Calculating total body length from rostrum-anus length in amputated bycaught dolphins

摘要

Total body length (TBL) is perhaps the cardinal dimension employed in descriptions to characterize cetaceans. It conveys a sense of body size, substitutes as an estimate of body mass (Trites and Pauly 1998), and provides an estimate of approximate age for individuals (Turner et al. 2006). Variance in TBL (e.g., based upon sex) can inform us of differences in reproductive strategy between the sexes (Ralls and Mesnick 2002). Variation of TBL within a species can reflect oceanographic or local differences between populations, as has been observed in Risso's dolphin (Grampus griseus) (Ross 1984, Amano and Miyazaki 2004), pantropical spotted dolphin (Stenella attenuata) (Perrin 2001), striped dolphin (Stenella coeruleoalba) (Di-Méglio et al. 1996), and Franciscana dolphin (Pontoporia blainvillei) (Barreto and Rosas 2006). Differences in TBL can also characterize a particular subgroup and help discriminate sympatric ecotypes, for example, fish-eating versus mammal-eating forms of killer whales (Orcinus orca) in Antarctica (Pitman et al. 2007). Thus, TBL is a simple and obvious attribute to help profile a local population, and therefore provide data useful for environmental management and conservation plans.