Thursday, September 12, 2013

A busy day with bull sharks in the Everglades with Phil Matich

We had another great day in the field on Saturday.  Dolphins, alligators, roseate spoonbills, and other birds added to the experience of catching six more sharks!  We caught one shark on each of the first three longlines - 1 two-year old which we implanted a transmitter into to track its movements, and 2 one-year-olds, one of which was a shark we caught in August.  The marks from collecting tissue samples were already incredibly well-healed! (see the picture below). 
On the fourth set we had a lot more activity - while deploying the longline I felt a tug on the line after putting out ~15 hooks and then an immediate splash at the surface.  When we investigated what had caused the splashed we found a small neonate that was born a within the last few months  and we processed it before continuing to set the line.  Immediately after we resumed setting the line, another little bull shark took the bait from the first hook in the water, so we processed her and then resumed setting the line.  The sharks allowed us to finish before any more bites, but when we pulled in the line another shark of the same size was on a hook.  Each of the three sharks had recently closed umbilical scars (see picture) telling us that they were born sometime during the summer and are probably still developing their foraging (hunting) skills - it can take sharks time to learn how to catch prey, and a free - or seemingly free - meal is  easier than catching a fish.  We put transmitters in each of the three newborns so we can track their movements to see what areas of the estuary newborn sharks are using compared to older individuals, and to investigate any individual variability in the movements of sharks as they grow . 
Hopefully our luck continues to be good when we go out again in 2 weeks - I’ll let you know.
A flat calm day!

Umbilical scar on a young shark.


No comments:

Post a Comment