A description and comparison of the four major methods available for studying conservation physiology of large whales, namely analysis of faecal, respiratory vapour, and skin/blubber biopsy samples, and photographs.

Cortisol is one of the main glucocorticoid hormones involved in both the mammalian stress response, and in fat metabolism and energy regulation, making it of increasing interest as a biomarker for stress, health and overall physiological state. However, transient stress responses to animal handling and sampling may be important sources of measurement artefact when investigating circulating concentrations of this hormone in wildlife. Here, cortisol concentrations were measured in the plasma and, for the first time, in the blubber of live captured adult harbour seals (Phoca vitulina). Plasma cortisol concentrations were positively correlated with capture time, suggesting that they were largely driven by a stress response to the capture event. In contrast, blubber cortisol concentrations were shown not to be significantly affected by capture time and varied significantly by sex and by season, with higher concentrations during natural fasting periods of their life cycle, particularly during the moult. These results suggest that cortisol may play a key role in increased fat metabolism during highly energetically demanding periods, and that blubber concentrations have the potential to be used as physiological state indicators in phocid seals.

Climate change has resulted in physical and biological changes in the world's oceans. How the effects of these changes are buffered by top predator populations, and therefore how much plasticity lies at the highest trophic levels, are largely unknown. Here endocrine profiling, longitudinal observations of known individuals over 15 years between 2004 and 2018, and environmental data are combined to examine how the reproductive success of a top marine predator is being affected by ecosystem change. The Gulf of St. Lawrence, Canada, is a major summer feeding ground for humpback whales (Megaptera novaeangliae) in the North Atlantic. Blubber biopsy samples (n = 185) of female humpback whales were used to investigate variation in pregnancy rates through the quantification of progesterone. Annual pregnancy rates showed considerable variability, with no overall change detected over the study. However, a total of 457 photo‐identified adult female sightings records with/without calves were collated, and showed that annual calving rates declined significantly. The probability of observing cow–calf pairs was related to favourable environmental conditions in the previous year; measured by herring spawning stock biomass, Calanus spp. abundance, overall copepod abundance and phytoplankton bloom magnitude. Approximately 39% of identified pregnancies were unsuccessful over the 15 years, and the average annual pregnancy rate was higher than the average annual calving rate at ~37% and ~23% respectively. Together, these data suggest that the declines in reproductive success could be, at least in part, the result of females being unable to accumulate the energy reserves necessary to maintain pregnancy and/or meet the energetic demands of lactation in years of poorer prey availability rather than solely an inability to become pregnant. The decline in calving rates over a period of major environmental variability may suggest that this population has limited resilience to such ecosystem change.

Mammalian body condition is an important individual fitness metric as it affects both survival and reproductive success. The ability to accurately measure condition has key implications for predicting individual and population health, and therefore monitoring the population‐level effects of changing environments. No consensus currently exists on the best measure to quantitatively estimate body condition in many species, including cetaceans. Here, two measures of body condition were investigated in the harbor porpoise (Phocoena phocoena). First, the most informative morphometric body condition index was identified. The mass/length2 ratio was the most appropriate morphometric index of 10 indices tested, explaining 50% of the variation in condition in stranded, male porpoises with different causes of death and across age classes (n = 291). Mass/length2 was then used to evaluate a second measure, blubber cortisol concentration, as a metabolic condition marker. Cortisol is the main glucocorticoid hormone involved in the regulation of lipolysis and overall energy balance in mammals, and concentrations could provide information on physiological state. Blubber cortisol concentrations did not significantly vary around the girth (n = 20), but there was significant vertical stratification through the blubber depth with highest concentrations in the innermost layer. Concentrations in the dorsal, outermost layer were representative of concentrations through the full blubber depth, showed variation by sex and age class, and were negatively correlated with mass/length2. Using this species as a model for live cetaceans from which standard morphometric measurements cannot be taken, but from which blubber biopsy samples are routinely collected, cortisol concentrations in the dorsal, outermost blubber layer could potentially be used as a biomarker of condition in free‐ranging animals.

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The fate and transportation of mercury in the marine environment are driven by combinations of anthropogenic atmospheric and aquatic sources, as well as natural geological inputs.Mercury bioaccumulates and biomagnifies up the food chain and can result in the accumulation of toxic concentrations in organisms even when the concentrations in the marine environment remain below the threshold level for direct toxicity. As a result, mercury exposure has been recognised as a health concern for both humans and top marine predators, including cetaceans.There appears to be no overall trend in the global measured concentrations reported in cetaceans between 1975 -2010, although differences between areas show that the highest concentrations in recent decades have been measured in the tissues of Mediterranean odontocetes. There is increasing concern for the impacts of mercury in the Arctic marine ecosystem with changes in water temperatures, ocean currents and prey availability all predicted to impact the exposure of Arctic species to mercury. The accumulation of mercury in various tissues has been linked to kidney and liver damage as well as other neurotoxic, genotoxic and immunotoxic effects. These effects have been documented through studies on stranded and by-caught individuals as well as in vitro cell culture experiments. Demethylation of methylmercury and protection by selenium have been suggested as possible mercury detoxification mechanisms in cetaceans that can help to explain the very high concentrations measured in tissues of some species with no apparent acute toxicity. Thus, the ratio of selenium to mercury is of importance when aiming to determine the potential toxicity of the contaminant load at an individual level. The long-term population level effects of mercury exposure are unknown, and continued monitoring of odontocete populations in particular is advised in order to predict the uptake and impact of mercury on marine food chains in the future.

Monitoring the body condition of free-ranging marine mammals at different life-history stages is essential to understand their ecology as they must accumulate sufficient energy reserves for survival and reproduction. However, assessing body condition in free-ranging marine mammals is challenging. We cross-validated two independent approaches to estimate the body condition of humpback whales ( Megaptera novaeangliae ) at two feeding grounds in Canada and Norway: animal-borne tags ( n = 59) and aerial photogrammetry ( n = 55). Whales that had a large length-standardized projected area in overhead images (i.e. whales looked fatter) had lower estimated tissue body density (TBD) (greater lipid stores) from tag data. Linking both measurements in a Bayesian hierarchical model to estimate the true underlying (hidden) tissue body density (uTBD), we found uTBD was lower (−3.5 kg m −3 ) in pregnant females compared to adult males and resting females, while in lactating females it was higher (+6.0 kg m −3 ). Whales were more negatively buoyant (+5.0 kg m −3 ) in Norway than Canada during the early feeding season, possibly owing to a longer migration from breeding areas. While uTBD decreased over the feeding season across life-history traits, whale tissues remained negatively buoyant (1035.3 ± 3.8 kg m −3 ) in the late feeding season. This study adds confidence to the effectiveness of these independent methods to estimate the body condition of free-ranging whales.

The separation and identification of proteins from cetacean blubber tissue will help to establish a database of potential health markers in species with limited sampling opportunities, and to assign novel functional roles to blubber in keeping with current understanding of the multi-functional role of adipose tissue in other mammals.