Abstract

Rough-toothed dolphins (Steno bredanensis) are a common mass stranding species in Florida. These large stranding events typically include a small number of sick or injured individuals and a much larger number of healthy individuals. Mortality in a stranding situation is a function of physical trauma, preexisting health status, and overall dispersal of individuals in the stranding event.¹ There is a clear need to be able to identify healthy individuals during triage to improve the outcomes associated with mass strandings. Applying length-to-weight comparisons as an objective assessment of health is becoming common practice with cetaceans.² The lack of standardized morphometric ranges is a significant limitation on the clinical care and rehabilitation of rough-toothed dolphins.

The objectives of this study were to analyze body mass index (BMI) and other morphometric measurements to determine their usefulness during triage, identify a suitable body condition level for release from rehabilitation, and to potentiate increased post-release success. We compared morphology and BMI in two rough-toothed dolphin mass stranding events in Florida: August 2004 (n=36) and March 2005 (n=32). Body mass index was calculated using methods published in 2017 comparing morphometric equations for body mass index in small cetaceans.³

The two groups were significantly different in morphologic measurements, with age- and sex-adjusted intake BMI significantly different (p<0.01) between groups. Only two parameters in the 2005 population proved to be connected to survival: a smaller intake length (p=0.038) and a smaller intake weight (p=0.03), indicating that younger, smaller animals had the greatest chances of enduring the initial stranding event as well as succeeding in rehabilitation. Ten animals from 2005 had weights tracked throughout the rehabilitation process. When comparing initial BMI by stranding outcome, individuals that were rehabilitated and released had a significantly higher (p<0.01) BMI than individuals who were euthanized; however, there was no difference between dolphins that died of natural causes (p=0.56) and animals successfully rehabilitated. According to data from the two stranding events, consequential rehabilitation, and post-release satellite monitoring, individuals found to be clinically stable and in good body condition were successfully rehabilitated with a BMI >0.50 (2004) and >0.53 (2005).

Acknowledgements

The authors would like to thank the many stranding network member participants, volunteers, and staff for their many contributions in the rescue, rehabilitation, and examination of the animals. The examination or treatment of animals was authorized through Scientific Research and Enhancement NMFS Permits. All work conducted for the 2004 stranding event occurred under the NOAA MMPA Permit 925‐1489‐05. All work conducted for the 2005 stranding event occurred under the NOAA MMPA Permit 932-1489-08.

Literature Cited

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2.  Perrin WF, Dolar MLL, Chan CM, Chivers SJ. 2005. Length-weight relationships in the spinner dolphin (Stenella longirostris). Mar Mamm Sci 21(4):765–778.

3.  Kershaw JL, Sherrill M, Davidson NJ, Brownlow A, Hall AJ. 2017. Evaluating morphometric and metabolic markers of body condition in a small cetacean, the harbor porpoise (Phocoena phocoena). Ecol Evol 7:3494–3506.