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Biological effects of El Nin
˜o on the Gala
´pagos penguin
F. Herna
´n Vargas
a,b
, Scott Harrison
a
, Solanda Rea
b
, David W. Macdonald
a,
*
a
Wildlife Conservation Research Unit, University of Oxford, Department of Zoology, South Parks Road, Oxford OX1 3PS, UK
b
Charles Darwin Research Station, Isla Santa Cruz, Gala
´pagos, Ecuador
ARTICLE INFO
Article history:
Received 24 May 2005
Available online 13 September 2005
Keywords:
El Nin
˜o
ENSO
Spheniscus
SST
Gala
´pagos
Penguin
ABSTRACT
Long-term monitoring of physical and biological parameters is essential for understanding
the effects of El Nin
˜o on bird populations, particularly for small or declining populations.
We examined the biological effects of El Nin
˜o activity from 1965 to 2004 using instrumental
sea-surface temperatures from the Gala
´pagos Islands and 20 years of census counts of the
Gala
´pagos penguin. Between 1965 and 2004, nine El Nin
˜o events were recorded of which
two were strong and seven were weak. The two strong El Nin
˜o events of 1982–1983 and
1997–1998 were followed by crashes of 77% and 65% of the penguin population, respec-
tively. The evidence suggests that the increased frequency of weak El Nin
˜o events limits
population recovery. The 2004 penguin population is estimated to be at less than 50% of
that prior to the strong 1982–1983 El Nin
˜o event. We discuss the biological effects of
increased El Nin
˜o intensity and frequency within the context of a 6000-year record of El
Nin
˜o influence and in the light of increasing anthropogenic threats operating after 1535,
when the Archipelago was discovered by Europeans.
Ó2005 Elsevier Ltd. All rights reserved.
1. Introduction
The Gala
´pagos penguin (Spheniscus mendiculus) is an endan-
gered species by virtue of its restricted range and fluctuating
population size (BirdLife International, 2000). Approximately,
95% of the population of Gala
´pagos penguins is distributed
primarily along the westernmost islands of Fernandina
(0°220000 S, 91°3102000W) and Isabela (0°2503000S, 91°70W); this dis-
tribution coincides with the major upwelling zones and the
most productive waters of the archipelago (Boersma, 1977,
1978). The remaining 5% of the population lives in small pop-
ulations inhabiting the islands of Floreana (1°170000 S,
90°260000 W), Santiago (0°1503000S, 90°43 03000 W), and Bartolome
´
(0°1605100 S, 90°3204800W). Birds nest opportunistically through-
out the year if conditions permit although peaks in egg laying
occur in April–May (Vargas, unpubl. data) and in August–Sep-
tember (Boersma, 1977). Based on capture-mark-resight
methods (Vargas et al., 2005), the population size of the Gala
´-
pagos penguin in 2004 was estimated at 1500 individuals (Var-
gas and Wiedenfeld, 2004).
Phylogenetic evidence suggests that the Spheniscus penguin
genus diverged from other penguin species between 100,000
and 800,000 years ago (Akst et al., 2002; Grant et al., 1994), and
subsequent association of S. mendiculus with the Gala
´pagos
means that historic El Nin
˜o episodes are likely to have shaped
specific breeding and survival strategies in this species for
thousands of years. Lake sediment deposits provide evidence
that El Nin
˜o activity has influenced the climate of the Gala
´pa-
gos Islands for at least the last 6000 years (Riedinger et al.,
2002) with it likely affecting the Gala
´pagos penguin (Boersma,
1998a; Valle and Coulter, 1987; Vargas, 1999), as it does other
seabirds, through a cascade of events (Chavez et al., 1999) that
lead to changes in the food web and predator–prey relation-
ships (Boersma, 1977). Of all the penguin species, only the Gala
´-
pagos penguin lives on the equator and is able to do so because
of the cold oceanic upwelling along the equator and the
0006-3207/$ - see front matter Ó2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biocon.2005.08.001
*Corresponding author: Fax: +44 0 1865 393100.
E-mail addresses: hernan.vargas@zoology.oxford.ac.uk (F.H. Vargas), david.macdonald@zoology.oxford.ac.uk (D.W. Macdonald).
BIOLOGICAL CONSERVATION 127 (2006) 107–114
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/biocon
Equatorial Under Current, also known as the Cromwell current
(Boersma, 1977, 1978). As the Equatorial Under Current hits the
western edge of the Gala
´pagos Archipelago, cold, nutrient-rich
water is forced to the surface (Houvenaghel, 1984) and provides
the shallow-diving Gala
´pagos penguin (Mills, 2000) with access
to its primary prey species.
El Nin
˜o events affect the biodiversity of the Gala
´pagos Is-
lands through dramatic changes to the environmental condi-
tions of the Islands. During El Nin
˜o, the Equatorial Under
Current weakens, the surface water warms, macronutrients
are reduced, primary production decreases (Chavez et al.,
1999), and fish numbers diminish; data from commercial fish-
eries indicated that the catch of mullets from the Gala
´pagos
during the 1997–1998 El Nin
˜o event was half that of the com-
mercial catch in 1999 when there was no El Nin
˜o event
(Nicolaides and Murillo, 2001). Similarly, the catch of sardines
along the coast of mainland Ecuador during the 1998 El Nin
˜o
year was the lowest of the last two decades (Ja
´come and Osp-
ina, 1999).
Recently, the frequency and severity of El Nin
˜o events ap-
pear to have increased and this is a concern for the conserva-
tion of endangered seabird species. El Nin
˜o events now occur
2–7 times more frequently than they did 7000–15,000 years
ago (Riedinger et al., 2002; Rodbell et al., 1999). Climate mod-
els suggest that most of the warming observed during the last
50 years is attributable to human activities (Karl and Tren-
berth, 2003) with an increased El Nin
˜o pulse in the last three
decades (Trenberth and Hoar, 1996, 1997). The 1982–1983 and
1997–1998 El Nin
˜o events were the strongest recorded in the
last century (Chavez et al., 1999) and had severe biological ef-
fects (Barber and Chavez, 1983; Hays, 1986; Valle et al., 1987).
Sea-surface temperatures and precipitation data collected
from the Gala
´pagos between 1965 and 1999 indicate that
1983 and 1998 were the hottest and wettest years on the Gala
´-
pagos Islands (Snell and Rea, 1999).
Here, we evaluate the effect of ENSO (El Nin
˜o Southern
Oscillation) on the population dynamics of the penguin and
determine the likely effects of climate change on the conser-
vation of Gala
´pagos penguins. Standard demographic param-
eters are inordinately difficult to obtain for this species
because the penguins are in small groups widely scattered
along the difficult terrain of the archipelago. However, we
present analysis from two long-running data sets: (1) the
number of adult and juvenile penguins recorded since 1970
and (2) the daily sea temperatures logged in the Gala
´pagos
since 1965.
2. Materials and methods
We examined the biological effects of El Nin
˜o using census
data of the Gala
´pagos penguin and instrumental sea-surface
temperature data from the Gala
´pagos Islands.
2.1. Penguin data
We conducted complete census counts each year as part of a
joint effort of the Charles Darwin Research Station (CDRS)
and the Gala
´pagos National Park Service (GNPS). Censuses
attempted to count all penguins using methods described
elsewhere (Boersma, 1974, 1977; Mills and Vargas, 1997). Sam-
pling bias was minimized by standardizing dates, duration of
the census, time of day, number of observers, field equip-
ment, survey zones, travel speed, and types of data collected.
The 10-day census occurred in late August and early Septem-
ber across the range of the Gala
´pagos penguin. We counted
penguins between 06:00 and 18:00 using a small dinghy to ap-
proach the coast as closely as possible. The birds were classi-
fied as adults, juveniles, and penguins of unknown age
(whose age could not be determined when birds were swim-
ming). Fledged juvenile birds, with juvenile plumage as aged
by Boersma (1977), were used as an index of reproduction
per year. For our statistical analysis, we assumed no migra-
tion and equal detectability of birds across all years (including
years of El Nin
˜o events). All known nesting areas were
checked to determine the extent of nesting activity. Here,
we present data on the combined total number of adult and
juvenile penguins.
2.2. Sea surface temperature
Sea surface temperature is a good indicator of El Nin
˜o events
(Trenberth and Stepaniak, 2001), so we used SST data col-
lected between 1965 and 2004 at the meteorological station lo-
cated at the CDRS (00°440200S, 90°1802400 W) on Santa Cruz
Island. Sea surface temperature were recorded at 06:00,
12:00, and 18:00 with a hand held thermometer in a bucket
of water pulled from the sea surface (Snell and Rea, 1999).
We calculated normalized SST anomalies for the period
1970–2004 relative to the base period of 1965–1979 from the
same data set. The base period was selected as it was consid-
ered representative and not biased by the warming and El
Nin
˜o events after 1979 (Trenberth, 1997; Trenberth and Hoar,
1996).
We determined El Nin
˜o events by identifying periods dur-
ing which the five-month running mean of SST anomalies
was above 0.5 °C for at least six consecutive months. This
definition follows the protocols of the Japan Meteorological
Agency (J.M.A.) and Trenberth (1997) with adjustment for
instrumental sea-surface temperature from the Gala
´pagos
Islands. These calculations also enabled us to determine
the duration, frequency, and intensity of warm El Nin
˜o and
cold La Nin
˜a events. La Nin
˜a events were determined by
identifying periods during which the 5-month running
means of SST was below 0.5 °C for at least six consecutive
months.
The El Nin
˜o events were classified as strong or weak
depending on the magnitude of the positive anomalies. We
considered anomalies between 0.5 and 2 °C as weak El Nin
˜o
and anomalies >2 °C as strong El Nin
˜o events. Despite some
differences in measurements of magnitude (intensity), our
frequency of ENSO (El Nin
˜o Southern Oscillation) events from
the Gala
´pagos is in most cases in agreement with the consen-
sus (ENSO) lists (http://ggweather.com/enso/years.htm) and
the Multivariate ENSO index (http://www.cdc.noaa.gov/
ENSO/enso.mei_index.html). The main difference is that the
1972–1973 event, classified as a strong El Nin
˜o by the consen-
sus list, appears only as a weak El Nin
˜o event in the Gala
´pagos
Islands.
108 BIOLOGICAL CONSERVATION 127 (2006) 107–114
3. Results
Analysis of SST indicates two strong (1982–1983 and 1997–
1998) and seven weak (1965–1966, 1968–1969, 1972–1973,
1976, 1986–1987, 1991–1992 and 1993) El Nin
˜o episodes in the
Gala
´pagos during the study period (Fig. 1). The two strong El
Nin
˜o events, in addition to showing anomalies greater than
2°C, also lasted for 17 and 18 months, respectively. The aver-
age duration of the weak episodes was 11.4 months (±3.4 SD,
range 6–16). The 1982–1983 and 1997–1998 strong El Nin
˜o
events were associated with reductions in the penguin popu-
lation of 77% and 65%, respectively, and the frequent, weak El
Nin
˜o events coincided with years when recovery in the pen-
guin population faltered (Fig. 1). The change in penguin num-
bers was significantly and strongly correlated with mean
normalised SST anomalies (Fig. 2). This model (F
1, 15
= 71.1,
p< 0.001, b
(adj)
= 0.81) predicts that strong El Nin
˜o events,
characterized by a rise in SST anomalies >2 °C above baseline
temperature, result in population crashes greater than 50%
(Fig. 2). In contrast, La Nin
˜a events, defined as a drop in SST
anomalies to 0.5 °C or lower below baseline temperatures,
are associated with periods of recovery in the population of
Gala
´pagos penguins (Fig. 2).
Fig. 1 illustrates that in the years of strong El Nin
˜o, the cen-
sus revealed fewer adults and juveniles than in other years
suggesting an association between El Nin
˜o, reduced fledgling
success (measured as the number of juveniles) and adult sur-
vival. Counts during weak El Nin
˜o events showed a low recov-
ery rate of the population indicating poor reproduction and
recruitment. The censuses also indicated an uncharacteristi-
cally low recovery rate of the penguin population between
1983 and 1997 coincident with a high frequency of weak Nin
˜o
events between the two strong events (Fig. 1).
During the 2004 census, we counted 858 penguins.
Although this represents nearly a doubling of the numbers
(444) after the last strong 1997–1998 El Nin
˜o event, the 2004
penguin numbers are less than half of numbers in the 1970s.
4. Discussion
4.1. Increased frequency and intensity of El Nin˜o
The CDRS SST data show that between 1965 and 1981 there
were no strong El Nin
˜o events in the Gala
´pagos that were
comparable to those of the 1980s and 1990s. We assert that
during these earlier years, the oceanographic conditions pro-
duced resources sufficient to support the high numbers of
penguins that we recorded in the first three counts of the
1970s and early 1980s (Fig. 1). In fact, recent investigations
suggest that a decrease of 25% in oceanic upwelling around
the equator after 1970 may have led to an increase of 0.8 °C
in SST (McPhaden and Zhang, 2002), probably reducing food
resources in Gala
´pagos. After 1980, the large fluctuations
and the slow recovery of the penguin population were proba-
bly linked to the increasing intensity and frequency of both
strong and weak El Nin
˜o events and the associated unproduc-
tive oceans.
Historically (before 1980), we presume that the penguin
population would recover in years following an El Nin
˜o, or
during cold La Nin
˜a events, with the associated abundance
of food. Our census data indicate that population recovery
during La Nin
˜a events have been only moderate (Fig. 2) and
have failed to restore the numbers typical of the period prior
to the 1980s (Fig. 1).
The modern pattern of more frequent and intense El Nin
˜o
episodes, including some events that are extreme by histori-
Fig. 1 – Sea-surface temperature (SST) anomalies from the Charles Darwin Research Station, Isla Santa Cruz, Gala
´pagos,
Ecuador. We calculated the normalized temperature anomalies (red and blue areas) by comparing the 5-month running mean
for SST of each month to the baseline SST from 1965 to 1979. SST anomalies that remain above 0.5 °C or below 0.5 °C
(beyond grey striped area) for at least six consecutive months define El Nin
˜o(n= 9) or La Nin
˜a(n= 9), respectively. The positive
temperature anomalies that exceeded 2 °C (dashed line) indicate strong El Nin
˜o events. Black bars are total number of
penguins. (For interpretation of the references to color in this figure legend, is referred to the web version of this paper.)
BIOLOGICAL CONSERVATION 127 (2006) 107–114 109
cal standards (1982–1983, 1997–1998), has cumulative effects
that diminishes the capacity of the penguin populations to re-
cover from previous El Nin
˜o events before the next event oc-
curs. This cycle leads to long-term reductions in penguin
numbers.
4.2. Strong El Nin˜ o events and population crashes
Our analysis indicates that strong El Nin
˜o events are cata-
strophic for the Gala
´pagos penguin causing declines greater
than 50% in the population of adult and juvenile birds (Fig. 2).
Starvation is the likely cause of this elevated mortality. Sim-
ilar mortality in seabirds, due to starvation, has been docu-
mented in productive ecosystems, such as those of the
Bengala Current during severe El Nin
˜o events. (La Cock, 1986).
The severity of strong El Nin
˜o, measured as duration and extent
of SST anomalies, explains this drastic effect on the Gala
´pagos
penguin. Only 29 juveniles werecounted in the two censuses of
1984 following the 1982–1983 El Nin
˜o event (Valle and Coulter,
1987). In September 1997, the effects of El Nin
˜o (initiated in
March 1997) on the penguin population were still imperceptible
(Fig. 1), and we counted 1284 penguins in the Archipelago of
which 17% were juveniles. The 1997–1998 El Nin
˜o ended in July
1998. By the time of the census of September 1998, no nests or
juveniles were recorded, and only 444 adults were observed.
These two strong warm events occurred when they would have
had the maximum impact on breeding success during two con-
secutive breeding seasons (1982–1983 and 1997–1998).
Although penguins can breed year round, the onset of a
strong El Nin
˜o events coinciding with the critical period of
pre-breeding food acquisition could have detrimental effects
on the population. Since one known preferred breeding time
is from April–May, it could have been that the two strong El
Nin
˜o events that started in May 1982 and March 1997 were
particularly detrimental to penguins because of the lack of
available food.
The high annual adult survival in penguins in general
(Crawford et al., 1999; Weimerskirch et al., 1992) would tend
to make their population trends extremely sensitive to small
changes in annual survival (Ratcliffe et al., 2002). Conse-
quently, the estimated low adult survival values of 0.23–0.35
for the Gala
´pagos penguin during strong El Nin
˜o events, in
addition to the direct impact on the dynamics of the breeding
population, could also reduce the penguin life expectancy
(Croxall et al., 2002) and affect the overall population trend
in the manner described in this paper. Therefore, we consider
adult mortality to be the main effect of El Nin
˜o on the Gala
´pa-
gos penguin.
4.3. Weak El Nin˜ o events and slow recovery rate of
penguin population
Weak El Nin
˜o events appear to affect only reproduction and
not adult survival because no population crashes were re-
corded during weak El Nin
˜o events. During the weak 1972–
1973 El Nin
˜o, Boersma (1998b) recorded only one surviving
chick from 92 nests. This suggests that penguins do lay eggs
during weak El Nin
˜o events, but we deduce that the food sup-
ply could be insufficient to achieve the survival and recruit-
ment of fledglings. The cumulative effects of weak El Nin
˜o
events on reproduction provide a plausible explanation for
the low recovery rate of the penguin population between
1983 and 1997 (Fig. 1). In fact, some authors have identified
the period between 1990 and 1995 as the longest El Nin
˜oon
record (Trenberth and Hoar, 1996). Poor recruitment rates
associated to post-fledgling mortality during repetitive weak
Fig. 2 – Percent change in penguin numbers in relation to the mean normalized sea-surface temperature (SST) anomalies for
the period December–April that preceded each penguin count. We calculated changes in the penguin population for counts
that were not more than 3 years apart (n= 17) (F
1, 15
= 71.1, p< 0.001, b
(adj)
= 0.81). We also tested the relationship without the 2
strong El Nin
˜o events in 1983 and 1998 to determine that the relationship remained significant without these extreme values
(F
1, 13
= 10.2, p= 0.007, b
(adj)
= 0.40). Dotted lines are 95% confidence limits. (For interpretation of the references to color in this
figure legend, is referred to the web version of this paper.)
110 BIOLOGICAL CONSERVATION 127 (2006) 107–114
El Nin
˜os are also expected to have a lag effect on population
size.
4.4. The mechanisms of El Nin˜ o events
Sinclair and Krebs (2002) state that food supply is the primary
factor determining the growth of animal populations. Fur-
thermore, there is accumulating evidence that changes in
the availability of food limits the production and survival of
the young, and that these changes are often driven by the
weather (White, 2004). At present, little is known about the
diet of the Gala
´pagos penguin. There are only opportunistic
observations of penguins foraging close to the shore that indi-
cate that prey species such as sardines (Sardinops sagax), piqu-
itingas (Lile stolifera), and mullets (Mugil sp.) are likely of
primary importance to the penguin diet (Mills, 2000; Vargas,
unpubl. data). If these schooling fish species migrate away
from the Gala
´pagos archipelago during El Nin
˜o events, the
penguin will not have access to prey. The Gala
´pagos penguin
will be constrained to the coastal areas by its inability to tra-
vel long distances (see Crawford and Shelton, 1978). In fact,
research on foraging behaviour suggests that feeding is exclu-
sively taking place in upwelling waters less than 2 km from
the coast where penguins perform dives of not more than
50 m (Mills, 2000; Steinfurth et al., unpubl. data).
The inability of the penguin populations to recover may
not be attributed solely to the time available between succes-
sive periods of impoverished food resources. The slow recov-
ery after El Nin
˜o events suggests that other factors might also
be at play. Boersma (1998b) noted higher mortality of females
than of males during strong El Nin
˜o events that lead to an
unbalanced sex ratio among survivors. The effect of such an
imbalance on the mating system of the penguins is unknown,
but a higher male:female ratio could dampen the recovery of
the population once released from the constraints of food
shortage. Flooding associated with El Nin
˜o could lead to nest
failure and desertion. In 1982–1983, over 2700 mm of rain was
recorded at Academy Bay (Santa Cruz) where the annual aver-
age (1965–2003) was only 500 mm. Flooding may be a particu-
lar problem for Gala
´pagos penguins as has been documented
for the Humboldt (Paredes and Zavalaga, 2001) and African
penguins (Wilson, 1985). Kelvin waves (eastward propagating
waves caused by fluctuations in wind speed at the ocean sur-
face at the Equator) in a strong El Nin
˜o create higher than nor-
mal sea levels around the Gala
´pagos, (Fig. 3., ftp://
ilikai.soest.hawaii.edu/islp/slpp.anomalies) and are expected
to increase risks of flooding. Most Gala
´pagos penguin nests
are usually sited less than 2 m above sea level (Vargas, unpubl.
data). In May 2004, a swell (wave) at Isla Mariela Mediana
(0°3503100 S, 91°5019.500 W) caused the loss of four nests with
eggs and chicks (two chicks were drowned in one of these
nests, Vargas, unpubl. data).
It is still unknown how the moult affects penguin survival
and breeding success during warm El Nin
˜o and cold La Nin
˜a
events. Some unanswered questions are whether penguins
are able to moult during El Nin
˜o or if penguins are capable
of moulting more than once in a year of La Nin
˜a when food
conditions would be favourable for laying multiple clutches.
Moulting requires energy and results in high thermoregula-
tion costs (Payne, 1972). Accordingly, the survival strategy of
this species of penguins would require that the penguins: (1)
build up energy reserves at sea, (2) moult on land, (3) return
to the sea to build up energy reserves again, and (4) begin
their breeding cycle. Preliminary data and incidental observa-
tions on the Gala
´pagos penguin suggest that, when not
moulting, this species is primarily at sea during the day and
on land at night (Boersma, 1977).
4.5. Implications for conservation
The data that we present here on the effects of El Nin
˜o on the
Gala
´pagos penguin is important to conservation biology be-
cause this species is endemic, rare, and, as we reveal, appar-
ently declining. We have demonstrated that the decline of the
Gala
´pagos penguin is associated with a change in climate that
is, at least, partly attributable to global human activity
(Houghton et al., 2001; Timmermann et al., 1999). Therefore,
the Gala
´pagos penguin is predicted to be at higher risk in
the 21st century as temperatures and precipitation will very
likely continue to rise as the ENSO shifts towards more warm-
ing events (Easterling et al., 2000; Houghton et al., 2001).
The fact that the Gala
´pagos penguin has survived for mil-
lennia in the face of El Nin
˜o (perhaps even stronger that those
of 1982–1983 and 1997–1998) is no cause for complacency as
other conditions have now changed. Before 1535, the Gala
´pa-
gos Islands were uninhabited by people. Whereas currently,
nearly 27,000 humans reside there and about 100,000 tourists
visit annually (Boersma et al., 2005). There are several human-
caused effects that can lead to further reductions of post-El
Nin
˜o populations of the Gala
´pagos Penguin. The commercial
fishery compete with penguins for the sardines and mullets,
particularly during El Nin
˜o events when fish populations are
reduced, and penguins become entangled in gillnets (Stein-
furth, pers. com., see Darby and Dawson, 2000). Furthermore,
mosquitoes (Culex quinquefasciatus) that arrived on the Gala
´-
pagos in the 1980s (Peck et al., 1998) because of human ac-
tions benefit from the warm and wet conditions of El Nin
˜o.
The C. quinquefasciatus mosquitoes represent a potential
new threat for Gala
´pagos penguin (Miller et al., 2001) because
C. quinquefasciatus are vectors for avian malaria (Fonseca
et al., 1998), and penguins in the genus Spheniscus are highly
susceptible to avian malaria (Fix et al., 1988; Graczyk et al.,
1995). There is also concern about the potential arrival to
Gala
´pagos of the mosquito-born West Nile virus (Wikelski
et al., 2004) that can infect penguins (Travis et al., submitted).
The threats outlined alone or in combination (see Huyser
et al., 2000) may be exacerbated by the low genetic diversity
of the Gala
´pagos penguin that could have arisen from the ef-
fects of population bottlenecks imposed by El Nin
˜o episodes
and coupled with the effects of increased human activity
(Akst et al., 2002).
In a population viability analysis (PVA) workshop in Febru-
ary 2005, researchers estimated that under the current El
Nin
˜o scenario, based on the frequency and intensity of El
Nin
˜o events described here, the Gala
´pagos penguin has a
30% probability of extinction within the next century (CBSG,
2005; Vargas et al., in preparation). The likelihood of extinc-
tion increases when other catastrophic factors such as
disease outbreaks, oil spills, or predation by introduced pre-
dators are added into the simulations (CBSG, 2005; Travis
BIOLOGICAL CONSERVATION 127 (2006) 107–114 111
et al., submitted). The Gala
´pagos penguin would be especially
at higher risk of extinction after strong El Nin
˜o events when
the population would be at lower levels.
Of course, direct management of the global human activi-
ties that probably underlie the increased frequency and sever-
ity of El Nin
˜o is beyond the scope of local strategies. However,
our results reveal that the situation of the Gala
´pagos penguin
is more fragile than previously realized and greater attention
should be paid to curtailing human activities that are increas-
ingly affecting this species.
4.6. Future perspectives and conservation
The diet of the Gala
´pagos penguin is virtually unknown. Con-
servation efforts will benefit from determination of seasonal
variation in diet. The distribution and abundance of prey spe-
cies could be better linked to changes in sea temperature,
underwater topography, and nutrient levels.
The population dynamics of the Gala
´pagos penguin living
in a climatically variable and unpredictable environment still
needs further study. Information on the age of first breeding,
longevity, annual breeding success and survival rates, recruit-
ment of juveniles, natal philopatry, and movements during
ENSO episodes is crucial for the conservation of this endan-
gered species.
Climatologists and wildlife managers should collaborate to
conserve the Gala
´pagos penguin. Climate models that suc-
cessfully predict El Nin
˜o events one or two years in advance
(see Chen et al., 2004) are of fundamental importance so that
timely and effective actions could be undertaken by wildlife
managers prior to extreme El Nin
˜o episodes.
Conservation actions should focus at reducing mortality of
adult birds, which could compensate, at least partially, for the
mortality losses during strong El Nin
˜o events. Reducing direct
and indirect anthropogenic-induced threats to the population
will enhance adult survival. Predation by exotic mammals,
entanglement in fishing nets, oil spills, and outbreaks of dis-
eases should be prevented (see CBSG, 2005, PVA report for
descriptions of research and management recommenda-
tions). Therefore, here we recommend the following priority
specific conservation actions:
1. Control feral cats (Felis catus) on Isabela. In early 2005, cats
were reported preying on adult penguins at Caleta Iguana,
Southern Isabela (Steinfurth, unpubl. data) Cats could also
prey on eggs and chicks in the nest.
2. Prohibit the use fishing nets within foraging ranges of pen-
guins. Fishing nets deployed for mullet and shark are
known to cause deaths by entanglement.
3. Prevent arrival of introduced vectors and diseases. Efforts
should be aimed at preventing the arrival of vectors (e.g.,
mosquitoes) and diseases, such as the West Nile virus
and avian malaria to which penguins are known to be
highly susceptible.
Acknowledgements
We are very grateful to P.D. Boersma for her invaluable exper-
tise on the Gala
´pagos penguin and critical evaluation of ear-
lier drafts of this manuscript. We thank K. Trenberth for
advice on SST analysis and on El Nin
˜o. P. Johnson helped with
statistics. M. Steinitz-Kannan, R. Wilson, E. Travis, and S. Bar-
low provided helpful comments. We are grateful to the staff of
the Charles Darwin Research Station (CDRS) and the Gala
´pa-
gos National Parks Service (GNPS) for assistance with the
recording of meteorological data and for participating in
penguin counts. The GNPS granted permission to carry out
the work and provided logistical support. Financial support
was provided by D. Swarovski & Co., Seaworld, and the Dar-
Fig. 3 – Gala
´pagos sea level anomalies from tide gauge at (0°4500 S, 90°1900 W) Santa Cruz, Gala
´pagos (January 1980–December
2004). The sea level reached 20–35 cm higher than average during the two strong El Nin
˜o events of 1982–1983 and 1997–1998.
Sea level in December 1997 was slightly higher than the maximum observed during the 1982–1983 El Nin
˜o (figure based on
monthly data available at: ftp://ilikai.soest.hawaii.edu/islp/slpp.anomalies).
112 BIOLOGICAL CONSERVATION 127 (2006) 107–114
win Initiative. Further support was provided by the Gala
´pagos
Conservation Trust, the Whitley Laing Foundation, and the
Swiss Friends of Gala
´pagos.
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