Study On Feeding Ecology And Food Relations Of Two High Trophic Level Fishes In Haizhou Bay

Seasonal bottom-traw] surveys were conducted in Haizhou Bay, China from March to December 2011. The high trophic levels of Conger myriaster and Saurida elongata stomach samples were analyzed to study their feeding ecology, including diet composition, feeding type, feeding intensity, trophic level, trophic niche and factors of affecting feeding by stomach contents analysis. The main results are as follows:The feeding ecology of C. myriaster and 5. elongata were studied.1) The results show that the prey items of C. myriaster included more than 40 species, and fish, decapods, and cephalopods were the dominant prey groups. Syngnathus acus, Chaeturichthys stigmatias, Alpheus distinguendus, and Loligo sp. were the major prey species of C. myriaster. Benthic animals were the dominant C. myriaster prey type, followed by swimming animals. The diet composition of C. myriaster had clear seasonal and length variations, and fish and shrimp were the major prey groups throughout all four seasons, whereas cephalopods were the most important prey during autumn. Loligo sp. were the dominant prey group of C. myriaster< 70 mm, whereas Callionymus beniteguri and A. distinguendus were the dominant prey groups of the 70-99-mm C. myriaster. Loligo sp., Syngnathus acus, and A. distinguendus were the dominant prey groups of C. myriaster> 99 mm. Percent of empty stomach and mean stomach fullness index of C. myriaster varied seasonally. The lowest and highest percent of empty stomach occurred in summer and spring, respectively. The mean stomach fullness index was lower in spring and higher in autumn. The C. myriaster trophic level was 4.17, indicating that it was in a high trophic position in the Haizhou Bay food web.The results show that the prey items of S. elongata included more than 30 species, fish was the dominant prey group, decapods and cephalopods were the minor prey groups. Engraulis japonicus, Loligo sp., Callionymus sagitta, Metapenaeopsis dalei, and Apogon lineatus were the major prey species of S. elongata. swimming animals were the dominant 5. elongata prey type. In addition, the prey items of S. elongata included 5. elongata, indicating the phenomenon of self-injurious in the growth and development. The diet composition of 5. elongata had clear seasonal and length variations and fish were the major prey groups throughout all three seasons, whereas decapods were the most important prey during autumn, and cephalopods were the most important prey during autumn. With length increaseing, the number of large fish was increasing. Percent of empty stomach of S. elongata varied seasonally, not length, however, mean stomach fullness index varied seasonally and length. The 5. elongata trophic level was 4.65, it had clear seasonal and length vsariations. The study found that the feeding ecology of C. myriaster and 5. elongata varied seasonally and ontogenetically, which was mainly due to variations in the dominant prey species.Trophic and spatial niche width, trophic-spatial niche overlap for the high trophic levels of C. myriaster and S. elongata in Haizhou Bay were studied using the Shannon-Wiener index and Pianka overlap index. The trophic-spatial niche overlap was calculated to describe the competition of C. myriaster and 5. elongata. The results showed that the trophic and spatial niche width of C. myriaster (3.04 and 3.06) were higher than S. elongata (2.51 and 2.96), respectively. The highest niche width of C. myriaster occurred in summer, however, S. elongata occurred in Autumn. The highest trophic niche overlap (0.55) and spatial niche overlap (0.31) occurred in autumn and summer, repectively. However, the highest trophic-spatail niche overlap (0.12) occurred in summer between C. myriaster and S. elongata. So the fishes with low trophic-spatail niche overlap were not likely to cause competition. The competitions between C. myriaster and S. elongata were reduced by partition of trophic and spatial niches. The canonical correspondence analysis (CCA) showed that depth, temperature and nutrients were the most important variables followed by length and salinity of C. myriaster. Length, depth and nutrients were the most important variables followed by temperature, pH and Latitude of S. elongata.