Forging Behvior of Fishes in Aqutic Plnts by Sherry L Hrrel, Eric D. Dibble, nd K. Jck Killgore PURPOSE: Forging behvior of juvenile bluegill (Lepomis mcrochirus) nd lrgemouth bss (Micropterus slmoides) ws observed in qutic plnts using underwter videogrphy. This note describes reltionships between plnt stem density nd forging of fish, nd discusses ppliction of these dt to evlute the hbitt vlue of qutic plnt beds. BACKGROUND: Smll species of fish nd juveniles of lrger species occupy qutic plnt ptches for food (Prdue 1973; Kest 1984) nd protection from predtors (Crowder nd Cooper 1982; Svino nd Stein 1989). Differences in density nd morphology of plnts influence forging intensity nd degree of predtor voidnce (Dionne nd Folt 1991; Lillie nd Budd 1992; Wycher et l. 1993; Dibble, Killgore, nd Dick 1996), which in turn influence fish growth nd survivl. Forging efficiency decreses in dense plnt beds (Svino nd Stein 1982; Anderson 1984), but plnt rchitecture (e.g., interstitil spce formed by the rrngement of stems nd leves) cn medite negtive effects (Lynch nd Johnson 1989; Lillie nd Budd 1992; Johnson 1993). High-density plnt beds, however, offer greter protection from predtors thn medium- or low-density beds (Hyse nd Wissing 1996). These trdeoffs, between reduced forging vlue nd incresed protection from predtors, mke ssessments of optiml or threshold densities of qutic plnts difficult. Behviorl studies of fish cn be used to ssess the functionl vlue of plnt densities, but such studies usully require direct observtion. In plnt beds, low turbidity llows observtion of individul fish behviors in structurlly complex hbitts. In this study, the effect of different plnt stem densities on forging strtegies of fish in Wisconsin lke ws evluted with underwter videogrphy. METHODS AND MATERIALS: This study ws conducted t Devil's Lke, Brboo, Wisconsin. The lke is cler, oligotrophic, nd hs shllow littorl res consisting of mixed ssemblges of ntive qutic plnts. Smpling efforts were concentrted long the southern nd southwestern shores where qutic plnts were the most bundnt nd diverse. Underwter Videogrphy. An underwter video cmer ws used to record bluegill nd lrgemouth bss distribution nd behvior in qutic plnt ptches of vrying densities (herein clled sites). Eight sites were recorded with video cmers in August 1995 nd 22 sites were recorded in August 1996. Wter depth mong the sites rnged from 0.7 to 1.6 m. A JVC VHS-C video cmer in wterproof housing ws mounted on t-post nd connected to monitor positioned on the bnk by 30-m cble. When plnt site ws rndomly locted, the cmer ws positioned nd mounted into the sediment. The cmer's field of vision ws pproximtely 1.56 m. Suspended sediment ws llowed to settle for 15-20 minutes, fter which time fish ctivity ws recorded for pproximtely 1 hr. Aqutic Plnt Mesurements. Immeditely fter videotping, stem density of ech plnt species ws mesured within 0.09-m 2 qudrt plced 0.5 m in front of the cmer. Plnts were DISTRIBUTION STATEMENT A Approved for Public Relese l OAAAn?HA fi A 1 Distribution Unlimited tuu I U DU 7 UO I
uprooted nd tken bck to the bnk, identified, nd totl stem density ws enumerted (Pringle 1984). Vlues were reported s number/m 2. Stem density of individul plnt species within site ws divided by totl stem density to determine percent composition. Behviorl Anlysis. Fifteen video smples were nlyzed for bluegill nd lrgemouth bss distribution nd forging behvior. Fifteen rndom, 1-minute focl smples were tken from ech video with the use of Pnsonic VG-1500 editing deck for totl of 3 hours nd 45 minutes observtion time. During ech focl smple, frequency (totl number of observtions) nd durtion (in minutes nd seconds) of visits of every bluegill nd lrgemouth bss were recorded, s well s frequency nd durtion of forging in the site. Forging behvior included serch nd orienttion (swim, stop, focus), chse (swimming bursts), strikes (open wter), nd glening (biting on plnt). Fish behviorl vribles were compred mong sites with different plnt stem densities. Histogrms were developed from frequency distributions nd Hbitt Suitbility Index (HSI) curves were constructed from the histogrms. HSI vlues, which rnge from 0 (no vlue) to 1 (mximum vlue), re used in the Hbitt Evlution Procedure to rte the qulity of prticulr hbitt (U.S. Fish nd Wildlife Service 1980). The y-xis (time) ws normlized by dividing time spent in ech clss intervl of plnt densities into the mximum time recorded in ny one clss (i.e., HSI = 1.0). A curve ws fitted to the distribution by drwing line through the midpoint of ech clss intervl. These nd other line-fitting techniques for constructing HSI curves re discussed in Bovee (1986) nd Bovee nd Zuboy (1988). RESULTS AND DISCUSSION Aqutic Plnt Species Composition. Totl qutic plnt stem densities in the study re rnged from 344 to 1600 stems/m 2, with men (±SD) of 817 ± 399. Stem densities rnged from low to modertely high vlues tht nturlly occur in vegetted wter bodies, lthough ggressively growing species such s Myriophyllum spictum cn exceed 1,700 stems/m (Lillie nd Budd 1992). Only one monospecific plnt site ws smpled, which precluded nlysis of species-specific effects on fish forging; other sites consisted of two to five qutic plnt species. The two most common qutic plnt species were Potmogeton robbinsii (Robbin's pondweed) nd Elode cndensis (Cndin elode) (Figure 1). These species hve contrsting growth forms. P. robbinsii hs long, crowded lternte simple leves tht re liner to lnceolte; stems re smooth, brnched, nd cn grow up to 0.60 m in length. E. cndensis is either rooted or free-floting (Aulbch-Smith nd de Kozlowski 1996), nd leves re whorled, elliptic, nd nrrow. Species tht were less common were P. illinoensis (Illinois pondweed), Njs flexilus (bushy pondweed), Certphyllum demersum (coontil), nd Vllisneri mericn (wter celery). Frequency nd Durtion of Fish Behvior. luvenile bluegill were observed 1,069 times, nd of these observtions, 306 were of forging (Tble 1). The men (±SD) totl length (mm) of bluegill ws 48 + 10 mm. Frequency of visits rnged between 6 nd 243, nd frequency of forging rnged between 0 nd 47. Durtion of visits by bluegill totled 187 min, 45 sec, nd durtion of forging totled 68 min, 41 sec. Durtion of visits rnged from 18 sec to 51 min, 39 sec. Durtion of forging rnged from 0 to 13 min, 37 sec.
ERDCTN-APCRP-MI-06 Certphyllum demersum. Vllisneri mericn Potmogeton illinoensis Njs flexilus Elode cndensis Potmogeton robbinsii 0 10 15 20 25 30 35 40 Percent Occurrence Figure 1. Percent occurrence of plnt species in Devil's Lke, Wisconsin Juvenile lrgemouth bss were observed 186 times, nd of these observtions, 25 were of forging (Tble 1). The men (+SD) totl length (mm) of lrgemouth bss ws 169 ± 57. Frequency of visits rnged from 0 to 30, nd frequency of forging rnged from 0 to 6. Durtion of visits totled 23 min, 24 sec, nd durtion of forging totled 6 min, 6 sec. Durtion of visits rnged from 0 to 4 min, 27 sec. Durtion of forging rnged from 0 to 2 min, 4 sec. Effect of Plnt Stem Density. Forging durtion by juvenile bluegill ws similr mong sites of different stem densities, but totl time (forging nd non-forging) ws greter in sites with intermedite to modertely high stem densities (Figure 2). In contrst, lrgemouth bss forged more frequently nd spent considerbly more time in sites with low stem densities. However, lrgemouth bss tended to "cruise" through plnts nd occupy ptch for less thn minute, wheres bluegill resided in one loction for significntly (p<0.001, ANOVA) greter period (Tble 1). An HSI curve ws constructed to illustrte how these dt cn be used to evlute hbitt qulity of mixed plnt communities (Figure 2). Highest hbitt vlue occurred t intermedite nd low stem densities for bluegill nd lrgemouth bss, respectively. In ddition, the reltionship between forging nd totl time suggests tht the primry function of plnts my differ between fish species. For bluegill, the disproportionte use of intermedite stem densities, with no increse in forging, suggests tht cover is the primry function. Conversely, the reltionship between forging nd totl
Tble 1 Frequency nd Durtion (in minutes:seconds) of Visits nd Forging by Juvenile Bluegill nd Lrgemouth Bss n Aqutic Plnts Bluegill Lrgemouth bss Site Visit Forge Visit Forge Visit Forge Visit Forge Freq Freq Dur Dur Freq Freq Dur Dur 1 56 23 7:13 3:52 9 2 1:03 0:13 2 36 13 6:19 4:14 27 5 4:27 2:04 3 6 1 1:04 0:30 30 1 3:01 0:11 4 30 10 13:35 3:08 7 0 0:21 0 5 80 34 19:56 11:45 8 0 0:31 0 6 103 42 15:07 7:34 14 2 2:23 0:54 7 110 47 26:52 13:37 23 6 3:48 1:28 8 19 1 1:08 0:09 7 0 0:49 0 9 70 16 5:07 1:58 6 2 0:56 0:14 10 165 41 15:35 4:55 15 0 0:43 0 11 8 0 0:18 0 11 0 1:06 0 12 243 34 51:39 5:44 9 0 1:48 0 13 41 11 5:24 2:17 6 1 0:23 0:06 14 49 14 8:37 3:40 0 0 0 0 15 53 19 9:51 5:18 14 6 2:05 0:56 Totl 1069 306 187:45 68:41 186 25 23:24 6:06 time in plnts by lrgemouth bss ws similr mong stem densities, indicting plnt beds re primrily being used s feeding res. Studies hve suggested tht juvenile bluegills select higher vegettion densities to reduce predtion, nd tht n increse in invertebrte bundnce with incresing vegettion density llows incresed encounter rtes, offsetting decresed cpture rtes (Svino nd Stein 1982; Gotceits nd Colgn 1987; Hyse nd Wissing 1996). The current study supports these conclusions, nd quntifies durtion of fish ctivities s function of plnt stem density. Behvior by lrgemouth bss my be regulted by similr fctors, except tht this species prefers to wit t the periphery of plnt beds or in less-structured res during non-forging periods. MANAGEMENT IMPLICATIONS: Forging rtes decline s mcrophyte density increses (Crowder nd Cooper 1982; Svino nd Stein 1982; Gotceits 1990), but prey re bundnt in densely vegetted res (Hyse nd Wissing 1996). As result, rtes of prey consumption my not decline in dense vegettion. In this study, fish spent only 30-40 percent of the time forging, nd durtion of forging mong sites with different plnt stem densities did not differ s much s totl
time. This indictes tht overll residence time in vegettion is more sensitive predictor of hbitt vlue thn just forging time. Juvenile bluegill prefer intermedite to modertely dense vegettion, nd bsed on HSI vlues derived in this study, stem densities of pproximtely 1,200 stems/m would provide optimum hbitt. Conversely, lrgemouth bss prefer to wit t the periphery of plnt beds or in res of lower plnt densities (300 stems/m 2 ). The hbitt vlue of littorl vegettion cn be rpidly ssessed nd monitored using stndrdized vlues, such s HSI's, nd trdeoffs mong fish species cn be determined for plnt control or fishery mngement ctions. Although this level of evlution does not include other fctors tht cn directly influence fish behvior, such s wter qulity, it does indicte tht dispersion of vegettion ptches is importnt when mnging the structurl lndscpe of littorl zones. Idelly, modertely dense ptches of vegettion surrounded by sprsely distributed plnts will provide optimum hbitt for most sunfishes.. 20 \ 15 10 I 5 ^ 0 3Foxgc l I Tril MSI Bluegill 300 600 1200 1500 Men Wnt Stem Density, m 2 Lrgemouth Bss 300 600 1200 1500 Men Plnt Stem Density, m 2 0.75 Figure 2. Forging nd totl time in qutic plnts over rnge of stem densities in Devil's Lke, Wisconsin for juvenile bluegill nd lrgemouth bss. Hbitt Suitbility Index vlues refer to totl time in ptch, nd rnge from 0 (no hbitt vlue) to 1.0 (optimum hbitt vlue) POINTS OF CONTACT: This technicl note ws written by Dr. Sherry L. Hrrel of the Deprtment of Biologicl Sciences, Estern Kentucky University, Richmond, KY, sherry.hrrel@eku.edu, Dr. Eric D. Dibble, MSU, (662-325-7494, edibble@cfr.msstte.edu), nd Dr. K. Jck Killgore, Environmentl Lbortory, Engineer Reserch nd Development Center, (601-634-3397, Jck.Killgore@erdc.usce.rmy.mil). For dditionl informtion, contct Dr. Killgore or the mngers of the Aqutic Plnt Control Reserch Progrm, Dr. John W. Brko, (601-634-3654, John.W.Brko@erdc.usce.rmy.mil) or Mr. Robert C. Gunkel, (601-634-3722, Robert.C.Gunkel@erdc.usce.rmy.mil). This technicl note should be cited s follows: Hrrel, S L., Dibble, E. D., nd Killgore, K. J. (2000). "Forging behvior of fishes in qutic plnts," APCRP Technicl Notes Collection (ERDC TN-APCRP-MI-06), U.S. Army Engineer Reserch nd Development Center, Vicksburg, MS. www. wes. rmy.mil/el/qu/qtn. html
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