A Critical Assessment of the Ecological Assumptions Underpinning Compensatory Mitigation of Salmon-Derived Nutrients

Collins, Scott F.; Marcarelli, Amy; Baxter, Colden V.; Wipfli, Mark S.

doi:10.1007/s00267-015-0538-5

Cited by 24 publications

(34 citation statements)

References 130 publications

(134 reference statements)

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“…Our findings mirror the results of a synthesis by Collins et al. (), where they showed that while nutrient addition was commonly associated with individual‐level responses, population‐level effects remain uncertain.…”

Section: Discussionsupporting

confidence: 89%

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The roles of extrinsic and intrinsic factors in the freshwater life‐history dynamics of a migratory salmonid

et al. 2018

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Key life‐cycle transitions, such as metamorphosis or migration, can be altered by a variety of external factors, such as climate variation, strong species interactions, and management intervention, or modulated by density dependence. Given that these life‐history transitions can influence population dynamics, understanding the simultaneous effects of intrinsic and extrinsic controls on life‐history expression is particularly relevant for species of management or conservation importance. Here, we examined how life histories of steelhead (Oncorhynchus mykiss) are affected by weather, pink salmon abundance (Oncorhynchus gorbuscha), experimental nutrient addition, and density‐dependent processes. We tested for impacts on the size of steelhead smolts (juveniles migrating to the sea), as well as their age and abundance across four decades in the Keogh River, British Columbia, Canada. Larger steelhead smolts were associated with warmer years and artificial nutrient addition. In addition, higher pink salmon abundance and artificial nutrient addition correlated with juvenile steelhead migrating at younger ages. While density dependence appeared to be the primary factor regulating the abundance of steelhead smolts, nutrient addition and temperature were positively and negatively associated with smolt production, respectively, prior to 1991, and pink salmon spawning abundance was positively associated with smolt production after 1990. Thus, this study provides evidence that the temporal dynamics of one species of salmon is linked to the juvenile life history of co‐occurring steelhead. A complex interplay of species interactions, nutrient subsidies, density dependence, and climatic variation can control the life‐history expression of species with complex life cycles.

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Section: Discussionsupporting

confidence: 89%

“…, Collins et al. ). Nutrient addition has generally increased individual growth rates in a variety of salmonid populations across multiple studies and locations (Johnston et al.…”

Section: Introductionmentioning

confidence: 99%

The roles of extrinsic and intrinsic factors in the freshwater life‐history dynamics of a migratory salmonid

et al. 2018

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“…migration from marine environments to freshwater spawning grounds is a textbook case of cross-ecosystem nutrient subsidies. For example, in the Columbia River Basin where Pacific salmon populations have declined, legislation requiring compensatory mitigation has led to nutrient enhancement programs, on the foundation that habitats have lost critical nutrients from salmon, and therefore, augmentation is necessary to maintain ecosystem function (Collins et al 2015). Declines in Pacific salmon populations in many areas, caused by human activities (overharvest, habitat degradation, dams; Gustafson et al 2007), and the concern over loss of MDN to coastal watersheds have made restoration of salmon nutrients a focal point for many management and mitigation strategies.…”

Section: Introductionmentioning

confidence: 99%

“…Experiments examining the contributions of MDN are often limited by short timescales, and relatively few experiments investigate changes in plant-available soil N pools important to plant nutrient uptake and growth (Collins et al 2015). Studies examining spatial and temporal impacts of salmon on soil inorganic N have identified highly localized responses (effects only observed <30 cm from carcasses) where soil ammonium (NH þ 4 ) and nitrate (NO À 3 ) increase for weeks to months (Drake et al 2005, Gende et al 2007, Holtgrieve et al 2009) and rarely consider longterm N retention in the system.…”

Section: Introductionmentioning

confidence: 99%

Riparian soil nitrogen cycling and isotopic enrichment in response to a long‐term salmon carcass manipulation experiment

et al. 2019

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Pacific salmon acquire most of their biomass in the ocean before returning to spawn and die in coastal streams and lakes, thus providing subsidies of marine-derived nitrogen (MDN) to freshwater and terrestrial ecosystems. Recent declines in salmon abundance have raised questions of whether managers should mitigate for losses of salmon MDN subsidies. To test the long-term importance of salmon subsidies to riparian ecosystems, we measured soil nitrogen cycling in response to a 20-yr manipulation where salmon carcasses were systematically removed from one bank and deposited on the opposite bank along a 2km stream in southwestern Alaska. Soil samples were taken at different distances from the stream bank along nine paired transects and measured for organic and inorganic nitrogen concentrations, and nitrogen transformation rates. Marine-derived nitrogen was measured using 15 N/ 14 N for bulk soils, and NH þ 4 and NO À 3 soil pools. Stable isotope analyses confirmed 15 N/ 14 N was elevated on the salmon-enhanced bank compared to the salmon-depleted bank. However, 15 N/ 14 N values of plant-available inorganic nitrogen exceeded the 15 N/ 14 N of salmon inputs, highlighting nitrogen isotope fractionation in soils that raises significant methodological issues with standard MDN assessments in riparian systems. Surprisingly, despite 20 yr of salmon supplementation, the presence of MDN did not cause a long-term increase in soil nitrogen availability. This finding indicates the importance of MDN to ecosystem nitrogen biogeochemistry, and riparian vegetation may be overestimated for some systems. Given that essential nutrients can also be pollutants, we urge more critical analyses of the role of MDN to inform compensatory mitigation programs targeting salmon nutrient enhancement.

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“…In response, salmon restoration programmes annually supplement spawning grounds with carcasses and carcass analogues in the Pacific Northwest to stimulate primary and invertebrate productivity in salmon streams (Kohler, Rugenski, & Taki, ; Kohler et al., , ). Yet the success of these mitigation measures and the pathways in which these nutrients move through food webs is not fully understood (Collins, Marcarelli, Baxter, & Wipfli, ; Ebel, Marcarelli, & Kohler, ). Although salmon have received much attention, other anadromous fish, including nonnatives, could also play significant roles in nutrient transport.…”

Section: Introductionmentioning

confidence: 99%

From salmon to shad: Shifting sources of marine‐derived nutrients in the Columbia River Basin

Haskell

2017

Ecology of Freshwater Fish

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Like Pacific salmon (Oncorhynchus spp.), nonnative American shad (Alosa sapidissima) have the potential to convey large quantities of nutrients between the Pacific Ocean and freshwater spawning areas in the Columbia River Basin (CRB). American shad are now the most numerous anadromous fish in the CRB, yet the magnitude of the resulting nutrient flux owing to the shift from salmon to shad is unknown. Nutrient flux models revealed that American shad conveyed over 15,000 kg of nitrogen (N) and 3,000 kg of phosphorus (P) annually to John Day Reservoir, the largest mainstem reservoir in the lower Columbia River. Shad were net importers of N, with juveniles and postspawners exporting just 31% of the N imported by adults. Shad were usually net importers of P, with juveniles and postspawners exporting 46% of the P imported by adults on average. American shad contributed <0.2% of the total annual P load into John Day Reservoir, but during June when most adult shad are migrating into John Day Reservoir, they contributed as much as 2.0% of the P load. Nutrient inputs by American shad were similar to current but far less than historical inputs of Pacific salmon owing to their smaller size. Given the relatively high background P levels and low retention times in lower Columbia River reservoirs, it is unlikely that shad marinederived nutrients affect nutrient balances or food web productivity through autotrophic pathways. However, a better understanding of shad spawning aggregations in the CRB is needed. K E Y W O R D Saquatic food webs, lake and reservoir management, nonnative species, nutrients, salmon, shad | INTRODUCTIONAnadromous fish are vectors of nutrient transport between marine and freshwater food webs. This phenomenon has been well documented for Pacific salmon (Oncorhynchus spp.; Holtgrieve & Schindler, 2011;Rex & Petticrew, 2008;Scheuerell, Levin, Zabel, Williams, & Sanderson, 2005;Vanni, 2002;Wipfli, Hudson, & Caouette, 1998), but is less explored for other anadromous fish. Pacific salmon are large-bodied nutrient vectors that contribute 3.0% of their body mass as nitrogen (N) and 0.36% of their body mass as phosphorus (P) in the form of excretions, gametes and carcasses to freshwater areas where they spawn (Brock, Leavitt, Schindler, & Quay, 2007). These nutrients can benefit progeny by increasing the productivity of rearing grounds but can also influence the productivity of entire ecosystems at multiple trophic levels. The decline of once great salmon runs in the Columbia River Basin (CRB) has reduced salmon-derived nutrient inputs to spawning grounds. Columbia River Basin salmon once numbered from 11 to 16 million per year and imported millions of kg of N and hundreds of thousands of kg of P annually (Gresh, Lichatowich, & Schoonmaker, 2000). These nutrient inputs have decreased by 90% with an associated decline in the productivity of salmon spawning grounds. This loss in productivity could inhibit ongoing salmon restoration efforts. In response, salmon restoration programmes annually supplement sp...

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A Critical Assessment of the Ecological Assumptions Underpinning Compensatory Mitigation of Salmon-Derived Nutrients

Cited by 24 publications

References 130 publications

The roles of extrinsic and intrinsic factors in the freshwater life‐history dynamics of a migratory salmonid

The roles of extrinsic and intrinsic factors in the freshwater life‐history dynamics of a migratory salmonid

Riparian soil nitrogen cycling and isotopic enrichment in response to a long‐term salmon carcass manipulation experiment

From salmon to shad: Shifting sources of marine‐derived nutrients in the Columbia River Basin

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