Sightings of marine mammals carried out during oceanographic surveys in the Argentine continental shelf

Study Extent

The Argentine continental shelf extends between the coast of Argentina and the continental slope, with a surface estimated of 1,000,000 km2 and depths less than 100 m in most of its extension (Fig. X). The continental shelf is dominated by two marine currents: the Malvinas Current and Brazil currents. The Malvinas current is a cold and rich in nutrients current that flows north along the continental slope of Argentina up to 38◦ S. The Brazil current is a warm and poor in nutrients current that enters the Argentine Sea from the north, along the slope, and moves south to meet Malvinas current. The collision of these two currents, known as the Brazil/Malvinas Confluence, is a transition area whose location varies seasonally between 30 and 46º S.

Sampling

Data were collected using line transect sampling methodology (Buckland et al. 2001).

Quality Control

During the census, all the individuals were identified at the lowest possible taxonomic level (species or genus) using reference guides of marine mammals (Folkens et al. 2002, Shirihai & Jarrett 2002, Shirihai et al. 2006, Bastida & Rodriguez 2010, Jefferson et al. 2011). All the scientific names of marine mammals were validated by matching them against World Register of Marine Species database (WoRMS, http://www.marinespecies.org/). The latitude and longitude of sightings were plotted on a GIS software to detect the outliers, which were corrected following the course of the ship.

Method steps

1. In the Coriolis II mission, one observer, in the roof of the wheelhouse, recorded all the marine mammals in a range of 300 meters in the side of the boat with better visibility using 7x50 binoculars. A screen connected to pilot’s cabin, shown in real time: ship position, ship speed and direction, wind speed and direction, latitude, and longitude. The census was conducted continuously during daylight hours (7-21 hours) when the ship was sailing at a relatively constant velocity of 10 knots. Species, number of individuals, behavior, sea state, ship speed and direction, wind speed and direction were recorded, and each observation was automatically recorded the position (latitude and longitude), date and time of day. In the other censuses, the marine mammals sightings were recorded on a portable handheld computer with integrated GPS (Trimble Juno ST), using the free software CyberTracker (CyberTracker Software (Pty) Ltd Reg. no. 97/01908/07, http://www.cybertracker.co.za). Surveys were conducted daily during daylight hours (~ 12 hrs) at a mean vessel speed of 10 knots. During the surveys, two observers collected the data from both sides of the vessel, through naked eye scans supplemented by use of 7x50 binoculars with internal compass and reticle. A third observer assisted in the scans and recorded observations. Observers switched between the three positions at 2 hour intervals. Data recorded for each sighting included GPS position, date and time, sighting distance, sighting angle, species, group size and composition. Vessel speed, air temperature, wind speed and direction, Beaufort Sea State (BSS), cloud cover and visibility were recorded at the start of each day and updated whenever they changed.

All individuals were identified to species level, except for some individuals that been identified until family and genus level. The dataset comprises 7 families, 14 genus and 18 species.

1. Arctocephalus australis
   common name: South American fur seal rank: species
2. Balaenoptera bonaerensis
   common name: Antarctic minke whale rank: species
3. Balaenoptera borealis
   common name: Sei whale rank: species
4. Cephalorhynchus commersonii
   common name: Commerson's dolphin rank: species
5. Delphinus delphis
   common name: Short-Beaked common dolphin rank: species
6. Eubalaena australis
   common name: Southern right whale rank: species
7. Globicephala melas
   common name: Long-finned pilot whale rank: species
8. Lagenorhynchus australis
   common name: Peale's dolphin rank: species
9. Lagenorhynchus cruciger
   common name: Hourglass dolphin rank: species
10. Lagenorhynchus obscurus
    common name: Dusky dolphin rank: species
11. Megaptera novaeangliae
    common name: Humpback whale rank: species
12. Mirounga leonina
    common name: Southern elephant seal rank: species
13. Orcinus orca
    common name: Killer whale rank: species
14. Otaria flavescens
    common name: South American sea lion rank: species
15. Phocoena dioptrica
    common name: Spectacled Porpoise rank: species
16. Physeter macrocephalus
    common name: Sperm whale rank: species
17. Tursiops truncatus
    common name: Common bottlenose dolphin rank: species
18. Balaenoptera
    common name: Baleen whales rank: genus
19. Balaenopteridae
    common name: Rorquals rank: family
20. Delphinidae
    common name: Dolphins rank: family

Argentine continental shelf (Southwest Atlantic Ocean)