Multi-population analysis of Puget Sound steelhead survival and migration behavior

Abstract

Until recently, research on mortality of anadromous fishes in the marine environment was largely limited to estimates of total mortality and association with group characteristics or the environment. Advances in sonic transmitter technology now allow estimates of survival in discrete marine habitats, yielding important information on species of conservation concern. Previous telemetry studies of steelhead Oncorhynchus mykiss smolts in Puget Sound, Washington, USA indicated that approx. 80% of fish entering marine waters did not survive to the Pacific Ocean. The present study re-examined data from previous research and incorporated data from additional Puget Sound populations (n = 7 wild and 6 hatchery populations) tagged during the same period (2006−2009) for a comprehensive analysis of steelhead early marine survival. We used mark-recapture models to examine the effects of several factors on smolt survival and to identify areas of Puget Sound where mortality rates were highest. Wild smolts had higher survival probabilities in general than hatchery smolts, with exceptions, and wild smolts released in early April and late May had a higher probability of survival than those released in early and mid-May. Steelhead smolts suffered greater instantaneous mortality rates in the central region of Puget Sound and from the north end of Hood Canal through Admiralty Inlet than in other monitored migration segments. Early marine survival rates were low (16.0 and 11.4% for wild and hatchery populations, respectively) and consistent among wild populations, indicating a common rather than watershed-specific mortality source. With segment-specific survival information we can begin to identify locations associated with high rates of mortality, and identify the mechanisms responsible.

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

“…While other studies have shown that hatchery and wild salmonids have different smolt survival patterns (Moore et al 2015;Raymond 1988;Zimmerman et al 2015), our MARSS models did not support separating hatchery and wild steelhead populations (⌬AIC c > 14 for the best of these models). This may be due to the lack of long-term wild steelhead smolt survival time series for all geographic areas.…”

“…This may be due to the lack of long-term wild steelhead smolt survival time series for all geographic areas. While no consistent differences in early marine survival (survival during the first few weeks in the ocean) of wild versus hatchery-reared BC steelhead were reported (Welch et al 2011), a similar study on Washington State fish showed higher early marine survival for wild fish (Moore et al 2015).…”

“…Puget Sound steelhead experience high levels of mortality in the Sound during their migration to the ocean despite relatively short migration distances, mortality rates that could not be sustained and have any adults return to spawn (Moore et al 2010b(Moore et al , 2015. Friedland et al (2014b) also suggested that punctuated, sizedmediated predation controls marine survival of Keogh River steelhead smolts.…”

“…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).…”

“…Recently, there has been increasing concern that poor marine survival of Pacific Northwest (including British Columbia (BC), Washington, and Oregon) steelhead may contribute to their declining abundance and lack of recovery (Moore et al 2015;Ward 2000 Beamish et al 2000;Beetz 2009;Coronado and Hilborn 1998a;Teo et al 2009;Zimmerman et al 2015; and Chinook salmon (Oncorhynchus tshawytscha): Coronado and Hilborn 1998b;Duffy and Beauchamp 2011;Kilduff et al 2014;Ruff et al 2017;Sharma and Liermann 2010;Sharma et al 2013), such an analysis has been done for only one steelhead population -the Keogh River of BC (Ward 2000;Ward and Slaney 1988). There are few large-scale mass mark-recapture or life-cycle monitoring studies (e.g., coded wire tag studies) on steelhead, and few populations are intercepted in marine fisheries, making it more difficult to estimate marine survival rates.…”