Research Document 2016/116

Multimodel assessment of population production and recommendations for sustainable harvest levels of anadromous Arctic Char, Salvelinus alpinus (L.), from the Hornaday River, Northwest Territories

By Zhu, X., Gallagher, C.P., Howland, K.L., Harwood, L.A., and Tallman, R.F.

Abstract

Arctic Char from the Hornaday River are an important subsistence resource for residents of Paulatuk, Northwest Territories. A commercial fishery operated concurrently with the subsistence harvest between 1968 and 1986 and was not opened since 1987 due to diminishing catches and reduced size of fish. Data from the Hornaday Char Monitoring Program collected between 1990 and 2013 in addition to data collected from periodic sampling from previous fisheries were used to;

1. characterize population production parameters such as growth and natural mortality;
2. standardize catch-per-unit-effort (CPUE), and;
3. assess the population using three different models in order to determine stock status and determine maximum sustainable yield.

The von Bertalanffy growth model and maximum likelihood estimates demonstrated differences in growth parameters between males (L∞ = 812 mm, K = 0.18) and females (L∞ = 748 mm, K= 0.18). Using growth parameters and age-related models, natural mortality was estimated to vary between 1.23 per year at age one and 0.2 per year at age 16. The nominal CPUEs were evaluated by a set of fixed-effect type I-III sum of squares, analysis of variance (ANOVA), generalized linear regression models (Poisson, quasi-Poisson, and negative binomial), and zero-inflated probability (hurdle, zero-inflated Poisson, zero-inflated negative binomial) regression models. The bias-corrected AIC weights were used to assess the relative goodness of the fit of the candidate models to the observed CPUEs in order to select a model.

Three different fisheries assessment models, depletion-based stock reduction analysis (DB-SRA), surplus production model (SPM), and statistical catch-at-age (SCA), were used to estimate the median maximum sustainable yield (MSY) and total abundance (NMSY), biomass (BMSY), fishing mortality (FMSY) and exploitation rate (UMSY) at MSY. The inverse weighted average (± 1SD) among the estimates produced an MSY of 2,496 ± 154 and 5,724 ± 187 in fishable abundance and biomass (kg), respectively. The NMSY was 14,635 ± 1,021 individuals while BMSY was 29,826 ± 1,851 kg. UMSY was estimated to be 0.15. Stock status of Arctic Char from Hornaday River has varied over time with evidence of overfishing observed between approximately 1977 and 1989, and in the mid-1990s. The modelling results indicate stock status is healthy as the stock is not being overfished given the harvest levels are currently below MSY.

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