Trophic ecology of three dominant myctophid species in the northern California Current region

Abstract

The feeding ecology of 3 dominant sympatric myctophid species (Tarletonbeania crenulans, Diaphus theta, and Stenobrachius leucopsarus) in the northern California Current System was investigated based on samples collected in June, August, and September of 2006. All 3 species fed predominantly on Euphausia pacifica, the most abundant euphausiid off the central Oregon coast. In contrast, the same 3 lanternfishes showed marked variation in utilization of other principal food categories, and stronger resource partitioning was evident in smaller individuals. The proportion of euphausiids in the diet of T. crenularis and S. leucopsarus gradually increased with increasing size. D. theta at intermediate sizes (31 to 60 mm) preyed heavily upon salps and hyperiid amphipods, whereas the largest specimens consumed mostly euphausiids. S. leucopsarus showed little changes in composition of principal food categories between months, while T. crenularis and D. theta consumed more hyperiid amphipods in June, euphausiids in August, and salps in September. No feeding on salps was recorded in S. leucopsarus for the entire study period. All 3 species showed variation in feeding intensity, stomach fullness, state of digestion, and number of prey species and prey items per stomach. A divergence in feeding strategies of these co-occurring lanternfishes appears to reflect their structural morphology and generally conforms to an ecological subdivision of this midwater family into 'active' and 'inactive' species. Active myctophids (T. crenularis and D. theta) consumed significantly larger amounts of protein-rich prey such as euphausiids, hyperiid amphipods, and salps, while inactive S. leucopsarus showed higher preference for slower-moving, lipid-rich Neocalanus copepods. © Inter-Research 2008.