Assessment of nutritional condition indices across reproductive states in the striped dolphin (Stenella coeruleoalba)

The aim of this study was to identify reliable and accurate nutritional condition indices in small cetaceans. Samples from 115 stranded striped dolphins along the eastern coast of Spain (Western Mediterranean) were collected during two die-off events (1990–1991 and 2007–2008), including animals of different reproductive states and varying nutritional conditions.We segmented the data according to sex and reproductive condition, because energetic demands vary considerably among these collectives, and they were considered a good sample to represent groups with different nutritional conditions.We compared five variables as indices to measure nutritional condition. They were: a) blubber lipid content, b) blubber trunk lipid mass (BTLM), c) muscle/blubber trunk mass ratio, d) maximum girth, and e) blubber thickness.Since the dolphins differed in size, each variable was regressed against standard body length, and the residuals of these regressions were used as indices of nutritional condition. Only the mean residuals of BTLM (p < 0.001) and blubber lipid content (p = 0.005) varied significantly among reproductive classes. However, the mean residuals of BTLM appeared to be the most sensitive index of nutritional condition, because it discriminated better among reproductive states.

Research highlights
► The index Blubber Trunk Lipid Mass (BTLM) most accurately reflects nutritional condition in striped dolphin.
► BTLM varied significantly among female reproductive states, confirming the central role of lipid reserves in the reproduction.
► No protein was mobilized for energy supply during periods of high energy demand, such as pregnancy of lactation.
► Blubber thickness or maximum girth failed to accurately reflect nutritional condition in the striped dolphin.