Integrating Stomach Content and Stable Isotope Analyses to Quantify the Diets of Pygoscelid Penguins

Abstract

Stomach content analysis (SCA) and more recently stable isotope analysis (SIA) integrated with isotopic mixing models have become common methods for dietary studies and provide insight into the foraging ecology of seabirds. However, both methods have drawbacks and biases that may result in difficulties in quantifying inter-annual and species-specific differences in diets. We used these two methods to simultaneously quantify the chick-rearing diet of Chinstrap (Pygoscelis antarctica) and Gentoo (P. papua) penguins and highlight methods of integrating SCA data to increase accuracy of diet composition estimates using SIA. SCA biomass estimates were highly variable and underestimated the importance of soft-bodied prey such as fish. Two-source, isotopic mixing model predictions were less variable and identified inter-annual and species-specific differences in the relative amounts of fish and krill in penguin diets not readily apparent using SCA. In contrast, multi-source isotopic mixing models had difficulty estimating the dietary contribution of fish species occupying similar trophic levels without refinement using SCA-derived otolith data. Overall, our ability to track inter-annual and species-specific differences in penguin diets using SIA was enhanced by integrating SCA data to isotopic mixing modes in three ways: 1) selecting appropriate prey sources, 2) weighting combinations of isotopically similar prey in two-source mixing models and 3) refining predicted contributions of isotopically similar prey in multi-source models.

Contrasting specialist and generalist patterns facilitate foraging niche partitioning in sympatric populations of Pygoscelis penguins

“…However, stomach content data reflect a 'snapshot' of recent diet and can be highly variable while underestimating the im portance of soft-bodied prey, such as fish and squid (Barrett et al 2007). Stable isotope analysis provides a complementary approach for examining the diets and ecological niches of penguins, which avoids many of the biases inherent to stomach content analysis (Polito et al 2011a). Nitrogen isotopic values (δ 15 N) are commonly used to infer trophic level and diets, while carbon isotopic values (δ 13 C) help trace trends in marine habitat use (inshore/benthic vs. offshore/pelagic; Cherel & Hobson 2007).…”

“…We collected stomach content samples during the chickrearing period (January to February) after chicks had reached the crèche stage (> 2.5 wk of age) using the water-offloading lavage technique following the methods of the Commission for the Con ser vation of Antarctic Marine Living Resources (CCAMLR) ecosystem monitoring program standard methods (CCAMLR 1997) as modified by Polito et al (2011a). We sampled breeding adults returning from foraging trips between 15:00 and 17:00 h local time at 5 to 7 d intervals, for a total of 10 to 15 gentoo penguins and 29 to 30 chinstrap penguins each year.…”

KARAKTERISTIKMORFOLOGI DANHUBUNGANMORFOMETRIK OTOLITH DENGAN UKURAN IKAN LEMURU (Sardinella lemuru Bleeker, 1853) DI SELAT BALI

“…Otolith menyajikan perekaman secara permanen terhadap sejarah hidup (life history) setiap individu ikan secara terus menerus (ICES, 2004) dan akan tetap tumbuh sepanjang hidup walaupun dalam kondisi stress (Mendoza, 2006) Otolith terdiri dari 3 bagian yaitu sagittae, lapillus dan asteriscus (Campana, 2004;Tuset et al, 2008), dimana sagittae mempunyai ukuran terbesar pada semua ikan, diikuti asteriscus dan lapillus sebagai yang terkecil (Jawad et al, 2008;Seyfabadi et al, 2014;Yilmaz et al, 2015). Sagittae relatif lebih mudah dikumpulkan (Bani et al, 2013) dan memiliki struktur yang lebih stabil dibanding astericus dan lapillus, serta memiliki ciri-ciri spesifik pada masingmasing spesies (Polito et al, 2011). Oleh karena itu, sagittae telah digunakan secara luas untuk memperoleh pemahaman yang lebih baik dalam studi taksonomi dan identifikasi spesies, sejarah hidup, pertumbuhan dan umur (Campana & Neilson, 1985;Sparre & Venema, 1999;Tuset et al, 2003).…”

Extreme intra-clutch egg size dimorphism is not coupled with corresponding differences in antioxidant capacity and stable isotopes between eggs

“…N values compared to other known prey consumed by rockhopper penguins (such as fish) (Polito et al, 2011;Dehnhard et al, 2016). Even though the underlying mechanisms remain unclear, this shows that female diet affects eggs differentially at least for isotopic compositions (Prediction 4), and that females with a low contribution of krill in their diet differentiate resources more strongly between A-and B-yolks.…”

“…Stable isotope analysis therefore represents an indirect method to assess foraging strategies, which can be used to determine the relative importance of feeding sources (Gauthier et al, 2003). For instance, penguins predominantly feeding on krill (with low δ 13 C and δ 15 N values) show low isotope values compared to penguins predominantly feeding on fish (with high δ 13 C and δ 15 N values) (Polito et al, 2011;Dehnhard et al, 2016). Krill also contains higher levels of lipophilic antioxidants (mostly astaxanthin) than fish (Tou et al, 2007).…”