COMMENTARY
COMMENTARY
Shifting patterns in Pacific climate, West Coast salmon survival rates, and increased volatility in ecosystem services Nathan J. Mantua1 Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Santa Cruz, CA 95060
Although Pacific salmon never swim within 2,000 km of the equatorial Pacific Ocean, this does not mean they are beyond the reach of El Niño and the Southern Oscillation (ENSO). Pacific salmon habitats are subject to robust long-distance climate linkages; tropical ENSO indicators are well correlated with the dominant pattern of North Pacific climate variations, the Pacific Decadal Oscillation (PDO), and with the dominant pattern of North America’s 20th-century salmon landings (1, 2). As such, might a change in the dominant flavor of ENSO variability and its link with North Pacific climate also affect patterns of Pacific salmon population dynamics? Kilduff et al. (3) show that, indeed, a shift in Pacific climate has a strong and previously unidentified signature in West Coast salmon survival rates; they also suggest that this shift increased the synchrony of survival rate variations for dozens of salmon populations across ∼2,000 km of coastline and destabilized the delivery of services these salmon provide to people and ecosystems. Coherent Patterns in Pacific Climate and Salmon Dynamics
The recent history of Pacific salmon (Onchorhynchus spp.) production offers valuable fodder for studies of climate impacts on aquatic ecosystems. As with many other species, scientists have uncovered clear evidence that large-scale climate variations synchronized aspects of Pacific salmon population dynamics (4). At the basin scale, variations in the PDO were especially important for variations in Alaska’s 20th-century pink, chum, and sockeye salmon production, which typically contributes ∼75% of the annual total salmon landings in North America (1, 2). At the same time, other research reveals a high level of asynchrony in the dynamics of near and distant individual salmon populations and regional-scale population groups (5). This apparent paradox has been hypothesized to result from the yin and yang of shared aggregate www.pnas.org/cgi/doi/10.1073/pnas.1513511112
population responses to common large-scale climate forcing versus localized divergent responses related to diversity in habitats, genetics, and life history traits that exist between and within individual populations (6). Kilduff et al. (3) analyze patterns of covariation in regionally aggregated postrelease survival rates for hatchery-origin Chinook and coho salmon populations from southeast
The dominant patterns of hatchery-origin coho and Chinook salmon survival rates from southeast Alaska to California show a strong negative correlation with the NPGO sea surface temperature pattern. Alaska to California. They find increasing synchrony in survival rates between the two species within shared regions from 1980 to 2006. Within both coho and Chinook salmon population groups, the degree of across-region covariation showed no obvious trends but remained high throughout the study period. They also find that, across regional groups from southeast Alaska to central California, dominant survival rate patterns are best correlated with a basin-scale pattern of Pacific climate variations, the North Pacific Gyre Oscillation (NPGO). They make the intriguing argument that increasing variance in the NPGO caused the observed increases in survival rate synchrony. This is a unique contribution for its focus on a changing ocean, rather than altered freshwater habitats and associated life history patterns, as the basis for increasing synchrony in the population dynamics of Pacific salmon. It also highlights the fact that there is more to
climate impacts on broad-scale patterns in Pacific salmon population dynamics than the PDO. Multiple studies have identified coherent patterns of salmon productivity, abundance, and survival rates at length scales spanning a few hundred kilometers of coastline. These studies have also found that warm coastal zone ocean temperatures just before and during the early marine period tend to coincide with increased production and abundance of northern pink, chum, and sockeye salmon population groups, but reduced production and abundance of more southern population groups (e.g., ref. 5 and references therein). Similar results were found with patterns of covarying survival rate variations for hatchery-origin Chinook salmon from southeast Alaska to California, again with regional-scale patterns of covariation, and an association between reduced survival rates and warmerthan-average coastal ocean temperatures near the ocean entry points in the first summer at sea (7). One way to understand the PDO’s effect on salmon production across broad spatial scales is that it tends to synchronize ocean temperature variations along the entire west coast of North America, which seems to be important for many Pacific salmon populations. What is new and intriguing about the analysis by Kilduff et al. (3) is that the dominant patterns of hatchery-origin coho and Chinook salmon survival rates from southeast Alaska to California show a strong negative correlation with the NPGO sea surface temperature pattern. The broad-scale survival rate pattern has maximum loadings on regional population groups between Vancouver Island and southern Oregon, in the heart of the range of these species where their ocean entry points are at the northern end of the highly productive but variable California Current System (CCS). Author contributions: N.J.M. wrote the paper. The author declares no conflict of interest. See companion article on page 10962. 1
Email: [email protected].
PNAS | September 1, 2015 | vol. 112 | no. 35 | 10823–10824
One possibility is that NPGO variations more optimally synchronize coastal zone ocean temperatures and related ocean properties for these populations than the PDO does (8). Evidence for important NPGO effects on CCS marine ecosystems includes high correlations between the NPGO index and transport in the North Pacific current, Northeast Pacific salinity, dissolved oxygen, nutrient concentrations, and West Coast plankton (8). Again, the coast-wide patterns of covarying coho and Chinook salmon survival rates are likely being coordinated by the NPGO pattern’s large spatial scale that overlays directly onto the region of ocean entry and early marine life for these salmon populations. Portfolio Effects in Pacific Salmon Population Complexes
In terms of aggregate salmon production and the ecosystem services salmon provide, asynchrony among the dynamics of individual populations (stocks) within a larger population complex (the portfolio) reduces the overall portfolio variance, the so-called portfolio effect, which is important for the reliability of services that salmon provide to fisheries and salmon-dependent ecosystems (9). A diminished portfolio effect over recent decades, expressed as increased synchrony in population dynamics among individual stocks within population complexes, has been noted for Chinook salmon in major production basins at the southern end of their range (10, 11). In these basins, freshwater habitats have been lost behind impassable dams and substantially degraded and/or simplified by land and water use practices, and hatchery-origin salmon production has increased substantially. Each factor can reduce the genetic, spatial, and life history diversity that supports a diverse suite of population-level responses to common environmental variations (6, 9). In contrast, no such declines have been detected in the portfolio effect for Bristol Bay, Alaska sockeye salmon, a 100% natural-origin complex of several hundred discrete populations that spawn and rear in pristine habitats and support an intense commercial fishery that began in the late 1800s (10). An issue not explored by Kilduff et al. (3) is the fact that their regional-scale averaging of individual hatchery population survival rate data can reduce fine-scale variance while emphasizing the regional-scale shared population responses. Because of data gaps for individual populations, they chose to aggregate 176 individual hatchery records into 10 coho and 8 Chinook salmon regional population groups with nearly continuous time series for the 27-y study period. Related analysis of the
10824 | www.pnas.org/cgi/doi/10.1073/pnas.1513511112
It has been suggested that the limited biodiversity of hatchery‐origin populations makes them more susceptible to synchronization in response to large‐scale climate forcing than natural-origin populations (14), and it is hard not to think that the combined influences of hatcheries and shifts in climate patterns contributed to the observed pattern of increased survival rate synchrony. For instance, a recent analysis of hatcheries in California’s Central Valley reveals substantial changes in late20th-century rearing and release practices that reduced early life history diversity and increased straying rates, and likely contributed to an increase in abundance synchrony within that basin’s Chinook salmon population complex (15). Of special interest here are hatchery and fishing practices that narrow similar aspects of salmon life history diversity across hatchery programs for these two species. For instance,
hatchery practices that concentrate the timing of juvenile release periods on similar dates, or produce ocean-ready juveniles of similar size, can increase the synchrony of postrelease survival rates (15, 16). Another potentially important mechanism is suggested by the population modeling done by Kilduff et al. (3) for natural-origin stocks, where they show that the closer that Chinook salmon age structure gets to that of coho salmon, the larger the impact that shared ocean survival rate variations have on synchronizing cross-species abundance variations. This is relevant because hatchery programs can produce Chinook salmon with a younger age at maturity than the natural populations they are founded on (closer to that of coho salmon) because of unnatural mating policies (17) and more rapid juvenile growth rates that are correlated with earlier age at maturity (18). Likewise, ocean harvest of immature Chinook salmon selects for a younger age at maturity (19). Future studies should explicitly evaluate how hatchery and harvest practices influence synchronization among populations within and between regions to illuminate the impact of management on the buffering capacity and stability of stock complexes and broader-scale groupings (14–16). More broadly, it is becoming increasingly important to evaluate hatchery and harvest practices, and restoration alternatives, with an eye toward protecting and improving portfolio performance to support the sustainability of salmonrelated ecosystem services (6, 9–11, 14–16).
1 Mantua NJ, Hare SR, Zhang Y, Wallace JM, Francis RC (1997) A Pacific interdecadal climate oscillation with impacts on salmon production. Bull Am Meteorol Soc 78(6):1069–1079. 2 Hare SR, Mantua NJ, Francis RC (1999) Inverse production regimes: Alaska and West Coast Pacific salmon. Fisheries 24(1):6–14. 3 Kilduff DP, Di Lorenzo E, Botsford LW, Teo SLH (2015) Changing central Pacific El Niños reduce stability of North American salmon survival rates. Proc Natl Acad Sci USA 112:10962–10966. 4 Beamish RJ (1993) Climate and exceptional fish production off the west coast of North America. Can J Fish Aquat Sci 50:2270–2291. 5 Mueter FJ, Pyper BJ, Peterman RM (2005) Relationships between coastal ocean conditions and survival rates of Northeast Pacific salmon at multiple lags. Trans Am Fish Soc 134(1):105–119. 6 Hilborn R, Quinn TP, Schindler DE, Rogers DE (2003) Biocomplexity and fisheries sustainability. Proc Natl Acad Sci USA 100(11):6564–6568. 7 Sharma R, et al. (2013) Relating spatial and temporal scales of climate and ocean variability to survival of Pacific Northwest Chinook salmon (Oncorhynchus tshawytscha). Fish Oceanogr 22(1):14–31. 8 Di Lorenzo E, et al. (2013) Synthesis of Pacific Ocean climate and ecosystem dynamics. Oceanogr 26(4):68–81. 9 Schindler DE, et al. (2010) Population diversity and the portfolio effect in an exploited species. Nature 465(7298):609–612. 10 Moore JW, McClure M, Rogers LA, Schindler DE (2010) Synchronization and portfolio performance of threatened salmon. Conserv Lett 3(5):340–348. 11 Carlson SM, Satterthwaite WH (2011) Weakened portfolio effect in a collapsed salmon population complex. Can J Fish Aquat Sci 68(9): 1579–1589.
12 Teo SLH, Botsford LW, Hastings A (2009) Spatio-temporal covariability in coho salmon (Oncorhynchus kisutch) survival, from California to southeast Alaska. Deep Sea Res Part II Top Stud Oceanogr 56(24):2570–2578. 13 Kilduff D, Botsford L, Teo S (2014) Spatial and temporal covariability in early ocean survival of Chinook salmon (Oncorhynchus tshawytscha) along the west coast of North America. ICES J Mar Sci 71(7):1671–1682. 14 Lindley ST, et al. (2009) What caused the Sacramento River fall Chinook stock collapse? NOAA Technical Memorandum. NMFS no. NOAA-TM-NMFS-SWFSC-447 (NOAA, Santa Cruz, CA). 15 Huber ER, Carlson SM (2015) Temporal trends in hatchery releases of fall-run Chinook salmon in California’s Central Valley. San Francisco Estuary and Watershed Sci 13(2):article 3. 16 Satterthwaite WH, et al. (2014) Match-mismatch dynamics and the relationship between ocean entry timing and relative ocean recoveries of Central Valley fall run Chinook salmon. Mar Ecol Prog Ser 511:237–248. 17 Hankin DG, Fitzgibbons J, Chen Y (2009) Unnatural random mating policies select for younger age at maturity in hatchery Chinook salmon populations. Can J Fish Aquat Sci 66(9): 1505–1521. 18 Vollestad LA, Peterson J, Quinn TP (2004) Effects of freshwater and marine growth rates on early maturity in male Coho and Chinook salmon. Trans Am Fish Soc 133(3):495–503. 19 Ricker WE (1981) Changes in the average size and average age of Pacific salmon. Can J Fish Aquat Sci 38(12):1636–1656.
same survival rate time series used by Kilduff et al. (3) included a wide range of pairwise correlation coefficients, from ∼1 to −0.25 at hatchery distances less than 250 km for both Chinook salmon and coho salmon (leastsquares fitted correlations at 250-km distance are about 0.4 for both species), respectively (12, 13). These results indicate that substantial response diversity does, indeed, exist within these hatchery-origin coho and Chinook salmon populations when their dynamics are considered at finer spatial scales. Interacting Influences of Climate, Hatcheries, and Fishing on Patterns of Salmon Synchrony
Mantua
COMMENTARY
Shifting patterns in Pacific climate, West Coast salmon survival rates, and increased volatility in ecosystem services Nathan J. Mantua1 Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Santa Cruz, CA 95060
Although Pacific salmon never swim within 2,000 km of the equatorial Pacific Ocean, this does not mean they are beyond the reach of El Niño and the Southern Oscillation (ENSO). Pacific salmon habitats are subject to robust long-distance climate linkages; tropical ENSO indicators are well correlated with the dominant pattern of North Pacific climate variations, the Pacific Decadal Oscillation (PDO), and with the dominant pattern of North America’s 20th-century salmon landings (1, 2). As such, might a change in the dominant flavor of ENSO variability and its link with North Pacific climate also affect patterns of Pacific salmon population dynamics? Kilduff et al. (3) show that, indeed, a shift in Pacific climate has a strong and previously unidentified signature in West Coast salmon survival rates; they also suggest that this shift increased the synchrony of survival rate variations for dozens of salmon populations across ∼2,000 km of coastline and destabilized the delivery of services these salmon provide to people and ecosystems. Coherent Patterns in Pacific Climate and Salmon Dynamics
The recent history of Pacific salmon (Onchorhynchus spp.) production offers valuable fodder for studies of climate impacts on aquatic ecosystems. As with many other species, scientists have uncovered clear evidence that large-scale climate variations synchronized aspects of Pacific salmon population dynamics (4). At the basin scale, variations in the PDO were especially important for variations in Alaska’s 20th-century pink, chum, and sockeye salmon production, which typically contributes ∼75% of the annual total salmon landings in North America (1, 2). At the same time, other research reveals a high level of asynchrony in the dynamics of near and distant individual salmon populations and regional-scale population groups (5). This apparent paradox has been hypothesized to result from the yin and yang of shared aggregate www.pnas.org/cgi/doi/10.1073/pnas.1513511112
population responses to common large-scale climate forcing versus localized divergent responses related to diversity in habitats, genetics, and life history traits that exist between and within individual populations (6). Kilduff et al. (3) analyze patterns of covariation in regionally aggregated postrelease survival rates for hatchery-origin Chinook and coho salmon populations from southeast
The dominant patterns of hatchery-origin coho and Chinook salmon survival rates from southeast Alaska to California show a strong negative correlation with the NPGO sea surface temperature pattern. Alaska to California. They find increasing synchrony in survival rates between the two species within shared regions from 1980 to 2006. Within both coho and Chinook salmon population groups, the degree of across-region covariation showed no obvious trends but remained high throughout the study period. They also find that, across regional groups from southeast Alaska to central California, dominant survival rate patterns are best correlated with a basin-scale pattern of Pacific climate variations, the North Pacific Gyre Oscillation (NPGO). They make the intriguing argument that increasing variance in the NPGO caused the observed increases in survival rate synchrony. This is a unique contribution for its focus on a changing ocean, rather than altered freshwater habitats and associated life history patterns, as the basis for increasing synchrony in the population dynamics of Pacific salmon. It also highlights the fact that there is more to
climate impacts on broad-scale patterns in Pacific salmon population dynamics than the PDO. Multiple studies have identified coherent patterns of salmon productivity, abundance, and survival rates at length scales spanning a few hundred kilometers of coastline. These studies have also found that warm coastal zone ocean temperatures just before and during the early marine period tend to coincide with increased production and abundance of northern pink, chum, and sockeye salmon population groups, but reduced production and abundance of more southern population groups (e.g., ref. 5 and references therein). Similar results were found with patterns of covarying survival rate variations for hatchery-origin Chinook salmon from southeast Alaska to California, again with regional-scale patterns of covariation, and an association between reduced survival rates and warmerthan-average coastal ocean temperatures near the ocean entry points in the first summer at sea (7). One way to understand the PDO’s effect on salmon production across broad spatial scales is that it tends to synchronize ocean temperature variations along the entire west coast of North America, which seems to be important for many Pacific salmon populations. What is new and intriguing about the analysis by Kilduff et al. (3) is that the dominant patterns of hatchery-origin coho and Chinook salmon survival rates from southeast Alaska to California show a strong negative correlation with the NPGO sea surface temperature pattern. The broad-scale survival rate pattern has maximum loadings on regional population groups between Vancouver Island and southern Oregon, in the heart of the range of these species where their ocean entry points are at the northern end of the highly productive but variable California Current System (CCS). Author contributions: N.J.M. wrote the paper. The author declares no conflict of interest. See companion article on page 10962. 1
Email: [email protected].
PNAS | September 1, 2015 | vol. 112 | no. 35 | 10823–10824
One possibility is that NPGO variations more optimally synchronize coastal zone ocean temperatures and related ocean properties for these populations than the PDO does (8). Evidence for important NPGO effects on CCS marine ecosystems includes high correlations between the NPGO index and transport in the North Pacific current, Northeast Pacific salinity, dissolved oxygen, nutrient concentrations, and West Coast plankton (8). Again, the coast-wide patterns of covarying coho and Chinook salmon survival rates are likely being coordinated by the NPGO pattern’s large spatial scale that overlays directly onto the region of ocean entry and early marine life for these salmon populations. Portfolio Effects in Pacific Salmon Population Complexes
In terms of aggregate salmon production and the ecosystem services salmon provide, asynchrony among the dynamics of individual populations (stocks) within a larger population complex (the portfolio) reduces the overall portfolio variance, the so-called portfolio effect, which is important for the reliability of services that salmon provide to fisheries and salmon-dependent ecosystems (9). A diminished portfolio effect over recent decades, expressed as increased synchrony in population dynamics among individual stocks within population complexes, has been noted for Chinook salmon in major production basins at the southern end of their range (10, 11). In these basins, freshwater habitats have been lost behind impassable dams and substantially degraded and/or simplified by land and water use practices, and hatchery-origin salmon production has increased substantially. Each factor can reduce the genetic, spatial, and life history diversity that supports a diverse suite of population-level responses to common environmental variations (6, 9). In contrast, no such declines have been detected in the portfolio effect for Bristol Bay, Alaska sockeye salmon, a 100% natural-origin complex of several hundred discrete populations that spawn and rear in pristine habitats and support an intense commercial fishery that began in the late 1800s (10). An issue not explored by Kilduff et al. (3) is the fact that their regional-scale averaging of individual hatchery population survival rate data can reduce fine-scale variance while emphasizing the regional-scale shared population responses. Because of data gaps for individual populations, they chose to aggregate 176 individual hatchery records into 10 coho and 8 Chinook salmon regional population groups with nearly continuous time series for the 27-y study period. Related analysis of the
10824 | www.pnas.org/cgi/doi/10.1073/pnas.1513511112
It has been suggested that the limited biodiversity of hatchery‐origin populations makes them more susceptible to synchronization in response to large‐scale climate forcing than natural-origin populations (14), and it is hard not to think that the combined influences of hatcheries and shifts in climate patterns contributed to the observed pattern of increased survival rate synchrony. For instance, a recent analysis of hatcheries in California’s Central Valley reveals substantial changes in late20th-century rearing and release practices that reduced early life history diversity and increased straying rates, and likely contributed to an increase in abundance synchrony within that basin’s Chinook salmon population complex (15). Of special interest here are hatchery and fishing practices that narrow similar aspects of salmon life history diversity across hatchery programs for these two species. For instance,
hatchery practices that concentrate the timing of juvenile release periods on similar dates, or produce ocean-ready juveniles of similar size, can increase the synchrony of postrelease survival rates (15, 16). Another potentially important mechanism is suggested by the population modeling done by Kilduff et al. (3) for natural-origin stocks, where they show that the closer that Chinook salmon age structure gets to that of coho salmon, the larger the impact that shared ocean survival rate variations have on synchronizing cross-species abundance variations. This is relevant because hatchery programs can produce Chinook salmon with a younger age at maturity than the natural populations they are founded on (closer to that of coho salmon) because of unnatural mating policies (17) and more rapid juvenile growth rates that are correlated with earlier age at maturity (18). Likewise, ocean harvest of immature Chinook salmon selects for a younger age at maturity (19). Future studies should explicitly evaluate how hatchery and harvest practices influence synchronization among populations within and between regions to illuminate the impact of management on the buffering capacity and stability of stock complexes and broader-scale groupings (14–16). More broadly, it is becoming increasingly important to evaluate hatchery and harvest practices, and restoration alternatives, with an eye toward protecting and improving portfolio performance to support the sustainability of salmonrelated ecosystem services (6, 9–11, 14–16).
1 Mantua NJ, Hare SR, Zhang Y, Wallace JM, Francis RC (1997) A Pacific interdecadal climate oscillation with impacts on salmon production. Bull Am Meteorol Soc 78(6):1069–1079. 2 Hare SR, Mantua NJ, Francis RC (1999) Inverse production regimes: Alaska and West Coast Pacific salmon. Fisheries 24(1):6–14. 3 Kilduff DP, Di Lorenzo E, Botsford LW, Teo SLH (2015) Changing central Pacific El Niños reduce stability of North American salmon survival rates. Proc Natl Acad Sci USA 112:10962–10966. 4 Beamish RJ (1993) Climate and exceptional fish production off the west coast of North America. Can J Fish Aquat Sci 50:2270–2291. 5 Mueter FJ, Pyper BJ, Peterman RM (2005) Relationships between coastal ocean conditions and survival rates of Northeast Pacific salmon at multiple lags. Trans Am Fish Soc 134(1):105–119. 6 Hilborn R, Quinn TP, Schindler DE, Rogers DE (2003) Biocomplexity and fisheries sustainability. Proc Natl Acad Sci USA 100(11):6564–6568. 7 Sharma R, et al. (2013) Relating spatial and temporal scales of climate and ocean variability to survival of Pacific Northwest Chinook salmon (Oncorhynchus tshawytscha). Fish Oceanogr 22(1):14–31. 8 Di Lorenzo E, et al. (2013) Synthesis of Pacific Ocean climate and ecosystem dynamics. Oceanogr 26(4):68–81. 9 Schindler DE, et al. (2010) Population diversity and the portfolio effect in an exploited species. Nature 465(7298):609–612. 10 Moore JW, McClure M, Rogers LA, Schindler DE (2010) Synchronization and portfolio performance of threatened salmon. Conserv Lett 3(5):340–348. 11 Carlson SM, Satterthwaite WH (2011) Weakened portfolio effect in a collapsed salmon population complex. Can J Fish Aquat Sci 68(9): 1579–1589.
12 Teo SLH, Botsford LW, Hastings A (2009) Spatio-temporal covariability in coho salmon (Oncorhynchus kisutch) survival, from California to southeast Alaska. Deep Sea Res Part II Top Stud Oceanogr 56(24):2570–2578. 13 Kilduff D, Botsford L, Teo S (2014) Spatial and temporal covariability in early ocean survival of Chinook salmon (Oncorhynchus tshawytscha) along the west coast of North America. ICES J Mar Sci 71(7):1671–1682. 14 Lindley ST, et al. (2009) What caused the Sacramento River fall Chinook stock collapse? NOAA Technical Memorandum. NMFS no. NOAA-TM-NMFS-SWFSC-447 (NOAA, Santa Cruz, CA). 15 Huber ER, Carlson SM (2015) Temporal trends in hatchery releases of fall-run Chinook salmon in California’s Central Valley. San Francisco Estuary and Watershed Sci 13(2):article 3. 16 Satterthwaite WH, et al. (2014) Match-mismatch dynamics and the relationship between ocean entry timing and relative ocean recoveries of Central Valley fall run Chinook salmon. Mar Ecol Prog Ser 511:237–248. 17 Hankin DG, Fitzgibbons J, Chen Y (2009) Unnatural random mating policies select for younger age at maturity in hatchery Chinook salmon populations. Can J Fish Aquat Sci 66(9): 1505–1521. 18 Vollestad LA, Peterson J, Quinn TP (2004) Effects of freshwater and marine growth rates on early maturity in male Coho and Chinook salmon. Trans Am Fish Soc 133(3):495–503. 19 Ricker WE (1981) Changes in the average size and average age of Pacific salmon. Can J Fish Aquat Sci 38(12):1636–1656.
same survival rate time series used by Kilduff et al. (3) included a wide range of pairwise correlation coefficients, from ∼1 to −0.25 at hatchery distances less than 250 km for both Chinook salmon and coho salmon (leastsquares fitted correlations at 250-km distance are about 0.4 for both species), respectively (12, 13). These results indicate that substantial response diversity does, indeed, exist within these hatchery-origin coho and Chinook salmon populations when their dynamics are considered at finer spatial scales. Interacting Influences of Climate, Hatcheries, and Fishing on Patterns of Salmon Synchrony
Mantua
