Tag Burden Research Articles

Determinants of riverine migration success by Atlantic salmon (Salmo salar) smolts from rivers across the UK and Ireland.

There is some evidence that the river migration success of Atlantic salmon smolts, on their first migration to sea, varies both spatially and temporally. However, we have only a poor understanding of what may be driving this variation. In this study, we used acoustic telemetry to quantify the spatial and temporal variations in river migration success in Atlantic salmon smolts on their first migration to sea. In total 4120 Atlantic salmon smolts migrating through 22 rivers in Scotland, England, Ireland, and Northern Ireland over multiple years were included in the study. Individuals were defined as successful migrants if detected leaving the river to enter marine waters. The results show significant temporal (up to 4 years) and spatial (river) variations in migration success, with overall between-river migration success varying from 3.4% to 97.0% and between years from 3.4% and 61.0%. Temporal variation in migration success was river specific, with some rivers being more temporally stable (exhibiting little variation between years) than others. Across all rivers and years, individual migration success was predicted positively by body condition and negatively by tag burden. The rate of migration success for a population (migration success standardized to a common river distance [proportion km-1]) was predicted by a number of environmental factors. The proportion of river catchment that comprised wetland and woodland positively predicted migration success, whereas the proportion of grassland and peatland in a catchment negatively predicted the rate of migration success. Although the mechanisms through which these effects may be operating were not directly examined in this study, we discuss some potential routes through which they may occur.

A comparison of acoustic tag sizes on wild Atlantic salmon Salmo salar L. smolt migration success and behaviour

AbstractTracking of animal migrations using telemetry technologies needs to take into consideration the burden that the tag exerts on the animal. Here, we examined the potential impacts of acoustic tags of two sizes (nominally a ‘V6’ [smaller] and ‘V7’ [larger]) on the downstream riverine migration success and behaviour of wild Atlantic salmon (Salmo salar L.) smolts. One hundred fish were tagged with either a V6 or V7 tag. Tag burden (tag: fish weight) ranged from 1.88% to 7.39% and differed significantly between fish tagged with the V6 (mean [SD] = 3.63% [0.51%]) and the V7 tags (mean [SD] = 5.84% [0.95%]). There was no significant difference in the in‐river migration failure between the two groups when tested with a time‐to‐event analysis. There were also no differences in other elements of the migratory behaviour (rate of movement, time of detection and residency time) between the two tagging groups. These data support the use of acoustic tracking for monitoring smolt migration and highlight that tagging of smaller smolts at up to 7.39% tag burden to gain a more representative understanding of migration success and behaviours across a smolt population.

Tagger effects in aquatic telemetry: Short‐term and delayed effects of surgery in Atlantic Salmon smolts

AbstractObjectiveAn assumption of biotelemetry is that animal performance is unaffected by the tagging process and tag burden, yet this assumption is often untested or not thoroughly explored. Our objective was to explore how transmitter implantation procedures influenced Atlantic Salmon Salmo salar smolt survival and migratory performance.MethodsWe monitored radio‐tagged smolts, first in the hatchery and then in a river with a receiver array. We assessed survival and in‐river performance in relation to surgeon, surgery duration, processing order, and fish size.ResultMortality was 13.3% during an 8‐day hatchery‐observation period but was higher for fish that were processed by one of two experienced surgeons (25% vs. 2%). Mortality peaked 3 days postsurgery and was higher for smaller fish and fish that were tagged during morning tagging sessions (versus afternoons). The size effect changed over time, being greatest during the first 2 days postsurgery and continuing thereafter at a diminished level. Fish performance once released into a river also differed between surgeons (migration initiation 66% vs. 82%; to‐lake migration success 22% vs. 43%) and, consistent with hatchery observations fish that were tagged in the morning by one surgeon, performed poorly once released.ConclusionWe highlight the immediate and lingering effects of surgical procedures on smolt survival that, if not accounted for, could bias inferences about the study population. Researchers should anticipate tagger effects during study design to ensure potential tagger effects (i.e., surgeon, order tagged, conditions during tagging) are balanced across study groups of interest. Testing for a fixed tagger effect in analyses may not always be adequate because a tagger effect may covary with processing order and fish size and may change over time.

Evaluating the viability of the use of T‐bar and radiotelemetry tags on prespawn Arctic Lampreys

AbstractObjectiveArctic Lampreys Lethenteron camtschaticum are harvested by subsistence and commercial fisheries in the Yukon–Kuskokwim River region of Alaska; however, baseline population data are deficient. For mark–recapture and telemetry studies to be effectively implemented to assess Arctic Lamprey abundance, migratory and dispersal patterns, and spawning locations, tags must not impact fish survival, physiology, or behavior.MethodsFor this laboratory evaluation, we examined survival, tag retention, swim endurance at short‐term (1 day posttreatment) and long‐term (43 days [~6 weeks] posttreatment) intervals, and incision healing for T‐bar‐tagged and radio‐tagged prespawn Yukon River Arctic Lampreys (N = 216). Six treatment groups were evaluated: control; sham surgery; external T‐bar anchor tag; and small (0.30 g; 0.1–0.4% tag burden [ratio of tag weight to fish body weight]), medium (0.57 g; 0.2–0.8% tag burden), and large (1.50 g; 0.6–1.9% tag burden) internal dummy radio transmitter tags.ResultAlthough all lampreys survived tagging and surgical procedures through the first 4 weeks of the experiment, a higher tag burden was associated with an increased mortality hazard up to 35 weeks postsurgery. Over the 14‐week experimental period, one T‐bar tag and one small radio tag were shed by lampreys. Although treatment was not a significant predictor of swim endurance, a higher tag burden led to reductions in swim endurance at 1 day posttreatment but not at 43 days posttreatment. Healing did not differ among surgical treatment groups, but persistent inflammation was observed at incision sites and skin erosion was observed at antenna protrusion locations.ConclusionThese results indicate that T‐bar anchor tags and internal radio tags are acceptable for Arctic Lamprey tagging studies if the radio tag burden is ≤1.3% for short‐term (≤14‐week) studies and ≤0.5% for long‐term (≥14‐week) studies.

Evaluation of double acoustic tagging techniques to track American shad Alosa sapidissima movements at multiple spatial scales

Enhancements to acoustic telemetry technology now allow for tracking aquatic animal movements at multiple spatial and temporal scales. While large acoustic arrays allow for broad-scale tracking of movement and migrations at scales of thousands of km across multiple years, more focused smaller arrays offer the potential to quantify fine-scale movement across shorter time frames. Investigators seeking to quantify movement at multiple scales may require a double-tagging approach if their telemetry systems and tag capabilities are different (e.g., 69 kHz for broad-scale, and 307 kHz for sub-meter fine-scale). We tested multiple double-tagging approaches (InnovaSea-Vemco V9 and HTI-495LY tags) for American shad Alosa sapidissima during three individual tank survival experiments including: 1) two free-floating acoustic tags and a dart tag, 2) two acoustic tags attached to one another and a dart tag, and 3) two acoustic tags attached to one another with no dart tag and revised handling and tagging techniques to reduce stress. In each experiment, we used a mixed effects Cox’s proportional hazard model to test for differences in relative survival between groups (double acoustic tagged and control fish). At the completion of each experiment, all fish were X-rayed to evaluate tag placement in the body cavity. During the first experiment, American shad that received two free-floating tags and a dart tag had significantly lower relative survival compared to control fish after three weeks. The second experiment with treatment fish receiving two attached tags and a dart tag still had lower survival compared to control fish, but the magnitude of survival differences between treatment and control was lower compared to experiment one. In the third experiment, when two attached tags were used, dart tags were eliminated, and changes to fish handling and tagging techniques were implemented (new tagging apparatus, addition of lubricant, and different fish orientation) survival was equal among treatment and control fish. X-ray images showed distinct differences in post-mortem tag positioning between the first experiment (misaligned tags) compared to the second and third experiments (tags horizontally aligned within intestinal tract). American shad are generally difficult to study experimentally and sensitive to collection, handling, and surgical implantation. Our study showed strong evidence that attaching two acoustic tags to one another to create a single, larger tag improved survival and reduced internal tag misalignment. Fine- and broad-scale acoustic telemetry studies can be achieved with aquatic animals, but care must be taken with all species, and particularly those susceptible to handing stress to minimize tagging effects (e.g., mortality, altered movement behaviors, and tag burden).

The effects of water temperature, acoustic tag type, size at tagging, and surgeon experience on juvenile Chinook salmon (Oncorhynchus tshawytscha) tag retention and growth

BackgroundAcoustic telemetry is a widely used tool to study the movement and survival of juvenile fish and often requires a surgical procedure to implant the transmitter, which may impact overall fitness and survival following release. This is an important consideration when implementing large-scale acoustic telemetry projects aimed at estimating outmigration survival. The objective of this study was to examine the effects of water temperature, tag type, size at tagging, and surgeon experience on tag retention and growth rate of juvenile Chinook salmon (Oncorhynchus tshawytscha). We tagged 128 spring-run Chinook salmon (81–97 mm fork length, 5.2–10.0 g, tag burden 2.4–6.0%) with one of two types of acoustic transmitters; a shorter, heavier model (‘standard’) and a longer, lighter model (‘injectable’). Fish were tagged by either a novice or experienced surgeon. An additional 64 untagged fish served as a control group and were split between temperature treatments. Fish were reared in either cool (mean 13.4 °C) or warm (mean 17.8 °C) water for 60 days, prior to being euthanized, weighed and measured.ResultsTag retention was similar for both transmitter types, but varied with water temperature, with significantly higher tag loss in the warm treatment (21.9%, 14 tags expelled), compared to the cold treatment (7.8%, 5 tags expelled). In the warm treatment, fish growth in the injectable tag group was significantly lower compared to the control group, and lower than the standard tag group, but not significantly lower. There was no significant difference between the control and standard tag groups for the warm treatment. In the cool temperature treatment, fish growth was not significantly different among any of the factors tested. Surgery time differed between surgeons; however, surgeon experience did not significantly affect tag shedding or growth.ConclusionTotal tag loss was 14.8% over the 60-day trial, with higher and earlier loss in the warmer treatment. Tag length may be a more important factor than tag weight in smaller size fish. This suggests that tag shedding is a significant factor to consider when estimating survival, as the actual survival rate may be higher than estimates based solely on receiver detections.

From 95 to 59 millimetres: a new active acoustic tag size guideline for salmon

Two laboratory studies evaluated small Chinook salmon (Oncorhynchus tshawytscha) (36–99 mm fork length (FL), 0.7%–26.7% tag burden) survival, tag retention, and growth (n = 539) and critical swimming speed (Ucrit; n = 241). Fish were implanted with a new active acoustic tag and compared with untagged controls at 12 and 17 °C. Across studies, no temperature differences were detected. All control fish survived. All tagged fish ≥58 mm FL survived and retained their tags. Regression models predicted ≥98.6% survival and retention for tagged fish ≥58.6 mm FL or ≥1.9 g (4.2% tag burden). No growth differences among treatments were identified. Spline regression analysis indicated Ucrit was similar for control and tagged fish that measured ≥57.3 mm FL. We recommend tagging salmon ≥59 mm FL or ≥1.9 g (≤4.2% tag burden), although the guideline should be confirmed in a field setting. Study results represent an important step towards using the new active tag in acoustic telemetry field studies that estimate short-term (30-day) survival of small salmonids.

Performance of Subyearling Fall Chinook Salmon Tagged with 8‐, 9‐, and 12‐mm Passive Integrated Transponder Tags in the Snake River

AbstractInferences based on tagged individuals from a population are limited in part by the minimum size of fish that can be tagged. Smaller tags allow a greater proportion of a population to be represented by tagging and should reduce potential tag effects on fish performance. We evaluated different performance metrics of juvenile fall Chinook Salmon Oncorhynchus tshawytscha tagged with 8‐, 9‐, and 12‐mm PIT tags in the Snake River. We did not find evidence that posttagging mortality of 45–49‐mm‐FL fish tagged with 8‐mm tags was higher than the posttagging mortality of larger fish tagged with 9‐ and 12‐mm tags. The incisions of fish tagged with 8‐mm tags using 14‐guage needles healed faster than those of fish tagged with larger tags using 12‐guage needles. For individuals that received 8‐mm tags, growth in length and mass was higher for 45–49‐mm fish than for 50–59‐mm fish and 60‐mm and larger fish. Growth of the larger size‐classes (50–59 and ≥60 mm) was also generally higher for those tagged with 8‐mm tags compared to those tagged with 9‐ and 12‐mm tags, respectively. There were no strong relationships between tag burden (i.e., tag weight expressed as a percentage of fish weight) at the time of tagging and growth metrics for any tag size or fish size‐class. Releases made to compare the detection efficiency of the three tag types in the juvenile fish bypass at Lower Granite Dam, Washington, showed that 99–100% of all fish were detected. Survival of fish from rearing areas to Lower Granite Dam generally increased with fish size and varied by year, but there was no strong evidence of a tag size effect. The 8‐mm PIT tag allowed us to represent a larger portion (i.e., 6.2–24.1%) of the subyearling fall Chinook Salmon population in the Snake River without compromising fish performance or detectability at the dam.

In situ experimental evaluation of tag burden and gill biopsy reveals survival impacts on migrating juvenile sockeye salmon

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 from release to the last marine receiver array was 1.51 times greater for the high tag burden group (25% surviving) compared with the low burden group (40% surviving). A biopsy effect was limited to the first migration segment (14 km), where mortality was 1.86 times greater for biopsied fish. These results demonstrate the importance of quantifying biopsy and tagging effects when survival estimates are prioritized.

Performance of a high-frequency (180\xa0kHz) acoustic array for tracking juvenile Pacific salmon in the coastal ocean

BackgroundAcoustic 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 duration are also reduced, introducing new challenges. The potential cost implications are not trivial. With these new transmitters in mind, we designed, deployed, and tested the performance of a dual-frequency receiver array design in the Discovery Islands region of British Columbia, Canada. We double-tagged 50 juvenile steelhead (Oncorhynchus mykiss) with large 69-kHz tags (VEMCO model V9-1H) and small 180-kHz tags (model V4-1H). The more powerful 69-kHz tags were used to determine fish presence in order to estimate the detection efficiency (DE) of the 180-kHz tags. We then compared the standard error of the survival estimate produced from the tracking data using the two tag types which has important implications for array performance and hypothesis testing in the sea.ResultsPerfect detection of the 69-kHz tags allowed us to determine the DE of the 180-kHz tags. Although the 180-kHz tags began to expire during the study, the estimated DE was acceptable at 76% (SE = 9%) when we include single detections. However, 95% confidence intervals on steelhead survival (64%) were 1.5 × larger for the 180-kHz tags (47–85% vs. 51–77% for 69 kHz) because of the reduced DE.ConclusionsThe array design performed well; however, single detections of the 180-kHz tags indicates that under slightly different circumstances the DE could have been compromised, emphasizing the need to carefully consider the interaction of animal migration characteristics, study design, and tag programming when designing telemetry arrays. To increase DE and improve the precision of 180 kHz-based survival estimates presented here requires either an increase in receiver density, an increase in tag sample size (and modified transmitter programming), or both. The optimal solution depends on transmitter costs, array infrastructure costs, annual maintenance costs, and array use (i.e., contributors). Importantly, the use of smaller tags reduces potential tag burden effects and allows early marine migration studies to be extended to Pacific salmon populations that have been previously impossible to study.

How Small Can We Go? Evaluating Survival, Tag Retention, and Growth of Juvenile Chinook Salmon Implanted with a New Acoustic Microtag

AbstractRecently, an acoustic microtag, called the Eel–Lamprey Acoustic Tag (ELAT), was developed for use in juvenile American Eel Anguilla rostrata and Pacific Lamprey Entosphenus tridentatus. The ELAT (12.0 × 2.0 mm; 0.088 g in air) has the potential to be used to study other small‐bodied fishes. In this pilot study, juvenile Chinook Salmon Oncorhynchus tshawytscha 52–99 mm fork length (FL) were surgically implanted with an ELAT (n = 99) or remained untagged (control; n = 101). Fish were held for 30 d to evaluate survival, tag retention, and growth. Survival did not differ significantly between control (n = 98 or 97.0%) and tagged fish (n = 95 or 95.9%). Logistic regression analysis suggested that survival was influenced by initial FL and tag burden. Mortalities only occurred in tagged fish with initial FLs of ≤65 mm (FL range = 57–65 mm; tag burdens = 3.8–5.9%). However, a tagged fish with an initial FL of 62 mm or an initial tag burden of 4.1% (FL range = 58–64 mm) was predicted to have a 90% chance of survival, and the smallest fish that survived the study was 54 mm FL (1.8 g; tag burden = 4.9%). Tag retention was high (99%), with only one fish expelling an ELAT during the study. Control fish grew slightly larger than the tagged individuals, but differences in final pooled FLs and weight gains were not significant. Our results demonstrate the successful surgical implantation of the ELAT into Chinook Salmon as small as 54 mm FL (1.8 g).

Effects of intracoelomic transmitter implantation on metabolic rate, swimming performance, growth and survival in juveniles of two salmonids.

In this study, we investigated the effects of acoustic tag implantation on standard and routine metabolic rate (SMR and RMR, estimated via oxygen consumption), critical swimming speed (Ucrit ), survival and growth in juveniles of rainbow trout Oncorhynchus mykiss and lake trout Salvelinus namaycush. Tag burdens ranged from 1.8% to 7.5% across the two species. Growth rates in acoustic-tagged fish were equal to or higher than those in other treatments. Acoustic-tagged S. namaycush had a marginally lower Ucrit than controls but that effect was not replicated in the O. mykiss experiment. Tagging did not have clear effects on metabolic rate but there was an interaction whereby SMR and RMR tended to increase with time since surgery in tagged O. mykiss but not in other treatments (the same trend did not occur in S. namaycush). Survival was high across treatments (mean 98% survival among O. mykiss, 97.5% among S. namaycush). There were no statistically significant effects of tag burden (percentage of body mass) except for a weak negative relationship with growth rate (across species) and a weak positive relationship with Ucrit but only in the O. mykiss. Collectively, our findings suggest there were minor, context-dependent effects of acoustic tagging in juvenile S. namaycush and O. mykiss during an eight-week laboratory experiment. Further research will be required to assess whether tagging can cause meaningful behavioural effects in these species in captivity or in the wild and whether there is a tag burden threshold above which deleterious effects consistently occur.

Evaluation of optimal surgical techniques for intracoelomic transmitter implantation in age-0 lake sturgeon

We evaluated the effects of incision placement (midline vs. lateral), closure method (absorbable monofilament suture vs. n‐butyl‐ester cyanoacrylate adhesive, Vetbond®, 3 M), and tag burden (PIT-tag only vs. PIT-tag and acoustic transmitter) on survival, post-operative complications (i.e., viscera expulsion, necrosis), incision dehiscence, incision apposition, transmitter retention, incision healing, inflammation, and growth for intracoelomic transmitter implantation in age-0 lake sturgeon (Acipenser fulvescens). The risk of death was 5.17 times higher and the risk of viscera expulsion was 6.21 times higher for sturgeon that had midline incisions closed with Vetbond compared to all other treatments. Incision dehiscence probabilities were low for all treatments, except for midline incisions closed with Vetbond. Time to complete incision apposition occurred most quickly in the lateral suture treatment followed closely by the midline suture and lateral vetbond treatment groups. Tissue strength was notably weaker in the midline region. Transmitter retention was 100% for all treatments except for midline incisions closed with Vetbond. Inflammation was low and slightly decreased over time for incisions closed with Vetbond, while incisions closed with suture exhibited significant increases in inflammation levels over time. Incisions closed with suture achieved better healing outcomes initially, but the healing process was 2–3 times more likely to relapse because of severe inflammation compared to lateral incisions closed with Vetbond. Sturgeon with midline incisions closed with Vetbond gained less weight compared to the other treatments, while sturgeon with lateral incisions closed with Vetbond gained similar amounts of weight relative to both suture treatments and the control group. Collectively, results suggest that Vetbond can be effectively used to close small lateral incisions (≤ 8 mm), with a lower risk of severe inflammation compared with sutures. For transmitter implantation, we recommend using a lateral incision through the hypaxial musculature and either closing the incision with suture or Vetbond.

Assessing Acoustic Tagging Effects on Survival, Growth, and Swimming Ability of Juvenile Lake Sturgeon

AbstractAcoustic telemetry is used to quantify fish movement, ecology, and habitat use and can contribute to assessing the success of species supplementation. In this field, a better understanding of the effects of tag burden (or the impact of an acoustic telemetry tag, which is related to the ratio of tag weight to body weight) is critical to ensure postrelease monitoring. Research on the effects of acoustic tag burden on imperiled fishes at different ontogenic stages, such as juvenile Lake Sturgeon Acipenser fulvescens, is limited. Our study provides key information for the selection of the largest acoustic tag with the greatest battery life possible (taking into account tag burden) to monitor the release success and movements of juvenile Lake Sturgeon stocked for reintroduction. We characterized tag burden effects by examining survival, TL, weight, Fulton's condition factor, and swim performance of individuals. We examined four groups of fish: control (anesthetized and no acoustic tag inserted; n = 24), sham control (anesthetized with incision sutured but no acoustic tag inserted; n = 24), Vemco V8 acoustic tag (2.0 g in air; n = 24), and Vemco V9 tag (4.4 g in air; n = 24). Acoustic tags were inserted into anesthetized fish, and the incision was sutured; tag burden (mean ± SE) ranged from 2.2 ± 0.06% to 4.6 ± 0.10% of total body weight. Results showed that the two tag burden treatments had no significant effects on growth or survival (compared to both control groups) across a 114‐d study period and that critical swim speed at 12–20 d postsurgery was not significantly impacted by increasing tag burden. Because neither of the acoustic tag sizes had significant deleterious effects on the metrics studied, we recommend using a larger V9 tag (i.e., the most powerful tag with the longest battery life) for postrelease monitoring of reintroduced juvenile Lake Sturgeon.

A field evaluation of the growth and survival of age-0 Oncorhynchus mykiss tagged with 8-mm passive integrated transponder (PIT) tags

BackgroundIn fish tagging studies, tag size limits the size of fish that can be tagged, the fraction of a population that can be represented, and ultimately inferences that can be made about the study population, particularly when juvenile fish are the subject of interest. Introduction of an 8-mm passive integrated transponder (PIT) reduced the minimum taggable size of fish, but it has not been evaluated in field trials. We evaluated the growth and survival of age-0 Oncorhynchus mykiss tagged with 8-mm PIT tags in four streams in southwest Washington, USA.ResultsA total of 351 PIT tagged fish and 340 control fish (marked with pelvic fin clips) were released, but recapture rates were low, particularly for control fish. Growth in length and mass did not differ between small (42–54 mm) and large (55–64 mm) PIT tagged fish. There was a slightly positive, but weak, relation between tag burden and growth in mass; however, there was considerable variability in this relation (R2 = 0.115). Summer to autumn joint probability of fish surviving and remaining in the study area estimated with a Bayesian mark-recapture model ranged from 0.228 to 0.478 in study streams. We found no significant relation between tag burden and survival, suggesting neither tag burden nor fish size at tagging affected survival.ConclusionsAlthough this study was limited in scope, it provided insight into how age-0 O. mykiss tagged with 8-mm PIT tags grew and survived under natural conditions. We showed that fish as small as 42 mm could be tagged without detrimental effects, which should allow researchers to represent a larger portion of study populations through PIT tagging.

The Influence of Smolt Age on Freshwater and Early Marine Behavior and Survival of Migrating Juvenile Sockeye Salmon

AbstractSockeye Salmon Oncorhynchus nerka smolts typically experience high mortality during out‐migration 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 populations. However, hatchery and larger wild smolts may not represent the majority of migrants. We used miniaturized acoustic transmitters (VEMCO V4) to track age‐1 Sockeye Salmon smolts (n = 200) for the first time over approximately 950 km from Chilko Lake, British Columbia, Canada, through the coastal environment by using large‐scale receiver arrays. We compared their survival with that of concomitantly tracked age‐2 smolts (n = 100) by using VEMCO V7 acoustic transmitters. Freshwater survival of tagged age‐1 smolts was double the age‐2 survival (56% versus 28%), potentially due to higher proportional tag burdens on age‐2 smolts. Age‐1 smolt cumulative survival was 16% to the last array capable of detecting age‐1 smolts (944 km from release) and was within the range of cumulative survival reported for age‐2 Chilko Lake Sockeye Salmon smolts in previous telemetry studies. Age‐2 smolt minimum cumulative survival to the final arrays (944 and 1,041 km) was about 2% and was lower than survival in previous years. Although survival differed between age‐classes in 2016, both experienced similar trends in landscape‐specific survival relative to age‐2 smolts tracked in previous years. Survival was particularly low in the upper Fraser River tributaries for age‐1 and age‐2 smolts (76% and 53%, respectively, over 13 km from release) and after ocean entry for age‐1 smolts (36% over 217 km). Migration rates of both age‐classes among landscapes were within the range observed for age‐2 smolts in earlier studies. Our study highlights the importance of expanding research to include smaller age‐1 smolts and provides survival estimates for an indicator population of Fraser River Sockeye Salmon.

Quantifying survival of age-2 Chilko Lake sockeye salmon during the first 50 days of migration

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 (distance and time) to compare across disproportionate habitats. We also refined our survival estimates by including individual covariates in our survival models and by re-investigating the detection efficiency of the final detection site. There was a tag burden effect in 2012 and a body size effect in 2013. Excluding 2010, survival during the 35- to 47-day migration to NEVI (range of annual mean travel time; 1044 km) ranged between 8% and 14%. Weekly survival rate (S·week−1) during downstream migration to the Fraser River estuary, through the central Strait of Georgia (CSOG), and NEVI was 25%–46%, 75%–90%, and 34%–64%, respectively. In addition to marked losses in freshwater tributaries, sockeye also experienced high losses north of the CSOG consistent with earlier results for Cultus Lake sockeye.

Survival, Tag Retention, Growth, and Wound Healing of Juvenile Chinook Salmon (Oncorhynchus tshawytscha) Surgically Implanted with a Dummy Acoustic Tag

Tag effect studies are paramount in interpreting the results of survival studies. The objective of this study was to analyze the influence of tag implantation and tag burden on the survival, tag retention, growth, and wound healing of juvenile Chinook Salmon 7.8 ± 0.9 g initial weight. Fish were obtained from the Merced River Hatchery, held for 7 d, and then surgically implanted with Juvenile Salmon Acoustic Telemetry System (JSATS) SS300 dummy tags (0.3 g in air). Tag burden ranged from 2.9–4.8% (3.86 ± 0.43%, mean ± standard deviation). Weight and fork length were taken immediately before tag implantation. All fish (i.e., control and dummy-tagged) were also implanted with a visible implant alpha tag next to the dorsal insertion. Control and dummy-tagged fish were held in a single tank for 30 d. Any fish that died during the 30-d period were noted. At the end of the holding period, all fish were euthanized, weighed, measured, and necropsied. All dummy-tagged fish retained their dummy tag, and survival rates between the two groups were similar. Wound healing was also similar across the range of tag burdens analyzed. Specific growth rates, however, differed significantly between the two groups, with control fish growing at a rate of 1.08 ± 0.38% d− 1 compared to 0.55 ± 0.48 % d− 1 in dummy-tagged fish (P < 0.001). Tag burdens and specific growth rates for dummy-tagged fish (P = 0.961) did not correlate, nor did initial weight and specific growth rate for control (P = 0.363) or dummy-tagged (P = 0.983) fish. The cause of the decreased growth rate in dummy-tagged fish remains unknown. Determining the cause of decreased growth in tagged juvenile Chinook Salmon, and how that decreased growth may influence survival in the wild, should be investigated further.

Juvenile Chinook Salmon Survival When Exposed to Simulated Dam Passage after Being Implanted with a New Microacoustic Transmitter

AbstractThe current minimum size for tagging Chinook Salmon Oncorhynchus tshawytscha in the Columbia River basin with acoustic transmitters is ≥95 mm FL. Using a newly developed cylindrical microacoustic transmitter (AT; weight in air, 0.22 g), our objective was to evaluate the minimum size of Chinook Salmon for tagging. We measured Chinook Salmon survival and the retention of transmitters and viscera after their exposure to rapid decompression (n = 399) or shear forces (n = 308) that simulated dam passage. Fish (69–107 mm FL) were implanted with an AT (AT‐only) or an AT and a PIT tag (weight in air = 0.10 g; AT+PIT) through a 3‐mm incision with no sutures, or did not receive an incision or tag (untagged control fish). Tag burden averaged 2.9% (range, 1.4–6.2%) in the AT‐only group and 4.2% (range, 2.0–7.9%) in the AT+PIT group. Proportional survival and the retention of transmitters and viscera was significantly lower for AT‐only (0.70) and AT+PIT (0.54) fish than for untagged fish (0.85) after their exposure to pressure change scenarios. No transmitters were fully expelled, but 9% of AT‐only and 22% of AT+PIT salmon had protruding viscera or transmitters. Following shear exposure, the proportional survival and retention of transmitters and viscera was significantly lower for AT‐only (0.70) and AT+PIT (0.61) fish than for untagged fish (0.98). Visceral expulsion was attributed to 90% and 93% of mortal injuries in AT‐only and AT+PIT fish, respectively. In both tests the tagged fish suffered more mortal injuries and death than did untagged fish over the range of tag burdens tested, and no tag burden threshold below which tagged and untagged fish performed similarly was found. As such, a generalized linear model that included tag burden as a predictor variable provided the best fit to the survival data. Without a significant tag burden threshold, we recommend the minimum size for tagging Chinook Salmon using the transmitters and PIT tags evaluated, applied with a 3‐mm incision and no sutures, should remain at 95 mm FL.

Effects of Surgically Implanted Acoustic Tags on Body Condition, Growth, and Survival in a Small, Laterally Compressed Forage Fish

AbstractTelemetry studies often assume a lack of adverse effects caused by tag attachment and presence in various species and size‐classes, which may lead to inaccurate conclusions about fish behavior in field studies. Studies that examine the effects of tagging are typically performed on salmonids and adult fishes rather than on the small fishes that are increasingly becoming the focus of telemetry studies. The objectives of this study were to assess the effects of intracoelomic acoustic tagging on growth, condition, survival, and tag retention in subadult hatchery Bloaters Coregonus hoyi (a focal species for restoration efforts in the Laurentian Great Lakes) and to determine the maximum tag burden below which tag effects are reduced. Fish were either tagged with one of three dummy acoustic transmitters (Vemco V6: n = 50; V7: n = 50; V9: n = 50) or were followed as controls (n = 50; anesthesia, PIT‐tagging, and handling only) or sham individuals (n = 49; anesthesia, surgery, suturing, and PIT‐tagging but no acoustic tag implanted). Tags represented 1.3–9.0% of body mass. All fish received a PIT tag for individual identification throughout the 6‐month monitoring period (November 2014–May 2015). Survival exceeded 90% in all treatment groups, and the tag retention rate was 100%. All surviving fish appeared healthy and in excellent condition at the conclusion of the experiment. The results of this study suggest that acoustic transmitters with a tag mass : body mass ratio of 9% or less can be successfully implanted intracoelomically into subadult Bloaters—small, laterally compressed pelagic fish—with no adverse effects.