Additional file 2: Table S1. of Evaluating taxonomic homogenization of freshwater fish assemblages in Chile

Native and non-native (alien) fishes present in inland waters in Chile. (DOCX 24 kb

Additional file 1: Appendix S1. of Evaluating taxonomic homogenization of freshwater fish assemblages in Chile

References used to build the presence-absence data set. (DOCX 69 kb

DataSheet1_Assessing Hybridization Risk Between ESA-Listed Native Bull Trout (Salvelinus confluentus) and Introduced Brook Trout (S. fontinalis) Using Habitat Modeling.PDF

The introduction of non-native species can negatively impact native species through reduced genetic fitness resulting from hybridization. The lack of spatiotemporal data on hybrid occurrences makes hybridization risk assessment difficult. Here, we developed a spatially-explicit Hybridization Risk Model (HRM) between native Oregon bull trout, an Endangered Species Act-listed Oregon species, and introduced brook trout by combining an intrinsic potential model (IPM) of brook trout spawning habitat and existing bull trout distribution and habitat use datasets in Oregon, United States. We created an expert-based brook trout IPM classification score (0–1) of streams based on the potential of geophysical attributes (i.e., temperature, discharge, gradient, and valley confinement) to sustain spawning habitats. The HRM included a risk matrix based on the presence/absence of both species as well as the type of habitat (spawning versus other) at 100-m stream segment resolution. We defined the hybridization risk as “extreme” when stream reaches contained bull trout spawning habitat and brook trout were present with IPM moderate or greater scores (IPM >0.5). Conversely, “low” risk reaches contained historic or non-spawning bull trout habitat, brook trout were absent, and IPM scores were low (IPM <0.25). Our HRM classified 34 km of streams with extreme risk of hybridization, 115 km with high risk, 178 km with moderate risk, and 6,023 km with low risk. Our HRM can identify a differential risk of hybridization at multiple spatial scales when either both species coexist in bull trout spawning habitat or are absent. The model can also identify stream reaches that would have higher risk of hybridization, but where brook trout are not currently present. Our modeling approach can be applied to other species, such as cutthroat trout and rainbow trout, Chinook and coho salmon, or similar species occurring elsewhere that potentially hybridize in freshwaters.</p

Hypothesized progression of the ecosystem-level water management cycle in reservoirs and ecological processes.

A full pool reservoir during summer is followed by (A) conventional lowering to minimum reservoir level or (B) experimental draining of the reservoir to riverbed during late fall, and refilling in spring. Under both scenarios, much of the benthos are exposed. In the case of Fall Creek Reservoir, this draining results in lotic conditions, with no holding pool, for one week annually. Sediments do not appear to desiccate during this period. The draining of a reservoir to riverbed assists anadromous Chinook Salmon with downstream migration, but acts as a pulse disturbance washing out many reservoir resident fishes. Upon refill, the reservoir in (B) has reduced densities of overwintering fish species (zooplankton and benthic invertebrates can quickly recover to previous densities from egg banks and resting stages). This results in shifts in the trophic dynamics for predatory fish, presumably through the reduction of small prey fishes. Though juvenile Chinook Salmon hatch in streams and move to the reservoirs in early spring, their densities are relatively low, making a piscivorous strategy which relies on them alone inefficient and thus, predaceous fishes now focus on invertebrate prey instead.</p

Evidence for lasting alterations to aquatic food webs with short-duration reservoir draining - Fig 2

Trophic levels of key taxa (top) and δ15N ratios for Largemouth Bass and Rainbow Trout (bottom). (A) Reference reservoir food chain compared to the (B) altered reservoir food chain observed in the previously drained reservoir. Additional species found in Willamette Basin reservoirs but not pictured here include: bullhead catfish, Largescale Sucker and sculpin (detritivores); dace, mosquitofish, Redside Shiner, and Threespine Stickleback (invertivores); Bull Trout, crappie, Northern Pikeminnow, Walleye and Yellow Perch (juvenile invertivores, adult piscivores). (C and D) δ15N ratios increase naturally with increasing size of fish in reference reservoirs. The threshold for piscivory is indicated by a red dashed line. The grey dotted vertical line indicates the 150 mm threshold, above which fish diets are predominantly piscivorous. Although both species are capable of consuming fish as prey when smaller than 150 mm, this size threshold was calculated as the intersection of these (C and D) reference ontogenetic trajectories and the predicted piscivory isotopic ratio. (E and F) δ15N values of large (>150 mm) (E) Largemouth Bass and (F) Rainbow Trout in Fall Creek Reservoir (shown in orange) are lower than in other reservoirs (shown in gray; S1 Table). Fall Creek experienced riverbed draining while other reservoirs maintained conservation pools. Lower δ15N values indicate that consumers are feeding lower on the food chain.</p

Unveiling growth and reproduction of a giant Patagonian galaxiid: an experimental rearing study

Understanding the life history of understudied native and threatened fishes is crucial to develop conservation strategies for freshwater ecosystems. Puye grande (Galaxias platei) is an endemic freshwater fish of Patagonia with little known about its life history traits. To bridge this information gap, comprehensive studies under controlled conditions could expand our basal understanding of puye grande’s life history. We conducted a long-term experimental study using one cohort of puye grande throughout its lifespan. We collected 423 postlarvae individuals from the Riñihue Lake (southern Chile) and reared them for 11 years under captivity. We documented the maximum longevity of this species as 11 years, with a survival rate of 0.47% for the entire study period. Hatchery-reared individuals showed isometric growth (b = 2.75). Parameters of the von Bertalanffy growth model were asymptotic total length L∞ = 20.80 cm, growth coefficient K = 0.75 yr−1, and theoretical age at-length zero t0 = 0.45 yr, including both sexes. Puye grande showed an iteroparous life history, with the first spawning event occurring at age 2+ and consecutive spawning events occurring mainly in fall and winter. Females had a mean (standard deviation) total fecundity of up to 58 500 (23 331) eggs individual−1 and a mean relative fecundity in fall of 621 (109) eggs g−1 wet mass; males had a mean spermatic density of 28.41 (4.18) × 109 spermatozoa mL−1. The embryonic development until eclosion occurred 432 h post fertilization (hpf) at 12 °C. Our valuable baseline findings about the life history of puye grande can contribute to future strategies for managing and conserving galaxiids under global environmental change in Patagonia.</p

δ¹⁵N values for other trophic levels and fish species in the four study reservoirs. Note that phyto- and zoo-plankton samples were bulk samples and likely represent a range of taxa.

δ15N values for other trophic levels and fish species in the four study reservoirs. Note that phyto- and zoo-plankton samples were bulk samples and likely represent a range of taxa.</p

Study sites and management characteristics.

(A) Map of the four Willamette Basin study reservoirs (purple). (B) The water control diagram with the conventional drawdown to conservation pool water level management (rule curve; black, solid) and the draining to riverbed (red, dashed) for the Fall Creek treatment reservoir. (C) Table of the conventional management characteristics of the study reservoirs. (D) Photographs from each reservoir in September, to illustrate exposed littoral area, when reservoirs are still accessible but water levels have begun to lower per conventional management. Photographs: C.A. Murphy. Fall Creek Reservoir is managed by short duration winter draining to riverbed (lowered by 49 m instead of the conventional 31 m) while the other reservoirs undergo conventional winter water level management (ranging from 29 m to 51 m in magnitude) and are reduced in lake levels but maintain a ‘minimum conservation pool’ (i.e. a small lake above riverbed). In conventional reservoir management each reservoir follows ‘rule curve’ diagrams for reservoir water levels to maintain downstream flow targets. During the winter, these large reservoirs are held at a reduced lake level, the ‘conservation pool’ that allows for the capture of peak inflows, reducing downstream flood risks. This period exposes littoral sediments. Captured water is used to fill the reservoir beginning late until ‘full pool’ is reached in spring. Stored water is then available to augment summer downstream flows as well as provide recreational opportunities in the reservoirs before the reservoir water level is reduced in the fall to the minimum lake level. The typical conservation pool is represented by a flat line during winter months and full pool by a flat line during summer months. Water control diagrams for all study reservoirs are available at: http://www.nwd-wc.usace.army.mil/nwp/teacup/willamette/.</p

Resilience of zooplankton communities in temperate reservoirs with extreme water level fluctuations

The importance of zooplankton as a food resource for higher trophic levels, including threatened and endangered salmon species, highlights the need to improve our understanding of the mechanisms that structure reservoir food webs. Pelagic plankton are the dominant primary and secondary producers in reservoirs experiencing extreme water level fluctuations (WLFs). In these systems, we might expect WLFs to promote predictable and homogenized biotic communities. Here we explored whether spring and summer zooplankton communities are homogenized in Pacific Northwest (USA) flood-control reservoirs managed with annual extreme WLFs. In addition, we evaluated whether community resilience is present in a reservoir that has been drained annually since 2011 for salmon passage. We sampled 4 reservoirs during spring and summer, including 1 that was fully drained, resulting in a lotic riverine environment, for 1 week each fall from 2012 to 2016. We found low beta diversity across reservoirs, indicating homogenized communities. Additionally, we did not observe changes across sample years or increased differences in species composition compared to historical data. Instead, we observed strong seasonal transitions that were predictably repeated each year. Our findings support the hypothesis that extreme WLFs, under which these reservoirs have been managed for >50 years, may have structured reservoir zooplankton communities such that they are resilient to even more dramatic draining. Understanding how WLFs and reservoir draining may impact zooplankton will be critical to minimizing unintended consequences of reservoir management on aquatic food webs.</p

Conceptual ichthyographs for Coho Salmon.

<p>Conceptual ichthyographs for Coho Salmon use by life stage of: (a) a mid-river location such as Winchester dam, and (b) throughout the river network with generalized patterns of streamflow and stream temperature for different drainage areas. These conceptual ichthyographs are based on the empirical data available in this system (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0168831#pone.0168831.g001" target="_blank">Fig 1</a>), but also incorporate informal data collected as part of ongoing fish management in this system, and the description of life-stage specific habitat characteristics that can be taken from the peer reviewed literature. Other species specific traits could be mapped in this way, as could other interpretations of fish habitat use beyond specific life stages. Empirical ichthyographs that map daily discharge, temperature, and fish use could also be mapped where data are available.</p