Estimating spawning habitat availability in flooded areas of the river Waal, the Netherlands

Fish spawning habitat availability in the river Waal is significantly influenced by seasonal and annual variations in discharge. In this paper we develop habitat suitability models, based on a literature survey of spawning preferences of the commonly occurring species roach (Rutilus rutilus), bream (Abramis brama), pikeperch (Sander lucioperca) and bleak (Alburnus alburnus). Within the resulting models water depth, flow velocity, water temperature and vegetation type were the most significant environmental parameters. Spatial data for the parameters were derived from a 2-D hydrodynamic model and detailed monitoring database. The area of suitable habitat available for spawning was calculated using the HABITAT software, based on species-specific suitability models and the environmental characteristics of two study sites on the river Waal over a 3 year period (1997-1999). The predicted available spawning area was compared with field data on the recruitment of young fish of each species for the same years and locations. There was a positive relationship between predicted available habitat and observed young of the year (YOY) densities for bream, roach and pikeperch. A negative relationship was recorded between predicted available area and observed YOY densities for bleak. The results indicate that optimal hydrological and hydraulic conditions differ even for species that are widely considered eurytopic. Moreover, annual differences in habitat availability indicate a strong influence of hydrological variability on population dynamics.