Swimming capabilities of deep-sea sharks through velocity, anatomical, physiological and morphological analyses

Louvain-La-Neuve

December 20, 2019

16 h

Place Croix du Sud 4-5 - Salle Jean-Baptiste Carnoy

The swimming capabilities of shallow-water shark species are nowadays well understood. However, similar information regarding deep-sea sharks is still poorly documented. Deep-sea sharks are believed to be slow and listless swimmers. This conclusion is mainly based on indirect measurements of their metabolism. Indeed, even with technological breakthroughs, it is still very difficult to study these elusive species.

In this context, this thesis was set up as the first multidisciplinary approach regarding the swimming capabilities of deep-sea sharks. It revealed that not all deep-sea sharks swim slowly, some of them, luminous species from Etmopteridae family, even display cruise swimming speed values similar to benthic shallow-water sharks. For these luminous species, higher swimming speed can be an advantage according to the isolume followers’ hypothesis (moving rapidly in the water column to stay at the depth where light equal their luminescence). In contrast, while the Greenland shark (Somniosus microcephalus) was previously described as the slowest shark in the world, our data have shown that the kitefin shark, Dalatias licha, displays an even slower cruising speed and hence becomes the new known slowest shark in the world. The study of metabolism also showed that aerobic metabolism and red muscles proportion can be related to the cruise swimming speed. Furthermore, sharks with a low cruise swimming speed display higher anaerobic metabolism and white muscle proportion which suggests efficient burst capabilities. The buoyancy of several deep-sea sharks was also estimated showing that deep-sea shark are closer to the neutral buoyancy that their shallow-water counterparts. Moreover, the red muscle proportion was inversely correlated with the buoyancy which confirmed, for the first time, the Bone’s hypothesis first mentioned in 1966. Finally, the first PCA morphological studies on Squaliformes sharks were performed revealing some differences in this group which was previously considered to be part of only one morphotype. Thanks to this study the ecology of deep-sea sharks was investigated in greater depth, adding new insights about the adaptations of different deep-sea sharks’ lifestyle.