Tag Loss Research Articles

High predation on small populations: avian predation on imperiled salmonids

Generalist predators can contribute to extinction risk of imperiled prey populations even through incidental predation. Quantifying predation on small populations is important to manage their recovery, however predation is often challenging to observe directly. Recovery of prey tags at predator colonies can indirectly provide minimum estimates of predation, however overall predation rates often remain unquantifiable because an unknown proportion of tags are deposited off‐colony. Here, we estimated overall predation rates on threatened wild juvenile steelhead (Oncorhynchus mykiss) by generalist adult Western Gulls (Larus occidentalis) in six central California (USA) watersheds. We estimated predation rates by gulls from the recapture of PIT (passive integrated transponder) tags that were originally inserted into steelhead and were subsequently deposited at a Western Gull breeding colony, Año Nuevo Island (ANI). We combined three independent datasets to isolate different processes: (1) the probability a tagged steelhead was consumed during predation, (2) the probability a consumed tag was transported to ANI, and (3) the probability a transported tag was detected at ANI. Together, these datasets parameterized a hierarchical Bayesian model to quantify overall predation rates while accounting for tag loss between when prey were tagged and subsequent tag detection at ANI. Results from the model suggest that low recovery rates of PIT tags from steelhead at ANI were mostly driven by low probabilities of transportation (≤0.167) of consumed tags to ANI. Low transportation probabilities equate to high per‐capita probabilities of predation (≥0.306/yr) at the three watersheds in closest proximity to ANI, whereas predation rates were uncertain at watersheds farther from ANI due to very low transportation rates. This study provides the first overall estimate of Western Gull predation rates on threatened wild juvenile steelhead and suggests gull predation on salmonids is a larger source of mortality than was previously estimated from minimum predation rates. This study thus represents an important example of high rates of incidental predation by a generalist consumer on an imperiled prey and provides a quantitative framework to inform robust estimates of predation rates on small populations that can be applied to other systems where direct observation of predation is not feasible.

A Comparison of Methods to Estimate Shovelnose Sturgeon Mortality in the Mississippi River Adjacent to Missouri and Illinois

AbstractMortality is a key parameter in understanding the dynamics of any fish population. We examined three methods to evaluate Shovelnose Sturgeon Scaphirhynchus platorynchus mortality (e.g., ratio of first year recruits to all recruits [Heincke's method], a linearized weighted catch curve, and an open system mark–recapture mortality approach). The Mississippi River was sampled in two distinct but connected geomorphic sections: upper Mississippi River (UMR; river kilometer 323–587) and the middle Mississippi River (MMR; river kilometer 0–322). All analyses were pooled across these areas due to potential emigration or immigration throughout both study reaches. Heincke's method estimated annual mortality at 16.9% for the full range of ages (9–23 years) with generally increasing estimates with decreasing age ranges considered (10–23, 11–23, 12–23, and so on). A linearized weighted catch curve that considered increasing estimates of mortality for the shorter age ranges generated an annual mortality estimate of 29.0%.d Four mark–recapture models were considered using the program MARK. The model with the greatest support was the model that provided estimates of annual mortality for each year and a single recapture probability. The annual mortality estimates from this model varied from 2.7% to 70.7% after correcting for tag loss. The best fit model with a single estimate of annual mortality was the one that estimated annual recapture probabilities for each year and had a mortality estimate of 34.6% (after correcting for tag loss, but not for immigration, emigration, or sampling effort). The three methods provided varying results, and our data indicated that a single method to estimate Shovlenose Sturgeon mortality rate may not be appropriate. As such, biologists must recognize that disparities in Shovelnose Sturgeon mortality rates may exist using various methods and should use caution when choosing which method will be employed to estimate sturgeon mortality.Received August 1, 2012; accepted May 16, 2013

Testing the effects of temperature and humidity on printed passive UHF RFID tags on paper substrate

This article is an interesting substrate material for environmental-friendly printable electronics. In this study, screen-printed RFID tags on paper substrate are examined. Their reliability was tested with low temperature, high temperature, slow temperature cycling, high temperature and high humidity and water dipping test. Environmental stresses affect the tag antenna impedance, losses and radiation characteristics due to their impact on the ink film and paper substrate. Low temperature, temperature cycling and high humidity did not have a radical effect on the measured parameters: threshold power, backscattered signal power or read range of the tags. However, the frequency response and the losses of the tags were slightly affected. Exposure to high temperature was found to even improve the tag performance due to the positive effect of high temperature on the ink film. The combined high humidity and high temperature had the most severe effect on the tag performance. The threshold power increased, backscattered power decreased and the read range was shortened. On the whole, the results showed that field use of these tags in high, low and changing temperature conditions and high humidity conditions is possible. Use of these tags in combined high-humidity and high-temperature conditions should be carefully considered.

Fishing and Natural Mortality Rates of Atlantic Halibut Estimated from Multiyear Tagging and Life History

AbstractFishing mortality and natural mortality rates for Atlantic HalibutHippoglossus hippoglossuson the Scotian Shelf and southern Grand Banks were estimated from a multiyear tagging study. Models that were used to estimate mortality rates incorporated tag loss. Between 2006 and 2008, 1,913 Atlantic Halibut were double‐tagged with t‐bar anchor tags; as of 26 August 2010, 368 of these fish had been recaptured. We estimated instantaneous fishing mortality (F) separately for each cohort in the first year (on average, 6 months) after release to allow newly tagged animals to mix with the population. A two‐parameter model was used to describe tag loss. Tag loss was estimated at 13% per year in the first year and 10% per year in the second and subsequent years. Using the multiyear model with incomplete mixing and assuming 90% tag reporting and 80% survival from tagging, average instantaneous natural mortality (M) of Atlantic Halibut was estimated to be 0.22 andFwas estimated to be 0.15 in 2007, 0.24 in 2008, and 0.18 in 2009. These estimates ofFwere comparable to those from the stock assessment population model. However, the estimates ofMwere higher than inferred estimates ofMbased on life history and growth. Estimates ofFandMwere sensitive to the minimum size of Atlantic Halibut at the time of release. An increase inFwith size is consistent with fishery size selectivity resulting from either gear selectivity or the distribution of fishing effort where there is spatial heterogeneity in the size composition. We suggest thatMmay have been overestimated because of emigration from the study area.

Comparison of 180-degree and 90-degree needle rotation to reduce wound size in PIT-injected juvenile Chinook salmon

Most telemetry studies require the implantation or attachment of passive transponders or active transmitters to monitor and assess fish stocks and conservation to gain an understanding of fish physiology and behavior. As new telemetry technologies become available, it is imperative to study the effect of the transmitter or implantation technique on species of interest. In this study, we investigated the effects of needle axial or bevel rotation (0-, 90-, 180-degree) on wound extent and healing, and tag loss in juvenile Chinook salmon injected with an 8-gauge needle, which is required for implantation of the injectable Juvenile Salmon Acoustic Telemetry Systems acoustic transmitter and some passive integrated transponders (PITs). Although the wounds were not closed after injection (e.g., with sutures or glue), there were no mortalities, dropped tags, or indications of fungus, ulceration, or redness around the wound. No axial rotation (0-degrees) resulted in the PIT tag frequently misloading or falling out before injection. On Day 0 and post-implantation Day 7, the 90-degree bevel rotation produced a significantly smaller wound extent than the 180-degree bevel rotation. Given the wound extent compared to size of fish, we recommend researchers should consider a 90-degree rotation over the 180-degree rotation when injecting transmitters.

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.

Group heterogeneity in the Jolly–Seber-Tag-Loss model

Mark–recapture experiments involve capturing individuals from populations of interest, marking and releasing them at an initial sample time, and recapturing individuals from the same populations on subsequent occasions. The Jolly–Seber model is widely used in open-population models since it can estimate important parameters such as population size, recruitment, and survival. However, one of the Jolly–Seber model assumptions that can be easily violated is that of no tag loss. Cowen and Schwarz [L. Cowen, C.J. Schwarz, The Jolly–Seber model with tag loss, Biometrics 62 (2006) 677–705] developed the Jolly–Seber-Tag-Loss (JSTL) model to avoid this violation; this model was extended to deal with group heterogeneity by Gonzalez and Cowen [S. Gonzalez, L. Cowen, The Jolly–Seber-tag-loss model with group heterogeneity, The Arbutus Review 1 (2010) 30–42]. In this paper, we studied the group heterogeneous JSTL (GJSTL) model through simulations and found that as sample size and fraction of double tagged individuals increased, bias of parameter estimates is reduced and precision increased. We applied this model to a study of rock lobsters Jasus edwardsii in Tasmania, Australia.

A comparison of single-suture and double-suture incision closures in seaward-migrating juvenile Chinook salmon implanted with acoustic transmitters: implications for research in river basins containing hydropower structures

BackgroundReductions in the size of acoustic transmitters implanted in migrating juvenile salmonids have resulted in the ability to make smaller incisions that may warrant using only a single suture for closure. However, it is not known if one suture will sufficiently hold the incision closed, particularly when outward pressure is placed on the surgical site, such as when migrating fish experience pressure changes associated with passage at hydroelectric dams. The objective of this research was to evaluate the effectiveness of single-suture incision closures on juvenile Chinook salmon (Oncorhynchus tshawytscha).ResultsJuvenile Chinook salmon were surgically implanted with a 2012 Juvenile Salmon Acoustic Telemetry System (JSATS) transmitter (0.30 g) and a passive integrated transponder tag (0.10 g), and incisions were closed with either one suture or two sutures. Mortality and tag retention were monitored, and tagged fish were examined after 7 and 14 d to evaluate tissue responses. In a separate experiment, surgically implanted fish were exposed to simulated turbine passage and then examined for expulsion of transmitters, expulsion of viscera through the incision and mortal injury. With incisions closed using a single suture, there was no mortality or tag loss and similar or reduced tissue reaction compared to incisions closed with two sutures. Furthermore, surgery time was significantly reduced when a single suture was used, which led to less handling time and time under anesthesia and consequently, stress. No tags were expelled during pressure scenarios. Expulsion of viscera occurred in two non–mortally injured fish (5%) with single sutures that were exposed to very high pressure changes, but no viscera expulsion was present in fish exposed to pressure scenarios, likely representative of hydroturbine passage at many Columbia River dams (for example, <2.7 ratio of pressure change, acclimation pressure of 146.2 absolute kPa and lowest exposure pressure of about 53.3 absolute kPa).ConclusionsWe recommend the use of a single suture for surgical implantation of transmitters with incisions that are approximately 5.5 mm long after tag insertion.

Development and testing of attachment methods for pop-up satellite archival transmitters in European eel

Four methods for attaching pop-up satellite transmitters to European eel were tested in the laboratory by recording long-term tag retention, growth and survival; short-term behavioral responses; and physical damage from attachments. All eels survived until they lost their tag, or until end of the six-month study. Specific growth rate did not differ between tagged fish and controls. Tag retention varied from 0% to 100% among attachment methods. A tagging method that uses the strength of the eel skin by attaching the tag to the skin at three points is recommended for ocean migration studies based on a long tag retention time, minimal behavioral reactions, negligible damage to the swimming muscle, and minimal physical damage both for fish retaining and losing the tag. Although tag retention was 50% over six months, those losing their tags still retained them for 114 to 134 days. Another method had higher tag retention (100%), but required the use of steel wires that moved upwards through the muscle over time. This method was regarded as less suitable because of a strong behavioral reaction in the first two days after tagging and damage to the swimming muscle. Results from 275 silver eels released on European coasts equipped with pop-up satellite transmitters or similarly sized pop-up data storage tags to study the ocean spawning migration indicated a large premature tag release. This was partly related to mechanical tag loss, but probably mainly to a high predation rate (>20% confirmed predations of eels with pop-up satellite transmitters). Mean time to premature tag release was 14 to 21 days (maximum nine months). Laboratory and field data showed that pop-up satellite transmitters attached to eels can remain attached for six to nine months, but that tag retention is a challenge. Hiding behavior in a structured habitat increased the risk of entanglement and tag loss. In ocean migration studies, consideration should be given to transportation and release off shore instead of in shallower areas where they are more likely to seek the seabed and hide in structured habitats. Behavioral reactions indicate that data recorded during the first two to three days after tagging may not reflect natural behavior.

Evaluation of passive integrated transponder tag retention from two tagging locations in juvenile pallid sturgeon

Summary Population augmentation and propagation of pallid sturgeon (Scaphirhynchus albus) have been a focus of scientists since the mid-1990s. Various tag types have been used to gain a better understanding of population characteristics, stocking success, and movement patterns. Passive integrated transponder (PIT) tags have been consistently used since the inception of recovery efforts to mark age-1 and older pallid sturgeon. This tag has been successfully used with other sturgeon species, and tagging protocols for pallid sturgeon were developed in response to those successes. Tag retention rates in pallid sturgeon have been reported as variable or unknown and there has been no formal study to determine PIT tag retention in pallid sturgeon, particularly with age-1 individuals that are propagated in hatcheries to be stocked into the wild. The objective was to evaluate retention rates of PIT tags inserted into the operculum and along the base of the dorsal fin of age-1 pallid sturgeon (total fork length [FL] range = 214–358 mm). Tagged sturgeon (n = 80) were held in a large holding tank and inspected for tag loss twice a month for a total of 189 days. Final tag retention was 83% for tags inserted into the operculum and 85% for tags inserted near the dorsal fin. Tags shed from the operculum were from smaller fish (mean FL = 265 mm) and losses occurred during the first 60 days of the experiment. Tags shed from the dorsal site were predominantly from larger individuals (mean FL = 305 mm) and losses were continual throughout the experiment. Future research should determine size-specific tag retention rates so that hatcheries can maximize retention in either tag placement location.

Survival and Population Dynamics of the Marabou Stork in an Isolated Population, Swaziland

Investigating the ecology of long lived birds is particularly challenging owing to the time scales involved. Here an analysis is presented of a long term study of the survival and population dynamics of the marabou stork (Leptoptilos crumeniferus), a wide ranging scavenging bird from Sub-Saharan Africa. Using resightings data of tagged nestlings and free flying birds we show that the stork population can be divided into three general life stages with unique survival probabilities and fecundities. Fecundity of the storks is inversely related to rainfall during their breeding season. Corroborative evidence for a metapopulation structure is discussed highlighting the impact of the Swaziland birds on the ecology of the species in the broader region. The importance of tag loss or illegibility over time is highlighted. Clearly, any attempt at conserving a species will require a detailed understanding of its population structure, of the sort examined here.

Size‐Dependent Effects of Coded Wire Tags on Mortality and Tag Retention in Redtail Culter Culter mongolicus

AbstractRedtail culter Culter mongolicus, a threatened piscivorous fish species in China's inland waters, has exhibited serious population decline. As part of a stock enhancement research project in shallow lakes of the Yangtze River basin, China, we evaluated the performance of coded wire tags (CWTs) for marking juvenile redtail culter. Through a short‐term indoor experiment, we marked hatchery‐reared juveniles from three size groups (mean ± SE, small: 46.85 ± 0.67 mm, intermediate: 53.76 ± 0.62 mm, large: 63.42 ± 1.05 mm) in the dorsal muscle with CWTs and tested whether marking effects on tag retention and mortality were size‐specific. Tag retention was more than 98% in all the three size groups and appeared to be unaffected by fish size. Tag losses were found only within 3 d of marking. Tagging‐induced mortality of small marked juveniles (58%) was significantly higher than those of intermediate (5%) and large (1%) marked juveniles and was also significantly higher than small unmarked ones (17%). The relationship of marked mortality and total length was quantitatively described by an exponential decay model. Mortality in small marked juveniles occurred mainly within 24 h after marking, which accounted for 71% of the mortality in this marked size. In order to avoid high posttagging mortality and biases in stocking assessment programs, we suggest it is worth the extra fish‐culture costs to use juveniles of at least 57 mm (which displayed 90% survival in our experiment) for stocking assessment programs that utilize CWTs for a handling‐sensitive species like redtail culter.Received December 1, 2011; accepted June 28, 2012

The implications of assuming independent tag loss in southern elephant seals

Survival and reproductive rate estimation requires following uniquely identified individuals through time, and many statistical models assume markings used to identify individuals are permanent. However, survival rates are underestimated when single marks are lost, since the models will effectively score those animals as dead. In order to account for mark loss, some researchers use a double‐mark approach, assuming the probability of losing one mark is independent of losing the other one. Therefore, mark loss can be estimated using animals that have lost one mark. Using a 17‐year dataset of southern elephant seals (Mirounga leonina) marked with permanent brands and two cattle tags in their hind flippers, we were able to compare tag loss and survival rate estimates with and without the assumption of independent tag loss with respect to age, sex, and wean mass. We demonstrate the assumption of independent tag loss is not valid, showing it is more likely for an animal to lose both tags than just one or the other. The assumption of independent tag loss leads to an underestimate of survival rates which in turn leads to underestimates of population growth rate. In addition, tag loss rates are different by sex and age, with older males more likely to lose tags. Tag loss is also a quadratic function of wean mass through age two, with smaller and larger animals more likely to lose both tags. Such differences are possibly due to differences in behavior, flipper growth, and immune response. Using a Bayesian approach, we will be able to use our tag loss estimates as priors in future analyses for a subset of marked animals that only have flipper tags. With this population, the independent tag loss models are more likely to incorrectly estimate a declining population (growth rate &lt; 1.0), potentially leading to unwarranted management action. To account for non‐independent mark loss in survival rate studies, we recommend researchers use at least two forms of marking on at least a subset of animals. However, neither form of marking need be permanent as long as mark loss is independent between the different forms.

Evaluation of Passive Integrated Transponders for Abalone: Tag Placement, Retention, and Effect on Survival

Since 1969, abalone populations have declined globally more than 50%, with many species now recognized as threatened, endangered, or species of concern. As monitoring progresses and restoration efforts evolve to include population supplementation, a reliable and robust method of tagging individual abalone is needed. Current abalone tagging methods are unsatisfactory, particularly for long-term studies as a result of tag loss, shell erosion, and encrustation. Observing tag numbers of cryptically positioned abalone can be difficult. To obviate these issues, we evaluated passive integrated transponders (PITs) as tags for pinto abalone (Haliotis kamtschatkana kamtschatkana). We applied 9-mm PITs with cyanoacrylate glue to the dorsal exterior of the shell and to the ventral anterior of the shell, and by injection into the foot muscle of small adults (trial 1), and applied PITs to the ventral anterior of the shell of juveniles (trial 2). We subsequently tracked growth, survival, and tag retention over 15 mo in trial 1 and 6 mo in trial 2 in captivity. Among small adults (trial 1), differences in relative growth rate and survival were not significant. PIT retention by adhesion to the ventral anterior and dorsal exterior was significantly greater than injection into the foot in trial 1. Between controls and tagged animals in trial 2, differences in survival were not significant. There was no significant difference in ventral anterior tag retention between trial 1 and trial 2. Gluing PITs on the ventral anterior of the shell is a promising method because abalone quickly formed nacre over the tags, incorporating them into the shell, which does not appear to affect tag detection by the PIT reader. Trials are underway to characterize PIT retention in natural habitats, to determine tag longevity, and to use PITs to track adults reintroduced to aggregations.

Survival and Growth of Juvenile Pacific Lampreys Tagged with Passive Integrated Transponders (PIT) in Freshwater and Seawater

AbstractTagging methods are needed for both adult and juvenile life stages of Pacific lampreys Lampetra tridentata to better understand their biology and factors contributing to their decline. We developed a safe and efficient technique for tagging juvenile Pacific lampreys with passive integrated transponder (PIT) tags. We tested the short‐term survival of PIT‐tagged juvenile lampreys in freshwater at four temperatures (9, 12, 15, and 18°C) and their long‐term growth and survival in seawater. For both experiments there was little to no tag loss, and juvenile lampreys in freshwater showed high survival at all temperatures at 7 d (95–100%) and 14 d (88–100%) posttagging. Prolonged holding (40 d) resulted in significantly lower survival (28–79%) at warmer temperatures (12–18°C). For juvenile lampreys tagged in freshwater and then transitioned to seawater, survival was 97% for tagged fish until day 94, and at the end of 6 months, survival was about 58% for both tagged and control fish. About half of the tagged and control fish that survived in seawater grew, but there was no difference in growth between the two groups. In freshwater, but not in seawater, most fish that died had an aquatic fungal infection. In both experiments, survival increased with increasing fish length at tagging. Our results indicate that tags similar in size to a 9‐mm PIT tag are a feasible option for tagging metamorphosed juvenile lampreys migrating downstream and that when fungal infections are mitigated—as in seawater—long‐term (at least 6 months) survival of tagged juvenile lampreys is high.

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.

Tag Retention of T‐Bar Anchor Tags and Passive Integrated Transponder Tags in Shovelnose Sturgeon

AbstractCapture–recapture methods are commonly used to estimate population parameters when the necessary assumptions are met. One of the broadest assumptions of capture–recapture models is that tags are not lost. Therefore, one must understand tag retention to be able to adjust estimates if tag loss occurs. Our objectives were to (1) determine retention rates of T‐bar anchor tags and passive integrated transponder (PIT) tags injected into the dorsal musculature of shovelnose sturgeon Scaphirhynchus platorynchus and (2) determine whether using an alternative PIT‐tagging location (the operculum) and a new tagging procedure (cyanoacrylate [i.e., superglue] to seal the tag insertion point) provided higher retention. The T‐bar tags had a retention rate of 100%; PIT tag retention, however, was more variable. Injection of PIT tags along the dorsal fin resulted in a retention rate of 73%, and tag loss was observed throughout the 98‐d experiment. The application of cyanoacrylate did not appear to deter PIT tag loss; retention rates before and after cyanoacrylate was applied were 73% and 77%, respectively. Further, we observed a similar trend of continual PIT tag loss throughout the experiment. The operculum location resulted in a 92% PIT tag retention rate and showed no trend in cumulative loss through time. The high retention rate of PIT tags placed in the operculum suggests that this location is a reliable alternative to inserting PIT tags along the dorsal fin of adult Scaphirhynchus species. In addition, the excellent retention of T‐bar tags makes them a viable option for use in Scaphirhynchus studies.Received October 8, 2011; accepted March 1, 2012

Evaluating population recovery for sea turtles under nesting beach protection while accounting for nesting behaviours and changes in availability

Summary1. Sea turtles and sea birds generally have high conservation importance world‐wide and are often difficult to survey except when present on nesting grounds. Consequently, many such surveys tag nesting individuals and use tag‐resighting models to estimate population size and assess anthropogenic impacts. However, the conventional Cormac–Jolly–Seber (CJS) tag‐resighting model is problematic for these species for three reasons: individuals often return to nesting areas in alternating years because of high energetic costs for nesting, estimated detectability confounds changes in survey efficiency with availability on the surveyed beach, and tag loss is confounded with mortality.2. We develop a robust design model that uses higher‐order Markovian transitions to approximate skip‐nesting behaviours and incorporates multiple observations for each nesting individual to estimate changes in availability (the probability of returning to the surveyed area rather than alternative nesting areas). We approximate time‐varying effects using a flexible spline method and demonstrate the model using data for leatherback sea turtles Dermochelys coriacea and loggerhead sea turtles Caretta caretta in South Africa.3. The apparent lack of recovery for leatherback sea turtles after implementing beach protection, as observed in nest count data, is likely to be due to declining detectability caused by decreased availability during population recovery (e.g. habitat expansion). By contrast, loggerhead sea turtles have approximately constant detectability and stable abundance since the 1970s.4. We find that increased fishing effort has no explanatory power regarding changes in survival for either species.5. Synthesis and applications. Based on study results, we recommend that future tag‐resighting programmes for sea turtles and birds are accompanied periodically by count surveys beyond the regularly monitored nesting areas to evaluate evidence of range expansion. However, the identification of range expansion in historical data is only possible using model‐based inference and robust design methods such as presented in this study.

Patterns in composition, abundance and scarring of whale sharks Rhincodon typus near Holbox Island, Mexico

Photo-identification and conventional tagging were used to estimate population size and structure of the whale shark Rhincodon typus near Holbox Island, Mexico. From 2005 to 2008, photographs of spot patterns behind the last gill slit and in a lateral view on the left side of each animal were used to identify individuals. Additionally, 578 R. typus were tagged using conventional marker tags. Of these and the 350 R. typus that were identified from 1184 photographs, 65% were male; 27%, female and 8%, indeterminate sex. Photographed R. typus ranged in size from 2·5 to 9·5 m total length. Size was bimodal with a large peak at 6 m and a smaller peak at 7 m. Photo-identification showed that there was considerable loss of marker tags. Few of these remained on the animals for more than a year, so that interannual re-sights using tagging could not be used in population modelling. Forty six interannual re-sightings were found in the photographic library; the interval between these re-sightings was typically 1 year. It was estimated that the R. typus aggregation near Holbox Island ranged from 521 to 809 individuals, based on mark-recapture models. From 13 to 33% of R. typus photographed had scars that were attributable to boat strikes. This study provides a baseline for assessing the status of R. typus near Holbox Island. This information is useful to understand drivers of local population size and distribution and potential concerns about increasing effects of tourism on R. typus in this area and for designing better management programmes for R. typus conservation.

CASE STUDY: Retention and readability of radio frequency identification transponders in beef cows over a 5-year period

ABSTRACT The objective of this study was to evaluate failure (loss or inability to read) of radio frequency identification (RFID) ear tags in beef cows over a 2- to 5-yr period under ranch conditions. One of 5 types of RFID tags (Allflex HDX, Allflex FDX, Y-Tex FDX, Z-Tag FDX, and Destron FDX) was applied in the ear of a total of 4,316 cows on 4 separate locations (ranches). Tags were evaluated at approximately yearly intervals for either 2 (ranch 1), 3 (ranch 2 and 3), or 5 yr. Percentages of tags that were lost or that failed to read were 1.4, 1.6, 3.7, 5.1, and 5.0 for the 5 consecutive annual evaluations, respectively, when averaged across ranches and RFID tag type. Cumulative losses of 3.0, 6.0, and 19.8% were observed when averaged over all tag types after 2 (all 4 ranches), 3 (3 ranches), and 5 yr (1 ranch). A ranch by tag type interaction was evident for failure of the 2 types of tags evaluated on all 4 ranches; a greater proportion of Allflex HDX tags were lost than Allflex FDX tags at ranch 4 (36 vs. 4%) but not at other ranches (4.7 vs. 5.1% cumulative loss–fail rate for HDX and FDX). This interaction may be due to differences in tag placement. Tags were placed in the top of the ear at ranch 4 but were attached between the second and third ribs of the ear at ranch 1, 2, and 3. Results indicate that loss of RFID tags increases with time after application and may exceed 5% after 3 yr.