Escape From the Heat: Thermal Stratification in a Well-Mixed Estuary and Implications for Fish Species Facing a Changing Climate

Climate change may cause organisms to seek thermal refuge from rising temperatures, either by shifting their ranges or seeking microrefugia within their existing ranges. We evaluate the potential for thermal stratification to provide refuge for two fish species in the San Francisco Estuary (SFE): Chinook Salmon (Oncorhynchus tshawytscha) and Delta Smelt (Hypomesus transpacificus). We compiled water temperature data from multiple monitoring programs to evaluate spatial, daily, hourly, intra-annual, and inter-annual trends in stratification using generalized additive models. We used our data and models to predict the locations and periods of time that the bottom of the water column could function as thermal refuge for salmon and smelt. Periods in which the bottom was cooler than surface primarily occurred during the peak of summer and during the afternoons, with more prominent stratification during warmer years. Although the SFE is often exceedingly warm for fish species and well-mixed overall, we identified potential for thermal refugia in a long and deep terminal channel for Delta Smelt, and in the periods bordering summer for Chinook Salmon. Thermal stratification may increase as the climate warms, and pockets of cooler water at depth, though limited, may become more important for at-risk fishes in the future.

El Modelling potential distribution of the endemic ringtail (Bassariscus astutus saxicola) on an island in the Gulf of California

Objective: Analyze the topography of the island with a digital elevation model (DEM) at 30 m spatial resolution and generate the first distribution model for an endemic carnivore from the islands of the Gulf of California. Design/Methodology/Approach: This study employed the Maxent species distribution model to find the distribution of the ringtail in its habitat on Espíritu Santo Island. In 2015–2016, through four surveys, ringtails were trapped in eight glens on the west of the island. A total of 74 individuals were captured, with nine recaptures. Results: The variables with the greatest contributions to the models were elevation, contributing 71.6%; heat load index 15% and ruggedness 11.8%. The model predicts > 0.5 probabilities of presence of this carnivore in 3,018 hectares of the island. We obtained a high AUC value (0.928), which indicates that the model is accurate, and subsequently confirmed it with a value of pAUC = 1.917. Study Limitations/Implications: The habitat of the ringtail (Bassariscus astutus saxicola) was little known mainly because it is an endemic species. And there was not a published article that will show its distribution within the island. Conclusions: This model shows that topographic variables are useful to explain the potential distribution of the ringtail, mainly because the topography is related to sites that can offer thermal refuge, abundance of food, and escape routes from predators, among other features.

Resource selection by the Endangered Arabian tahr: identifying critical habitats for conservation and climate change adaptation

The Arabian tahr is an Endangered mountain ungulate endemic to the Hajar Mountains of Arabia. The Arabian tahr population is in decline and threats to tahr habitat are intensifying, in addition new potential challenges from climate change are emerging. Fundamental to future conservation planning is understanding tahr habitat selection patterns, so we can prioritise habitat protection, and understand how habitat may be used to provide thermal refuge and allow adaptation to climate change impacts. We used GPS collars and resource selection functions to characterise Arabian tahr habitat preferences in Wadi Sareen Nature Reserve, Oman. We found tahr habitat selection was dependent on scale, sex and season. Vegetation resources were only selected at the smallest scales of selection and avoided at other scales. Habitat providing low heat load and thermal refuge were intensely selected at small and medium scales, by both sexes and in both seasons, suggesting the importance of thermal refuges in facilitating thermoregulation. Higher elevations, steep slopes and rugged habitats were selected across all scales tested here, and in previous landscape-scale studies, indicating the fundamental importance of these habitats in supporting Arabian tahr populations. Our results identified critical habitats required to sustain Arabian tahr, and demonstrated the importance of thermal refuges to species living in the hot climates such as the Arabian Peninsula. Given the accessibility of habitat layers, and ease in which the identified habitats can be mapped using a geographical information system, understanding the habitat selection of tahr and other species is a crucial step to increasing conservation management capacity of threatened species. Given our uncertainty of how to conserve wildlife under future climate change, understanding the availability and distribution of wildlife habitat is an important baseline from where we can plan, connect and preserve the resources necessary for wildlife conservation.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—The Ozark Plateau is located at the southern extent of native Smallmouth Bass <em>Micropterus dolomieu </em>range and water temperature and drought conditions during summer months may potentially affect growth of Smallmouth Bass in this region. Groundwater streams in the region do not warm to the same extent as runoff streams during summer months and could provide a thermal refuge habitat for Smallmouth Bass from high summer temperatures and drought conditions. Our study objective was to examine differences in body condition and diet of Smallmouth Bass through summer months between groundwater and runoff streams. We sampled Smallmouth Bass from eight streams across two flow regimes monthly from June–September from 2014 to 2016 in the Ozark Plateau of Arkansas and Missouri. Relative weights were calculated and diet contents were examined for each fish. Linear mixed model analyses indicated that relative weights declined in both stream types in 2014 and 2015, but not in 2016. Surprisingly, there was no significant difference in change in relative weights between runoff and groundwater streams in any year. No diet shifts over the course of the summer were noted in any year, and no differences were seen between stream types. Our results suggest that further work should investigate the refuge qualities of groundwater streams for Smallmouth Bass in this region as Smallmouth Bass from both stream types may currently respond similarly to summer conditions.

Understanding summertime thermal refuge use by adult Atlantic salmon using remote sensing, river temperature monitoring, and acoustic telemetry

Adult Atlantic salmon (Salmo salar) return to natal rivers several months before spawning and during summer can be subjected to temperatures that exceed their upper temperature tolerance limits. Salmon use thermal refuges to minimize exposure to high temperatures, but little information exists regarding behavioral thermoregulation by adult Atlantic salmon. We examined behavioral thermoregulation by Atlantic salmon during summer in-river residence in a Quebec river with a novel combination of thermal infrared remote sensing, river temperature monitoring, and acoustic telemetry. Adults engaged in behavioural thermoregulation at cooler ambient river temperatures (17–19 °C) than previously recorded for this species and maintained body temperature within a narrow range (16–20 °C) via use of cool and warm refuges. Adults used large, stable, stratified pools as refuges, allowing multiple individuals to thermoregulate simultaneously without leaving the pool. Low river discharge and high temperatures can be physical barriers to salmon migration, preventing them from accessing suitable refuges (e.g., pools). Identifying and maintaining connectivity to thermal refuges may be critical for persistence of Atlantic salmon populations as climate changes and rivers warm.