A puffadder shyshark with a rocksucker in its mouth, upside down.
In close-up.
Another view.
Swimming with the large rocksucker in its mouth.
In detail
Two rocksuckers which are not lunch.
All photos Guido Zsilavecz
During a dive at Castle Rocks (at about lunch time) some commotion between two shysharks (Haploblepharus edwardsii)- one was chasing the other - alerted us that someting interesting was going on. We noticed that the shark being chased had something in its mouth, so as to have a closer look we caught it - and discovered it was holding a rather large rocksucker (Chorisochismus dentex)! Rocksuckers, as the last image shows, have a wide head with a tapering, narrow tail. The tail fitted perfectly in the shark, but how it was going to swallow the rest is beyond us - not only is the head wide, but a spike on each of the gill covers would surely prevent it from being swallowed.
Rocksuckers, as their common name implies, suck themselves onto rocks using modified pelvic fins. They eat limpets which they manage to pry off the rocks by slipping their sharp lower teeth under the shell and performing a somersault to get enough leverage required to overcome the shell's hold.
How the shark (a male, as can be seen from the large claspers) managed to pry the rocksucker of its rock is not known, let alone why it managed to get it off upside down! The incident must have happened only just before we saw it, with the second shyshark probably hoping for a shared meal, but neither had any in the end, as somehow the rocksucker managed to escape and swim away, seemingly quite unharmed by the experience.
For more information on rocksuckers and shysharks, see "Coastal Fishes of the Cape Peninsula and False Bay", available directly from SURG and better Cape Town dive stores.
Coastal Fishes of the Cape Peninsula and False Bay, Guido Zsilavecz, 2005.