Observations On Brook Trout

Author : Brooks Fost
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (992 download)

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Download or read book PH Preference and Avoidance of Adult Brook Trout and Brown Trout written by Brooks Fost and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A recent analysis of Pennsylvania Fish and Boat Commission historical data collected fromstreams throughout Pennsylvania containing trout concluded that base-flow pH is stronglycorrelated to the observed segregation of Brook Trout (Salvelinus fontinalis) and Brown Trout(Salmo trutta). Populations of Brook Trout, which are native to Pennsylvania, predominated atpH7.0 (mostly headwaters), while Brown Trout, an introduced species that has becomenaturalized in much of Pennsylvania, predominated at pH7.0 (lower reaches). The decline ofhistoric Brook Trout populations has been linked in part to competition with Brown Trout (Hudy2005). The relationship between the segregation pattern observed and pH is significant becauselow pH may be acting as a barrier that prevents further invasion of Brown Trout into theheadwaters, where Brook Trout populations remain strong.The overall goal of this study was to examine the influence of pH and species interactions on thedistribution of Brook Trout and Brown Trout in Pennsylvania streams. The first study examinedshifts in Brook Trout and Brown Trout pH preference/avoidance after exposure to different pHconditions. Adaptation to pH is important because the results of behavioral studies may differdepending on pH exposure history. Adaptation to pH is particularly important for Brook Troutand 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 howthe behavioral response differed between the two species, it was necessary to determine if pHexposure history altered behavioral response. Thus, hatchery-reared Brook Trout and BrownTrout were exposed to different holding pH treatments for seven days prior to determining theirbehavioral 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.ivI found that hatchery-reared Brook Trout and Brown Trout pH preference was not influenced byholding pH. Results of pH avoidance trials were similar to that of preference studies, in thatholding pH did not alter pH avoidance of either species. This study suggested that individuals ofthese species can be held in the laboratory at a pH different from the source waterbody for ashort period of time without altering preference or avoidance behavior. Thus, the pH of thelaboratory source water was not adjusted for the purposes of examining preference andavoidance behavior of wild fish.The second study investigated the pH preference and avoidance of wild, adult Brook Trout andBrown Trout using the same methodology applied in the first study. The behavioral response ofBrook Trout and Brown Trout to low pH is one of factor that may lead to the observedsegregation pattern of the two species in Pennsylvania streams. The observed segregationpattern and behavioral responses to episodic events suggest that differences in the pH preferredor 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 notprefer any pH within the range tested (pH 4.0 7.0). Adult Brown Trout displayed a lack ofavoidance at pH below 5.0, which is similar to that reported for juvenile Brown Trout. Theavoidance pH of wild, adult Brook Trout (between pH 5.5 and 6.0) and Brown Trout (betweenpH 6.5 and 7.0) did not differ appreciably from earlier study results for the avoidance pH ofjuvenile Brook Trout and Brown Trout. A comparison of confidence intervals around theseavoidance estimates indicates avoidance pH is similar among adult Brook Trout and BrownTrout in this study. However, the limited overlap of confidence intervals for avoidance pHvalues for the two species suggests that some Brown Trout will display avoidance at a higher pHvwhen 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 thatcompetition with Brown Trout could be mediating the occurrence of Brook Trout at some pHlevels. The preference and avoidance pH results from this study were used to design fieldexperiments involving species interactions and pH.The final study examined the effects of acidification and species interactions on the distributionof Brook Trout and Brown Trout. Although pH appeared to be correlated with the observeddistribution patterns of Brook Trout and Brown Trout in Pennsylvania streams, our laboratorystudies examining the avoidance pH of wild, adult Brook Trout and Brown Trout did notconclusively find that avoidance pH differs between these species. The lack of conclusivedifference in the pH avoidance threshold did not rule out pH as a mediating factor. Interactionsbetween Brook Trout and Brown Trout could lead to habitat partitioning in a stream. BrownTrout are considered superior competitors, but a physiological advantage may allow Brook Troutto 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 reachesthat 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 0seconds on the treatment side during the control observation period) responded to acidificationby 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 causedtheir avoidance at a higher pH. Indwelling Brown Trout spent less time in the acid conditionsduring the acid treatment (44 4%) than during a control period (98 1%). The proportion ofvitime 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 oftime spent in the acidic conditions. The results of this study do not support the hypothesis thatacidification mediates the segregation of Brook Trout and Brown Trout in Pennsylvania streams.Confounding factors, relating to changes in CO2 associated with the acid manipulation, andissues relating to stocking density need further investigation to identify what role these may haveplayed.