Geology topics

James R. Bence

Publications and source records attributed to James R. Bence.

26 records · Page 2Linked to original sources

USGS2011

Population dynamics of Lake Ontario lake trout during 1985-2007

Lake trout Salvelinus namaycush were extirpated from Lake Ontario circa 1950 owing to commercial and recreational fishing, predation by sea lampreys Petromyzon marinus , and habitat degradation. Since the 1970s, substantial efforts have been devoted to reestablishing a self-sustaining population through stocking, sea lamprey control, and harvest reduction. Although a stocking-supported population has been established, only limited natural reproduction has been detected. Since the 1990s, surveys have indicated a continuing decline in overall abundance despite fairly static stocking levels. We constructed a statistical catch-at-age model to describe the dynamics of Lake Ontario lake trout from 1985 to 2007 and explore what factor(s) could be causing the declines in abundance. Model estimates indicated that abundance had declined by approximately 76% since 1985. The factor that appeared most responsible for this was an increase in age-1 natural mortality rates from approximately 0.9 to 2.5 between 1985 and 2002. The largest source of mortality for age-2 and older fish was sea lamprey predation, followed by natural and recreational fishing mortality. Exploitation was low, harvest levels being uncertain and categorized by length rather than age. Accurate predictions of fishery harvest and survey catch per unit effort were obtained despite low harvest levels by using atypical data (e.g., numbers stocked as an absolute measure of recruitment) and a flexible modeling approach. Flexible approaches such as this might allow similar assessments for a wide range of lightly exploited stocks. The mechanisms responsible for declining age-1 lake trout survival are unknown, but the declines were coincident with an increase in the proportion of stocked fish that were of the Seneca strain and a decrease in the overall stocking rate. It is possible that earlier studies suggesting that Seneca strain lake trout would be successful in Lake Ontario are no longer applicable given the large ecosystem changes that have occurred subsequent to invasion by dreissenid mussels.

North American Journal of Fisheries Management↗

USGS2010

Dreissenid mussels are not a "dead end" in Great Lakes food webs

Dreissenid mussels have been regarded as a “dead end” in Great Lakes food webs because the degree of predation on dreissenid mussels, on a lakewide basis, is believed to be low. Waterfowl predation on dreissenid mussels in the Great Lakes has primarily been confined to bays, and therefore its effects on the dreissenid mussel population have been localized rather than operating on a lakewide level. Based on results from a previous study, annual consumption of dreissenid mussels by the round goby (Neogobius melanostomus) population in central Lake Erie averaged only 6 kilotonnes (kt; 1 kt = one thousand metric tons) during 1995–2002. In contrast, our coupling of lake whitefish (Coregonus clupeaformis) population models with a lake whitefish bioenergetics model revealed that lake whitefish populations in Lakes Michigan and Huron consumed 109 and 820 kt, respectively, of dreissenid mussels each year. Our results indicated that lake whitefish can be an important predator on dreissenid mussels in the Great Lakes, and that dreissenid mussels do not represent a “dead end” in Great Lakes food webs. The Lake Michigan dreissenid mussel population has been estimated to be growing more than three times faster than the Lake Huron dreissenid mussel population during the 2000s. One plausible explanation for the higher population growth rate in Lake Michigan would be the substantially higher predation rate by lake whitefish on dreissenid mussels in Lake Huron.

Journal of Great Lakes Research↗

USGS2005

Ecology of the Lake Huron fish community, 1970-1999

We review the status of the Lake Huron fish community between 1970 and 1999 and explore the effects of key stressors. Offshore waters changed little in terms of nutrient enrichment, while phosphorus levels declined in inner Saginaw Bay. Introduced mussels ( Dreissena spp.) proliferated and may have caused a decline in Diporeia spp. This introduction could have caused a decline in lake whitefish ( Coregonus clupeaformis ) growth and condition, with serious repercussions for commercial fisheries. Bythotrephes , an exotic predatory cladoceran, and other new exotics may be influencing the fish community. Sea lampreys ( Petromyzon marinus ) remained prevalent, but intensive control efforts on the St. Mary's River may reduce their predation on salmonines. Overfishing was less of a problem than in the past, although fishing continued to reduce the amount of lake trout ( Salvelinus namaycush ) spawning biomass resulting from hatchery-reared fish planted to rehabilitate this species. Massive stocking programs have increased the abundance of top predators, but lake trout were rehabilitated in only one area. Successful lake trout rehabilitation may require lower densities of introduced pelagic prey fish than were seen in the 1990s, along with continued stocking of hatchery-reared lake trout and control of sea lamprey. Such reductions in prey fish could limit Pacific salmon ( Oncorhynchus spp.) fisheries.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2003

Estimating parasitic sea lamprey abundance in Lake Huron from heterogenous data sources

The Great Lakes Fishery Commission uses time series of transformer, parasitic, and spawning population estimates to evaluate the effectiveness of its sea lamprey ( Petromyzon marinus ) control program. This study used an inverse variance weighting method to integrate Lake Huron sea lamprey population estimates derived from two estimation procedures: 1) prediction of the lake-wide spawning population from a regression model based on stream size and, 2) whole-lake mark and recapture estimates. In addition, we used a re-sampling procedure to evaluate the effect of trading off sampling effort between the regression and mark-recapture models. Population estimates derived from the regression model ranged from 132,000 to 377,000 while mark-recapture estimates of marked recently metamorphosed juveniles and parasitic sea lampreys ranged from 536,000 to 634,000 and 484,000 to 1,608,000, respectively. The precision of the estimates varied greatly among estimation procedures and years. The integrated estimate of the mark-recapture and spawner regression procedures ranged from 252,000 to 702,000 transformers. The re-sampling procedure indicated that the regression model is more sensitive to reduction in sampling effort than the mark-recapture model. Reliance on either the regression or mark-recapture model alone could produce misleading estimates of abundance of sea lampreys and the effect of the control program on sea lamprey abundance. These analyses indicate that the precision of the lakewide population estimate can be maximized by re-allocating sampling effort from marking sea lampreys to trapping additional streams.

Journal of Great Lakes Research↗

USGS2003

Classifying sea lamprey marks on Great Lakes lake trout: observer agreement, evidence on healing times between classes and recommendations for reporting of marking statistics

In 1997 and 1998 two workshops were held to evaluate how consistent observers were at classifying sea lamprey ( Petromyzon marinus ) marks on Great Lakes lake trout ( Salvelinus namaycush ) as described in the King classification system. Two trials were held at each workshop, with group discussion between trials. Variation in counting and classifying marks was considerable, such that reporting rates for A1–A3 marks varied two to three-fold among observers of the same lake trout. Observer variation was greater for classification of healing or healed marks than for fresh marks. The workshops highlighted, as causes for inconsistent mark classification, both departures from the accepted protocol for classifying marks by some agencies, and differences in how sliding and multiple marks were interpreted. Group discussions led to greater agreement in classifying marks. We recommend ways to improve the reliability of marking statistics, including the use of a dichotomous key to classify marks. Laboratory data show that healing times of marks on lake trout were much longer at 4°C and 1°C than at 10°C and varied greatly among individuals. Reported A1–A3 and B1–B3 marks observed in late summer and fall collections likely result from a mixture of attacks by two year classes of sea lamprey. It is likely that a substantial but highly uncertain proportion of attacks that occur in late summer and fall lead to marks that are classified as A1–A3 the next spring. We recommend additional research on mark stage duration.

Journal of Great Lakes Research↗

USGS2003

Modeling time-varying growth using a generalized von Bertalanffy model with application to bloater (Coregonus hoyi) growth dynamics in Lake Michigan

A concurrent increase in lakewide abundance and decrease in size-at-age of bloater ( Coregonus hoyi ) in Lake Michigan have suggested density-dependent growth regulation. We investigated these temporal patterns by fitting a dynamic von Bertalanffy model and lengthweight relationship with time-varying parameters to mean length- and weight-at-ages (ages 17) from annual surveys (1965-1999). We modeled yearling length, asymptotic size ( L &permil;), and the parameters of a power relationship between mean weight and mean length (α and β) as changing slowly over time using a random walk model. The Brody growth coefficient ( k ) was modeled as a linear function of L &permil; with year-specific random deviations. Our results support a positive relationship between L &permil; and k , indicating that under conditions supporting larger asymptotic lengths, individuals approach the asymptote more rapidly. We explored the relationship between year-specific growth parameters and indices of lakewide bloater abundance and found evidence of density-dependent growth. However, in the most recent years, L &permil; and yearling length have remained low in Lake Michigan despite low bloater abundances, suggesting the occurrence of a fundamental shift in the food web.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2002

Measurement error associated with surveys of fish abundance in Lake Michigan

In fisheries, imprecise measurements in catch data from surveys add uncertainty to the results of fishery stock assessments. The USGS Great Lakes Science Center (GLSC) began to survey the fall fish community of Lake Michigan in 1962 with bottom trawls. The measurement error was evaluated at the level of individual tows for nine fish species collected in this survey by applying a measurementerror regression model to replicated trawl data. It was found that the estimates of measurement-error variance ranged from 0.37 (deepwater sculpin, Myoxocephalus thompsoni ) to 1.23 (alewife, Alosa pseudoharengus ) on a logarithmic scale corresponding to a coefficient of variation = 66 to 156%. The estimates appeared to increase with the range of temperature occupied by the fish species. This association may be a result of the variability in the fall thermal structure of the lake. The estimates may also be influenced by other factors, such as pelagic behavior and schooling. Measurement error might be reduced by surveying the fish community during other seasons and/or by using additional technologies, such as acoustics. Measurement-error estimates should be considered when interpreting results of assessments that use abundance information from USGS-GLSC surveys of Lake Michigan and could be used if the survey design was altered. This study is the first to report estimates of measurement-error variance associated with this survey.

Lake Michigan↗

USGS2002

Dynamics of the Lake Michigan food web, 1970-2000

Herein, we document changes in the Lake Michigan food web between 1970 and 2000 and identify the factors responsible for these changes. Control of sea lamprey ( Petromyzon marinus ) and alewife ( Alosa pseudoharengus ) populations in Lake Michigan, beginning in the 1950s and 1960s, had profound effects on the food web. Recoveries of lake whitefish ( Coregonus clupeaformis ) and burbot ( Lota lota ) populations, as well as the buildup of salmonine populations, were attributable, at least in part, to sea lamprey control. Based on our analyses, predation by salmonines was primarily responsible for the reduction in alewife abundance during the 1970s and early 1980s. In turn, the decrease in alewife abundance likely contributed to recoveries of deepwater sculpin ( Myoxocephalus thompsoni ), yellow perch ( Perca flavescens ), and burbot populations during the 1970s and 1980s. Decrease in the abundance of all three dominant benthic macroinvertebrate groups, including Diporeia , oligochaetes, and sphaeriids, during the 1980s in nearshore waters ( 50 m deep) of Lake Michigan, was attributable to a decrease in primary production linked to a decline in phosphorus loadings. Continued decrease in Diporeia abundance during the 1990s was associated with the zebra mussel ( Dreissena polymorpha ) invasion, but specific mechanisms for zebra mussels affecting Diporeia abundance remain unidentified.

Canadian Journal of Fisheries and Aquatic Sciences↗