Historical abundance of Puget Sound steelhead, Oncorhynchus mykiss, estimated from catch record data

Abstract

We used reported commercial catch data and historical information regarding unreported catches to estimate the abundance of winter steelhead, Oncorhynchus mykiss, in Puget Sound rivers in 1895, the year in which the peak commercial catch of steelhead occurred. We employed a Bayesian analysis to address the uncertainties associated with the estimation process and report abundance estimates for four large northern Puget Sound rivers and for the remaining aggregate of rivers and streams in Puget Sound. The central 90% of the posterior distribution of total abundance ranged from 485 000 to 930 000, with a mode of 622 000. Compared with the 25-year average abundance for all of Puget Sound of 22 000 for the 1980-2004 period, our results show that current abundance is likely only 1%-4% of what it was prior to the turn of the 20th century. Loss of freshwater habitat alone can account for this reduction in abundance only if there was an extraordinary decline in productivity. Our estimates of historical abundance should better inform the development of recovery goals for Puget Sound steelhead.

Declining patterns of Pacific Northwest steelhead trout (Oncorhynchus mykiss) adult abundance and smolt survival in the ocean

“…However, steelhead populations appear to have declined in abundance over time throughout much of the southern part of their range (Busby et al 1996), and there are specific concerns about the viability of populations in various regions, especially Puget Sound (NMFS 2006(NMFS , 2007Berejikian et al 2016;Ford 2011;Gayeski et al 2011;Moore et al 2015).…”

An integrated population model for estimating the relative effects of natural and anthropogenic factors on a threatened population of Pacific trout

“…Our analysis suggests that such effects have scaled up to the entire population level to govern patterns of steelhead productivity in the Skagit River basin. Importantly, we found strong evidence for density dependent interactions despite the fact that contemporary population censuses are well below historical estimates (Gayeski, McMillan & Trotter 2011). Similar results have been observed in populations of coho salmon Oncorhynchus kisutch Walbaum 1792 in Oregon (Buhle et al .…”

Abundance of Skeena River Chum Salmon during the Early Rise of Commercial Fishing

“…(1) We followed the general approach of Gayeski et al (2011) to estimate the principal parameter of interest, the terminal Chum Salmon run size (N), from the total catch and estimates of the harvest rate applied to the total run. We employed a negative binomial likelihood based on the gamma-Poisson parameterization (see the appendix for justification) and treated the total commercial Chum Salmon catch (C) as a Poisson random variable in which the Poisson rate parameter (λ) is drawn from an underlying gamma distribution with a constant scale parameter (β) equal to the underlying average harvest rate (ChHR) and a shape parameter (α) equal to the total run from which the catch was obtained, that is, C ∼ Poisson(λ); Bin λ ∼ gamma(N, ChHR).…”

“…But data deficiency aside, we believe that the difference between our historical abundance estimate and that for the contemporary period far exceeds even the most exaggerated estimate of decline due to spawning habitat loss. For example, habitat loss for the steelhead returning to Puget Sound (a region of high-density urban and industrial development) was recently estimated to be no more than 33% (Gayeski et al 2011). Notably, this loss in habitat was deemed negligible in the context of a 25-fold reduction in steelhead abundance.…”