بررسي پراكنش گاوماهي شني (Neogobius fluviatilis pallasi) در سواحل جنوب غربي درياي خزر(آب‏هاي استان گيلان)

Studying distribution of sand goby, Neogobius fluviatilis pallasi (Gobiidae) in the South-west coast of Caspian Sea (Guilan Province)

This study carried out on distribution of sand goby in the south west coast of the Caspian Sea (from Astara to Chaboksar) from October 2005 to September 2006 during 1 year. Samples were collected from 3 stations (Astara, Anzali, and Chaboksar coasts) from 0 to 15 meters of depth. They have been captured monthly by bottom trawl. It has been determined Caspian sand goby density per trawling and its relative and absolute abundance in station. The minimum abundance (7.70% of total catch) took place in the study in January 2006 and the maximum abundance (32.85% of total catch) in December 2005. The minimum and maximum catch for sand gobies made up 9.98% and 41.64%, of the total catch respectively for Caspian Sea gobies area was recorded. A significant decrease in density of sand gobies specimens was observed with an increase in depth. Among studied coast, Abundance of N. fluviatilis was the most amount in Astara Coast. An interacting effect among the different factors was also seen (non-parametric Spearsman,s test) indicating that among depth, sampling station and depth-sampling station only depth influences on absolute density of the fish. Correlation coefficient between N. fluviatilis pallasi abundance and biotic factors and abiotic factors were tested using Spearman non-parametric test. Significant correlation was observed between abundance of sand goby and factors of total catch (0.703), abundance of gobies (0.672), temperature (0.683) and dissolved oxygen (0.419) at 99% confidence level, however negative correlations existed between abundance of sand goby and zooplankton (-0.300) and phytoplanktons (-0.388)). No correlations were observed between abundance of sand goby, N. fluviatilis pallasi and other studied parameters. The closest linked factor (PCA) to absolute abundance and biomass of sand gobies (biomass) were gobies, total catch, temperature and dissolved oxygen in order of their reference.