Evaluating cetacean body condition; a review of traditional approaches and new developments

Abstract

The ability to accurately gauge the body condition of free‐swimming cetaceans is invaluable in population and conservation biology, due to the direct implications that this measure has on individual fitness, survival, and reproductive success. Furthermore, monitoring temporal change in body condition offers insight into foraging success over time, and therefore the health of the supporting ecosystem, as well as a species’ resilience. These parameters are particularly relevant in the context of widespread and accelerated, climate‐induced habitat change. There are, however, significant logistical challenges involved with research and monitoring of large cetaceans, which often preclude direct measure of body condition of live individuals. Consequently, a wide variety of indirect approaches, or proxies, for estimating energetic stores have been proposed over past decades. To date, no single, standardized, approach has been shown to serve as a robust estimation of body condition across species, age categories, and in both live and dead individuals. Nonetheless, it is clear that streamlining and advancing body condition measures would carry significant benefits for diverse areas of cetacean research and management. Here, we review traditional approaches and new applications for the evaluation of cetacean energetic reserves. Specific attention is given to the criteria of measure performance (sensitivity and accuracy), level of invasiveness, cost and effort required for implementation, as well as versatility e.g. applicability across different species, age groups, as well as living versus deceased animals. Measures have been benchmarked against these criteria in an effort to identify key candidates for further development, and key research priorities in the field.

Assessing the effects of lipid extraction and lipid correction on stable isotope values (δ13C and δ15N) of blubber and skin from southern hemisphere humpback whales

“…7,35,36 Glycogen is a source of carbon, which could increase the C:N ratio 15,35 and therefore result in an overestimated lipid content using the aforementioned calculations. Although empirically measured lipid data do not match the modelled values, it cannot be confidently determined whether this is a limitation of lipid extraction protocols that have been outlined extensively in recent literature 37 or whether it is a model overestimate. This uncertainty means that the true lipid content could lie somewhere between 4% and 14%, and therefore, it is reasonable that chemical lipid extraction has some impact on δ 13 C values.…”

Rapid weight loss in free ranging pygmy killer whales (Feresa attenuata) and the implications for anthropogenic disturbance of odontocetes

“…In this study, anthropogenic disturbance leading to the observed foraging disruption was not documented and it is unknown in this case what led to the prolonged stranding event. The ability to detect small changes in body condition has been demonstrated using various techniques 26 and the ability to detect them over a short period of time, as presented here, can be applied to determine the potential impacts of other human-caused interactions. These could include commercial fisheries, chemical pollution, military sonar, and vessel traffic that bring odontocetes into direct conflict with humans and can lead to reduced fitness, disturbance, and disruptions in foraging efficiency 9 , 32 , 32 , 51 , 53 .…”

“…Given the difficulty of quantifying feeding requirements and the energetic needs for free-ranging odontocetes, most studies have largely relied on extrapolations 7 with appropriate data for model validation lacking for many species 23 . The use of UASs to estimate morphometric characteristics is well established 24 , 25 and has been used to quantify body conditions 26 for a variety of marine mammals 27 – 29 . The initial application of UAS technology largely focused on photogrammetry of baleen whales 27 , but it is currently being used for a variety of research applications and species 30 , including odontocetes 22 .…”

Uso de veículos aéreos não tripulados (VANT’s) para monitoramento de condição corporal de pequenos cetáceos sul americanos

“…Medidas indiretas permitem estimar a condição corporal quando não é possível pesar os animais (BOYD;BOWEN;IVERSON, 2010). Medidas como a circunferências ao longo do corpo, proporção da circunferência ou larguras pelo comprimento do corpo, circunferência e largura cranial, são as principais abordagens indiretas utilizadas para inferir condição corporal em mamíferos marinhos, em especial por permitirem estimar o peso dos animais a partir de relações morfométricas (BURNETT et al, 2019;CASTRILLON;BENGTSON NASH, 2020;LEMOS et al, 2013;LOCKYER, 2007;MILLER et al, 2012).…”

“…Nos últimos anos, técnicas de fotogrametria aérea baseadas em imagens de drones tem sido uma abordagem amplamente adotada no monitoramento de condição corporal em diversas espécies de mamíferos marinhos (CHRISTIANSEN et al, 2016;FEARNBACH et al, 2018;ALLAN et al, 2019;BURNETT et al, 2019;NOREN et al, 2019). A popularização dos drones deve-se principalmente pela facilidade em controlar o equipamento, por ser uma abordagem não invasiva, bem como pelo custo reduzido do equipamento, mostrando-se mais acessível que o monitoramento aéreo tripulado (ANGLISS et al, 2018;FERGUSON et al, 2018;CASTRILLON;BENGTSON NASH, 2020). Inúmeros modelos estão disponíveis no mercado, que variam quanto a autonomia de voo, tamanho, peso do equipamento, qualidade de câmeras e sensores, entre outros parâmetros, que devem ser selecionados de acordo com a necessidade da pesquisa (COLEFAX; BUTCHER; KELAHER, 2018).…”