Effects of trammel nets on native Arizona fishes using cortisol as a stress index

Authors: Teresa A. Hunt, Catherine R. Propper, Alice C. Gibb

Year: 2008 (xl)

Abstract

Sampling and handling fish is critical for surveying fish populations, but such sampling should have minimal impacts on those populations surveyed. Trammel nets are commonly used to sample fish; however, little is known about post-capture effects. We evaluated the impact of trammel net sampling on survival of razorback sucker, Xyrauchen texanus, bonytail, Gila elegans, and roundtail chub, Gila robusta, at 15, 20 and 25°C using plasma cortisol concentrations as a potential indicator of stress. Fish between 139 and 388 mm in total length were obtained from both captive hatchery-stock and wild populations, quarantined for 2 weeks, and acclimated in two 18,000-L artificial tanks for 13 days. ‘Treatment’ fish were entangled in a trammel net for two hours and ‘control’ fish were captured with a seine net. After capture, all fish were weighed, measured and PIT tagged according to established field procedures. We extracted on average 0.37 mL (no more then 0.5 ml) of blood from the caudal vasculature from 56% of the total number of experimental fish. Fish were then placed in a 36,000-L recovery/holding tank and monitored for survivorship for 13 days. Although the species varied in the magnitude of their response (p<0.05), cortisol levels were higher for fish captured by trammel nets then for fish captured by seine (p<0.05). Fish captured at the highest temperature (25°C) were more likely to have elevated cortisol levels than fish captured in the same way at lower temperatures (p<0.05). We also note that significantly more fish died after capture by trammel net (p<0.05), and more fish died at the highest experimental temperature 20 and 25°C (p<0.05). For bonytail and razorback suckers, elevated cortisol levels were an effective predictor of mortality (p<0.05); however, in this study, roundtail chub did not demonstrate a significant association between cortisol levels and subsequent mortality. These results suggest that cortisol is a potential index of stress and post-capture mortality, at least for some species. Our results also suggest researchers and managers should consider the risk of delayed mortality when using trammel nets, especially in warm water environments where temperatures exceed 20°C.