Meeting Abstract
37.6 Jan. 5 Life history strategy affects escape performance of endangered Colorado River fish species GIBB, A. C.*; FERRY-GRAHAM, L. A.; Northern Arizona University; Moss Landing Marine Laboratories Alice.Gibb@nau.edu
Many native fishes of the Colorado River are Cypriniformes (Teleostei). Because cypriniform fish have no parental care and produce eggs with small yolks, their larvae are free swimming when the axial skeleton and fins have not yet formed. Many introduced game fish are in the teleost orders Perciformes (e.g. largemouth bass; Centrarchidae) or Salmoniformes (e.g. brown trout; Salmonidae). Salmonid eggs have large yolks, and larvae become free swimming at an advanced state of morphological development; centrarchids have parental care of eggs and young larvae. Thus, these species become free swimming as advanced larvae (i.e. near metamorphosis), when the axial skeleton and fins approach adult morphology. We measured escape response performance (time to complete preparatory phase, max. velocity, time to max. velocity) from larvae and juveniles (20-70 ind.) from three species (each representing one of the three teleost lineages) in the laboratory. For all species, improvements in performance were correlated with the development of specific adult morphologies (e.g. the caudal fin), and small juveniles produced more effective escape responses than did larvae. We suggest that cypriniform fish populations may be reduced by predators because larvae are free living but produce ineffective escape responses. The creation of a series of dams and reservoirs on the Colorado River exacerbates this problem. Decreased water temperature retards development of native fishes, extending their period of increased vulnerability. Decreased turbidity improves the ability of visual predators (particularly introduced nektivores) to target larvae in the water column. Finally, damming modifies the habitat in a manner conducive to the nesting success of introduced game fish, and does not confer any benefit to native fishes.
