Tasmania is in the middle of peak whale-watching season, but at least one species has been notably rare.

Marine biologist Kris Carlyon takes calls on the Department of Environment's whale hotline, but said fewer southern right whales have been reported since migration began last month.

"It's been another relatively quiet year compared to the big year we had in 2012 where we had up to 12 animals socialising off Bruny Island and Frederick Henry Bay, so a quiet year for that species," he told ABC Radio Hobart.

"They are still coming through at the moment and we are particularly keen to hear of any sightings of that species."

Photos help identify individual animals by their unique markings. ( Supplied: James Stone )

Many people are posting images on social media but Dr Carlyon said the hotline — 0427 WHALES (0427 942 537) — was also a valuable tool.

"By all means chuck things up on social media but please remember to call us," he said.

"It contributes really valuable information to long-term monitoring of humpbacks, southern rights and all other cetaceans."

Scientists are seeking more data on behaviour, location, time and colour.

"Number one is what we are looking at. We try to get to the bottom of the species and often that can be tricky. Sometimes they are seen right off in the distance," Dr Carlyon said.

"We're interested in behaviour, we are interested in direction of travel, we are interested in group size, whether there are any calves.

"Quite basic information but it all adds up to tell us a lot over the course of the season.

"Potentially we can predict where those animals might be if we know what time they were seen in the first place and we know what direction they were travelling in and time of day.

"That tells us whether our sightings are being duplicated if we get sightings further down the coast."

Migrating humpbacks have been seen regularly this season. ( Supplied: Patrick Tigges )

The low numbers of southern right whales this season has scientists puzzled.

"Estimates vary from between a couple of hundred to potentially up to five or six hundred," he said.

"They are very difficult to get a handle [on] numbers, they are quite distinct genetically and spatially from other populations.

"So there is actually very limited evidence that this population is increasing much at all.

"We're unsure why that is, there are potentially some issues around just how built-up the environment is in the south-east of Australia and whether that is contributing.

"So we're not sure, we know they're keen to show up and they have big years where they see lots and they have lower years.

"This year for example, South Australia, Argentina, South Africa all had record years and and showed record numbers whereas in the south-east of Australia we're just not seeing that many.

"We're hopeful next year might be another another big year like 2012 but it's hard to predict."