Estimating survival of the tayatea Astacopsis gouldi (crustacea, decapoda, parastacidae), an iconic, threatened freshwater invertebrate.
(Protection and preservation)
Crayfish (Protection and preservation)
Biological diversity conservation (Methods)
Green, Bridget S.
|Publication:||Name: Journal of Shellfish Research Publisher: National Shellfisheries Association, Inc. Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Zoology and wildlife conservation Copyright: COPYRIGHT 2011 National Shellfisheries Association, Inc. ISSN: 0730-8000|
|Issue:||Date: April, 2011 Source Volume: 30 Source Issue: 1|
|Product:||Product Code: 9106283 Endangered Species NAICS Code: 92412 Administration of Conservation Programs|
|Geographic:||Geographic Scope: Australia Geographic Code: 8AUST Australia|
ABSTRACT Populations of the world's largest freshwater
invertebrate Astacopsis gouldi (tayatea, or giant Tasmanian freshwater
crayfish) have declined because of land use changes and poaching. The
species is endemic to northern Tasmania and is listed as
"vulnerable" under the Commonwealth of Australia Environment
Protection and Biodiversity Conservation Act of 1999 and the Tasmanian
Threatened Species Protection Act of 1995. Mark-recapture models were
tested for their suitability in estimating survival of a population of
A. gouldi in a remote river. Tayatea were marked with passive integrated
transponder (PIT) tags during a 7-mo period. Catchability of tagged and
untagged A. gouldi was size and sex specific. Larger animals and females
were more readily trapped throughout the sampling period, which spanned
the austral autumn/winter. Catchability of male tayatea increased during
May, and was strongly influenced by environmental conditions such as
water temperature and river level. Results suggest that PIT tagging
combined with mark recapture methods are a feasible approach for
estimating survival in tayatea, given sample sizes that can be achieved
with reasonable effort. Precision of estimates could be improved by
concentrating sampling around peak catchability during spring and
autumn, and minor flood conditions during winter. This method provides a
tool to estimate A. gouldi mortality as a result of illegal fishing and
detrimental land use practices, thus providing better information for
management. This strategy is essential to monitor progress toward the
milestone of reducing their "vulnerable" classification under
the Commonwealth and Tasmanian legislation within 14 y (1 generation)
from the implementation of the plan.
KEY WORDS: Astacopsis gouldi, crayfish, mark-recapture, PIT tagging, tayatea, threatened species
Freshwater ecosystems have frequently been cited as being among the most altered and threatened by human activities (Saunders et al. 2002). As a result, lotic environments feature some of the highest proportions of threatened species (Duncan & Lockwood 2001), and understanding their biodiversity distribution patterns is a central issue for scientists and managers concerned with extinction processes (Clavero et al. 2004). Species listed as Threatened are those that are officially recognized as possibly facing extinction (International Union for the Conservation of Nature and Natural Resources (IUCN 2008)). Under the IUCN Red List criteria, species are allocated to categories of "vulnerable," "endangered," and "critically endangered" using quantitative rules based on population size, range areas, and rates of decline in these metrics (Akcakaya et al. 2006, IUCN 2008). In comparison, species that are regarded as "rare" can be defined as taxa that occur at low frequency compared with the size of the entire community (Cao & Williams 1998).
Rare and threatened species are of high management concern because of their low density, limited geographical distribution, and lack of information on their demographics (Akcakaya et al. 2006). However, these factors also imply low detection probability and, hence, difficulty in achieving accurate survival estimates. Mark-recapture strategies that cater to animals present at low densities can increase detection probability and thus the accuracy of survival estimates (Thompson 2004).
Astacopsis gouldi (Clark 1936) is the world's largest freshwater invertebrate, reaching weights of 4 kg or more and living for decades; females reach sexual maturity at 14 y and males at 9 y (Hamr unpubl.) The species is endemic to streams in northern Tasmania, where it was the target of recreational fishery until January 1998 (Threatened Species Section 2006). Declining population numbers resulting from overfishing and land clearance resulted in the species being listed as "vulnerable" under the Tasmanian Threatened Species Protection Act of 1995. This was followed by a listing of "vulnerable" under the Commonwealth of Australia Environment Protection and Biodiversity Conservation Act of 1999, and the species is also recognized in the IUCN Red List. It was known to aboriginal Tasmanians as "tayatea," and this name is preferred to "crayfish" or "lobster," both of which have connotations of edibility and consequently are not helpful in conserving the species.
This study focused on the development of a technique for estimating survival of A. gouldi. Survival can sometimes be the demographic parameter with the greatest potential impact on population change (Crone 2001). Prediction of survival probabilities provides information on the most critical determinant of the growth rate of populations of long-lived, slowly maturing animals such as tayatea (Lindeque & VanJaarsveld 1993, Schmidt et al. 2005). Reliable estimates of survival rate allow managers to compare and implement programs that prevent extinction or overexploitation of animals with high conservation value (Powell & Proulx 2003). In the case of A. gouldi, a robust technique to estimate survival would enable research to be conducted on the effects of possible threats (e.g., siltation from forestry) or the effectiveness of remediation measures (e.g., poaching surveillance programs).
MATERIALS AND METHODS
Tagging of A. gouldi was conducted in the Flowerdale River in northwestern Tasmania (Fig. 1). The river was not subject to artificial water regulation, but river height variations occurred during the sampling period. The study site was located in a remote gorge characterized by pool riffle pool sequences with many in-stream logs; occasional, large in-stream rocky outcrops; and a coarse substratum. Some of the deeper pools had silt bottoms whereas the riffles consisted of gravel and small cobbles. The vegetation was temperate rainforest, including plant species such as Nothofagus cunninghamii, Eucalyptus obliqua, Atherosperma moschatum, Anopterus glandulosus, and Dicksonia antarctica. Access to the site was difficult, and levels of poaching were considered very low, according to compliance officers working in the region (Inland Fisheries Service, Tasmania; pers. comm.).
The survey section of the river was 1.5 km in length and was divided up into 4 pools. The small scale of the site assisted in testing the effectiveness of the mark-recapture design, because it was relatively easy to expose all tayatea in a stretch of river to a baited trap in each survey. The scale of this sampling was also intended to simulate the scale of sampling that would be feasible for future research or monitoring. Each pool was large (mean surface area, 120 [m.sup.2]), which is the preferred habitat of adult A. gouldi specimens (Hamr unpubl.). Water temperature was recorded on arrival at each sampling trip.
Mark-Recapture Data Collection
To estimate survival rates and abundance densities of A. gouldi at the Flowerdale River, 9 irregularly spaced mark-recapture sampling sessions of 1 or 2 days were conducted between March 6, 2007, and September 2, 2007. Tayatea were captured predominantly through the use of ring nets (mesh size, 5 cm) and hookless strings baited with fish, depending on the depth and turbidity of the water. Ring nets were most effective in deep sections of a pool or when the water was turbid. Occasionally, polarizing sunglasses were used to spot individual animals, which were then captured by hand or net. Upon capture, all tayatea of 70-mm carapace length (CL) or greater were tagged with a glass (12 x 1.8 mm) or plastic (11 x 2.4 mm) passive integrated transponder (PIT) tag (Hallprint Pty Ltd, South Australia). Crayfish smaller than 70 mm CL were released unharmed. The tag was inserted ventrally into the second abdominal segment, to the right or left of the midline to avoid damage to the medial ventral nerve cord or intestine (Bubb et al. 2002). Needles were sterilized with 100% ethanol prior to tagging to prevent the transmission of disease (Speare et al. 1998). Animals were double tagged by snipping a triangle in the telson to aid in identification of recaptured specimens if the PIT malfunctioned or was lost. These marks are known to last through at least 1 molt (Hamr unpubl.).
[FIGURE 1 OMITTED]
Capture site (GPS location), sex, CL (millimeters), and weight (grams) were recorded whenever an animal was captured or recaptured. Evidence of regeneration or damage, such as missing appendages, was recorded on recaptured animals to indicate any ill effects of tagging or handling. CL was measured from the rostral apex to the posterior median edge of the carapace with Vernier calipers (Robinson et al. 2000). Increases in CL and, to a lesser extent, decreases in fouling on the exoskeleton (density of Temnocephala flatworms) were used to determine whether molting had occurred since the last capture. Tag number was recorded using a digital scanner (RFID electronic reader; Allflex). The entire tagging and measuring procedure involved handling the animals for approximately 2 min. All tayatea were returned to their point of capture.
Survival and Catchability Analysis
We examined the possibility that size or sex affected capture probability by testing the null hypotheses that capture probability was independent of size and that the sex ratio in catch samples was constant through the year. The program MARK was used for analyses per Cooch and White (2007). The Jolly-Seber model was selected for analyses because it allows for survival estimation of open populations, which is relevant to A. gouldi, because they occasionally move more than a kilometer (Webb & Richardson 2004).
Running an analysis for the more complex encounter histories data, when the data included individual covariates, produced an extensive list of models. Goodness-of-fit (GOF) tests ([??] and bootstrap) were carried out in MARK to test whether the data fit the model adequately (Cooch & White 2007). In cases when the [??] (quasi likelihood parameter) estimate indicated lack of fit, then [??] was adjusted by dividing the observed [??] by the mean bootstrap [??]. This reduced bias toward models with fewer parameters, which can occur with uneven distribution of data (Cooch & White 2007). Adjusting converted Akaike's information criterion (AIC) to a quasi estimate (QAIC). This process was used to compare model parsimony. Models that did not fit the data adequately when assessed using bootstrap and [??] GOF tests were discarded.
Temporal gaps between surveys were expressed as days so that model estimates of survival rate and encounter probability were expressed as daily values. Daily survival estimates were converted into annual estimates by raising to the power of 365.
Sixty-six A. gouldi were tagged between March and September in the Flowerdale River; 37 were recaptured (Fig. 2). Animals ranged in size from 70-201 mm CL (mean size, 152.81 mm CL). The overall sex ratio of captured animals was 1:1.49 (male to female), but this varied depending upon the time of year (Fig. 3). For example, although 13 males and 14 females were captured on March 3, the catch on April 16 and 17 comprised 11 females (Fig. 3). Male tayatea were only caught at the beginning of April, and none were caught during the middle and end of this month (Fig. 3). Tayatea typically remained in their home pool throughout the sampling period, with a single individual (female, 180 mm CL) moving approximately 200 m between 2 pools. Retention of glass and plastic PIT tags in recaptured A. gouldi (70-201 mm CL) was 100%.
Tayatea survival and recapture rate estimates were obtained by calculating the logit value for each size class. This was done using the beta values located in the logit link function parameters (Table 1) output file for each model in MARK.
Survival and recapture rate were both influenced by size; therefore, the most parsimonious model based on the QAICc weight was ([phi] (size) p (size); Table 2).
Logit ([phi]) = [beta]0 + [beta]1 x size (Eq. 1)
Logit ([phi]) = [beta]2 + [beta]3 x size
To get a true survival or recapture estimate, the logit value was converted using the reverse transformation of
e^logit/(1 + e^1ogit) (Eq. 2)
This was calculated by
EXP(logit)/(l + EXP(logit))
Models that included sex as a factor to explain changes in catchability between samples failed GOF testing, which appeared to be an issue of overparameterization of a small data set. Temporal models are not presented because they failed GOF testing. However, we note that the temporal trends in the sex ratio presented earlier suggest that gender differences in temporal catchability (Fig. 3) and recatchability (Fig. 4) are important.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Overall catchability was highest in March (autumn) and lowest in June (winter) (Fig. 2). Total catch generally increased with water temperature (Fig. 2). Increases in river height after rain on sampling occasion 5 (May 8 and 9), and to a lesser degree on sampling occasion 8 (August 7 and 8), resulted in higher catch rates of A. gouldi (Fig. 2). Tayatea catchability and recatchability levels was not always correlated with warmer water temperatures, but they did appear to rise after increases in water temperature in late winter on sampling occasion 8 (August 7 and 8; Fig. 2).
The annual survival estimates for the A. gouldi population from the model in which survival and catchability were affected by size was 95.5% (Table 2), which implies the species is long-lived and that this population was not poached or otherwise heavily affected. Survival rate of A. gouldi apparently decreased with size; however, recapture rate increased with size (Fig. 5).
Recatchability was highest for females in the size range of 170-179 mm CL (27%) and for males in the 130-139-mm CL size range (10.8%; Fig. 4). No tayatea in the size range of 70-110 mm were recaptured (Fig. 4). Recapture rate for males and females combined increased with size, whereas survival rate of large animals decreased with size (i.e., animals with a CL greater than 190 mm were only captured once; Fig. 5). On a number of sampling occasions, tayatea were recaptured within hours of tagging.
This pilot study has shown that A. gouldi can be successfully captured and individually identified after marking with PIT tags. The effort involved required 2 persons for 2 days on each capture occasion, suggesting that this approach could he used to monitor populations of A. gouldi at several sites throughout northern Tasmania 3 or 4 times per year. This field program would allow for accurate survival estimation by allowing for variance in catchability, which occurs as a result of the behavioral characteristics of tayatea and the effect of environmental conditions.
The methodology outlined is a useful tool for threatened species conservation, because of its ability to provide a means of obtaining accurate A. gouldi survival estimates, which is a key gap outlined in the recovery plan for the species (Threatened Species Section 2006). The methodology could be used to measure the relative effect of different threatening processes by comparing survival at different sites or before and after events such as land clearing.
Effect of PIT Tagging, on Tayatea Survival
Although tagging procedures can affect animal behavior (Powell & Proulx 2003), handling and abdominal insertion of PIT tags did not appear to affect the likelihood of recapture of A. gouldi. A number of A. gouldi were recaptured within hours of being tagged and released, suggesting that animals do not become trap shy and can be readily recaptured (Hamr unpubl., Walsh unpubl.). PIT tags have also been used effectively to mark other smaller crayfish species such as Orconectes limosus and Pacifastacus leniusculus (Bubb et al. 2002, Buric et al. 2008).
[FIGURE 4 OMITTED]
Associated tank trials demonstrated that the mortality rate of identically PIT tagged Astacopsis franklinii, a smaller congeneric species, was 92.5%; the tags did not significantly affect growth, and myodegeneration and melanization in surrounding musculature tissue were also low (Shepherd unpubl.). It is likely that the physical impact of these tags on the significantly larger A. gouldi would be less. High tag-related mortality has been reported in the laboratory and wild for the smaller Orconectes compressus (slender crayfish; <30 mm CL; Black et al. 2010)), but past tagging studies have demonstrated the resilience of A. gouldi to capture/tagging procedures (Hamr unpubl., Walsh unpubl.).
Effect of Size on Tayatea Survival Estimation Accuracy
Survival and catchability of A. gouldi was size specific. Estimated survival of large animals (both sexes) was relatively low compared with small ones; however, recapture rate also increased with size. This suggests that although the apparent decline in survival of large tayatea could have been caused by poaching or natural mortality, another likely cause is inactivity of these larger animals. In a radio-tracking study, Webb and Richardson (2004) noted that large animals may spend days at a time inactive in their home refuge. Detected movement was not a factor in the current study, with only 1 animal (female, 180 mm CL) moving between 2 pools.
[FIGURE 5 OMITTED]
Although some large A. gouldi, appeared to be inactive at times (Webb & Richardson 2004), other large specimens had a higher recapture rate, suggesting that this size class is susceptible to poaching. The population size of a long-lived species, such as A. gouldi (Hamr unpubl.), is dependent on the survival of mature animals. The presence of suitable densities of sexually mature individuals ensures successful reproduction and, therefore, continued population growth (Heppell 1998). Thus, mortality of large, sexually mature specimens resulting from illegal fishing or unsustainable land use could have dire consequences for the conservation of A. gouldi. The current scale of A. gouldi mortality from poaching is unknown; however, the cumulative effects of past (legal) and current (illegal) taking of adult tayatea has devastated populations of A. gouldi in many northern Tasmanian rivers (Threatened Species Section 2006).
The high capture rate of some large A. gouldi may be a result of their dominance over smaller individuals. During peak activity, large animals would be captured first at a site, followed by the smaller tayatea, suggesting the existence of a feeding hierarchy. High levels on intraspecific competition between A. gouldi individuals were observed as tayatea fought over bait, and there was evidence of limb loss and scarring in some animals. Intense intraspecific competition between crustaceans in and around traps occurs in other species of crustaceans. Large lobsters, Homarus americanus, chase smaller animals out of traps, and only 11% of all animals that approached the trap fully enter it (Jury et al. 2001). The large southern rock lobster, Jasus edwardsii, also inhibits small animals from entering traps; however, as large animals are removed from a population, the capture rate of small animals increases (Frusher et al. 2003).
Season may play a role in the relationship of size versus catchability in A. gouldi, with strong behavioral interactions in winter possibly resulting in the less frequent capture of small J. edwardsii in comparison with their larger counterparts (Ziegler et al. 2002a, Ziegler et al. 2002b). Part of this study was undertaken during the breeding season (April/May) (Hamr unpubl.), when intraspecific competition would be high, which may have prevented a high recapture rate of small A. gouldi. Another reason for a low rate of catchability in juvenile A. gouldi might be that they inhabit different (shallow) sections of river in the sample sites (deep pools) (Hamr unpubl.), which were dominated by large A. gouldi. The smallest A. gouldi (120 mm and 126 mm CL) radio tracked in the Dip River were found to move the greatest distances, possibly because of displacement by larger, territorial specimens (Webb & Richardson 2004). The gear used was successful in capturing juvenile A. gouldi (60-70 mm CL) in a separate study on the Inglis River (Shepherd unpubl.); therefore, gear size is an unlikely source of size bias in capture rates observed. In future monitoring, portable transceiver systems could be tested to detect PIT-tagged juvenile tayatea (i.e., <60 mm) that may not regularly respond to bait. They can be initially captured by turning over large rocks or logs in riffle zones (Hamr unpubl.).
Effect of Sex on Tayatea Survival Estimation Accuracy
Astacopsis gouldi survival estimates were strongly sex specific in these studies, and the very low capture rates of male A. gouldi during April were a significant contributor to the lower overall recapture of males. Catch rates in J. edwardsii also seem sex dependent, with male catch numbers declining in winter (Ziegler et al. 2002a), probably as a result of gender differences in the molt cycle. It is unlikely that the inactivity of males observed in the current study was a result of ecdysis, because this occurs biennially during summer (Hamr unpubl.). Male inactivity t is more likely a result of reproductive behavior. Mating occurs in April/May (Hamr unpubl.), and although the breeding behavior of male A. gouldi is unknown, it is possible that they defend a female, rather than foraging, therefore reducing catchability--as occurs in several decapod species (Miller 1990) such as H. americanus (Bushmann & Atema 1997). Female A. gouldi breed biennially (Hamr unpubl.) so, on average, half the female population is not breeding and thus may have higher catchability during April.
Low male recapture may also be the result of an uneven sex ratio, because males accounted for 33% of the overall captures in the current study, and skewed sex ratios were observed in the nearby Dip River (1:1.88, male to female (Webb unpubl.)).
Breeding behavior may also have affected sampling of female tayatea during winter. We did not capture any berried females, similarly to other studies on this species (Lyall 2001). During winter, when female A. gouldi are ovigerous, it is possible that they reduce foraging activity to protect their broods (Hamr unpubl.), reducing likelihood of capture. One female tayatea (180 mm CL) was captured during 4 of the first 5 samples, but was not seen again after early May during the last 5 sampling occasions, possibly because it became ovigerous (and therefore inactive). These sex-dependent results demonstrate the value of undertaking sampling at times of the year when catchability is less affected by reproductive events.
Effect of Environmental Conditions on Tayatea Catchability
Although temporal models failed GOF testing, anecdotal evidence suggests that catchability of A. gouldi can be strongly correlated to seasonal conditions. Water temperature is a likely influence on A. gouldi catch rate. In the current study and others, A. gouldi were not active at temperatures less than 8[degrees]C, and catch rates declined in winter (Lyall 2001, Hamr unpubl.). Catchability of tayatea has also been found to decline in temperatures higher than 18[degrees]C (Lyall 2001). Tayatea activity peaked in March and mid April when temperatures were relatively mild (12.5-15[degrees]C). In contrast, no animals were caught when water temperatures were very low (4.8[degrees]C and 4.9[degrees]C, on June 14, 2007, and June, 15, 2007, respectively). The gradual increase of water temperature during spring was associated with an increase in A. gouldi catchability (Walsh unpubl.). However, during summer, radiotelemetry showed that A. gouldi activity increased when water temperatures decreased (Webb & Richardson, 2004). The highest total daily catch (n = 27 on March 3) occurred during cool weather, following a prolonged hot spell, when A. gouldi at the site became very inactive.
These observations suggest that tayatea are active within a range of temperatures, but also that sharp temperature changes may influence activity. Rainfall and water levels are also likely to affect activity, because minor flood conditions in winter improve catchability. A. gouldi catchability was highest from mid morning to early afternoon (1000-1400 HR). The species is not strictly nocturnal or diurnal (Webb & Richardson 2004), unlike many other decapods (e.g., J. edwardsii) that are most frequently captured in low-light conditions.
Limitations and Future Sampling Recommendations
Despite the effectiveness of this methodology as a tool for estimating survival in the cryptic and threatened tayatea, several opportunities to improve the methodology were apparent. Recapture rates were low in this study for small and large tayatea. Regular (e.g., monthly) sampling is less important than maximizing recapture rates, particularly in such a long-lived species. Focusing sampling at specific times throughout the year, under optimal environmental conditions, will maximize the capture of tagged and untagged tayatea of both sexes and most size classes (i.e., >70 mm CL) (Hamr unpubl., Shepherd unpubl., Walsh unpubl.). Such periods include autumn (e.g., March) and spring (e.g., September to November), when water temperatures are not excessive (e.g., such as in peak summer) (Walsh unpubl.) and both sexes are active. Sampling under such conditions will increase the accuracy of survival estimates. Minor flood conditions during winter (June to August) may also be conducive to maximizing the capture of tagged and untagged tayatea.
In situations when their range is sufficient, in situ PIT tag readers could be used in combination with mark recapture studies to increase the recapture rate (Black et al. 2010). This technique would also be suitable for identifying juvenile and adult tayatea that at certain times may not respond to baited traps. Smaller PIT tags (e.g., 8.5 mm long with a diameter of 2.12 mm) could be slightly less intrusive for identifying small juvenile tayatea (30-70 mm CL), and could tested (Black et al. 2010).
This is an example of a field program that can be applied to obtain accurate survival estimates of a freshwater species that is otherwise difficult to detect because of its rare status and cryptic behavioral characteristics. Measuring survival across multiple sites or through time could be conducted to measure the scale of impact from suspected threats such as poaching or forestry. This information could then be applied to management strategies for that waterway/catchment to fulfill the requirements outlined in the recovery plan (Threatened Species Section 2006), such as reducing their "vulnerable" classification under the Commonwealth and Tasmanian legislation within 14 y (1 generation) from the implementation of the plan (implemented in 2006). This will ensure the conservation of this iconic freshwater invertebrate and will be another step in reducing the number of threatened species associated with altered riverine environments globally (Duncan & Lockwood 2001, Clavero et al. 2004).
Thanks to the Tasmanian Aquaculture and Fisheries Institute (TAFI) and University of Tasmania (UTAS) for providing the necessary resources and equipment for catching Astacopsis gouldi. We thank Keith Martin-Smith for assistance with Program MARK. A special mention goes to Todd Walsh for his study site recommendation, expert tayatea fishing know-how, and field assistance.
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TIM SHEPHERD, (1) * CALEB GARDNER, (2) BRIDGET S. GREEN (2) AND ALASTAIR RICHARDSON (3)
(1) 23 Park Drive, Ambleside, Tasmania, 7310; (2) Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, Private Bag 49, Hobart, Tasmania, 7001; (3) School of Zoology, University of Tasmania, Private Bag 5, Hobart, Tasmania, Australia 7001
* Corresponding author. E-mail: firstname.lastname@example.org
TABLE 1. Logit link function parameters for most parsimonions model: [psi[ (size), p (size). Parameter Beta Vlue and Symbol 1 31.752754 = [beta]0 2 -0.1490379 = [beta]1 3 -11.807080 = [beta]2 4 0.0609236 = [beta]3 TABLE 2. Results demonstrating the strength of each model along with annual Astacopsis gouldi survival rates. Delta QAICc Model * QAICc QAICc Weight [phi] (size) p (size) 137.97 0.00 0.6 [phi] (.) p (size) 141.18 3.21 0.13 [phi] (sex X size) p (sex X size) 142.61 4.64 0.06 [phi] (.) p (g) 142.98 5.01 0.05 [phi] (size) p (.) 143.35 5.37 0.04 [phi] (sex + size) p (sex + size) 144.68 6.70 0.02 [phi] (g) p (g) 144.91 6.93 0.02 [phi] (sex) p (sex X size) 145.31 7.33 0.02 [phi] (sex X size) p (sex) 145.59 7.62 0.01 [phi] (.) p (.) 145.90 7.93 0.01 [phi] (g) p (.) 146.06 8.09 0.01 Model Annual Survival Model * Likelihood Rate [phi] (size) p (size) 1.00 0.95 [phi] (.) p (size) 0.20 0.03 [phi] (sex X size) p (sex X size) 0.10 0.58 [phi] (.) p (g) 0.08 0.04 [phi] (size) p (.) 0.07 0.02 [phi] (sex + size) p (sex + size) 0.04 0.81 [phi] (g) p (g) 0.03 0.26 [phi] (sex) p (sex X size) 0.03 0.26 [phi] (sex X size) p (sex) 0.02 0.89 [phi] (.) p (.) 0.02 0.02 [phi] (g) p (.) 0.02 0.00 * Jolly-Seber model selected for analyses because A. gouldi are an open population (Webb & Richardson 2004). c adjusted = 1.49. [phi], survival; p, encounter rate; ., constant over time; g, sex.
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