Habitat Preferences, Movement, Size Frequency Patterns and Reproductive Seasonality of the Lesser Electric Ray, Narcine Brasilie
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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.