Conservation implications of loss of both blubber and muscle mass in cetaceans

Abstract

Marine mammals may lose body mass for many different reasons such as disease and reduced food availability due to overfishing and/or climate change. This loss in body mass may have detrimental effects on the animal’s health and ability to survive. We studied the relative distribution of tissues (body composition) in different species of cetaceans to assess what occurs when an animal losses body mass. We performed mass dissections on multiple individuals with different body conditions from three cetacean species (Stenella coeruloalba, Delphinus delphis, and Mesoplodon densirostris). Our results indicated that animals in poor body condition lost both blubber and muscle mass. The animal with the worst body condition lost half of its blubber and muscle mass. A loss in blubber mass implies a loss in thermal isolation, which results in a higher metabolic rate for thermoregulation. Moreover, the loss in total body mass results in increased massspecific metabolic rate, and the loss of muscle mass reduces the total O2 store resulting in a reduction in the aerobic dive limit (ADL). This together reduces the foraging time. Consequently, an animal with poor body condition will have to spend more energy to obtain the same amount of prey at a higher energetic cost, resulting in greater body mass loss, leading to a snowball effect that can have fatal consequences. Reduction of the ADL might be more critical to deep diving species that unavoidably need longer dives to reach their prey. Loss of body mass may have a greater implication for individual animal survival and marine mammal conservation than previously thought, especially given the reduction of available food resources due to climate change and/or overfishing, and merits further investigations.