Geology topics

Donald Mraz

Publications and source records attributed to Donald Mraz.

3 recordsLinked to original sources

USGS1964

Age and growth of the round whitefish in Lake Michigan

The round whitefish, though rarely abundant, is widely distributed in northern waters. It is one of the least studied of the coregonines; the present report is but the second for Great Lakes waters. Commercial production in Lake Michigan has been tightly confined to the northern portion. The period 1924-30 showed the best production: 200,000 to 359,000 pounds. Since 1956, production has been around 10,000 pounds or less. The present age and growth study is based on 208 fish collected by gill net in December 1951. The relation between total length in inches (L) and the weight in ounces ( W ) is described by the equation log W = -2.7232 + 3.2940 log L. Age-group III made up 66.3 percent, and age-group IV, 20.6 percent of the sample; age-groups V, VI, and VII combined contributed only 5.9 percent. The average length for all fish in the sample was 14.5 inches. Growth was calculated from a previously published linear body-scale relation with an intercept of 1.1 inches on the axis of fish length. The increments of calculated length declined steadily from a maximum of 4.6 inches the first year to 1.0 inch the eighth. A 3-year-old Lake Michigan fish (12.3 inches) is as long as a 5-year-old Lake Superior fish, and an 8-year-old Lake Michigan fish (18.9 inches) is 0.9 inch longer than the oldest (12 years) from Lake Superior. The smallest mature males and females were in the length intervals 12.0-12.4 inches and 13.0-13.4 inches, respectively. All males over 1.4 inches and all females over 14.9 inches were mature. The youngest mature males were in age-group II; 36 percent of II-group males but none of the females were mature. All fish older than age-group III were mature.

Transactions of the American Fisheries Society↗

USGS1964

Age, growth, sex ratio, and maturity of the whitefish in central Green Bay and adjacent waters of Lake Michigan

This study is based on 1,023 whitefish, Coregonus clupeaformis (Mitchill)--819 in seven samples from five localitites in central Green Bay in 1948-49 and 1851-52 and 204 in a single 1948 collection from northwestern Lake Michigan proper. Records of age indicated unusual strength for only one year class--1943 which strongly dominated the 1948 sample from Lake Michigan and the 1949 sample from Green Bay and was well represented in the 1948 collection from green Bay. Collection of 1951-52 without exception were dominated by age group III. Length distributions of samples varied widely according to the age composition. Among fish more than 2 years old, the length distributions of age groups overlapped broadly. Several 1-inch intervals included fish of four age groups. The length-weight relation varied considerably among central Green Bay samples, but differences among localitites were nearly equalled by the year-to-year difference at a single locality. Lake Michigan whitefish were generally lighter than those from Green Bay. Weight increased to the 3.386 power of length in Green Bay (combined samples) and the 3.359 power in Lake Michigan. Growth in length, calculated by direct proportion from diameter measurements of growth fields on scales, differed among localities in central Green Bay and between samples of different years at a single locality. If permanent locality differences exist they are not large and can be obscured by the evident annual fluctuations of growth. The grand average calculated length of Green Bay whitefish (combined collections) exceeded that of Lake Michigan fish in all years of life. The advantage was greatest (2.2 inches) at 3 years (calculated lengths of 16.0 inches and 13.8 inches) and subsequently declined to 0.5 inch at 9 years (lengths of 24.6 and 24.1 inches). Both groups reached the minimum legal length of 17 inches during the fourth growing season. Green Bay whitefish also had the larger calculated weights. The advantage reached 9.3 ounces in 3 years (calculated weights of 22.4 and 13.1 ounces). In years of life 4-9, the weight advantage over Lake Michigan fish ranged from 8.7 ounces, (seventh year; weights of 74.4 and 65.7 ounces) to 12.2 ounces (ninth year; weights of 96.2 and 84.0 ounces). Comparison of growth of whitefish at four localities in northern Lake Michigan indicates that fastest growth is in central Green Bay and slowest near the Fox Islands. Growth is intermediate and similar in northwestern Lake Michigan proper and sorthern Green Bay. Youngest mature male whitefish in green Bay belonged to age group II and youngest mature females to age group III. All IV-group fish were mature. Shortest mature males were at 14.5-14.9 inches and shortest mature females at 16.5-16.9 inches. All males longer than 17.9 inches and all females longer than 18.4 inches were mature.

Fishery Bulletin of the U.S. Fish and Wildlife Ser↗

USGS1952

Movements of yellow perch marked in southern Green Bay, Lake Michigan, in 1950

To obtain information on the post-spawning movements of yellow perch that spawn in southern Green Bay, Lake Michigan, 4,172 fish caught in drop nets were marked by tagging with monel-metal strap tags attached to the right operculum and 24,799 were marked by clipping off the second or membranous dorsal fin. Marking was done during the period from May 3 to 17, 1950, at six main stations, all located in the southern end of Green Bay. The average length of the tagged perch was 7.3 inches and all fell within the range 5.5–14.4 inches. Most (90.9 percent) of the fish were below the minimum legal length of 8.0 inches. The follow-up procedure consisted of informing commercial and sports fishermen of the program and enlisting their cooperation in watching for marked fish; accounts of the investigation were released through newspapers and descriptive posters were distributed. The personnel connected with the investigation examined catches frequently. The large majority (101 or 79.5 percent) of the 127 tagged perch recaptured in the experimental nets during the marking operations were retaken at the tagging station at which they were released. Of the 108 tagged perch captured by commercial fishermen and anglers following the opening of the season on May 20, 96 were taken by drop nets, 6 by gill nets, and 6 by hook and line. The mean lengths for the three groups were 7.7, 7.1, and 9.25 inches, respectively. All recoveries were made in the Wisconsin waters of Green Bay. Most of the “open-season” recoveries (86 fish; 79.6 percent) were made during the period May 20-May 31. Recaptures during subsequent months were: June–14; July–7; August–none; September–1. Of the 86 perch recaptured May 20–31, 70 were retaken inside and 16 outside the tagging area. The majority (14 of 22) of those recovered after May 31 were retaken outside the tagging area. The average length of the 20 tagged yellow perch recaptured by drop nets (data restricted to fish from a single type of net to avoid bias from gear selectivity) outside the tagging area (8.42 inches) was 0.96 inch greater than the mean length (7.46 inches) of the 76 fish retaken inside the area. This statistically highly significant difference lends support to the belief of commercial fishermen that the larger of the yellow perch that spawn in southern Green Bay move out soon after spawning. The percentage of recapture of tagged perch increased sharply with increase in the size of the fish. Not one of 169 tagged fish less than 6.5 inches long was recovered. The rates of recapture at greater lengths were: 6.5 to 8.9 inches–2.5 percent; 9.0 to 9.9 inches–11.4 percent; 10.0 to 14.4 inches–16.7 percent. Among the several factors suggested in explanation of this relationship, the most important appear to be the lesser ability of the smaller fish to survive the rigors of handling and tagging, greater loss of tags from the smaller fish, and the greater likelihood of overlooking the smaller of the tagged fish in the sorting of the catch. The factors just mentioned and the lack of knowledge of the efficiency of measures taken to obtain records of recoveries preclude the 2.6-percent return of all tagged fish from being accepted as an approximation of the rate of recapture. Neither should the 6.6-percent return of tagged fish of legal size (8 inches and longer) be taken as an estimate of the rate of exploitation. Although 465 fin-clipped perch were recovered in the experimental nets during the marking operations, only 68 of 24,799 fish so marked were recovered after the fishing season opened. All but one of these 68 were retaken near the point of marking. The difficulty of detecting a perch with a missing membranous dorsal is believed to be a major cause of the poor returns from fin-clipped fish. These investigations have demonstrated that for studying migration of yellow perch, tagging is superior to fin-clipping as a method of marking. The technique of the tagging, however, needs to be improved, and better means must be found to trace tagged fish of small size. Furthermore certain small regions in the bay not at present open to commercial fishing must be explored in order to obtain more comprehensive information as to migration.

Transactions of the American Fisheries Society↗