George R. Spangler

Lake Huron Fish Community Structure Based on Gill-Net Catches Corrected for Selectivity and Encounter Probability

Abstract This paper describes the depth distributions and numeric abundance of fishes in the Canadian waters of Lake Huron based upon size-corrected results of experimental netting from 1958 through 1968. Gill-net catches were corrected for encounter probabilities based on the positive correlation between fish size and swimming speed and for retention probability offish of different sizes once they encounter the net. A 3-parameter gamma function was used to fit net-selectivity curves for 13 Great Lakes species. Comparison of raw with corrected catches for Georgian Bay showed that the former exaggerated the relative abundance of deep-water coregonines Coregonus spp. in the deepest strata and overrepresented the abundance of yellow perch Perca flavescens and lake chub Couesius plumbeus in the shallowest waters. Corrections resulted in status changes for several species that are major segments of the fish community. Nearly two decades after the collapse of the top-level native piscivores, Georgian Bay retain...

Effect That Providing Fishing Information Has on Angler Expectations and Satisfaction

Abstract Anglers on Lake Miltona, Minnesota, who were given fishing information (catch rate and average weight of available species) generally did not show significant differences in satisfaction or expectations from a control group of anglers who were not provided with this information. Exceptions were the successful anglers for walleye Stizostedion vitreum and largemouth bass Micropterus salmoides. Anglers were more satisfied with nonconsumptive aspects of the fishing experience (natural beauty of the lake, water quality, weather, quality of the access to the lake by boats) than with consumptive aspects (size and number of fish caught). Expectations of fish size were more realistic than expectations of catch rate: 67% of the anglers evaluated the average walleye (determined by creel surveys to be 2.1 lb) as “about what I expected,” whereas 47% evaluated the average walleye catch rate (0.2 fish/h) as “less than I expected.” Walleye anglers showed higher expectations of walleye catch rate than other angle...

Dynamics of Rainbow Smelt during and after Exploitation in South Bay, Lake Huron

Abstract We examined population dynamics of rainbow smelt Osmerus mordax in South Bay of Lake Huron during intensive fishing of the spring spawning runs (1948–1957) and after exploitation was stopped (1958–1970). Modal ages of spawning rainbow smelt changed from 2 to 3 during the intensive fishing period to 3 and 4 after 1959. Percentage males in the spawning run samples from dip nets increased from 60% (1950–1957) to 78% (1958–1964). Percentage males in summer samples from gill nets increased from 39% to 50% between the same periods. Total annual mortality rate averaged 90% during exploitation and 67% after fishing stopped. Instantaneous natural mortality rate during 1948–1970 was estimated as 1.1. Relative stock sizes, estimated from cohort analysis, sharply increased after 1957; an extremely large 1960 year-class caused a peak in 1962. Growth of rainbow smelt to age 1 and to age 2 was decreasing while their own abundance and that of alewives Alosa pseudoharengus were increasing. Growth after age 2 was ...

Use of Biochronology to Examine Interactions of Freshwater Drum, Walleye and Yellow Perch in the Red Lakes of Minnesota

Growth histories for freshwater drum, Aplodinotus grunniens, walleye, Stizostedion vitreum, and yellow perch, Perca flavescens, were constructed using calcified structures for the period 1947 through 1996 for the Red Lakes, Minnesota. Increased walleye growth and decreased yellow perch growth were observed over the period from 1983 to 1996, which are attributed to intensive fishing resulting in decreased intraspecific competition in walleye and increased intraspecific competition in yellow perch through release from predation. Strong year-classes of yellow perch were positively correlated with walleye growth (r=0.57, p-value=0.042). There was no evidence for interactions of walleye or yellow perch with freshwater drum. Freshwater drum growth (r=0.680, p-value=0.0001) was more highly correlated with temperature than were walleye (r=0.386, p-value=0.006) and yellow perch growth (r=0.303, p-value=0.036).

Development and utilization of a population growth history of Red Lake walleye, Stizostedion vitreum

SynopsisAn environmental growth history of commercially harvested walleye, Stizostedion vitreum, in Red Lakes, Minnesota, was constructed for the years 1944–1992. This was accomplished using a linear model which was fitted to annular scale increment measurements. Increment size was separated into one component due to a combination of environmental factors, an environmental growth coefficient, and one due to the age of the fish. Our hypothesis was that variables such as air temperature, walleye year-class strength, catch-per-unit-effort (CPUE) of walleye, and CPUE of yellow perch, Perca flavescens, affect walleye growth, and therefore a historical series of these variables would show coherence to the series of walleye growth coefficients. Multiple regression techniques were used to test these hypotheses. Significant predictors of the growth of walleye after age one were average February temperature, cumulative degree days in July, walleye year-class strength, and growth of young-of-the-year (YOY) walleye. We hypothesized that YOY walleye respond to a different set of factors than walleye after age one, thus, a series of YOY growth measurements would show coherence to a different set of environmental factors. Significant predictors of YOY walleye growth were May, June, and August cumulative degree days, as well as the growth of older walleye. We expected the set of factors which affect freshwater drum, Aplodinotus grunniens, to include factors that affect walleye, such as temperature, shared prey availability, and abundance of both walleye and drum. As a test, environmental growth coefficients computed by Pereira (1992) for freshwater drum were compared to walleye growth coefficients. The growth coefficients of drum were significantly positively correlated with the walleye coefficients, and the significance increased if the poorest walleye growth years were excluded.

Stock-Specific Growth Rates of Lake Herring, Coregonus artedi, in Western Lake Superior

We constructed environmental growth histories, termed biochronologies, for lake herring, Coregonus artedi, from four areas of western Lake Superior using scale samples from historical collections. We created chronologies using a linear growth model (LGM) to describe individual somatic growth as the sum of both intrinsic and environmental factors. We built a master chronology using all possible scale samples age five or younger, then examined subsets of the data according to collection site (Bayfield Wisconsin, Black Bay Ontario, French River Minnesota, and Thunder Bay Ontario). The LGM best fit the site-specific data, indicating statistically different stock-specific growth rates. These differences were primarily due to environmental growth, as age effects were similar across sites. We show that the LGM is a useful tool for identifying lake herring stocks in western Lake Superior, a situation where genetic stock identification techniques have been unsuccessful. Our findings demonstrate that the stocks at these four sites are growing at different rates and therefore require different management strategies according to the unit stock concept. Further refinement of these chronologies and coupling with abundance data may allow managers to determine the degree of stock rehabilitation.

A Tool for Age Determination

Abstract A master growth chronology for walleye Stizostedion vitreum was developed to complement age determination by hard-part analysis. A master chronology documents year-to-year fluctuations of growth in body size of individuals in the population in response to environmental conditions, as inferred through the magnitudes of their growth increments. The master chronology was constructed by using a linear growth model that separated measured growth increments on reliably aged fish into age-specific and environmental components. Year-classes of a sample of unknown-aged older fish were predicted by three methods: visual inspection of their scales, matching their individual growth histories to the master chronology through an algebraic concordance sum of squares method, and matching the individual histories to the master chronology by correlation. The results of the algebraic concordance sum of squares method corresponded more closely to the results of visual inspection than did the results of the simple co...

Population Characteristics of Adult Pink Salmon in Two Minnesota Tributaries to Lake Superior

Pink salmon, Oncorhynchus gorbuscha, have adapted well to the Lake Superior environment and have become a significant member of the Great Lakes salmonid community. However, to properly manage pink salmon in this new environment, an improved understanding of their population characteristics is necessary. To gather population information, the following parameters were estimated for the 1981 and 1982 runs of pink salmon in the Cascade and Cross rivers, Minnesota: 1) absolute abundance of spawners, 2) age, size, and sex distribution of the spawners, 3) fecundity and growth of returning adults, and 4) egg deposition, egg fertilization rates, and embryo development. Trap nets were used to collect upstream migrant pink salmon, while electrofishing, carcass counts, and creel censuses were used to obtain recaptures. Left pectoral fin rays were used for aging and growth back-calculation. Redd samples were collected to estimate egg fertilization rates and embryo development. It was found that Lake Superior pink salmon are similar to their Pacific Coast counterparts, except that they are smaller and 3-year-old fish are common. The latter may preclude the genetic divergence based on spawning stock which is apparent in the Pacific. The sex distribution of 3-year-old pink salmon was highly skewed towards females. Three-year-old female pink salmon had a lower fecundity and a poorer egg quality than 2-year-old females. The major factor controlling the abundance of Lake Superior pink salmon appears to be limited spawning habitat.

Check Formation on the Scales of Hatchery-Reared Lake Trout Prior to and Soon after Release into Lake Superior

Abstract We investigated two assumptions about scales of hatchery-reared lake trout Salvelinus namaycush stocked as yearlings into Lake Superior: (1) only one check is formed during hatchery life and (2) a “stocking check” forms when the fish are released. We examined four scales from each of 176 fish prior to release from five hatcheries and 55 fish soon after release. Prior to release, 91 % of the lake trout had only one check. This percentage was 81–100% for individual hatcheries. Evidence for a stocking check was observed only on fish whose scales had grown substantially between release and subsequent recapture. All measures of variability were less and check conspicuousness was greater for fish raised in hatcheries with seasonal cycles of temperature and photoperiod than for those reared with nearly constant water temperatures and darkness. We conclude that the assumption of only one check prior to stocking was not grossly violated when several scales from the same fish were interpreted and that ther...

Great Lakes Fisheries: Are Explicit Controls Necessary?

This is an essay on the current state of fisheries management in the Laurentian Great Lakes. It is presented here to introduce the subject to an audience of control specialists who may have somewhat different theoretical and ecological perspectives on fishery management than do biologists practicing in the Great Lakes region. Following a brief history of Great Lakes fishery problems2, I will review the corrective measures that have been taken and identify the critical uncertainties surrounding past and present management activities. Where possible, I will identify those processes which may be amenable to significant intervention or control by management agencies.