Proportion Of Recaptures Research Articles

Estimating the natural mortality rate of saucer scallops (Ylistrum balloti) on the Queensland east coast from tag-recaptures

Saucer scallops (Ylistrum balloti) were tagged and released on four occasions inside two areas closed to fishing (Hervey Bay A, HBA; and Yeppoon B, YB) on the Queensland (Australia) east coast and their subsequent recaptures over the following months were used to measure the instantaneous rate of natural mortality (M). A total of 13,295 scallops were tagged and 526 recaptured over the 15 month-long experiment (May 2018 to August 2019). Three statistical approaches were applied to the experimental design and analysis of the tagging data, based on 1) the Brownie model, 2) a modified version of the Brownie model, and 3) a binomial logistic regression model of recaptures. Estimates of M based on the Brownie model were much higher for tagged scallops that were at liberty over summer months compared to those at liberty over the winter months, possibly indicating seasonal variation. The logistic model parameter estimates indicated the proportion of recaptures differed significantly with the lunar phase at recapture, scallop size class, the number of days the scallops were at liberty and the interaction between days-at-liberty and closure. All three approaches indicated M was higher in HBA compared to YB. Mean estimates of M for the whole fishery, derived by averaging estimates from both closures, ranged from a minimum of 1.461 year–1 for the logistic model, to 1.501 year–1 for the Brownie model, to 1.548 year–1 (variable recapture rate) and 1.594 year–1 (fixed recapture rate) for the modified Brownie model. Estimates from all three approaches were higher than the previous estimate that was published over 40 years ago and possible reasons for the increase are discussed.

Conventional tagging of sharks in Western Australia: the main commercial species exhibit contrasting movement patterns

Understanding movement patterns underlies effective management and conservation measures. The current study summarises the main findings from a tagging program of Western Australian sharks to provide insights into the movement patterns of the main commercial shark species: dusky (Carcharhinus obscurus), sandbar (C. plumbeus), gummy (Mustelus antarcticus) and whiskery (Furgaleus macki) sharks. Between 1993 and 2020, >12 000 individuals from 52 taxonomic groups were implanted with conventional tags in Western Australia, of which 8.5% were recaptured. Most of the tagged (74.5%) and recaptured (95.8%) individuals belong to the four main commercial shark species. Recaptured individuals of these species, as well as tiger (Galeocerdo cuvier) and bronze whaler (C. brachyurus) sharks showed displacements of >1000 km and rates of movement (ROMs) of >10 km day–1, with the exception of whiskery sharks, which showed much slower ROMs (<3 km day–1). Despite tagged dusky and sandbar sharks being predominately small individuals and gummy and whiskery sharks being large individuals, dusky and sandbar sharks had faster ROMs and a greater proportion of recaptures outside the release zone. Our study provided the information required for estimating movement rates across different fishing zones and therefore defining the spatial scale for managing these shark species.

Light Trap Effectiveness to Capture Razorback Sucker Larvae in a Large Floodplain Wetland

AbstractLight trap captures of larval Razorback Sucker Xyrauchen texanus are used to trigger flow releases from Flaming Gorge Reservoir, which inundate floodplain wetland nursery habitat in the Green River, Utah. However, because little is known about the efficacy of traps to capture or retain larvae under field‐relevant conditions, we conducted an exploratory study using releases of unmarked and marked (oxytetracycline hydrochloride) early life stages of Razorback Sucker (mesolarval life stage, hereafter called “larvae”) in the 53‐ha Leota‐10 wetland of the middle Green River. Batches of 10, 50, 250, or 1,000 larvae were released 3‐ or 10‐m from light traps. Light traps had either chemical light stick or LED light sources, and releases were made on two successive evenings to assess recapture proportions. Light traps recaptured larvae each night and at all release abundances in this large and open habitat. Recapture proportions (number recaptured per number released) for individual traps ranged from 0 to 0.68 (mean = 0.11) over the two release nights. Because recapture proportions were similar over all release abundances, light trap captures may be an index of larvae abundance. In addition, recapture proportions of larvae in traps (light sources combined) were not influenced by release distance. Nonsignificant tests for release distance and release abundance effects had low statistical power resulting from high sample variability and modest sample sizes, so additional experiments are required to confirm those results. The ANCOVA also indicated that traps with an LED light source had consistently higher recapture proportions than traps lit with chemical light sticks, in support of laboratory findings. Although additional experiments with greater replication are needed to better understand attraction distance, release abundance, and retention effects, light traps may be a useful tool to monitor presence and abundance of larvae. This information will aid management and conservation of endangered Razorback Sucker in the Colorado River basin.

Evaluation of a Deepwater Release Method for Hatchery‐Reared Lake Sturgeon

AbstractHatchery rearing and stocking of young Lake Sturgeon Acipenser fulvescens have become key management and species recovery tools in many jurisdictions, yet there has been relatively little investigation into the optimization of release methods. Based on the contemporary understanding of the species’ ecology in Boreal Shield rivers, it was hypothesized that poststocking survival and/or within‐reach retention could be improved via release of hatchery‐reared fish directly into the deepwater habitats that are preferred by juvenile and subadult life stages. Acoustic telemetry and mark–recapture methods were used to evaluate this hypothesis. In total, 390 PIT‐tagged age‐1 Lake Sturgeon (mean ± SD of length measured 1 week prior to stocking = 242 ± 29 mm FL) were released during spring 2015 from shore at the base of a set of falls on the Nelson River, Manitoba (mimicking the status quo stocking procedure for the reach), and 391 PIT‐tagged individuals (240 ± 27 mm FL) were released approximately 4.2 river kilometers downstream of the shore release location into an approximately 750‐m‐long patch of deepwater habitat (maximum depth = 15 m) using the deepwater release method. Of the released fish, 30 (15 per stocking method) were implanted with acoustic transmitters. In total, 23% and 22% of the stocked fish were recaptured in gill‐net surveys conducted during fall 2015 and 2016, respectively. Recapture proportions associated with the two release types were not significantly different. Acoustic telemetry revealed considerable variation among individuals and offered general insight into poststocking behavior but provided no direct support for the primary hypothesis. Despite the null results of the current study, optimization of release methods for Lake Sturgeon may warrant further investigation.

Measuring the Host-Seeking Ability of Aedes aegypti Destined for Field Release.

Host seeking is an essential process in mosquito reproduction. Field releases of modified mosquitoes for population replacement rely on successful host seeking by female mosquitoes, but host-seeking ability is rarely tested in a realistic context. We tested the host-seeking ability of female Aedes aegypti mosquitoes using a semi-field system. Females with different Wolbachia infection types (wMel-, wAlbB-infected, and uninfected) or from different origins (laboratory and field) were released at one end of a semi-field cage and recaptured as they landed on human experimenters 15 m away. Mosquitoes from each population were then identified with molecular tools or through minimal dusting with fluorescent powder. Wolbachia-infected and uninfected populations had similar average durations to landing and overall recapture proportions, as did laboratory and field-sourced Ae. aegypti. These results indicate that the host-seeking ability of mosquitoes is not negatively affected by Wolbachia infection or long-term laboratory maintenance. This method provides an approach to study the host-seeking ability of mosquitoes in a realistic setting, which will be useful when evaluating strains of mosquitoes that are planned for releases into the field to suppress arbovirus transmission.

Prescribed fire alters surface activity and movement behavior of a terrestrial salamander

AbstractPrescribed fire has become a commonly used forest management tool for reducing the occurrence of severe wildfires, decreasing fuel loads and reestablishing the historic ecological influences of fire. Investigating population‐level wildlife responses to prescribed fire is important for evaluating the effects of fire management on animals, but in order to predict and simulate wildlife responses to potential management actions, mechanistic studies that elucidate individual‐level responses are also necessary. We used radio‐frequency identification to investigate individual‐level responses of western slimy salamanders Plethodon albagula to prescribed fire. We compared the salamander home‐range sizes [minimum convex polygons (MCP)], movement behaviors, and activity levels before and after prescribed fire using a randomized block experiment. We initiated the study at three plots in 2011, and added two new plots in 2012. We captured, tagged and released ≥38 salamanders at each plot from May 2011–May 2012 (total N = 205). We recorded 918 total recaptures of 142 unique salamanders; 31% of tagged salamanders were never recaptured. Across all years and treatments, only 14% of relocations were surface‐active (i.e. visually confirmed) salamanders; the others were underground. Following prescribed fire, the surface‐active proportion of recaptures was nearly seven times greater in control versus burned areas, which indicates that P. albagula respond to post‐prescribed fire conditions by spending more time belowground. We did not find evidence of direct mortality of salamanders from fires; the proportion of known‐alive individuals did not differ between treatments. Maximum daily displacement was 43.3% higher among burn‐area than control‐area salamanders, and MCP varied in a similar pattern; this may indicate salamanders were attempting to find more hospitable microenvironments or other resources, such as prey. Together, these individual‐level observations corroborate our findings from a population‐level study of a congeneric terrestrial salamander and contribute to our understanding of the behavioral mechanisms underlying population dynamics.

Competitive effects between rainbow trout and Atlantic salmon in natural and artificial streams

AbstractCompetition with non‐native species may impede the restoration of native species, but differences in competitive abilities among intraspecific native populations may make some populations more suitable for reintroduction than others. Here, juvenile Atlantic salmon (Salmo salar) from two allopatric populations (LaHave and Sebago) being used for reintroduction into Lake Ontario were placed into two natural stream sites differing in the presence of ecologically similar rainbow trout (Oncorhynchus mykiss). We assessed the effects of competition in the natural streams on fitness‐related traits and habitat use of the Atlantic salmon. We then compared these effects to those observed in artificial streams from a previous study. Atlantic salmon in natural streams had reduced fitness‐related traits that were associated with suboptimal microhabitats in the presence of rainbow trout, but utilised optimal microhabitats in their absence. In the presence of rainbow trout, the two Atlantic salmon populations exhibited comparable recapture proportions to each other, but the individuals from the Sebago population had better performance (body size and condition) than those from the LaHave population. Responses of both Atlantic salmon populations to competition with rainbow trout were generally similar in both direction and magnitude when compared to results from the artificial stream study. The combined results suggest that native species restoration efforts should be focused on candidate populations that are ecologically suitable to reintroduction environments, as well as on suitable habitats that do not contain exotic competitors. Moreover, this study highlights the value of controlled experiments in artificial environments for predicting fitness‐related performance in natural environments.

Autumn Migration Of The Thrush Nightingale (Luscinia Luscinia) In Northern Hungary

Abstract Kováts D. 2012. Autumn migration of the Thrush Nightingale (Luscinia luscinia) in northern Hungary. Ring 34: 23-36. The autumn migration of the Thrush Nightingale was studied in Szalonna in northern Hungary in 1989-2010. Birds were mist-netted, ringed, aged, measured, weighed and fat scored. In total, 193 Thrush Nightingales were ringed during 22 years. Relations between arrival time and biometrical measurements were determined. Within the study period (6 August - 26 September) the migration curve was bimodal showing maximum on 22 August and 27 August. Immature birds arrived significantly earlier with lower body mass and shorter wing length and had more pointed wings in the first half of their passage. The distribution of fat score classes did not differ significantly between the early and late periods of the most intensive migration, although the mean of the deposited fat was the lowest during the peak of migration. Fat reserve distribution was bimodal in autumn suggesting that Thrush Nightingales probably start their journey from different breeding ranges (populations) or follow still undiscovered migration strategies of sex/age groups. The low proportion of recaptures proved that the area was not used as a stopover site or premigratory fattening area. Within 22 years of study, the median date of autumn migration of Thrush Nightingales shifted 7.9 days earlier, probably due to current climate change.

Movement patterns of solitary bees in a threatened fragmented habitat

Fragmentation and loss of natural habitats are major threats to many bee species. Large, long-distance flying bees are predicted to be more efficient in utilizing resources and at the same time may function as important pollinators in a fragmented landscape. Using mark-recapture experiments, this study evaluates the movement of bees belonging to the “large, long-tongue” guild in a threatened, fragmented habitat. Bee movement between the sampling plots was limited, despite high recapture proportions within the plots. A maximum likelihood model has estimated a high degree (60 % of all marked bees) of site fidelity to the source plots and a mean traveling distance of 357 m for the bees that left the plots. Additional observations on the bees’ foraging behavior suggest that some anthophorine bee species can be important pollinators in the studied habitat. We suggest that the bees’ site fidelity and flower constancy are the main causes for their observed conservative movement pattern.

Efficacy of Dry Ice-Baited Traps for Sampling Amblyomma americanum (Acari: Ixodidae) Varies With Life Stage But Not Habitat

The carbon dioxide-baited trap is the most common and effective method for sampling vector life-stage Amblyomma americanum (L.) (Acari: Ixodidae), although confounding environmental variables are rarely considered. A mark-recapture experiment was designed to compare recapture proportions of A. americanum nymphs and adults between two habitat types: old field and oak-hickory forest. Powdered fluorescent dye was used to mark A. americanum ticks released in 1-m increments from carbon dioxide-baited traps. Adults were recaptured in significantly higher proportion than nymphs, but habitat type had no significant effect on recapture proportions. Tick abundance is an important parameter in the estimation of human risk of exposure to tick-borne disease and the influence of life stage on capture rates should be considered when calculating entomological risk.

Genotypic variation does not explain differences in growth of mummichogs Fundulus heteroclitus from simple and complex tidal marsh landscapes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 386:207-219 (2009) - DOI: https://doi.org/10.3354/meps08068 Genotypic variation does not explain differences in growth of mummichogs Fundulus heteroclitus from simple and complex tidal marsh landscapes R. T. Kneib* The University of Georgia Marine Institute, Sapelo Island, Georgia 31327, USA *Email: rtkneib@uga.edu ABSTRACT: Decimal coded wire tags were used to measure individual growth rates of mummichogs (Pisces: Fundulidae) within tidal marshes on Sapelo Island, Georgia, USA. Mummichogs (n = 17508) were marked and released at 3 sites with different levels of complexity in their tidal channel drainage networks. The proportion of recaptures (average 19%), which varied from 6.4 to 43.3% among sites and release dates, was inversely related to relative complexity of the tidal drainage networks. Gender-specific differences were detected in size metrics and growth rates. Mean (± SD) growth rates (mm d–1 total length, TL) of individuals at large for 28 to 56 d prior to recapture ranged from 0.062 ± 0.044 to 0.274 ± 0.060 for males and 0.071 ± 0.036 to 0.279 ± 0.062 for females, with the least and most rapid growth rates associated with complex and simple tidal drainage networks, respectively. A ‘common garden’ experiment was conducted to test the hypothesis that there were genotypic differences in growth potential seemingly associated with landscape structure. Two size classes (40–50 and 55–65 mm TL) of individually marked mummichogs from drainage networks characterized as simple (high growth) and complex (low growth) were raised in the laboratory for 42 d on each of 2 daily rations (10 and 30% wet body mass) of minced fresh-frozen grass shrimp. There was no significant difference in mean (± SD) daily growth rates of mummichogs from the 2 sites (simple: 0.283 ± 0.124 and complex: 0.299 ± 0.131) when reared under the same conditions. Although there was no evidence of a genotypic difference in growth potential between these local populations of mummichogs, a possible association between landscape structure and gene expression reflected in the spatial variation of fish growth within tidal marsh ecosystems remains to be explored. KEY WORDS: Coded wire tags · Estuary · Genome · Fundulus heteroclitus · Killifish · Mummichog · Wetlands Full text in pdf format PreviousNextCite this article as: Kneib RT (2009) Genotypic variation does not explain differences in growth of mummichogs Fundulus heteroclitus from simple and complex tidal marsh landscapes. Mar Ecol Prog Ser 386:207-219. https://doi.org/10.3354/meps08068 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 386. Online publication date: July 02, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Capture efficiency of insect natural enemies from tall and short vegetation using vacuum sampling

SUMMARYExperiments were conducted in lucerne to determine the efficiency of vacuum sampling of insects and whether this was affected by the height of vegetation sampled. Three insects of significance as predators of pests in Australian lucerne were studied: transverse ladybird beetle (Coccinella transversalisFabricius), pollen beetle (Dicranolaius bellulus(Guérin‐Méneville)), and spined predatory shield bug (Oechalia schellembergii(Guérin‐Méneville)). In a preliminary experiment comparing a commercially harvested area of lucerne with an unharvested area within the same crop, the proportions of released insects recaptured from unharvested lucerne were significantly lower than recoveries from the shorter, harvested lucerne. Resampling the tall lucerne after it was cut by hand gave cumulative recapture proportions which did not differ from those observed for the harvested lucerne. A second experiment with a randomised replicated design re‐tested the hypotheses of the preliminary experiment for two insect species. Very similar results were obtained. This verification showed that recapture efficiencies from tall lucerne ranged between 0.60 and 0.74 but that resampling after hand cutting gave cumulative recapture proportions in excess of 0.86 which did not differ from recapture proportions from short lucerne.

Mobility, population size and life time pattern of <i>Carabus glabratus</i> (Coleoptera, Carabidae) under extreme northern forest conditions.

The study was carried out in the Vaniotunturi fell area (67°44'N, 29°37 'E) under northern taiga forest conditions. The habitat, a Pinus heath is extremely poor and monotonous. Altogether 196 pitfall traps 10 metres apart (Ø 8.5 cm, height 10.3 cm, with a lid 5 cm above the trap) arranged in a quadrat were used in 1991, and the same field with an additional40 traps placed one trap at each end of a two-metre wall was used from 1992 to 1994. The individuals of Carabus glabratus were marked with a small label cut off from a traffic sign sticker in 1991 and 1992. Only these captured and marked ones were recorded in the following years. In 1994 the trapping was done by killing the beetles. 524 individuals were marked. Males dominated in both years. The recapture proportion was significantly higher for the beetles marked in 1992 than for those of the previous year. The marked beetles were recaptured within four days on average. The estimated maximal population size in 1991 was 1400 individuals, occurring at the beginning of July, while in 1992 it was 3000 exx., in the middle of June. About 15% of the beetles marked in 1991 were caught at least once during the year of marking. Two years after marking, the proportion of recaptures decreased to 2%, but one male marked in 1991 was still captured in 1994.

Population Ecology of Green Snakes (Opheodrys aestivus) Revisited

A population of rough green snakes (Opheodrys aestivus) was studied by markrecapture at Ransom Lake (RL) in north-central Arkansas over 7 yr (1986-1992). Results are compared to those obtained previously from a population in similar habitat located 12 km distant (Bald Knob Lake, BKL). Over 2700 captures made along the RL shoreline were nonrandomly distributed within areas of dense vegetation. Green snakes lived within home ranges averaging 67 m in shoreline length and differing in location between years by about 50 m. Individuals were recaptured on average every 19 days, in which time they had moved linearly along the shoreline about 28 m. About 3% of all movements were over water. Each of these spatial parameters at RL was very similar to those obtained at BKL. Growth rates of individual snakes decreased linearly with snout-vent length (SVL) and were similar to those characterizing snakes at BKL. However, greater variance in growth rates at RL resulted in a weaker relationship between body size and age. Females grew to be larger than males. Body size of females was slightly larger at RL than at BKL. Younger age groups were proportionally larger at RL than at BKL. Sex ratio was 1:1 both in adults and in all snakes combined. In 1987 and 1988 when about 60% of the population consisted of adult snakes, sex and age structure of the population were similar between years. Maximum population density was about 800 snakes/ha. Catchability of individual snakes in monthly samples was equal in 1987 but equivocal in 1988. Survivorship was measured directly by agespecific recapture proportions. Adult survivorship (males 28%, females 41%) was less at RL than at BKL. Calculated overall first-year survivorship (21.5%) was similar to that at BKL and was slightly greater than hatchling survivorship measured directly by recapture (15-19%). Survivorship for ages -0 in both sexes showed a linear logarithmic decline with age (type II survivorship curve). As at BKL, overall clutch size at RL averaged 6 eggs. Unlike at BKL, clutch size at RL differed among years concordant with body condition (weight-length ratio) of snakes. As at BKL, the net reproductive rate at RL (RO = 0.60) was insufficient for sustaining the population over the long term. Estimated population size varied fivefold over 7 yr and decreased from approximately 350-500 snakes in the first 3 yr (1986-1988) to 100-200 in the last 4 yr (1989-1992). The rapid population decline apparently was due to unusually high mortality among adults, and the increased mortality, in turn, was correlated with unusually hot and dry weather leading to a decrease in the body condition of snakes. Predation by snakes and birds may have contributed to the decline. Although snake populations are often regarded as being relatively stable, this study demonstrates that populations of a small insectivorous species are not immune to environmental vagaries and may respond by decreasing density as do other vertebrates.

Site tenacity and survival rates of Wrens Troglodytes troglodytes and Treecreepers Certhia familiaris in a Nottinghamshire wood

Mark‐recapture data from 20 years of standardized mist‐netting were used to investigate site tenacity and adult survival rates of Wrens Troglodytes troglodytes and Treecreepers Certhia familiaris in an English woodland. Within breeding seasons, a high proportion of Wren (but not Treecreeper) recaptures occurred in the same part of the wood as the original capture. Between breeding seasons, a high proportion of recaptures of adult males (but not of adult females) occurred in the same part of the wood as the original capture. Both species experienced exceptionally high mortality during the severe winters of 1978–1979 and 1985–1986, and, in the case of Wren, all or almost all birds which had previously bred in the wood probably died. Outside of these two cold winters, apparent (minimum) adult survival rates of Wrens and Treecreepers showed very different temporal patterns of variation. Wren survival rates were negatively correlated with the number of snow days in winter, whilst Treecreeper survival was negatively correlated with the amount of winter rainfall. After allowing for the influence of winter weather, apparent survival rates of adult Wrens were density dependent, indicating that either mortality or permanent emigration out of the wood was density dependent. There was some evidence from British and Irish ringing recoveries that movements of adult Wrens may be density dependent. The apparent survival rate of adult Wrens was probably an important factor determining the size of the local breeding population.

The influence of age and season on dispersal and recapture of Anopheles culicifacies in Sri Lanka

Abstract. 1. Three mark—release—recapture experiments with Anopheles culicifacies were carried out at different seasons in Sri Lanka. Blood fed females were collected daily in cattle baited huts, marked with fluorescent powder and released in the same village. In two of the experiments males and females were reared, marked when newly emerged, and released. The recapture rates were recorded in the same village and in a second village 2 km away.2. The mosquitoes marked when already mature yielded an estimate that 2–7% of the mosquitoes in the second village had flown from the first. The recapture rate of reared mosquitoes in the first village was much lower than with those marked when already mature. This difference could be at least partly attributed to a tendency to disperse when young, as shown by the considerable number of recaptures of young mosquitoes in the second village.3. By varying the colour used for marking, estimates were made of the amount of dispersal from hut to hut in the first village, the daily survival rate and the proportion of the wild population resting in the collecting huts each day.4. Using the latter two estimates equations have been solved predicting the rate of build‐up of the proportion of recaptures. These predictions were compared with the observed results. The data on dispersal are discussed in relation to possible method for delaying the build‐up of insecticide resistance.

The Analysis of an Animal Population

IN a previous paper (Jackson, 1936) an account was given of the estimation of a tsetse-fly population through the year by means of the Lincoln Index . Since then certain amendments have become necessary as the mathematical treatment has improved, and the method has been extended to provide estimates of rates of birth, death and dispersal which were previously unobtainable. It is the purpose of this paper to explain and describe these improvements and extensions, as the use of the method seems potentially of wide application in problems of animal ecology. The principle is simple. A random sample of individuals is marked: at some later time a random sample is caught and examined: either the initial marking or the later catching is done evenly over the area selected for study. The second catch includes a certain proportion of individuals recognized by their marks as having been caught in the first sample. Then, subject to conditions considered below, the proportion of recaptures to total taken in the second catch ought to be the same as the proportion initially marked to the total population. That is, the population is equal to

The physiology and activity of the bed-bug (Cimex lectulariusL.) in a natural infestation

A natural infestation of bed-bugs which has existed for several years in an animal room has been studied. The bugs feed on the rats kept in cages in the room.Methods are described by which the bugs were trapped during their periods of normal activity.Adult bugs appear to feed on an average once every 5 or 6 days when the temperature is in the region of 20–27° C. (68–80·6° F.). Most of the female bugs lay a continuous series of eggs at the rate of nearly three per day.Female bugs are not usually fertilized more than once a week in this wild population. In laboratory cultures copulation is much more frequent.In the animal house the bugs were most active between 3 a.m. and 6 a.m. This activity seems to be controlled by some inherent rhythm.Some marked bugs were released and the proportion of recaptures to others in the total catch was noted. From this a rough estimate of the population was made. It appears that few adults live more than 29 days as they are probably killed by the rats when trying to feed.