Warm Rivers and Disease
The El Nino year has brought some interesting variation in air and stream temperatures. As many of you know I have been collecting water temperature and steelhead spawning data in the Quileute River basin since 1997 (excluding the two years I left for school). This year, to no surprise, the streams (SolDuc and Calawah) are running warmer than any other January I have on record. Typically, streams run 38 - 42F in January, this year they are running 42 - 45F.
Because of the warm water temperatures the steelhead spawn timing is shifting this year. I have counted at least 50 steelhead redds over the past three weeks in the Sol Duc and Calawah Rivers. Interestingly, many of these redds are in the middle and lower sections of the rivers. If you remember the paper I published a few years ago, I found that steelhead spawned earlier in the upper river sections and later in the lower sections. There are fish spawning up high this year - the high water facilitated their migration. However, there are also many fish spawning in areas further downstream, which is unusual. I have already caught 4 female kelts, including 2 Snider Ck. hatchery fish and 2 wild fish. I wondered if WDFW and the Tribes were aware that this early spawning and trying to account for the activity by initiating redd surveys earlier than normal? It will be interesting to see how this plays out over the course of the season.
Because of the early spawning wild fish and the large Chambers Creek hatchery run, there is a lot of opportunity for interbreeding between wild and hatchery fish this year (and potentially other El Nino years). In fact, I am catching and seeing Chambers Creek males hanging out in sections of the SolDuc where I have never previously observed them. Right now there are still several Chambers Creek rip males in both of the aforementioned rivers. There are also numerous Snider Creek males. Given the IHN outbreak in the hatchery fish, surely transmission from adult to offspring is occurring via hatchery males fertilizing wild females. There is simply too many wilds spawning activity right now and too many hatchery males for that not to occur.
I imagine that the managers are aware of the typical modes of IHNV transmission. However, four days ago I caught a male Chambers Creek fish in the middle SolDuc. As I removed him from the water at least 20 leeches evacuated his gills. Another 10 or so slithered away after I beached him.
The leeches raised a question in my mind: Can they transmit IHNV? Guess what, leeches and copepods can carry IHNV and presumably transmit to wild fish. I have attached a nice paper that found very high infection levels in leeches, so high in fact that alost all of the leeches on the spawning grounds were infected. I am wondering if WDFW has considered this transmission pathway? I saw an email from Heather Bartlett and she rattled off the normal modes of transmission but did not mention leeches or copepods. Perhaps my observations and the attached paper will raise some questions.
Lastly, IHNV has a fairly narrow range of temps that it survives under (46 - 59F). As I previously mentioned, in your typical year water temps range from 38 - 42F during the time of overlap between Chambers Creek and wild steelhead. The cold water temps would limit survival and transmission of IHNV. This year though, with the El Nino, the water temps are around 46F and the intragravel temps are at least 46F, meaning that INHV survival and transmission is highly possible.
This could be the worst mix of conditions WDFW could ask for with their hatchery program. It is not a surprise though. IHNV outbreaks are nearly always the worst in good ocean years. Couple their abundance with very warm stream temps and I believe the potential for heightened transmission of INHV from hatchery to wild steelhead needs to be evaluated.
Mass transmissions are difficult to track and find in nature. I understand that. In this case though, it seems imperative to determine if transmission is occurring.
I hope you are finding this year to be as interesting, and potentially disappointing, as I am.