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.
Dolphin and whale watching has become a blooming activity in the tourism industry in Sri Lanka. Proper scientific data is lacking for the understanding and management of dolphin and whale watching activities particularly in the Southern coast. Based from Mirissa, a shipboard survey was conducted for 43 days from January to May 2012 covering 940 km 2 .The diversity and distribution of cetaceans inhabits in the continental shelf and slope were recorded from shipboard sighting data. Their species composition, pod size, behavioral pattern were observed and the distribution pattern was mapped. Total of 8 species of cetaceans were recorded during the study period. They were spinner dolphin (Stenella longirostris), bottlenose dolphin (Tursiops truncates), melon headed whale (Peponocephala electra), fin whale (Balaenoptera physalus), killer whale (Orcinus orca), short finned pilot whale (Globicephala melas), sperm whale (Physeter macrocephalus) and blue whale (Balaenoptera musculus). Distribution pattern and pod size varied with the species. Out of 6675total sightings, 5382 were spinner dolphins and 843 were bottlenose dolphins. Depth levels showed a significant relationship with different cetacean species (p < 0.05). Spinner dolphins, bottlenose dolphins and melon headed whales were always observed near to the shore at relatively shallow areas around 100m depth contours. Fin whales, killer whales and short finned pilot whales were observed around 500 m to 650 m depth while sperm whales and blue whales were observed around 1000 m depth level located further away from the shoreline. Most of the dolphin groups were consisted with relatively large number of individuals about 160 while, most baleen whales were found solitary or small pods consisted with few individuals. Large toothed whales such as sperm whale pods were observed with intermediate number groups about 20 individuals. Those findings can be directly used to conserve and protect cetaceans and prepare a proper management plan to regulate whale watching industry.
Sea urchins are keystone herbivores in many marine benthic habitats. They can significantly influence coral-algae phase shifts and impact on reef carbonate budgets through grazing. Hall Bank reef in Western Australia is unique among other reefs in the region being high latitude with a high hermatypic coral cover but lacking macroalgae and soft corals. Since the reef status is thought to result from high densities of the urchin Centrostephanus tenuispinus limiting the growth of macroalgae, the present study was focused on evaluating their role as bio-eroders. Monthly samples of 26 urchins were collected from 2014–2016 and gut composition was analyzed. Gut evacuation rates were calculated using 50 urchins dissected at time intervals (0, 4, 8, 16, 24, 36, 48, 60, 72 and 96 h). Reworked calcium carbonate was calculated using 30 urchins maintained in five cages in a seagrass bed adjacent to the reef site. Mean percentages for organic component, calcium carbonate and other siliceous components were 86.29 ± 3.23%, 10.32 ± 2.76% and 3.39 ± 1.52% respectively. Gut evacuation rates for autumn, winter, spring and summer were 0.70, 0.24, 0.48 and 0.72 (day− 1). Bio-erosion rates were significantly higher in Summer-16 (3.52 g CaCO3 m− 2 day− 1) and lower in winter (1.32 g CaCO3 m− 2 day− 1) (F = 101.580, p < 0.000). High erosion rates were recorded for large urchins (F = 37.789, P < 0.001. Annual urchin bio-erosion was 1017.69 g CaCO3 m− 2 a− 1. Differences in food ingestion rates in response to seawater temperature changes are thought to be the main cause for the significant differences in seasonal bio-erosion rates.
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