Crab Density Research Articles

A field-based investigation of behavioural interactions between invasive green crab (Carcinus maenas), rock crab (Cancer irroratus), and American lobster (Homarus americanus) in southern Newfoundland.

Marine species invasions pose a global threat to native biodiversity and commercial fisheries. The European green crab (Carcinus maenas) is one of the most successful marine invaders worldwide and has, in the last decade, invaded the southern and western coastal waters of the island of Newfoundland, Newfoundland and Labrador (NL), Canada. Impacts of green crab on the American lobster (Homarus americanus), which are native to Newfoundland, are not well understood, particularly for interactions around deployed fishing gear. Declines in lobster catch rates in invaded systems (i.e., Placentia Bay, NL), have prompted concerns among lobster fishers that green crab are interfering with lobster catch. Here, we conducted a field experiment in a recently-invaded bay (2013) in which we deployed lobster traps pre-stocked with green crab, native rock crab (Cancer irroratus) (a procedural control), or empty (control). We compared catch per unit effort across each category, and used underwater cameras to directly observe trap performance in situ. In addition, we used SCUBA surveys to determine the correlation between ambient density of lobster and green crab in the ecosystem and the catch processes of lobster in traps. We found: (1) Regardless of the species of crab stocked, crab presence reduced the total number of lobster that attempted to enter the trap, and also reduced entry success rate, (2) lobster consumed green crab, rock crab and other lobster inside traps and (3) there was a positive association between lobster catch and ambient lobster density. Our results suggest that while there was a relationship between in-trap crab density and trap catch rates, it was not linked to the non-native/native status of the crab species.

Association of Epialtus brasiliensis Dana, 1852 (Brachyura, Majoidea) with different species of seaweed

Abstract Seaweed aggregates form secondary substrates on rocky shores, providing habitats for phytal organisms such as the spider crab Epialtus brasiliensis Dana, 1852. This species is one of the most abundant macroinvertebrate component from seaweed communities. Although the literature suggests that E. brasiliensis lives in many species of seaweed, their density has only been reported in communities of Sargassum spp. This study assessed the density of the spider crab E. brasiliensis associated with the seaweed Sargassum cymosum Agardh, 1820, Hypnea musciformis (Wulfen) Lamouroux and Acanthophora spicifera (Vahl) Borgesen. We expected to observe a higher density of E. brasiliensis in S. cymosum, which shows greater morphological complexity, followed by H. musciformis, with intermediate complexity, and then by A. spicifera, with low complexity. We found that the density of these crabs can be as abundant in H. musciformis as has been previously reported for S. cymosum, but in both species, the density was higher than in A. spicifera. Overall, our findings improve the knowledge of the phytal habitats used by E. brasiliensis in rocky shore environments.

Food source and feeding habit of Helice tientsinensis from the common reed vegetation in high marsh of Yellow River Delta, China

Investigating the composition of food sources with stable isotope method can provide direct evidence for the top-down control in the coastal wetland. In this study, we examined food source and feeding habit of Helice tientsinensis of common reed (Phragmites australis) vegetation in high marsh of Yellow River Delta. The results showed that the density of crab was (5.5±1.5) ind·m-2, with the behavior of climbing P. australis to feed on the leaves at night. Under the same indoor experimental condition, H. tientsinensis showed feeding preference on fresh leaves of P. aus-tralis. The stable isotope food source analysis showed that the leaves of P. australis were one of the important food sources of H. tientsinensis in the field. There were temporal variations in the proportion of fresh leaves [May: (6.4±4.9)%, July: (5.8±4.9)%, September: (12.5±8.8)%] and dead leaves [May: (12.4±7.8)%, July: (15.5±9.9)%, September: (15.1±9.4)%]. Therefore, H. tientsinensis could inhibit P. australis's growth and affect litter decomposition through feeding disturbance behavior.

Population Structure of Alien Snow Crabs (Chionoecetes opilio) in the Kara Sea (Trawl and Video Sampling)

The paper presents the results from a study of the population structure of alien snow crabs Chionoecetes opilio in the western Kara Sea near the Kara Strait using two methods: Sigsby trawling and video surveillance. The towed unmanned underwater vehicle Videomodule was used to estimate the population density of crabs: 0.55 ind/m2 in 2016, and 0.17 and 0.09 ind/m2 in 2017. No differences were revealed when comparing the size structure of the crab population based on the two methods. An exception is possible underestimation of younglings with a carapace width <20 mm when using the Videomodule. The minimum observed carapace size was ~10 mm, and the maximum, 127 mm. Both methods revealed the presence of all stages of crab growth, which indicates successful survival and growth of this crab in the western Kara Sea. An adequate assessment of the development of invasion of alien C. opilio in the Kara Sea requires annual video observations in the regions representing characteristic biotopes at different distances from the Kara Strait.

Mangrove planting on dredged material: three decades of nature-based coastal defence along a causeway in the Arabian Gulf

Nature-based coastal defence approaches are increasingly being explored to protect shorelines from erosion and climate change-related threats such as sea level rise, storms and coastal flooding. At Mubarraz, near Abu Dhabi in the Arabian Gulf, mass plantings of &amp;gt;500000 nursery-reared seedlings of the mangrove Avicennia marina were conducted over 30 years in response to erosion of an artificially created, 17-km-long causeway of dredged material. Planting efforts resulted in successfully established mangrove vegetation along 6.7km of shoreline, covering an area of 16.5ha. Survival rates of planted mangrove seedlings to healthy saplings or trees were in the order of 26% averaged over all years, with best results obtained at planting sites established in artificial tidal channels excavated parallel to the causeway, ensuring appropriate tidal hydrological conditions. The mangroves and causeway have attracted a high diversity of birds (48 species), some of which breed on the island, and there are significant densities of crabs and gastropod snails in the mangroves. These results demonstrate that planting mangroves on dredged material is feasible (even under extreme climatic conditions) and may offer a cost-effective alternative for shoreline protection, with added benefits for biodiversity through the creation of new habitats.

Temporal changes in the growth of a crustacean species, Portunus armatus, in a temperate marine embayment: evidence of density dependence

AbstractGrowth is a key attribute influencing population dynamics and fishery production, and understanding factors that affect the growth of individuals in a population is essential in fisheries science and management. This study analyses 18 years of fishery-independent trawl data to determine the relationships among temperature, density, primary productivity and growth of the blue swimmer crab, Portunus armatus, in a temperate marine embayment. Growth was modelled using mixture distribution analyses and cohort-specific seasonal growth curves to estimate the size of crabs at the age of 0.5 and 1.5 years. Growth was highly seasonal, with size-at-age increasing during the austral summer periods and slowing/ceasing during the cooler winter months. The results from the mixture models were used to estimate the mean size of the 0.5- and 1.5-year-old crabs in each year. Linear models showed that the mean size of adult P. armatus at 1.5 years was negatively related to the density of juvenile (0.5 year) crabs in the previous year (i.e. the same cohort) and chlorophyll a concentrations in this year. Increased chlorophyll a levels may increase the survival of larval and megalopal P. armatus, leading to density-dependent effects such as increased competition among juveniles for food and spatial resources, and ultimately, reduced growth.

High temperature and crab density reduce atmospheric nitrogen fixation in Red Sea mangrove sediments

Mangrove ecosystems are highly productive and provide important ecosystem services. However, in the Red Sea mangroves are under severe nutrient-limiting conditions, reflected in dwarf plants. The nutrient limitation is especially acute for iron, as verified experimentally, although the low carbon-to-nutrient stoichiometric ratios reported for Red Sea mangrove leaves are indicative of general nutrient depletion. Therefore, atmospheric nitrogen (N2) fixation in mangrove sediments might be particularly important considering the minimal nitrogen inputs from land. Here, we tested the effect of temperature and crab density on sediment N2 fixation rates in mature and juvenile mangrove (Avicennia marina) stands in the central Red Sea. The average N2 fixation rates (from 0.002 ± 0.002 to 0.46 ± 0.12 mg N m−2 d−1) fall in the low range of N2 fixation rates reported in mangroves elsewhere, which is in agreement with the small size of the mangrove plants. Mature mangrove sediments hold higher N2 fixation rates than the juvenile mangrove sediment, related to a higher sediment organic matter and carbon content. We found a detrimental effect of temperature and crab density on sediment N2 fixation rates. Maximum N2 fixation rates were detected at 28 °C with a sharp decrease at 35 °C. Similarly, high crab-density reduced N2 fixation, likely due to the sediment oxygenation or the grazing of cyanobacteria by crabs. This is supported by i) previously reported higher oxygen concentration and redox around burrows compared to undisturbed sediment and ii) lighter sediment carbon isotopic composition in high crab-density than in low crab-density sediments, indicating a higher contribution of microphytobenthos in the mature sediments supporting low crab-density. Our data document temperature and crab density as factors affecting N2 fixation in the Red Sea mangrove sediments.

Wastewater bioremediation by mangrove ecosystems impacts crab ecophysiology: In-situ caging experiment

Mangroves are tidal wetlands that are often under strong anthropogenic pressures, despite the numerous ecosystem services they provide. Pollution from urban runoffs is one such threats, yet some mangroves are used as a bioremediation tool for wastewater (WW) treatment. This practice can impact mangrove crabs, which are key engineer species of the ecosystem. Using an experimental area with controlled WW releases, this study aimed to determine from an ecological and ecotoxicological perspective, the effects of WW on the red mangrove crab Neosarmatium africanum. Burrow density and salinity levels (used as a proxy of WW dispersion) were recorded, and a 3-week caging experiment was performed. Hemolymph osmolality, gill Na+/K+-ATPase (NKA) activity and gill redox balance were assessed in anterior and posterior gills of N. africanum. Burrow density decreased according to salinity decreases around the discharged area. Crabs from the impacted area had a lower osmoregulatory capacity despite gill NKA activity remaining undisturbed. The decrease of the superoxide dismutase activity indicates changes in redox metabolism. However, both catalase activity and oxidative damage remained unchanged in both areas but were higher in posterior gills. These results indicate that WW release may induce osmoregulatory and redox imbalances, potentially explaining the decrease in crab density. Based on these results we conclude that WW release should be carefully monitored as crabs are key players involved in the bioremediation process.

Combining data from different sampling methods to study the development of an alien crabChionoecetes opilioinvasion in the remote and pristine Arctic Kara Sea

Data obtained using three different types of sampling gear is compared and combined to assess the size composition and density of a non-indigenous snow crab population Chionoecetes opilio in the previously free of alien species Kara Sea benthos. The Sigsbee trawl has small mesh and catches even recently settled crabs. The large bottom trawl is able to catch large crabs, but does not retain younger crabs, due to its large mesh. Video sampling allows the observation of larger crabs, although some smaller crabs can also be spotted. The combined use of such gear could provide full scope data of the existing size groups in a population. The density of the crabs was calculated from the video footage. The highest figures were in Blagopoluchiya Bay at 0.87 crabs/m2, where the settlement seems to be reaching its first peak of population growth after the introduction. High density in the Kara Gates Strait at 0.55 crabs/m2, could be due to the close proximity of the Barents Sea from where the crabs can enter by both larval dispersal and active adult migration. All size groups have been present in most sampled areas, which suggest successful settlement and growth of crabs over a number of years. Again, this was not the case in Blagopoluchiya Bay with high density of small crabs (<30 mm CW), which confirms its recent population growth. Male to female ratio was strikingly different between the bays of the Novaya Zemlya Archipelago and west of the Yamal Peninsula (0.8 and 3.8 respectively). Seventy five ovigerous females were caught in 2016, which confirms the presence of a reproducing population in the Kara Sea. The spatial structure of the snow crab population in the Kara Sea is still in the process of formation. The presented data indicates that this process may lead to a complex system, which is based on local recruitment and transport of larvae from the Barents Sea and across the western Kara shelf; formation of nursery grounds; active migration of adults and their concentration in the areas of the shelf with appropriate feeding conditions.

Experimental evidence for the decline of submerged vegetation in freshwater ecosystems by the invasive Chinese mitten crab (Eriocheir sinensis)

The Chinese mitten crab (Eriocheir sinensis) is a damaging invader which is designated as a species of Union Concern within the European Union. A negative impact of the crabs on macrophyte vegetation in lowland rivers is suspected but not yet proven or quantified. We have performed a mesocosm study that combines a density gradient of Chinese mitten crabs (0, 0.3, 1.0 and 2.5 ind. m−2) with chemical stress (2350 µg EDTA L−1 + 258 µg glyphosate L−1) or light limitation stress (− 70% irradiance compared to control) on water plants (Myriophyllum spicatum). The results clearly demonstrate that the crabs are capable of removing plant shoots effectively which can lead to a complete elimination of the vegetation. Generally, the higher the crab density, the sooner the plants started to disappear and the sooner the vegetation was completely removed. Additional light and chemical stress accelerated this process: plant disappearance at a crab density of 0.3 ind. m−2 compared to 1.0 ind. m−2 in the control treatments. Video recording, plant strength and crab pinch strength measurements and stable isotope signatures of δ13C and δ15N in the Chinese mitten crabs and their possible food sources showed that directly eating the plants is causing only minor damage to the plants. Most damage comes from the movement of the crabs and crab–crab interactions during which they use their chelae to grasp the shoots. We conclude that a decline of vegetation as a consequence of Chinese mitten crab behaviour can be a realistic scenario in freshwater ecosystems and warrants close attention and monitoring. Being primary producers and ecological engineers, macrophytes are key species in these ecosystems, whose services are lost when they disappear and are difficult to restore.

Population Decline of the Invasive Asian Shore Crab (Hemigrapsus sanguineus) and Dynamics of Associated Intertidal Invertebrates on Cape Cod, Massachusetts

A few moderately long-term studies have documented population dynamics of the invasive Hemigrapsus sanguineus (Asian Shore Crab) and species with which it interacts. One such study on Cape Cod reported exponential growth of the Asian Shore Crab through 2012, concurrent with declines in 2 resident species, but recent data at nearby sites suggest considerable geographic variation in population dynamics, with modest recovery of resident crab populations. We monitored the Cape Cod population for an additional 5 years to determine whether population growth of the Asian Shore Crab had slowed and whether there was any change in population dynamics of Carcinus maenas (Green Crab), Littorina littorea (Common Periwinkle), or Mytilus edulis (Blue Mussel). Asian Shore Crab density declined by nearly 90% since 2012. There was no evidence of recovery by the Green Crab, but the Blue Mussel experienced a brief but substantial increase in density in 2015, when both crab species displayed >70% reductions in density from the previous year. The pattern of population dynamics of the Asian Shore Crab from 2003 to 2017 is consistent with boom–bust dynamics, but it remains unclear whether the population will equilibrate near its current density or undergo recurrent boom–bust cycles.

Sex related differences in density, selectivity and vulnerability of the Atlantic blue crab, Callinectes sapidus (Rathbun, 1896), in the southern Gulf of Mexico

The density, selectivity and vulnerability by sex of Atlantic blue crab (Callinectes sapidus) in the Yucatan coast were estimated using a Jolly–Seber mark–recapture model. A total of 614 individuals of C. sapidus were captured, of which 336 were marked and of these 20 were recaptured. Overall male:female ratio was 1:3.78. The selectivity of fishing gear (L50) was estimated at 143.9 and 141.4 mm carapace width for females and males, respectively. Catch per unit effort (CPUE) was estimated at 0.41 (males) and 1.55 (females) individuals trap−1. With the model of Jolly–Seber density was estimated at 39 males ha−1 and 323 females ha−1. The average catchability (q) of the males was 0.0340 and 0.0243 for the females, and the relative vulnerability was higher for males of small sizes and females of large sizes. Our results indicated that sex related demographic variations should be considered in further design and application of fishery management measures since differences in density, selectivity, catchability and vulnerability by sex were found.

Evaluating the potential impact of bird predation on the SW Atlantic fiddler crab Leptuca uruguayensis

The southernmost permanent population of the fiddler crab Leptuca uruguayensis occurs along the Samborombón Bay (36°22′S, 56°45′W, Argentina), an important feeding site for many bird species, including ruddy turnstones (Arenaria interpres), whimbrels (Numenius phaeopus), grey plovers (Pluvialis squatarola), american golden plovers (Pluvialis dominica) and gull-billed terns (Gelochelidon nilotica). Although all these birds are known to prey on many fiddler crab species worldwide, there is no estimation of their joint predation impacts, probably due to the difficulty in conducting experiments on an appropriate spatial scale. In these situations, computer simulation methods are useful tools. By using Monte Carlo methods and field data, we modeled the decrease of a fiddler crab population due to bird predation. The model found that under current bird occurrences and crab densities, birds do not consume more than 0.03% of the studied fiddler crab populations. Birds only consume more than 10% of the population if crab density is below 0.02 crabs m2, or if bird occurrences are at least 3 orders of magnitude higher than currently observed. Both situations are unlikely, as mean crab density is 140 crabs m2, and bird density is never so high. Furthermore, by monitoring three different fiddler crab patches, we found that bird predation cannot account for temporal density changes, suggesting that other population processes are more important than bird predation. In conclusion, even though fiddler crabs may exhibit strong predator-avoidance behavior, direct lethal effects of bird predation are currently small.

The development of habitat suitability models for fiddler crabs residing in subtropical tidal flats

Fiddler crabs are deposit feeders that play critical roles as ecological engineers in tidal flats. Recently, anthropogenic disturbances have led to fiddler crab habitat loss and/or degradation; therefore, we developed a mathematically derived habitat suitability index (HSI) model to aid in habitat assessments of fiddler crabs. Based on what is known about the life histories of fiddler crabs, the variables of an HSI model included submersion time, interstitial salinity, and soil 1) grain size, 2) organic matter content, and 3) heat capacity. We acquired density data from four fiddler crab species—Xeruca formosensis, Tubuca arcuata, Austruca lactea, and Gelasimus borealis— at five sites on the western coast of Taiwan to develop the HSI models. Significant positive correlations existed between the HSI output and fiddler crab density for all target species except for those X. formosensis inhabiting the topsoil layer (0–20 cm). For the deep burrowers X. formosensis, however, a positive linear relationship was documented when only those data from the 40–60 cm layers were considered and if the habitat was a sand-covered mudflat. Mapping for each species was conducted using the HSI models with the highest reliability, and four classification levels were established for the habitat suitability of each species at one of the study sites. Based on this field test of a fiddler crab HSI model, we have developed a platform for the proactive conservation of fiddler crabs inhabiting subtropical tidal flats.

Habitat alteration by invasive European green crab (Carcinus maenas) causes eelgrass loss in British Columbia, Canada

Dominant, habitat-forming plant species, such as seagrasses, are key components of coastal ecosystems worldwide. Multiple stressors, including invasive species that directly alter, remove, or replace the foundation plant species, threaten these ecosystems. On the Atlantic coast of North America, ecosystem engineering by invasive European green crab (Carcinus maenas) has been linked to the loss of some eelgrass (Zostera marina) beds. However, the interaction of the same co-occurring species on the Pacific coast has not been investigated. We conducted an enclosure experiment in Barkley Sound, British Columbia, to determine if the engineering impacts of green crabs on Pacific eelgrass ecosystems mirror those previously identified on the Atlantic coast. Eelgrass shoot density declined rapidly over 4 weeks, with a 73–81% greater loss in enclosures with high crab density compared to the low-density and control treatments. The low ratio of eelgrass blades to rhizomes in the high-density treatment suggests that blade shredding, rather than bioturbation of whole plants, was the main mechanism of eelgrass loss. Eelgrass was detected in green crab stomach contents, consistent with observations from the Atlantic coast. Crab density did not have a detectable effect on the biomass or community composition of benthic fauna associated with eelgrass over the duration of the experiment. The eelgrass loss we observed was consistent with losses observed on the Atlantic coast, which raises management concerns on the Pacific coast, particularly in areas where green crabs co-occur with other coastal stressors and with ecologically and economically important species such as salmon.

Physiochemical factors and heavy metal pollution, affecting the population abundance of Coenobita scaevola.

Hermit crabs (Coenobita scaevola) affect the environmental health. The effects of different physiochemical factors and heavy metals, on the population abundance of hermit crabs, collected from two different coastal stations in the Kish Island of Persian Gulf, Iran, were determined. The non-parametric Kruskal-Wallis test indicated the significant differences between hermit crab density, water pH, organic matter (OM), and slope, in the two stations. The tissue concentrations of Pb were 22.49 ± 5.11 and 19.36 ± 5.66 mg/kg, and of Cd were 2.38 ± 0.38 and 1.8 ± 0.36 mg/kg in the Stations 1 and 2, respectively. The corresponding values in the sediments were equal to 68.75 ± 0.7 and 60.22 ± 16.03 mg/kg for Pb, and 3.25 ± 0.17 and 2.77 ± 0.63 for Cd. PCA results indicated sediment OM, slope, and water pH were the three main parameters significantly affecting C. scaevola density. The significance of C. scaevola for biomonitoring the marine ecosystems, has been presented.

Impact of fiddler crab activity on microphytobenthic communities in a South African mangrove forest

Microphytobenthos (MPB) are important primary producers in mangroves, where they are an important source of food for fiddler crabs. The St Lucia mangroves are currently disconnected from the sea and thus considered a non-tidal mangrove ecosystem. Fiddler crabs occur close by, along with sympatric sesarmid crabs. This study examined the foraging effects of the fiddler crab Austruca occidentalis on MPB biomass and composition. The effects of two dominant sesarmids, Chiromantes eulimene and Neosarmatium africanum, on A. occidentalis were also investigated as sesarmids are known to interfere with fiddler crab surface activities such as foraging and burrow maintenance.In situ experimental plots contained fiddler crabs at three different densities, combinations of fiddler crabs and sesarmids, and controls with no crabs. The biomass of three main microalgal groups were measured (i.e. diatoms, cyanobacteria and green algae) using a fluoroprobe and overall MPB biomass was measured using acetone extraction analysis.Austruca occidentalis affected cyanobacteria and diatoms, allowing green algae to increase in biomass during the experimental period. The presence of sesarmids was shown to affect cyanobacteria biomass more than either of the other two algal groups. Overall, MPB biomass was unaffected by fiddler crab density or sesarmid presence, suggesting that abiotic factors played a more important role in controlling biomass while biotic grazing and interference only affected microalgal group composition.

Synergistic effect of extreme climatic events and urbanization on population density of the ghost crab Ocypode quadrata (Fabricius, 1787)

AbstractThe combined effects of urbanization and extreme climatic events were examined on the ghost crab Ocypode quadrata, a well‐recognized ecological indicator in sandy beaches. The effect of storm waves was assessed before and after these climate events in beaches with different levels of urbanization in the coast of Brazil, Tropical Atlantic Ocean. The number of burrows was used as a metric for the population size of O. quadrata and the number of humans along the beaches as a proxy for the urbanization level. Significant differences were recorded in this species’ population density according to the human pressure. Our core modelling approach showed that the number of O. quadrata burrows was lower after storm waves in urbanized zones, compared to non‐urbanized ones. The interaction between storm waves and urbanization impacted the number of O. quadrata burrows negatively, and suggest that species’ populations are more vulnerable to the combined effects of extreme climatic events and urbanization. Extreme events are predicted to increase in frequency in the next few decades, and may modify or impair ecosystem functioning in sandy beaches by reducing populations of the O. quadrata, an important beach scavenger, which markedly contribute to the flux of energy in coastal trophic webs.

Study of Fiddler Crab (Uca sp.)Community in Mangrove Ecosystem of Mangrove Areas Curahsawo Probolinggo, East Java

Fiddler crab (Uca sp.)one of the crabs that inhabit the intertidal area, especially around the mangrove forest research was conducted in the mangrove areas Curahsawo, district of Gending, Probolinggo, East Java in April 2017. The aim of this study is to determine the structure community violin crabs in the mangrove areas Curahsawo Probolinggo. The measured parameters namely pH, soil organic matter and soil texture. Sampling point there are three stations, namely station 1 is mangrove area, station 2 is in the pond area, the station 3 is the estuary area. Results of measurement of environmental quality at the location of research is soil pH among 7.09 to 8.03, soil organic matter among 1.027% to 3.106%, and the type of soil is sandy clay and dusty clay. fiddler crabs are found in mangrove ecosystem Curahsawo there are 6 types of Uca rosea, Uca lactea, vocans Uca, Uca perplexa, dussumieri Uca, Uca demani. The highest density of crabs is Uca perplexa as much as 16 ind/m2, the lowest type of Uca demani 4 ind/m2. Value diversity fiddler crabs in mangrove ecosystem Sawo relatively standart is 1,56. The value of existing dominance is 0,96. Index violin crab distribution patterns in the Mangrove Ecosystem Munitions Sawo is uniform for Uca lactea, Uca vocans, Uca dussumieri , Uca demani and clumped to Uca rosea and Uca perplexa. The result of the spread of fiddler crab to the type of soil texture is very visible on the Uca perplexa since spread across all points of soil sampling with the number 6 ind/m2 to 16 ind/m2 in the texture of clay and sandy loam.

Use of winter habitat at an early age: spatial ecology and association with human activities of juvenile Olrog’s GullLarus atlanticus

SummaryOlrog’s GullLarus atlanticusis an endemic species of the Atlantic coast of southern South America and is currently listed as ‘Near Threatened’ on the IUCN Red List. The species breeds in coastal wetlands of Buenos Aires and Chubut provinces of Argentina and during winter migrates northwards as far as southern Brazil. During the breeding season the species is considered to have a specialised diet, foraging mostly on crabs. However, during the non-breeding season the gull presents a wider dietary spectrum (including fish) as a result of a potential association with commercial and sport fishing activities. The main goal of this study was to analyse the habitat use and overlap with natural and anthropogenic food resources of juvenile Olrog’s Gull during the winter in Mar Chiquita Lagoon, Buenos Aires. Twenty-two GPS devices were deployed during the winters of 2013 and 2014. A total of 1,088 fixes was gathered by GSM (both seasons combined). Analysis showed that the individuals were (kernel 95%) distributed in a limited area along the mouth of the lagoon. The core area (kernel 50%) covered only 0.3 km2and was located in the south of the mouth. The overlap between juveniles and crab densities was lower than expected, while the overlap between juveniles and fishing effort was higher than expected during weekdays and lower during weekends. These results are of value for the further development of marine conservation measures for wintering areas which have so far been somewhat neglected while addressing the conservation status of the species.