• Abstract and Figures
• Public Full-text

A FEVIEW OF THE OCEANOGRAPHY AND FISHERY OF ONSLOW BAY, NORTH CAROLINA by William L. Kruczynski Department of Biology Hartwick College Oneonta, New York Research supported by Environmental Analysts, Inc., Garden City, New York Printing of this publication was financed by the North Carolina Division of Commercial and Sports Fisheries, Department of Natural and Economic Resources, and incorporated as Information Series Number 6 in the Division's information series. Printed: May, 1974 CONTENTS General description ........... " " "." .... page I Biogeography ............................... I weather .................. " . •. 2 Depth •..................................... 2 lleef s Shelf edge........ .. .. .. .. .. .. .. ... 2 Coral heads.. .. J Water movements Tides ................................. J Currents. .. J Geology .................................... 4 Salini ty •.............•............. , ...... 5 Tempera ture .............................. " 5 Density ....................•............... 6 Tur bidi ty. • . • . .. 6 pH •.•••••.•..••.••..•••••••••...•••.•..••.• 6 Oxygen .........•......................... " 6 Nutrients. .. 7 Benthic algae Genera1. .... , . " ........ , ..•.......... 7 Coral heads ............. ". .. 7 She].f -edge reef.. • . .. 8 Near shore algae... .. 8 Phytoplankton. • . .. 8 Zooplan.ltton. .• 8 Benthic invertebrates InfaUIl£i. • . .. 9 EpifaUIla ..•........................... 9 Commercially important species •....... IO Fishes Genera1. ........... , .............. , " .11 Commercial areas~ ........... ~ ....... .. 12 Fishery statistics ....•........•.....• 13 CODMercially important species •....... 13 Sports fishing ........................ 15 CONTENTS (cont.) Birds ..••...••.....•.•..••..................•.....••• Page 1'5 Turtles ..•.......•..•.•. " ....•.•.......• , •.•.•.•.••••.... 16 Mammal s .....•...•....••.•.....••.......•.••..••••...•.•..• 16 List of tables Table 1. Climatological data ........................ 17 2. Physical and chemical data .••.•.••.•..•...• 18 3. Benthic algae on coral heads .••.•.•.•.....• 19 4. Benthic algae near shore .••.•.....•••.••..• 20 5. Benthic algae in Beaufort harbor ••.••...••• 21 6. Phytoplankton .•••..•...••......•...•.•....• 22 7. Seasonal occurrence of zooplankton ••.•....• 24 8. Common benthic invertebrates .•••...••..•••• 25 9. Common fishes .............................. 28 10. Fishes on coral heads .••.•••..•••....••.•.• 30 11. Fishery data, 1971. ........................ 31 12. Sport fi shing facilitie s ..•.•••..•••••••••. 32 13. Oceani 0 bird s ••.••••••••.••••.••••••••••.•• 33 Figure 1. East coast of the United States .....•...... 34 2. IDeation of coral patched and shelf-edge reef .•..........•.......................... 35 3. IDcation of calico scallop beds .•.......... 36 4. Loca tion of conunercial shrimp grounds ...... 37 5. IDeation of menhaden fishing grounds ....... 38 Li tera ture oi ted. .. .39-47 1 GENERAL DESCRIPTION The waters off North Carolina have been intensively studied because of their unique biogeographic position and the presence of three rrarine laboratories in the Beaufort-Morehead City area. This paper is a review of the phYSical, chemical, and biological oceanography of On aIm. Bay, North Carolina and a summary of fishery statistics of the area. The coastline of North Carolina is composed of a series of outer banks which enclose an extensive estuarine system. A main feature of the outer banks is a series of capes which protrude into the ocean and delineate three embayments: 11i11eigh Bay, Onslow Bay, and Long Bay (Figure 1). The outer edge of these bays, the edge of the continental shelf, occurs at about the 100 fathom contour which ranges from less than 16 miles off Cape Hatteras to greater than 60 miles south of Cape Fear. In all there is about 10,450 square miles of shelf area off North Carolina (Varshall, 1951) ,lith an average slope of less than 1: 900 (Newton and Pilkey, 1969). Onslow Bay is typical of coastal waters of the Carolinas. It is bounded to the north by Cape Lookout and to the south by Cape Fear and has about 100 miles of shoreline. The origin of it and other Carolina Bays has been subject to much speculation. Abbe (1895) suggested that a back eddy of the Gulf Stream, which passes offshore, may have produced the bays. This hypothesis is supported by the south and southwest movements of inlets and shore prominences and MacCarthy's (1931) jntc;rpretation of currents as indicated by sand grain size. Rude (1922) op­ posed Allbe i s theory and stated that main currents correspond to wind direction, and suggestl3d that strong winds must have molded the shoreline. J'ohnson (1919) discussed certain types of norrral wave action and the influence s of prominences of the inner shoreline as alternative explanations for the cuspate coast. The Bays have also been discussed by Richards (1950). The forrration of the capes which border the Bays has also been investigated. Cape Fear, for instance, had its origin in the falling Talbot Sea which exposed Cape Fear coquina rock (Wells, 19~,~,). Shore changes which have occurred at Cape Hatteras are reported by Rude (1922). BIOGEOGRAPHY The east coast of the United States is divided into three marine biogeographic provinces containing assemblages of organisms which typify the areas. Good general accounts of marine biogeography are given by Hutchins (1949), Hedgpeth (1957) and Glover (1961). The Virginian Province occurs north of Cape Hatteras to Cape Kennedy, and the Tropical Province occurs from Cape Kennedy southward. The warm-water Gulf Stream flows from the Straits of Florida along the edge of the continental shelf at a velocity of about 3 knotts off Cape Kennedy and 1 knot off Cape Hatteras. At Hatteras the Gulf Stream turns seaward and continues flowing north Dome distance off the coast. There thus is a sharp terr.perature barrier at northern forms above the cape (Vernberg and Vernberg, 1970a). Judging from relict shelf biota, a similar delrarkation waS present during the 1'1eistocene (MIlliman, Pilkey and Blackwe1der, 1968). 2 AnLnal and plant distribution in Onslow Bay is complicated seasonally since the Gulf Stream regularly moves closer to shore in the Carolinas by the actIon of the wind, particularly in the summer during prolonged south- went blows. Webster (1961) and Blanton (1971) noted that tbis warm water nJaos can move as milCh as lC km closer to the shore, thus extending the Trop­ ical Province over the continental shelf. During the winter, the Gulf Stream l!JOve,," farther offshore and a tongue of cold Virginian coastal water moves into Raleigh and Onslow Bays (Gray and Gerame-Vivas, 1963). Virginian forms can thus enter Carolinian waters, such as the northern mussel, Mytilus edulus (Wells and Gray, 1960). Cerame-Vivas and Gray (1966) discussed the distribution of benthic invertebrates on the Carolina continental shelf in light of what is mown about seasonal shifts in this al'ea~ WEATHER The coa<3t of North Carolina has a mild climate. Summer days are usually cooler than the mainland and temperatures greater than 95()F are a rarity. The following data are summarized from NOAA Cape Hatteras weather station for 197L Carney (1955) gives nearly identical data. Mean annual temperature is 62.Jo F, annual precipitation about 55" and 26 days per year are below freezing. Average temperature in Ju~y and August is 78. 90 F and the wind is predominantly from the southwest. Mean monUtly values of temperature, rain, and wind for 1971 are given in Table 1. Storms along the coast are common and one hurricane warning per year can be expected. Bad weather has accounted for many shipwrecks, especially at the capes, 'lhose attendant shoals produce powerful currents and seas. Newton, Pilkey and Blanton (1971) give the following summary of storms: The storms on the Carolina coast tend to be cyclic and can be categorized as either hurricanes or coastal lows associated with passage of cold fronts. Both types of storms have produced massive disasters to the Carolinas during historic times. Hurricanes normally occur from June to October and passage of cold fronts normally during November through ]Varch. The passage of cold fronts results in clockwi se shifts in wind direction from southwest to north­ east. Ships .seeking shelter from southwest winds in the lee of the capes have been pushed into the shoals as the wind shifts to northeast. No less th.an 150 ships are on the bottom of Onslow Bay, most occurring at Cape Fear and Cape Lookout. DEP'l'll Newton and Pilkey (1969) and Newton, Pilkey and Blanton (1971) give detailed maps of the bottom of the continental shelf and edge off North Carolina. Minor surface undulations have been found to occur along the shelf, being particularly prominant near the capes. The shoals near the capes are the largest topographic features on the shelf. The depth 1 to :3 miles from tne shore is 40 to 50 feet. She] f Edge At the rJhelf break in Onslow Bay the bottom is raised to about 40 to 80 meters for a distance of about 80 miles parallel to the shore (Figure 2). J This reef area is about 70 km from shore and has been dated at about 20,000 years B.P. It probably represents the edge of the sea at that time (MacIntyre and Milliman, 1970). Thi3 reef has been built by a calcareous algae (Litho­ tharnnion) and no reef-buUding corals have been found (Menzies et a1., 1966). Biota of this reef area are described in Pearce and WUliams, (1951) and Menzies et al. (1966). The latter give a detaUed description of the topography, hydrography, geology and biota

Load more

  51

Copy Link