Comparison of visual survey and seining methods for estimating abundance of an endangered, benthic stream fish

Abstract

We compared visual survey and seining methods for estimating abundance of endangered Okaloosa darters, Etheostoma okaloosae, in 12 replicate stream reaches during August 2001. For each 20-m stream reach, two divers systematically located and marked the position of darters and then a second crew of three to five people came through with a small-mesh seine and exhaustively sampled the same area. Visual surveys required little extra time to complete. Visual counts (24.2 ± 12.0; mean ± one SD) considerably exceeded seine captures (7.4 ± 4.8), and counts from the two methods were uncorrelated. Visual surveys, but not seines, detected the presence of Okaloosa darters at one site with low population densities. In 2003, we performed a depletion removal study in 10 replicate stream reaches to assess the accuracy of the visual survey method. Visual surveys detected 59% of Okaloosa darters present, and visual counts and removal estimates were positively correlated. Taken together, our comparisons indicate that visual surveys more accurately and precisely estimate abundance of Okaloosa darters than seining and more reliably detect presence at low population densities. We recommend evaluation of visual survey methods when designing programs to monitor abundance of benthic fishes in clear streams, especially for threatened and endangered species that may be sensitive to handling and habitat disturbance.

SmeltCam: Underwater Video Codend for Trawled Nets with an Application to the Distribution of the Imperiled Delta Smelt

“…In particular, underwater video systems are becoming increasingly popular for studying fishes in marine [7], [8], estuarine [9], [10], [11] and freshwater habitats [12], [13]. They are especially desirable when a key objective is to minimize or avoid the adverse effects of handling stress associated with traditional sampling methods [14], [15].…”

Estimating Occupancy of Rare Fishes using Visual Surveys, with a Comparison to Backpack Electrofishing

“…Our study indicated that the relative effectiveness of these two methods differed among species and that snorkel sampling was comparable or in some cases superior to electrofi shing for estimating site occupancy. Jordan et al (2008) found that snorkel sampling was more accurate and precise than seining for estimating the abundance of Etheostoma okaloosae (Fowler) Okaloosa Darter. Thurow et al (2006) documented higher detection rates for single-pass backpack electrofi shing compared to daytime snorkeling for Salvelinus confl uentis (Suckley) (Bull Trout), emphasizing that the relative effectiveness of these different methods varies across species and systems.…”

“…Snorkel sampling has an obvious advantage over electrofi shing because it greatly reduces handling stress and mortality, which is an important consideration when assessing the status of imperiled fi shes (Bohl et al 2009, Jordan et al 2008, Poos et al 2007). Our study indicated that the relative effectiveness of these two methods differed among species and that snorkel sampling was comparable or in some cases superior to electrofi shing for estimating site occupancy.…”

“…This problem was ignored in the past, but it is becoming increasingly more common to account for incomplete species detection in surveys for rare fi shes (e.g., Albanese et al 2007, Burdick et al 2008, Wenger et al 2008. Another challenge is the need to minimize handling stress and the risk of mortality for legally protected fi shes (Jordan et al 2008), which may restrict or preclude the use of effective but potentially harmful sampling methods such as electrofi shing (Bohl et al 2009). …”

“…Other advantages include lower cost and the ability to target habitats that may be too deep or structurally complex to sample by seining or electrofi shing (Thurow et al 2006). While visual observation techniques are routinely applied, only a few studies have specifi cally examined their effectiveness compared to other methods (e.g., Ensign et al 1995, Jordan et al 2008, Thurow et al 2006 or accounted for incomplete species detection (Peterson et al 2002). This latter issue could be particularly problematic for rare southeastern fi shes because they are typically small-bodied and cryptobenthic (Jenkins and Burkhead 1993).…”