Evaluation of external operculum loop tags to individually identify cage-cultured Atlantic halibut Hippoglossus hippoglossus in commercial research trials

The growth, survival and tag retention of double-tagged [external FT4 lock-on (FT4) and internal passive integrated transponder (PIT)-tagged] Atlantic halibut Hippoglossus hippoglossus were compared to internal PIT-tagged controls in a randomized trial. The objective was to assess the suitability of these tags for monitoring the performance of individual fish in longitudinal trials under commercial cage-culture conditions in the lower Bay of Fundy, New Brunswick, Canada. The FT4 tags were chosen due to their similarity to tags used by investigators to track H. hippoglossus in the wild. A subset of the population randomly received an external FT4 tag inserted through the operculum and were monitored over a 1105 day period. The specific growth rate of FT4-tagged fish was significantly reduced in the first sea summer with no significant difference observed for the remainder of the trial. The differential growth in the first sea summer created a relative size advantage, permitting controls to increase in size significantly faster than FT4 fish in all subsequent periods. The FT4 tags did not significantly influence survival under normal commercial cage-culture conditions. Results, however, suggest that the survival of FT4-tagged H. hippoglossus may be compromised during stressful handling events. Tag retention of FT4 tags was acceptable with 76% of tags remaining at the end of the 1105 day trial. FT4 tags proved to be an effective method to identify individual H. hippoglossus, with the caveat that they seriously bias productivity measures in commercial research trials.     

Effects of tag type on red snapper Lutjanus campechanus tag retention,growth and survival under hatchery conditions

Management of red snapper stocks is one of the most controversial issues in the Gulf of Mexico fisheries. Fish tagging programs can help to address many management issues if an appropriate tag is selected. In the study three types of tags were tested to determine tag retention and effects on red snapper growth and survival. Hatchery‐produced juveniles (43.7 ± 5.6 g) were either not tagged or given: internal anchor tags anchored in the abdominal cavity; passive integrated transponders (PIT) tags injected into the body cavity; or metal self‐piercing fish tags clamped around the dentary bone. Fish were stocked at 25 m^?3 in three replicate circular tanks/tag type, and fed a commercial feed for a 150 days period. Fish survival did not differ by treatment. Average weight gains after 150 days were similar. Tag retention differed by treatment (P = 0.0002), with 100% retention of PIT tags, 98.4 ± 2.8% retention of jaw tags, and 90.4 ± 1.6% retention of internal anchor tags. Loss of internal anchor tags occurred primarily within the first month. Inflammation was frequently observed at the internal anchor tag insertion site. Irritation and cell proliferation was sometimes observed in areas around the jaw tags.     

A Field Evaluation of an External and Neutrally Buoyant Acoustic Transmitter for Juvenile Salmon: Implications for Estimating Hydroturbine Passage Survival

Turbine-passed fish are exposed to rapid decreases in pressure which can cause barotrauma. The presence of an implanted telemetry tag increases the likelihood of injury or death from exposure to pressure changes, thus potentially biasing studies evaluating survival of turbine-passed fish. Therefore, a neutrally buoyant externally attached tag was developed to eliminate this bias in turbine passage studies. This new tag was designed not to add excess mass in water or take up space in the coelom, having an effective tag burden of zero with the goal of reducing pressure related biases to turbine survival studies. To determine if this new tag affects fish performance or susceptibility to predation, it was evaluated in the field relative to internally implanted acoustic transmitters (JSATS; Juvenile Salmon Acoustic Telemetry System) used widely for survival studies of juvenile salmonids. Survival and travel time through the study reach was compared between fish with either tag type in an area of high predation in the Snake and Columbia rivers, Washington. An additional group of fish affixed with neutrally-buoyant dummy external tags were implanted with passive integrated transponder (PIT) tags and recovered further downstream to assess external tag retention and injury. There were no significant differences in survival to the first detection site, 12 river kilometers (rkm) downstream of release. Travel times were also similar between groups. Conversely, externally-tagged fish had reduced survival (or elevated tag loss) to the second detection site, 65 rkm downstream. In addition, the retention study revealed that tag loss was first observed in fish recaptured approximately 9 days after release. Results suggest that this new tag may be viable for short term (<8 days) single-dam turbine-passage studies and under these situations, may alleviate the turbine passage-related bias encountered when using internal tags, however further research is needed to confirm this.     

Retention of loop,monel, and passive integrated transponder tags by wild,free‐ranging Lake Sturgeon (Acipenser fulvescens Rafinesque, 1817)

Tagging or marking of fish is instrumental to fisheries biologists and managers seeking to distinguish groups of fish, track movement or migration patterns, and monitor population characteristics. However, tag loss can inhibit the ability of biologists and managers to reach these objectives. The ability of Lake Sturgeon to live for long periods of time and reach large sizes, in combination with their dynamic spawning activity, requires tags to be retained under a variety of environmental and physically demanding conditions. This study evaluated tag retention of loop, monel, and passive integrated transponder (PIT) tags on wild, free‐ranging Lake Sturgeon in Lake Huron and the St. Clair – Detroit River System. Lake Sturgeon in this study were double‐tagged with both a PIT tag under one of the three anterior‐most dorsal scutes and an external tag (loop or monel) at the base of the dorsal fin. Fish were at large for up to 16 years. Overall, tag loss for PIT tags was 1% followed by monel tags at 12% and loop tags at 36%. Tag loss for loop tags was higher when the initial length of Lake Sturgeon tagged was smaller. Tag loss for monel tags increased with time at large but was not related to length at initial tagging. Monel tags left behind abrasion marks when attached to smaller Lake Sturgeon. PIT tag retention was higher than reported in previous studies that tagged other sturgeon species in different body locations. Monel tag retention was higher than other external tag types evaluated in previous studies while loop tags had similar retention rates to external tag types. Most previous studies on tag retention of sturgeon species were of shorter duration and conducted in laboratory settings, therefore loop tags may have performed more favorably during studies under short term laboratory settings. Results of this study suggest that PIT tags inserted below dorsal scutes represent a viable option for long‐term tracking of Lake Sturgeon. Monel tags attached at the base of the dorsal fin also seem to be a viable option relative to other external tag types, but should be limited to larger sturgeon as they can leave behind abrasion marks.     

Growth, survival, and tag retention of steelhead trout (Oncorhynchus mykiss) and its application to survival estimates

Steelhead trout, Oncorhynchus mykiss, are known to expel acoustic tags which can negatively bias population survival estimates. Tag burden may also affect the development and behavior of smolts, thereby impacting the results of population and behavioral studies. We monitored the growth, condition, and tag expulsion rate of steelhead trout in similar-sized individuals and used these data to adjust survival rates from an acoustic telemetry study conducted in the Sacramento River. Eighty fish were surgically implanted with tags—40 with cylindrical tags of 9 mm diameter and 21 or 24 mm length (V9, Vemco Ltd) and 40 with a 7 mm diameter and 20 mm length tag (V7, Vemco Ltd)—to examine the impact of tag size on peritoneal retention and survival rate of juvenile steelhead trout. A total of 20 % (16/80) of all tags were expelled by smolts during the 143-day study. Ten V9 tags were expelled between day 18 and day 66. Six V7 tags were expelled between day 21 and day 143. A statistical difference was found for retention rate by surgeon even though the surgeons were of equal experience and received the same training. There were no significant differences in the tag retention rate in relation to the tag/body weight ratio, or in growth (weight or fork length) among the control, V7 or V9 treatment groups over the duration of the study. All individuals survived throughout the experiment. Two methods were used to adjust the survival estimates of an acoustic telemetry data set from the Sacramento River based on the tag retention study. First, a simple individual censorship approach in Program MARK was utilized and next ATLAS, a software program designed to compensate for bias in survival estimates caused by tag failures was used. The results of the adjusted survival estimates were not significantly different from the unadjusted rates suggesting that it may be more important to focus on improving surgical techniques to reduce tag expulsion rather than adjusting survival estimates dependent on the study. The surgical techniques utilized in this study did not have significant impacts on the growth rates of either of the tag treatment groups compared to the control. However, tag retention was an issue regardless of the size and weight of the implanted tag and the size of the steelhead.     

Novel Use of PIT Tags in Sea Cucumbers: Promising Results with the Commercial Species Cucumaria frondosa

The lack of a reliable and innocuous mark-recapture method has limited studies that would provide essential information for the management of commercial sea cucumbers. Tagging sea cucumbers is notoriously difficult because of their plastic nature and autolysis capacities. The markers that have so far been tested, mainly on or through the body wall, were either lost rapidly or had major drawbacks (e.g. suitable only for batch identification, requiring complex analysis, causing infections, necrosis, behavioural changes and mortality). The present study explored the efficacy of passive integrated transponder (PIT) tags for individually marking sea cucumbers by assessing retention rates and long-term side effects of tags inserted in previously unstudied tissues/organs. Individuals of the species Cucumaria frondosa were tagged in the body wall, aquapharyngeal bulb and at the base of the oral tentacles. They were monitored closely for evidence of stress, infection, change in feeding and spawning behaviour and tag retention rate. Implanting the tag in an oral tentacle to reach the hydrovascular system of the aquapharyngeal bulb achieved the best retention rates in full-size individuals: from a maximum of 92% after 30 days to 68% at the end of the experimental period (300 days). Efficacy was lower in smaller individuals (84% after 30 d and 42% after 300 d). Following a slight increase in cloacal movements for 15 h post tagging, no side effect was noted in sea cucumbers tagged in the aquapharyngeal bulb via the tentacles. Feeding and spawning behaviours were not affected and no signs of infections or abnormal cell development in the vicinity of the tags were observed. This study indicates that marking sea cucumbers with 8.2 mm long PIT tags implanted via the oral tentacle is an effective technique, yielding relatively high retention rates over long periods without any detectable physiological or behavioural effects.     

Effects of surgically implanted PIT tags on growth, survival and tag retention of yellow shortfin eels Anguilla australis under laboratory conditions

This study evaluated the effects of surgically implanted passive integrated transponder (PIT) tags on growth rate, survival and tag retention of yellow shortfin eels Anguilla australis with an initial mean mass of 101 g. There were no significant differences in body mass, total length, specific growth rate and survival between tagged and untagged A. australis in a 108 day laboratory trial. This tagging method was very reliable, with a tag retention of >95%.     

Long-term retention of internal elastomer tags in a wild population of painted crayfish (Panulirus versicolor [Latreille]) on the Great Barrier Reef

Many crustaceans are highly exploited fisheries species, but determining the population parameters of these animals via mark-recapture techniques is problematic, primarily due to tag-loss during moulting of the exoskeleton. Recently developed internal elastomer tags may overcome this challenging problem, since they are completely encased in the tissues beneath the exoskeleton. In this study, we evaluated the effectiveness of internal elastomer tags in a wild population of painted crayfish (Panulirus versicolor) over an 18-month period. Seventy animals were double-tagged in the abdominal musculature, with individuality obtained using different combinations of tag colour and tag location. Forty individuals were recaptured after 6, 12 and (or) 18 months, giving an overall recapture rate of 57%. Annual tag retention was estimated to be 98%, since only one instance of tag-loss was observed, despite numerous episodes of moulting among tagged individuals. The majority of tags (95%) were easily visible, even after 18 months at liberty. Nonetheless, small reductions in tag condition were observed after the first six months (mostly due to fading and [or] fragmentation), but this did not interfere with overall tag readability. Tag condition did not decline in the following 12 months, nor did it vary with gender or tag location. It is concluded that internal elastomer tags are an effective method for marking wild crayfish over long-term periods. Given the durability of elastomer, and the capacity for individual identification of large numbers of animals, such tags may be suitable for commercial-scale fishery applications.     

Tag retention and mortality of adult Atlantic salmon Salmo salar gastrically tagged with different sized telemetry transmitters

A batch of 1 sea winter pre‐spawning adult Salmo salar from the Bush river in Northern Ireland, U.K., were gastrically tagged with large (13 mm diameter) and small (9 mm diameter) dummy acoustic telemetry tags alongside untagged control fish. Survival differed between control and tagged fish and the estimated probability of survival by the end of the study for control fish with no tag was 0·94, small tags was 0·90 and large tags was 0·72. Tag loss through regurgitation was slightly higher for fish tagged with larger tags than for fish tagged with smaller tags and the estimated probability of tag loss for fish with a small tag was 0·10 and for large tags was 0·14.     

The potential use of PIT telemetry for identifying and tracking crayfish in their natural environment

A method for tracking crayfish and other benthic animals in rivers and streams, based on passive integrated transponder (PIT) technology, using a portable detector was investigated. The effect of implanting crayfish with PIT tags and the efficiency of the PIT tag detector system at locating tags is described. In a laboratory study 30 signal crayfish Pacifastacus leniusculus (>33.7 mm carapace length) were internally implanted with PIT tags (12-mm long×2.1-mm diameter) and 30 crayfish matched for size and sex were kept as controls and maintained for 6 months. Tagging had no significant effect on survival, moulting or growth of crayfish, and tag retention was 100%. The reader unit consists of an antenna coil mounted on a pole and designed to be moved over the streambed to search for tagged crayfish. Efficiency testing indicated that more than 80% of tags were identified and located when hidden within different stream microhabitats.     

A Comparison of Floy and Soft VIalpha tags on Hatchery Arctic Charr, with Emphasis on Tag Retention, Growth and Survival

The Floy FTF-69 'fingerling' tag and the soft VIalpha tag are designed to be used on small salmonid fishes (> 100 and > 150mm, respectively). The two tags were compared for 160 days on hatchery-reared Arctic charr, Salvelinus alpinus, (170–209mm). Tag retention and effects on growth rate and survival were analysed. VIalpha-tagged and untagged control fish had similar growth rates and grew significantly faster than Floy-tagged fish during the experiment. Tag retention was significantly higher for Floy tags (94%) than for VIalpha tags (78%). Most VIalpha tag loss (11%) took place within the first 10 days of tagging while there were no Floy tags lost during this period. Survival rates were about equal for all three groups (96–98%), and thus the tags did not seem to affect the survival of charr under hatchery conditions.     

Suitability of surgically implanted 8-mm passive integrated transponder tags for small-bodied fishes

Innovative tools that benefit conservation are critical as freshwater fishes are lost at unprecedented rates. Mark-recapture methods can characterize population demographics and life-history traits of diverse fishes, but suitable techniques for tagging for individual recognition of small-bodied fishes are rare. Passive integrated transponder (PIT) tag technology may facilitate the tagging of small fishes and early life stages of larger species. However, relatively little research has evaluated the suitability of these small (8.4 × 1.4 mm) tags for many groups of small fishes. Tag loss (retention and survival) and growth of individuals implanted with PIT tags relative to control and sham treatments were compared for eight fishes of differing morphologies. Additionally, the utility of cyanoacrylate to improve tag retention was tested on a subset of taxa. Fish of each species were equally divided and randomly assigned to one of three treatment groups (handled [control], surgical incision [sham], or surgical incision and PIT tag implantation [PIT]). During the 42-d study period, mortalities and expelled tags were counted daily and growth was measured weekly. Researchers can generally expect little tag loss and uncompromised growth rates for a variety of small-bodied fishes; however, initial fish length was related to the magnitude of physiological effects for some taxa (i.e., blacknose dace Rhinichthys atratulus, johnny darter Etheostoma nigrum, juvenile white sucker Catostomus commersonii). Relatively poor survival (<80%) was observed for two benthic species: johnny darter and blacknose dace, often when incision wounds became inflamed before healing. Prevalent tag loss for johnny darter, tadpole madtom Noturus gyrinus, and a dorsal-laterally compressed cyprinid can be reduced by closing the wounds with cyanoacrylate, but with substantially increased mortality rates. This research demonstrates the broad applicability of PIT tagging technology for ecological studies of small-bodied fishes and alleviates many concerns when surgically implanting tags into several fishes.     

Differential survival of male and female partially resistant horn flies (Diptera: Muscidae) on steers treated with permethrin

Males and females from a heterozygous, resistant strain (SR) of the horn fly, Haematobia irritans (L.), were tested for survival until reproductive maturity on steers with ear tags in outdoor, screened enclosures and on steers sprayed on the neck in an indoor isolation room. After 6 d, female SR flies on outdoor steers with one tag had 10 times greater survival than males; almost no SR flies on steers with two ear tags survived. Survival of male and female SR flies on steers sprayed on the neck was reduced during the first 24 h, but not thereafter. Lower survival of males compared with females on treated steers reflected differential survival of the sexes during exposure to treated cloths in a laboratory bioassay. Hair samples from neck, back, rump, and lower legs of steers with ear tags in outdoor pens were tested for toxicity to the SR flies. These bioassays indicated high localization of insecticide on the neck of steers with ear tags.     

Physiological responses of Pacific halibut, <Emphasis Type="Italic">Hippoglossus stenolepis</Emphasis>, to intracoelomic implantation of electronic archival tags,with a review of tag implantation techniques employed in flatfishes

Management of Pacific halibut (Hippoglossus stenolepis), a long-lived flatfish, is complicated by possible ontogenic and sex-specific variation in migration. Archival tags promise the ability to help uncover long-term movement patterns at the individual level, if the tags can be retained and recovered from healthy fish. We examined fifteen individuals (69–90 cm fork length) for long-term physiological response to intracoelomic implantation of three types of archival tags: fully internal, internal with right angle protruding light stalk, and internal with straight protruding light stalk. Tags represented 0.05–0.16% of initial fish weights. Fish were reared at 10.8 ± 1.1°C for 59 weeks post-surgery. One fish died after 39 weeks from thermal stress unrelated to the surgical procedure. Temporal variation in behavior of tagged fish was indistinguishable from that of controls (n = 15 tagged, 5 controls). Treatment and control-group fish grew at similar rates. No tag expulsion or physiological response was evident in the individual that died at 39 weeks, but nine of eleven individuals dissected at the end of 59 weeks had developed internal responses. These responses ranged from deposition of fibrous protein and/or calcitic material on tag surfaces to partial or full tag encapsulation in either the visceral peritoneal layer (fully-internal tags) or the intestinal mesenteries (stalk-bearing tags). The responses were within the range reported for other pleuronectids implanted with tags of similar configuration and may have implications for design and interpretation of long-term tagging studies. Encapsulation may reduce the probability of tag recoveries even in the absence of tag expulsion, especially in species eviscerated at sea.     

In situ tagging technique for fishes provides insight into growth and movement of invasive lionfish

Information on fish movement and growth is primarily obtained through the marking and tracking of individuals with external tags, which are usually affixed to anesthetized individuals at the surface. However, the quantity and quality of data obtained by this method is often limited by small sample sizes owing to the time associated with the tagging process, high rates of tagging‐related mortality, and displacement of tagged individuals from the initial capture location. To address these issues, we describe a technique for applying external streamer and dart tags in situ, which uses SCUBA divers to capture and tag individual fish on the sea floor without the use of anesthetic. We demonstrate this method for Indo‐Pacific lionfish (Pterois volitans/P. miles), species which are particularly vulnerable to barotrauma when transported to and handled at the surface. To test our method, we tagged 161 individuals inhabiting 26 coral reef locations in the Bahamas over a period of 3 years. Our method resulted in no instances of barotrauma, reduced handling and recovery time, and minimal post‐tagging release displacement compared with conventional ex situ tag application. Opportunistic resighting and recapture of tagged individuals reveals that lionfish exhibit highly variable site fidelity, movement patterns, and growth rates on invaded coral reef habitats. In total, 24% of lionfish were resighted between 29 and 188 days after tagging. Of these, 90% were located at the site of capture, while the remaining individuals were resighted between 200 m and 1.1 km from initial site of capture over 29 days later. In situ growth rates ranged between 0.1 and 0.6 mm/day. While individuals tagged with streamer tags posted slower growth rates with increasing size, as expected, there was no relationship between growth rate and fish size for individuals marked with dart tags, potentially because of large effects of tag presence on the activities of small bodied lionfish (i.e., <150 mm), where the tag was up to 7.6% of the lionfish's mass. Our study offers a novel in situ tagging technique that can be used to provide critical information on fish site fidelity, movement patterns, and growth in cases where ex situ tagging is not feasible.     

Maximum tag to body size ratios for an endangered coho salmon (<Emphasis Type="Italic">O. kisutch</Emphasis>) stock based on physiology and performance

Many coho salmon stocks (Oncorhynchus kisutch) have been in decline during the past three decades. Canada’s most endangered salmon stock, the Thompson River coho salmon, is being studied extensively as managers attempt to reverse these population declines. Investigators are using acoustic telemetry to track the migratory behaviour and survival of the Thompson River (and other) coho salmon stocks. Coho salmon pre-smolts are relatively small compared with salmonid species that are typically studied using acoustic telemetry; therefore the identification of the appropriate sizes of fish and tags to use is critical. This study tested the effects of surgically implanting the three smallest sizes of acoustic tags currently available on the growth, survival, tag retention, swimming performance and physical condition of coho salmon pre-smolts for 300 days post-surgery. Maximum tag size to body size ratios ranged from 15–17% by fork length and 7–8% by mass for the three tag sizes (11 cm fork length for a 6 × 19 mm tag, 12.5 cm for a 7 × 19 mm tag, and 14 cm for a 9 × 21 mm tag). Based on our results, it is unlikely that coho salmon pre-smolts implanted with acoustic transmitters following these size guidelines would have poor survival in studies of freshwater migratory behaviour as a result of the surgery or the tag.     

An experimental evaluation of the effects of geolocator design and attachment method on between‐year survival on whinchats Saxicola rubetra

Data from location logging tags have revolutionised our understanding of migration ecology, but methods of tagging that do not compromise survival need to be identified. We compared resighting rates for 156 geolocator‐tagged and 316 colour ringed‐only whinchats on their African wintering grounds after migration to and from eastern Europe in two separate years. We experimentally varied both light stalk length (0, 5 and 10 mm) and harness material (elastic or non‐elastic nylon braid tied on, leg‐loop ‘Rappole’ harnesses) in the second year using a reasonably balanced design (all tags in the first year used an elastic harness and 10 mm light stalk). Tags weighed 0.63 g (0.01 SE), representing 4.1% of average body mass. There was no overall significant reduction in between‐year resighting rate (our proxy for survival) comparing tagged and untagged birds in either year. When comparing within tagged birds, however, using a tied harness significantly reduced resighting rate by 53% on average compared to using an elastic harness (in all models), but stalk length effects were not statistically significant in any model considered. There was no strong evidence that the fit (relative tightness) or added tag mass affected survival, although tied tags were fitted more tightly later in the study, and birds fitted with tied tags later may have had lower survival. Overall, on a precautionary principle, deploying tags with non‐elastic tied harnesses should be avoided because the necessary fit, so as not to reduce survival, is time‐consuming to achieve and does not necessarily improve with experience. Geolocator tags of the recommended percentage of body mass fitted with elastic leg‐loop harnesses and with short light stalks can be used without survival effects in small long‐distance migrant birds.     

Efficacy of chemical markers and physical tags for large-scale release of an exploited holothurian

Hatchery-produced juveniles need to be distinguished from wild conspecifics in order to evaluate the success of restocking experiments and stock enhancement. The commercially valuable sea cucumber Holothuria scabra, or ‘sandfish’, has potential for stock enhancement but cheap, long-lasting tags have not yet been developed. We evaluated five non-genetic tags against several criteria: cost, ease of application, retention rate, and ease of detection. In a 1-month trial, T-bar tags and visible elastomer implants proved unsuitable on hatchery-produced sandfish juveniles. Coded-wire tags and two fluorochromes, tetracycline and calcein, showed more promise, so retention rates of these tags were tested on juveniles held in an earthen seawater pond for 1 year. Sixty percent of juveniles retained at least one of two coded-wire tags for 1 year. Under UV illumination, spicules from the body wall of sandfish immersed in solutions of tetracycline are yellow, whereas calcein-stained spicules are green. From months 1 to 12 after immersion, the average percentage of stained spicules declined from 40% to 8% with tetracycline and 54% to 5% with calcein. After 1 year stained spicules were detected in all immersed animals, i.e. mark retention was 100%. Stained spicules from the ventral body wall of juveniles were generally in greater proportions, and fluoresced brighter, than those from the dorsal body wall. Spicule density exceeded 7000 spicules per mm² of body wall in juveniles of 2-13 g, and decreased with sandfish weight. Fluorescence provides a simple diagnostic tool for identifying marked individuals and the sampling is non-destructive. Several mm² of outer body wall is ample for tag identification. Immersion-staining with fluorochromes is preferred to coded-wire tags and provided a cheap and reliable batch-mark for distinguishing released and wild sandfish.     

Growth,survival, and tag retention of steelhead trout (<Emphasis Type="Italic">O. mykiss</Emphasis>) surgically implanted with dummy acoustic tags

Recent advances in micro-electronics make the study of the migration of even small marine animals (>12 cm) over many 1000s of kilometres a serious possibility. Important assumptions in long-term studies are that rates of tag loss caused by mortality or tag shedding are low, and that the tagging procedure does not have an unacceptable negative effect on the animal. This paper reports results from a study to examine the retention of relatively large (24 × 8 mm) surgically-implanted dummy acoustic tags over a 7-month period in steelhead pre-smolts (O. mykiss), and the effects of implantation on growth and survival. Although there was some influence on growth to week 12, survival was high for animals > 13 cm FL. In the following 16-week period, growth of surgically implanted pre-smolts was the same as the control population and there was little tag loss from mortality or shedding. Currently available acoustic tags can be implanted in salmonid fish ≥12 cm FL, although combined losses from mortality and tag shedding were 33–40% for animals in the 12 and 13 cm FL size classes. By 14 cm FL, combined rates of tag loss (mortality plus tag shedding) for surgically implanted tags dropped to <15% and growth following surgery was close to that of the controls. Our results suggest that studies of ocean migration and survival over periods of many months are now feasible even for animals as small as salmon smolts. Surgically implanted salmon smolts are therefore good candidates for freshwater and coastal ocean-tracking studies on relatively long time scales (months). On such time scales, even relatively small salmon smolts may move thousands of kilometers in the ocean.     

Activation of sea urchin eggs by inositol phosphates is independent of external calcium.

We investigated the contribution of external calcium ions to inositol phosphate-induced exocytosis in sea urchin eggs. We show that: (a) inositol phosphates activate eggs of the sea urchin species Lytechinus pictus and Lytechinus variegatus independently of external calcium ions; (b) the magnitude and duration of the inositol phosphate induced calcium changes are independent of external calcium; (c) in calcium-free seawater, increasing the volume of inositol trisphosphate solution injected decreased the extent of egg activation; (d) eggs in calcium-free sea water are more easily damaged by microinjection; microinjection of larger volumes increased leakage from eggs pre-loaded with fluorescent dye. We conclude that inositol phosphates do not require external calcium ions to activate sea urchin eggs. This is entirely consistent with their role as internal messengers at fertilization. The increased damage caused to eggs in calcium-free seawater injected with large volumes may allow the EGTA present in the seawater to enter the egg and chelate any calcium released by the inositol phosphates. This may explain the discrepancy between this and earlier reports.