Abstract
Baleen tissue accumulates stress hormones (glucocorticoids, GC) as it grows, along with other adrenal, gonadal and thyroid hormones. The hormones are deposited in a linear fashion such that a single plate of baleen allows retrospective assessment and evaluation of long-term trends in the whales' physiological condition. In whale calves, a single piece of baleen contains hormones deposited across the lifespan of the animal, with the tip of the baleen representing prenatally grown baleen. This suggests that baleen recovered from stranded carcasses of whale calves could be used to examine lifetime patterns of stress physiology. Here we report lifetime profiles of cortisol and corticosterone in baleen of a North Atlantic right whale ('NARW'-Eubalaena glacialis) calf that died from a vessel strike, as well as four southern right whale ('SRW'-Eubalaena australis) calves that were found dead with varying severity of chronic wounding from Kelp Gull (Larus dominicanus) attacks. In all five calves, prenatally grown baleen exhibited a distinctive profile of elevated glucocorticoids that declined shortly before birth, similar to GC profiles reported from baleen of pregnant females. After birth, GC profiles in calf baleen corresponded with the degree of wounding. The NARW calf and two SRW calves with no or few gull wounds had relatively low and constant GC content throughout life, while two SRW calves with high numbers of gull wounds had pronounced elevations in baleen GC content in postnatal baleen followed by a precipitous decline shortly before death, a profile suggestive of prolonged chronic stress. Baleen samples may present a promising and valuable tool for defining the baseline physiology of whale calves and may prove useful for addressing conservation-relevant questions such as distinguishing acute from chronic stress and, potentially, determining cause of death.
Highlights
Understanding the impacts of natural and anthropogenic disturbances on the behaviour and physiology of wildlife is critical to predicting resiliencies and vulnerabilities to environmental change
We report lifetime profiles of cortisol and corticosterone in baleen of a North Atlantic right whale (‘NARW’—Eubalaena glacialis) calf that died from a vessel strike, as well as four southern right whale (‘SRW’—Eubalaena australis) calves that were found dead with varying severity of chronic wounding from Kelp Gull (Larus dominicanus) attacks
The NARW calf and two SRW calves with no or few gull wounds had relatively low and constant GC content throughout life, while two SRW calves with high numbers of gull wounds had pronounced elevations in baleen GC content in postnatal baleen followed by a precipitous decline shortly before death, a profile suggestive of prolonged chronic stress
Summary
Understanding the impacts of natural and anthropogenic disturbances on the behaviour and physiology of wildlife is critical to predicting resiliencies and vulnerabilities to environmental change. The habits, body size and longevity of large whales present numerous logistical complications that have severely challenged collection of data needed to elucidate basic natural history parameters as well as impacts of natural and anthropogenic disturbances on their population (Meyer-Gutbord and Greene, 2017). Little is known of the responses of individual whales to environmental change, including potential impacts of natural or anthropogenic stressors on health, mortality risk and future reproduction. A large body of literature exists linking glucocorticoid measures to acute and chronic stress in both terrestrial and marine wildlife (Haukenes and Buck, 2006; Fridinger et al, 2007; Brewer et al, 2008a, b; Williams et al, 2008; Hunt et al, 2013; Romero and Wingfield, 2016). Little information exists on patterns of glucocorticoids with repeated or chronic stress in mysticete whales, largely because whales are remarkably difficult to access and study
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