study on effects of depth variation on bycatch rate and fish size of shrimp trawl net in the fishing grounds of hormuzgan waters

with regard to bycatch problem, this is the first study of the shrimp trawl bycatch in different depth variation in hormuzgan coastal waters. samples were collected during shrimp season in october 2011 and november 2012. the study area was divided into two regions: hormuz-keshtisoukhte (56°, 27ʹ e/27°, 07ʹ n) to (56°, 18ʹ e/27°, 06ʹ n) and keshtisoukhte-toola (56°, 18ʹ e/27°, 06ʹ n) to (55°, 58ʹ e/26°, 58ʹ n). to compare the mean cpue of bycatch among different depths, sampling zone were divided into 3 depths: 1 to 10, 10 to 20 and 20 to 30 m. in 30 hauls, 1028.2 kg of shrimp and 3388 kg of bycatch were caught in the trawl net. bycatch-to-shrimp ratio was calculated 2.80:1 and 3.77:1 in 2011 and 2012 respectively. bycatch-to-shrimp ratio in 2011 was less than 2012, in all depth category. in the depth of 10 to 20 m, the less bycatch and bycatch-to-shrimp ratio in two years of study be obtained. also, the cpue and mean cpue of bycatch in 2012 was higher than 2011. in investigation of the mean cpue of bycatch between seasons 2011 and 2012 (f=2.544; p>0.05) also, among different depths (f=2.264; p>0.05) and in depths in combination with seasons (f=0.579; p>0.05) with using two-factor analysis of variance (anova), no significant difference were detected.