Chief Mate Jacques de Requin was a sailor on board the Lankester.
De Requin served under Captain Callany. He discovered a Mermaid called Amphitrite whom he named Amy Ivans and took aboard the ship, hoping to sell her. He also captured her daughter and hid her in a wall compartment. In 1901, Callany was planning his retirement, at which point he told de Requin he would hand over the ship to him. De Requin was poisoning Amy with small doses of mercury.
Jacques arrested the Sixth Doctor on Callany's orders after the murder of Crawford. Later, he freed the Doctor on Callany's orders, and had him and Peri Brown treat Amy Ivans.
While the Doctor was elsewhere, de Requin tried to have Peri drink mercury, to prevent her telling the Doctor of Amy's secret. They fought and Amy's wheelchair was knocked over, revealing her true form.
Amy died and Peri escaped with Galatea. She confronted Jacques, who threatened her into compliance with a gun. He then tried to force Callany into preparing him a lifeboat to escape. Callany refused and told him there was none. He then fired at Callany, killing him. He began to laugh insanely and descended into madness.
He was taken by Nereus and his people, who said he would use him as freakshow as he had intended to use his daughter and granddaughter while he is pulled under by his people. (AUDIO: Cryptobiosis)