After being in the water hundreds of times with thousands of silvertips, I had a unique experience during my last trip to Papua New Guinea. I was diving southeast of Milne Bay in the Louisiade Archipelago. This was highly exploratory diving (i.e. no regular dive boat goes to these islands). We had amazing shark dives for the 3 weeks we were there. On one dive, we were diving one of the outer reefs - a very sheer wall. My friend Elizabeth was first down the wall at about 70 feet. I was about 20 feet above her. I looked down and approaching Elizabeth coming up from deeper water was a very large silvertip. I saw it at the same time she did. She turned to give me the shark signal. As she turned, another 3 equally large silvertips also appeared from the deep. I signalled back to her, "no, you look behind you at the sharks, there are now 4." Now my experience with silvertips are that they come up from deep water, check you out, perhaps stay with you for a little while, but then head back into deep water (the exception being in Kavieng at a place where they have regularly fed the silvertips, but that's another story). Well, these 4, then 5 large silvertips stayed with us. Another bunch of smaller silvertips as well as a slew of grey reef sharks also joined the large silvertips.
We proceeded at around 100 feet along the wall. The silvertips kept circling out in front of us. We headed back up a little shallower. The sharks followed. We went up to 40 feet. The sharks followed, circling even closer. Ever few minutes one of the larger sharks would head in straight for one of us. If you faced it and stood your ground, the shark would veer off. However, the distance at which they would veer off was getting shorter and shorter. Eventually, we hit a spot on the wall where instead of being a sheer drop, it was much more sloping. The sharks disappeared. I thought, "wow, that was incredible, but now I can relax and start looking at the critters on the wall." However, the instant the wall again turned sheer, the sharks reappeared, this time charging even closer. Even when we were back up at 20 feet, the sharks stayed with us. I felt bumping was imminent. I've never felt threatened by sharks before, but I decided it was time to get out of the water (it was about 45 minutes into the dive -- the sharks had been with us for at least 40 of it). We hung out along a crevice where we had walls on 3 sides doing a safety stop. We got out of the water, being careful to not hang out on the surface for long.