Comparative ecology of the brook trout (Salvelinus fontinalis Mitchill) in two natural and one fertilized lake in central insular Newfoundland

Clancy, Sean Richard (2001) Comparative ecology of the brook trout (Salvelinus fontinalis Mitchill) in two natural and one fertilized lake in central insular Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

This study compares aspects of the feeding, physiological, population dynamics, ecology, and the life history of the brook trout, Salvelinus fontinalis Mitchill in three ponds of the Experimental Ponds Area (EPA), central Newfoundland. Two of the ponds were natural control ecosystems while the third had been fertilized with nitrogen and phosphorus each summer since 1991. -- Analysis of stomach contents was used to evaluate feeding intensity and diet composition. Feeding intensity generally decreased throughout the summer. Brook trout were predominantly benthic feeders and switched from a diet dominated by odonate nymphs (Corduliidae) in the spring to one composed of snails (Gastropoda), smaller-sized insect taxa (Trichoptera, Corixidae) and organisms found on or near the surface waters of the pond later in the summer and early fall (Diptera, Hymenoptera). Modest variation in the prey groups selected by male and female trout indicated spatial differences where each gender feeds within the lake ecosystem. Large fish fed on larger-sized prey taxa and had a greater mean ration in comparison to small fish. -- Analysis of somatic-visceral percent lipid content was used to document the seasonal change in physiological condition of large, maturing male, and female trout. The monthly mean lipid content increased from spring to a maximum in mid-summer, then decreased through to fall for each gender. Lipid accumulation coincided with the period when mean ration was greatest, while lipid depletion coincided with a decrease in feeding intensity, an increase in metabolism inferred from higher water temperatures and the diversion of lipid into gonadal mass. Percent lipid content was positively correlated with two indices of condition and negatively correlated with water content which can be used to predict lipid content. -- Analysis of annual seasonal population census data from 1991 to 1996 and electro-fishing data collected in 1996 facilitated the description of the life history and growth characteristics of brook trout in the three ponds. Young-of-the-year were most predominant in the streams and cohort patterns indicated trout enter the ponds at ages 1+ and 2+. The lack of older fish in the streams suggests that death may be the principle source of loss for pond fish aged 2+ and older. The maximum age observed was age 5+. Male trout matured at a smaller size and at a younger age, on average, than females; the majority of reproductive individuals were age 3+. Female brook trout produced an average of 236 eggs per female with a mean egg diameter of 3.23 mm. EPA brook trout displayed generally smaller fork lengths at age than fish in other lakes on the mainland and insular Newfoundland. -- Comparison of the temporal change in the brook trout population abundance, population structure and growth characteristics in the experimental pond relative to the controls facilitated the investigation of the potential effects of the whole-lake fertilization experiment. There was an increase in brook trout density in the experimental pond relative to the controls during the fourth year of fertilization, consistent with an expected 'bottom-up' response to increased macroinvertebrate abundance, followed by increased mortality rates possibly attributable to a 'top-down' impact by loons. Fertilization appears not to have increased growth rates of fish in the experimental pond, as indicated by the comparisons of age-class fall weight, however the growth patterns of experimental pond fish varied less among individuals than those of the control ponds across years.

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