Search

Factors influencing the health of sockeye salmon Oncorhynchus nerka in British Columbia, Canada, are important for fisheries management and conservation. Juvenile salmon originating from the Fraser River were screened for 3 enzootic parasites (Myxobolus arcticus, Parvicapsula minibicornis, Ceratonova shasta) and the bacterium Renibacterium salmoninarum. Fish were collected from the Strait of Georgia in 2010, 2011 and 2012 and genotyped to stock of origin. Trends in infection status were estimated by year, spawning zone and catch area. The annual prevalences of P. minibicornis (n = 1448) were 23.3, 6.5 and 8.1%, and for M. arcticus (n = 1343), annual prevalences were 40.4, 66.3 and 27.4%, respectively. Logistic regression showed that P. minibicornis was most strongly associated with salmon from the lower Fraser River spawning zone and increased with distance caught from the mouth of the Fraser River. In contrast, infection with M. arcticus was most strongly associated with salmon from the middle Fraser River spawning zone, and there was no trend related to distance from the Fraser River. Neither R. salmoninarum nor C. shasta were detected. These observations are discussed in the context of salmon life history and pathogen biology.

Survival during early marine life stages is hypothesized to contribute disproportionately to variation in salmonid recruitment, yet estimates of cumulative mortality are constrained by knowledge of how long juveniles reside in specific regions. We used otolith microstructure techniques to examine the relationship between migratory rate and ocean entry characteristics of juvenile sockeye salmon (Oncorhynchus nerka). We observed differences in migratory rate between catch locations that are consistent with divergent migratory behaviours. Individuals captured in northern regions were typically older, larger at ocean entry, and migrated more rapidly. Migratory rate was also correlated with entry size, phenology, population group, and year. Next, we compared “lingering” individuals captured nearshore during fall surveys to juveniles from the same populations captured during the peak summer migratory period. We determined that individuals that entered after 24 May and at smaller sizes (

We examined how individual processes contribute to a latitudinal gradient in body size within populations of migrating juvenile sockeye salmon (Oncorhynchus nerka) while simultaneously testing for size-selective mortality, a potentially confounding population scale process. Using otolith microstructure techniques and structural equation modeling, we determined that ocean entry size and phenology had strong, direct effects on size at capture. Population identity and freshwater age also had strong indirect effects, moderated by size at entry. Conversely, marine growth rates immediately after entry or before capture were relatively weak predictors of size during migration. We next tested for shifts in size distribution indicative of selective mortality, but detected no evidence of smaller individuals experiencing lower survival during early marine migrations. These results indicate that the migratory distributions of juvenile sockeye salmon are influenced by body size and that this variation is predominantly driven by traits present prior to freshwater outmigration, rather than marine growth or differential survival. We suggest integrating individual variation in migratory characteristics with the effects of environmental conditions experienced en route to provide an improved understanding of migratory species.

The phenology of long-distance migrations can influence individual fitness, moderate population dynamics and regulate the availability of ecosystem services to other trophic levels. Phenology varies within and among populations, and can be influenced by conditions individuals experience both prior to departure and encounter en route. Assessing how intrinsic and extrinsic factors (e.g., individual physical condition vs. environmental conditions) interact to influence variation in migratory phenologies across ecological scales is often limited due to logistical constraints associated with tracking large numbers of individuals from multiple populations simultaneously. We used two natural tags, DNA and otolith microstructure analysis, to estimate the relative influence of individual traits (life-history strategy, body size at departure and growth during migration), population-specific behaviours and interannual variability on the phenology of marine migrations in juvenile sockeye salmon Oncorhynchus nerka. We show that the timing and duration of juvenile sockeye salmon migrations were correlated with both life-history strategy and body size, while migration duration was also correlated with departure timing and growth rates during migration. Even after accounting for the effect of individual traits, several populations exhibited distinct migration phenologies. Finally, we observed substantial interannual and residual variation, suggesting stochastic environmental conditions moderate the influence of carry-over effects that develop prior to departure, as well as population-specific strategies. Migratory phenologies are shaped by complex interactions between drivers acting at multiple ecological and temporal scales. Given evidence that intraspecific diversity can stabilize ecological systems, conservation efforts should seek to maintain migratory variation among populations and preserve locally adapted phenotypes; however, variation within populations, which may buffer systems from environmental stochasticity, should also be regularly assessed and preserved.

Mortality in the early marine period in a particular habitat is related to the severity of the factors causing mortality and the time that juvenile Pacific salmon Oncorhynchus spp. spend in the habitat. Juvenile sockeye salmon O. nerka produced in the Fraser River rear in the Strait of Georgia immediately upon leaving freshwater. We used catches from trawl and purse seine surveys to develop two estimates of their average residence time in the Strait of Georgia and present a third estimate which pertains to Chilko Lake smolts in particular. The average time between the entry of the last 1% of juvenile sockeye salmon into the Strait of Georgia and the departure of the last juveniles was 54 d. The average time between the point when the maximum number of juvenile sockeye salmon entered the Strait of Georgia and the point when the maximum abundance in the strait occurred was 43 d. Individuals from the Chilko Lake population were shown to spend a minimum of 31–43 d in the Strait of Georgia, indicating...

Trawl studies from 1998 to 2009 indicated that juvenile Pacific salmon Oncorhynchus spp. and Pacific herring Clupea pallasii represented 98% of the fish in the surface waters of the Strait of Georgia during the day in the spring and early summer. Standardized catches of all juvenile Pacific salmon in the trawl surveys were lowest in 2007. Catches of young-of-the-year Pacific herring were also extremely low in 2007. Three years later, the 2007 year-class had the lowest recruitment to the fishery in recorded history. In 2007, juvenile coho salmon O. kisutch and Chinook salmon O. tshawytscha were small and had the lowest condition of the fish in all surveys as well as a high percentage of empty stomachs. The early marine survival of coho salmon in 2007 and the total survival in 2008 were exceptionally poor. Trawl catches of juvenile chum salmon O. keta in 2007 were the lowest of all surveys. Adult chum salmon from these juveniles that returned in 2010 had extremely poor survival. Juvenile sockeye sa...

The migration of juvenile coho salmon Oncorhynchus kisutch out of the Strait of Georgia in 2006 was investigated by means of acoustic telemetry. During July and September, 173 juvenile coho salmon were caught in the strait with a purse seine, surgically implanted with acoustic tags, and released the same day. In 2006, approximately 19% of the fish tagged in July and 52% of those tagged in September left the Strait of Georgia. Most of these fish did so in October and November through Juan de Fuca Strait and not by a northward migration through Queen Charlotte Strait. This movement was several months later than that observed for coho salmon migrating out of Puget Sound. A small number of coho salmon that moved out of the Strait of Georgia migrated south to areas off the coast of Washington and Oregon. The documentation of a movement out of the Strait of Georgia late in the year was important, as it shows that population changes of the juvenile coho salmon that enter the strait during spring and sum...

An analysis of the results of a 10-year study of the population ecology of juvenile hatchery and wild coho salmon Oncorhynchus kisutch in the Strait of Georgia produced new information about the interannual and interseasonal fluctuations in abundance and marine survival. A decline in the percentage of hatchery coho salmon was related to declines in hatchery fish abundance and marine survival; wild coho salmon abundance was more stable. The declining marine survival of hatchery coho salmon appeared to be related to a fixed average date of release from hatcheries and a possibility of earlier prey production. The relatively stable abundance of wild coho salmon may relate to a natural trend toward earlier ocean entry dates. Oscillations in hatchery coho salmon percentage and abundance were related to oscillations in abundance of juvenile pink salmon O. gorbuscha. The impact of oscillating density affected marine survival of hatchery coho salmon more than that of wild coho salmon. Marine survival and ...

The sea louse, Lepeophtheirus salmonis, is commonly found on Pacific salmon that are rearing in the central North Pacific Ocean and adjacent seas (subarctic Pacific). Large numbers of sea lice have also been observed on all species of adult Pacific salmon when they return to coastal marine areas in the summer during their spawning migration. We propose that the transport of sea lice into coastal areas is a strategy employed by L. salmonis to improve their productivity by improving the transmission potential of the infectious stage when host densities are decreased in the open ocean and increased in the coastal areas. Juveniles of the species of Pacific salmon inhabit the same areas at the same time as the returning adult salmon and, according to the proposed strategy, will become infected from sea lice on the adult Pacific salmon. Juvenile pink, chum and sockeye salmon will carry these sea lice into the open ocean when they migrate away from the coastal areas later in the year. The offspring of these sea lice on pink, chum and sockeye would infect Pacific salmon on the high seas and thus maintain high abundances of sea lice. Juvenile coho and chinook salmon that remain in the coastal areas would serve as hosts for the sea lice over the winter. The sea lice on these resident coho and chinook salmon would infect juvenile Pacific salmon that enter the ocean in the early spring. The strategy would result in the infection of juvenile Pacific salmon throughout their range in all coastal areas.

Juvenile pink salmon that entered a marine ecosystem along the eastern margin of Queen Charlotte Strait in 2003 and returned as adults in 2004 had very high marine survival. The early seaward migration and midsummer rearing in 2003 were in an area containing 16 active Atlantic salmon farms. Two species of sea louse, Lepeophtheirus salmonis and Caligus clemensi, were commonly found on farmed salmon and juvenile Pacific salmon during the early rearing period of the pink salmon. Mobile L. salmonis and C. clemensi were most abundant on farmed Atlantic salmon from February to May and on pink salmon in June. Chalimus stages were the dominant stages on pink salmon to the end of May. Mobile stages of C. clemensi were the dominant stages and species of sea louse on farmed Atlantic salmon and pink salmon at about the same time in June. DNA studies showed that local juvenile pink salmon were in the area until August. The exceptional returns of the brood year suggest that pink salmon populations and farmed Atlantic salmon coexisted successfully during 2003 within an environment that included sea lice and farmed Atlantic salmon. The processes responsible for the high marine survival cannot be identified with certainty, but they could include increased freshwater discharge in 2003, which may have resulted in lower salinity less favourable to sea louse production, increased inflow of nutrient-rich water to the study area, and the introduction of a Provincial Action Plan that required mandatory louse monitoring and established a fallowed migration corridor for pink salmon.

Adult Pacific salmon were captured individually during their coastal migration and examined for sea lice in two marine areas in the central coast area of British Columbia. Virtually all salmon had sea lice. Pink, chum, and sockeye salmon had average intensities ranging from 41.5 to 52.0 sea lice. Chinook and coho salmon had average intensities ranging from 16.1 to 18.5 sea lice. Chinook salmon had the lowest intensities of sea lice and the smallest number of chalimus stages. The prevalence and intensities of sea lice were similar in each study area, one of which had salmon farms and one that had no salmon farms. Lepeoptheirus salmonis were about twice as numerous as Caligus clemensi. Most C. clemensi were in the chalimus stage and most L. salmonis were in the mobile stage. Gravid female L. salmonis represented 33.3% of all mobile stages. Gravid female C. clemensi were rare. In general, two species of sea lice were observed to be a common parasite on five species of Pacific salmon in the area that contained salmon farms and the reference area that had no farms.

The relationships between the spawning stock and the subsequent recruitment of pink salmon Oncorhynchus gorbuscha and sockeye salmon O. nerka from the Fraser River improve significantly when the data are separated by climate and ocean regimes. Our analyses show changes in these relationships as regimes shift, indicating that the trend in marine survival of pink and sockeye salmon changes on a decadal scale. In general, the climate and ocean regime from 1977 to 1988 was productive for pink and sockeye salmon. However, the regime in the 1990s was characterized by reduced productivity for both species. The occurrence of a natural shift in the trend of pink and sockeye salmon production on a decadal scale should be incorporated into the management of Pacific salmon stocks to ensure that annual catches, escapements, and planned stock abundances are consistent with the productivity of a particular regime.

Beginning in 2000, juvenile Pacific salmon Oncorhynchus spp. in the Strait of Georgia, British Columbia, fed more frequently, contained greater volumes of prey in their stomachs compared with the previous 3 years, and increased in size. Abundances in July also increased in 2000 and 2001. Marine survival increased, as indicated by the early marine survival of coho salmon O. kisutch in 2000 and 2001, which improved to more than twice the annual survival estimates for 1997–1999. Other indicators of improved marine survival included exceptional returns of pink salmon O. gorbuscha to the Fraser River in 2001 and sockeye salmon O. nerka in 2002. The change to a more productive regime for juvenile Pacific salmon was a lagged response to an abrupt change in climate in 1998, as shown by regional, basin-scale, and planetary indices.

Otoliths, or ‘ear stones’, are calcium carbonate structures found in all vertebrates. In teleosts, they have a number of sensory functions, including hearing. Daily growth increments of these structures have permitted advanced age and population studies of teleosts. Whereas ‘normal’ otoliths are composed of crystals imbedded within a protein matrix as aragonite, a ‘crystalline’ form of calcium carbonate termed vaterite is also found. A review of the otolith literature demonstrates a significant level of understanding of the structure and function of otoliths, but the cause for crystalline otolith structure remains speculative. Pairs of otoliths from hatchery and wild juvenile and adult coho salmon (Oncorhynchus kisutch) were examined visually for determination of otolith microstructure type. The vateritic or crystalline otoliths were found in much higher percentages in juvenile hatchery-reared coho salmon than in juvenile wild coho salmon, supporting previous studies. There did not seem to be any negative impact on size or survival. There was also no correlation between crystalline otoliths and premature maturation in coho males. A preliminary study of adult coho salmon returning to Big Qualicum and Chilliwack hatcheries showed even higher ratios of vateritic otoliths than observed in juveniles.

Coho salmon Oncorhynchus kisutch from the Strait of Georgia were used to test the hypothesis that slower growing fish in their first ocean year had lower survival over the late fall and winter than faster growing fish. The Strait of Georgia provided a suitable area for this study because it is a semi-enclosed rearing area for juvenile Pacific salmon that is distinct from the open marine rearing areas off the west coast. Coho salmon that survived the winter had significantly larger spacing between circuli on scales, indicating that brood year strength is related to growth in the first marine year. Other studies have shown that smaller fish of a cohort are less able to survive periods of energy deficit than larger fish. Thus, size-related mortality in the first marine fall and winter may be an important determinant of brood year strength of some coho salmon stocks and stocks of other species of Pacific salmon.

The percentage of hatchery-reared coho salmon Oncorhynchus kisutch in the Strait of Georgia, British Columbia, increased from nearly 0% in the early 1970s to more than 70% by 2001. These estimates were derived from fin clip and coded wire tag data collected from commercial and sport fisheries, research surveys conducted in the summer and fall of 1997 to 2000, and examination of the microstructure of otoliths extracted from juvenile coho salmon collected during our marine surveys. The increasing trend may be related to the proportions of hatchery and wild smolts entering saltwater, fishing rates, and changes in the ecological processes regulating coho salmon production in the ocean. The consequence for management is that the abundance of wild spawning salmon (escapement) depends on hatchery as well as wild production. The consequence for policy makers is that future enhancement activities need to have clear policies for assessing the effects of hatchery fish on the population dynamics of wild fish...

The abundance of Fraser River sockeye salmon (Oncorhynchus nerka) stocks was low in the 1960s, increased to high levels in the 1980s, and possibly entered a period of low abundance in recent years. The abundance changes of the combined stocks can be separated into productivity regimes that correspond to changes in climate trends. The most distinct change occurred when there was a major change in the climate over the Pacific Ocean in the winter of 1976-1977. The existence of natural shifts in abundance trends means that the high returns that occur during periods of high productivity would not be expected to occur during the low-productivity periods. The response of Fraser River sockeye to climate changes may be a specific example of a more general response by a number of species of fishes in the Pacific and perhaps in other oceans. Because the shift from one regime to the other occurred quickly in the 1970s, future shifts could also occur quickly. It is necessary to detect natural shifts in productivity when attempting to manage fishing impacts to ensure that economic expectations are sound and that overfishing does not occur.

River lamprey (Lampetra ayresi) enter the Strait of Georgia from the Fraser River and feed almost exclusively on Pacific herring (Clupea harengus) and salmon (Oncorhynchus spp.). Although the major prey of river lamprey is Pacific herring, the greater effect of lamprey predation was on the populations of chinook (O. tshawytscha) and coho (O. kisutch) salmon. In 1990 and 1991, river lamprey killed a minimum of 20 million and 18 million chinook salmon, respectively, and a minimum of 2 million and 10 million coho salmon in the same years. In 1991, river lamprey in the Fraser River plume killed an equivalent of approximately 65 and 25% of the total Canadian hatchery and wild production of coho and chinook salmon, respectively. These estimates are probably low because river lamprey also feed in other areas and the abundance estimates are conservative. These high mortality rates indicate that river lamprey predation must be considered as a major source of natural mortality of chinook and coho salmon in the Strait of Georgia.

We identified years of anomalously high and low discharge from the Fraser River and compared these years with indices of anomalously high and low production of Pacific salmon (Oncorhynchus spp.) and Pacific herring (Clupea pallasi). For chinook (O. tshawytscha) and coho salmon (O. kisutch), we found that brood years that went to sea in a year when the Fraser River discharge was very high compared with the previous year virtually never had an index of production that was higher than the previous year. Similarly, brood years that went to sea in a year when the Fraser River discharge was very low compared with the previous year almost never had an index of productivity that was lower than the previous year. The analysis identified a weaker association between extreme discharge anomalies and chum salmon (O. keta) production. A close association was not found between extreme discharge anomalies and pink salmon (O. gorbuscha), sockeye salmon (O. nerka), or herring production. The relationships identify a connection between annual fluctuations in river flow and production of some marine fishes and may be of use in forecasting abundance changes.

An increase in infections with two species of sea lice occurred on farmed salmon farthest up an inlet in the Broughton Island area of British Columbia during the winter of 2005/2006. The increase in the chalimus stage started at the end of November 2005 at a rate of 0.03 lice/day for Lepeophtheirus salmonis and 0.015 lice/day for Caligus clemensi. The increase in the infection started at a time of high salinity and low sea surface temperatures with very few gravid sea lice detected on the farmed fish. The mobile stages increased in early January about one month after the increase in the chalimus stage. Gravid lice increased in abundance about the time the farmed fish were treated with SLICE® in early February. This pattern of an increase in infection in the winter was similar in two nearby farms. In January of 2008 the three farms in the study area were either treated with SLICE® or the fish were harvested. Despite the reduced capacity of the salmon farms to produce sea lice, the juvenile stages remained abundant on sticklebacks ( Gasterosteus aculeatus ) around the farms in February and March of 2008. Sticklebacks were heavily infected with sea lice but were not a host of gravid lice. Trawl studies in the vicinity of the farms did not find an abundance of hosts except for sticklebacks. Some of the infection on the sticklebacks could originate from a low level of gravid lice on the farmed fish in the study area. However, we speculated that a major source of the winter infection on the sticklebacks could result from the transport of infectious stages in the deeper water that flows into the area as a consequence of the estuarine circulation. The source of these lice and the lice in the 2005/2006 study could be natural or from untreated fish farms farther down the inlet or both. Continued research is needed to understand the biology and population ecology of both species of sea lice in order to manage their production

The anadromous parasitic Pacific lamprey (Lampetra tridentata) does not feed during metamorphosis or its spawning migration. To assess the utilization of body reserves, we compared the compositions of an adult lamprey held for 2 yr without food, recently metamorphosed lampreys, and lampreys starved for 6 mo. Moisture was higher and soluble ash and lipid levels were lower in tissue of the 2-yr-starved than in metamorphosed lampreys (2.67 and 3.39 kj∙g−1, respectively). Fatty acid profiles of 2-yr-starved and metamorphosed lampreys were qualitatively similar except for the presence of 15:0 in the latter. Substantially lower levels of 14:0 and 16:1 n7 and higher levels of polyunsaturated fatty acids occurred in starved lampreys. Changes in composition of lampreys starved for 6 mo were similar to changes between the 2-yr-starved and metamorphosed lampreys. Maintenance energy in a normalized 1-g lamprey starved for 6 mo was derived from catabolism of 71% lipid and 29% protein; total loss was 2.56 kJ or 49% of the original energy. The ability to survive extended periods on endogenous reserves, which may have allowed L. tridentata to survive past environmental catastrophes, allows it to migrate considerable distances to spawning areas in the headwaters of rivers.

Dorsal aorta blood samples were taken from cannulated rainbow trout (Salmo gairdneri) exposed to pH 4.0 (acid group) or pH 7.0 (controls) in normocapnic conditions at 10 °C. Over a 5-d period there was a significant gradual decrease in pH and total CO2 in the acid group but no significant difference in pO2 and lactate compared to the controls. After uncannulated rainbow trout were exposed to the same conditions for 12 d there were significant increases in hemoglobin, hematocrit, and erythrocyte levels in caudal vein samples from the acid group. The results show that rainbow trout exposed to acid without hypercapnia develop acidaemia which is not a result of anaerobic respiration. The increase in erythrocyte concentration probably offsets the effects of acidaemia upon blood oxygen carrying capacity. Differences in ambient pCO2 and/or species differences could account for varying acid-base values in acid exposed fish reported by different workers. Key words: environmental acidification, acidaemia, lactate, pH, total carbonate, fish

An initial 1- to 2-h exposure of juvenile rainbow trout (Salmo gairdneri) to 2.8 μM (= μmol∙L−1) inorganic aluminum caused increased ventilation and activity responses ranging from slight to severe depending on the ambient pH. The severity of physiological response after 6–11 d of exposure was similar to that of the initial response. This was severe at pH 6.1, 4.5, and 4.0, slight to moderate at pH 5.0 and 5.5, but minimal at pH 6.5. In the severe response groups, 40–90% of the fish died after a few days of exposure. Death was due primarily to hypoxia at pH 6.1 and to electrolyte loss at pH 4.5 and 4.0. Between pH 5.5 and 5.0 there was a transition between the two mechanisms. With 8–10 mg natural organic acids∙L−1the response to the same concentration of inorganic aluminum was unchanged at pH 5.0 but was slightly increased at pH 4.5. Fish kills of salmonids that have occurred in South Norway could have been predicted from these results. In North America the presence of refuge areas and the prevalence of more tolerant species could account for the occurrence of sublethal rather than lethal responses.

The population dynamics of chinook salmon (Oncorhynchus tshawytscha) from the Cowichan River on Vancouver Island, British Columbia, Canada are used by the Pacific Salmon Commission as an index of the general state of chinook salmon coast wide. In recent years the production declined to very low levels despite the use of a hatchery that was intended to increase production by improving the number of smolts entering the ocean. In 2008, we carried out an extensive study of the early marine survival of the hatchery and wild juvenile chinook salmon. We found that both rearing types mostly remained within the Gulf Islands study area during the period when most of the marine mortality occurred for the hatchery fish. By mid September, approximately 1.3% of all hatchery fish survived, compared to 7.8%–31.5% for wild fish. This six to 24 times difference in survival could negate an estimated increased egg-to-smolt survival of about 13% that is theorized to result through the use of a hatchery. Estimates of the early marine survival are approximate, but sufficient to show a dramatic difference in the response of the two rearing types to the marine nursery area. If the declining trend in production continues for both rearing types, modifications to the hatchery program are needed to improve survival or an emphasis on improving the abundances of wild stocks is necessary, or both. The discovery that the juvenile Cowichan River chinook salmon remain within a relatively confined area of the Gulf Islands within the Strait of Georgia offers an excellent opportunity to research the mechanisms that cause the early marine mortalities and hopefully contribute to a management that improves the production.