Geology topics

C.T. Knight

Publications and source records attributed to C.T. Knight.

5 recordsLinked to original sources

USGS2010

Night sampling improves indices used for management of yellow perch in Lake Erie

Catch rate (catch per hour) was examined for age-0 and age-1 yellow perch, Perca flavescens (Mitchill), captured in bottom trawls from 1991 to 2005 in western Lake Erie: (1) to examine variation of catch rate among years, seasons, diel periods and their interactions; and (2) to determine whether sampling during particular diel periods improved the management value of CPH data used in models to project abundance of age-2 yellow perch. Catch rate varied with year, season and the diel period during which sampling was conducted as well as by the interaction between year and season. Indices of abundance of age-0 and age-1 yellow perch estimated from night samples typically produced better fitting models and lower estimates of age-2 abundance than those using morning or afternoon samples, whereas indices using afternoon samples typically produced less precise and higher estimates of abundance. The diel period during which sampling is conducted will not affect observed population trends but may affect estimates of abundance of age-0 and age-1 yellow perch, which in turn affect recommended allowable harvest. A field experiment throughout western Lake Erie is recommended to examine potential benefits of night sampling to management of yellow perch. Published 2010. The article is a US Government work and is in the public domain in the USA.

Fisheries Management and Ecology↗

USGS2006

Intercalibration of research survey vessels on Lake Erie

Fish abundance indices obtained from annual research trawl surveys are an integral part of fisheries stock assessment and management in the Great Lakes. It is difficult, however, to administer trawl surveys using a single vessel-gear combination owing to the large size of these systems, the jurisdictional boundaries that bisect the Great Lakes, and changes in vessels as a result of fleet replacement. When trawl surveys are administered by multiple vessel-gear combinations, systematic error may be introduced in combining catch-per-unit-effort (CPUE) data across vessels. This bias is associated with relative differences in catchability among vessel-gear combinations. In Lake Erie, five different research vessels conduct seasonal trawl surveys in the western half of the lake. To eliminate this systematic bias, the Lake Erie agencies conducted a side-by-side trawling experiment in 2003 to develop correction factors for CPUE data associated with different vessel-gear combinations. Correcting for systematic bias in CPUE data should lead to more accurate and comparable estimates of species density and biomass. We estimated correction factors for the 10 most commonly collected species age-groups for each vessel during the experiment. Most of the correction factors (70%) ranged from 0.5 to 2.0, indicating that the systematic bias associated with different vessel-gear combinations was not large. Differences in CPUE were most evident for vessels using different sampling gears, although significant differences also existed for vessels using the same gears. These results suggest that standardizing gear is important for multiple-vessel surveys, but there will still be significant differences in catchability stemming from the vessel effects and agencies must correct for this. With standardized estimates of CPUE, the Lake Erie agencies will have the ability to directly compare and combine time series for species abundance. ?? Copyright by the American Fisheries Society 2006.

North American Journal of Fisheries Management↗

USGS2005

A potential new energy pathway in Central Lake Erie: The round goby connection

Round gobies, invasive fish that entered Lake Erie in 1994, are altering energy, contaminant, and nutrient pathways. Our objective was to quantify how they alter energy pathways in the central basin of Lake Erie by describing their diet and identifying the degree to which predatory fish feed upon round gobies. We used bioenergetic models parameterized with data collected in the central basin between 1995 and 2002 to estimate the type and amount of prey eaten, the biomass accumulation rate for the round goby population, and a partitioning of the food energy into “new” energy derived from dreissenids as opposed to existing energy derived from zooplankton and non-dreissenid benthic prey. Mean (± SE) prey consumption peaked at 5.98 ± 2.17×10 4 tonnes wet mass in 1999 coincident with the maximum population size of 4.2 ± 1.5 billion round gobies. Zooplankton (40.2% by biomass) and dreissenid mussels (38.3%) dominated the prey consumed. Almost 90% of the zooplankton biomass was consumed by age-0 round gobies, while over 80% of the dreissenids were eaten by older ages. Standing stock biomass of round gobies ranged between 203 and 4,803 tonnes y −1 (interannual range), with an additional 475 to 8,943 tonnes of biomass accumulating through growth each year. Piscivorous fish showed an increasing reliance on round gobies as prey, with round gobies being the dominant prey fish in the diets of benthic-oriented predators. Hence, by being one of the few benthivores that exploit dreissenid mussels as prey, our analyses reveal that round gobies transfer new energy up the central Lake Erie food web.

Journal of Great Lakes Research↗

USGS2005

The impact of introduced round gobies (Neogobius melanostomus) on phosphorus cycling in central Lake Erie

We used an individual-based bioenergetic model to simulate the phosphorus flux of the round goby (Neogobius melanostomus) population in central Lake Erie during 1995-2002. Estimates of round goby diet composition, growth rates, and population abundance were derived from field sampling. As an abundant introduced fish, we predicted that round gobies would influence phosphorus cycling both directly, through excretion, and indirectly, through consumption of dreissenid mussels, whose high mass-specific phosphorus excretion enhances recycling. In 1999, when age-1+ round gobies reached peak abundance near 350 million (2.4 kg??ha-1), annual phosphorus excretion was estimated at 7 t (1.4 ?? 10-3 mg P??m-2??day -1). From an ecosystem perspective, however, round gobies excreted only 0.4% of the phosphorus needed by the benthic community for primary production. Indirectly, round gobies consumed <0.2% of dreissenid population biomass, indicating that round gobies did not reduce nutrient availability by consuming dreissenids. Compared with previous studies that have revealed introduced species to influence phosphorus cycling, round gobies likely did not attain a sufficiently high biomass density to influence phosphorus cycling in Lake Erie. ?? 2005 NRC Canada.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2002

Evaluation of fish sampling using rotenone in a navigation lock

Annual sampling in locks with rotenone has been a principal means of assessing fish populations in the commercially navigable portions of the Ohio River. Despite extensive use, sampling in locks with rotenone and interpretation of the data obtained have not been adequately evaluated. The purpose of our study was to determine the degree of inter- and intraseasonal variation in lock samples, estimate correction factors (CFs) for fish recovery rates, and compare lock samples to other fish collections from the navigational pools above and below the lock. Lock samples from all seasons had a greater proportion of pelagic and demersal fish than samples from the navigational pools, which contained greater proportions of littoral species. CF for non-recovery of fish were determined. Spring and summer lock collections yielded several more species and estimates of overall fish biomass were an order of magnitude higher than fall collections. Within season variation between lock samples was relatively low; however, variation in lock samples among seasons was high, equivalent to that seen among the annual samples from the 1980s. Thus, single-season sampling may not be adequate, and fall may be the least preferred season.

Fisheries Research↗