Patterns of cortisol and corticosterone concentrations in humpback whale (Megaptera novaeangliae) baleen are associated with different causes of death

Abstract

Baleen whales are subject to a myriad of natural and anthropogenic stressors, but understanding how these stressors affect physiology is difficult. Measurement of adrenal glucocorticoid (GC) hormones involved in the vertebrate stress response (cortisol and corticosterone) in baleen could help fill this data gap. Baleen analysis is a powerful tool, allowing for a retrospective re-creation of multiple years of GC hormone concentrations at approximately a monthly resolution. We hypothesized that whales that died from acute causes (e.g. ship strike) would have lower levels of baleen GCs than whales that died from extended illness or injury (e.g. long-term entanglement in fishing gear). To test this hypothesis, we extracted hormones from baleen plates of four humpback whales (Megaptera novaeangliae) with well-documented deaths including multiple and chronic entanglements (n = 1, female), ship strike (n = 2, male and female) and chronic illness with nutritional stress (n = 1, male). Over ~3 years of baleen growth and during multiple entanglements, the entangled whale had average corticosterone levels of 80–187% higher than the other three whales but cortisol levels were similar to two of the other three whales. The nutritionally stressed and chronically ill whale showed a slow increase in both cortisol and corticosterone spanning ~3 years, followed by a sharp decline in both hormones before death, possibly indicative of adrenal failure in this moribund individual. This whale’s correlation between cortisol and corticosterone was significant but there were no correlations in the other three whales. Our results show that cortisol and corticosterone concentrations vary according to the type and duration of illness or injury. Single-point GC concentrations should be interpreted with caution as low values can occur in whales experiencing pronounced stress and individual baselines can be highly variable. Baleen analysis is a promising tissue type for retrospective analyses of physiological responses to various stressors affecting baleen whales.

Whales in the carbon cycle: can recovery remove carbon dioxide?

“…abundance [19] and body size [20], modern populations continue to face threats from fisheries entanglement [21], climate-change-induced shifts in prey distribution and abundance [22], noise pollution [23], ship strikes [24], marine debris [25], and, in some areas, continued commercial whaling [26].…”

Whale Baleen To Monitor Per- and Polyfluoroalkyl Substances (PFAS) in Marine Environments

“…Furthermore, the necropsy report indicated that the cause of death was probable blunt trauma from a vessel strike. An acute cause of death (e.g., vessel strike) reduces the possibility of other factors (e.g., chronic stress, starvation, or a change in habitat use following injury or entanglement in fishing gear) causing long-term changes in body chemistry that can be reflected on a baleen plate. ,, …”

“…As the baleen grows from the gum tissue (i.e., the Zwischensubstanz), it continually erodes on the lingual side, creating a dense fringe mat, which acts as the filter. As the plates grow dorsoventrally, at an average of ∼20 cm/year (range of 12–32 cm/year), the chemical signature acquired when the baleen first emerged is preserved, as in human hair. − This makes baleen a useful tissue for investigating key physiological and phenological variables over time, including individual movements and diet patterns via stable isotopes, − hormonal changes related to breeding and feeding, − and variation in exposure to trace metal pollution . However, only a limited time window for analysis is available (the most recent 3–13 years) as the plate eventually erodes distally and is replaced by new keratinous tissue.…”

(Almost) all the humpback whales of the North Pacific: A collaborative and comprehensive photo-ID dataset

“…For research collaborators, this has inspired studies that would not have been possible without the large collective investment in building a platform and populating it with a comprehensive and contemporary dataset 48,49 . To date the NPPID collaboration has contributed data to seven other peer reviewed papers 17,26,27,[50][51][52][53] . Accessible information about North Paci c humpback whale individuals has also proven very useful for resource managers, for example tracking shing gear entanglement cases and individual identi cation and past sighting histories of dead or stranded whales 54 .…”