Temporal Spawning Patterns of Several Surgeonfishes and Wrasses in American Samoa 1

Transcription

1 Pacfc Scence (1998), vol. 52, no. 1: by Unversty of Hawa' Press. All rghts reserved Temporal Spawnng Patterns of Several Surgeonfshes and rasses n Amercan Samoa 1 ABSTRACT: Three coral reef surgeonfshes (Acanthurus guttatus, A. trostegus, A. lneatus) and two wrasses (Thalassoma qunquevttatum, T hardwck) spawned year-round n Amercan Samoa. Spawnng occurred n or adjacent to the channel dranng the frngng reef at specfc tmes of day: dawn (A. lneatus), daytme (T qunquevttatum, T hardwck), or dusk (A. guttatus, A. trostegus); and spawnng tme tracked seasonal changes n day length. Egg predaton was hgh for the surgeonfshes, but predaton by pscvores appeared to be low. ABOUT TEMPORAL spawnng patterns of coral reef fshes has accumulated over the past three decades (e.g., overvews by Johannes 1978, Thresher 1984, Robertson 1991, Sadovy 1996). However, only a small proporton of the thousands of coral reef speces have been examned, and data are avalable for few locatons across the vast South Pacfc. Ths report summarzes tmeof-day and monthly spawnng records for several common coral reef fshes n Amercan Samoa: three surgeonfshes (Acanthurus guttatus Bloch & Schneder, A. trostegus Lnnaeus, A. lneatus Lnnaeus) and two wrasses (Thalassoma qunquevttatum Lay & Bennett, T hardwck Bennett). Of these, A. lneatus s a major component of local harvests (Crag et al. 1997). NFORMATON MATERALS AND METHODS Amercan Samoa (14 S, 17 ) conssts of several small volcanc slands n the central South Pacfc. Observatons of spawnng were made on the frngng coral reef at Afao vllage on Tutula sland. The reef flat there -- --rtjsstudywassupported by the Federal Ad fn Sportfsh Restoraton Act. Manuscrpt accepted 2 March Department of Marne and ldlfe Resources, Box 373, Pago Pago, Amercan Samoa Current address: Box 532, Klamath, Calforna was 25 m wde, dropped abruptly to a depth of 3-6 m, and descended gradually thereafter to 2 m. A sngle channel draned the reef flat. Nearshore water temperatures were measured seaward of the reef flat at a depth of.3 m (n = 295 daly measurements). Sunrse and sunset tmes were obtaned from the NOAA weather staton n Amercan Samoa. Durng , approxmately 35 snorkelng surveys were made on nearshore portons of ths reef at varous tmes of day. For the surgeonfshes, made observatons durng all months of the year at known spawnng locatons; observatons of the wrasses were opportunstc encounters. Confrmaton of spawnng was determned by the upward rush of fsh, culmnatng n the producton of vsble mlt clouds. Observatons were generally made at md to hgh tde; no attempt was made to assess tdal or lunar effects. Data are summarzed by plottng multple-year spawnng records over a sngle annual cycle. Spawnng tmes lsted for dawn spawners tended to be at the end of ther spawnng perod, whereas the reverse occurred for dusk spawners. Because the full duraton of each spawnng perod was not montored, observed rates of predaton were mnmum estmates. RESULTS Two varables that commonly nfluence the tme when fshes spawn, water tempera35

2 PACFC SCENCE, Volume 52, January Acanthurus guttatus, a nonterrtoral surgeonfsh, mgrated to a specfc ("tradtonal") o. (/)3,., : area n the outer reef channel and spawned above several large coral blocks n waters -H 4-7 m deep. Groups of 5-5 fsh began w 29'" " :: :: ::::l.' spawnng near sunset, and the tme of : spawnng tracked seasonal changes n sunset 28 (Fgure 2). Spawners had pale/slvery sdes ' wth fant bars and dots, dark edges on dora.. r sal and ventral body, and brght yellow on 27 L pelvc fns and a porton of the caudal fn..,, Egg predators (prmarly the snapper Macolor nger Forskl) fed on the eggs durng at least 57% of observed spawnng perods on 22 dates. Two attacks on the spawners were observed, once each by a dogtooth tuna (Gymnosarda uncolor Ruppell) and a bluefn trevally (Caranx melampygus Cuver). 12 Acanthurus trostegus also spawned near Z sunset (Fgure 2) n large groups (2-2) -l along the reeftop adjacent to the reef channel 11.. and along the outer channel floor. ater depths were.8-6 m. Spawnng color was as "" l...-_--'---._ descrbed by Robertson (1983). Egg predamar MAY JUL SEP NOV JAN tors (M. nger) were observed feedng on the FGURE. Seasonal changes n nearshore water temeggs durng at least 64% of observed spawnperature (lop) and day length (bottom). ng perods on 28 dates. Eghteen attacks on the spawners were observed, 17 by bluefn ture and day length, vared only slghtly trevally and one by an undentfed fsh. through the year because of Samoa's oceanc Acanthurus lneatus, a terrtoral surgeonlocaton near the equator. Seasonal changes fsh, mgrated at dawn to a "tradtonal" ste amounted to 2SC and 1.8 hr day length that partally overlapped the spawnng ste used by A. guttatus n the outer porton of (Fgure 1). Three surgeonflshes (A. guttatus, A. tro- the reef outlet channel. Groups of 5-2 stegus, A. lneatus) and two wrasses (T fsh began spawnng at least 5-15 mn before qunquevttatum, T hardwck) spawned sunrse (Fgure 2) n water depths of 3-5 m. throughout the year n water temperatures Spawnng color was as descrbed by Robrangng from 27 to 3 C. Vrtually all ob- ertson (1983). Typcally 1-3 egg predators served spawnng occurred n or adjacent to (M nger) hovered nearby and fed on the the outlet channel of the reef flat where water eggs durng all spawnng perods observed currents flowed n a seaward drecton. Two on 27 dates. One attack was observed on of the surgeonfshes spawned at nearly the the spawners, apparently by Lutjanus bohar same ste n the outer porton of the channel, Forskl. and the other speces spawned over a slghtly Thalassoma qunquevttatum spawned broader area wthn or near the channel. All throughout the daytme (Fgure 2) on the were group spawnngs, except as noted. Prn- shallow reef flat adjacent to the channel cpal-olferences among speces--were-'1:he-- (water--depth--:-7=1-m1:--almost-ah-were tmes of day that they spawned and the rates group spawnngs consstng of 1-2 small of egg predaton by other fshes, as descrbed fsh (8-1 cm). Multple spawnngs were obbelow. None of the spawnng aggregatons served on each of 49 dates. No predators or was targeted by local fshermen. egg predators were seen. On three occasons, ::: t9._..._,._..j......l...-

3 Spawnng Patterns of Surgeonfshes and rasses-crag 37 Bpm t o.l. o - 3pm L 1am 5 am rl---'---'--_' ' ' '_--' l------' -'------L---'-----' 8pm L ---: r- * B o o * * * Ok 3pm r- o T. qunq. (;t. * T. hardwck lfo * 1 am, B r,=: 5am MONTH * A. guttatus o A. trostegus A. lneatus FGURE 2. Tme of day of spawnng throughout the year for three surgeonfshes (top) and two wrasses (bottom) n relaton to tmes of sunrse and sunset (lnes). par spawnngs were observed between a small fsh and a larger termnal-phase fsh at the edge of the reef fat. On one of the latter occasons, a juvenle M nger fed on the eggs. Thalassoma hardwck probably spawned 'yeafnmnd-(fgure-2r--on'n-akfes, 'group spawnngs of 1-4 fsh were observed durng daytme hours on the reef fat near the nner channel (water depth.7-1 m). No predators or egg predators were seen durng spawnngs. DSCUSSON t has long been noted that tropcal fshes spawn over an extended season compared wth fshes from hgher lattudes (e.g., Qasm r9'sorye'a--=found spawnng, as'observe(cn Samoa, has been documented or nferred for a number of other tropcal fshes (Randall 1961a, Randall and Randall 1963, Myrberg 1972, Munro et al. 1973, arner et al. 1975,

4 38 PACFC SCENCE, Volume 52, January 1998 Robertson and Hoffman 1977, Thresher 1984, Grmes 1987, alsh 1987, Coln and Clavjo 1988, Gladstone and estoby 1988, Robertson 199). Despte such prolonged breedng, Russell et al. (1977) emphaszed that most spawnng effort by tropcal fshes occurs durng a seasonal perod. Ths holds true for at least one ofthe fshes descrbed n ths paper: A. lnea- only dawn-spawnng speces was one that defended feedng terrtores. LTERATURE CTED COLN, P., and L. BELL Aspects of the spawnng of labrd and scard fshes at Enewetak Atoll, Marshall slands wth tus spawns prmarly durng the austral notes on other famles. Envron. Bo. sprng and summer months of September- Fshes 31: February (Crag et al. 1997), even though COLN, P., and 1. CLAVJO Spawnng some spawnng occurred monty. Smlarly, actvty of fshes producng pelagc eggs A. trostegus n Hawa' has a seasonal on a shelf edge coral reef, southwestern spawnng peak although some year-round Puerto Rco. Bull. Mar. Sc. 43: spawnng occurs (Randall 1961a). Although CRAG, P ntertdal terrtoralty and a seasonal spawnng peak may be talored tme-budget of the surgeonfsh, Acanthuto a partcular tme that s favorable for rus lneatus, n Amercan Samoa. Envron. ether adult spawners or the survval of ther Bo. Fshes 46: young, year-round spawnng seems to be a CRAG, P., H. CHOAT, L. AxE, and S. "bet-hedgng" strategy to cope wth losses SAUCERMAN Populaton bology and of young caused by envronmental vagares harvest ofthe coral reef surgeonfsh Acan- (Robertson 199, 1991). thurus lneatus n Amercan Samoa. Fsh. The tme ofday that spawnng occurred n Bull. 95(4): ths study was smlar to that reported else- GLADSTONE,., and M. ESTOBY where for the same speces. Acanthurus lne- Growth and reproducton n Canthgaster atus spawned at dawn n Palau (Johannes valentn: A comparson of a toxc reef 1981, Robertson 1983); A. trostegus spawned fsh wth other reef fshes. Envron. Bo. at dusk n the Socety slands (Randall Fshes 21: b); T qunquevttatum and T hardwck GRMES, C Reproductve bology of were daytme spawners n the Marshall the Lutjandae: A revew. Pages slands (Coln and Bell 1991). For one of n J. Polovna and S. Ralston, eds. Tropthese speces, the herbvorous and strongly cal snappers and groupers: Bology and terrtoral A. lneatus (Crag 1996), the tme fsheres management. estvew Press, of day when t spawns s thought to be a London. strategy to mnmze loss of food from ts JOHANNES, R Reproductve strateges terrtory (Robertson 1983, 1991, Kohda of coastal marne fshes n the tropcs. 1988); that s, f a herbvorous terrtoral fsh Envron. Bo. Fshes 3: must leave ts terrtory unguarded when t ords of the lagoon. Unverspawns, t would be best to do so n the sty ofcalforna Press, Berkeley. mornng when herbvorous compettors typ- KOHDA, M Durnal perodcty of cally have low feedng rates. spawnng actvty of permanently terrto- n all, the Samoan spawnng data ft ral damselfshes (Teleoste: Pomacenwell nto what was predcted based on ltera- trdae). Envron. Bo. Fshes 21 :91-1. ture from dstant tropcal areas: spawnng MUNRO, J., V. GAUT, R. THOMPSON, and P. occurred over an extended tme perod, at REEsoN The spawnng seasons of - specfctmes- ofaay, often ac"lraotonal"- --earbbe-,rn-re'ef-fshes:-jfsh:--bol-;-5-:69= stes where there was a seaward current away 84. from the reef. n addton, the surgeonfshes MYRBERG, A Ethology of the bcolor adopted specalzed spawnng coloraton, egg damselfsh, Eupomacentrus parttus (psces: predaton was hgh at some stes, and the Pomacentrdae), a comparatve analyss

5 Spawnng Patterns of Surgeonfshes and rasses-crag 39 of laboratory and feld behavor. Anm. Behav. Monogr. 5: QASM, S Tme and duraton of the spawnng season n some marne teleosts n relaton to ther dstrbuton. J. Cons. nt. Explor. Mer 21: RANDALL, J. 1961a. A contrbuton to the bology of the convct surgeonfsh of the Hawaan slands, Acanthurus trostegus sandvcenss. Pac. Sc. 15: b. Observatons on the spawnng of surgeonfshes (Acanthurdae) n the Socety slands. Copea 1961: RANDALL, J., and H. RANDALL The spawnng and early development of the Atlantc parrotfsh Sparsoma rubrpnne, wth notes on other scard and labrd fshes. Zoologca (N.Y.) 48:49-6. ROBERTSON, D. R On the spawnng behavor and spawnng cycles of eght surgeonfshes (Acanthurdae) from the ndo-pacfc. Envron. Bo. Fshes 9: Dfferences n the seasonaltes of spawnng and recrutment of some small neotropcal reef fshes. J. Exp. Mar. Bo. Eco. 144: The role of adult bology n the tmng of spawnng of tropcal reef fshes. Pages n P. Sale, ed. The ecology of fshes on coral reefs. Academc Press, San Dego. ROBERTSON, D. R., and S. HOFFMAN The role of female mate choce and predaton n the matng systems of tropcal labrod fshes. Z. Terpsycho. 45: RUSSELL, B., G. ANDERSON, and F. TALBOT Seasonalty and recrutment of coral reef fshes. Aust. J. Mar. Freshwater Res. 28: SADoVY, Y Reproducton of reef fshery speces. Pages n N. Polunn and C. Roberts, eds. Reef fsheres. Chapman and Hall, New York. THRESHER, R Reproducton n reef fshes. T.F.H. Publcatons, Neptune Cty, New Jersey. ALSH, Patterns of recrutment and spawnng n Hawaan reef fshes. Envron. Bo. Fshes 18: ARNER, R., D. ROBERTSON, and E. LEGH Sex change and sexual selecton. Scence (ashngton, D.C.) 19: