Dive Meeting Report: Gary Goss's Research on Sharks 9/903 at PBCRRT

Professor Gary Goss spoke at the PBCRRT meeting last Tuesday night. He gave a great perspective on sharks over his 30+ years living in Florida.

He spoke about working on a long lining boats and catching sharks and discarding them as by catch. Private boats fished for sharks, took pictures with these huge monsters and then threw the fish away. People thought they were doing good by getting rid of these creatures that could bite you.

As fish stock dwindle, sharks are commercially viable for their skin, oil, meat, and fins. Overfishing is causing decline in populations. Unlike bony fish that release 1000s of eggs per spawn, sharks only live birth a couple of pups per cycle. There numbers will take a lot longer to recover.

15ft sawfish sharks were a common site off Florida. Now they are extremely rare and almost extinct. I just got an email some have been spotted of Jupiter.

How sharks hunt according to Gary Goss:

**Note these are general guidelines. Sharks use a combination of their senses at different ranges in hunting.**

1000 yards away
Sharks have HUGE ears inside their head and they pick up low frequency vibration from fish. Everyone is familiar with the Goliath Grouper's "boom" but Snappers and Grunts were named after the sounds they made when caught out of the water. Most fish make sound from their swim bladder, we just can't hear it. Spearing a fish and not killing it is like ringing a giant gong, "Dinner is served" you just can't hear it!

100 yards away
Sharks rely on smell to pick up blood in the water of hurt fish OR they can smell the slimy fish coating. Schools of fish leave a huge smell trail. Sharks swim in an S pattern to lock in on the smell

100 ft away
Sharks have good eye site and can determine size and shape. Most shark attacks are in Volusia county because there are a lot of swimmers and surfers in turbid water where sharks can't see and have to use their other senses.

10 ft away
Sharks can feel water pressure through their lateral line. Just like other fish, tiny hairs detect changes in the water pressure and alert the fish to danger and lead the shark to prey.

1 ft away
Sharks pick up on electrical fields with their Ampullae of Lorenzini which are all up in their nose. They can pick up the irregular heartbeat of a dying fish. Often sharks "bump" their prey before biting and scientists think this bump is for a close up electrical look at its prey.

- 6 inches
Sharks bite and can "taste" their prey. Scientist believe the Great White can taste the difference between a fatty seal and human meat. They are also not used to the thick arm and leg bones when they take a bite. Most shark "attacks" are actually "bites" and the shark leaves you alone once it figures out you are not on the menu or listed on the marine version of the Atkins diet. Depending on the shark, the "bite" can be fatal.

Categories for Bites and Attacks

1. Resemble Prey (Black wetsuit and fins swimming with seals)
2. Blood in the water (Spearfishing or boating accidents)
3. Turbid Water (swimming among schools of fish in no visibility

That's the highlights I got out of my notes.

--Matt