Andrew W. Hafs

Smallmouth Bass Summer Habitat Use, Movement, and Survival in Response to Low Flow in the Illinois Bayou, Arkansas

Abstract The southwestern edge of the natural range of smallmouth bass Micropterus dolomieu contains streams that become disconnected pools during summer primarily owing to hydrogeologic conditions, including high evapotranspiration rates. These conditions may complicate fisheries management by affecting fish behavior or mortality rates. The objectives of this study were to characterize summer habitat use by smallmouth bass, estimate the changes in the extent of available habitat, describe summer movement patterns, and estimate summer survival rates. Radio transmitters were implanted into 60 smallmouth bass during May 2006, and the fish were tracked until October in the forks of the Illinois Bayou, which drains a portion of the Ozark National Forest. Habitat characteristics were measured as the summer progressed, and during this time most riffle–run habitat dried completely, resulting in a series of disconnected pools. The decreases in wetted area exceeded 55% in certain 2-km study reaches; however, small...

Efficiency of Gastric Lavage on Age-0 Brook Trout and the Influence on Growth and Survival

Abstract Accurate knowledge of food webs is important in understanding aquatic ecology. One common way to determine the food web structure of an aquatic ecosystem is to perform stomach content analysis. Gastric lavage has developed into the preferred method for collecting dietary data from live fish. The objective of this study was to determine the efficiency of gastric lavage for age-0 brook trout Salvelinus fontinalis. Also, to assess the effects on short- and long-term growth and survival, age-0 brook trout were monitored for 2 months following the gastric lavage procedure. Gastric lavage was extremely efficient (>97% of dry weight; >98% by number) at removing Ephemeroptera, Plecoptera, and Trichoptera larvae fed live to age-0 brook trout larger than 50 mm total length (TL). Neither growth nor survival was significantly influenced by gastric lavage. Long-term survival was excellent (94%) and did not differ from that of control fish. Gastric lavage is thus an efficient, safe method for stomach content a...

Influences of Acid Mine Drainage and Thermal Enrichment on Stream Fish Reproduction and Larval Survival

Abstract Potential effects of acid mine drainage (AMD) and thermal enrichment on the reproduction of fishes were investigated through a larval-trapping survey in the Stony River watershed, Grant County, WV. Trapping was conducted at seven sites from 26 March to 2 July 2004. Overall larval catch was low (379 individuals in 220 hours of trapping). More larval White Suckers were captured than all other species. Vectors fitted to nonparametric multidimensional scaling ordinations suggested that temperature was highly correlated to fish communities captured at our sites. Survival of larval Fathead Minnows was examined in situ at six sites from 13 May to 11 June 2004 in the same system. Larval survival was lower, but not significantly different between sites directly downstream of AMD-impacted tributaries (40% survival) and non-AMD sites (52% survival). The lower survival was caused by a significant mortality event at one site that coincided with acute pH depression in an AMD tributary immediately upstream of the site. Results from a Cox proportional hazard test suggests that low pH is having a significant negative influence on larval fish survival in this system. The results from this research indicate that the combination of low pH events and elevated temperature are negatively influencing the larval fish populations of the Stony River watershed. Management actions that address these problems would have the potential to substantially increase both reproduction rates and larval survival, therefore greatly enhancing the fishery.

Bioelectrical Impedance Analysis: A New Tool for Assessing Fish Condition

Bioelectrical impedance analysis (BIA) is commonly used in human health and nutrition fields but has only recently been considered as a potential tool for assessing fish condition. Once BIA is calibrated, it estimates fat/moisture levels and energy content without the need to kill fish. Despite the promise held by BIA, published studies have been divided on whether BIA can provide accurate estimates of body composition in fish. In cases where BIA was not successful, the models lacked the range of fat levels or sample sizes we determined were needed for model success (range of dry fat levels of 29%, n = 60, yielding an R2 of 0.8). Reduced range of fat levels requires an increased sample size to achieve that benchmark; therefore, standardization of methods is needed. Here we discuss standardized methods based on a decade of research, identify sources of error, discuss where BIA is headed, and suggest areas for future research.

Quantification of Walleye Spawning Substrate in a Northern Minnesota River using Side-Scan Sonar

AbstractEvaluating aquatic habitats is an important component of many ecological studies and natural resource assessments, but traditional habitat evaluations are time and labor intensive and do not provide continuous data. Side-scan sonar (SSS) can provide a low-cost method that collects continuous aquatic habitat data. We used SSS mapping to quantify suitable spawning substrate available to Walleye Sander vitreus during the 2015 spring spawning migration in a 10.8-km reach of the Tamarac River, Minnesota. The SSS map had 78.0% agreement with reference points classified in the field, and the proportion of reference points predicted as suitable using the SSS map was not significantly different than the proportion of reference points observed to be suitable. Suitable substrate for Walleye spawning comprised 8.4% (26,392 m2) of the total area mapped. The estimated number of females that suitable substrate could support was lower than the number that likely migrate up the Tamarac River and suggests that acce...

Seasonal Changes in Condition of Appalachian Brook Trout

AbstractReliable fish condition estimates help managers better understand ecosystem population dynamics. Therefore, our study objectives were to measure seasonal changes in percent dry weight and energy density (physiological-based measures of condition) of stream-dwelling Appalachian Brook Trout Salvelinus fontinalis, field-validate bioelectrical impedance analysis (BIA) models, and compare reliability of BIA and morphometric-based estimates of condition. Percent dry weight was highly correlated to energy density (R2 = 0.93; J/g wet weight = −1,803.5 + 286.43 ∙ [percent dry weight]), and the relationship was clearly different from those published previously for other salmonids. Significant seasonal changes in adult Brook Trout condition were observed and likely related to energy depletion from reproduction and changes in terrestrial invertebrate consumption. Adult percent dry weight peaked in early September and was lowest in February. Age-0 fish did not have large changes in measured condition between s...