David W Welch

The role that open‐net‐pen farms for Atlantic Salmon Salmo salar play in the global decline of stocks of wild salmonids (Salmo spp. and Oncorhynchus spp.) is contentious; Canada’s west coast is no exception. We identified the proportion of acoustic‐tagged juvenile Sockeye Salmon Oncorhynchus nerka migrating through the main migration routes of the...

Background Animal biotelemetry and individual-based modeling (IBM) are natural complements, but there are few published examples where they are applied together to address fundamental or applied ecological questions. Existing studies are often found in the modeling literature and frequently re-use small datasets collected for purposes other than th...

Although telemetry is commonly used to study fishes, researchers rarely design experiments that facilitate in situ quantification of tagging-related impacts to survival. We experimentally applied high (mean burden = 9.6%) and low (2.6%) acoustic tag burdens and gill clip biopsies to migrating juvenile sockeye salmon (Oncorhynchus nerka). Mortality...

We collated smolt-to-adult return rate (SAR) data for Chinook salmon from all available regions of the Pacific coast of North America to examine the large-scale patterns of salmon survival. For consistency, our analyses primarily used coded wire tag-based (CWT) SAR estimates. Survival collapsed over the past half century by roughly a factor of thre...

Background: Acoustic telemetry is now a key research tool used to quantify juvenile salmon survival, but transmitter size has limited past studies to larger smolts (> 130 mm fork length). New, smaller, higher-frequency transmitters (“tags”) allow studies on a larger fraction of the smolt size spectrum (> 95 mm); however, detection range and study d...

Background. Animal biotelemetry and individual-based modeling (IBM) are natural complements, but there are very few published examples where they are applied together to address fundamental or applied ecological questions. Existing studies are often found in the modeling literature and draw opportunistically on small datasets collected for purposes...

Background. Animal biotelemetry and individual-based modeling (IBM) are natural complements, but there are few published examples where they are applied together to address fundamental or applied ecological questions. Existing studies are often found in the modeling literature and frequently re-use small datasets collected for purposes other than t...

White sturgeon are the largest freshwater fish in North America and are the focus of an intense catch-and-release (C&R) fishery; the effects are largely unknown. We assessed the effect of fight and handling time, water temperature, river discharge rate, and fish size on physiological and reflex impairment responses of wild white sturgeon to angling...

In some salmonid populations, multiple smolt age classes co-emigrate owing to variation in the duration of freshwater residence. While it is assumed that smolts prolong freshwater residence to maximize survival, infectious agent profiles and host gene expression (GE) have not been compared between concurrently migrating age classes. We coupled mole...

Sockeye Salmon Oncorhynchus nerka smolts typically experience high mortality during outmigration through freshwater and the early marine environment. Due to tag burden (tag mass relative to fish mass) constraints, telemetry studies investigating migration survival have focused on tracking hatchery smolts or larger individuals within wild population...

Accelerating decreases in survival are evident for northern Hemisphere salmon populations. We collated smolt survival and smolt-to-adult (marine) survival data for all regions of the Pacific coast of North America excluding California to examine the forces shaping salmon returns. A total of 3,055 years of annual survival estimates were available fo...

Behavioral decisions during periods of vulnerability to predation risk, such as migrations during the juvenile life-history stage, may strongly affect the probability of survival. Habitats through which animals migrate are heterogeneous, and risk-reducing behaviors may be more important in some habitats than others. Using biotelemetry data, diurnal...

• In Fig. 2 on page 163, the release sites on the right-hand side of the figure were incorrect. The legend remains the same. • In Fig. 4 on page 166, the two upper panels were shown as hatchery data only, but are actually hatchery and wild data combined. The legend has been changed accordingly. • Furthermore, in the legend to Fig. 3 on page 165, ‘d...

Pacific salmon from multiple species and stocks have experienced large declines in the number of returning adult over a wide region of the Pacific Northwest due to poor marine survival (low smolt‐to‐adult survival rates). One possible explanation for reduced survival is thiamine deficiency. Thiamine (Vitamin B1) is an essential vitamin with an inte...

We used acoustic telemetry to investigate survival of age-2 sockeye salmon (Oncorhynchus nerka) as they emigrated from Chilko Lake, British Columbia, Canada, to northeastern Vancouver Island (NEVI) from 2010 to 2014. We built on our previously reported results by including an additional year of data and by converting survival estimates into rates (...

For anadromous Pacific salmonid (Oncorhynchus spp.) smolts, the physiological state of individuals can influence migration fate. This critical life stage is typically associated with poor survival and influences population productivity, highlighting the need to identify intrinsic factors associated with outmigration fate. To better understand and i...

To better understand the mechanisms that lead to marine mortality of homing adult sockeye salmon (Oncorhynchus nerka), gill and blood biopsies were used in combination with biotelemetry to demonstrate how survival to freshwater entry is related to gene expression and physiological indices of stress. Microarray analysis of gene expression indicated...

To investigate the causal basis for patterns of seabird foraging distributions during breeding we integrated data from ship-board seabird and zooplankton surveys, aerial radio telemetry, and colony-based research programs. We examined the marine distributions of Cassin's Auklet (Ptychoramphus aleuticus) breeding on Triangle Island, in the Northeast...

For migratory species, spatiotemporal variability in movement patterns, such as routes, has the potential to influence survival, but this aspect of movement ecology is poorly understood. For anadromous steelhead Oncorhynchus mykiss smolts, little is known about important migratory corridors used during early marine migration. To investigate route-s...

Background Access to harvestable surpluses of sockeye salmon is often limited by incidental harvest of Chinook salmon in the mixed-species gillnet fishery of Cook Inlet, Alaska, particularly in years of low Chinook abundance. This is restricting economic opportunity and creating allocation conflict between user groups. Prior work quantified differe...

In 2011, unusually high flows caused total dissolved gas (TDG) levels in the Columbia River, USA, to escalate well above the 120% regulatory limit that was imposed to prevent harmful impacts to aquatic organisms. After observing gas bubble trauma (GBT) in dead yearling Chinook Salmon Oncorhynchus tshawytscha (smolts) held in tanks, we compared esti...

Few estimates of migration rates or descriptions of behavior or survival exist for wild populations of out-migrating Pacific salmon smolts from natal freshwater rearing areas to the ocean. Using acoustic transmitters and fixed receiver arrays across four years (2010-2013), we tracked the migration of >1850 wild sockeye salmon (Oncorhynchus nerka) s...

Variability in animal migratory behavior is expected to influence fitness, but few empirical examples demonstrating this relationship exist. The initial marine phase in the migration of juvenile salmon smolts has been identified as a potentially critical life history stage to overall population productivity, yet how fine-scale migration routes may...

The reproductive migration of anadromous salmonids through estuarine waters is one of the most challenging stages of their life cycle, yet little is known about the environmental and physiological conditions that influence migratory behaviour. We captured, sampled tissues, tagged and released 365 sockeye salmon (Oncorhynchus nerka) homing through i...

Worsening recruitment of Alaskan Chinook salmon over the past decade has created major conservation problems. In Cook Inlet, lucrative Sockeye salmon fisheries are severely limited because of Chinook bycatch, restricting economic opportunity and creating political conflict between user groups. Although Chinook are thought to migrate at deeper depth...

We present the first data to link physiological responses and pathogen presence with subsequent fate during migration of wild salmonid smolts. We tagged and non-lethally sampled gill tissue from sockeye salmon (Oncorhynchus nerka) smolts as they left their nursery lake (Chilko Lake, BC, Canada) to compare gene expression profiles and freshwater pat...

Chum salmon (Oncorhynchus keta) in the North Pacific Ocean are anadromous fish, and spend most of their life in the sea until spawning in natal streams. To identify the stock and habitat characteristics of chum salmon, the composition of chemical elements (Ca, Mn, Sr, Zn, and Ba) in otolith was examined using laser ablation inductively coupled plas...

The population of anadromous steelhead Oncorhynchus mykiss in the Keogh River has been studied intensively, in part because of its pattern of declining recruitment, which is largely attributed to poor marine survival. Climate variability has changed the productivity of salmonid species in all regions of the North Pacific, with areas alternately shi...

We observed large survival differences between wild and hatchery-reared steelhead trout (Oncorhynchus mykiss) during the juvenile downstream migration immediately after release, which persisted through adult life. Following a railway spill of sodium hydroxide into the Cheakamus River, British Columbia, a short-term conservation hatchery rearing pro...

Although behaviour and physiology of the reproductive migration of Pacific salmon Oncorhynchus spp. have been studied for the upriver migration, equivalent information for the coastal marine migratory phase has been difficult to obtain. Acoustic acceleration transmitters equipped with pressure sensors provide a tool to study swimming activity and m...

The impact of oceanographic processes on early marine survival of Pacific salmon is typically estimated upon adult return, 1 to 5 yr after ocean entry, and many 1000s of kilometers after initial exposure. Here, we use direct estimates of early marine survival obtained from acoustic-tagged yearling Chinook salmon Oncorhynchus tshawytscha that entere...

Juvenile Snake River Chinook salmon pass through eight major hydroelectric dams during their >700 km migration to the sea, or are transported downriver to avoid these dams. Both of these anthropogenic processes are thought to be sufficiently stressful that they reduce subsequent estuarine and early marine survival, and thus reduce the rate adults r...

In our report (1), we set out to explicitly control for the ecological differences Haeseker (2) cites so that we could assess the effect of a critical policy issue: whether Snake River dam passage results in poorer early marine survival of juvenile Snake River spring Chinook salmon. Thus, we selected smolts of common size and manipulated release ti...

Between december 2004 and January 2007, we studied the movements of six Black Rockfish (Sebastes melanops) that had been fitted with acoustic transmitters and reintroduced into a fjord environment at the edge of vancouver Harbour, British Columbia. The Black Rockfish were released in december 2004 and april 2005 at a reef characterized by complex r...

To assess the potential impact of “tag effect” on seaward-migrating Coho Salmon Oncorhynchus kisutch, presmolt juveniles were surgically implanted with acoustic transmitters followed by exposure to freshwater (FW, 0‰ salinity) or seawater (SW; 30‰ salinity) for 24 h and then subjected to repeated critical swimming speed (U crit) trials. Three diffe...

Multiple dam passage during seaward migration is thought to reduce the subsequent survival of Snake River Chinook salmon. This hypothesis developed because juvenile Chinook salmon from the Snake River, the Columbia River's largest tributary, migrate >700 km through eight hydropower dams and have lower adult return rates than downstream populations...

Juvenile hatchery-reared Sockeye Salmon Oncorhynchus nerka from Cultus Lake, British Columbia, were implanted during their smolt phase with one of three sizes of dummy acoustic tags to assess how tag burden (tag mass: body mass ratios ranging from 1.3% to 13.6% in air) influenced prolonged swimming performance, survival, and postsurgical wound heal...

Marine survival rates of many juvenile salmon populations have declined in recent decades. Although several potential causes have been proposed, there has been little conclusive evidence for which factors are responsible or not responsible for these declines. We experimentally addressed the hypothesis that exposure of coho salmon Oncorhynchus kisut...

Many juvenile Snake River Chinook salmon are transported downriver to avoid hydroelectric dams in the Columbia River basin. As mortality to the final dam is ∼50%, transported fish should return as adults at roughly double the rate of nontransported fish; however, the benefit of transportation has not been realized consistently. "Delayed" mortality...

Supplementary Info Rechisky

While recent studies have evaluated the stock-specific coastal migration of juvenile Chinook salmon, it remains unclear if these seasonal patterns are consistent between years, particularly when ocean conditions change dramatically. Here we contrast the abundance, distribution and seasonal stock compositions of juvenile Chinook salmon between years...

We investigated the marine migratory behavior and survival of Sakinaw Lake sockeye salmon Oncorhynchus nerka during their outbound migration as juve-niles and return migration as adults two or more years later by tracking individuals that had been implanted with Vemco acoustic tags programmed to have two periods of active transmission. We tracked b...

With declines in sockeye salmon abundance, researchers are turning to telemetry studies to uncover movements and survival of Pacific salmon smolts during their outmigration to sea. Resulting data are used to make general conclusions at the population level with an underlying assumption that the tags do not affect behavior, survival, or physiology o...

Large-scale declines in marine survival of many Pacific salmon populations occurred over the last three decades. We examined when in the life history this mortality was expressed using the POST prototype array. We first compared the size at tagging of released smolts and of the survivors at distant marine array locations, hundreds of kilometers a...

The ocean feeding grounds of juvenile Pacific salmon Oncorhynchus spp. range over several thousand kilometers in which ocean conditions, prey quality and abundance, and predator assemblages vary greatly. Therefore, the fate of individual stocks may depend on where they migrate and how much time they spend in different regions. Juvenile (n = 6,266)...

Many salmon populations in both the Pacific and Atlantic Oceans have experienced sharply decreasing returns and high ocean mortality in the past two decades, with some populations facing extirpation if current marine survival trends continue. Our inability to monitor the movements of marine fish or to directly measure their survival precludes exper...

The diet of chum salmon (Oncorhynchus keta) can range from a primarily arthropod to a primarily gelatinous composition. Because no data exist for the digestion rates of gelatinous prey in any fish, it has not been possible to convert data on stomach contents to feeding rates. We measured rates of digestion to address this issue. In freely feeding a...

The 1997–1998 El Niño was one of the strongest ocean warming events in the historical record followed by an equally strong cold La Niña event in 1999. We observed a rapid shift in the marine zooplankton assemblage found in the transitional area between the California Current domain and the Alaska Gyre domain. Nonmetric multidimensional scaling reve...

Pacific salmon are normally thought to be distributed throughout the Subarctic Pacific, an area where they form the dominant fish fauna. We use a series of generalized additive models to show that salmon exhibit a sharp step-function response to temperature in the oceanic eastern north Pacific in spring. The critical temperature defining the southe...

Archival tags record information about the environment of tagged animals over long periods of time (months to years). In theory, position can be estimated from a record of changes in light intensity with time. We describe two approaches to estimating geoposition based on estimating either the time of maximal rate of change in light intensity or the...

Intraregional similarities and interregional differences in wild steelhead (Oncorhynchus mykiss) abundance trends over time throughout British Columbia were identified using catch-per-angler-day (CpAD) as an index of abundance. This index was calculated using sport angler catch and effort data obtained by an ongoing mail-out questionnaire begun in...

A new approach is described for removing part of the density-independent noise present in stock–recruitment (SR) data. The method is based on filtering the time series of recruitment data in the frequency domain, an approach that allows complete removal of the identifiable environmental noise without reducing the length of the time series. Results...

The information content of stock–recruitment (SR) data is examined for three population models incorporating different life history characteristics. These models represent (i) a population whose recruitment is totally independent of stock size, (ii) a semelparous population whose recruitment is dependent on the abundance of the adult age group, and...

A maximum likelihood methodology for the analysis of maturity-at-length data is presented, and illustrated with data for female Pacific cod (Gadus macrocephalus) from Hecate Strait, British Columbia. Our approach explicitly accounts for the binomial nature of maturity data. Estimated maturity–length relationships show substantial differences for fe...

We examined escapement policies for a stock-recruitment model with negative between-year interactions. Regardless of the degree of interaction present, the optimal policy is to always equalize escapement. Parameter estimates obtained for the Adams River sockeye salmon (Oncorhynchus nerka) indicate that between-year interactions may occur, but confi...

Adult Pacific salmon (Oncorhynchus spp.) returning from offshore waters to spawn frequently bear a wide range of wounds and scars. One of the most common wounds is a single slash mark on the posterior third of one side of the body, running posteroventrally from near the dorsal fin at a roughly 45° angle. The evidence is reviewed for the occurrence...

We examined the sampling statistics of Pacific salmon (Oncorhynchus spp.) caught in a series of experimental gillnet sets on the high seas and demonstrate how the reliability of the catch statistics varies with the amount of sampling effort. Our analysis indicates that the replicate catches, which were made under essentially identical conditions, a...

Theory is introduced which permits the identification and removal of part of the environmental (density-independent) noise influencing the recruitment to age-structured populations. The biological assumptions under which this noise may be safely removed from the recruitment data without distorting the analysis of the density-dependent dynamics are...

The abundance of North Pacific salmon (Oncorhynchus spp.) has nearly doubled during the period 1975-1993. As salmon population numbers have increased, there have been corresponding decreases in average adult size at return (maturity). As nearly all of the growth of Pacific salmon occurs in the ocean, the ocean plays an important role in determining...

Summary of results following the 2007 health assessment sampling of Seymour River steelhead. Fish were sampled at the Seymour Hatchery prior to release. Results are expressed as mean standard error (n = 30 per group). * indicate significant differences between the groups for a particular parameter. (0.06 MB DOC)

Description of scoring system for the necropsy based health assessments performed on the Seymour steelhead smolts sampled in 2007–2009. The higher score indicates a greater disparity from the appearance of those tissues from normal tissues (i.e., a score of 0 indicates a completely normal healthy appearing fish, while a score of 23 indicates a fish...

Summary of results following the 2009 health assessment of summer steelhead. Eight groups of fish were sampled (n = 12 per group, except pathogen prevalence testing which was performed on 30 per group). Vaccinated and unvaccinated fish were sampled at the hatchery, and from buckets placed into the transport tank. Unvaccinated fish were also sampled...

Summary of results following the 2008 health assessment of Seymour River summer steelhead. River release (FW) fish were sampled at the point of release into the Seymour River; Hatchery fish were sampled under resting conditions at the Seymour Hatchery; Marine Release (SW) fish were sampled following a 6 hour transport, at the point of release (13°C...

Summary of survival data of the various treatment groups of Seymour steelhead released from 2006–2009. Percent survival was based on the ratio of survivors to total number per designated segment of the migration up to and including the Northern Strait of Georgia (NSOG) and Queen Charlotte Strait (QCS). Overall survival from the river release site t...

Early marine migratory behaviour and apparent survival of hatchery-reared Seymour River steelhead (Oncorhynchus mykiss) smolts was examined over a four year period (2006-2009) to assess the impact of various management strategies on improving early marine survival. Acoustically tagged smolts were released to measure their survival using estuary and...

The stomach (but not the intestine) of chum salmon (Oncorhynchus keta) is greatly enlarged relative to that of other species of Pacific salmon. This permits the exploitation of gelatinous zooplankton (jellyfish, ctenophores, and salps), an abundant but low-energy prey unused by other species of salmon, as a major food source. The unique gut structu...

Model selection results for comparison of fixed effects in models for length-adjusted travel speeds. (0.04 MB DOC)

Histograms of travel speeds of tagged fish during the downstream and coastal migrations under alternate travel speed measures. Panels A–D show absolute speeds, while panels E–H show length-adjusted speeds. Frequency distributions are truncated at 100 km⋅d−1 and 10 BL⋅s−1, as few fish had speeds faster than these. Number of fish is indicated for eac...