The "humane destruction" of seals following encounters with salmon farm divers in Tasmania has been described as "way out of proportion" by a vet, with deterrents like shotgun "beanbags" and underwater explosives blasted by animal welfare advocates.

Key points: Only two workers have filed seal injury reports since 2013

Only two workers have filed seal injury reports since 2013 Seal deterrent use out of proportion with injuries, advocates say

Seal deterrent use out of proportion with injuries, advocates say Vet calls for independent investigation

The ABC can reveal only two Tasmanian fish farm workers have filed reports about being injured by seals in the past five years, despite industry claims they are a threat, with critics calling for a review of the methods used to ward off the hungry animals.

Seals vs salmon farmers in numbers Permits "to deter" approved since 2013 — 2,539

Permits "to deter" approved since 2013 — 2,539 Uses of beanbag shotgun shells to deter in 2017 — 1,000

Uses of beanbag shotgun shells to deter in 2017 — 1,000 Uses of underwater explosives to deter in 2017 — 28,748

Uses of underwater explosives to deter in 2017 — 28,748 Diver encounters with seals resulting in "humane destruction" of animal — 8

Diver encounters with seals resulting in "humane destruction" of animal — 8 Reports of diver encounters ending in seal destruction publicly released — 2 Source: DPIPWE (documents obtained under RTI legislation)

Documents obtained under right to information legislation show eight applications have been lodged with the Department of Primary Industries, Parks, Water and Environment (DPIPWE) to remove seals "by humane destruction" since 2013.

One incident report reveals a diver suffered a "nip" from a juvenile seal, with the animal later destroyed.

Another report details how a diver injured himself while evading an "aggressive lunge" from a seal at Tassal's North West Bay lease in southern Tasmania, with that seal also destroyed.

In the period between November 1, 2017, and June 26, 2018, the department approved a number of "permit to deter" applications from salmon producers — Tassal lodged 331, Huon Aquaculture 151 and Petuna filed 22 applications.

Since 2013, none of the 2,539 applications for "permits to deter" were rejected.

Hungry seals are a problem for Tasmanian salmon farmers. ( Department of Environment )

The number of times "direct injury to a person happened due to a seal" is recorded since 2013 is four. The offending seal was "destroyed" in two of these cases.

While four injuries were recorded, only two of these resulted in "incident reports" made by divers, both of whom were working for Tassal at the time.

Dr Barrie Wells, a retired vet with specialist knowledge of seal biology, said he would "love to see an independent investigation into this issue".

"The industry's response to these injuries of their workers is way out of proportion," he said.

First-timers on the job with 'stubborn' seal

One report describes an interaction involving four Tassal divers who were "returning from lunch" to find two seals inside an enclosure, with other seals lurking outside the pen, on June 4 this year at Tassal's North West Bay lease.

Despite eight interactions between divers and seals since 2013 ending in the death of the animal, only two reports were lodged. ( Huon Aquaculture )

"We dropped a few crackers on the outside of the pen to keep the other seals out, then a few inside the pen," one of the workers wrote, adding it was "my first time as a dive supervisor".

"After about 10 minutes the first seal exited the pen but the second one was being stubborn and didn't show any signs of wanting to get out. The seals on the outside were getting more game and coming closer to the gap."

The Tassal supervisor wrote that after 45 minutes, the decision was made for two divers to enter the water to check the enclosure's nets for holes and complete a "collection of morts" — gathering dead fish from the bottom of the pen.

"I heard [redacted] go 'ooh' followed by [redacted] saying 'have you just got bitten?' " the supervisor wrote, adding that once it was confirmed, he "immediately aborted the dive and instructed both to exit the pen".

With the victim out of the water, the wetsuit was removed and "that's when we saw the puncture wound on his arm".

Salmon farmers are moving towards pens that can withstand attacks from seals. ( Supplied: Tassal )

"[Redacted] was in a little bit of shock, giving short sharp answers to any questions I asked him," the supervisor wrote.

The culprit was a "small seal of about 100 kilograms" which had not "displayed any aggressive behaviour before the dive", the report noted.

The first-time dive supervisor also recorded that it was the other diver's "first time performing this task with us" but that the other worker had "done this several times beforehand".

'No aggressive behaviour' on display

The non-lethal ammunition is used by police and law enforcement agencies. ( Supplied: Security Devices Inc )

The account from the diver who was bitten records he was "working my way around the netting when I felt something go past and next thing I know, the seal had bitten me on my right arm. Similar to a dog bite, it let go straight away and swam off".

The diver, whose identity was not released, wrote that "prior to the dive, I was comfortable and not nervous about diving the pen with a seal inside", also noting: "The seal was not displaying any aggressive behaviour prior to the dive to make anyone concerned".

Another incident report records an interaction at Tassal's Dover lease, in southern Tasmania, on 8 August, 2016.

"I was performing seal pen maintenance … when a seal took a lunge at me," the worker wrote.

"I shot one seal scare dart at it with no effect. Before I could reload, the seal took another aggressive lunge at me, coming out of the water.

"I quickly moved out of the way before it could bite me, straining my shoulder."

Programs to relocate seals caused an outcry from fishers. ( Supplied: Tassal )

Earlier this month, the ABC reported 8,795 shotgun-fired beanbag rounds and more than 130,000 underwater explosives were used as part of a seal deterrent regime by the industry, endorsed by DPIPWE.

"This is really disproportionate, it's an astonishing number of uses of these highly dangerous deterrents," said Malcolm Caulfield, founder and principal lawyer of the Animal Welfare Community Legal Centre in Tasmania.

The deterrents have up until recently been used alongside a program of relocating seals, a practice which the Tasmanian Government ceased after an outcry by fishers who said the newly-arrived seals were causing havoc in their new surrounds.

The ABC's application for more information regarding seal interactions is being opposed by a third party whose identity is being withheld, but is not one of the three major salmon-producing companies.

Huon has said it was investing $90 million in seal-proof "fortress" pens, while Tassal has said it was investing $70 million.

Both companies said seal deterrents were key to ensuring duty of care for staff.