their habitat impacting both survival and health. In these situations, baseline surveys and abundance estimates are important in order to guide and monitor species protection and habitat management (Kuit et al, 2021;Avila et al, 2018;de Vere et al, 2018).…”