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Possible Future Studies or Areas of Exploration

As I read through articles related to diving mechanisms in seals and sea lions I realized that most research has been done on free-diving true seals (the phocids), whereas less was truly known about fur seals and sea lions (the otariids).  However, although most assume their diving techniques to be similar, the “relatively large differences in oxygen stores between the two orders suggest they are likely to use different physiological strategies (Kooyman & Ponganis 1998).  More specifically, approximately 30-35% of oxygen is stored in the muscle in both orders, but only 5% of oxygen is stored in the lung of phocids compared to the 60-65% in the blood (Kooyman 1985).  Further, current studies suggest that a much larger portion (19%) of oxygen is stored in the lungs of otariids compared with 47% in the blood, and these seals dive with inflated lungs (Hooker 2005).  Due to these differences in biological makeup and perhaps different diving mechanisms, I think that future studies should take this in to account when looking at the diving mechanisms of seals.  Although the phocids have been our model species up to this point, it is time to start looking at the affects of deep-sea diving in others. 

Another study needs to continue looking at the causes of why seal invariably expel air during the ascent phase of dives, particularly when such a behavior is energetically costly!  It has been shown that Humpback whales emit bubbles during dive ascents to concentrate prey swarms, but no prey have been observed in association with seal bubbles (Hooker 2005).  Future studies will need to determine if these bubbles really are physiologically related and if so, why.

Also, I wanted to mention a study I read about that involved observing the locomotor gaits of different marine mammals.  Because despite independent evolution of swimming in cetaceans and pinnipeds, and differences in body size and propulsive mechanisms, the study done by Williams in 2000 found that Weddell seals, elephant seals, bottlenose dolphins, and the blue whale, all shared similar sequences in locomotor gaits during diving.

 

This figure shows the locomotor activity of the four marine mammals Williams observed during a deep dive.  The grey part of the line corresponds to when the animal was stroking and the blue part of the line represents when the animal was gliding.  Notice that each animal has extended glides on the decent.  (Figure adapted from Williams 2000.)

Looking closer at this figure, observe that almost each animal begins to dive at the same depth.  Interestingly enough although each animal observed varies so much from the other, some adaptations for successful prolonged diving can be shared.  This study makes me wonder who other features among marine mammals are similar and/or different.

Finally, some other factors that these experiments need to take into account are volitional, appetitive, emotional, arousal, and circadian drives (Stephenson 2005).  It would be interesting to see how these additional factors play a part in either regulating, determining, or affecting the ability to deep-sea dive.

 

Photo provided by Corel with permission

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This website was created as a part of a class project in the
Animal Physiology Class at Davidson College.

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