Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Marine Ecosystems Research Department
species of deep-sea hydromedusa polyps obtained to
date, and gathered data on regeneration, growth and
reproduction of hydromedusa polyps, the budding of
medusa from polyps, and medusa rearing techniques.
As for rearing samples in particular, we had been
rearing samples at the same water temperature of ˚C
as their habitat, but we gradually raised the temperature
for both medusae and polyps to about ˚C,
and this gave us excellent results in polyp reproduction,
and medusa budding and growth. By rearing
medusae until maturity and clarifying their life cycle,
and keeping deep-sea medusae in the laboratory at
any time, we believe we will be able to obtain
detailed data that would otherwise be too difficult to
access in the field.
Our achievements to date have been published in
journals, and presented at domestic and international
symposiums.
Fig.19 Polyp of a deep-sea hydromedusa budding a medusa
(top), and the medusa released from the polyp (bottom).
Research on the spawning characteristics of the
Japanese eel (Anguilla japonica)
Period : FY-FY
This joint research between JAMSTEC and Ocean
Research Institute (ORI), Tokyo University aimed at
clarifying the spawning characteristics and environmental
conditions under spawning, and migration
process of the Japanese eel (Anguilla japonica) to contribute
to marine biology and fisheries.
The seamount hypothesis conjectures that the
spawning field of the Anguilla japonica is in the area
˚E-˚E at about ˚N. However there have been
no reported sightings of A. japonica around the
seamounts in this region, and the hypothesis was merely
conjecture covering a broad sea area. To verify the
seamount hypothesis, we carried out surveys around
the Pathfinder, Arakane and Suruga Seamounts in the
southern edge of the West Mariana Ridge. Survey were
conducted during the new moon period of August -,
in line with the A. japonica new moon hypothesis
(hatching takes place during new moon).
Our observations (KY-) were mainly at night
using the deep tow camera system. We recorded the
location, depth, water temperature and salinity at each
point where anguilliform fishes observed, and analyzed
environmental factors that characterized the distribution
of these fishes.
Eighty-five Anguilliformes individuals observed in
our survey at the three seamounts (Fig.). It was very
difficult to identify species of Anguilliformes, because
the deep-tow camera was not high definition.
The survey was carried out at a depth of -,m,
but focused mainly on the depth range of -m
(.% of the total line of observation). When standardizing
the number of anguilliform fishes for every
m depth, we estimate a distribution of one individual
per kilometer up to a depth of ,m (Fig.). We
also conducted surveys at two seamounts whose peaks
are at depths of and ,m for comparison with
the area around the three seamounts, and found a low
density of the anguilliform fishes. It is suggested that
61