Deer Lake is truly a unique project for NSRAA, with a long and complex history. Situated in the South Baranof Wilderness Area, Deer Lake is a 977-acre lake located at 400 feet elevation on the southeastern shore of Baranof Island. The lake is steep-sided, with a maximum depth of 870 feet, and non-anadromous because of the 330 foot falls that barriers it from the sea. NSRAA has operated a coho enhancement program at Deer Lake since the mid-eighties. The program began as part of NSRAA’s Coho Lake Rearing Project, which stocked numerous lakes on Baranof and Chichagof Islands. The project at Deer Lake has gone through numerous changes over the years described below. In the lake stocking phase of the program smolt production peaked from 1995-1999; subsequently the project began experiencing the profound impact of a growing rainbow trout population in the lake. We have now taken a new approach, utilizing in-lake net pens for fry rearing. Production is currently 2-3 million fry transferred from Hidden Falls Hatchery via float plane and reared in the lake each year. Present goals for the program care for a 2.2 million smolt release.
Fry transfers to Deer Lake.
Net Pen Rearing
Beginning in 2005, in place of planting fry in the lake, fry were planted in net pens in Deer Lake and reared on fish food to around 18 grams before being released into the lake. The first lake release was in late September and October when the lake’s temperatures were 12 and 7 degrees Celsius, respectively. For each respective release date, 18 percent and 22 percent of the fry migrated to their death over the falls within days of release. Later, in 2006, less than one-tenth of 1 percent migrated over the falls when they were released mid-November when the lake had cooled to 4 degrees Celsius. This indicated that as the lake turns over and cools , water temperatures near the surface and at depth become cold enough to lower the coho fry’s dietary needs, so their motivation to seek over-winter holding habitat outside the lake diminishes. As a result, fish are now reared in net pens until this lake turning effect is observed (generally late December). At this time, up to 75% of the fish reared in net pens are released into the lake. The remainder are held for further captive rearing in the event that an over winter exodus would occur. Fish that are pre-designated for either lake release or net pen over winter are each tagged with a unique code for adult survival evaluation.
Pumping fish out of the net pens and to the weir.
Annual weir construction.
Smolt Emigration
Smolts leaving Deer Lake for the ocean are intercepted in the lake’s outlet stream, above the 330-foot high falls, with an inclined-screen trap that separates them from most of the creek’s water. The fish are then transported over the falls in pipelines that wind a half mile downhill to net pens anchored in Mist Cove. There, smolts are passed through an electronic counter, examined for size and condition, held a few days, and then released.
See videos featuring the outmigration process below:
1 of 3: from the pens to the weir.
2 of 3: from the Lake to the cove.
:
3 of 3: from the cove and beyond.
Adult Returns
Adult coho return to the Deer Lake’s outlet stream in Mist Cove after 15 months at sea. During their time at sea, recovery of tagged adults is used to estimate marine survival and contribution to the commercial fisheries. Marine survival of smolts to adults has ranged widely from 1.2 to 24 percent, while commercial interception averages roughly 50 percent, with the majority of the commercial harvest going to trollers, while some are intercepted in traditional seine fisheries. Deer Lake coho do not migrate through gillnet fishing areas, hence this project does not contribute to that gear group. The adult coho that evade capture in the commercial fishery and enter Mist Cove each year are targeted by chartered and private sport fishermen with any remaining fish harvested for cost recovery.
Commercial and sport boats targeting coho at Mist Cove.
Developmental Years
Work on Deer Lake began in 1984 with a pre-stocking study, and then about 800 thousand coho fry were stocked in the lake the following year, with almost half emigrating as smolts in the spring of 1986. No fry were planted in 1986 to allow the depleted food resources–zooplankton, amphipods, and aquatic insects–time to replenish. In 1987, another 800,000 fry were planted in the lake with similar results to the 1985 plant.
Beginning in 1988, liquid fertilizer was applied to the lake to increase the phytoplankton (microscopic algae) population so that zooplankton (cyclopodia and bosmina), a larger food source for coho fry would proliferate by feeding on the abundant algae.
The increased food base allowed for much greater stocking densities in the lake. Numbers of stocked fry jumped from 800 thousand every other year to 2.5 million each year. Thus for any two year period, 5 million fry—a six fold increase over the non-fertilization stocking levels—were reared with fertilization induced zooplankton blooms. From 1988-2004, an average of 2.1 million fry were stocked in 15 of the 17 years. In-lake survival of these fry ranged from 30 percent to 73 percent, and averaged 52 percent over the period. On average, Deer Lake has produced around 1.1 million smolts per year for the 15 years coho fry have been stocked. Peak years saw production of 1.6 to 1.8 million smolts.
In-lake survivals began to decline in the late 1990’s primarily due to increased predation by non-native rainbow trout. Rainbow trout from nearby Sashin Lake were planted in the lake in 1938; in 1967, a second planting of rainbows from Montana and Washington State occurred. But as coho fry stocking increased in the lake, so did the rainbow trout population until predation caused smolt production to drop to around half of earlier levels.
Pictured above: NSRAA staff from initial fry planting project era.