Backpack electrofishing effort and imperfect detection: Influence on riverine fish inventories and monitoring

Abstract

Summary An increased electrofishing sampling effort will increase detection probabilities of riverine fishes. In this study, a repeat‐sampling approach was used in small to medium‐sized Ontario (Canada) rivers to estimate: (i) species‐specific detection probabilities of freshwater fishes, (ii) the number of sampling events required to confidently detect species, and (iii) the power of timed‐search surveys to detect future distribution (or occupancy) declines. Wadeable habitats at 36 sites were sampled with a backpack electrofisher on four separate dates during the summer low‐flow period in 2013 and 2014. Forty‐two species were collected, including three species of conservation concern (American eel Anguilla rostrata Lacépède, 1802, channel darter Percina copelandi Jordan, 1877, northern sunfish Lepomis peltastes Cope, 1870), and two recreationally important species (largemouth bass Micropterus salmoides Lacépède, 1802 and smallmouth bass Micropterus dolomieu Lacépède, 1802). A hierarchical Bayesian modelling approach was used to estimate detection probabilities and site occupancy for 18 species at four levels of effort: 250, 500, 750 and 1,000 s. In all cases, species detection was imperfect. Search effort had a positive effect on estimates of detection probability and site occupancy and the power to detect declines in future distribution. Detection probabilities ranged from 0.11 to 0.66 with an effort of 250 s, and 0.27 to 0.92 with an effort of 1,000 s. For 13 species, detection and power to detect changes in distribution were significantly improved by increasing sampling effort from 250 to 750 s or 1,000 s. For the channel darter and northern sunfish, three replicate sampling visits (of 750 or 1,000 s duration) are recommended for confident detection.

Coastal river connectivity and the distribution of ascending juvenile European eel (Anguilla anguilla L.): Implications for conservation strategies regarding fish‐passage solutions

“…On the other hand, Baldwin and Aprahamian () showed that sampling focused on salmonids could give good estimates of eel abundance, with catch efficiencies similar to those of other species. Nevertheless, good estimates of occurrence may be difficult to obtain if the abundance is low, and the sampling effort is consequently a key factor for collecting high‐quality presence/absence data (Reid & Haxton, ). The strong effect of temperature on eel occurrence was expected, as eels may be considered a warm‐water species (Tesch, ) and the immigration to fresh water is often initiated at water temperatures of 14–16°C (Knights & White, ; White & Knights, ).…”

“…As occurrence data (presence/absence and not density estimates) were used, sampling effort must be controlled for in the statistical model. Logically, the probability of encountering an individual is positively related to sampling effort (Reid & Haxton, ). Although electrofishing in Sweden is standardized, the sampled areas of the sites included varied greatly (ranging from 12 to 700 m 2 , with a mean of 166 m 2 ), and were positively correlated with the river width (Spearman's rho = 0.71, P < 0.001, n = 1917).…”

Gear effectiveness and size selectivity for five cryptic madtom species ( Noturus spp.)

“…Many previous studies have assessed the utility of different sampling gears for stream fish assemblages (Onorato, Angus, & Marion, ; Vincent, ; Yoder & Smith, ). However, to our knowledge, no studies have specifically focused on madtoms, although differences in relative abundance (Neebling & Quist, ; Tiemann & Tiemann, ; Wilkinson, ) and detection probability (Gibson‐Reinemer et al, ; Peoples & Frimpong, ; Reid & Haxton, ) have been noted as part of stream assemblage studies. Herein, gear choice affected the probability that we detected each species during low water conditions, typical of autumn in southeastern streams, having implications for future efforts to describe the presence and absence of these fishes, while explicitly accounting for the size biases related to gear selection.…”

“…1998; Vincent, 1971;Yoder & Smith, 1999). However, to our knowledge, no studies have specifically focused on madtoms, although differences in relative abundance (Neebling & Quist, 2011;Tiemann & Tiemann, 2004;Wilkinson, 2012) and detection probability (Gibson-Reinemer et al, 2016;Peoples & Frimpong, 2011;Reid & Haxton, 2017) have been noted as part of stream assemblage studies. Herein, Electrofishing is one of the most common methods for ecological monitoring in wadeable streams, but is occasionally avoided due to increased potential for mortality of threatened and endangered species Note.…”

“…Without understanding potential gear biases, which can influence catch rates and size-structure, surveys may poorly describe species status and population demographics. Understanding these gear biases is particularly important when sampling madtoms, which are notoriously difficult to detect (Gibson-Reinemer, Stewart, Fritts, DeBoer, & Casper, 2016;Peoples & Frimpong, 2011;Reid & Haxton, 2017) due to their reclusive nocturnal behavior and cryptic color patterns.…”