Environmental regulation of migratory movements by juvenile brown trout (Salmo trutta)
|dc.contributor.author||Jones, Douglas Allan|
|dc.identifier.citation||Jones, D. A. (2018). Environmental regulation of migratory movements by juvenile brown trout (Salmo trutta) (Thesis, Doctor of Philosophy). University of Otago. Retrieved from http://hdl.handle.net/10523/7937||en|
|dc.description.abstract||This thesis explores the role that environment and geographic landscape features have on migratory response in juvenile brown trout (Salmo trutta). Migratory strategy was found to be related to landscape features at the catchment scale. Migratory populations occurred at lower elevations where migratory journeys were less costly. Furthermore, migratory populations were characterised by high juvenile density and suppressed growth rates, indicating competition for resources. Invertebrate biomass interacted with landscape features, presumably by alleviating competition where invertebrate biomass was high, and played a role in out-migration. A temporal study on a migratory population of brown trout showed that space resources became constrained over a season. In situ filming of fish showed that the number of foraging stations first increased and then decreased, as stream flow and discharge decreased over the season. This was presumably due to a reduction in the number of profitable foraging stations available and offers a mechanistic explanation for the decline in fish numbers - losers in competitive interactions for foraging stations are forced to migrate. The effects of intra-cohort competition could be observed in declining individual condition factors and loss of fish (out-migration) from the stream. The role of food as a proximal cue regulating out-migration has received increasing attention as salmonid restocking programs try to increase the return rate of released fish. Producing a fish similar to wild types, including migratory tendencies, is difficult. A simple method might be to reduce the amount of food rations given to fish, creating leaner individuals more inclined to migrate on release. In this thesis, I find that food rations could affect the degree of smolting (physiological change prior to migration) under standard hatchery conditions. Fish fed low rations in spring prior to out-migration showed a greater degree of smoltification. A meta-analysis on the effect of food on migration in salmonids found that rationing food had different effects on different species of salmonid. Rationing had a direct effect on migratory response in more irruptive migratory species (trout), but not so in more regular migratory species (salmon). The terms irruptive and regular migration have their roots in avian ecology, but I propose they are equally applicable to salmonids. The findings of this thesis are used to form a hypothesis for the environmental regulation of patterns of residency and migration in brown trout.|
|dc.publisher||University of Otago|
|dc.rights||All items in OUR Archive are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.|
|dc.title||Environmental regulation of migratory movements by juvenile brown trout (Salmo trutta)|
|thesis.degree.name||Doctor of Philosophy|
|thesis.degree.grantor||University of Otago|
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