Warmwater Temperatures (≥ 20°C) as a Threat to Pacific Lamprey: Implications of Climate Change

Climate change is understood to have myriad effects on fish physiology, fish distribution, and fish communities (Ficke et al. 2007; Lynch et al. 2016; Whitney et al. 2016). The effects of climate change include alterations in the hydrogeomorphic cycle that result in less seasonal instream flow and higher water temperatures. Fishes are poikilotherms; thus, their metabolism, behavior, and ecology are controlled by water temperature. Depending on the temperature tolerances and optima of fish species, these decreased river flows and increased water temperatures can have significant impacts at the organismal level that reverberate up to the population level (Ficke et al. 2007).

Lampreys (Petromyzontiformes) occur in temperate regions of the northern and southern hemispheres (Potter et al. 2015), and recent reviews and analyses suggest that over time anadromous lamprey populations will disproportionately lose habitats in lower latitudes while gaining habitats in higher latitudes because of warming water temperatures, especially in areas where other threats occur. This is predicted to result in the movement of anadromous lamprey populations toward the poles (e.g., Lassalle and Rochard 2009; Wang et al. 2021). Here, I draw attention to the region-specific status and thermal ecology of one species, the Pacific Lamprey Entosphenus tridentatus.

The Pacific Lamprey is an anadromous and semelparous fish distributed in the North Pacific Ocean and associated freshwater drainages (Renaud 2011). The status of Pacific Lamprey on the West Coast of North America, from California to Washington (USA), declines from “imperiled” in most watersheds to “critically imperiled” and “presumed extirpated” moving inland from the coast (U.S. Fish and Wildlife Service [USFWS] 2019). These interior drainages are generally arid and exhibit warmer water temperatures and lower river flows because of a combination of climate and human water withdrawals for various uses. Poor water quality and low water quantity are two identified threats to lamprey populations (Maitland et al. 2015; USFWS 2019; Clemens et al. 2021a). However, moving eastward from coastal Oregon (USA), it is difficult to disentangle the effects of warmwater temperatures and low river flows in inland drainages from the increased occurrences of hydropower and flood control dams and water diversions for irrigation. For example, the magnitude of water withdrawals in Oregon is high in the arid areas of eastern Oregon (Franczyk and Chang 2009). The presence of these structures can prohibit the ability of adult Pacific Lamprey to access cooler water that may occur upstream in some drainages. Both water quality and water quantity are impacted by climate change (Ficke et al. 2007; Wang et al. 2021), which will affect the physiology, phenology, and distribution of native lampreys (Wang et al. 2021).

I briefly summarize the results of previous research and field observations pertaining to water temperature (and correlated river flow) and the thermal ecology (i.e., the physiology, behavior, and survival) of adult Pacific Lamprey in fresh water, including information from a tagging study in the Umatilla River (eastern Oregon; Jackson and Moser 2012). I then describe new observations of prespawn mortalities of adult Pacific Lamprey in the South Umpqua River (coastal Oregon) that occurred during a recent heat wave when water temperatures exceeded 20°C. The Umpqua River drainage is under several threats, with passage, predation, climate change, stream and floodplain degradation, lack of awareness, water quality, and water quantity being the highest threats or limiting factors (USFWS 2019; Oregon Department of Fish and Wildlife [ODFW] 2020). A separate assessment found the Umpqua River drainage to be vulnerable to climate change (Wang et al. 2020). Taken together, this information suggests that warmwater temperatures (≥ 20°C) are a threat to adult Pacific Lamprey within the Columbia River drainage, including the Umatilla River of eastern Oregon and Willamette River of western Oregon (Clemens et al. 2016) and the Umpqua River of coastal Oregon. Adult Pacific Lamprey occur in fresh water year-round, either holding, migrating, or spawning (and then dying afterward); thus, water temperature could have a profound effect on these behaviors.

The Q10 of fishes is a quantitative description of the extent to which the metabolic rate changes over a 10°C in water temperature (Schmidt-Nielsen 1997; Clarke and Johnston 1999). The Q10 of adult Pacific Lamprey increases from a scaling coefficient of 1.6 over the 10° span of 5–15°C to a scaling coefficient of 6.0 over the 5° span of 15–20°C, signaling a substantial increase in metabolic demand as water temperature approaches 20°C (Johansen et al. 1973). By comparison, a statistical model fitted to data from various teleost fishes revealed a Q10 coefficient of 1.8 across a wider temperature range of 0–30°C. In addition, 14 studies reported Q10 coefficients of 3.4 or less in teleost fishes (Clarke and Johnston 1999). The details of the measurement and estimation of Q10 clearly matter, but at 15–20°C, adult Pacific Lamprey exhibit a significant increase in Q10 relative to lower water temperatures and relative to other fishes.

High water temperature is the most prevalent cause of water quality impairment in Oregon (ODFW 2020). Several rivers throughout Oregon display long, uninterrupted stretches of > 20°C during the summer (Fullerton et al. 2018). Adult Pacific Lamprey are generally active at 10–23°C (Figure 1; Clemens et al. 2016) and tend to select water temperatures of 16–17°C (in the laboratory; Lemons and Crawshaw 1978 [this publication reported no further details]). At summertime water temperatures of ≥ 20°C, several different morbidities, mortalities, and changes to behavior have been documented. For example, adult Pacific Lamprey in the Willamette drainage (western Oregon) exhibited the following: damaged oocytes and testes (evidenced via gonadal histology); mortalities (Figure 2A); skewed sex ratios (toward males; Clemens et al. 2016); slowed and in some cases halted upstream migration of tagged individuals (Clemens et al. 2012, 2017; Clemens and Schreck 2021); and triggering of sexual maturation in the laboratory (Clemens et al. 2009). This information suggests that warmwater temperatures may damage reproductive organs and cause mortalities on one hand, or halt upstream migration and expedite sexual maturation on the other. Thus, warmwater temperatures may inhibit adult lamprey from reaching upper watersheds in some situations (Clemens et al. 2016). In addition, the maximum ventilatory and heart rates of adult Pacific Lamprey occur at 25°C (Johansen et al. 1973), and incipient lethal levels can occur at ≥ 28°C (Potter and Beamish 1975; Macey and Potter 1978). Finally, the studies of the development and survival of Pacific Lamprey embryos in the laboratory revealed that across water temperatures of 10, 14, 18, and 22°C, the highest proportion of developmental abnormalities occurred at 22°C and the highest survival occurred at 18 and 14°C (Meeuwig et al. 2005). Therefore, the weight of evidence suggests that exposure of Pacific Lamprey to water temperatures of greater than or equal to 20°C is associated with myriad physiological, behavioral, and survival challenges that pose a threat to this species.

Three prespawn mortalities of adult Pacific Lamprey were found in the Umpqua River drainage (coastal Oregon; during a heat wave in 2021 [Figures 2B and 2C] and presumed to be caused by very high temperatures [daily average of 26.6°C; range: 20.8–30.6°C; Figure 3; Table 1]). Two of these mortalities from the lower South Umpqua River were observed on June 30 and a third was observed approximately 62.3 river kilometers (rkm) upstream between July 5 and July 8. These mortalities showed no obvious signs of injury or predation (R. Nichols, U.S. Forest Service, personal communication; B.J.C., personal observations of images in Figures 2B and 2C). The external morphology and arrival timing of these Pacific Lamprey are consistent with sexually immature adults, not postspawn carcasses (Figure 2). Although we do not have information on the prevalence of live, dead, or dying Pacific Lamprey, nor do we have individual records of the water temperatures that these dead Pacific Lamprey endured before death, these observations nevertheless underscore the repercussions of warmwater temperatures on Pacific Lamprey mortality.

Water temperature is often correlated with river flow such that high temperatures tend to occur with less river discharge and vice versa (Clemens et al. 2016). Worldwide, lampreys are attracted to increased river flows while migrating toward spawning grounds (reviewed in Moser et al. 2015; see also Arakawa et al. 2019), including Pacific Lamprey (Moser and Mesa 2009; reviewed in Clemens et al. 2016). Conversely, static flow is not conducive to promoting upstream migration (e.g., Sea Lamprey Petromyzon marinus; Daniels 2001).

Adult Pacific Lamprey can avoid warmwater temperatures by moving into cooler reaches upstream or using coldwater refuges (Clemens and Schreck 2021; see Torgerson et al. 2012 for a definition of coldwater refuges). Adult Pacific Lamprey occur in fresh water year-round, holding, actively migrating, or spawning (Clemens et al. 2010). In the lower Columbia River, adult Pacific Lamprey migrate upstream past Bonneville Dam (rkm ∼ 235.1) earlier in warm, low-flow years (July), with cumulative averages of approximately 50% migrating upstream at approximately 19°C and approximately 80% migrating at approximately 21–23°C (average daily temperatures at Bonneville Dam; Keefer et al. 2009). At the Willamette Falls dam complex in the Willamette River, the number of adult Pacific Lamprey that passed increased during water temperature of approximately 23°C (Mesa et al. 2010). Clemens et al. (2016) hypothesized that these increased upstream migrations of adult Pacific Lamprey may have been “. . .  an active response by the fish to escape warming temperatures of ∼21–23°C.” In the Umatilla River (∼226.8 river kilometers upstream of Bonneville Dam), a telemetry study that assessed passage of adult Pacific Lamprey at lowhead barrier dams found that low summertime river flows and a long period (July–October) of 20°C water temperature resulted in a lack of upstream migration, with some fish falling back downstream. These fall backs were attributed to “handling and release at high temperature”(Jackson and Moser 2012).

Although lampreys have persisted through many climate change events and four global mass extinction events over their 360–550-million-year history (Gess et al. 2006; Barnosky et al. 2011; Smith et al. 2013; Docker et al. 2015), they are now subjected to multiple human-related threats that are associated with significant declines in their populations from about the 1900s onward (Maitland et al. 2015; Clemens et al. 2021a). Up until the 1900s, lampreys have not had to adapt to the rapid environmental changes and human threats that now occur. Climate change exacerbates human-made threats to ecosystems and species (e.g., Meyer et al. 1999; Independent Scientific Advisory Board [ISAB] 2007; Williams et al. 2015).

Although the effects of climate change at specific geographical locations, across lamprey species, and across their life cycles will be difficult to predict (Clemens et al. 2021a; Wang et al. 2021), assessments have been made regarding the vulnerability of Pacific Lamprey to climate change in some areas of the Pacific Northwest (USA; Sharma et al. 2016; Wang et al. 2020). Wang et al. (2020) conducted a vulnerability assessment in several drainages where Pacific Lamprey were historically present and found that the Umpqua drainage was extremely vulnerable to climate change. Habitat degradation and resulting reduction in aquatic connectivity were the primary threats contributing to the high vulnerability ranking. In addition, expanding warmwater temperatures in the Umpqua drainage are predicted to facilitate the expansion of the nonnative Smallmouth Bass Micropterus dolomieu (Jones et al. 2020), a known predator of larval Pacific Lamprey (Schultz et al. 2017). Thus, it is becoming increasingly evident that Pacific Lamprey face many threats in the Umpqua drainage, which may explain the low estimated abundance of adults in this drainage relative to other coastal drainages (Clemens et al. 2021b). Are the warmwater temperatures in the Umpqua drainage and associated prespawn mortalities (Figure 2) a harbinger of things to come in that basin?

As individual species, anadromous lampreys worldwide may be able to mitigate the threat of climate change by moving their distribution poleward (Wang et al. 2021). However, without conservation interventions, Pacific Lamprey may become extirpated in some temperate drainages in North America. If this happens, the cultural benefits (e.g., Close et al. 2002) and ecosystem services (Docker et al. 2015; Clemens and Wang 2021) associated with Pacific Lamprey would be lost from these drainages. The appropriate conservation intervention will depend upon the logistical, financial, biological, and socially acceptable practices in a particular geographical region, in a specific location, and at a particular time. The conservation practice may include any one of the following or some combination thereof: translocating adult Pacific Lamprey from lower drainages into upper drainages (Ward et al. 2012); providing passage to allow the Pacific Lamprey to access preferable habitats (e.g., Moser et al. 2021); restoring riparian habitats to ameliorate the effects of climate change (Rahel et al. 2008; Lawrence et al. 2014); and working with the social aspects of curtailing excessive water use for humans to leave more water in-stream for fishes where and when possible. In conclusion, the accumulating evidence within the Columbia and Umpqua drainages suggests that warmwater temperatures (≥ 20°C) pose a threat to Pacific Lamprey, particularly as climate change is likely to increase the occurrences of these water temperatures.

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Reference S1.[ISAB] Independent Scientific Advisory Board. 2007. Climate change impacts on Columbia River Basin fish and wildlife. Portland, Oregon: Northwest Power and Conservation Council.

Available: https://doi.org/10.3996/JFWM-21-087.S1 (2.683 MB PDF) and https://www.nwcouncil.org/media/filer_public/a2/c6/a2c6bc00-1882-47c2-a4a6-9dfa0a172bbb/isab2007_2.pdf

Reference S2.[ODFW] Oregon Department of Fish and Wildlife. 2020. Coastal, Columbia, and Snake conservation plan for lampreys in Oregon: Pacific lamprey, western river lamprey, western brook lamprey, and Pacific brook lamprey. Salem: Oregon Department of Fish and Wildlife.

Available: https://doi.org/10.3996/JFWM-21-087.S2 (9.073 MB PDF) and https://www.dfw.state.or.us/fish/CRP/docs/coastal_columbia_snake_lamprey/CPL%20-%20Final%202-14-20.pdf

Reference S3. Torgerson CE, Ebersole JL, Keenan DN. 2012. Primer for identifying cold-water refuges to protect and restore thermal diversity in riverine landscapes. Seattle: U.S. Environmental Protection Agency, Report prepared for Region 10, under EPA interagency agreement DW-14-95755001-0.

Available: https://doi.org/10.3996/JFWM-21-087.S3 (20.618 MB PDF) and https://nepis.epa.gov/Exe/ZyPDF.cgi/P100E45N.PDF?Dockey=P100E45N.PDF

Reference S4.[USFWS] U.S. Fish and Wildlife Service. 2019. Pacific lamprey Entosphenus tridentatus assessment.

Available: https://doi.org/10.3996/JFWM-21-087.S4 (7.120 MB PDF) and https://www.pacificlamprey.org/wp-content/uploads/2022/02/Pacific-Lamprey-Entosphenus-tridentatus-Assessment-%E2%80%93-2018-Revision.pdf

This paper is a by-product of the third Sea Lamprey International Symposium. I thank Robert Nichols, Karie Wiltshire, and Greg Huchko for sharing the information on the prespawn mortalities from the South Umpqua River. Sandy Lyon of the Partnership for the Umpqua Rivers provided the water temperature data for the South Umpqua River. This paper benefitted from an early review by Jon Hess, discussion with Michael Siefkes and Rob McLaughlin, and reviews by Tom Stahl and Kara Anlauf-Dunn. I thank the editors and two anonymous reviewers for their constructive reviews.

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