| Summary: | This thesis explores how competition and predation by coexisting fish species affect recruitment (number of hatched larvae recruiting into the population). The study is primarily based on field manipulations on a series of eight lakes found in two parallel watersheds, each with two species of fish: rainbow trout (Oncorhynchus mykiss, referred to as trout) and northern pikeminnow (Ptychocheilus oregonensis, referred to as pikeminnow). Different lakes had adults of one species or the other depleted to observe how recruitment changed in response. However, earlier research discovered that pikeminnow populations ontogenetically move between lakes so that each watershed was a single treatment rather than individual lakes. The lakes were followed for up to eight years to examine how interspecific interactions affect survival of hatched trout and resultant recruitment into each lake. My first objective was to estimate variation in growth and consumption of each population over the course of the study. I first evaluated estimates of growth and consumption provided by a new bioenergetics model, called the general bioenergetics model and compared them with estimates from the most commonly used bioenergetics model for fish called the Wisconsin model. Estimates of growth were improved over that from the Wisconsin model, although estimates of consumption were similar between models. I then adapted the general bioenergetics model to permit net consumption rate, to vary over time and across populations. Results showed that growth was quite variable over time for trout, and less so for pikeminnow. Growth responses did not appear to be related to density manipulations. My second objective was to incorporate estimated growth into a length-based age-structured mark recapture model, which estimates density and recruitment for each species and population. Although recruitment appeared to respond to depletion of the same species, manipulation of the other species did not appear to have a noticeable impact. My final objective was to develop a multi-species recruitment model to see how competition and predation across species would impact larval survival. Results were inconclusive, but generated useful hypotheses regarding the strength of competitive and predatory impacts in this particular study system.
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