ISSN 10630740, Russian Journal of Marine Biology, 2010, Vol. 36, No. 3, pp. 157–166. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.V. Zavolokin, 2010, published in Biologiya Morya.
To date, little information is available on the jelly
fish of the Sea of Okhotsk. The most recent prominent
works dealing with the taxonomy and biogeography of
cnidarians of the Sea of Okhotsk were published about
a century ago [8, 9]. Various aspects of the ecology of
jellyfish, such as distribution, total biomass and abun
dance, nutrition, trophic relationships, etc., have been
Some information on the distribution and abun
dance of jellyfish in the Sea of Okhotsk can be
obtained from trawl surveys, which have been annually
performed during the last several decades by the staff
of the Pacific Fisheries Research Center (TINRO
Center). The trawling gear used in these surveys is pri
marily designed for fish and squid abundance assess
ment; however, it permits an approximate estimation
of the occurrence and abundance of large jellyfish (>
Estimates of jellyfish abundance in the Sea of
Okhotsk based on trawl survey data were first provided
by Shuntov et al. . These authors have shown that
gelatinous zooplankton have a significant biomass and
can obviously play a substantial role in the pelagic
communities. Results of the study of jellyfish species
composition, distribution, and abundance were after
wards supplemented by information on diets and the
trophic status of gelatinous zooplankton [2, 6, 7].
However, the published data are limited to shortterm
The article was translated by the authors.
observation series (1–5 years), usually relating to one
season and only to the epipelagic zone. In the present
paper, we summarize the results of the study of jellyfish
distribution and abundance in the epi and mesope
lagic zones of the Sea of Okhotsk in 1992–2005.
MATERIAL AND METHODS
This work uses trawl survey data on the quantitative
composition of jellyfish in the epipelagic and mesope
lagic zones of the Sea of Okhotsk in 1992–2005. A
total of about 4600 trawlings were performed (Table 1).
The epipelagic zone was studied most completely:
about 80% of the trawl stations were made in the
200 m layer. In the mesopelagic zone, the surveys
were limited to the 500 m depth. The region of study
included the entire northern Sea of Okhotsk, as well as
waters of western Kamchatka and eastern Sakhalin.
For a more correct analysis of the seasonal and inter
annual dynamics of jellyfish, it was divided into four
large areas: eastern Sakhalin, western Kamchatka,
northern Sea of Okhotsk, and Shelikhov Bay (Fig. 1).
Jellyfish were caught using RT80 and RT108
pelagic trawls (vertical opening 30–60 m) with a
smallsize meshed (1 cm) insertion at the cod end.
The abundance (biomass) of jellyfish was determined
by the formula
Distribution and Abundance Dynamics of Jellyfish
in the Sea of Okhotsk
A. V. Zavolokin
Pacific Fisheries Research Center, Vladivostok, 690950 Russia
Received November 19, 2009
—The seasonal and interannual trends in the distribution and abundance of jellyfish (Scyphozoa and
Hydrozoa) in the epipelagic and mesopelagic areas of the Sea of Okhotsk during 1992–2005 were examined
on the basis of trawl survey data. The area of occurrence, biomass, and the numbers of Scyphozoa in the epi
pelagic layer were the smallest in spring; in summer and fall their abundance sharply increased and then
decreased in winter. In contrast to the epipelagic zone, the numbers of scyphomedusae in the mesopelagic
layer were significantly lower in the summer than in the winter and spring. This probably indicates that a part
of scyphomedusae winter in the mesopelagic. Hydrozoa in both the epi and mesopelagic areas were more
numerous in the winter and spring. Jellyfish biomass and abundance greatly changed from year to year. Thus,
in fall the biomass of scyphomedusae and hydromedusae in the epipelagic zone varied from 166 to 1271 and
from 6 to 49 kg/km
Scyphozoa, Hydrozoa, jellyfish, biomass, abundance, distribution, Sea of Okhotsk.