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Just as for epipelagic fish (those that live in the first 100 m of depth, see Figure above), deep-sea species must successfully spawn, grow and return to the area of the adult habitat. The extreme conditions of the deep-sea are reflected in the variety of reproductive strategies that exist. Low population sizes notwithstanding, hermaphroditism, extreme sexual dimorphism and unbalanced sex ratios occur. Sebastes spp, certain ophidioids, as well as deep-sea sharks can be live bearers and the pseudotriakid, Pseudotrakis microdon, is oviphagous. Despite the fewer number of species in the deep-seas, those that occur display a variety of reproductive methods ranging from strongly K-selected species, which may be semelparous (e.g. Coryphaenoides armatus, a widely occurring macrourid) through ovoviviparous and oviparous species, to those that are strongly r-selected. And, in the perpetual darkness of the abyss, many species depend on photophores and sound production for intra-species recognition required for successful reproduction. Many deep-sea species grow slowly, so slowly in fact that determination of their actual age remains difficult and contentious. For some species, particularly orange roughy (Hoplostethus atlanticus), no convincing case has yet emerged for any particular ageing technique based on interpretation of otolith microstructure. Depending on the assumptions made, this species may have longevity ranging from 21 to more than one hundred years. Because of these biological characteristics, most deep-sea species are very fragile with reduced resilience to intensive fishing.

 

The grenadier (Coryphaenoides armatus) has a wide distribution. Along with the species C. yaquinaen, it has an estimated global biomass of 15 million tonnes
The grenadier (Coryphaenoides armatus) has a wide distribution. Along with the species C. yaquinaen, it has an estimated global biomass of 15 million tonnes
FAO/Fisheries & Aquaculture Department

Distribution maps of deep-sea species extracted from the Compilation of Aquatic Species Distribution Maps of Interest to Fisheries

 
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