Reproductive behaviour of the ocean triggerfish Canthidermis sufflamen (Tetraodontiformes: Balistidae) in the shallow waters of the marine-protected area of El Hierro Island (Canary Islands).

The abundance of Canthidermis sufflamen has increased worldwide, including around the Canary Islands, due to global ocean warming. The reproductive behaviour of this species was studied within a marine-protected area (MPA) and its adjacent areas off the island of El Hierro (Canary Islands). This oceanic species starts to move from pelagic habitats to inshore waters at the end of April. Spawning takes place asynchronously from June to September, with peak activity in July-August. Males establish territories and build several benthic nests on sandy bottom for multiple females. Each male covers an area ranging from ~21 to 135 m². The maximum number of territorial males was observed in July-August, whereas the minimum was recorded in May. A polygynous mating system was observed, with a sex ratio skewed towards females during the reproductive period. In each male territory within the MPA, one to five females were observed, whereas only one to three females were recorded outside the MPA. During the spawning season, males exhibit a darker body colouration, indicative of sexual dichromatism. Reproductive activity ends in September, although some males and females remain until October, providing biparental care. Females care for benthic eggs, staying within ~2 m of the nest. By the end of October, all individuals leave inshore waters and return to the ocean pelagic habitats. No specimens are present in coastal waters from November to March. The MPA plays a key role in ensuring successful reproduction of this species, acting as a source of colonisation for the surrounding regions and neighbouring islands.