Effects of location and flood characteristics on fish growth in the Volga floodplain

ABSTRACT The flood pulse concept states that periodical flooding is the main driver of productivity in river floodplain systems. Given the importance of floodplains as nursery and foraging habitat for many fish species we hypothesize that the yearly variation in flood characteristics will also result in growth variability. We studied this hypothesis in a large floodplain (100 x 30 km) of the lower Volga River (Russian Federation), where annual floodings occur. We focused on bream (Abramis brama) and roach (Rutilus rutilus), both common, and commercially important species that use the floodplain for spawning and feeding. Fish were caught at two locations in the floodplain, in the middle part, consisting mainly of (flooded) grasslands and large lakes, and close to the main channel of the Volga River, consisting of small channels and lakes. Scales were collected and age and back-calculated growth were determined of 200 bream and 150 roach, using the Fraser-Lee method. For bream we found that the annual growth increment per age-class of individuals from the middle part of the floodplain was higher than that of those caught closer to the main channel, especially for age 3-5. Also, the yearly variation in growth increment per age-class was less for individuals caught in the middle of the plain than that of those caught closer to the main channel. For roach the annual growth increment per age-class showed yearly variation (for age 3-4), however there was no difference between locations. Increased growth occurred during 2005, a year with a high and prolonged flood discharge. The results indicate variation in growth in response to flooding variation, for both species especially for age-class 3 and 4. In addition, bream growth is increased and less influenced by flooding variation when growing in the middle part of the area. This suggests that the middle part is more profitable than the area near the main channel and the scale of home ranges might be limited.