Sexual differences in the foraging ecology of 19th century beluga whales (Delphinapterus leucas) from the Canadian High Arctic

Abstract

Marine mammals often exhibit significant sexual segregation in their diet and habitat use but these differences have not been studied systematically in historic or ancient populations due to the difficulties associated with determining the sex of skeletal elements based on gross morphology. Using a combined ancient DNA and stable isotope approach, we document a sexual difference in the foraging ecology of late 19th century beluga whales (Delphinapterus leucas) from the Canadian High Arctic. Using two PCR assays that coamplify fragments of the Y‐linked SRY and X‐linked ZFX genes, we assigned reproducible sex identities to 35 beluga specimens. This provided a basis for investigating sex‐specific differences in foraging ecology using stable carbon and nitrogen isotope analyses of bone collagen. These isotopic data demonstrate that although both males and females primarily consumed Arctic cod, males utilized a wider range of prey than females, feeding on high trophic level benthic prey (sculpins) to a greater extent. Because bone collagen integrates prey isotopic compositions over the course of several years these sex‐based differences in beluga bone collagen isotopic compositions reflect long‐term and sustained sexual differences in foraging.

Population-specific sex and size variation in long-term foraging ecology of belugas and narwhals

“…We did not include prey isotopic data, as these are available from soft tissue samples only [43,44,65] and reflect the short-term seasonal diet of the prey species, while our cetacean stable isotope data from bone collagen reflect the consumer diet over several years. We attempted to incorporate prey data [43,44,65] but the resulting mixing polygon was inconsistent with the isotopic compositions observed in belugas and narwhals after correcting for the Suess effect, which was done for the consumers following Szpak et al 2019 [66] and trophic enrichment [67]. This suggests that the prey isotopic data are not representative of what would have been consumed by these cetaceans either because isotopic compositions are inaccurate, certain prey sources are missing, or a combination of the two.…”

Quality control for modern bone collagen stable carbon and nitrogen isotope measurements

“…Burton et al., 2001; Guiry, Needs‐Howarth, et al, 2016; Guiry, Orchard, Royle, Cheung, & Yang, 2020; Misarti, Finney, Maschner, & Wooller, 2009; Szpak, Orchard, McKechnie, & Gröcke, 2012). These studies are particularly important because they can allow for more accurate reconstructions of preindustrial environmental conditions as well as provide detailed insights into how humans have altered ecosystem dynamics throughout the Anthropocene (Braje et al., 2017; Guiry, Beglane, et al, 2018; Guiry, Buckley, et al, 2020; Szpak, Buckley, Darwent, & Richards, 2018; Szpak et al., 2019)—both of which, in turn, can provide context for guiding future conservation policy and environmental restoration efforts (Rick & Lockwood, 2013; Swetnam, Allen, & Betancourt, 1999).…”

Diet of St. Lawrence Estuary Beluga (<i>Delphinapterus leucas</i>) in a changing ecosystem

“…Beluga are size dimorphic, with males being larger than females (Lesage et al 2014). Allometric relationships predict that males would be able to ingest larger prey items and a wider range of species (Wilson 1975), and reach deeper depths than females (Schreer and Kovacs 1997), predictions that were verified in other Beluga populations (Seaman et al 1982;Lowry et al 1985;Szpak et al 2019). In the SLE, differential prey access by sexes due to diving capacity is unlikely given that maximum bottom depth (350 m) is shallower than the species diving capacity (in excess of 1100 m; Richard et al 1997).…”

“…Age was determined from tooth dentinal layers, using a longitudinal midline section or half tooth, and highresolution (4800 dpi optical resolution, 24-bit colour) digital imagery (Epson scanner Perfection V500 photo, Epson Canada Limited, Markham, Ontario, Canada) to allow for magnification, light, and contrast adjustments. One growth layer group (GLG) was assumed to be depos ited each year (Stewart et al 2006;Hohn et al 2016;Waugh et al 2018).…”