and GMW left Kiritirnati on 24 April and sailed to Starbuck (30 April, no landing) then south to Motu One (Bellingshausen Island), in the north-west. Society Group ...
)/ Sea Swallow 45 Seabirds at sea in the Line Islands and NW French Polynesia, Central Pacific by N. John Phillips, Martin C. Garnett, A. Kay Kepler, Mark D. Linsley, Annabel J. Seddon, and Graham M. Wragg" "Authors are listed alphabetically (except senior author)
Rcseut:hV('SSCI
"TeManu"
Introduction This paper reports at-sea seabird observations during a c. 7600 km voyage through the Line Islands (Kiribati) and Society Islands (French Polynesia), in the central Pacific. Observations were made from the 1 Om motor-sailing Research Vessel 'Te Manu' (skipper Graham Wragg), during March-May 1990. The distribution of seabirds in this region, particularly around the southern Line Islands, is little known. Observations are described and discussed with special reference to Kepler et al. (I 992) and Garnett (1983). This study formed part of the 1990 ICBP Line Islands Expedition (Kepler 1990). For a more detailed report see Phillips & Wragg (1993). PERSONNEL AND ITINERARY The expedition was initiated by MCG, AKK, and GMW. On the northbound leg (6 Mar. to 2 Apr.) AKK, MDL, NJP, AJS and GMW, with Alve Henricson (Mate), left Tahiti (Berkeley University Research Station, Cook's Bay, Moorea) after dark on 6 March and sailed north to Caroline Atoll (where we were ashore from 11-14th), then to Flint Island (ashore 16-18th) and Vostok Island (ashore 20-21st). From here we continued via Starbuck and Malden Islands (where landing was impossible) to Kiritimati (Christmas Island), arriving on 2 April. On the southbound leg MCG, AKK, MDL, AJS and GMW left Kiritirnati on 24 April and sailed to Starbuck (30 April, no landing) then south to Motu One (Bellingshausen Island), in the north-west Society Group, where we landed for two hours on 10 May. Thence we tracked south to c.17.5°S, north-east to Caroline Atoll (ashore 18-25 May), and south to Tahiti, arriving on 31 May. The boat's position was ascertained by CPS satellite fixes and sextant. The cruise track (Fig. l) was derived from these readings and from the Te Manu 's log. METIIODS Seawatching and recording methods were based on those of the Pacific Ocean Biological Survey Program (POBSP) of the US National Museum, Smithsonian Institution (King 1970; Gould, 1974 ), with reference to other studies (Haney 1985; Tasker et al. 1984; Gould & Forsell 1989). A virtually constant daylight watch was maintained while at sea. Watches usually began c.10 minutes before sunrise and ended c.] 0 minutes after sunset. They were occasionally interrupted by heavy rain squalls or for sailing duties, and were discontinued within c.5km of islands. Fifty days were spent at sea 71
)I
Sea Swallow 45
during which 7,600km were travelled, of this 367Skm were spent seawatching for a total of SOS hours of observation. At least one observer was on watch at any time, with regular changes every two hours. At times more than one observer was active, with a maximum (rarely) of four. Observations were usually carried out from a forward-facing position on top of the boat's cockpit, c.2.Sm above the waterline. A single observer in this position could observe the sea over a c.200 degree arc. Adding further observer(s) added at most only a small percentage of seabird sightings. References to periods of time for which observations were carried out relate to the number of hours spent watching, irrespective of the number of observers on watch. Every seabird sighting was logged with details of species, including time (local), number of birds, direction of flight, and whether in directed flight or feeding. All sightings have been included in the species accounts and in the discussion of feeding flocks. It should be borne in mind that our observations were carried out from a low elevation and so are likely to have missed a proportion of small and low-flying species, especially beyond c.400m. Most birds seen were within c. l ,OOOm. The speed of 'Te lvlanu' during this cruise, whether under sail or engine varied, with a maximum of c.6 knots (c. l l km/hr), and an average of 3-4 knots. Accordingly, numbers of birds seen per hour, rather than numbers per unit distance or unit area, are used when discussing bird densities. The majority of observations related to birds in flight past the boat. The numbers seen per hour are less subject to variability - due to the boat's speed - than numbers per km or km". The number of stationary birds (i.e. for the most part, feeding flocks) encountered per hour will vary with the boat's speed, but this is unlikely to have a major effect on the aspects discussed here.
l
o = Atolls
High Islands
• =
I
I
I
160"W
150"W
Track ol the Research Vessel
'to ssonu:
-Equator
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