October 2000

Summary

Green Lake in Seattle has suffered for many years from diminished water quality, excessive vegetation growth and unbalanced fish populations. These problems have in turn reduced recreational opportunity. A number of organizations, including the Seattle Department of Parks and Recreation (SDPR) and Washington Department of Fish and Wildlife (WDFW) have an interest in improving these conditions for the benefit of the local community and the general public. A number of projects have already been implemented in Green Lake to address these concerns. For example, a lake-wide phosphorus reduction treatment and mechanical aquatic plant harvesting program were implemented based on recommendations arising from consulting firm and WDFW research. The next project implemented by WDFW with support from SDPR will be the stocking of the sterile apex predator, tiger muskellunge (commonly known as "tiger muskie"), to control the dominant and deleterious common carp population and to restore balance to the fish community. Following are additional details describing the background, goals, and objectives of this project, and basic facts regarding the biology of tiger muskellunge.

Background

1. Green Lake historically provided substantial fishing recreation within the urban region of Seattle.
   
   
2. Water diversions from the lake and widespread introductions of non-native species have impacted water quality, altered lake productivity and decimated this once-popular fishery.
   
   
3. For years SDPR and WDFW have struggled with various approaches to solving these problems and restoring fisheries in Green Lake, which would be accessible to large numbers of urban youth and local citizens.
   
   
4. Following recommendations outlined in a 1995 lake restoration study, a lake-wide alum treatment was applied to Green Lake. This treatment was intended to bind the critical algal nutrient, phosphorus, and make it unavailable in the sediments, thus reducing incidents of lake-wide blooms. While a small and temporary measure of success was achieved, the loading of phosphorus into the sediments has shifted lake productivity from algae to aquatic plants, which now dominate the extensive littoral zone of this shallow lake.
   
   
5. Further exacerbating these water quality problems, a large population of common carp has expanded unchecked in the lake and now dominates the biomass of the fish community, reducing resources for more desirable species such as trout, bass, and catfish. Common carp stir the sediments extensively through their foraging activities and resuspend the phosphorus. This behavior combined with the excretions of these fish is thought significantly diminish water quality. Furthermore, because of their rapid growth, Green Lake common carp rapidly reach sizes that make them invulnerable to the lake's resident predators.

Goals

1. Restore recreational mixed-species fisheries to Green Lake
   
   
2. Improve water quality
   
   
3. Create angling opportunities for urban youth

Objectives (Phase I)

1. Reduce carp populations, relieve competition for resources for other fish species, reduce internal phosphorus loading, and restore ecosystem function by stocking the sterile apex predator, tiger muskellunge
   
   
2. Provide an additional angling opportunity to fish for these desirable game fish

Tiger Muskellunge biology

1. Tiger muskellunge are a sterile hybrid of northern pike and muskellunge
   
   
2. Tiger muskellunge grow rapidly, attaining a length of 20 inches in their first year and 30 inches in their second year. Growth slows dramatically after they reach 36 inches but some individuals may attain a length of 50 inches under ideal growth conditions. Although there are records of these fish living as long as 15 years, few have been observed to live longer the eight to ten years.
   
   
3. Tiger muskellunge prefer shallow, weedy habitats characterized by dense aquatic vegetation in summer and fall and tend to move into deeper water during winter months.
   
   
4. Numerous studies have revealed that these fish are ambush predators feeding primarily on other fish, and show distinct preferences for carp where these fish are present.
   
   
5. Like all esocid species, tiger muskellunge are reclusive and avoid contact with humans.
   
   
6. The WDFW has stocked tiger muskellunge in a number of lakes in both eastern and western Washington.

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