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- 검색키워드
- 저자 : Fost, Brooks A (검색결과 1 건)
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Fost, Brooks A The Pennsylvania State University ProQuest Dissert 2017 해외박사(DDOD)
A recent analysis of Pennsylvania Fish and Boat Commission historical data collected from streams throughout Pennsylvania containing trout concluded that base-flow pH is strongly correlated to the observed segregation of Brook Trout (Salvelinus fontinalis) and Brown Trout (Salmo trutta). Populations of Brook Trout, which are native to Pennsylvania, predominated at pH<7.0 (mostly headwaters), while Brown Trout, an introduced species that has become naturalized in much of Pennsylvania, predominated at pH>7.0 (lower reaches). The decline of historic Brook Trout populations has been linked in part to competition with Brown Trout (Hudy 2005). The relationship between the segregation pattern observed and pH is significant because low pH may be acting as a barrier that prevents further invasion of Brown Trout into the headwaters, where Brook Trout populations remain strong. The overall goal of this study was to examine the influence of pH and species interactions on the distribution of Brook Trout and Brown Trout in Pennsylvania streams. The first study examined shifts in Brook Trout and Brown Trout pH preference/avoidance after exposure to different pH conditions. Adaptation to pH is important because the results of behavioral studies may differ depending on pH exposure history. Adaptation to pH is particularly important for Brook Trout and Brown Trout because these species are often segregated in streams with a pH gradient, suggesting that behavioral responses to pH differ between the two species. In order to study how the behavioral response differed between the two species, it was necessary to determine if pH exposure history altered behavioral response. Thus, hatchery-reared Brook Trout and Brown Trout were exposed to different holding pH treatments for seven days prior to determining their behavioral response to pH. Preference was determined in a long trough where a gradient of pH (4.0-7.0) was presented to fish. Steep gradient choice tanks were used to determine avoidance. I found that hatchery-reared Brook Trout and Brown Trout pH preference was not influenced by holding pH. Results of pH avoidance trials were similar to that of preference studies, in that holding pH did not alter pH avoidance of either species. This study suggested that individuals of these species can be held in the laboratory at a pH different from the source waterbody for a short period of time without altering preference or avoidance behavior. Thus, the pH of the laboratory source water was not adjusted for the purposes of examining preference and avoidance behavior of wild fish. The second study investigated the pH preference and avoidance of wild, adult Brook Trout and Brown Trout using the same methodology applied in the first study. The behavioral response of Brook Trout and Brown Trout to low pH is one of factor that may lead to the observed segregation pattern of the two species in Pennsylvania streams. The observed segregation pattern and behavioral responses to episodic events suggest that differences in the pH preferred or avoided may exist. Although pH preference and avoidance of juveniles have been established, the preference and avoidance of adults have not been examined. Wild, adult Brown Trout showed a preference for pH 4.0 while wild, adult Brook Trout did not prefer any pH within the range tested (pH 4.0 -- 7.0). Adult Brown Trout displayed a lack of avoidance at pH below 5.0, which is similar to that reported for juvenile Brown Trout. The avoidance pH of wild, adult Brook Trout (between pH 5.5 and 6.0) and Brown Trout (between pH 6.5 and 7.0) did not differ appreciably from earlier study results for the avoidance pH of juvenile Brook Trout and Brown Trout. A comparison of confidence intervals around these avoidance estimates indicates avoidance pH is similar among adult Brook Trout and Brown Trout in this study. However, the limited overlap of confidence intervals for avoidance pH values for the two species suggests that some Brown Trout will display avoidance at a higher pH when Brook Trout will not. The results of this laboratory study indicate that adult Brook Trout -- Brown Trout segregation patterns in Pennsylvania streams could be related to pH and that competition with Brown Trout could be mediating the occurrence of Brook Trout at some pH levels. The preference and avoidance pH results from this study were used to design field experiments involving species interactions and pH. The final study examined the effects of acidification and species interactions on the distribution of Brook Trout and Brown Trout. Although pH appeared to be correlated with the observed distribution patterns of Brook Trout and Brown Trout in Pennsylvania streams, our laboratory studies examining the avoidance pH of wild, adult Brook Trout and Brown Trout did not conclusively find that avoidance pH differs between these species. The lack of conclusive difference in the pH avoidance threshold did not rule out pH as a mediating factor. Interactions between Brook Trout and Brown Trout could lead to habitat partitioning in a stream. Brown Trout are considered superior competitors, but a physiological advantage may allow Brook Trout to dominate Brown Trout in headwaters, particularly if pH is lower. Thus, the behavior of wild, adult Brook Trout and Brown Trout (alone and in combination) was observed in study reaches that were manipulated to vary the level of acidity and CO2. In the artificial stream channel, the majority of indwelling fish (fish that spent greater than 0 seconds on the treatment side during the control observation period) responded to acidification by moving to more neutral conditions (62% of Brook Trout and 68% of Brown Trout). Indwelling Brook Trout spent less time in acidic conditions during the acid treatment (41 +/- 5%) than during the control period (94 +/- 2%). However, elevated levels of CO2 may have caused their avoidance at a higher pH. Indwelling Brown Trout spent less time in the acid conditions during the acid treatment (44 +/- 4%) than during a control period (98 +/- 1%). The proportion of time spent in the acid water by indwelling trout decreased as negative interactions with other fish (such as chasing) increased. Presence of the opposite species did not influence the proportion of time spent in the acidic conditions. The results of this study do not support the hypothesis that acidification mediates the segregation of Brook Trout and Brown Trout in Pennsylvania streams. Confounding factors, relating to changes in CO2 associated with the acid manipulation, and issues relating to stocking density need further investigation to identify what role these may have played.
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