Field and Laboratory Observations on Larval Atlantic Sailfish (<I

BULLETIN OF MARINE SCIENCE. 60(3): 1026--1034. 1997

FIELD AND LABORATORY OBSERVATIONS ON LARVAL ATLANTIC SAILFISH (ISTIOPHORUS PLATYPTERUS) AND SWORDFISH (XIPHIAS GLADIUS)

James T. Post, Joseph E. Serafy, Jerald S. Ault, Thomas R. Capo and Donald P. de Sylva

ABSTRACT We conducted a 2-year study off Miami, Florida, to verify the presence and seasonality of larval billfish, particularly sailfish (lstiophorus platypterus) and swordfish (Xiphias gladius), and, to examine the feasibility of obtaining laboratory observations on feeding, behavior, and growth. The Gulf Stream's western edge was sampled from April to October 1994, and from March to October 1995, with a I-mm-mesh plankton net. A total of 315 samples yielded 288 larval sailfish and 2 larval swordfish. Sailfish larvae were present from May to October with a May to July peak, while the two swordfish were captured in May and July. Highest sailfish catches were made from 07:00 to 08:00. No swordfish survived capture at sea. Of the 288 sailfish larvae captured, 87 were alive immediately after capture and these were transported to the University of Miami's experimental hatchery. Of the sailfish captured alive, 23 survived 24 h, 7 survived 48 h, and I survived 72 h. Dissection confirmed that one larval sailfish ingested Artemia introduced as food. This is the first reported observation of larval sailfish feeding.

The istiophorids and xiphiids are pelagic billfishes found in all tropical oceans (Nakamura, 1974; Robins and Ray, 1986). Observations of adult billfish are dif- ficult because they are large, migratory fish typically found many miles offshore. Hence our understanding of these fishes is limited (Radtke and Shepherd, 1991; Prince and Brown, 1994). The quantitative scientific information available has been derived from mature adults captured by the fishery; consequently, little is known about the distribution, behavior, ecology, physiology, or population dynamics of the earliest life stages. Most studies on sailfish (Istiophorus platypterus) and swordfish (Xiphias gladius) larvae have examined development, diet, abundance, and vertical and hori- zontal distribution (Sanzo, 1922; Sanzo, 1930; Nakamura, 1932; Nakamura, 1940; Nakamura et al., 1951; Voss, 1953; Yabe, 1953; Arata, 1954; Gehringer, 1956; Jones, 1959; Yabe et al., 1959; Sun, 1960; Ueyanagi and Watanabe, 1962; Uey- anagi, 1963; Ueyanagi and Watanabe, 1964; Gehringer, 1970; Lipskaya and Gor- bunova, 1977; Yasuda et al., 1978; Harada et al., 1980). The few studies on live larval billfish have all been on swordfish. Working at sea in the Straits of Messina, Mediterranean Sea, Sanzo (1922) collected fertilized swordfish eggs. These hatched and were maintained for 13 days. Yasuda et al. (1978) and Harada et al. (1980) strip-spawned adult swordfish from Sicilian waters with the resulting larvae surviving for 9 d after fertilization. Billfish larvae were not observed to feed in either of these studies. The goal of our study was to verify the presence and seasonality of larval Atlantic billfish in the surface waters off Miami, Florida, and to examine the feasibility of obtaining observations on feeding, behavior, and growth.

MATERIALS AND METHODS

Larval billfish collections were made during two periods: April to October 1994; and. March to October 1995. Sampling was conducted along the western edge of the strong, northward-moving Gulf Stream (Fig. I), an area known to have enhanced primary and secondary productivity (Olson et aI.,

1026 POST ET AL.: BEHAVIOR-LARVAL ATLANTIC BlLLRSHES 1027

Figure I. Map of Caribbean Basin and major hydrodynamic regimes with inset showing the study area and sample locations. Figure adapted from Lee et at. (1994: fig. 1).

1994). The sampling gear was a I-m diameter plankton net with I-mm mesh and a I-liter plastic cod- end equipped with a flowmeter. Tow duration was set at 2 min to reduce mechanical damage to captured larvae. Larval billfish identifications were based on publications by Ueyanagi (1963), Uey- anagi and Watanabe (1964), Richards (1974), Ueyanagi (l974a, 1974b), and Nishikawa and Rimmer (1987). Catch-per-unit-effort (CPUE) was standardized as the number of individuals caught per 10,000 mJ of water filtered. Recorded at each sampling station were: latitude, longitude, time of day, volume filtered, surface water temperature, and salinity. After each tow, samples were poured into a clear plastic bag to allow visual inspection for billfish larvae. Using a 6-mm diameter glass tube, live larval billfish were sep- arated from the sample and transferred to opaque plastic containers which were then charged with pure oxygen, covered, and secured for transport to the laboratory. Dead or clearly moribund individuals were immediately placed on ice and later frozen. All specimens arrived at the laboratory within 8 h of capture. In the laboratory, surviving billfish larvae were placed in dark green 400-liter or black 1,060-liter cylindrical fiberglass tanks connected to the University of Miami's flow-through system which receives oceanic water from an adjacent pass. The 400-liter tanks measured 85 cm in diameter by 70 cm deep. The 1,060-liter tanks measured 150 em in diameter by 85 cm deep. Five live foods were introduced into tanks: brine shrimp (Artemia spp.), wild copepods, larval red drum (Sciaenops ocellatus), larval spotted seatrout (Cynoscion nebulosus), and larval dolphin (Coryphaena hippurus). Invertebrate foods were introduced at densities ranging from I to 10 items·ml-', while vertebrate food densities ranged from 0.03 to 0.10 items·ml-I.

RESULTS During the study, a total of 315 tows captured 2 larval swordfish and 288 larval sailfish (Table 1). The swordfish larvae measured 6.7 and 7.7 mm total length (TL), in May and July, respectively, Larval sailfish first appeared in the collections during the month of May in both years. Sailfish larvae were captured from surface waters ranging in temperature from 27.0°C to 30.4°C and salinity from 34.9%0 to 37.4%0. Captured larval sailfish ranged from 2.9 to 15.7 mm TL (mean = 5.1, standard deviation = 1.6) over the study period. Monthly mean size of sailfish larvae remained relatively constant. In both years, the highest CPUEs were ob- tained from May through July (Fig, 2). Sailfish larvae were least abundant during 1028 BULLETIN OF MARINE SCIENCE. VOL. 60, NO.3. 1997

Table I. Details of field and laboratory observations on captured larval swordfish and sailfish, For each sampling day data are: number of tows, total volume of water filtered (m3), number of billfish larvae captured, and the numbers surviving to at least the hours listed.

Sampling date Survivors at x hour Tolal volume Number Species Tows filtered captured 0 8 24 48 72 >72 Swordfish 5/24/94 13 17,803 1 0 7/21/95 11 15,782 I 0 Total 24 33,585 2 0 Sailfish 5/9/94 7 8,646 0 5/13/94 16 19,219 29 17 3 3 3 0 5/17/94 12 15,000 3 2 2 2 0 5/24/94 13 17,803 37 12 5 5 0 6/1/94 8 10,254 21 7 0 6/20/94 5 6,256 0 6/21/94 10 13,465 13 3 1 0 7/1/94 13 17,097 26 14 0 7/19/94 9 12,043 3 0 8/2/94 11 14,111 2 1 0 8/8/94 21 30,692 13 3 0 8/9/94 7 10,295 10 5 2 2 0 8/31/94 12 18,318 8 3 2 2 0 9/7/94 5 7,537 1 0 10/11/94 14 21,502 7 1 0 3/23/95 10 16,602 0 4/13/95 6 8,568 0 5/12/95 11 20,696 10 0 5/14/95 5 8,895 2 0 5/17/95 10 15,203 17 0 5/18/95 12 18,128 15 0 6/19/95 4 7,003 1 0 6/28/95 11 15,256 8 3 2 0 6/30/95 10 13,399 18 0 7/21/95 11 15,782 22 5 4 3 1 0 8/10/95 4 5,220 5 3 2 2 1 0 8/11/95 12 16,618 5 1 1 1 0 8/14/95 6 7,364 1 0 8/17/95 12 17,356 0 8/22/95 8 11,360 8 5 0 9/19/95 10 14,076 2 1 1 0 10/20/95 10 15,407 1 1 0 Total 315 449,171 288 87 26 23 7 0 the first quarter of the moon (Fig. 3). Highest CPUEs were observed from 07:00 to 10:00 hours (Fig, 4). Of the 288 sailfish larvae captured, 87 were alive immediately after capture. While none died during transfer from the plastic inspection bag to transport containers, 26 larvae survived transport to the laboratory. Of these, 23 survived 24 h, 7 survived 48 h, and 1 survived 72 h (Table 1). Laboratory and field water conditions were not identical. In the first few sampling trips, laboratory water temperatures differed from those measured at capture sites by as much as 2.5°C. As techniques were refined, temperatures were kept within 0.5°C; however, laboratory salinities averaged 1.1%0 lower than field conditions (Fig. 5). In the laboratory, most sailfish displayed similar behavior patterns, i.e., ex- tremely rapid swimming that led to contact with the tank sides and bottom. Typ- ically, fish maintained this pattern until their death. Apparently healthy individual POST ET AL.: BEHAVIOR-LARVAL ATLANTIC BILLFISHES 1029

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1994 1995 Year and Month

Figure 2. Sailfish mean catch-per-unit-effort (larvae per 10,000 m3) by month sampled during 1994 and 1995. Venical bars arc:!: I SE.

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Moon Phase

Figure 3. Sailfish mean catch-per-unit-effon (larvae per 10,000 m3) by moon phase. Each category represents:!: 3.5 days around the moon phase. Venical bars are:!: I SE. 1030 BULLETIN OF MARINE SCIENCE, VOL. 60. NO.3, 1997

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Time of Day (Hours)

Figure 4, Sailfish mean catch-per-unit-effort (larvae per 10.000 mJ) by time-of-day sampled (i.e., 06:00 to 16:00 h), Vertical bars are ± I SE. sailfish were observed to strike and seize prey. Dissection of one sailfish larva revealed cultured Artemia in its gut confirming feeding in the laboratory (Fig. 6). This is the first reported observation of larval sailfish feeding.

DISCUSSION The number and apparent abundance of larval sailfish captured in the present study exceeds those reported in previous studies. The Nankai Regional Fisheries Laboratory, Japan, conducted a 15-year survey of larval tunas and istiophorids in the Pacific and Indian oceans which yielded 129 sailfish larvae from approxi- mately 2,600 15-min plankton tows (Ueyanagi, 1964). Jolley (1977) reported that only 149 istiophorid larvae were collected in 12 years of plankton surveys off the east coast of Florida. The presence and abundance of larval sailfish in the Straits of Florida off Miami in our study appear to indicate a May to October spawning season which has been reported previously (LaMonte and Marcy, 1941; Voss, 1953; Gehringer, 1956; de Sylva, 1957; Jolley, 1977). Lack of any pattern in monthly mean sizes of sailfish larvae may reflect gear avoidance by larger larvae and/or a protracted spawning period over the summer months. The size range of sailfish larvae in our study (2.9 to 15.7 mm TL) was similar to that of Gehringer (1956) off Georgia (i.e., 3.4 to 38.8 mm TL), but was larger than that of Leis et al. (1987) off Australia (i.e., 2.5-3.8 mm TL). Swordfish larvae were smaller than those reported in other studies (Grall et al., 1983). Precisely why we observed lower catches during the first quarter of the moon is unclear. The observed distribution of larval sailfish in the surface waters during the morning hours is consistent with previous studies. Gehringer (1956) captured most of 26 sailfish larvae off Georgia at the surface during the day. Ueyanagi (1964) found Indo-Pacific istiophorid larvae concentrated in surface waters during the day, but scattered through the upper 50 m at night. Of 14 sailfish larvae that Lipskaya and Gorbunova (1977) captured in the surface waters of the Pacific and Indian oceans, 10 were caught in the morning (05:00-11:00). Off Australia, Leis et al. (1987) collected 13 sailfish larvae in the upper 6 m during the day. Collec- tively, these studies suggest that larval sailfish concentrate in surface waters during daylight hours; however, further depth-stratified sampling, particularly at night, is required. Despite the fact that we used a short tow duration (i.e., 2 min), most billfish larvae did not survive the capture process. This was possibly due to a combination of mechanical effects such as contact with, and compression against, the sides and cod-end of the net, floating debris, and other animals such as jellyfish and amphipods. Some of these problems might be ameliorated by further reduction 1032 BULLETIN OF MARINE SCIENCE, VOL. 60, NO.3. 1997

Figure 6. A dead 5.5-mm sailfish larva that survived in the laboratory for 2 d. Larva is shown (A) intact; and (B) dissected. The gut of this larval sailfish was full of cultured Artemia which were introduced into holding tanks. of tow duration combined with a much larger (i.e., > 10 liter) cod-end design which has successfully captured live ctenophores (Baker and Reeve, 1974). During transport to the laboratory, some principal factors that may have induced mortality were elevated water temperatures, high light levels, and abrupt physical disturbances associated with wave action. We observed larval sailfish pushing bill-first against the sides of transport containers. In this position, they appeared to be subject to energy transferred from the impact of the vessel against ocean waves. While transport containers were padded to reduce shock, it is unlikely that these effects were eliminated. This behavior is apparently a stress response to be prevented if survival in captivity is to improve. POST ET AL.: BEHAVIOR-LARVAL ATLANTIC BILLFISHES 1033

While the exact causes of mortality in the laboratory were not determined, these likely can be attributed to some combination of injuries incurred during capture, interruptions in feeding, and suboptimal water quality conditions. Every attempt was made to match field and laboratory water quality conditions, but this was not always possible with our flow-through system which was subject to tidal fluctuations. Future studies could reduce differences between field and laboratory water quality by using closed recirculating systems filled with the oceanic water taken from collection sites. Successful feeding in the laboratory suggests that larval billfish maintenance is to some extent possible, even with somewhat rudimentary methods and equip- ment. Refinements in the techniques applied here hold promise for the live capture and laboratory observation of billfish larvae as a means of increasing our knowl- edge of the behavior, early life history, and population dynamics of these impor- tant pelagic species.

ACKNOWLEDGMENTS

This research was funded by T. Choate, ARTMARINA, the Mostyn Foundation, Inc., and the Yamaha Miami Billfish Tournament. K. Mertz and H. Augustus provided technical support. Thanks are due to P. Walsh, B. Rosendahl, and M. E. Clarke for suggestions on collecting and maintaining billfish larvae. R. Schaeffer facilitated acquisition of federal billfish collection permits. D. de Sylva acknowledges Ihe previous support provided by the National Science Foundation and the Pompano Beach (Florida) Fishing Rodeo. This manuscript benefitted greatly from the insightful comments of an anonymous reviewer.

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DATEACCEPTED:September 4, 1996.

ADDRESS: University of Miami, Rosenstiel School of Marine and Atmospheric Science, Division of Marine Biology and Fisheries, 4600 Rickenbacker Causeway, Miami, Florida 33149 USA.