Special Web Article from OceanWanderers

Frontispiece: Juan Fernandez Petrel. Photo by Hadoram Shirihai ©2003.

As part of my ongoing work, the forthcoming tubenoses monograph and the Marine Mammal Guide (for A. C. Black, and Princeton Univ. Press for the UK and US editions, respectively), I recently joined a research vessel for a cruise in the Eastern Pacific Ocean. This three weeks voyage, aboard the NOAA ship McArthur II, departed from Costa Rica on 6 October and traveling westwards via the Galapagos Archipelago, to survey Pacific waters to a point c. 2500 Km from land, where we shifted eastward, and returned to South America, traveling through the rich Humboldt Current to make landfall at Callao in Peru.

The expedition is part of a large scale marine mammal and ecosystem sampling project known as 'Stenella abundance research', under the organisation of Chief Scientist Dr. Lisa Ballance of the Southwest Fisheries Science Centre, La Jolla, California, National Marine Fisheries Service, US Department of Commerce. There is another ship, the David Starr Jordan, that was operating simultaneously in the area to the north of us.

Fig. 1. Pink-footed Shearwater. Photo by Hadoram Shirihai ©2003.

I can find no better way than refering to this voyage as the 'petrel cocktail', the list of petrel species we encountered is given below (with approximate numbers and tubenoses species*) and speaks for itself:

Waved Albatross Phoebastria irrorata (80)

Cape Petrel Daption capensis (1)

Kermadec Petrel Pterodroma neglecta (120)

Herald Petrel Pterodroma arminjoniana (15)

Henderson Petrel Pterodroma atrata (30, see note below)

Murphy's Petrel Pterodroma ultima (23)

Juan Fernandez Petrel Pterodroma externa (150)

Galapagos Petrel Pterodroma phaeopygia (225)

Gould's Petrel Pterodroma leucoptera (250)

Stejneger's Petrel Pterodroma longirostris (30)

Defilippe's Petrel Pterodroma defilippiana (250)

Cook's Petrel Pterodroma cookii (11)

Tahiti Petrel Pseudobulweria rostrata (15)

White-chinned Petrel Procellaria aequinoctialis (20)

Parkinson's Petrel Procellaria parkinsoni (12)

Pink-footed Shearwater Puffinus creatopus (55)

Wedge-tailed Shearwater Puffinus pacificus (50)

Christmas Shearwater Puffinus nativitatis (6)

Sooty Shearwater Puffinus griseus (90)

Short-tailed Shearwater Puffinus tenuirostris (1)

Audubon's Shearwater Puffinus lherminieri (110)

Wilson's Storm Petrel Oceanites oceanicus (1)

White-vented Storm Petrel Oceanites gracilis (80)

White-bellied Storm Petrel Fregetta grallaria (150)

Wedge-rumped Storm Petrel Oceanodroma tethys (2100)

White-faced Storm Petrel Pelagodroma marina (4)

Hornby's Storm Petrel Oceanodroma hornbyi (350)

White-throated Storm Petrel Nesofregetta fuliginosa (4)

Madeiran Storm Petrel Oceanodroma castro (800)

Leach's Storm Petrel Oceanodroma leucorhoa (750)

Markham's Storm Petrel Oceanodroma markhami (150)

Peruvian Diving Petrel Pelecanoides garnotii (15)

(*The above numbers represent birds at optimal views allowing definite identification, of course many more petrels observed at a greater distances and not included here).

Figs. 2 & 3. Hornby's Storm-Petrel. Photo by Hadoram Shirihai ©2003.

Fig. 4. Markham's Storm-Petrel. Photo by Hadoram Shirihai ©2003.

Besides the amazing spectacle of up to 7 species of gadfly petrels in a day, we also observed many frigatebirds, skuas, boobies, terns, a number of oceanic dolphin species, a few Blue (see discussion below) and Bryde's Whales, and an amazing observation of the rare Fraser's Dolphin, Lagenodelphis hosei.

Fig. 5. Fraser's Dolphin. Photo by Hadoram Shirihai ©2003.

Beside gaining at-sea experience with the many different species of petrels that occur in this area, I also gathered a number of interesting behavioural and distributional facts. For example, it is clear that in the deep pelagic zone, some 2000 km from land, the sea belongs almost exclusively to the gadfly petrels - and the fortunate people who go after them. In the very deepest water, we encountered Herald, Henderson, Juan Fernandez, Gould's and Stejneger's Petrels with regularity, whereas we found Galapagos, Defilippe's and Cook's Petrels to be more abundant slightly closer to the continent Defilippe's and Cook's Petrels tended to occurs farther south than the others and primarily in the Humboldt Current.

Fig. 6. Galapagos Petrel. Photo by Hadoram Shirihai ©2003.

The storm-petrels and the small number of Kermadec Petrels were scattered throughout the cruise track. As might be expected, Galapagos Petrel, Madeiran Storm-Petrel and Galapagos Storm-Petrel were most numerous in the vicinity of their nesting islands, although surprisingly they were sometimes encountered well away from the Galapagos Islands as well. Bear in mind that this is probably an over simplification of a complex situation. We noticed that several species were forming post breeding moult concentrations in different areas, such as a gathering of 1000's of Galapagos Storm-Petrels southwest of the islands, which resulted in some birds taking on a very odd Madeiran Storm Petrel-like appearance. At this time of year, Defilippe's Petrel were in active molt allowing easy separation of this species at a distance from the fresh and unmolted Cook's Petrels.

Fig. 7. Defilippe's Petrel. Photo by Hadoram Shirihai ©2003.

Other noteworthy observations included the amazing ability of Juan Fernandez Petrels to catch flying fish in the air, while Kermadec Petrels frequently "mimic" Stercorarius-Skuas in plumage, flight mode and appearance (especially the intermediate and dark morphs), enabling them to challenge other petrels to give up their food. Another interesting observation was the propensity of White-bellied Storm-Petrels to be found associating with pilot whales.

In the last few days 300-600 nautical miles off Peru and west of the cooler Humboldt / Peruvian Current at about 10-15°S, we encountered five sightings of probable 'Pygmy' Blue Whales (see photo below). The total body length of most of these animals were estimated at 15-20 meters with a general appearance of being more attenuated and noticeably compact (in comparison to both the nominate Baelenoptera m. musculus which both Richard Rowlett and myself have observed in the Northern Hemisphere, B. m. intermedia of the Southern Hemisphere, which is believed to reach north to about 22°S in the Pacific off South America, perhaps even as far north as to the Galapagos Islands, as well as B. m. indica of the N Indian Ocean).

Fig. 8. Blue Whale sp. - possibly Pygmy Blue Whale. Photo by Hadoram Shirihai ©2003.

Thus, these animals most likely represent Pygmy Blue Whales B. m. brevicauda, which appear to possess a proportionally shorter rostrum (area forward of blow hole) and very shortened and slender caudal peduncle (area between the dorsal fin and base of the flukes). The small nub-like dorsal fin was located on the last 1/3 to 1/4 of the back and about 3 meters forward of the flukes thus highlighting this diagnostic characteristic. Fluke width was estimated to be about 1/4 the total body length and flippers were proportionally long as well. Apart from showing 'blue' below the surface, the proportions of these animals seem quite rotund in the middle third and somewhat suggestive of a Right Whale in appearance. Compared to the larger 'True' Blue Whales, these animals observed off Peru appeared less mottled and more uniform colored gray-blue. 'Pygmy' Blue Whales are generally best known to occur in Subantarctic waters of the Indian and southwest Pacific Oceans where we have seen them during our previous travels and research there. We can also add that all animals we have seen so far were about the same in size, proportion, coloration, behaviour, and most likely full grown adults. All of our sightings were maintaining an unwaivering course to the SSE at about 4 knots.

Interestingly enough, Rice (1998) mentioned [without additional details] that a population inhabiting the Peru Current along the coasts of Peru and Chile may also be Pygmy Blue Whales and our sightings may support this. However, identification of these forms at sea is very difficult and still not fully established; moreover, their taxonomic status remains unclear. that said, I will not be surprised if Pygmy Blue Whale is found to merit specific recognition.

The research team on board have taken biopsy samples and acoustic recordings from several of these animals for DNA analysis and comparison, and it will be interesting to match these with details of the features we noted or photographed at sea. There is on going blue whale research (mainly by a US team), including identifying and studying various stocks which could in the future help to understand the taxonomy and the ID of the blue whale populations, which are indeed complex and remain a work in progress.

Fig. 9. Possible Henderson Petrel. Photo by Hadoram Shirihai ©2003.

Another unresolved issue on this voyage is the status and identification of Henderson Petrel (see above photo), which should perhaps be considered a tentative sighting on our trip. Seeing these birds raises some important questions: Are all dark "Herald Petrels" in the Pacific Ocean in fact Henderson Petrels? Conversely, is there a dark-morph Pacific Herald Petrel with which Henderson Petrel can be confused? If so, how does one separate the two species at sea!!??

Fig. 10. Author/photographer at work. Photo by Michael Force ©2003.

Acknowledgements It was also extremely useful for my work to meet such a group of experts and professional observers on this voyage, and especially I like to thank seabird observers Michael Force and Chris Hoefer and senior mammal observer Richard Rowlett, the official observers on the voyage and with whom the above observations were made, as well as Cruise Leader, Dr. Susan Chivers and Chief Scientist, Dr. Lisa Ballance, for much help and great hospitality on board, and for permission to publish the above records. Also thanks to Michael Force and Richard Rowlett for many hours of interesting seabird and marine mammal discussions as well as providing valuable comments during this cruise and for this report. Other observers on board which should receive my thanks, and sorry if I was asking sometimes too many questions on taxonomy and identification, but it was great to share with you these amazing animals. They are: marine mammal observers Juan Carlos Salinas, Annie Douglas, Erin Labrecque, Michael Richlen, and Holly Fearnbach, and acousticians Shannon Rankin and Megan Ferguson.

This is an exclusive publication by OceanWanderers.com: readers referring this article requested to refer it as "Shirihai (2003)" and "Shirihai 2003. Petrel cocktail. Oceanwanderers.com Special Electronic Publication."

Fig. 11. Swallow-tailed Gull. Photo by Hadoram Shirihai ©2003.

Hadoram Shirihai is the author of the The Complete Guide to Antarctic Wildlife: Birds and Marine Mammals of the Antarctic Continent and the Southern Ocean, illustrated by Brett Jarrett and published in 2002 by Alula Press and Princeton University Press. In addition, Shirihai is the author of numerous identification articles and books on European and Middle Eastern birds. He is a leading authority on the birds of the Middle East, especially his native Israel and the Horn of Africa.

Text and photos copyright of Hadoram Shirihai© 2003 or Michael Force© 2003. All rights reserved. Page layout copyright of Angus Wilson© 2003 All rights reserved.
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