Do Endangered Razorback Suckers Have Poor Larval Escape Performance Relative to Introduced Rainbow Trout?

Abstract

Poor recruitment has generated the hypothesis that the endangered razorback sucker Xyrauchen texanus is particularly vulnerable to predation early in its life history. We compared the escape responses of razorback suckers, which are adapted to the historically warm waters of the Colorado River, with those of rainbow trout Oncorhynchus mykiss, an introduced coldwater species, throughout early development at water temperatures of 12°C and 18°C. We quantified escape performance using maximum velocity, acceleration, and time to maximum velocity and acceleration. Both species showed complete temperature compensation for escape performance; individuals reared at 12°C performed as well as those reared at 18°C. Performance was also similar between species, although two variables exhibited a species × size interaction. Small razorback suckers were faster (greater maximum velocity and acceleration) than small rainbow trout, while large larvae performed similarly. We also determined that razorback sucker larval escape performance falls within the range reported for other fishes. Therefore, we conclude that razorback suckers do not have “poor” escape performance and that temperature does not directly cause decreased performance. However, a cold temperature reduces growth rates and delays razorback suckers' attainment of a “predator‐proof” size. Small larvae are also more likely to perform uncoordinated, ineffective escape responses. Hence, razorback sucker performance is indirectly diminished by temperature.

Trade-offs between size and energy reserves reflect alternative strategies for optimizing larval survival potential in rockfish

“…Taken together, their positive association with body size across species suggests that larger larvae will have substantially greater success in avoiding predation and are likely to do much better than smaller larvae under conditions of high predator density. Increasing escape capabilities with increasing body size have been commonly observed for larval fishes and amphibians (Batty et al 1993, Williams et al 1996, Fuiman et al 1999, Wesp & Gibb 2003, Eidietis 2005. We did not observe a correlation between larval size and startle performance within species, but this was likely due to the relatively narrow size range within individual species (CV ranged from 2.9 to 3.3% within a species, but was 6.0% for the means of each of the 5 species).…”

“…When converted to a relative scale (per unit body length), average swimming speeds during the startle response were similar for all species (approximately 17 to 18 bl s -1 ), were slightly slower than those recorded for subtropical fish larvae (20 to 30 bl s -1 ; Fuiman et al 1999), and fell mid-range when compared with a broad range of teleost larvae measured at similar temperatures (Wesp & Gibb 2003).…”

Heterochrony and the development of the escape response: prehatching movements in the rainbow trout Oncorhynchus mykiss

“…C-starts are present at (or immediately after) hatching in cod, drum, pollock, herring, various species of flatfish, carp, razorback sucker and zebrafish (Kimmel et al, '74;Bailey and Batty, '84;Yin and Blaxter, '87;Gibson and Johnston, '95;Wakeling et al, '99;Wesp and Gibb, 2003;Smith and Fuiman, 2004;Gibb et al, 2006). Thus, for both marine and freshwater teleosts with indirect development, coordination of the elements that produce the escape response is achieved before hatching, even though adult morphology has not been attained.…”

“…Relatively few studies, have examined the escape response in species with intermediate development. However, C-start behavior is present at hatching in the few species with intermediate development examined to date (Hale, '99;Wesp and Gibb, 2003). Thus, it seems that coordinated C-starts are present at hatching in teleosts with indirect and intermediate development.…”

Simulation and validation of larval sucker dispersal and retention through the restored Williamson River Delta and Upper Klamath Lake system, Oregon

“…The maximum burst speed for razorback sucker larvae with a standard length of 19 mm has been determined to be 464 mm/s or 24 body lengths (BL) per second (BL/s) (Wesp and Gibb, 2003). Prolonged swim speeds (50 percent of fish held this speed for 1 hr) were determined to average 5.8 BL/s (range of 5.3 to 6.5 BL/s) for robust redhorse sucker larvae with a standard length of 13.1-20.4 mm (Ruetz and Jennings, 2000).…”