Mark T. Porath

Estimating Fish Body Condition with Quantile Regression

Abstract We used quantile regression to compare the body condition of walleye Sander vitreus and white bass Morone chrysops before (1980–1988) and after (1989–2004) the establishment of alewives Alosa pseudoharengus in Lake McConaughy, Nebraska. Higher quantiles (percentiles = 100% × quantiles (0, 1)) of weight (W) at the same total length (TL) were indicative of better body condition in an allometric growth model that included separate slopes and intercepts for the before and after groups. All quantiles of walleye weights by TL increased in the years after alewife introduction, ranging from 1.01 to 1.12 times weights in the years before alewife introduction, with greatest increases for the lower (<0.50) quantiles and greater TLs. Quantiles up to 0.25 (the lowest 25th percentiles) of white bass weights were reduced in years after alewife introduction for TLs less than 300 mm, ranging from 0.78 to 0.98 times weights in the years before alewife introduction. However, quantiles greater than or equal to 0.50 ...

Effects of Waterbody Type and Management Actions on Bluegill Growth Rates

Abstract Managers have conducted a number of activities to improve the growth rates of bluegill Lepomis macrochirus. However, attempts to compare the effectiveness of management actions often ignore basic differences in growth related to the type of water body in which populations reside. Bluegill age and growth data were collected from four different water body types in Nebraska between 1994 and 2001. Model analysis detected significant differences in the previous years growth increments by water body type. When compared with other water body types, growth increments were greater in Sandhill lakes for age-2 and age-3 bluegills and mean length at capture was greater for age −6 and −7 bluegills. Several significant age × management activity interactions were detected within water body types. The application of supplemental feed and the absence of gizzard shad Dorosoma cepedianum increased bluegill growth increments in borrow and sand– gravel mining pits, while in flood control reservoirs, the presence of ...

Impact of Alewife Introduction on Walleye and White Bass Condition in Lake McConaughy, Nebraska, 1980-1995

Abstract We examined relative weight (W r) relationships of walleye Stizostedion vitreum and white bass Morone chrysops before and after the addition of alewife Alosa pseudoharengus in Lake McConaughy, Nebraska, where gizzard shad Dorosoma cepedianum had been the primary prey. Walleyes and white bass were collected in fall gillnetting surveys from 1980 to 1995. A general linear model was constructed to determine the least-squares means of walleye and white bass W rs by length category and year. Contrast statements were used to test for significant differences in the annual W rs of walleye and white bass population length categories before and after the establishment of alewives. The annual mean W rs of walleyes of stock to quality (S-Q), quality to preferred (Q-P), and preferred to memorable (P-M) lengths and Q-P-length white bass increased significantly, whereas that of S-Q-length and P-M-length white bass decreased significantly after 1988. The introduction of alewives changed the body condition of wall...

Flathead Catfish Habitat Use and Predation on a Stunted White Perch Population in Branched Oak Reservoir, Nebraska

ABSTRACT Flathead catfish (Pylodictis olivaris) were stocked for recreational angling in Branched Oak Reservoir, Nebraska in 1981 and subsequently in 1994 through 1996. During 1999 and 2000, additional fish were stocked to act as predators on an abundant white perch (Morone americana) population. We studied food habits and habitat use of flathead catfish to evaluate their utilization of white perch. Flathead catfish were sampled by electrofishing every other week from May through September of 2001. Flathead catfish were separated into five size classes and pulsed gastric lavage was performed on up to six individuals per size class. One flathead catfish per 250 mm size class and ten white perch (150–175 mm) were placed in each of eight experimental feeding enclosures to establish baseline consumption rates. Seventy four percent of all captured flathead catfish were found near rocky habitat, which comprised only 25% of the reservoir shoreline. Flathead catfish consumed mostly white perch and crayfish. Flathead catfish confined in enclosures fed on white perch at a lower than expected rate.

Reservoir Rehabilitations: Seeking the Fountain of Youth

Aging of reservoirs alters the functions, and associated services, of these systems through time. The goal of habitat rehabilitation is often to alter the trajectory of the aging process such that the duration of the desired state is prolonged. There are two important characteristics in alteration of the trajectory—the amplitude relative to current state and the subsequent rate of change, or aging—that ultimately determine the duration of extension for the desired state. Rehabilitation processes largely fall into three main categories: fish community manipulation, water quality manipulation, and physical habitat manipulation. We can slow aging of reservoirs through carefully implemented management actions, perhaps even turning back the hands of time, but we cannot stop aging. We call for new, innovative perspectives that incorporate an understanding of aging processes in all steps of rehabilitation of reservoirs, especially in planning and assessing.

Evaluating Supplemental Feeding of a Bluegill Population and Validating Species Utilization by Application of a Toxic Fish Food

ABSTRACT Mechanical fish feeders were placed throughout the littoral zone of a flood control reservoir and operated for four growing seasons to improve growth rates of bluegill. Analysis of previous year growth increments suggested that only age 5 bluegill benefited from the supplemental feeding program. To validate utilization by the target species, toxic fish bait was applied through the feeders. Gizzard shad were the only species captured through this method. These results suggest that the presence of gizzard shad may reduce the effectiveness of supplemental feeding programs for bluegill.

Using standardized fishery data to inform rehabilitation efforts

Abstract Lakes and reservoirs progress through an aging process often accelerated by human activities, resulting in degradation or loss of ecosystem services. Resource managers thus attempt to slow or reverse the negative effects of aging using a myriad of rehabilitation strategies. Sustained monitoring programs to assess the efficacy of rehabilitation strategies are often limited; however, long-term standardized fishery surveys may be a valuable data source from which to begin evaluation. We present 3 case studies using standardized fishery survey data to assess rehabilitation efforts stemming from the Nebraska Aquatic Habitat Plan, a large-scale program with the mission to rehabilitate waterbodies within the state. The case studies highlight that biotic responses to rehabilitation efforts can be assessed, to an extent, using standardized fishery data; however, there were specific areas where minor increases in effort would clarify the effectiveness of rehabilitation techniques. Management of lakes and reservoirs can be streamlined by maximizing the utility of such datasets to work smarter, not harder. To facilitate such efforts, we stress collecting both biotic (e.g., fish lengths and weight) and abiotic (e.g., dissolved oxygen, pH, and turbidity) data during standardized fishery surveys and designing rehabilitation actions with an appropriate experimental design.