Evaluation of the use of portable ultrasonography to determine pregnancy status and fecundity in bonnethead shark Sphyrna tiburo.

This study examined the usefulness of portable ultrasonography in accurately predicting pregnancy and fecundity in the bonnethead shark Sphyrna tiburo by comparing ultrasound-obtained data with those obtained from animal dissection, the gold standard for elasmobranch reproduction studies. Mature female S. tiburo (n = 66) were collected throughout the period of reproduction and examined via portable ultrasonography using two different ultrasound transducers (8-5 MHz linear array transducer and a 5.0-2.5 MHz curvilinear array transducer) to determine pregnancy status and fecundity. Ultrasound-derived data were compared with validated assessments of pregnancy and litter size obtained using animal dissection to determine the level of agreement between the two approaches. Overall, there was strong agreement (90.9%) between pregnancy determinations obtained using ultrasonography and dissection. However, the effectiveness of portable ultrasonography in accurately determining specific stages of maturity and pregnancy differed slightly between transducer types (linear = 61.3%; curvilinear = 88.9%). Measurements of fecundity also agreed well between ultrasonography and dissection and there were no significant differences between mean fecundity estimates obtained using the two methods. In general, portable ultrasonography was found to be a good alternative to lethal sampling and animal dissection in obtaining reproductive data critical for the management and conservation of elasmobranchs. Special attention should be given to factors that can influence the reliability of ultrasound-derived data such as transducer type, embryo size and sound wave interference due to gut contents.