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Swimming Muscle Physiology of Thresher Sharks

The Functional Significance of Divergent Locomotor Designs in Pelagic Fish (National Science Foundation IOB-0617384)

Collaborative Researchers: Diego Bernal, Ph.D. (University of Massachusetts)
Jeanine Donley, Ph.D (Mira Costa College)
Douglas Syme, Ph.D. (University of Calgary, Canada)

This project  compared several aspects of locomotor muscle function and design within a single family of large pelagic sharks, the thresher sharks (Alopiidae). Within the thresher family there are three different species (common thresher, bigeye thresher and pelagic thresher) that all possess an extremely elongate upper caudal lobe, which is as long as their entire body.

Superficially, all three thresher species appear to be very similar, however, recent studies have shown that the internal anatomy of the common thresher is surprisingly distinct from the pelagic and bigeye threshers (Sepulveda et al. 2005).

In the common thresher, the red muscle (sometimes referred to as the blood-line) is condensed in to a solid, piston-like muscle mass that is predominantly distributed over the anterior body in a medial position (i.e. near the vertebral column). Anatomically, this layout is strikingly similar to that of tunas and lamnid sharks, two groups known for specialized swimming muscle physiology. Common threshers also differ from the other two species in having a blood supply to the RM through a set of lateral vessels that give rise to a countercurrent heat exchange system. This heat exchange system allows for RM temperature elevation, just as it does in tunas and lamnid sharks (Bernal et al., 2005).

Figure.  Whole-body reconstructions of the three thresher shark species, showing the very different positions of the red, aerobic locomotor muscle (RM).



The threshers are the only group known to posses both regionally endothermic and ectothermic taxa, and represent the ideal system for testing hypotheses on the evolution of divergent locomotor mechanisms.  



This study examined the swimming biomechanics and twitch kinetics of this group and compared these data to other high performnce species (i.e., mako sharks). 

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The Pfleger Institute of Environmental Research, PIER, is a non-profit 501(c)(3) organization based in Oceanside, California.