Understanding sockeye salmon production in the Kvichak Ray Hilborn thanks to T. Quinn for data and ideas, Tyler Dann and Wes Larson for genetics

Counting Tower

What causes the cyclic dominance? Depletion of food in lakes Increase in predators Disease Depensatory fishing Substock structure

Recruits per spawner Calculate how many adult fish return from the ocean for every fish that spawned You need to know the number of spawners counted at the counting tower, the catch in each year, and the age composition of the catch and escapement If you have less than 1 recruit per spawner there is no sustainable yield

Maybe there are two curves, one when ocean conditions are good and one when they are bad

Productivity in Markov Model Relative Productivity

Habitats Rivers and streams Island beaches Mainland beaches Spring fed ponds

Quinn’s observations Island beach populations have greatly diminished Island beaches have lower recruits per spawner than other habitats

Slim Morstad 2014 Kvichak manager for last 15 years “I don’t want to put more than 3 million fish up the Kvichak because they just don’t seem to do well”

The hypothesis Island beaches have lower egg to fry survival than rivers, streams and mainland beaches Island beach stocks have been depleted Increased escapements in the absence of island beach stocks will encounter carrying capacity limits and not be able to produce very large runs Island beaches have much larger potential spawning area than other habitats Rebuilding island beach stocks is required to produce very large runs

Estimates returns per escapement to five Iliamna Lake spawning sites (Brood Years 1958 – 1982, Blair 1989).   From T. Quinn

Why Island Beaches have lower survival Fish in rivers rely on water flow to aerate the eggs and alevins Fish on mainland beaches rely on underground water flow to do the same Island beaches rely on wind driven currents, much more subject to vagaries of weather, ice cover, and warming lake temperatures Note that beach spawner production was much better in cold times

The hypothesis Island beaches have lower egg to fry survival than Rivers, streams and mainland beaches Island beach stocks have been depleted Island beaches have much larger potential spawning area than other habitats Increased escapements in the absence of island beach stocks will encounter carrying capacity limits and not be able to produce 20+ million runs Rebuilding island beach stocks is required to produce 20+ million fish

Where the fish spawn Aerial Surveys

Analysis of air survey data

A model of aerial counts C y,s = T y p s . The observed count in a year and site is a total number that where visible in the year (Ty) times the proportion of fish that go to each site (ps)

Genetics data from Kvichak catch confirm air counts proportions

This allows us to estimate the total number of fish in Island Beaches (blue) and for rivers and streams (orange)

The proportion in Island Beaches has declined dramatically

The p’s Woody Triangle Isl Porcupine

The hypothesis Island beaches have lower egg to fry survival than Rivers, streams and mainland beaches Island beach stocks have been depleted Increased escapements in the absence of island beach stocks will encounter carrying capacity limits and not be able to produce the big runs Island beaches have much larger potential spawning area than other habitats Rebuilding island beach stocks is required to produce 20+ million fish

Where are the River Fish? % of fish Area (1000 sq m) Copper River 17% 412 Newhalen River 15% 3,065 Iliamna River 12% 2,000 Tazimina River 8% 163 Gibraltar Creek 9% 66 Lower Talarik Creek 6% 29

A general rule of thumb for sockeye salmon 1 spawning fish per square meter of good river habitat

Potential River Habitat 2-4 million spawners in good habitat Admittedly a bit of a handwave but clearly the fish don’t “like” the big Iliamna and Newhalen rivers as much as they do Copper, Gibraltar, Tazimina, and Lower Talarik

The hypothesis Island beaches have lower egg to fry survival than Rivers, streams and mainland beaches Island beach stocks have been depleted Increased escapements in the absence of island beach stocks will encounter carrying capacity limits and not be able to produce very largeruns Island beaches have much larger potential spawning area than other habitats Rebuilding island beach stocks is required to produce 20+ million fish

How much Island beach habitat is there?

From Kerns and Donaldson 1968

Total area (1965) That is 1.3 million square meters with 3 million fish 1965 Estimate is that there were 10 million Island beach spawners

A quick calculation of area If the surveyed sites had 3 out out of 10 million fish, then perhaps there are 4 million square meters of Island beach habitat capable of having densities of 2 fish per square meter

The hypothesis Island beaches have lower egg to fry survival than Rivers, streams and mainland beaches Island beach stocks have been depleted Increased escapements in the absence of island beach stocks will encounter carrying capacity limits and not be able to produce very large runs Island beaches have potential spawning area than as large or larger than other habitats Rebuilding island beach stocks is required to produce very large runs

A two stock life history model 2nd stock has lower survival than 1st stock

The low survival stock disappears

Flies in the ointment

Non island habitat has returned large runs Year Total Return %Island Non Isl Return 1965 48,627,305 66% 16,447,183 1980 37,931,680 23% 29,078,010 1970 34,839,685 40% 20,816,793 1995 28,422,825 17,123,522 1979 24,927,042 9% 22,581,566

The aerial count sees 9% of the tower count

Explanations for missing fish Not all spawning sites surveyed Not all fish are in the rivers when surveys are done Visibility of fish is less than 1 1965 comparison between on water counts and air counts for Woody and Porcupine beaches showed water count was twice aerial count

The research agenda Redo brood tables with most recent data for individual types of habitat Understand the capacity of each Understand why aerial surveys see such a small portion of the fish On water calibration studies Understand amount and quality of Island beach habitats Explore environmental changes on Island beach survival (wind, temperature, ice etc).

More research How to rebuild Island beach spawners? Is there differential run timing? Genetic composition of catch and escapement data Is there potential for selective fishing based on size? What harvest strategy could rebuild Island beaches, at what cost to yield?

Final research thoughts The role of Island beaches cannot be considered in isolation of the two other critical Kvichak issues What causes the period changes in productivity? Understanding cyclic dominance

A final note Island beaches have produced over 20 million sockeye salmon in a given year This habitat is, in effect, one of the largest two sockeye population in the world It appears to be severely depleted and almost commercially extinct It probably qualifies as endangered under ESA

The End

Study questions What do we mean by recruits per spawner Why do island beach spawning fish have lower recruits per spawner Why are island beach spawning fish genetically different from river and stream spawners What explanations are possible for the fact that the aerial counts only see about 9% of the fish counted past the counting tower Can the production of the Kvichak sockeye population be sustained without Island beach spawning fish? Explain in two or three sentences.