Survival probability estimates for the endangered loggerhead sea turtle resident in southern Great Barrier Reef waters

Sex- and age-class-specific survival of a loggerhead turtle population resident in southern Great Barrier Reef waters was estimated using a long-term capture-mark-recapture (CMR) study and the Cormack-Jolly-Seber modelling approach. The CMR history profiles for 271 loggerheads tagged over 9 years (1984-1992) were classified into two age classes (adult, immature) based on somatic growth and reproductive traits. The sex and maturity status of each turtle was determined from visual examination of reproductive organs using laparoscopy. A reduced-parameter model accounting for constant survival with sex- and time-specific recapture was adequate for estimating age-class-specific survival probabilities, but inclusion of time-specific transient behaviour was informative for the immature age class. The annual fluctuations in the estimated proportion of transient immatures was not a function of sampling effort, but could be due to anomalous oceanographic conditions affecting dispersal of the immature class. There was no sex-specific difference in survival probabilities for either age class, but females were more likely to be recaptured than males, which might be related to behavioural differences such as sex-biased dispersal. The expected annual survival probability for adults was 0.875 (95% CI: 0.84-0.91). The expected annual survival probability for immatures was 0.859 (95% CI: 0.83-0.89), but when the transients were accounted for, the expected annual survival for the resident immature loggerheads was 0.918 (95% CI: 0.88-0.96). These are the first substantive estimates of annual survival probabilities for any loggerhead sea-turtle stock and provide a basis for developing a better understanding of loggerhead population dynamics.     

Estimating demographic parameters for a critically endangered marine species with frequent reproductive omission: hawksbill turtles nesting at Varanus Island,Western Australia

The hawksbill marine turtle (Eretmochelys imbricata) is listed on the IUCN Red List as critically endangered but little is known about its demography to support robust diagnosis of population trends. Moreover, adult female hawksbills do not nest each year due to environmentally mediated physiological constraints and this skipped breeding behaviour presents a major challenge in data collection and for estimating demographic parameters from such data sets. We estimated demographic parameters such as survival and breeding probabilities for a major Indo-Pacific nesting hawksbill population using a capture-mark-recapture (CMR) study and a multistate open robust design statistical modelling approach, which accounts for breeding omission and the staggered arrival and departure of nesters during each season. Our study used CMR histories for 413 nesting hawksbills tagged on Varanus Island (Western Australia) over a 4-month sampling period each year for 20 austral summer nesting seasons between 1987 and 2007. The estimated annual survival probability for these nesting hawksbills was constant over the 20 years at ca. 0.947 (95% CI: 0.91–0.97), which is encouragingly high for a population associated with industry. The estimated annual conditional nesting (breeding) probability for female hawksbills that had skipped the previous nesting season was time-specific ranging from 0.07 to 0.29 (mean = 0.18, CV = 41.3%), which presumably reflects the interaction between turtle physiology and in-water habitat quality. The mean conditional probability of breeding again having skipped 2 prior consecutive nesting seasons was ca. 0.83 (95% CI: 0.73–0.89), indicating a high frequency of breeding season omission. The annual nesting probability for females that had nested the previous season was 0, reflecting known obligate skipped breeding (reproductive omission) that is characteristic of hawksbill populations in response to high energy demands of vitellogenesis and breeding migration. These are the first estimates of annual survival and state-dependent breeding probabilities for any Indo-Pacific hawksbill stock that provide a basis for developing a better understanding of regional population dynamics for this critically endangered species.     

Variation in adult annual survival probability and remigration intervals of sea turtles

We analyzed a large dataset to quantify adult annual survival probability and remigration intervals for the Tortuguero, Costa Rica green turtle population. Annual survival probability was estimated at 0.85 (95% CI 0.75–0.92) using a recovery model and at 0.85 (95% CI 0.83–0.87) using an open robust design model. The two most common modes of remigration are 2 and 3 years. Annual survival probability is lower and remigration intervals are shorter than for other green turtle populations. Explanations for short remigration intervals include reproductive compensation due to historic population declines, availability of better quality food items, favorable environmental conditions, and short distance to the main foraging grounds. Variation in survival and remigration intervals have profound consequences for management and life history evolution. The short remigration intervals of Tortuguero green turtles partly offset mortality caused by turtle fishing in Nicaragua and mean that low juvenile survival represents a more urgent threat to the population than low adult survival. Low adult survival probability could result in selective pressure for earlier age at maturity.     

Estimating Sonoran pronghorn abundance and survival with fecal DNA and capture–recapture methods

Population abundance estimates are important for management but can be challenging to determine in low‐density, wide‐ranging, and endangered species, such as Sonoran pronghorn (Antilocapra americana sonoriensis). The Sonoran pronghorn population has been increasing; however, population estimates are currently derived from a biennial aerial count that does not provide survival or recruitment estimates. We identified individuals through noninvasively collected fecal DNA and used robust‐design capture–recapture to estimate abundance and survival for Sonoran pronghorn in the United States from 2013 to 2014. In 2014 we generated separate population estimates for pronghorn gathered near 13 different artificial water holes and for pronghorn not near water holes. The population using artificial water holes had 116 (95% CI 102–131) and 121 individuals (95% CI 112–132) in 2013 and 2014, respectively. For all locations, we estimated there were 144 individuals (95% CI 132–157). Adults had higher annual survival probabilities (0.83, 95% CI 0.69–0.92) than fawns (0.41, 95% CI 0.21–0.65). Our use of targeted noninvasive genetic sampling and capture–recapture with Sonoran pronghorn fecal DNA was an effective method for monitoring a large proportion of the population. Our results provided the first survival estimates for this population in over 2 decades and precise estimates of the population using artificial water holes. Our method could be used for targeted sampling of broadly distributed species in other systems, such as in African savanna ecosystems, where many species congregate at watering sites.     

Abundance and survival rates of green turtles in an urban environment: coexistence of humans and an endangered species

Longitudinal capture-mark-recapture data were used to estimate abundance and survival rates for green turtles (Chelonia mydas) in San Diego Bay, California, USA. These turtles were closely associated with warm effluent from a power plant during winter months. The life stage distribution of green turtles in the bay ranged from post-pelagic juveniles to adults (44.0–110.4 cm straight carapace length). During 99 capture sessions between December 2, 1990, and March 25, 2009, 96 individual green turtles were caught. To estimate abundance and survival rates, robust-design mark-recapture models were fitted to capture-recapture histories using software MARK. The estimated annual survival rate was 0.861 (SE = 0.147, 95% CI = 0.356–0.986), whereas annual abundance ranged from 16 (SE = 6.3, 95% CI = 4–29) to 61 (SE = 13.2, 95% CI = 36–88). This study provides the first survival rate and abundance estimates for a green turtle foraging population in the highly industrialized San Diego Bay.     

Survival and remigration probabilities for loggerhead turtles (Caretta caretta) nesting in the eastern Gulf of Mexico

Few long-term mark-recapture tagging datasets exist to estimate population parameters for loggerhead sea turtle (Caretta caretta) recovery units. Using a two-state open robust design model, we analyzed a 20-year (1990–2009) mark-recapture dataset from the Keewaydin Island loggerhead nesting assemblage off the southwest coast of Florida (USA) in the eastern Gulf of Mexico. For this analysis, 2,292 turtle encounters were evaluated, representing 841 individual nesting turtles. Survival was estimated at 0.73 (95 % CI 0.69–0.76). This estimate is comparable with survival estimates elsewhere in the Peninsular Florida subpopulation and is among the lowest estimates for the Northwest Atlantic loggerhead population. We documented no changes in remigration rates or clutch frequency over time. These are the first survival and remigration probabilities estimated for a loggerhead nesting assemblage in the eastern Gulf of Mexico.     

The adaptive significance of male subadult plumage in purple martins: plumage dyeing experiments

Summary I tested two hypotheses for the adaptive significance of subadult plumage in male purple martins (Progne subis) : the female mimicry and subordinance signaling hypotheses. Subadult males were at a competitive disadvantage in obtaining territories, as they arrived later in the spring than adult males. Contrary to the predictions of both hypotheses, adult male territory owners were not less aggressive toward subadult male than adult male intruders. The subadult plumage was not effective in mimicking females, as adult male owners were significantly more aggressive toward subadult male than female intruders. Summer adaptation hypotheses predict that young males in subadult plumage are more successful in acquiring territories and mates than they would be with an adult plumage. I tested this prediction by dyeing the plumage of floater subadult males to mimic the appearance of adult males. In 13/17 paired experiments, dyed subadults obtained territories before control subadults. There was no difference in the time it took dyed and control males to attract a mate after they obtained a territory. These results suggest that the subadult plumage is not an advantage to young males in competing with adult males for breeding resources. In late winter, subadult males were growing mostly femalelike feathers on their underside, suggesting that the subadult plumage is not the result of a molt constraint. The subadult plumage could enhance survival of yearlings in winter roosts if it improves access to good roost sites or reduces the risk of predation.     

Offspring number in pygmy marmosets, Cebuella pygmaea *, in relation to group size and the number of adult males

In many species of birds and mammals with a co-operative breeding and rearing system, offspring survival is positively related to the number of helpers. In the New World callitrichine primates (marmosets and tamarins), adult males are considered as particularly valuable helpers, and female reproductive success may depend strongly on the males' contribution to infant care. We analysed the number of offspring (infants, juveniles) in groups of wild pygmy marmosets, Cebuella pygmaea (Callitrichinae, Cebidae, Primates), in relation to the number of adult males and to the number of adult and subadult group members. In contrast to other callitrichines with a co-operative system of infant care, no relationship was found between the number of adult males and the number of infants and offspring. However, there was a significant positive relationship between the number of juveniles and the number of adult and subadult group members. The lack of a relationship between infant and adult-male number is interpreted as resulting from the reduced importance of adult males as helpers in pygmy marmosets in comparison to other callitrichines, probably due to the reduced costs of infant care. The relationship between the number of juveniles and the number of adult and subadult group members is in accordance with increased offspring survival in larger groups, as observed in other primates. Received: 1 February 1999 / Received in revised form: 5 June 1999 / Accepted: 29 June 1999     

Spatial and temporal variability in somatic growth of green sea turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) resident in the Hawaiian Archipelago

The somatic growth dynamics of green turtles (Chelonia mydas) resident in five separate foraging grounds within the Hawaiian Archipelago were assessed using a robust non-parametric regression modelling approach. The foraging grounds range from coral reef habitats at the north-western end of the archipelago, to coastal habitats around the main islands at the south-eastern end of the archipelago. Pelagic juveniles recruit to these neritic foraging grounds from ca. 35 cm SCL or 5 kg (~6 years of age), but grow at foraging-ground-specific rates, which results in quite different size- and age-specific growth rate functions. Growth rates were estimated for the five populations as change in straight carapace length (cm SCL year^–1) and, for two of the populations, also as change in body mass (kg year^–1). Expected growth rates varied from ca. 0–2.5 cm SCL year^–1, depending on the foraging-ground population, which is indicative of slow growth and decades to sexual maturity, since expected size of first-time nesters is 80 cm SCL. The expected size-specific growth rate functions for four populations sampled in the south-eastern archipelago displayed a non-monotonic function, with an immature growth spurt at ca. 50–53 cm SCL (~18–23 kg) or ca. 13–19 years of age. The growth spurt for the Midway atoll population in the north-western archipelago occurs at a much larger size (ca. 65 cm SCL or 36 kg), because of slower immature growth rates that might be due to a limited food stock and cooler sea surface temperature. Expected age-at-maturity was estimated to be ca. 35–40 years for the four populations sampled at the south-eastern end of the archipelago, but it might well be >50 years for the Midway population. The Hawaiian stock comprises mainly the same mtDNA haplotype, with no differences in mtDNA stock composition between foraging-ground populations, so that the geographic variability in somatic growth rates within the archipelago is more likely due to local environmental factors rather than genetic factors. Significant temporal variability was also evident, with expected growth rates declining over the last 10–20 years, while green turtle abundance within the archipelago has increased significantly since the mid-1970s. This inverse relationship between somatic growth rates and population abundance suggests a density-dependent effect on somatic growth dynamics that has also been reported recently for a Caribbean green turtle stock. The Hawaiian green turtle stock is characterised by slow growth rates displaying significant spatial and temporal variation and an immature growth spurt. This is consistent with similar findings for a Great Barrier Reef green turtle stock that also comprises many foraging-ground populations spanning a wide geographic range.Communicated by P.W. Sammarco, Chauvin     

Habitat fragmentation lowers survival of a tropical forest bird.

Population ecology research has long been focused on linking environmental features with the viability of populations. The majority of this work has largely been carried out in temperate systems and, until recently, has examined the effects of habitat fragmentation on survival. In contrast, we looked at the effect of forest fragmentation on apparent survival of individuals of the White-ruffed Manakin (Corapipo altera) in southern Costa Rica. Survival and recapture rates were estimated using mark-recapture analyses, based on capture histories from 1993 to 2006. We sampled four forest patches ranging in size from 0.9 to 25 ha, and four sites in the larger 227-ha Las Cruces Biological Station Forest Reserve (LCBSFR). We found a significant difference in annual adult apparent survival rates for individuals marked and recaptured in forest fragments vs. individuals marked and recaptured in the larger LCBSFR. Contrary to our expectation, survival and recapture probabilities did not differ between male and female manakins. Also, there was no support for the existence of annual variation in survival within each study site. Our results suggest that forest fragmentation is likely having an effect on population dynamics for the White-ruffed Manakin in this landscape. Therefore, populations that appear to be persisting in fragmented landscapes might still be at risk of local extinction, and conservation action for tropical birds should be aimed at identifying and reducing sources of adult mortality. Future studies in fragmentation effects on reproductive success and survival, across broad geographical scales, will be needed before it is possible to achieve a clear understanding of the effects of habitat fragmentation on populations for both tropical and temperate regions.     

Hidden demographic impacts of fishing and environmental drivers of fecundity in a sea turtle population

Fisheries bycatch is a critical threat to sea turtle populations worldwide, particularly because turtles are vulnerable to multiple gear types. The Canary Current is an intensely fished region, yet there has been no demographic assessment integrating bycatch and population management information of the globally significant Cabo Verde loggerhead turtle (Caretta caretta) population. Using Boa Vista island (Eastern Cabo Verde) subpopulation data from capture–recapture and nest monitoring (2013–2019), we evaluated population viability and estimated regional bycatch rates (2016–2020) in longline, trawl, purse-seine, and artisanal fisheries. We further evaluated current nesting trends in the context of bycatch estimates, existing hatchery conservation measures, and environmental (net primary productivity) variability in turtle foraging grounds. We projected that current bycatch mortality rates would lead to the near extinction of the Boa Vista subpopulation. Bycatch reduction in longline fisheries and all fisheries combined would increase finite population growth rate by 1.76% and 1.95%, respectively. Hatchery conservation increased hatchling production and reduced extinction risk, but alone it could not achieve population growth. Short-term increases in nest counts (2013–2021), putatively driven by temporary increases in net primary productivity, may be masking ongoing long-term population declines. When fecundity was linked to net primary productivity, our hindcast models simultaneously predicted these opposing long-term and short-term trends. Consequently, our results showed conservation management must diversify from land-based management. The masking effect we found has broad-reaching implications for monitoring sea turtle populations worldwide, demonstrating the importance of directly estimating adult survival and that nest counts might inadequately reflect underlying population trends.     

Modeling survival and mark loss in molting animals: recapture, dead recoveries, and exuvia recoveries

Capture-mark-recapture (CMR) analyses aim primarily at estimating relevant life history parameters, despite the fact that some individuals are not always recaptured, even if alive on the study site. Applying such approaches to species with a complex life cycle, such as insects, remains challenging because each change of stage tends to cause mark loss through molting. We developed a multistate model based on three exclusive events ("dead", "surviving and molting", and "surviving and staying in the same larval stage") to estimate probabilities of survival and mark loss. Estimates of biologically relevant parameters were derived from those of the probabilities of transition between these states. The model was applied to data from radio-tracking diodes glued on grasshoppers. The estimates of recapture probabilities decreased throughout the season for animals remaining alive, while the detection of dead animals and lost diodes was exhaustive. The survival probability was higher for larvae than for adults (0.98 vs. 0.96), and mark loss was stronger in larvae than in adults (0.09 vs. 0.06). We show that the survival rate of a species with a high rate of mark loss can be estimated using multistate models, provided that marks can be recovered after being lost. These models are flexible enough to test for several effects that potentially affect survival and mark loss probabilities.     

Delayed plumage maturation in the orchard oriole (Icterus spurius): tests of winter adaptation hypotheses

Summary Explanations of delayed plumage maturation (DPM) in passerines have focused on potential breeding season advantages for non-definitive (subadult) plumage. In contrast, the molt constraint hypothesis (Rohwer and Butcher 1988) proposes that subadult plumage is a winter adaptation, increasing winter survivorship by decreasing intraspecific aggression (the winter status signaling hypothesis) or predation (the winter crypsis hypothesis). Under the molt constraint hypothesis, nondefinitive breeding plumage is non-adaptive, resulting from species-specific constraints on the number of feathers replaced during the pre-alternate (spring) molt. In studies conducted on an overwintering population of orchard orioles in Panama, I tested predictions of both the winter status signaling and molt constraint hypotheses. Contrary to predictions of winter status signaling, I found no evidence that subadult plumage reduces adult male aggression toward subadults. Agonistic encounters occurred at random with respect to plumage and the intensity of adult male/subadult male encounters was not lower than the intensity of encounters occurring within age classes. Contrary to the molt constraint hypothesis, I found no evidence that the number of feathers exchanged by subadults in their pre-alternate molt is the sole constraint on the development of subadult breeding plumage. The majority of feathers grown by molting subadult orioles during January and February were of non-definitive coloration. These results, together with results of earlier breeding season experiments which tested summer communication hypotheses for DPM in this species, suggest that subadult plumage in the orchard oriole may be non-adaptive and the result of constraints on plumage development. They also indicate, however, that the extent of the pre-alternate molt is not the sole source of that constraint.     

Ecology of loggerhead marine turtles Caretta caretta in a neritic foraging habitat: movements, sex ratios and growth rates

Much is still to be learned about the spatial ecology of foraging marine turtles, especially for juveniles and adult males which have received comparatively little attention. Additionally, there is a paucity of ecological information on growth rates, size and age at maturity, and sex ratios at different life stages; data vital for successful population modelling. Here, we present results of a long-term (2002–2011) study on the movements, residency, growth and sex ratio of loggerhead turtles (Caretta caretta) in Amvrakikos Gulf (39°0′N 21°0′E), Greece, using satellite telemetry (N = 8) and ongoing capture–mark–recapture (CMR; N = 300 individuals). Individuals encountered at sea ranged from large juvenile to adult (46.2–91.5 cm straight carapace length) and demonstrated growth rates within published norms (<2.7 cm yr^?1) that slowed with increasing body size. We revealed that an unexpectedly high proportion of animals were male (>44 % of captures above 65 cm straight carapace length), compared to region-wide female-biased hatchling production, indicating sex-biased survival or possible behavioural drivers for likelihood of capture in the region. Satellite tracking confirmed that some turtles establish discrete, protracted periods of residency spanning more than 1 year, whilst others migrated away from the site. These findings are underlined by CMR results with individual capture histories spanning up to 7 years, and only 18 % of individuals being recaptured.     

An EM algorithm for capture-recapture estimation

Analysis of capture—recapture data often involves maximizing a complex likelihood function with many unknown parameters. Statistical inference based on selection of a proper model depends on successful attainment of this maximum. An EM algorithm is developed for obtaining maximum likelihood estimates of capture and survival probabilities conditional on first capture from standard capture—recapture data. The algorithm does not require the use of numerical derivatives which may improve precision and stability relative to other estimation schemes. The asymptotic covariance matrix of the estimated parameters can be obtained using the supplemented EM algorithm. The EM algorithm is compared to a more traditional Newton-Raphson algorithm with both a simulated and a real dataset. The two algorithms result in the same parameter estimates, but Newton-Raphson variance estimates depend on a numerically estimated Hessian matrix that is sensitive to step size choice.     

Reproductive consequences of variation in the composition of howler monkey (Alouatta spp.) groups

At least three general categories of environmental pressure - predation, resource distribution, and demographics - shape the costs and benefits of group-living for animals. Among the demographic factors that influence individual survival and reproduction, the composition of social groups can play an important role. Census data drawn from 26 populations of howler monkeys (Alouatta spp.) were used to determine if the composition of groups explained variation in their reproductive performance. Each group's reproductive performance was estimated by calculating the difference between the observed number of immatures and the number expected from its population average. Of four group structure variables tested, only one - the residual of the adult and subadult sex ratio - was a consistent correlate of reproductive performance across the howler monkey populations. Groups with a greater proportion of adult and subadult males contained more juveniles than expected from the population average. I propose that the survival or retention of immatures within howler monkey groups depends in part on the behavior of resident males. Of particular importance, the relative proportions of resident males and females were more informative than the absolute number of males or females. On this basis, I evaluate the possible role of males in protection from predation, conspecific aggression, and resource competition. The techniques used here can also be used to forecast major changes in demographic structure within populations.     

Distribution of Juvenile,subadult and adult Scylla serrata (Crustacea: Portunidae) on tidal flats in Australia

In Deception Bay, northern Australia, during 1979–1981, a study was made of the distribution of Scylla serrata (Forskal) in an area having a broad intertidal zone. Juveniles (20 to 99 mm carapace width) were resident in the mangrove zone, remaining there during low tide. The majority of subadult crabs (100 to 149 mm) migrated into the intertidal zone to feed at high tide and retreated to subtidal waters at low tide. Adults (150 mm and larger) were caught mainly subtidally and only small numbers were captured in the intertidal at high tide. Few crabs were captured in the coolest months (May to August). Adults were captured on the flats mainly in the warmest months (January to April), but subadults could be captured over the entire summer (September to March). Juveniles were found in the upper intertidal throughout the year.     

Abundances,growth rates,and production of tropical neritic copepods off Kingston,Jamaica

Weekly samples were collected near Kingston, Jamaica in 27 m vertical hauls, using 200 and 64µm mesh plankton nets, from July 1985 to January 1987. Thirtytwo copepod species were identified; nauplii and all copepodite stages were enumerated. Total copepod abundance ranged from 2.56 to 87.3 × 10⁴ m^–2. The annual abundance cycle was bimodal with peaks in October–November and May–June corresponding to the rainy seasons. Mean annual copepodite biomass was 0.15 g AFDW m^–2 ranging from 0.03 to 0.41 g AFDW m^–2. Mean generation time (from egg to adult) at 28°C was 19.5 d for the common speciesCentropages velificatus, Paracalanus aculeatus, andTemora turbinata. Isochronal development was demonstrated for copepodites ofP. aculeatus andT. turbinata, but not forC. velificatus. Mean daily specific growth rates (G) were 0.63, 0.63, and 0.48 d^–1 forC. velificatus, P. aculeatus, andT. turbinata, respectively. In general, daily specific growth rates decreased in the later copepodite stages. Thus, it is postulated that growth of later stages and egg production may be food limited. Annual copepodite production was estimated as 419 kJ m^–2 yr^–1, while annual exuvial production and naupliar production were 35 and 50 kJ m^–2 yr^–1, respectively. Egg production was estimated as 44% (184 kJ m^–2 yr^–1) of the total copepodite production. Thus, mean total annual copepod production was 688 kJ m^–2 yr^–1. This estimate is within the range of copepod production estimates in coastal temperate regions.     

Feeding ecology of the three juvenile phases of the spiny lobster<Emphasis Type="Italic"> Panulirus argus</Emphasis> in a tropical reef lagoon

The three juvenile phases of the spiny lobster Panulirus argus (algal phase: 5-15 mm carapace length, CL; postalgal phase: 15-45 mm CL, and subadults: 45-80 mm CL) occur in the reef lagoon at Puerto Morelos, Mexico. The algal phase abounds in this lagoon, which is covered by extensive seagrass-algal meadows, but the density of postalgal and subadult juveniles is low, owing to the scarcity of crevice-type shelters suitable for these phases. The feeding ecology of the three juvenile phases was investigated to examine whether spatial or temporal differences in food intake, diet composition, or nutritional condition occurred among phases and could partially account for the low abundance of the larger juveniles. Juveniles were collected by divers at night, from January to November 1995, throughout the mid-lagoon and back-reef zones. Percent stomach fullness, relative weight of the digestive gland (RWDG, an index of nutritional condition), percent frequency of occurrence and percent volume of food categories in the diet were compared between sexes, juvenile phases, molt stages (postmolt, intermolt, premolt), seasons, and sampling zones (mid-lagoon and back-reef zones). Significant differences in stomach fullness occurred only among molt stages, mainly because postmolt individuals had emptier stomachs. The main food categories in all juvenile phases were crustaceans (mostly hermit crabs and brachyurans) and gastropods, but the food spectrum was wide, including many other animal taxa as well as plant matter. In June 1995, the epibenthic macrofauna was sampled in five sites in the lagoon that differed in their amount of vegetation. The most abundant taxa in all sites were decapods and gastropods, but density and diversity measures showed that the distribution of these potential prey taxa for juvenile P. argus was rather patchy. Diet overlap in juvenile lobsters was high between sexes, juvenile phases, sampling zones, seasons, and molting stages, indicating that all juveniles fed on the same general food categories throughout time. The only factor that affected the RWDG was the juvenile phase. RWDG was significantly lower in subadults than in algal and postalgal phases, suggesting a poorer nutritional condition in the largest juveniles. This may be related to the scarcity of suitable shelters for large juveniles throughout the lagoon, which may preclude subadults from exploiting food resources in areas of the lagoon where shelter is limited.