James R. Irvine

Evaluations of Visible Implant Fluorescent Tags for Marking Coho Salmon Smolts

Abstract Groups of about 10,000 smolts of coho salmon Oncorhynchus kisutch were marked with one of two types of fluorescent tags: visible implant fluorescent filament (VIF) and visible implant fluorescent elastomer (VIE). Fish were also tagged with coded wire tags and adipose fin clipped to assess fluorescent tag retention and marine survival. Ocean recoveries were reported through the coastwide mark–recovery database. Returning fish were examined for the presence of tags, and survival and exploitation data were compared among groups. Fluorescent tags in approximately 90% of fish bearing them were easily seen in natural light. Probabilities of recovery, either in fisheries or spawning escapements after fisheries, and survival rates, did not differ significantly between coded-wire-tagged fish with and without fluorescent tags (either type). Short-term losses of fluorescent marks were about 5%; long-term losses between application and recovery were about 28% for VIE but were not statistically significant fo...

Reliability of indicators of decline in abundance.

Although there are many indicators of endangerment (i.e., whether populations or species meet criteria that justify conservation action), their reliability has rarely been tested. Such indicators may fail to identify that a population or species meets criteria for conservation action (false negative) or may incorrectly show that such criteria have been met (false positive). To quantify the rate of both types of error for 20 commonly used indicators of declining abundance (threat indicators), we used receiver operating characteristic curves derived from historical (1938-2007) data for 18 sockeye salmon (Oncorhynchus nerka) populations in the Fraser River, British Columbia, Canada. We retrospectively determined each populations yearly status (reflected by change in abundance over time) on the basis of each indicator. We then compared that populations status in a given year with the status in subsequent years (determined by the magnitude of decline in abundance across those years). For each sockeye population, we calculated how often each indicator of past status matched subsequent status. No single threat indicator provided error-free estimates of status, but indicators that reflected the extent (i.e., magnitude) of past decline in abundance (through comparison of current abundance with some historical baseline abundance) tended to better reflect status in subsequent years than the rate of decline over the previous 3 generations (a widely used indicator). We recommend that when possible, the reliability of various threat indicators be evaluated with empirical analyses before such indicators are used to determine the need for conservation action. These indicators should include estimates from the entire data set to take into account a historical baseline.

Genetic and Coded Wire Tag Results Combine to Allow More-Precise Management of a Complex Chinook Salmon Aggregate

Abstract Conservation concerns for small, relatively unproductive populations of Chinook salmon Oncorhynchus tshawytscha limit the utility of fisheries in Canadas Fraser River. To identify population-specific migration time and to index abundance, we analyzed 4,822 fish sampled for genetic variation in 2000 and 2001 and 580 fish with coded wire tags (CWTs) caught from 1987 to 2004 in a test fishery near the river mouth. Population sizes estimated from microsatellite variation were within 3.4% of the known-origin population composition and were unbiased in comparison with known-origin population sizes. All but 1 of the 30 populations detected by both genetic methods and CWTs had overlapping migration times, but these times differed significantly for only 7 populations. Migration times were identified for another 23 untagged populations identified by using genetics, which resulted in the assignment of migration timing groups (peak passage) for 53 populations as spring (March–May), early summer (June), mids...

Understanding Smolt Survival Trends in Sockeye Salmon

Abstract Many populations of Sockeye Salmon Oncorhynchus nerka in the eastern North Pacific Ocean experienced significant productivity declines that began about 1990, but there is no consensus on the mechanisms responsible. To better understand Sockeye Salmon survival trends, we examined the 50-year time series for two age-classes of Sockeye Salmon smolts from Chilko Lake in central British Columbia. Arranging survival time series for both age-classes by ocean entry year and combining them, weighted by a proxy model of sampling variance, reduced the sampling variance in the original age-1 smolt survivals sufficiently to indicate a linear trend of increasing survival from 1960 to 1990 that suddenly changed at or near 1991 to a lower and declining trend from 1992 to 2008. Neither density nor mean length influenced smolt survival. Returns in a given year were not good predictors of siblings returning in subsequent years. Time spent at sea increased linearly beginning around 1970. Although smolt survivals differed between ecosystem regimes, there was only the one clear pattern break about 1991. To improve our understanding of mechanisms, survival trends were compared with environmental indices that included catches and hatchery releases of potentially competing salmon from around the North Pacific Ocean. Smolt survivals were more similar to abundance indices of Sockeye Salmon, Chum Salmon O. keta, and Pink Salmon O. gorbuscha than to indices of global, regional, or local ocean climate. Our results are consistent with the hypothesis that salmon productivity in the North Pacific declined soon after 1990. We present a simple model to illustrate how increased competition at sea, related to the release of large numbers of hatchery salmon, in conjunction with changes in ocean productivity, may have played a significant role in improving Sockeye Salmon survivals while reducing their growth before 1991. After 1991, these factors may have acted to reduce survivals while the growth of survivors showed no effect.

Sulfur isotopes in otoliths allow discrimination of anadromous and non-anadromous ecotypes of sockeye salmon (Oncorhynchus nerka)

Oncorhynchus nerka occur both as anadromous sockeye salmon that spend most of their life in the ocean, and as non-anadromous kokanee salmon that remain in fresh water their entire lives. We assessed whether stable isotopes of sulfur (δ34S) in otoliths could be used to distinguish sockeye salmon and kokanee ecotypes that are otherwise difficult to identify when they share a common freshwater rearing environment. We also investigated the chemical link between salmon and their diet by measuring δ34S in various fish tissues (eggs, muscle, scales) and zooplankton. δ34S (mean±SE) in sockeye salmon eggs (18.7 ± 0.4‰) and marine zooplankton (20.5 ± 0.1‰) were enriched by 10–14‰ compared with kokanee eggs and freshwater zooplankton. δ34S in the otolith cores of sockeye salmon (19.2 ± 0.7‰) and kokanee salmon (5.3 ± 1.1‰) were similar to δ34S in marine and freshwater zooplankton, respectively, indicating that the core is derived from maternal yolk tissue and reflects the maternal diet. δ34S in the freshwater growth zone of otoliths did not differ significantly between sockeye (5.9 ± 1.1‰) and kokanee salmon (4.4 ± 1.2‰), and was similar to freshwater zooplankton. The mean difference between δ34S in the otolith core and first year of growth was 13.3 ± 1.4‰ for sockeye and 0.65 ± 1.3‰ for kokanee salmon. A quadratic discriminant function developed from measurements of δ34S in otoliths of known maternal origin provided perfect classification rates in cross-validation tests. Thus, sulfur isotope ratios in otoliths are effective in discriminating between anadromous and non-anadromous ecotypes of O. nerka.

Spatial and Temporal Patterns in Smolt Survival of Wild and Hatchery Coho Salmon in the Salish Sea

Abstract Understanding the factors contributing to declining smolt-to-adult survival (hereafter “smolt survival”) of Coho Salmon Oncorhynchus kisutch originating in the Salish Sea of southwestern British Columbia and Washington State is a high priority for fish management agencies. Uncertainty regarding the relative importance of mortality operating at different spatial scales hinders the prioritization of science and management activities. We therefore examined spatial and temporal coherence in smolt survivals for Coho Salmon based on a decision tree framework organized by spatial hierarchy. Smolt survival patterns of populations that entered marine waters within the Salish Sea were analyzed and compared with Pacific coast reference populations at similar latitudes. In all areas, wild Coho Salmon had higher survival than hatchery Coho Salmon. Coherence in Coho Salmon smolt survival occurred at multiple spatial scales during ocean entry years 1977–2010. The primary pattern within the Salish Sea was a declining smolt survival trend over this period. In comparison, smolt survival of Pacific coast reference populations was low in the 1990s but subsequently increased. Within the Salish Sea, smolt survival in the Strait of Georgia declined faster than it did in Puget Sound. Spatial synchrony was stronger among neighboring Salish Sea populations and occurred at a broader spatial scale immediately following the 1989 ecosystem regime shift in the North Pacific Ocean than before or after. Smolt survival of Coho Salmon was synchronized at a more local scale than reported by other researchers for Chinook Salmon O. tshawytscha, Pink Salmon O. gorbuscha, Chum Salmon O. keta, and Sockeye Salmon O. nerka, suggesting that early marine conditions are especially important for Coho Salmon in the Salish Sea. Further exploration of ecosystem variables at multiple spatial scales is needed to effectively address linkages between the marine ecosystem and Coho Salmon smolt survival within the Salish Sea. Since the relative importance of particular variables may have changed during our period of record, researchers will need to carefully match spatial and temporal scales to their questions of interest.

Canada's Species at Risk Act

Abstract Canadian salmon are now eligible for protection under a federal Species at Risk Act proclaimed in June 2003 and fully implemented in June 2004. The act has four major steps dealing with species at risk of extinction: (1) an independent scientific committee assesses biological status and designates those at risk, (2) Federal Cabinet decides, following consideration of socioeconomic implications, which species to add to the legal list of species at risk, (3) legal protection, and (4) recovery planning and implementation. The committee has designated five distinct populations of salmon as endangered—one Atlantic salmon (Salmo salar), one coho salmon (Oncorhynchus kisutch), two sockeye salmon (O. nerka), and one Chinook salmon (O. tshawytscha). Only the Atlantic salmon is currently listed under the act; Cabinet decided not to list the two sockeye after considering socioeconomic implications and decisions on listing coho and Chinook are pending socioeconomic assessment. Both the Species at Risk Act in...

Size-Dependent Smolt Yield and Overwinter Survival of Hatchery-Reared Masu Salmon Released in Fall

Abstract To increase commercial marine catches of masu salmon Oncorhynchus masou in northern Japan, hatchery-reared juveniles are stocked at several life stages. To minimize mortality from freshwater angling, fish are often stocked in the fall when the fishing season is almost finished. In the fall of 1994–1998, we experimentally stocked hatchery-reared age-0 masu salmon (mean weights, 4.1–13.9 g) in the Masuhoro River of northern Japan. Mark–recapture experiments were conducted to estimate the numbers of hatchery-origin masu salmon smolts in the spring. Numbers of masu salmon parr in the river were estimated in July 1998–1999 when the smolt runs were almost finished. The proportion of fish smolting at age 1 (2.2–15.7%) was positively correlated with mean weight at release. Overwinter survival (9.0–17.0%) was also correlated with fish weight at release. Our study showed that size at release is an important factor when stocking age-0 masu salmon in the fall to maximize the number of smolts produced and the...

Distinguishing benchmarks of biological status from management reference points: A case study on Pacific salmon in Canada

For fisheries with multiple, competing objectives, identifying and applying reference points for management can present difficult trade-offs between long-term biological and shorter-term socioeconomic considerations. The term biological benchmarks is proposed to demarcate zones of population status based on conservation and production considerations. These scientifically derived benchmarks contrast with management reference points that generally require additional shorter-term socioeconomic information best obtained through public consultations. This paper illustrates the distinction between biological benchmarks and management reference points with a case study on Pacific salmon ( Oncorhynchus spp.). In Canada, the management and assessment of wild Pacific salmon are guided by a major 2005 conservation policy, which calls for the identification of biological benchmarks to categorize status of demographically isolated populations, and decision-support tools, such as management reference points, to integrate biological information with appropriate social and economic information. In the Fraser River (British Columbia, Canada), the selection of management reference points for sockeye salmon ( O. nerka ) fisheries explicitly considered trade-offs between the probability of meeting long-term biological objectives on component populations and harvest objectives on population aggregates. Decisions about reference points were made in a consultative process that included extensive stakeholder engagement. Other agencies are urged to distinguish biological benchmarks from management reference points to ensure transparency in the relative influence of biological versus socioeconomic information in decision making.

Standardizing Spawner Escapement Data: A Case Study of the Nechako River Chinook Salmon

Abstract Spawner escapements for Pacific salmon Oncorhynchus spp. are frequently estimated by using a variety of methods over time. To evaluate temporal patterns in escapements, the data must be standardized. In our study, we standardized escapement data from 1980 to 1998 for the chinook salmon O. tshawytscha of the Nechako River in British Columbia. This particular stock and period were chosen because (1) escapement had been estimated by several methods that could be standardized and (2) escapement estimation methods and data had previously been summarized in detail and were readily available. The area-under-the-curve method of estimating escapement had been used since 1987, and after minor adjustments in 1989, methods had remained constant. To evaluate whether differences in methods for earlier years affected analysis of trends in escapement over time, we converted the data for years 1980–1988 to area-under-the-curve equivalents. The mean of reported escapements for the 1980–1988 period increased from 1...