Taking the bait: in situ voluntary ingestion of acoustic transmitters by Atlantic cod (Gadus morhua)

Voluntary ingestion of acoustic transmitters by Atlantic cod (Gadus morhua) was investigated under field conditions in the shallow inshore waters off Newfoundland. A surface-controlled tagging frame was used to suspend and monitor baited transmitters (16×45 mm up to 16×108 mm) near the seafloor at depths ranging from 12.5 to 39.0 m. The behaviour of cod toward the transmitters was quantified using an underwater video camera. Cod ranging in size from 11 to 92 cm approached and touched the transmitters. Both biting and ingestion were size-dependent. Eight successful taggings were completed with cod ranging in size from 34 to 92 cm. Transmitters deployed in the morning were consumed faster (mean soak time = 3.3 h) than transmitters deployed in the afternoon (mean soak time = 9.1 h). Tracking revealed that cod were active immediately following tagging, suggesting no effect of the tagging procedure. Individual fish were tracked for periods ranging from 5.6 to 18.8 d, with none of the fish regurgitating transmitters during the period for which they were tracked.     

A field and experimental evaluation of the effect of data storage tags on the growth of cod

The effect of electronic data storage tags (DSTs) on the growth of cod Gadus morhua was evaluated in laboratory and field experiments. In the first laboratory experiment, large DSTs (60 × 18 mm, 3 g in water ) attached externally for 3 months did not have any effect ( anova , P  > 0·05) on the growth of adult cod (mean ±  s . d . 65 ± 4·5 cm total length) relative to untagged adult cod. In a second experiment, small DSTs (34 × 11 mm, 1·5 g in water) implanted into young cod (48·1 ± 4·4 cm) for an 8 month period did not have any effect upon the growth relative to untagged controls ( anova , P  > 0·05). Length data returned from tagging experiments conducted on adult cod (57·3 ± 7·5 cm) in the North Sea showed that the growth of fish tagged either externally or internally with large DSTs was not different ( t ‐test, P  > 0·05). Attachment wounds, however, provided evidence that external attachment of DSTs should be avoided unless sensor configuration requires access to the external environment, and that internal implantation should be preferred whenever possible.     

Evaluation of VIE and PIT tagging methods for juvenile cyprinid fishes

Retention and mortality associated with visible implant elastomer (VIE) and passive integrated transponder (PIT) tagged juvenile chub [ Leuciscus cephalus (L.)], dace [ Leuciscus leuciscus (L.)] and roach [ Rutilus rutilus (L.)] were evaluated. PIT tag retention (96.6–100%) was higher than VIE over the 6-month duration of the experiment. VIE retention was significantly better in the head (96.3–98.8%) than in the fins (78.8–90.9%) the first month after tagging, but the opposite was found after 6 months (head = 21.5–57.5%; fins = 77.2–88.8%). Survival was not significantly different from controls for any treatment, except dace tagged with 23-mm PIT (significantly influenced by mass of fish at tagging) and sham PIT tagged dace, because of initial losses. PIT tags are recommended as the most suitable method for tagging individual juvenile chub, dace and roach based on high retention and survival. VIE implantation in the head (studies < 30 days) and fins (studies > 30 days) could provide a cheap, batch-marking alternative, provided retention rates are monitored.     

Cod migration and transplantation experiments in the Baltic

In the first half of the paper a review is given of the occurrence and migratory habits of Baltic cod based on experience since the 1950s, results of extensive tagging experiments combined with information on changes in allele frequency for haemoglobin types, in meristic characters, and in otolith types. The latter pan of the paper is an account of about 15 transplantation experiments with tagged cod to study a potential homing ability of the fish. The very great importance of the threshold areas inside the Baltic and out to the Kattegat is stressed, and so are the hydrographic conditions in general for cod recruitment and migration. The waters west of Bornholm constitute an area of hydrographic instability with varying cod migrations and passive transport of fry with the currents. The migration east of Bornholm refers—except for local stocks and a varying contribution from the west-mainly to fish grown up in the central Baltic proper and northern areas. The latter fish migrate primarily southward for spawning, and as adults they usually stay in the southern waters east and north of Bornholm. The results of the transplantation experiments support a strong direct linkage of cod migration and hydrographic factors. Cod that were tagged and transplanted to a new area behaved and moved in the same way as the local stock. Indications of “homing” can be found in areas with suitable hydrographic gradients, such as changes in salinity, for example in the Öresund.     

Effects of surgically implanted transmitters on swimming performance, food consumption and growth of wild Atlantic salmon parr

Experiments were conducted on wild Atlantic salmon Salmo salar parr to determine the effect of surgically implanted dummy transmitters on swimming performance, food consumption and growth. Swimming performance of tagged fish (tag 1·7–3·7% of fish mass) was similar to that of control fish 1, 5 and 10 days after surgery. Negative effects on growth, however, were found up to day 36 of a 45 day experiment (tag 0·9–2·6% of fish mass). Consumption rates were similar between tagged and control fish and did not explain differences in growth.     

Learning from unsuccessful radio tagging of common carp in a Namibian reservoir

Radio tagged common carp Cyprinus carpio in a Namibian reservoir, where this species has been introduced, experienced 100% mortality or tag loss (  n  = 13) with surgically implanted transmitters and 100% survival (  n  = 5) with externally attached transmitters at water temperatures of 24–25° C. It seems that the negative effects of the tagging were greater for surgical implantation than for external attachment. The body shape of common carp make them well suited for external tagging, and this tagging method is recommended for common carp studies at high water temperatures or under other stressful conditions.     

Predicting the factors influencing the inter- and intraspecific survival rates of riverine fishes implanted with acoustic transmitters

Biotelemetry is a central tool for fisheries management, with the implantation of transmitters into animals requiring refined surgical techniques that maximize retention rates and fish welfare. Even following successful surgery, long-term post-release survival rates can vary considerably, although knowledge is limited for many species. The aim here was to investigate the post-tagging survival rates in the wild of two lowland river fish species, common bream Abramis brama and northern pike Esox lucius, following their intra-peritoneal double-tagging with acoustic transmitters and passive integrated transponder (PIT) tags. Survival over a 2-year period was assessed using acoustic transmitter data in Cox proportional hazards models. Post-tagging survival rates were lowest in the reproductive periods of both species, but in bream, fish tagged just prior to spawning actually had the highest subsequent survival rates. Pike survival was influenced by sex, with males generally surviving longer than females. PIT tag detections at fixed stations identified bream that remained active, despite loss of an acoustic transmitter signal. In these instances, loss of the acoustic signal occurred up to 215 days post-tagging and only during late spring or summer, indicating a role of elevated temperature, while PIT detections occurred between 18 and 359 days after the final acoustic detections. Biotelemetry studies must thus always consider the date of tagging as a fundamental component of study designs to avoid tagged fish having premature end points within telemetry studies.     

Efficacy of tagging European catfish Silurus glanis (L., 1758) released into ponds

The efficacy and sub‐lethal consequences of single and double tagging European catfish Silurus glanis with Petersen disc and passive integrated transponder (PIT) tags were examined in short (laboratory) and longer‐term (field) experiments. Tag retention in the laboratory was 100%, with normal behaviour (i.e. feeding) in all fish returning within 36 h. In the field, 65 of 120 tagged S. glanis were recaptured from five small study ponds, with 85% retaining their PIT tags, though recapture rates and tagging efficacy were highly variable amongst locations. This is consistent with literature for other fishes, suggesting that tagging efficiency is variable across species and largely context dependent (fish length, tagging location, habitat).     

Effects of acoustic tagging on juvenile green sturgeon incision healing,swimming performance,and growth

Ultrasonic telemetry is a preferred method for fish-movement studies. Despite surgical tag implantation being the most common method for affixing tags, many studies lack tests addressing the assumption that tagging has no effect on fish performance or survival. The threatened, anadromous green sturgeon, Acipenser medirostris, has little documentation concerning its movements. We evaluated the effects of surgery and tag implantation in juveniles. We compared three groups: tagged fish with dummy transmitters implanted in the peritoneal cavity, sham fish that underwent surgery without tag implantation, and control fish that were handled and anesthetized but did not undergo surgery. We found no differences in growth or critical swimming velocity among groups. Photos of incisions were taken towards the beginning and at the end of the study to assess inflammation and to score each incision for closure and suture retention. Inflammation declined similarly for tagged and sham fish during the study. U_crit was not related to the extent of inflammation or to post-surgery time. All fish showed healing during the study (ca. 140 day duration) and 10 % of tagged and sham fish showed signs of inflammation by the study end. These results suggest that current ultrasonic surgical tagging methods do not significantly affect the short-term growth or swimming performance of juvenile green sturgeon. Additionally, effects of surgery can be mitigated by minimizing the number of suture entry points and by using rapid-absorbing sutures.     

Behaviour and diet of sea trout post-smolts in a Norwegian fjord system

In order to study the behaviour of sea trout Salmo trutta L., in the early post-smolt phase, reared smolts were tagged with acoustic transmitters and released in the estuary of the River Aurland (Western Norway) and observed for 31–137·5 h. The study was conducted in May-June 1991 and 1995 on a total of seven tagged smolts. The fish moved back and forth along the littoral zone close to the surface and migrated net distances of 100–8000 m. In 1991 the tagged fish were usually observed in schools averaging 24–55 fish, while the tendency to school was less pronounced in 1995. Post-smolts of wild and reared origin were caught by 25 m long gillnets in the littoral zone. In 1991 the mean distance to shore at capture was 4·3 m and the mean depth 0·6 m, and the corresponding numbers in 1995 were 8·0 and 0·8 m. The distribution of the post-smolts is explained by a general preference for shallow water caused by osmoregulatory problems in high-salinity deep water, together with a preference for the sheltered littoral zone and a strong predation pressure in the open sea from fast swimming pelagic fish predators and gulls Larus sp. Schooling seemed to restrict predation by cod Gadus morhua L., in the littoral zone in 1991, while no cod were observed in this habitat in 1995. In both years the stomach contents of the netted fish consisted mainly of terrestrial insects. Reared fish chose prey items similar to those taken by wild fish, but consumed less food.     

The effect of external dummy transmitters on oxygen consumption and performance of swimming Atlantic cod

Decreased critical swimming speed and increased oxygen consumption (     ) was found for externally tagged Atlantic cod Gadus morhua swimming at a high speed of 0·9 body length (total length, L _T) s⁻¹. No difference was found in the standard metabolic rate, indicating that the higher     for tagged cod was due to drag force rather than increased costs to keep buoyancy.     

Movements and Site Fidelity of two Juvenile Fish Species Using Surf Zone Nursery Habitats Along The Southeastern North Carolina Coast

We examined the extent of movements of juvenile Florida pompano, Trachinotus carolinus, and gulf kingfish, Menticirrhus littoralis, along an open ocean beach. Fishes were collected by seine at three sites along Masonboro Island and Carolina Beach, NC between 7 June and 7 July 1995. All specimens 40 mm standard length (SL) were tagged with coded wire tags and released at the capture sites. Between 7 July and 9 August and on 15–16 September Masonboro Island and northern Carolina Beach were surveyed for tagged fish. A controlled tag mortality/retention study was conducted for both species. Overall, 1569 Florida pompano (40–135 mm SL) were tagged. Sixty-one (3.9%) of these were recaptured, and only eight moved away from the original tagging sites. The largest movements by two Florida pompano were 2.1 and 10.5 km. Many fish remained at their original tagging sites for 21–27 days. Of 488 gulf kingfish (36–158 mm SL) tagged, 16 (3.3%) were recaptured. Gulf kingfish also exhibited little movement away from tagging sites during the study, with individuals remaining at original tagging sites up to 21 days. Stock size estimates for Florida pompano ranged from 3354 to 4670 among the tagging sites, with densities ranging from 1.9 to 2.6 fish m^–2. The remarkable site fidelity exhibited by these two species suggests that resources were not limiting or that predation pressure was not high enough to cause large scale movements during the study. This implies that local disturbances could impact behavior or survival of juvenile fishes in the surf zone.     

Fin-spines attachment,a novel external attachment method for the ultrasonic transmitters on hard fin-spines fish (Sparidae)

The purpose of this study was to develop a novel method for the external attachment of ultrasonic transmitters on hard fin-spines fish (Sparidae). Acanthopagrus latus, one of the main stocking Sparidae fishes in the northern South China Sea, was employed to conduct the 40-day tank experiment by using dummy ultrasonic transmitters. The experiment consisted of 3 treatment groups, i.e., drilling on dorsal fin-spine (DD) group, drilling on anal fin-spine (DA) group, and control (C) group, with each group having 3 replicates and 30 fish per replicate. The feasibilities of DD and DA for the external attachment of ultrasonic transmitters were tested and evaluated using parameters: the specific growth rate, survival rate, and tag retention rate of each group. And the tagging procedures for the external attachment of hard fin-spines fish were also proposed. The results showed that there were no significant differences in the specific growth rate of fish between groups. Both the survival rates of DD group (96.67%) and DA group (94.44%) were less (but not significant) than C group (97.78%), while the tag retention rate of DA group (100%) was higher (but not significant) than DD group (98.89%). These results demonstrate that drilling on dorsal or anal fin-spines is feasible as an external attachment method of ultrasonic transmitters on Sparidae fishes. In addition, considering the friction between the tagged transmitters and rocks at the bottom of natural waters, which possibly affect the fish behaviors such as swimming, feeding, etc., or lead to tag loss, so drilling on the dorsal fin-spine is preferred for rocky-bottom Sparidae fishes like A. latus as small as 14 cm body length.     

Diel activity pattern and food search behaviour in cod, Gadus morhua

Food search behaviour in cod, Gadus morhua, was studied by means of a stationary positioning system. Six fish in a fjord in northern Norway were tagged in situ by allowing them to shallow bait-wrapped acoustic tags, and their swimming behaviour was continuously recorded. The fish exhibited a diel activity rhythm, with higher swimming speeds and a larger range during the day than at night. Chemically mediated food search was studied in periods of both high and low activity by setting a string of baits in the morning and at night. During the period of high activity, more fish localized the baits (70 versus 45% of the observations) and the time to localization was 50% shorter, indicating that high swimming activity increased the probability of encountering the odour plume and the odour source. No diel variations in the response threshold to olfactory stimuli were found, as the proportion of fish in the odour plume that responded rheotactically, and their response distances were similar in the two periods (240 and 227 m respectively). Cod performed area-restricted searches on encountering the string of baits during the day. The probability of cod detecting prey by taste receptors, encountering the odour plume of prey or localizing a stationary food source after olfactory stimulation should be relatively independent of light, and this could explain why cod were active throughout the 24 h cycle. On the other hand, the visual detection distance and the ability to capture active prey are influenced by the light level, resulting in higher activity during the day.     

Subcutaneous injection of visible implant elastomer in sterlet (Acipenser ruthenus Linnaeus, 1758): a study on compatibility and retention

The purpose of this study was to mark endangered sterlet (Acipenser ruthenus) with visible implant elastomer (VIE) in order to assess mortality, compatibility, retention, persistence and histological reactions resulting from this tagging technique. It was hypothesized there would be only minor effects on the fishes' health, and assumed that acute effects would be more pronounced than long‐term effects. On 11 September 2013, 20 specimens were tagged ventrally with visible implant elastomer, 20 received a subcutaneous injection with 0.9% NaCl solution, and another 20 served as untreated control. Mean total length was 28.0 ± 1.8 cm and mean body mass 64.1 ± 12.0 g. The sterlets were kept in four 4,000‐L tanks filled with 2,400‐L water. Acute effects were monitored for 95 days, where fish were held at temperatures between 2.4°C and 15.2°C, reflecting outdoor conditions. Chronic effects were examined 282 days post‐tagging through histological sections of the tagging region in five sterlets. During the first 95 days of observation, tag retention was 100%. No signs of incompatibility were detected. Body mass did not significantly differ between VIE‐tagged fish and controls. At day 282 post‐tagging, however, distinct tissue reactions were visible at the tagging sites of nine fish. Histological examination of five fish revealed a variable degree of infiltration with leukocytes in the areas around the elastomer, which did not necessarily correspond with the externally visible degree of inflammation. After medical treatment, the lesions healed without complications, whereas the retention rate of the VIE tags was 5%. According to the findings, the tag location rather than the tag itself was responsible for the externally visible irritations, indicating that the ventral subcutis of sterlet is not a suitable site, even for small VIE tags in long‐term studies. The results of this study also suggest that VIE marking should in general be critically evaluated before application in field studies.     

Mitochondrial DNA sequence variation and genetic stock structure of Atlantic cod (Gadus morhua) from bay and offshore locations on the Newfoundland continental shelf

Bay cod, Atlantic cod (Gadus morhua) that over-winter in the deep-water bays of northeastern Newfoundland, have historically been regarded as distinct in migration and spawning behaviour from offshore (Grand Bank) cod stocks. To investigate their genetic relationships, we determined the DNA sequence of a 307-base-pair portion of the mitochondrial cytochrome b gene for 236 adult cod taken from the waters off northeastern Newfoundland, including fish found over-wintering and spawning in Trinity Bay. Although 17 genotypes were found, a single common genotype occurs at a frequency of greater than 80% in all samples, and no alternative genotype occurs at a frequency of greater than 3%. Genotype proportions did not differ significantly among samples. Measures of genetic subdivision among sampling locations are nil. Cod over-wintering in Trinity Bay are not genetically distinct from offshore cod. In combination with tagging and physiological studies, these data suggest that there is sufficient movement of cod between bay and offshore locations to prevent the development or maintenance of independent inshore stocks. Adult cod that over-winter in Trinity Bay appear to represent an assemblage of temporarily nonmigratory fish that have become physiologically acclimated to cold-water inshore environments. The pattern of genetic variation in northern cod suggests a recent population structure characterized by extensive movement of contemporary individuals superimposed on an older structure characterized by a bottleneck in the population size of cod in the north-western Atlantic.     

A passive integrated transponder tag implanted by a new alternative surgical method: effects on the oriental weather loach (Misgurnus anguillicaudatus) and application in a small irrigation system

We validated the effects of a passive integrated transponder (PIT) tagging process on the oriental weather loach Misgurnus anguillicaudatus. Laboratory experiments were conducted to assess the effects of PIT tagging on fish survival, growth, wound healing, and tag omission. Two tagging protocols, standard syringe injection versus insertion through a small hole pierced by a fine needle-shaped awl, were compared using a 12.5 × 2.07 mm² tag. A control group was also included. In comparison with the awl technique, syringe injection heightened the mortality of the loach and delayed healing of the wound caused by tag insertion. No effects of either PIT tagging method were detected on the growth of surviving loach. We also field-tested similarly tagged populations within a river-based irrigation system of Sado Island, Japan. Two different sized tags (long, 12.5 × 2.07 mm²; short, 8.5 × 2.12 mm²) were compared by using antenna loggers which detected fish movement through gates and automatically logged tagged fish’s tag IDs and timestamps. By comparing logged data and actual fish collection surveys both below and above the gates, 77% and 30% of actual loach movements were confirmed to have been successfully logged for the long and short tags, respectively. The awl insertion technique with the longer tag is therefore recommended for use in similar studies of smaller fish species.     

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.     

Effects of Body Size and Food Ration on Over-winter Survival and Growth of Age-0 Atlantic cod, Gadus morhua

This study examined the effects of body size and food ration on over-winter survival of age-0 Atlantic cod. Cod were divided into two groups based on standard length (large=76.95±1.10 mm SL; small=57.65±1.02 mm SL; mean±1 SE) and wet weight (large=4.02± 0.21 g; small=1.52±0.09 g). Replicate tanks (n=2) of 10 large and 10 small cod were exposed to one of two food rations (0.25% and 1.0% body weight day^-1) for the entire experiment (December to June). Tanks were examined daily for mortalities and feeding was adjusted accordingly. The experiment was run under ambient light and seawater conditions. All but large age-0 cod exposed to the low food ration grew over the course of the experiment. The specific growth rate (SGR) of small cod was significantly higher (0.2425% wet weight day^-1) than that of the large fish (0.0443% wet weight day^-1). Food ration had no significant influence on SGR or over-winter survival. Significantly more of the large age-0 cod survived the winter (58.5% of those originally introduced) compared to the smaller fish (14%). Our results are consistent with those from studies of several other fish species, and are discussed in relation to the ecology of age-0 cod, and their potential use in aquaculture in Newfoundland.     

Distinct patterns of Arctic cod (<Emphasis Type="Italic">Boreogadus saida</Emphasis>) presence and absence in a shallow high Arctic embayment,revealed across open-water and ice-covered periods through acoustic telemetry

With climate change resulting in unpredictable sea ice conditions between years, it is crucial to gain a more comprehensive understanding of the subsequent effects on Arctic marine ecosystems. Arctic cod (Boreogadus saida) play a key role in the Arctic marine food web, serving as a food source that is estimated to contribute up to 75 % of energy transfer to higher trophic levels. To investigate Arctic cod residency and distribution in Resolute Bay (74°44′N, 095°04′W), 85 individuals from four locations in the bay were captured, measured, weighed, implanted with acoustic tags and subsequently tracked on an acoustic array of 49 receivers. Two main periods of residence in the bay were identified, the first in open water and the second under ice cover, and both concluded with a collective mass departure of fish. A generalised linear mixed model was used to investigate the influence of variables on Arctic cod presence/absence in the bay, indicating that ingress and egress were influenced by environmental changes, particularly those associated with the transition from open-water to the ice-covered period. Timing and distribution, during the study period, appeared to be influenced by a combination of physiological acclimation, and a balance between resource availability and refuge from predators. Receiver site Residence Index (RI) analysis revealed strong site fidelity of fish towards the northern areas of the bay, and this behaviour was consistent between tagging groups and individuals, indicating that the majority of tagged cod were representative of a single school. This study represents the first employment of acoustic telemetry to monitor the movements of individual Arctic cod over 9 months, incorporating both open-water and ice-covered periods.