They are surveying, looking for something, completely uninterested in marine life. We are as of yet unable to determine what they're searching for, but it cannot be anything good. They were left behind when the first anomalies retired to space, we managed to capture one and dismantle it, nothing too noteworthy on the insides, however, they do seem to be operated by a small organic brain like matter, whether this is naturally or synthetically created, we just don't know.