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Mary C. Fabrizio

Publications and source records attributed to Mary C. Fabrizio.

At least 19 recordsLinked to original sources
USGS2025

Management strategy evaluation to assess trade-offs associated with invasive Blue Catfish fisheries and predation impacts

Objective Many species are intentionally introduced beyond their native range to provide benefits to humans (e.g., food, recreation, or biocontrol). However, introduced species can become invasive and can harm native species, prompting resource managers to explore options to simultaneously conserve native biota and enhance fishing opportunities. Management of Chesapeake Bay Blue Catfish Ictalurus furcatus is complicated because the species supports a renowned trophy fishery and commercial and recreational harvest but also negatively affects native species. Consequently, there is uncertainty and disagreement on how to balance trade-offs associated with varying stakeholder interests. Methods We used a management strategy evaluation to project Blue Catfish population dynamics into the future under different fishery policies to understand whether fishery yield, trophy fishing opportunities, and predation on the economically and ecologically important blue crab Callinectes sapidus could be optimized in the James River, a Chesapeake Bay subestuary. Results Simulated population trajectories indicated that objectives related to maintaining fisheries and conserving prey populations were in conflict. Policies that increased the yield and abundance of trophy-size Blue Catfish (≥100 cm total length) generally increased predation on the blue crab, which supports a valuable fishery. Intense harvest of smaller length-classes and protection of larger Blue Catfish yielded outcomes in which trophy fish abundance increased and blue crab predation declined compared to baseline conditions. However, these outcomes were generally associated with lower Blue Catfish yields after 25 years. There were zero scenarios in which the fishery yield increased and blue crab predation decreased after 25 years. Policies limiting the harvest of small Blue Catfish resulted in large population abundances, suggesting that reducing the abundance of small fish could be important for reducing impacts on native species. Conclusions This study supports the importance of management planning to develop objectives and performance measures based on an improved understanding of trade-offs associated with harvest management for a nonnative fish with economic value.

Virginia↗
USGS2022

A size-based stock assessment model for invasive blue catfish in a Chesapeake Bay sub-estuary during 2001–2016

Stock assessment modeling provides a means to estimate the population dynamics of invasive fishes and may do so despite data limitations. Blue catfish ( Ictalurus furcatus ) were introduced to the Chesapeake Bay watershed to support recreational fisheries but also consume species of conservation need and economic importance. To assess management tradeoffs, managers need to understand the current status of the population and anticipate future population abundance and trends. A Bayesian size-based stock assessment model was used to estimate blue catfish abundance, fishing mortality, and size structure over time (2001–2016) in the tidal James River. The model estimated population size increases until around 2006, with declines in total abundance after 2011 and large blue catfish (≥80 cm total length) after 2001. These first estimates of blue catfish population dynamics in the Chesapeake Bay region provide inputs for projection models to evaluate prospective management actions and identify monitoring needs.

Virginia↗
USGS2002

Procedures for formation of composite samples from segmented populations

We used a simulation approach to investigate the implication of two methods of forming composite samples to characterize segmented populations. We illustrate the case where the weight of individual segments varies randomly, a situation common with fish samples. Composite samples from segments such as whole fish or muscle tissue should be formed by homogenizing each segment separately and combining equal-sized portions randomly drawn from each homogenate. This approach permits unbiased estimation of the mean concentration per fish. Estimates of mean contaminant concentration varied little with variation in the number of composite samples analyzed or with composite size (number of segments in a composite sample). However, for a fixed number of composite samples, the precision of the variance estimate increases as composite size increased. In addition, for a fixed number of composites, the estimate of the variance stabilized as more segments were included in the composite samples. Estimates of the variance among fish or other population segments can be recovered using appropriate compositing procedures and specially-designed studies.

Environmental Science & Technology↗
USGS2001

Dynamics of individual growth in a recovering population of lake trout (Salvelinus namaycush)

In 1976, the Wisconsin Department of Natural Resources established a refuge for a nearly depleted population of lake trout (Salvelinus namaycush) at Gull Island Shoal, Lake Superior. The refuge was intended to reduce fishing mortality by protecting adult lake trout. We examined the growth dynamics of these lake trout during the period of recovery by comparing estimates of ndividual growth before and after the refuge was established. Our estimates are based on an annual mark-recapture survey conducted at the spawning area since 1969. We developed a model that allowed mean growth rates to differ among individuals of different sizes and that accommodated variation in growth rates of individuals of the same size. Likelihood ratio tests were used to determine if the mean growth increments of lake trout changed ater the refuge was established. Our results suggest that growth of mature lake trout (particularly wild fish) decreased significantly in the postrefuge period. This decreased growth may have been associated with a reduction in food availability. We also observed reductions in growth as wild fish grew older and larger, which suggests that the growth of these fish may be adequately approximated by a von Bertalanffy growth model if it becomes possible to obtain accurate ages.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2000

Using linear models with correlated errors to analyze changes in abundance of Lake Michigan fishes: 1973-1992

We examined annual changes in relative abundance of Lake Michigan fishes using linear models with correlated errors in space and time. Abundance of bloater ( Coregonus hoyi ), deepwater sculpin ( Myoxocephalus thompsoni ), slimy sculpin ( Cottus cognatus ), alewife ( Alosa pseudoharengus ), and rainbow smelt ( Osmerus mordax ) was monitored with bottom trawls at 10 discrete depths (between 18 and 110 m) off eight fixed ports from 1973 to 1992. The model describing abundance included fixed effects of year, port, depth, and interaction terms as well as quadratic and cubic effects of year and depth because changes in abundance were not strictly linear. Observed temporal trends in abundance varied with species and depth. Additionally, trends in alewife and slimy sculpin abundances depended on port. Cubic trends in the abundance of bloater and quadratic trends in deepwater sculpin and rainbow smelt abundances were similar among ports, permitting lakewide inferences for these species. Mean bloater abundance was low throughout the 1970s, increased during the 1980s, and reached high levels by 1990. Mean abundances of deepwater sculpin and rainbow smelt increased from 1973 to the mid-1980s and declined thereafter. The linear model with correlated errors can be readily applied to repeated-measures data from other fixed-station fishery surveys and is appropriate for data exhibiting spatial and temporal autocorrelations.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1999

Predation on lake trout eggs and fry: A modeling approach

A general model was developed to examine the effects of multiple predators on survival of eggs and fry of lake trout, Salvelinus namaycush , associated with spawning reefs. Three kinds of predation were simulated: epibenthic egg predators consuming eggs on the substrate surface during spawning, interstitial egg predators that can move in rocky substrate and consume incubating eggs, and fry predators. Also simulated was the effect of water temperature on predation rates. The model predicted that interstitial predation on eggs accounted for most (76 to 81%) of the predation on early life history stages of lake trout; epibenthic egg predation (12 to 19%) and fry predation (0 to 12%) had less effect on lake trout survival. Initial predation conditions chosen for the model were: epibenthic egg predation peaked at 2 eggs/m 2 /d over 30 d, interstitial egg predation at 2 eggs/m 2 /d over 180 d, and fry predation at 1 fry/m 2 /d over 60 d. With a starting egg density of 100 eggs/m 2 and initial predation conditions, no lake trout were estimated to survive to swim-up. At egg densities of 250 eggs/m 2 , 36% of the lake trout survived. At the highest egg densities examined, 500 to 1,000 eggs/m 2 , estimated survival increased to about 70 to 80%. Simulated survival rates of lake trout decreased dramatically as predation rate increased but were not as sensitive to increases in the duration of predation.

Journal of Great Lakes Research↗
USGS1999

Modeling data from double-tagging experiments to estimate heterogeneous rates of tag shedding in lake trout (Salvelinus namaycush)

Data from mark-recapture studies are used to estimate population rates such as exploitation, survival, and growth. Many of these applications assume negligible tag loss, so tag shedding can be a significant problem. Various tag shedding models have been developed for use with data from double-tagging experiments, including models to estimate constant instantaneous rates, time-dependent rates, and type I and II shedding rates. In this study, we used conditional (on recaptures) multinomial models implemented using the program SURVIV (G.C. White. 1983. J. Wildl. Manage. 47: 716-728) to estimate tag shedding rates of lake trout (Salvelinus namaycush) and explore various potential sources of variation in these rates. We applied the models to data from several long-term double-tagging experiments with Lake Superior lake trout and estimated shedding rates for anchor tags in hatchery-reared and wild fish and for various tag types applied in these experiments. Estimates of annual tag retention rates for lake trout were fairly high (80-90%), but we found evidence (among wild fish only) that retention rates may be significantly lower in the first year due to type I losses. Annual retention rates for some tag types varied between male and female fish, but there was no consistent pattern across years. Our estimates of annual tag retention rates will be used in future studies of survival rates for these fish.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1998

Longevity of Lake Superior lake trout

The age structure of mature lake trout Salvelinus namaycush from the Wisconsin waters of Lake Superior increased following a population recovery that has taken place since the 1960s. As the population aged, it became apparent that scales were unreliable aging structures. Beginning in 1986, we examined both scale and sagittal otolith ages from tagged fish with a known period at liberty. We found large discrepancies in scale and sagittal otolith ages of mature fish, such that scale ages were biased low. We estimated lake trout living up to 42 years, which is greater than previously reported from Lake Superior. Investigators studying lake trout population dynamics in the Great Lakes should be aware that lake trout can live longer than previously thought.

North American Journal of Fisheries Management↗
USGS1997

Assessing prey fish populations in Lake Michigan: Comparison of simultaneous acoustic-midwater trawling with bottom trawling

The Lake Michigan fish community has been monitored since the 1960s with bottom trawls, and since the late 1980s with acoustics and midwater trawls. These sampling tools are limited to different habitats: bottom trawls sample fish near bottom in areas with smooth substrates, and acoustic methods sample fish throughout the water column above all substrate types. We compared estimates of fish densities and species richness from daytime bottom trawling with those estimated from night-time acoustic and midwater trawling at a range of depths in northeastern Lake Michigan in summer 1995. We examined estimates of total fish density as well as densities of alewife Alosa pseudoharengus (Wilson), bloater Coregonus hoyi (Gill), and rainbow smelt Osmerus mordax (Mitchell) because these three species are the dominant forage of large piscivores in Lake Michigan. In shallow water (18 m), we detected more species but fewer fish (in fish/ha and kg/ha) with bottom trawls than with acoustic-midwater trawling. Large aggregations of rainbow smelt were detected by acoustic-midwater trawling at 18 m and contributed to the differences in total fish density estimates between gears at this depth. Numerical and biomass densitites of bloaters from all depths were significantly higher when based on bottom trawl samples than on acoustic-midwater trawling, and this probably contributed to the observed significant difference between methods for total fish densities (kg/ha) at 55 m. Significantly fewer alewives per ha were estimated from bottom trawling than from acoustics-midwater trawling at 55 m, and in deeper waters, no alewives were taken by bottom trawling. The differences detected between gears resulted from alewife, bloater, and rainbow smelt vertical distributions, which varied with lake depth and time of day. Because Lake Michigan fishes are both demersal and pelagic, a single sampling method cannot be used to completely describe characteristics of the fish community.

Fisheries Research↗
USGS1997

An empirical comparison of stock identification techniques applied to striped bass

Managers of migratory striped bass stocks that mix along the Atlantic coast of the USA require periodic estimates of the relative contributions of the individual stocks to coastal mixed- stock fisheries; however, to date, a standard approach has not been adopted. We compared the performances of alternative stock identification approaches, using samples taken from the same sets of fish. Reference (known) samples were collected from three Atlantic coast spawning systems: the Hudson River, Chesapeake Bay, and the Roanoke River. Striped bass of mixed-stock origin were collected from eastern Long Island, New York, and were used as test (unknown) samples. The approaches applied were discriminant analysis of morphometric data and of meristic data, logistic regression analysis of combined meristic and morphometric data, discriminant analysis of scale-shape features, discriminant analysis of immunoassay data, and mixed-stock analysis of mitochondrial DNA (mtDNA) data. Overall correct classification rates of reference samples ranged from 94% to 66% when just the Hudson and Chesapeake stocks were considered and were comparable when the Chesapeake and Roanoke stocks were grouped as the ''southern'' stock. When all three stocks were treated independently, correct classification rates ranged from 82% to 49%. Despite the moderate range in correct classification rates, bias due to misallocation was relatively low for all methods, suggesting that resulting stock composition estimates should be fairly accurate. However, relative contribution estimates for the mixed-stock sample varied widely (e.g., from 81% to 47% for the Hudson River stock, when only the Hudson River and Chesapeake Bay stocks were considered). Discrepancies may be related to the reliance by all of these approaches (except mtDNA) on phenotypic features. Our results support future use of either a morphometrics-based approach (among the phenotypic methods) or a genotypic approach based on mtDNA analysis. We further recommend a conservative strategy of reliance on a single approach in tracking changes in relative contributions of striped bass stocks to coastal fisheries.

Transactions of the American Fisheries Society↗
USGS1997

Survival rates of adult lake trout in northwestern Lake Michigan, 1983-1993

The restoration of lake trout Salvelinus namaycush in Lake Michigan has been an elusive goal of resource management agencies in the Great Lakes region. In this study, we estimated annual survival rates of adult lake trout from an area in northwestern Lake Michigan known as the Clay Banks refuge. We tagged and recaptured fish with gill nets during the fall spawning season ( N = 12,175; 1983–1989 and 1991–1993) and with pound nets in the spring ( N = 52,035; 1984–1990 and 1992–1993). We fit Cormack–Jolly–Seber models to the two sets of data. We had insufficient data to analyze annual differences in survival rates of fall-tagged fish, but we were able to estimate an overall annual survival rate of 0.67. Annual survival rates of spring-tagged fish varied between 0.53 and 0.88 and increased after 1987–1988. In addition to the mark–recapture studies, we analyzed catch rates of lake trout from gill-net and pound-net surveys to estimate survival rates using catch curve analyses; these annual rates were generally lower than those estimated from mark–recapture analyses of tagged fish. However, survival rates of lake trout from the Clay Banks refuge appeared to meet the minimum rate believed necessary for restoration of this species in Lake Michigan. Furthermore, adult survival rates have been increasing in recent years, and lake trout restoration in Lake Michigan is not hampered by low survival of adult fish. We hypothesize that the recent decrease in abundance of adult lake trout is primarily due to decreases in survival rates of lake trout younger than 6 years.

North American Journal of Fisheries Management↗
USGS1996

Comparison of three nonlinear models to describe long-term tag shedding by lake trout

We estimated long-term tag-shedding rates for lake trout Salvelinus namaycush using two existing models and a model we developed to account for the observed permanence of some tags. Because tag design changed over the course of the study, we examined tag-shedding rates for three types of numbered anchor tags (Floy tags FD-67, FD-67C, and FD-68BC) and an unprinted anchor tag (FD-67F). Lake trout from the Gull Island Shoal region, Lake Superior, were double-tagged, and subsequent recaptures were monitored in annual surveys conducted from 1974 to 1992. We modeled tag-shedding rates, using time at liberty and probabilities of tag shedding estimated from fish released in 1974 and 1978–1983 and later recaptured. Long-term shedding of numbered anchor tags in lake trout was best described by a nonlinear model with two parameters: an instantaneous tag-shedding rate and a constant representing the proportion of tags that were never shed. Although our estimates of annual shedding rates varied with tag type (0.300 for FD-67, 0.441 for FD-67C, and 0.656 for FD-68BC), differences were not significant. About 36% of tags remained permanently affixed to the fish. Of the numbered tags that were shed (about 64%), two mechanisms contributed to tag loss: disintegration and dislodgment. Tags from about 11% of recaptured fish had disintegrated, but most tags were dislodged. Unprinted tags were shed at a significant but low rate immediately after release, but the long-term, annual shedding rate of these tags was only 0.013. Compared with unprinted tags, numbered tags dislodged at higher annual rates; we hypothesized that this was due to the greater frictional drag associated with the larger cross-sectional area of numbered tags.

Transactions of the American Fisheries Society↗
USGS1996

Commercial Fisheries Surveys

In this chapter, we describe methods for sampling commercial fisheries and identify factors affecting the design of sampling plans. When sampled properly, commercial fisheries can provide important information on the response of aquatic organisms to exploitation; such information can be used by management agencies to develop regulations for ensuring long-term production of the resource and long-term economic benefit. Fishery statistics are typically used to estimate abundance, mortality, recruitment, growth, and other vital characterisitcs of populations. Fishery statistics can also be used to study changes in fish community composition resulting from differential exploitation of species.

Book chapter↗
USGS1995

Age-at-maturity estimates for Atlantic coast female striped bass

This study was undertaken to estimate the percentage of mature female striped bass Morone saxatilis present in each age-class during annual coastal feeding migration. Migratory striped bass (N = 302) were sampled in coastal Rhode Island waters during spring (May-June) and fall (September-November) from 1985 to 1987. Stocks were identified by analysis of morphometric characters and isoelectric focusing of eye-lens proteins. Histological sections of ovarian tissue were used to categorize maturity state. Fish were considered mature if a class of oocytes measuring at least 150 μm and containing cytoplasmic inclusions was found in the ovarian sections. All females whose age at next potential spawning was 7 and older were mature. Our empirical observations indicated that 12% of fish in age-class 4, 34% of fish in age-class 5, and 77% of fish in age-class 6 were mature. The estimate of the proportion of mature fish in age-class 5 differs significantly from that of Merriman (1941), who also examined coastal migrants. No significant differences were found in maturity estimates of fish from stocks of different origin.

Transactions of the American Fisheries Society↗
USGS1995

Limitations to lake trout (Salvelinus namaycush) rehabilitation in the Great Lakes imposed by biotic interactions occurring at early life stages

We examine evidence that biotic factors, particularly predation, may be limiting early survival of wild lake trout (Salvelinus namaycush) juveniles in many areas of the Great Lakes. The Great Lakes contain numerous potential predators of lake trout eggs and fry, some of which are recent invaders, and most of which were probably absent when lake trout most recently re-invaded the Great Lakes after the last ice age. Simple quantitative models of predation suggest that plausible assumptions about prey densities, predator feeding rates, and duration of exposure of predator to prey can lead to very high estimates of predation mortality, in some instances approaching 100%. Indirect evidence from inter-Great Lake comparisons and inland lake examples also suggest that biotic factors may impede successful lake trout colonization. Our synthesis of the evidence leads to recommendations for research to better define field feeding rates of lake trout egg and fry predators and comparative studies of densities of potential egg and fry predators on lake trout spawning reefs. Management options should be designed to provide useful information as well as achieve short-term goals. From a management standpoint we recommend that: newly constructed lake trout reefs should be placed well away from concentrations of potential predators; offshore spawning reefs should be stocked; salmonine stocking, nutrient abatement, and commercial harvest of alewives should all be considered as options to enhance survival of young lake trout; hatchery lake trout should not be stocked at sites where wild lake trout are showing signs of recovery; and exotic species expansions or introductions must be curtailed to maintain or improve on our recent successes in lake trout rehabilitation.

Journal of Great Lakes Research↗