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

Abstract

More than half of the diminutive North American catfish species known as madtoms (Noturus spp.) are considered imperiled due to range reductions from habitat fragmentation and degradation. In response, government agencies regularly conduct sampling that targets these cryptic fishes. Unfortunately, the effectiveness and biases associated with common sampling gears has rarely been quantified for non‐game fish, including madtoms. To improve sampling protocols for diverse madtom species, we: (a) quantified the detection probabilities and effort necessary to detect five species of madtom with relative certainty using complimentary sampling gears, and (b) described biases associated with size‐selectivity of the same gears when used to sample madtoms. Five madtom species that are native to Mississippi streams and have two distinct coloration patterns were selected: uniform pattern, Brown Madtom (Noturus phaeus) and Freckled Madtom (Noturus nocturnus); patterned, Piebald Madtom (Noturus gladiator), Least Madtom (Noturus hildebrandi), and Brindled Madtom (Noturus miurus). These species were captured using four standardized sampling gears (i.e., backpack electrofisher, seine, dipnet, and Gee‐style minnow trap) from 13 isolated stream reaches in Mississippi during baseflow conditions between August and November 2016. Each gear was randomly assigned to up to five transects at each site resulting in a maximum of 20 unique samples per stream reach. We estimated the detection probability of each species with each gear using presence–absence capture data. Cumulative detection probabilities were calculated for each species and gear combination to describe the number of samples necessary to achieve a detection probability of 0.95. Additionally, we pooled all capture data across sampling sites to compare madtom size distributions among gears. Electrofishing was generally the most efficient gear for detecting madtoms, but slightly overestimated fish size distributions. By seining, managers can expect to capture all species evaluated with a modest amount of effort; however, are likely to catch relatively small individuals. Seining was the most effective gear for only Piebald Madtom, a species petitioned for listing under the Endangered Species Act. To be relatively certain that Piebald Madtom are absent from a stream reach would require sampling ten 100 m transects by seining. In contrast, the same certainty would require more than twenty 100 m electrofishing transects. Minnow traps and dipnetting generally performed poorly and failed to detect some species at occupied sites. Biologists can now consider using each of these complimentary gears assessed when evaluating species status and population structure for diverse madtom species, while explicitly acknowledging the biases associated with each gear.

Suitability of passive integrated transponder tags and a new monitoring technique for at-risk madtoms (Noturus spp.)

“…Cryptic madtoms are difficult to detect during frequent survey attempts to monitor at-risk populations, which has hindered efforts to monitor conservation actions (Wagner et al 2019). As a result, relatively little is known about the effectiveness of available conservation actions such as targeted reintroductions.…”

“…Surgically implanted tags are seemingly applicable to diverse studies of patterned madtoms, as re searchers can rea- sonably expect rapid healing of the surgical wounds and minimal tag loss. Because of widespread conservation concerns (Wagner et al 2019), diverse madtom species are regularly targeted by surveys to inform management decisions. Previous efforts have demonstrated the effectiveness of artificial cover units as a method to passively describe madtom occurrence patterns and monitor populations relative to traditional sampling methods (Midway et al 2010a,b, Cope et al 2019.…”

“…The frecklebelly madtom is a small, non-game catfish that inhabits gravel shoals in large rivers and contributing tributaries in the southeastern USA (Shepard et al 1997). This species can be locally abundant (Wagner et al 2019), but declines have occurred throughout its native range (Shepard et al 1997, Piller et al 2004, Millican et al 2006, Bennett et al 2008. Although the frecklebelly madtom is now being considered for federal listing under the Endangered Species Act, the imperilment of this species has been recognized for more than a decade.…”

“…), a monophyletic group of small catfish endemic to North America, are considered at risk of extinction by state or federal authorities (Bennett et al 2008, Page et al 2013. Although madtom species are difficult to detect due to their nocturnal behaviors and cryptic body patterns, frequent surveys are conducted to monitor their conservation status and inform management decisions (Peoples & Frimpong 2011, Gibson-Reinemer et al 2016, Reid & Haxton 2017, Wagner et al 2019.…”

“…Representative knowledge of fish distributional patterns and population structure are essential for effective conservation decision making (Smith et al 2018). However, the effectiveness of traditional sampling efforts may poorly quantify status, occurrence, and population demographics for species that are difficult to detect (Hubert et al 2012, Schloesser et al 2012, Pregler et al 2015, including madtoms (Midway et al 2010a, Wagner et al 2019. The development of standardized, species-specific sampling protocols has decreased concerns for many sportfish species (Neumann & Allen 2007, Doyle et al 2008; however, alternative sampling methods are not often available for small-bodied nongame fishes.…”