Monday, 8 December 2008

Biological Observations

The dominant bird species on the cruise is the Sooty Tern Sterna fuscata. Almost 90 hours of observation have been completed so far producing almost 2000 birds. In the north Common Noddy Anous stolidus, threatened some competition, but this waned as the survey progressed south. Tropical (formerly Audobon’s) Shearwater Puffinus Iherminieri and Parasitic Jeager Stercorarius parasiticus (harassing Sooty Terns) was of interest in the north.

Several feeding aggregations of terns were observed throughout the survey (but not the 6 December), the group size varying from 50 – 480 birds. All the aggregations were associated with feeding activity of small tuna. Some Sooty Terns were seen to grab small slender silver fish. A bird aboard at night regurgitated several small squid, a species taken frequently in trawls conducted to date. Other species were few and far between, but the most productive area for diversity seemed to be on the approaches to Madagascar and northward towards Juan da Nova Island. Of interest in this region was Great Frigatebird Fregata minor, Red-footed Booby Sula sula, White-tailed Tropicbird Phaethon lepturus, Wedge-tailed Shearwater Puffinis pacificus, Jouanin’s Petrel Bulwaria fallax, Black-bellied Storm Petrel Fregetta tropica and Wilson’s Storm Petrel Oceanites oceanicus. The survey moved across to the Mozambican coastline and the steady flow of birds dried up. We await a clearer picture to see where and why the birds numbers improve as the survey progresses. Oddities included Madagascar Squacco Heron and Cattle Egret.

Cetaceans were scarce, but when seen exhibited a reluctance to be remotely close to the vessel, which severely inhibited their identification. This behaviour may result from the acoustic equipment used for fish location. However, despite this Sperm Whale Physeter macrocephalus, Minke Whale Balaenoptera acutororostrata, Cuvier’s Beaked Whale Ziphius cavirostris, Short-finned Pilot Whale Globicephala macrorhynchus, False Killer Whale Pseudorca crassidens, Bottle-nosed Dolphin Tursiops truncatus, Common Dolphin Delphinus delphis and Spinner Dolphin Stenella longirostris, have been positively identified. I might add that only the Minke Whale sightings have been relatively close to the vessel.

False Killer Whales
Sooty Tern

written by Bruce Dyer – MCM, Top Predator observer (photos: S Kaehler)

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