The purpose of this section is to define the general hypothesis which were used to guide the research, the general objectives, and the research design. Specific objectives for research on particular taxa and detailed methods are reported in other sections.

The project has been reviewed annually, prior to each field season, by a panel of nationally distinguished scientists. The panel has played an important role in structuring the research by evaluating progress annually and recommending directions of future research.

Research in NOCA is complicated by the rugged terrain of the park, which creates logistical problems, the relatively short period of time available for field work, and relatively unpredictable weather. Field work is restricted to the period of time between ice-out (mid-June to early July) and the onset of inclement weather in fall (approximately mid-September). There is no road access to the lakes; they can be reached only by hiking or helicopter.

A three-year program of field research, funded through the NPS Natural Resource Preservation Program, was initiated in FY 1989 to investigate ecological impacts of stocked trout on naturally fishless lake communities in NOCA. Little was known about native biota and physical and chemical conditions in NOCA lakes prior to initiation of this research. The objective of the 1989 field season was to conduct an extensive survey of NOCA lakes to begin to define biotic and abiotic conditions in major lake ecosystem classes. Lake ecosystem classes were defined based on vegetation zone (alpine, subalpine, and forest) and location east or west of the crest of the northern Cascade Mountains (see Lake Classification section). Sixty-one lakes were sampled in 1989 (Table 1). Most of the lakes were sampled only once. Sampling focused on lake morphometry, chemistry, phytoplankton, zooplankton, and benthic macro-invertebrates. The presence of fish and amphibians was noted, but densities were not estimated.

Based on the 1989 park-wide survey, we designed more systematic research for 1990 and 1991. We hypothesized that fish effects on native lake biota (salamanders, zooplankton, and benthic macro-invertebrates) increased along a gradient of increasing fish predation intensity. Results of the 1989 survey suggested that the effects of fish predation included reductions in densities and elimination of some species (e.g., salamanders, large bodied zooplankton) from lakes. Furthermore, the 1989 survey indicated that abiotic conditions and species composition of the native biota varied among vegetation zones.

For policy reasons, stocking of fish into fishless lakes was not an experimental option at NOCA. Thus, we had to infer effects of fish by comparison of community structure in lakes with fish to that in fishless lakes. Although we lacked specific information on densities of fish, fish appeared to reach much higher densities in lakes where natural reproduction occurred than in lakes where fish did not reproduce. In lakes without natural reproduction, fry are stocked periodically at relatively low densities. Thus, to approximate a gradient of increasing fish predation intensity, we stratified lakes into fishless lakes, lakes with non-reproducing fish, and lakes with reproducing fish (Table 1). We also stratified sampling by vegetation zone. We sampled subalpine lakes in 1990 and forest lakes in 1991 (Table 1). Few lakes in the alpine vegetation zone support fish. Our intention was to sample lakes 2-3 times during the field season depending on the length of the ice-free period. Sometimes weather conditions limited the number of times a lake was sampled. The objectives of the research were to:

1. Determine physical (lake morphometry, temperature, benthic habitat) and chemical abiotic conditions in lakes.

2. Determine the structure of pelagic (crustacean, zooplankton, rotifers, and phytoplankton) and benthic (benthic macro-invertebrates) systems. Structure included taxa composition (species or higher level taxa if identification to species was not possible), average body size (or biovolume) of major taxa, absolute and relative densities of taxa, and habitat utilized by benthic macro-invertebrates.

3. Determine species composition, age and size structure, diet, and densities of reproducing and non-reproducing trout.

4. Determine species composition, abundance of aquatic life stages (egg masses, larvae, and neotenes), and habitat utilization by salamanders.

5. Compare the composition, size structure, and densities of taxa between fishless lakes, lakes with non-reproducing fish, and lakes with reproducing fish. Develop inferences of community organization that involve the effects of fish and abiotic conditions on native species.

6. In cooperation with NPS personnel, develop a program for continual monitoring of lakes in NOCA relative to the question of fish impacts on naturally fishless lakes.

Table 1. Sampling frequency of NOCA lakes from 1989 to 1993. Vegetation zone indicated as A = alpine, S = Subalpine, F = Forest, W = West, E = East. Asterisks denote manipulated lakes.

In 1990 we began manipulations of a few small lakes (LS1, MR11, MR13-2, Lower Panther, Upper Panther, Table 1). The purpose of the manipulations was to evaluate impacts on native biota of changes through time in body size and density of a cohort of stocked fish. During the summer of 1990 the lakes were sampled and in early fall fish were removed and fry were stocked in all lakes except Upper Panther (see Fish section). Upper Panther provided a reference for Lower Panther, which was only a few meters away.

A small amount of funds remained after the first three years of scheduled work and a limited field season was added to the program in 1992. The field effort in 1992 focused on sampling the manipulated lakes and obtaining better estimates of fish densities in selected lakes.

Results of research through 1992 provided evidence of fish impacts on crustacean zooplankton and salamanders and served to further focus our hypothesis. More research, including more extensive sampling of both eastslope and westslope lakes, was needed. A proposal for a second phase of the project was submitted to the NPS Natural Resource Preservation Program in 1991 and funded in 1993. Some of the results of the second phase of the NOCA project (1993 field season) are presented in this report because the results are relevant to the evaluations of the first phase of the project.