"Where once fishermen were lucky to see, let alone catch an octopus, now they are finding up to 300 a time as the creatures invade the creels in search of the same bait that is used to attract lobsters and crabs," Duncan MacInnes of the Western Isles Fisherman's Association told The Observer.

MacInnes said that while the octopus are a commercial catch, they also eat the lobsters, which fetch more at market.

Other species showing up in unusual numbers are squid, Japanese skeleton shrimp, John Dory and red blenny.

"The waters are certainly getting a warmer. Species that would have been typical for the south coast are now moving increasingly northwards," said Dr. Anuschka Miller of the Scottish Association for Marine Science.

MacInnes said some cold-water species could be moving northward from Scotland. He suggested cod may be rare now, not because of over-fishing but because the water is becoming too warm for them.