Chinook Salmon Supplementation in the Imnaha River Basin- A Comparative Look at Changes in Abundance and Productivity Chinook Salmon Supplementation in the Imnaha River Basin- A Comparative Look at Changes in Abundance and Productivity Richard W. Carmichael and Tim Hoffnagle Oregon Department of Fish and Wildlife Eastern Oregon University La Grande, OR 97850

Management Objectives Enhance natural production while maintaining long term fitness (productivity) of the natural population. Re-establish historic tribal and recreational fisheries Operate the hatchery program so we maintain the genetic and life history characteristics of the natural population and hatchery fish characteristics mimic those of the wild fish, while achieving management objectives.

Today’s Presentation Illustrate one approach to assessing success in supplementation programs Has the Imnaha Chinook salmon supplementation program increased the number of total spawners and natural origin spawners? How has the hatchery program influenced natural spawner productivity? Are the life history and spawning characteristics of hatchery origin fish the same as natural origin fish?

Broodstock Development History Wild adults were collected for broodstock beginning in The majority of broodstock were wild through Wild and hatchery adults were used for broodstock from (14 to 71% wild). Due to logistical constraints of weir installation, the broodstock comes from middle to end of run. In 2007, it appears that we were able to collect broodstock from across the entire run.

Management of Wild Returns and Natural Escapement Nearly all wild salmon collected were kept for broodstock from Percentage of wild salmon retained for broodstock after 1986 was 50% or less, except Few hatchery salmon were released to spawn naturally until Naturally spawning hatchery fish were those that passed the weir site prior to weir installation and those that spawned below the weir. The percent of naturally spawning salmon that were hatchery origin has ranged from 30-80% since 1990.

Abundance/Productivity Comparison Approach Compiled spawner and recruit adult abundance and productivity (R/S) datasets for Imnaha and unsupplemented Idaho Salmon River Chinook populations (ICTRT/ODFW/IDFG) including harvest adjusted values. Determined level of correlation in abundance and productivity between Idaho and Imnaha populations for the pre-supplementation time period (late 1950’s-1985 for abundance and late 1950’s-1981 for productivity) to evaluate adequacy as reference populations. Calculated and compared Imnaha-to-Idaho population ratios for total spawner abundance, natural origin spawner abundance and productivity (year specific and means) for pre- and post-supplementation time periods (abundance return years and R/S broodyears). If we have increased natural origin abundance then the ratio should be higher in post supplementation period and if we have maintained productivity the post period ratio should be equal to or higher than pre period ratio.

Abundance/Productivity Comparison Stocks

Natural Origin Abundance Imnaha River

Abundance of Total Spawners

(harvest adjusted)

Abundance of Natural Origin Spawners

Abundance of Natural Origin Recruits (harvest adjusted)

Recruits per Spawner Ratio

Pre-Supplementation Natural-Origin Abundance Correlations Imnaha Population vs. Idaho Populations Natural origin abundanceR:S ratio Idaho streamrhoP-valuerhoP-value Bear Valley Creek Big Creek Camas Creek Lemhi River Loon Creek Marsh Creek Sulphur Creek Valley Creek <

Total Abundance Ratio (Imnaha River / Bear Valley Creek)

Total Spawner Abundance Ratios (Imnaha Abundance / Unsupplemented Abundance) Mean Stream Pre- supplementation Post- supplementation P-value (t-test) Bear Valley Creek Big Creek Camas Creek Lemhi River < Loon Creek Marsh Creek Sulphur Creek Valley Creek

Imnaha River Recruits per Spawner

Natural-Origin Abundance Ratio (Imnaha River / Bear Valley Creek)

Natural Origin Abundance Ratios (Imnaha Abundance / Unsupplemented Abundance) Mean Stream Pre- supplementation Post- supplementation P-value (t-test) Bear Valley Creek Big Creek Camas Creek Lemhi River Loon Creek Marsh Creek Sulphur Creek Valley Creek

Recruits per Spawner Ratio (Imnaha River R:S / Bear Valley Creek R:S)

Recruit per Spawner Ratios (Imnaha R:S / Unsupplemented R:S) (Imnaha R:S / Unsupplemented R:S) Mean Stream Pre- supplementation Post- supplementation P-value (t-test) Bear Valley Creek Big Creek Camas Creek Lemhi River Loon Creek Marsh Creek Sulphur Creek Valley Creek

Imnaha Recruit-per-Spawner Ratios Brood year Recruits per Spawner Natural Hatchery

Abundance and Productivity Summary We have not observed a trend of increased number of natural- origin spawners through time since supplementation started. We have achieved a significant life cycle survival advantage for hatchery fish with progeny-to-parent advantage of seven to one. Recruits per spawner for naturally spawning hatchery and natural fish have averaged less than one and have been above one for only four of the last fifteen broodyears. It does not appear that we have increased natural origin abundance with supplementation even though we have increased the total number of spawners. It appears that we have depressed productivity of the natural spawners in the Imnaha population since supplementation was initiated.

Life History and Spawning Comparison Approach Compiled data from weir collections, spawning ground surveys, and hatchery spawning to examine: Age composition – based on tags and scales to determine age Run timing – based on time of arrival at the weir and the composition of marked and unmarked carcasses recovered on spawning ground surveys. Spawn timing – based on time of collection of female carcasses on spawning ground surveys and time of spawning of females at Lookingglass Fish Hatchery. Spawning distribution – based on the location of female carcass recovery on spawning ground surveys. Spawning characteristics (age, size, fecundity, egg size, ovosomatic index, timing) – based on females spawned at Lookingglass Fish Hatchery. Our objective is for hatchery origin fish to have the same life history and spawning characteristics as natural origin fish.

Life History and Hatchery Spawning Summary Hatchery adults return at an earlier age for both males and females. Younger females means smaller females that are less fecund and have smaller eggs, on average, than natural females. Smaller hatchery smolt size-at-release has not resulted in an older age at return. Hatchery salmon typically return later than natural salmon. Hatchery salmon spawn later, in both nature and the hatchery, and mean spawn date of natural females is shifting to later. Hatchery salmon are distributed more downstream, near the smolt release location. Life history and spawning characteristics of hatchery salmon are not matching those of natural salmon.

Why Not More Natural Origin Fish and Why Does Productivity Appear Depressed? Some Hypotheses Poor reproductive success of hatchery fish? Likely given the relatively low PNI, selective broodstock and resulting life history effects (spawn timing and younger age) Competitive and other ecological effects on natural origin juveniles? Highly uncertain due to lack of information, however the number of hatchery produced smolts far exceeds the natural smolt production Other genetic and ecological effects? Likely given selective broodstock collection, high proportion of hatchery origin fish spawning naturally, differences in spawn timing and spawning distribution of natural and hatchery origin fish, unnaturally high proportions of jacks spawning in nature and potential weir effects on adult spawning distribution Density dependent effects of increased total spawners Likely some influence, however many post supplemetation years were low spawner abundance ( ) in the Imnaha

What To Do Improve adult collection to get broodstock in a non selective manner Increase proportion of natural origin broodstock Reduce proportion of hatchery spawners in nature Reduce the size of the program Distribute juvenile releases throughout the spawning area Harvest as many hatchery fish as possible