Bodies of the slaughtered seals, including some newborn pups, were found late last week at the colony north of Kaikoura.
DOC spokeswoman Trish Grant told NZPA no new deaths had been discovered since yesterday but staff would be checking the seals carefully, particularly the pups who may have lost their mothers in the attack.
"We will keep an eye on them and it will be concerning if some look poorly. They can only be fed by their own mothers, I believe."
Ms Grant said the department was working its way through calls about the attacks and "bits and pieces of information" from the public but more help was needed.
"It could be something they saw happening at the colony or people talking about being involved in what has happened. People have also been calling up expressing concern and horror so it is good to see such public support."
DOC South Marlborough area manager Dave Hayes said it appeared the "callous and cowardly" attacks had been carried out by a person of some strength with a bat or similar club-like object.
They would likely have been spattered with seal blood during the attacks, he said.
Ohau Point is a popular tourist spot for viewing fur seals and is visited by thousands of people each year.
Matt Chambers, the manager of the 23-year-old tourism venture Seal Swim Kaikoura, told NZPA the massacre was the sort of incident that could lead to the point being blocked off to the public.
"If somebody is stupid enough to do this they are going to be stupid enough to open their mouths."
A person can be jailed for up to six months or fined up to $250,000 for killing or harming fur seals or other marine mammals.
In July Kaikoura's Hayden John Ingram, 17, was fined $500 and sentenced to 200 hours' community work for shooting a seal with a paintball gun, bashing it with a metal bar and running over a seal pup, killing both.
In 2005 current All Black Andrew Hore was one of three men each fined $3500 for shooting at seals on the Otago coast and killing one.
The lobby group People for the Ethical Treatment of Animals is offering up to $2500 for information leading to the arrest and conviction of those responsible.
DOC has reported the attack to police.
