A Review of Long Term Lake Fertilization Projects in South Central Alaska – FRED's Legacy

The Alaska Department of Fish and Game use of lake fertilization to enhance salmon production in Alaska became a common practice in the mid-1980’s. The Division of Fisheries Restoration, Enhancement and Development (FRED) at some level pioneered this application of lake fertilization with an intensive program of monitoring basic lacustrine ecosystem functions. In this use lake fertilization is intended to increase the forage base for juvenile salmon and thereby increase growth and ultimately survival. During that time the FRED limnology program was investigating lakes statewide to develop a limnological data archive. Key variables related to productivity evaluations were basic nutrients (nitrogen, phosphorus and other trace elements), primary production pigments (chlorophyll a and phaeophyton), secondary production (zooplankton) and ultimately tertiary production (fish). This led FRED to develop the commonly used Limnology Field and Laboratory Manual which guided the Lake Enrichment and Lake Stocking Programs. A Lake Fertilization Policy was also developed to guide these activities and has become the ‘go-to’ operating procedures adopted for many lake fertilization projects in AK and beyond. The lake fertilization projects implemented in the 1980’s were spread across coastal Alaska and met with mixed success. Two of the original projects Bear and Leisure lakes were started in the 1980s and continue today. These long term projects provide an opportunity to evaluate the efficacy of lake fertilization. Leisure Lake, is a ‘poster child’ for successful lake fertilization with a long and consistent period of fertilization (15 tons annually for 15 years). In the past decade fertilization was drastically reduced and sporadic yet sockeye stocking rates remained the same. The ecosystem response is reflected in multiple trophic levels with reduced primary, secondary and tertiary production indicators. Similarly, Bear Lake has a long history of lake fertilization with detailed monitoring that provide insight into lake trophic structure and fisheries enhancement.