Geology topics

George R. King

Publications and source records attributed to George R. King.

4 recordsLinked to original sources

USGS1975

Changes in the lake trout population of southern Lake Superior in relation to the fishery, the sea lamprey, and stocking, 1950-70

Commercial catch and effort statistics for 1929-70, samples of commercial catches in 1959-62, and records of examinations of all lake trout (Salvelinus namaycush) taken commercially in inshore waters of Michigan and Wisconsin in 1962-70 were the basis for descriptions of changes in the population in 1929-70. Abundance fluctuated cyclically and gradually downward in 1929-49, whereas fishing intensity tended to increase during the same period. In 1950-52, a change from cotton to nylon twine in gillnets raised effective fishing effort to 305% of the 1929-43 average in Michigan waters and to 228% in Wisconsin waters; production held near average. Abundance fell to 18% of average in Michigan in 1953-61 and to 25% of average in Wisconsin in 1956-61; in the same periods, production fell to 11% of average in Michigan and to 19% in Wisconsin. In 1962-70 abundance rose to 160% in Michigan and 246% in Wisconsin while production and fishing intensity were held low (3-14%) by regulation. Changes in abundance of lake trout were attributable to a sequence of developments in successive series of years; intensive fishing in the early 1950's; severe sea lamprey predation in the late 1950's; an 85% reduction in abundance of sea lampreys in mid 1961; and the combination of sea lamprey control, intensive stocking of yearling lake trout, and restrictions on fishing in 1962-70. A decline in average size of lake trout and the near elimination of spawning stocks in 1953-61 curtailed recruitment of native lake trout in the mid 1960's. Stocking of fin-clipped lake trout replaced natural reproduction in the early 1960's. In 1965-70, the lake trout population was composed mainly of hatchery-reared fish. Natural reproduction was reestablished on one major spawning shoal in Wisconsin in 1965, but in 1970 only 10% of the legal (17-inch and longer) and 17% of the undersize lake trout in Wisconsin were native fish. Reduction of sea lamprey abundance resulted in an immediate increase in survival and abundance of lake trout, especially of the larger sizes. As abundance of lake trout progressively increased in 1962-70, survival of the smaller legal-size lake trout increased, probably due to reduction of the predator-prey ratio and an increase in availability of larger lake trout preferred by sea lampreys. Abundance of spawning-size lake trout was limited by high natural mortality in 1965-70. Circumstantial evidence suggested that sea lamprey predation contributed a major part of the high natural mortality.

Technical Report↗

USGS1968

Rehabilitation of lake trout in the Apostle Islands region of Lake Superior

Marked success of rehabilitation of lake trout in Lake Superior has been due principally to the control of the sea lamprey and closure of the lake trout fishery in 1962 and large-scale plantings of yearling lake trout in 1959-66. After the sea lamprey became established in the late 1940s, spawning stocks of lake trout began to decrease and were almost nonexistent by 1960-61. After control of the sea lamprey and closure of the commercial fishery for lake trout in 1962, the abundance of spawning stocks began to rise and reached the highest levels on record in 1964-66. Successful spawning in 1964 and 1965 was demonstrated by catches of age-0 lake trout in 1965 and 1966, the first evidence of natural reproduction since 1959. Plantings of hatchery-reared lake trout in Wisconsin waters of Lake Superior began in 1952. The percentage of hatchery-reared fish in catches of juvenile lake trout increased almost steadily from 1953 to 1965 (when nearly all were of hatchery origin). The abundance of juvenile fish increased from 1959 to 1962 and remained nearly constant in 1962-66. The success of lake trout plantings was highest in 1959-61 but generally declined after 1961; the success of the plantings was inversely related to the abundance of older lake trout. Annual increments of growth of hatchery-reared lake trout varied from 1.1 to 5.0 inches after planting. The average lengths of fish of identical age-groups varied according to gear of capture, depth of water, and season. More than 65% of the season's growth of age-III lake trout took place after September. The findings indicate that the present rate of stocking lake trout may be higher than necessary to maintain optimum abundance.

Journal of the Fisheries Research Board of Canada↗

USGS1967

Returns of hatchery-reared lake trout in southern Lake Superior, 1955-62

Experimental plantings of fin-clipped lake trout (Salvelinus namaycush) of various ages have been made in southern Lake Superior since 1952. The catch of planted lake trout by the commercial fishery was used to measure the success of stocking. Estimates of total returns were based on samples of 8.2 to 21.2% of the Wisconsin catches in 1955-62 and 36.4 to 46.8% of the Michigan catches in 1959-62. Marked lake trout were assigned to various plantings according to the fin mark, length of fish, readings of age from scales, and locations of capture. Estimated returns from Wisconsin plantings of 9-month-old lake trout varied from 2.1 to 6.4%. Wisconsin releases of 16-month-old fish yielded returns of 5.7 to 37.3%. Returns from plantings in Michigan were 0.3% for 9-month-old fish and 1.5 to 3.8% for 16-month-old fish. The ratios of the returns from plantings of 16-month-old fish to those of 9-month-old fish were 3.9:1 for Wisconsin releases and 6.7:1 for Michigan releases. Lake trout planted in Wisconsin generally survived better than those released in Michigan. Returns from fish planted at ages of 17 to 40 months in Michigan in 1958-59 were far greater than those from 16-month-old fish released in Michigan, but were not as high as from the most successful plantings of 16-month-old fish in Wisconsin. Lake trout released in 1960 from shore and from boats survived equally well. Average size of lake trout at release was more closely related to survival than any other factor. All except 1 of 10 highly successful releases were of fish larger than 22 per lb, and all 6 poor releases were of fish smaller than 34 per lb. Fish that ran 22 to 33 per lb survived only moderately well. A size of 17 to 20 fish per lb appears to be close to optimum. Abundance of native lake trout, American smelt (Osmerus mordax), and sea lampreys (Petromyzon marinus) all appeared to be unrelated to stocking success. The only apparent method of rapidly improving the success of stocking is to rear all lake trout to an average size of 17 to 20 per lb.

Journal of the Fisheries Research Board of Canada↗

USGS1965

Movements of hatchery-reared lake trout in Lake Superior

The history of stocking of lake trout (Salvelinus namaycush) in the Great Lakes is reviewed. The study of movements is based on capture of 24,275 fin-clipped lake trout taken in experimental gill nets and trawls and commercial gill nets. Yearling lake trout planted from shore dispersed to 15-fath (27-m) depths in 3A? hr. Most fish remained within 2 miles (3.2 km) of the planting site 2 months, but within 4 months some fish had moved as much as 17 miles (27 km). The highest abundance of planted lake trout was in areas 2-4 miles (3.2-6.4 km) from the planting site even 3 years after release. Distance moved and size of fish were not correlated. Dispersal of lake trout begins at planting and probably continues until the fish are mature. Most movement was eastward in southern Lake Superior and followed the counterclockwise surface currents. Movement is most rapid in areas of strong currents and slowest in areas of weak currents or eddies. Movement to areas west of the Keweenaw Peninsula was insignificant from plantings in Keweenaw Bay and nil from other plantings farther east. Lake trout planted in the eastern third of the lake dispersed more randomly than those planted farther west. Few fish moved farther offshore than the 50-fath (91-m) contour. Lake trout planted in Canadian waters made insignificant contributions to populations in US waters.

Journal of the Fisheries Research Board of Canada↗