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An examination of metadata associated with a population of sockeye salmon (Oncorhynchus nerka) changed our interpretation of the purported benefi ts of salmon enhancement projects and improved our understanding of the stock-recruitment relationship. Eff orts to increase the production of sockeye salmon from Chilko Lake (Fraser River watershed in British Columbia, Canada) included simultaneously fertilizing the lake and operating a spawning channel. To investigate the eff ects of these manipulations, we analyzed data for spawners, smolts, and returns including metadata associated with these fi sh and their watershed. Incorporating factors derived from metadata in stock-recruit analyses reduced the total variance to be explained before considering stock density eff ects, and allowed us to explore the eff ect of imprecise data. When Beverton and Holt models were applied to data for smolts from spawners and returns from spawners, estimates of productivity and capacity for broods aff ected by the spawning channel (1988–2003) were lower than for broods before and after its operation. Observations during this period suggested that many salmon fry, emerging from natural spawning areas downstream of the channel and destined for Chilko Lake, entered the channel or could not pass it, and perished. Applying metadata related to the precision of annual return estimates reduced our confi dence in published conclusions about a positive eff ect on egg-to-smolt survival from adding fertilizer to Chilko Lake. We further investigated a factor for smolt-to-adult survival based on the survival of other populations of Fraser River sockeye, noting that this factor, and others, aff ect estimates for both capacity and productivity. Lastly we investigated changes in the fecundity of spawners and in the primary productivity of Chilko Lake, establishing that both have changed on a decadal scale. In summary, adding categorical and ordinal variables (factors) to account for natural and manmade habitat manipulations reduced the variance to be explained by stock-recruit models, thereby enabling more eff ective analyses of habitat capacity and density-dependent survival, which should lead to improved fi sheries management decisions. The importance of analysts becoming familiar with metadata cannot be overstated.

Habitat Manipulations Confound the Interpretation of Sockeye Salmon Recruitment Patterns at Chilko Lake, British Columbia