zombie84 said:

To be honest in all likelihood that was erased by mistake, whether human or computer.

Yeah, I think this quote from "Jaws expert" Jim Beller suggests it was erased by mistake:

"For those who asked if the boat in the background during the quick scene of Brody trying to tie the "little brown eel" rope is still there. No, it's not anymore. The boat was the ferry going (or leaving) Oak Bluffs and was seen in the background in all other past versions of the film. They digitally took it out I guess. Although......
They missed another scene where you see the ferry in the background. That scene is still there, untouched with digital fixing."

A great article on the restoration: http://magazine.creativecow.net/article/restoring-jaws

This is what I was referring to in my earlier post, from that article:

In addition to the bigger challenges of color and brightness shifts, Dunn also dealt with a host of more minor issues. "There were some shots where there is production equipment in part of the shot," he says. "No one would notice, but we did. We got permission first from the production company and then removed it digitally or positioned it out." In one case Dunn recalls, he could see the shadow of a boom mic in the water off the boat. "It's safe to say that people who work in post have seen a lot of these things," he says. "Enough that we tend to catch them. But they tend to be subtle. A glint in the water might be mistaken for dirt, and you have to be careful about that."

I think they did a fantastic job with this restoration, the blu-ray looks excellent IMO, I was a little worried about the color timing being off with all the bad attempts to make old films look more modern, like we often see these days, but it looks perfect. Now if only Star Wars could be treated in the same way.