Effects of Hypoxia on Ichthyoplankton and Micronekton Communities off the Oregon Coast
1. Effects of Hypoxia on Ichthyoplankton and Micronekton Communities off the Oregon and Washington Coasts Johnson, A., Ciannelli, L., Barth, J., Brodeur, R., and Wakefield, W. Oregon State University; NOAA Northwest Fisheries
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3. Hypoxia History on the Oregon Coast (Chan et al. 2008) Dissolved oxygen (ml l -1 ) Depth (m) 1950 to 1999 2000 to 2005 2006 N ~ 4000 hydrocasts
15. Groups a: ≤1.7 ml/L b: 1.7-4.0 ml/L c: >4.0 ml/L Figure 2: Sampling sites along NH Line, in green (left); Modified beam trawl (right) Abundance : On both sample dates, abundance was highest at the tow site of 40 meters depth and gradually decreased as tow depth increased ( Figure 3) Length : On both sample dates, average length tended to increase with tow depth. Furthermore, the tow site of 40 meters depth saw the greatest spread in lengths of individual fishes ( Figure 4 ) Escape Frequency: On both sample dates, escape frequency increased as tow depth increased ( Figure 5 ) Figure 1: DO levels, 1950-2006 on Oregon’s coast (Chan et al, 2004) Figure 3: Abundance of fish plotted against tow location and DO levels for July 26 th (left) and August 11 th (right). Figure 4: Average length of fish plotted against tow locations and DO levels for July 26 th (left) and August 11 th (center); Distribution of fish lengths at tow locations (right). Time to React, Endurance and Duration of Reaction: On both sample dates, no clear patterns or trends were observed between these times and their corresponding tow depth or DO levels and ANOVA tests showed no significant difference ( Figure 6, p-values given on graphs) Figure 5: Escape frequency in percent of fish plotted against tow locations and DO levels from July 26 th (left) and August 11 th (right). Figure 6: (Clockwise from top left) Average time to react in seconds plotted against tow location and DO level; Endurance times in seconds plotted against tow location and DO level; duration of reaction in seconds against tow location and DO level. Behavior: The most common behavior type was “running” followed by “hopping,” though no relationship seen among behaviors, tow locations or DO levels ( Figure 7 ) Figure 7 : Combined frequency of all behaviors for both dates at all tow locations and at all DO levels (left); percentage of each behavior type at each tow location with corresponding DO levels (right). Figure 8: endurance times against grouped DO levels Figure 9: physical samples from beam trawl tows