Broadscale Population Structure and Hatchery Introgression of Midwestern Brook Trout

To present evidence of acid-induced stress, we studied the population structure and distribution of brook trout (Salvelinus fontinalis) in acidified Lac Tantaré, Quebec. Trout greater than 21 cm (FL) represented only 16.2 and 10% of the population sampled in 1979 and 1980, respectively. Survival rates of trout from 1979 to 1980 indicated higher survival among individuals > 25 cm, mortality occurring primarily among fish of 13–25 cm. The marked decline in numbers of fish occurring at 21 cm coincided with the size at which 50% of the female trout population reached sexual maturity, suggesting that postspawning mortality contributes to the high mortality observed among these fish. Comparisons of population and individual growth rates revealed that smaller fish of age-classes 1 to 5 suffer higher mortality than do the larger individuals of these age-classes, implicating mortality agents other than those related to spawning. We provide evidence to support the hypothesis that the most probable cause of mortality is size-related differential exposure to toxic stress whereby small brook trout (< 25 cm) are found in lake areas (brooks) exhibiting the most potentially toxic combination of pH and aluminum, thus enhancing the exposure of the most susceptible part of the population to toxic stress. Large brook trout [Formula: see text] are found in the "safest" lake areas (springs), thus diminishing the exposure of the least susceptible part of the population to toxic stress and enhancing survival. Female trout exhibit delayed sexual maturity relative to other Quebec populations, attaining 50% maturity at age 3 and a length of 21–24 cm such that the major part of the population's reproductive effort is provided by those fish representing only 15% of the population in 1979 and 1980. During the October spawning season, 20% of potential spawners exhibited retarded oogenesis. These reductions in reproductive effort and changes in spawning site selection provide evidence in support of the hypothesis that recruitment failure may be occurring in the Tantaré brook trout population.

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Exploitation of Self-Sustaining Ontario Stream Populations of Brown Trout (Salmo trutta) and Brook Trout (Salvelinus fontinalis)

Journal of the Fisheries Research Board of Canada ◽

10.1139/f70-124 ◽

1970 ◽

Vol 27 (6) ◽

pp. 1087-1102 ◽

Cited By ~ 7

Author(s):

T. Lawrence Marshall ◽

Hugh R. MacCrimmon

Keyword(s):

Population Structure ◽

Brown Trout ◽

Brook Trout ◽

Standing Crop ◽

Salmo Trutta ◽

Salvelinus Fontinalis ◽

Catch Per Unit Effort ◽

High Quality ◽

Exploitation Rate ◽

Brown Trout Salmo Trutta

The August standing crop of harvestable brown trout (Salmo trutta, 90%), and brook trout (Salvelinus fontinalis, 9%) in the upper Sydenham River, Ont., was estimated at 499 trout/ha (63.2 kg/ha) during 1966 and 1967. Brown trout were of age I (68%), age II (23%), and the remainder of ages III, IV, V, and XIII. Brook trout were ages I (95%) and II only.The average annual harvest by 1501 anglers was 1135 fish (64% brown, 35% brook trout) at a rate of 0.34 fish/hr. Exploitation of the preseason standing populations of brown and brook trout was 23 and 59%, respectively. Catch per unit effort from the downriver section (all brown trout of ages II–IV and mean length of 34.0 cm) averaged 0.10 at an angling pressure of 264 hr/ha. An upriver section occupied predominantly (90%) by brown trout of age I–III and mean length of 26.8 cm yielded 0.67 trout/hr at an angling pressure of 251 hr/ha.The population structure, growth, and exploitation rate of naturalized brown trout favours its use in providing continuous angling of creditable quality in heavily fished headwater streams. Coexistence of self-sustaining populations of brown and brook trout provide a sustained, high-quality mixed fishery.

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