I bet we all think we know what a steelhead is: a rainbow trout that goes to the ocean and returns to spawn in freshwater. I agree.
But, new research indicates that the definition may not be so simple.
Jason Hall, a researcher with NOAA in Seattle at the Montlake Lab (Northwest Fisheries Science Center), recently published a study on the life history diversity of steelhead in two small rivers on the Olympic Peninsula. The West and Twin Rivers, really just creeks in size, drain into the Strait of Juan de Fuca about 20-30 miles west of Port Angeles, WA. The neighboring rivers – mouths less than two miles apart – are part of the Intensively Monitored Watershed system where agencies and tribes conduct restoration actions and intensive monitoring to get a better understanding of the fish, their habitat and the efficacy of restoration actions.
Jason, along with several co-authors (including myself), found something that makes steelhead a little bit more complex than we thought – but more on that later.
The first result is we found 18 different life history combinations. While that is only about half of what was found in the Klamath and Skeena studies, these rivers are a fraction of their size. Each watershed drains only about 13-14 square miles, while the Klamath and Skeena drain over 15,000 and 21,000 square miles, respectively. Not bad for two little streams.
Second, smolt age was variable, but most commonly fish migrated to the ocean at age-2, and it influenced the length of time adults spent in the ocean. For instance, all age-1 smolts spent three years at sea while age-2 and -3 year smolts spent 1-3 years at sea. This is somewhat common in steelhead, with younger smolts often – but not always (these are steelhead remember!) – spending a longer time in the ocean than older smolts. The oldest total adult age was 6 years.
Third, while Jason and others were only able to sample a fairly small number of adults and of those, a small percentage were repeat spawners. Repeat spawners are those fish that survive spawning, go back to the ocean and return to spawn again. Many repeat spawners spend only summer in the ocean before returning to spawn again, which does not give them much time to grow. Instead they reinvest in egg or milt production. However, some of the repeat spawners in the Twins spent two summers in the ocean before returning to spawn again. Those fish are referred to as “skip spawners” because they skip returning to spawn after the normal one year in the ocean. They are important because they tend to grow larger after spending the extra time in the ocean and thus, end up carrying more eggs. It’s riskier, but the benefits are also great. Ultimately, we are not sure why this happens, but several other studies have found similar diversity in repeat spawning steelhead.
Lastly, and the coolest of all, is that we documented two cool life histories. Some fish left the river at age-1 during the summer as parr, not the spring when most fish smolt, and then returned in late-fall before eventually migrating out to the ocean for good at age-2. Sound like a half-pounder? Further, some age-0 fish (fry) migrated to the ocean, though none were documented to survive to adulthood. More remarkable, about 1% of those age-0 migrants left one of the Twin Rivers, entered the ocean and then swam up the other river. A few fish even then returned back to the ocean and swam up the river from which they first came. We are not aware of this behavior being previously documented, but it is likely the same behavior is occurring in other watersheds. Regardless, those are some indecisive fish. Reminds me of Goldilocks.
The study underscores that there really is no normal steelhead, and that frankly, it appears that the way we define a steelhead is more complex than ever. Such studies, and the data they produce, are absolutely critical to understanding the fish and improving management and conservation. For example the study indicates there steelhead do not just smolt in the spring, and therefore, to fully account for smolt production managers will also have to document fish that migrate to the ocean during fall and summer.
The research was possible because of an incredible amount of work, including installation of tagging arrays, modems to send the data from the field to the office on a daily basis, maintenance of the whole operation (the Twins get a lot of rain and the floods wreak havoc on the tagging arrays), and the field work to capture, measure and tag fish. In this case we owe thanks to NOAA/NWFSC, Lower Elwha Klallam Tribe, and Weyerhauser for making the study possible.
Here is the study abstract: http://www.tandfonline.com/doi/abs/10.1080/00028487.2016.1194893?journalCode=utaf20
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