Ballance,L.T,Pitman,R.L.
Cetaceans of the Western Tropical Indian Ocean: Distribution, Relative Abundance, and comparisons with Cetacean Communities of Two other Tropical Ecosystems Journal Article
In: Marine Mammal Science, vol. 14, no. 321, pp. 429-459, 1998.
Abstract | BibTeX | Tags: abundance, cetacean, cetaceans, Distribution, dolphin, dolphins, Gulf of Mexico, habitat preference, Indian Ocean, Maldives, Mexico, Oman, relative abundance, seabirds, survey, whale
@article{,
title = {Cetaceans of the Western Tropical Indian Ocean: Distribution, Relative Abundance, and comparisons with Cetacean Communities of Two other Tropical Ecosystems},
author = {Ballance,L.T,Pitman,R.L.},
year = {1998},
date = {1998-01-01},
journal = {Marine Mammal Science},
volume = {14},
number = {321},
pages = {429-459},
abstract = {We conducted a cetacean survey in the pelagic western tropical Indian Ocean (WTIO) aboard an 85-m research vessel from March to July 1995, covering 9,784 linear km. Using 25x binoculars and line-transect methods, we recorded 589 sightings of 21 species. Stenella longirostris was the most abundant cetacean, in terms of number of individuals sighted, by an order of magnitude above any other species, while Physeter macrocephalus was the most frequently sighted, in terms of number of schools. Twelve species were widespread, seven were rare, and two were localized; our sightings include new distributional records for 12 species. Significant observations included the following: (1) Delphinus cf. tropicalis was abundant off the coast of Oman (16 sightings) and readily distinguishable in the field from D. delphis and D. capensis, (2) Balaenoptera musculus was fairly common and localized in the area of the Maldives (17 sightings), and (3) three sightings were made of an unidentified bottlenose whale tentatively referred to as Indopacetus (i.e., Mesoplodon) pacificus. We recorded 26 mixed-species cetacean schools, 43 schools with which seabirds associated, and 17 schools associated with tuna. Notable among these were mixed aggregations of Stenella attenuata, S. longirostris, yellowfin tuna, and seabirds. The cetacean community of the WTIO was similar to that of the eastern tropical Pacific (ETP) and the Gulf of Mexico (GM) in several respects. First, differences in abundance rank of individual species were small, with the result that common species were common and rare species were rare, regardless of ocean. Second, these differences in abundance were due primarily to differences in encounter rate, which varied with ocean by as much as 3,000%, and less so to school size, which generally varied less than 100%. Third, regardless of ocean, three species comprised the majority of cetaceans in the community, Stenella attenuata, S. longirostris, and S. coeruleoalba, representing 62%-82% of all individuals for all species. However, the rank order of abundance for these three species differed with ocean. Most notably, S. attenuata was abundant in the ETP and GM (abundance rank = 2 and 1, respectively) but much less common in the WTIO (abundance rank = 6). Although habitat preferences for S. attenuata appear to overlap considerably with those of S. longirostris in the ETP, our results suggest there may actually be significant differences between these two species. Detailed analysis of oceanographic correlates of distribution will be necessary in order to understand fully the habitat requirements of these pelagic dolphins, often the most conspicuous elements of tropical cetacean communities around the world.},
keywords = {abundance, cetacean, cetaceans, Distribution, dolphin, dolphins, Gulf of Mexico, habitat preference, Indian Ocean, Maldives, Mexico, Oman, relative abundance, seabirds, survey, whale},
pubstate = {published},
tppubtype = {article}
}
We conducted a cetacean survey in the pelagic western tropical Indian Ocean (WTIO) aboard an 85-m research vessel from March to July 1995, covering 9,784 linear km. Using 25x binoculars and line-transect methods, we recorded 589 sightings of 21 species. Stenella longirostris was the most abundant cetacean, in terms of number of individuals sighted, by an order of magnitude above any other species, while Physeter macrocephalus was the most frequently sighted, in terms of number of schools. Twelve species were widespread, seven were rare, and two were localized; our sightings include new distributional records for 12 species. Significant observations included the following: (1) Delphinus cf. tropicalis was abundant off the coast of Oman (16 sightings) and readily distinguishable in the field from D. delphis and D. capensis, (2) Balaenoptera musculus was fairly common and localized in the area of the Maldives (17 sightings), and (3) three sightings were made of an unidentified bottlenose whale tentatively referred to as Indopacetus (i.e., Mesoplodon) pacificus. We recorded 26 mixed-species cetacean schools, 43 schools with which seabirds associated, and 17 schools associated with tuna. Notable among these were mixed aggregations of Stenella attenuata, S. longirostris, yellowfin tuna, and seabirds. The cetacean community of the WTIO was similar to that of the eastern tropical Pacific (ETP) and the Gulf of Mexico (GM) in several respects. First, differences in abundance rank of individual species were small, with the result that common species were common and rare species were rare, regardless of ocean. Second, these differences in abundance were due primarily to differences in encounter rate, which varied with ocean by as much as 3,000%, and less so to school size, which generally varied less than 100%. Third, regardless of ocean, three species comprised the majority of cetaceans in the community, Stenella attenuata, S. longirostris, and S. coeruleoalba, representing 62%-82% of all individuals for all species. However, the rank order of abundance for these three species differed with ocean. Most notably, S. attenuata was abundant in the ETP and GM (abundance rank = 2 and 1, respectively) but much less common in the WTIO (abundance rank = 6). Although habitat preferences for S. attenuata appear to overlap considerably with those of S. longirostris in the ETP, our results suggest there may actually be significant differences between these two species. Detailed analysis of oceanographic correlates of distribution will be necessary in order to understand fully the habitat requirements of these pelagic dolphins, often the most conspicuous elements of tropical cetacean communities around the world.
Salm,R.V.,Jensen,R.A.C.,Papastavrou,V.
Marine fauna of Oman: Cetaceans, turtles, seabirds and shallow water corals Technical Report
no. 469, 1993.
Abstract | BibTeX | Tags: cetacean, cetaceans, coastal zone management, coral, dolphin, dolphins, management, marine, minke whale, minke whales, Oman, seabirds, Strandings, survey, turtles, whale, whales
@techreport{,
title = {Marine fauna of Oman: Cetaceans, turtles, seabirds and shallow water corals},
author = {Salm,R.V.,Jensen,R.A.C.,Papastavrou,V.},
year = {1993},
date = {1993-01-01},
number = {469},
pages = {1-66},
publisher = {IUCN},
abstract = {This is the final compilation report that summarises all the data in the sub-reports on cetaceans and turtles etc. Cetacean stranding an sighting info from the surveys conducted between 1984 and 1992. 210 sightings of live cetaceans were made from the shore, boats and helicopters. Most sightings were of animals within four km of shore. The sightings, which were incidental to other coastal zone management studies do not include any related observer effort. The majority of boat-based searching occurred in the capital area, with remaining boat distributed equally between Musandam and Dhofar. There was less observation from boats along the stretch of central coast, but more time spent driving on beaches.There are also 173 records of beached cetacean material. these include the remains of 25 dolphins butchered by fishermen. The sightings and strandings are summarised in a table including 16 species (including both sei and minke whales). 90% of all beached cetacean remains were found south of Ras al Hadd along the central coast, and was most abundant between 20 and 21 N.},
keywords = {cetacean, cetaceans, coastal zone management, coral, dolphin, dolphins, management, marine, minke whale, minke whales, Oman, seabirds, Strandings, survey, turtles, whale, whales},
pubstate = {published},
tppubtype = {techreport}
}
This is the final compilation report that summarises all the data in the sub-reports on cetaceans and turtles etc. Cetacean stranding an sighting info from the surveys conducted between 1984 and 1992. 210 sightings of live cetaceans were made from the shore, boats and helicopters. Most sightings were of animals within four km of shore. The sightings, which were incidental to other coastal zone management studies do not include any related observer effort. The majority of boat-based searching occurred in the capital area, with remaining boat distributed equally between Musandam and Dhofar. There was less observation from boats along the stretch of central coast, but more time spent driving on beaches.There are also 173 records of beached cetacean material. these include the remains of 25 dolphins butchered by fishermen. The sightings and strandings are summarised in a table including 16 species (including both sei and minke whales). 90% of all beached cetacean remains were found south of Ras al Hadd along the central coast, and was most abundant between 20 and 21 N.