Introduction
Gentoo penguins (
Pygoscelis papua) have a circumpolar range with an estimated global population of 387,000 breeding pairs (Lynch
2013). Important breeding sites occur along the West Antarctic Peninsula (WAP) and across the Scotia Sea (Harris et al.
2015; Lynch et al.
2012), where approximately 80% of the global population breeds (IUCN
2016). The WAP and Scotia Sea are both experiencing significant environmental change (Forcada et al.
2006; SCAR
2009; Turner et al.
2016), with increases in air (Turner et al.
2016) and ocean temperatures (Gille
2008) and reductions in the regional duration and extent of seasonal sea-ice (Stammerjohn et al.
2008a,
b). Recent gentoo population surveys at a number of sites across the WAP and Scotia Sea showed different trends at different sites; some were stable while others increased, or expanded southwards (Baylis et al.
2013; Clucas et al.
2014; Ducklow et al.
2007; Dunn et al.
2016; Juáres et al.
2013; Lynch
2013; Lynch et al.
2008). Following a recent reappraisal of population trends, the gentoo penguin is currently designated as “Least Concern” by the IUCN, having previously been classified as “Near Threatened” in 2012 (IUCN
2016).
Changes in penguin population size are a useful indicator of ecosystem status (Boersma
2008; Che-Castaldo et al.
2017; Croxall et al.
2002; Forcada and Trathan
2009; Fraser et al.
1992; Hinke et al.
2007; Lynch et al.
2010; Lynch and LaRue
2014; Murphy et al.
2007; Trathan et al.
2007; Trivelpiece et al.
2011; UKAHT
2016). Currently, a number of ecological programmes exist that include gentoo penguins as one of the species monitored; this includes the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Ecosystem Monitoring Program, CEMP (CCAMLR
2004). CEMP records a range of parameters for penguins in order to monitor the status of the marine ecosystem in areas used by fisheries, to determine whether observed changes might be ascribed to fishery impacts or to natural environmental variation (Agnew
1997). At Goudier Island, we used CEMP protocols to monitor key penguin parameters. The standardised monitoring programme at Goudier Island was established during the 1996/1997 breeding season to assess the effects of tourist visitors on the gentoo population (Cobley and Shears
1999). Since then, numbers of breeding pairs and crèching chicks, as well as visitor numbers, were counted annually at all colonies.
Gentoo penguins first established breeding colonies at Goudier Island, Port Lockroy in 1985 (Cobley and Shears
1999; Trathan et al.
2008) and became a tourist attraction shortly thereafter. There are currently 10 colonies on Goudier Island and the site has become one of the most heavily visited tourist sites anywhere in the Antarctic, receiving an average of approximately 11,200 visitors per austral summer (November to March). In 2012/2013, more than 16,000 passenger landings took place on Goudier Island (Bender et al.
2016; IAATO
2017; Lynch et al.
2010). During the austral summer, tourist vessels visit Goudier Island nearly every day to view the penguins and the restored historical British Antarctic Survey (BAS) base which is currently managed and maintained by the UK Antarctic Heritage Trust (UKAHT
2016). The number of tourists landing on the WAP has increased dramatically since the late 1980s: between the 1989/1990 and 2013/2014 austral summers the number of visitors landing increased by 6 ± 1% per annum (Bender et al.
2016). The first tourist ships arrive at Goudier Island and nearby Jougla Point as early as mid-November (15 November in 2016), and daily visits continue until late February or March (28 February in 2017, 4 March in 2016), resulting in a complete overlap of tourist visits across the entire breeding season of the resident gentoo penguins (Black
2016; Cobley and Shears
1999). Tour ships visiting Goudier Island frequently incorporate visitor landings at nearby Jougla Point where a maximum of 100 people are permitted to land at a time (see
http://www.ats.aq/devAS/ats_other_template.aspx?lang=e&id=168cbdd8-56ae-45ad-8682-cdb7196f754e). Each visit to Goudier Island is carefully managed by UKAHT staff in accordance with current International Association of Antarctica Tour Operators (IAATO) visitor guidelines and the Antarctic Treaty System (ATS
2016; IAATO
2017; UKAHT
2016): a maximum of 60 visitors are permitted ashore at any one time and they are only permitted to travel along designated pathways under the supervision of UKAHT staff and ship-based guides. Nevertheless, the small size of the island makes it inevitable that visitors and station personnel are regularly within very close proximity (less than several metres) of nesting or transiting gentoo penguins and their chicks, despite a general recommendation of a 5 m minimum approach distance (IAATO
2017).
An initial study by Cobley and Shears (
1999) found that gentoo penguin breeding success at Goudier Island during the 1996/1997 austral summer was similar to that elsewhere in the region, concluding that tourist disturbance was unlikely to have had an impact in that season. A more comprehensive study by Trathan et al. (
2008), using data from 12 years (1996/1997–2007/2008), found high inter-annual variability in numbers of breeding pairs and observed productivity (number of chicks divided by number of nests with eggs), a result that reflects gentoo behaviour elsewhere (Holmes
2007; Putz et al.
2001). Six of the 10 Goudier Island colonies are directly visited by tourists, while four colonies are not. However, penguins nesting in these four colonies have to move through areas accessed by visitors to transit to and from the sea. Trathan et al. (
2008) reported that breeding numbers in two of the six visited colonies declined significantly but breeding success remained unchanged, and interpreted this as likely due to small scale movement of breeding pairs between locally-situated colonies, as is commonly recorded in this species (Bost and Jouventin
1990).
The programme at Goudier Island is the longest-running study measuring potential tourist disturbance to breeding penguins in the Antarctic. Each year large numbers of tourists visit penguin breeding sites in Antarctica (Bender et al.
2016; IAATO
2017). Thus, the ongoing monitoring of Goudier Island remains of high conservation and management value. Here we present a 21-year dataset (1996/1997 to 2016/2017); data were collected in a consistent manner and conformed to the CEMP methodology. We compare the colonies visited by tourists with those not directly visited. In addition, we examine the influence of environmental variability and compare our observations with records from a neighbouring breeding site at Jougla Point on Wiencke Island, as well as with other sites within the local region (within 50 km range).
Discussion
Our study focuses on the longest-running study examining visitor numbers and penguin population processes in the Antarctic. The dynamics of the gentoo colonies on Goudier Island are of interest in themselves, being situated within one of the fastest warming parts of the planet. That said, the study was initiated to explore interactions between visitors and penguins, so in this paper we focus much of our discussion upon this issue.
Population trends
The total number of gentoo penguin breeding pairs recorded on Goudier Island and at Jougla Point varied considerably between years but has fallen substantially at both sites since 1996/1997. Breeding success at these two sites also decreased over the same period. However, the population decreases at both Goudier Island and Jougla Point contrast with the majority of recent surveys at other gentoo breeding sites across the WAP/Scotia Arc. Excluding Goudier Island and Jougla Point, the general pattern has been broadly one of stable or increasing penguin populations and a gradual extension southward of the breeding range of this species (Baylis et al.
2013; Casanovas et al.
2015; Clucas et al.
2014; Ducklow et al.
2007; Dunn et al.
2016; Forcada et al.
2006; Humphries et al.
2017; IUCN
2016; Juáres et al.
2013; Lynch et al.
2012,
2008). In reviewing other study sites where potential tourism impacts are high, we found that three gentoo penguin colonies located within 50 km of Goudier Island (Cuverville Island, Danco Island and Waterboat Point) have all shown increasing numbers of breeding pairs in parallel to increasing numbers of tourists between 2001/2002 and 2015/2016. None of these three gentoo sites are however located in as small an area as Goudier Island in which tourists and breeding penguins overlap, suggesting caution in attempting to draw parallels. We also note that a study carried out between 2003/2004 and 2007/2008 at Petermann Island (65°10′S, 64°10′W), approximately 48 km south east of Goudier Island and which also experiences high levels of tourism, found an increasing gentoo penguin population (Lynch et al.
2010). However the population trend at Peterman Island closely resembled that of Goudier Island over the same 5 year period to 2007/2008. More recent data from this location would therefore be valuable for determining whether the recent decline in gentoo penguin population size and breeding success at Goudier Island is occurring at this second, comparable site.
Population drivers and future directions
Stochastic environmental factors, such as snow coverage and air temperature can exert temporal and spatial effects, frequently on a local scale (Cobley and Shears
1999; Micol and Jouventin
2001; Southwell et al.
2013; Van Franeker et al.
2001). Sea ice, oceanographic and weather conditions are all known to influence penguin population size and breeding success (Boersma
2008; Forcada and Trathan
2009). Our models for nest counts suggested a negative effect of higher temperatures and a positive effect of day of maximum sea ice; the best model indicated negative effects during years of extreme sea ice and increased surface air temperature on numbers of gentoo breeding pairs and breeding success in visited and unvisited/control colonies at Goudier Island. These effects are consistent with similar observations in other parts of the range of this species and support results from the Petermann Island study (Lynch et al.
2010) where breeding success was significantly correlated with total December precipitation (rain and/or snow). Both findings are of particular interest given the increase in precipitation across the WAP (Lynch et al.
2010; Turner et al.
2005).
The best nest count model found the interaction of year and visitors was highly significant; recent years in which higher numbers of tourists visited Goudier Island had a more negative effect on numbers of gentoo breeding pairs both in visited and unvisited colonies. This decline was best modelled by a linear trend (variable “syear”). There was a strong correlation between decreasing numbers of penguin pairs and increasing numbers of tourists over time, potentially confounding the importance of both time and tourist effects on nest counts. However, the best model had only the interaction term, thus resolving this issue, and suggested that there was strong support for a negative effect of visitors on nest counts.
Between 1996/1997 and 2007/2008, Trathan et al. (
2008) found a significant decline in breeding pairs (nests counted) in the colonies visited by tourists and stable or increasing pair numbers in the unvisited control colonies at Goudier Island. A similar trend was found by Lynch et al. (
2010) at Petermann Island between 2003/2004 and 2007/2008, with gentoo penguin reproductive success lowest in colonies frequently visited by tourists, as opposed to colonies that remained visitor-free. Our results show a continuation of the declining trend in numbers of breeding pairs within the visited colonies, but also reveal an almost identical rate of pair decline in the unvisited colonies (a reduction of 24% and 25%, respectively, over the entire 21-year period). This represents a significant change at Goudier Island, and future surveys carried out at Petermann Island would be most useful in establishing whether such a change has also taken place on that island. The small size of Goudier Island makes a certain degree of close contact between penguins breeding in the control areas and humans inevitable, despite best efforts to minimalize disturbance to these control colonies. Regardless of colony location, most penguins enter and leave the water from several main sections of shoreline, most of which are located within the visited part of the island. They use common pathways across the island which again require birds from both visited and control colonies to travel through the “visited areas” (UK Antarctic Heritage Trust unpublished data). The unvisited control colonies are located less than 100 m from the main buildings and walkways that form the focal points for visiting tourist parties, and the boundary zone dividing these colonies from the rest of the island runs adjacent to control colony one and four, facilitating the approach of tourists to within several metres of penguins nesting in these colonies. Consequently penguin breeding pairs in both visited and unvisited colony areas may be equally susceptible to negative behavioural or physiological responses brought about by the continued season-long presence of large numbers of visitors (Bender et al.
2016; Holmes
2007; Southwell et al.
2013).
Practically all available penguin nesting areas on Goudier Island have been occupied by breeding pairs. Consequently it is plausible to assume that the carrying capacity (K) of the island has been reached, with pair numbers currently likely to be fluctuating around the maximum sustainable number. However, we found no significant effects of density dependence when testing as a possible explanatory variable. Trathan et al. (
2008) noted the plausibility of movement by individual birds between colonies on Goudier Island and between Goudier Island and adjacent Wiencke Island (Jougla Point) as a likely cause of local scale variation in population size. The declining trend detected at both Goudier Island and Jougla Point in this study appears to dispel the possibility of such movement as the main driver of population decline.
During the 21 years of this study both Goudier Island and Jougla Point experienced a 22% per annum increase in visitor numbers, and are amongst the most intensively visited areas anywhere in the WAP (Bender et al.
2016; IAATO
2017; Lynch et al.
2010). For example, in 2015/2016 Goudier Island received a total of 19,834 visitors over a 112 day period; an average of 177 people every day, despite a further 16 tourist ships cancelling their planned visits due to increased levels of sea ice (UK Antarctic Heritage Trust unpublished data). This is a very significant increase from the 35-55 tourists visiting the same site every 1–2 days (262 people in total) in 1996/1997 (IAATO
2017) and represents a disproportionate growth in tourist numbers and visits relative to the rest of the WAP (Bender et al.
2016; IAATO
2017; Lynch et al.
2010). Although we found no statistical correlation between the number of tourists and sea ice variables, increased sea ice might affect the arrival of cruise ships to Goudier Island, although this would be unlikely during the summer months when tourist visits take place. Recent predictive analyses suggest likely further increases in the number of tourists visiting the Antarctic, including at Goudier Island and Jougla Point, particularly as winter sea ice continues to decline in extent and duration (Bender et al.
2016; Lynch et al.
2010; Stammerjohn et al.
2008a). However, given the time lag associated with scheduling additional tourist cruises, it is unlikely that additional cruises could be organised at short notice in any given year to take advantage of prevailing sea ice conditions. Thus, disentangling the impact of the presence of tourists from environmental factors may remain a complex problem, requiring more detailed data collection protocols than are currently in place.
Human disturbance can have a significant negative effect on Antarctic wildlife (Coetzee and Chown
2016). Stress to incubating birds, obstruction of foraging pathways and land routes to and from colonies, depressed recruitment at breeding sites and physiological disruption have all been cited as potential consequences of tourism close to sensitive penguin populations (Bender et al.
2016; Coetzee and Chown
2016; Ellenberg et al.
2006,
2007; Lynch et al.
2010; Trathan et al.
2015). Magellanic
Spheniscus magellanicus, Humboldt
S. humboldti and yellow eyed
Megadyptes antipodes penguins exposed to human visitors all responded with elevated heart rates; the severity of disturbance and time taken for heart rate to return to normal was directly related to the length of exposure (Ellenberg et al.
2013), including at distances of up to 150 m (Ellenberg et al.
2006). However, such studies should be treated with caution when intimating cause and effect in our study due to variation in sensitivity to human disturbance between penguin species and location (Trathan et al.
2008; Villanueva et al.
2014; Walker et al.
2005). Future monitoring of physical and physiological responses, such as heart rate, hormonal levels or body temperature, amongst gentoo penguins at Goudier Island could help to determine if and to what extent penguins within the visited and control colonies are exhibiting stress symptoms (Bejder et al.
2009), although the feasibility of carrying out increased levels of fieldwork at study sites of such high tourist intensity would require careful evaluation.
Conclusion
Over the past 21 years there has been a significant change in the gentoo penguin population at Goudier Island and Jougla Point, Port Lockroy. However, the processes driving these local-scale changes remains unclear. Despite the evident decline in the numbers of breeding pairs and breeding success at both Goudier Island and Jougla Point, we advise caution when attempting to interpret the factors influencing these trends. Che-Castaldo et al. (
2017) demonstrated that the effects of random fluctuating dynamics and “process noise” can significantly influence abundance shifts in penguin populations, particularly at the local scale of individual colonies, and subsequently complicate accurate interpretation of the drivers responsible. Our data suggest a degree of complexity, with gentoo penguin population trends at Goudier Island (and Jougla Point) influenced by a number of potentially subtle drivers acting together.
Given the high level of human visitation, on-going annual monitoring of the Goudier Island and Jougla Point gentoo penguin breeding populations should remain a high priority, including collecting information on numbers of visitors per day and length of visits to test for any specific visitor effects on each breeding stage (e.g. arrival, incubation, brood guard, crèche). Additional surveys using standard methodologies at other breeding sites of gentoo penguins within the Palmer Archipelago/WAP region would provide valuable comparisons and context to the changes taking place at Goudier Island (Che-Castaldo et al.
2017), where current population trends differ from those at some other regional sites. Noting the highly significant interactions between increasing human visitation and decreasing numbers of gentoo penguin breeding pairs at Goudier Island and Jougla Point, the current levels of tourist numbers could be seen in contradiction to a precautionary approach. Arguably, a potential annual cap on total numbers of tourists visiting Goudier Island and Jougla Point and restrictions to the landing season at settlement should be considered. Continued collection of meteorological data, such as air temperature and snow cover, would be useful to evaluate ongoing stochastic environmental factors (Southwell et al.
2013; Trathan et al.
2008; Van Franeker et al.
2001). Only by improving our understanding of the causes that manifest as population declines on both local and regional scales will we be able to implement management strategies to safeguard penguin populations at Port Lockroy and elsewhere, and balance the demands of the tourism industry with the needs of the penguins.