BULLETIN OF MARINE SCIENCE, 45( I): 15-25, 1989 BIOLOGY OF THE BLUNTNOSE STINGRAY, DASYATIS SAYI, IN FLORIDA COASTAL LAGOONS Franklin F. Snelson, Jr" Sherry E. Williams-Hooper and Thomas H. Schmid ABSTRACT Dasyatis sayi is a common year-round resident in the brackish Indian River lagoon system on the central east coast of Florida. We studied the species in the Cape Canaveral area from July 1975 to January 1978. Catch-per-unit-effort generally peaked in the spring and fall, was depressed in winter, and usually was significantly higher at night than during the day. Catch rates were always highest in Mosquito Lagoon, the most saline section of the study area. Females reached a size of 73 cm DW and 21 kg; males reached 52 cm and 7 kg. Fema]es matured between 50-54 cm DW and males between 30-36 cm. The reproductive cycle was significantly different from that of the sympatric D. sabina. Ovarian egg size and male gonaso- matic index both peaked in May, indicating that mating occurred in spring. Uterine eggs were present from June through the following March but no embryonic development was evident. Fetal development began in early April and parturition occurred in middle to late May, followed immediately by ovulation. There were 1-6 young per brood and neonates were 15-17 cm DW at birth. The bluntnose stingray, Dasyatis sayi, is distributed in western Atlantic coastal waters from Massachusetts to southern Brazil, including the Gulf of Mexico and many islands in the Greater Antilles. Although it is common to abundant in some parts of its range (Bigelow and Schroeder, 1953), it is the most poorly known of the four Dasyatis species inhabiting Atlantic and Gulf coastal waters of the United States. The discovery of large, accessible stingray populations in lagoons and estuaries on the central east coast of Florida (Snelson and Williams, 1981) prompt- ed a comparative study of the natural history of D, sayi and the related D. sabina (Snelson et al., 1988). This is the third in a series of papers dealing with the biology of rays in the Indian River Lagoon system. STUDY AREA AND METHODS The Indian River Lagoon system has been described and mapped by a number of recent authors (Gilmore, 1977; Snelson and Williams, 198]; Snelson, 1983; Snelson et aI., 1988), Our studies have been concentrated in the northern part of the system, specifically Mosquito Lagoon, Indian River, and Banana River in Brevard County, Florida, Data for this report were collected between July 1975 and January 1978, During that time, data were taken from 2,421 D. sayi. We observed rays from small drifting boats and by wading in clear, shallow water. Animals were collected by means of trawls, seines, tangle nets, dip nets, cast nets, and gigs, Depth, salinity and substrate were recorded at the time of observation or capture for most animals. The majority of D. sayi specimens were collected with braided-nylon tangle nets 90-229 m long, 3.7 m deep, with 30.5-40.6-cm stretch mesh. These nets were set in water from 1.5-4 m deep. Rays swimming into the nets became entangled by their caudal spines, with the retrorse marginal hooks snaring the filaments of the nylon twine. Subsequent thrashing usually resulted in the ray becoming thoroughly entangled in the net. The animals were always alive and usually in good condition when removed from the net, even after an overnight set. From November 1976 to November 1977, tangle nets were used to collect samples of approximately 25 adult D. sayi per month for reproductive analysis. Major netting sites are identified elsewhere (Snelson et aI., 1988), Because detailed records were kept on all collecting with tangle nets, it was possible to quantify the sampling effort, A 24-h net day (NetDay24) was defined as 100 m of net fished for 24 h, calculated as follows: NetDay24 = (m of net deployed! I00) x (h net deployed!24). Fishing effort was also calculated separately for daylight and night-time sampling as follows: NetDayl2 (or NetNight]2) = 15 16 BULLETIN OF MARINE SCIENCE, VOL. 45, NO.1, 1989 Table 1. Effort devoted to fishing with tangle nets in the three main sections of the Indian River lagoon system in northern Brevard County, Florida Mosquito Lagoon Indian River Banana River Year/season Hours NetDay24 Hours NetDay24 Hours NetDay24 1976 Summer 22.5 2.1 112.0 10.7 Fall 208.5 19.9 119.0 11.4 1977 Winter 116.0 11.1 224.0 21.4 Spring 437.5 51.0 208.5 19.3 24.5 2.3 Summer 842.8 106.6 235.0 29.6 68.5 10.2 Fall 912.1 83.1 166.2 20.9 24.0 3.8 1978 Winter 127.7 12.2 89.3 8.5 48.5 4.6 Spring 641.2 51.4 169.3 15.8 24.5 2.3 Summer 577.5 51.6 88.0 8.4 25.6 2.4 Fall 298.4 28.0 89.0 7.9 25.8 2.2 (m of net deployed/lOa) x (day (or night) h net deployed/12). The hours of 0600 and 1800 were designated as the changcover times between night and day. Catch-per-unit-effort data were summarized by season as follows: December-February = Winter, March-May = Spring, June-August = Summer, September-November = Fall. Retained specimens were returned to the laboratory on ice, sexed externally, weighed wet after blotting on a top-loading electronic balance or mechanical platform balance, and then examined immediately (usually) or frozen for study later. Disk width and length were measured for all specimens with forester's tree calipers to the nearest 0.1 cm (Hubbs and Ishiyama, 1968). Clasper length was measured with dial calipers to the nearest millimeter from the posterior end of the cloacal slit to the tip of the longest clasper with the specimen laying on its dorsum and the clasper supported to eliminate sag. The gonads and reproductive tracts were removed, wrapped in cheesecloth, and preserved in 10% formalin for later analysis. Specimens were assigned to one offour reproductive stages: Males-(1) immature, testes and claspers undeveloped; (2) mature but nonreproductive, claspers fully developed and testes enlarged but without secondary lobes; (3) mature and reproductive, testes with secondary lobes indicative of active sperm production (Babel, 1967; Lewis, 1982); (4) mature and sexually active, sperm present in vas deferens, sperm sac, or clasper groove; Females-(1) immature, no ovarian development; (2) mature but non- reproductive, developing eggs in left ovary; (3) mature and sexually active, mature ova in left ovary and/or left uterus; (4) pregnant, embryos in left uterus. We saw no evidence that the right ovary or uterus was functional. After associated mesentaries were removed, the gonads (both testes, left ovary) were blotted and weighed wet to the nearest gram on a top-loading electronic balance and were examined for reproductive activity. Gonasomatic index (GSI) was calculated as: (gonad wt/(body wt - gonad wt) x 100. In mature females, eggs were dissected from the left ovary. One group of eggs was always distinctly larger than the remainder. These enlarged eggs were measured with dial calipers. Since the fixed eggs were often ovoid in shape, length and width were averaged to give egg diameter to the nearest 0.1 mm. The presence of uterine eggs was recorded and the ova were preserved when possible. Any embryos present were removed, weighed after blotting, measured, and sexed when possible. RESULTS Distribution, Occurrence, and Abundance. - Dasyatis sayi was found throughout the study area and it was taken in every month of the year. Captures spanned a water temperature range of 12.5-32.5°C and a salinity range of 25-430/00.Adults were not often found on shallow seagrass flats and were usually taken in water deeper than I m. Only young-of-the-year and small juveniles were seen regularly on the shoals, and they were found there primarily in fall and winter months. SNELSON ET AL.: BLUNTNOSE STINGRAY IN FLORIDA LAGOONS 17 10 6 ~ Mosqurto lagoon Ii: Indian River Ii: 5 0 8 • Banana River o Day It ~ • Night W ... ~ 4 t: 6 z Z :::l ~ 3 Ii: II: w 4 w Q. i ~ 2 0 0 ~ 2 ~ 0 0 1 0 0 S S F S F W S S F W S S F 1977 1978 1976 1977 1978 Figure I (Left). Seasonal CPUE for Dasyatis sayi taken in tangle nets in the Indian River lagoon system between summer, 1976 and fall, 1978. The asterisk represents a CPUE of zero for both Indian and Banana rivers in the winter of 1978. Figure 2 (Right). Day and night CPUE for Dasyatis sayi taken in tangle nets in Mosquito Lagoon between summer, 1976 and fall, 1978. Despite being infrequently observed on shoals, D. sayi was abundant in the lagoons as suggested by the large number of individuals taken in tangle nets set in water 1-3 m deep. Fishing effort varied in the three main sections of the lagoon system (Table 1). After the winter of 1977, effort was consistently highest in Mosquito Lagoon and moderate effort was expended in Indian River throughout the study. Sampling in Banana River did not begin until April 1977 and effort was always low there due to logistic constraints. Seasonal CPUE's for the three bodies of water sampled are shown in Figure 1. Capture rates were usually low in the Banana and Indian rivers, with an overall mean CPUE of 1.4 animals per NetDay24.