Search This Blog

Sunday, January 18, 2015

The Reproductive Ecology of Oncorhynchus mykiss in Tributary Streams of the Mid Skagit River Basin

Bill McMillan generously shared the documents below on his ongoing study of the Mid-Skagit tributaries.  Bill has tirelessly conducted spawning surveys on these tributaries and he has collected, graphed, and interpreted this data through scientific methods.  Of note is the presence of hatchery steelhead on the spawning grounds in these tributaries and also significant spawning activity before the supposed March 15 timeline of supposed wild steelhead spawning commencement.  My hope is that the evidence in this study will be a harbinger of further wild steelhead recovery on the Skagit with the complete cessation of hatchery plants.  

Kudos and much gratitude to Bill for his dedicated study of wild steelhead on the Skagit, and beyond, and for his immeasurable contributions to wild steelhead conservation.

Links to the documents provided below and I've copied over the summary of Bill's draft.


McMillan, B. 2015. The Reproductive Ecology of Oncorhynchus mykiss in Tributary Streams of the Mid Skagit River Basin.
The information provided is pertinent to the present public process related to the Draft Environmental Impact Statement (DEIS) on Two Joint State and Tribal Resource Management Plans for Puget Sound Salmon and Steelhead Hatchery Programs.  Some of those who provide comments to the DEIS will be citing this Summary (and the report it represents).  
The 2010-2014 Mid Skagit tributary spawning surveys were independently done by me as a retired field biologist (Wild Fish Conservancy for 10 years) motivated by both a personal and scientific interest of living on the Mid Skagit River in order to fill a temporal void in steelhead spawning information that I knew existed.  There was no funding provided by anyone.  This void in steelhead spawning information has long existed in much of Western Washington and has resulted in much misunderstanding about the life histories of wild winter-run steelhead and their sharing of spawning habitat with feral Chambers Creek hatchery steelhead.

The Reproductive Ecology of Oncorhynchus mykiss
in Tributary Streams of the Mid Skagit River Basin
(A Final Summary with the full report still in Draft form)

Bill McMillan
(January 15, 2015)
40104 Savage Road
Concrete, WA 98237

Acknowledgments:  In great appreciation for the several reviews and helpful comments provided by George Pess of NOAA’s Northwest Fisheries Science Center in the drafting of the Summary and the full report it represents; to Nora Kammer of Skagit River System Cooperative tribes for Savage Creek pond observations; and to Brett Barkdull of Washington Department of Fish and Wildlife for a 2014 Skagit basin steelhead spawning escapement estimate.


From October of 2009 to June of 2014 regular spawning surveys were independently and voluntarily made for personal fishery interests as a retired field biologist at five Mid Skagit basin tributary streams that support the spawning of the anadromous life history of Oncorhynchus mykiss (O. mykiss) commonly known as steelhead.  The most intensive of these five years of surveys were those from October 2013 to June of 2014 with a total of 125 spawning surveys made at these five tributaries.  Puget Sound Steelhead in Washington are listed under the Endangered Species Act (ESA) as Threatened, including those of the Skagit River basin.  Several and perhaps all of the same tributaries also support resident O. mykiss populations commonly known as rainbow trout.  All of the same tributaries also have spawning populations of coho salmon (O. kisutch) and pink salmon (O. gorbuscha) as well as coastal cutthroat trout (O. clarki clarki) of both anadromous and resident life histories.  Four of the streams also have spawning chum salmon (O. keta) and three have spawning returns of ESA listed Chinook salmon (O. tshawytscha). 

Winter steelhead spawning surveys in the Skagit basin by Washington Department of Fish and Wildlife (WDFW) have targeted an initiation time of March 15th in the supposition that is when wild steelhead begin to spawn.  In fact, management of winter steelhead has been based on the belief that hatchery steelhead spawn prior to March 15th and wild after with little potential for spawning interactions between the two to occur.  However, no recent history was found of steelhead spawning surveys that regularly occurred prior to March 15th from which to justify this conclusion in the Skagit basin.  Historic evidence from the early 1900s indicates Skagit basin winter steelhead began to spawn by early February and Mid Skagit tributary entry for spawning began by January.  On the Northwest Coast of Washington where spawning surveys were initiated in January by Washington Department of Natural Resources (WDNR) from 1973 to 1980, and similarly so during independent surveys by the Wild Salmon Center (WSC) from 1999 to 2003, it was found that wild winter steelhead spawning begins by early January.  Other areas of the Pacific Northwest also exhibit early steelhead spawning. For instance, the State of Oregon’s spawning survey protocol for coastal rivers is from mid-January through mid-May.  In British Columbia wild winter steelhead spawning historically began as early as January on central Vancouver Island and in more recent history by January or February at least as far north as the Queen Charlotte Islands and Southeast Alaska.  

The 2009-10 to 2013-14 spawning surveys at the five Mid Skagit tributaries were initiated with the first fall storms that stimulate the upstream migration of anadromous spawning runs.  This was to insure that no steelhead spawning was missed and to determine what the overlaps between steelhead spawning time with other salmonids may be.  Over the five years the
earliest steelhead spawning redd found was January 16th and the latest June 6th.  Coho salmon and steelhead were found to have slight overlapping spawning times some years but it was
typically minimal.   Sea-run and resident cutthroat were found to have significant spawning time overlaps with steelhead.  Hatchery steelhead were included in the O. mykiss spawning population mix and steelhead mating (both wild and feral hatchery) included wild resident male life histories.  

There were 104 total steelhead redds counted in the five years of Mid Skagit tributary surveys (Table 1).  Almost half (49%) of the redds were found prior to March 15th, the assumed initiation date of wild steelhead spawning.  Over half (53%) of the steelhead were estimated to have spawned prior to March 15th when redd sightings were adjusted for spawn timing (Figure 1).  In the five years of surveys a total of 18 O. mykiss (14 steelhead, 2 male residents, and 2 undetermined male steelhead or residents) were observed at 7 active spawning redds between January and June (Table 2).  The hatchery proportion of the steelhead in the spawning mix was 40%.  If the wild male resident life history was included it decreased to 33% hatchery.  Both wild and hatchery origin steelhead were found spawning in the early time period of January to mid March.  The hatchery proportion of the steelhead spawning mix prior to March 15th was 67% (Table 3).  If the wild male resident life history was included it decreased to 50% hatchery. Although no hatchery steelhead were found spawning after March 15th the unknown origin steelhead after that date were 20% of the total steelhead observed.  Of particular concern, hatchery steelhead were found spawning to the maximum upstream anadromous extent of the smallest tributaries in the Mid Skagit basin.   

The spawning time of steelhead was found to vary between tributaries. Over 50% of the spawning occurred prior to March 15th in three of the tributaries. The two other tributaries had 50% of the spawning occurring after March 15th.  Air/water temperature, precipitation, streamflow, and intermittent or perennial hydrology were all examined as potential explanations for the spawn timing differences.  Streamflow hydrology best explained the steelhead spawn timing differences. Specifically, whether a tributary’s hydrology was intermittent or perennial was found to be a particularly probable driver regarding whether most steelhead spawned prior to March 15th or most thereafter (Figure 3).  This was hypothesized to be due to the need for spawning to be early enough for significant numbers of emergent steelhead fry to move either downstream to perennial waters prior to late June to early July when intermittent flows began to disconnect these tributaries from larger downstream water bodies, or upstream if that option were available. Although intermittency is predicted to increase in northward expansion with climate change, and is sometimes perceived as a great limitation on steelhead reproductive success, there are examples of high steelhead productivity that occurs in intermittent streams and where gravel accumulations may actually provide better spawning habitat if steelhead life histories have effectively adapted with early spawning and emergence.

From the limited specific tributary water temperatures taken, the coldest stream had the latest steelhead spawn timing and the four warmer streams earlier. At the cumulative level of all five tributaries a highly significant correlation was found between average monthly air temperature and steelhead redds per month when adjusted to spawning date if 50-67% of the redds during the early spawning period were eliminated to better reflect wild steelhead spawning (Figure 2). Spawn timing also varied by year. In one tributary with significant spawners in 2010 and 2014 the warmer year (2010) had a month earlier spawning peak than the colder year (2014).  Active spawning was found to most commonly occur shortly after a flow peak on a falling hydrograph at all tributaries and on cloudy days and/or at late afternoon to evening.

Underwater photographs found and confirmed that steelhead fry emergence occurred by late May at one of the intermittent tributaries and at another with side channels going intermittent by May.  Steelhead fry were likely present dating to at least mid May but they could not be clearly identified in the photographs.  It is important to note that photographs were not taken prior to mid May which might have captured even earlier emergence. 

The one stream attribute identified that resulted in more intensive steelhead spawning was that of a well contained channel with least difference between wetted and bankfull widths (bankfull width/wetted width ratio) during the steelhead spawning period.  This was found to be the case at the entire length of the one stream with the greatest steelhead redds/km, and at one particularly heavily used side channel of a stream that otherwise had a broad and actively moving mainstem channel.

Shifts in the monthly pattern of air temperatures and precipitation since 1909 (Tables 4 and 5) were examined as were relevant streamflows dating to 1928 (Table 6).  Shifts are occurring that are particularly correlated with the steelhead spawning period of January to May.  Air temperature trends include warmer air temperatures in January, less variable temperatures in February, and cooler temperatures in the remaining months. More precipitation now occurs in each of the months except February, as well as greater average streamflow, with the exception of February and May.  Historically peak spring streamflow occurred in May, now peak spring streamflow occurs in March. Steelhead spawn timing must adapt to these climate related changes.  It is important to note that the one month with least change is February.  It may provide an important temporal point of climatic stability for steelhead spawning that has remained little changed the past 100 years. 

For historic comparison, three of the five Mid Skagit tributaries regularly surveyed in 2014 were also surveyed in 1978-1981.  The steelhead redds/km found in 2014 were 35%-78% of that in the earlier time period (Table 7).  Mid Skagit tributaries are now apparently much less productive for wild steelhead than was the case about 35 years ago.  This may not necessarily be explained by habitat loss and/or ocean conditions alone.  It may be at least as significantly related to loss of steelhead life histories (such as early run-timing and/or early spawning) that can no longer fill formerly productive and widespread habitat that is increasingly left depleted or vacated.  At that earlier time, the smaller tributaries were found to support 65-80% of all steelhead spawning in the Skagit basin despite an average escapement estimate of 5,700 wild steelhead, over 63% less than the preliminary escapement estimate of over 9,000 in 2014 (Table 8).  If tributaries were at former productivity levels, presumably the 2014 wild steelhead return would have been greater than it was.  Identifying and resolving the present limitations for tributary steelhead productivity in the Skagit basin may lead to considerable wild steelhead recovery progress. 

The 67% of hatchery steelhead found spawning in Mid Skagit tributaries prior to March 15th was of particular concern that would be anticipated to be most problematic for wild O. mykiss populations (that include both anadromous and resident life histories) at tributaries typified by warmer winter flows and/or intermittent hydrology.  Four of the five tributaries regularly surveyed had these characteristics.  Regarding future genetic studies that may occur, it will be important to recognize the early period of time when steelhead spawning can occur in Skagit basin tributary streams with subsequent early fry emergence.  To indicatively represent the hatchery signal sampling should occur that includes the earliest fry stage prior to significant depletion through natural selection from early May to mid June.  After that time increasingly high depletion of hatchery and hybrid fry whose life histories may well exclude effective movements from intermittent streams or stream sections would be anticipated.  In general, hatchery heritage would be anticipated to result in increased fry/parr loss over time due to greater vulnerability to predation, or due to other factors that commonly limit hatchery related characteristics to survive as well as wild.  The least effective time to find a hatchery genetic signal would be anticipated in juvenile sampling occurring from July onward, and least of all from returning adult steelhead.

These independent 2010-2014 Mid Skagit tributary surveys provide a baseline for the
full period of steelhead spawning that has otherwise been lacking from which to monitor wild steelhead escapements, the hatchery component of the escapements, and how the steelhead spawning is variable in time and quantity by individual tributaries that have similarly variable characteristics that need to be understood.  Recovery planning can be anticipated to be more effective if it is based on information that effectively represents the reproductive ecology of wild O. mykiss populations that include both anadromous and resident life histories.  This can occur with further refinement of this spawning survey and reproductive evaluation template that includes habitat differences along with the differing adaptive life history strategies of the fish themselves.