ISSN 1063-0740, Russian Journal of Marine Biology, 2009, Vol. 35, No. 3, pp. 250–254. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.S. Sokolovskii, T.G. Sokolovskaya, 2009, published in Biologiya Morya.
The signiﬁcance of ichthyoplankton studies in the
entire complex of ichthyofauna monitoring is espe-
cially obvious in the areas where the studies have been
conducted during a long time span. In the Sea of Japan,
the Peter the Great Bay has been an area of regular ich-
thyoplankton surveys since 1949 [1–3, 5, 7–9].
The eastern part of the Peter the Great Bay, with its
inner second-order bays, such as Strelok, Vostok, and
Nakhodka, is of great interest regarding monitoring stud-
ies. At these sites, scientists from the Paciﬁc Research
Fisheries Center and the Institute of Oceanology of the
USSR Academy of Sciences carried out joint ichthy-
oplankton surveys in June–July 1951 and 1952 . The
survey season was chosen to coincide with the time of
mass spawning of commercial ﬂatﬁsh species in near-
shore shallow waters, which occurs in the spring–sum-
mer period [4, 6]. The ﬂatﬁsh egg-counting technique
allows the estimation of the reproductive efﬁciency of
these species in various parts of the bay.
Since 2003, annual complex ichthyologic works,
including ichthyoplankton sampling, have been con-
ducted in Vostok Bay and the adjacent areas . The
area of studies was greatly widened in June–July 2007.
In order to provide the long-term monitoring of the
state of ichthyofauna, we tried to repeat the ichthy-
oplankton surveys of the 1950s and compare the latest
results with half a century old data to obtain a more reli-
able evaluation of the signiﬁcance of this area for ﬂat-
MATERIAL AND METHODS
In June and July of 2007, two ichthyoplankton sur-
veys were performed on the RV
The network of stations, catching techniques and gear
were mostly the same as those in the 1951–1952 sur-
veys. (Fig. 1).
Ichthyoplankton samples were taken with a special
egg net (IKS-80) designed for collecting ﬁsh eggs and lar-
vae. Horizontal or surface catches were made with a half
submerged net at the vessel’s lowest speed, 3.0 knots.
Catches were conducted in the daytime; each event lasted
for 10 min. At some stations with abundant free-ﬂoating
sargassum or other macrophytes, the duration of the
catches was cut to 2–5 min to avoid damage to the ichthy-
oplankton net. The results of catches like those were sub-
sequently evaluated in 10-min catches.
Ichthyoplankton samples were conveyed to the Ich-
thyology Laboratory at A.V. Zhirmunskii Institute of
Marine Biology of the FEB RAS, and analyzed by
means of Olympus SZX9 and MBS-10 binocular
microscopes according to the methods used earlier
. Identiﬁcation of the eggs of ﬂatﬁsh and other ﬁsh
species was based on the works by Pertseva–Ostrou-
mova [8, 9]. The diameter of each egg, yolk and oil
globule (if present) was measured through the eyepiece
micrometer of the MBS-10 microscope. Small ﬁsh lar-
vae were measured to 0.1 mm with the eyepiece
micrometer, and larger ones, with a millimeter ruler.
To deﬁne the taxonomy of ﬁsh larvae, we used ref-
erence samples of the collection of larval and juvenile
ﬁshes from the northwestern Paciﬁc (up to 200 spe-
Distribution of Ichthyoplankton in the Eastern Peter
the Great Bay, Sea of Japan, in June and July of 2007
A. S. Sokolovskii and T. G. Sokolovskaya
Institute of Marine Biology, Far East Department of Russian Academy of Sciences, Vladivostok, 690041 Russia
Received November 20, 2008
—Comparison of the results of ichthyoplankton surveys conducted at 97 stations in the eastern part of
the Peter the Great Bay of the Sea of Japan, in June–July 2007 with the similar research data of the 1950s shows
that at present, as was the case 50 years ago, ﬂatﬁsh eggs belonging mainly to the yellowﬁn sole
and brown sole
prevail in the local ichthyoplankton (up to 86%). The highest
concentrations of these species’ eggs were recorded in the Vostok Bay and Strelok Bay. The spawning activity
of ﬂatﬁsh in 2007 is found to be lower than in the mid 1900s, but the signiﬁcance of the eastern part of the Peter
the Great Bay for ﬂatﬁsh reproduction remains large. The importance of long-term monitoring in this area,
which is being subjected to steadily growing anthropogenic impacts, is also proven.
ichthyoplankton surveys, spatial distribution, eggs, ﬁsh larvae, concentration, monitoring, ﬂatﬁsh