Article A Skagit Bull Trout Bio


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Spring is still several months away in a North Cascade stream valley; the evergreen tree’s limbs are sagging under a load of snow and the forest floor and stream gravel bars have a "virginal" white blank of snow. Several miles of this ice rimmed stream flows through a relatively flat valley located more than 2,000 feet above sea level and more than 100 river miles from Puget Sound. In gravel below the frigid stream water life is beginning to stir. The cleanest and most stable gravels coupled with water temperatures just barely above freezing is providing a near ideal environment for the eggs of one of the Pacific Northwest’s enigmatic species. The next generation of native char of the region are preparing to hatch.

It seems appropriate that the parents of those eggs after several months of ghost like hiding the char began their spawning as Halloween approached. The spawning of those native char or bull trout as they are commonly called is triggered by the dropping stream temperatures associated with the fall season. Their spawning activity is triggered as the temperature drops below 8 degrees C or 46 degrees F. The adult fish had begun arriving near the spawning grounds as early as June with numbers of fish building throughout the summer. The migrating adult fish take advantage of the higher flows associated with the snow run-off to find their way pass waterfalls, log jams and cascades. While some of the earlier migrants had been able to reach the spawning areas the later fish held in large pools, log jams, and deep runs well downstream of the spawning areas for weeks or months waiting for the first of the fall freshets to provide the flows needed to complete their journey. Typically the pre-spawn bull trout stage at the lower part of the potential spawning area in the water they find most secure (log jam, under cut bank, deep pool, run with cover, etc.

As the stream temperature drops below that 8 degree C trigger point the females begin moving from the staging areas up on to the spawning gravels. The females can be seen actively moving about and checking potential spawning sites. It is common to see such females to pause and apparently testing various gravels with an arched body or a test dig. The ideal spawning site would be side channel area or tail out with up welling flow through large substrate over laid with smaller gravel. Having some stream side cover (an over hanging limb, root wad, or log) would be an added bonus. Once a satisfactory site is located the spawning process is similar to that of many other salmonids. The female will turn on her side and using hydraulic pressure from downward thrust of her tail/body lift the stones from the bottom allowing the current to carry them downstream.

Once the female begins redd construction the males (who have been holding nearby) quickly move into position to attend the spawning . The male will typically hold downstream of the digging female and to the outer side (that away from the nearest bank) of the female. As the female is ready to release some of her eggs the male will move along side of her with their vents near each other with body arching, gaping and shuddering the eggs and sperm are jointly released. This process with be repeated multiple times with the female releasing may 5 to 10% of her eggs per spawning attempt. The larger the female the more eggs (higher fecundity) she will have with dramatic increases with size increases. The largest of the females may have 10,000 or more eggs while the small resident fish may have only a few hundred. Surprisedly the eggs of a very large female (say a 30 inch fish) may not be much larger than a more normal size one (say 18 or 20 inch fish).

It is not uncommon for the males spawning with a female to be of a different life history or to have single spawning female attended by multiple males. Early and late in the spawning season (which can be only a few weeks long) it is common to see only one male with an actively spawning female. However when the population’s spawning activity is at a peak the female maybe attended by 4 or 5 males. In those cases there can be considerable "jockeying" for position and spawning "rights". Those confrontations can be quite violent at times with extensive chasing and even activity that can only be characterized as fighting. The fighting includes bumping, biting and grasping and shaking of a competitor. On occasion large males have been seen to grasp and physically tossing a smaller fish; at times that toss can result in the smaller fish being thrown from the stream. In that fighting it is the norm for the largest male to establish dominance however the fighting between the males can be so intense that while larger males are fighting for spawning rights a lesser male can sneak in an accomplish the deed.

The spawning males develop some spectacular colors; a dark back (black to dark green) bright pink/red spots, and brilliant white leading edges of the pectoral, ventral and anal fins. The most dominate male will always have the most brilliant colors. If that dominance changes the most brilliant color male will also change. With a demotion the former dominant male will exhibit a fading coloration rather quickly (within minutes) with the new dominate males color intensifying.

While not to the degree seen with the males the females will also demonstrate aggressive behavior during spawning. They will actively defend their spawning site by attempting to "bully" a competing female. Typically the dominant female will turn sideways to her competitor arching her side and pushing towards the other fish. Usually one or two "rushes" are all that are required to establish dominance. The females attempt to create 5 or 6 feet of space between the redd sites. Once spawning is complete the female quickly vacates the site. In habitats with limit spawning sites and/or high densities of spawning adults it is not uncommon to see individual redd sites used multiple times in a single spawning season. At high spawning densities superimposition of redds is very common. In ideal locations (that with larger substrates over laid with smaller gravels) the eggs from an early spawning will fall deep in the spaces of that larger substrate with little impact from following spawns.

Unlikely many salmonids both the females and males vacate the spawning areas quickly post spawn. By the tail end of the spawning season very few fish (either males or females) remain on the spawning grounds. Post spawn the fish are typically shadows of their former selves. They may loss 50% of the body weight during the spawning migration, holding and spawning - that entire process can stretch over 4 or 5 months with little feeding being done by the staging adults. Between the damage from the fighting males, the physical injuries from the rigors of the upstream migration and various predator attacks (in some cases 10 to 20% of the adults are lost to predators - such animals as otters, bears, racoons, blue herons, eagles, ospreys, etc. The survivors often have a variety of injuries and scars.

The spawning grounds for the north Puget Sound bull trout is typically at the upper limits of the basin accessible to the migrating salmonids. The spawning headwater areas are commonly in areas that are snow covered for most of the winter. In basins like the Skagit that means that much of that critical habitats can be found in Parks and wilderness areas. In some cases only bull trout are found in those waters but at other times resident rainbows, steelhead (winters or summers), spring Chinook or coho share at least some of that habitat. Bull trout seem to particularly adept at migrating beyond areas that can be barriers to salmon and steelhead. They have the ability to jump some significant size barriers but more importantly they can often find ways around significant falls by taking advantage of alternate paths even in those cases that those path ways are only available for limit periods of time. Major log jams that may stop spring Chinook or even steelhead can be easily passed by bull trout as they take advantage of small side flows to wiggle their away around the barrier; more snake like than fish like. Those types of barriers that are barriers to the brute strength of the Chinook or the acrobatic ability of steelhead are only minor obstacles to the cunning and guile of the bull trout.

The region’s bull trout express as wide of a diversity in behaviors and life histories as any of the salmonids found in the area rivers. It is not long after the fry emerge from the gravel in the spring that individual fish begin showing some of that diversity. Some of those young fry are destined to spend their entire lives within a very short distance of their natal gravels. The biologist call the fish with that life history "resident" fish. They remain life long residents of those head water streams. These fish are slow growing individuals typically maturing at age 4 or 5 as smallish adults of only 10 inches or so. A 14 inch individual would be a true trophy and likely an ancient individual. All the various life histories will ultimately end up spawning in the same locations at the same time and often together. For the "resident" the majority of the adult will be males that often successfully spawn as "sneakers" - that is males that sneak in to spawn with a larger female on either the off side of the dominate male or while the larger males are occupied fighting among themselves. Those males also spawn with the resident females who often spawn in smallish side channels or areas with smaller gravels used by the larger fish. Those females construct a "cute" redd that typically is no larger than diner plate.

The majority of the juvenile bull trout in headwater areas eventually leave their natal areas to rear in downstream habitats. Those fish can leave the area anytime in their first couple years; the timing of which appears to be at least partial related to the bull trout densities. It is these fish that will become the larger individual in the populations. Depending on the type of habitat that those juveniles achieve the bulk of their growth they are assigned different life histories; adfluvial -lake dwelling, fluvial-river dwelling or anadromous - marine going. While it seems to be human nature to place the fish in this nice neat boxes the reality is that like many fish bull trout resist that simple classification. Not only do all the various life histories interact on the spawning grounds studies have found that individual fish of a given life history can change rear strategies during its life. For example post spawn anadromous adult may elect not to return to the salt and instead spend the next growing season in the river or a fish that matured as a resident fish may opt to take advantage of downstream habitats. In one two year study 8% of the adult bull trout sampled had changed life histories.

Most anglers are probably most familiar with the anadromous life history of Skagit bull trout. The fish opting for this rearing strategy typically leave the river as two year smolts at approximately 6 inches in length in the spring of the year (peak migration in mid-May). In the salt bull trout are more like sea-run cutthroat than salmon or steelhead and stay relatively close to their natal rivers. Like the cutthroat they seem to spend the majority of their time in the shallow near shore areas taking advantage of the diverse forage found in that habitat. The fish range up and down the sound’s shoreline with radio tagged Skagit fish track as far south as Seattle. That first summer the smolt grow quickly and by late summer or early fall they make their way back to freshwater areas as sub-adult fish. Those immature fish are typically 10 to 14 inches in length and while most return to the Skagit to over winter some will find their way to other near by river basins. Those that over-winter in the Skagit do so in the lower river with the vast majority found from tide water upstream to the middle Skagit (mostly downstream of Lyman). After taking advantage of whatever food resources that were available (salmon flesh, fry , insects, etc) they make their way back to the marine waters in the late winter through most of the spring though some may never actually leave the tidal influenced waters of the Skagit. Tagging work demonstrated at least some of the fish return to virtually the identical forage areas used the previous year. By mid-summer most of the sub-adult fish have become maturing adults of 16 to 19 inches and have begun their migration to the spawning grounds. Once that migration starts the fish move quickly upstream until well up river typically reach the spawn staging areas in advance of the fall spawning period. Of the non-resident foraging strategy most of the population seems to opt for the anadromous option.

The second most common migratory foraging strategy is one focused on in-river rearing. The strong hold for this fluvial fish are the large main stem pools. The areas with the highest density of fluvial fish are those reaches with significant numbers of large/deep pools that provide both access to major foraging areas (salmon spawning areas for example) as well as security during the course of the year in a wide variety of environment conditions (summer low flows, floods, etc). Like their anadromous brothers and sister the majority of the fluvial fish reach maturity as 4 year old fish. This mature fluvial fish at a given age tend to be smaller than the anadromous fish. At age 4 these fish are typically 15 to 17 inches long.

Once the sub-adult fish find a suitable pool they exhibit a high fidelity to that "home pool". The fish tend remain in those pools for extended periods often only leaving as adult as they migrate to their spawning grounds. Post spawn many of the fish that have established a "home pool" will return to that pool within months of spawning. A river like the Skagit has dozens of such large pools and each of those pools have bull trout that use it as a "home pool". A post spawn adult will often swim through a number of such pools to find its own "home".

The smaller fry and parr that will adopt the fluvial life history move downstream from the spawning/early rearing habitats over the course of a couple years and tend to shotgun throughout downstream areas. Those juvenile fish can be found in almost any downstream habitats that are accessible to anadromous fish. As a result in a system with robust bull trout populations individual fish can be found in some surprising areas/habitats. Often those habitats are well outside of the "book" of what is typically considered bull habitats. In many ways that kind of diverse habitat uses is an indicator of a robust population.

The fourth rearing strategy shown by bull trout is a lake dwelling or adfluvial. Like the fluvial fish the juvenile fish move downstream and in this case take up residency in the lake in the system. Depending the lake system the fish with this rearing strategy can be the fastest growing bull trout in a basin and across the species’ range the largest individuals often are of the adfluvial type. Historical the adfluvial type habitat was not very common in the north Puget Sound region (Baker Lake on the Skagit and Chester Morse on the Cedar are examples of historical bull trout lakes) thus were found in few areas. However in keeping with the incredibly and surprising adaptability of bull trout adfluvial fish are more commonly found in the region today. Those populations have taking advantage of reservoirs that are accessible to a bull trout population. Like the other rearing strategy options the adfluvial fish mature at age 4 (sometimes older) but exhibit a greater diversity in that size at maturity. In systems of low productivity those adult fish may be similar in size to fluvial fish at first spawning and in other more productive systems they may be reach 24 inches at first maturity.

Bull trout regardless of their life history can a relatively long lived salmonid and here in the north Puget Sound region some fish can live to be teenagers. Unlike salmon they can and do survive spawning with some individuals spawning multiple times. In this area it is not uncommon for ½ or more of the spawning population to consist of fish that have spawned previously. With the exception of some adfluvial fish it is typical for bull trout to spawn annually once they reach maturity. The growth between once spawning and the next can be highly variable. The extensive migration and extended time period that bull trout dedicate to their spawning takes a pretty heavy toll on the fish. Not only is there a high annual mortality for the fish once they reach maturity (maybe only half will survive from one year to the next) there is a high physical toll with individual spawners losing a substantial portion of their body weight. How quickly the fish recovers from the rigors of spawning is highly depending on the food resources available to the post spawn fish. Depending on that availability it may take weeks to an entire year for the fish to recover. As a result the year to year growth of the repeat spawners is also highly variable. For anadromous fish growth from one spawn to the next may average 2 or 3 inches a year though it will vary from no growth to 6 inches or more in a single year.

The largest fish found in the population are obviously those fish that not only live the longest but also grow the fastest. Both the males and females pay a heavy price in their migrations and spawning though it appears the price maybe higher for the females. The vast majority of the very largest individuals in the population (more than 95%) are males.

With the mixing of multiple life histories and age classes of fish in the population and the variable growth rates it can hardly be surprising that for the angler or even a trained biologists it is difficult to pigeon hole an individual fish. Has that 22 inched spawned twice or even three or four times and has it had fluvial or anadromous or both life history? While those kinds of question may be of interest to the angler it isn’t that important to the overall bull trout population. On the spawning grounds the varies life histories freely interbreed and clearly are a single population. The critical factor here is that the population by hedging its survival bets with complex life histories and age structures coupled with much of the species historic still intact is insuring its long term survival of the Skagit bull trout.

Any discussion of the region’s bull trout would be incomplete without consideration of would for a lack of better term the fish’s personality. Bull trout’s personality can best be characterized as "laid back". That trait is expressed at a vary of ways during the fish’s life. When feeding the bull trout is very efficient; feeding heavily when forage is readily available and conditions favor that activity. On main stem rivers post spawn the fish take advantage of the spawning salmon feeding on loose eggs, dislodged insects and fishes and salmon flesh. During the period between the salmon spawn and before the fry begin emerging from the gravels the fish tend to hunker down in the deeper/slower water. For the angler that means that they may experience good catch rates during the spawn and fry emergent times and little action in the lull between when the fish are not very active. Something similar can be seen in the summer in the salt where it is common to see bull trout laying on or near the bottom for long periods of time with little activity only to see them spring into a short burst of intense feeding activity when conditions change (for example strong currents trapping bait fish in the shallows). The same sort of behaviors is seen in the fish’s migration where they move along stream edges in lower velocity areas or the areas where they opt to hold for extended periods which typically have low velocities as well as adequate cover (in the form of depth, over head cover, etc). A final example of how this "laid back" attitude benefits the species is seen when the fish face severe injuries. It has become common to see bull trout surviving a completely torn gill arch. Even though heavy bleeding is associated with this type of the injury the fish seem to react calmly to such injuries and typically seek a refuge beneath logs or boulders where they lay stationary with virtually no movement for extended periods. It seems that allows the blood flow to slow and clot much more efficiently than with other salmonids.

That whole "laid back/efficient" behavior is further highlighted when the growth and behavior of anadromous bull trout is contrasted with the sea-run cutthroat in the same basin. As state before the bull trout smolts typically are about 6 inches long when the move to the salt and in two years they grow to 18 inch adults. The cutthroat tend to have larger smolts and as they mature as 4 years old they typically only 12 inches long and it may take an additional 3 or 4 years for that fish to reach 18 inches. This is in spite of the fish sharing very similar migration patterns and feeding areas. As mentioned earlier the bull trout tend to forage on larger food items and in short periods when the forage is most vulnerable. The cutthroat feed over longer periods of time on smaller items often in inefficient ways; a classic example is sea-runs feeding on blue wing olive may flies where the fish will rise through several feet of water to take a very small insect only to return to the bottom before rising again. As a result an individual fish will swim 8 or 10 or more feet to consume a single size 18 mayfly repeating that for hours - have to wonder about how energy efficient that behavior is.

It is this diverse life history and complex behaviors that contribute to the attraction of the bull trout to anglers. That coupled with the large size attained by the species and when the fish are in prime condition their tough dogged resistence to capture make them worth of angler interest. Further in basins such as the Skagit where robust populations exist the angler can find very good catch rates with fish responding to a vary of presentations by the fly angler over much of the watershed and over the entire angling year. Current angling regulations have contributed to the rebound of bull trout numbers in basins like the Skagit and seem to be adequate for the long term survival of this attractive and interesting critter.

A bull trout fan
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wadin' boot

Donny, you're out of your element...
Curt- given the efficiencies of the Bull, why aren't they far more prolific? Historical perceptions as a junk fish maybe? A couple of things that always blow my mind when there's one on the end of the line- how truly spectacular the coloring and spotting patterns are. To my way of thinking they always look like they got their jewels on. That and the ribs are often far easier to see, alternatively with a bend in the fish the sides can almost look wrinkled or eel like. Thanks for this- looking forward to more... (addendum- Curt answered these questions in this thread...

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