Temperature dynamics in Klamath River off-channel floodplain restoration sites depend on location within the watershed

The mid-Klamath River is heavily impacted by altered streamflow and warm water temperatures, which contribute to the decline of native salmonids. In an effort to restore critical salmonid habitat, the Karuk Tribe, National Forest Service, and Mid-Klamath Watershed Council have created a variety of off-channel floodplain ponds that provide habitat for juvenile Coho Salmon (Oncorhynchus kisutch) and other juvenile salmonids such as Steelhead (O. mykiss). One purpose of these ponds is to provide cool water refuges for juvenile salmonids during high summer water temperatures. However, no studies have quantified how these ponds vary in temperature regimes across the river floodplain. In July 2020, we placed 30 temperature sensors in 9 off-channel ponds and 2 creeks (Seiad Creek and Horse Creek) in the mid-Klamath floodplain. We used a multivariate auto-regressive state space (MARSS) models to determine the number and spatial arrangement of distinct thermal regimes in floodplain ponds and tributaries. We found that pond temperatures have lower daily maximums and fluctuate less than tributary temperatures. We also found that Seiad Creek, Seiad Creek ponds, Horse Creek, and Horse Creek ponds all have different patterns of temperature change throughout the summer. Historical data (2010-2019) for Alexander and Stender Ponds showed that over time, daily fluctuations in pond water temperature became less drastic. This pattern was also observed by MKWC in their reports on Alexander and Stender Ponds (MKWC 2020; Wickman et al. 2020). More stable water temperatures in the ponds contrast to creek temperatures, which continue to fluctuate widely on a daily basis during summer. Fish monitoring data from MKWC show that coho growth rates are higher in these two ponds, which suggests that coho experience a metabolic benefit from more stable water temperatures (MKWC 2020; Wickman et al. 2020). Overall, our analysis provides deeper insight into the thermal benefits of floodplain habitats and off-channel ponds on the mid-Klamath River, and informs the future collection of fish data that will reveal more precise information about how floodplains benefit salmonids.

INFECTION OF COREGONIDS OF CHIVYRKUISKY BAY OF LAKE BAIKAL AND TSIPO-TSIPICANSKIYE LAKES BY TRIAENOPHORUS CRASSUS PLEROCERCOIDS

Triaenophorus crassus is the causative agent of muscular trienophorosis in fish, especially pathogenic for juvenile salmonids and coregonids. The purpose of this work was to analyze the infection of coregonids with T. crassus plerocercoids in the Chivyrkuisky Bay of the Lake Baikal and Tsipo-Tsipikanskiye (Bauntovskie) lakes (basin of the Lena River, Transbaikalia). Level of infection with plerocercoids T. crassus in coregonids from 1976 to 2013 in the Chivyrkuisky Bay of the Lake Baikal did not cause concern: the prevalence in the Baikal omul did not exceed 23.6%; intensity was no more than 6 specimens; the prevalence in the Baikal whitefish is up to 5.0%. At the same time, in 1954, in the Chivyrkuisky Bay, a higher level of infection of the Baikal omul was noted (the prevalence was 44.4%; the intensity was 1–9 specimens), which does not allow us to exclude a recurrence of this situation in the future. There was a sharply different situation in terms of infection of coregonids with T. crassus plerocercoids in two lakes of the Tsipo-Tsipikanskaya group: in the lake Bolshoye Kapilyushi, the prevalence of this cestoda is ten times higher than in the lake Baunt. It is likely that such contrasting levels of infection were associated with the difference in the location of the habitats of pike (the definitive host of T. crassus) and coregonids in these lakes: the coincidence in the lake Bolshoye Kapylyushi and divergence in the lake Baunt.

Effects of landscape-scale hypoxia on Salish sucker and salmonid habitat associations: implications for endangered species recovery and management

To understand the effects of widespread urbanization and agricultural impacts on recovery of Salish sucker, a federally threatened Catostomid endemic to the lower Fraser Valley of British Columbia, we assessed i) the current extent and effects of hypoxia on the distribution of Salish sucker and juvenile salmonids, ii) potential drivers of hypoxia, and iii) management options for hypoxia mitigation. Over 40% of sucker critical habitat experiences hypoxia (dissolved oxygen (DO) < 4 mg·l-I) by late summer, indicating widespread non-compliance with water quality guidelines. The strong positive relationship between seasonal hypoxia and temperature (R2= 0.53) and negative relationship with streamflow (R2= 0.78) indicates that hypoxia is driven by a synergy between low summer flows, elevated temperatures, and high primary production associated with nutrient enrichment (eutrophication). Sucker show strong selection against high water temperatures and weaker negative selection against low DO; juvenile salmonids show very strong selection against both high temperatures and low DO. Climate projections for declining summer flows and elevated temperatures indicate worsening trends in DO without intensive watershed-scale management to reduce nutrient loads.

POTENTIAL OF UTILIZATION OF ALLOCHTHONOUS INVERTEBRATES BY GAMMARUS KOREANUS UÉNO (AMPHIPODA)

In an isolating experiment on feeding only on arthropods of terrestrial origin, the potential of their consump-tion by amphipods from a fishless water-course is studied. The data obtained confirm the hypothesis that, on the basis of experiments on feeding exclusively on arthropods, it is possible to determine the maximum proportion of their biomass that selected consumers are able to utilize. The results of such works can be used to quantitative assessment of the level of possible losses of allochthonous matter and energy for the recipient communities of waterbodies due to feeding activity of consumers from their tributaries. Assessments of this kind may be relevant when deciding on the food availability for juvenile salmonids, inhabiting recipient waterbodies.

Systematic review and meta-analysis of PIT tagging effects on mortality and growth of juvenile salmonids

A systematic review and meta-analysis was conducted to evaluate the appropriate tag:fish size ratio when tagging juvenile salmonids (genera Oncorhynchus, Salmo, and Salvelinus). The review yielded 18 publications with 211 control and treatment groups reporting results from laboratory studies on the effects of passive integrated transponder (PIT) tags, plus a small number of additional studies on acoustic transmitters. A meta-analysis of the PIT tagging studies showed significant heterogeneity among studies with respect to mortality. Meta-regression revealed that juvenile salmonid mortality increased curvilinearly with the tag:fish length ratio, indicating that mortality risk is rapidly enhanced as smaller fish or larger tag sizes are used. The tag:fish length ratio effect on daily length or mass gain increased linearly. The results provide an estimate of the effects of the tag:fish length ratio on mortality and growth parameters in juvenile salmonids. Based on this, we suggest that researchers can follow best practices for tagging juvenile salmonids with tags that are not greater than 17.5% of fish total length (TL). This equates a minimum size threshold of 131 mm TL for tagging salmonids with 23-mm PIT tags, and 69 mm TL with 12-mm PIT tags. This information can assist researchers, managers, and welfare agencies striving to use the best possible evidence to make informed decisions regarding fish tagging.

Carcass additions increase juvenile salmonid growth, condition, and size in an interior Columbia River Basin tributary

Numbers of anadromous fish returning to freshwater ecosystems have declined precipitously across much of western North America, reducing a potentially important resource subsidy for juvenile salmonids. We added carcasses to three sections of a Snake River tributary and assessed juvenile Chinook salmon (Oncorhynchus tshawytcha) and steelhead trout (Oncorhynchus mykiss) growth, body condition, size, and diet responses in summer and early fall. Juvenile salmonids consumed an abundance of eggs and carcass tissue, which increased energy rations. Within 3 weeks of carcass additions, juvenile Chinook and steelhead growth rates were 1.1–5 and 6–23 times greater in treatment reaches relative to control reaches, respectively. We used long-term tagging and detection data from this system to assess the relationship between juvenile Chinook size and emigration survival for two different juvenile life histories. The increased growth rates and body size in response to carcass additions, coupled with a positive relationship between body size and survival, suggest that juvenile salmonid rearing productivity and emigration survival may be limited by depressed returns of anadromous fishes in this system and potentially other tributaries of the Columbia Basin.