Institute of Marine Sciences, University of North Carolina, Morehead City, North Carolina, USA
Received date: June 29, 2016; Accepted date: July 15, 2016; Published date: July 30, 2016
Citation: Schwartz FJ, Perschbacher PW (2016) Callinectid Crab Abundances, and Movements of Tagged Blue Crabs (Callinectes sapidus) in the Cape Fear River and Adjacent Waters, North Carolina. J Fisheries Livest Prod 4:196. doi: 10.4172/2332-2608.1000196
Copyright: © 2016 Schwartz FJ, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Callinectes sapidus; Blue crabs; Tagging; Cape Fear River; Impinged
An intensive six year survey of the Cape Fear River and adjacent waters (1973-1978) was initiated to determine of the effects of the CP&L (now Duke) Brunswick 1,979 MW nuclear power plant, located four km north of Southport, North Carolina (Brunswick County) on the biota, especially crabs, of the area. Blue crabs, Callinectes sapidus Rathbun, 1869, are an important North Carolina resource for commercial fisherman and the public. Blue crabs are captured as hard and soft shell crabs using: dip nets, troll lines, baited crab pots, gill nets, pound nets, haul seines and otter trawls, sell for as much as $55/dozen. Would the power plant manmade intake canal flow affect the blue crabs frequenting the Cape Fear River and adjacent waters? Would tagged blue crabs, by sex, stay in the river? What were their environmental conditions: water temperatures, oxygen contents, salinities they endured during the six year surveys?
Cape Fear River flowing southward of Wilmington, NC (New Hanover County is a coastal, two-layered, 1.2-3.2 km wide estuary. It experiences 2 m tides, southeast and southwest winds, tropical storms and hurricanes. Its coffee brown waters exit into the Atlantic Ocean via Carolina Beach Inlet on the northeast, the ocean mouth at Southport and the CP&L power plant canal that passes around Southport and into the ocean west of Southport (Figure 1). Abundant precipitation of 127.5 cm/yr (43% is dissipated as runoff, 85 cm is lost to evaporation and transportation) produces flows of 258,000-7.2 million m3/month (Wheeler Pers. Obs.). East and west river shoal substrates are sandy to silty-sand, river navigation substrates are muddy and strewn throughout with water logged trees and stumps, and the substrate is rocky at buoy 18.
Surface and bottom water samples were obtained using a three liter brass Kemmerer sampler. Water temperatures were recorded using hand held Taylor Mercury thermometers. Oxygen contents were determined using the Winkler titration methods. Salinities were determined by using A/O refractometers. Fourteen river channel (1973) and 23 river-shoal stations (1974-1978) stations were sampled using gill nets and semi-balloon otter trawls  (Table 1) Sampling was weekly and daily (five days per week) January-May, September- November, and one week during June, July, and August. The number of stations visited daily depended on available daylight.
|Total Catch All Gears||32,279||35,279||57,996||85,642||1,07,906||1,10,395||4,29,497|
Table 1: Total number of callinectes captured by species and year in the capefear river and adjacent waters 1973-1978 by gill nets, small and large trawls.
Monofilament No. 208 nylon gill nets (91.4 m long, 65 meshes deep, 89 cm stretch mesh) were set at 24 east and west river shoal stations. Soak time was one hour/set. A 6.1 m skiff towed a 9.2 m wide semiballoon otter trawl for 15 minutes at all shoal stations. Deep water, CBI and intake canal stations (Figure 1) were sampled by either the 13.3 m R/V Sara Helen or the 19.3 m R/V Machapunga towing a 12.5 or 15.5 m semi-balloon otter trawl.
Varied numbered and addressed, colored 6 × 24 mm plastic strap tags, held in place by wires wound around the lateral carapace spines, were attached across 120-170 mm crab carapaces. Tag number changed every 1,000 specimens. Most blue crabs were tagged during September- October of each year. A small reward was paid for the return recapture information, location, and date located on the numbered and addressed tags. Additionally, large number of fish and shrimp were tagged and recaptures analyzed .
Numbers of impinged tagged crabs were determined from sampling of screens from the inflow of river water in the intake canal (Figure 1) by the North Carolina State University concurrent study. Percentage impingement was determined by dividing the number impinged by the number tagged at various stations.
Surface river waters flowed faster than substrate waters (Pers. Obs.). Water temperatures were lowest in January (mean 4°C) with extreme lows in 1976-1977 that froze many shallow areas of the river, and highest in July and August (mean 23°C). Oxygen levels were highest in January (mean 12.2 ppm) lowest in July-August (mean 3.2 ppm). Salinities were 0-4 ppt at buoy 42 and increased to 32 ppt at the river mouth.
Overall, 429,497 fish, shrimp, and crabs were collected during this six year survey. Callinectid crabs accounted for 81,208 (Table 1): Callinectes larvatus (8, Callinectes danae (3) C. ornatus (436), C. sapidus (58,087), and C. similus (11,048). C. sapidus Rathbun 1869, the most abundant crab, occurred throughout the fresh water and saline river waters; and was especially caught at the canal mouth (5,048) CBI inlet (4,240) and buoy 19 (1,756) (Table 2). They tolerated water temperatures 4-32°C, oxygen 4-12 ppt, and salinities 0-32 ppt. C. larvatus Ordway 1863, C. similus, C. danae, and C. ornatus preferred higher saline waters south of buoy 18 and at CBI inlet (Figure 1 and Table 3).
Table 2: Total effort and number of blue crabs tagged by station and years, 1973-1978, in the Cape Fear River and adjacent areas.
|Adjacent ocean||Lower river 1||Middle river 2||Upper river 3||Total|
Table 3: Number of blue crabs tagged by major geographic areas of the Cape Fear River, 1973-1978.
Male C. sapidus preferred low level salinities (Table 2). Males moved throughout the river, mated, and wintered in the river substrates. A few moved into the Atlantic Ocean and moved north to Chesapeake Bay. Maximum distance of tag returns by males was short – 25.1-50.0 km, although one moved to Hoopersville, MD, 617 km (Table 4).
Table 4: Male and female blue crabs tagged in the cape fear river, north Carolina.
Female C. sapidus preferred higher saline river waters (Table 2), moved throughout the river system, mated, and exited the river via CBI and the river mouth into adjacent Atlantic Ocean to spawn and live for one or two years before returning to the river. Females traveled longer distances, up to 1,256 km (Table 4) to the Gulf of Mexico just west of Key West, Fl. The oddest female blue crab (No. 4326) was tagged near buoy 18, 13 May 1975 and was recaptured alive 2359 days later in the lower Cape Fear River 26 October 1985 . That recapture established a new survival record, as the blue crabrarely live as long as 18 months.
Female catches and those tagged out numbered (25,330) males caught and tagged (9,198) (Table 5). Tagged blue crabs were released at their capture site. Blue crabs tagged with orange-colored plastic strap tags dominated the recaptures, 1,282, yellow were 492, red 593, and green 88. Tags of blue crabs were usually returned within one to three years; although tags shed, caught, or unearthed following storms were periodically returned as late as 2011. Maximum recaptures of both males and females were between 2.1 and 10.0 km from the release points (Table 5). Blue crabs tagged in the CP&L power intake canal were rarely impinged (159, or 3.1% from 1973-1978) in the nearby screens. Only 180 of 34,528 (0.5%) total tagged blue crabs were impinged on the intake canal screens.
|Total of Females for 1974-1978||1626|
|Total of Males for 1974-1978||1178|
Table 5: Blue Crab recapture by distance travelled after tagged during 1973-1978.
Even though others have studied blue crab movements and abundance in North Carolina ; Eggleston et al.  Hill and Fowler 1989 ; Judy and Dudley ; Ramach et al. ; Rittschof et al.  Schwartz ; Schwartz et al. ; Schwartz , their observations while similar to the Cape Fear River and adjacent waters study  did not address power plant intake effects. The low number impinged from this study from blue crabs tagged and released in the canal (3.1% from one of the major capture sites) and from total tagged in the Cape Fear River and adjacent waters (0.5%) indicates little impact from power plant canal screen impingement .
A staff of 52 collected and analyzed the Cape Fear data and published it in six volumes. CP&L funded the 1973-1978 study of the Cape Fear River. Ginni Purifoy typed the text.
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