Pacific salmon (<i>Oncorhynchus</i> spp.) runs and consumer fitness: growth and energy storage in stream-dwelling salmonids increase with salmon spawner density

Abstract. Organisms transporting nutrients from highly productive ecosystems can subsidize food webs and alter ecosystem processes. For example, the carcasses and eggs of migratory Pacific salmon (Oncorhynchus spp.) provide a high-quality food source that could potentially benefit other species of salmon rearing in fresh water. We investigated relationships between spawning chum (O. keta) and pink (O. gorbuscha) salmon density, and the body size and age of juvenile coho salmon (O. kisutch) in 17 streams on the central coast of British Columbia, Canada. Chum salmon density was the most consistently important and positive correlate of coho body size, in comparison with pink salmon density, juvenile coho salmon density, and numerous characteristics of habitats. This was shown by comparisons both among and within streams, and between sites above and below natural barriers to spawning chum and pink salmon. In addition, streams that had higher chum and pink salmon spawning densities had a higher proportion of age 0 coho (less age 1), suggesting earlier juvenile coho salmon migration to the ocean with increased spawning salmon nutrient availability. Most of the coho salmon sampled had little or no direct contact with spawning chum and pink salmon, which suggests an indirect, time-delayed influence on coho salmon body size.

Section: Discussionsupporting

confidence: 89%

Effects of subsidies from spawning chum and pink salmon on juvenile coho salmon body size and migration timing

Nelson

Reynolds

2015

“…This study demonstrated that seasonally pulsed MDN resources can persist for many months in some biota and, together with other studies (Verspoor et al 2010, Rinella et al 2012, suggests that salmon can have prolonged effects in ecosystems where they spawn. While MDN persisted in most taxa sampled over the threeseason course of this study, we were unable to determine the full duration of its presence.…”

supporting

confidence: 75%

“…Substrate disturbance during salmon spawning, however, can offset these effects and reduce overall periphyton and macroinvertebrate biomass Schindler 2008, Verspoor et al 2010), especially in streams with fine sediments (Janetski et al 2009). Growth and energy storage among stream-dwelling fishes is increased by MDN (Bilby et al 1996, Wipfli et al 2003, Heintz et al 2004, Rinella et al 2012) and the direct consumption of eggs and carcass material appears to be more important than bottom-up pathways for conveying MDN benefits (Scheuerell et al 2007, Denton et al 2009, Armstong et al 2010. MDN is transferred to the riparian environment by hyporheic processes, flooding, and terrestrial scavengers (Cederholm et al 1989, Ben-David et al 1998, Hilderbrand et al 1999, O'Keefe and Edwards 2002), where it enriches riparian soils (Bartz andNaiman 2005, Drake et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Seasonal persistence of marine‐derived nutrients in south‐central Alaskan salmon streams

Rinella

Wipfli

Walker³

et al. 2013

Abstract. Spawning salmon deliver annual pulses of marine-derived nutrients (MDN) to riverine ecosystems around the Pacific Rim, leading to increased growth and condition in aquatic and riparian biota. The influence of pulsed resources may last for extended periods of time when recipient food webs have effective storage mechanisms, yet few studies have tracked the seasonal persistence of MDN. With this as our goal, we sampled stream water chemistry and selected stream and riparian biota spring through fall at 18 stations (in six watersheds) that vary widely in spawner abundance and at nine stations (in three watersheds) where salmon runs were blocked by waterfalls. We then developed regression models that related dissolved nutrient concentrations and biochemical measures of MDN assimilation to localized spawner density across these 27 stations. Stream water ammonium-N and orthophosphate-P concentrations increased with spawner density during the summer salmon runs, but responses did not persist into the following fall. The effect of spawner density on d 15 N in generalist macroinvertebrates and three independent MDN metrics (d 15 N, d 34 S, and x3:x6 fatty acids) in juvenile Dolly Varden (Salvelinus malma) was positive and similar during each season, indicating that MDN levels in biota increased with spawner abundance and were maintained for at least nine months after inputs. Delta 15 N in a riparian plant, horsetail (Equisetum fluviatile), and scraper macroinvertebrates did not vary with spawner density in any season, suggesting a lack of MDN assimilation by these lower trophic levels. Our results demonstrate the ready assimilation of MDN by generalist consumers and the persistence of this pulsed subsidy in these organisms through the winter and into the next growing season.

“…4). While prior studies have shown that salmon subsidies can positively impact the nutritional status of stream-dwelling salmonids (e.g., Bilby et al 1996, Wipfli et al 2003, Rinella et al 2012), we uniquely (1) demonstrated that the foraging and growth response of resident fishes can substantially vary across a wide naturally occurring range of salmon densities, (2) documented how varying levels of background in situ productivity can affect the relative impacts of the subsidy, and (3) showed that the magnitude of resource pulses can affect competing species differently.…”

Section: Discussionmentioning

confidence: 99%

Foraging and growth responses of stream‐dwelling fishes to inter‐annual variation in a pulsed resource subsidy

Bentley¹,

Schindler²,

Armstrong³

et al. 2012

Abstract. Pulsed resource subsidies generate ephemeral fluxes of nutrients and energy among ecosystems. The effects of pulsed subsidies should depend on the magnitude of the pulse, the in situ productivity of the recipient system, and the ability of consumers to capitalize on the resources, yet empirical data on these relationships are limited. We assessed the ecological consequences of variation in resource pulse magnitude, as represented by anadromous salmon returns, for the foraging and growth responses of two species of stream-dwelling salmonids in two streams that vary in productivity in southwestern Alaska. Over 11 years and across a greater than 10-fold variation in sockeye salmon (Oncorhynchus nerka) density, both rainbow trout (O. mykiss) and Arctic grayling (Thymallus arcticus) exhibited a relatively similar, but mechanistically different, non-linear saturating growth response to increasing salmon density. This growth response was driven by both an increase in consumption of salmon eggs and also a decrease in dietary overlap between the two species. However, the relative change in growth from low to high salmon densities was different between streams and depended on in situ stream productivity. In low salmon density years the growth of resident consumers fell 46-68% relative to high years in the low productivity stream, but only by 26-34% in the high productivity stream. Our study provides strong evidence that understanding of both the foraging ecology of consumers and the in situ productivity of recipient ecosystems, which together regulate the ecological consequences of variation in resource subsidies, is required for successful implementation of ecosystem-based management in systems dependent on pulsed resource subsidies.