The fish in this season’s Bristol Bay sockeye run are older than usual - having spent more years in the open ocean - and significantly bigger, according to fisheries management researchers. KDLG’s Jessie Sheldon talked with Stacy Vega, area research biologist for commercial fisheries with the Alaska Department of Fish and Game to learn more.
This interview has been edited for length and clarity.
Jessie Sheldon, KDLG: Hi, Stacey, thanks for taking the time to chat today.
Stacey Vega: Yeah, no problem.
KDLG: This weekend, we got the latest age composition data from the Port Moller Test Fishery, that includes data from around the whole bay. And I just wanted to take the time to dive into the numbers with you because they look unusual this year. So can you tell me generally what we're seeing for the age composition of the fish both passing through Port Moller and arriving at the different districts?
Vega: Yeah the most striking thing that we're noticing with the composition is the smaller amount of "two ocean" fish than we were anticipating returning this year. So the majority of the fish that are returning bay wide are “three ocean” fish. So either one or two years in the freshwater, and then three years in the ocean. And we were expecting a pretty large “one-three” run, or “three ocean” run, but we are definitely coming up short a little in the “two ocean” fish component pretty much bay wide.
KDLG: How much extra weight does a year in freshwater, or a year in saltwater add to a sockeye?
Vega: Yeah, so this year, the difference between a “one-two” fish or, one year freshwater and two ocean, versus a one year freshwater and three ocean is about a pound and a half or more. But an extra year is an entire growing season and can add a significant amount of length or weight. So the average “one ocean” fish this year is about 4.2 pounds, and then an average “one-three” fish is pushing six.
KDLG: Wow, so does an additional year in freshwater then not have as much of an impact on weight?
Vega: The smolt size is bigger. So they out-migrate from the lakes or rivers at a larger size, which increases their opportunity for survival. But in terms of weight that the adult fish comes back with, it's not too drastic of a change.
KDLG: So this higher proportion of older and larger fish that we're seeing this year, how drastic of a difference is this compared to previous years?
Vega: So we certainly have seen some years in the recent past, mainly last year, and 2019 or 2020, where we had some pretty large, "one-three" returns in some systems. Bay wide however, having this large of a discrepancy between "one-threes" and "one-twos" is somewhat unusual. It's just not common to see this kind of out-of-whack proportion certainly is a little different than what we were expecting.
KDLG: There are a lot more older fish than were predicted by the age composition forecast. Can you talk about how the age composition forecast is determined?
Vega: Well, we forecast each river and the four major age classes for each river, nine river systems in the bay. And we do that using different linear regression models based on age and returns that we might expect to see based on ages we've seen return already. So say a "one-two" fish returning this year, that will give us an idea of what we can expect to see in "one-threes" next year, because they're the same brood year fish. So we basically model some different regressions and see what the historical dataset looks like. And we can kind of get an idea of what we might be seeing for that specific age and that specific river based on what we've seen in the past.
KDLG: Any ideas as to why we might be seeing older and bigger fish this year?
Vega: Yeah, so it's confusing, it's certainly not something I have an answer for or a smoking gun. The brood year for the "one-two" age class would be 2019. We do know that that was a very warm year, we had a lot of heat, heat stress on fish, that certainly could be part of the problem. The marine environment is always kind of a large mystery as to how fish are doing each year out in the ocean. Definitely, probably a part of it, marine conditions for the out-migrating smolts and for the growing juveniles. So it's just not one thing you can kind of pin it on, and I certainly don't have the answer. But yeah, it is confusing. And there are a multitude of factors that it could possibly be.
KDLG: Then I guess the “why” is kind of two parts. So for the why might we be seeing fewer of those younger fish, you talked about 2019 being a hot year. But so then why would we be seeing so many of the two-threes, the oldest fish?
Vega: Yeah, like I said, I can't tell you one way or the other what the reason is, for any reason the fish are going to do what they're going to do. And the conditions that they're growing in are constantly changing. These brood years from the "one-threes" and the "two-threes" that we're seeing this year, so those will be brood years 2018 and 2017, those were really, really prolific years. That 2017 brood year is having great, great returns from it. Those fish just did really well bay wide. So yeah, it's a mixture of growing conditions when they're in the freshwater environment. And then once they get out to sea, they have a whole other suite of issues to deal with. And these age classes, these brood years, the parents that spawned these fish did it in a year that was beneficial, certainly.
KDLG: Well, lucky for them!
Vega: Yeah, lucky them! Yeah, I mean, it's good. It's nice to see big, healthy fish. Certainly everyone's to get a lot of comments, but really large fish, really good looking healthy fish, they're definitely larger in size by age than they have been in recent years. And that is great. It is something missing, or missing a lot of the younger fishes, is somewhat problematic, or at least somewhat concerning. But there's things we just can't answer. Every year, every river, every transition of these fishes’ lifecycle kind of has an extra layer of complexity and difficulty that they have to get through and survive through. So there is no one easy answer.
KDLG: As a last question, what overall does this different age composition mean for folks out on the water.
Vega: It means heavier fish! Yeah, it means bigger, prettier fish to catch. Certainly I know that people probably are bummed that there's not as many as there have been, but, we've been in some record years lately, and we expected that to not last forever. So yeah, I won't speak to the processing or catching side of it, that's definitely not my wheelhouse. But certainly there's bigger fish out there.
KDLG: Great. Thank you so much, Stacy.
Vega: No problem, anytime.
Get in touch with the author at jessie@kdlg.org or 907-842-2200.
