The biology of anadromous Salvelinus fontinalis (Mitchill, 1815) and Salmo trutta Linnaeus, 1758 in river systems flowing into Placentia Bay and St. Mary's Bay, Newfoundland

O'Connell, M. F. (Michael Francis) (1982) The biology of anadromous Salvelinus fontinalis (Mitchill, 1815) and Salmo trutta Linnaeus, 1758 in river systems flowing into Placentia Bay and St. Mary's Bay, Newfoundland. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The biology of anadromous brook trout (indigenous) and brown trout (introduced) was studied for several river systems flowing into Placentia and St. Mary's Bays, Newfoundland. Outward movements of brook trout were observed from April to June; inward movements occurred in July-August. Movements between fresh and salt water in Northeast and Southeast Arms, Placentia appear to occur throughout the year. Outward movements of brown trout occurred concurrently with brook trout (North Harbour River, S.M.B.) while inward movements were observed from July through September. Smolt age of brook trout ranged from 1.⁺ to 7.⁺ years and that of brown trout from 1.⁺ to 8.⁺ years. Modal smolt age of brook trout ranged from 2.⁺ to 4.⁺ while for brown trout it was 2.⁺ to 3.⁺. The great majority of all samples for both species were comprised of smolt/post-smolt. It is possible that specimens of brown trout with a history of sea life leave North Harbour River, S.M.B. in a discrete run prior to the one observed in April-May which was comprised almost exclusively of smolt. There was some indication that homing occurs to Southeast River and its tributary Beaver River for brook trout. -- Growth in freshwater was slower than previously reported for the freshwater form of each species in lakes on the Avalon Peninsula. Growth in freshwater and salt water was slower than that reported for anadromous populations elsewhere in North America (brook trout) and in Europe (brown trout). The slow growth of brown trout in salt water could partially result from the relatively small portion of the yearly increment attained during the winter with temperature being the dominant determining factor. Newfoundland populations overwintering in estuarine and coastal areas likely experience temperatures of 0°C and less compared with 5-6°C for certain European populations. There was a dramatic increase in growth rate in salt water compared with freshwater for both species; also there was a tendency towards attainment of a greater ultimate size the younger the smolt age. -- All age groups of smolt on North Harbour River, S.M.B. were significantly smaller than observed for the other areas. This appears to be the result; of overwintering in flowing water on that river as opposed to lakes for the others. Lakes afford better temperature and feeding regimes as well as more living space. Based on the fact that the growth increment attained at the end of the growing season for parr remaining in North Harbour River, S.M.B. is similar to that of the other areas, it does not appear that the size difference in smolt has an adaptive basis but rather reflects a homeostatic compensatory response to temporal environmental conditions. -- While size has been reported to be an important factor in smoltification and the development of salinity tolerance, it is not the only one. Smolt in the present study were substantially smaller than those reported in the literature as suffering high mortality upon direct transfer to seawater. These phenomena appear to be the result of a synergistic process involving several variables such as temperature, photoperiod, water level and living space. -- Except for some differences in percent occurrence of items in gut contents, the food of brook trout and brown trout were similar in both fresh and salt water. -- Spawning time varied with area for brook trout (first three weeks in October for North Harbour River, S.M.B, and first three weeks in November for Southeast River); no spawning concentrations of brown trout were located. Sex ratio was significantly in favor of females for brook trout in virtually all cases, no significance and no consistent trend in favor of either sex was found for brown trout. Age at first maturity for brook trout was 2⁺ for both sexes; for brown trout it was 2⁺ for males and 3⁺ for females. The percentage of brook trout males reaching maturity in a given age group was higher than than of females in the majority of cases; there was no consistent trend for brown trout. For both species there was a tendency for a lower percentage of anadromous fish to reach maturity in a given age group than reported for their counterparts in freshwater. Both sexes of brook trout appear to be alternate spawners; there was evidence for the same for female brown trout. For brook trout, parr and specimens with a sea history spawn together; kelts of each sex showed evidence of spawning and parr. Male brown trout can spawn as parr. -- Reproduction in anadromous brook trout and brown trout is spread over the maximum number of years. Delay of maturity until a larger size is attained probably results in a higher reproductive effort and juvenile survival. Atlantic salmon cohabiting the same rivers are more r-selected in that the overall life span is shorter and they probably produce a higher reproductive effort. Salmon are consecutive spawners as opposed to alternate spawners. -- Brown trout introduced to Newfoundland were mainly British and were of the freshwater form. They have since become anadromous in Newfoundland waters. Growth rate in freshwater and salt water is lower than that published for British anadromous populations (as already pointed out) and age at first maturity and longevity are greater. Alternate spawning is exhibited instead of consecutive spawning. Differences in exploitation between Newfoundland and Great Britain over the years could compound any assumptions based on life history theory predictions. -- Since their introduction in the 1880's through early 1900's, the spread of brown trout (colonization by means of the sea) was rather slow. This could be the result of a combination of the following factors: (1) straying rate, (2) slow growth and hence low egg deposition potential, and (3) the fact that a relatively large number of specimens of both sexes may not mature after entering a river. For one of the rivers studied, the establishment of a population of brown trout has been to the detriment of brook trout. It is not possible in light of present data to say if resource competition in freshwater has contributed to an observed decline in numbers of anadromous brook trout concomitant with an increase in numbers of brown trout on that river. However, there is evidence to suggest that a combination of greater vulnerability to angling on the part of brook trout, angler preference and adjustments in the length and timing of the licenced angling season have in part brought about this result.

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