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Fig. 1 _ Juvenile injured by predators. Fish A is normal. EFFECT OF PREDA TO RS ON JUVENILE MENHADEN IN CLEAR & TURBID ESTUARIES

Richard L. Kroger and J am e s F . Guthrie

L ittle is known about the effects of pre da­ P redators Reduce Schools tion on juvenile menhaden during their 6 to 9 months of est u a r i n e life (Reintje s a nd Observations by fishermen and rat of Pacheco,1966). Numerous published report s s c arring suggest that the number of juveml s have de scribed the occurrence of juvenile in Steinhatchee River decreases steadily as menhaden in stomach samples of other spe­ a r e s ult of . Fishermen who live by cies (Reintjes, Christmas and Collins, 1960). t he r iver reported that schools of juvel1l:f' No studies have mentioned scarring rates in m e nhaden are usually 20 to 30 feet in diam­ populations of juvenile menhaden from dif ­ e te r in April. But, by July of each year, the ferent-type estuaries, or the kind of injurie s s c h ools which are about the same in numb I' incurred by juveniles that escape after be ing are r e duced by the abundant predator popula­ bitten by predators. tiont o t he 5 - to 10-feet- diameter schools we saw. These observations are supported by A sample of 682 juvenile Gulf menhade n) c alculations - -based on the fact that 197'0 of Brevoortia pat ron us (mean for k le ngth t he fis h wer e injured, and the assuP1ption that 62 mm), asp ott e d sea t r ou t) Cy nosci on one of 10 bitten juveniles survives. Thes nebulosus, and a blue runner,) cry s os) indi cate that our sample of 682 fish was th were collected in Steinhatchee River, , r emains of an original group of 1,852 juve­ on July 13, 1971, with a cast net. We ex­ niles (682 x .197-.1 + 552 = 1852). This esti­ amined the menhaden immediately and de ­ mate should be greater if scars disapp aI', termined t hat 19% had been i nj u r ed by or if rate of predation increases on injured pre-dators . Injuries ranged from single tooth menhaden. slashes to missing fins and chunks of fle sh The precise number of injured juvemle (Figure 1). It can be assumed that m ost menhaden in samples from other clear-water injuries occurred recently if rapid r egener­ and turbid estuaries was not obtained because ation and healing obscures injuries in this we did not immediately examine each fish river, as observed for fin -clipped and t a gged when fresh. After the samples were pre­ juvenile menhaden in other estuarie s and in served, only major injuries were discermble. the laboratory (Kroger and Dryfoos , 1972), Based on field calculations, however, we or if injured menhaden in schools are preyed know that at least 10% of the juve nile Atlantic upon at a greater rate than noninjure d m en­ menhaden, B . tyrannus) were injured in sam­ haden (Gunter and Ward, 1961). pIes collected from two Rhode Island and clear -water est u a r i e s in Most injuries were probably c aused by 1969-71. Water clarity in these estuaries trout and other sight-feeding predatory fish, was such that the bottom was visible in over such as blue runners (Simmons a nd B reuer, 2 m of water. Typical abundant predatory 1950 and Reintjes, 1969). We saw the s e spe­ fish captured in the haul seine with the in­ ci es make 20 predatory attacks in 1 h our on jured menhaden, and whose stomachs con­ menhaden schools at the surface i n a s mall tained menhaden, included chub mack r I, cove. Water clarity, as indicated by secchi Sc omber c olias) and b I u e f ish) Pomatomus disk readings, reg i s t er e d greater than saltatrix. Other probable menhaden preda­ 100 cm (the length of our s ecchi stick). We tors were caught, but their stomachs were consider this very clear and ideal for s ight­ not examined; these included crevalle Jack" feeding predators. Caranx hippos) and northern sennet,Sphyraena borealis.

Mr. Kroger is Fishe'Y Biologist and Mr. Guthrie is Technician, National Marine Fisheries Service, AtI"nuc Est nn~ F r- ies Center, Beaufort, North Carolina 28516 .

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Contrast of Turbid Estuaries the samples, or were present only in small numbers. In contrast, while capturing juvenile men­ hadenfor tagging and yearly abundance stud­ The high rate of scarring we observed in ies from 1956 to 1 971 on the Atlantic and populations of juvenile menhaden in clear Gulf coasts, we have never observed more water, relative to turbid water, indicates than one or two injured juvenile menhaden in either a different rate of escapement when any of several thousand samples collected in juveniles are bitten by the resident preda­ over 50 turbid estuaries where secchi read­ tors--or a different rate of predation on the ings ranged from 10 to 50 cm. Stomachs of juveniles in the two types of estuaries. We ladyfish)Elops sauruE1captured in these sam­ believe the great amount of scarring indi­ pIes have been examined and shown to con­ cates a higher rate of predation on the men­ tain a high percentage of juvenile menhaden haden. In our opinion, abundant predators (Sekavec, 1971). The only other t ypical severely reduce the number of juvenile men­ predatory fish captured with the juveniles in haden in some clear -water estuaries, whereas these turbid estuaries, and which stomach in turbid estuaries rates of predation on analysis showed they fed on menhaden, in­ menhaden are much lower (Kroger and cluded longnose and alligator gars, Lepisos­ Guthrie, 1973). Additional studies of the in­ teus osseus and L. spatula. These turbid­ teraction of menhaden and predator popula­ water predators usually were absent from tions in clear and turbid est u a r i e s are needed.

LITERA TURE CITED

GUNTER, G. and J. W. WARD REINTJES, J. W. andA. L. PACHECO 1961. Some fish that survive exteme injuries, and some 1966. The relation of menhaden to estuaries. Amer. Fish. aspects of tenacity of life . Copeia 1961: 456-462 . Soc. Spec. Publ. No .3: 50-58.

KROGER, R. L. and R. L. DRYFOOS 1972. Tagging and tag recoveIY experiments with Atlantic 1969. The Gulf menhaden and our changing estuaries . menhaden, Brevoortiatyrannus. U.S. Dep. Comm. Proc . Gulf Fish. Inst., 22nd Annual Nat. Mar. Fish Serv., Spec. Sci. Rep.-Fish. In Session, 87 -9~. press . SEKAVEC, G. B. and J. F. GUTHRIE 1971. Gross morphology of the digestive tract of the lady­ -'1"'97"'3'. Migrations of tagged juvenile Atlantic menhaden. fish, £lops saurus. Chesapeake Sci. 12(4): 275-276. Trans . Amer. Fish. Soc. 102 (2). In press. SIMMONS, E. G. and J. p. BREUER REINTJES, J. W., J. Y . CHRISTMAS, Jr. and 1959. The Texas menhaden fisheIY. Texas Parks Wildl. R. A. COLLINS Dept. Bull. No. 45A., 16 p. 1960. Annotated bibliography on biology of American men­ haden. U.S. Fish. Wildl. Servo Fish. Byll. 60: 297-322.