Free-ranging bottlenose dolphin calves may consume milk as either a sole or combined energy source for the first several years of life. Our project aimed to determine the nutritional value of milk received by known-age bottlenose dolphin calves in Sarasota Bay including the percentage of fat, protein, water, sugar and caloric content. We were also interested in the relationship between milk and calf survivorship, age, size and body condition of both mothers and calves. Additionally, our group began research to determine when Sarasota Bay’s dolphin calves are able to obtain nutritional resources (prey fish) for themselves. This objective was met through the first time application of a novel dietary biomarker technique to establish if any given dolphin has recently fed on solid food.
Our study results were obtained by the proximate analysis of forty-six milk samples that were collected between 1988 and 2006 during the temporary capture and release of 30 individually identified bottlenose dolphin mothers from Sarasota Bay. There was no significant relationship between calf survivorship and milk composition. However, calf mass increased significantly with the percentage of milk fat and varied inversely with milk water and potassium content. We have also analyzed serum samples obtained during temporary capture and release efforts from a number of known age mother and calf pairs in Sarasota Bay. These samples have been analyzed to determine the amount of dietary biomarkers which provide insight into recent feed history of the individual dolphins. A significant relationship was apparent between the ranking of biomarker concentrations in the paired mothers and calves. This suggests that paired mothers and calves do not forage separately, but instead if the mother is eating a large meal, the calf is likely to be simultaneously ingesting a substantial amount of food. It is likely that dolphin calves learn about foraging grounds and prey capture techniques from their mothers while continuing to suckle. Additionally, the concentration of dietary biomarker and age were significantly related in the Sarasota dolphin calves. It is likely that this reflects an increasing amount of solid food intake in growing calves. Our wild dolphin calves were aged between almost 2 years of age and 5 years, a period of rapid growth probably fueled by increased food intake.
Further investigations into dolphin calf nutrition are needed, but our research indicates that it is vital that sufficient prey is available for lactating mothers. This is important to ensure high fat milk can be provided to dolphin calves and that resources are available for simultaneous foraging of mothers and their calves.
This research was supported by the Harbor Branch Oceanographic Institution’s Protect Wild Dolphins program, and samples were collected through Dolphin Quest’s support of capture-release operations for health assessment.