• Ecological effects of invasive European bird cherry (Prunus padus) on salmonid food webs in Anchorage, Alaska streams

      Roon, David A.; Wipfli, Mark; Prakash, Anupma; Wurtz, Tricia (2011-08)
      Invasive species are a concern worldwide as they can displace native species, reduce biodiversity, and disrupt ecological processes. European bird cherry (Prunus padus) (EBC) is an invasive ornamental tree that is rapidly spreading and possibly displacing native trees along streams in parts of urban Alaska. The objectives of this study were to: 1) map the current distribution of EBC along two Anchorage streams, Campbell and Chester creeks, and 2) determine the effects of EBC on selected ecological processes linked to stream salmon food webs. Data from the 2009 and 2010 field seasons showed: EBC was widely distributed along Campbell and Chester creeks; EBC leaf litter in streams broke down rapidly and supported similar shredder communities to native tree species; and EBC foliage supported significantly less terrestrial invertebrate biomass relative to native deciduous tree species, and contributed significantly less terrestrial invertebrate biomass to streams compared to mixed native vegetation, but riparian EBC did not appear to affect the amount of terrestrial invertebrate prey ingested by juvenile coho salmon (Oncorhynchus kisutch). Although ecological processes did not seem to be dramatically affected by EBC presence, lowered prey abundance as measured in this study may have long-term consequences for stream-rearing fishes as EBC continues to spread over time.
    • Impacts of a top predator (Esox lucius) on salmonids in Southcentral Alaska: genetics, connectivity, and vulnerability

      Jalbert, Chase S.; Falke, Jeffrey; Westley, Peter; López, J. Andrés; Dunker, Kristine (2018-12)
      Worldwide invasion and range expansion of northern pike (pike; Esox lucius) have been linked to the decline of native fishes and new techniques are needed to assess the effects of invasion over broad geographic scales. In Alaska, pike are native north and west of the Alaska Mountain Range but were introduced into Southcentral Alaska in the 1950s and again in the 1970s. To investigate the history of the invasion into Southcentral Alaska, I identified 7,889 single nucleotide polymorphisms (SNPs) from three native and seven introduced populations in Alaska and examined genetic diversity, structure, and affinities of native and invasive pike. Pike exhibited low genetic variability in native populations (mean heterozygosity = 0.0360 and mean π = 0.000241) and further reductions in introduced populations (mean heterozygosity = 0.0227 and mean π = 0.000131), which suggests a bottleneck following introduction. Population differentiation was high among some populations (global FST = 0.424; max FST = 0.668) when compared to other freshwater fishes. I identified five genetically distinct clusters of populations, consisting of three native groups, a single Susitna River basin invasive group, and a Kenai Peninsula group, with little evidence of admixture among groups. The extremely reduced genetic diversity observed in invasive northern pike populations does not appear to affect their invasion success as the species range Southcentral Alaska continues to expand. To assess the vulnerability of five species of Pacific salmon (Oncorhynchus spp.) to the invasion, I combined intrinsic potential habitat modeling, connectivity estimates, and Bayesian networks across 22,875km of stream reaches in the Matanuska-Susitna basin, Alaska, USA. Pink salmon were the most vulnerable species, with 15.2% (2,458 km) of their range identified as "highly" vulnerable. They were followed closely by chum salmon (14.8%) and coho salmon (14.7%). Finally, analysis of the intersection of vulnerable salmon habitats revealed 1,001 km of streams that were highly vulnerable for all five Pacific salmon. This framework is easy to implement, adaptable to any species or region, and cost effective. With increasing threats of species introductions, fishery managers need new tools like those described here to efficiently identify critical areas shared by multiple species, where management actions can have the greatest impact.
    • The use of aerial imagery to map in-stream physical habitat related to summer distribution of juvenile salmonids in a Southcentral Alaskan stream

      Perschbacher, Jeff; Margraf, F. Joseph; Hasbrouck, James; Wipfli, Mark; Prakash, Anupma (2011-12)
      Airborne remote sensing (3-band multispectral imagery) was used to assess in-stream physical habitat related to summer distributions of juvenile salmonids in a Southcentral Alaskan stream. The objectives of this study were to test the accuracy of using remote sensing spectral and spatial classification techniques to map in-stream physical habitat, and test hypotheses of spatial segregation of ranked densities of juvenile chinook salmon Oncorhynchus tschwytscha, coho salmon O. kisutch, and rainbow trout O. mykiss, related to stream order and drainage. To relate habitat measured with remote sensing to fish densities, a supervised classification technique based on spectral signature was used to classify riffles, non-riffles, vegetation, shade, gravel, and eddy drop zones, with a spatial technique used to classify large woody debris. Combining the two classification techniques resulted in an overall user's accuracy of 85%, compared to results from similar studies (11-80%). Densities of juvenile salmonids was found to be significantly different between stream orders, but not between the two major drainages. Habitat data collected along a 500-meter stream reach were used successfully to map in-stream physical habitat for six river-kilometers of a fourth-order streams. The use of relatively inexpensive aerial imagery to classify in-stream physical habitats is cost effective and repeatable for mapping over large areas, and should be considered an effective tool for fisheries and land-use managers.