Sharvit praised the lifeguard, David Shalom, for handing the rare relic over to authorities, rather than pocketing it as many others have been suspected of doing.
"This was an act of good citizenry," he told the AP.
Shalom said he was snorkeling when he caught a glimpse of the disc and dived to get it.
"It captured my curiosity, so I asked someone what it was," he said. "I didn't think it was something so important, but I'm very happy that it is."
The port city of Yavne-Yam was first settled in the Middle Bronze Age and was inhabited until the Middle Ages. The modern city of Yavne is currently located nearby.
Archaeological surveys in the region since the 1980s have turned up other maritime artifacts, such as anchors, weights, fishing equipment, ovens for cooking, storage jars, bowls and cooking pots that date to the Late Bronze Age, Persian, Hellenistic, Roman and Byzantine periods.
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