Tag Shedding Research Articles

Estimating internal transmitter and external tag retention by Walleye in the Laurentian Great Lakes over multiple years

AbstractObjectiveBoth electronic tags (e.g., acoustic and radio transmitters) and conventional external tags are used to evaluate movement and population dynamics of fish. External tags are also sometimes used to facilitate the recovery of internal electronic tags or other instrumentation because healing can make it difficult to identify fish with internal tags based on appearance alone. With both tag types, tag shedding and failure of electronic tags can affect accuracy and precision of study results.MethodsWe used a decade (2011–2021) of recapture data for Walleye Sander vitreus tagged in the Laurentian Great Lakes, where fish were double‐ or triple‐tagged with external tags (T‐bar, loop, or internal anchor tags) and internal acoustic transmitters, to quantify external tag and internal transmitter shedding and transmitter failure rates.ResultIn total, 1125 (33%) Walleye were recovered that had retained at least one external tag or internal transmitter. No confirmed cases of transmitter shedding were observed; 15 of 899 transmitters (2%) that were checked for functionality failed prior to the expected battery expiration. The retention of external T‐bar tags 1 year after release differed depending on whether the tag was placed anterior or posterior to the secondary dorsal fin (anterior, fish length = 420 mm: 73% retention; anterior, fish length = 700 mm: 73%, posterior: 63%) but was <26% after 4 years for both tag positions and fish sizes. Internal anchor tags had an 88% 1‐year retention probability and 81% 4‐year retention probability. Loop tags had the highest 1‐year retention (89%) but after 4 years retention (28–34% depending on agency) was comparable to that of T‐bar tags.ConclusionBetter understanding of tag retention characteristics through long‐term tagging studies such as this can inform study design, be considered in model design, and ultimately improve inferences from mark–recapture studies.

The fate of intracoelomic acoustic transmitters in Atlantic salmon (Salmo salar) post-smolts and wider considerations for causal factors driving tag retention and mortality in fishes

Acoustic telemetry is a widely used method in assessing behavioural dynamics in fishes. Telemetry transmitters (tags) are often surgically implanted in the coelom of the animal with limited in situ testing and sometimes only assuming that they have minimal rates of post-release tag shedding and mortality. However, fish are capable of expelling tags and mortalities do occur following release, with the mechanism (s) underlying these effects not well-understood. The purpose of this research was to address causal factors underlying tag expulsion and tagging mortality in fishes. We conducted an empirical assessment of tag retention and post-surgical mortality rates in post-smolt Atlantic salmon (Salmo salar) fitted with dummy (non-transmitting) acoustic tags over a 92-day monitoring period. This was complimented with a meta-analysis of factors affecting tag retention and post-surgical mortality rates in the wider literature. Post-smolt salmon had high rates of tag expulsion (54.8%), impaired growth, and a foreign body response evident but exhibited low rates of mortality following tag implantation (≤ 5.1%). The meta-analysis showed that mortality was generally low across all studies (12.4%) and was largely unaffected by model cofactors. Tag retention rates were high among the studies investigated here (86.7%) and had a weak negative relationship with tag:body mass ratios. Our results suggest that while mortality is often low among tagging studies, including this one, caution must be exercised in assessing stationary tag location data as they may represent an expelled tag rather than a mortality event. Our results also indicate that tag dimensions are not nearly as important as the tag:body mass ratio.

Times are changing, but has natural mortality? Estimation of mortality rates for tropical tunas in the western and central Pacific Ocean

A variety of density-dependent and -independent processes have been proposed to influence natural mortality rates, potentially leading to variation through time. Processes of natural mortalities are rarely directly observed, making estimation of natural mortality rates difficult. Mark-recapture data allow estimation of total mortality rates, which can be separated into natural and fishing mortality with information on rates of tag reporting, tag shedding and tag-induced mortality. We fitted attrition models and length-based Brownie models to four decades of mark-recapture data from skipjack and yellowfin tuna in the Western and Central Pacific Ocean, a period representing a sustained expansion of associated fisheries in the region as well as rapid changes to the marine environment. The modelled dataset included c. 250,000 skipjack and 100,000 yellowfin tag releases, with 45,000 and 17,000 recoveries of skipjack and yellowfin respectively, released from 1977 to 2017. Increases in fishing mortality were detected over this time for both skipjack and yellowfin, with evidence of temporal changes in selectivity for yellowfin. Estimates of natural mortality were highest for the smallest size class and generally lower for larger sizes, though there was large uncertainty in the largest size groups due to lower sample sizes of tagged fish. There was no clear evidence of temporal changes in natural mortality rates for either species, though there was some evidence of changes in natural mortality for the smaller yellowfin size classes (< 61 cm). However, there was likely insufficient statistical power to test for plausible changes in natural mortality rates for yellowfin due to low precision of estimates during the earlier years of the tag dataset.

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

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

Feasibility of using surgical implantation methods for acoustically tagging alewife (Alosa pseudoharengus) with V5 acoustic transmitters.

Anadromous alewives (Alosa pseudoharengus) are abundant in the Canadian Maritimes, where they support lucrative commercial fisheries. Little is known about their coastal movement, and their potential to interact with anthropogenic structures. Acoustic telemetry can provide detailed information on the spatiotemporal distribution and survival of fishes in coastal areas, using information transmitted from tagged fishes and recorded by moored receivers. However, few acoustic telemetry studies have been performed on clupeids as they are extremely sensitive to handling, and are often compromised by surgical tag implantation. This research assesses the feasibility of a surgical tagging protocol using novel High Residency acoustic tags in alewives, and establishes a baseline of short-term tagging effects. Alewives from the Gaspereau River population were tagged between 2018 (n = 29) and 2019 (n = 96) with non-transmitting models of Vemco/Innovasea V5 HR tags. Tagging effects were evaluated based on recovery rate, reflex impairment, and necropsy-based health assessments. Alewives responded well to tagging, with low mortality (3%) and no observed instances of tag shedding 72 hours post-surgery. The use of sutures to close the incision site had no effect on recovery times. Water temperature and spawning condition had the greatest effect on the behavioural response of fish to tagging. Our findings suggest that, with proper handling and smaller acoustic tags, telemetry studies on alewives are feasible.

Retention of T‐Bar Anchor Tags for Channel Catfish in the Red River of the North

AbstractTagging fish for mark–recapture studies is a common practice in fisheries science that is used to estimate population parameters. However, biased estimates may result from an incomplete understanding of tag retention. The objective of this study was to assess tag retention for a large‐river population of Channel Catfish Ictalurus punctatus over a 2,196‐d period by using both discrete and instantaneous tag‐retention models. A total of 3,827 Channel Catfish were double tagged with T‐bar anchor tags in the Red River of the North from 2013 to 2016. The number of tagged Channel Catfish that were recaptured from 2013 to 2019 was 227, with 177 individuals retaining both tags and 50 individuals retaining one tag. Tag retention was estimated at 88% over the study interval by using a discrete tag‐retention estimator. An instantaneous tag‐retention model suggested that initial tag retention was high, while instantaneous tag shedding was 0.00028 (95% CI = 0.00021 to 0.00038). Based on the instantaneous model, tag retention was predicted as 90% (95% CI = 87% to 93%) at the end of the first year and 54% (95% CI = 44% to 64%) at the end of the study interval. When instantaneous estimates of tag retention are obtained, T‐bar anchor tags may be appropriate for studies that evaluate population parameters for Channel Catfish over extended periods.

Parameter estimation performance of a recapture-conditioned integrated tagging catch-at-age analysis model

Recapture-conditioned models are infrequently used to analyze tag-recovery data, but have been proposed as an alternative to release-conditioned models for estimating movement from tagging studies when tag-loss processes (e.g., tag reporting, tag shedding) can be assumed constant and estimates of these processes are not available. Through simulations, we investigated the performance (bias and precision) of a recapture-conditioned integrated tagging catch-at-age analysis (ITCAAN) that assumes yearly natal homing under varying model complexities and intermixing rates and compared the results to those from a release-conditioned ITCAAN. We also investigated how misspecification of natural mortality, parity in population productivities, tag shedding, and spatially-varying reporting rates affected estimation of model parameters. At low intermixing rates, estimation of total abundance and spawning population abundances was accurate and precise, with precision decreasing when natural mortality was estimated for the recapture-conditioned ITCAAN. Accuracy and precision of individual population abundances declined with higher intermixing rates, with the largest bias and lowest precision occurring when estimating relative reporting rates. Assuming reporting rates were spatially constant in the ITCAAN when they varied regionally in the operating model led to biased estimation of movement rates and population abundances for both ITCAANs; attempting to estimate relative reporting when reporting varied spatially greatly improved parameter estimation compared to assuming spatially constant reporting. When tag shedding was simulated to occur, the recapture-conditioned ITCAAN yielded relatively unbiased estimation of total abundance without additional data on the tag-shedding rate, whereas the release-conditioned ITCAAN requires external data to inform this tag shedding process. Incorrect specification of tag-shedding rates by 20% resulted in only a 5% bias in estimation of total abundance from the release-conditioned ITCAAN. To avoid biased estimation from the release-conditioned model, externally derived data for all tag loss rates (e.g. tag shedding and tag-induced mortality) must be provided to the ITCAAN. Movement rates in the recapture-conditioned ITCAAN framework are theoretically unbiased by spatially uniform loss rates, but yielded biased estimates at high movement rates in this simulation study as a consequence of the model's poor ability to estimate population-specific abundances. For most scenarios investigated, estimation by the release-conditioned ITCAAN was less biased and more precise compared to the estimation by the recapture-conditioned ITCAAN presumably as a consequence of the former providing additional information on region-specific survival. However, both models performed poorly in estimating population specific abundances for scenarios with high intermixing rates and when reporting rates varied regionally but were assumed to be regionally constant in the ITCAANs.

First marlin archival tagging study suggests new direction for research

Decades of billfish tagging studies have been hindered by below-par conventional tag recovery rates and high rates of premature satellite pop-up tag shedding. With hopes of obtaining long-term tracking data, we performed the world’s first archival tagging study on an istiophorid, surgically implanting 99 archival tags into the peritoneal cavity of striped marlin (Kajikia audax) off the coast of Baja California, Mexico. Marlin were also tagged externally with a conventional tag before release. Ten archival tags (10.1%) were recovered with days at liberty (DAL) ranging from 400 to 2795. Nine recoveries were from Mexican waters, whereas one marlin was recaptured off Ecuador. In total, 100% of the light stalks on the archival tags failed, with nine failing within the first 3 months of deployment; because the light data are used to estimate the geographic position of the tagged fish, tracking data were compromised. The absence of conventional tags on all recaptured marlin indicates that studies of marlin using conventional tags have been hindered by tag shedding rather than tagging-associated mortality or underreporting. Our high recapture rate and long DAL suggest istiophorid science could be greatly advanced by archival tagging if new tag designs or methods can eliminate tag failure.

Impact of two telemetry transmitter implantation incision suturing methods on the physiological state and condition of perch (Perca fluviatilis)

Abstract The aim of this work was to determine the impact on European perch, Perca fluviatilis L. (mean body weight – 78.33 g) of the intraperitoneal implantation of telemetry transmitters using different suturing methods. In the first experiment silk sutures were used (experiment I – group ST), while in the second tissue adhesive was used (experiment II – group GT). Following the procedure, the fish were kept for 42 days in a recirculating system. Differences in growth and condition parameters were only noted in the first week of the experiment. Specimens from group GT had lower values for DGR (daily growth rate) and SGR (specific growth rate), but a higher value for FCR (feed conversion ratio) values. For the hematological parameters, lower values of MCV (mean corpuscular volume) and PLT (blood platelets) were noted in group GT, while for the biochemical parameters, lowered ALP (alkaline phosphatase) activity and Mg (magnesium) concentrations were noted in group ST. In group ST, 33.3% of the specimens loss their tags, while in group GT 77.8% did so. Differences in incision healing were only noted in the second week, when specimens in group ST were observed to have fully closed incisions, while in group GT 50% of the incisions were open. Despite the high percentage of implantation incision healing in both groups, because of the high values of tag loss rate, neither method can be recommended for perch. It might be more effective to use tag with external antennae in this species. The method use for closing implantation incisions also must be improved to eliminate tag shedding.

Survival of Atlantic halibut (Hippoglossus hippoglossus) following catch-and-release angling

Catch-and-release (C&R) of Atlantic halibut (Hippoglossus hippoglossus) has been heavily debated as a management strategy to reduce fishing mortality of this species while maintaining angling opportunities in Norwegian recreational fisheries. However, little information exists on what proportion of the fish survive post release. To test if C&R affects short- and long-term survival of Atlantic halibut, halibut (>120cm; N=11) were caught on angling gear using commonly used fishing lures, and tagged with both pop-up satellite archival tags (PSATs) and acoustic transmitters. Survival was determined by the vertical migration patterns of individuals measured by the tags during individual monitoring periods ranging from 3 to 248days (median 80 days) after the C&R event. No short-term mortality was observed post release. In terms of long-term survival, eight halibut were confirmed to have survived the monitoring periods while one halibut had insufficient data. For the other two individuals, the acoustic transmitters showed a cessation of vertical movement after 38 and 44 days, which could neither be verified nor disproven by the PSAT recordings (due to earlier detachment and tag malfunction of the PSATs). Since premature tag shedding was frequent in this study, it cannot be concluded if the cessation of vertical movement was because of tag shedding or delayed mortality. The results of this study indicate that Atlantic halibut is resilient to C&R angling, and that C&R of Atlantic halibut may be an effective management strategy to reduce fishing-induced mortality. However, the effects of severe hooking injuries, impacts on smaller individuals, and potential sublethal consequences of C&R were not covered in this study, and are still poorly understood. To minimize negative impacts of C&R and to promote fish welfare, fisheries managers are encouraged to implement best practice C&R angling guidelines for Atlantic halibut.

Life, Death, and Resurrection: Accounting for State Uncertainty in Survival Estimation from Tagged Grass Carp

AbstractInformation about Grass Carp Ctenopharyngodon idella survival would be useful for improving the management of fish used for aquatic weed control. Reliable methods for estimating annual poststocking survival of Grass Carp from radiotelemetry data do not exist because the fish remain sedentary for prolonged periods between movements, giving the false impression of death, only to be observed alive (i.e., “resurrected”) at a later date. We constructed a state‐space, multistate mark–recapture survival model accounting for uncertainty in the live/dead states of tagged Grass Carp in a large (8,500 ha) reservoir, and we estimated monthly and annual survival. Model results were compared with life history‐based methods for estimating survival, and survival estimates that were corrected for state misclassification were compared with uncorrected estimates. Corrected estimates of annual survival (mean = 0.23; 95% credible interval [CRI] = 0.15–0.41) contained less bias than uncorrected estimates (0.12; 95% CRI = 0.08–0.18). However, both corrected and uncorrected estimates were substantially lower than the survival expected based on life history theory (mean = 0.69; 95% confidence interval = 0.52–0.78), suggesting that mark–recapture survival estimates for Grass Carp might be negatively biased due to tag shedding, tag‐related mortality, or both. Our model effectively reduced bias in monthly and annual survival estimates due to state misclassification, illustrating the potential for application of existing mark–recapture frameworks to estimate Grass Carp survival with telemetry data, despite the behavioral idiosyncrasies of the species. Furthermore, these methods may have application for studies of other animals that undergo periodic quiescence between movements, such as salmonids, ictalurids, and reef fishes. To account for bias resulting from tag loss, future mark–recapture studies of Grass Carp could incorporate tag shedding rates within the framework developed here.Received July 19, 2014; accepted December 3, 2014

Tag retention, wound healing, and subsequent reproductive history of southern right whales following satellite‐tagging

AbstractThis paper presents data from 48 resightings of 16 southern right whales that were satellite‐tagged on the South African coast in September 2001, up to and including 2012. Tag performance in terms of number of days with locations received was significantly higher in males than females, and lowest in cows with calves, and attributed to behavioral differences leading to variable degrees of antenna damage. Resightings occurred from 4 to 4,054 d after tagging: tags were retained in all whales seen within 27 mo, but were apparently shed in all but one individual seen within 36 mo of tagging. The exception was a whale that still had the tag present 11 yr after tagging. Healing at the tag site occurred gradually and within 5 yr of tagging (and 2 yr after tag shedding). No significant difference in the subsequent frequency of calving was detected between 12 tagged and 382 untagged females photographed contemporaneously, and although statistical power was low, a 21% or greater reduction in calving rate in tagged females would seem incompatible with the observations. The death of one female 3 yr after tagging was more likely attributable to a ship strike on an animal debilitated by a prolapsed uterus.

Covariates of release mortality and tag loss in large-scale tuna tagging experiments

The data from tag-recapture experiments, which are used to help understand animal behaviour and dynamics, and to provide input data for population models such as stock assessments, are affected by mortality associated with tagging and by tag shedding. These processes introduce bias and uncertainty into parameters estimated in population models such as tuna stock assessments. The causes and magnitudes of tag shedding and post-release mortality in tuna tagging experiments are not well understood. We analysed data from tuna tagging experiments in the Western Pacific (330,000 releases) and Indian Oceans (168,000 releases) to investigate factors affecting post-release mortality and tag shedding. Tag return rates were modelled as functions of the tagger identity, tagger experience, tagging assistant, tagging station, treatment of the fish, use of oxytetracycline, tuna species, and size at release. The release event was included in models as a fixed effect, so that differences in recapture rate among release events did not affect other parameter estimates. We found differences in tag return rates among taggers and tagging assistants, with tagger experience, and between tagging stations. Substantially lower return rates were associated with some types of damage to fish and with internally implanted tags, and when oxytetracycline was injected. Return rates varied with tuna size and species. In the Western Pacific yellowfin and bigeye return rates were more affected by some covariates than were skipjack, while differences were not observed in the Indian Ocean, where sample sizes were smaller. Results suggest that tagging mortality may be quite high, and that more care and better recording of fish treatment would increase the reliability of assessment inputs. We provide new effective release numbers that have been adjusted to allow for estimated tagging mortality and tag shedding.

Tag shedding by tropical tunas in the Indian Ocean and other factors affecting the shedding rate

A key objective of the Regional Tuna Tagging Project—Indian Ocean was to estimate tag-shedding rates, Type-I (immediate tag shedding) and Type-II (long-term tag shedding). To assess this, a series of double-tagging experiments (26,899 double tags released with 4555 recoveries) were conducted as part of the broader tagging program. After omitting data from tags placed by less experienced taggers, the results of our analyses did not show any evidence that individual differences between taggers (i.e., a tagger effect) impacted estimates of tag-shedding rates. However, it was shown that the probability of retaining the second tag (inserted in the left side of the fish) was larger than retaining the first tag (inserted in the right side, i.e., the side typically tagged in single-tagging experiments). We used a Bayesian model averaging approach to account for model uncertainty in the estimates of the parameters α and L used to calculate the probability of tag retention Q(t)=α e−(L t) for the right tag. The parameter estimates were α=0.993 and L (per year)=0.030 (skipjack); α=0.972 and L (per year)=0.040 (yellowfin); and α=0.990 and L (per year)=0.021 (bigeye). These results agree with estimates obtained by other large-scale tropical tuna tagging projects. We showed that tag loss has a moderate impact on the underestimation of the exploitation rate (bias=2–6% depending on the tuna species). However, non-reporting leads to a bias of around 7% when using the high reporting rate estimate of purse seiners. Finally, tag shedding (specifically Type-II shedding) modified the individual weights of the samples of recaptures. Consequently, the total instantaneous mortality estimates (Z; calculated from mean times-at-large) were reduced by a range of 1–3%.

Assessment of biases in the estimation of tag shedding rates through a mark-resight experiment

Several flexible methods for estimating tag loss rates through mark-resight data have been developed recently. They allow evaluation of different tag shedding modalities and relax the usual assumption of independence between the loss of tags made in classical double-tagging methods. Two conditions limit the applicability of these methods: (1) tagged individuals must have permanent marks so that they can still be identified after losing their tags, and (2) a large number of observations is required to obtain precise estimates. Here we evaluate the performance of alternative estimators of tag shedding rates when these conditions are not met, a situation that is very common in mark-resight experiments on reef fishes. We simulated resighting data using a simple exponential model of tag shedding under different scenarios created by varying the probabilities of fish detection and fish emigration from the reef, and the tagging schedule. The model was conditioned on actual data from a short-term (∼1.5 years) double-tagging study conducted on the Argentine sandperch Pseudopercis semifasciata (Cuvier 1829) in rocky reefs of northern Patagonia. We tested eight estimation procedures: three variants of an individual-based method, two based on a binomial likelihood function for exact or pooled times-at-liberty data, and three regression methods. Although the individual-based approach produced unbiased and most precise estimates when individuals that had lost both tags were identifiable, it performed poorly in the absence of permanent tags. In contrast, conditional methods, which do not require identification of individuals that have lost both tags, were more robust, providing unbiased and precise estimates. The pros and cons of the different methods for analyzing small-scale mark-resight experiments are discussed.

Tag loss in the lobster Palinurus elephas (Fabricius, 1787) and implications for population assessment with capture-mark-recapture methods

Assessments of animal populations by mark-recapture methods rest on the assumption that all marked animals are recognizable, yet a variety of processes, such as molting in crustaceans, can lead to tag shedding. In this paper we estimate the shedding rate of T-bar anchor tags in the European spiny lobster Palinurus elephas from double tagging experiments conducted in the wild. During four annual consecutive surveys (1999–2002) lobsters were caught, double-tagged and released. The evolution of the subsequent double- and single-tag recaptures was traced during the following ten years (2000–2009). The estimated instantaneous rate of tag loss was 6.8%year−1 in males and 5.0%year−1 in females tagged during intermolt. These tag-shedding rates are low compared to most published values for similar species. Data also suggested that there is poorer tag retention when tagging immature individuals or during premolt. We simulate and discuss the impact of undetected recaptures on the return rate and the implications for population assessment in the particular case of P. elephas.

Estimation of Tag Shedding and Reporting Rates for Lake Erie Jaw-Tagged Walleyes

Since 1990, walleyes Sander vitreus in Lake Erie have been tagged annually with jaw tags to better understand the population dynamics and ecological characteristics of individual spawning populations. Although the data collected from this tagging program have been used for a variety of management purposes (e.g., estimating migration patterns, stock intermixing, and mortality rates), there has been only cursory examination of the shedding and reporting rates associated with the program. We used double tagging and high-reward tagging experiments to estimate tag shedding and reporting rates for jaw-tagged walleyes in Lake Erie. Double tagging of walleyes with jaw and passive integrated transponder (PIT) tags suggested that the tagging method and tagging agency contributed to the observed variability in both immediate (within 21 d of tagging) retention and chronic jaw tag shedding rates. Agency-specific model-averaged estimates of immediate tag retention ranged from 95% to 99%. For chronic shedding, model-averaged instantaneous rates (annual) ranged from 0.07 to 0.28. Jaw tag reporting rates, estimated via releases of high-reward tags in 1990 and 2000, varied among tagging years, tagging basins, and commercial and recreational fisheries. In general, tag reporting rates were higher for the recreational fishery (range, 33–55%) than for the commercial fishery (10–17%), and the reporting rates for both fisheries and tagging basins were found to have declined between 1990 and 2000. Uncertainty in the tag reporting rates was greater for the recreational fishery than for the commercial fishery. Our findings will benefit management of the economically important Lake Erie walleye fisheries by providing managers with robust tag shedding and reporting rate estimates, providing more reliable estimates of important dynamic rates (e.g., fishing and natural mortality) by correcting the long-term jaw tagging data set for these previously unaccounted for biases. Received September 13, 2011; accepted November 30, 2011

Dispersal of Adult Black Marlin (Istiompax indica) from a Great Barrier Reef Spawning Aggregation

The black marlin (Istiompax indica) is one of the largest bony fishes in the world with females capable of reaching a mass of over 700 kg. This highly migratory predator occurs in the tropical regions of the Pacific and Indian Oceans, and is the target of regional recreational and commercial fisheries. Through the sampling of ichthyoplankton and ovaries we provide evidence that the relatively high seasonal abundance of black marlin off the Great Barrier Reef is, in fact, a spawning aggregation. Furthermore, through the tracking of individual black marlin via satellite popup tags, we document the dispersal of adult black marlin away from the spawning aggregation, thereby identifying the catchment area for this spawning stock. Although tag shedding is an issue when studying billfish, we tentatively identify the catchment area for this stock of black marlin to extend throughout the Coral Sea, including the waters of Papua New Guinea, the Solomon Islands, Micronesia, New Caledonia, Kiribati, Vanuatu, Fiji, Tuvalu and Nauru.

Feasibility of Surgically Implanting Acoustic Tags into Pacific Herring

AbstractInternally implanted acoustic tags represent a potentially valuable approach to assessing the seasonal migration and distribution patterns of Pacific herring Clupea palasii. We examined the feasibility of implanting two sizes of dummy acoustic tags (9 mm in diameter × 21 mm long, 1.6 g; and 7 mm in diameter × 18 mm long, 0.7 g) in Pacific herring that had been held in captivity for nearly a year and that ranged from 165 to 215 mm in fork length (FL) and from 41.6 to 142.6 g. Relatively low mortality (4%) and tag shedding (4%), as well as growth similar to that observed in control fish after 135 d, indicate that, with proper handling, Pacific herring are amenable to surgical implantation of acoustic tags.

Sensitivity of tag-recovery mortality estimates to inaccuracies in tag shedding, handling mortality, and tag reporting

ABSTRACT We used Monte Carlo simulations to evaluate the sensitivity of tag-recovery mortality estimates to inaccuracies in tag shedding, handling mortality, and tag reporting. The data-generating model used in the simulations assumed that tagging was conducted annually for 4 years with tag recoveries occurring over a 4-year period. Several different combinations of instantaneous fishing (F) and natural (M) mortality were evaluated in the simulations. The data-generating model additionally assumed that immediate-shedding and handling-mortality rates equaled 2.5% and 0%, respectively, and that chronic shedding was a sigmoidal function of months since tagging. Two spatial patterns of reporting rates were considered-one where reporting was a function of distance from the tagging site and one where reporting was a random generation across the study area. Maximum likelihood estimates of F and M were calculated from the recovery of tags from the data-generating model under different assumed rates of tag sheddin...