ABSTRACTS ALPHABETIZED BY FIRST AUTHOR / RESUMENES EN ORDEN ALFABETICO POR PRIMER AUTOR Bestgen, K. R.*; Beyers, D. W.; Haines, G. B.; Rice, J. A.(KRB and DWB - Larval Fish Laboratory, Department of Fishery and Wildlife Biology, Colorado State University; GBH - U.S. Fish and Wildlife Service, Colorado River Fishery Project; JAR - Department of Zoology, North Carolina State University) Importance of red shiner predation on survival of Colorado squawfish larvae: an experimental and individual-based modeling analysis

Authors: DFC HYDROLOGIC BASIN, AGENCY REPORT COORDINATORS………………………….. …………….. 71

Year: 1998 (xxx)

Abstract

Red shiner, Cyprinella lutrensis , an introduced cyprinid in the Colorado River basin, is abundant in backwater habitat used by larvae of endangered Colorado squawfish Ptychocheilus lucius. Red shiners prey upon fish larvae in backwaters and may be an important source of mortality for Colorado squawfish. We used experimental data and an individual-based simulation model to evaluate the potential importance of this source of mortality. The model incorporated experimental estimates of: joint encounter-attack rate predicted by prey size, predator feeding strategy, water turbidity, and availability of alternative prey; size-dependent capture probability; and temperature-dependent growth of larvae. Experiments suggested that Colorado squawfish larvae 10 to 19mm TL were attacked an average of once per minute by red shiners that were 38 to 69mm TL. Probability of capture peaked at about 25% for the smallest larvae attacked by the largest red shiners and declined to near zero for small shiners that attacked large larvae. The largest red shiners captured Colorado squawfish up to 22mm TL. Model simulations suggested that red shiner predation may substantially reduce survival of Colorado squawfish larvae even with turbid water and alternate prey. In simulations with warm water temperatures and 3 predators/m2, squawfish survival at the end of the growing season was 15% for cohorts hatched 1 June, 25% for cohorts hatched 1 July, and 13% for cohorts hatched 1 August. Survival was reduced an additional one third or more in cool-water simulations. Survival of larvae with growth rates of 0.6 and 0.2mm/d were 44-52% and 5- 10%, respectively, and decreased with increasing predator density from 53-63% with 1 shiner/m 2 to 3-7% with 6 shiners/m2.

Resumen

Importancia de la depredación por la carpa roja en la sobrevivencia de larvas de la carpa gigante del Colorado: un análisis experimental y de modelación basado en individuos La carpa roja, Cyprinella lutrensis, un ciprínido introducido a la cuenca del Río Colorado, es abundante en el hábitat de remanso utilizado por las larvas de la carpa gigante del Colorado, Ptychochilus lucius, especie en peligro de extinción. Las carpas roja se alimentan de larvas de peces encontradas en los remansos del río y podría ser una causa importante de mortandad de la carpa gigante del Colorado. Utilizando datos experimentales y un modelo de simulación basado en individuos, evaluamos la importancia potencial de dicha causa de mortandad. El modelo incorporó estimaciones experimentales de: la tasa encuentro-ataque pronosticada por el tamaño de la presa, estrategia de alimentación del predador, turbidez del agua, y disponibilidad de presas alternativas; la probabilidad de captura dependiente del tamaño; y el crecimiento de las larvas dependiente de la temperatura. Los experimentos sugieren que las larvas de la carpa gigante del Colorado de 10 a 19mm de longitud total (LT) fueron atacadas a una razón promedio de una por minuto por las carpas roja de 38 a 69mm LT. La probabilidad de captura llegó a su máximo de cerca de 25% para las larvas más pequeñas atacadas por las carpas roja más grandes y declinó hasta cerca de cero para las carpas roja pequeñas que atacaron a las larvas