Appendix 4 workshop 1

H. Negarestan, S. Hosseini, F. Parafkandeh, and A. Roohi
Iranian Fisheries Research Organization and Department of Environment, I. R. Iran

Abstract

Presence of the comb-jelly, Mnemiopsis leidyi, in the Caspian Sea has certainly resulted in a sharp decline of Kilka stocks. A catch of 85000 tones in 1999 now is hoped to reach 30000 tones. Iranian Fisheries Research Organization is conducting 3 research studies on invasion of the Caspian environment by this ctenophore. Series of laboratory based studies were performed on ways to combat the problem, which will be presented by Drs. Shiganova and Finenco here. Another study is in progress on feeding behavior of this species in the Caspian. Biomass studies are presented in this paper.

A plankton net (Judy net) with a mesh size of 0.5 mm was used to collect samples of Mnemiopsis. Sampling was done in 0-5, 0-10, 1-20, and 0-50 meters (Kideys et al. 2001). Samples were counted in 6 length classes. Using length-weight relationships a formulae of W=al^b was used to estimate biomass.

The present study looked into fluctuations of Mnemiopsis biomass. The presence of this ctenophore increased in summer, and in 20 m as the maximum layer of biomass from 0.6 Kg/m² reached a biomass 2.1 Kg/m² in September 2001 in Amirabad Mazandaran. The biomass in 20 m depth in November has decreased and for Amirabad became 0.8 Kg/m². The maximum biomass layer in November was not 20 m anymore and it was 50 m where a biomass of 1.1 Kg/m² in Amirabad was observed.

Introduction

Presence of the comb jelly, Mnemiopsis leidyi, in the Caspian Sea by ship ballast water exchange has resulted in a sharp decline of Kilka stocks. A cartch of 85000 tones in 1999 in the south Caspian reduced to 65000 tones in 2000 and now it is so much declined that it may reach 30000 tones by the end of Iranian year 1380 (2001-2). Iranian Fisheries Research Organization, Russian Fisheries Research Institute (CaspNirkh) and Azarbalikh were the 3 research institutions which presented research work at First International Workshop on Invasion of Caspian Sea by Mnemiopsis held in Baku, 2001 (Negarestan et al. 2001, Ivanov 2001, Shiganova 2001, and Kasimov 2001). Following this workshop Caspian Sea littoral States with the support of CEP have conducted studies on biomass of this ctenophore. Iranian Fisheries Research Organization has participated in this research. In addition to this, IFRO conducted 2 research studies on invasion of the Caspian environment by Mnemiopsis. Series of laboratory based studies in Mazandaran Fisheries Research Center of IFRO were performed on ways to combat the problem, which will be presented by Drs. T. Shiganova and G. Finenko here. Another study is in progress on feeding behavior of this species in the Caspian. The main aim of biomass studies is to monitor concentrations of invading species. It is hoped that looking into the results of studies on biomass and ways to control this invading organism a practicable conclusion could be reached in this workshop.

Materials and Methods

A plankton net (Judy net) with a mesh size of 0.5 mm was used to collect samples of Mnemiopsis. Sampling was done in 0-5, 0-10, 0-20, and 0-50 meters (Kideys et al. 2001). Samples were counted in 6 length classes. Using length-weight relationships a formulae of W=al^b was used to estimate biomass.

Results

The present study looked into fluctuations of Mnemiopsis biomass. The presence of this ctenophore increased in summer and in 20 m as the maximum layer of biomass from 0.6 Kg/m²reached a biomass 2.1 Kg/m² in September 2001 in Amirabad Mazandaran. The biomass in 20 m depth in November has decreased and for Amirabad became 0.8 Kg/m². The maximum biomass layer in November was not 20 m anymore and it was 50 m where a biomass of 1.1 Kg/m² in Amirabad was observed (Table 1).

Table 1. Biomass of Mnemiopsis in south Caspian coastal waters in 2001 (gr/m²)