Meeting Abstract
We compared the internal force-generating structures of tunas and other pelagic predatory fish, identifying key biomechanical adaptations that characterize thunniform swimming. In particular, we describe the role of the bony peduncular keel unique to tunas as a guide for the great lateral tendon (GLT), increasing mechanical advantage of the associated muscle myomeres and improving efficiency of the tail stroke. In tunas, centralized red muscle enables endothermy and powers cruising. Without the keel, this muscle would have a poor angle with low mechanical advantage to move the tail. Mechanical advantage is related to the angle of the force applied – the closer to perpendicular, the greater the torque produced by an equal force. For this case study, we developed a novel dissection approach to measure the GLT incidence angle in 3 skipjack tuna (Katsuwonus pelamis), 4 yellowfin tuna (Thunnus albacares), and 4 bluefin tuna (Thunnus thynnus). In the skipjack, this angle increased with curved fork length (13 to 19 deg). This may indicate that as a skipjack grows, swimming efficiency becomes more valuable than speed. At a similar length, skipjack had a smaller angle than yellowfin and bluefin, which may imply yellowfin and bluefin are more tuned for speed than skipjack. Yellowfin and bluefin maintained a fairly constant angle (around 14 deg) for fork lengths of 70 to 180 cm. These internal structures that power the caudal fin and peduncle in tunas can be connected to the motion observed in in situ video from a camera tag, or from overhead in a flume. By understanding how tunas actuate their main propulsive foil, we can look to future applications in bio-informed robotics by identifying key features that drive thunniform locomotion.
