Morrison 1
Kinsey Morrrison
Darwin, Evolution, and the Galápagos
October 12, 2015
Tropical Penguins are on Thin Ice
Introduction:
According to legend, the Galápagos Islands mystically rise and fall from the sea as sailors pass by them in the fog. While that’s only true on a geological time scale, The Enchanted Islands unquestionably deserve their name: much of what visitors can see, often just an arm’s length away, would have them believe they’re in a dream. An iguana diving as deep as a cormorant; a hawk unafraid to land on Darwin’s gun (or maybe your camera lens); a sea turtle swimming on the left while you pass a cactus grove on your right. But the most surprising sight may be the Galápagos penguin (Spheniscusmendiculus): an Antarctic bird that, remarkably, has found a home in a place where the sun twice as bright as in California.
Theirs is the only penguin species found north of the equator in the wild: the birds’ decreased body weight (4.8 lb for males, 3.7 lb for females; about the size of a half-gallon milk carton) is an adaptation to the warmer Galápagos climate since they don’t need to store so much energy in body fat (De Roy, 2009). Ironically, these penguins used to life on ice can only survive in the Galápagos because the islands because have volcanoes — most birds nest inside the cool lava tubes that are left aftereruptions (De Roy, 2009). Their largest populations are on the islands of Isabela and Fernandina, as these are closest to the cold Cromwell Current which is critical to the species’ success (Boersma, 1998): it’s namesake nutrient upwelling sustains the penguins, as well the marine iguanas and flightless cormorants mentioned earlier.
Unfortunately, after four million years of evolution from their closest ancestor, the endangered penguins now face a 30% chance of extinction in the next century (De Roy, 2009). Fire in the mountains provides them with a home, but when waters heat up during El Niño years, their food supply is decimated as cold currents weaken and waters more resemble those of a tropical climate. The most severe El Niños of the past few decades (1982-83 and 1997-98) have decreased their numbers by 77% and 66% respectively (IUCN Redlist, Spheniscusmendiculus). Even before these bottleneck events, they were the world’s rarest penguin species, and in 2009, the endemic Galápagos population hovered at just over 1,000 birds (Alava and Haase, 2011). With some scientists predicting a “Super El Niño” in late 2015, rivaling the strongest on record, penguins deserve a place at the forefront of the islands’ conservation efforts. NASA climatologist Bill Patzert explains, “There’s no longer a possibility that [the 2015] El Niño wimps out at this point. It’s too big to fail (Lin II).”
But while this climate phenomenon is understandably devastating for the species in the short-term, they should be able to rebound in the long-term: El Niño is only one half of an oscillation, followed by balancing La Niña years that strengthen the Cromwell upwelling and rescue many sea-going species that can only survive in cold waters (De Roy, 2009). While the Galápagos cormorant population also swiftly declined during the 1982 and 1997 El Niños, the species has steadily recovered since then: their population rose from a record-low 500 in 1982 to 1,400 in 2009 (Alava and Haase, 2011). Similarly, though marine iguanas have suffered 85% mortality in the worst El Niños, their population has bounced back as well — according to the most recent census, there are at least 15,000-30,000 of the lizards on Santa FéIsland alone (IUCN Redlist).
It’s not that the penguins haven’t recovered at all — to some degree, they have. They have even adapted to molt before breeding in order to conserve energy in case there is a drop in food supply during the mating season (De Roy, 2009). But while El Niño causes downward spikes on an upward trend for the cormorants, La Niña provides upward spikes on an overall downward trend for the penguins (see Figure 1 and 2). In 1971, they had a population of 1,950: 95% higher than in 2009 (Vargas, Lougheed, Snell, 2005). Why are Galápagos penguins losing to El Niño when some other affected marine species are thriving in spite of it?
Hypothesis 1:
My first hypothesis is that El Niño disproportionately affects female penguins, slowing down population recovery. That differential, if supported by the evidence, could depress breeding for perhaps decades after an initial crash of the population (Vargas et al 2007). In 1998, Boersma noted that females lost body weight at a faster rate than males during periods of food shortage, likely causing a higher mortality rate among females during strong El Niño events that would lead to an unbalanced sex ratio among survivors[1].
On average, females weighed 2.1 kg during the 1971 La Niña, and dropped to less than 1.8 kg during the 1972 El Niño; males on the other hand started off heavier at 2.45 kg, and lost 50% less weight than females, with most at 2.25 kg in 1972 (Figure 3) (Boersma, 1998). Even if they did survive, the females’ significant weight loss would likely cause them to have a much harder time reproducing than in years of abundance (Vargas et al 2007). The Boersma study adds, “For Galápagos Penguins, reproduction and body condition appear to be tightly linked to oceanic conditions.”
The penguins’ unbalanced sex ratio is exacerbated because they are monogamous; in contrast, flightless cormorants can sometimes breed through facultative sequential polyandry. This strategy can increase the number of cormorant chicks that survive and reproduce, especially given circumstances where the risks outweigh the benefits: typically when the young reach at least 2.5 months and food is relatively abundant (Paz-y-Miño-C and Espinosa, 2013). Why don’t female penguins systematically abandon their nests, too?
First, while male cormorants are 40% heavier than females, male penguins are only 16% heavier; the increased sexual size dimorphism (SSD) among cormorants means the males are notably better food providers and can usually raise a single-young brood alone even when resources are limited (Boersma, 1998; Paz-y-Miño-C and Espinosa, 2013).
Second, penguins have evolved from life on a continent where the average winter temperature is -60° F (-51° C) and six months of the year are spent in almost complete darkness (Browne, 1994). Just staying alive in those conditions — let alone raising young — is so strenuous that it likely requires monogamy, and the teamwork and pair-bond that comes with it. Even with some selective pressure away from that breeding strategy in the Galápagos, it remains the most viable option for the endemic birds: due to both the species’ evolutionary history and lack of SSD, if a female penguin left her mate alone, their chick would probably starve. Hypothesis 1 is therefore supported by the data: El Niño does disproportionately affect females, and because of their monogamy, this especially hinders their reproduction and subsequent population growth during La Niñas.
Hypothesis 2:
My second hypothesis is that since the penguins forage in open water, Galápagos fishermen compete with them for food. Fortunately for the birds, the evidence quickly showed this wasn’t true: Spheniscusmendiculusmost commonly feeds on anchovies, sardines, pilchards, and mullets, where as humans predominantly seek out fish far larger than the penguins themselves, like tuna, billfish, and groupers (Fitter, J; Fitter, D; Hosking, D., 2000). As you can see from Figure 4, mullets are the only fish that both people and penguins commonly hunt for in Galápagos waters (Schiller et al 2014)[2].
But that doesn’t mean that people pose no threat to the species: island fishermen often inadvertently kill the birds since floating nets from fishing boats can drown them (IUCN Redlist, Spheniscusmendiculus). Longline fishing has especially troubling implications (for many different endangered marine animals): they can be up to 15 miles long with hundreds or even thousands of baited hooks (PBS, 2008) with no way for the people on the boats to regulate what they’re catching before it’s often too late (Vargas et al 2006). In the Galápagos Marine Reserve specifically, bycatch accounts for 40.3% of any given haul: nearly half of the animals fishermen bring on board are not what they meant to catch (Zimmerhackel et al 2015). Bycatch mortality accounts for 12.6% (see Image 1), while 27.7% of animals unintentionally caught are discarded alive, but often injured (Figure 5).
These results raise major concern for both conservation and the economy in the Galápagos as high bycatch rates are as inefficient for fishermen as they are threatening for the marine community as a whole. With that said, because the bycatch mortality is spread out among a variety of species (sharks, sea birds, unmarketable fish, etc.) it’s effect on penguins in particular is probably not large enough to account for such a notable population decline spanning more than four decades[3].
Hypothesis 3:
Perhaps though, my third hypothesis is widespread enough to explain the long-term downward trend: human-induced climate change has increased Pacific water temperatures and the frequency of El Niño events, endangering the Galápagos penguins. Since 1950, La Niña events have gotten generally gotten shorter, less intense, and further apart, while El Niño periods have gotten somewhat longer, and considerably more intense and frequent (NOAA, 2015) (see Figure 6).” While these short-term shifts are important, they reflect a large-scale change as well. El Niño events now occur 2–7 times more frequently than they did 7000–15,000 years ago (Vargas et al 2006). Not only is the penguins’ food supply limited, but flooding associated with El Niño can lead to nest failure and desertion (Vargas et al 2006).
In addition to having more El Niños that push Pacific water temperatures especially high, climate change is raising the baseline sea surface temperature. In 1880, the temperature anomaly from the 1971-2000 global average was -0.5°F; in 2014, it was 0.7°F (EPA, 2014) (see Figure 7). Interestingly though, while Hypothesis 3 is supported in the long term, it may actually be incorrect in the short term, fortunately for the penguins.
New evidence shows that due to climate change, the Cromwell Current — 1,000 times the volume of the Mississippi River — is moving northward, expanding the Galápagos Cold Pool so that it further surrounds the tip of Isabela Island (Karnauskas et al 2015). As we can see from Figure 8, this doesn’t just mean the penguins have access to more of the current, they also get access to the best part of it: the especially cool epicenter now nearly touching the western shore of Fernandina. Could this surprising oceanographic shift single-handedly reverse the penguin population’s downward trend? Probably not in the long-term if climate change overall isn’t drastically slowed down, but it could certainly help them survive the upcoming El Niño with less of a bottleneck than in 1982 and 1997, possibly pushing them back from endangered to vulnerable on the IUCN Redlist (Karnauskas et al 2015).
While this new finding is incredibly promising, it can’t be emphasized enough that climate change overall ultimately hurts the penguins — it doesn’t matter how large the cold pool is if the water isn’t cold. Still, the Karnauskas study underscores why we have to look at climate shifts on a local scale as well as global; certainly, more research should be completed on this subject to explore its implications, and similar studies should be considered for other currents with major ecosystem impacts.
Additional Challenges:
First, like all penguins, Spheniscusmendiculusis flightless; since the birds are marine feeders, this doesn’t typically harm their fitness, but it does mean they can’t fly to another island or the mainland when food is scarce, as some other Galápagos birds are able to do. The blue-footed booby for example has been found as far as California during low-resource years on the islands, a coping strategy totally out of a penguin’s range (IUCN Redlist, Sula nebouxii).
Second, the growing number of foreign travelers to the islands pose an added risk to the species by introducing diseases and predators, for example, feral dogs; when created, the master plan of the Galápagos National Park called for a maximum of 12,000 visitors per year, but there was no mention of how to achieve this (Groot, 1983). Now Galápagos tourism is one of the fastest growing economies in the world (Brewington, 2012). Scientists have recently found the introduced Plasmodium blood parasite (Avian malaria) in some Galápagos penguins, and it remains unclear how much this might threaten the species (Levin et al 2009). 97.2% of penguins sampled in one study showed seroprevalence of malarial antibodies which suggests high exposure to the parasite but low Plasmodium-induced mortality (Palmer et al 2013). Whatever level of harm Avian malaria may cause, it would likely be worsened by strong El Niños, as bottleneck events lower genetic diversity which in turn decreases immunological resistance. Though one of the penguins’ greatest struggles in their remarkable journey to Galápagos was the islands’ isolation, recreating that isolation now might be the only way to protect them.
A Promising Conservation Strategy:
Many nests used in the 1970s (when the penguin population was the highest ever recorded) have been flooded, are used by marine iguanas, or no longer exist. To help alleviate this barrier to the species’ success, Dr. Dee Boersma (partnering with the University of Washington) built 120 high-quality “penguin condos” with natural materials such as lava rock, to provide cool and shady homes for the birds that still resemble their typical Galápagos habitat. Near Elizabeth Bay, constructed nests account for up to 43% of penguin breeding activity (G. Conservancy). This idea seems to have great potential, and though most of my project focused on marine-based threats to the penguins, could address one of their largest problems on land.
Conclusion:
The Galápagos penguin’s declining population remains troubling, but their situation is certainly not without hope. The most potent threats they face include increasingly strong and frequent El Niño events (which disproportionately affects females), a rising global sea surface temperature, fishery bycatch, and also, flightlessness, foreign visitors, and Avian malaria. But their population could reverse its decline if the shifting Cromwell Current (which is expanding the Galápagos Cold Pool), combined with new artificial nests on land, lessen the bottleneck effect of the 2015-2016 El Niño and those beyond it.
This project highlights the need for researchers zooming in on local trends within a global phenomenon, as climate change has provided a surprising benefit to penguins despite its overall harm to them. But it’s also critical to zoom out, especially when looking at population trends: it’s possible the 40-year decline I’ve noted is merely one of many valleys we would see if we had earlier census data, and if given enough time, the penguins would rise back to their relative peak numbers of 1971.
To make sure they have that time, we must act swiftly but strategically in conservation efforts, as much as possible keeping accurate and consistent data on population numbers, water temperatures, sex ratios, bycatch mortality, Plasmodium prevalence, and penguin condo success in order to prioritize the efforts that most help these unique, resilient (and of course, adorable) animals. It would be disheartening — and I think, tragic — to lose the penguins now because of preventable human errors, especially when they have survived for so long in a near-opposite environment to that of their ancestors’. The Baltra airport had it right (Image 2): if we can help the penguins to thrive, we will have left a indelible mark on the world’s natural paradise.
Bibliography:
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