Life History of Large Gadiformes Over Slope Depths (to 1300 m) in the Western Mediterranean: Relationship With Environmental Factors

ABSTRACT This study examines the distribution, reproductive biology, and trophic strategies of three deep‐sea gadiform species ( Phycis blennoides , Trachyrincus scabrus , and Mora moro ) in the Balearic Basin (western Mediterranean). All three showed a depth‐related size trend, but with distinct spatial distributions and life cycles. P. blennoides and T. scabrus were mainly found along the mainland slope, whereas M. moro was more abundant on the insular slope of the Balearic Islands. These patterns were linked to species‐specific trophic strategies and reproductive traits. Adults of P. blennoides and T. scabrus (benthic feeders) were mostly found below 1000 m, associated with higher organic matter and dissolved oxygen, whereas M. moro (a benthopelagic feeder) was related to higher dissolved oxygen and fluorescence (a proxy for chlorophyll a ). Juveniles of P. blennoides and M. moro were associated with high dissolved oxygen and turbidity, respectively. All three species showed ontogenetic migration, with juveniles in shallower waters (< 600 m) and larger, reproductive individuals at deeper depths (> 800 m). Reproductive hotspots for P. blennoides and T. scabrus were located on the mainland slope near submarine canyons (> 900 m), where elevated dissolved oxygen levels may enhance fertilization and egg survival. Although trawling does not reach these depths, rising deep‐water temperature and salinity—possibly due to climate change—may affect the distribution and success of spawners. These findings emphasize the key role of environmental conditions in structuring deep‐sea fish populations and the need for further research into anthropogenic impacts on deep marine ecosystems.