Relationship between smolt gill Na⁺, K⁺ ATPase activity and migration timing to avian predation risk of steelhead trout (Oncorhynchus mykiss) in a large estuary

Abstract

We examined avian predation risk of juvenile steelhead trout (Oncorhynchus mykiss) migrating through the Columbia River Estuary in relation to their osmoregulatory physiology, body length, rearing conditions (hatchery or wild), migration timing, and migration year. From 2003 to 2006, mean gill Na+, K+ ATPase activity of migrating wild steelhead was greater than hatchery steelhead. Hatchery steelhead were always longer than wild steelhead. Wild steelhead never had higher plasma [Na+] or osmolality levels than hatchery fish after seawater challenge trials conducted in 2004, 2005, and 2006. More passive integrated transponder (PIT) tags from hatchery fish (19%; 126 of 678 fish) were detected on East Sand Island among bird nesting colonies than PIT tags of wild fish (14%; 70 of 509 fish), presumably consumed by birds. As gill Na+, K+ ATPase activity and migration date within a year increased, the probability of an individual fish being eaten by an avian predator decreased. Length, rear type, and year were not related to predation risk. These results show that physiology and migration timing of juvenile steelhead play an important role in a migrant’s risk to avian predation within an estuary.

Susceptibility of Juvenile Steelhead to Avian Predation: the Influence of Individual Fish Characteristics and River Conditions

“…These results corroborate previous work suggesting that the susceptibility of Chinook salmon O. tshawytscha smolts to predation by Caspian terns in the Columbia River estuary was influenced by the incidence of disease in the out-migrating smolts (Schreck et al 2006). Kennedy et al (2007) found similar relationships between decreased saltwater preparedness and increased susceptibility of juvenile steelhead to avian predation in the Columbia River estuary, thus supporting the hypothesis that salmonid susceptibility to avian predation is associated with individual fish characteristics and condition.…”

“…Several studies in the Columbia River estuary have noted that hatchery-reared salmonids were more susceptible to avian predation than their wild counterparts (Collis et al 2001;Ryan et al 2003;Kennedy et al 2007). Our results indicate that hatchery-reared steelhead were more susceptible to some avian predators in freshwater systems: double-crested cormorants disproportionately consumed hatchery-reared steelhead relative to wild-origin steelhead, but this was not the case for Caspian terns.…”

“…Within populations of Pacific salmon Oncorhynchus spp., increased susceptibility to predation by piscivorous fish and birds has been attributed to differences in fish behavior, condition, size, rearing, and environmental conditions (Gregory and Levings 1998;Mesa et al 1998;Collis et al 2002;Schreck et al 2006;Kennedy et al 2007). Environmental conditions experienced by juvenile salmonids during out-migration (e.g., water flow, turbidity, or factors associated with migration timing) are known to increase stress, reduce fish performance, and increase susceptibility to predation (Raymond 1979;Gregory and Levings 1998;Budy et al 2002;Schreck et al 2006).…”

Seaward migrating Atlantic salmon smolts with low levels of gill Na+, K+ -ATPase activity; is sea entry delayed?

“…Several studies have shown that post-smolts are exposed to high predation immediately after sea entry (Reitan et al 1987;Hvidsten and Lund 1988;Dieperink et al 2002) and that the risk of predation increases if fish suffers from osmotic stress (Järvi 1989;Handeland et al 1996;Kennedy et al 2007). It may therefore be suggested that the extended residency of the first smolt group in the lower part of the river was related to their low gill Na + , K + -ATPase activity and a need to improve seawater tolerance before entering seawater.…”

Loss of Genetic Integrity in Hatchery Steelhead Produced by Juvenile‐Based Broodstock and Wild Integration: Conflicts in Production and Conservation Goals

“…Samples from smolts produced in brood year 2002 were degraded and were not considered in the analyses. We sampled wild smolts using either a screw trap operated at the mouth of Abernathy Creek or from archived tissues collected during annual electrofishing surveys from individuals later determined to have emigrated as smolts (Kennedy et al 2007) from the creek via a PIT tag reader near the mouth of the creek. Collection efforts at the screw trap took place between March and June each year to capture the distribution of emigration timing.…”