'I’ve seen a lot of stuff out here… but this is the biggest I’ve ever seen, ever,' he told the local NBC affiliate.
Dolphins typically travel in groups of anywhere between 15 and 200 which are called pods.
What Mr Dutra spotted on Thursday however is best described as a super mega pod given the astonishing size of the group.
He estimated that the trail of dolphins was seven miles long and five miles wide, and he was able to steer the boat alongside them for over an hour.
Experts are unable to pinpoint any specific reason as to why so many of the mammals were traveling together on this particular night.
'They’re definitely social animals, they stick together in small groups. But sometimes, the schools come together,' marine expert Sarah Wilkin told NBC.
While it does seem like a once-in-a-lifetime experience, a very similar flock of thousands of dolphins were seen swimming together about this time last year.
At the end of February in 2012, an unspecified group of dolphins was spotted swimming about 65 miles north of San Diego, implying that there may be an unacknowledged migratory pattern.