Evaluating morphometric and metabolic markers of body condition in a small cetacean, the harbor porpoise (Phocoena phocoena)

Abstract

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.

Pathology findings and correlation with body condition index in stranded killer whales (Orcinus orca) in the northeastern Pacific and Hawaii from 2004 to 2013

“…be associated with poor body condition [32]. T-tests (normality confirmed by a Shapiro-Wilk test and equal variance confirmed by a Brown-Forsythe test) or Mann-Whitney Rank Sum Tests (when the normality test failed) were used to evaluate differences in body length, blubber thickness measurements, and BCI between killer whales that died from trauma and killer whales that died from infectious or nutritional CODs (combined).…”

Not just fat: investigating the proteome of cetacean blubber tissue

“…Other studies have established the reproductive status of individuals through the measurement of concentrations of reproductive hormones in blubber, specifically progesterone and testosterone ( Kellar et al , 2009 , 2013 ). The concentrations of blubber cortisol have been measured in terms of both an indicator of physiological state and body condition ( Kershaw et al , 2017 ) as well as the stress response ( Kellar et al , 2015 ; Champagne et al , 2017 ). Moving forward, the identification and quantification of different hormones and proteins involved in various metabolic pathways within blubber tissue could lead to the development of potential new protein markers of interest that can be quantified to provide information on a range of physiological processes and life history states.…”

“…Blubber tissue can typically make up anywhere between 15% and 55% of the body mass of cetacean species ( Ryg et al 1993 ; McLellan et al 2002 ). To date, most studies in cetaceans have focused on the physical properties of this tissue ( Ackman et al , 1975 ; McClelland et al , 2012 ), the lipid content ( Aguilar and Borrell, 1990 ; Evans et al , 2003 ; Gómez-Campos et al , 2011 ), variation in fatty acid profiles ( Olsen and Grahl-Nielsen, 2003 ), and the quantification of lipophilic steroid hormones ( Kellar et al , 2009 ; Trego et al , 2013 ; Kershaw et al , 2017 ) and contaminants ( Torres et al , 2015 ; Jepson et al , 2016 ). Adipose tissue in other mammals is known to be highly metabolically active and is increasingly being recognized as an endocrine organ in its own right ( Kershaw and Flier, 2004 ; Gimeno and Klaman, 2005 ).…”

Evaluation of body mass index as a prognostic indicator from two rough‐toothed dolphin (Steno bredanensis) mass strandings in Florida

“…Body mass index was calculated using methods published by Kershaw et al () comparing morphometric equations for body mass index in small cetaceans suggesting that normalizing the data can be achieved using a simple calculation:…”

“…Applying length‐to‐weight comparisons as an objective assessment of health is becoming common practice in cetaceans (Perrin, Dolar, Chan, & Chivers, ), though further research is required to improve precision and species‐specific reference ranges. There is currently no consensus on the best morphometric index with which to calculate body condition, let alone what healthy ranges look like (Kershaw, Sherrill, Davidson, Brownlow, & Hall, ). In a recent study, the length‐to‐girth ratio for stranded common dolphins ( Delphinus delphis ) was found to be significantly different between animals with postrelease success and failure; whereas, the length‐to‐weight ratio was not found to be a good prognostic indicator (Sharp et al, ).…”