Article O. Mykiss Diversity In North Puget Sound

Discussion in 'Articles & Reference Info' started by Smalma, Apr 6, 2012.

  1. Smalma Active Member

    Posts: 2,741
    Marysville, Washington
    Ratings: +538 / 0
    Hope the reader find this of interest -

    O. Mykiss diversity found in North Puget Sound Rivers

    Over the last 50 years as an avid angler and field biologist I found myself in an unique position to investigate the wide diversity expressed by the O. Mykiss populations found in our North Pguet Sound rivers. With observations from decades of fishing, hiking streams, extensive creel surveys, spawning surveys, brood stock collections and spawning of steelhead at various hatcheries I have had the unique opportunity to view diversity expressed by our local populations thanks a large number of individual observations. During those years not only was I able to review the results of huge amounts of data and a make a number of field observations I also was in a position look at greater detail at off-beat fish that were outside of the norm for local populations. The following is an attempt to capture some of that diversity seen in our wild populations.

    It should be noted that the more time I spend with the resource and thinking about the implications of what I was seeing the more certain I became that our O. mykiss populations contain multiple life histories which of course is part of the diversity of the over all populations. The foundation of my discussion will be the Skagit basin fish though information from other basins will be included were appropriate (for example the Deer Creek summer steelhead). I will attempt to follow the fish from their emergence from the gravel until they completed the cycle with surviving adults spawning. Unless noted in the discussion I will be taking about winter fish.

    Throughout the north Puget Sound region we see wild steelhead fry emerging from the spawning gravels from late June into September. The timing of that emergence varies from basin to basin. The peak emerge timing seems to be strongly influenced by the duration of the snow melt run-off for each basin in the region with peak emergence timed to occur on the falling hydro-graph of the run-off. For example consistently the peak emergence for the Skagit is in early August while the peak on basins like the Snohomish it occurs in early/mid-July. There appears to trade offs between the fry emerging early in the growing season to assure the largest size and fat reserves to survive that first winter and coming out of the gravel late enough to find favorable flow conditions.

    There are considerable trades in that timing though it is clear that over several decades there times that favor a timing other than what is the "average or norm" for the population. One example would those late emerging fry in September. This fish have a very short growing season in which to prepare for the winter. Most years there are significant survival costs for this late strategy but on those rare years with large and prolong run-offs it would be a wining approach. As aside those late emerging fish are so late that they are just forming scales as they enter the winter; as a result aging such fish based on scale samples may underestimate their total age when sampled later in their lives.

    Whether the fish is likely to ultimately become either a resident rainbow or a steelhead the first couple years of the young fish are similar. O. mykiss is basically a fish of moderate size streams with the largest densities of rear fry seen in large creeks and small rivers. It is typical to see a downstream shift to large waters as the fish get older. The next bench mark in the diversity equation is the age at which those fish destined to become steelhead smolt. Commonly steelhead smolts of the region are in that 6 to 8 inch size range as they smolt in the spring. That size is a critical threshold for successful smolting with the age at smolting strongly related to the time it takes for the young fish to reach that size. Across the region the most common /dominate age of a smolt is age 2 (two winters in freshwater) though age 1 and age 3 fish are seen in most populations. Those basins with earlier fry emergence, warm water and better growing conditions have more 1 year smolts than those at the other end of the spectrum of rearing conditions.

    Those smolts leave the river over a 3 month period (from late March to early June) with the peak out-migration in mid-May. The parr that did not smolt in the spring and opted for a freshwater life history over the next year typically show a downstream migration taking up residence in the pools/runs found in the larger tributaries and main stems. It is at this stage that those resident fish are positioned to take advantage of the abundant food resources provided by the returning salmon. You will see them along with the whitefish and bull trout among and behind the active fall spawning salmon, During the winter they are more than willing to take advantage of any available salmon flesh and the emerging and migrating salmon fry/smolts from the late winter through the spring period. During the next two years before reaching sexual maturity those rainbows may double their length and increase their weight by more than 10 fold.

    It is once the steelhead leave our rivers and begin their ocean feeding phase that we as anglers begin see the expression of the fish’s diversity. Those feeding fish may spend as little as single summer feeding or as much as 5 years. The majority of the fish spend 2 summers (2 salts) feeding at the ocean before returning to the rivers to spawn as 3 to 5 year old fish (depending on the age of smolting). Those fish with a 2 salt history return as adults typically at a size of 8 to 12#s). The majority of the other fish return as 3 salt fish and are those teenage size fish with some of the fasts growing males exceeding that magic 20# mark. Those fish returning after just a single summer of feeding are those males returning as what is commonly called "Jacks". The fish are typically only 15 to 18 inches long but are fully mature fish capable of fertilizing a much larger females eggs. The fish at the other end of the spectrum (those 5 salt fish) are also males that return as giants of the species (over 30#).

    A couple of other salt water feeding periods that are occasionally seen are fish that return during the same season (usually in the fall) as the year they smolted. These fish are commonly called "half-pounders". These are immature fish that over-winter in the river but do not spawn. I have only seen 3 such fish (all caught while chasing sea-runs on the lower Skagit). They were in that 14 to 16 inch range and a year or two younger than similar sized sea-run cutthroat. Just as rare are those fish that spend more than 5 years at sea feeding; they return at a size that defies belief.

    The fish that opted to spend their time in the river as rainbows typically mature at age 4. Their size depends in large part on the areas that they have spend the last growing seasons. Those fish living in the larger tributary and main stem areas are often in that 14 to 15 inch size range, those from the smaller tribs will be smaller; maybe 10 to 12 inches in length. Those from the extreme headwater areas often mature at older ages and a much smaller size (in some cases only 6 to 8 inches in length). It often requires determining the rearing history of an individual fish from a scale sample looking at growth patterns. Though to be fair an angler with a lot of experience at looking at the diversity across the population can make an "educated guess" at an individual’s life history; especially at certain times of the year.

    The Deer Creek summer steelhead provide an interesting contrast to the complex rearing patterns seen with the Skagit winter fish. A sample of more than 150 Deer Creek summers collected over two years found that nearly 95% of the first returning fish were of a single age. They had smolted at age two and returned during the second summer at sea to spawn the following spring as 4 year old fish. A small handful of the fish had migrated as 1 or 3 year old smolts and a single fish had returned as a "3 salt" adult. While the average size of these summer steelhead were 24 to 25 inches in length (5#s or so) there was a pretty wide range in size. In spite of being the same age there were fish as short as 19 inches and one or two were over 30 inches.

    The run timing for the Skagit winter fish have long been noted as late returning fish though it should be no surprise by now that there is a some variation in that timing. Enos Bardner in his "Northwest Angling" published in 1950 before significant success of the hatchery program in the basin noted in his discussion of the winter run fishing on the Skagit "The Skagit is the undoubtedly the greatest producer of steelhead trout in the Northwest....It is fished very little in December but January is good, and the period from Washington’s Birthday until the end of March is the best." Today the run timing remains the same. As with most characteristics with steelhead with run timing we see a fair amount of variability.

    Tribal nets sometimes catch the first Skagit wild winter fish of the year below Mt Vernon in late October. The earliest that I personal caught a wild Skagit was gorgeous hen on the Sauk the first week of November. However as mentioned by Bardner there aren’t many wild Skagit fish until well into the New Year and I don’t really expect to see consistent catches of wild winters until late February with the run picking up from there with numbers of fish entering the river in late March/early April. The numbers of newly arriving fish taper off pretty quickly after that point though there must be new fish well into May. Throughout the region the peak of the wild runs seem to occur roughly 6 to 10 weeks prior to the peak of the wild spawning activity.

    On the Skagit the peak of the spawning of the wild winters happens the second or third week of May nearly every year. It seems that the first wild fish spawn in early to mid-March every year but the level of active remains low until nearly the first of May. It is rare for date when 10% of the wild redds in the basin to have been dug to happen before the 20th or 25th of April. From that point the numbers of active spawning fish increases rapidly until the peak. From the peak the action tapers off fair quickly though there are still fish actively spawning well into the summer with fish seen actively spawning as late as the last week of July.

    The distribution of redds in the Skagit basin is pretty interesting with some found barely above sea-level and others as much as 115 miles from the mouth of the river and at an elevation of nearly 3,000 feet. The timing of the spawning varies little no matter were the fish spawn. The overall timing of the spawning in the lower basin tributaries tends to be earlier than elsewhere though that may as much as a function of dropping flows as the spring progress making access to those smaller streams more challenging for the fish. The fish found the farthest from mouth of the river (South Fork of Sauk near Monte Cristo) spawn with much the same timing as those much lower in the basin (for example the Sauk below Darrington).

    It is common for O. Mykiss individuals to survive spawning to spawn a second time. While the repeat spawning rates in this region is lower than elsewhere across the species range repeat spawning rates of 5 to 15% or more is the norm. One thing of note is the portion of the population that survives to spawn a second time seems to have declined over time with the average in recent years being only about ½ of what it was a couple decades. Obviously having those repeat spawners in the population provides some stability to the population’s productivity. With the low repeat spawning rate as expected it is rare to see individual steelhead surviving to spawn more than 2 or 3 times. The resident rainbows seem to be better equipped to survive to spawn multiple times; have seen several fish that had survive 5 spawnings and seem to be well on their way to spawning a 6th time; fish in their 10th year of life.

    Combining the complex fresh and salt water age structure of the returning adults with the ability to spawn multiple times it is common to see 15 to 20 age/life histories combination in any decent sample of wild fish. Clearly having resident and anadromous fish of 5 of 6 year classes overlaid with repeat spawning fish interacting on the spawning grounds not only provides stability it enhances the diversity of the population.

    In the wild Skagit steelhead populations I have caught wild winters every month of the year. Unspawned fish from November into July and kelts from April to October. You find wide range of sizes for the adult O. mykiss. The resident fish may be as small as 6 inches in high elevation tributaries or some of the main stem repeat spawners can be more than 24 inches long. The anadromous branch of the family tree have spawners as small as 14 or 15 inches and gaints stretching into the mid-40 inch range.

    In short while the steelhead populations of the Skagit and other Puget Sound basins are clearly at depressed levels the diversity essential to support the long term survival of the species in the region seems to largely intact.

    A former steelheader
    Curt
    Bert Kinghorn, aplTyler, JS and 7 others like this.
  2. o mykiss Active Member

    Posts: 1,280
    .
    Ratings: +138 / 0
    Very interesting read, Curt. Thanks for sharing.
  3. Steelie Mike Active Member

    Posts: 1,600
    Camas, WA
    Ratings: +24 / 0
    Great read Curt.