Browsing by Subject "Blue crab (Callinectes sapidus)"

Now showing 1 - 7 of 7

Open Access
Estuarine Ingress of the Blue Crab Callinectes Sapidus
(2008-04-21) Ogburn, Matthew Bryan
This dissertation investigated ingress of postlarval blue crabs Callinectes sapidus to the Newport River estuary, North Carolina, USA. Data from C. similis, Menippe mercenaria, Pachygrapsus transversus, and Arenaeus cribrarius are included in some chapters for comparison. Changes in tolerance to low salinity were examined by: 1) exposing postlarvae (megalopae) collected in coastal and estuarine areas to a range of salinities and 2) determining the cue that stimulates acclimation of coastal megalopae to low salinities, the time to acclimation, and the decrease in salinity necessary for acclimation. Coastal megalopae were less tolerant to salinities of 5 and 10 than megalopae from the estuary. Coastal megalopae became acclimated to low salinities within 12 h when salinity was reduced from 35 to 31. Spatial patterns in abundance during ingress were investigated simultaneously in coastal and estuarine areas. Coastal distributions were determined using nighttime surface plankton tows at slack water after ebb tide and slack water after flood tide on four nights; two each during spring and neap tides. Estuarine distributions were determined using nightly settlement on 'hog's hair' collectors. C. sapidus megalopae were most abundant at the coast east of Beaufort Inlet, but settlement was restricted to western channels of the estuary. Species-specific patterns in abundance were maintained during two spring/neap cycles, possibly due to interactions between larval behavior and physical forcing. Biophysical mechanisms of estuarine ingress were investigated by comparing nightly abundance in coastal and estuarine areas with environmental variables. Comparisons were made using cross-correlation and cross-fourier analyses. High estuarine abundances were associated with wind-driven estuarine inflow and nighttime flood tides. The seasonal pattern of estuarine ingress was strongly associated with the seasonal pattern of alongshore wind stress, suggesting that inter-annual variations in atmospheric forcing may determine the yearly abundance of megalopae arriving in estuarine nursery habitats. The effect of sampling interval on annual megalopal abundance estimates was determined using an 11-year dataset of nightly settlement. Variability in abundance estimates increased with increasing sampling interval. Switching from a one day to two day sampling interval resulted in a 20 % decrease in the likelihood of detecting a significant correlation between annual abundance and CPUE in the North Carolina blue crab pot fishery.
Open Access
Managing the North Carolina Blue Crab Fishery: Engaging Fishermen in the Analysis of Soft and Peeler Crab Regulations
(2006) Greene, Emily
In September of 2005, the North Carolina Marine Fisheries Commission approved regulations in the blue crab fishery for reducing wasteful fishing practices and preserving the spawning stock. Interviews of soft and peeler crab fishermen in Carteret County, North Carolina revealed the perceived effects of these and other regulations on their individual operations and on the health of the fishery as a whole. The results of these interviews are discussed in the following report. Additionally, the extent to which the 1998 and 2004 North Carolina Blue Crab Fishery Management Plans reflect the major findings of the interviews is considered and recommendations for future management plans are offered.
Open Access
Migratory behavior of adult female blue crabs, Callinectes sapidus, in Pamlico Sound: implications for assessment and protection of the spawning stock
(2007-08-30) Goldman, Margaret
The blue crab, Callinectes sapidus, supports North Carolina’s largest and most valuable commercial fishery, but according to the 2004 stock assessment, recent fishery-dependent and -independent data suggest the population is in decline. Of particular concern is the status of the spawning stock. Annual recruitment is largely dependent on the size of the spawning stock. A decline in spawning stock abundance and biomass predicts future decline in the population. In order to develop effective management strategies to protect the spawning stock, it is first necessary to (1) understand the migratory behavior of adult female crabs within the Croatan Albemarle Pamlico Estuary System (CAPES) and (2) acquire data that can be used to accurately assess the status of the spawning stock. Assessment of the spawning stock in the CAPES is currently based on the assumptions that crabs remain in the estuary to spawn and that mature female abundance peaks in the estuary in late summer/early fall. However, recent studies on blue crab reproduction and migration indicate that blue crabs have multiple clutches, migrating seaward with each successive clutch. Upon reaching coastal waters, crabs do not reenter the estuary. Instead, they continue to spawn in the ocean. Based on this new model, peak spawning occurs in the ocean in the fall. In this study, I examine trawl and gill net survey data collected by the NCDMF to evaluate the use of these surveys in assessing the spawning stock. The demographics of female crabs caught in each survey indicate that gill net survey data collected year-round in east Pamlico Sound may provide a better estimate of spawning stock abundance than trawl survey data collected in June and September in central and west Pamlico Sound. A comparison of the east gill net survey data with post-larval settlement in the estuary suggests that a cumulative index, which would provide us with an estimate of the total number of crabs migrating to the ocean each year, would be a more accurate reflection of the spawning population than a monthly index.
Open Access
REDUCING SEA TURTLE DAMAGE TO CRAB POTS USING A LOW-PROFILE POT DESIGN IN CORE SOUND, NORTH CAROLINA
(2002) Marsh, Jesse C.
The blue crab (Callinectes sapidus) supports North Carolina's most valuable commercial fishery; the value of hard blue crabs landed in 2000 was over $30 million dollars. This lucrative fishery may be adversely affected by loggerhead sea turtles (Caretta caretta), which are listed as threatened under the Endangered Species Act of 1973. Crabbers in Core Sound, North Carolina, report that sea turtle damage to crab pots has become an increasingly serious issue. Turtles damage crab pots by overturning them while trying to get the bait, tearing up the bottoms and sides of the pots; this damage results in higher gear replacement costs and losses in crab catch. Experimental fishing was conducted to test for differences in crab catch and pot damage using three types of crab pots: low-profile, square mesh, and hexagonal mesh. The hexagonal mesh pot is the most common pot type used by crabbers in Core Sound, and the low-profile pot was designed to reduce the sea turtles' ability to overturn the pots. The number and size of all crabs caught in the experimental pots were recorded. An analysis of variance (ANDVA) was used to analyze the relationship between number of crabs caught per pot and the effect of pot type, location, date, the interaction of date and location, and the interaction of pot type and location. Tukey-Kramer multiple comparison tests were used to determine significant differences among treatments. There was no significant difference in crab catch between the low-profile and the square mesh pots at any of the three experimental fishing locations. There was a significant difference in catch between the low-profile and hexagonal mesh pots at one location. The lowprofile pots sustained considerably less damage than both the square mesh and hexagonal mesh pot types. In interviews with 19 Core and Pamlico Sound crabbers, crabbers estimated that 62% of all crab pot damage, and 37% of lost crab catch, is due to sea turtle damage. The low-profile crab pot has the potential to improve this situation by allowing crabbers to maintain crab catch with a reduction in gear replacement costs.
Open Access
Sea Turtle Damage and Bycatch in North Carolina's Blue Crab Fishery
(2006) Avissar, Naomi
In North Carolina’s sounds, loggerhead sea turtles are causing significant economic problems for blue crab fishermen by damaging crab pots, stealing bait, and reducing crab catch. This may be causing the fishermen to change their fishing locations, moving their crab pots further towards shore where they potentially encounter more bycatch of species that tend to be found near shore, such as diamondback terrapins. Loggerheads are a federally threatened species, and most of the loggerheads that interact with crab pots in North Carolina’s sounds are large juveniles, one of the most sensitive stages of their life cycle (Crouse et al. 1987). To exacerbate the problem, the state’s blue crab fishery is threatened by pollution, nitrification, and overfishing, and is listed in the “concern” category by the NC Division of Marine Fisheries. The loggerhead-fishery conflict could worsen as blue crabs are depleted, because turtles and fishermen that are drawn to the same prey may aggregate in smaller patches of crab availability, increasing probability of overlap. Due to these issues, and those associated with bycatch, careful management of the blue crab resource and the turtle interaction in the fishery is crucial. I conducted a collaborative fishing study with commercial crabbers to characterize location, timing, and extent of sea turtle damage to their crab pots, and tracked crab catch and bycatch in each pot. I examined spatial and temporal overlaps of crabbing with sea turtles and bycatch, and documented turtle-damage hotspots. Though over 990 animals were captured as bycatch, no clear spatial pattern was detected. My results may guide crabbers to times and areas of minimal overlap, where they should concentrate their fishing effort to minimize economic and ecological damages. This document describes the results of this research, and provides ecological, economic, and political analysis of the conflict.
Open Access
Spawning Biology of Female Blue Crabs, Callinectes Sapidus
(2009) Darnell, Michael Zachary
This dissertation investigated spawning biology of female blue crabs, Callinectes sapidus. Females mate following the terminal molt and undertake a spawning migration seaward, producing multiple clutches of larvae. To examine lifetime reproductive potential of female crabs, individual crabs were confined in the field from terminal molt to death. Crabs produced up to 7 clutches over 1-2 spawning seasons and survived up to 394 d after the terminal molt. Time to first clutch and time between clutches were positively correlated with carapace width and best described by degree-days. Size at maturity was negatively correlated with water temperature on the day of the terminal molt. Most measurements of clutch quality and larval fitness were similar for all clutches. The percentage of embryos developing normally decreased 40% from clutch 1 to clutch 4 and clutch volume decreased 50% from clutch 1 to clutch 5. Thus, most of a crab's reproductive output is from the first few clutches.
Using swimming and abdominal pumping assays, the roles of pheromones in larval release and migratory behavior were investigated. Following delivery of egg extract, bradykinin (a pheromone mimic), and trypsin (an enzyme that generates peptide pheromones), ovigerous crabs responded with increased abdominal pumping, indicating that peptide pheromones stimulate larval release in blue crabs. Ovigerous crabs responded with increased swimming following delivery of egg extract, but not following delivery of a peptide pheromone mimic or an enzyme that produces peptide pheromones. These results suggest that some substance generated from the egg mass stimulates vertical swimming, but that peptides alone do not stimulate swimming. A blend of molecules, possibly including sugars, may be the cue that stimulates swimming behavior.
Endogenous rhythms in vertical swimming, a mechanism underlying migration in tidal estuaries, were examined in the laboratory under constant conditions in juvenile females, recently-molted females, and females with mature ovaries from Beaufort, NC. Rhythms were variable in each stage, though circatidal rhythms consistent with ebb tide transport were observed in juvenile females and recently-molted females. Crabs with mature ovaries typically swam around the time of high tide. Rhythms were also examined for ovigerous females collected from estuaries with three different tidal regimes: semi-diurnal, diurnal, and non-tidal. Crabs from the tidal estuaries had circatidal or circalunidian swimming rhythms with period lengths corresponding to the tidal period of their home estuary. Swimming occurred primarily on ebb tide. Crabs from the non-tidal estuary had a circadian rhythm of vertical swimming around the time of sunset. Such a rhythm has no obvious migratory significance and migration likely takes place though another mechanism.
Swimming behavior was also examined in the field in one non-tidal site and three tidal sites. Crabs were tethered in the field and swimming was monitored using archival pressure tags. Crabs tethered in the non-tidal site did not swim, possibly due to the lack of necessary environmental cues. Crabs at the tidal sites swam primarily on ebb tides. Swimming was greatest at the deepest site, which also had the strongest currents. This site is known to be a migratory area for spawning blue crabs. Decreased swimming behavior was observed at the two shallower sites, including one site that is known to be habitat for all stages of blue crabs. These results indicate that swimming behavior is variable among different areas in a single estuary. In areas where swimming is reduced, crabs may continue migrating seaward by walking or may spend additional time in that area to forage. Within each site, peak swimming generally occurred during the time of the most rapid decrease in water level, suggesting that hydrostatic pressure may serve as a cue for swimming.
Mark-recapture studies were conducted in three rivers (North River, South River, Adams Creek) in eastern North Carolina, and recently-molted female crabs were tagged to ensure a relatively constant time since molting. Most crabs traveled relatively short distances and were recaptured before producing a clutch of eggs. Individuals that moved substantial distances typically moved down-estuary. The Adams Creek canal, connecting Adams Creek with the Newport River estuary, functioned as a migratory corridor, as crabs from both Adams Creek and South River migrated down the canal, presumably using ebb tide transport. Many of the crabs that migrated down the canal into the Newport River were recaptured while ovigerous. Results of this study support the hypothesis that rapid long-distance migratory movements do not begin until production of the first clutch of eggs, though some down-estuary movement takes place by prior to production of the first clutch of eggs.
Female blue crabs mate following the terminal molt and begin moving seaward soon thereafter by walking and swimming. Once the appropriate salinity (> 22 ppt) is reached, the first clutch of eggs is produced and migration rate rapidly increases. Blue crab spawning biology should be similar throughout the range of the species. After taking latitudinal temperature variation and other local variables into account, results presented here should be applicable not only to blue crabs in North Carolina, but in other areas as well.
Open Access
What can be done to save the east coast blue crab fishery?
(2009-04-24T17:24:37Z) Sartwell, Tim
The blue crab (Callinectes sapidus) is a decapod crustacean that inhabits estuarine and marine ecosystems of the western Atlantic Ocean. Blue crab is the largest and most valuable fishery for Maryland, Virginia and North Carolina. In 2007 the blue crab fishery in the Chesapeake Bay crashed. Maryland and Virginia experienced the lowest landing levels since landings data were first recorded in 1950. As a result, I chose to investigate the east coast blue crab fishery and develop recommendations to improve blue crab populations of the Atlantic states. I analyzed blue crab landings data and management for all east coast states that report commercial landings to the National Marine Fisheries Service. In 2007 approximately 81.5 million pounds of blue crabs were landed by New York, New Jersey, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia and the east coast of Florida. The Atlantic coast landed almost 14 million pounds less blue crabs in 2007 than in 2006. Maryland saw the largest drop between 2006 and 2007 at almost seven million pounds, while Virginia and North Carolina both saw a drop of over three million pounds each. Most of the states analyzed showed a recurring pattern of a peak harvest in the mid-1990’s followed by a profound crash to the low landings seen today. As a result of the crashing blue crab populations, I developed a suite of recommendations to improve populations coast wide as well as coordinate blue crab management. First, blue crabs should be managed in two regions, North and South, split at Cape Hatteras, North Carolina. Second, female crabs need to be protected from havest pressures, especially sponge crabs. Third, dredging for crabs disproportionately targets fecund females so crab dredging should be banned coast wide. Finally, coastal ecosystems are severely degraded and tougher regulations and enforcement is required to preserve blue crab habitat.