Adipose Fin Clips Research Articles

Coded-Wire Tag Sampling: The Case for Electronic-Field Detection

A clipped adipose fin served as an effective external mark indicating presence of a coded-wire tag (CWT) in salmon (Oncorhynchus spp.) from the 1960s until the mid 1990s when hatcheries in the Pacific Northwest began mass marking released fish with an adipose fin clip, but not necessarily a CWT. Since then, many CWT sampling programs of commercial fisheries have transitioned to electronic-field detection, while others are still visual-field only, examining snouts from all adipose-clipped salmon, even those without CWTs. Because some CWT salmon are released from hatcheries without any external marks, visual-field only programs also fail to sample these CWTs. In 2012, we used electronic tag detection at a processing plant in Kodiak, Alaska, to scan 1,201 Chinook salmon (O. tschawytscha) caught as bycatch in the US North Pacific groundfish fisheries in the Gulf of Alaska (GOA). Chinook salmon bycatch were also electronically scanned in partnerships with private industry: 3,713 salmon in the 2013–2016 US rockfish fishery in the central GOA, and 611 salmon in testing of salmon excluder devices in 2013 in the central GOA groundfish fisheries. Electronic-field detection increased CWT recovery rates by 20–24% over visual-field detection of adipose-clipped Chinook salmon, and an estimated 64–74% of adipose-clipped Chinook salmon sampled had no CWTs. Visual-field only CWT sampling programs may unnecessarily process large numbers of untagged, adipose-clipped salmon while also recovering fewer CWTs than comparable electronic sampling programs.

A review of fish identification methods applied on small fish

AbstractMost of the research on marking of aquatic organisms has been done using large organisms since they tend to have better retention rates, their swimming behaviour is less affected by the size of the tag, they have less trauma due to injectable tags or from the injector itself and they are easier to handle and able to withstand the stress of tagging and recapture. The development of small tags has grown from a necessity to study smaller fish species, earlier life stages of fish and to study other small aquatic organisms. As an endangered species, delta smelt (Hypomesus transpacificus) are being intensively studied in the upper San Francisco Estuary (CA, USA). A crucial part of many of these studies is tracking delta smelt, which requires a distinctive mark on each individual or group of fish. Unfortunately, many of the experimental fish suffer inadvertent mortality, as delta smelt are very sensitive to environmental and handling stress. The purpose of this review was to synthesize the different tagging and marking studies on small fish and aquatic organisms and to evaluate the advantages and disadvantages of each method for applications on sensitive species such as delta smelt. This review suggests the most effective methods for tracking delta smelt are visible implant alphanumeric (VIA) tagging and adipose fin clips for subadult to adult fish and calcein marks for young life stages. Among these methods, only VIA tagging currently provides individual organism identification.

Factors Affecting Prestocking Coded Wire Tag Loss in Lake Trout Tagged by an Automated System

AbstractTag loss is an important consideration in tagging studies. We used two approaches to describe prestocking coded wire tag (CWT) loss in Lake Trout Salvelinus namaycush tagged by an automated tagging system and released in the Laurentian Great Lakes. First, four strains of Lake Trout tagged by an automated system through the Great Lakes Mass Marking Program were observed for up to 254 d to describe how tag loss and adipose fin clip success relates to time posttagging. Second, we also evaluated final tag loss and fin clip success from 197 tag lots from 2011 to 2013 that were tagged with an automated system to explore the factors affecting tag loss and fin clip success, and to compare tag loss and fin clip success rates with those from 1,080 tag lots from 1985 to 2003 that were manually tagged. Coded wire tag losses from experimental lots of four strains of Lake Trout were low and ranged from 2.8% to 5.7%. Coded wire tag losses stabilized 150 d posttagging, when fish had a mean length of 131 mm, which is far longer than that reported for other salmonines (30 d). We developed a descriptive model to correct for time effects on tag loss; tag loss could be estimated with high confidence after 100 d posttagging. Coded wire tag losses varied by genetic strain, possibly due to differences in body size and shape. Fish that lost a CWT were significantly smaller than fish retaining a CWT. In our comparison of the automated system with manual tagging, CWT loss across 197 automated tag lots was highly variable (0.0–14.0%), but it was <5.5% in 86% of samples and less than the loss rates from manually tagged fish (<5.5% in 72% of samples). Our results provide important details for CWT studies on Lake Trout and other species.Received July 28, 2015; accepted February 7, 2016 Published online June 1, 2016

The Influence of Size at Release on Performance of Imnaha River Chinook Salmon Hatchery Smolts

AbstractTen brood years (BYs 1988–1990 and 1992–1998) of spring–summer Chinook Salmon Oncorhynchus tshawytscha smolts that were reared at Lookingglass Fish Hatchery (Oregon) and released from the Imnaha River Weir and Acclimation Facility were evaluated to determine whether size at release affected juvenile migration survival, smolt‐to‐adult survival (SAS) rate, smolt‐to‐adult return (SAR) rate, production efficiency, age composition, straying rate, or harvest rate. Smolts were marked with adipose fin clips and were tagged with coded wire tags (all BYs) and PIT tags (BYs 1992–1998). For BYs 1992–1998, the out‐migration survival rate to Lower Granite Dam (LGD) on the Snake River was greater for large smolts (30–38 g) than for small smolts (18–23 g). This juvenile survival difference did not translate to an adult survival difference, as the total (ages 3–5) and adult (ages 4–5) SAR and SAS rates did not differ between large and small smolts. Straying rates were less than 0.02% and harvest rates were less than 0.05% for both treatments, and we found no significant differences between groups. Total production efficiency (number of mature salmon/10 kg of smolts released) was greater for small smolts than for large smolts but not significantly so. Small smolts produced significantly more (~10%) age‐5 females than did large smolts. Treatments (smolt size at release) did not differ in sex ratio or the age composition of male returns. Because broodstock availability limited production in 5 of the 10 years, we also compared size at release within standard‐density (14.8‒22.2 kg/m3) and low‐density (2.2‒8.6 kg/m3) rearing years. At standard density but not at low density, juvenile survival to LGD was significantly greater for large smolts than for small smolts. Adult and total SAR and SAS rates, total production efficiency, and straying rates did not differ between standard‐density and low‐density rearing years. Harvest rate of the small smolts was significantly greater than that of the large smolts at low density but not at standard density. We found no performance benefit in rearing large Chinook Salmon smolts instead of small smolts.Received April 27, 2015; accepted December 2, 2015 Published online March 30, 2016

Coded-Wire Tag Expansion Factors for Chinook Salmon Carcass Surveys in California: Estimating the Numbers and Proportions of Hatchery-Origin Fish

Recovery of fish with adipose fin clips (adc) and coded-wire tags (cwt) in escapement surveys allows calculation of expansion factors used in estimation of the total number of fish from each adc,cwt release group, allowing escapement to be resolved by age and stock of origin. Expanded recoveries are used to derive important estimates such as the total number and proportion of hatchery-origin fish present. The standard estimation scheme assumes accurate visual classification of adc status, which can be problematic for decomposing carcasses. Failure to account for this potential misclassification can lead to significant estimation bias. We reviewed sample expansion factors used for the California Central Valley Chinook salmon 2010 carcass surveys in this context. For upper Sacramento River fall-run and late fall-run carcass surveys, the estimated proportions of adc,cwt fish for fresh and non-fresh carcasses differed substantially, likely from the under-recognition of adc fish in non-fresh carcasses. The resulting estimated proportions of hatchery-origin fish in the upper Sacramento River fall-run and late fall-run carcass surveys were 2.33 to 2.89 times higher if only fresh carcasses are considered. Similar biases can be avoided by consideration of only fresh carcasses for which determination of adc status is relatively straightforward; however, restricting the analysis entirely to fresh carcasses may limit precision because of reduced sample size, and is only possible if protocols for sampling and recording data ensure that the sample data and results for fresh carcasses can be extracted. Thus we recommend sampling protocols that are clearly documented and separately track fresh versus non-fresh carcasses, either collecting only definitively adc fish or that carefully track non-fresh carcasses that are definitively adc versus those that are possibly adc. This would allow judicious use of non-fresh carcass data when sample sizes are otherwise inadequate.

Aquaculture Methods for a Genetically Managed Population of Endangered Delta Smelt

AbstractIn response to Federal listing of the Delta Smelt Hypomesus transpacificus as a threatened species in 1993, intensive fish culture techniques were developed to provide a supply of fish for research activities. The Delta Smelt was listed as endangered by the state of California in 2009, and several agencies worked quickly to develop a captive refuge population under genetic management. Captive 2‐year‐old wild‐origin Delta Smelt served as the founding population in 2008. Each year, 250 genetically selected, single pair crosses are made in vitro, and the resultant full‐sibling families are combined to rear in multifamily groups. Typically, eight families are reared together from egg to adult stage, with 80% or more of the initial families represented at the adult stage. Multifamily rearing provides an efficient way of achieving a breeding population of 500 in a smaller facility. Juvenile survival increased from 18% in 2009 to 39% in 2010, as facilities and methodologies improved. Growth rate also increased significantly from 2009 to 2010 (from 0.19 to 0.25 mm/d). Subdermal alphanumeric tags identified individuals and allowed spawning of select individuals to preserve genetic diversity in the refuge population. Group marking, by adipose fin clip, provided efficiencies in time and space. Tagging and genetic analyses enabled in vitro spawning of recommended pair crosses each year. At present, we recommend completing the majority of spawning from February to mid‐May and continuing to augment the refuge population with wild fish each year. The refuge population provides one type of safeguard against species extinction and provides an example for endangered fish culture.

Influences of Hatchery Supplementation, Spawner Distribution, and Habitat on Genetic Structure of Chinook Salmon in the South Fork Salmon River, Idaho

We evaluated the genetic influence of hatchery supplementation on distinct naturally spawning populations of Chinook salmon Oncorhynchus tshawytscha in the South Fork Salmon River (SFSR), Idaho. Genetic tissue samples were collected from unmarked natural-origin and McCall Fish Hatchery (MFH)-reared Chinook salmon carcasses, and fish were identified by an adipose fin clip at five main-stem sites located both upstream and downstream of a seasonal exclusionary weir in the upper SFSR. We evaluated allele frequency data across 95 single-nucleotide polymorphism loci to determine the extent of genetic differentiation among collections. Genetic distance analyses and homogeneity tests indicated little subpopulation distinction in the upper SFSR. The weak overall genetic structure (global F ST = 0.010) is likely reflective of a population diversity similar to the historical structure with introgression by MFH stock in the naturally spawning population of the upper SFSR. Further analyses were conducted to evaluate the genetic structure among the upper SFSR and spawning aggregates in two adjacent SFSR tributaries: the Secesh River, which is devoid of any hatchery stocking, and Johnson Creek, where a discrete supplementation program has been implemented using only Johnson Creek fish. Our results indicated variable abundances of SFSR hatchery spawners distributed spatially among the three main watersheds. Gene flow appears to be restricted and genetic differentiation to be relatively large despite substantial hatchery releases in the upper SFSR. Three historical aggregates of Chinook salmon appear to persist in the SFSR metapopulation, where variable hatchery influences are coincident with the distribution of suitable spawning habitat and watershed-specific management objectives. Received January 5, 2011; accepted December 12, 2011

Distribution, Size, and Origin of Juvenile Chinook Salmon in Shallow‐Water Habitats of the Lower Columbia River and Estuary, 2002–2007

AbstractWe monitored fish assemblages monthly at estuarine and tidal freshwater sites in the lower Columbia River and estuary from January 2002 through September 2007 in order to identify specific salmon stocks and migration stages that may benefit from habitat restoration initiatives. We report landscape‐scale and seasonal variation in abundance, size, hatchery production (based on adipose fin clips), and genetic stock of origin of juvenile Chinook salmon Oncorhynchus tshawytscha. From fish implanted with coded wire tags (CWTs), we also determined the sites of release and inferred migration patterns. Chinook salmon were found in diverse life history stages and forms, including fry migrants, fingerlings, and (fewer) yearlings. Abundance increased in February and decreased in August, but salmon were present in all months each year. Spatial gradients in abundance and size were strong, with fewer but larger fish in brackish than in tidal freshwater zones. Overall, 30% of the Chinook salmon measured were fry (≤60 mm) that were likely naturally produced fish. These occurred at higher mean monthly proportions in tidal freshwater than in estuarine zones. In contrast, most larger fish were probably raised in hatcheries. Genetic stock assessment revealed that the majority of the Chinook salmon analyzed were from fall‐run stock groups originating in the lower Columbia River, with 15% originating from other stock groups. Of these minority contributors, about 6% were identified as upper Columbia River summer–fall‐run Chinook salmon while seven other stock groups accounted for the remainder, including 3% from transplants originating in southern Oregon's Rogue River. Recaptures of tagged fish revealed maximum migration times of 143 d for subyearlings and 52 d for yearlings, and both CWT and genetic data indicated that fall Chinook salmon from coastal rivers occasionally entered the estuary. These data demonstrated a widespread temporal and spatial distribution of subyearling Chinook salmon in shallow‐water habitats of the lower Columbia River and estuary.Received June 28, 2011; accepted February 28, 2012

Evaluation of Calcein as a Mass Mark for Rainbow Trout Raised in Outdoor Hatchery Raceways

AbstractMass marks are useful for evaluating releases of hatchery fishes for management and research purposes. Calcein is a chemical that shows potential for producing a cost‐effective batch mark that can be easily applied to large numbers of small fish and can be detected externally by nonlethal means. However, calcein shows some drawbacks related to mark deterioration when exposed to direct sunlight. We evaluated calcein mark retention over time in rainbow trout Oncorhynchus mykiss by using both external (head, fins) and internal structures (otoliths), and we compared mark retention between fish reared in normal outdoor raceways under ambient light conditions and those reared indoors in shaded circular tanks. Calcein marks on rainbow trout that were marked as fry and reared in outdoor raceways deteriorated significantly within 8 d of marking and remained at low or undetectable levels throughout the study. Mark quality was much better for rainbow trout reared indoors but still degraded over the 7‐month evaluation period. Calcein marks were visible over the entire study period for otoliths of fish reared both indoors and outdoors, with better results being obtained for fish reared indoors. While calcein shows potential for generating a successful nonlethal batch mark, it may have limited use in situations where fish are exposed to sunlight, which can degrade the external mark. Marks in otoliths were retained well but required time‐consuming processing and lethal sampling. For use of otolith marks, we recommend combining calcein with some other external mark (e.g., adipose fin clip) to aid in identifying chemically marked individuals.

δ13C and δ15N Signatures in Muscle and Fin Tissues: Nonlethal Sampling Methods for Stable Isotope Analysis of Salmonids

AbstractStable isotope analysis has emerged as an important tool in aquatic ecology. For fish, dorsal muscle from sacrificed individuals has traditionally been used in stable isotope studies; however, there are many instances when lethal sampling is undesirable. We evaluated the feasibility of using adipose and caudal fin clips as alternatives to muscle in stable isotope studies for five species of salmonids. Because fish size and water temperature can affect stable isotope ratios, we also determined whether fish length and sampling date affected the difference in isotope signatures between fins and muscle. Biopsied muscle plugs and fin clips were collected from rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, and lake trout S. namaycush as well as lake whitefish Coregonus clupeaformis and pygmy whitefish Prosopium coulterii and analyzed for stable isotopes of carbon and nitrogen. The isotope signatures of both adipose and caudal fins were significantly correlated (0.33 < R2 < 0.97) with those of dorsal muscle from the five salmonid species studied, and in some cases the signatures of fins did not differ from those of muscle. Fish length and sampling date occasionally had a small effect (0.042 < R2 < 0.49) on the relationship between the isotope signatures of fin and muscle. Although muscle biopsy provides a viable, nonlethal method of collecting muscle tissue from suitably sized fish, the strong relationships between the isotope signatures of fin and muscle demonstrate that fin clips should be considered good surrogates for muscle in stable isotope studies of salmonids.

Comparing Two Methods Used to Mark Juvenile Chinook Salmon: Automated and Manual Marking

AbstractHatcheries in the U.S. Pacific Northwest are increasingly implementing programs that use an adipose fin clip and coded wire tag to mark a large number of juvenile salmonids Oncorhynchus spp. Traditionally, fin‐clipping and tagging were done by hand, but the need to mass‐mark large numbers of fish has led to the development of an automated tagging trailer system (Northwest Marine Technology, Inc.). We compared the adipose fin clip quality, coded wire tag retention, and injury rates of juvenile stream‐type spring Chinook salmon O. tshawytscha marked and tagged at automated and manual tagging trailers at Warm Springs National Fish Hatchery (NFH) and Carson NFH, two hatcheries located in the Columbia River basin. Clip quality (99% good clips), tag retention (>98%), and injury rates (<7%) were similar between the two types of trailers at Carson NFH, where the manual markers had several years' experience clipping and tagging fish. At Warm Springs NFH, where the majority of manual markers had no previous experience, injury rates were similar (<14%) but the fish marked and tagged in the automated trailer had significantly higher clip quality (95% good clips) and tag retention (98%) than those marked and tagged in the manual trailer (70% good clips, 87% retention), where the clip quality and tag retention were poorest during the first day of tagging. Our results show that automated and manual trailers can perform similarly with regard to fin clip quality, tag retention rate, and injury rate when staffed by experienced markers. We recommend focusing efforts on training and quality control during the initial days of tagging and incorporating postmarking clip quality and coded wire tag retention sampling into all marking programs.

Returns of Hatchery Steelhead with Different Fin Clips and Coded Wire Tag Lengths

AbstractLeft ventral (LV) fin clips have routinely been used in the Columbia River basin to visually identify the presence of a coded wire tag (CWT) in steelhead Oncorhynchus mykiss. Managers and researchers alike have expressed concern that the ventral fin clip may negatively affect survival. Adult returns from summer steelhead smolts released from Lyons Ferry Hatchery (LFH), Washington State, between 1996 and 1999 having combinations of adipose (AD) and LV fin clips and 1.1‐ or 1.6‐mm‐long CWTs were compared. The CWT loss rate calculated from release to adult recovery was 1.9% and the LV fin clip regeneration rate was 2.4%; neither of these rates influenced our recovery results. We found slight, nonsignificant differences in return rates between fish with AD fin clips and those with both AD and LV fin clips (ADLV) and between fish with 1.1‐mm CWTs and those with 1.6‐mm CWTs. Overall, fish with ADLV fin clips had LFH return rates that were 5% greater than those of fish with AD‐only clips, and fish with 1.6‐mm CWTs had LFH return rates that were 6% higher than those of fish with 1.1‐mm CWTs. Increased straying because of the 1.6‐mm CWT length was not evident, although there was likely sampling bias at other hatcheries or traps that did not conduct electronic CWT scans of fish that lacked LV clips. Two variables that may have influenced our results were examined, but neither was determined to be a factor in our results. Our study results suggest that a ventral fin clip or longer CWT does not impair adult returns (survival) of hatchery summer steelhead. Unfortunately, study limitations reduced our statistical power to definitively conclude that there was no significant difference in survival, and additional study may be necessary. However, our study provides sufficient information for fishery managers to consider use of the LV clip on hatchery steelhead as a visual cue for CWT recovery when electronic scanning of fish will be inconsistently used or is unavailable. Also, we suggest the use of 1.6‐mm CWTs if electronic detection is to be the primary recovery method as it does not appear to affect survival in hatchery steelhead. We strongly caution managers to ensure that 100% electronic scanning of fish occurs throughout the region before foregoing standard LV fin clip marks on steelhead that contain CWTs.

Relative Survival of Lake Trout Stocked at Different Sizes and Quality in Lake Michigan

Beginning in 1995, the size of yearling lake trout ( Salvelinus namaycush) stocked into the upper Great Lakes was increased based on the assumption that these fish would be healthier and survive better since natural mortality is thought to be inversely proportional to body size. We compared the postrelease, relative survival of paired stockings of lake trout reared to 44 fish/kg (standard size) with larger fish reared to 22–26 fish/kg (enhanced size) in Lake Michigan. About 60,000 lake trout each of the standard and enhanced sizes for the 1994–1997 year classes were released as yearlings in spring near Clay Banks Reef, Wisconsin, and identified with coded-wire tags and an adipose fin-clip. Recaptures were made from 1997 to 2003 in four gill net surveys conducted in spring and fall near the release location. Comparisons of catch-per-unit of effort corrected for numbers stocked generally indicated no significant differences in relative survival of standard and enhanced lake trout. An autopsy-based assessment of overall fish health and condition indicated few measures where significantly different between standard and enhanced lake trout prior to stocking. Size differences between standard and enhanced fish remained statistically significant at all observed ages at recapture; however growth rates were the same for the two groups. Stocking numbers at certain sites on Lake Michigan were reduced concurrent with the change to larger yearlings with the expectation of increased survival, which did not occur; hence recruitment was essentially reduced in these areas for the restoration program.

Detection of Early Stages of Myxobolus Cerebralis in Fin Clips from Rainbow Trout (Onchorynchus Mykiss)

A nested polymerase chain reaction (PCR) assay was used to detect early stages of Myxobolus cerebralis in caudal and adipose fin samples from rainbow trout (RT). To determine sensitivity, groups of 10 RT were exposed to 2,000 M. cerebralis triactinomyxons/fish for 1 hour at 15 degrees C and subsequently moved to clean recirculating water. Fish were held for 2 and 6 hours and 1, 2, 3, 5, 7, 10, 30, and 60 days before sampling by nonlethal fin biopsy. Nested PCR performed on fin clips showed that M. cerebralis DNA was detected in caudal fin tissue in 100% of fish up to 5 days postexposure. At days 7 and 10 postexposure, 80% of fish were positive, and at 60 days postexposure, 60% of fish were positive using this technique. Conversely, testing on adipose fin clips proved less sensitive, as positive fish dropped from 80% at day 7 to below 20% at day 10 postinfection. Since detection of M. cerebralis infection using caudal fin samples coupled with nested PCR is an effective method for detection of early parasite stages, use of this technique provides for accurate, nonlethal testing.

Cost Comparison of Marks, Tags, and Mark-with-Tag Combinations Used in Salmonid Research

Abstract Modern fishery management requires knowledge of fish survival and distribution that is best acquired by marking and subsequent recapture. To aid cost-effective analysis for marking Pacific salmon Oncorhynchus spp. and steelhead O. mykiss, 16 marks, 6 tags, and 3 mark–tag combinations were compared for application and decoding costs per fish. Application costs (1999 US$) ranged from negligible for thermal otolith marks to $6.50/fish for a combination of an adipose fin clip, a coded wire tag, and a passive integrated transponder tag. Decoding costs ranged from negligible for fin clips to $50.00/sample for strontium marked scales.

Growth, Mortality, and Mark Retention of Hatchery Brook Trout Marked with Visible Implant Tags, Jaw Tags, and Adipose Fin Clips

Abstract Growth, mortality, mark retention, and mark readability were compared among control and treatment groups of 197–265-mm hatchery brook trout Salvelinus fonitinalis marked with visible implant (VI) tags, adipose tin (AD) clips, or stainless steel circularstrap jaw tags. Based on growth rates calculated for individual fish after 90 d, brook trout marked with VI tags grew faster than those with jaw tags (P G 0.03). Mortality was higher after 251 d for jaw-tagged fish (45%) than the cumulative mortality (8.3%) observed among VI-tagged, AD clipped, and control fish, Mark retention was 759c for VI tags, 99% for jaw tags, and 100% for AD clips, Visible implant tag loss was greatest within 7 d after insertion. After 251 d. 37% of the VI tags were unreadable. but 92% of the “unreadable” tags were readable if magnification and light were used. Unreadability could limit the usefulness of VI tags in multiyear studies unless problem tags can be removed from the fish to read tag codes.

Short-Term Mortality and Injury of Rainbow Trout Caused by Three-Pass AC Electrofishing in a Southern Appalachian Stream

Short-term (7-d) mortality and injury rates were determined for 227 wild rainbow trout Oncorhynchus mykiss sampled by three-pass AC electrofishing (500 V) in a low-conductivity stream typical of those in the southern Appalachian Mountains. An additional 67 rainbow trout were captured by angling and served as controls. Half the fish in each group were anesthetized, measured for total length and weight, marked with an adipose fin clip, and sampled for scales to simulate the effects of a typical handling regimen; the other half were not handled. All fish were held in a partitioned raceway adjacent to the study stream. Two fish died during sampling (1%) and five other fish died within 24 h of the completion of electrofishing. All control fish survived. Thirteen electroshocked fish could not be accounted for after the 7-d observation period and were treated as sampling deaths. Mortality rates were 9% overall, 10% for handled fish, 7% for unhandled fish, and 12, 9, and 4% for the first, second, and third electrofishing passes, respectively. Mortality did not differ significantly between handled and unhandled fish or among electrofishing passes. Mortality rates for age-0 (< 100 mm) and adult (100-234 mm) fish (20 and 6%, respectively) were significantly different. Seventy-six fish, including all 7 of the recovered fish that died, 57 survivors (including handled and unhandled fish from all passes), and 12 controls (handled and unhandled), were X-rayed and dissected to determine the incidence of spinal injuries and hemorrhages. Two electroshocked rainbow trout (3%) had spinal injuries and two others (3%) had hemorrhages along the spinal column but no spinal injuries; no injuries were detected among the seven fish that died or the controls. Based on these results and 4 years of data from a nearby monitoring station, we conclude that rainbow trout mortality and injury rates caused by three-pass depletion sampling with AC are tolerable. This conclusion is limited, however, to relatively small, short-lived fish inhabiting low-conductivity waters that characterize southern Appalachian streams.

Homing of Atlantic salmon ( Salmo salar L.) to a tributary spawning stream in a major river catchment

At the Girnock Burn, a tributary of the River Dee in Scotland, a substantial part of the annual production of migrant juvenile salmon ( Salmo salar L.) leaves the stream in autumn rather than in spring. Previously, the status of the autumn migrants was uncertain because Carlin tagging indicated that they returned to the stream with a lower frequency than smolts tagged in spring. The difference was not attributable to the smolting of autumn migrants outside of the Girnock Burn and their homing to these new locations since adults tagged as autumn parr were also under-represented in fisheries distant from the home stream. Instead, the differences were probably artifactual and attributable to a seasonal effect of the Carlin tagging procedure itself. When juveniles were tagged instead with wire microtags, recapture rates were similar for autumn and spring migrants. This is consistent with the hypothesis that the autumn migration is an aspect of smolting. Microtagging of all juvenile migrants (paired with adipose fin clipping) indicated that the homing of adult spawners to the Girnock Burn was substantially accurate. Over the period of study 45% of fish of the sea-age classes that were expected to bear adipose fin clips did so.

Relative Survival of Unmarked and Fin-Clipped Coho Salmon from Bear Lake, Alaska

Abstract Some of the completely censused smolts of coho salmon (Oncorhynchus kisutch) emigrating from Bear Lake, Alaska, during the years 1967–1969 and 1977–1989 received a variety of fin clips: left and right ventral clips, adipose clips (with and without coded wire tags), and combinations thereof. Coho salmon adults returning to Bear Lake were censused and examined for missing fins. As measured by the return rates of unmarked and fin-clipped coho salmon, fish that had received ventral fin clips as smolts suffered significantly higher mortality than did unmarked fish. In contrast, fish that had received adipose fin clips and implanted coded wire tags did not exhibit significantly higher mortality than unmarked fish.

Evaluation of Coded Wire Tags for Marking Lake Trout

Abstract Among hatchery-reared lake trout (Salvelinus namaycush) of the 1979-1982 year classes stocked in New York waters of Lake Ontario, more than 3 million fish were marked with a coded wire tag (CWT) plus an adipose fin clip, and 1.5 million with only conventional fin clips. Altogether, 7,640 tags were recovered from fish collected with bottom trawls and gill nets or caught by anglers during 1980-1983. One person was able to extract and decipher 200 or more CWTs per day with about a 1% error rate in reading and recording codes. Presence of the CWT did not affect growth. The adipose fin clip did not regenerate. The occurrence of fish with an adipose fin clip but no CWT resulted primarily from the regeneration of paired fins among fish marked with a combination of the adipose fin and a paired fin. Loss of CWTs between marking and stocking (generally 4-5 months for fish stocked in spring and 1-8 d for fish stocked in fall) declined from nearly 11% for the 1979 year class stocked as fall fingerlings to le...