On the Age and Growth of Meso-Bathypelagic Fishes, with Case Studies of Omosudis lowii, Stomias affinis and Lampanyctus lineatus from the Gulf of Mexico

Mesopelagic fishes provide important ecosystem services, such as carbon sequestration via the biological pump and provision of food for economically important (billfishes and tuna) and federally protected (cetaceans and seabirds) species. These attributes are becoming increasingly recognized, while simultaneously mesopelagic fisheries are becoming of interest as coastal fisheries have become overexploited. Additionally, climate change, ocean acidification, and seabed mining threaten deep-sea fishes. With increasing interest in deep-sea fisheries and anthropogenic threats, age and growth information on these fishes is a necessity for management. With increasing threats, age and growth information on deep-pelagic fishes is needed for management. A limitation for deep-pelagic research, conservation, and management is that very few age estimations of fishes have been validated. Additionally, the majority of age and growth studies have been performed on the family Myctophidae (lanternfishes) due to their presumed importance in food chains via vertical migration; most other taxa remain relatively uninvestigated. In order to address these information gaps, age estimations and otolith shape and microincrement descriptions linked to life histories will be presented for the meso/bathypelagic fish species Omosudis lowii, Stomias affinis, and Lampanyctus lineatus These fishes were collected during seven research cruises from 2010 – 2011, as part of the NOAA supported Offshore Nekton Sampling and Analysis Program, and during six research cruises from 2015 – 2018, as part of the GOMRI-supported Deep Pelagic Nekton Dynamics of the Gulf of Mexico (DEEPEND). We found that the dragonfish Stomias affinis grows exponentially, with a slow initial growth followed by a rapid increase in growth with time. The hammerjaw Omosudis lowii and the deep-living lanternfish Lampanyctus lineatus grow isometrically, which is the normal growth pattern for most fishes. These are the first growth curves produced of these species for the Gulf of Mexico, which serves as an analog for the world’s low-latitude, oligotrophic domain.