Improving habitat for fish with artificial structures in rivers

A flier (Centrarchus macropterus). Drawing by Duane Raver.A new study from researchers at West Virginia University finds that dike structures in rivers can provide important habitat for native fish.

Kyle Hartman and Jennifer Titus tested the benefit of these artificial habitat features by looking at dikes that were installed in the Kanawha River in West Virginia as mitigation to offset negative impacts from a project to increase barge traffic on the waterway. The dike structures were made of rip and rap and placed either at an angle or parallel to the shore.

The researchers surveyed fish in 2002 and 2003 during the day and night at the dikes and at natural reference sites that were either high quality (i.e many complex habitat features such as wood debris, aquatic vegetation, etc) or low quality (i.e. few complex habitat features).

They found that fish abundance and species richness were greater in the dike areas than low quality reference sites and either equal or greater than the high quality reference sites.  These study results show that dikes and other artificial features can be used as tools to increase habitat complexity and compensate somewhat for the negative impacts to riverine habitat.

The complex, meandering morphology of rivers throughout much of the world have been transformed into straight, narrow, deep systems for the purpose of controlling flooding and improving navigability. While these modifications have provided benefits to people they have come at a cost to fish in part by homogenizing the environment.

The authors believe that the dikes improve habitat by providing refuge from predators, shelter from high velocity flows, and niches for feeding. The evidence supports this. The study measured water velocity and found that it was much slower in the area of the dikes. They also found that the average fish catch at the dikes increased with higher river flows during the day. 

Certain groups of fish such as sunfish (Centrarchidae) were particularly more abundant in the artificial habitat areas. The authors write,

"The mechanisms responsible for increased use of dikes by Centrarchidae species may be related to two habitat changes the dikes provide that favour these taxa. Velocity profiles showed dikes offer extended areas of lower velocity currents than reference areas. As most of the sunfish taxa we collected represent species that prefer pools and lentic systems areas of lower velocity likely provide zones of increased habitat quality for sunfish...Dikes also increase heterogeneity of substrate by providing both structural relief and crevices in which to hide and forage. As a result, dike areas would score high on two axes in habitat suitability and this combination of habitat features likely leads to the increased use of dike structures by centrarchids relative to reference sites."

--Reviewed by Rob Goldstein

Hartman, K., & Titus, J. (2009). Fish use of artificial dike structures in a navigable river River Research and Applications DOI: 10.1002/rra.1329