Foraging range and habitat associations of non‑breeding Tristan albatrosses: overlap with fisheries and implications for conservation

Abstract

The Tristan albatross Diomedea dabbanena is Critically Endangered: >99% of adults breed at Gough Island, central South Atlantic Ocean, where chicks are threatened by introduced predators. At sea they mostly remain within the South Atlantic Ocean, where they are threatened by incidental capture in longline fisheries. Conservation measures to reduce seabird mortality in pelagic longline fisheries are confined largely to fishing effort south of 25°S. This covers the core range of breeding Tristan albatrosses, but the distribution of non-breeding adults and immature birds is unknown. We tracked 14 non-breeding adult Tristan albatrosses from Gough Island for up to 3 yr, from 2004 to 2006, using geolocating loggers. All birds remained in the South Atlantic or southern Indian Oceans, and showed distributions centred on the Sub-Tropical Convergence. They used the SW Atlantic during the austral summer and the SE Atlantic and Indian Oceans as far east as Australia during the austral winter. Foraging effort was concentrated in areas of upwelling and increased productivity. The distribution of the tracked birds overlapped with a range of pelagic longline fisheries, especially off southern Africa. Of particular concern was that 2 birds spent several months off the coast of Namibia and in adjacent high seas north of 25°S, where there are currently no regulations to prevent seabird bycatch during pelagic longline fishing operations.

Full text

ENDANGERED SPECIES RESEARCH
Endang Species Res
Vol. 22: 39– 49, 2013
doi: 10.3354/esr00528 Published online November 7
INTRODUCTION
Of all the groups of birds in the world, seabirds are
the most threatened (Croxall et al. 2012). Albatrosses
are particularly at risk, with 17 of the 22 species listed
as threatened by the International Union for the Con-
servation of Nature (IUCN) (BirdLife International
2012). Seabirds face a range of threats, including
fisheries mortality at sea, depletion of prey by fish-
eries, habitat destruction (either at sea or on land)
and predation by introduced mammals at breeding
islands (Moors & Atkinson 1984, Tuck et al. 2003,
Cuthbert et al. 2005, Wanless et al. 2009, Žydelis et
al. 2009, Finkelstein et al. 2010). Marine threats are
particularly difficult to study, given the limited moni-
toring of many fishing fleets and the resultant paucity
© Inter-Research 2013 · www.int-res.com*Corresponding author. Email: rosswanless@gmail.com
Foraging range and habitat associations of
non-breeding Tristan albatrosses: overlap with
fisheries and implications for conservation
Timothy A. Reid1, Ross M. Wanless1,2,*, Geoff M. Hilton3, 5, Richard A. Phillips4,
Peter G. Ryan1
1Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa
2Seabird Division, BirdLife South Africa, PO Box 7119, Roggebaai, 8012, South Africa
3Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK
4British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
5Present address: Wildfowl and Wetlands Trust, Slimbridge, Gloucestershire GL2 7BT, UK
ABSTRACT: The Tristan albatross Diomedea dabbenena is Critically Endangered: > 99% of adults
breed at Gough Island, central South Atlantic Ocean, where chicks are threatened by introduced
predators. At sea they mostly remain within the South Atlantic Ocean, where they are threatened
by incidental capture in longline fisheries. Conservation measures to reduce seabird mortality in
pelagic longline fisheries are confined largely to fishing effort south of 25°S. This covers the core
range of breeding Tristan albatrosses, but the distribution of non-breeding adults and immature
birds is unknown. We tracked 14 non-breeding adult Tristan albatrosses from Gough Island for up
to 3 yr, from 2004 to 2006, using geolocating loggers. All birds remained in the South Atlantic or
southern Indian Oceans, and showed distributions centred on the Sub-Tropical Convergence.
They used the SW Atlantic during the austral summer and the SE Atlantic and Indian Oceans as
far east as Australia during the austral winter. Foraging effort was concentrated in areas of
upwelling and increased productivity. The distribution of the tracked birds overlapped with a
range of pelagic longline fisheries, especially off southern Africa. Of particular concern was that
2 birds spent several months off the coast of Namibia and in adjacent high seas north of 25°S,
where there are currently no regulations to prevent seabird bycatch during pelagic longline fish-
ing operations.
KEY WORDS: Atlantic Ocean · Indian Ocean · Longline · Bycatch · Diomedea dabbenena ·
Namibia
Resale or republication not permitted without written consent of the publisher

Endang Species Res 22: 39– 49, 2013
of reliable data on bird bycatch. In addition, many
species of seabirds range over vast areas and are thus
likely to encounter multiple threats at sea in a variety
of management jurisdictions (both national Exclusive
Economic Zones [EEZs] and high seas areas) and to
interact with fleets that vary widely in terms of com-
pliance with conservation measures where these are
in place.
The Tristan albatross Diomedea dabbenena breeds
almost exclusively on Gough Island in the central
South Atlantic Ocean. It is classified as Critically
Endangered by the IUCN because of population
declines caused by mortality on longlines and preda-
tion of chicks by introduced mice Mus musculus
(Wanless et al. 2007, 2009, BirdLife International
2012). The population is estimated to be decreasing
by almost 3% yr−1, with annual mortality from long-
line fishing estimated to be around 250 individuals
(Wanless et al. 2009). Tristan albatrosses have been
killed by pelagic longline fisheries off Brazil (Olmos
1997, Cuthbert et al. 2005) and southern Africa
(Petersen et al. 2009). A recent assessment conducted
under the auspices of the International Commission
for the Conservation of Atlantic Tunas (ICCAT) con-
cluded that the Tristan albatross was one of the spe-
cies most at risk from longline fishing within the
ICCAT area of jurisdiction (Tuck et al. 2011). A qual-
itative risk assessment for seabirds in the area man-
aged by the Indian Ocean Tuna Commission (IOTC)
came to a similar conclusion in terms of the threat to
Tristan albatrosses from fishing in the Indian Ocean
(Baker & Wanless 2010).
Identifying the main foraging areas of the Tristan
albatross is complicated because at sea they are diffi-
cult to distinguish from other great albatrosses
Diomedea spp.; indeed, separation from wandering
albatross D. exulans requires measurements of birds
in the hand (Cuthbert et al. 2003, Ryan 2007). The
only published assessment of their foraging range is
derived from tracking data for breeding birds in
2000. In that study, birds remained predominantly in
the central South Atlantic, though some travelled as
far as South America and South Africa (Cuthbert et
al. 2005). However, foraging ranges of adult alba-
trosses can be substantially larger in the non-breed-
ing period, when they are not constrained to return to
a central location to incubate or provision their chick
(BirdLife International 2004, Phillips et al. 2005,
Weimerskirch et al. 2012). Given the ongoing threat
to this Critically Endangered species, it is imperative
to better understand their movement patterns and
habitat use during all life-cycle stages. Here we pres-
ent new information on the distribution of non-
breeding Tristan albatrosses in relation to longline
fishing effort and environmental characteristics.
MATERIALS AND METHODS
Tristan albatrosses Diomedea dabbenena breed
biennially, and are currently restricted to breeding at
2 sites in the South Atlantic Ocean. At Gough Island
(40° 19’ S, 9° 56’ W) around 1400 pairs breed annu-
ally. At Inaccessible Island (37°18’ S, 12° 40’ W), a
tiny number of pairs breed and, on average, <1 chick
fledges each year from Inaccessible Island (Wanless
et al. 2009).
Position-tagging devices
Global location sensor (GLS) loggers (British
Antarctic Survey, Cambridge, UK), often referred to
as geolocators, were attached to leg bands on 43 Tris-
tan albatrosses breeding on Gough Island. Devices
were ground-truthed for 2 wk at the colony, and then
fitted to adults feeding large chicks in August and
September 2004. The devices weighed 9 g, equiva-
lent to <0.2% of the weight of a mature Tristan alba-
tross (>7 kg), well below the load that might be
expected to affect foraging behaviour (Phillips et al.
2003, Passos et al. 2010).
GLS loggers measured light intensity every minute
and recorded the maximum in each 10 min period.
Downloaded light data were processed to estimate
the time of sunrise, sunset and, hence, local midday
relative to GMT/UTC, and daylength. From these
parameters, it is possible to estimate latitude and lon-
gitude. However, there are inaccuracies in positions
derived in this way due to factors such as cloud cover,
shading of the light sensor by feathers, or rapid
movements by flying birds. Positions are accurate to
roughly 200 km, except around the equinoxes when
latitudinal errors increase (Phillips et al. 2004). An
iterative speed filter was used to identify unlikely
locations (McConnell et al. 1992). For this, an aver-
age was taken over 5 positions, and those positions
that required a maximum average speed of > 80 km
h−1 (Weimerskirch et al. 1993) were filtered using the
tripEstimation package (Version 0.0-37). To estimate
the areas used most frequently, we applied kernel
smoothing to the filtered positions using the ks pack-
age (Version 1.8.12) in R. Most frequently used areas
were presented as percentage volume contours, such
that 50% contours show the most dense 50% of all
locations (Tancell et al. 2013). All statistical analyses
40

Reid et al.: Non-breeding Tristan albatross distributions
were conducted in R, Version 2.15.0 (R Development
Core Team 2012).
Devices deployed in late 2004 were retrieved dur-
ing the 2006 breeding season, and, hence, the study
included the end of the 2004 breeding period, the
entire 2005 sabbatical year and the start of the 2006
breeding period. Based on the GLS positional data,
none of the study birds appeared to breed during
2005 (there was no researcher on the island that
breeding season to confirm their absence from the
breeding colony). Breeding/non-breeding activity
was classed based on known breeding history and
movement patterns (e.g. birds regularly attending
the island were assumed to be breeding). Only data
from the non-breeding period (including both failed
and successful breeders at the previous attempt) are
presented here. Data for breeding birds suggested
the use of similar areas to those described in Cuth-
bert et al. (2005).
Longline fishing effort distribution
Longline fishing effort data are presented here at
the finest spatial resolution available. Quarterly data
at a 5° × 5° resolution over 5 yr (2001 to 2006) were
obtained from the ICCAT for the Atlantic Ocean
(www. iccat. es/ en/ accesingdb. htm), and monthly data
for the Indian Ocean were obtained from the IOTC
(www. iotc. org/ English/ data/ databases. php# dl).
Modelling effects of environmental conditions
To test how non-breeding Tristan albatrosses were
distributed in relation to environmental conditions,
we followed the approach of Aarts et al. (2008) and
Wakefield et al. (2011). Tracking data are presence
only, so we created pseudo-absences in order to ex-
amine habitat preferences using logistic regressions,
where records of birds were given a value of 1, and
pseudo-absences, a value of 0. Pseudo-absence data
are derived from positions chosen from areas available
to the population (Aarts et al. 2008). Choice of pseudo-
absence position is important, and overcomplicating
models of possible areas can lead to poor prediction
(Wisz & Guisan 2009). In the present study, possible
pseudo-absences were confined to areas to which the
study birds could realistically move. Because non-
breeders are not constrained to return to their nests,
this was considered to be the maximum extent of the
area used during this study, i.e. from 15 to 60°S in the
Atlantic Ocean and 30 to 60°S in the Indian Ocean; no
birds visited the Pacific Ocean. During summer (No-
vember to April), all birds remained within the At-
lantic Ocean. Thus, pseudo-absences were randomly
chosen from within these spatio-temporal constraints.
We generated 100 points bird−1 mo−1 throughout the
year, giving 4085 presences and 15 535 absences.
Monthly sea-surface temperature (SST) and Aqua
Modis chlorophyll a(chl a) in milligrams per cubic
metre at 4 km resolution were downloaded from
SeaWifs via http:// oceancolor. gsfc. nasa. gov/, and
monthly mean sea-level anomaly (SLA) data, from
Aviso at www.aviso.oceanobs.com at a 0.333° ×
0.333° grid scale. Variables chosen were ones that
have previously been demonstrated to correlate with
distributions of other seabird species (e.g. Phillips et
al. 2006, Wakefield et al. 2011). We modelled the
tracking data using a generalised additive mixed
model (GAMM) using the mgcv (Version 1.7-13)
package in R. Individual bird identity was treated as
a random effect. Fixed effects were latitude and lon-
gitude as interacting terms, SST, chl a, water depth
and mean SLA). We took a Bayesian view that all
variables chosen for fixed effects were components of
the world, and therefore should be presented, rather
than using any form of model selection to narrow the
suite of variables (Bolker 2008). This was considered
appropriate as the model was descriptive rather than
predictive.
RESULTS
Of the 43 GLS loggers deployed, 35 (81%) were
retrieved, but data were obtained from only 15
devices (the others failed to download data). Four-
teen contained data on non-breeding movements of
Tristan albatrosses (13 post-breeding and 1 late fail-
ure), while 1 only contained data for the breeding
period. The core areas (i.e. 50% kernels) of most
birds were between ~25 and ~45° S, year-round.
Most positions were around the Sub-Tropical Con-
vergence and farther north, typically in waters of 10
to 20°C (range: 0 to 24°C; Fig. 1). Distributions were
largely centred in oceanic waters (> 3000 m deep).
Non-breeding adult Tristan albatrosses ranged
across the Atlantic and Indian Oceans, encompass-
ing half the globe from the east coast of South Amer-
ica (50° W) to the Great Australian Bight (130° E).
However, most locations (86%) were in the Atlantic
Ocean (west of 20° E), and only 2 birds ranged well
into the Indian Ocean. Non-breeding adults
occurred predominantly in the SW Atlantic from
January to March (Fig. 2a–c), shifting to the SE
41

Endang Species Res 22: 39– 49, 2013
Atlantic from March to May (Fig.
2c–e). During austral winter (May to
September), most time was spent in
the SE Atlantic off South Africa
(Fig. 2e–i) and eastward into the
Indian Ocean to ~40° E (Fig. 3b–f).
Two birds moved to Namibia in late-
March and remained there until
June, with 1 of these returning dur-
ing August (Fig. 2c–f, h). In April, 2
individuals (14% of tracked birds)
began moving to SW Australia, arriv-
ing in June. They returned west-
ward, against the prevailing winds,
in September (Fig. 3), resulting in
their winter foraging ranges being
predominantly in the Indian Ocean.
In spring (October), prior to the onset
of breeding, adults started to return
to the SW Atlantic (Fig. 2j), and all
birds were in this area in November
(Fig. 2k). By De cember, immediately
before breeding commenced, all
tracked birds were concentrated in
the central South Atlantic around
Gough Island (Fig. 2k).
Tristan albatross distributions over lapped with
high levels of longline fishing effort from April to
August off South Africa, where birds spent most of
their time in areas of eddies and mixing associated
with the Agulhas Current (Figs. 2d –f & 3b–d, Table
1). The intensity of fishing effort in the areas used by
non-breeding Tristan albatross during this study was
greater in the Indian Ocean than in the Atlantic
Ocean, with a maximum of 2.76 million hooks set
during a month in a single 5° × 5° block in the Indian
Ocean, compared with an average of 1.1 million
hooks set over 3 mo during 2001 to 2006 in the block
with the greatest effort in the Atlantic Ocean. Most
overlap between adult Tristan albatrosses and long-
line fishing effort occurred during winter (Quarters 2
and 3; Table 1); during Quarter 3, all tracked birds
visited a 5° × 5° square in which fishing effort had
averaged >500 000 hooks yr−1 from 2001 to 2006.
The GAMMs comparing presences and pseudo-ab-
sences suggested that Tristan albatrosses were signif-
icantly more likely to occur in the SW or SE Atlantic
Ocean or off SW Australia (estimated degrees of free-
dom, edf = 27.0; F= 58.7; p < 0.01). They preferred
waters ~3000 to 5000 m deep, with surface tempera-
tures of 15 to 20°C (Fig. 4a; edf = 5.9; F= 15.5; p <
0.01) and enhanced chl aconcentrations (Fig. 4b;
edf = 1.0; F= 6.0; p = 0.01), and avoided shelf waters
42
Quarter
1 (14) 2 (13) 3 (11) 4(7)
ICCAT
Blocks with fishing effort 100 100 100 100
Blocks with high fishing effort 3 2 1 2
No. of birds visiting a block with high effort 0 8 4 0
IOTC
Blocks with fishing effort 141 141 148 148
Blocks with high fishing effort 23 23 49 46
No. of birds visiting a block with high effort 0 0 9 1
Tracked birds visiting block with high effort (%) 0 62 100 14
Table 1. Diomedea dabbenena. Overlap of tracked non-breeding Tristan alba-
trosses and longline fishing in the South Atlantic and Indian Oceans. Values in
parentheses beside quarters show no. of tracked birds. ICCAT: International
Commission for the Conservation of Atlantic Tuna; IOTC: Indian Ocean Tuna
Commission. No. of tracked birds: no. of individuals in that year quarter;
blocks with fishing effort: no. of 5° × 5° squares which had some fishing effort
during the quarter in 2001 to 2006; blocks with high fishing effort: no. of 5° × 5°
squares where an annual average of > 500 000 hooks was set between 2001
and 2006; no. of birds visiting a block with high effort: no. of individual Tristan
albatrosses that visited a square where > 500 000 hooks were set each year;
tracked birds visiting a square with high effort: percentage of total tracked in-
dividuals that visited a square with >500 000 hooks yr−1 (note that in Quarter 3
two birds visited squares with > 500 000 hooks set in both the Atlantic and
Indian Oceans)
January March May July September Decembe
r
0
5
10
15
20
26
SST (°C)
Fig. 1. Variation in sea-surface temperature (SST) encoun-
tered by non-breeding Tristan albatrosses Diomedea dabbe-
nena by month during 2005. The box shows the 25 and 75%
quartiles (the inner quartiles), the notch occurs at ±1.58 ×
IQR/sqrt(n), where IQR is the inner quartile range and n is
the number of observations in that month. Whiskers are
drawn at 1.5 × IQR beyond the inner quartiles

Reid et al.: Non-breeding Tristan albatross distributions 43
Fig. 2. Diomedea dabbenena. (a to l) Kernel plots (50, 75 and 90% isopleths) of non-breeding adult Tristan albatross distribu-
tions within the South Atlantic Ocean in 2005, overlaid on fishing effort by pelagic longliners targeting tuna and other bill-
fishes (red: 50%; orange: 75%; yellow: 90 %). Fishing effort is mean quarterly number of hooks set within 5° × 5° blocks for the
period of 2001 to 2006, with circles proportional to the number of hooks set (maximum number of hooks set in Quarter 1: 1.0
million, Quarter 2: 1.0 million, Quarter 3: 0.6 million, Quarter 4: 1.1 million)
(Fig. 2 continued on next page)

Endang Species Res 22: 39– 49, 2013
(Fig. 4c; edf = 4.1; F= 4.3; p < 0.01). Mean SLAs had
less influence on their distribution, except for a weak
tendency of Tristan albatrosses to favour areas with
reduced mean SLA values (Fig. 4d; edf = 1.0; F= 4.3;
p = 0.04). However, when mean SLAs were examined
in isolation, tracked Tristan albatrosses were least
likely to visit areas where there was no mean SLA.
The overall model had an ad justed r2of 0.26.
DISCUSSION
Overlap with breeding birds and other species
The ranges of non-breeding Tristan albatrosses
were substantially greater than those of breeding
adults (Cuthbert et al. 2005; Fig. 5), which are
required to return regularly to Gough Island to incu-
bate or to provision their chick. Breeding birds
remain predominantly in waters of the central South
Atlantic Ocean around Tristan da Cunha and Gough
Islands, with east−west movements largely confined
to the area from 15°E to 50°W (Cuthbert et al. 2005).
Although non-breeders spent most of their time in
the South Atlantic Ocean, there was little overlap in
their distribution with the core areas used by breed-
ers (in the central Atlantic), suggesting spatial niche
partitioning between adults of different status. Gen-
erally, Tristan albatrosses occur in subtropical waters
or around the Sub-Tropical Convergence, rather
than in more southerly waters. While there was some
overlap with wandering albatrosses from their more
southerly colonies on South Georgia, the Prince
Edward Islands, Iles Crozet and Kerguelen (Prince et
al. 1992, Weimerskirch et al. 1993, Nel et al. 2002,
BirdLife International 2004), Tristan albatrosses for-
aged predominantly to the north of adult wandering
albatrosses and were more likely to overlap with
female and non-breeding wandering albatrosses
than with breeding males.
Non-breeding movements
Non-breeding Tristan albatrosses move exten-
sively throughout 2 southern ocean basins. The areas
they utilise off both South America and southern
Africa are associated with eddies and mixing zones
(Figs. 6 & 7), which are typically highly productive
(Wainer et al. 2000) There were clear seasonal pat-
44
Fig. 2. (continued)

Reid et al.: Non-breeding Tristan albatross distributions
terns to their movements, with all tracked birds con-
centrating in the SW Atlantic during austral summer,
but travelling eastward and dispersing more widely
during austral winter, mostly to the SE Atlantic and
SW Indian Ocean off South Africa. However, 2 birds
moved to waters off northern Namibia and 2 to south-
ern Australia. It is important to note that, although
we present results from 2005 only, the limited track-
ing data available for non-breeding birds in 2004 and
2006 showed a broadly similar pattern.
Overlap with oceanography
Our analyses indicate that although Tristan alba-
trosses tend to concentrate in productive areas at
frontal zones and around eddies, their overall distri-
bution includes waters that vary widely in terms of
primary productivity. There are several possible
explanations. Tristan albatrosses may be able to get
sufficient food to meet their energetic requirements,
while avoiding competition, by remaining in slightly
lower quality areas. Alternatively, there may be
a mismatch between chlorophyll ameasured by
satellite imagery (which is at the lowest trophic level)
and the distributions of higher trophic-level organ-
isms that Tristan albatrosses are likely to target (fish
and squid; Imber 1992). In addition, the GLS data
used in the modelling are inherently imprecise,
which means that habitat can only be described at
broad spatial scales. In order to investigate habitat
preferences more closely, more accurate tracking
data from GPS loggers or satellite-tags would be
required.
45
Fig. 3. Diomedea dabbenena. (a to f) Kernel plots (50, 75 and 90% isopleths) of non-breeding adult Tristan albatross distribu-
tions within the Indian Ocean in 2005 (red: 50%; orange: 75%; yellow: 90 %), overlaid on fishing effort by pelagic longliners
targeting tuna and other billfishes. Fishing effort is total hooks set monthly within 5° × 5° blocks (maximum number of hooks
set in a block during a month in observation period: 2.8 million), with circles proportional to the number of hooks set

Endang Species Res 22: 39– 49, 2013
During austral summer, non-breeding Tristan alba-
trosses occurred predominantly in the SW Atlantic
Ocean between 30 and 45° S and 0 and 50° W. This
area is influenced by a number of strong oceano-
graphic features, including the Sub-Tropical Conver-
gence between the Brazil/ Malvinas (Falklands) Con-
fluence (Fig. 6), that result in eddies and vertical
mixing that enhance local production. This area has
consistently high productivity in summer and low pro-
ductivity in winter (Wainer et al. 2000), supporting the
conclusion that its importance to seabirds is likely to
vary seasonally. It is a key foraging area for other mar-
ine predators in summer, including black-browed al-
batrosses Thalassarche melanophris (Wakefield et al.
2011) and white-chinned petrels Procellaria ae-
quinoctialis (Phillips et al. 2006) from South Georgia,
southern elephant seals Mirounga leonina from Ar-
gentina (Campagna et al. 2006), and migrant Cory’s
Calonectris diomedea (Dias et al. 2011), sooty Puffinus
griseus (Hedd et al. 2012) and Manx P. puffinus (Guil-
ford et al. 2009) shearwaters.
46
0
ab
cd
15 20 25510
2
1
0
–1
–2
–3
–4
2
1
0
–1
–2
–3
–4
2
1
0
–1
–2
–3
–4
2
1
0
–1
–2
–3
–4
sst
s(sst,5.92)
0 5 10 15
Chl a
s(chla,1)
–6000 –4000 –2000 0
Depth
s(depth,4.11)
–50 0 50
msla
s(msla,1)
Fig. 4. Diomedea dabbenena. Plots of some fixed effects of the model of non-breeding Tristan albatrosses during 2005. The
y-axes show the partial residuals once the effect of other variables has been removed. Solid lines are means and dashed lines
are estimated 95% CIs; ‘s’ is a smoothing term, with values in parentheses the effective degrees of freedom. (a) Sea-surface
temperature (SST, °C), (b) chlorophyll a(chl a, mg m−3), (c) depth (m), (d) mean sea-level anomaly (SLA, cm)
60° 40° 20° W 0° 20° E
60°
50°
40°
30°
20°
10°
S
Fig. 5. Diomedea dabbenena. Kernel plots (50, 75 and 90%
isopleths) of breeding adult Tristan albatrosses tracked from
2004 to 2006 (red: 50%; orange: 75%; yellow: 90 %)

Despite the high productivity in summer, this area
experiences relatively low pelagic longline fishing
effort in this season, limiting the risk to Tristan alba-
trosses. Most seabird bycatch in longline fisheries off
Uruguay and southern Brazil occurs in winter, and
the apparent paucity of Tristan albatrosses in these
waters in winter may explain their scarcity in bycatch
records from these fisheries (Bugoni et al. 2008,
Jimenez et al. 2009). Other fisheries that can impact
seabirds, such as demersal longlining and trawling,
do not occur in these deep, offshore waters. In winter,
when the SW Atlantic is less productive (Wainer et al.
2000), Tristan albatrosses dispersed more widely.
Most tracked birds concentrated to the south and
west of South Africa in areas associ-
ated with the Agulhas and Benguela
Currents Stramma & England 1999),
and 2 birds visited sub-Antarctic and
Antarctic waters to ~55° S during
April, May and August.
Overlap with fisheries
All the non-breeding Tristan alba-
trosses visited areas of high fishing
effort in winter, particularly off south-
ern Africa and in the Indian Ocean.
Fortunately, their catch rate in this
region appears to be fairly low pro-
vided appropriate mitigation meas-
ures (e.g. setting only between nauti-
cal dusk and dawn, mandatory use of
bird scaring lines, etc.). Petersen et al.
(2009) recorded only 3 Tristan alba-
trosses killed, 0.3% of birds returned
to port by fishery observers in the
South African large pelagic longline
fishery between 1998 and 2005. And
since 2005, no further mortalities of
this species have been recorded in
this fishery. Until recently, appropri-
ate mitigation has not been required
in high seas fisheries in this region,
but the ICCAT and IOTC will soon re -
quire vessels operating south of 25° S
to use 2 mitigation measures for all
longline sets, from a choice of 3 possi-
ble measures: bird scaring lines, night
setting, or line weighting (ICCAT
2011, IOTC 2012). The Commission
for the Conservation of Southern
Bluefin Tuna requires vessels catch-
ing southern bluefin tuna Thunnus maccoyi to use
the conservation measures of the relevant ocean
in which they operate. Thus, Tristan albatrosses
will be afforded some protection from longline
bycatch across their longitudinal range, but only
south of 25° S.
Two Tristan albatrosses (14% of tracked birds)
spent approximately 4 mo off the coast of Namibia,
north of 25° S, where neither the ICCAT nor the gov-
ernment of Namibia require any measures to reduce
seabird by catch in tuna longline operations. This
suggests that an appreciable proportion of non-
breeding Tristan albatrosses remain at risk from
pelagic longline fishing off Namibia. Seabird bycatch
Reid et al.: Non-breeding Tristan albatross distributions 47
60° 40° 20° W 0° 20° E
60°
50°
40°
30°
20°
10°
S
−50
0
50
100
SLA
50
75
75
90
90
60° 40° 20°W 0° 20° E
60°
50°
40°
30°
20°
10°
S
−50
0
50
SLA
50
75
75
75
90
90
90
Fig. 6. Diomedea dabbenena. Kernel plots of non-breeding adult Tristan alba-
trosses during January 2005 overlaid on mean sea-level anomaly (SLA, cm) in
Atlantic and SW Indian Oceans (solid line: 50%; dashed line: 75 %; dotted
line: 90%)
Fig. 7. Diomedea dabbenena. Kernel plots of non-breeding Tristan albatrosses
in the South Atlantic Ocean during June 2005 overlaid on mean sea-level
anomaly (SLA, cm) in Atlantic and SW Indian Oceans (solid line: 50%;
dashed line: 75%; dotted line: 90 %)

Endang Species Res 22: 39– 49, 2013
on pelagic longliners occurs in these waters (Ander-
son et al. 2011), so it is imperative that the ICCAT and
the government of Namibia afford protection for this
Critically Endangered species by extending the area
of application of the ICCAT conservation measure
(Recommendation 11-09). Our results suggest that
current ICCAT seabird conservation measures
should be extended north from 25 to 15° S in the area
from 0° E to the Namibian coast. This would also ben-
efit other species susceptible to mortality in longline
fisheries in the region, including spectacled Procel-
laria conspicillata and white-chinned P. aequi -
noctialis petrels, and Atlantic yellow-nosed Thalas-
sarche chloro rhynchos and shy/white-capped T.
cauta/ steadi albatrosses (Camphuysen & van der
Meer 2000).
Acknowledgements. Andrea Angel, Marie-Helene Burle,
John Cooper and Johnny Wilson assisted with deployment
and retrieval of devices. Phil Taylor of BirdLife International
kindly supplied cleaned and vetted longline fishing effort
data from the ICCAT area of competence.
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49
Editorial responsibility: Rory Wilson,
Swansea, UK
Submitted: April 9, 2013; Accepted: July 4, 2013
Proofs received from author(s): October 16, 2013
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