Sediment Deposition within Fry Emergence Traps: A Confounding Factor in Estimating Survival to Emergence

Abstract

We provide evidence that the effects of sediment infiltration and deposition within fry emergence traps can lead to a potential negative bias when estimating survival to emergence (STE) of salmonid fry. Fry emergence traps were placed over 12 redds of brown trout Salmo trutta located in sections of three streams in the upper Clark Fork River system in Montana. The redds were capped in March 1989 and monitored through June 1989. During this period, sediment deposition became noticeable inside 8 of the 12 traps. During the final removal of the traps, substrate core samples were collected from a location inside and outside of each emergence trap. Substrate size gradation analysis indicated that concentrations of fine sediments (≤0.84 mm in diameter) were significantly higher in samples collected inside the traps than outside. These results suggested that the local sediment transport capacity was reduced within the emergence traps, resulting in increased deposition of fines. An understanding of the hydrology, ambient sediment concentrations, and sediment transport capabilities of river systems is important when considering the use of fry emergence traps. Without consideration for this potential confounding factor, STE estimates that involve the use of fry emergence traps may underestimate actual STE values.

Sand Seals in Coho Salmon Redds: Do They Improve Egg Survival?

“…The problem was that, unlike any other year, the peak discharge for 1992 (Table 4) occurred during the emergence period and when the fry traps were on the redds. The force of the high flows against the trap net appeared to cause sand to unnaturally accumulate at high levels on the surface of the redds (similar to Reiser et al [1998]). Also, 1992 was the only year the traps were on for a prolonged period of two months before initial emergence.…”

Parental Effect as a Primary Factor Limiting Egg‐to‐Fry Survival of Spring Chinook Salmon in the Upper Yakima River Basin

“…Studies estimating salmonid egg-to-fry survival normally utilize one of three primary field methods: excavation of naturally produced redds prior to first emergence, trapping of emergent fry from naturally produced redds, or planting known numbers of eggs in artificially constructed redds (Rubin 1995). Potential biases in the estimation of survival have been well documented for each of these methodologies due to various factors such as adult fecundity, egg deposition, fertilization rate, siltation, flow dynamics, escapement, and predation (Claire and Phillips 1968;Chapman 1988;Young et al 1990;Rubin 1995;Reiser et al 1998). Due to the scale and replication required, we chose to use egg boxes to estimate survival.…”

A new method to evaluate egg‐to‐fry survival in salmonids, trials with Atlantic salmon

“…Many studies have tried to quantify ETF survival and two main methods have been used. The first consists in capping redds using trap nets or covering the redds with fine mesh screen cages to trap emergent fry (Phillips & Koski, 1969; Scrivener, 1988; Marty & Beall, 1989; Reiser et al ., 1998; Dumas & Darolles, 1999; Ingendahl, 2001). This technique, however, has several problems including the estimation of the initial egg number deposited in natural redds, difficulty in positioning the trap, risk of fry escaping through the intragravel interstices, and vulnerability of the device to high flows (Chapman, 1988; Rubin, 1995; Crisp, 1996; Dumas & Darolles, 1999).…”