Where did all the monkeys go?

A few months ago, I posted a blog about my kayak trip down the Silver River near Ocala. Then I told you about the monkeys and alligators. Well Monday we took another trip up the river, but there wasn't a single monkey to be found. As much as I was scared of them the first time, I was a little disappointed that they weren't there.
As it was, myself, Rudy, John and Ashlee paddled up river again into Silver Springs and floated back down to the boat ramp. The whole trip took us 6 1/2 hours. The paddle up river was kind of tiring because it seemed to me that the current was a little bit swifter than the last time.
The trip back was amazing. We didn't see another soul on the river. At one point it started to rain and we could hear thunder in the near distance. We all started paddling like crazy, not wanting to get stuck in a thunderstorm, but after about 5 minutes the rain passed, we all stopped paddling and just were. It was amazing. The silence was deafening. All you could hear was a gurgle of water and the wild life.
We floated like that for a while and then started paddling again, because it was getting late. There is one point on the river were it is really easy to stop and park your kayak and get out and swim for a bit. After all the crazy paddling we did it was nice to take a dip in the cool water.
The Silver River is crystal clear and very narrow, but there aren't alot of places that you can get out and swim.
The trip starts out in the Silver River State Park and then about 3/4 of the way to Silver Springs attraction you enter the Silver River refuge. They have very strict rules about no swimming or getting out onto the banks or anything. Not even when you get up into the attraction at the main spring. It is pretty cool though because there you are kayaking and he glass bottom boats are floating past you with all these tourists taking your picture and taking videos of you. I waved to one guy who was more interested in us than what his tour guide was saying.
Unfortunately, I didn't get any pictures this time, but Rudy and Ashlee did and as soon as I get them, I will try to post.
Oh yeah, Amy I wanted to ask you something:
We saw this thing that was labeled 'USGS' for United States Geological Survey and I wondered if you knew what it was for. It was just down river from Silver springs attraction, kind of off in the water, but near the bank. I thought I recalled that you worked with them, so I thought you might know what it was.