Distribution and diet of Cyclothone microdon (Gonostomatidae) in a submarine canyon

S.E Thompson,T.J Kenchington

doi:10.1017/s0025315416000916

Abstract

The primarily bathypelagic gonostomatid Cyclothone microdon, amongst the most abundant of all vertebrates, remains poorly known. We describe its diet in The Gully, a very large submarine canyon off Nova Scotia, Canada, based on the stomach contents of specimens caught by midwater trawl. In The Gully, C. microdon had a shallower distribution than in open ocean and primarily fed at mesopelagic depths. Most of its diet comprised vertically migrant calanoid copepods, while its secondary prey was conchoeciinid ostracods. Both were typical of the food eaten in other regions by its mesopelagic congeners and were consistent with the results of the only previous dietary study of C. microdon.

Highlights

Following Marshall (1954), Cyclothone (Gonostomatidae, Stomiiformes) is often claimed to be the most abundant of all vertebrate genera
Most of its 13 species have depth ranges centred in the mesopelagic zone, where what little they eat comprises vertically migrant calanoid copepods, with lesser quantities of ostracods, plus trace amounts of other mesozooplankton (De Witt & Cailliett, 1972; Gorelova, 1980; Maynard, 1982; Mauchline & Gordon, 1983; Roe & Badcock, 1984; Gordon et al, 1985; Palma, 1990; Yoon et al, 2007; McClain-Counts, 2010)
Since Cyclothone spp. show little evidence of vertical migration, C. microdon might be expected to sustain itself on the scarce resources available below the depths reached by mesopelagic diel migrants

Summary

INTRODUCTION

Following Marshall (1954), Cyclothone (Gonostomatidae, Stomiiformes) is often claimed to be the most abundant of all vertebrate genera. Only Mauchline & Gordon (1983) have provided substantial information on the diet of that species, which they derived from 68 stomachs containing identifiable prey, taken from specimens caught in the Rockall Trough at unreported depths. Those individuals had consumed similar prey to that of their shallower-dwelling congeners. The canyon supports an endangered population of northern bottlenose whales, Hyperoodon ampullatus (Forster 1770), which feed there at depths of 500–1500 m. To provide a context for the prey data, we first examine the spatio-temporal distribution of Cyclothone spp. in The Gully and outline the sizes, sexes and maturation stages of the specimens

MATERIALS AND METHODS

Laboratory methods

RESULTS

DISCUSSION