As it is that time of year I thought I would post up this e mail thread that is part of a conversation on Steelhead survival or reproductive rates. The link in the original post ( at the bottom of the page ) is to a paper that is interesting reading.



The concept of mykiss spawning and then smolting is something that I believe I saw at Snow Creek but it took a couple of decades for it to work to the forepart of my brain. While it still hasn't been confirmed for mykiss...................



Atlantic salmon males can spawn as parr (sneaky) and then smolt and spawn as 1 SW (grilse) or as 2 SW fish. Males are often sequential repeat spawners. Females seldom spawn as 1 SW, with 2 SW and rarely 3 SW maiden female spawners - then spawning is alternate year. Life history strategies are very complex in the North East Atlantic (River Teno Erkinaro)

Population resilience depends on a mix of smolt ages and maiden and repeat spawner ages. Populations reduced to limited life history strategies are the ones most in peril. Those listed as endangered in USA and Canada are down to one dominant life history strategy.

Joan



Subject: Re: Commission adopts new sportfishing regulations (steelhead, etc.)

Iteroparous salmonids are significantly more complex than even suggested here.

Males in some species (Atlantic Salmon come to mind) never smolt. There are apparently survival tradeoffs while the females go to sea to grow big eggs (simplified). Then, there are the mykiss that appear to spawn and then smolt. Finally, some Argentine populations of anadromous mykiss spawn up to eight times.

This all gets back to why would a species spawn/breed more than once. I believe that they multiple spawn because a single spawning/breeding does not produce sufficient future spawners; it is not a sustainable life history pattern. This gets most obvious when you look at something like albatross. There is a female Laysan Albatross (named Wisdom) who is banded and is known to be well over 60 years old. And, she laid an egg again this year. For argument sake, assume she started to breed at 10 and laid an egg every year since. So, she has laid at least 50 eggs. For the albatross population to be stable, she needs to have produced 2 adults, or a success of 4%. This is, actually, less because she is still laying. Put another way, that means an egg-adult LOSS of 96% annually can result in stability.

For mykiss, we nave seen populations with 50-90% repeats and they can spawn up to 8 times. Just what sort of marine smolt-adult survival would this be? At Snow Creek we had 800-1200 smolts while I was there. 50 spawners could produce this. 50/800 is 6.3% and 50/1200 is 4.2% id R/S is 1:1 which it almost never is. So, the "low" marine survivals seen in recent years are low only in the sense that they aren't large enough to support the fisheries we "want".



Here’s a relevant article re: Hal’s concerns about the importance of repeat spawning for steelhead-population viability, being particularly important for males (given additional growth between breeding seasons):

Seamons, T.R., and T.P. Quinn. 2010. Sex-specific patterns of lifetime reproductive success in single and repeat breeding steelhead trout (Oncorhynchus mykiss). Behavioral Ecology and Sociobiology 64: 505-513 (https://drive.google.com/uc?export=download&id=0B_sa2AnC9DW4VlhLcXFNUTRXVDg).