Introduced northern pike predation on salmonids in southcentral alaska

Northern pike (Esox lucius) are opportunistic predators that can switch to alternative prey species after preferred prey have declined. This trophic adaptability allows invasive pike to have negative effects on aquatic food webs. In Southcentral Alaska, invasive pike are a substantial concern because they have spread to important spawning and rearing habitat for salmonids and are hypothesised to be responsible for recent salmonid declines. We described the relative importance of salmonids and other prey species to pike diets in the Deshka River and Alexander Creek in Southcentral Alaska. Salmonids were once abundant in both rivers, but they are now rare in Alexander Creek. In the Deshka River, we found that juvenile Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) dominated pike diets and that small pike consumed more of these salmonids than large pike. In Alexander Creek, pike diets reflected the distribution of spawning salmonids, which decrease with distance upstream. Although salmonids dominated pike diets in the lowest reach of the stream, Arctic lamprey (Lampetra camtschatica) and slimy sculpin (Cottus cognatus) dominated pike diets in the middle and upper reaches. In both rivers, pike density did not influence diet and pike consumed smaller prey items than predicted by their gape-width. Our data suggest that (1) juvenile salmonids are a dominant prey item for pike, (2) small pike are the primary consumers of juvenile salmonids and (3) pike consume other native fish species when juvenile salmonids are less abundant. Implications of this trophic adaptability are that invasive pike can continue to increase while driving multiple species to low abundance

Potential of Environmental DNA to Evaluate Northern Pike (Esox lucius) Eradication Efforts: An Experimental Test and Case Study.

Determining the success of invasive species eradication efforts is challenging because populations at very low abundance are difficult to detect. Environmental DNA (eDNA) sampling has recently emerged as a powerful tool for detecting rare aquatic animals; however, detectable fragments of DNA can persist over time despite absence of the targeted taxa and can therefore complicate eDNA sampling after an eradication event. This complication is a large concern for fish eradication efforts in lakes since killed fish can sink to the bottom and slowly decay. DNA released from these carcasses may remain detectable for long periods. Here, we evaluated the efficacy of eDNA sampling to detect invasive Northern pike (Esox lucius) following piscicide eradication efforts in southcentral Alaskan lakes. We used field observations and experiments to test the sensitivity of our Northern pike eDNA assay and to evaluate the persistence of detectable DNA emitted from Northern pike carcasses. We then used eDNA sampling and traditional sampling (i.e., gillnets) to test for presence of Northern pike in four lakes subjected to a piscicide-treatment designed to eradicate this species. We found that our assay could detect an abundant, free-roaming population of Northern pike and could also detect low-densities of Northern pike held in cages. For these caged Northern pike, probability of detection decreased with distance from the cage. We then stocked three lakes with Northern pike carcasses and collected eDNA samples 7, 35 and 70 days post-stocking. We detected DNA at 7 and 35 days, but not at 70 days. Finally, we collected eDNA samples ~ 230 days after four lakes were subjected to piscicide-treatments and detected Northern pike DNA in 3 of 179 samples, with a single detection at each of three lakes, though we did not catch any Northern pike in gillnets. Taken together, we found that eDNA can help to inform eradication efforts if used in conjunction with multiple lines of inquiry and sampling is delayed long enough to allow full degradation of DNA in the water

Correction: Potential of Environmental DNA to Evaluate Northern Pike (Esox lucius) Eradication Efforts: An Experimental Test and Case Study.

[This corrects the article DOI: 10.1371/journal.pone.0162277.]

Data from: Potential of environmental DNA to evaluate Northern pike (Esox lucius) eradication efforts: an experimental test and case study

Determining the success of invasive species eradication efforts is challenging because populations at very low abundance are difficult to detect. Environmental DNA (eDNA) sampling has recently emerged as a powerful tool for detecting rare aquatic animals; however, detectable fragments of DNA can persist over time despite absence of the targeted taxa and can therefore complicate eDNA sampling after an eradication event. This complication is a large concern for fish eradication efforts in lakes since killed fish can sink to the bottom and slowly decay. DNA released from these carcasses may remain detectable for long periods. Here, we evaluated the efficacy of eDNA sampling to detect invasive Northern pike (Esox lucius) following piscicide eradication efforts in southcentral Alaskan lakes. We used field observations and experiments to test the sensitivity of our Northern pike eDNA assay and to evaluate the persistence of detectable DNA emitted from Northern pike carcasses. We then used eDNA sampling and traditional sampling (i.e., gillnets) to test for presence of Northern pike in four lakes subjected to a piscicide-treatment designed to eradicate this species. We found that our assay could detect an abundant, free-roaming population of Northern pike and could also detect low-densities of Northern pike held in cages. For these caged Northern pike, probability of detection decreased with distance from the cage. We then stocked three lakes with Northern pike carcasses and collected eDNA samples 7, 35 and 70 days post-stocking. We detected DNA at 7 and 35 days, but not at 70 days. Finally, we collected eDNA samples ~ 230 days after four lakes were subjected to piscicide-treatments and detected Northern pike DNA in 3 of 179 samples, with a single detection at each of three lakes, though we did not catch any Northern pike in gillnets. Taken together, we found that eDNA can help to inform eradication efforts if used in conjunction with multiple lines of inquiry and sampling is delayed long enough to allow full degradation of DNA in the water

Genomics reveal the origins and current structure of a genetically depauperate freshwater species in its introduced Alaskan range

Abstract Invasive species are a major threat to global biodiversity, yet also represent large‐scale unplanned ecological and evolutionary experiments to address fundamental questions in nature. Here we analyzed both native and invasive populations of predatory northern pike (Esox lucius) to characterize landscape genetic variation, determine the most likely origins of introduced populations, and investigate a presumably postglacial population from Southeast Alaska of unclear provenance. Using a set of 4329 SNPs from 351 individual Alaskan northern pike representing the most widespread geographic sampling to date, our results confirm low levels of genetic diversity in native populations (average of 3.18 × 10−4) and even less in invasive populations (average of 2.68 × 10−4) consistent with bottleneck effects. Our analyses indicate that invasive northern pike likely came from multiple introductions from different native Alaskan populations and subsequently dispersed from original introduction sites. At the broadest scale, invasive populations appear to have been founded from two distinct regions of Alaska, indicative of two independent introduction events. Genetic admixture resulting from introductions from multiple source populations may have mitigated the negative effects associated with genetic bottlenecks in this species with naturally low levels of genetic diversity. Genomic signatures strongly suggest an excess of rare, population‐specific alleles, pointing to a small number of founding individuals in both native and introduced populations consistent with a species' life history of limited dispersal and gene flow. Lastly, the results strongly suggest that a small isolated population of pike, located in Southeast Alaska, is native in origin rather than stemming from a contemporary introduction event. Although theory predicts that lack of genetic variation may limit colonization success of novel environments, we detected no evidence that a lack of standing variation limited the success of this genetically depauperate apex predator

Raw_data

Quantification cycle values and scores for Northern pike DNA in water samples collected at multiple lakes across time

Schematic of the locations of eDNA sampling.

<p>Locations of pre (○)and post (●)-rotenone treatments are identified in Derks, East Mackey, Union, and West Mackey Lakes near Soldotna, AK. Post-treatment samples were collected at all pre-treatment sample locations. The background base map is exclusive property of Environmental Systems Research Institute, Inc. (Esri).</p

Physical habitat and fish stocking data for caged and carcass experiments.

<p>Physical habitat and fish stocking data for caged and carcass experiments.</p

Schematic of the locations of Northern pike cages relative to eDNA sampling locations.

<p>Northern pike carcass locations were identical to cage locations in Tiny, Gensle, Little Bear, and Denise lakes near Soldotna, AK. The background base map is exclusive property of Environmental Systems Research Institute, Inc. (Esri).</p