Are the diets of sympatric Pygoscelid penguins more similar than previously thought?

Abstract

In recent years, functional changes in Southern Ocean are becoming more noticeable, due to climate change and increasing human impacts, including a growing fishery that is concentrating in the Antarctic Peninsula (AP) region. Antarctic krill Euphausia superba is often the primary prey species for animals such as Pygoscelis penguins, a sentinel species for ecosystem monitoring and management. During the last two decades in the AP gentoo penguin numbers (Pygoscelis papua) have increased and their range has shifted southward, in contrast to the decline in numbers of Adélie (P. adeliae) and chinstrap (P. antarcticus) penguins. Given divergent population trends, the goal of this study was to examine differences in their diet, and size structure of Antarctic krill recovered from penguin diet samples. The study is based on diet samples collected during the austral summers on King George Island (South Shetland Islands) where P. adeliae, P. antarcticus, and P. papua breed in mixed colonies. Results indicate that the penguins consumed krill of similar sizes during the breeding period. In contrast to prior diet studies, we found higher proportions of krill in the gentoo diet and changes in the percentage of krill in the diet relative obtained during 1970s. The similarity in diets among all three species suggests that the availability prey items (e. g., fishes) may be changing and driving higher dietary overlap. Moreover, we also check differences in krill length among penguin individuals and we did not find any statistically significant differences. We also found plastic debris in penguin stomachs during both summers.

Quantifying Antarctic krill connectivity across the West Antarctic Peninsula and its role in large-scale Pygoscelis penguin population dynamics

“…Pygoscelis penguins primarily consume krill during the austral summer 33 , 43 , 86 . Krill distributions along the WAP are spatially and temporally heterogeneous 1 – 6 , 31 and are facing increasing pressures from a growing krill fishery 17 .…”

“…Post-larval krill distributions along the WAP during this critical season are well studied 2 , 7 , 25 , 31 , however, the connectivity within the krill population during the austral summer is poorly understood. Because krill distributions in this region are spatially heterogeneous 32 , connectivity among regions can have an important influence on krill availability not only for predators, such as breeding Pygoscelis penguins that feed primarily on krill 33 , but also for a growing krill fishery 17 , 19 , 34 , 35 .…”

“…Moreover, gentoos and chinstraps, whose core breeding habitat is further north in the sub-Antarctic, are better adapted to milder conditions 37 , 44 . During the critical breeding period, all three species act as central place foragers and have similar diets 33 , 42 . While gentoos have higher diet plasticity, all three species primarily consume krill during the chick-rearing period 33 .…”

“…During the critical breeding period, all three species act as central place foragers and have similar diets 33 , 42 . While gentoos have higher diet plasticity, all three species primarily consume krill during the chick-rearing period 33 . Due to differences in clutch initiation, breeding pygoscelid penguins consume differing amounts of krill in different periods of the austral summer, with Adélies consuming more krill earlier in the season than their counterparts 42 .…”

Examining the Connectivity of Antarctic Krill on the West Antarctic Peninsula: Implications for Pygoscelis Penguin Biogeography and Population Dynamics

“…Pygoscelis penguins primarily consume krill during the austral summer 66, 74,75 . Krill distributions along the WAP are spatially and temporally heterogeneous [1][2][3][4][5][6]26 and, therefore, could play a role in penguin biogeography around the Adélie gap.…”