Northeast Gulf Science Volume 10 Article 4 Number 2 Number 2

8-1989 Habitat Preferences, Movement, Size Frequency Patterns and Reproductive Seasonality of the Lesser Electric Ray, Narcine brasiliensis Anne Rudlow Gulf Specimen Marine Laboratory

DOI: 10.18785/negs.1002.04 Follow this and additional works at: https://aquila.usm.edu/goms

Recommended Citation Rudlow, A. 1989. Habitat Preferences, Movement, Size Frequency Patterns and Reproductive Seasonality of the Lesser Electric Ray, Narcine brasiliensis. Northeast Gulf Science 10 (2). Retrieved from https://aquila.usm.edu/goms/vol10/iss2/4

This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf of Mexico Science by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. Rudlow: Habitat Preferences, Movement, Size Frequency Patterns and Reprod Northeast Gulf Science Vol. 10, No.2 August 1989 p. 103-112

HABITAT PREFERENCES, MOVEMENT, SIZE FREQUENCY PATTERNS AND REPRODUCTIVE SEASONALITY OF THE LESSER ELECTRIC RAY, Narcine brasiliensis

Anne Rudloe Gulf Specimen Marine Laboratory P. 0. Box 237 Panacea, Florida 32346

ABSTRACT: The lesser electric ray, Narcine brasiliensis, is often used in neurochemical studies of cholinergic neurons. Data on habitat preferences, seasonal movements, growth rates and reproductive seasonality are presented. Narcine brasiliensis is highly localized within an area, concentrating in surf zones adjacent to barrier beaches and on offshore sand bars in warm months and moving offshore in winter. Females larger than 29 em total length are reproductively active and give birth to less than 20 young in August and September. Young are estimated to attain a size of 20 · 29 em TL at the end of their first year. This species is potentially vulnerable to overharvest as a result of its low rate of reproduction and localized distribution.

Over the past decade there has been been the model used in 45 neuro­ a growing use of electric rays of the chemical studies reported in Biological family Torpedinidae, order Rajiformes, in Abstracts since 1968. neurophysiological and biochemical In view of the importance of Narcine research. From 1980 to 1984, over 900 in the neurophysiological laboratory, the papers dealing with the biochemistry and dearth of information on its life history neurophysiology of Torpedo california and ecology is remarkable. Bigelow and and Torpedo nobiliana were cited in Schroeder (1953) reported that poly­ Biological Abstracts. Torpedo are large chaete annelids are its primary diet. It (approximately 2m total length), deep occurs inshore during the summer water, cold temperature rays that are months in Mississippi Sound in the vicin­ difficult to keep in the laboratory. ity of passes between barrier islands The lesser electric ray, Narcine (Funicelli, 1975; Migdalski & Fichter, brasiliensis, which is roughly one third 1976). The taxonomy of the family has the size of Torpedo, is perhaps more suit­ most recently been reviewed by Fech­ able as a laboratory animal. Occurring in helm and McEachran (1984). shallow warm water from Argentina to Studies of behavior and electric North Carolina, it is locally common in organ discharge using various species of the Gulf of Mexico and off the south­ the genus Torpedo are reported by Bray eastern coast of the United States, mak­ and Hixon (1978), Belbenoit (1986, 1977), ing it potentially available for a routine Michaelson eta/. (1979) and Mellinger et and dependable supply to researchers. at. (1978). However, these larger, cold Unlike Torpedo a refrigerated sea water water species of electric ray are piscivor­ system is not necessary. It provides a ous. A recent review of the evolution and neurophysiological preparation compar­ function of electric organs in fishes is able to Torpedo in that both genera have provided by Bass (1986). electric organs densely innervated with This two year investigation of popu­ exclusively cholinergic neurons and has lation characteristics and movement

103 Published by The Aquila Digital Community, 1988 1 Gulf of Mexico Science, Vol. 10 [1988], No. 2, Art. 4 104 Rudloe, A.

patterns of Narcine brasiliensis was part tative sampling was done in waters in of an exploration of the feasibility of and just beyond the surf zone at Dog routinely providing Narclne brasiliensis Island, St. George Island and Little St. for biomedical laboratories. Methods George Island, Franklin County, Florida developed for maintaining Narcine in (Figure 1) and at a site approximately 15 laboratory are reported elsewhere (Rudloe, miles offshore from St. George Island in 1989). approximately 30 meters depth (C Tower site). STUDY AREA METHODS The study was conducted in coastal waters from Alligator Point, Franklin A 21 m vessel pulling two 12m County, Florida, to Cape San Bias, Gulf trawls was used to sample offshore County, Florida. Four offshore stations while a shallow drafted nine m trawler were used, one in a depth of 10m and pulling one 12m trawl was used for the one in 16m several miles south of St. inshore sampling. Trawling was the only George Island, one at West Pass between feasible sampling method due to highly St. George Island and St. Vincent Island, turbid conditions and the necessity to and one at Cape San Bias, Gulf County, sample at night when animals were Florida. active. Trawling was considered an The West Pass and Cape San Bias efficient sampling method for this sites are both regions of sand bars and species in view of its sluggish swimming gullies at depths of 8-10 meters. The behavior and benthic feeding habits. The West Pass site ("ray bar") is perpen­ offshore stations south of St. George dicular to the west end of St. George Island and at West Pass were sampled Island at West Pass between St. George twice a month from March 1985 to Febru­ and St. Vincent Island, and the other is ary 1986, except in August 1985 (equip­ part of a large complex of underwater ment failure). The Cape San Bias station bars south of Cape San Bias. They are was sampled twice a month from June offshore from passes between barrier 1985, to January, 1986. The inshore sta­ islands that carry most of the outflow tion at Alligator Point was sampled once from estuarine Apalachicola Bay (Living­ a month from April 1986 to March 1987. ston, 1983) and are characterized by The other 3 beach sites were sampled strong currents and high turbidity. qualitatively a total of 13 times between Temperatures ranged from 14.6°C to June 1985 and March 1987. 31 °C and salinities varied from 22-35 ppt A one hour tow was made at each during the study. station. Stations which yielded rays were One inshore station was located at then sampled further using up to eight Alligator Point, Franklin County, Florida, additional 1 hour tows per station. All in and just beyond the surf zone. The sta­ electric rays captured were measured tions were chosen based on preliminary and sexed and all individuals longer than sampling from December 1984, to Febru­ 20 em TL were tagged with a plastic dart ary 1985, and during the preceding sum­ tag (FT-6) manufactured by Floy Tag and mer. Sampling was designed to include Manufacturing, Seattle, Washington. The areas utilized by the species at various barbed shaft was inserted into the mus­ seasons as the fish move on and off­ culature posterior to the body disc. In shore through the year. In addition quali- animals held in captivity, tagging did not https://aquila.usm.edu/goms/vol10/iss2/4 2 DOI: 10.18785/negs.1002.04 Rudlow: Habitat Preferences, Movement, Size Frequency Patterns and Reprod Habitat Preferences of the Lesser Electric Ray 105

TALLAHASSEE• 110 females were dissected and their ovaries weighed periodically from March + 1985 through April 1986. Swollen clas­ 8km N H pers were noted on males.

RESULTS

A total of 3,913 rays were captured from March 1985 to March 1987 from all sites. Of these 3,229 were returned to shore, 455 tagged and released and 229 released untagged due to small size. Ten tagged rays were recaptured (Table 1).

OFF SHORE SITES

Figure 1. Sampling sites for electric rays, March The catch per unit effort (CPUE) of 1985- March 1987. the four offshore stations offshore from impede the fish, or cause infection or the barrier beaches is plotted Figure 2. necrosis and <1% tag loss was ob­ The CPUE at the sites ranged from served. All body lengths are expressed as 3-31 rays/hour. However, rays were con­ total length. centrated over an extremely limited area Surface water temperature and sal­ on each bar. As little as several tens of inity, and wind and sea state were meters change in position could deter­ recorded at each station. Bottom temper­ mine whether there were two or 20 rays atures were recorded in December 1985 in the catch. CPUE of rays declined dur­ and January 1986. Trawling began at ing the August-September birthing dark and continued until shortly after season (see section on Reproductive dawn. The majority of animals were Seasonality) at these sites and then returned to shore with tag numbers used increased in October. Adults left the area to track individuals in subsequent neuro­ in November. Only young of the year chemical or culture methods studies were present in December. The 10m and (Rud loe, 1989). 16m stations were frequented primarily Animals not needed for laboratory in November and February, periods im­ research were released at the collection mediately preceding and following the site. Posters offering a reward for season of occupancy of the ray bars and returned tags were placed at seafood beaches. plants within 160 km of the study area. The length frequency distribution of To determine reproductive seasonality rays taken at Cape San Bias and West

Table 1. Trawling Summary of animals collected, March 1985- March, 1987.

Offshore Inshore Total

Rays Caught 2,198 1,715 3,913 Rays Released, Tagged 335 120 455 Rays Released, Untagged 194 35 229 Rays Returned to Shore 1,669 1,560 3,229 Tag Recoveries 8 2 10 (2%)

Published by The Aquila Digital Community, 1988 3 Gulf of Mexico Science, Vol. 10 [1988], No. 2, Art. 4 106 Rud\oe, A.

animals 14-19.9 em TL increased from

CAPE SAN BLAS -WEST PASS 6% in April to 27% in July for males and ---- !0 m STATION ·-·- 16m STATION from 1% in April to 33% in July for 40 females at West Pass. The large increase 36 NO RAYS 32 CAUGHT UJ in this size range coincided with a ~ 28 u 24 decline in the smaller <14 em class, sug­ 20 16 ··· ..... ·····" ·· ... gesting rapid growth of young during the 12 ··...... ··· 8 ,~. spring. Animals 14-19.9 em TL declined ~ =::.~::::-.-_. ___ ,___ ,.,..~.::::.-::.~::..~~. ,/ from July through September at both A M J A S 0 N D J M sites concurrently with increases in ani­ MONTH Figure 2. Catch per unit effort in rays per hour at mals 20-29 em total length (Figure 3, 4). tour offshore stations, April 1985 ·March 1986. Newborn rays less than 14 em TL reappeared abruptly in the trawl catch in Pass from April 1985 to March 1986 September, concurrently with August­ expressed as percent of the sample in September birthing observed in inshore each size category for both males and rays, but peaked in November at West females is given in Table 2. Females Pass and December at Cape San Bias appear to attain larger sizes than do (Figure 3, 4). males. The proportion comprised of Females >30 em TL with developed

Table 2. Size frequency of males and females by month as percent of total catch, April1985. March 1986.

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

West Pass MALES n = 102 145 22 83 5 65 6 19 0 0 10 <14 em 9 3 0 0 20 9 86 47 0 0 10 14·19.9 em 6 17 23 27 0 6 0 42 0 0 20 20-29.9 em 43 57 50 23 60 48 7 11 0 0 50 30·39.9 em 42 23 27 29 20 37 7 0 0 0 20 >40cm 0 0 0 4 0 0 0 0 0 0 0 FEMALES n = 94 98 25 78 3 52 20 14 0 2 10 <14 em 10 4 0 1 0 6 75 43 0 50 20 14-19.9 em 1 18 16 33 33 4 5 57 0 0 50 20-29.9 em 26 59 48 53 67 44 10 0 0 50 10 30-39.9 em 50 17 28 12 0 36 5 0 0 0 10 >40cm 13 2 12 1 0 10 5 0 0 0 10

Cape San Bias MALES n = 65 63 25 27 19 23 0 <14cm 4 0 12 22 5 70 0 14-19.8 em 54 44 16 19 11 26 0 20-29.9 em 31 35 28 41 42 0 0 30-39.9 em 11 21 44 18 42 4 0 >40cm 0 0 0 0 0 0 0 FEMALES n = 64 89 26 45 13 20 0 <14cm 5 1 15 2 8 65 0 14-19.9 em 65 65 8 15 31 35 0 20·29.9 em 17 22 27 55 23 0 0 30-39.9 em 5 4 27 24 23 0 0 >40cm 8 8 23 4 15 0 0 https://aquila.usm.edu/goms/vol10/iss2/4 4 DOI: 10.18785/negs.1002.04 Rudlow: Habitat Preferences, Movement, Size Frequency Patterns and Reprod Habitat Preferences of the Lesser Electric Ray 107

ovaries (see Reproductive Seasonality TOTALLENGTH (em) <14 section) declined in number at West Pass --- 14-19.9 - 20-29.9 from an April peak of 63% of the females collected to a low of 0 in September and NO RAYS then increased in October to 46% of the CAUGHT females collected. Sampling at Cape San t Bias from June-September 1985, however indicated that the occurrence of these ...... ··· females peaked 50% in September, sug­ ...... , gesting that birthing females may have A M A S 0 N MONTH remained on the site. Figure 4. Size frequency of immature rays, (<30 em total length), Cape San Bias. WINTER DISTRIBUTION trated at the C tower site in February. Lesser electric rays remained on the They returned to the ray bar sites as in offshore bars in all months except the previous year by March 1987. Males January and February. Larger animals slightly outnumbered females in the disappeared from the catch at both sites catch at C Tower in winter 1987 with no in November, leaving predominately young of the year (M/F ratio: 1.5/1). young animals at each site in December. In addition to the systematic sam­ During January and February 1986, no pling described above, 20 60 minute rays were caught at any of the offshore tows were made at a variety of other off­ stations. However, 186 rays were caught shore locations from Dog Island to Cape in February at the C tower site. This area San Bias throughout the study. No rays had been heavily trawled the preceding were found at any other site. Extensive month but yielded no specimens. These interviews with commercial shrimp rays were predominately 20-40 em TL trawlers revealed few rays captured at with no young of the year and only two any other sites. No tag returns were animals less than 20 em TL. No rays were recovered from other sites. caught at any site when bottom tempera­ tures fell below 17°C. BARRIER BEACH SITES A total of 132 rays were collected from December 1986 to February 1987. During August and September 1985, Rays were collected at the 16m station lesser electric rays were located in through January. They again concen- waters of less than three meters at two barrier beach sites: Alligator Point and

TOTAL LENGTii (em) <14 Dog Island (Figure 1). Intermittent quali­ ~-w--- 14-14,9 - 20-29.9 tative sampling continued until rays left the area in December 1985. Routine monitoring of the Alligator Point surf zone by shrimpers working with us on other projects produced no \ ... ,I 1'•, I·.'· rays in the area from December 1985 I I through February 1986. In March 1986

ASONOJFM MONTH rays returned to these sites. Twelve Figure 3. Size frequency of immature rays, months of monthly quantitative sampling (<30 em total length), West Pass. at Alligator Point was conducted from

Published by The Aquila Digital Community, 1988 5 Gulf of Mexico Science, Vol. 10 [1988], No. 2, Art. 4 108 Rudloe, A.

March 1986 - February 1987 using the Table 3. Catch summary of rays adjacent to bar­ same procedures described previously. rier beach at Alligator Point showing proportion of Rays were taken in the surf zone at newborn rays, CPUE and sex ratio of mature rays. Alligator Point from March-December CPUE Male/Female (Table 3). Date N % <14 em TL Rays/hr >29 em TL Rays were also consistently caught 3/86 29 8 710 at three additional surf zone sites (Dog 4/86 101 0 Island, Little St. George and St. George) 5/86 51 0 4.0 10/1 6/86 jellyfish precluded sampling between June 1985, and March 1987, with 7/86 35 0 5.1 1.0/.6 CPUE ranging from 1-35 rays per hour. At 8/86 jellyfish precluded sampling all sites, samples taken in August and 9/86 6 17 6.0 1/4 September had a predominance of new­ 10/86 106 12 3.4 0/4 11/86 67 0 0/6 born rays and large females. Animals 12/86 297 6 29.0 0/2 greater than 29 em were predominantly 1/87 0 .7 0 females in the surf zone. Sex ratios at 2/87 0 .6 0 Dog Island in August and September 1985 reflected female dominance as did from 5.4-198.1 g wet weight. Ovaries all surf zone samples at Little St. George ranged from 20-76 g wet weight in May Island (Table 4). 1985 (n =20) and the tissue was now Lesser rays between 14-19.9 em organized in all females examined into appeared on these sites in early spring clearly defined segments with vasculari­ and grew into the 20-29 em TL range over zation extending from the entire inner the summer. These rays were then joined surface of the membrane into the ovary in August and September by large preg­ to a depth of approximately one em. nant females and their newborn young. Females examined in June 1985 Pregnant females gave birth in (n = 9) had macroscopically visible August and September. Rapidly growing embryos ranging from 9-17 in number, newborn rays dominated in the surf zone with a mean length of 4.5 em (range in September and grew into 14-19.9 em 3.6-4.9 em). By late July, all females size range during the fall. During January larger than 29 em both in captivity and /February no rays were caught. In March, collected from the field were visibly preg­ the young born the previous August nant. Female rays >29 em dissected in reappeared in the trawls and grew to the July (n = 4) carried embryos. Eight em­ 20-29.9 em range during the following bryos surgically removed from a live spring and summer. The changing pro­ female were all 8.7 em in length and portions of immature (less than 30 em survived independently for several days. TL) rays in these two size catagories at They gave electric shocks if prodded and Alligator Point is plotted in Figure 5. could swim. External yolk sacs were still evident. REPRODUCTIVE SEASONALITY Two females gave birth in August in captivity, one to six young ranging from All dissected female rays above 10.9-11.9 em TL and one to three young 20 em (n = 81) had large well developed each 9.5 em TL. Several weeks prior to oocytes and all less than 29 em (n =29) giving birth the vent became enlarged did not. In March (N =24) ovaries con­ and remained so for several weeks after sisted of macroscopically undifferen­ birth. Thus pregnant and post birthing tiated yolk material and varied in weight females were readily identified in the https://aquila.usm.edu/goms/vol10/iss2/4 6 DOI: 10.18785/negs.1002.04 Rudlow: Habitat Preferences, Movement, Size Frequency Patterns and Reprod Habitat Preferences of the Lesser Electric Ray 109

Table 4. Summary of qualitative sampling at 3 ad­ tween April 1985 and March 1987. Ten ditional barrier beach localities, showing proportion rays were recaptured, six females, three of newborn rays, CPUE and sex ratio of mature rays. males and one of unknown sex. Four Three samples had no trawl time, so CPUE could not be calculated: indicated by -. mature females moved from West Pass to Cape San Bias and were recovered Location CPUE Males/Females between one and five months after Date N % <14 em TL Rays/hr >29 em TL release. Three (two males, one female) Dog Island were recovered at the point of release 6/85 4 0 2.7 1/0 after periods of one to two months at 8/85 17 29 7.1 0/6 9/85 32 91 0/5 liberty. One moved from West Pass west­ 4/86 25 4 5.0 1/3 ward to Indian Pass. Two mature females 5/86 17 6 17.0 1/3 tagged at Little St. George Island in May 7/86 6 50 0/1 1986 both moved offshore and were Little St. George Island 4/86 176 13 35.0 1/3.4 recovered offshore at West Pass and 5/86 339 4 32.0 1/2.2 slightly south of West Pass after four 8/86 13 5 1.0 0/3 and seven months respectively. Two rays St. George Island recaptured by us and remeasured had 5/86 59 7 27.5 1/.1 grown 2.4 em (a male after two months) 6/86 26 0 6.5 4/0 12/86 68 47 0/1 and 5 em (a female after five months) in 3/87 63 40 5.7 1/1.2 total length, indicating summer field growth rates of approximately one em per month for these two animals. field by mid summer. Forty-one addi­ tional female rays >29.0 em TL were DISCUSSION collected from the field and dissected from October 1985 to April1986, to com­ This study indicates that Narcine plete twelve months of monitoring gona­ brasiliensis can be collected in most dal development. Female gonads totally months of the year once specific locali­ regressed by February and were develop­ ties occupied by the animal are located. ing again in April 1986. The tag recovery locations plus the ap­ The only time during the total sam­ parent general scarcity of rays in other pling period when females carried viable areas, as indicated by our sampling and young was August and September. This reported by fishermen, suggest that rays was consistent with the field data indi­ are localized in their habitats during cating presence of young of the year in August and September.

Males above 22 em TL had mature TOTAL LENGTH (em) ••..•••• <14.0 claspers. Nineteen males with swollen ----- 14-19.9 - 20-29.9 claspers suggestive of breeding activity NO RAYS

were collected in December, 1985 in 18 '-.., _...... 1 ~\ CA~UGHT ...... , \ meters depth south of the West Pass ',\ ./ \ site. The mean size of these rays was ', I \ ',, I / \I \ / \ 31.7 em (range 28.0-38.1 em TL). ' I ' I I ' I I TAGGING STUDY ...... ~>.7.~~·~~~-~~/t ······ .. ·· ...... ········· \ MAMJJASON OJ MONTH A total of 455 Narcine was tagged Figure 5. Size frequency of immature rays, and released at the point of capture be- (<30 em total length), Alligator Point.

Published by The Aquila Digital Community, 1988 7 Gulf of Mexico Science, Vol. 10 [1988], No. 2, Art. 4 110 Rudloe, A.

warm months at least, and move directly 14 em TL, and growth is rapid in the fall. from one preferred locality to another or Growth is dormant over January and remain in one area over a period of weeks February and resumes in March. Thus a to months. They then move to deeper female ray born in August is estimated water in the winter. Since the 10 and 16 to grow to 15-19 em by March of the next meter stations were occupied primarily year, approximately 20-28 em by Septem­ during November and February, it is ber of that year, and to become a repro­ likely that animals taken there were tran­ ductively active adult (>29 em) the sient, moving between ray bar or beach following year at age two. Very large rays habitat in the warmer months and off­ (>40 em) might then be three to four shore in the winter. years old. Preferred habitats are in the vicinity If males become reproductively of barrier beach surf zones and on bars active at approximately 30 em TL as is adjacent to passes between estuarine suggested by the limited sample of barrier islands. This is consistent with males with swollen claspers, this model summer distributions reported from the would apply to them as well. However, Mississippi Sound by Funicelli (1975). In the small sample size precludes definite addition, eight specimens were collected conclusions. If mating does occur in off a bar adjacent to the mouth of the December, sperm may be stored for Suriname River, Republic of Surinam, in some months prior to ovulation and South America in September 1978, sug­ fertilization, as is common with other gesting that the habitat preferences elasmobranchs (Wourms, 1977). Whether described for the northern Gulf of Mexico the birthing seasons or growth rates are valid throughout the species' range. observed in this study are applicable to The period of winter inactivity at shal­ other parts of the species' range is not lower sites might however be shorter or known at this point. nonexistent in the tropical parts of the Data on mortality are not yet avail­ species' range and longer in more north­ able, but the low birth rates as well as the erly water. potent defensive organs of this species The presence of larger females and suggest limited predation. Tagged rays newborn rays in the surf zones in August released off trawlers were repeatedly and September, together with the decline observed to be actively avoided by both in mature females but not mature males sharks and porpoises that fed heavily on at West Pass in September suggests other rays and bony fishes as they were movement of females away from the culled overboard. West Pass area and onto the beach. The Whether the November and Decem­ movement of two tagged rays out of the ber peak in newborn rays at West Pass surf zone to the West Pass site also and Cape San Bias was a result of immi­ supported an hypothesized movement gration of young from the beach is not pattern of females to the surf zone to clear. The absence of small animals at give birth and then back offshore to the "C" tower site in winter suggests that winter. young may remain on the ray bar sta­ Females larger than 29 em TL ap­ tions, but buried, over the winter when pear to give birth to 2-17 live young in adults move offshore. August and September in the surf zone As was noted, additional trawls and at some but not all of summer off­ were made only if the first sample shore sites. Young are born at less than yielded rays. While the necessity to https://aquila.usm.edu/goms/vol10/iss2/4 8 DOI: 10.18785/negs.1002.04 Rudlow: Habitat Preferences, Movement, Size Frequency Patterns and Reprod Habitat Preferences of the Lesser Electric Ray 111

collect large numbers of animals for Howard Hughes Medical Institute in sup­ laboratory use in the limited time avail· port of neurochemical work in the labor­ able demanded this approach, it never­ atory of Dr. Robert Johnson, Howard theless made comparisons of CPUE diffi­ Hughes Medical Institute, University of cult and may underestimate numbers Pennsylvania. Special thanks to the present. skills and determination of Jack Rudloe, The use of different size sampling Edward Keith, and Johnny Keith without gear at the inshore as compared to off­ whose efforts this project would have shore stations precludes direct compari­ been impossible. Numerous reviewers son of CPUE figures between inshore contributed greatly to the clarity of the and offshore sites. The inshore CPUE manuscript. I also acknowledge with values did however suggest larger gratitude the aid of the Turtle Mother. numbers at Little St. George Island and St. George Island than east at Alligator LITERATURE CITED Point and Dog Island. These sites are ad­ jacent to the ray bar off West Pass, St. Bass, A. H., 1986. Electric organ George Island, a major offshore ray site. revisited. Evolution of a vertebrate Rays were also reported by fishermen to communication and orientation organ. consistently occupy the surf zone in late In Bullock, T. H. and W. Heiligenberg summer at Cape San Bias, adjacent to (ED.). Electroreception. Wiley series in the second major offshore ray site. neurobiology, N.Y. 13-70. Estimates of population size or sub­ Belbenoit, P. 1986. Fine analysis of stainable yield cannot yet be made. How­ predatory and defensive motor events ever, it is likely that if this species is in Torpedo marmorata (Pisces). J. Exp. fished on a substained basis for labora­ Bioi. 121:197-226. tory use, its low rate of reproduction and Belbenoit, P., 1977. Electric organ dis­ localized distribution make it highly vul­ charge of Torpedo marmorata (Pisces): nerable to over fishing. In addition, its Basic pattern and ontogenetic changes. relative abundance might readily be over J. Physiol. (Paris). 75(4) 435-441. estimated depending on sampling sites Bigelow, H. B. and W. S. Schroeder, 1953. chosen. Ongoing monitoring of catch per Fishes of the Western North Atlantic. unit effort at each site and changes in Part 2. Sawfishes, quitar fishes, skates, size frequency on a site as well as rays and chimearoids. Mem. Sears spreading collecting efforts over as Found. Mar. Res. (12) 588 pp. many collecting sites as possible will be Bray, R.N. & M.A. Hixon, 1978. Night essential to protect the long term future shocker: predatory behavior of the of this species as a marine resource. Pacific electric ray, Torpedo califor­ The relation of the detailed topo­ nica. Science 200:333-334. graphy of the ray bars to concentrations Fechhelm, J. D. & J. D. McEachran, 1984. of animals as well as the orientational A revision of the electric ray genus mechanisms used by these animals in Dip/abatis with notes on the inter­ their seasonal movements will be pro­ relationships of Narcinidae (Chon­ ductive areas for future research. drichthyes, Torpediniformes), Bull. Fla. St. Mus. 29(5):171-209. ACKNOWLEDGMENTS Funicelli, N. A., 1975. Taxonomy, Feeding, limiting factors and sex ratios of This research was funded by the Dasyatis sabina, Dasyatis americana,

Published by The Aquila Digital Community, 1988 9 Gulf of Mexico Science, Vol. 10 [1988], No. 2, Art. 4 112 Rudloe, A.

Dasyatis say, and Narcine brasiliensis. Ph.D. Diss. University of Southern Mississippi. Livingston, R. J. 1983. Resource Atlas of the Apalachicola Estuary. Fla. Sea Grant College Program. Rep. No. 55. Mellinger, J., P. Belbenoit, M. Ravaille, & T. Szabo, 1978. Electric organ develop­ ment in Torpedo marmorata (Chon­ drichthyes). Dev. Bioi. 67(1):167-188. Michaelson, D. M., D. Sternberg, & J. Fishelson, 1979. Observations on feeding growth and electric discharge on new born Torpedo ocel!ata (Chon­ drichthyes, Batoidei) J. Fish. Bioi. 15(2): 159-164. Migdalski, E. C. and G. S. Fichter, 1976. The fresh and salt water fishes of the world. KnopL New York, N.Y. 71-73 pp. Rudloe, A., 1989. Captive maintenance of the Lesser Electric Ray, Narcine bra­ siliensis with observations of feeding behavior. Prog. Fish Cult. 51(1):37-41. Wourms, J.P. 1977. Reproduction and development in chondrichthyan fishes. Am. Zoo!. 17:379-410.

https://aquila.usm.edu/goms/vol10/iss2/4 10 DOI: 10.18785/negs.1002.04