Diversity and distribution of cetaceans off Mirissa in the southern coast of Sri Lanka II. Relationship with sea surface temperature, salinity and water density

Abstract

Lack of proper scientific data on the behaviour of cetaceans is a major constraint in managing whale and dolphin watching activities without affecting cetacean populations in marine waters off Mirissa, where it has become a high income generating tourist activity. Therefore a shipboard surveys were conducted using a special whale watching boat for 43 days from January to April 2012 in an area of about 940 km 2 in Mirissa, southern coast of Sri Lanka to identify the environmental parameters that affect the abundance of cetaceans. During this study, 8 cetacean species including 6 toothed whale species (Physeter macrocephalus, Globicephala melas, Peponocephala electra, Orcinus orca, Tursiops truncates and Stenella longirostris) and two baleen whale species (Balaenoptera musculus and Balaenoptera physalus) were identified. Results of the study revealed that relationship between species occurrence and the measured water quality parameters (temperature, salinity and density) was significant (p < 0.05). From the identified species blue whale and melon headed whale can tolerate high density (1.02±0.0) and salinity (blue whale-36.35±0.75; melon headed-35.55±0.51) range while blue whale (28.53±0.89), sperm whale (28.47±0.93) and spinner whale (28.66±1.04) can tolerate widee temperature range.

Distribution and Abundance of the Blue Whale (Balaenoptera musculus indica) off Sri Lanka during the Southwest Monsoon 2018

“…Dense aggregations of blue whales were observed from Dondra point to Galle on the continental shelf break, especially at a depth range of 500-2000 m. This was consistent with the results of the previous surveys in a survey area of 150 × 50 km, 30-47 km off of the southern coast of Sri Lanka (off Bundala to Galle) to assess the whale distribution in relation to the major shipping lanes [6]. Many studies have shown high levels of blue whale occurrence within this area; however, surveys during the southwest monsoon (SW) period are limited [6,14,41]. The present survey, conducted during the SW monsoon, also reveals a similar pattern of blue whale aggregations along the continental shelf off Dondra to Galle and their distribution towards the deep sea in the south.…”

Cetacean occurrence and diversity in whale‐watching waters off Mirissa, Southern Sri Lanka

“…The whale-watching activity mainly occurs in the island's southern coastal waters off Mirissa, where is popularly known as the "land of the blue whale" (Ilangakoon 2013;Randage et al 2014;Buultjens et al 2017). To date, there are over 30 whale-watching boats in Mirissa, attracting over 79 000 tourists per year (Thilakarathne et al 2015;Buultjens et al 2016). Some conservation groups and scientists have hypothesized that the growing whale-watching activities can lead to short-term behavioral disturbances resulting in negative impacts on cetaceans including changes in vocalization and respiration patterns, swimming behavior and surfacing, feeding times and group size (Parsons 2012), and undermines long-term population fitness such as chronic levels of stress resulting in negative effects on health as well as reduced reproductive rates (Stockin et al 2008).…”

“…To date, there are over 30 whale‐watching boats in Mirissa, attracting over 79 000 tourists per year (Thilakarathne et al . 2015; Buultjens et al . 2016).…”