عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The aim of the present research is to survey the effects of environmental and biological factors on Rutilus frisii kutum migration in the southwest region of Caspian sea. For this purpose Sampling was carried out by gillnet cooperatives company in Tonekabon city from November 2013 to April 2014. The total catch per unit effort was calculated as 220 kg. Rutilus frisii kutum contains 69% of the total catch in fishing cooperatives. Samples age range were in age groups of 1-7 age which among the age groups listed, had 4-year age group with the highest frequency rate ( 51/1%) and 1-year age group had the lowest frequency ( 0/8%). The highest frequency of Rutilus frisii kutum length classes Has been in the range of 38-42 cm and a frequency of 34/7 percent. The Rutilus frisii kutum weight changes range in caught samples were 240-2240 kg. The most frequency of weight class has been in the 840-640 weight class which are included 30/5 percent. Male fishes were more than female fish. The results showed quantitatively remarkably increase in Rutilus frisii kutum stocks over the past decade, as indicated elevated levels of catch rate than when the rivers was in very good condition. But we observed changes in stocks qualitatively that the most important growth factors such as length, weight and age of Rutilus frisii kutum than in past years. The findings indicate that the impact of environmental factors on biological factors. As well as biological factors rather than environmental factors were a greater impact on catch and migration.