Ji X. He

Evidence of Widespread Natural Reproduction by Lake Trout Salvelinus namaycush in the Michigan Waters of Lake Huron

ABSTRACT Localized natural reproduction of lake trout Salvelinus namaycush in Lake Huron has occurred since the 1980s near Thunder Bay, Michigan. During 2004–2006, USGS spring and fall bottom trawl surveys captured 63 wild juvenile lake trout at depths ranging from 37–73 m at four of five ports in the Michigan waters of the main basin of Lake Huron, more than five times the total number captured in the previous 30-year history of the surveys. Relatively high catches of wild juvenile lake trout in bottom trawls during 2004–2006 suggest that natural reproduction by lake trout has increased and occurred throughout the Michigan waters of the main basin. Increased catches of wild juvenile lake trout in the USGS fall bottom trawl survey were coincident with a drastic decline in alewife abundance, but data were insufficient to determine what mechanism may be responsible for increased natural reproduction by lake trout. We recommend further monitoring of juvenile lake trout abundance and research into early life history of lake trout in Lake Huron.

Modeling Annual Growth Variation using a Hierarchical Bayesian Approach and the von Bertalanffy Growth Function, with Application to Lake Trout in Southern Lake Huron

We compared two models for time-varying growth using a hierarchical Bayesian approach to inference. Both models were derived from the same time-invariant von Bertalanffy growth function (VBGF), and our model comparisons were based on the deviance information criterion. We fit models to length and age data for 15,675 individual lake trout Salvelinus namaycush collected during annual spring gill-net surveys in southern Lake Huron from 1976 to 2004. We found that a model structured with both year and cohort effects outperformed a model that only used the same year-specific VBGF parameters for all age-groups. For the better model, the full version that allowed all VBGF parameters to vary over time also outperformed alternatives for which some parameters were constant. Length at age changed greatly over the 1976-2004 period, and in some years different ages changed in different directions. These complex patterns, which were due to the combination of cohort-specific growth and year-specific changes in growth environment, were well captured by our model. When we modeled growth as varying over time, inferences about VBGF parameters differed between the two models, and correlations among VBGF parameters also differed from the usually reported relations based on time-invariant models.

Lake Trout Status in the Main Basin of Lake Huron, 1973–2010

Abstract We developed indices of lake trout Salvelinus namaycush status in the main basin of Lake Huron (1973–2010) to understand increases in the relative abundance of wild year-classes during 1995–2010. Sea lamprey Petromyzon marinus wounds per 100 lake trout declined from 23.63 in 2000 to 5.86–10.64 in 2002–2010. The average age-7 lake trout catch per effort per recruitment (CPE/R; fish·305 m of gill net−1·million stocked yearlings−1) increased from 0.56 for the 1973–1990 year-classes to 0.92 for the 1991–2001 year-classes. Total CPE (fish/305 m of gill net) declined from 16.4 fish in 1996 to 4.1 fish in 2010, but the percentage of age-5 and younger lake trout steadily decreased from more than 70% before 1996 to less than 10% by 2009. The modal age in gill-net catches increased from age 5 before 1996 to age 7 by 2005. The average adult CPE increased from 2.8 fish/305 m of gill net during 1978–1995 to 5.34 fish/305 m of gill net during 1996–2010. The 1995–2010 year-classes of wild fish were more abundan...

Modeling Variation in Mass-Length Relations and Condition Indices of Lake Trout and Chinook Salmon in Lake Huron: a Hierarchical Bayesian Approach

Abstract Commonly used approaches to studying mass-length relations and condition indices often do not adequately address covariance between mass-length parameters, usually ignore heterogeneity in individual variance for body mass at a given length, and assume that length distributions of fish samples are similar across regions and years. We used body mass at selected lengths as condition indices based on statistical modeling and a hierarchical Bayesian approach to inferences, and our approach allowed us to avoid using restrictive assumptions. We estimated spatial and annual variation in mass-length relations, where the process errors in parameters are drawn from a multivariate distribution. We also estimated region-, year-, and size-group-specific variance for individual variation in mass at given lengths. We applied our approach to study mass-length relations of lake trout Salvelinus namaycush (1977-2005) and Chinook salmon Oncorhynchus tshawytscha (1983-2004) in U.S. waters of Lake Huron. We found that...

A Comparison of the Scale and Otolith Methods of Age Estimation for Lake Whitefish in Lake Huron

Abstract We compared sagittal otolith and scale age estimation methodologies for lake whitefish Coregonus clupeaformis collected in Georgian Bay and the main basin of Lake Huron between 2002 and 2004 in terms of the age, growth, and mortality estimates generated by the two methodologies. In general, otolith age estimates were higher than scale age estimates. Forty-nine percent of the fish aged by otoliths were judged to be greater than 10 years of age, compared with 5% of the fish aged by scales, and more age-classes were found when otoliths were used. Otolith and scale ages agreed for 16% (n = 60) of Georgian Bay fish and only 9% (n = 27) of main-basin fish. The overall coefficients of variation for the otolith and scale age estimation methodologies pooled across years and basins were 5.52% and 2.68%, respectively. Mean length at age based on otoliths was significantly lower than mean length at age based on scales. Variation in the mean length at age was greatest for fish age 7 and older. Otolith-based c...

Growth and Maturity of Hatchery and Wild Lean Lake Trout during Population Recovery in Michigan Waters of Lake Superior

Abstract The recovery of populations of wild lake trout Salvelinus namaycush in Lake Superior was the first success among Great Lakes—wide rehabilitation efforts for this species. Knowledge of changes in major demographic factors (e.g., growth and maturity schedules) is very important for enhancing our understanding of stock status during the recovery process, particularly for a fish population with a relatively long life span, such as lake trout in Lake Superior. We separated the recovery time line into three periods—hatchery dominant (1970–1979), transitional (1980–1985), and wild dominant (1986–2003)—and compared growth and sexual maturity (1) between hatchery- and wild-origin lake trout within each period and (2) among the three periods for a given origin. In all three periods, the lengths at old ages (age >6) were similar between wild and hatchery lake trout, but wild fish had smaller lengths at ages 4–6 and at maturity than did hatchery fish. Consequently, wild lake trout had a lower wounding rate b...

Rehabilitation Stocking of Walleyes and Lake Trout: Restoration of Reproducing Stocks in Michigan Waters of Lake Huron

AbstractLake Trout Salvelinus namaycush and Walleye Sander vitreus, native keystone predators of the upper Great Lakes, were nearly extirpated from Lake Huron in the 1940s. Efforts to restore these species in the Great Lakes constitute one of North Americans largest-scaled native keystone predator recovery projects. From 1973 to 2012 nearly 49 million yearling-equivalent Lake Trout and 21 million spring-fingerling Walleyes were stocked in western Lake Huron. We used assessment catch rates and biological data, statistical catch-at-age models, and harvest statistics to evaluate whether the objectives of rehabilitation stocking and management have been achieved in the Main Basin of Lake Huron, with emphasis on the period from 2003 to 2012. Key measures of progress were the biomass of older, spawning stock and evidence of natural reproduction. Until 2000, excessive Sea Lamprey Petromyzon marinus– and fishing-induced mortality caused few Lake Trout to survive to spawning age. Lake Trout broodstock biomass ros...

Using Maxillae to Estimate Ages of Lake Trout

AbstractPrevious evaluations of calcified structures used to estimate fish ages have not included maxillae. While otoliths are considered the superior structure for assessing the age of Lake Trout Salvelinus namaycush, it can be difficult to collect and analyze sufficient samples for annual stock assessment, particularly from recreational fisheries. We used maxilla sections to estimate ages of 1,145 Lake Trout collected from Lake Huron in 2013, including 83 fish of known age with coded wire tags (CWT). Maxilla removal was 287% faster than extraction of otoliths. Maxilla sections were cut using inexpensive tools commonly used for processing spines and fin rays. Multiple sections could be made easily from each maxilla, allowing for the use of a superior section that exhibited easily identifiable annuli; in contrast, a single cracked otolith yields only two opportunities to assign age since the cut must be made through the otolith focus. From blind estimates by two independent estimators, made without prior ...

Revised fish aging techniques improve fish contaminant trend analyses in the face of changing Great Lakes food webs

Incorporation of fish age into the assessment of status and trends for persistent, bioaccumulative and toxic chemicals in the Great Lakes has become an important step for the U.S. EPAs Great Lakes Fish Monitoring and Surveillance Program (GLFMSP). A slowing in the rate of decline for total PCBs in Lake Huron beginning in 2000, led the Program to complete a retrospective analysis to assess how chemical contamination may be influenced by fish age. Analytical results suggest that fish age is an important variable when assessing contaminant trends and that the Program needed to revise its compositing scheme to group fish according to age, rather than by length, prior to homogenization and chemical analysis. An Interlaboratory comparison study of multiple age structures was performed to identify the most appropriate age estimation structure for the Program. The lake trout (Salvelinus namaycush) maxillae was selected, over the otolith, as the most precise, accurate, and rapidly assessed structure for the Program when compared between laboratories and against the known age from the coded wire tag (CWT). Age-normalization practices can now be implemented when assessing contaminant concentrations and trends for the GLFMSP.

Recreational Postrelease Mortality of Lake Trout in Lakes Superior and Huron

AbstractThe effectiveness of fishing regulations that result in the release of some angler-caught fish depends on accurate knowledge of the postrelease mortality of those individuals. In the Laurentian Great Lakes, Lake Trout Salvelinus namaycush are a major component of recreational fisheries; across large regions of the lakes, they are managed with length limit and daily quota regulations assuming a 15% postrelease mortality rate. Due to concerns regarding the accuracy of that rate, we conducted a tagging study to estimate Lake Trout postrelease mortality in Lakes Superior and Huron, and we examined environmental and fishing factors that influenced the return rates of tagged fish. The basic study design was to compare tag return rates between two groups: (1) a treatment group comprising fish that were caught and released by anglers; and (2) a control group comprising fish that were caught via trap net and released. Tag return rates for the angler-caught group were evaluated in relation to depth of captu...