Michael C. Healey

The effect of temperature on swimming performance and oxygen consumption in adult sockeye (Oncorhynchus nerka) and coho (O. kisutch) salmon stocks

SUMMARY Our knowledge of the swimming capabilities and metabolic rates of adult salmon, and particularly the influence of temperature on them, is extremely limited, and yet this information is critical to understanding the remarkable upstream migrations that these fish can make. To remedy this situation, we examined the effects of temperature on swimming performance and metabolic rates of 107 adult fish taken from three stocks of sockeye salmon Oncorhynchus nerka and one stock of coho salmon O. kisutch at various field and laboratory locations, using large, portable, swim tunnels. The salmon stocks were selected because of differences in their ambient water temperature (ranging from 5°C to 20°C) and the total distance of their in-river migrations (ranging from ∼100 km for coastal stocks to ∼1100 km for interior stocks). As anticipated, differences in routine metabolic rate observed among salmon stocks were largely explained by an exponential dependence on ambient water temperature. However, the relationship between water temperature and maximum oxygen consumption (ṀO2max), i.e. the ṀO2 measured at the critical swimming speed (Ucrit), revealed temperature optima for ṀO2max that were stock-specific. These temperature optima were very similar to the average ambient water temperatures for the natal stream of a given stock. Furthermore, at a comparable water temperature, the salmon stocks that experienced a long and energetically costly in-river migration were characterized by a higher ṀO2max, a higher scope for activity, a higher Ucrit and, in some cases, a higher cost of transport, relative to the coastal salmon stocks that experience a short in-river migration. We conclude that high-caliber respirometry can be performed in a field setting and that stock-specific differences in swimming performance of adult salmon may be important for understanding upstream migration energetics and abilities.

Abnormal migration timing and high en route mortality of sockeye salmon in the Fraser River, British Columbia

Abstract Since 1995, several stocks of Fraser River sockeye salmon (Oncorhynchus nerka) have begun upriver spawning migrations significantly earlier than previously observed. In some years, the timing of peak migration has shifted more than 6 weeks. Coincident with this early migration are high levels of en route and pre-spawning mortality, occasionally exceeding 90%. These phenomena pose risks to the perpetuation of these fisheries resources. At present, although there are many competing hypotheses (e.g., energetics, osmoregulatory dysfunction, oceanic conditions, parasites) that may account for early migration and high mortality, there are no definitive answers, nor any causal evidence that link these issues. With poor predictive ability in the face of uncertainty, fisheries managers have been unable to effectively allocate harvest quotas, while ensuring that sufficient fish are able to not only reach the spawning sites, but also successfully reproduce. If trends in mortality rates continue, several imp...

Excess post-exercise oxygen consumption in adult sockeye ( Oncorhynchus nerka) and coho (O. kisutch) salmon following critical speed swimming

SUMMARY The present study measured the excess post-exercise oxygen cost (EPOC) following tests at critical swimming speed (Ucrit) in three stocks of adult, wild, Pacific salmon (Oncorhynchus sp.) and used EPOC to estimate the time required to return to their routine level of oxygen consumption (recovery time) and the total oxygen cost of swimming to Ucrit. Following exhaustion at Ucrit, recovery time was 42–78 min, depending upon the fish stock. The recovery times are several-fold shorter than previously reported for juvenile, hatchery-raised salmonids. EPOC varied fivefold among the fish stocks, being greatest for Gates Creek sockeye salmon (O. nerka), which was the salmon stock that had the longest in-river migration, experienced the warmest temperature and achieved the highest maximum oxygen consumption compared with the other salmon stocks that were studied. EPOC was related to Ucrit, which in turn was directly influenced by ambient test temperature. The non-aerobic cost of swimming to Ucrit was estimated to add an additional 21.4–50.5% to the oxygen consumption measured at Ucrit. While these non-aerobic contributions to swimming did not affect the minimum cost of transport, they were up to three times higher than the value used previously for an energetic model of salmon migration in the Fraser River, BC, Canada. As such, the underestimate of non-aerobic swimming costs may require a reevaluation of the importance of how in-river barriers like rapids and bypass facilities at dams, and year-to-year changes in river flows and temperatures, affect energy use and hence migration success.

Aggression and self-regulation of population size in deermice

Sadleir (1965) proposes that seasonal changes in the survival of juvenile deermice are determined by seasonal changes in the aggressiveness of the adult population. The purpose of the study is to examine some of the consequences of Sadleirs hypothesis experimentally. Laboratory studies confirmed Sadleirs observations on seasonal changes in the aggressiveness of male deermice. Similarly, in the laboratory, juvenile deermice grew poorly when competing with adults in their home cage. Further analysis showed that only aggressive males are capable of inhibiting juvenile growth. In order to avoid the crowded conditions and confinement implicit in the laboratory experiments, the relations between adult aggressiveness and juvenile growth and survival was reexamined in field experiments. Artificial populations or docile male deermice were established in field plots. Juveniles were then released onto the plots, and their growth and survival followed. Juveniles again grew poorly when competing with aggressive adults, but in the field juveniles also disappeared rapidly from the experimental plots when the adult population was aggressive. The success of immigrants onto trapped out plots and plots with a resident population was examined as well. Immigrants were more successful in establishing themselves on trapped out plots. All the data collected support Sadleirs hypothesis, and it is concluded that the correlation he drew between adult aggressiveness and juvenile survival is real. The data also provide some clues to the organization of deermouse populations. An organization is proposed in which the social units is an animal and its immediate neighbours. Within the social unit mutual antagonism is reduced. But the members of the unit remain highly aggressive, and are intolerant of any stranger that wanders into their home ranges. The system proposed prevents immigrants from settling, the helps to regulate population size, while conserving energy by reducing antagonism between familiar animals.

Effects of River Discharge, Temperature, and Future Climates on Energetics and Mortality of Adult Migrating Fraser River Sockeye Salmon

Abstract We evaluated the effects of past and future trends in temperature and discharge in the Fraser River on the migratory performance of the early Stuart population of sockeye salmon Oncorhynchus nerka. Fish of lower condition exhibited disproportionately higher mortality during the spawning run, elucidating a critical link between energetic condition and a fishs ability to reach the spawning grounds. We simulated spawning migrations by accounting for energetic demands for an average individual in the population from the time of entry into the Fraser River estuary to arrival on the spawning grounds (about 1,200 km upstream) and estimated energy expenditures for the average migrant during 1950–2001. The model output indicates relatively high interannual variability in migration energy use and a marked increase in energy demands in recent years related to unusually high discharges (e.g., 1997) and warmer than average water temperature (e.g., 1998). We examined how global climate change might effect dis...

Flow refugia for benthic macroinvertebrates during flooding of a large river

Benthic macroinvertebrates shifted from deep water to shallow water of the shore zone during annual flooding of a large, gravel-bed river. The shore zone is seasonally inundated during flooding for up to 4 mo of the year, and is a geomorphic feature of many large rivers in northern latitudes with limited floodplain habitat. We collected samples of invertebrates along with measures of several hydraulic and sedimentary variables 5 times through the flood cycle from 4 fixed water depths; stations shifted laterally over a distance of 30 m between baseflow and peak flow. In deep water (1.5 and 3.0 m), shear velocity and substrate mobility increased as a result of flooding. At shallow depths (0.2 and 0.5 m) within the shore zone, stable substrate and low hydraulic stress remained throughout the flood cycle, providing flow refugia to benthic invertebrates. Invertebrate density and species richness were similar during months on the rising limb of the hydrograph while the wetted area of the channel markedly increased. Persistence of the invertebrate community appears to have been facilitated by a shift in a large proportion of organisms from deep water to shallow depths of the shore zone during flooding. Total density and the density of most collector-gatherers such as Rhithrogena and Baetis was highest at 1.5 m prior to flooding but shifted to depths of 0.5 and 0.2 m at peak flow. The filter-feeding caddisfly Hydropsyche was most abundant at 1.5 m in all months of the study while the location of 1.5 m samples shifted laterally over a distance of 30 m through the flood cycle. The ecological importance of the shore zone as a flow refugium was demonstrated by the broad diversity of species with varying feeding behaviors and morphologies that concentrated in this zone during flooding.

Sex‐Specific Life History Tactics and Risk‐Taking in Coho Salmon

Differences in size and abundance between males and female at sexual ma- turity are common in vertebrates. Evolutionary explanations for these differences generally assume a consistent pattern within a species. Among Pacific salmon (Oncorhynchus spp.) and coho salmon (0. kisutch) in particular, however, sexual size dimorphism and sex ratio are not consistent among or within populations, making extant explanations unsatisfactory. In this paper we describe the variation size dimorphism and sex ratio within and among coho salmon populations and propose a model to account for this variation. Our data consist of a 16-yr study of coho salmon in Carnation Creek, British Columbia, and shorter term studies of 30 other coho populations ranging from California to Alaska. Among mature coho salmon in Carnation Creek males outnumbered females but fe- males were larger, and the male/female sex ratio varied directly with the female/male size ratio. Mean female size was constant over 16 yr, while male size varied inversely with the male/female sex ratio. Females apparently had higher mortality rates than males, and the difference in mortality rates appeared to increase as the animals neared maturity. Sex- and size-ratio data from other coho salmon populations indicate that there are two general population types. In one type males outnumber females, and females are larger at maturity. In the other type the sexes are equally abundant and equal in size. We propose that the range of size for successful reproduction in coho salmon is set by conditions in the breeding environment, and that the range differs for males and females because of the different roles that the sexes play in reproduction. The sex-specific constraints on reproductive size lead to sex-specific foraging strategies and risk-taking. Interpopulation differences in size and sex ratio are determined by differences in physical characteristics of the breeding environment, spawning population density, and the relative riskiness of ocean nursery areas. Within populations, variation is determined by the interaction of sex- specific foraging strategies with interannual variation in ocean feeding conditions and predator abundance.

MECHANISTIC BASIS OF INDIVIDUAL MORTALITY IN PACIFIC SALMON DURING SPAWNING MIGRATIONS

Reproductive-based migration is a challenging period for many animals, but particularly for Pacific salmonids, which must navigate from the high seas to freshwater natal streams. For the first time, we attempt to answer the question as to why some migratory adult Pacific salmon die en route to spawning grounds. Summer-run sockeye salmon (Oncorhynchus nerka) were used as a model, and the migration behavior of 301 fish was followed by intercepting them in the ocean about 215 km from the mouth of the Fraser River, British Columbia, Canada, and implanting a gastric radio transmitter. Before release, telemetered fish were also bio-sampled, which included drawing a blood sample, collecting a gill biopsy, and quantifying energetic status with a microwave energy meter. We tested the predictions that the fish that died prematurely would be characterized by low energy reserves, advanced reproductive development, elevated indicators of stress, and low osmoregulatory preparedness compared with fish that completed their river migration. Just over half (52.3%) of the sockeye tagged were subsequently detected in the Fraser River. Salmon that failed to enter the river had exhibited indicators of stress (e.g., elevated plasma lactate, glucose, and cortisol). Contrary to our prediction, fish that failed to enter the river tended to have higher gross somatic energy and be larger at the time of sampling in the ocean than fish that successfully entered the river. Of the fish that were detected in the river (i.e., 134 fish excluding fishery removals), 9.7% did not migrate beyond the lower reaches (approximately 250 km from ocean), and a further 14.2% reached the upper reaches but failed to reach natal sub-watersheds, whereas the remainder (76.1%) reached natal sub-watersheds. Of these, fish unsuccessful in the lower reaches tended to have a high plasma osmolality in the ocean, whereas fish failing in the upper reaches had lower levels of reproductive hormones in the ocean.

Use of Electromyogram Telemetry to Assess Difficult Passage Areas for River-Migrating Adult Sockeye Salmon

Abstract We conducted laboratory respirometry trials using adult sockeye salmon Oncorhynchus nerka implanted with electromyogram (EMG) radio transmitters to investigate the relationship between oxygen consumption and EMG pulse interval. The strong association that was observed suggested that EMG telemetry could be used to assess activity and, thus, relative energy expenditure in freely migrating sockeye salmon. Using EMG telemetry, we then assessed the relative energy costs of upstream migration by adult sockeye salmon through specific reaches of the Fraser River, British Columbia. Greatest energy costs were incurred during migration through Hells Gate fishways, a known point of difficult passage. Another energetically demanding area was a gravel bar that had not been previously identified as difficult for passage. Three other areas that historically had been identified as difficult for passage were energetically less expensive to migrate through during our study. Our results demonstrate that EMG telemet...

Swimming patterns and behaviour of upriver-migrating adult pink (Oncorhynchus gorbuscha) and sockeye (O. nerka) salmon as assessed by EMG telemetry in the Fraser River, British Columbia, Canada

Little is known about the behaviour patterns and swimming speed strategies of anadromous upriver migrating fish. We used electromyogram telemetry to estimate instantaneous swimming speeds for individual sockeye (Oncorhynchus nerka) and pink salmon (O. gorbuscha) during their spawning migrations through reaches which spanned a gradient in river hydraulic features in the Fraser River, British Columbia. Our main objectives were to describe patterns of individual-specific swim speeds and behaviours, identify swimming speed strategies and contrast these between sexes, species and reaches. Although mean swimming speeds did not differ between pink salmon (2.21 BL s−1) and sockeye salmon (1.60 BL s−1), sockeye salmon were over twice as variable (mean CV; 54.78) in swimming speeds as pink salmon (mean CV; 22.54). Using laboratory-derived criteria, we classified swimming speeds as sustained (<2.5 BL s−1), prolonged (2.5–3.2 BL s−1), or burst (>3.2 BL s−1). We found no differences between sexes or species in the proportion of total time swimming in these categories – sustained (0.76), prolonged (0.18), burst (0.06); numbers are based on species and sexes combined. Reaches with relatively complex hydraulics and fast surface currents had migrants with relatively high levels of swimming speed variation (e.g., high swimming speed CV, reduced proportions of sustained speeds, elevated proportions of burst speeds, and high rates of bursts) and high frequency of river crossings. We speculate that complex current patterns generated by river constrictions created confusing migration cues, which impeded a salmons ability to locate appropriate pathways.