Japanese Journal of Ichthyology Vol.31,No.3 1984 魚 類 学 雑 誌 31巻3号1984年

Mobbing Behavior by Stegastes albifasciatus interatctions(Donaldson,1981).The study Pomacentridae),a Territorial( sites are described as follows: Mosaic Damselfish Site 1.Located at Tanguisson Reef on a reef flat 20m above the surge zone in a depth of 1.5 m. The substratum consisted mainly of coral rock Terry J.Donaldson pavement and rubble interspersed with patches (Received February 21,1984) Acropora,Favia,and Pocillopora spp.corals. Inhabitants of the territorial mosaic included Mobbing of potential predators,a behavior Stegastes albifasciatus,and the pomacentrids long known for birds,has only recently been re- Chrysiptera leucopomas(Lesson),and C.leuco- ported for fishes.Mobbing by fishes has been pomas-amabilis phase(Allen,1975). simply defined as the assemblage of individuals Site 2.Located in Tumon Bay on a reef around a potentially dangerous predator(Do- flat 50m above the surge zone in a depth of miney,1983).Possible functions of this be- 1.0 m.The substratum consisted of coral sand havior include advertisement of the presence of and rubble,and patches of Acropora aspera. a predator(Dominey,1983),driving the pred- Inhabitants of this mosaic were S.albifasciatus, ator from a given area,or cultural transmission and the pomacentrids S.lividus(Bloch et of predator identity(Curio,1978).Mobbing Schneider),S.nigricans(Lacepede),and Dascyl- behavior has been reported chiefly from colonial- lus aruanus(Linnaeus). ly nesting fishes,and serves to protect nesting Site 3.Located in Pago Bay on a reef flat adults rather than eggs present in a nest(Fricke, 30m above the surge zone in a depth of 1.5 m. 1973;Dominey,1983).It has also been reported The substratum consisted of broken coral rock for non-territorial and occasionally territorial pavement,coral rubble and sand.Benthic coral-reef species(Motta,1983).Here I report algal growth was considerable.Inhabitants mobbing behavior by the damselfish Stegastes of this mosaic included S.albifasciatus,and the albifasciatus(Schlegel et Miiller),a non-nesting pomacentrids S.nigricans,Chrysiptera biocellatus inhabitant of coral reef flat territorial mosaics. (Quoy et Gaimard)and C.glaucus(Cuvier). A territorial mosaic consists of contiguous territories occupied for long periods of time by Results single animals(Keenleyside,1979).Pomacen- No evidence of nesting by S.albifasciatus on trid territorial mosaics are characterized by hav- any of the study sites was observed.Rather, ing single adults of both sexes occupying and damselfishes were observed feeding,clustering defending small areas of the substrate,usually (Thresher,1980),sheltering and engaging in in patches of coral rubble(Sale,1974).Ter- intra-and interspecific agonistic behavior. ritories are relatively stable and non-overlapping A total of seven separate observations of (Keenleyside,1979),except in heterospecific mobbing behavior were made between the three mosaics where territory boundary overlap can study sites(Table 1)during one hour observation occur(Donaldson,1981).Mosaic territories sup- periods.They are described as follows: port feeding,breeding(courtship and nesting), Site 1.Mobbing behavior by S.albifasciatus sheltering and resting activities(Keenleyside, was observed on four consecutive mornings 1979)but function primarily as a means for pro- tecting a limited food source,usually benthic (0900-1100 h)in June,1980.Mobbing was di- rected against a pair of scorpionfishes,Scorpa- algae(Low,1971;Vine,1974;Ebersole,1977; enopsis diabolus(Cuvier),each measuring ap- Hixon,1980). proximately 30cm SL,which occasionally en- tered the study site mosaic.The intruders were Methods almost always positioned parallel to one another Observations of mobbing behavior by Steg- and occasionally their bodies touched.A single astes albifasciatus were made at three 5 m2 reef S.albifasciatus,resident in the territory where flat study sites on Guam,Mariana Islands, the intrusion occurred,rose above the territory, during a 1980-81 study of damselfish species milled about(Thresher,1980)and then ap-

―345― 魚 類 学 雑 誌Japan.J.Ichthyoi.31(3),1984 proached the scorpionfishes from either the side the second observation. or the back of the intruders but never from the Discussion region of the head.During the approach the Patterns of mobbing behavior directed against damselfish was joined by two to five damselfishes of the mosaic in a similar manner.Mobbing intruding predators by Stegastes albifasciatus damselfishes repeatedly dove to within approxi- were essentially the same at all three sites.Dif- mately 20cm of the heads of the scopionfish ferences existed however in the proximity and under attack,performed lateral displays,often direction of approach relative to the position of with erect dorsal fins,exhibited bodyshaking, the head of the intruder.Mobbing damsel- fishes tended to orientate towards and approach and then spun away with a flip of the caudal fin,often passing well above the intruder's head. closer to the heads of intruding eels but did not do so with intruding scorpionfishes.The be- The intruding scorpionfishes appeared to ignore the mobbing at first and then slowly swam out havior towards scorpionfishes suggests the pos- of the mosaic.Pursuit of the intruders,once sibility of some form of predator recognition outside of the mosaic,was not observed. ability in mobbing damselfishes.An ability to Site 2.A single observation of mobbing be- recognize potential predators would be useful havior was observed at this site during an after- in conveying information of the relative danger- noon(1400 h)in March,1981.A single juvenile ousness of the intruder(Dominey,1983).While moray eel,Lycodontis javanicus(Bleeker),ca. eels and scorpionfishes are both successful pred- 80cm SL,entered the mosaic through an ad- ators,their methods of feeding are different. Scorpionfishes possess a highly specialized jacent patch of Acropora aspera.Five S.al- bifasciatus,joined by a single S.lividus from the method of suction feeding which is quite efficient mosaic,commenced milling above the eel and in capturing nearby prey(Grobecker,1983). then alternately mobbed the head region of the Mobbing damselfishes passing too closely to the eel,passing within approximately 10cm of the head of a scorpionfish could fall victim to such side and back of the head,but avoiding the a means of predation.Moray eels,lacking this mouth.Lateral displays,dorsal fin erections ability,appear to lunge at prey and may also and body-shaking were also observed of the restrict most of their feeding to nocturnal periods mobbing damselfishes.Pursuit by two S.al- when potential prey are resting and less capable bifasciatus continued 0.5 m past the boundary of avoiding predation(Hiatt and Strasburg,1960, of the mosaic as the eel left the mosaic. but see Hobson,1968,1974).Mobbing dam- Site 3.During two late afternoon(1700- selfishes,if responsive to the difference in pred- 1800 h)observations in Pago Bay during April, ator feeding ability,practice a different means 1981,mobbing by 5-7 S.albifasciatus and 1 C. of approach while mobbing eels which allow them biocellatus was directed against a small(ca.45cm to pass much closer to the intruder.The but- SL)eel,Echidna nebulosa(Ahl),which foraged on terflyfishes,Chaetodon frembili Bennett,C.uni- the mosaic.Methods of approach and agonis- maculatus Bloch and C.auriga Forsskal,ap- tic behavior were the same as those described parently mobbing moray eels,Gymnothorax for Site 2,except that pursuit of the intruder (=Lycodontis)meleagris(Shaw et Nodder),G. extended 1 m past the mosaic boundary during eurostus(Abbott)and Muraenidae sp.,passed

Table 1.Summary of mobbing events by damselfish observed in three study sites at Guam,Mariana Islands.

(*Denotes 5 Stegastes albifasciatus plus 1 S.lividus.**Denotes 5-7 S.albifasciatus plus 1 Chrysiptera biocellatus.)

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close to and even touched the heads of these mobbing fishes might very well be tempered by predators(Motta,1983). their ability to recognise and determine the rel- Recognition of apparent predators and their ative dangerousness of the predator. subsequent harassment by potential prey ap- parently occurs among Caesio cuning(Bloch) Acknowledgments confronted by moray eels(Eibl-Eibesfeldt,1962), I with to thank C.Birkeland,R.N.Clayshulte, and Dascyllus trimaculatus(Riippell),a nesting and G.B.Constantino for their assistance,and damselfish which harasses barracuda(Sphyra- W.J.Dominey,J.T.Moyer and the late J.A. enidae),triggerfishes(Balistidae)and even octo- Ward for their comments on fish mobbing be- pus(Fricke,1973).Dominey(1983)reported havior.The suggestions of an anonymous that bluegill sunfish,Lepomis macrochirus Ra- reviewer improved portions of the manuscript. finesque,mobbed snapping turtles Chelydra J.M.Fitzsimons and R.F.Myers are thanked serpentina serpentina,effective ambush pred- for critically reading the manuscript.Mrs.M. ators which intrude upon colonial nests,but Richard kindly typed the final draft.This did not respond to intruding painted turtles, Chrysemys picta picta,which offer no apparent paper was written with the generous support of the Department of Ichthyology,California A- threat.Adult bluegills also did not respond to cademy of Sciences,for which I am very grateful. largemouth bass,Micropterus salmoides(La- Contribution No.204,University of Guam, cepede),and chain pickerel,Esox niger Lesueur, Marine Laboratory. which are effective predators of juveniles. Advertisement of the apparently recognised intruding predator was also indicated.Each Literature cited episode of mobbing commenced with a single Allen, G. R. 1975. Damselfishes of the south individual responding to a violation of its ter- seas. TFH Publ., Neptune City, New Jersey, ritorial area and it was joined by other damsel- 240 pp. fishes over time.Advertisement is useful in alert- Curio, E. 1978. The adaptive significance of avian mobbing. I. Teleonomic hypotheses and pre- ing members of the mosaic to the potential dictions. Z. Tierpsychol., 48: 175-183. threat of the intruder.Since scorpionfishes and Dominey, W. J. 1983. Mobbing in colonially eels rely upon the element of surprise in capturing nesting fishes, especially the bluegill, Lepomis their prey,advertisement of their presence by macrochirus. Copeia, 1983 (4): 1086-1088. mobbing reduces predator success.Such an Donaldson, T. J. 1981. Serial territories of the outcome has been suggested for bluegill sunfish damselfish Stegastes albifasciatus in three coral which mobbed intruding snapping turtles and habitats on Guam. Proc. 4th Internl. Coral effectively deterred this ambush predator by Reef Symp., 2: 587. advertising its presence(Dominey,1983). Ebersole, J. P. 1977. The adaptive significance of interspecific territoriality in the reef fish Eu- The degree of aggression during mobbing pomacentrus leucostictus. Ecology, 58: 914-920. while driving away predators varies in fishes. Eibl-Eibesfeldt, I. 1962. Freiwasserbeobachtungen Although intruding predators were eventually zur Deutung des Schwarmverhaltens verschiedener driven from territorial mosaics by mobbing dam- Fische. Z. Tierpsychol., 19: 165-182. selfishes,the extent of aggression displayed was Frick, H. W. 1973. Okologie and Sozialverhalten limited to behavioral displays with only occasion- des Korallenbarsches Dascyllus trimaculatus(Pisces, al pursuit.No contact between the intruding Pomacentridae). Z. Tierpsychol., 32: 225-256. predator and the mobbing damselfishes was ever Grobecker, D. B. 1983. The" lie in wait" feeding observed although such activity occurs among mode of a cryptic teleost, Synanceia verrucosa, pp. some butterfiyfishes(Motta,1983).Damaging 29-40. In D. L. G. Noakes, D. G. Lindquist, G. aggression(Curio,1978)during mobbing has S. Helfman, and J. A. Ward, eds., Predators and been observed of black basses(Micropterus spp.) prey in fishes. Dr. W. Junk, Publ., Hague. Hiatt, R. W., and D. W. Strasburg. 1960. Eco- which repeatedly attacked an intruding softshell logical relationships of the fish fauna on coral turtle(Trionyx ferox)by biting and grabbing reefs of the Marshall Islands. Ecol. Monogr., its tail and legs(Dominey,1983).The ability 30: 65-127. to successfully inflict damaging aggression by Hixon, M. A. 1980. Food production and corn-

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petitor density as the determinants of feeding (Museum of Natural Science, 119 Foster Hall, Lou- territory size. Amer. Natur., 115 (4): 510-530. isiana State University, Baton Rouge, Louisiana Hobson, E. S. 1968. Predatory behavior of some 79803-3216 USA) shore fishes in the Gulf of California. U. S. Bur. キ オ ビス ズ メダ イのmobbing行 動 Sports Fish. Wildl., Res. Rept., 73: 1-92. Hobson, E. S. 1974. Feeding relationships of Terry J.Donaldson teleostean fishes on coral reefs in Kona, Hawaii. 鳥 類 で 古 く か ら 知 られ ていたmobbing行 動 が,魚 Fish. Bull., 72 (4): 915-1031. 類 で も最 近 明 ら か に さ れ つ つ あ る.魚 類 のmobbing Keenleyside, M. H. A. 1979. Diversity and adap- は 捕 食 者 の 周 囲 に 群 ら が る 行 動 と定 義 さ れ て い る. tation in fish behaviour. Springer-Verlag, New mobbingは 捕 食 者 の 存 在 を 知 ら せ,追い 払 う た め に York, xii+208 pp. 行 な わ れ る と 考 え ら れ てい る.mobbing行 動 は 主 と Low, R. M. 1971. Interspecific territoriality in a し て 巣 を 形 成 す る 魚 類 に 見 出 さ れ て い る. pomacentrid reef fish, Pomacentrus flavicauda Guam島 の ス ズ メ ダ イ 科 魚 類 の 種 間 関 係 の 研 究 中 Whitley. Ecology, 52: 648-654. に,キ オ ビ ス ズ メ ダ イ のmobbing行 動 が 観 察 さ れ Motta, P. J. 1983. Response by potential prey to た.観 察 を 行 な っ た 際 に 本 種 は 巣 を 形 成 し て い な か っ coral reef fish predators. Anim. Behay., 31: た が,サ ツ マ カ サ ゴ と ド ク ウ ツ ボ に 対 し てmobbing 1257-1259. 行 動 を 示 し た. Sale, P. F. 1974. Mechanisms of co-existence in 2尾 の サ ツ マ カ サ ゴ が な わ ば り 内 に 侵 入 す る と1尾 a guild of territorial fishes at Heron Island. Proc. の キ オ ビ ス ズ メ ダ イ が な わ ば り 内 で 上 昇 し,侵 入 者 の 2nd Internl. Coral Reef Symp., 1: 192-200. 背 後 や 側 方 か ら接 近 し た.こ の 間 に2～5尾 の キ オ ビ Thresher, R. E. 1980. Clustering: non-agonistic ス ズ メ ダ イ が 加 わ り,体 側 面 を 誇 示 し た り,体 を ふ る group contact in territorial reef fishes, with special わ せ た り,背 鰭 を た て た り,尾 鰭 を 振 り な が ら 回 転 し reference to the Sea of Cortez damselfish, Eu- た り,侵 入 者 の 頭 上 を 横 切 っ た り し た.侵 入 者 が な わ pomacentrus rectifraenum. Bull. Mar. Sci., 30: ば り外 へ 去 る と,キ オ ビ ス ズ メ ダ イ は 追 跡 は し な か っ 252-260. た. Vine, P. J. 1974. Effects of algal grazing and ド ク ウ ツ ボ に 対 し て は5尾 の キ オ ビ ス ズ メ ダ イ が aggressive behavior of the fishes Pomacentrus mobbing行 動 を 示 し た.ド ク ウ ツ ボ の 頭 部 背 面 や 側 lividus and Acanthurus sohal on coral reef ecology. 面 を10cmの 距 離 を 保 っ て 何 回 も 通 過 し た.こ の 際, Mar. Biol., 24: 131-136. 口 の 周 囲 は 通 ら な か っ た.体 を ふ る わ せ た り,背 鰭 を た て た り,体 側 面 を 誇 示 す る 行 動 も 観 察 さ れ た.

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