Quick viewing(Text Mode)

Shrimp Stocking, Salmon Collapse, and Eagle Displacement

Shrimp Stocking, Salmon Collapse, and Eagle Displacement

University of ScholarWorks at University of Montana

Biological Sciences Faculty Publications Biological Sciences

1-1991

Shrimp Stocking, Collapse, and Eagle Displacement

Craig N. Spencer

B. Riley McClelland

Jack Arthur Stanford The University of Montana, [email protected]

Follow this and additional works at: https://scholarworks.umt.edu/biosci_pubs

Part of the Biology Commons Let us know how access to this document benefits ou.y

Recommended Citation Spencer, Craig N.; McClelland, B. Riley; and Stanford, Jack Arthur, "Shrimp Stocking, Salmon Collapse, and Eagle Displacement" (1991). Biological Sciences Faculty Publications. 292. https://scholarworks.umt.edu/biosci_pubs/292

This Article is brought to you for free and open access by the Biological Sciences at ScholarWorks at University of Montana. It has been accepted for inclusion in Biological Sciences Faculty Publications by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. Shrimp Stocking, Salmon Collapse, and Eagle Displacement Cascading interactions in the food web of a large aquaticecosystem

CraigN. Spencer,B. RileyMcClelland, and Jack A. Stanford

tocking of nonnative fish and 1986). In 1949, the shrimp were fish-food organisms has long introduced experimentally into been used by fishery managers Benefitsproduced by Kootenay , , to enhance production of freshwater introductionshave with the intention of enhancing rain- fisheries. Indeed, more than 25% of bow trout. However, they were the caught by anglers come at considerable largely responsible for a dramatic in- in the continental is cost crease in the growth rate and size of from nonnative stocks (Moyle et al. (Oncorhynchus 1986). I nerka; Northcote 1972, 1973). After Recent studies, however, report this initial introduction, opossum negative effects of such introductions, tions have been described as the shrimp were stocked into more than especially on the native species Frankensteineffect by Moyle et al. 100 in the northwestern United (Moyle 1986, Schoenherr 1981, Tay- (1986). Althoughthe most serious,or States and , primarily to stim- lor et al. 1984). For example, intro- at least most widely reported,effects ulate production of kokanee (Lasenby duced rainbow trout (Oncorhynchus appear to be on native fish popula- et al. 1986, Martinez and Bergersen mykiss) have displaced native west- tions, other organisms also may be 1989, Northcote in press). slope (Salmo clarki affectedby introducedspecies. Between 1968 and 1975, opossum lewisi) in many Rocky Mountain In this article,we documentpartic- shrimp were introduced into three streams (Allendorf and Leary 1988), ularly widespreadchanges cascading lakes in the upper portion of the and introduced brown trout (Salmo throughthe food web of the Flathead Flathead catchment of northwest trutta) have largely replaced native River-Lakeecosystem (Figure 1) after Montana (Figure 2) by the Montana brook trout (Salvelinusfontinalis) in the introduction of the opossum Department of Fish, Wildlife, and various streams in the Midwest shrimp(Mysis relicta). Owing to pre- Parks. The shrimp drifted down- (Moyle et al. 1986). In the Southwest, dation by the shrimp, copepod and stream, and in 1981 they appeared in native Gila topminnows (Poeciliopsis cladoceranzooplankton populations , one of the largest nat- occidentalis) have been widely re- declineddramatically, contributing to ural freshwater lakes in the western placed by introduced mosquitofish the collapseof an importantplanktiv- United States (surface area 482 km2, (Gambusia affinis; Schoenherr 1981, orous fish population. Loss of this mean depth 52 m). Shortly thereafter, Stanford and Ward 1986). The result- formerlyabundant forage fish caused they began to alter the existing food ing negative, long-range, or broad- displacementof birds and mammals web. scale consequences of such introduc- that had fed on them in an upstream tributary within National Impacton zooplankton Park. and Craig N. Spenceris a researchassistant phytoplankton professorand Jack A. Stanfordis director Shrimpintroduction Opossum shrimp are voracious pred- and BiermanProfessor of Ecology at the ators of zooplankton (Figure 1); FlatheadLake BiologicalStation, Univer- are 1-2- are but clado- of MT 59860. B. Opossum shrimp small, copepods consumed, sity Montana, Polson, cold-water crusta- cerans are because Riley McClellandis a researchscientist at centimeter-long, preferred prey they GlacierNational Park,West Glacier,MT ceans that carry their young in a swim more slowly and are easier to 59936 and professor in the School of brood pouch, hence their name. They capture (Cooper and Goldman 1980, Forestry, University of Montana, Mis- are native to a limited number of Grossnickle 1982, Nero and Sprules soula, MT 59812. ? 1991 AmericanIn- large, deep lakes in North America 1986). After the appearance of opos- stitute of BiologicalSciences. and coastal Sweden (Lasenbyet al. sum shrimp in Flathead Lake, clado-

14 BioScienceVol. 41 No. 1

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions , n phytoplankton McDonald Creek {f~ ~Dj~ ~ copepod

cladoceran

kopkanee salmon opossum shrimp

Flathead Lake

Figure1. The food web of the FlatheadRiver-Lake ecosystem, emphasizing those componentsaffected by the introductionof opossumshrimp. Eagles and bearsfeed on spawningkokanee, lake trouteat kokaneeand shrimp,kokanee and shrimpeat zooplankton(copepods and cladocerans), and zooplankton feed on phytoplankton.The organisms are not drawn to scale;they range in sizefrom several micrometers (phytoplankton) to meters(grizzly bears). cerans declined dramatically, with and 1989, two cladocerans,D. lon- increased nutrient loading.1 Thus it mean annualabundances reduced sig- giremis and L. kindtii, reappearedin appearsthat the phytoplanktoncom- nificantly (p < 0.0001, Student's t FlatheadLake for the first time since munity in FlatheadLake is regulated test) from 2.8 to 0.35 organisms/I 1985, albeit at low densities. largelyby "bottom-up"controls (nu- (Figure3a, also Beattie and Clancey Hrbaceket al. (1961), Spencerand trients), whereas top-down controls, in press). Two of the four principal King (1984), and Carpenter et al. involving changes in the upper cladoceranspecies (Daphnia longire- (1985) have suggestedthat predator- trophic levels, may play a largerrole mis and Leptodora kindtii) disap- induced alterations to the herbivo- in regulatingphytoplankton produc- peared from lake samples, and the rous zooplankton community can tion in eutrophiclakes. other two (Daphnia thorata and cause "top-down" effects potentially Bosmina longirostris) persisted, but regulating the abundance of phyto- Impact on fish at greatly reduced densities. Cope- plankton (free-floatingalgae) and the pods also declined significantly(p < appearanceof algal blooms in lakes. Although top-down effects extending 0.0001; Figure3b). Althoughdeclines For example, increased densities of to the phytoplanktonare not appar- in cladoceranshave been well docu- planktivorousfish have been linkedto ent in Flathead Lake, the effects of mented after opossum shrimp intro- decreasedzooplankton densities and predationby opossum shrimpon the ductionsin other lakes (Morganet al. greatly increased phytoplankton zooplanktonare widespreadand have 1978, Richardset al. 1975, Rieman abundancein nutrient-rich(eutrophic) carried over to upper trophic level and Falter 1981), similar declines in lakes. Mean annual phytoplankton organisms, including the kokanee copepods have not been reported, productionhas increasedslightly since salmon. Kokanee (landlocked sock- suggestinga higher level of predation 1978 in FlatheadLake, a nutrient-poor eye salmon) were introduced into by the shrimpon zooplanktonin Flat- (oligotrophic)lake (Stanfordand Ellis FlatheadLake in 1916, and thereafter head Lake. 1988). they replaced the native westslope After peaking in 1986, opossum However, recent experimentsindi- cutthroattrout as the dominantsport shrimp densities declined for three cate that increased phytoplankton fish (Tables 1 and 2). successiveyears (Figure4). The zoo- production after the appearance of Kokanee normally lived 3-4 years plankton community appears to be opossumshrimp is not due to declines respondingto this reductionin opos- in zooplankton grazing pressure in 'C. N. Spencer,J. A. Stanford,and B. K. Ellis, sum shrimpabundance. During 1988 FlatheadLake, but ratheris relatedto 1990, unpublisheddata.

January1991 15

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions (Fraley et al. 1986). From 1979 to 1985, the peak annual number of kokanee spawners varied between 26,000 and 118,000 (Figure4). By 1985, the density of opossum shrimp in FlatheadLake had increasedto 49 organisms/m2,illustrating the rapid growth of this invading species. Within two years, the kokaneepopu- lation was noticeably reduced. In 1987, only 330 kokanee migrated into McDonald Creek, and only 50 spawnedin 1989. The salmondemise also was reflectedin the annualcatch by angler fishermen,which often ex- ceeded 100,000 kokanee through 1985 (Beattie et al. 1988). As the shrimp population grew, angler har- vest declined precipitouslyto fewer than 6000 in 1987 (Beattie et al. 1988), followed by no reported catchesin 1988 and 1989. Previousintroductions of opossum shrimp into , / ; Lake Pend Oreille, ; Ashley ad Lake Granby, ; and many Lake other lakes produced few, if any, River long-lastingbenefits to the fish (pri- marilykokanee) that were targetedas opossum shrimp predators (Lasenby et al. 1986, Martinez and Bergerson 1989, Northcote in press). Several N interactivemechanisms may explain Flathead \ South Fork these results. First, opossum shrimp commonly did not become a significantcompo- Lake nent of the kokaneediet, even though 20 km they were originally introducedas a supplemental prey (Beattie et al. 1988, Bowles et al. in press, Rieman and Bowler 1980). Although both 'KerrDam species occupy the offshore (pelagic) zone, kokanee normally are found nearerthe surfacein the top 30 m of Figure2. TheFlathead River-Lake catchment (22,241 km2) in Montana.Location of the water where introducedin 1968 and column, they concen- upstreamlakes where opossum shrimp were (Whitefish Ashley tratetheir activities the lakes)and 1975 (SwanLake) are shown.Two hydroelectricdams affect kokanee feeding during spawninggrounds: Kerr on FlatheadLake (completed in 1938)and Hungry Horse day, especially around dawn and Damon thesouth fork of theFlathead River (completed in 1952).The major kokanee dusk (Cordoneet al. 1971, Doble and spawningstream and site of baldeagle concentrations is located on McDonaldCreek Eggers1978, Finnelland Reed 1969). in GlacierNational Park. We referto the catchmentshown here as the Flathead Conversely, opossum shrimp spend River-Lakeecosystem. the daylight hours on or near the bottom at depths below 30 m, and I they migrateupwards at night to feed in FlatheadLake before spawningin cobble riffles interspersed between on zooplankton (Figure 5; Beeton tributarystreams or along the lake- deep pools, and the water tempera- 1960). Because kokanee do not feed shore. The primaryspawning stream tures and streamdischarges are mod- effectively on opossum shrimp at was McDonald Creekin GlacierNa- eratedby Lake McDonald. night, the vertical migration of the tional Park,located 100 km upstream Beginningin 1979, biweekly esti- shrimpto deep watersduring the day- from Flathead Lake (Figure2). This matesof kokaneespawner abundance time largely precludeskokanee from four-kilometerstream has favorable were made each autumn in McDon- exploiting this new potentialprey. conditionsfor kokanee spawning,in- ald Creek by the Montana Depart- Enhancementof kokaneegrowth did cludingloosely compactedgravel and ment of Fish, Wildlife, and Parks occur in KootenayLake shortly after

16 BioScienceVol. 41 No. 1

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions C' lapse of the kokanee spawningrun in I'll to -0- Pre-Mysis a. McDonald Creek is linked the ap- 4- -4- Post-Mysis pearanceof opossum shrimpin Flat- head Lake, the situation is compli- cated kokanee declines in 3- by past ' other areasof the Flatheadecosystem. #/L These declinesmay be partiallyattrib- 2- uted to water-levelfluctuations caused by hydroelectricdams on both the 1- southfork of the FlatheadRiver and on Flathead Lake (Figure 2). Changing n w LI Ih. . . . I. from of F M A M J J A S O N D J F MA MJ J A S O N D waterlevels resulting operation J these causedkokanee Month Month reportedly spawningareas in both the river and Figure3. Seasonalabundance of cladocerans(a) and copepods(b) measuredin Flathead along the lakeshoreto become dessi- Lakeat our midlakesampling station (95 m deep),before the introductionof opossum cated,killing kokanee eggs (Fraleyet al. shrimp(May-December 1972 and January-April1973; from Potter 1978) and after 1986, 1989, Fraley and Decker-Hess the introductionof opossumshrimp (January-December 1988). Data are meandaytime 1987). The kokanee also may have plankton densities estimatedfrom duplicatevertical hauls (50 m to surface)using a been stressedby intensiveannual har- 64-micrometer-meshplankton net. vests by anglers,which often removed 50% or more of the adult kokanee population(Beattie et al. 1988). the introductionof the shrimp,owing shrimpfrom the centralregion of this Although the kokanee were likely to unusual hydrologic conditions in deep lake into a shallow bay, where affected by these long-term stresses which upwelling currentscarried the theylacked a deepwaterdaytime refuge (the dams were constructed more (Northcote1972). However,after two than 35 years ago), a sustained ko- 150 KokaneeX 1000 decadesof increasedkokanee produc- kanee population and fisheryexisted ? Eagles X 7 tion in the kokanee in Flathead Lake the mid- - Kootenay Lake, through Mysis declinedsignificantly in the 1970s, re- 1980s, with adult kokanee popula- 100- portedlydue to complexchanges in the tions of several hundred thousand lake decreasednutrient load- and naturalkokanee recruitment -. including fish, 0 ing and constructionof a large up- of 9 million or more fry per year 0 0 -1 streamdam, which alteredhydrologic cominglargely from undisturbedMc- flows andtrapped nutrients (Northcote Donald Creekin recentyears (Beattie in press). et al. 1988, Clancey and Fraley 1979 1981 1983 1985 1987 1989 A second explanationfor the com- 1986). Then, in just a few years after Year mon failure of opossum shrimp to the establishmentof opossumshrimp, stimulate kokanee is in- the kokanee almost com- Figure4. Shrimp,salmon, and eagle abun- production collapsed dance. Mean annual autumn lakewide terspecific competition for food re- pletely. abundance of opossum shrimp (Mysis; sources. Like opossum shrimp, ko- Comparabledeclines have beendoc- number/m2)in Flathead Lake estimated kanee are planktivores throughout umentedelsewhere, in which fish pop- fromvertical net hauls (bottomto surface) their existence in the lake environ- collectedat 25-40 randomlychosen loca- ment (Cooper and Goldman 1980, 0, tions throughout the lake. Collections Leathe and Graham 1982, Rieman 10 were made on moonless nights using a and Falter1981, Vinyardet al. 1982). 20 1-meter-diameter, 500-micron-mesh Thus previous kokanee declines that planktonnet. Opossumshrimp data from 40 1981 to 1986 are from Bukantis and followed introduction of opossum Depth have been attributedto (m) s50 Bukantis(1987). The errorbars represent shrimp largely I 2400 hrs 95% confidenceintervals for each lake- interspecific competition for a se- 70 1200 hrs wide estimate.(Error bars 1984-1986 are verely depletedsupply of cladocerans 80 fromR. Bukantis,1990, personalcommu- (Lasenby et al. 1986, Northcote in botormF-. "----.\\^.M.."." .".." .""'-' ^ nication.Montana Water Quality Bureau, press). Competition for scarce food 0 2 4 6 8 10 158 Helena, MT.) Eagle and kokanee abun- resourcesis not restrictedjust to juve- Abundance(#/m3 ) dance data are annual peaks of weekly nile kokanee and opossum shrimp. (eagles) and biweekly (kokanee) counts Adult kokanee also feed primarilyon Figure5. Verticaldistribution of opossum made along the entire 4-kilometerreach cladocerans,probably explainingthe shrimp measuredon 16 August 1988 at of McDonaldCreek. These data are abso- our midlakesampling station in Flathead lute counts of the total local dramaticdecline in kokaneespawners Lakeat population, from FlatheadLake in middayand midnight.Collections and thus no error estimationis possible. 1987, just two were made using vertical hauls with a To obtain specificeagle and kokaneeden- years after the initial large increasein closing net (1-meter-diameter, 500- sities from the figure, the values shown opossumshrimp abundance (Figure 4). micrometer mesh). Note all opossum must be multipliedby 7 and 1000, respec- Although the prevailing evidence shrimpat midday were found at the bot- tively. strongly suggests that the recent col- tom of the lake.

January 1991 17

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions tumn migration along McDonald bly related. Both of the newer loca- Creek(Figure 6). The firstrecord of a tions supported eagle concentrations concentrationin this areais before the kokanee collapse in Flat- from 1939, when 37 eagles were re- headLake. Intensive observations near ported; kokanee had been first ob- Koocanusa Reservoir from 1983 to servedin 1935 (McClelland1973). 1989 (186 eagles were recordedin a Systematiccounts of eagles along single count in 1988) documentedno McDonald Creek were conductedby more than one marked eagle from canoe once each week duringautumn McDonald Creek in any one year ei- beginningin 1965 (McClellandet al. ther before or after the collapse.4No 1982). Peak numbersof eagles were markedeagles have been reportedat stronglycorrelated with peak numbers HauserReservoir. Furthermore, ongo- of kokanee spawners(Figure 7; Mc- ing studies5indicate that at least sev- Clelland and McClelland 1986). In eral hundredeagles still pass through 1981, for example,more than 100,000 the McDonald Creekarea duringmi- kokaneespawners and 639 bald eagles gration, quickly moving southward were talliedduring a singlecount. For toward wintering areas, not toward many years, the autumncongregation the Koocanusaor Hauserreservoirs. of bald eagles on McDonald Creek The collapseof the McDonaldCreek (Figure8) was the densestconcentra- spawningrun clearly represents the loss tion of the species south of Canada. of a valuablefood resourcefor the bald in numbersof an or threatened ,:. Then, beginning 1987, eagle, endangered spe- eagles declinedprecipitously concomi- cies in the . Figure6. An immaturebald eagle with a tant with the demise of the kokanee Althoughkokanee salmon are not na- kokanee salmon taken from McDonald food resource,reaching a low of 25 tive to Flathead Lake or McDonald Creekin GlacierNational Park. Photo: eaglescounted in 1989 (Figure4). Creek,migrating bald eagles took ad- B. Riley McClelland. Migration routes of eagles along vantageof this abundantfood resource McDonald Creek have been studied for more than 50 years,when manyof since 1977; orange wing markers their historical prey species were no ulations, already under stress, have were placed on 121 eagles and 66 longercommon. beenrapidly eliminated after invasions were equipped with radio transmit- The eagles cannot respond to the of nonnativespecies. For example,the ters. Trackingof transmitter-equippedloss of Flathead Lake kokanee by classic case history of Lake Michigan eagles before the kokanee collapse simply returningto native prey else- includes a productive showed that nearly all the eagles mi- where. The once-abundantcarrion of (Salvelinusnamaycush) fishery, which gratedto McDonaldCreek from sum- bison (Bison bison) and elk (Cervis persistedin the 1930s and early 1940s meringareas in northwesternCanada. elaphus)on the plains east of Glacier in spite of overexploitationby com- After salmon numberswere depleted National Park, and the anadromous mercialfishermen and apparentlyde- each autumn, the eagles continued salmon in headwatersof the Colum- graded habitat. After the invasion of south to winteringareas elsewherein bia River to the west, are now much the exotic sea lamprey (Petromyzon the western United States (Young reduced or absent (Netboy 1980, marinus), the lake trout population 1983, Younget al. 1983). Schmidt and Gilbert 1978, Schultz collapsedalmost completelyduring a Recent increasesin the number of 1919). Therefore,loss of the kokanee period of just 4-5 years, as sea lam- reported eagles at two reservoirsin spawning run could lead to higher preys preyed on the already-stressed western Montana, where introduced eagle mortality during migration or lake trout population (Christie1974, kokanee populationshave expanded, duringwinter, especiallyamong juve- Wells and McLain 1972). led to speculationby the local press nile eagles (McClellandet al. 1983, that the McDonald Creekeagles rap- Newton 1979, Stalmasterand Gessa- on birdsand mammals idly shiftedto these new food sources. man 1984), if adequatealternate food Impact In 1989, more than 200 bald eagles resourcesare not available. Collapse of the kokanee population were counted near Hauser Reservoir, Other wildlife speciesthat were at- has affectedother componentsof the 270 km southeast of Glacier Park,2 tracted to the spawning run in Mc- food web, including the wildlife on and more than 100 were seen near Donald Creekalso have been affected tributariesof FlatheadLake. The most KoocanusaReservoir, 100 km west of by the kokanee collapse. Herringgull intenselystudied location, McDonald the park.3 (Larus argentatus), California gull Creek(Figures 1 and 2), attractedeach Although these sightings followed (Larus californicus), common mer- autumn a spectacular diversity and the declineat McDonaldCreek, we do ganser (Mergusmerganser), and mal- abundance of birds and mammals, not believe these events are apprecia- lard (Anas platyrhynchos)fed on ko- which fed on spawningkokanee, their kanee, whereas other bird species, carcasses,and kokaneeeggs. 2A. Harmata,1989, personalcommunication. Baldeagles were the most prominent MontanaState University, Bozeman. 4Seefootnote 3. of the predatorsand scavengers,gath- 3M. Swanson,1989, personalcommunication. 5B. R. McClelland,1990, manuscriptin prep- eringby the hundredsduring their au- U.S. ForestService volunteer. aration.

18 BioScienceVol. 41 No. 1

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions 7nnUVVr ure 5). Already, it appears that two newly expandingfish populations,as

600 such species, lake whitefish (Corego- well as reducedprey availability(Fig- nus and small-sized ure Several cladoceran u) 500 * / clupeaformis) 3). species 0) lake trout, have become more abun- have reappearedin the last two years, Y 400 a) dant in Flathead Lake, as has been presumably in response to the re- 0 300 in other lakes afterthe intro- ducedabundance of shrimp. *0^^ ~2 reported opossum m 200 r =0.876 duction of opossum shrimp (Morgan We expect that opossum shrimp 100 et al. 1978, Wydoski and Bennett and zooplankton populations will n ! 1981). We suspectthat enhancedsur- continue to exhibit cyclic oscillations 0 50000 100000 150000 vival and growth of young lake trout, characteristicof some predator-prey Kokanee spawners as a result of the opossum shrimp interactions.If predationon opossum have contributed other fish continues Figure7. Relationshipbetween peak num- introduction, may shrimpby species bersof kokaneespawners and bald eagles to the kokanee decline, because lake to intensify,further reducing the den- alongMcDonald Creek, 1979-1989. The trout prey heavily on kokanee. sities of this kokaneecompetitor, then relationshipis significantat the p = Although the mean size of lake kokanee populationsmay respondto 0.0001level. trout appears to have declined after a limitedextent. Suchtrends have not the introductionof opossum shrimp, been observedelsewhere, however. including common goldeneye (Buce- the smallerlake trout are more desir- It is likely that many bald eagles phala clangula), Barrow's goldeneye able to some anglers.When the larger gradually will shift their southward (Bucephalaislandica), and American lake trout fed on kokanee, they had migrationroute away from the imme- dipper (Cinclus mexicanus), fed on an oily taste. Many of the smallerlake diate area of McDonald Creek in kokaneeeggs. trout caught recently seem less oily, search of alternate prey. However, Coyotes(Canis latrans), mink (Mus- presumablydue in part to their con- becauseMcDonald Creek is within a tela vison),river otter (Lutracanaden- sumption of opossum shrimp. How- well-establishedraptor migration cor- sis), and even white-tailed deer ever, trophy lake trout (10-20 kg) ridor,we expect that some eagleswill (Odocoileusvirginianus; Shea 1973), currentlyappear to be less abundant continue to use this route. also madeuse of the abundantkokanee than in years when kokanee were Although the Flathead ecosystem, food resource.Grizzly bears (Ursus arc- abundant. We do not know the im- which includes much of GlacierNa- tos) trappedspawning kokanee in shal- pact of opossumshrimp on important tional Park, is considered relatively low rifflesand dove to the bottom of native sportfishin FlatheadLake, in- pristineand largelyundisturbed (sup- five-meter-deeppools to recoverdead cluding (Salvelinusconflu- portinga naturalassemblage of only 10 salmon from the creek bottom. One entus) and westslope cutthroattrout. native fish species), it has been per- individualbear, distinctivebecause of After peaking in 1986, opossum turbedover the yearsthrough introduc- the absenceof one ear, was observed shrimp densities have declined for tions of at least 17 nonnativefish (Ta- for 11 consecutive autumns. During three successiveyears (Figure4), ap- ble 2), crayfish (Orchonectesvirilis), yearsof abundant,late-season kokanee parently due to predation from the and most recently opossum shrimp. spawningruns, several grizzlieswere activemuch later than the usual onset of hibernation.Since the kokaneecol- lapse, bears and most other kokanee feeders have been far less common alongMcDonald Creek in the autumn. Finally, collapse of the kokanee spawning run has diminished the numberof human visitors to Glacier National Parkin autumn.At a desig- nated viewing area on McDonald Creek, park visitors often could see more than 100 eagles at one time. Since the collapse, visits to the view- ing area have declined from a maxi- mum of 46,500 in 1983 to fewer than 1000 in 1989.

The future We expect that the Flathead Lake food web will shift from pelagic ko- kanee toward benthic-feeding fish species, which can exploit the abun- dant daytime opossum shrimp con- Figure8. In some years,more than 500 bald eaglescongregated along the four- centrationson the lake bottom (Fig- kilometerstretch of McDonaldCreek. Photo: B. RileyMcClelland.

January 1991 19

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions Table 1. Native fish species within the Flat- of many native species, a public than two decades; H. L. Allen, R. E. head River-Lakeecosystem. largelyuninformed about the value of Bennetts, E. M. Caton, J. G. Cren- Commonname (Latinname) nongame species and natural biodi- shaw, D. E. Lange,M. E. McFadzen, because the Bull trout (Salvelinusconfluentus) versity management E. B. Spettigue,R. M. Williams,R. E. Westslopecutthroat trout (Oncorhynchus agencies have typically stressed only Yates, and L. S. Young for assistance clarkilewisi) the benefits of the new species, and in various phases of GlacierPark ea- Mountainwhitefish (Prosopium williamsoni) numerousmanagement problems cre- gle research;R. T. Bukantisfor opos- Pygmywhitefish (Prosopium coulteri) ated by unstablefish populationsand sum shrimpdata from 1981 to 1986 Peamouth(Mylocheilus caurinus) food webs (Moyle et al. 1986). and discussions regardingzooplank- Northernsquawfish (Ptychocheilus In recentyears, many agencieshave ton analysis; D. S. Potter for pre- oregonensis) more conservative Longnosesucker ( catostomus) adopted policiesre- opossum shrimp zooplankton data; Largescalesucker (Catostomus gardingintroduction of nonnativespe- the Montana Department of Fish, macrocheilus) cies; nevertheless,introductions con- Wildlife, and Parks for cooperation Redsideshiner (Richardsonius balteatus) tinue at an alarmingrate. Some are and use of kokanee data (however, Slimysculpin (Cottus cognatus) intentional(via agency efforts or illegal interpretationsof these data are the fish plantingsby privatecitizens), and authors'); R. Petty for Figure 1; J. The practiceof stockingnonnative spe- some occur via accidentalmeans, in- Craft,J. B. Imbert,R. Steinkraus,and cies, in FlatheadLake and aroundthe cludingdownstream drift or even acci- J. Tohtz for assistancewith opossum world, has been a cornerstoneof fish- dentaltransport on boats,as evidenced shrimp and zooplankton sampling eries management for many years. by the recentdiscovery in the Lauren- and counting;B. K. Ellisfor help with Some introductionshave resulted in tian Great Lakes of nuisance zebra sampling on Flathead Lake and pri- popularsport fisheries, whereas others mussels(Dreissena polymorpha) and a mary productiondata; and M. Spen- have produced inadvertentbenefits, predatory cladoceran (Bythetrephes cer, K. Fausch,A. Covich,W. Beattie, suchas the opportunityfor baldeagles cederstroemi)apparently released in J. Fraley, R. Hutto, and C. Hall for to preyon introducedkokanee in Gla- ballastwater from ships traveling from helpful commentson the manuscript. cier NationalPark. Eurasia(Lange and Cap 1986, Roberts Funding for Flathead Lake research Nevertheless, many of the per- 1990). We encouragestricter controls providedby JessieBierman, Lakeside, ceivedbenefits of nonnativeintroduc- aimed at preventingfurther introduc- MT; the FlatheadBasin Commission, tions are short-liveddue to instabili- tions, particularlyuntil we can predict Kalispell,MT; and the Montana De- ties in disturbedfood webs, such as cascadingeffects within food webs of partmentof Fish, Wildlife,and Parks. the loss of bald eagle/kokaneecongre- aquaticecosystems. Baldeagle researchwas fundedby the gations in GlacierNational Park and USDI National Park Service, Mon- the eventual decline in the kokanee Acknowledgments tana Forest and ConservationExper- fisheryin Kootenay Lake. More im- iment Station, Wildlife Management portant, the benefitsproduced by in- We thank P. T. McClellandand D. S. Institute,National Audubon Society, troductions have come at consider- Shea for their work on eagle research Alberta Fish and Wildlife Division, able costs, includingloss or reduction in Glacier National Park for more ParksCanada, Canadian Department of Indian and Northern Affairs (Ge- Table 2. Nonnativefish speciesintroduced within the FlatheadRiver-Lake ecosystem. ology Division), Northwest Territo- Yearfirst Currentrange in ries Wildlife Service,Canadian Wild- Nonnativespecies introduced* the ecosystem life Service,and Echo Bay Mines. Largemouthbass (Micropterussalmoides) 1898t Limited Laketrout (Salvelinusnamaycush) 1905 Extensive Referencescited Lakewhitefish (Coregonus clupeaformis) 1909 Extensive Pumpkinseed(Lepomis gibbosus) 1910 Moderate Allendorf,F. R., and R. Leary.1988. Conser- White crappie(Pomoxis annularis) 1910 Limited vation and distributionof genetic variation in a the cutthroattrout. Smallmouthbass (Micropterusdolomieui) 1910 Limited polytypic species, Blackbullhead melas) 1910 Limited Conserv.Biol. 2: 170-184. (Ictalurus Beattie,W. P., and P. In Effects Yellow 1910 Moderate Clancey. press. perch (Percaflavescens) of the establishmentof opossum shrimp Brooktrout (Salvelinusfontinalis) 193t Limited (Mysisrelicta) on the zooplanktoncommu- Yellowstonecutthroat trout (Salmoclarki bouvieri) 1913t Limited nity, and coincidentdecline in the survivalof Arcticgrayling (Thymallus arcticus) 1913 Limited kokanee (Oncorhynchusnerka) in Flathead Rainbowtrout (Oncorhynchusmykiss) 1914t Moderate Lake,Montana. Am. Fish. Soc. specialpub- Kokaneesalmon (Oncorhynchusnerka) 1916t Moderate lication. Chinooksalmon (Oncorhynchustschawytscha) 1916 Absent Beattie,W., P. Clancey,and R. Zubik. 1988. Goldentrout (Oncorhynchusaguabonita) 1938* Limited Effectof the operationof Kerrand Hungry Horse on the Northernpike (Esox lucius) 1965s Limited dams reproductionsuccess of kokaneein the Flathead no. Coho salmon 1969 Absent system.Project (Oncorhynchuskisutch) 81-S-5. Reportto the BonnevillePower Ad- *Modifiedfrom Hanzel 1969. ministration,Portland, OR. Montana De- tSpeciesintroduced on multipleoccasions after the initialintroduction. partmentof Fish, Wildlife,and Parks,Kalis- tB. Cheff, 1988, personalcommunication, Charlo, MT. pell, MT. SUnauthorizedintroduction of pike was apparentlycarried out by privatecitizens. The date of the Beeton,A. M. 1960. The verticalmigration of firstintroduction is unknown;the firstrecorded observation of pike in the ecosystemwas in 1965 Mysisrelicta in LakesHuron and Michigan. (Hanzel1976). J. Fish. Res. Bd. Can. 17: 517-539.

20 BioScienceVol. 41 No. 1

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions Bowles,E. C., B. E. Rieman,G. R. Mauser,and Cladocera):a new recordfor Lake Ontario. and R. Wickwire.1975. Wherehave all the D. H. Bennett. In press. Effects of mysid J. Gt. Lakes Res. 12: 142-143. daphniagone? The declineof a majorclado- introductionson fisheryresources in north- Lasenby,D. C., T. G. Northcote,and M. Furst. ceran in Lake Tahoe, California-Nevada. ernIdaho. Am. Fish.Soc. specialpublication. 1986. Theory,practice, and effectsof Mysis Verhandlungen Internationale Vereinege Bukantis, R. T., and J. G. Bukantis. 1987. relictaintroductions to North Americanand Limnologie19: 835-842. Mandibles.Montana Outdoors 18: 15-17, Scandinavianlakes. Can.J. Fish.Aquat. Sci. Rieman,B. E., and B. Bowler. 1980. Kokanee 26. 43: 1277-1284. trophic ecology and limnology in Pend Carpenter,S. R., J. F. Kitchell, and J. R. Leathe,S. A., and P. J. Graham.1982. Flathead OreilleLake. FisheriesBulletin no. 1. Idaho Hodgson. 1985. Cascadingtrophic interac- LakeFish Food HabitsStudy. Final report to Departmentof Fish and Game,Boise. tions and lake productivity.BioScience 35: EPA,Denver, CO. MontanaDepartment of Rieman,B. E., and C. M. Falter.1981. Effects 634-639. Fish, Wildlife,and Parks,Kalispell, MT. of the establishmentof Mysis relictaon the Christie,W. J. 1974. Changes in fish species Martinez, P. J., and E. P. Bergersen.1989. macrozooplanktonof a large lake. Trans. compositionof the GreatLakes. J. Fish. Res. Proposed biological managementof Mysis Am. Fish. Soc. 110: 613-620. Bd. Can. 31: 827-854. relictain Coloradolakes and reservoirs.N. Roberts,L. 1990. Zebramussel invasion threat- Clancey,P., and J. Fraley.1986. Effectsof the Am. J. Fish. Manage.9: 1-11. ens U.S. waters.Science 249: 1370-1372. operationof Kerrand HungryHorse Dams McClelland,B.R. 1973. Autumnconcentration Schmidt,J. L., and D. L. Gilbert,eds. 1978. Big on the kokaneefishery in the FlatheadRiver of bald eagles in Glacier National Park. Gameof North America:Ecology and Man- system. Project No. 81-S-5. Report to the Condor75: 121-123. agement.Stackpole Books, Harrisburg,PA. BonnevillePower Administration,Portland, McClelland, B. R., and P. T. McClelland. Schoenherr,A. A. 1981. The roleof competition OR. MontanaDepartment of Fish, Wildlife, 1986. Baldeagles and kokaneesalmon: ren- in the replacementof nativespecies by intro- and Parks,Kalispell, MT. dezvous in Glacier National Park. West. ducedspecies. Pages 173-203 in R. J. Naiman Cooper, S. D., and C. R. Goldman. 1980. Wildlands11: 7-11. andD. L. Soltz,eds. Fishesin NorthAmerican Opossum shrimp (Mysis relicta) predation McClelland,B. R., L. S. Young,D. S. Shea,P. T. Deserts.John Wiley & Sons,. on zooplankton.Can. J. Fish.Aquat. Sci. 37: McClelland,H. L. Allen,and E. B. Spettigue. Schultz,J. W. 1919. Rising Wolf, the White 909-919. 1982. The baldeagle concentration in Glacier Blackfoot.Houghton-Mifflin, Boston. Cordone,A. J., S. J. Nicola, P. H. Baker,and T. NationalPark: origin, growth, and variation in Shea, D. S. 1973. White-taileddeer eating C. Frantz. 1971. The kokanee salmon in numbers.Living Bird 19: 133-155. salmon.Murrelet 54: 23. Lake Tahoe. CaliforniaFish and Game 57: . 1983. The bald eagle concentrationin Spencer,C. N., and D. L. King. 1984. Role of 28-43. GlacierNational Park, Montana: an interna- fish in regulationof plant and com- Doble, B. D., and D. M. Eggers. 1978. Diel tional perspective for management.Pages munitiesin lakes. CanJ. Fish.Aquat. Sci. 41: feeding chronology, rate of gastric evacua- 69-77 in D. M. Bird,ed. Biology and Man- 1851-1855. tion, dailyration, and preyselectivity in Lake agementof Bald Eagles and Ospreys.Har- Stalmaster,M. V., and J. A. Gessaman.1984. Washingtonjuvenile (Onco- pell Press,Quebec. Ecologicalenergetics and foragingbehavior rhynchusnerka). Trans. Am. Fish.Soc. 107: Morgan, M. D., S. T. Threlkeld, and C. R. of overwinteringbald eagles. Ecol. Monogr. 26-45. Goldman.1978. Impactof the introduction 54: 407-428. Finnell,L. M., and E. B. Reed. 1969. The diel of kokanee(Oncorhynchus nerka) and opos- Stanford,J. A., and B. K. Ellis. 1988. Pages verticalmovements of kokaneesalmon, On- sum shrimp (Mysis relicta) on a subalpine 11-32 in Our Clean Water:Flathead's Re- corhynchusnerka, in GranbyReservoir, Col- lake. J. Fish. Res. Bd. Can. 35: 1572-1579. source of the Future.Flathead Basin Com- orado. Trans.Am. Fish. Soc. 98: 245-252. Moyle, P. B. 1986. Fish introductionsinto mission,Helena, MT. Fraley,J., and J. Decker-Hess.1987. Effectsof North America:patterns and ecologicalim- Stanford,J. A., and J. V. Ward. 1986. Fish of streamand lake regulationon reproductive pact. In H. Mooney and J. A. Drake, eds. the Colorado system. Pages 385-402 in B. success of kokanee in the Biological Invasions in North America. Daviesand K. Walker,eds. Ecologyof River system,Montana, U.S.A. Regul. RiversRes. Springer-Verlag,New York. Systems. Dr. W. Junk Publ., The Hague, & Manage.1: 257-265. Moyle, P. B., H. W. Li, and B. A. Barton.1986. Netherlands. Fraley,J., B. Marotz,J. Decker-Hess,W. Beat- The Frankensteineffect: impact of intro- Taylor, J. N., W. R. Courtenay,and J. A. tie, and R. Zubik. 1989. Mitigation, com- ducedfishes on nativefishes in North Amer- McCann. 1984. Known impacts of exotic pensation, and future protection for fish ica. Pages415-426 in R. H. Stroud,ed. Fish fish introductionsin the continentalUnited populationsaffected by hydropowerdevel- Culturein FisheriesManagement. American States. Pages 322-373 in W. R. Courtenay opment in the Upper Columbia system, FisheriesSociety, Bethesda, MD. Jr. and J. R. Stouffer,eds. Distribution,Bi- Montana,U.S.A. Regul.Rivers Res. & Man- Nero, R. W., and W. G. Sprules.1986. Preda- ology and Managementof Exotic Fishes. age. 3: 3-18. tion by threeglacial opportunists on natural Johns HopkinsUniversity Press, Baltimore. Fraley,J. J., S. L. McMullin,and P. J. Graham. zooplanktoncommunities. Can. J. Zool. 64: Vinyard,G. L., R. W. Drenner,and D. A. Han- 1986. Effectsof hydroelectricoperations on 57-64. zel. 1982. Feedingsuccess of hatcheryreared the kokanee populations in the Flathead Netboy, A. 1980. The ColumbiaRiver Salmon kokaneesalmon when presentedwith zoop- River system, Montana. N. Am. J. Fish. and SteelheadTrout: Their Fight for Survival. lanktonprey. Prog. Fish-Cult. 44: 37-39. Manage.6: 560-568. Universityof WashingtonPress, Seattle. Wells, L., and A. McLain. 1972. Lake Michi- Grossnickle,N. E. 1982. Feedingshabits of Newton, I. 1979. PopulationEcology of Rap- gan: effects of exploitation, introductions, Mysis relicta-an overview. Hydrobiologia tors. Buteo Books, Vermillion,SD. and eutrophicationof the salmonidcommu- 93: 101-107. Northcote,T. G. 1972. Some effectsof mysid nity. J. Fish. Res. Bd. Can. 29: 889-898. Hanzel, D. A. 1969. FlatheadLake, investiga- introductionand nutrientenrichment on an Wydoski, R. S., and D. H. Bennett. 1981. tion of its fish populationsand its chemical oligotrophiclake and its salmonids.Verhan- Foragespecies in lakes and reservoirsof the and physical characteristics.Project F-33- dlung InternationaleVereinege Limnologie westernUnited States. Trans. Am. Fish. Soc. R-3, job no. I, finalreport. Montana Depart- 18: 1096-1106. 110: 764-771. ment of Fish and Game, Kalispell,MT. . 1973. Some impacts of man on Young, L. S. 1983. Movementsof bald eagles .1976. Historyof northernpike in the KootenayLake and its salmonids.Great Lakes associated with autumn concentrationsin Flathead River. Montana Department of FisheriesCommittee Technical Report no. 25. GlacierNational Park, Montana. M.S. dis- Fish and Game, Kalispell,MT. . In press. Successes, problems, and sertation,University of Montana,Missoula. Hrbacek,J., M. Dvorakova,V. Korinek,and L. control of introducedmysid populationsin Young,L. S., B. R. McClelland,H. L. Allen,P. T. Prochazkova.1961. Demonstrationof the ef- lakesand reservoirs.N. Am.J. Fish.Manage. McClelland,and J. G. Crenshaw.1983. Long- fectof fishstock on the speciescomposition of Potter, D. S. 1978. The zooplanktonof Flat- range movementsof bald eagles associated zooplanktonand the intensityof metabolism head Lake:an historicalreview with sugges- with autumn concentrationsin GlacierNa- of the whole planktonassemblage. Int. Ver. tions for continuinglake resourcemanage- tional Park,Montana: a preliminaryreport. Theor.Angew. Limnol. Verh. 14: 192-195. ment. Ph.D. dissertation, University of Page 325 in D. M. Bird, ed. Biology and Lange, C., and R. Cap. 1986. Bythetrephes Montana,Missoula. Managementof BaldEagles and .Har- cederstroemi, (Schodleri). (Cercopagidae: Richards,R. C., C. R. Goldman,T. C. Frantz, pell Press,Ste. Annede Belluvue,Quebec.

January1991 21

This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:54:27 PM All use subject to JSTOR Terms and Conditions

Top View