Crab Size Research Articles

Fishing characteristics and spatial distribution of blue swimming crab size (Portunus pelagicus) in the waters of Pati District, Central Java Province

The increasing Blue swimming crab/BSC fishing activity is a response to the high demand of the international market. One of the potential coastal waters for BSC capture fisheries is Pati Regency. However, biological information related to BSC resources is still limited in this area. Therefore, the purpose of this study is to analyze the characteristics of BSC fishing and the size structure of the caught BSC. The study was conducted from December 2020 to March 2021. The method of data collection is observation and interview with fishermen, while the analysis is carried out descriptively. The location of BSC fishing is divided into 3 zones. The characteristics of BSC fishing locations include those related to the distance from the coastline, technical aspects and types of fishing gear, as well as the operational system of capture. The distance from the coastline in zone 1 is about 1-2 miles, zone 2 is about 2-3 miles, and zone 3 is more than 3 miles. The types of fishing gear used in zone 1 are bottom gill net, zone 2 and zone 3 are trapnet. The operational system of capture in zone 1 and zone 2 is carried out with daily trips, while in zone 3 it is carried out with weekly trips (babang). The distribution of carapace width sizes in zone 1 ranges from 44.00-139.00 mm (average 104.80±11.00 mm), in zone 2 it ranges from 72.10-138.00 mm (average 107.90±12.30 mm), and in zone 3 it ranges from 101.40-177.60 mm (average 126.50±11.50 mm).

From Descriptive to Accurate Horseshoe Crab Size Variations in Wild Populations

From Descriptive to Accurate Horseshoe Crab Size Variations in Wild Populations

PROPORTION OF LEGALLY SIZE BLUE SWIMMING CRABS CAUGHT BY FISHERMEN IN BETAHWALANG VILLAGE

Blue swimming crab is a fishery product with high economic value in Indonesia. Betahwalang Village, Demak, is one of the crab fisheries locations in the province of Central Java. High selling prices and processing industry demand encourages fishing activities. One issue brought on by increased fishing activity is the smaller crab size. It will impact the crab fishing industry in Betahwalang. The majority of the fisherman in Betahwalang Village catch crabs using arad nets, simple gill nets, and traps. This study aims to evaluate the size of crab catch results on fishing gear used by fishermen and recommend proper fishing gear for catching crabs. This research was conducted in April 2019. The catch size of crab was the primary data collected for this study, also with data on fishing grounds, methods, and characteristics of fishing gear. Data were collected by observation, interviews, and measurements of fishing gear and the carapace width of the crab. The results of data collection and processing were analyzed descriptively. The results showed that the highest proportion of legal size crabs (carapace width ≥10 cm) was caught in traps, while the proportion of unlegal size crabs caught was mostly in bottom gillnets and mini trawl.

Why Mesolithic Populations Started Eating Crabs on the European Atlantic Façade Only Over the Past 15 Years?

AbstractMesolithic populations from coastal areas are known as hunter-gatherer-fishers. This way of life is visible in the landscape owing to the presence of large accumulations of shells named shell middens. These anthropogenic refuse heaps are composed of high proportions of marine resources, yet studies dedicated to marine components are relatively recent. Efforts have been made to record marine molluscs, but other minorities are still invisible as a result of the small sizes of archaeological remains. Crustaceans are one of these minorities and this article will focus on one of them: crabs. Why are these decapods persistently ignored by most of archaeologists? Is this due to the scant presence of their remains in Mesolithic shell middens? An overview of published data on crabs is presented here for the Mesolithic period on the European Atlantic façade. The proportions of shell middens comprising these crustaceans is evaluated, as well as quantities and identified species. We endeavour to identify the potential impact of excavation methods and sampling on our knowledge of this marine resource. We present the methods developed to extract data from small archaeological crab remains and show how, from a fragment of a crab finger extremity, we can identify the species and estimate the original size of crabs. This methodological challenge has a major impact on our knowledge of past maritime populations.

Species composition, abundance, size distribution, sex ratios, and movement of Scylla mud crabs within the mangrove ecosystem at Setiu Wetland, Terengganu, Malaysia

The aim of the present study was to determine the movement patterns of mud crabs, genus Scylla, within the mangrove area of the Setiu Wetland in Terengganu, Malaysia. Mark-release-recapture technique were conducted during 24 sampling trips. A fluorescent visible implant elastomer (VIE) tag was inserted within the crab’s shell and they were released at the same capture stations over an interval of two weeks before the next sampling. A total of 288 crabs of various sizes, sex and species were identified, measured, tagged and recorded. The numbers of male crabs were higher than females. Three species were present, dominated by S. olivacea at 54.2% and S.tranquebarica at 26.4%, with S. paramamosain in third place at 19.4%. Among the 288 crabs that were tagged and released, 26.38% were recaptured. The tagged crabs did not move very far from the release station based on the recapture data. The greatest mean chance of being recaptured within 24 h was 44.5%, and there were no tagged crabs recaptured after 48 h even on sampling trips at several points from the release site. Knowledge of movement patterns is essential to understand migration and population dynamics and the relationship between reproduction and local distribution.

Higher survival but smaller size of juvenile Dungeness crab (Metacarcinus magister) in high CO2

Dungeness crab (Metacarcinus magister) are the most valuable fishery on the U.S. West Coast and both larval and adult Dungeness crabs are important components of regional food webs. Previous experiments have shown decreased survival and a slower development rate for Dungeness crab zoea reared in water with high CO2, indicating a susceptibility to ocean acidification. In this study we reared late-stage megalopae and juvenile Dungeness crabs in both ambient and high CO2 conditions for over 300 days. Counter to expectations, crabs reared in high CO2 had a higher survival rate than those reared in ambient conditions and crabs in high CO2 transitioned more quickly in one of the stages (J5 to J6). However, crabs reared in high CO2 were generally smaller and had a higher resting metabolic rate than crabs in ambient CO2. We hypothesized that two separate mechanisms were in effect, with one process driving survival and a second process driving size and respiration rate. We further hypothesized that increased mortality in ambient CO2 could be caused by a CO2-sensitive microbial pathogen, but that size and respiration differences were caused by the direct effects of CO2 on the crabs themselves. Overall, the zoea stages seem more sensitive to CO2 than the megalopae and juvenile stages.

Local fisher knowledge reveals changes in size of blue swimmer crabs in small-scale fisheries

Fisheries stock status is generally based on time series catch and effort data sourced from independent surveys and the fishery. These methods are often expensive and can be limited temporally and spatially. Alternative methods include the use of local fisher knowledge (LFK) to identify observed changes in catch. The blue swimmer crab (Portunus armatus) supports a small-scale commercial fishery and one of the most popular recreational fisheries in south-western Australia. Previous studies identified concerns from recreational fishers over its long-term sustainability. To understand if fishers’ perceptions of change provide useful information on actual changes in the fisheries, a triangulation approach was used to assess changes in size and abundance of crabs in two estuaries (Peel-Harvey and Swan-Canning). Three types of data were used: (i) fisher recollections from 1940s to 2010s, including face-to-face interviews and online surveys; (ii) historical records from newspaper articles from 1900 to 2000; and (iii) quantitative data on size between 2006/07 and 2018/19. Results identified: (i) crabs were smaller in the Peel-Harvey, a consistent difference identified in all data sources; (ii) crab size was perceived to have decreased in the Peel-Harvey; (iii) inter-generational differences in fishers’ perceptions regarding size changes over time; and (iv) historical evidence of persistent fishers’ concerns and perceptions of changes in the fishery and wider environment. These findings are evidence of a likely decline in the average size of crabs in south-western Australia over the last century, particularly in the Peel-Harvey, and demonstrate that LFK may be a valuable source of information particularly when other data sources are lacking.

Predation of the crab Acanthocyclus albatrossis on seeds of the bivalve Mytilus chilensis under different environmental conditions: Importance of prey and predator size

Predation is one of the most important interactions in biology, playing a fundamental role in the ecology of populations and communities. In southern Chile, the mussel Mytilus chilensis supports a large aquaculture industry. This species cohabits with one of its predators, the crab Acanthocyclus albatrossis, both in wild bivalve beds and in suspended culture systems. In this investigation, we assessed the predator-prey interaction between these two species, addressing the following aspects: a) the vulnerability pattern of M. chilensis to predation by A. albatrossis; b) prey sizes that are free of predation (the refuge in size); c) the attack rate and d) the effects of temperature and salinity on predation by different-sized A. albatrossis crabs. The prey sizes most likely to be attacked were 7.5, 12 and 14 mm (valve length) respectively for the three predator size categories evaluated. The sizes of the mussels that are free of predation were > 12, > 18 and > 22 mm respectively for each predator size. The mean attack rate was affected by the size of M. chilensis, with the smallest prey (6–12 mm) exposed the highest predation pressure. Temperature exhibited a positive linear effect on the median attack rate only for crabs in the smallest size category; no pattern was observed for the effect of temperature on the other sizes of crabs. Salinity showed no evident effects on the median attack rate at any size category. Our results indicate that A. albatrossis could be an important predator of M. chilensis recruits in wild bivalve beds, and of seeds in suspended culture systems.

A note on sex ratio, size at maturity, fecundity and breeding season of the portunid crab, Thranita crenata (Rüppell, 1830) from the Pakistani coast

Abstract Specimens of the portunid crab, Thranita crenata (Rüppell, 1830), commonly known as spiny rock crab or crenate swimming crab, were collected from Buleji rocky shore, in Karachi, during March 2015 to February 2016. The size (recorded as carapace width measured between the tips of the 5th spines) at which male and female crabs attain maturity was 42.6 mm and 42.4 mm CW, respectively. The smallest size of an ovigerous female crab was 38 mm CW. Although there were some more male crabs than female crabs in the samples, the male to female ratio was not significantly different from 11 (). Sex ratios in different size groups and different months were also found insignificantly different from a 11 ratio. Ovigerous females were found throughout the year, with a major peak in May and a minor peak in October when, respectively, 30.04% and 25.12% of the female crabs were ovigerous. The minimum and maximum fecundities recorded were 42 800 and 193 433 in females of 35 mm and 77 mm CW, respectively, and the average fecundity was 107 856 ± 50 331 over all berried females.

Understanding and predicting the effect of entrance cone diameters on the catch efficiency of snow crabs (Chionoecetes opilio) in conical pots

Conical pots with a plastic entrance cone on the top are a type of fishing gear used to harvest snow crabs (Chionoecetes opilio) in Arctic regions. In this study, we assessed the effect of pot entrance diameter on the catch efficiency of snow crabs. We used catch data collected during sea trials of pots with different entrance cone diameters, and we conducted laboratory experiments where morphological characteristics of snow crabs were investigated to estimate the extent of the different body parts of the animal that are decisive for the catch efficiency of the pot entrance. The results show that body parts larger than the carapace affected pot entrance efficiency. We predicted that entrance diameter is a key factor determining catch efficiency and that the experimental pots used in this study would experience significant reductions in the catch of marketable size crab, compared to pots currently used in the fishery.

Burrow utilization by the Japanese mitten crab <i>Eriocheir japonica</i> in the clay sediment of a freshwater river of Kyushu, Japan

This is the first record of the burrows of the Japanese mitten crab Eriocheir japonica. Morphologies of the burrows found in the clay sediment used by this crab were recorded by excavating them in a small freshwater river in Japan. Only E. japonica was found inside 2 of the 10 burrows examined (15 crabs and one crab, respectively), and the other 8 were empty. Crabs of various sizes (6.1–47.0 mm in carapace width) were collected from inside the occupied burrows. Burrow morphology ranged from single tunnels to complex burrows with multiple openings and tunnels. Openings (2–10 cm in diameter) were mostly located underwater. The single tunnels were 14–65 cm long. Considering the different digging habits of other burrowing animals found in this area, it can be concluded that E. japonica constructed these burrows. Burrows resembled those of the Chinese mitten crab E. sinensis, but were different in their location (freshwater vs. tidal), sediment type (clay vs. sand and silt), opening placement (mainly underwater vs. intertidal) and occupation rate (low vs. high). The low occupation rate suggests that E. japonica do not always rest in their burrows and rather prefer to hide beneath the riverbed’s large rocks. These results reflect the adaptation of E. japonica to the unstable environment of Japanese rivers.

Heterochely and cheliped dimorphism in the porcellanid crab Petrolisthes japonicus (De Haan, 1849) (Decapoda: Porcellanidae)

Cheliped dimorphism is common in decapod crustaceans, and many decapods have a pair of different-sized chelipeds, i.e., one side being larger (major) than the other (minor), a phenomenon known as heterochely. Anomuran crabs from the family Porcellanidae exhibit a true crab-like body shape, with relatively large chelipeds for their body size, and they show a sexual size dimorphism of chelipeds (i.e., males with larger chelipeds). However, very little is known about heterochely in porcellanid crabs. Therefore, we aim to elucidate heterochely and cheliped dimorphism in the porcellanid crab Petrolisthes japonicus (De Haan, 1849). We examined the laterality of the chelipeds and performed allometric growth analyses of the cheliped dimensions. Heterochely was observed in most of the specimens, and major chelipeds occurred randomly on either the right or left sides of the body, regardless of the crab size. Major and minor cheliped size of males surpassed female cheliped size, and males increased the growth of both major and minor chelipeds to the same degree during the breeding season, thereby inducing the distinct intersexual size dimorphism of the cheliped. This is probably attributable to sexual selection (i.e., male-male competition). Intersexual dimorphism as an energy allocation strategy was also evident with females allocating their energy evenly to both major and minor cheliped growth without changing the chela shape; regardless of the body size, whereas males were investing more energy in major cheliped growth, resulting in wider chelae with increasing body size. Consequently, the major cheliped may have a greater role in male-male competition in P. japonicus.

A reflex action mortality predictor (RAMP) for commercially fished blue crab Callinectes sapidus in Florida

The paucity of data on discard mortality in the commercial blue crab fishery contributes significant uncertainty to stock assessments. The reflex action mortality predictor (RAMP) method is used to predict mortality of commercially fished species by establishing a relationship between reflex impairment and the likelihood of mortality (RAMP curve). The present study adapted the RAMP method to commercially fished blue crabs in two unique habitats in Florida, the Tampa Bay estuary and the St. Johns River. The euryhaline nature of blue crabs permits the fishery to operate in myriad habitats, which adds complexity to cumulative effects that influence discard mortality. A total of 697 crabs were assessed, and a RAMP curve was generated. Logistic regression analyses determined that reflex impairment score, injury score, and salinity are strong predictors of discard mortality, with 91% of predictions correct. For every 1-unit increase in reflex impairment and injury score, mortality was 2.71 and 1.65 times more likely, respectively. Additionally, for every 1-SD (11.35 ppt) increase in salinity, mortality was 2.17 times more likely. Crab size, sex, water temperature, and emersion time minimally influenced mortality. The present study is the first crustacean RAMP research that included water quality and demonstrated that its inclusion increases the predictability of discard mortality. The RAMP curve can be used as a tool to estimate discard mortality aboard commercial vessels and discard mortality in future stock assessments.

Structural Changes and Mechanical Resistance of Claws and Denticles in Coconut Crabs of Different Sizes.

Simple SummaryUnderstanding the diverse mechanisms by which organisms achieve exceptionally high mechanical properties may enable the development of unique, biologically inspired materials. We assessed the microstructure, composition, and mechanical resistance of the pinching side with denticles and of the outer side without denticles in robust claws of coconut crabs with body weight (BW) of 300 g to 1650 g. Surprisingly, they were independent of BW except for low hardness near the surface of the denticles of a small crab of 300 g. Although the microstructure of the denticles was clearly different from that of the exocuticle, their mechanical resistance indicated the same maximum value. The denticle can be regarded as a bulge of the cuticle without phosphorus. The design principles found in the exoskeleton provided promising opportunities for the research and development of novel structural materials.The exoskeleton of the pinching side of claws with denticles and of the outer side without them on the coconut crab, Birgus latro, which is a rare organism, were studied using a materials science approach. The mechanical resistance of three claws of different sizes was investigated along the exoskeleton thickness from the outer surface to the inner surface, and the results were compared, including the contribution of the microstructure and chemical compositions. Mechanical properties, hardness (H) and stiffness (Er), were probed through nanoindentation tests. The results showed the H, Er, microstructures, and chemical components of the exocuticle and endocuticle layers were almost the same, in a BW range of 300 g to 1650 g. At the same time, the H and Er near the surface of the denticles of a small coconut crab of 300 g were lower than those of other large coconut crabs. The microstructure of the denticles was clearly different from that of the exocuticle, but the maximum mechanical properties near their surface indicated almost the same values, Hmax = 4 GPa and Er(max) = 70 GPa, regardless of being on the pinching side or the outer side. A denticle can be regarded as a bulge of the cuticle without phosphorus and with high magnesium. The results provided novel information that expanded our knowledge about the claw microstructure of coconut crabs with different body sizes, and may be used in further studies

The Effect Of Different Additional Feed On The Growth Of Raw Crab (Scylla serrata)

This study aims to determine the effect of different supplementary feeds on the growth of mud crab (Scylla serrata). This research was conducted from January 2 to March 2, 2021, at the Joint Pond Owner in Kandang Village, Kampung Melayu District, Bengkulu City. The container used is a plastic basket with a design size of 37 cm high, a circle diameter of 34 cm with a test crab size of 100-110 grams, totaling 48 tails. The design used in this study was a completely randomized design (CRD) which consisted of three treatments, namely experiment 1 (trash fish feed), Experiment 2 (mangrove snail feed), and Experiment 3 (cut chicken intestine feed) with eight replications, so that in getting twenty-four treatment units. To determine the effect or not, analysis of variance was carried out at the level of 5% and 1%, while to determine the effect of the best feed, the BNT Advanced Test (Least Significant Difference) was carried out. 5%. The parameters observed were weight growth of crabs, carapace length, carapace width, feed conversion, feed efficiency, and survival of mud crabs. The results showed that different supplementary feeding had a significant effect on the weight growth of mud crabs but had no significant effect on carapace length growth, carapace width, feed conversion, feed efficiency and survival of mangrove crabs. The best feed for the growth of mangrove crabs is chicken intestine with an initial weight of 105.2 grams and a final weight of 173.4 grams.

Improving size selectivity of round pot for Charybdis japonica by configuring escape vents in the Yellow Sea, China.

Sustainable development of the important economic species, Asian paddle crab (Charybdis japonica), has attracted attention in the coastal waters of the Yellow Sea, China. The commonly used round pots are almost nonselective, resulting in severe bycatch of juveniles. In this study, we explored a method to improve the size selectivity for C. japonica by mounting escape vents on the side panels of each pot. The selectivity of pots with escape vent sizes of 70 mm × 20 mm, 70 mm × 25 mm, 70 mm × 30 mm, and 70 mm × 35 mm was tested using a catch comparison method. The estimated minimum landing size (MLS) of carapace height (27 mm), according to the regulated MLS of carapace length (50 mm), was used as a reference point to explain the results. Significant increases in the size of crabs caught by pots were found with the enlargement of escape vent size (Kruskal–Wallis test, P < 0.01). The pots with 70 mm × 20 mm, 70 mm × 25 mm and 70 mm × 30 mm escape vents released nearly 50%, 75% and 95% of undersized individuals, respectively, and these three types of pots retained approximately 90% of legal-sized individuals compared with the control pots without escape vents. The pots with 70 mm × 35 mm escape vents released nearly all undersized individuals, but they also released most legal-sized individuals. Pots with an escape vent size of 70 mm × 30 mm were recommended for the sustainable development of C. japonica in the Yellow Sea of China. The results of this study reiterate the importance of carapace height for determining the size selectivity, which can serve as a reference to formulate management regulations in the coastal waters of the Yellow Sea, China.

Catches in abandoned snow crab (Chionoecetes opilio) pots in the Barents Sea

During a 2018 retrieval cruise for abandoned snow crab (Chionoecetes opilio) pots in the Barents Sea, approximately 8600 pots abandoned 1.5 years earlier were recovered. Forty-three percent of a subsample of 1000 pots contained snow crabs, with an average of three crabs per pot. Most of the crabs were alive (~98%) and dominated by large males. Pinch injuries and limb loss were common and tended to decline with increasing crab size. Reflex testing showed that the crabs were vital (i.e. the crabs moved their legs, chelipeds and maxillipeds when stimulated), which was supported by a relatively high meat content. However, energy reserves in the digestive glands (hepatopancreas reserves) were low, indicating overall energy deficiencies. Our results indicate considerable unaccounted mortality due to self-baiting, continued catch and cannibalism. The findings demonstrate that snow crab pots which are lost or abandoned in the Barents Sea fishery maintain huge potential for ghost-fishing impacts.

The fishing season and the exploitation status of mud crab (Scylla serrata) in Asahan Sea, North Sumatera, Indonesia

Crab is one of the resources that can be found in almost all areas in Indonesia, and its export increases every year. However, increase in its exploitation and mangrove forest damage affect crab availability. Scylla serrata is one of the crab commodities for export in Asahan sea, North Sumatera. Scientific studies are necessary to determine the fishing season and the exploitation status of crabs in the area. Therefore, this study was carried out for 3 years, i.e. in April–December 2018, February–December 2019, and March–December 2020, at one crab landing site in Asahan. The fishing season for S. serrata in this area occurred all year long, with peak seasons in April–June and September–December. The crab’s carapace width (CW) was 65–175 mm, where 71.2% of which were below 120 mm. Its carapace width at first capture (CWc) increased from 103.2 mm to 112.1 mm. Its fishing mortality (F) was 1.40 per year, higher than its natural mortality (M) (0.84 per year). Therefore, its exploitation rate (E) was 0.63, indicating that the species was already overfished. Suggested measures to control the fishing activity include limiting the crab size for capture in accordance with the Regulation of the Minister of Marine Affairs and Fisheries No. 12 Year 2020 and improving the environment of mangrove habitats.

Population level differences in overwintering survivorship of blue crabs (Callinectes sapidus): A caution on extrapolating climate sensitivities along latitudinal gradients.

Winter mortality can strongly affect the population dynamics of blue crabs (Callinectes sapidus) near poleward range limits. We simulated winter in the lab to test the effects of temperature, salinity, and estuary of origin on blue crab winter mortality over three years using a broad range of crab sizes from both Great South Bay and Chesapeake Bay. We fit accelerated failure time models to our data and to data from prior blue crab winter mortality experiments, illustrating that, in a widely distributed, commercially valuable marine decapod, temperature, salinity, size, estuary of origin, and winter duration were important predictors of winter mortality. Furthermore, our results suggest that extrapolation of a Chesapeake Bay based survivorship model to crabs from New York estuaries yielded poor fits. As such, the severity and duration of winter can impact northern blue crab populations differently along latitudinal gradients. In the context of climate change, future warming could possibility confer a benefit to crab populations near the range edge that are currently limited by temperature-induced winter mortality by shifting their range edge poleward, but care must be taken in generalizing from models that are developed based on populations from one part of the range to populations near the edges, especially for species that occupy large geographical areas.

Impact of unilateral eyestalk ablation on Callinectes arcuatus (Ordway, 1863) under laboratory conditions: behavioral evaluation

Eyestalk ablation allows the removal of neurohormones that inhibit early reproduction and decreases the time to complete the molting cycle. The present study evaluated the impact of unilateral eyestalk ablation on the behavior of blue crab breeders Callinectes arcuatus in the short term under laboratory conditions. Immature male and female crabs and individuals in the intermolt stage were collected in Ohuira Bay, Ahome, Sinaloa, Mexico. Three bioassays were performed: males, females, and male-females each with three treatments; control + xylocaine (50 μL, 5%), squash ablation + xylocaine (50 μL, 5%), ablation by string ligation + xylocaine (50 μL, 5%), each with three replicas and three periods of evaluation after the ablation procedure (10 min, 2 h, and 24 h). Kruskal-Wallis and Chi-square (χ2) tests were used to evaluate significances (P &lt; 0.05) in the behavior of C. arcuatus. The sizes of blue crab C. arcuatus were 9.72 ± 1.0 cm of carapace width. The feeding behavior of the male-females bioassay was significant at 2 h (P &lt; 0.05). The results obtained were satisfactory using two techniques, unilateral eyestalk ablation by squash and ligation in which pain and aggressiveness indicators were mitigated. Disorientation and aggressiveness in males were significant at 2 h (P &lt; 0.05), and in females after 10 min, and 2 h after ablation (P &lt; 0.05). In the male-females bioassay, aggressiveness was significant at 2 h (P &lt; 0.05). Courtship and copulation were recorded in those crabs subjected to unilateral eyestalk squash ablation (13 and 8, respectively).