SCH WART/ AND PORTER: FISHES. MACROINVERTEBRATES OFF NORTH CAROLINA 



TABLE 2.— North Carolina calico scallop production, 1972. ' 

 (No production in November and December] 



'Data supplied by the National Marine Fisheries Service Statistical Office. 

 Beaufort. N.C.. and Chestnut and Davis 1975. 



METHODS 



Sampling Vessels 



Two types of vessels were used to sample the 

 offshore North Carolina calico scallop beds. Com- 

 mercial fishing vessels, from which most of the 

 samples were obtained, were the 25-m MV Ensign, 

 a side trawler of Gloucester design and the 15-m 

 MV Seven Brothers, a double rigged shrimper de- 

 sign. Research vessels include the RV Beveridge, a 

 17-m shrimp trawler which was chartered 

 monthly to collect additional samples or to main- 

 tain anchored equipment, and the Duke Univer- 

 sity 33-m RV Eastward, a side trawler of Glouces- 

 ter design. One bottom observational cruise was 

 accomplished by using RUFAS (Anonymous 1969) 

 aboard NOAA RV George M. Bowers. Two addi- 

 tional samples, 23 April and 27 June, were also 

 obtained while returning from other Eastward 

 projects. 



All commercial or chartered vessels towed one 

 or two 10-12 m scallop trawls (Rivers 1962) which 

 were modified to have heavily weighted foot lines 

 and heavy-duty chaff gear on the cod end. The 

 trawl on theBeveridge was rigged the same as that 

 of the commercial vessels except that the foot line 

 was the standard weighted loop chain design pre- 

 ceded by a light tickler chain. Mesh size of all 

 trawls was the standard flat shrimp type. Sam- 

 pling tow interval varied on the commercial ves- 

 sels by season as a function of scallop abundance. 

 Beveridge or Eastward tows were kept to 15 min. 

 Sample tow distances, by commercial vessels, var- 

 ied Va-V-z km, whereas Beveridge and Eastward 

 tows were Va km. No effort, by type of vessel, was 

 made to sample with or against the current. 



Environmental Data 



Salinities were determined from the water sam- 

 ple by using a direct reading American Optical 

 Corp. 2 refractiometer. 



Chlorophyll a was determined spec- 

 trophotometrically for 19 stations (Figure 2) fol- 

 lowing the methods of Strickland and Parsons 

 < 1968) and expressed as milligrams per cubic me- 

 ter. 



A Braincon 381 current meter was anchored and 

 buoyed at the northwestern edge of the commer- 

 cial grounds. Excessive fouling during much of the 

 sample year by hydroids, sponges, and tunicates 

 prevented precise long-term bottom current data 

 being recorded at the surface of the bed. After 

 rebouying the meter to record currents 30 cm 

 above the bed, current data obtained over a 26-day 

 period, mid-August to mid-September, indicated a 

 northeastward current drift component 

 (Schumacker 1974). 



Sediment samples taken by Peterson (Bev- 

 eridge) and Shipek (Eastward) grabs (Figure 3) 

 were frozen until grain size and organic determi- 

 nations could be made. Pretreatment for grain- 

 size analysis included washing each sample in a 

 large volume of fresh water and then decanting 

 after all sediment had settled. Washing was done 

 to reduce weighing errors induced by salt crystals. 

 Following decanting, sediments were oven dried 

 at 85°C and separated into sediment sizes by a U.S. 

 Standard Sieve Series and mechanical sieve 

 shaker. All samples were in the shaker for at least 

 2 h. Analysis of data followed Morgans (1956). 



Percent organic material was determined from 

 1 to 2 g unwashed subsamples which had been 

 oven dried for 48 h at 85°C. The amount of organics 

 was assumed to be the difference in sample 

 weights before and after firing at 500°C for 2 h. 

 This followed a technique used in the Marine Sed- 

 iments Laboratories of Oregon State University 

 (J. Paul Dauphin pers. commun.). 



An attempt was made to develop a fast method 

 for percent organic determinations of marine sed- 

 iments through the manufacturer's suggested use 

 of a Coleman Model 33 Carbon-Hydrogen 

 Analyzer, rented from the Duke University 

 Marine Laboratory. Comparison of data, by statis- 

 tical means, showed no correlation between 

 analyzer and ovenfired organic values from 

 offshore marine sediments. 



Water temperatures were obtained with a mer- 

 cury thermometer immersed in bottom water ob- 

 tained by a 3.1-liter Kemmerer sampler. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



429 



