Crab Pots Research Articles

Sustainable co-location solutions for offshore wind farms and fisheries need to account for socio-ecological trade-offs

The spatial expansion of offshore wind farms (OWFs) is key for the transition to a carbon free energy sector. In the North Sea, the sprawl of OWFs is regulated by marine spatial planning (MSP) and results in an increasing loss of space for other sectors such as fisheries. Understanding fisheries benefits of OWFs and mitigating the loss of fishing grounds is key for co-location solutions in MSP. For the German exclusive economic zone (EEZ) of the North Sea we conducted a novel socio-ecological assessment of fisheries benefits which combines exploring potential spill-over from an OWF with an experimental brown crab (Cancer pagurus) pot fishery and an economic viability analysis of such a fishery. We arrayed a total of 205 baited pots along transects from an OWF located near the island of Helgoland. After a soaking time of 24 h we retrieved the pots and measured the carapace width (mm), weight (g), and sex of each individual crab. To conclude on cumulative spill-over potentials from all OWFs in the German EEZ and drivers of passive gear fisheries we analysed vessel monitoring system (VMS)-data and computed random forest regressions. Local spill-over mechanisms occurred up to distances of 300 to 500 m to the nearest turbines and revealed an increasing attraction of pot fishing activities to particular OWFs. This corresponds to the observation of constantly increasing fishing effort targeting brown crab likely due to both a growing international demand and stable resource populations at suitable habitats, including OWFs. Our break-even scenarios showed that beam trawlers have the capacities to conduct during summer an opportunistic but economically viable pot fishery. We argue that particularly in the North Sea, where space becomes limited, integrated assessments of the wider environmental and socio-economic effects of planning are crucial for a sustainable co-location of OWFs and fisheries.

Length-weight relationship (LWR) of mud crabs (Scylla sp.) in mangrove waters Peukan Bada Aceh Besar as the basic for waters resources development

Mud crab (Scylla sp.) is one of the aquatic resources that has high economic value so that the information on length-weight relationships is important for sustainable fisheries management. The objectives of this study were to determine the abundance of mud crab (Scylla sp.), the sex ratio of mud crab (Scylla sp.) and to analyze the length-weight relationship of mud crabs (Scylla sp.). This study was conducted in April 2019. Sampling of mud crabs (Scylla sp.) was carried out by using a bubu crab trap with the random sampling method. The bubu size is in length 47 cm, width 31 cm and height 19 cm. The sampling at ach station was repeated three times during low tide conditions. Sampling location was determined by using the stratified random sampling method. The results of the analysis showed that sampled number of mud crabs (Scylla sp.) in the mangrove waters of Peukan Bada were 90 individu, consisting of 50 ind female mud crabs and 40 ind male mud crabs. Therefore, sex-ratio in mud crabs (Scylla sp.) shows that the sex ratio between male and female individuals is still in a balanced state. The growth pattern were negative allometric (b<3), which means that the growth pattern of carapace length is faster than the body weight of mud crabs. The results also showed that the correlation coefficient (r) values for male and female mud crabs were 0.89 and 0.94, respectively. This indicates a close relationship between length and weight of mud crabs. Environmental parameter factors such as salinity and temperature greatly affect the growth pattern of mud crabs and sex ratio in the mangrove waters Peukan Bada, Aceh Besar.

Home ranges and Movements of Two Diamondback Terrapins (Malaclemys terrapin macrospilota) in Northwest Florida

The diamondback terrapin (Malaclemys terrapin) is a small estuarine turtle distributed along the Atlantic and Gulf Coasts of the USA that is threatened by drowning in crab pots, road mortality, exploitation in the pet trade, and habitat loss. Little is known about the movement patterns and home ranges of these turtles, particularly along the U.S. Gulf of Mexico coast. Satellite tags were deployed on two adult female terrapins captured at two distinct sites in Northwest Florida. A first-difference correlated random walk approach was used to determine distances traveled and estimate home range for each individual. The two terrapins were tracked for 146 and 147 days, and the total distance traveled for each terrapin was 70.1 km and 723.0 km, respectively. The maximum distance moved from capture location was 11.3 km and 49.6 km. Home ranges here were much larger than those previously reported in other studies. The movements we documented were greater than expected and indicate habitat protection for this species may need to be expanded to incorporate more distant foraging sites.

Assessment of Mud Crab Fishery in Panguil Bay

The last assessment of three commercially important mud crab species (Scylla tranquebarica, S. olivacea and S. serrata) in the mangrove dominated Panguil Bay was in 2005; there was already an indication of the stock decline. This study aimed to continue the assessment but focused on production, growth parameters, total mortality, and exploitation rate of the three mud crab species at seven mud crab landing sites from March 2017 to March 2019 following standard fisheries enumeration protocols. Results showed that the total resource production in Panguil Bay decreased from 201.1 MT in 2005 to 103.0 MT in 2017-2019. Growth parameters of the three species for male and female, respectively are as follows: S. tranquebarica (L∞ = 11.5 cm and 11.7 cm, annual growth coefficient K = 0.6 and 0.6, exploitation rate E of 0.5 and 0.5); S. olivacea (L∞ =10.9 cm and 11.4 cm, K = 0.5 and 0.6, E = 0.6 and 0.5); and S. serrata (L∞ = 12.3 cm and 12.9 cm, K = 0.7 and 0.6, E = 0.6 and 0.6). Total production of mud crabs increased, and the three species are highly exploited, but exploitation rates are already slightly below or above maximum sustainable yield (Emax). A total of 1,848 fishers were recorded owning 2,015 boats composed of 1,419 motorized and 596 non-motorized. An inventory showed an increase of 5.36% in the number of motorized boats from the last assessment in 2005. A total of 15 types of gear were recorded, in which the top three include fish corral, crab pot, and gill net. Consequently, this study recommends reducing the present fishing pressure or effort of the three mud crab species, particularly during the spawning season occurring on wet months (July to October), for sustained mud crab fisheries in Panguil Bay.

Modelling the effect of mesh size and opening angle on size selection and capture pattern in a snow crab (Chionoecetes opilio) pot fishery

Size selection in commercial snow crab (Chionoecetes opilio) pot fisheries is important for reducing on-board sorting and unintended mortality of undersized individuals. In this paper, we tested whether snow crab of various sizes geometrically could pass through diamond meshes of different sizes and opening angles, to estimate a model for predicting the effect of mesh size and mesh opening angle on snow crab size selectivity. The model was able to explain the size selection results from earlier sea trials using commercial snow crab pots. Size selection was strongly dependent on mesh opening angle, making it less well-defined for the conical pots often used in snow crab fisheries where mesh opening angle varies. We predicted the optimal mesh size for the Norwegian snow crab fishery is 140 mm with a 65° opening angle, resulting in high capture efficiency for target size snow crab (larger than 100 mm carapace width) and low sorting effort, with approximately 10% of the catch consisting of undersized snow crab. Our model can potentially be used for other snow crab fisheries.

Effects of the trap entrance designs on the catch efficiency of swimming crab Charybdis feriata fishery

The swimming crab Charybdis feriata fishery is important to the coastal fishing communities of Vietnam, particularly in the province of Quang Nam. Trapping is considered a low impact and fuel-efficient fisheries capture technique that is drawing increasing attention as concerns regarding the impact of fisheries on ecosystems and the environment grow. However, traps typically have low capture efficiency for most crab species and there is considerable interest to improve catchability. In this study we investigated the impact of modifying the number of trap entrances on a traditional trap design, and also the colour of entrance-netting, on the catch rate of swimming crab in the Vietnam trap fishery. In the first experiment we compared catch rates between a traditional three-entrance trap and a modified one-entrance trap design, and found that the modified one-entrance trap had a 24 % higher catch rate. In second experiment, we compared catch rates of one-entrance traps having green or yellow entrance-netting and found that yellow netting increased catch rates by 31 %. This study shows that fishing enterprises could improve their swimming crab trap fishery by using modified one-entrance traps with yellow entrance netting.

Proportion and Total of Commodities Blue Swimming Crab (Portunus pelagicus Linnaeus, 1758) Catches in Gebang Mekar Village, Cirebon Regency, West Java Using Crab Gillnet and Collapsible Crab Trap

Blue swimming crab (Portunus pelagicus) is one of the high economic value commodities which causes increased efforts to catch blue swimming crab in Indonesia. The effort of catching continues to increase the blue swimming crab resources in the nature that has decreased. Cirebon Regency is one of the largest blue swimming crab fishing centers in West Java with a total value of blue swimming crab production in 2017 by 7,347 tons/year. This research was conducted to determine the selecitivity level of the crab gillnet and collapsible crab trap based on the proportion and total of catches obtained in Gebang Mekar Village, Cirebon Regency. Research was conducted in September 2019 – October 2019 in Gebang Mekar Village. For this research we used are primary data; collected directly during the observations includes catch type and weight of the catches and then interviews with several crab gillnet and collapsible crab trap fisherman and secondary data; data from official agencies and some literature. Our research suppose the moonlight phase effect of the blue swimming crab catch. Based on the research, it can be concluded that the crab gillnet with 3.5 inch mesh size and collapsible crab trap that operated in Gebang Mekar Village may be called a selective fishing gears but crab gillnet is more eficient as compared to collapsible crab.

Estimating the Benefits of Derelict Crab Trap Removal in the Gulf of Mexico

Ghost fishing in derelict blue crab traps is ubiquitous and causes incidental mortality which can be reduced by trap removal programs. In an effort to scale the benefits of such removal programs, in the context of restoring the Gulf of Mexico after the Deepwater Horizon oil spill, this paper calculates the ecological benefits of trap removal by estimating the extent of derelict blue crab traps across Gulf of Mexico waterbodies and combining these estimates with Gulf-specific crab and finfish mortality rates due to ghost fishing. The highest numbers and densities of traps are found in Louisiana, with estimates ranging up to 203,000 derelict traps across the state and up to 41 traps per square kilometer in areas such as Terrebonne Bay. Mortality rates are estimated at 26 crabs per trap per year and 8 fish per trap per year. The results of this analysis indicate a Gulf-wide removal program targeting 10% of derelict traps over the course of 5 years would lead to a combined benefit of more than 691,000 kg of crabs and fish prevented from mortality in ghost fishing traps. These results emphasize the importance of ongoing derelict trap removal programs. Future work could assess additional benefits of trap removal programs, such as fewer entanglements of marine organisms, improved esthetics, and increases in harvestable catch. Lastly, this model could be utilized by fishery managers to calculate the benefits of other management options designed to decrease the extent and impact of derelict fishing gear.

Effect of escape vents on retention and size selectivity of crab pots for swimming crab Portunus trituberculatus in the East China Sea

An increase in the crab pot fishery in the East China Sea has caused great pressure on swimming crab Portunus trituberculatus resources. Thus, it is essential to implement suitable measures to release sublegal-sized crabs to increase the number of recruits for legal-sized crabs. One of the measures considered is the installation of escape vents on crab pots. We tested crab pots with one and two escape vents and compared the catchability and size selectivity of these pots with control pots without an escape vent. Pots with one escape vent located on single side of the pot, top or bottom (SS), and another on both sides at top and bottom edges (BS) were tested in sea trial experiments following typical commercial fishing practice. The results show that both SS pots and BS pots caught significantly smaller number of sublegal-sized crabs (<116 mm carapace width, CW), but the difference in catch between the two types of crab pots is not significant. The 50% selective CWs (CW50) and the selective ranges (SRs) of both BS pots are slightly larger than those of SS pots. However, 95% confidence intervals of CW50s and SRs are overlapped, indicating that the discrepancy between them is small. Then, in a mixed effect model, the effect of locations of escape vents, taken as the fixed effect, on selectivity parameters and indexes was analyzed by hypothesis testing. The results show that null hypothesis of no effect of location of vents on size selectivity cannot be rejected, indicating that there is no significant difference in size selectivity between the two types of pots for P. trituberculatus.

Impacts of sampling design on the abundance estimation of Portunus trituberculatus using crab pots

Fishery-independent surveys can provide high-quality data and support fishery assessment and management. Optimization of sampling design is crucial to increase the quality of fishery surveys. Crab pots are important fishing gears used to catch crabs. We analyzed the impacts of sampling design of crab pots on the abundance of Portunus trituberculatus in the Changjiang (Yangtze) River estuary to the Hangzhou Bay and its adjacent waters in East China Sea. The crab pots were cylindrical, 240 mm in height and 600 mm in diameter of the iron ring. Our sampling designs (including fixed-station sampling, simple random sampling, stratified fixed-station sampling, and stratified random sampling), three number of stations (9, 16, and 24), and three numbers of crab pots (500, 1 000, and 3 000) were simulated and compared with the “true” abundance that obtained from bottom trawl surveys in the study area in 2007. The scenarios with 16 stations were set in stratification as a control group for comparison with unstratified designs. Results show that simple random sampling can obtain more stable results than fixed-station sampling in the abundance estimation of P. trituberculatus. In addition, stratified sampling resulted in more accurate abundance than unstratified sampling. The accuracy of the simulated results improved with the increase of the number of stations. No remarkable differences in the results were found among the scenarios of different number of crab pots at each station. However, resource-intensive areas exerted great impacts on simulation results. Thus, prior information or pre-survey results about resource abundance and density distribution are necessary. This study may serve as a reference for future sampling designs of crab pots of P. trituberculatus and other species.

Blue Crab Abundance and Survival in a Fragmenting Coastal Marsh System

Louisiana’s coastal marshes are becoming increasingly fragmented due to sea level rise, subsidence, reduced sediment inflow from the Mississippi River, and saltwater intrusion. Many commercially and recreationally fished species rely on the marsh system as nursery habitat, and the resilience of species to further marsh loss and marsh fragmentation is uncertain. We examined the impacts of marsh fragmentation on the blue crab, Callinectes sapidus, a species supporting one of the largest fisheries in coastal Louisiana and which uses marsh edge as nursery habitat. Juvenile and adult abundances were quantified in multiple habitats (bare sediment, marsh edge, and submerged aquatic vegetation [SAV]) within an actively fragmenting coastal marsh. Adult blue crabs were sampled using crab pots, while juveniles were sampled using a throw trap. In general, blue crab density was unrelated to marsh fragmentation, but was instead related to local-scale patterns of habitat availability, including presence and type of vegetation. In tethering experiments to examine predation rates on juvenile blue crabs across habitats, predation rates were lowest in SAV compared with marsh edge or bare sediment. While direct effects of marsh fragmentation on local-scale patterns of blue crab abundance were not observed, marsh fragmentation will likely have indirect effects on blue crab populations through changes in habitat availability. Unless SAV expands into newly created open water areas, providing an alternative nursery habitat for blue crabs, continued marsh fragmentation and loss are expected to have negative impacts on blue crab populations and fisheries through a decrease in available nursery habitat.

Aerial drone technology can assist compliance of trap fisheries

AbstractIllegal fishing is a global issue that threatens the viability of fishing industries and biodiversity conservation. Management agencies typically use on‐ground surveillance to monitor and minimise illegal fishing practices, the efficacy of which may be enhanced by integrating emerging remote sensing technology. Affordable drones may contribute to cost‐effective detection of illegal fishing activity and associated gear, although their application has yet to be evaluated in many types of fisheries. Here, the utility of drones for the detection of crab traps and floats set in a shallow estuary was quantitatively tested, and the effects of survey altitudes, cameras and monitor screens on detection rates were determined. It was found that drone flight altitude and float colour influenced the detection rates of common crab trap floats, with infrared cameras improving the detection of floats camouflaged by black paint. However, the type of monitor screen used by the drone operator had no influence on the detection of crab traps. Overall, it appears drones can contribute to cost‐effective compliance in estuarine trap fisheries, and the approach can contribute to evidence‐based standard operating procedures.

Fishery of mud crab Scylla serrata of Kotania Bay, Western Seram District: potency, stock status and sustainable management

Study on the fishery of mud crab Scylla sp. of Portunid crab at Kotania Bay of Western Seram District was conducted between March and August 2018. The objectives of this study were to analyze biological parameters, the potency, stock status, sustainability, and to propose a sustainable management plan for this fishery. A total of 592 individual mud crab sample were collected from local fisher for biological parameters analysis. Historical catch data from local fisher, mud crab collector and fishery enumerator were used to analyze stock biomass, fishing intensity and stock status using Graham-Schaefer dynamic model. Rapfish analysis was used to analyze the sustainability of the stock. The carapace width ranged from 7.80 - 23.50 cm with an average of 13.68 cm (±2.25). There was a strong relationship between carapace width-weight (r = 0.9405) with overall growth pattern of isometric. The estimated stock biomass of mud crab of Kotania Bay was 130,000 t with BMSY of 22,425 t.yr−1, and mud crab fishery was under overfishing status. The overall sustainability was 46.92% and was considered as less sustain according to the ecosystem approach to fisheries management. Most sensitive attributes affecting sustainability were catching before maturity, consumer attitude towards sustainability, gear side effect, just governance, and government quality. Law enforcement, education and training on ecosystem approach to fisheries management, mud crab pot with escape gab, community based fishery management as well as monitoring and reporting should be conducted for mud crab sustainability.

Drones detect illegal and derelict crab traps in a shallow water estuary

AbstractThe issues surrounding illegal, unregulated and unreported fishing, and that of abandoned, lost and discarded fishing gears, leading to ghost fishing, are intensifying. Estuarine crab trapping is likely subject to high levels of illegal and potential ghost fishing, because it also has good economic incentives regarding potential catch, low gear acquisition costs and accessible fishing grounds. To improve the efficiency and effectiveness of fisheries monitoring, control and surveillance operations, the efficacy of small consumer‐grade drones for sighting traps in an estuary in NSW, Australia, was tested. Twelve sets of two flights were undertaken at 20 and 30 m altitude over a 600‐m stretch of estuary for 5 days to quantify the detectability of submerged mesh traps of three different mesh colours. The drone was able to detect the majority of traps efficiently, with depth in relation to water clarity being the main factor affecting detection. In shallow water, detection rates were high for all mesh colours, but in the slightly deeper placements, orange traps were more readily detected. This study demonstrates that drones could be an efficient and reliable tool for rapidly assessing areas for illegal and derelict traps and can be supplemented into land or vessel‐based fisheries operations.

Effect of gear soak time on size selection in the snow crab pot fishery

In the commercial pot fishery for snow crab (Chionocetes opilio), size selection by the pots is important for reducing catch sorting and unintended mortality. In addition to mesh size and shape, selection in the pots relies on every crab contacting the netting meshes, which makes the process complex because the odour of the bait tends to keep all sizes of crab in the pots. Thus, soak time may affect the extent of the use of the selective potential of the pots. This study was designed to assess the influence of soak time on size selectivity, and the methodology was applied to snow crab data collected in the Barents Sea. The results showed that a minimum soak time is required to reach the full size-selective potential of the pots. Specifically, a fraction of the small crabs inside a pot will not attempt to escape through the pot meshes when the pots are soaked for short periods of time (under nine days). Further, with short soak time, some of the crabs inside a pot will not make selectivity contact with the netting. Therefore, some crabs will not utilize the escape options through the pot meshes. This finding confirms the need for using a selection model that explicitly accounts for such a process when assessing snow crab size selection. Lastly, this study outlines how the concept of selectivity contact can formally be applied to model the effect of soak time on the size selectivity of the snow crab pot fishery.

Influence of Crab Trap Geometry and Wind Direction over the Catch Fluctuations in a Neotropical Coastal Lagoon

Blue crabs (Callinectes spp.) are widely distributed around coastal regions being usually exploited by artisanal fishing through specific fishing gears, like as crab traps. Notably, two crab traps types are adopted in Brazil: (I) rectangular crab traps and (II) circular crab traps. Empirically, fishermen suggest that the geometry of these fishing gears amongst the wind regimes in shallow waters are directly related to the catch success, that is, the blue crabs capture into the crab traps. However, these empirical observations have not been proven by academy. Thus, the present study analysed the performance of circular and rectangular traps during twenty campaigns in a coastal lagoon located in Laguna, Santa Catarina–Brazil. The results showed that circular crab traps obtained the highest catches of Callinectes spp. than rectangular crab traps. We observed that wind direction can influence the catch performance in both fishing gears and the best catch performance in our study region were during NE and SO wind quadrants.

Особенности поведения камчатского краба в зоне действия конусной ловушки

Особенности поведения камчатского краба в зоне действия конусной ловушки

Assessment of Portunus (Portunus) trituberculatus (Miers, 1876) stock in the northern East China Sea

Portunus (Portnus) trituberculatus (Miers, 1876) is one of the important commercial crustaceans in the northern East China Sea. Although extensive research on aquaculture of the species is being carried out, the wild stock is scientifically unassessed. In this paper, the total catch of P. trituberculatus in the northern East China Sea during 2001 and 2015 were classified into 4 carapace width (CW) groups (150 mm), for estimation of the maximum sustainable yield (MSY) and the spawner-recruitment relationships for wild stock and released stock were built, respectively. Standing biomass, spawning biomass and catch were predicted under the assumptions that fishing intensity and quantity of P. trituberculatus released were kept at the levels of those in 2015. The results showed that the MSY of P. trituberculatus is about 14.2×104 t and the corresponding fishing effort (EMSY) is about 14.8×104 tonnage (both the crab pot vessels and trawl vessels were standardised to gillnet vessels). In future, if fishing effort level and the release number equals to those in 2015, the biomass, spawning biomass and catch of P. trituberculatus would remain at 58.9×104 t, 53.1×104 t and 15.6×104 t, respectively. The present stock assessment study was conducted with limited data and further survey data in future may provide more accurate stock assessment to evolve management strategies.

The curious case of the missing face: Death of California sea lion by Dungeness crab trap

Marine mammals frequently interact with human detritus due to their proximity to shores and shared target foods. Sea lions have been known to attempt to obtain bait inside crab traps. A case is described in which the pattern of decomposition of a California Sea Lion, Zalophus californianus , suggests that it likely became entangled and drowned while attempting to get Dungeness crab trap bait. This represents the first case of California Sea Lion death related to interaction with a crab trap.

Low Back Pain and its Assessment among Commercial Fishermen in Agenebode: An Ergonomic Perspective

In a research done amongst commercial fishermen in Agenebode (Lat. 7.11oN, 6.69oE), the problem low back pain is significant in the fishing business. Research information is scarce on the investigation of the ergonomic stress of professional fishing. Moreover, there is no prior analysis, which investigates the relationship between low back stress (LBS) and low back pain (LBP) in fishing activities. This paper aims to measure the LBS during the gillnet and commercial crab fishing activities as well as to verify the correlation between the low back pain occurrences and those stresses reported in study of Agenebode commercial fishermen during the period (April 2017 – July 2017). A sample of 30 commercial fishermen considered in this study were exposed to LBS and the frequency of the fishing activities was assessed using questionnaire with crab pot and gillnet fishermen. The occurrence rate ratios (RR, 95% CI) of low back pain, which interrupted fishing, exposed to the high LBS and self-reported task was modelled on the basis of the multivariate generalised Poisson regression. It was observed that increased rates of low back pain correlates with the percent of time fishermen were exposed to discomforted postures. Handling of heavy loads during the loading and unloading activities generated lifting indices and high compression values, but with little overall work time (&lt;15%). The results establish that neither ergonomic measure nor fishing task frequency alone can accurately predict LBP. Conversely, ageing, history of the LBP and self-selection out of tasks, perhaps, are significant factors that contributes to the LBS and outcomes observed