Hatchery Reform: Reducing Risk of Cumulative Impact of Hatchery Fish on Wild Fish in the Columbia River Estuary

There is a strong consensus that estuaries are important in terms of providing rearing habitat for growth, potential refuge from predation and a physiological transition before emigrating to higher salinity in the marine environment (Quinn 2005, Thorpe 1994). The Columbia River (CR) estuary bordering Washington and Oregon has suffered a major loss of shallow water rearing habitat in the past century. The loss of wetland habitat in the CR estuary since 1870 has been a major factor in the capacity of the estuary to support juvenile salmon (Bottom et al. 2005). Given the limited habitat in the CR estuary this sets the stage for the potential impact of more abundant hatchery origin fish (HOF) on their natural origin fish (NOF) counterparts in terms of spatial and temporal overlap of habitat. Based on actual smolt release data from 2007 that was reported in the Mitchell Act DEIS, 86% of the salmonid smolts or approximately 108 million that reach the CR estuary are HOF and 14% or 17.8 million are NOF. Given the larger numbers of HOF the potential risks of ecological interactions (competition, predation and disease transfer) are greater based upon the limited estuary habitat. The method used to illustrate the risk of larger numbers of HOF compared to NOF smolts in the estuary was to calculate a simple density metric in an effort to quantify the effect. Both intraspecific and interspecific interactions have been quantified in this manner. Since the CR estuary in contemporary times is much smaller than historically it tends to exacerbate the impact of spatial and temporal overlap between HOF and NOF. One method of control over the risk of ecological interactions is to manipulate the temporal component of overlap between HOF and NOF by spreading out hatchery fish releases. Another aspect of hatchery reform could result from sequencing the releases of hatchery salmon to coincide with peak availability of marine prey in the near shore marine environment. This concept is hypothesized to improve marine survival and potentially reduce hatchery release numbers by producing the same number of adult returns. The application of this approach was originally proposed and implemented by the Japanese in their chum salmon hatchery program and subsequently used in Alaska with hatchery pink and chum.