Assessing Juvenile Salmonid Response to Gas Supersaturation Using a General Multivariate Dose–Response Model

Abstract

Based on data compiled from the literature, we investigate the effects of excess total gas pressure (TGP%) on juvenile salmonids (chinook, Oncorhynchus tshawytscha; coho, O. kisutch; sockeye, O. nerka; and steelhead, Salmo gairdneri). Our study relates exposure time to 50% mortality (ET50) to TGP%, component levels of dissolved oxygen (O2%) and nitrogen (N2%), water depth, temperature, barometric pressure (BP), and fish size. We employ a new device, called a tabular histogram, for exploratory data analysis. We also formulate and test statistical hypotheses by applying the general multivariate dose–response model described in a companion paper (Can. J. Fish. Aquat. Sci. 43: 1684–1693). When modeled in response to TGP%, ET50 follows a typical exponential dose–response relationship. Based on our full data set, two ancillary factors, water depth and fish length, significantly improve the model's ability to explain variations in ET50. Furthermore, based on a smaller subset of the data, either of the factors O2% or N2% also improve the model fit significantly. For 50-d exposures, apparently "safe" levels of TGP% range from 103.8 to 114.8%, depending on associated factor levels of water depth and fish size.