Western Australia's Department of Fisheries is cracking down on crayfish theft in the lead-up to Christmas.

Four boats have already been seized this season and offenders face massive fines.

North Metropolitan Compliance Manager Todd A'Vard said interest in crayfish was peaking.

"The catches have really picked up in the last week or so and obviously the activity in terms of people participating has really gone through the roof," he said.

"Typical of every boat ramp in the metropolitan area, everyone's trying to get out and get a feed of rock lobster for Christmas."

But some were doing the wrong thing.

Since the end of October, four boats have been seized after their owners allegedly interfered with lobster pots and seven people have been apprehended.

Crayfish catches have increased in the past week and boat harbours like Hillarys have been busy. ( ABC News: David Weber )

Mr A'Vard said three seizures have occurred south of Perth, while the fourth and most recent had happened at Ocean Reef.

"We've taken a very hard line this season, we're seizing boats where people are interfering with other peoples' fishing gear."

"The maximum fine for interfering with fishing gear is $25,000 and actually up to one year imprisonment, so the courts take it very seriously as well."

Theft of equipment and tampering seemed to be rife with cray fishermen speak of having pots stolen or moved every season.

Mr A'Vard said that while it was a challenge to police the state's waters, there had been a commitment to target crayfish theft.

"Operation Bagana that we've got going at the moment is sort of targeting between Dawesville and Kalbarri we've got probably around about 50 fisheries officers that are focused on that operation across that area.

"Whilst it's a big area, we're putting a lot of resources into it.

"We're getting some good results, we're getting some good information from the public to assist us through our Fishwatch number."

There is also an effort to target those who are taking more than the allowable eight per person and a maximum of 24 per boat.

"Bags and size limits, we're certainly focused on that as well, there's a tendency for people at this time of year when their craypots come up full of lobster they think that well, you know, 'we'll try and find a way of getting a few more into shore than we're allowed to'.

This boat was seized in 2014 and is now used at various ramps along the coast to set an example. ( ABC News: David Weber )

"Penalties up to $5,000 plus there's an additional penalty which is $250 a lobster which is quite severe."

The department has warned that some of those who have been apprehended for tampering or theft had unknowingly been monitored for some time.

While social media is awash with stories about crayfish thefts, officials must formally receive information in order to act.

"Hopefully the message will get out there, there's plenty of lobster out there if you just fish your own rock lobster pots," Mr A'Vard said.