A major animal welfare organisation has defended its record on protecting seals amid claims that a scheme it backs has failed to stem killings by fish farms.

The RSPCA has always stipulated in its welfare standards for farmed Scottish salmon that the shooting of seals has to be a "last resort".

But campaigners allege seals are still being needlessly shot despite the rise in use of anti-predator nets that should protect salmon stocks from seals.

New Marine Scotland figures show the percentage of fish farms that had made use of anti-predator nets, seen as a way of deterring seals, has risen from 13 per cent in 2011/12 to 79 per cent in 2014/2015.

The percentage of those that made use of seal blinds, to prevent seals seeing fish that they can prey on, has fallen from 29 per cent in 2012/13 to 18 per cent in 2014/15.

It has coincided with a decline in the number of seals killed from 241 on 235 individual fish farms in 2011 to some 80 across 214 farms in 2014.

But the latest figures for 2015 show that salmon farming has been responsible for the shooting of 49 seals in the first half of 2015. That's eight more than the same period the last year.

Meanwhile the RSPCA's welfare standards that need to be complied with to become RSPCA approved state: "The repeated shooting of seals without having deployed all of the measures leading to a last resort scenario, will result in the site being suspended from the scheme pending further investigation."

Producers of farmed salmon are issued with licences which allow seals to be shot to protect fish stocks.

Salmon farmers say they sometimes need to kill seals as a last resort to prevent them attacking nets and eating fish. However, campaigners, argue that better nets and 'seal-scarers' should eliminate the need for killing.

The Global Alliance Against Industrial Aquaculture campaign group said in response to the figures: "The leap in use of anti-predator nets shows how easy (albeit expensive) it is to take steps to avoid shooting and killing seals.

"These figures blow out of the water the industry's claim that seals are shot as a 'last resort'. Even now, one in five salmon farms still don't use anti-predator nets.

"The RSPCA, who certify over 70% of Scottish farmed salmon as 'welfare friendly', must now tighten the net on salmon farms who shoot seals first rather than as a 'last resort'."

The RSPCA insisted it was "equally concerned" about the welfare of all animals whether they be farmed salmon and wild animals such as seals, which may prey upon them.

"The shooting of one seal is still one too many and the RSPCA and its RSPCA Assured scheme are working closely with the Salmon, Aquaculture and Seals Working Group (of which we were founder members) to find further new ways to reduce the use of a lethal method of predator control to zero as soon as practically possible. The group is made up of concerned animal welfarists, salmon farmers, academics specialising in sea mammals and retailers.

"All members of the RSPCA Assured scheme must record and demonstrate that rigorous measures are taken at all times to deter predator attacks on their salmon. These measures must - in accordance with RSPCA standards - focus on physical exclusion, including the proper use of acoustic devices, properly tensioned and weighted nets and the efficient removal of dead and moribund fish from the bottom of the nets.

"However it is a sad reality of salmon farming - as it is with predator attacks on terrestrial livestock farming - that from time to time a determined predator may be able to bypass all efforts to exclude them and attack on the fish. Such attacks can cause serious welfare problems, with potentially hundreds of fish being killed and/or caused great suffering. In these cases, the predator must be dealt with in a humane way by a suitably trained and competent person. This method of control must only be enacted as a last resort.

"RSPCA Assured scheme members must report any incidents of seals being shot to the scheme management within 72 hours.

"If a member of the RSPCA Assured scheme cannot demonstrate that any lethal action was taken only as a last resort, and that all required non-lethal deterrents were in place and fully functional, then the member will automatically be suspended from the scheme."

The Scottish SPCA does not certify salmon farms but its chief superintendent Mike Flynn said: "All non-lethal control measures must be exhausted before any lethal measure is considered.”