Distribution of small cetaceans in the nearshore waters of Sarawak, East Malaysia

The Sarawak Dolphin Project, Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak

Between June 2008 and September 2009, 56 days of small boat surveys were conducted off the coast of Sarawak, Malaysia with the aim of recording cetacean distribution. These surveys, which focused on the Miri, Bintulu-Similajau and Kuching regions, comprised 173 hours of survey effort and covered 2851 km of pre-determined systematic tracks. Surveys were clustered into three sets of seasonal snapshots: June-July, September-October and March-April. A total of 115 cetacean sightings were made, of which 65 were on-effort and used in analyses of cetacean encounter rates in relation to habitat characteristics. Species observed included (in order of frequency) Irrawaddy dolphins (Orcaella brevirostris),
finless porpoises (Neophocaena phocaenoides), Indo-Pacific bottlenose dolphins (Tursiops aduncus) and
Indo-Pacific humpback dolphins (Sousa chinensis).
One hundred and ten of 115 sightings were made in less than 10 m water depth, highlighting the importance of nearshore coastal habitats for these species. Despite an apparent overlap in habitat, Irrawaddy dolphins showed a statistically significant affiliation with areas of shallower depth and closer proximity to shore and river mouths than finless porpoises or bottlenose dolphins. This preference for nearshore areas renders the species vulnerable to threats such as fisheries by-catch and habitat degradation from coastal development. Irrawaddy dolphins were more frequently encountered in Kuching, while the highest encounter rate for finless porpoises was in the Bintulu-Similajau region. The highest encounter rates in both Kuching and Similajau occurred in areas that are destined for major coastal developments.

A series of small boat surveys was conducted in three locations along Sarawak’s coastline with the aims of:
1) assessing more accurately the species composition,
distribution and habitat requirements of coastal cetaceans
in the region;
2) collecting baseline data on dolphin distribution and habitat use; and
3) facilitating management and conservation efforts.

The results of these surveys should enable managers and researchers to identify areas of key importance for future conservation and research efforts and lay the foundation for more detailed and targeted study both within Sarawak and in other parts of the species’ range.

Effort data are available through request from the original data providers.

Overview

This section explains attributes included in the original dataset. OBIS-SEAMAP restricts the attributes available to the public to date/time, lat/lon and species names/counts only. Should you need other attributes described here, you are encouraged to contact the data provider.

Attributes described below represent those in the original dataset provided by the provider.
Only minimum required attributes are visible and downloadable online. Other attributes may be obtained upon provider's permission.

Attributes in dataset

Attribute (table column)	Description
oid	Unique ID number (generated by SEAMAP)
obs_date	Observed date
obs_time	Observed time
sp_tsn	Species ITIS TSN
sp_obs	Species observed
engname	English name observed
sightrecnum	Sighting record number
sitename	Site name
latitude	Latitude of observation
longitude	Longitude of observation
obs_count	Observed count (best estimate number)
effort	Effort level code
depth	Observed depth (m)
tideht	Observed tide height
notes	Notes for when observation was not identified to species level and English name was used