Ecology of Lahille's bottlenose dolphin Tursiops truncatus gephyreus in the Patos Lagoon estuary and adjacent marine coast

Study Extent

The area sampled is 140 km2 and encompasses the lower portion of the PLE (40 km2) and adjacent marine coast (50 km2 south and 50 km2 north of PLE in the coastal zone). Temporal coverage: January 2009 to December 2016.

Sampling

Distribution patterns and habitat use: All field work was carry out onboard a 5.6m inflatable boat equipped with 90 hp outboard engine, VHF radio, echo sounder and GPS. Boat-based surveys were conducted year-round on the core area of Patos Lagoon estuary (PLE) dolphin community. Surveys in estuarine waters were conducted following predefined zigzag transects whereas in the adjacent marine coast we run either zigzag or parallel-to-shore transects up to 20 km north and south of the estuary mouth, depending on the sea conditions. Surveys were halted when the sea state (Beaufort scale) were > 3. Transects were run at speeds between 18 and 22 km/h. Two observers positioned in the bow searched for dolphins visually. Whenever a dolphin group was sighted, the survey route was abandoned to approach the animals for photo-identification and to obtain data of group size and composition, sighting depth and geographical position. After a sufficient number of good-quality digital photographs of the dorsal fins of all presumed animals were taken, the survey was resumed.

Method steps

1. Estimates of abundance, reproductive and survival rates: Abundance estimates were based on mark-recapture models for closed populations that deals with heterogeneity in capture probabilities. Survival rates were also estimated from mark-recapture models, but in this case, using open population models. The identification and monitoring of mother-calf pairs over time, from the beginning of the breeding season, were designed to allow approximate calculations of birth intervals and reproductive rates and their temporal trends.

Collected species: Lahillee’s bottlenose dolphins (Tursiops truncatus gephyreus Montagu, 1821).

1. Tursiops truncatus gephyreus
   common name: Lahillee's bottlenose dolphins rank: species
2. Animalia
   rank: kingdom
3. Chordata
   rank: phylum
4. Mammalia
   rank: class
5. Cetartiodactyla
   rank: order
6. Cetacea
   rank: infraorder
7. Odontoceti
   rank: superfamily
8. Delphinidae
   rank: family
9. Tursiops
   rank: genus

The study area of 140km² was divided in three major areas: estuary, with 40km² and the coastal areas south and north, each one with 50km². These three areas were subdivided in more three sub-areas: inner estuary (31° 58,94’S/52° 04,33’W; 31° 58,69’S/052° 03,30’W; 32° 03,00’S/052° 02,87’W and 32° 02,99’S/052° 04,24’W); medium estuary (32° 02,99’S/052° 04,24’W; 32° 03,00’S/052° 02,87’W; 32° 07,99’S/052° 05,66’W and 32° 08,00’S/052° 06,19’W); mouth of estuary (32° 08,00’S/052° 06,19’W; 32° 07,99’S/052° 05,66’W; 32° 11,21’S/052° 04,47’W and 32° 11,27’S/052° 04,83’W); adjacency south (32° 09,97’S/052° 05,90’W; 32° 11,27’S/052° 04,83’W; 32° 12,17’S/052° 07,84’W and 32° 11,40’S/052° 08,72’W); medium south (32° 11,40’S/052° 08,72’W; 32° 12,17’S/052° 07,84’W; 32° 16,01’S/052° 12,16’W and 32° 15,31’S/052° 13,12’W); further south (32° 15,31’S/052° 13,12’W; 32° 16,01’S/052° 12,16’W; 32° 20,42’S/052° 15,57’W and 32° 19,82’S/052° 16,60’W); adjacency north (32° 09,61’S/052° 04,85’W; 32° 11,20’S/052° 04,47’W; 32° 07,93’S/052° 02,33’W and 32° 07,20’S/052° 03,27’W); medium north (32° 07,20’S/052° 03,27’W; 32° 07,93’S/052° 02,33’W; 32° 03,73’S/051° 58,25’W and 32° 03,07’S/051° 59,24’W) and further north (32° 03,07’S/051° 59,24’W; 32° 03,73’S/051° 58,25’W; 31° 59,71’S/051° 53,95’W and 31° 59,03’S/051° 54,93’W).