A man has been slapped with a $5,000 fine, banned from boarding certain boats and had his diving gear confiscated after he was found to be in possession of over 100 abalone, many of which were well under the legal size for fishing.

The Victorian Fisheries Authority (VFA) revealed this week that the Melbourne man, aged in his 50s, illegally took 113 abalone from Port Phillip back in March -- 108 of which were under the legal minimum size of 10cm. Abalone can sell for over $100 a kilo at fish markets.

Taking undersized abalone can have serious environmental consequences, and undermine efforts to sustain healthy populations, the VFA warned.

"The smallest measured less than 8cm, and the man admitted to the officers that he intended to sell them," the agency stated.

Excessive abalone collection and its illegal sale on the black market threaten the sustainability of wild populations, undermine legitimate commercial fishers, and compromise food safety standards for consumers, the VFA added.

Last week, the man was found guilty of five separate charges, including trafficking a commercial quantity of abalone. "Victoria's abalone fishery is the state's most valuable commercial fishery, and the species is highly regarded by recreational divers," the VFA said.

The magistrate issued a prohibition order preventing the man from possessing abalone or any commercial fishing equipment within 1 km of Victoria's marine or estuarine waters.

He was also banned from being on a boat under 20 metres in length with abalone fishing equipment and prohibited from abalone fishing for life, unless a court decides otherwise.

It comes just weeks after the VFA alleged three Melbourne men were found in possession of 467 crabs, more than five times the daily limit. In photos of the haul, multiple buckets and even a backpack were filled with live crabs.

"Red shore crabs play an important role in the intertidal environment, helping to cycle nutrients by consuming decaying organic matter, and serving as food for predators like fish and birds," the department said.

Officers seized all the crabs and returned them to the water alive. The men will be charged on summons and could face fines of up to $4,000 each.

Earlier this year, another angler copped a $2,000 fine after authorities discovered he was allegedly using live carp as fishing bait, a serious breach of the law. He was also found to have deployed illegal set-lines.

The VFA encourages the public to call 13FISH (133474) if they see or suspect illegal fishing.

Aussie fisherman gets lifetime ban and $5,000 fine after illegal haul seized