Using the DIDSON to Evaluate the Effectiveness of Different Fish Attractors in Turbid Reservoirs

Fish attractors have been widely used by fisheries managers to enhance fish habitat and increase the concentration of fish at known locations.  However, fish attractors are often deployed without any validation for how well they meet management goals.  The objective of this project was to evaluate the effectiveness of four different types of fish attractors to concentrate fish in North Carolina Piedmont reservoirs.  ANOVA using a complete block design with repeated measurements was used to compare fish abundance from three types of artificial attractors, one natural attractor, and a control area devoid of structure.  Attractors encompassed a volume of approximately 3.375 m³, but the materials and general designs varied from a structure constructed from PVC pipes and plastic barrels, a structure built from PVC pipes and corrugated plastic pipes, a commercially available PVC product called the Porcupine, and a bundle of three evergreen trees.  Fish abundance at unmarked attractors was evaluated once per season during a three year period using instantaneous counts from images taken by a dual-frequency identification sonar device.  We found that all attractors held significantly (α =0.05) more fish than the control area and that significantly more fish concentrated around the corrugated pipe structure as compared to the other structures.  A year-by-year analyses was also performed.  During years one and two, the only significant difference was between fish attractors and the control area.  In year three, the corrugated pipe structure held significantly more fish than the barrel and porcupine structure, which held significant more fish than the tree structure, and all structures held more fish than the control area.  Schools of small bait fish were also attracted to these structures and using binary logistic regression we found that relative to the control only the three synthetic attractors had significantly higher odds of having these schools present.  We also found that by the third year the tree structure had significant structural breakdown, but all of the synthetic attractors were still intact.  This study validates the effectiveness of fish attractors to concentrate fish, highlights the benefits of artificial structures as compared to natural structure, and will help fisheries managers make informed decisions when attempting to enhance angling opportunities.