UNDERSTANDING LONG DISTANCE MIGRATION PATTERNS, TROPHIC DYNAMICS, AND HABITAT USES OF MOLIDS IN THE WESTERN PACIFIC OCEAN

Abstract

Members of the family of Molidae have a circumglobal distribution from tropical to temperate regions and they can undergo long-distance migration in the western Pacific Ocean. Molids plays a unique ecological role as predators of gelatinous zooplankton in the food web. Due to their slow growth rate and high bycatch, it is important to know Molidae trophic ecology across regions, which allows development of effective management strategies and policies. The overarching goal of this research is to explore the migration patterns, habitat use and feeding ecology of molids using electronic tagging, stomach content analysis (SCA) and stable carbon and nitrogen isotopic data (SIA) in the western Pacific Ocean. First, the tagging data revealed that molids made norward movements from Taiwan to Japan, and southward movements from Taiwan to the southern hemisphere. The N–S migrants demonstrate different habitat utilization patterns. Instead of using prevailing currents, the northward movements of molid cohorts exhibit extensive use of mesoscale eddies. Southward movement patterns are associated with major currents and thermal stratification of the water column. Second, isotope data suggested that some large molids found in Japan and Taiwan might have migrated from the warm pool region and one molid from New Caledonia might have migrated from Taiwan, consistent with satellite tagging data. Coupled with the captured timing of these large migrants and the spawning period of molids in Taiwan and Japan, it is suggested that the migration of the molids from the warm pool is likely related to spawning behavior. Third, a comprehensive diet description, breadth and overlap of each species in the Family Molidae were examined by literature review, SIA, and SCA. The literature review revealed that molids are predators of gelatinous plankton but exhibit broader diets than previously characterized as predators of gelatinous plankton almost exclusively. Ocean sunfish, bumphead sunfish, and hoodwinker sunfish reportedly consume prey from epi/mesopelagic environments, while sharptail sunfish and slender sunfish consume prey from both epi/mesopelagic environments and benthic habitats. Off Taiwan, ocean sunfish and bumphead sunfish had similar and relatively narrow diet breadths, differing from sharptail sunfish, which exhibited a broader diet. Unlike other moildes that typically feed on scyphozoans, sharptail sunfish primarily consumed tunicates. The diet of sharptail sunfish changed significantly with size and seasons. This study provides new insights into the movement and feeding ecology of molids in the western Pacific Ocean.