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 3 million fry reared in net pens each year. Present goals for the program call for the rearing the fry with a 70% in lake survival resulting in 2.2 million smolts which on average should return 160,000 to 220,000 adults.
Net Pen Rearing
In 2005, in place of planting fry in the lake, 600 thousand fry were planted in net pens in Deer Lake and reared on fish food to around 18 grams before being released into the lake 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. In contrast, 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. When the lake surface reaches 4 degrees C, this colder and therefore denser surface water sinks when the warmer, deeper water moves to the surface. 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 and they remain in the lake instead of migrating over the falls. In addition, freshets and high water events are rare after November, a phenomenon that is known to push fish out of the lake.
To further address the problem of losing production to fall emigration over the falls, we’ve developed a system which allows the fry to remain in net pens over winter.
With the exception of the loss of fry over the falls in the first year, the net pen rearing strategy has worked well. Production was increased to 3 million fry beginning in the summer of 2011. We hope to see fry to smolt survival of 70-75%, which would produce an annual smolt release of 2.0 – 2.2 million smolts. Update for 2012 & 2013: records were broken with 2.0 and 2.4 million smolt respectively. Fry to smolt survival was over 85% both years and average smolt size was 20 grams.
Smolt Emigration & Adult Returns
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, coded wire tagged, held a few days, and then released.
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 and averages 13.2 percent, while commercial interception averages 52 percent, with 41 percent going to trollers and 11 percent to seiners. Deer Lake coho do not migrate through gillnet fishing areas, hence this project does not contribute to that gear group. In terms of numbers, commercial catches of Deer Lake coho average 44 thousand for trollers and 17 thousand for seiners. The value of commercially-caught coho from Deer Lake has been as high as $1.2 million but typically varies between $150 and $700 thousand. The Deer Lake project has a cumulative benefit: cost ratio of 2:1. the benefit to cost will certainly increase now that NSRAA has developed a successful strategy to raise 85% of the fry to smolt and safely to saltwater. For example by the third week of August in 2013 trollers had already harvested 80,000 coho valued at over a million dollars.
Usually about one-third of the returning adult coho evade capture in the commercial fishery and enter Mist Cove each year. Around 1,200 of those fish are caught by chartered and private sport fishermen. The royalty rights to harvest the returning coho in the terminal harvest area are sold to processors to help with the costs of perpetuating the program.
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.