Proportion Of Crabs Research Articles

Feeding habits of the marbled rockfish Sebastiscus marmoratus in the marine ranching off Ma'an Archipelago, China

Marine ranching is considered as an efficient tool to protect and restore the coastal fishe-ries resource. In order to assess the ecological impacts of the construction of marine ranching on rocky fishes, the feeding habits of Sebastiscus marmoratus collected at the marine ranching area off Ma'an Archipelago were studied using stomach contents analyses and stable isotope analyses. Results showed that S. marmoratus mainly preyed on amphipoda, crabs and cephalopods before the construction of marine ranching. The dominant prey species were Caprella sp., Loligo japonica, Charybdis japonica, Petrolisthes japonicas and Amphiura vadicola. Proportion of crabs in the diet of S. marmoratus increased with the increase of fish size, whereas the proportion of amphipoda decreased. After the construction of marine ranching, S. marmoratus fed mainly on crabs, amphipoda, and fishes. The dominant prey species were C. bimaculata, C. japonica, Caprella sp. and Thryssa kammalensis. Proportions of fishes and crabs in the diet of S. marmoratus increased with the increase of fish size, whereas the proportion of amphipoda increased and then decreased. Results of the stable isotope analyses suggested that S. marmoratus populations in the marine ranching area off Ma'an Archipelago could be divided into three feeding groups based on size variations: <10.0 cm BL, 10.0-14.0 cm BL, and ≥14.0 cm BL. The mean trophic level of S. marmoratus was estimated as 3.40.

Determination of Size Selectivity of Traps for Blue Crab (Callinectes sapidus Rathbun, 1896) in the Mediterranean Sea

This study investigates the effects of trap selectivity of various mesh size on escape success of the blue crab (Callinectes sapidus). The study was carried out Camlik Lagoon of Yumurtalik Gulf in the Mediterranean Sea and total of 1051 blue crabs were caught by rectangular baited trap. Using traps constructed with 30, 35, 40, 45 and 50 mm square mesh the proportion of crabs escaping through each mesh size was measured for each half centimetre carapace width (CW) class. A logistic model was fitted to the size frequency data of the retained and escaped blue crabs for each mesh size in the experiment. L50 and selection range (SR) for the 30, 35, 40, 45 and 50 mm (bar length) square meshes tested in this study was 8.47 cm and 0.85 cm; 9.31 cm and 0.39 cm; 10.40 cm and 0.31 cm; 11.72 cm and 1.17 cm; 13.17 cm and 0.89 cm respectively. The 50 mm square mesh of the trap showed relatively better selectivity considering the size at 50% sexual maturity of blue crab Callinectes sapidus, and the high rate of immature escapers. Keywords: Blue crab Callinectes sapidus; Trap; Size selectivity; Mediterranean Sea

The Diet of Eurasian Otters in the Jajrood River System, Iran

Abstract The diet and feeding habits of Eurasian otters (Lutra lutra) were studied by spraint analysis over a one year period on the four sections of the Jajrood River, eastern Tehran. Two methods were used to estimate the proportions of different prey consumed: frequency of occurrence and score-bulk estimate. The number of prey categories in a spraint varied between one and four. Fish, crabs, birds and insects were found in the spraints. Fish is the main prey. Otters mainly eat fish, preferring three species: the chub (Leuciscus cephalus), riffle minnow (Alburnoides bipunctatus) and various barbel (Capoeta spp.) species. The otters' diet differed significantly across four sites positive for otter sign. Seasonal variation was also found: birds were taken more in the cold season and insects in the warm season. The proportion of crab in the diet was almost constant throughout the year. Leuciscus cephalus was the most taken fish species in the cold season and Capoeta spp. in the warm season. Only L. Cephalus...

Collision-based computing implemented by soldier crab swarms

Collision-based computing schemes are implemented using propagating and interacting localisations. When two or more travelling localisations collide, they may reflect or merge into a new localisation. Presence/absence of a localisation in a specified site of a physical space represents True/False values of Boolean variables. Incoming trajectories symbolise inputs and outgoing trajectories are outputs. Logical gates are implemented by collisions between the localisations. We demonstrate how primitives of the collision-based computing can be implemented using swarms of soldier crabs in laboratory experiments. Soldier crabs, Mictyris guinotae, exhibit coherent collective behaviour on an intertidal flat at a daytime low-tide period. The soldier crabs' swarm often moves as a single entity with definite yet dynamically changing boundary. We utilise swarms of soldier crabs to implement a Boolean logic gate. The gate has two inputs and three outputs. Values of the inputs and outputs are represented by crab swarm size or a proportion of crabs in the input and output channels. We demonstrate that the gate performs logical conjunction and negation.

Seasonal and temporal variations in population dynamics of theCarcinus maenas(L.): the effect of an extreme drought event in a southern European estuary

The temporal and spatial variability in population dynamics of the European crabCarcinus maenas(L.) was studied between June 2003 and September 2007 in the Mondego estuary. An extreme climate event (extreme drought) occurred in 2004 and 2005 with a low freshwater flow discharge into the estuary, leading to an increase in salinity. Juveniles' recruitment was continuous throughout each year with a high proportion of young recruits being recorded in the spring of 2005. The proportion of green crabs clearly increased from the mouth to the upstream areas and the proportion of crabs actually in moult followed the same pattern. Parasitization by the endoparasitic barnacle,Sacculina carciniwas observed, principally at the mouth of the estuary. TheC. maenaspopulation showed a regular size–frequency distribution and structure for both sexes during the study. Secondary production (P) ofC. maenasestimated for the 4-year study period was different between years though, P/B ratios were similar during the whole study period. During the drought period, catches of the crab recruits were higher, particularly in the spring, probably due to the increase in salinity, which emphasizes the importance of these extreme events in controlling the abundances of coastal populations.

Parasitism of the rhizocephalan Briarosaccus callosus on the crab Paralomis verrilli (Crustacea: Lithodidae) in the waters of southeast Sakhalin

The crab Paralomis verrilli in the waters of southeast Sakhalin is infected by the parasitic rhizocephalan barnacle Briarosaccus callosus. The prevalence of parasitic infection was on the average 4.36% (6.29% for females, 3.28% for males) and varied between samples from none up to 14.9%. The degree of prevalence was not related to the average carapace width and the sex ratio of crabs in samples. Sterilization of female P. verrilli was caused by the B. callosus infestation or its consequences. No more than two parasite externae per crab were found. Crabs with two externae made up 5.6% of all infected specimens. The infestation of crab hosts with two B. callosus externae negatively influenced the growth of the externae. A positive relationship was found between the width of the crab carapace and the length of the parasitic externae. The survival rate of P. verrilli with either one or two parasite B. callosus externae did not differ substantially. The proportion of crabs with externae and those with “scars” (12.2% in our case) can be taken as the index of survival of the parasitized crabs.

Biology, population dynamics and secondary production of the green crab Carcinus maenas (L.) in a temperate estuary

The biological features, population dynamics and secondary production of Carcinus maenas were studied between June 2003 and June 2004 in four areas within the Mondego estuary, Portugal. Benthic samples were collected monthly, during the night, at high water of spring tides using a 2-m beam trawl, and plankton samples were collected monthly, during the day, at high tide with a Bongo net. Only the first zoeae stage of C. maenas larvae was found in the plankton; it was collected at all sampling stations throughout the year. A continuous pattern of benthic recruitment was observed in the upstream areas of the estuary with the highest peaks occurring in the spring 2004. Females carrying eggs were also caught through the year, although mainly in downstream areas. Juveniles' sex-ratio was favourable to males at almost all the sites sampled. Ventral carapace colour varied between green and orange-red, with the proportion of the green morphotype increasing with the increasing distance from the mouth of the estuary. The proportion of crabs in moult also increased from downstream to upstream areas. For both sexes the crab population showed a similar size structure throughout the year. The upstream areas of the estuary were characterized by the dominance of juveniles, with adults migrating to downstream areas. The average annual production of C. maenas, P (growth production), was estimated at 0.08 g m −2 y −1 AFDW, and the average annual biomass ( B ¯ ) was estimated at 0.058 g m −2, resulting in a P / B ¯ ratio of 1.4.

Autotomy and regeneration of limbs in the male blue king crabParalithodes platypus from the Bering Sea and the Sea of Okhotsk

Limb loss and the frequency of regeneration was investigated in the male blue king crabParalithodes platypus collected in the Sea of Okhotsk and the Bering Sea. TheP. platypus population in the Bering Sea is characterized by an anomalously high proportion of crabs with missing limbs, which is largely due to the intensive fishing. The present approach to the exploitation of the Bering Sea population, in which large intact crabs are removed and injured crabs are left to recover to the normal state, may result in a decline in the reproductive potential of this population as early as this coming year.

EPIBIOSIS AND RHIZOCEPHALAN INFESTATION PATTERNS IN RELATION TO THE REPRODUCTIVE BIOLOGY OF LITHODES FEROX (FILHOL, 1885) (ANOMURA: LITHODIDAE)

ABSTRACT Aspects of the reproductive biology of Lithodes ferox, namely, size dimorphism, rhizocephalan infestation, occurrence of ovigerous females, morphometrics of chelae, and incidence of epibionts, were studied in individuals collected from fishery research cruises off southern Namibia between 1983 and 1989. All these aspects appeared closely related to each other. A small proportion of the population was infested by the rhizocephalan cirripede Briarosaccus callosus. We found no strong evidence of seasonality in reproduction. Two discontinuities in male chela allometry were identified: juvenile-immature, and immature-adult. Relative chela growth in females was closer to isometry. Size at maturity was estimated at 108-mm CL for males, based on chela allometry, and 83-mm CL for females, based on the presence of eggs on the pleopod setae. Fecundity increased with female size. Females carried up to 8,000 eggs each. Epibiosis by the thoracican cirripede Poecilasma kaempferi was more prevalent in females than in males, and in ovigerous rather than in nonovigerous females. The pattern shown by the proportion of crabs with epibionts within each host size class varied between the sexes. There is a good fit between maturity and epibiosis patterns with size in females. The high levels of epibiosis in mature females are probably due to a reduction in molt frequency on maturation.

Growth Estimates for Male Stone Crabs along the Southwest Coast of Florida: A Synthesis of Available Data and Methods

Little is known about the growth of male stone crabs Menippe mercenaria in Florida waters. For the most part, information from laboratory and tagging data has not been analyzed thoroughly to obtain a growth curve for the species. In this paper, I synthesized existing and new methods to construct a growth curve from available data. Two components of growth were estimated in detail: the relationship between postmolt and premolt size and the relationship between intermolt period and premolt size. The first relationship was estimated from data from captive crabs by relating the sizes before and after ecdysis with a segmented regression model. The relationship between intermolt period and premolt size was estimated from data from laboratory studies in which crabs were allowed to molt once and the subsequent intermolt periods were recorded exactly. Because long exposure to laboratory conditions may affect growth rates, the molt–frequency relationship also was estimated with methods that require one of two types of information that can be gathered in a shorter period of time: the time to first molt in captivity or the proportion of crabs that molt after an observation time of arbitrary duration. The intermolt period–size relationship also was estimated from mark–recapture data from wild crabs that comprised individual records of initial size, time from release to recapture, and a binary variable that indicated whether or not each animal had molted. I then used simulation analysis to develop a growth curve for a hypothetical stone crab cohort; individual (stochastic) variability in the two components of growth was considered in the analysis. The simulation used growth increments predicted by the estimates from the laboratory data and molt frequencies predicted by the estimates from the tagging data. The results suggested that, on the average, male stone crabs are recruited into the fishery at age 2.25 years and can live to be at least 8 years old.