Early Survival and Recruitment of Smallmouth Bass in Northern Michigan

Abstract

Survival for six life-history stages from egg to fall fingerling was estimated for the 1967, 1968, and 1969 cohorts of smallmouth bass (Micropterus dolomieui) in Katherine Lake in the Upper Peninsula of Michigan near the northern limit of the species' range. The percentages of egg potentials that were deposited on nests were low (15-34 percent). Survival between egg deposition and the postlarval stage was consistent in all years (26-33 percent). Although there was no correlation between firstyear survival of the 1967-69 year classes and temperature, there was a significant correlation between strength of the 1959-66 year classes (as estimated from adjusted population numbers at age IV) and air temperatures during the first summer of life. Since dominant year classes produced in the three years (1959, 1963, and 1966) which had the warmest June-October temperatures contributed greatly to the correlation, the discrepancy between the 1959-66 and 1967-69 data probably resulted from the lack of overall average or above-average temperatures during any year of the latter period. J. WILDL. MANAGE. 39(1):194-200 Fry and Watt (1957) found that populations of smallmouth bass on Manitoulin Island in Lake Huron produced strong year classes in years of high summer air temperatures. Comprehensive studies of the South Bay, Manitoulin Island, population (Watt 1959) indicated that 94 percent of the variation in numbers of bass recruited to the fishery was due to temperatures in the summer the cohort was spawned. Watt suggested that temperature may regulate abundance of smallmouth bass populations near the northern limit of their range. Forney (1972) suggested that, at such latitudes, low temperatures throughout the first growing season may limit survival. The objective of this study was to determine the precise stage at which temperature influenced recruitment of year classes of smallmouth bass in Katherine Lake in northern Michigan, also near the species' northern limit. Survivals during the egg, fry, and fingerling stages and year-class strength in the autumn were estimated for the 1967-69 cohorts and examined for correlation with air temperatures during the first summer. Adjusted numbers at age IV for year classes already recruited by 1967 (1959-66) also were compared with temperatures during their first growing season. C. Harris, B. Otterpohl, T. Cannon, and J. Kowalis aided in the field studies. J. McFadden, W. C. Latta, G. Cooper, F. Hooper, J. Forney, and D. Karna offered valuable criticisms. A. Sutton drafted the figure. This paper is based on a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The University of Michigan. STUDY AREA AND METHODS Katherine Lake is in the Sylvania Recreation Area, Gogebic County, in Michigan's Upper Peninsula. It has an area of 19.4 ha (47.9 acres) and a maximum depth of 17.7 m (58 ft). There is no inlet or outlet. Total alkalinity was 3 ppm and pH was 5.7 in 1969. Smallmouth bass and the central mudminnow (Umbra limi) were the only species of fish in the lake. Although primary productivity was not measured, sev'A contribution from Dingell-Johnson Project F-28-R, Michigan. 2 Present address: Department of Natural Resources, Cornell University, Ithaca, New York 14853. 194 J. Wildl. Manage. 39(1):1975 This content downloaded from 207.46.13.37 on Wed, 03 Aug 2016 04:59:25 UTC All use subject to http://about.jstor.org/terms BASS SURVIVAL AND RECRUITMENT * Clady 195 eral characteristics of Katherine Lake (e.g., few larger aquatic plants, abundant organic materials in the bottom, low electrolyte content, low pH, floating mats of Sphagnum and other bog plants, and brown-stained water) indicate a progressive state of lake succession in which biological productivity is generally low (Welch 1952). Estimation of the proportion of egg potential spawned, and the survival from egg to postlarva and postlarva to fall fingerling required estimates of the number of survivors at each subsequent stage. Annual egg potential was equal to the average fecundity of mature size groups multiplied by one-half the spring population estimate for that group. Populations of adult smallmouth bass were estimated by the mark and recapture method and the formula of Schumacher and Eschmeyer (1943) during each May and June, 1967 through 1969. Four trap nets were set at randomly selected sites in 1967, but in 1968 and 1969 nets were moved almost daily among sites which proved productive in 1967. Fish were measured, fin-clipped, and released in an area remote from any net lead. The number of census days was 17 in 1967, 18 in 1968, and 17 in 1969. Estimates of size groups were converted into estimates of age groups after aging a representative sample of scales from fish of each of 8 size groups between 228 and 430 mm. Fecundities were estimated from counts of clear, large eggs taken from subsamples of ovaries preserved in 10 percent formalin. Bass nests were observed with a water telescope during the last week of May and the first two weeks of June. Collections of eggs and postlarvae were made with a glass tube siphon (Carbine 1939) from 10 percent of the nests, which were mostly in water 1 to 2 m deep. A nest was siphoned until no more eggs or larvae could be seen or taken. Collections were strained and preserved in 10 percent formalin. In each of the three years, counts were made of the total number of nests, and, with one exception, of the number of eggs and postlarvae in five nests. Total numbers of eggs deposited and postlarvae emerging were estimated by multiplying the number of nests observed by mean counts of eggs and larvae per nest. Populations of fall fingerlings were estimated by mark-and-recapture and the Schumacher-Eschmeyer formula in late August and early September, 1967-69. Fish were captured by electrofishing at night from a fiberglass boat equipped with a boom and five electrodes. Output from a 2,500-watt, AC/DC generator was modified by a control unit with a variable voltage transformer to produce an electrical field of up to 560 volts AC. All areas of the lake less than 2 m deep were fished on 10 days in 1967, 6 in 1968, and 10 in 1969. Air temperatures from June through October, 1959-69, for the western Upper Peninsula, recorded by the National Weather Service, were expressed as the algebraic sum of the monthly deviations from the long-term mean air temperature (Fry and Watt 1957). For cohorts recruited from 1959 through 1966, annual natural mortalities of 50 percent for the second, third, and fourth years of life and 30 percent thereafter were used to adjust the populations measured in 1967 to an estimate of the numbers of fish in each year class that would have been present at age IV. These rates were approximate mean natural mortalities for juveniles and adults as determined from population estimates made in 1967, 1968, and 1969 (Clady 1970). Ranks were then assigned to the adjusted populations at age IV to evaluate the comparative strengths of the year classes. J. Wildl. Manage. 39 (1) :1975 This content downloaded from 207.46.13.37 on Wed, 03 Aug 2016 04:59:25 UTC All use subject to http://about.jstor.org/terms 196 BASS SURVIVAL AND RECRUITMENT * Clady Table 1. Estimated number and fecundity of mature female smallmouth bass, by size groups, in Katherine Lake, 1967-69. Size group Year of Females Females Mean (mm) observation present examined fecundity 228-252 1967 6 1 2,910 253-278 1967 23 2 3,183 1968 33 1 2,757 1969 14 1 3,567 279-303 1967 32 2 4,539 1968 42 4 5,177 1969 50 3 4,179 304-328 1967 21 2 5,65