Significant changes in pelagic fish stocks of Clupeonella spp. in the south Caspian Sea

 The present study was carried out
during 2006-2007 along the southern Caspian Sea. The species composition showed that the common kilka, Clupeonella cultriventris caspia, is
dominant species with 89% and then anchovy, C. engrauliformis, has shown only 8.7% while it was already dominant
species in the past decades. The overall results indicated that common kilka was
replaced with anchovy kilka as previous dominant kilka species due to invasion
of Mnemiopsis leidyi to the southern Caspian Sea. Anchovy suffered greatly from M. leidyi so
that the total catch dropped from 95000 mt in 1999 to less than 20000 mt in 2007. In our survey, 1415 fish
specimens were collected randomly, including 221 anchovy, 281 bigeye and 913
common kilka. The mean length of anchovy was 117.8 ± 0.27 mm, while it was
about 93.0 mm during 1995 to 1998 before the invasion of M. leidyi. Analysis
of age classes indicated the mean age of 4.5 ± 0.04 years for anchovy, 3.6 ±
0.03 for common kilka and 4.6 ± 0.08 for big eye C. grimmi. According to the age and the length structure of the specimens in this
study, it could be concluded that in recent years, young fish population of
anchovy has been decreased in comparison with the last decade. The results
showed that some biological characteristics of kilka population were affected
by M. leidyi. Recently
fishing activities take place in shallow waters where schools of kilka are in
suitable density for fishing. According to our results,
ctenophore occupied the anchovy habitat where it was mainly more than 50 m
depth. The fishing has moved to areas with depths less
than 50 meters where it was the main reason to change in species composition.