THE OCCURRENCE OF ELVERS OF 



SYNAPHOBRANCHUS AFFINIS ON 



THE CONTINENTAL SLOPE OFF 



NORTH CAROLINA' 



Members of the family Synaphobranchidae are 

 demersal eels which are widely distributed in the 

 Atlantic and Indo-Pacific oceans (Castle 1964). 

 Data from a June 1973 cruise in the Norfolk 

 Canyon area indicate that they are an important 

 part of the fish community in both numbers and 

 biomass in depths around 1,000 m (Virginia Insti- 

 tute of Marine Science unpubl. data). Bruun (1937) 

 reported on the life histories and larval develop- 

 ment of several synaphobranchids, and Castle 

 (1964) listed synonomies in addition to keys to 

 genera and species. Robins (1971) gave os- 

 teological, meristic, and morphometric data and 

 also discussed the life history and ecology (Robins 

 1968). 



Although Robins (1971) intensively examined 46 

 Synaphobranchus affinis Gunter 1877 greater than 

 193 mm in total length, the occurrence of elvers or 

 unpigmented juveniles of this species is unre- 

 ported. The purpose of this report is to provide a 

 record of capture, meristic and morphometric da- 

 ta, and some observations in food habits of S. 

 affinis elvers. 



Materials and Methods 



A total of 89 elvers of S. affinis (Figure 1) were 

 collected during a y2-h otter trawl haul from 1745 

 to 1815 h EST aboard the RV Eastward on 29 April 

 1973 at Eastward station 22039, lat. 34°03.2'N, 

 long. 75°52.0'W at depths from 550 to 600 m. The 

 gear used was a 30-foot shrimp trawl with a \4-inch 

 stretch-mesh cod end liner. 



Total length of all specimens was measured to 

 the nearest millimeter. A subsample of 40 elvers 

 was taken for meristic analysis using a table of 

 random numbers (Rohlf and Sokal 1969). Elvers 

 were cleared in 2% potassium hydroxide, stained 

 with alizarin red-S in 2% KOH, passed through a 

 graded series of glycerine, and stored in 100% 

 glycerine to which thymol was added. Three 

 replicate counts were made of the following 

 meristic characters: total vertebrae; dorsal, anal, 

 caudal, and left and right pectoral fin rays; left and 

 right branchiostegals. The presence and position of 

 vertebral deformities (fused or partially fused 



'Virginia Institute of Marine Science contribution no. 652. 



vertebral centra; extra, fused, or distorted neural 

 or hemal spines) were noted and representative 

 types were drawn with the aid of a camera lucida. 



To determine if osteological deformities might 

 result in differential mortality of 5. affinis during 

 later life, 40 additional specimens (^ total length = 

 220 mm, extremes 173-305 mm) collected on 13 

 June 1973 aboard the RV Columbus Iselin in 630 m 

 of water with a 45-foot otter trawl at lat. 

 37°03.2'N, long. 74°34.1'W were examined. These 

 fishes were X-rayed, vertebrae counted, and the 

 presence or absence of deformities noted. 

 Frequency of occurrence of deformities in elvers 

 and larger fish were compared by X^ analysis (Sokal 

 and Rohlf 1969). 



Morphometric measurements were taken 

 following the method of Robins (1971) with either 

 dividers and dial calipers or a binocular microscope 

 fitted with a calibrated ocular micrometer. 



Results and Discussion 



Eels of the genus Synaphobranchus are 

 characterized by confluent branchial apertures 

 with a slitlike opening on the midline of the throat 

 (Robins 1971). Synaphobranchid eels commonly 

 encountered in trawls on the continental slope 

 near Cape Hatteras, N.C. are Synaphobranchus 

 kaupi, S. affinis, and Ryophis brunneus (Markle 

 1972; Virginia Institute of Marine Science unpubl. 

 trawl records). Members of this group show vary- 

 ing degrees of plasticity and overlap in 

 morphometric characters but also show mean 

 differences (Robins 1971). The specific identifica- 

 tion of these elvers as S. affinis, therefore, was 

 based on vertebral counts. 



Mean, 95% confidence interval, and the 

 frequency distribution of vertebral counts are 

 shown in Figure 2. Vertebral counts of the 40 

 specimens had extremes of 130 and 136 with a 

 mode of 134. This is within the range of values for 

 44 S. affinis given by Robins (1971) (x = 133.1, 

 extremes 128-139) and outside the range of the 

 other species of synaphobranchids common to this 

 region {S. kaupi: x = 148.0, extremes 146-150; 

 Ryophis brunneus: x = 147.5, extremes 144-151). 

 Means, 95% confidence intervals, and frequency 

 distributions of other meristic characters are 

 found in Figure 2. Paired t tests (Sokal and Rohlf 

 1969) showed no significant differences between 

 the number of left and right pectoral fin rays (t = 

 1.00, df = 39) or the number of left and right 

 branchiostegals {t = 0.42, df = 39). Dorsal and 



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