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Age composition of subsistence harvests and total return of sockeye salmon from the Kvichak River

Citation

Agler, Beverly; Dann, Tyler (2021), Age composition of subsistence harvests and total return of sockeye salmon from the Kvichak River, Dryad, Dataset, https://doi.org/10.5061/dryad.gqnk98sn1

Abstract

This project aged samples of sockeye salmon harvested in the subsistence fishery in the Kvichak River watershed in 2018 and 2019. Age data were vital to previously funded AKSSF Project #44362 ("Stock Composition of Subsistence Harvests and Total Return of Sockeye Salmon from the Kvichak River"). It was determined in that project’s first year that scale reabsorption necessitated using otoliths to age samples rather than scales. Ages from otolith reading combined with stock composition estimates from genetic mixed stock analysis were used to evaluate survival and productivity of brood years 2012–2015 at smolt and returning adult life stages. This project only produced the age reads from otoliths.

Knowing the age composition of harvests permits reconstruction of the sockeye salmon return and examination of cohort returns and estimation of marine survival. This project dovetailed with AKSSF Project #44362 (Stock Composition of Subsistence Harvests and Total Return of Sockeye Salmon from the Kvichak River) by pairing age composition data with genetic stock composition data. Accurate age data are key to fisheries management. Harvests from in five communities along the Kvichak River were sampled (Kokhanok, Pedro Bay, Iliamna-Newhalen, Nondalton and Port Alsworth). Otoliths were collected during 2017, 2018, and 2019 to use to estimate the age.

Methods

Otolith collection and transfer to MTA Lab

Otoliths were collected from sockeye salmon caught in subsistence fisheries in five communities in the Kvichak River watershed. During 2018, each pair of otoliths from one fish was stored in a coin envelope and paired with an axillary process for genetic analysis. During 2019, each pair of otoliths was stored in 96-cell genetics trays by site and date.  Otoliths were shipped to the MTA Lab in Juneau each year.

Otolith cleaning and tray review

Upon receipt, otoliths were cleaned with a 5% chlorine solution to remove any remaining tissue. Trays were then rinsed with 0.7% thiosulfate and water to stop the process. Data associated with each otolith pair, including number, species, life stage, statistical week, source, gear type, location, stream code, collectors, comments, shipping method, and number of otoliths were entered into the Mark, Tag, and Age Lab (Alaska Department of Fish and Game) Oracle database. Samples were tracked by bar-codes.

Preparation for and ageing of otoliths

Prior to estimating age of these sockeye salmon otoliths, readers studied examples of known age otoliths. Although we expected the estimated age of most fish would be one of four ages (1.2, 2.2, 1.3, and 2.3, most common ages, European age notation), all ages were studied. To estimate age, a reader placed a whole otolith on a petri dish sulcus side down and examined it under a dissecting microscope to count the annuli (Figure 2). Once a specimen was examined, age was entered in the database, and the otolith was returned to the tray.

Quality Control/Quality Assurance

First and Second Reads

Because we did not have access to any known age otoliths from the Kvichak River watershed, laboratory personnel practiced estimating age of using samples from Southeast Alaska that either had a thermal mark or a scale age. Readers read these “known age” samples until their reader agreement was > 90%. All sockeye salmon otoliths for this project were examined at least three times.  In other words, the age of an otolith was estimated by a reader, and then age was estimated for same otolith by a second and/or a third independent reader. Disagreements among readers were resolved by a final examination of the age by senior personnel (Final age; Fishery Biologist and/or Crew Leader). During the final read, the reader was aware of previous results.

Read Assessment Methods

For this project, we assessed reader reliability with: agreement matrices, Kappa statistics, mean coefficient of variation (CV), and percent error.

Usage Notes

Description of data: 

  • year: 2017, 2018, 2019
  • SampSpec: sockeye salmon
  • SURVEY_SITE: 5 sites in Kvichak River, AK*
  • Final age: multiple
  • READ_STATUS: completed

* Kokhanok, Pedro Bay, Iliamna-Newhalen, Nondalton, Port Alsworth

Questions? Contact Bev Agler: bev.agler@alaska.gov

Funding

NOAA (AK Sustainable Salmon Fund), Award: 44374

NOAA (AK Sustainable Salmon Fund), Award: 44374