Date of Award:

1979

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Natural Resources

Department name when degree awarded

Wildlife Science

Advisor/Chair:

Richard S. Wydoski

Abstract

Certain aspects of the biology of two species of fish, bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides), and the assessment of fishing pressure upon the sport fishery of Pelican Lake, Uintah County, Utah, a 680 ha warmwater lake, were studied between April 1, 1976 and June 30, 1978. The growth rate of bluegills (sexes combined) was fairly rapid; the mean back-calculated total lengths from ages one through nine were 55, 112, 166, 194, 211, 229, 245, 256 and 259 mm. The growth of largemouth bass was 104, 194, 271, 316, 350, 405 and 416 mm total length for ages one through seven for the combined sexes. Male bluegills matured earlier in life than females. Bluegills spawned continually from the first of June to the first of September, although the peak spawning occurred in June of both years. Gonadal weight to body weight ratios (maturity index) were greatest in the first of June for both male and female bluegills. Fecundity estimates ranged from 1 1,102 mature ova for an age II bluegill to 4 6, 281 mature ova for an age V bluegill. Fecundity estimates for largemouth bass ranged from 4,810 mature ova for a II year old to 31, 719 mature ova for a V year old. Largemouth bass spawned primarily in late May in 1976 and early June in 1977.

Angler use of the lake was estimated to be 10,054 angler days fished in 1975, culminating a seven-year increase in use, with subsequent declines in angling to 8,001 angler days in 1976 and 5,027 in 1977. A significant winter fishery developed in 1978. Anglers harvested an estimated 58,277, 44,918 and 22,469 bluegills and 5,791, 2,747 and 4,176 largemouth bass in 1975, 1976 and 1977, respectively. Angler catch rates for bluegills in respective years were 1.520, 1.640 and 1.130 fish/hr and 0.204, 0.094 and 0.213 fish/hr for largemouth bass. Bluegill age groups IV and V and largemouth bass age group III composed the majority of angler harvested fish in 1976 and 1977. Age and size composition of angler harvested bluegills indicated no statistically significant change between 1976 and 1977. Bass harvested by anglers in 1977 were significantly greater in weight than those harvested in 1976. The total annual mortality determined from scale analyses of angler harvested fish was 59.9% for bluegill and 71.6% for bass. A significant number of male bluegills was harvested by anglers in June 1977, the period of peak nesting activity. Anglers released 5,158 bluegills in 1977, of which an estimated 11% (565) were lost to hooking mortality. Of various hook sizes used to assess hooking mortality, number 8 regular shank hooks yielded the highest total mortality (18%). The lowest hooking mortality was with number 6 regular shank jig hooks (0%) and where the leader was cut and the hook allowed to remain (0%). Higher mortality of worm-hooked fish was attributed largely to anatomical location of hooking. Of the total (19) bluegill mortalities, 63% were hooked in the esophagus and 37% in the gill/gill arch.

Postwinter population sampling in May 1977 indicated the estimated standing crop weight was 40% less than the prewinter standing crop weight in Au gust 1976. A similar loss in standing crop (37%) was noted in weight from August 1977 to June 1978. The greatest loss in numbers was in young-of-the-year bluegill that suffered an estimated 98% overwinter mortality. Midwinter water quality analyses indicated that anoxic conditions occurred from 2.0 m below the ice to the bottom. An increase in hydrogen sulfide levels was also detected.

Recommendations for the fishery were (1) adjustment of the daily bag limit for the bluegill sport fishery with fluctuations in angling use; (2) continuation of a creel census from April 1 through July 31 similar to the design used in this study to annually assess angling use, catch rates, total harvest and the size and age composition of this harvest; (3) stomach analyses of potential predators to assess the overwinter mortality of blue gills; (4) retainment of the current bag limit on largemouth bass with future consideration of utilizing a 12-15-in (305-381 mm) total length limit to increase the numbers of larger, older bass in the population; (5) nonrestrictive use of terminal gear by anglers since hooking mortality of bluegills caught and released by anglers in the summer of 1977 was insignificant; (6 ) no size length restrictions on the bluegills retained by anglers; and (7) consideration of purchasing additional water storage from the irrigation company.

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