Sources : Sea-fox

Pliny the Elder [1st century CE] (Natural History, Book 9, 67): Sea-foxes [vulpes marinae] on the other hand in a similar emergency [being caught with a hook] gulp down more of the line till they reach its weak part where they may easily gnaw it off. - [Rackham translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.88): The sea-fox [vulpes marine], as Pliny says, when it has swallowed the hook and is in danger, is drawn up to the weak part of the line, and easily bites through it. These fish signify some of the faithful in the Church who, when they see themselves enticed to some delight of pleasure by the enemy's cunning, at once reject the perceived danger in the offered sweetness, and gnaw it away with a biting knowledge. - [Badke translation/paraphrase]