BULLETIN OF MARINE SCIENCE, 61(2): 327–342, 1997 BIOLOGY OF THE STRIPED CUSK-EEL, OPHIDION MARGINATUM, FROM NORTH CAROLINA Frank J. Schwartz ABSTRACT Nearly 2500 striped cusk-eels, Ophidion marginatum, were collected during a 6-yr intensive, 22-station trawl sampling of the Cape Fear River and nearby Sound and Atlan- tic Ocean areas in 1973-1978. Problems existed in confirming the specimens were O. marginatum rather than the similar appearing and ranging crested cusk-eel, O. welshi. The taxonomy remains unresolved but radiographs confirmed the North Carolina speci- mens were O. marginatum. Catch/effort and repetitive yearly sampling was compared by month, capture by size and station, morphometric relationships, age and growth, crest development, and food analyses. The study revealed O. marginatum was more active than previously believed, males and some females developed head crests, females were larger than males in size and many body-organ relationships, and females attain age 4 while males live for 3 yrs. O. marginatum feeds on a variety of foods, primarily crusta- ceans and fishes. Much remains to be learned of this elusive and systematically confus- ing species. Cohen and Nielsen (1978) reviewed the taxonomy of the Ophidiiform fishes, a group that includes the subfamily Ophidiinae (Pisces: Ophidiidae) which are mostly shelf- water inhabiting species (Gordon et al., 1984; Nelson, 1994). At least two similar and perhaps conspecific species pairs of cusk-eels, genus Ophidion, occur in the western Atlantic Ocean (Lea, 1980). One pair includes Ophidion (= Rissola) marginatum (DeKay, 1842) (striped cusk-eel) and O. welshi (Nichols and Breder, 1922) (crested cusk-eel). O. marginatum ranges from New York to northeastern Florida, O. welshi, from Georgia to northwestern Florida and the northern Gulf of Mexico (Fahay, 1992; Robins and Ray, 1986). Larvae and transformed specimens of O. welshi are now known from at least New Jersey southward (Fahay, pers. comm.). O. marginatum and O. welshi are similar in appearance, but their taxonomy is far from resolved. Both species possess horizontal stripes on the body and adult males are known to develop crests. Although Fahay (1992), Gordon et al. (1984), and Miller and Jorgensen (1973) presented meristic data that was intended to separate the two species, broad over- laps exist in meristic counts. Clearly the taxonomic relationships of the two species is not resolved. Little or no detailed information pertains to life history aspects of either species, other than size and sexual dimorphism (Robins, 1960) and nocturnal and burrowing behavior (Greenfield, 1968; Herrera et al., 1985; Hoese and Moore, 1977; Retzer 1991; Robins and Böhlke, 1959). Retzer (1991) examined life history aspects of 390 O. welshi from off Texas, and Courtenay (1971) and Rose (1981) noted crest development in O. marginatum from the western Atlantic. Capture of 2420 O. marginatum from 1973-1978 in the Cape Fear River North Caro- lina permitted studies of sizes, crest development by sex, morphometric and body organ relationships, length-weight relationships, catch effort, ages, and food habits. 327 328 BULLETIN OF MARINE SCIENCE, 61(2): 327–342, 1997 METHODS From 1973 to 1978, a 22-station survey was made of a 7854 ha area, that included the Cape Fear River and nearby areas, Masonboro Sound, the river from buoy 42 near Wilmington, North Caro- lina, southward for 17 km to and including the adjacent Atlantic Ocean (Fig. 1). Sampling was done with 7.6 and 12.2 m semi-balloon otter trawls and consisted of 3196 small (38.6%) and 5088 large otter trawl tows (61.4%). Sampling occurred during 0.25 h daylight tows. Time and direction of sampling usually was influenced by prevailing water currents, numerous hangs, and commercial ship traffic. Sampling occurred twice each January, weekly from February through May and Sep- tember through November, and half of December. June, July, and August of each year were sampled monthly. See Schwartz et al. (1982) for additional descriptions of each station’s substrates, physi- cal, and chemical features. Species determinations were made by examining and comparing radiographs produced by a Picker Hot-shot X-ray unit of O. marginatum from North Carolina and O. welshi (UF O37996) from the Gulf of Mexico: Fifty-eight percent of the specimens captured (1403) were measured and exam- ined in detail for sex, age and growth, body-organ and morphometric relationships, and food analy- ses, 210 (8.7%) were measured but not worked up or sexed, and no lengths were taken of 807 (33.3%) specimens (Table 1). Several lots of the 1973 specimens were deposited in the IMS-UNC fish collection at Morehead City, North Carolina. Largest catches occurred in 1974 (1088 speci- mens) and 1978 (589). All O. marginatum were immediately preserved in the field in 10% formalin. Laboratory analy- ses consisted of measuring head (HL), eye (E), standard (SL), and total (TL) lengths in millimeters (mm). Total body (BW), liver, and intestines were weighed to the nearest 0.01 g. Eye, heart, gonads, kidneys, and spleen weights were expressed in milligrams. Several body relationships were examined for each sex: SL/TL, HL/SL, E/SL, E/HL, SL/BW, TL/BW, and E/BW. Morphometric and body-organ weight relationships were determined by the formula log y = a + b log x. Ages were determined by noting evident annuli on each vertebra. Measurements from the focus to each annulus and the outer edge of each vertebra permitted back calculations of length at each age using the formula log y = a + b log x. Stomach and intestine food contents were examined in 549 males and 854 females. Each food eaten was determined as percent fullness, percent vol- ume, and percent frequency of number. Each food item was determined to the lowest possible taxon and an index of relative importance (IRI, Pinkas et al., 1971) was calculated where IRI = (%N + %V) . %F, N = numerical percentage, V = volumetric percentage, and F = frequency of occur- rence percentage, as a means of ranking the percent each food was found in either the stomach or intestine. Head crest formation was determined by external and internal visual examination of each speci- men, as external examinations alone were often misleading. Crests, depending on sex and time of year captured, were often not visible on males or females. Gonads were examined and verified the sex of each individual. OBSERVATIONS Combining ranges given by Fahay (1992), Gordon et al. (1984), and Miller and Jorgensen (1973), O. marginatum has 52-55 caudal vertebrae (vs. 50-52 in O. welshi), 138-162 dorsal rays (vs. 128-150) and 116-131 anal rays (vs. 105-122). North Carolina specimens possess 15 precaudal, 53-54 caudal vertebrae (total 68-69), 149-155 dorsal, and 118-124 anal rays indicating the study specimens were O. marginatum. CATCH/EFFORT. — Over 2 million fishes were collected during the 6-yr sampling period (Schwartz et al., 1982) of which 2420 were O. marginatum. Two hundred thirty-five of the 2420 O. marginatum were captured during the 6-yr sampling efforts in small trawls SCHWARTZ: BIOLOGY OF THE STRIPED CUSK-EEL 329 Figure 1. Location of river-channel and shoal otter trawl stations ( ■ ) sampled in the Cape Fear River and adjacent waters between 1973 and 1978. Buoys ( ● ), CS = CPL intake Canal Screen Station. 330 BULLETIN OF MARINE SCIENCE, 61(2): 327–342, 1997 fosrebmuN.1elbaT mutanigram.O ro,dexestontubderusaem,dexesdnaderusaem,thguac reviRraeFepaCehtni)htuosothtron(snoitats22taslwartegraldnallamsyb,nekathtgnelon .8791-3791saeratnecajdadna laohSdnalennahC raeY S3noitat 149715971697179718971l97Tota 433732E 1 4112 46172W C246BIN C4BIS3222331317 121274 31283 227 1421 233E 14252513 213 132533532001 29W3 383963187 C8S 985815641611 C1B2 3610 C2B1 158 C2M8111 179E1413111174 189 11081116247 18W9 12545263 12E8 8125121301 188 1071814856 198W 124117 O5C1,23644312723742 T0lato 281180820152569850242 Mderusae— 04001625057211131%4058.0 wdekroup Measured— 93923 7033012%7.8 notworkeduporsexed N7el.onshtg 111834388354478%033.3 Eot-troffws S3martllawl 304417459766674156319 L1egraartwl 51761919500151506884508 Cnahlenoitatssn=42,22,71,31,98 Shlaooitatssn=424,E2WC,BINC,B1,SI72,432,E3W1,91,E9W1,81,E8W Powre-tnalpClanaoitatssn=C,SCB,2CB,ICM 0=O,naecCS=ClanaSsneerc while 2185 were collected by large trawls. Largest, combined sampling efforts occurred in 1975-1977, with 1662, 1684, and 1681 tows made each year respectively (Table 1). SIZE/YEAR. —Overall, captured O. marginatum ranged from 41-245 mm TL (Table 2, Fig. 2). Mean sizes for the 1403 specimens measured and examined in detail (Table 2), regardless of sex, ranged 132.8 (in 1977) to 161.1 mm TL (1978). Smallest specimens were collected in 1976 and 1977 while the largest individuals occurred in 1974 (Table 2). SCHWARTZ: BIOLOGY OF THE STRIPED CUSK-EEL 331 Table 2. Numbers, sizes, and ranges of 1,403 O. marginatum captured in the Cape Fear River and adjacent areas 1974-1978; regardless of month and station of capture. YNXerae Rang 189749391548.89-24 14975 2341135.48-22 16976 601048.41-21 14977 281332.42-20 11978 711061.50-23 NUMBER/MONTH/YEAR. —Most specimens were captured between March-May or De- cember (1971 specimens) with lesser numbers during other months (Table 3). Mean sizes and ranges (Table 3) varied greatly between month and years captured. May 1975 (48 mm TL) and March 1977 (42 mm TL) produced the smallest specimens captured. Largest individuals were caught May 1974 and 1978 respectively (245 and 230 mm TL) (Table 3). CAPTURE/SIZE/STATION. —The Carolina Power and Light Company intake canal screens station with a newly dug muddy substrate (CS, Fig. 1, Table 3) produced 1161 specimens, 988 of which were captured in 1974. Eighty-three (92-220 mm TL) of the 988 were captured in February 1974, 163 (91-224) in March, 292 (103-210 mm TL) in April, 242 (115-212) in May, 45 (134-217) in June-July, two in October (97-157), and 171 (112-123) in December.