Heithaus Lab Blog: Moorea Reef Sharks Day 4

October 23, 2103

Today was underwater construction day! We started out with a snorkel in an area near the shark feeding site. After about half an hour we had the right spot picked out. We didn’t want to be right at the shark feeding site, but a ways off. That way we wouldn’t see the effects of a lot of fish being attracted to bait and have to worry about the effects of the divers. Instead we wanted to be far enough away to avoid those effects but still have higher shark abundances than more “normal” parts of the reef.

We donned our SCUBA gear and descended with three stakes, a really heavy mallet, and a bag full of the camera housings that we will be attaching to the stakes tomorrow. It was a good thing we did that test – one of the housings leaked! But its nothing a bit of silicon can’t fix! It took us about a half hour to put the three stakes –spaced several hundred yards apart - in at about 50’ depth. During the dive it was obvious that we were at a good distance for the work. We saw at least three blacktip reef sharks – a couple of them individuals that Johann recognized from his previous work. He could tell based on their fin markings. We also saw three female sickle fin lemon sharks. They are quite a bit bigger than the blacktips and were cruising slowly along the reef slope. One of them had fresh mating scars.

The reefs here on the northern coastline of Moorea aren’t what you might expect for a remote island in the tropical Pacific. Instead of tons of living coral everywhere, on the forereef much of the coral is dead. A combination of a crown-of-thorns starfish outbreak – which resulted in a lot of coral being eaten – and then a cyclone in 2010 really impacted the reef. But, everywhere you could see new corals growing as the reef begins to recover. And, although the coral wasn’t what it will be once it recovers the fish life was really amazing. We saw what must have been dozens of species in our short dive.

We had to make a quick trip back to CRIOBE to switch tanks and to grab our shark-cam that we want to deploy soon. This is our advanced camera that should get 60 hours or more of video so we need to make sure that it floats and test how far the VHF signal will go. Of course, we also managed to squeeze in a nice pasta lunch that Jeremy made…hey, we needed the time between dives!

The second dive was to a site far from shark feeding, but the same depth, basic reef characteristics, and distance from the lagoon pass as the shark site. It was another amazing dive with well over 100’ visibility (I can’t tell you how much over because I am used to less than 10’)! We got the three poles in fast and had time for a bit of a tour around the area. We saw plenty of fish but no sharks in a similar dive time to this morning. I can’t wait to get the data from these two sites!

Since we had a little time left in the afternoon we tested the advanced shark cam – plenty of range on the transmitter and it floats perfectly! It will be ready to go tomorrow if we have any luck. However, we might try our less advanced (and, well less expensive) shark cam tomorrow to see how it goes. I am excited about a final modification we made to it so it should get great images and data with no disturbance to the shark!

Jeremy doing hammering a stake into a small sand patch in the reef. The bag floating above Johann has the housings for the cameras we will put on the stakes starting tomorrow!