Imitating the physical properties of drifting semibuoyant fish (Cyprinidae) eggs with artificial eggs

Six Rio Grande basin cyprinid taxa compose a reproductive guild that spawns during increases in stream flow and broadcasts semibuoyant (drifting) eggs in the current. Spawning by guild members is naturally initiated by elevat ed flows during spring snow-melt or summer rainstorms, but reservoir releas es now also result in spawning. Location or development of a material that mimics the physical properties of semibuoyant eggs of,guild members would e nable quantification of the displacement of drifting eggs and assessment of the additive impacts of stream flow, instream barriers, and habitat modifi cations on populations of these fishes. To initiate this search, the size a nd terminal velocity of guild members' eggs was determined and their specif ic gravity (SG=1.00589 +/- 0.00011) calculated. Products with specific grav ities similar to semibuoyant eggs were obtained, and tests were conducted o n their rates of travel and settling times when exposed to current. Materia ls with specific gravities slightly greater than semibuoyant cyprinid eggs (SG>1.01) sank too rapidly, while materials less dense than water (SG<1.00) traveled downstream more rapidly than guild members' eggs. Particle size, not shape, noticeably affected rates of travel and settling times. Laborato ry and field tests indicated that a modified nylon 12 particle (SG=1.00457 +/- 0.00017) most closely mimicked the properties of semibuoyant cyprinid e ggs.