The snowball effect of loosing body mass: diving and health implications

Abstract

The body condition of an animal is an index that provides information about the individual’s health. An estimation used for body condition determination is the relationship between length and weight. In the current study, we studied the relative distribution of tissues (body composition) in different species of cetaceans to assess what occurs when an animal is in poor body condition, and how this affects body composition. We performed mass dissections in several species (Stenella coeruloalba, Delphinus delphis, and Mesoplodon densirostris) with different body conditions. Our results indicated that animals in poor body condition lost both, blubber and muscle mass. The animal with the worst body condition lost 52% of blubber mass and 49% of muscle mass. As the mass-specific metabolic rate increases with a decrease in body mass, the loss in body mass in the animal with the poorest body condition would have resulted in an increase of mass-specific basal metabolic rate of 61%. With a concurrent reduction in relative muscle mass, and therefore a reduction in oxygen muscle mass storage (49%), this would result in a decrease in the aerobic dive limit of 48%. Consequently, changes in body condition would alter the diving capacity and foraging efficiency with the animal having to spend more energy to obtain the same amount of prey at a higher energetic cost, resulting in greater body mass loss. Our results show that body condition has direct implications for body composition and body compartments. The studied animals presented a poor body condition. More extreme results should be expected for animals in very poor body condition. Further studies should be performed in more species, and in a larger sample size. The implications of body condition in the dive capabilities merits further investigations.