Samantha M. Wilson

Effects of post-capture ventilation assistance and elevated water temperature on sockeye salmon in a simulated capture-and-release experiment

The authors evaluated a method of assisting the ventilation of adult sockeye salmon in an attempt to enhance post-release survival after fisheries capture at moderate and peak water temperatures. Though comparable recovery methods are often used by recreational anglers, the authors found this to be ineffective in enhancing post-release survival.

Burst Swimming in Areas of High Flow: Delayed Consequences of Anaerobiosis in Wild Adult Sockeye Salmon

Wild riverine fishes are known to rely on burst swimming to traverse hydraulically challenging reaches, and yet there has been little investigation as to whether swimming anaerobically in areas of high flow can lead to delayed mortality. Using acoustic accelerometer transmitters, we estimated the anaerobic activity of anadromous adult sockeye salmon (Oncorhynchus nerka) in the tailrace of a diversion dam in British Columbia, Canada, and its effects on the remaining 50 km of their freshwater spawning migration. Consistent with our hypothesis, migrants that elicited burst swimming behaviors in high flows were more likely to succumb to mortality following dam passage. Females swam with more anaerobic effort compared to males, providing a mechanism for the female-biased migration mortality observed in this watershed. Alterations to dam operations prevented the release of hypolimnetic water from an upstream lake, exposing some migrants to supraoptimal, near-lethal water temperatures (i.e., 24°C) that inhibited their ability to locate, enter, and ascend a vertical-slot fishway. Findings from this study have shown delayed post–dam passage survival consequences of high-flow-induced burst swimming in sockeye salmon. We highlight the need for studies to investigate whether dams can impose other carryover effects on wild aquatic animals.

Calibrating acoustic acceleration transmitters for estimating energy use by wild adult Pacific salmon.

This study is the first to calibrate acceleration transmitters with energy expenditure using a vertebrate model species. We quantified the relationship between acoustic accelerometer output and oxygen consumption across a range of swim speeds and water temperatures for Harrison River adult sockeye salmon (Oncorhynchus nerka). First, we verified that acceleration transmitters with a sampling frequency of 10 Hz could be used as a proxy for movement in sockeye salmon. Using a mixed effects model, we determined that tailbeat frequency and acceleration were positively correlated (p<0.0001), independent of tag ID. Acceleration (p<0.0001) was positively related to swim speed while fork length (p=0.051) was negatively related to swim speed. Oxygen consumption and accelerometer output (p<0.0001) had a positive linear relationship and were temperature dependent (p<0.0001). There were no differences in swim performance (F(2,12)=1.023, p=0.820) or oxygen consumption (F(1,12)=0.054, p=0.332) between tagged and untagged individuals. Five tagged fish were released into the Fraser River estuary and manually tracked. Of the five fish, three were successfully tracked for 1h. The above relationships were used to determine that the average swim speed was 1.25±0.03 body lengths s(-1) and cost of transport was 3.39±0.17 mg O(2) kg(-1)min(-1), averaged across the three detected fish. Acceleration transmitters can be effectively used to remotely evaluate fine-scale behavior and estimate energy consumption of adult Pacific salmon throughout their homeward spawning migration.

Low cardiac and aerobic scope in a coastal population of sockeye salmon Oncorhynchus nerka with a short upriver migration.

This study showed that a coastal population (Harrison) of Fraser River sockeye salmon Oncorhynchus nerka had a lower aerobic and cardiac scope compared with interior populations with more challenging upriver spawning migrations, providing additional support to the idea that Fraser River O. nerka populations have adapted physiologically to their local migratory environment.

Facing the river gauntlet: understanding the effects of fisheries capture and water temperature on the physiology of coho salmon.

An improved understanding of bycatch mortality can be achieved by complementing field studies with laboratory experiments that use physiological assessments. This study examined the effects of water temperature and the duration of net entanglement on physiological disturbance and recovery in coho salmon (Oncorhynchus kisutch) after release from a simulated beach seine capture. Heart rate was monitored using implanted electrocardiogram biologgers that allowed fish to swim freely before and after release. A subset of fish was recovered in respirometers to monitor metabolic recovery, and separate groups of fish were sacrificed at different times to assess blood and white muscle biochemistry. One hour after release, fish had elevated lactate in muscle and blood plasma, depleted tissue energy stores, and altered osmoregulatory status, particularly in warmer (15 vs. 10°C) and longer (15 vs. 2 min) capture treatments. A significant effect of entanglement duration on blood and muscle metabolites remained after 4 h. Oxygen consumption rate recovered to baseline within 7–10 h. However, recovery of heart rate to routine levels was longer and more variable, with most fish taking over 10 h, and 33% of fish failing to recover within 24 h. There were no significant treatment effects on either oxygen consumption or heart rate recovery. Our results indicate that fishers should minimize handling time for bycatch and maximize oxygen supply during crowding, especially when temperatures are elevated. Physiological data, such as those presented here, can be used to understand mechanisms that underlie bycatch impairment and mortality, and thus inform best practices that ensure the welfare and conservation of affected species.

Oxidative stress associated with paternal care in smallmouth bass (Micropterus dolomieu)

In species that provide parental care, care for offspring is often accompanied by an increase in locomotor activity and a decrease in feeding opportunities which can negatively impact endogenous energy reserves. Depletion of parental energy stores and declines in nutritional condition can cause physiological disturbances, such as an imbalance between free radical production and available antioxidants, known as oxidative stress. Using the teleost smallmouth bass (Micropterus dolomieu) as a model, we tested if the energetic challenge associated with sole paternal care was associated with oxidative stress. Blood samples from parental males were collected throughout parental care, during egg, embryo, and larval stages of offspring development, and assayed for both antioxidant capacity and oxidative damage. A reduction in oxygen radical absorbance capacity was observed during the parental care period, indicating a decrease in resistance to oxidative stress. Although no change was observed in the reduced:total thiol ratio, a significant increase in the concentration of both oxidized and total thiols occurred during the parental care period. No increase in the oxidative stress markers 8-hydroxy-2-deoxyguanosine, protein carbonyls and lipid peroxides was observed. We concluded that oxidative stress did not occur as a result of parental care in the male smallmouth bass. This study provides evidence that participation in energetically taxing activities, such as parental care, can result in a decrease in antioxidant resources, but may not always result in oxidative stress.

A physiological comparison of three techniques for reviving sockeye salmon exposed to a severe capture stressor during upriver migration

We used physiological measurements to compare different methods for reviving salmon after a severe capture stressor that involved 3 min of air exposure. Both a powered recovery box and a flow-through in-river recovery bag enabled revival, but prolonged confinement appeared to act as an additional stressor.

Is there a pace-of-life syndrome linking boldness and metabolic capacity for locomotion in bluegill sunfish?

The concept of behavioural syndromes (i.e. correlations between behavioural traits) has provided an important framework for understanding individual variation in animal behaviour and its link to individual variation in physiology and life-history traits. The pace-of-life syndrome concept posits that behavioural, physiological and life-history traits coevolve in response to correlated selection pressures, and therefore predicts a positive correlation between boldness (i.e. exploration and risk taking) and metabolic capacity for locomotor performance in individuals. We tested for a pace-of-life syndrome linking boldness and metabolic capacity for locomotor activity in juvenile bluegill sunfish, Lepomis macrochirus. Individual fish were screened and classified as bold or shy using an established refuge emergence test. Subsequently, the aerobic and anaerobic metabolisms of bold and shy individuals were quantified using respirometry and by measuring the metabolic by-products of white muscle anaerobic glycolysis following exhaustive exercise, respectively. Bold fish demonstrated 25% greater metabolic scope for activity (i.e. aerobic capacity) than shy fish, which was attributable to a 15% greater maximum metabolic rate. However, there was no significant difference in resting metabolic rate or anaerobic energy expenditure (i.e. anaerobic capacity) between bold and shy fish. These results partially support a pace-of-life syndrome linking boldness and aerobic metabolism in juvenile bluegill sunfish, but did not reveal a link between boldness and anaerobic metabolism. Our findings suggest that aerobic and anaerobic capacities may be subject to different selection pressures, and that physiological processes governing maximum anaerobic performance in fishes are independent from behavioural and physiological traits related to boldness.

Are there intergenerational and population-specific effects of oxidative stress in sockeye salmon (Oncorhynchus nerka)?

Intergenerational effects of stress have been reported in a wide range of taxa; however, few researchers have examined the intergenerational consequences of oxidative stress. Oxidative stress occurs in living organisms when reactive oxygen species remain unquenched by antioxidant defense systems and become detrimental to cells. In fish, it is unknown how maternal oxidative stress and antioxidant capacity influence offspring quality. The semelparous, migratory life history of Pacific salmon (Oncorhynchus spp.) provides a unique opportunity to explore intergenerational effects of oxidative stress. This study examined the effects of population origin on maternal and developing offspring oxidative stress and antioxidant capacity, and elucidated intergenerational relationships among populations of sockeye salmon (Oncorhynchus nerka) with varying migration effort. For three geographically distinct populations of Fraser River sockeye salmon (British Columbia, Canada), antioxidant capacity and oxidative stress were measured in adult female plasma, heart, brain, and liver, as well as in developing offspring until time of emergence. Maternal and offspring oxidative stress and antioxidant capacity varied among populations but patterns were not consistent across tissue/developmental stage. Furthermore, maternal oxidative stress and antioxidant capacity did not affect offspring oxidative stress and antioxidant capacity across any of the developmental stages or populations sampled. Our results revealed that offspring develop their endogenous antioxidant systems at varying rates across populations; however, this variability is overcome by the time of emergence. While offspring may be relying on maternally derived antioxidants in the initial stages of development, they rapidly develop their own antioxidant systems (mainly glutathione) during later stages of development.

Sex-specific consequences of experimental cortisol elevation in pre-reproductive wild largemouth bass.

Experimental implants were used to investigate the effect of elevated cortisol (the primary stress hormone in teleost fish) on energetic and physiological condition prior to reproduction in male and female largemouth bass (Micropterus salmoides). Fish were wild-caught from lakes in Illinois, and held in experimental ponds for the duration of the study. Between 9 and 13 days after cortisol treatment, and immediately prior to the start of the reproductive period, treated and control animals were sampled. Females exhibited lower muscle lipid content, lower liver glycogen content, and higher hepatosomatic indices than males, regardless of treatment. Also, cortisol-treated females had higher hepatosomatic indices and lower final mass than control females, whereas males showed no differences between treatment groups. Finally, cortisol-treated females had higher gonadal cortisol concentrations than control females. In general, we found evidence of reduced energetic stores in female fish relative to male fish, likely due to timing differences in the allocation of resources during reproduction between males and females. Perhaps driven by the difference in energetic reserves, our data further suggest that females are more sensitive than males to elevated cortisol during the period immediately prior to reproduction.