The seabirds of the Conrad Rise, Southern Ocean

2009·6.3 MB·

by  Peter G Ryan

The seabirds of the Conrad Rise, Southern Ocean
Peter G. Ryan
Les oiseaux de mer du Conrad Rise, Ocean austral. A l’occasion d un inventaire
oceanographiquedu Conrad Rise (51-55°S et39-47°E) enavril 2008, les oiseauxdemerontete
recenses. Le Conrad Rise est une vaste zone relativement peu profonde oil le fond sous-marin
s’eleve a <3.000 m, situee juste au sud du Front polaire antarctique et 330-700 km au sud des
lies du Prince Edouard et Crozet. Au moins 28 especes ont ete observees, parmi lesquelles les
puffinures Pelecanoides spp., le Prion bleu Halobaena caerulea et le Petrel de Kerguelen Lugensa
(Aphodroma) brevirostris etaient les plus abondants, tandis que le Manchot royal Aptenodytes
patagonicusetle GorfoudoreEudypteschrysolophusrepresentaientlabiomasselaplus importante.
Le Petrel bleu et le Puffin a menton blanc Procellaria aequinoctialis etaient les plus abondants
pendant quele navire etaitimmobile, malgre le fait que l’Albatros hurleurDiomedea exulansetle
Petrel de Hall Macronectes halli etaient les especes les plus attirees par le navire. La plupart des
especes etaient plus abondantes au nord de lazone prospectee, mais le Puffin fuligineux Puffinus
griseus a uniquement ete recense au sud de 56°30’S. Des photos numeriques ont permis de
confirmer 1'identification des groupes d'especes difFiciles adistingueren mer, surtoutles prions.
Le Prion de Belcher Pachyptila belcheri et le Prion colombe P turtur etaient les prions les plus
abondants, tandis que le Prion de la Desolation P. desolata a ete observe en petit nombre, et le
Prion de Salvin Psalvinipas du tout. Relativement peu de mammiferes marins ont ete observes;
le Rorqual commun Balaenopteraphysalusetait toutefois commun au sud de 56°S. Le resultatdes
transects n’indique pas une abondance avienne plus importante dans les eaux peu profondes
(<250 m). La frequentation du navire par les oiseaux etait toutefois la plus grande sur le Banc
O’b, ce qui est peut-etre indicatifd’activites de peche recentes. La peripherie du Conrad Rise
sembleetreuneimportantezonedenourrissagepourlespuffinuresetlesmanchotsacetteepoque
de l’annee.
Summary. Seabirds were counted during an oceanographic survey ofthe Conrad Rise (51-55°S
and39-47°E) inApril2008.TheConradRiseis alargeareaofshallowerwaterwheretheseafloor
rises to < 3,000 m deep, lyingjust south oftheAntarctic Polar Front and 550-700 km south of
the Prince EdwardandCrozetarchipelagos.Atleast28 specieswereobserved, with divingpetrels
Pelecanoidesspp., and Blue Halobaena caerulea and Kerguelen Petrels Lugensa {Aphodroma) brevi-
rostris most abundant, but King Aptenodytes patagonicus and Macaroni Penguins Eudyptes
chrysolophus dominating in terms ofbiomass. Blue Petrels andWhite-chinned Petrels Procellaria
aequinoctialiswere mostabundantwhile theshipwas stationary, althoughWanderingAlbatrosses
Diomedea exulans and Northern Giant Petrels Macronectes halliwere most strongly attracted to
theship. Mostspeciesweremoreabundantin thenorth ofthesurveyarea, butSootyShearwaters
Puffinusgriseuswere onlyrecorded south of56°30’S. Digital photographywas useful to confirm
the identification of species groups that are tricky to discriminate at sea, especially prions.
Slender-billed Prion Pachyptila belcheriand Fairy Prion P. turturwere the most abundant prions,
with only small numbers of Antarctic Prions P. desolata, and no Salvin’s Prions P. salvini.
Relativelyfewmarine mammals were observed, but FinWhales Balaenopteraphysaluswere com-
monsouthof56°S.Transectsprovidedno evidenceofincreasedbirdabundanceatshallow(<250
m) seamounts, but ship attendance peaked on the O’b Bank, possibly reflecting recent fishing
activities. The periphery ofthe Conrad Rise appears to be an important foraging area for diving
petrels and penguins at this time ofyear.
T m
he Conrad Rise is a large area of shallower from the abyssal plain >4,000 deep to < 3,000
m
water in the Southern Ocean between deep (Fig. 1). This change in bottom topogra-
51-55°S and 39-47°E, where the seafloor rises phyapparentlyinfluenceslocaloceaniccirculation
Theseabirdsofthe ConradRise, Southern Ocean:Ryan BullABCVol16No 1 (2009)-67
patterns, resultingineastwardjetsnorthandsouth
ofthe rise. The Conrad Rise lies just south ofthe
Antarctic Polar Front, c.550 km south-southeast
ofthe Prince Edward Islands and 700 km south-
west ofthe Crozet Islands. Both archipelagos are
breeding sites for globally important seabird pop-
ulations, notably large numbers of penguins,
albatrosses and petrels (Williams 1995, Brooke
2004, Ryan & Bester 2008). The Conrad Rise lies
in an area used extensively by King Penguins
Aptenodytespatagonicus from the Crozets (Piitz et
&
al. 1999, Charrassin Bost 2001), and a
Macaroni Penguin Eudyptes chrysolophus tracked
during its pre-moult fattening trip travelled 700
km south ofthe islands into the generalvicinityof
the rise (Hockey etal. 2005).
TheConradRiseincludestwoseamounts, O’b
Bank and Lena Seamount, which extend to with-
in 250 m of the surface. Another, unnamed
seamount lies just east ofthe Rise (Fig. 1). These Figure 1.Thestudyareain relationto thePrinceEdward
andCrozetislandsandregionalbathymetry, showingthe
seamounts have been fished for Patagonian tooth-
cruisetrack, witharrows indicatingthedirection oftrav-
fish Dissostichus eleginoides, but there are no el. Circles alongthecruisetrackare CTD stations (open
published observations on the region’s birds. = daylight, closed= night).
Albatrosses and petrels at risk from long-line fish- Lazoned’etudeparrapportauxlies duPrinceEdouard
ing have been tracked into the general area south etCrozetetlabathymetrie regionale, avecletrajetdu
of the Prince Edwards and Crozets (BirdLife navire, les fleches indiquantladirectiondunavire. Les
International 2004). I accompanied an oceano- cercleslelongdutrajetdunaviresontdesstations CTD
graphic survey of the region in April 2008 to (conductivity, temperature, profondeur) (ouvert = de
record the distribution and abundance ofseabirds jour, ferme = denuit).
associated with the Conrad Rise. The survey especially when the sea is rough. All birds were
included the surrounding seas between 48-57°S recorded to the nearest minute, but were pooled
and 38-48°E (Fig. 1), and took place in autumn, into 30-minute minimum count blocks.
when sea-ice conditions were minimal around Identification of tricky groups was confirmed,
Antarctica. A satellite ice image for 4 April 2008 wherepossible, byphotographingbirdswithadig-
indicated no sea-ice north of64°S in the sector of ital SLRand 500-mm telephoto lens.
the Southern Ocean between 30-60° E. The oceanographic survey departed Marion
Island on 3 April, and commenced sampling at
Methods 49°S 38°E on 4 April. Initially a widely spaced
Seabirds were counted during the day (roughly grid was run with north-south legs at 38°E, 44°E
06.30-17.30 hrs local time) on standard steaming and 48°E (Fig. 1). On these legs, CTD (conduc-
transects (Tasker etal. 1984) as well as at oceano- tivity, temperature, depth) stations were
graphic stations. Transects were conducted from conducted every 30 nautical miles. This required
m
the ship’s bridge (9 above sea level), looking the ship to stop on station for c.70-90 minutes
beyond the bow on that side ofthe ship offering while the CTD was lowered to 2,000 m. Stations
best visibility. Flying birds were counted, using were shorter where the water was shallower.
binoculars, every minute by scanning a 300 m- Between stations, the ship steamed at 9-12 knots
block extending forward from the bow. Ship (16.5-22 km.lr1), permitting 2.0-2.5 hours of
followers that repeatedly circled the ship were transect counts. Counts did not commence until
excluded. More frequent scans were made of the the ship had attained full speed and had left the
same area for birds on thewater, such as penguins laststation byatleast2 km. On average, 5.3 hours
and diving petrels, which are easily overlooked, of transects were conducted daily (3.5-7.5), all
68-BullABCVol16No 1(2009) Theseabirdsofthe ConradRise, Southern Ocean:Ryan
made by the same observer. Crude estimates of Results and Discussion
seabird density (numbers.knr2) were made assum- At least 28 seabird species were recorded, 24 dur-
ing the transect counts accurately reflected the ing 80 hours ofsteaming transects and 25 at 35
abundance of flying birds in the 300-m wide oceanographic stations or during ten stern counts
count area. Apart from 18 April, when seas were (Table 1). The most abundant birds during tran-
exceptionally calm, no penguin groups were sects were diving petrels Peleconoides spp., Blue
m
observed >200 from the ship (80% <100 m, Petrels Halobaena caerulea Kerguelen Petrels
,
n-96 groups), and so a conservative estimate of Lugensa Aphodroma brevirostris and crested pen-
( )
200-m wide effective transect width was assumed guins Eudyptes spp., whereas on stations Blue
for all days except 18 April (300 m). Petrels and White-chinned Petrels Procellaria
At each CTD station, counts ofbirds attend- aequinoctialis predominated (Table 1). Most alba-
ing the ship (within c.500 m) were made for ten trosses and petrels exhibited a high index ofship
minutes shortly after arrival at the station, and attraction (Table 1), with Northern Giant Petrels
again after30 and 60 minutes. Dumpingofgalley Macronectes halli and Wandering Albatrosses
waste (the only material dumped at sea) was only Diomedea exulans highest, followed by White-
conducted after dark each evening and thus chinned Petrels, sooty albatrosses Phoebetria spp.,
should not have overly influenced the behaviour Southern Giant Petrels Macronectes giganteus
,
of birds to the ship. After testing for consistent Pintado Petrels Daption capense and Grey Petrels
patterns in numbers ofbirds attending as a func- Procellaria cinerea. Only specialist diving species
tion of time on station, a single count for each (diving petrels, penguins and shearwaters) were
station was taken to be the maximum number of encountered much more frequently during tran-
each species seen during the three counts. Only sects than attending the ship (Table 1).
one or two counts were made at stations conduct- Species richness decreasedwith increasinglati-
ed at dawn or dusk and at some shallow-water tude due to several species failing to penetrate
sites.Typicallythreestationswereconducteddaily, south of 52°S (e.g. Soft-plumaged Petrel
but on some days there were longer steams Pterodroma mollis Little Shearwater Puffinus
,
between stations (transits from 38-44°E, assimilis). Other species occurred further south,
44-48°E, 48°E to Lena Seamount, between Lena but were more abundant in the north (e.g. Sooty
Seamount and O’b Bank, and from O’b Bank en Albatross Phoebetria fusca Great-winged Petrel
,
route to Marion Island). Stern counts ofbirds fol- Pterodroma macroptera Grey Petrel). Sooty
,
lowing the ship were made during these legs and Shearwater Puffinus griseus was the only species
used in lieu ofstation counts to bring the sample that was recorded in the south ofthe survey area
sizeforeachdayto threecounts.Theratio ofbirds but was absent further north. The following sec-
attending the ship to those counted during tran- tions report the distribution and abundance
sects was used to provide a crude index of ship patterns ofthe species encountered.
attraction.
Thecoursegridconcludedat 56°S 48°Eon 13 Penguins
April. The ship then travelled to Lena Seamount, Given the general paucity ofsightings at sea away
where 13 CTD stationswere conducted 20 nauti- from colonies in the Southern Ocean (Enticott
&
cal miles apart and to O’b Bank, where nine 1986, Marchant Higgins 1990), alargenumber
stations were conducted 13 nautical miles apart ofpenguins was counted. However, some groups
(Lig. 1). This permitted 1.0-1.3 hours oftransect doubtless were overlooked, especially in rough
observations between stations, finally, the ship seas, so the number counted represents a mini-
returned to Marion Island, arriving early on 19 mum estimate of penguin abundance. Most
April. Steaming transects were conducted until observations were of crested penguins. Both
48°S. During the surveywe visited one iceberg at Macaroni and Southern Rockhopper Penguins
33°36’S 47°21’E on 13 April. The only other ice Eudyptes chrysocome may occur in the region, but
encountered was three distant icebergs (>20 km all crested penguins positively identified were
offthe cruise track) between 54°45’S and 55°20’S Macaroni Penguins. Only four of70 groups were
at 38°00’E on 6 April. No other shipping was thought to be possible Rockhoppers (one at
encountered during the survey. 49°05’S 37°59’E, two at49°15’S44°00’Eandone
Theseabirdsofthe ConradRise, Southern Ocean:Ryan BullABCVol16No 1(2009)-69
Table 1. Numbersofbirdscounted during steamingtransects (80 hours)and attendingtheship (maximum countsat35
stationsandten stern countswhilesteaming). Frequencyofoccurrence reportsthe percentageof30-minutetransectcounts
(n=160)and shipcounts (n=45)forwhich a specieswas present.
Tableau 1. Nombred’oiseauxde merrecensesen parcourantlestransects (80 heures)etfrequentantle navire (totaux
maximauxsur35stationsetdixcomptagesa partirde la poupeen navigant). Lafrequencede presence indiquele
pourcentagedescomptagesdetransectsde30 minutes(n=160)etdescomptagesautourdu navire (n=45)pendant
lesquelles I’especeetaitpresente.
Species Transects Stations Total Ship
n %freq. n %freq. attraction*
—
EmperorPenguinAptenodytesforsteri 0 0 1 2 1
KingPenguinAptenodytespategonicus 132 16 3 4 135
AdeliePenguinPygoscelisadeliae 1 1 0 0 1 —
CrestedpenguinsEudyptesspp. 232 29 33 11 265
WanderingAlbatrossDiomedeaexulans 6 4 89 80 95 +++
Grey-headedAlbatrossThalassarchechrysostoma 14 9 44 69 58 +
SootyAlbatrossPhoebetriafusca 4 3 13 29 17 ++
Light-mantledSootyAlbatrossPhoebetriapalpebrata 16 11 36 56 52 +
SouthernGiantPetrelMacronectesgiganteus 5 3 37 53 42 ++
NorthernGiantPetrelMacronecteshalli 4 2 109 71 113 +++
SouthernFulmarFulmarusglacialoides 0 0 3 7 3
PintadoPetrelDaptioncapense 2 1 22 36 24 +++
BluePetrelHalobaenacaerulea 286 84 478 100 764
AntarcticPrionPachyptiladesolata 17 8 12 20 29
Slender-billedPrionPachyptilabelcheri 65 29 112 71 177
FairyPrionPachyptilaturtur 48 23 71 67 119
KerguelenPetrelLugensa(Aphodroma)brevirostris 174 71 84 84 258 -
Soft-plumagedPetrelPterodromamollis 9 5 3 7 12
White-headedPetrelPterodromalessonii 18 11 11 24 29
Great-wingedPetrelPterodromamacroptera 12 8 11 22 23
White-chinnedPetrelProcellariaaequinoctialis 33 20 263 98 296 ++
—
GreyPetrelProcellariacinerea 5 3 12 24 17 +
SootyShearwaterPuffinusgriseus 96 3 2 2 98
—
LittleShearwaterPuffinusassimilis 2 1 0 0 2
DivingpetrelsPelecanoidesspp. 378 66 10 22 388
Wilson’sStormPetrelOceanitesoceanicus 1 1 0 0 1
Black-belliedStormPetrelFregettatropica 34 17 28 42 62
SubantarcticSkuaCatharactaantarctica + 0 0 0 +
ArcticTemSternaparadisaea 0 0 1 2 1
Total 1,593 1,487 3,082
*ratiooftransecttoshipcounts;+indicatesmoreoftenattheship-moreoftenontransects.Numberofsymbolsdenotesstrengthofdifference:+++/—>tenfold,++/—
5-10fold,+/-2-5folddifference(nosymbolimplieseitherthesamplesizeistoosmall,ordifference<twofold).
at 49°06’S 44°50’E), but none was photographed 72=5). The few at-sea sightings of Macaroni
to confirm identification. All groups pho- Penguins suggest theymove south ofthe breeding
tographed {n=23) were correctly identified as islands in thesouth-westIndian Ocean (Marchant
&
Macaroni Penguins (broad crest and large pink Higgins 1990). Macaroni Penguins from
gape). Theywere observed south to 53°2l’S, with Marion Island in the Prince Edwards have been
peak densities at 50-52°S (Fig. 2). The density trackedto 700 km south ofthe islandduringtheir
between 48-49°S is perhaps biased because the pre-moult fatteningtrip (Hockeyetal. 2005; R.J.
transects were relatively close to Marion Island. M. Crawford pers. comm.).
Group size during transects was 3.5 ± 3.6 {n=65 King Penguins generallywere easier to spot at
groups, mode 2, range 1-20), and all pho- sea than crested penguins, especially among large
tographed birds were adults (based on waves, because they usually extended their long
well-developed crests). Macaroni Penguins also necks to peer at the vessel. Unlike crested pen-
were observed at five stations, where group sizes guins, they seldom porpoised away from the ship.
averaged slightly larger (6.6 ± 4.5, range 2-14, However, they were less often seen at stations,
70-BullABCVol16No 1(2009) Theseabirdsofthe ConradRise, Southern Ocean:Ryan
despite being more curious of ships than crested resulting in display and calling. The predomi-
penguins close to the Prince Edward Islands (pers. nance of adult males further south corroborates
obs.). KingPenguinswere most common between previous observations and tracking data in the
51°30’S and 34°S, although small numbers were southern Indian Ocean (Weimerskirch &
seen further north (Fig. 2). Like diving petrels, Jouventin 1987,Weimerskirch 1998). However, it
there was a tendency for a lower density over the is unlikely that many breeding birds were in the
shallows of the Conrad Rise compared to the area, as the survey took place during the
periphery. Group size during transects 4.3 ± 3.6 brood/guardphase, when foragingtrips tendto be
[n-31 groups, mode 2, range 1-18) was greater localised around the breeding islands
than that of groups visiting the ship on station (Weimerskirch 1998, Nel et al. 2002). Based on
(1.3 ± 0.7, range 1-2, n=2). All but one (a lone limited tracking data, it is more likely the birds
immature at 53°S 38°E on 5 April) were adults encountered came from the Crozets rather than
with bright orange neck patches. King Penguins the Prince Edwards or Kerguelen (BirdLife
from the Crozet Islands forage south of45°S irre- International 2004).
spective of season, travelling 500-750 km from Grey-headed Albatross Thalassarche chrysos-
colonies in summer and up to 1,800 km during toma was the next most abundant albatross and
winter, including into the pack-ice to 62°S (Piitz again adults predominated, with only four imma-
&
etal. 1999, Charrassin Bost 2001). tures (7%) seen. However, at least one apparent
A single immature Emperor Penguin adult that was photographed still had a dark nail,
Aptenodytesforsterivisitedtheshipwhileonstation indicating it was a subadult, perhaps 3-4 years
at 53°S 38°E on 5 April. Itwas next to a group of old. Three of the immatures were seen north of
Macaroni Penguins, andtherewere KingPenguins 52°S (11% ofbirds in this area), with the other
at the same station. Itwas readily identified by its immature at 56°15’S 42°25’E (4% ofbirds south
large size, relatively short neck and bill, diffuse of 52°S). Latitudinal segregation of adults and
white neck patch, and humped back that pro- immatures has not been reported in this species
trudes much furtherabove thesurfacethan thatof (Tickell 2000), although almost all records north
aKingPenguin.The onlypenguin observedsouth of40°S are immatures (Hockey etal. 2005).
of 54°S was tentatively identified as an adult Light-mantled Sooty Albatross Phoebetria
Adelie Penguin Pygoscelis adeliae based on its all- palpebratawas thealbatrossleaststronglyattracted
dark head and throat, and short bill. However, to the ship, although they were still more abun-
lightconditionswerepoor, and thereis achanceit dant in station counts than during transects. A
was a crested penguin (albeit well south of all higher proportion of this species (37%) was in
otherrecords). BothEmperorandAdeliePenguins mottled immature plumage and, unlike the other
typically remain further south, but vagrants reach albatross species, immatures tended to be more
the subantarctic (Marchant & Higgins 1990). common further south (21% north of52°S, 29%
between 52-54°S and 60% south of54°S). Sooty
Albatrosses Albatrosswas relativelyscarce. Allwere adults and
Only four species of albatross were observed, were onlycountednorth of53°S, butan adultvis-
although two others (Black-browed Thalassarche itedtheshipbrieflyat55°50’S 38°00’Eon6April.
melanophrisand Shy T. cauta) followed the ship at SootyAlbatrosses breeding at both Marion Island
46°59’S 38°10’Esouth-eastofMarion Islandon 3 and the Crozets remain north of the Antarctic
April. Wandering Albatross was the most abun- Polar Frontataround 50°S (Berruti 1979, Cooper
&
dant albatross overall, with most atstations (Table Klages 1995, Weimerskirch 1998), whereas
1). The largest aggregation was observed on O’b Light-mantled Sooty Albatrosses forage south of
Bank on 17 April, when up to 11 gathered at the the Front (R. J. M. Crawford unpubl.). However,
ship. With the exception of a stage 2 (‘leopard Jouventin etal. (1981) reported both species to be
stage’) bird observed at 49°S 44°E, all were in common south to 56°S in the south Indian
adult plumage (Gibson stages 5-8), and south of Ocean, and they occasionally eat Antarctic krill
53°S mostwere terminal stage’, presumably adult Euphausiasuperba which mustbe caughtsouthof
,
males. The youngster (an apparent female based the Front (Ridoux 1994).
on bill size and shape) landed with three adults,
TheseabirdsoftheConradRise, Southern Ocean:Ryan BullABCVol16No 1(2009)-71
KingPenguin Crested Divingpetrels BluePetrel KerguelenPetrel
Aptenodytes penguins Pelecanoidesspp. Halobaena Lugensa
patagonicus Eudyptesspp. c=aerulea brevirostris
H
I m i
3 4
; 1
ZZG
j l 1
1 i H .. . ] SB J 1
1 i i 1
=1
m 1 . !
in
1 1
i 1
0 1 0 1 2 0 1 2 0 1 0 0.5
Numberofbirds.km-2
Figure2.Averagedensityofthemostabundantseabirds countedinsteamingtransects asafunctionoflatitude.
Densitemoyennedes oiseauxdemerlesplus abondants recenses enparcourantlestransects enfonction delalatitude.
Fulmarine petrels a few hundred metres of the bow, but some
Giantpetrels occurredthroughoutthesurveyarea, undoubtedly returned after flying further ahead
with Northern outnumbering Southern. No and may have been counted in error. Although
white-morph Southern Giant Petrels were most were adults, some fresh-plumaged juveniles
observed. Both species were attracted to the ship, were photographed, distinguished by their more
followingwhileitwas travellingandeithercircling prominent pale feather fringes and paler crown
orrestingon thewaternextto the ship on station. and breast-band. BreedingBlue Petrels forageover
Thelargestnumbersofgiantpetrelswereobserved a wide latitudinal range, often travelling into
on O’b Bank on 17 April, when up to 27 (24 Antarctic waters >1,000 km from the breeding
NorthernandthreeSouthern) gatheredattheship islands (Cherel etal. 2002). Stable isotope analysis
while on station. The greater aggregation ofship- ofadultfeathers suggests thattheyremain in these
attendant species on O’b Bank may possibly waters during the moultingperiod.
reflect recent fishing activities. Reliable information on the distribution and
Other fulmarine petrels were surprisingly relative abundance of prions at sea is limited by
scarce, withonlysmall numbers ofPintado Petrels the difficulty of positively identifying them to
and Southern Fulmars Fulmarusglacialoides seen. species (Marchant & Higgins 1990). The use of
Itwaspresumablyjusttooearlyforthesespecies to digital photography was essential in this regard.
have dispersed north from their breeding areas On several occasions the presence ofa species was
&
(Marchant Higgins 1990).Therewas no signof only confirmed by examining photographs taken
the ice-specialist Snow Pagodroma nivea or at a station. Three species ofprions were observed
Antarctic Petrels Thalassoica antarctica. in the area: Antarctic Prion Pachyptila desolata,
Fairy Prion P. turtur and Slender-billed Prion P.
Blue Petrels and prions Pachyptila belcheri. FairyandSlender-billed Prionsweremost
Blue Petrels occurred throughout the survey area, abundant and occurred throughout the survey
with a tendency for higher densities at 54-56°S area, althoughFairyPrionsweremoreabundantin
(Fig. 2), supported by larger mean numbers the north, whereas Slender-billed Prions were
attending the ship at these latitudes. It was the more common further south, mainly south ofthe
most abundant species at stations, occurring at Antarctic Polar Front, with the greatest numbers
every station (Table 1), and, although second to at 54-56°S.The Slender-billed Prions presumably
diving petrels in terms ofabundance during tran- come from the large Kerguelen breeding popula-
sects, had the highest frequency ofoccurrence in tion (Brooke 2004).
half-hourtransect blocks (86%). Accurate transect Antarctic Prions were relatively scarce and
counts were complicated by the habit of petrels were only recorded south of 50°S. However,
accompanying the ship to fly ahead of it. It was Antarctic Prions also were fairly common at
possible to ignore such birds ifthey turned within 39-40°S on 28 March, en route between Cape
72-BullABCVol16No 1(2009) Theseabirdsofthe ConradRise, Southern Ocean:Ryan
Town and Marion Island. Interestingly, most of followers, seldom remainingat thevessel for more
these more northerly prions were moulting their than a minute or two. All were north of53°30’S.
primaries, whereas none of the birds south of Shearwaters generally were uncommon in the
Marionwas replacingtheflightfeathers. Onlyone area. Sooty Shearwaters were only seen on the
prion amongsthundredsphotographedin thesur- morning of7 April, when numerous flocks ofup
vey area was moulting its primaries: a to 30 were seen from dawn until 10.00 hrs. All
Slender-billedPrion completingits primarymoult were south of 56°30’S and travelling south-east.
on 10April at 49°S 44°E. Thiswas the onlydayofthe surveyspentsouth of
No Salvins Prions P. salvini were observed, 56°S. Little Shearwaters were rare, with two
either offMarion Island or further south, despite observed during transects at 50°30—51’30°S.
thatalargepopulationbreedsatthePrinceEdward Neither species evinced anyinterest in the ship.
&
and Crozet archipelagos (Marchant Higgins
1990). Smallnumberswerephotographednorthof Diving petrels
Marion Island (39-44°S) en route between the Diving petrels were the most abundant species
island and Cape Town in late March and the end recorded during transect counts (Table 1). Both
ofApril, supporting their preference for warmer Common Pelecanoides urinatrix and South
&
waters (Marchant Higgins 1990). Georgian DivingPetrels P.georgicuscan be expect-
ed to occur in the region, although Common
Gadfly petrels Diving Petrels apparently tend to remain closer to
Kerguelen Petrel was the third commonest bird their breedingislands, at least duringthe breeding
during transects, occurring throughout the region season, than do South Georgian Diving Petrels
&
(Fig. 2). Although regularly attracted to the ship (Marchant Higgins 1990, Bocher etal. 2000).
on station, they were more abundant in transect Even when photographed, the criteria to separate
counts. On station, they tended to hang off the the two species in the field are not definitive
stern, fluttering high in the sky, or circle the ship (Shirihai 2007). The eight diving petrels pho-
a few times then depart. White-headed Petrels tographed sufficientlywell to identifyappeared to
Pterodroma lessonii were the most abundant be South Georgian (based on clean, black and
Pterodroma also occurring throughout the area, whiteplumage, relativelybroadwhitetrailingedge
,
but were relatively scarce. The other two gadfly to secondaries, and the presence of a pale ‘C’
petrels, Great-winged and Soft-plumaged Petrels, around the ear-coverts). My impression is that
werebothuncommon,withSoft-plumagedPetrels most birdswere this species, butsome ratherplain
onlyrecordednorthof32°S andallbuttwo Great- birds with dark heads and breasts may have been
winged Petrels north of52°30’S (furthest south at Common Diving Petrels. Based on stable-isotope
55°35’S 38°00’E). signatures in feathers from adults, both species
apparently forage on the same prey in offshore
Procellaria petrels and shearwaters waters while moulting (Bocher etal. 2000).
White-chinned Petrel was the second most abun- Diving petrels occurred throughout the study
dant species at stations, occurring at all but one area, but were most abundant at 51-52°S and
station. Relatively few were counted during tran- 53-54°S, on the periphery of the Conrad Rise
sects but, like Blue Petrels, transect counts were (Fig. 2). The highest abundance occurred south-
complicated byWhite-chinned Petrels circlingthe east of Lena Seamount, where there were 10
ship, and often ‘running’ well ahead of the ship. petrels.km2. I have not seen anything like these
Their numbers typically increased during the first densities away from breeding colonies previously.
hourofdaylight, thenremainedrelativelyconstant The area around the Conrad Rise appears to be a
all day, suggesting the same individuals remained keyforaging area, at least at this time ofyear.
with the ship throughout the day. White-chinned
Petrels have a very broad foraging range, from Storm petrels
Antarcticto temperatewaters (Weimerskirch etal. Although Grey-backed Storm Petrel Oceanites
1999). Grey Petrels were much less common than nereis was observed close to Marion Island on 3
White-chinned Petrels, and although most were April, only two species ofstorm petrel were seen
recordedonstations, theywerelessassiduousship- during the survey. Black-bellied Storm Petrel
TheseabirdsoftheConradRise, Southern Ocean:Ryan BullABCVol16No 1(2009)-73
Figure 3. Prionsarenotoriouslydifficultto identifyatsea. Photographingbirdshelps greatly, althoughnotall individu-
als canbeidentifiedwithcertainty, especiallybetween Slender-billedPachyptilabelcheri,AntarcticP.desolataandSalvin’s
PrionsPsalvini(whichwasnotrecordedduringthesurvey).The imageshereshowtypicalbirds: (E) Salvin’s Prion
(notelargehead, deep-basedbill andsteep forehead), (C)AntarcticPrion (smallerbillandmoreroundedforehead), (D)
Slender-billedPrion (narrowbill, ratherpaleheadwithaprominentsuperciliumbroadeningbehindtheeyeandnarrow
blacktail tip) and (A& B) FairyPrionP. turtur(short, stubbybillandmoreextensiveblacktailtip). MostFairyPrions
showratherplain faces, butsomehavestrongerfacialmarkings (PeterRyan)
II est notoirequeles prions sontdifficilesaidentifieren mer. Memesi photographierles oiseauxrendlatachebeaucoup
plus facile, il ne faut pass’attendre apouvoiridentifiertous les individusaveccertitude, surtoutquandils’agitd’especes
commele Prion de BelcherPachyptilabelcheri, le PriondelaDesolationP.desolataoulePriondeSalvinPsalvini(qui
n’apasete notependantlerecensement). Lesphotos presentees ici montrentdes oiseauxtypiques : (E) lePrionde
Salvin (noterlateteetlebeefortsetlefrontabrupt), (C) lePrion delaDesolation (beepluspetit, frontplusbombe),
(D) le Prion de Belcher (beemince, teteplutotpaleavecunsourciltres marques’elargissantderrierel’oeil, queueavec
etroitebarreterminale noire) et (A & B) le PrioncolombePturtur(beecourtettronque, queueavecbarreterminale
noire plus large). Laplupartdes Prionscolombesontlescotes delateteplutotunis, mais certains individuspresentent
des marques facialescontrastees (PeterRyan)
74-BullABCVol16No 1(2009) Theseabirdsofthe ConradRise, Southern Ocean:Ryan
Figure4.TheLittle ShearwatersPuffinusassimilisencounteredwereofthesubantarcticform elegans,whichis treatedas
adistinctspeciesbysomeauthorities (PeterRyan)
Les Petits PuffinsPuffinusassimilisobservesetaientdelaformesubantarctiqueelegans quiesttraiteecommeuneespece
,
distincteparcertainsauteurs (PeterRyan)
Figure 5. BluePetrelsHalobaenacaeruleaare notusuallyregardedashavingadistinctjuvenileplumage, butin addition
tohavingpalefringesto theirupperpartfeathers, fresh-plumagedjuveniles (b) typicallyhavepalerandless extensive
darkfeatheringonthecrown, faceandbreastthanadults (a) (PeterRyan)
D’habitudele PrionbleuHalobaenacaerulean’estpassupposeavoirunplumagejuveniledistinct, mais enplusdes
liserespalesauxplumes des partiessuperieures, lesjuvenilesenplumagefrais (a) differenttypiquementdesadultes
(b) enayantlacalotte, les cotesdelateteetlapoitrinepluspales (PeterRyan)
Figure 6. Black-belliedStormPetrelsFregettatropicawerethemostabundantstormpetrels in thearea, butbecame
scarcesouthof50°S.Theyfrequently‘water-ski’ acrossthesurfaceon onefoot, makingadistinctive ‘rooster-tail’ splash
(PeterRyan)
L’OceaniteaventrenoirFregettatropicaetaitl’oceaniteleplusabondantdans lazone, mais ildevenaitplus rareausud
de 50°S. II ‘glisse’ frequemment surunpiedalasurfacedel’eau, produisantun eclaboussementcaracteristique (Peter
Ryan)
Figure7. OneofthemanygroupsofMacaroni PenguinsEudyptesclorysolophusobservedaroundthe Conrad Rise
(PeterRyan)
Un desnombreuxgroupes deGorfous doresEudypteschrysolophusobservesautourduConradRise (PeterRyan)
Theseabirdsofthe ConradRise, Southern Ocean:Ryan BullABCVol16No1(2009)-75
Fregetta tropica occurred throughout, but was six to the absence ofsea-ice.Theonlybirds associated
times more abundant north of 50°S (averaging with the sole iceberg encountered on the survey
0.18 km2 comparedwith 0.03 knr2 south of30°S were a mixed flock of15-20 Blue Petrels and pri-
in transect counts). Comparable data for station ons flying close below the cliffs of the iceberg.
counts were 2.1 and 0.3 birds per station north TherewasnosignofChinstrap PenguinsPygoscelis
and south of 30°S. One Wilson’s Storm Petrel antarctica which are common in spring around
,
Oceanites oceanicuswas observed at 50°S 38°E on 55°S (pers. obs.). The low diversity also results
4April. from the failure of many subantarctic species to
penetrate southwards much beyond the Antarctic
Other birds and marine mammals Polar Front.
Only two non-procellariiform seabirds were The cumulative abundance of Blue and
observed: a Subantarctic Skua Catharactaantarcti- Kerguelen Petrels and Slender-billed Prions, espe-
ca at 56°35’S 40°20’E on 7 April, and an cially from 54-56°S, is intriguing given the
immatureArcticTern Sternaparadisaeavisited the irruption ofall three species into temperatewaters
ship on station, at 52°43’S 45°39’E, on Lena off South Africa, Australia and eastern South
Seamount on 15 April. A Cattle Egret Bubulcus America in the austral winter of1984 (Ryan etal.
ibis briefly landed on the ship while on station at 1989). It suggests that something peculiar hap-
50°S 48°Eon 11 April. Itwas quiteweak, andhad pened at these latitudes that year causing large
trouble perching. Itwas blown offthe ship after a numbers ofbirds ofall three species to move well
few minutes and presumablyperished. north oftheir usual range. Blue Petrels breedingat
Relatively few marine mammals were Kerguelen experience periodic population crashes
observed. Fin Whales Balaenoptera physalus were linked to increased winter mortality in anom-
commonon7Aprilbetween 56°35’S 40°20’Eand alously warm years (Barbraud & Weimerskirch
56°14’S 42°10’E, with an estimated 30 animals 2003). Unfortunately, records do not extend to
seen in eight groups (positively identified as Fin the early 1980s, but this epoch corresponds with
Whales inthreegroups). Severalgroupscomprised the end ofa sustained period ofunusually warm
whalesthatapparentlywerefeeding, surgingto the years in theAntarctic that resulted in an apparent
surface, and lying on their sides, thrashing their shift in the functioning of pelagic ecosystems in
tail flukes out ofthe water. No birds were closely the Southern Ocean (Jenouvrier etal. 2005).
associated with any ofthese whales. Another Fin Perhaps the most interesting finding of the
Whale was photographed at 48°48’S 39°10’E on studywas the large numbers ofdiving petrels and
18April,with anothertwowhales blowingfurther penguins encountered. Diving petrels were the
away. A single large baleen whale (possibly a Fin most abundant bird encountered during steaming
Whale) approached the ship on station at 51°S transects, and penguins comprised some 80% of
44°E on 9 April. Only three other cetaceans were theavian biomass on transects. Clearlytheperiph-
observed: an unidentified, 3-4-m dolphin showed ery of the Conrad Rise is an important foraging
briefly near 56°4l’S 39°52’E on 7 April, a proba- areafordivingpetrels andpenguins, atleastatthis
ble beaked whale breached several times near season. Although there was no evidence of
50°42’S 48°00’E on 11 April, and a suspected increased bird abundance in transects on the
Sperm Whale Physeter macrocephaluswas blowing seamounts, ship attendance peaked on O’b Bank,
at 51°55’S 4l°12’E on 17 April. No seals were and is possiblyaconsequence ofpastfishingactiv-
seen, which is perhaps not too surprising given ity on the seamounts.
that seals from the Prince Edward Islands typical-
ly forage south-west of the islands along the Acknowledgements
&
Southwest Indian Ridge (Ryan Bester 2008). I am extremely grateful to Dr Isabelle Ansorge,
University ofCape Town, for the opportunity to join
Conclusions thesurveyandforexplainingthephysicaloceanography
Species richness in these peri-Antarctic waters is ofthe region. I also thank the oceanography team and
MV
relatively low. With the exception ofthe Emperor the officers and crew ofthe S.A. Agulhas for their
Penguin and possible Adelie Penguin, no truly support and assistance. The survey was funded by the
Antarctic species were observed, presumably due SouthAfrican NationalAntarctic Programme, through
76-BullABCVol16No 1(2009) Theseabirdsofthe ConradRise, Southern Ocean:Ryan