Residency and Anadromy in O. mykiss, May 25, 2011

BTW, this here fish is a hatchery steelhead that was released into the South Santiam in April or May, and was still hanging out in the river in September, where it gulped a size 16 Renegade and was then released back into the river to compete with wild rainbow, cutthroat, and chinook juveniles.

Wow, what a complex question, that faced by a rainbow/steelhead trout which is now actually a member of  Oncorhynchus, not as it formerly was, of Salmo, and as such is a member of the Pacific Salmon family.

What was the question?  Oh yes.  I am a little O mykiss (rainbow) living in Hood River.  My mom and dad might have been anadromous (like they swam to the ocean and came back) or they might have both matured somewhere in Hood River, mated and produced me.  But now, gosh darn it, I have this strong impuse to head off downstream myself, swim out into the ocean and migrate way up between Alaska and Russia in the Alaskan Gyre (Google that if you will), hang out for a few years, and then come on home to the Hood.  (play on words?)

This blog ain’t gonna answer the question completely, as this would take more time and dilligence than I have at the moment.  But here is the deal.

O. mykiss is good at exploiting habitat and ecological opportunities.  Some fascinating research in Kamchatka indicates that rivers with very fertile feed production tend to produce more “residency” in mykiss, although a proportion of the rainbow do practice anadromy (as if they need practice) and head out to sea and back, thusly becoming steelhead.

Conversely, the anadromous life history was more common in rivers where we would consider food production to be on the stingy side.  This makes sense.  If there isn’t much to eat, then let’s go to sea, grow, make lots of big eggs, and then come home to spawn.  If on the other hand, there is a ton of food in the river, then why bother?

One cool aspect of this tendency to express fundamentally an anadromous or resident life history, with lots of interbreeding among both “types” of fish, is that it shows how O. mykiss can exploit significantly different ecological conditions by mostly staying in the river to mature or mostly going to sea to mature.

But I ramble, as per usual.  Go to southern CA, at the extreme southern edge of where steelhead persist these days.  Little streams.  Harsh warm climate.  Unpredictable stream flow patterns.  And on top of all that, a few impassable dams.  O. mykiss persists above these dams, sending some number of little fish downstream over the barrier each year, and amazingly, if there is water in the creek, there may be two,or three or six or heck, even a dozen or so steelhead come back to the creek in some years.

Many studies in Columbia River, if not all, have found that resident mykiss parents can produce anadromous offspring, anadromous parents can produce off spring that mature in the river, and parental pairings can include any possible combination of anadromous and non anadromous fish.

Jon McMillan has observed non-ocean going O. mykiss spawning with anadromous steelhead in Olympic Peninsula rivers.  If it goes on in those coastal WA populations, then why not here in Oregon?

In oregon, ask the coastal biologists if we have “resident” rainbow and they will almost universally say that we do not.  My guess is that there are indeed offspring of anadromous mykiss that stay in the river and spawn with non ocean going or ocean going mates, producing mostly offspring that go to sea, but an occasional little guy or gal that matures in the river.

What about steelhead through Ballard Locks?  I find it difficult to believe that the mostly river resident rainbow in upriver tributaries don’t produce at lease a few little guys and gals who do in fact migrate to the ocean and try to return as big adults.  It may simply be that this life history is so scant that no one notices these fish, or that survival is so low that none survive to make it back through Ballard Locks, but common, there have to be a few offspring of the upriver O. mykiss that are trying to express an anadromous life history, don’t ya think?

Our Oregon coastal rivers could be an example of an ecological setting where food supplies, rationed across many species of Pacific Salmon, are slim enough that the residency life history is so rare compared to the anadromous life history.  But to think that the stay at home in the river to mature life history is completely missing in Oregon coastal mykiss populations seems a stretch, given what we have seen in most every place where we have really looked closely.

Most every place, not every place, I should add.  Let’s consider the McKenzie River, in the upper Willamette River basin.  This river is big and bold, it grows tons (not that I have weighed the critters, but a lot of rainbow at any rate) of what we call resident rainbow.  We call ‘en resident rainbow because they live out their entire life cycle in the McKenzie, Willamette, and various tributaries of same.  These O. mykiss are in a river close to 200 miles from the ocean.  There is what I would consider decent food supply in the river, and it seems that these mykiss have evolved to be stay-at-homes to such a great extent, that we don’t believe that there are any anadromous offspring of these rainbow.

Hummmmm.  If so, is this because there was such a clear disadvantabe to make the long migration to and from the ocean that the anadromous life history pretty much got weeded out of the population?  Are McKenzie mykiss derived from stream capture of an interior mykiss ancestor that had even less tendency to go clear to the ocean than to stay close to home?

So, yes, I think if one goes far enough inland, and looks at”rainbow” that have been isolated from the ocean long enough, you will see anadromy pretty much lacking from the life history expressions.

The Elwah?  I do not know enough about the specifics to be an expert and recommend a breeding program to re-establish runs of anadromous Pacific Salmon.  But your proposal should be considered.  And it really grates on my sensibilities to think about flooding the system with hatchery fish to restore anadromy to the upper basin.  I do not know exactly what has survived below and above the dam.  I am sure that a hundred years of isolation has had some genetic effects on the up and downstream mykiss.  So too, the below-dam Pacific Salmon in the Elwah, may have been influenced by hatchery programs.  Wouldn’t this be a great opportunity to restore an all wild assemblage of many species of Pacific Salmon in this gorgeous basin that has been strangled by the dam for so long?

Ooops.  Editorializing.  Again.

But hey, here’s an idea, if it is deemed essential to use hatchery fish to restore a wild run, what about limiting the program to one life cycle and prohibiting any fishing on the river for three life cycles?  I know, none of my business.  But an honest to goodness conservation/restoration effort shouldn’t get mired in harvest battles, and should give the fish a decent shot at making the re-introuduction on their own, because these are amazing resilient fish, given half a chance, and especially considering the quality of the upriver habitat in the Elwah.

And how would anyone know that there are not any anadromous mykiss returning to the Elwah from above-dam resident rainbow?

Jay Nicholas, May 25, 2011

Coastal Oregon Chinook: Spring and Fall Run Populations


Following my recent post on Oregon coastal steelhead populations, why not review ODFW’s classifications of fall and spring chinook Species Management Units (SMUs) and populations?

Juicy stuff, for all you fish science and salmon management geeks out there.

Oregon coastal Chinook are categorized by ODFW into two Species Management Units,the Coastal and Rogue SMU>

These SMUs are further divided into roughly 28 populations of fall run fish, and only nine historical  populations of spring run fish (at least two are currently thought to be extinct).

Spring chinook salmon are far less widely distributed than fall run fish, but are not nearly as rare as native runs of summer steelhead in Oregon coastal rivers.

This information was compiled from the ODFW Native Fish Status Report.

http://www.dfw.state.or.us/fish/ONFSR/report.asp#fall_chinook

Anyone wonder why spring chinook might be more common than summer steelhead?

JN

Coastal Oregon Steelhead – Winter and Summer Run Populations

The summer steelhead pictured here, just prior to its release, is a hatchery fish that was stocked and  caught on the Middle Fork of the Willamette.

The Middle Fork hatchery steelhead program is remarkable from the standpoint that it supports a robust recreational fishery during the spring, summer, and autumn, within minutes of zillions of people who live in the Eugene & Springfield area.

Winter steelhead are not native to the Middle fork, and the naive run of wild spring chinook has been all but erased by the salmon problems associated with Dexter Dam, Lookout Point Dam, and Hills Creek Dam.

This is a preamble to a question: do you ever wonder how many populations of summer and winter steelhead the Oregon Department of Fish and Wildlife categorizes on the Oregon Coast?  The majority of anglers I have met spend most of their time trying to figure out how to catch a steelhead, or how to catch more steelhead, than pondering population classifications and steelhead management policy.

Just to keep the science of steelhead management on the table for anyone who cares to discuss such matters, I assembled the following table that summarizes, as closely as I could, ODFW’s list of native, coastal steelhead populations.

Among the key  concepts that this table displays, is that there are two Species Management Units on the Oregon coast,Coastal and Rogue SMUs;  but only three native summer steelhead populations, compared to roughly 31 winter steelhead populations.

One could ask whether or not classification of these population units could be informed by more or newer data, but it is clear that native populations of summer steelhead are rare in Oregon coastal rivers, even more rare than the populations of spring-run Chinook classified by ODFW.

FYI, this information was compiled from the ODFW Native Fish Status Report.

http://www.dfw.state.or.us/fish/ONFSR/report.asp#fall_chinook

Hope you find this interesting.

JN

Buck and Hen Salmon: How to distinguish sex.

Sexing Salmon:  Bucks and Hens.

How to tell male from female salmon and steelhead.

Last year, 2009, the Oregon Department of Fish and wildlife considered the option of allowing anglers to harvest (retain, kill) only male Chinook, and if I remember correctly, there would also have been a size slot within which harvest would have been allowed.  The purpose of the proposed regulation was to allow some fishing, and some harvest, of male salmon in a certain age class.

When the dust settled, the proposal was not adopted.  ODFW biologists believed that the proposal had some biological merit, but were unsure whether anglers would be able to accurately distinguish between male and female kings.  Then too, the State Police expressed concern regarding their officer’s ability to monitor compliance, conduct education with anglers, and enforce this regulation, if it had been adopted.

Personally, I found the proposal most intriguing.  I appreciated the proposal’s biological basis, and also understood the social and administrative challenges that adoption of the regulation would have created.

Bottom line – this regulation, or something like it, could become a normal part of our angling future. A continuation of poor ocean survival conditions,  vastly fluctuating survival between brood years, a general decline in the freshwater capacity of our rivers, or even social pressures, could change the landscape for salmon anglers.

Think it sounds silly to contemplate a bucks-only harvest restriction on king salmon?  Isn’t there more social than biological basis for hunting regulations that target bucks?  Not a wildlife biologist, so this is dangerous territory for me to dabble.

I simply want to make the point that our regulation landscape, and our value-based thinking about harvesting salmon could evolve in the future.  The day could dawn when our opportunity to fish at all depends on releasing hens.

For now, let’s just talk about the next time one of us is lucky enough to catch an actual salmon or steelhead.  What should we look at to decide if it is male or female, buck or hen?

Here is a short list of the body characteristics I look for to decide if I am looking at a buck or a hen.  Head shape; relative head size; body cross-section; adipose fin size; jaw shape; my, how sharp your teeth are; the presence or absence of distended vent; and body color.

All of these morphological traits are useful to distinguish male from female salmon, and to a less dramatic extent, to distinguish male and female steelhead also.  My remarks and the photos I will show are principally limited to Chinook and steelhead.  Some of us anglers take it that an understanding of distinguishing between male and female salmon is simple.  To many anglers, though, it is not.

First thing to note is that the differences between males and females becomes much more obvious as salmon approach sexual maturity.  Recognizing sex differences in immature ocean salmon is more difficult, and I have little personal experience (like none) so I won’t talk about this situation.  Suffice to say that it is far more complicated to distinguish both species and sex of immature salmon in the ocean.

As salmon approach sexual maturity, however, the difference between species – and between bucks and hens – becomes far more obvious.  In Pink salmon, the males develop a great hump (hence Humpie) but the females do not.  In Chum salmon, bucks develop a huge hooked jaw with fang-like teeth, but the hens do not.  These extreme morphological changes are directly associated, we think, with mating rituals, fighting among males for dominant status to spawn with a specific female.

Here is pretty much what  a male Sockeye looks near sexual maturity.

The striking physical differences between each salmon species probably helps the species recognize their own, and helps minimize hybridization – although there are many other factors like olfaction (sense of small), body size, spawning season, homing, and spawning habitat selection – that all contribute to the salmon’s ability to maintain their species’ distinction.

Blah blah.  Sorry.

Head shape. Buck Chinook salmon have a convex sloped forehead; hens have a convex sloped head.  This is the case for steelhead also, although the differences we see in steelhead are usually not quite as dramatic as they are in king salmon.

The Chinook above is a hen.  The Chinook below is a buck.

Relative head size. This can be subtle, but bucks have larger heads than hens, when one looks at similar sized fish.

Body cross-section. Bucks tend to be laterally compressed, hens tend to be round.  This means that a buck will be narrower and taller – a hen will tend to be rounder and shorter for fish of similar weight.  A view of a maturing buck from above, or head-on, helps one see these differences more clearly and the differences increase as the buck salmon becomes more mature.

Adipose fin size. Wish I had a good photo to show this distinguishing feature.  Suffice to say, bucks have much larger adipose fins than hens.  Big bucks have huge adipose fins and they can be 2-3 times larger than the adipose fin on a similar weight hen.

Jaw shape. Make king salmon develop a hooked nose –a kype – and the teeth of bucks grow larger than the teeth of hens.  King salmon do not develop kypes as dramatic as do, for example, Coho salmon, Atlantic salmon, or Chum salmon – but the kype of buck Chinook is noticeable; females do not develop kypes.

Fangs. Male king salmon exhibit larger teeth than hens.  Male king salmon do not develop fangs as dramatically as do male Chum salmon, but development of long, foreboding teeth on the males of both species is noticeable.  Female Chinook to not develop fangs like the males.

Check out the fangs on the male chum salmon pictured above.  My, grandma, what big teeth you have.  This male also shows the developing kype of the jaw, a characteristic you would not see on the female.

A distended vent on ripening females. As female salmon and steelhead become more sexually mature, as they ripen, their vent begins to protrude slightly.

Body color. Male king salmon develop a distinctive copper-bronze hue as they approach maturity.  Hen Chinook can be fully mature and still appear to be fairly “bright.”  These fish are not really what we would consider “chrome”, they just have not become dramatically colored as the males. Buck Sockeye and Coho salmon develop much brighter body hues than do Chinook bucks.  Point is, the bucks sport the most dramatic colors on the spawning grounds.

Here is the body color of a male Chinook, above, the bonze hue I mention.  Note also that the adipose fin is big and the vent is not distended.

Here is a mature Chinook female. Note that this hen does not have the “bronze color” of a male at a similar stage of maturation, could be mistaken as a bright fish, (had fresh sea lice), but has a well distended vent.

Hope these notes and photos help.

Steelhead?  The morphological differentiation between male and female steelhead are not as drastic as the differences displayed by Chinook, Chum, Pink, coho, and Sockeye salmon, even though all are classified as Pacific salmon.  Below, check out the head shape of a bright male (first photo) and female (second photo).  Both of these steelhead are hatchery fish.


Finally, here are three sketches. The first, of a pair of kings as seen from above;  the buck is the slimmer of the two fish.  The next sketch is a classic male Chinook – large head, concave slope of the forehead, no distension of the vent, and large adipose fin.  The final sketch s a female Chinook salmon approaching maturity – smaller head, rounded forehead, small adipose fin, and a slightly protruding vent.

We are fortunate to share the salmon’s rivers.

JN

Sea Lice or Leeches – Answers to the Blogosphere

Sea Lice – Not Leeches….

Let’s do a quick review, prompted by many sincere requests from folks who have caught steelhead and were unsure if they were seeing sea lice on the fish – or not.

This is an especially troubling question for anglers who have not caught very many fish and who catch a kelt, a spawned-out steelhead, that has re-chromed and is enroute back to the ocean.

Kelt steelhead present the dilemma of appearing shiny and are often carrying many external parasites.  The novice angler, having heard about “sea lice” associated with “bright” fish, might well be confused.

So, nuthin’ like a photo, right?

These are freshwater leeches, parasites acquired after freshwater residence.  They are dark brown to blackish wormy lookin’ things with little sucker mouths that tend to attach under pectoral fins or near the anal fin, but they could take refuge from the current behind any fin.

These are sea lice on a fresh-from-the-salt salmon. Note that they are translucent-white.  Note that some have lost their tails, but that a few of the very long tails remain attached.

Sea lice that have lost tails, turned dark gray or brown, are dying after being out of the salt for several days.

JN

Chrome or Kelt?

Let’s go back to March of 2006.  I was fishing with two good friends and one of us hooked a steelhead.  Off downstream it ran, well into the backing to make a great head-over-heels leap.  “Chrome!”  one of my friends remarked.  “I’m pretty sure it’s a kelt,” I said.  My buddies weren’t quite convinced, but soon we had the fish close enough to see that it was, indeed a post-spawning female.

By the way, the term kelt refers to a spawned-out salmon or steelhead.  The term was in use on Atlantic Salmon waters for centuries and is used my many here in the Pacific Northwest also.  More often, anglers in this region will use terms like spawn-out, snake, downstreamer, or run-back to identify a steelhead that has finished its reproductive activity and is headed back to the ocean.

The freshly spawned-out female pictured above is what they expected to see, not the silvery fish that we had hooked.  This female still has the rosy opercle and faint but noticeable lateral blush common to sexually mature female steelhead.  The fish’s sex is easily noted by the fact that the head slopes in a smooth convex curve from top of head to the snout.  A male steelhead would have a subtle but noticeable concave dip in this forehead shape.

Female steelhead undergo a striking change in appearance, reflecting hormonal changes, after they spawn.  These post-spawning females will lose their rosy cheeks and lateral stripe, regaining perfectly clean silvery sides and white bellies.  Over the years, I have found a surprising number of steelhead anglers who have not learned to recognize silvered-up kelts from fresh run, chrome steelhead.

Both male and female steelhead change physiologically as they mature prior to spawning.  The physical changes are far more striking in the males than females.  Males become redder, narrower, and their head shape changes more as they mature sexually.  Females to not change their appearance nearly as much as males, although they get quite plump as their ovaries mature and the rosy cheek and red lateral stripe becomes prominent as they approach spawning condition.

Here’s the tricky part.  Shortly after a female steelhead spawns, the henfish experiences a hormonal shift that triggers a seaward migration behavior and a shift to a “smolt-like” appearance.  Exactly how quickly this occurs, I’m not sure.  I suspect it occurs over a few days rather than weeks.  Ideas, anyone?

Post-spawning females transform from exhibiting a broad red lateral stripe to being very shiny.  Their backs will usually be an olive-green instead of the gun metal blue characteristic of a fresh-from-the-ocean, “chrome” steelhead.

Male steelhead are different.  I don’t remember ever seeing a silvered-up male steelhead kelt, although I have seen plenty of male steelhead that were sexually mature and could have been “finished” with spawning activity.

Whereas a female will head back towards the ocean rather quickly after spawning, the spawning activity of a male steelhead is far more protracted; a male  will persist, moving around the river, looking for more females to spawn with and more males to fight.

When a female steelhead deposits her eggs, she’s done.  End of spawning activity.  Hormonal changes and seaward migration usually commences fairly quickly.  Males?  Not so.  They keep at it for a month, two months, before getting the cue to cease and desist.

I don’t remember ever seeing a chromed-up post spawning male steelhead.  I have seen a lot of silvered-up females.  It is common for post spawning steelhead to feed actively on their return to the ocean also, so they can be voracious biters.

This photo shows a fresh run winter steelhead hen.  This female is sexually immature and is a relative newcomer to the river.

This photo shows a ripe male winter steelhead.  Note the distinct red opercle and the slope of the fish’s forehead; both are striking characteristics of sexually mature, “ripe” male.  The maxillary bone is also very dark, another sign of an advanced stage of maturity.

This photo shows a close-to-ripe female winter steelhead.  Note that this fish has only a slight rosy hue at lateral line and on opercle.  This is common for female winter steelhead hens to not display striking sexual characteristics.

This photo shows a post spawning hen steelhead.  This fish is very slim and has regained a “silvery” appearance that could be mistakenly associated with a “fresh-run” fish.  This steelhead was handled gently, photographed, and released.

How often have any of you heard anglers report having caught “chrome” steelhead that had “pale flesh” and “tasted terrible”?   When questioned, I have heard these same anglers say that the fish were fresh because the eggs were “really small.”

I’m guessing that these steelhead were silvered-up kelts: slim, sleek, shiny, and holding next year’s tiny eggs nestled in healing ovary tissues.

I encourage anglers to learn as much as they can about the life history of the fish they so love to catch.  The more we understand and respect these magnificent fish, the more effectively we will be able to advocate for their protection.

JN