EXECUTIVE SUMMARY:
17 August 2015
Severe hypoxia in southern Hood Canal continues: Will there be a fish kill this year?
Starting last fall and continuing this year, the seawater conditions in Hood Canal have been abnormal
and continue to evolve in unprecedented ways. Our ability to answer the question of whether there will
be a fish kill in southern Hood Canal is somewhat limited by this. Real-time data from the UW ORCA
buoys, part of the NANOOS system, reveal changes occurred in early August that could favor fish kills,
but because things set up a month early, maybe this will not happen. The risk for a fish kill is because
subsurface waters near Hoodsport have less than 1 mg/L oxygen content. Hypoxia is defined as less
than 2 mg/L; the southern Hood Canal waters are so oxygen-deprived that they can be lethal. As of mid
August, these conditions are found deep, between 20-40 meters (60-120 feet). If strong southerly winds
blow, as we typically get during September, this can cause the hypoxic conditions to rise to the surface,
killing fish. However, the warm weather and high pressure conditions that we are having this summer
mean that the southerly wind storms may not occur, or will be delayed. The hypoxic waters may be
flushed out already since that process started 1-2 months early this year, a condition influenced by the
“blob” of very warm Pacific Ocean waters that invaded Puget Sound last fall. So, the oxygen
concentrations are extremely low in areas like Twanoh and Hoodsport but whether we see fish kills
depends on two processes (south winds and flushing), both of which are being influenced by the
abnormal weather and ocean conditions this year. We can’t answer the question, but the public can
view the real-time oxygen data and updates at: http://orca.ocean.washington.edu and
http://www.nanoos.org.
SCIENTIFIC SUMMARY:
14 August 2015
Conditions in 2014-15 are historically anomalous and continue to evolve in unprecedented ways.
Flushing started early this year: The seasonal oceanic intrusion of higher density seawater into Hood
Canal was evident at Hoodsport starting in early August, which is about a month or two earlier than that
observed in the last 10 years (Figure 1).
Relative to the seawater conditions around Hoodsport prior to the intrusion, this oceanic water mass
has relatively higher oxygen (~3.5 mg/L), higher temperatures, and higher salinity.
Flushing, or the replacement of the ambient waters with the intrusion waters, has the potential to be
very effective this year, because the waters that intruded last year were affected by the “blob” resulting
in spring and early summer 2015 deep waters that were the least dense in the last 10 years (Figure 2).
Consequently, these deep waters are easily displaced by this year’s intrusion waters. Whether this
strong flushing will continue or not, depends on outer coastal dynamics (see below).
Changes are occurring rapidly: The hypoxic layer at Hoodsport was ~100 m thick on 31 July and on 9
August was only ~20 m thick (Figure 3). During this time, the subsurface oxygen minimum concentration
decreased and is currently less than 1 mg/L. Past observations suggest that the decrease in the
minimum dissolved oxygen concentration that occurs after the intrusion begins is a consequence of
near-anoxic water flushing out of Lynch Cove and Lower Hood Canal.
Currently, the hypoxic layer at Hoodsport starts at about 20 m and is very low (<1 mg/L). Twanoh
remains near anoxic at depth, with concentrations of dissolved oxygen essentially below detection.
Other Puget Sound buoys do not show hypoxia (Figure 4), though are lower than typical at those sites.
Will there be a fish kill?
The chance of a fish kill depends on the timing of local southerly storms relative to flushing of hypoxic
waters out of Lower Hood Canal and near Hoodsport. If a subsurface hypoxic signature:
• Continues* and strong sustained S winds blow**, this is high risk for a fish kill
• goes away and strong sustained S winds blow, this is low risk for a fish kill
• continues and strong sustained S winds do not blow, this is low risk for a fish kill
*Continue? The subsurface hypoxia may continue, until Lower Hood Canal (as evidenced by conditions
at Twanoh) fully flushes. Deep oxygen in the lower 10 m at Twanoh is essentially anoxic (~ 0 mg/L).
**S winds blow? They may not blow, because the high pressure associated with blob phenomenon may
prevent or delay development of these storms. Also we are earlier in the year now than when fish kills
have been observed in the past (e.g. Sept. 2006) with climatologically lower chances for strong southerly
winds. We are in undocumented conditions: the subsurface oxygen minima during fish kill years looks
similar to conditions now, but we are in August, not September, when this has been observed before.
Coastal dynamics are odd this year: Coastal upwelling was strong early this summer and may have
favored a denser oceanic intrusion. Seawater temperatures along the coast of Washington in the
upwelling region during May-June 2015 were cooler than normal. However, conditions during July 2015
are different and somewhat confusing: upwelling-favorable winds persist yet buoys and satellites show
waters much warmer than normal in the upwelling region (Figure 5). An effect from El Niño (northward
transport of warmer waters along the coast) or due to changes in the upwelling source waters (blob
effects) may be involved. How this recent shift will affect Puget Sound dynamics remains to be
determined.
Figure 1. Seawater temperature at 80 meters at Hoodsport ORCA buoy, showing warm 2015 conditions.
http://orca.ocean.washington.edu/climatologies/climatology_HP_80_temp.png
Figure 2. Seawater density at 80 meters at Hoodsport ORCA buoy, showing very light densities in early
2015 (note late 2014 data not available). Figure is URL below with one bad data spike removed.
http://orca.ocean.washington.edu/climatologies/climatology_HP_80_sigma.png
Figure 3. Oxygen profiles at Hoodsport ORCA buoy before (July 31) and after 2015 oceanic intrusion
(August 9) and from prior to September 2006 fish kill.
Figure 4. Most recent oxygen profiles at all ORCA buoys. While lower Hood Canal is the only location to
exhibit hypoxia, other sites may be lower than typical. For instance, Carr Inlet is almost 2 mg/L lower
than its average (see http://orca.ocean.washington.edu/climatologies/climatology_CI_35_oxy_mgL.png)
but the current oxygen concentration at depth there is more than 4 mg/L.
Figure 5. Sea surface temperature anomaly values from the MODIS satellite in June 2015 (upper) and
July 2015 (lower) showing strong temporal change within the upwelling-affected coastal area. See
http://nvs.nanoos.org/Climatology