Despite comprising the largest biome on Earth, the bathypelagic zone inhabitants represent a “black hole” in the understanding of deep-oceanic functioning due to physical and monetary limitations. The characteristics of the global bathypelagic realm create a limiting environment only inhabitable by specially adapted fauna. These include whalefishes (Stephanoberycoidei: Cetomimidae), which are a taxonomically and systematically challenging group of primarily bathypelagic fishes.
Cetomimids were collected in the Gulf of Mexico using high-speed rope trawls and a multiple-opening-and-closing net system. Population dynamics were described using morphometric analysis. Vertical distributions, including diel variation, were described using a modified boxplot of abundance standardized by volume of filtered water. Finally, trophic ecology of male and larval Cetomimus/Gyrinomimus was described through gut-content analysis.
In total, 493 Cetomimidae were collected, including six new records for the region (Cetomimus compunctus, C. picklei, Danacetichthys galathenus, Gyrinomimus bruuni, G. grahami, and male Cetomimus/Gyrinomimus TBD) and one new record for the Atlantic Ocean (C. compunctus). The assemblage is dominated by Cetostoma regani and Ditropichthys storeri and is highly skewed to favor adult females. Cetomimids were collected most often in the upper bathypelagic zone, including the smaller males and larvae. Asynchronous diel vertical migration is likely in C. regani and D. storeri and possible in species of Gyrinomimus. Specimen SL and depth of capture were not correlated. Male Cetomimus/Gyrinomimus primarily consume copepods although opportunistic feeding of larger crustacea including euphausiids and/or mysids is likely. Larvae gorge on copepods (in quantities reaching 1709) and may display a selective feeding strategy targeting swarming copepods
