When spring rolls around, steelhead anglers wonder when to take a few days off. The burning question involves what really triggers movements into rivers. Most of us probably think we already know, because a huge influx of steelhead in spring always follows rainfall and rising water levels.
But what if it doesn’t rain? What if rivers don’t rise? What if they do but we don’t really know what causes anything to happen at all, when it comes to steelhead movements?
Fall-run steelhead often spawn and leave before the spring run begins. During winters with little rain or snow pack, it might be weeks, in fact, before any significant numbers of spring steelhead enter the river after the last fall-run fish have dropped back (see “Ghosts Of The River,” In-Fisherman, January 2008). In spring, most steelhead need to enter the river eventually. It approaches a biological imperative, but female steelhead can refuse to run and instead reabsorb their eggs, like other fish do in adverse conditions, if the river stays too low.
This is why some biologists hypothesized steelhead were so immense in some Michigan streams 4 or 5 years back. During a solid week of fishing that year, the smallest steelhead our group of seven was able to bank weighed 10 pounds. Most of the fish looked to be 15 pounds or better, with some real behemoths in the mix. Of course, it was generally a short look, as they reentered the water like torpedoes on a direct bearing for the nearest wood. After our best sticks suffered a few 0-for-12 days, we reconsidered our normal habit of “counting coup,” wherein a touched fish is considered banked. Instead, we adopted a bullriding motif: Whoever stays on longest wins.
If rivers stay low throughout spring, will some steelhead simply refuse to run? Could several drought years in a row cause a high percentage of steelhead to hold off and wait another year to spawn, resulting in an inordinately high number of 5-year-old fish in the system? “It’s certainly possible, though we have no data to support it,” says Jim Dexter, steelhead program director for the Michigan DNR.
The opposite happened this past year, after another drought. Inordinately high numbers of precocious fish ran the rivers between early and mid-fall. Most weighed between 3 and 5 pounds, apparently having spent only 1 or 2 years in the big lake. What happened?
Spring floods were the norm for many decades, but low snowfall during the past few winters caused lower-than-normal flows in many rivers. The way we’ve understood this phenomenon for the past decade or so, steelhead wait until the end of their spawning window (or “day length” window, referring to their innate ability to sense the lengthening of days) when rivers remain low. The window is a block of time ultimately determined by survival. Those that spawn late, beyond the window, produce progeny that, historically, did not have time to reach a size that allowed them to survive the following winter.
When rivers stay extremely low, many steelhead may refuse to run, staying in the big lake for another year. It would not be at all surprising to discover that the highest percentage of those that refuse to run are quite large already, especially when their target river is small. “That’s an interesting point,” Dexter says. “We have no data on it, but it is possible that smaller fish feel safe enough to enter small rivers in low flows when larger fish don’t. Stream conditions certainly seem to play a role.
“We do know that temperature can be a limiting if not a determining factor with regard to timing,” he continues. “I observed at the fish ladder on the St. Joseph River many times in spring, counting the fish that go through. Until water temperatures rise above 39°F, no fish will ascend the ladder. At 41°F to 42°F, the movement increases dramatically. When we get quick warm-ups from winter right into summer, the fish ram in, spawn, and disappear. As a fisherman, of course, I don’t like that.
