Geology topics

Charles P. Madenjian

Publications and source records attributed to Charles P. Madenjian.

At least 55 records · Page 3Linked to original sources

USGS2019

Age truncation of alewife in Lake Michigan

Empirical evidence has shown increased variability in harvest and recruitment of exploited fish populations, which can result directly from exploitation or indirectly from interactions between external drivers and the internal dynamics of age-structured populations. We investigated whether predation in a freshwater system could affect a prey fish population, in the same way fishing affects targeted populations. Using fishery-independent trawl survey data and a suite of quantitative indicators, we evaluated changes in the alewife population in Lake Michigan. Our results provide evidence for a reduction in the mean spawner age, a reduction in the diversity of age classes and the distribution of biomass across them, and increased variability in the proportion of first time spawners in the spawning stock. We used wavelet analysis and estimates of lifetime egg production to demonstrate how the alewife population displays behaviors of instability as the overall biomass declines. Our results provide evidence that predation pressure can influence prey fish populations in a similar manner to fishing on harvested populations, and that conservation of a broad reproducing age structure is likely to be important for buffering against adverse environmental fluctuations and for sustainable management of fish populations.

Lake Michigan↗

USGS2019

Status and trends of prey fish populations in Lake Michigan, 2018

The U.S. Geological Survey Great Lakes Science Center has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12 m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The survey provides relative abundance and biomass estimates between the 5 m and 114 m depth contours of the lake for prey fish populations, as well as for burbot and yellow perch. The resulting data are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2018, although depths 64 m and greater offshore of Frankfort could not be completed due to excessive dreissenid mussel biomass on our multiple tow attempts. Mean biomass of alewives in 2018 was estimated at 0.54 kg/ha, which was the highest value since 2013, but still only 6.7% of the long-term average (7.96 kg/ha). Age distribution of alewives remained truncated with no alewife age exceeding 5 years. Bloater biomass was 2.60 kg/ha in 2018, relatively unchanged from 2017, but still only 14% of the long-term average. Round goby biomass was 1.25 kg/ha in 2018, the 3rd largest estimate in the time series and 62% higher than the average since they were first sampled in 2003. Rainbow smelt biomass was 0.45 kg/ha, which was the highest since 2006 but only 21% of the long-term average. Likewise, deepwater sculpin biomass was 1.30 kg/ha in 2018, which was the highest since 2007 but only 20% of the long-term average. Slimy sculpin biomass was only 0.07 kg/ha in 2018, and similar to the very low levels estimated since 2012 and only 17% of the long-term average. Ninespine stickleback remained very rare in 2018 (0.004 kg/ha), and only 1% of the long-term average. Overall, the total prey fish biomass (sum of alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, round goby, and ninespine stickleback) in 2018 was 6.22 kg/ha, roughly 65% greater than in 2017 but still only 17% of the long-term average. With respect to other species of interest, burbot biomass was only 0.04 kg/ha in 2018 (18% of the long-term average) and no age-0 yellow perch were caught in 2018, indicating a weak year-class.

Lake Michigan↗

USGS2018

Mercury isotopes reveal an ontogenetic shift in habitat use by walleye in lower Green Bay of Lake Michigan

In general, fish residing in rivers differ from fish residing in lakes in their mercury (Hg) isotope ratios. Specifically, fish residing in lakes typically show enriched values for the isotope ratios of δ 202 Hg (mass-dependent fractionation of isotope 202 Hg) and Δ 199 Hg (mass-independent fractionation of isotope 199 Hg) compared with fish residing in rivers, because photochemical effects acting on Hg isotope ratios are stronger in lakes than in rivers. Whole-fish determinations of Hg isotope ratios in age-0 and adult (ages 4–11) walleye ( Sander vitreus ) caught in the Fox River, the main tributary to lower Green Bay of Lake Michigan, were dissimilar. Age-0 fish exhibited a river signature for δ 202 Hg and Δ 199 Hg, with means equal to 0.00 and 0.26‰, respectively. Significantly elevated levels of δ 202 Hg and Δ 199 Hg were observed in adult fish, indicating that adult fish primarily resided in the bay. Our results implied that the Fox River serves as a nursery area for juvenile walleye in the Fox River–lower Green Bay ecosystem. Moreover, corrections for photochemical fractionation of δ 202 Hg revealed that age-0 and adult walleye shared the same source of Hg in this ecosystem. In addition, Hg isotope ratios did not significantly differ between the sexes of adult walleye, suggesting that these ratios did not fractionate during the Hg elimination process.

Environmental Science & Technology Letters↗

USGS2018

Ratio of mercury concentration to PCB concentration varies with sex of white sucker (Catostomus commersonii)

The whole-fish total mercury (Hg) concentrations were determined in 25 mature female and 26 mature male white suckers ( Catostomus commersonii ) caught during their spawning run in the Kewaunee River, a tributary to Lake Michigan. The age of each fish was estimated using thin-sectioned otoliths, and total length (TL) and weight were determined for each fish. When adjusted for the effect of age, males were found to be 7% higher in Hg concentration than females. Nearly all (about 98%) of the Hg found in the white suckers was determined to be methylmercury. In an earlier study on the same 51 white suckers from the Kewaunee River spawning run, males were found to be 18% higher than females in polychlorinated biphenyl (PCB) concentration. We determined that the ratio of Hg concentration to PCB concentration in females was significantly higher than that in males. Thus, sex significantly interacted with contaminant type (Hg or PCBs) in determining contaminant concentrations. The most plausible explanation for this interaction was that males eliminated Hg at a faster rate than females, most likely due to the boosting of the Hg-elimination rate by certain androgens such as testosterone and 11-ketotestosterone. Hg concentrations in the white suckers were well below federal guidelines for fish consumption.

Environments↗

USGS2018

Distributions of PCB congeners and homologues in white sucker and coho salmon from Lake Michigan

We tested the hypothesis of the proportion of higher chlorinated biphenyl (PCB) congeners increasing with increasing trophic level by comparing the respective PCB homologue distributions in an omnivore, white sucker ( Catostomus commerson i), and a top predator, coho salmon ( Oncorhynchus kisutch ), from Lake Michigan. Adult females had the same congener and homologue proportions of total PCB concentration (ΣPCB) as adult males in both species. Hexachlorinated congeners comprised the largest proportion (32%) found in white sucker, followed by heptachlorinated (21%) and octochlorinated (18%) congeners. In contrast, pentachlorinated congeners comprised the largest proportion (33%) of ΣPCB found in coho salmon, followed by hexachlorinated (26%) and tetrachlorinated (24%) congeners. Coho salmon contained significantly higher proportions of tri-, tetra-, and pentachlorinated congeners, whereas white sucker contained significantly higher proportions of hexa- through decachlorinated congeners. Our results were opposite of the hypothesis of greater degree of PCB chlorination with increasing trophic level, and supported the contention that the PCB congener proportions in fish depends mainly on diet, and does not necessarily reflect the trophic level of the fish. Our results also supported the contention that diets do not vary between the sexes in most fish populations.

Environmental Science & Technology↗

USGS2018

Temperature regimes, growth, and food consumption for female and male adult walleye in Lake Huron and Lake Erie: a bioenergetics analysis

Bioenergetics modeling was used to assess the relative importance of food availability and water temperature in determining walleye ( Sander vitreus ) growth. Temperature regimes experienced by both female and male adult walleye in three basins of Lake Huron and in Lake Erie were determined by use of surgically implanted temperature loggers and acoustic telemetry. Temperatures experienced by walleye were higher in Lake Erie than in Lake Huron. Walleye from Lake Erie grew at nearly double the rate of walleye from Lake Huron, and mass at age for adult females averaged about 50% greater than that for adult males in both lakes. Food consumption rate for an average adult walleye in Lake Erie was nearly twice as high as that in Lake Huron. Interbasin and interlake variability in temperature regimes accounted for a moderate degree of variability in walleye growth. We concluded that the driver for faster growth in Lake Erie compared with Lake Huron was higher food availability in Lake Erie compared with Lake Huron. The sex difference in temperature regimes explained 15% of the sex difference in Lake Erie walleye growth.

Lake Erie, Lake Huron↗

USGS2018

Are changes in lower trophic levels limiting prey-fish biomass and production in Lake Michigan?

To improve understanding of how recent changes in lower trophic levels in Lake Michigan could be affecting prey-fish biomass and production, the Lake Michigan Committee (LMC) convened a Lower Trophic Level Task Group and provided several charges that are responded to in this report. First, we compiled a comprehensive summary of lower trophiclevel data in Lake Michigan, separating out nearshore versus offshore trends over time. Declining trends were prevalent in offshore time series for phosphorus, chlorophyll a, biomass of total crustacean zooplankton, biomass of herbivorous cladocerans, and density of Diporeia spp. In the nearshore, declining trends were evident only for biomass of cyclopoid copepods and density of Diporeia spp. Second, we hypothesized specific mechanisms by which changes in lower trophic levels could affect prey-fish biomass and production and described the degree of empirical support for each mechanism. The best-supported hypothesis was that declining invertebrate prey (especially Diporeia spp.) was responsible for declining growth of prey fish, especially over the last decade when competition for prey resources should otherwise have been lessened due to declining prey-fish densities. As a result, declining growth potentially limits the prey-fish biomass that could have been attained had growth been maintained at the levels that were achieved in the 1980s and earlier. Third, we prioritized several lower trophic-level indicators that fishery managers could use to better inform decision making. The top-ranked indicator was annual reporting of Alewife (Alosa pseudoharengus) condition. Fourth, we prioritized the key monitoring and research gaps that limit our current understanding of how lower trophic levels influence fish production. The highest-priority monitoring gap was coordinated sampling of the nearshore, which, if accomplished, would complement annual reporting on offshore sampling. The top-ranked knowledge gap was identifying bottlenecks that regulate fish recruitment, given that recent changes in zooplankton distribution and abundance could be suppressing survival of larval fish and, ultimately, the biomass and production of prey fish. We provided three specific recommendations for the LMC to consider as they seek to better incorporate lower trophiclevel changes into their management decision process: (1) implement a coordinated and standardized nearshore monitoring program, (2) encourage funding agencies to use our prioritized lists in their decision processes, and (3) foster the already improved dialogue between those researching lower trophic levels and those researching fisheries.

Miscellaneous Publication↗

USGS2017

Fish Bioenergetics 4.0: An R-based modeling application

Bioenergetics modeling is a widely used tool in fisheries management and research. Although popular, currently available software (i.e., Fish Bioenergetics 3.0) has not been updated in over 20 years and is incompatible with newer operating systems (i.e., 64‐bit). Moreover, since the release of Fish Bioenergetics 3.0 in 1997, the number of published bioenergetics models has increased appreciably from 56 to 105 models representing 73 species. In this article, we provide an overview of Fish Bioenergetics 4.0 (FB4), a newly developed modeling application that consists of a graphical user interface (Shiny by RStudio) combined with a modeling package used in the R computing environment. While including the same capabilities as previous versions, Fish Bioenergetics 4.0 allows for timely updates and bug fixes and can be continuously improved based on feedback from users. In addition, users can add new or modified parameter sets for additional species and formulate and incorporate modifications such as habitat‐dependent functions (e.g., dissolved oxygen, salinity) that are not part of the default package. We hope that advances in the new modeling platform will attract a broad range of users while facilitating continued application of bioenergetics modeling to a wide spectrum of questions in fish biology, ecology, and management.

Fisheries Magazine↗

USGS2017

Changes in movements of Chinook Salmon between lakes Huron and Michigan after Alewife population collapse

Alewives Alosa pseudoharengus are the preferred food of Chinook Salmon Oncorhynchus tshawytscha in the Laurentian Great Lakes. Alewife populations collapsed in Lake Huron in 2003 but remained comparatively abundant in Lake Michigan. We analyzed capture locations of coded-wire-tagged Chinook Salmon before, during, and after Alewife collapse (1993–2014). We contrasted the pattern of tag recoveries for Chinook Salmon released at the Swan River in northern Lake Huron and Medusa Creek in northern Lake Michigan. We examined patterns during April–July, when Chinook Salmon were primarily occupied by feeding, and August–October, when the salmon were primarily occupied by spawning. We found evidence that Swan River fish shifted their feeding location from Lake Huron to Lake Michigan after the collapse. Over years, proportions of Swan River Chinook Salmon captured in Lake Michigan increased in correspondence with the Alewife decline in Lake Huron. Mean proportions of Swan River fish captured in Lake Michigan were 0.13 (SD = 0.14) before collapse (1993–1997) and 0.82 (SD = 0.22) after collapse (2008–2014) and were significantly different. In contrast, proportions of Medusa Creek fish captured in Lake Michigan did not change; means were 0.98 (SD = 0.05) before collapse and 0.99 (SD = 0.01) after collapse. The mean distance to the center of the coastal distribution of Swan River fish during April–July shifted 357 km (SD = 169) from central Lake Huron before collapse to central Lake Michigan after collapse. The coastal distributions during August–October were centered on the respective sites of origin, suggesting that Chinook Salmon returned to release sites to spawn regardless of their feeding locations. Regarding the impact on Alewife populations, this shift in interlake movement would be equivalent to increasing the Chinook Salmon stocking rate within Lake Michigan by 30%. The primary management implication is that interlake coordination of Chinook Salmon stocking policies would be expected to benefit the recreational fishery.

Lake Huron, Lake Michigan↗

USGS2017

Testing for synchrony in recruitment among four Lake Michigan fish species

In the Great Lakes region, multiple fish species display intra-specific spatial synchrony in 28 recruitment success, with inter-annual climate variation hypothesized as the most likely driver. 29 In Lake Michigan, we evaluated whether climatic or other physical variables could also induce 30 spatial synchrony across multiple species, including bloater ( Coregonus hoyi ), rainbow smelt 31 ( Osmerus mordax ), yellow perch ( Perca flavescens ), and alewife ( Alosa pseudoharengus ). The 32 residuals from stock-recruitment relationships revealed yellow perch recruitment to be correlated 33 with recruitment of both rainbow smelt (r = 0.37) and alewife (r = 0.36). Across all four species, 34 higher than expected recruitment occurred in 5 years between 1978 and 1987 and then switched 35 to lower than expected recruitment in 5 years between 1996 and 2004. Generalized additive 36 models revealed warmer spring and summer water temperatures and lower wind speeds 37 corresponded to higher than expected recruitment for the nearshore-spawning species, and 38 overall variance explained ranged from 14% (yellow perch) to 61% (alewife). For all species 39 but rainbow smelt, higher recruitment also occurred in extremely high or low years of the North 40 Atlantic Oscillation index. Future development of indices that describe the physical Great Lakes 41 environment could improve understanding of how climate can synchronize fish populations 42 within and across species.

Great Lakes↗

USGS2017

Sex difference in PCB concentrations of a catostomid fish

Unraveling the complexities associated with the relative differences in contaminant concentrations between the sexes of mature fish may provide insights into important behavioral and physiological differences between the sexes of not just fish but higher vertebrates as well. Whole-fish polychlorinated biphenyl (PCB) concentrations were determined in 25 mature female white suckers (Catostomus commersoni) and 26 mature male white suckers caught during their spawning run in the Kewaunee River, a tributary to Lake Michigan. Total length and weight were measured for each fish, and age of each fish was estimated from thin-sectioned otoliths. PCB concentration significantly increased with increasing total length, weight, and age. Consequently, three analysis of covariance (ANCOVA) models were fitted to the data to assess the effect of sex on white sucker PCB concentration. Based on model averaging, estimates of mean PCB concentrations in female and male white suckers were 185 and 219 ng/g, respectively. Thus, males were 18% greater in PCB concentration than females. We conclude that this difference between the sexes was most likely mainly driven by a higher rate of energy expenditure in males compared with females. Greater energy expenditure, owing to greater swimming activity and a higher resting metabolic rate , resulted in a higher rate of food consumption, which in turn led to a greater rate of PCB accumulation. Higher whole-fish PCB concentration in males compared with females has now been shown in nine different fish species. Our study represented the first documentation of this type of sex difference in a catostomid fish.

Kewaunee River, Lake Michigan↗

USGS2017

2016 Lake Michigan Lake Trout Working Group Report

This report provides a review on the progression of lake trout rehabilitation towards meeting the Salmonine Fish Community Objectives (FCOs) for Lake Michigan (Eshenroder et. al. 1995) and the interim goal and evaluation objectives articulated in A Fisheries Management Implementation Strategy for the Rehabilitation of Lake Trout in Lake Michigan (Dexter et al. 2011); we also include data describing lake trout stocking and mortality to portray the present state of progress towards lake trout rehabilitation.

Report↗

USGS2016

Feeding ecology of the walleye (Percidae, Sander vitreus), a resurgent piscivore in Lake Huron (Laurentian Great Lakes) after shifts in the prey community

Recovering populations of piscivores can challenge understanding of ecosystem function due to impacts on prey and to potentially altered food webs supporting their production. Stocks of walleye (Percidae, Sander vitreus ), an apex predator in the Laurentian Great Lakes, crashed in the mid‐1900s. Management efforts led to recovery by 2009, but recovery coincided with environmental and fish community changes that also had implications for the feeding ecology of walleye. To evaluate potential changes in feeding ecology for this apex predator, we assessed diets in the main basin of Lake Huron and in Saginaw Bay, a large embayment of Lake Huron, during 2009–2011. Walleye switched their diets differently in the main basin and Saginaw Bay, with non‐native round goby (Gobiidae, Neogobius melanostomus ) and rainbow smelt (Osmeridae, Osmerus mordax ) more prevalent in diets in the main basin, and invertebrates, yellow perch (Percidae, Perca flavescens ) and gizzard shad (Clupeidae, Dorosoma cepedianum ) more prevalent in diets in the bay. Feeding strategy plots indicated that there was a high degree of individual specialisation by walleye in the bay and the main basin. Bioenergetic simulations indicated that walleye in Saginaw Bay need to consume 10%–18% more food than a walleye that spends part or all of the year in the main basin, respectively, in order to achieve the same growth rate. The differences in diets between the bay and main basin highlight the flexibility of this apex predator in the face of environmental changes, but changes in diet can alter energy pathways supporting piscivore production.

Ecology of Freshwater Fish↗

USGS2016

Sex differences in contaminant concentrations of fish: a synthesis

Comparison of whole-fish polychlorinated biphenyl (PCB) and total mercury (Hg) concentrations in mature males with those in mature females may provide insights into sex differences in behavior, metabolism, and other physiological processes. In eight species of fish, we observed that males exceeded females in whole-fish PCB concentration by 17 to 43%. Based on results from hypothesis testing, we concluded that these sex differences were most likely primarily driven by a higher rate of energy expenditure, stemming from higher resting metabolic rate (or standard metabolic rate (SMR)) and higher swimming activity, in males compared with females. A higher rate of energy expenditure led to a higher rate of food consumption, which, in turn, resulted in a higher rate of PCB accumulation. For two fish species, the growth dilution effect also made a substantial contribution to the sex difference in PCB concentrations, although the higher energy expenditure rate for males was still the primary driver. Hg concentration data were available for five of the eight species. For four of these five species, the ratio of PCB concentration in males to PCB concentration in females was substantially greater than the ratio of Hg concentration in males to Hg concentration in females. In sea lamprey (Petromyzon marinus), a very primitive fish, the two ratios were nearly identical. The most plausible explanation for this pattern was that certain androgens, such as testosterone and 11-ketotestosterone, enhanced Hg-elimination rate in males. In contrast, long-term elimination of PCBs is negligible for both sexes. According to this explanation, males ingest Hg at a higher rate than females, but also eliminate Hg at a higher rate than females, in fish species other than sea lamprey. Male sea lamprey do not possess either of the above-specified androgens. These apparent sex differences in SMRs, activities, and Hg-elimination rates in teleost fishes may also apply, to some degree, to higher vertebrates including humans. Our synthesis findings will be useful in: (1) developing sex-specific bioenergetics models for fish, (2) developing sex-specific risk assessment models for exposure of humans and wildlife to contaminants, and (3) refining Hg mass balance models for fish and higher vertebrates.

Biology of Sex Differences↗

USGS2016

Population ecology of the sea lamprey ( Petromyzon marinus ) as an invasive species in the Laurentian Great Lakes and an imperiled species in Europe

The sea lamprey Petromyzon marinus (Linnaeus) is both an invasive non-native species in the Laurentian Great Lakes of North America and an imperiled species in much of its native range in North America and Europe. To compare and contrast how understanding of population ecology is useful for control programs in the Great Lakes and restoration programs in Europe, we review current understanding of the population ecology of the sea lamprey in its native and introduced range. Some attributes of sea lamprey population ecology are particularly useful for both control programs in the Great Lakes and restoration programs in the native range. First, traps within fish ladders are beneficial for removing sea lampreys in Great Lakes streams and passing sea lampreys in the native range. Second, attractants and repellants are suitable for luring sea lampreys into traps for control in the Great Lakes and guiding sea lamprey passage for conservation in the native range. Third, assessment methods used for targeting sea lamprey control in the Great Lakes are useful for targeting habitat protection in the native range. Last, assessment methods used to quantify numbers of all life stages of sea lampreys would be appropriate for measuring success of control in the Great Lakes and success of conservation in the native range.

Reviews in Fish Biology and Fisheries↗

USGS2016

Mercury accumulation, and the mercury-PCB-sex interaction, in lake whitefish ( Coregonus clupeaformis )

We determined whole-fish Hg concentrations of 26 female and 34 male adult lake whitefish (Coregonus clupeaformis) from northern Lake Huron captured during November 2010. Subsampling from these 60 fish, Hg concentration was also determined in both the somatic tissue and ovaries (n=5), while methylmercury (MeHg) concentration was determined in whole fish (n=18). Bioenergetics modeling was used to assess the growth dilution effect on the difference in Hg concentrations between the sexes. Mean whole-fish Hg concentration in females (59.9 ng/g) was not significantly different from mean whole-fish Hg concentration in males (54.4 ng/g). MeHg accounted for 91% of the mercury found in the lake whitefish. Bioenergetics modeling results indicated that the growth dilution effect did not contribute to a difference in Hg concentration between the sexes. We estimated that females increased in Hg concentration by 17.9%, on average, immediately after spawning due to release of eggs. Using PCB data for the same 60 lake whitefish from a previous study, we detected a significant interaction between sex and contaminant type (Hg or PCBs), which was attributable to males being significantly higher in PCB concentration than females. Males may be eliminating Hg at a faster rate than females.

Lake Huron↗

USGS2016

Differences in energy expenditures and growth dilution explain higher PCB concentrations in male summer flounder

Comparison of polychlorinated biphenyl (PCB) concentrations between the sexes of mature fish may reveal important behavioral and physiological differences between the sexes. We determined whole-fish PCB concentrations in 23 female summer flounder Paralichthys dentatus and 27 male summer flounder from New Jersey coastal waters. To investigate the potential for differences in diet or habitat utilization between the sexes, carbon and nitrogen stable isotope ratios were also determined. In 5 of the 23 female summer flounder, PCB concentrations in the somatic tissue and ovaries were determined. In addition, we used bioenergetics modeling to assess the contribution of the growth dilution effect to the observed difference in PCB concentrations between the sexes. Whole-fish PCB concentrations for females and males averaged 87 and 124 ng/g, respectively; thus males were 43% higher in PCB concentration compared with females. Carbon and nitrogen stable isotope ratios did not significantly differ between the sexes, suggesting that diet composition and habitat utilization did not vary between the sexes. Based on PCB determinations in the somatic tissue and ovaries, we predicted that PCB concentration of females would increase by 0.6%, on average, immediately after spawning due to release of eggs. Thus, the change in PCB concentration due to release of eggs did not explain the higher PCB concentrations observed in males. Bioenergetics modeling results indicated that the growth dilution effect could account for males being 19% higher in PCB concentration compared with females. Thus, the bulk of the observed difference in PCB concentrations between the sexes was not explained by growth dilution. We concluded that a higher rate of energy expenditure in males, stemming from greater activity and a greater resting metabolic rate, was most likely the primary driver for the observed difference in PCB concentrations between the sexes.

New Jersey↗

USGS2016

Age and growth of round gobies in Lake Huron: Implications for food web dynamics

Although the round goby ( Neogobius melanostomus ) has become established throughout the Laurentian Great Lakes, information is scarce on spatial variation in round goby growth between and within lakes. Based on a sample of 754 specimens captured in 2014, age, growth, and mortality of round gobies at four locations in Lake Huron were assessed via otolith analysis. Total length ( TL ) of round gobies ranged from 44 to 111 mm for Saginaw Bay, from 45 to 115 mm for Rockport, from 50 to 123 mm for Hammond Bay, and from 51 to 118 mm for Thunder Bay. Estimated ages of round gobies ranged from 2 to 5 years for Saginaw Bay, from 2 to 6 years for Rockport, and from 2 to 7 years for Hammond Bay and Thunder Bay. Sex-specific, body–otolith relationships were used to back-calculate total lengths at age, which were then fitted to von Bertalanffy growth models. For each sex, round goby growth showed significant spatial variation among the four locations within Lake Huron. At all four locations in Lake Huron, males grew significantly faster than females and attained a larger asymptotic length than females. Annual mortality rate estimates were high (62 to 85%), based on catch-curve analysis, suggesting that round gobies may be under predatory control in Lake Huron.

Michigan↗