Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries

<em>Abstract.</em>—Grenadiers are the most dominant fish species of the demersal fish community in the waters off northeastern Taiwan. Due to their relative large size and high abundance, they are major predators in the local demersal community. Three congeneric species of grenadiers, <em>Coelorinchus kishinouyei</em>, <em>C. leptorhinus </em>and <em>C. multispinulosus </em>were collected by bottom trawler at depths of 100–600 m in the study area. The diets and depth distributions of these fishes were analyzed to investigate: 1) whether resource partitioning exists among these three congeneric grenadier species by water depths or feeding habits; and 2) whether ontogenetic shifts in diet or distribution depth exist for grenadiers with different developmental stages. Results showed that <em>C. multispinulosus </em>mainly occupied depths of 100–200 m, <em>C. kishinouyei </em>200–400 m and <em>C. leptorhinus </em>400–600 m. Two grenadier species pairs coexisted at some depths, <em>C. kishinouyei </em>and <em>C. multispinulosus </em>at 200 m, and <em>C. kishinouyei </em>and <em>C. leptorhinus </em>at 400 m. Diet analyses of these pairs reveal apparent resource partitioning resulting from interspecies competitions. When species coexistence occurred, the numerically dominant species would retain its preferred diet while the less abundant species made adjustments on its food habits. The distribution of body size for <em>C. leptorhinus </em>suggested separation into two size groups. The smaller size-group (4–9 cm PAL) was feeding mainly copepoda and polychaeta while the larger size-group (10–15 cm PAL) on shrimp and polychaeta, suggesting an ontogenetic diet shift. The previously described “bigger-deeper” phenomenon was not supported because of inconsistent patterns observed between body size and distributional depths of the three grenadier species studied.