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Sockeye salmon population dynamics over the past 4000years in Upper Russian Lake, south-central Alaska

Sockeye salmon population dynamics over the past 4000years in Upper Russian Lake, south-central... J Paleolimnol (2018) 60:67–75 https://doi.org/10.1007/s10933-018-0024-1 ORIGINAL PAPER Sockeye salmon population dynamics over the past 4000 years in Upper Russian Lake, south-central Alaska . . Molly D. McCarthy Daniel J. Rinella Bruce P. Finney Received: 1 June 2017 / Accepted: 2 March 2018 / Published online: 13 March 2018 The Author(s) 2018 Abstract Stable nitrogen isotope (d N) data from coincides with large reductions in sockeye salmon sediment cores taken in clear-water Upper Russian abundance identified previously in Karluk and Aka- Lake (Kenai River Watershed, Alaska, USA) indicate lura lakes on Kodiak Island, [ 400 km southwest, that sockeye salmon (Oncorhynchus nerka) popula- supporting the possibility of regionally synchronous, tions varied significantly over the past 4000 years, multi-centennial production regimes that may origi- with a prominent * 650-year period of lower salmon nate from shifts in oceanographic conditions such as abundance from * 100 BCE to 550 CE. Sediment biological productivity in the northeastern Pacific characteristics during this * 650-year interval reflect Ocean. Under such a scenario, coincidence with glacial sediment input, which may have contributed to watershed glacial activity indicates a common driver, the salmon decline by degrading spawning habitat and i.e. regional climate change. Climate conditions that reducing carrying capacity. The decline, however, led to significant glacial advances in this part of the Kenai Peninsula (cold and/or wet conditions) may have also created unfavorable ocean conditions during M. D. McCarthy (&)  D. J. Rinella critical periods in the marine phase for these stocks of Department of Biological Sciences, University of Alaska Gulf of Alaska sockeye salmon. Future climate Anchorage, Beatrice G McDonald Hall, 2400 W Campus projections and management strategies should focus Dr, Anchorage, AK 99508, USA e-mail: mmccarthy3@alaska.edu on how climate regimes impact not only prey avail- ability for salmon at sea, but also local conditions for D. J. Rinella e-mail: daniel_rinella@fws.gov spawners and juveniles. D. J. Rinella Keywords Salmon  Nitrogen  Sediment  Alaska Alaska Center for Conservation Science and Department d N  Climate of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA B. P. Finney Departments of Biological Sciences and Geosciences, Introduction Idaho State University, Pocatello, ID 83209, USA e-mail: finney@isu.edu Paleolimnological analyses have led to reconstruc- Present Address: tions of sockeye salmon (Oncorhynchus nerka) abun- D. J. Rinella dance spanning hundreds or thousands of years in U.S. Fish and Wildlife Service, Anchorage Fish and Wildlife Conservation Office, Anchorage, AK 99507, USA 123 68 J Paleolimnol (2018) 60:67–75 many nursery lakes (Finney 1998, 2000, 2002; Gre- from investigating trends in long-term abundance, gory-Eaves et al. 2003; Rogers et al. 2013). These paleolimnological reconstructions of salmon abun- insights are possible because adult sockeye salmon, dance had not been conducted previously. after gaining nearly all of their body mass at sea, return to natal river systems where they spawn and die, Study area primarily in lakes and associated feeder streams. Marine-derived nitrogen (MDN) from decomposing The Kenai River Watershed (Kenai Peninsula, south- 15 2 salmon carcasses, which is enriched in N relative to central Alaska) drains 56,600 km of icefields, rugged watershed sources, is subsequently preserved in lake mountains, and boreal forest (Fig. 1). The mainstem sediments and represents a time-series proxy of past Kenai River begins at the outlet of Kenai Lake and abundance that can be sampled by coring lake flows 132 km westward to Cook Inlet, passing through sediments. Skilak Lake along the way. Several tributaries drain A synthesis of paleolimnological data spanning montane glaciers in the eastern part of the watershed, * 500 years from 20 nursery lakes in southwestern carrying cold, sediment-rich meltwater into Kenai and south-central Alaska, the center of wild sockeye Lake, Skilak Lake, and the mainstem Kenai River. salmon abundance, reveals substantial shifts in salmon Numerous clear-water tributaries also join the system, productivity within individual lakes that often lasted ranging from montane streams that drain persistent for decades or centuries (Rogers et al. 2013). These snowpack to lowland streams that drain extensive productivity regimes were often asynchronous among forest and wetlands. Additional lakes are found on lakes, presumably related to differential responses of both glacial and clear-water tributaries. habitats and salmon populations to regional climatic This mosaic of freshwater habitats supports all five conditions, resulting in a ‘‘portfolio effect’’ that species of North American Pacific salmon, with stabilizes regional salmon returns over time (Rogers sockeye being the most abundant. The total sockeye et al. 2013). When viewed across longer time scales, salmon run to the Kenai River Watershed averages 3.1 however, there is evidence for regionally coherent million fish; on average, 2.4 million of these are climate-related shifts in abundance that may synchro- harvested and 700,000 escape to spawn and die nize the dynamics of different populations. Paleolim- (1976–2008 average; Tobias and Willette 2013). nological data from two nursery lakes on Kodiak Spawning occurs throughout much of the watershed Island, covering * 2200 years, showed large, syn- in multiple substocks and juveniles typically rear in chronous declines in sockeye salmon that began several different glacier-fed and clear-water lakes for around * 100 BCE and lasted for several hun- 1 or 2 years before going to sea. dred years (Finney et al. 2002). Examination of We chose to study Upper Russian Lake (Fig. 1; temporal variation at similarly long timescales in 60.339N, 149.880W) because it is the Kenai River distant river systems will provide insights into the Watershed’s most productive clear-water sockeye temporal and spatial scales over which population salmon nursery lake (DeCino and Willette trends of different stocks are synchronized or not. 2011, 2014) and because its relatively high escape- The Kenai River is the most productive sockeye ment density (* 20,000 spawners/km ) makes it salmon system in south-central Alaska’s Cook Inlet amenable to paleolimnological reconstruction of Watershed, producing over half of the Inlet’s average salmon abundance (Finney et al. 2000). Upper Russian annual return of 5.2 million sockeye salmon (Willette Lake is a relatively small lake (4.6 km ) drained by the and Shields 2015; Schoen et al. 2017). The Cook Inlet Russian River, which in turn flows into the Kenai commercial fishery harvests an average of 2.9 million River 119 km upstream from its mouth at Cook Inlet. sockeye salmon with an ex-vessel value of $26.3 Two genetically distinct sockeye salmon runs use this million (1966–2014 data; Shields and Dupuis 2016). river system: the early run spawns in early July in Within a 3-h drive of nearly two-thirds of Alaska’s Upper Russian Lake’s main tributary and the late run human population, the Kenai River also supports the spawns in August throughout Upper Russian Lake, in most popular personal-use and sport fisheries in the main tributary, and in the lake outlet (Nelson Alaska. Despite the importance of the Kenai River’s 1983). Escapement to the Russian River, which has sockeye salmon and the insights that may be gained been counted annually at a weir on the lower Russian 123 J Paleolimnol (2018) 60:67–75 69 Fig. 1 The Kenai River watershed, including the Russian River watershed (highlighted in gray) River since 1965, ranges from * 2000 to 86,000 for Materials and methods the early run and * 21,000–158,000 for the late run Sediment coring and analysis (Fair et al. 2013) (Table 1). The purpose of this study was to expand our We collected twelve undisturbed surface sediment knowledge of past salmon populations in south-central Alaska. Our objectives were (1) to reconstruct relative cores that ranged from 0.5 to 1.2 m in length from Upper Russian Lake between 2014 and 2015 using a changes in past salmon abundance over multi-millen- nial timescales using sediment d N in Upper Russian hand-operated universal percussion corer (Universal Lake (2) compare our results to previously published Percussion Corer, Aquatic Research Instruments, paleolimnological reconstructions of salmon abun- Hope, ID). Most cores were obtained from the dance, and (3) examine paleoclimate changes that may southern end of the lake in a deep, flat basin. We used have influenced salmon productivity over time. Zorbitrol and floral foam immediately upon obtaining Although our focus was on Alaskan systems, under- cores to preserve surface sediments, which remained intact through shipping. We shipped whole cores to the standing the nature of past variability, and any connections to climate change, have broad implica- National Lacustrine Core (LacCore) Facility at the University of Minnesota where they were run through tions for salmon conservation and management throughout their range. a Geotek Multi-Sensor Core Logger (MSCL) to measure magnetic susceptibility and gamma density, 123 70 J Paleolimnol (2018) 60:67–75 Table 1 Limnological characteristics for Upper Russian Lake Water residence Escapement density Surface Volume Turbidity Euphotic zone Zooplankton density 2 2 6 3 -2 time (years) (spawners/km ) Area (km ) (9 10 m ) (NTU) depth (m) (mg m ) * 1.1 * 20,000 4.6 122 n/a 13.0 * 1400 (1) (3) (3) (1) (2) Data are from Koenings et al. (1986) (1); Koenings and Kyle (1997) (2); Spafard and Edmundson (2000) (3); N/A indicates that no data could be found then split and imaged. We chose a * 110-cm-long To isolate terrestrial macrofossils, we sieved and master core based on the presence of terrestrial plant rinsed (with distilled water) the remaining material in macrofossils (for radiocarbon dating), uniform hori- each of the 215 sediment core subsamples; macrofos- zontal laminations, and the absence of turbidites or sils with adequate mass for AMS radiocarbon dating other event-driven sediment deposits (Fig. 2). We were sent to the Center for Applied Isotope Studies at believe the master core covers the longest period of the University of Georgia for analysis. We calibrated time, based on the presence of a distinct white tephra all raw dates using the IntCal13 terrestrial calibration (volcanic ash) deposit located near the base of the curve in the CALIB Program, version 7.1 (Reimer core, which was not present in other cores (Fig. 2). et al. 2013; Stuiver et al. 2017; Stuiver and Reimer We subsampled sediment from the master core 1993). Tephras identified visually and by spikes in continuously at 0.5-cm intervals, yielding a total of magnetic susceptibility were sampled and wet sieved 215 subsamples. We mixed each of these subsamples to remove particles\ 63 lm, and dried. We analyzed and removed small aliquots that were homogenized, glass shards from tephra samples by electron probe dried, and subsequently analyzed for d N as a proxy microanalysis (EPMA) using a JEOL 8900 electron for past salmon abundance, in addition to %C, %N, microprobe equipped with 5 wavelength x-ray spec- and d C. These analyses were run on a Costech ECS trometers at the USGS, Menlo Park, California. 4010 elemental analyzer (Costech, Valencia, CA) in Standards for EPMA analysis included Si-RLS-132, line with a Thermo Scientific Delta V Advantage Fe, Mg, Ca-VG2 (basaltic glass), K, Al-Or1, Na- continuous-flow isotope ratio mass spectrometer TibAlbite, Cl-sodalite, P-Wilberforce apatite, Ti– (Thermo Scientific, Bremen, Germany) calibrated TiO and Mn–Mn O . We attempted to identify 11 2 2 3 with international reference standards from the Inter- tephra events by geochemically correlating them to national Atomic Energy Agency (IAEA-N1, IAEA- dated reference tephras archived at the USGS Alaska CH7, IAEA-C3, and IAEA-600) and the USGS Tephra Laboratory and Data Center in Anchorage, (USGS-25, USGS-40, and USGS-41). We included AK. Our age model utilized all dated macrofossils and internal standards of purified methionine (Alfa Aesar, tephras and assumed a constant sedimentation rate 13 15- %C = 40.25, %N = 9.39, d C= - 34.6, d between adjacent dated layers. N= - 0.9%) and homogenized peach leaf (NIST 1547, %C = 46.79, %N = 2.94 d C= - 25.8%, d N = 1.9%) with all subsamples as quality controls. Results Stable isotope values are reported in standard d notation of parts per mil (%) and are referenced to Laminated brown and gray silts (Munsell colors: 5Y Vienna Pee Dee Belemnite (VPDB) for d C and to air 5/2, 5Y 6/1, 5GY 6/1; Goddard et al. 1975) intermixed for d N. Long-term records of internal standards yield with blue/gray clastic bands (Munsell colors: 5PB 7/2, an analytical precision of 0.03% for %N, 0.22% for 5B 7/1, 5B 7/6, 5B 5/6), black organic bands, and 15 13 %C, 0.1% for d N, and 0.1% for d C. Analyses several tephra layers of varying color (Munsell colors: were conducted at the University of Alaska Anchorage 5YR 3/4, 10YR 8/2, 10YR 2/2) were common across stable isotope facility. cores (Fig. 2). All cores were dominated by silts To construct an age model, we radiocarbon dated (0.002–0.05 mm), but they also contained layers of terrestrial macrofossils and geochemically identified very fine-grained sands (0.05–0.125 mm) and clays previously dated tephras throughout the master core. (\ 0.002 mm) (Fig. 2). Tephras were composed of 123 J Paleolimnol (2018) 60:67–75 71 Fig. 2 Photograph showing sediment core stratigraphy from sedimentary d N, a proxy for salmon abundance; C:N ratio (by the Upper Russian Lake master core in relation to the dated mass); d C; %C; and %N. In the age column, UW stands for layers used for the age model; magnetic susceptibility (MS) used unidentified wood and T stands for tephra to identify tephras; bulk density, an indicator of sediment type; fine to medium-grained ash (\ 0.0625–0.125 mm; a 2-cm-thick deposit centered at a core depth of 17 cm, Fig. 2). which correlated with a 505 ± 25 year BP tephra Our age model was based on 4 radiocarbon-dated layer found in a peat core from Seldovia, Alaska (AT- wood fragments and 1 dateable tephra, for a total of 5 3508, unpublished data). Sedimentation rates, based dated layers (Table 2). The macrofossils were found at on linear interpolation between each of the 5 dated depths of 5–80 cm below the lake floor and corre- layers, varied from 0.014 to 0.047 cm/year and was sponded to ages between 229 ± 24 at 5 cm and highest between the topmost and underlying dated 3626 ± 23 year BP at 80 cm. The dateable tephra was layers (Fig. 3). At these relatively slow sedimentation 123 72 J Paleolimnol (2018) 60:67–75 rates, each 0.5-cm subsample represents 10–34 years Upp er Russian Lake Age Model (y ear and co re d epth) and the dated portion of the core represents * 4000 years (Fig. 3). C:N (by mass) was relatively low (7.7–11.0 1500 throughout the dated portion of the core), suggesting that organic matter was predominantly from aquatic sources, thereby indicating limited potential for alter- ation of MDN signals by inputs of terrestrial organic matter (Holtham et al. 2004). The d C, which ranged from - 27.2 to - 24.5, was consistent with aquatic sources, though it also generally fell within the range of terrestrial plants. The recent decline in d C to the lowest values observed in the record likely reflects the influence of anthropogenic CO in the atmosphere, i.e. -500 the Suess effect (Verburg 2007). The d N values averaged 4.7% throughout the dated portion of the core, which is substantially higher -1000 than in salmon-free control lakes and generally consistent with expected values for similar spawning densities, suggesting that variation in d N was related -1500 to MDN input (Finney et al. 2000; Rogers et al. 2013). For the first 1900 years (* 2000 BCE to 100 BCE) of -2000 the * 4000-year time series represented in the core, 0 204060 80 100 d N averaged 4.9% (Figs. 2, 4). Over the period from Core Depth (cm) * 100 BCE to 550 CE, d N abruptly declined to an average of 2.7%, which is closer to values * 2.3% Fig. 3 Age at depth for the Upper Russian Lake master core, constructed from the 4 radiocarbon-dated macrofossils and 1 observed in sediments of salmon-free reference lakes dateable tephra and assuming constant sedimentation rates elsewhere in Alaska (Finney et al. 2002; Rogers et al. between successive dated layers 2013) and suggests a significant, multi-centennial Table 2 Radiocarbon sample material, core depth, measured age of sample and calibration output for 5 samples used to construct Upper Russian Lake age model Sample Core depth Age ( C Median cal years 2-r age ranges, cal years Relative age range material (cm) years) (CALIB 7.1) (CALIB 7.1) probability Unidentified 5 229 ± 24 1673 CE 1642–1679 CE 0.533 wood 1764–1800 0.398 1939–1950 0.069 Tephra 17 505 ± 25 1422 CE 1403–1443 CE 1 Unidentified 36 1581 ± 25 482 CE 417–541 CE 1 wood Unidentified 60 2517 ± 24 640 BCE 790–732 BCE 0.293 wood 690–661 0.159 649–545 0.548 Unidentified 80 3626 ± 23 1987 BCE 2114–2099 BCE 0.025 wood 2037–1917 0.975 All radiocarbon ages are given as calibrated ages in years BCE/CE Age BCE/CE J Paleolimnol (2018) 60:67–75 73 decline of Upper Russian Lake sockeye salmon low-frequency climate patterns synchronize produc- abundance. The d N in sediments accumulated since tion regimes across the North Pacific (Finney et al. this decline (550 CE–present) averaged 5.0%, with 2002). the exception of another decline from 900 CE to 1000 In addition to unfavorable conditions at sea, it is CE, during which d N in sediments averaged 2.9%. possible that salmon declines in Upper Russian Lake The relatively high values and narrow range in d N were also associated with changes in its watershed. prior to and since the decline, suggest that salmon Concurrent with the salmon decline inferred from were returning to the lake in numbers similar to d N, the sediment character shifted towards finer- present day during those intervals. grain materials with lower organic matter content (Fig. 2), reflecting glacio-lacustrine processes. With regional evidence of glacial advance during this time Discussion period (Wiles and Calkin 1994), it is possible that the primary inlet stream to Upper Russian Lake was Sediment d N in Upper Russian Lake has fluctuated impacted by glacial ice that extended northward from around a mean of 4.5% for most of the * 4000 years the nearby Harding Icefield. Inputs of silt-rich, turbid represented in our core, suggesting that spawner glacial meltwater could have led to degraded salmon abundance has been relatively consistent on time- spawning conditions in the inlet stream and, by scales similar to or greater than sampling resolution limiting light penetration, to reduced sockeye salmon over much of this time period. A major multi- carrying capacity in the lake (Koenings et al. 1986; centennial decline in inferred salmon abundance, Milner and Petts 1994). however, occurred from * 100 BCE to 550 CE Most Alaska nursery lakes show clear trends toward followed by a shorter decline from * 900 to 1000 CE. lower d N since the late 1800s, following the onset of These shifts coincide with inferred salmon declines in commercial salmon fisheries (Finney et al. 2002; both Karluk and Akalura Lakes on Kodiak Island, Rogers et al. 2013), which typically harvest half or [ 400 km southwest of our study area (Fig. 4), the more of each year’s spawning run. Upper Russian only other lakes with salmon reconstructions dating Lake sediments, however, show no sign of such back to this time period (Finney et al. 2002). This depletion. Several other nursery lakes that have been finding provides further evidence for an ancient, studied, however, also fail to display lower d Nin prolonged and widespread decline in salmon produc- upper sediments, presumably a consequence of the tion, and supports the hypothesis that high-magnitude, relatively recent development of commercial fisheries Fig. 4 Comparison of Karluk Upper Russian Akalura salmonreconstruction 10 6.5 among UpperRussian Lake, and Akaluraand Karluk lakes on KodiakIsland (Finney et al. 2002) 5.5 4.5 3.5 2 3 -250 0 250 500 750 1000 1250 1500 1750 2000 BCE Calendar Age CE Karluk and Upper Russian δ N (‰) Akalura δ N (‰) 74 J Paleolimnol (2018) 60:67–75 that intercept stocks bound for these lakes (Rogers Further research into the ocean environment during et al. 2013). An unknown portion of the Russian these times may shed light on how climate influences River’s late run has been harvested by Cook Inlet’s salmon production in the ocean. As a working commercial fisheries since they began, shown in hypothesis, the climate conditions that led to signif- recent years by genetic stock identification, to average icant first-millennium AD glacial advances (Wiles and 28% (2006–2008 data; Eskelin et al. 2013), so it is Calkin 1994) in this part of the Kenai Peninsula (cold possible that commercial harvest has not impacted and/or wet conditions), may have created unfavorable escapement enough to elicit the dramatic N deple- ocean conditions during critical times during the tion seen in other systems. Harvest rates on Russian marine phase of these stocks of Gulf of Alaska River salmon have presumably increased in recent sockeye. Interestingly, these conditions were different decades (Schoen et al. 2017), with the growth of sport from those during glacial advances in the Little Ice fisheries that harvest approximately 50% of the early Age, a time for which most available sediment core run and 29% of the late run and a personal-use fishery data from Alaskan sites suggests high salmon abun- that harvests 7% of the late run (Begich and Pawluk dance (Finney et al. 2002; Rogers et al. 2013). Our 2007; Eskelin et al. 2013; Fair et al. 2013). This Upper Russian core, uniquely from a primarily clear- additional harvest may be too recent to be reflected in water lake with periodic glacial influence, also shows Upper Russian Lake sediments (Rogers et al. 2013), relatively high d N during the Little Ice Age. Future especially given the relatively low temporal resolution climate projections and management strategies should of our core subsampling. Additionally, these fisheries focus on understanding how climate regimes not only developed during a period of favorable ocean condi- impact prey availability for salmon at sea, but also tions and exceptionally high abundance for many influence local conditions for spawners and juveniles. salmon stocks, including Cook Inlet sockeye salmon Acknowledgements This analysis was part of a larger project (Irvine and Ruggerone 2016). funded by Alaska EPSCoR National Science Foundation award Our results provide further evidence for synchrony #O1A-1208927 and the State of Alaska. Support for Bruce in salmon production regimes at centennial timescales Finney was assisted by NSF award #1521365. We thank Kristi over the last few millennia (Finney et al. 2002). Wallace from USGS for tephra analysis, as well as use of her tephra lab for a variety of sampling activities. We acknowledge Fluctuations in Upper Russian Lake salmon abun- the many researchers who work for the Alaska Department of dance inferred from d N over the last 500 years are, Fish and Game and collected long-term data on commercial and however, relatively minor compared to records from sport catch and escapement of Kenai River and Russian River other Alaskan nursery lakes (Rogers et al. 2013). salmon, and especially Mark Willette for providing initial guidance. We also thank Dr. David Fortin, Nore Preat, Koen Du Resolving this scale of fluctuation is likely compro- Ryker, Phillip Kempf, Nicole Warner, Courtney Breest, Scott mised because of the low time-resolution of our Cunfer, Nancy McCarthy, and Frank McCarthy for field and record, but it could also reflect the fact that individual laboratory assistance. The findings and conclusionsin this article systems may react differently to regional climate are those of theauthors and do not necessarilyrepresent the view of the U.S.Fish and Wildlife Service. change on decadal scales (Rogers et al. 2013). The temporal resolution of our data are sufficient to Open Access This article is distributed under the terms of the compare over longer timescales, and suggest coherent Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits unre- patterns of higher magnitude and longer duration at stricted use, distribution, and reproduction in any medium, centennial and longer scales. provided you give appropriate credit to the original In summary, our results from Upper Russian Lake, author(s) and the source, provide a link to the Creative Com- together with previous research (Finney et al. 2002), mons license, and indicate if changes were made. suggest dramatic multi-centennial periods of lower salmon abundance in multiple systems across a wide area of the northern Gulf of Alaska. 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Sockeye salmon population dynamics over the past 4000years in Upper Russian Lake, south-central Alaska

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Springer Journals
Copyright
Copyright © 2018 by The Author(s)
Subject
Earth Sciences; Paleontology; Sedimentology; Climate Change; Physical Geography; Freshwater & Marine Ecology; Geology
ISSN
0921-2728
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1573-0417
DOI
10.1007/s10933-018-0024-1
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J Paleolimnol (2018) 60:67–75 https://doi.org/10.1007/s10933-018-0024-1 ORIGINAL PAPER Sockeye salmon population dynamics over the past 4000 years in Upper Russian Lake, south-central Alaska . . Molly D. McCarthy Daniel J. Rinella Bruce P. Finney Received: 1 June 2017 / Accepted: 2 March 2018 / Published online: 13 March 2018 The Author(s) 2018 Abstract Stable nitrogen isotope (d N) data from coincides with large reductions in sockeye salmon sediment cores taken in clear-water Upper Russian abundance identified previously in Karluk and Aka- Lake (Kenai River Watershed, Alaska, USA) indicate lura lakes on Kodiak Island, [ 400 km southwest, that sockeye salmon (Oncorhynchus nerka) popula- supporting the possibility of regionally synchronous, tions varied significantly over the past 4000 years, multi-centennial production regimes that may origi- with a prominent * 650-year period of lower salmon nate from shifts in oceanographic conditions such as abundance from * 100 BCE to 550 CE. Sediment biological productivity in the northeastern Pacific characteristics during this * 650-year interval reflect Ocean. Under such a scenario, coincidence with glacial sediment input, which may have contributed to watershed glacial activity indicates a common driver, the salmon decline by degrading spawning habitat and i.e. regional climate change. Climate conditions that reducing carrying capacity. The decline, however, led to significant glacial advances in this part of the Kenai Peninsula (cold and/or wet conditions) may have also created unfavorable ocean conditions during M. D. McCarthy (&)  D. J. Rinella critical periods in the marine phase for these stocks of Department of Biological Sciences, University of Alaska Gulf of Alaska sockeye salmon. Future climate Anchorage, Beatrice G McDonald Hall, 2400 W Campus projections and management strategies should focus Dr, Anchorage, AK 99508, USA e-mail: mmccarthy3@alaska.edu on how climate regimes impact not only prey avail- ability for salmon at sea, but also local conditions for D. J. Rinella e-mail: daniel_rinella@fws.gov spawners and juveniles. D. J. Rinella Keywords Salmon  Nitrogen  Sediment  Alaska Alaska Center for Conservation Science and Department d N  Climate of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA B. P. Finney Departments of Biological Sciences and Geosciences, Introduction Idaho State University, Pocatello, ID 83209, USA e-mail: finney@isu.edu Paleolimnological analyses have led to reconstruc- Present Address: tions of sockeye salmon (Oncorhynchus nerka) abun- D. J. Rinella dance spanning hundreds or thousands of years in U.S. Fish and Wildlife Service, Anchorage Fish and Wildlife Conservation Office, Anchorage, AK 99507, USA 123 68 J Paleolimnol (2018) 60:67–75 many nursery lakes (Finney 1998, 2000, 2002; Gre- from investigating trends in long-term abundance, gory-Eaves et al. 2003; Rogers et al. 2013). These paleolimnological reconstructions of salmon abun- insights are possible because adult sockeye salmon, dance had not been conducted previously. after gaining nearly all of their body mass at sea, return to natal river systems where they spawn and die, Study area primarily in lakes and associated feeder streams. Marine-derived nitrogen (MDN) from decomposing The Kenai River Watershed (Kenai Peninsula, south- 15 2 salmon carcasses, which is enriched in N relative to central Alaska) drains 56,600 km of icefields, rugged watershed sources, is subsequently preserved in lake mountains, and boreal forest (Fig. 1). The mainstem sediments and represents a time-series proxy of past Kenai River begins at the outlet of Kenai Lake and abundance that can be sampled by coring lake flows 132 km westward to Cook Inlet, passing through sediments. Skilak Lake along the way. Several tributaries drain A synthesis of paleolimnological data spanning montane glaciers in the eastern part of the watershed, * 500 years from 20 nursery lakes in southwestern carrying cold, sediment-rich meltwater into Kenai and south-central Alaska, the center of wild sockeye Lake, Skilak Lake, and the mainstem Kenai River. salmon abundance, reveals substantial shifts in salmon Numerous clear-water tributaries also join the system, productivity within individual lakes that often lasted ranging from montane streams that drain persistent for decades or centuries (Rogers et al. 2013). These snowpack to lowland streams that drain extensive productivity regimes were often asynchronous among forest and wetlands. Additional lakes are found on lakes, presumably related to differential responses of both glacial and clear-water tributaries. habitats and salmon populations to regional climatic This mosaic of freshwater habitats supports all five conditions, resulting in a ‘‘portfolio effect’’ that species of North American Pacific salmon, with stabilizes regional salmon returns over time (Rogers sockeye being the most abundant. The total sockeye et al. 2013). When viewed across longer time scales, salmon run to the Kenai River Watershed averages 3.1 however, there is evidence for regionally coherent million fish; on average, 2.4 million of these are climate-related shifts in abundance that may synchro- harvested and 700,000 escape to spawn and die nize the dynamics of different populations. Paleolim- (1976–2008 average; Tobias and Willette 2013). nological data from two nursery lakes on Kodiak Spawning occurs throughout much of the watershed Island, covering * 2200 years, showed large, syn- in multiple substocks and juveniles typically rear in chronous declines in sockeye salmon that began several different glacier-fed and clear-water lakes for around * 100 BCE and lasted for several hun- 1 or 2 years before going to sea. dred years (Finney et al. 2002). Examination of We chose to study Upper Russian Lake (Fig. 1; temporal variation at similarly long timescales in 60.339N, 149.880W) because it is the Kenai River distant river systems will provide insights into the Watershed’s most productive clear-water sockeye temporal and spatial scales over which population salmon nursery lake (DeCino and Willette trends of different stocks are synchronized or not. 2011, 2014) and because its relatively high escape- The Kenai River is the most productive sockeye ment density (* 20,000 spawners/km ) makes it salmon system in south-central Alaska’s Cook Inlet amenable to paleolimnological reconstruction of Watershed, producing over half of the Inlet’s average salmon abundance (Finney et al. 2000). Upper Russian annual return of 5.2 million sockeye salmon (Willette Lake is a relatively small lake (4.6 km ) drained by the and Shields 2015; Schoen et al. 2017). The Cook Inlet Russian River, which in turn flows into the Kenai commercial fishery harvests an average of 2.9 million River 119 km upstream from its mouth at Cook Inlet. sockeye salmon with an ex-vessel value of $26.3 Two genetically distinct sockeye salmon runs use this million (1966–2014 data; Shields and Dupuis 2016). river system: the early run spawns in early July in Within a 3-h drive of nearly two-thirds of Alaska’s Upper Russian Lake’s main tributary and the late run human population, the Kenai River also supports the spawns in August throughout Upper Russian Lake, in most popular personal-use and sport fisheries in the main tributary, and in the lake outlet (Nelson Alaska. Despite the importance of the Kenai River’s 1983). Escapement to the Russian River, which has sockeye salmon and the insights that may be gained been counted annually at a weir on the lower Russian 123 J Paleolimnol (2018) 60:67–75 69 Fig. 1 The Kenai River watershed, including the Russian River watershed (highlighted in gray) River since 1965, ranges from * 2000 to 86,000 for Materials and methods the early run and * 21,000–158,000 for the late run Sediment coring and analysis (Fair et al. 2013) (Table 1). The purpose of this study was to expand our We collected twelve undisturbed surface sediment knowledge of past salmon populations in south-central Alaska. Our objectives were (1) to reconstruct relative cores that ranged from 0.5 to 1.2 m in length from Upper Russian Lake between 2014 and 2015 using a changes in past salmon abundance over multi-millen- nial timescales using sediment d N in Upper Russian hand-operated universal percussion corer (Universal Lake (2) compare our results to previously published Percussion Corer, Aquatic Research Instruments, paleolimnological reconstructions of salmon abun- Hope, ID). Most cores were obtained from the dance, and (3) examine paleoclimate changes that may southern end of the lake in a deep, flat basin. We used have influenced salmon productivity over time. Zorbitrol and floral foam immediately upon obtaining Although our focus was on Alaskan systems, under- cores to preserve surface sediments, which remained intact through shipping. We shipped whole cores to the standing the nature of past variability, and any connections to climate change, have broad implica- National Lacustrine Core (LacCore) Facility at the University of Minnesota where they were run through tions for salmon conservation and management throughout their range. a Geotek Multi-Sensor Core Logger (MSCL) to measure magnetic susceptibility and gamma density, 123 70 J Paleolimnol (2018) 60:67–75 Table 1 Limnological characteristics for Upper Russian Lake Water residence Escapement density Surface Volume Turbidity Euphotic zone Zooplankton density 2 2 6 3 -2 time (years) (spawners/km ) Area (km ) (9 10 m ) (NTU) depth (m) (mg m ) * 1.1 * 20,000 4.6 122 n/a 13.0 * 1400 (1) (3) (3) (1) (2) Data are from Koenings et al. (1986) (1); Koenings and Kyle (1997) (2); Spafard and Edmundson (2000) (3); N/A indicates that no data could be found then split and imaged. We chose a * 110-cm-long To isolate terrestrial macrofossils, we sieved and master core based on the presence of terrestrial plant rinsed (with distilled water) the remaining material in macrofossils (for radiocarbon dating), uniform hori- each of the 215 sediment core subsamples; macrofos- zontal laminations, and the absence of turbidites or sils with adequate mass for AMS radiocarbon dating other event-driven sediment deposits (Fig. 2). We were sent to the Center for Applied Isotope Studies at believe the master core covers the longest period of the University of Georgia for analysis. We calibrated time, based on the presence of a distinct white tephra all raw dates using the IntCal13 terrestrial calibration (volcanic ash) deposit located near the base of the curve in the CALIB Program, version 7.1 (Reimer core, which was not present in other cores (Fig. 2). et al. 2013; Stuiver et al. 2017; Stuiver and Reimer We subsampled sediment from the master core 1993). Tephras identified visually and by spikes in continuously at 0.5-cm intervals, yielding a total of magnetic susceptibility were sampled and wet sieved 215 subsamples. We mixed each of these subsamples to remove particles\ 63 lm, and dried. We analyzed and removed small aliquots that were homogenized, glass shards from tephra samples by electron probe dried, and subsequently analyzed for d N as a proxy microanalysis (EPMA) using a JEOL 8900 electron for past salmon abundance, in addition to %C, %N, microprobe equipped with 5 wavelength x-ray spec- and d C. These analyses were run on a Costech ECS trometers at the USGS, Menlo Park, California. 4010 elemental analyzer (Costech, Valencia, CA) in Standards for EPMA analysis included Si-RLS-132, line with a Thermo Scientific Delta V Advantage Fe, Mg, Ca-VG2 (basaltic glass), K, Al-Or1, Na- continuous-flow isotope ratio mass spectrometer TibAlbite, Cl-sodalite, P-Wilberforce apatite, Ti– (Thermo Scientific, Bremen, Germany) calibrated TiO and Mn–Mn O . We attempted to identify 11 2 2 3 with international reference standards from the Inter- tephra events by geochemically correlating them to national Atomic Energy Agency (IAEA-N1, IAEA- dated reference tephras archived at the USGS Alaska CH7, IAEA-C3, and IAEA-600) and the USGS Tephra Laboratory and Data Center in Anchorage, (USGS-25, USGS-40, and USGS-41). We included AK. Our age model utilized all dated macrofossils and internal standards of purified methionine (Alfa Aesar, tephras and assumed a constant sedimentation rate 13 15- %C = 40.25, %N = 9.39, d C= - 34.6, d between adjacent dated layers. N= - 0.9%) and homogenized peach leaf (NIST 1547, %C = 46.79, %N = 2.94 d C= - 25.8%, d N = 1.9%) with all subsamples as quality controls. Results Stable isotope values are reported in standard d notation of parts per mil (%) and are referenced to Laminated brown and gray silts (Munsell colors: 5Y Vienna Pee Dee Belemnite (VPDB) for d C and to air 5/2, 5Y 6/1, 5GY 6/1; Goddard et al. 1975) intermixed for d N. Long-term records of internal standards yield with blue/gray clastic bands (Munsell colors: 5PB 7/2, an analytical precision of 0.03% for %N, 0.22% for 5B 7/1, 5B 7/6, 5B 5/6), black organic bands, and 15 13 %C, 0.1% for d N, and 0.1% for d C. Analyses several tephra layers of varying color (Munsell colors: were conducted at the University of Alaska Anchorage 5YR 3/4, 10YR 8/2, 10YR 2/2) were common across stable isotope facility. cores (Fig. 2). All cores were dominated by silts To construct an age model, we radiocarbon dated (0.002–0.05 mm), but they also contained layers of terrestrial macrofossils and geochemically identified very fine-grained sands (0.05–0.125 mm) and clays previously dated tephras throughout the master core. (\ 0.002 mm) (Fig. 2). Tephras were composed of 123 J Paleolimnol (2018) 60:67–75 71 Fig. 2 Photograph showing sediment core stratigraphy from sedimentary d N, a proxy for salmon abundance; C:N ratio (by the Upper Russian Lake master core in relation to the dated mass); d C; %C; and %N. In the age column, UW stands for layers used for the age model; magnetic susceptibility (MS) used unidentified wood and T stands for tephra to identify tephras; bulk density, an indicator of sediment type; fine to medium-grained ash (\ 0.0625–0.125 mm; a 2-cm-thick deposit centered at a core depth of 17 cm, Fig. 2). which correlated with a 505 ± 25 year BP tephra Our age model was based on 4 radiocarbon-dated layer found in a peat core from Seldovia, Alaska (AT- wood fragments and 1 dateable tephra, for a total of 5 3508, unpublished data). Sedimentation rates, based dated layers (Table 2). The macrofossils were found at on linear interpolation between each of the 5 dated depths of 5–80 cm below the lake floor and corre- layers, varied from 0.014 to 0.047 cm/year and was sponded to ages between 229 ± 24 at 5 cm and highest between the topmost and underlying dated 3626 ± 23 year BP at 80 cm. The dateable tephra was layers (Fig. 3). At these relatively slow sedimentation 123 72 J Paleolimnol (2018) 60:67–75 rates, each 0.5-cm subsample represents 10–34 years Upp er Russian Lake Age Model (y ear and co re d epth) and the dated portion of the core represents * 4000 years (Fig. 3). C:N (by mass) was relatively low (7.7–11.0 1500 throughout the dated portion of the core), suggesting that organic matter was predominantly from aquatic sources, thereby indicating limited potential for alter- ation of MDN signals by inputs of terrestrial organic matter (Holtham et al. 2004). The d C, which ranged from - 27.2 to - 24.5, was consistent with aquatic sources, though it also generally fell within the range of terrestrial plants. The recent decline in d C to the lowest values observed in the record likely reflects the influence of anthropogenic CO in the atmosphere, i.e. -500 the Suess effect (Verburg 2007). The d N values averaged 4.7% throughout the dated portion of the core, which is substantially higher -1000 than in salmon-free control lakes and generally consistent with expected values for similar spawning densities, suggesting that variation in d N was related -1500 to MDN input (Finney et al. 2000; Rogers et al. 2013). For the first 1900 years (* 2000 BCE to 100 BCE) of -2000 the * 4000-year time series represented in the core, 0 204060 80 100 d N averaged 4.9% (Figs. 2, 4). Over the period from Core Depth (cm) * 100 BCE to 550 CE, d N abruptly declined to an average of 2.7%, which is closer to values * 2.3% Fig. 3 Age at depth for the Upper Russian Lake master core, constructed from the 4 radiocarbon-dated macrofossils and 1 observed in sediments of salmon-free reference lakes dateable tephra and assuming constant sedimentation rates elsewhere in Alaska (Finney et al. 2002; Rogers et al. between successive dated layers 2013) and suggests a significant, multi-centennial Table 2 Radiocarbon sample material, core depth, measured age of sample and calibration output for 5 samples used to construct Upper Russian Lake age model Sample Core depth Age ( C Median cal years 2-r age ranges, cal years Relative age range material (cm) years) (CALIB 7.1) (CALIB 7.1) probability Unidentified 5 229 ± 24 1673 CE 1642–1679 CE 0.533 wood 1764–1800 0.398 1939–1950 0.069 Tephra 17 505 ± 25 1422 CE 1403–1443 CE 1 Unidentified 36 1581 ± 25 482 CE 417–541 CE 1 wood Unidentified 60 2517 ± 24 640 BCE 790–732 BCE 0.293 wood 690–661 0.159 649–545 0.548 Unidentified 80 3626 ± 23 1987 BCE 2114–2099 BCE 0.025 wood 2037–1917 0.975 All radiocarbon ages are given as calibrated ages in years BCE/CE Age BCE/CE J Paleolimnol (2018) 60:67–75 73 decline of Upper Russian Lake sockeye salmon low-frequency climate patterns synchronize produc- abundance. The d N in sediments accumulated since tion regimes across the North Pacific (Finney et al. this decline (550 CE–present) averaged 5.0%, with 2002). the exception of another decline from 900 CE to 1000 In addition to unfavorable conditions at sea, it is CE, during which d N in sediments averaged 2.9%. possible that salmon declines in Upper Russian Lake The relatively high values and narrow range in d N were also associated with changes in its watershed. prior to and since the decline, suggest that salmon Concurrent with the salmon decline inferred from were returning to the lake in numbers similar to d N, the sediment character shifted towards finer- present day during those intervals. grain materials with lower organic matter content (Fig. 2), reflecting glacio-lacustrine processes. With regional evidence of glacial advance during this time Discussion period (Wiles and Calkin 1994), it is possible that the primary inlet stream to Upper Russian Lake was Sediment d N in Upper Russian Lake has fluctuated impacted by glacial ice that extended northward from around a mean of 4.5% for most of the * 4000 years the nearby Harding Icefield. Inputs of silt-rich, turbid represented in our core, suggesting that spawner glacial meltwater could have led to degraded salmon abundance has been relatively consistent on time- spawning conditions in the inlet stream and, by scales similar to or greater than sampling resolution limiting light penetration, to reduced sockeye salmon over much of this time period. A major multi- carrying capacity in the lake (Koenings et al. 1986; centennial decline in inferred salmon abundance, Milner and Petts 1994). however, occurred from * 100 BCE to 550 CE Most Alaska nursery lakes show clear trends toward followed by a shorter decline from * 900 to 1000 CE. lower d N since the late 1800s, following the onset of These shifts coincide with inferred salmon declines in commercial salmon fisheries (Finney et al. 2002; both Karluk and Akalura Lakes on Kodiak Island, Rogers et al. 2013), which typically harvest half or [ 400 km southwest of our study area (Fig. 4), the more of each year’s spawning run. Upper Russian only other lakes with salmon reconstructions dating Lake sediments, however, show no sign of such back to this time period (Finney et al. 2002). This depletion. Several other nursery lakes that have been finding provides further evidence for an ancient, studied, however, also fail to display lower d Nin prolonged and widespread decline in salmon produc- upper sediments, presumably a consequence of the tion, and supports the hypothesis that high-magnitude, relatively recent development of commercial fisheries Fig. 4 Comparison of Karluk Upper Russian Akalura salmonreconstruction 10 6.5 among UpperRussian Lake, and Akaluraand Karluk lakes on KodiakIsland (Finney et al. 2002) 5.5 4.5 3.5 2 3 -250 0 250 500 750 1000 1250 1500 1750 2000 BCE Calendar Age CE Karluk and Upper Russian δ N (‰) Akalura δ N (‰) 74 J Paleolimnol (2018) 60:67–75 that intercept stocks bound for these lakes (Rogers Further research into the ocean environment during et al. 2013). An unknown portion of the Russian these times may shed light on how climate influences River’s late run has been harvested by Cook Inlet’s salmon production in the ocean. As a working commercial fisheries since they began, shown in hypothesis, the climate conditions that led to signif- recent years by genetic stock identification, to average icant first-millennium AD glacial advances (Wiles and 28% (2006–2008 data; Eskelin et al. 2013), so it is Calkin 1994) in this part of the Kenai Peninsula (cold possible that commercial harvest has not impacted and/or wet conditions), may have created unfavorable escapement enough to elicit the dramatic N deple- ocean conditions during critical times during the tion seen in other systems. Harvest rates on Russian marine phase of these stocks of Gulf of Alaska River salmon have presumably increased in recent sockeye. Interestingly, these conditions were different decades (Schoen et al. 2017), with the growth of sport from those during glacial advances in the Little Ice fisheries that harvest approximately 50% of the early Age, a time for which most available sediment core run and 29% of the late run and a personal-use fishery data from Alaskan sites suggests high salmon abun- that harvests 7% of the late run (Begich and Pawluk dance (Finney et al. 2002; Rogers et al. 2013). Our 2007; Eskelin et al. 2013; Fair et al. 2013). This Upper Russian core, uniquely from a primarily clear- additional harvest may be too recent to be reflected in water lake with periodic glacial influence, also shows Upper Russian Lake sediments (Rogers et al. 2013), relatively high d N during the Little Ice Age. Future especially given the relatively low temporal resolution climate projections and management strategies should of our core subsampling. Additionally, these fisheries focus on understanding how climate regimes not only developed during a period of favorable ocean condi- impact prey availability for salmon at sea, but also tions and exceptionally high abundance for many influence local conditions for spawners and juveniles. salmon stocks, including Cook Inlet sockeye salmon Acknowledgements This analysis was part of a larger project (Irvine and Ruggerone 2016). funded by Alaska EPSCoR National Science Foundation award Our results provide further evidence for synchrony #O1A-1208927 and the State of Alaska. Support for Bruce in salmon production regimes at centennial timescales Finney was assisted by NSF award #1521365. We thank Kristi over the last few millennia (Finney et al. 2002). Wallace from USGS for tephra analysis, as well as use of her tephra lab for a variety of sampling activities. We acknowledge Fluctuations in Upper Russian Lake salmon abun- the many researchers who work for the Alaska Department of dance inferred from d N over the last 500 years are, Fish and Game and collected long-term data on commercial and however, relatively minor compared to records from sport catch and escapement of Kenai River and Russian River other Alaskan nursery lakes (Rogers et al. 2013). salmon, and especially Mark Willette for providing initial guidance. We also thank Dr. David Fortin, Nore Preat, Koen Du Resolving this scale of fluctuation is likely compro- Ryker, Phillip Kempf, Nicole Warner, Courtney Breest, Scott mised because of the low time-resolution of our Cunfer, Nancy McCarthy, and Frank McCarthy for field and record, but it could also reflect the fact that individual laboratory assistance. The findings and conclusionsin this article systems may react differently to regional climate are those of theauthors and do not necessarilyrepresent the view of the U.S.Fish and Wildlife Service. change on decadal scales (Rogers et al. 2013). The temporal resolution of our data are sufficient to Open Access This article is distributed under the terms of the compare over longer timescales, and suggest coherent Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits unre- patterns of higher magnitude and longer duration at stricted use, distribution, and reproduction in any medium, centennial and longer scales. provided you give appropriate credit to the original In summary, our results from Upper Russian Lake, author(s) and the source, provide a link to the Creative Com- together with previous research (Finney et al. 2002), mons license, and indicate if changes were made. suggest dramatic multi-centennial periods of lower salmon abundance in multiple systems across a wide area of the northern Gulf of Alaska. 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Journal of Paleolimnology – Springer Journals

Published: Mar 13, 2018

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