Abstract
Fish abundance in the main-stem ecosystem surrounding its confluences with burned, burned + debris flow, and unburned streams was estimated by underwater surveys with mask and snorkel. Snorkel surveys encompassed habitat above and below each confluence. We drew maps of the surveyed area and estimated width, depth, and length of each habitat to calculate approximate volume available to fish within habitat units. We identified fish in each habitat unit to species and estimated their length to the nearest 5-cm increment. This information allowed us to determine if fish were preferentially using confluence habitat and to what extent they did so. Selection for a particular habitat was determined if the proportion of total fish occupying a particular habitat / proportion of total habitat volume available was > 1. In August 2010, we conducted daytime snorkel surveys in the main-stem habitat encompassing the confluence with each tributary. Each survey lasted between 45 and 60 min and encompassed a stream length of 75-100 m.