Amphibian Use of Chehalis River Floodplain Wetlands

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<ul><li><p>Amphibian Use of Chehalis River Floodplain WetlandsAuthor(s): Julie A. Henning and Greg SchiratoSource: Northwestern Naturalist, Vol. 87, No. 3 (Winter, 2006), pp. 209-214Published by: Society for Northwestern Vertebrate BiologyStable URL: http://www.jstor.org/stable/4501964 .Accessed: 12/06/2014 23:18</p><p>Your use of the JSTOR archive indicates your acceptance of the Terms &amp; Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp</p><p> .JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact support@jstor.org.</p><p> .</p><p>Society for Northwestern Vertebrate Biology is collaborating with JSTOR to digitize, preserve and extendaccess to Northwestern Naturalist.</p><p>http://www.jstor.org </p><p>This content downloaded from 188.72.126.41 on Thu, 12 Jun 2014 23:18:42 PMAll use subject to JSTOR Terms and Conditions</p><p>http://www.jstor.org/action/showPublisher?publisherCode=snwvbhttp://www.jstor.org/stable/4501964?origin=JSTOR-pdfhttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsp</p></li><li><p>NORTHWESTERN NATURALIST 87:209-214 WINTER 2006 </p><p>AMPHIBIAN USE OF CHEHALIS RIVER FLOODPLAIN WETLANDS </p><p>JULIE A HENNING1 </p><p>Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331- 3803; hennijah@dfw.wa.gov </p><p>GREG SCHIRATO </p><p>Washington Department of Fish and Wildlife, 48 Devonshire Road, Montesano, Washington 98563 </p><p>ABSTRACT-The use of isolated emergent wetlands by amphibians has been well documented. </p><p>However, amphibian habitats such as emergent wetlands in floodplains may differ from isolated wetlands because of their high disturbance (water fluctuation) related to riverine flooding, pres- ence of fish species, and increased connectivity among aquatic habitats. We compared the am- </p><p>phibian assemblages at 6 freshwater wetland habitats in the Chehalis River floodplain and ex- amined the effect of wetland restoration on amphibians. We sampled 6 wetlands during the </p><p>breeding season in 2003 and 2004 and captured over 15,000 adults, tadpoles, and larvae from 6 species. The red-legged frog (Rana aurora) was the most abundant species captured. The rough skinned newt (Taricha granulose) was the only amphibian captured at all sampled sites. Although it is more desirable to prevent wetland degradation from occurring, restored and enhanced wet- lands in floodplains do provide breeding habitat for amphibians. Amphibian species captured in reference wetlands were also captured in restored wetlands. Water control structures, which were used to facilitate wetland restoration, did not seem to influence utilization by amphibians; however, hydroperiod seemed to affect amphibian abundances. Wetlands with intermediate hy- droperiods had the highest amphibian abundance compared to wetlands with temporary or </p><p>permanent water. Fish were captured in all wetlands, and those with the greatest abundance of native non-game fishes had the highest abundance of amphibians. Our results suggest that </p><p>emergent wetlands in floodplains are dynamic habitats that can offer breeding opportunities, but microhabitat suitability needs to be considered when managing amphibian habitats. </p><p>Key words: red-legged frog, Rana aurora, Pacific treefrog, Pseudacris regilla, bullfrog, Rana ca- tesbeiana, rough-skinned newt, Taricha granulosa, northwestern salamander, Ambystoma gracile, long-toed salamander, Ambystoma macrodactylum, amphibians, wetlands, floodplains, restora- </p><p>tion, habitat, Chehalis River, Washington </p><p>Freshwater emergent wetlands are common features of large river-floodplain systems. Flood disturbances enhance the productivity of these wetlands, increase wetland water fluctu- ation, and allow riverine fish to access flood- </p><p>plain habitats (Bayley 1991, 1995). Many am- </p><p>phibians use wetlands for mating, oviposition, and larval growth and development (Semlitsch and others 1996). Studies of amphibian use of </p><p>river-floodplain wetlands in the Pacific North- </p><p>west, however, are infrequent. Most of the pub- lished work to date has dealt with amphibian use of inland wetlands and isolated palustrine </p><p>habitats (such as Richter and Azous 1995). These habitats differ from isolated wetlands because river-floodplain wetlands have higher levels of disturbance (water fluctuation) related to riverine flooding, have increased connectiv- </p><p>ity among aquatic habitats, and often contain fish. Water level fluctuations or the presence of exotic fish have been shown to decrease am- </p><p>phibian richness (Richter and Azous 1999; Pearl and others 2005). </p><p>Freshwater wetland restoration projects in </p><p>floodplain environments are designed and </p><p>managed for emergent vegetation, fishes, and waterfowl. Amphibians are rarely a manage- ment focus. Consequently, our goal for this </p><p>study was to describe the amphibian assem- 1 Present Address: Washington Department of Fish and Wildlife, 1182 Spencer Road, Toledo, Washington 98591. </p><p>209 </p><p>This content downloaded from 188.72.126.41 on Thu, 12 Jun 2014 23:18:42 PMAll use subject to JSTOR Terms and Conditions</p><p>http://www.jstor.org/page/info/about/policies/terms.jsp</p></li><li><p>210 NORTHWESTERN NATURALIST 87(3) </p><p>blages in floodplain wetland habitats of the Chehalis River Valley in southwestern Wash- </p><p>ington. Our specific study objectives were to </p><p>quantify and compare amphibian use across the floodplain at 6 study sites and to determine the effect of wetland restoration on amphibi- ans. Subsequently, we evaluated the potential influence of hydroperiod on amphibian use at the study sites. </p><p>METHODS AND STUDY AREA </p><p>The study was conducted in Grays Harbor </p><p>County in an agricultural floodplain landscape of the Chehalis River. The Chehalis River Basin has a drainage area of approximately 6900 km2 and is the 3rd largest river basin in the State of </p><p>Washington. The study sites were located in the lower Chehalis Basin (below river kilometer 60) where the river is unconstrained and sinuously moves through the floodplain in the broad flat </p><p>valley floor. The basin was chosen for sampling because of its large size and relatively intact and minimally degraded floodplain. </p><p>Six sites were studied: 4 emergent wetlands and 2 oxbow wetlands in the Chehalis River </p><p>floodplain between river kilometer 27 and 60. Two of the 4 emergent wetlands were restored sites with water control structures (R1 and R2), and 2 were reference wetlands (N1 and N2). The reference wetlands were naturally occur- </p><p>ring and had not been impacted by ditching. The oxbow habitat site, 01, was a remnant ox- bow with a beaver dam that contained perma- nent water. The other oxbow habitat site, 02, was a seasonal side-channel wetland off the river's main-channel. All study sites contained fish species (see Henning and others 2006). </p><p>Restored wetlands R1 and R2 contained ren- nie and salzer clays (USDA SCS 1986) and were drained as part of a local drainage district pro- ject to facilitate farming. Wetland enhance- ments in 1997-98 involved blocking drainage ditches by constructing water control struc- tures and levees. The water control structures enhanced wetland hydrology by retaining wa- ter, and levees kept water within the project area to avoid flooding adjacent lands. Water ac- cumulation provided conditions for a diversity of emergent vegetation and reduced nonnative reed canarygrass (Phalaris arundinacea). Winter water depths were similar at the restored sites (1 to 1.5 m). R1 during the summer desiccated to 0.5 ha, but R2 retained about 1 ha of standing </p><p>water. Dense, monotypic stands of invasive reed canarygrass dominated the vegetation at both wetlands before enhancement. After res- toration at R1, native emergent vegetation in- creased and included narrowleaf bur-reed </p><p>(Sparganium angustifolium), swamp smartweed </p><p>(Polygonum hydropiperoides), waterpurslane (Di- diplis diandria), mannagrass (Glyceria sp.), slough sedge (Carex obnupta), and yellow pond- lily (Nuphar lutea). The R2 wetland was drawn down to allow vegetation to germinate during the growing season. Dominant vegetation was reed canarygrass, spotted ladysthumb (Polyg- onum persicaria), narrowleaf bur-reed, marsh cudweed (Gnaphalium uliginosum), slough sedge, and bentgrass (Agrostis sp.). </p><p>The N1 and N2 reference sites lacked water control structures and were chosen based on their proximity and similarity to the restored wetlands, R1 and R2, respectively. The refer- ence wetlands had not been ditched or drained and contained rennie and salzer clays. Re- stored and reference sites connected to com- mon water bodies and exhibited similar hydro- logical patterns and river flows. The wetlands had free-flowing hydrologic connections to the river's mainstem during periods of peak dis- </p><p>charge. However, the reference wetlands did not have surface water outlets, and surface wa- ter disappeared by May at N1 and in July at N2. </p><p>Emergent vegetation colonized the wetlands </p><p>during desiccation. N1 was dominated by reed </p><p>canarygrass. N2 vegetation consisted of reed </p><p>canarygrass, common spikerush (Eleocharis pal- ustris), narrowleaf bur-reed, sedge (Carex sp.), and waterpurslane. </p><p>The oxbow habitats (01 and 02) did not con- tain water control structures or emergent wet- land characteristics. The sites had free-flowing hydrologic connection to the river during most of the sampling season. The 01 study site was a remnant channel with permanent water and connected upstream to the same drainage as N1 and R1. Water permanence in the oxbow was retained by spring inputs and a beaver dam. 01 also had steep channel slopes, mini- mal emergent vegetation, and an abundance of </p><p>large wood. Dominant vegetation was yellow pond-lily and largeleaf pondweed (Potamogeton amplifolius), and the site was bordered by reed canarygrass, willow (Salix sp.), Sitka spruce (Picea sitchensis), and Himalayan blackberry (Rubus discolor). The 02 study site was a sea- </p><p>This content downloaded from 188.72.126.41 on Thu, 12 Jun 2014 23:18:42 PMAll use subject to JSTOR Terms and Conditions</p><p>http://www.jstor.org/page/info/about/policies/terms.jsp</p></li><li><p>WINTER 2006 HENNING AND SCHIRATO: AMPHIBIANS IN FLOODPLAINS 211 </p><p>sonal channel directly connected to the river in winter. Site depth and discharge were depen- dent on river stage. 02 desiccated by mid-May and reed canarygrass dominated the oxbow. </p><p>Relative amphibian abundance was evaluat- ed using fyke nets from January to May 2003. Each net consisted of a 5-ringed steel hoop net with 2 trapping throats that were 4.5 m long, 1.2 m wide, and covered with 4.76-mm mesh </p><p>netting. Nets were set perpendicular to the shoreline along the wetland perimeter and sep- arated to maintain independence during each 24-h sampling period. The number of nets per site was proportional to the wetland surface area and nets were set to not exceed a maxi- mum density of 1 net/ha in each wetland. Abundance was expressed as catch-per-unit-ef- fort (CPUE), which was defined as the number of amphibians captured in a fyke net over a pe- riod of 24 h. Catch-per-unit-effort estimates for each month of sampling were combined to ob- tain an average monthly CPUE for each study site. </p><p>One-way emigrant traps were installed downstream of study sites that contained a de- fined outlet (R1, R2, 01, and 02) to examine </p><p>amphibian abundance and emigration. The </p><p>traps were operated from 4 March to 5 June 2003. Abundances at R1 and R2 were reexam- ined using emigrant traps from 7 January to 4 </p><p>June 2004. Each emigrant trap consisted of a </p><p>0.6-m X 1.2-m holding box attached to wing nets that channeled amphibians into the box for identification and counting. The traps operated continuously except during floods when trap- ping became inefficient or when the site des- iccated and the trap became dry. </p><p>RESULTS </p><p>Amphibians utilized all of the river-flood- </p><p>plain wetlands studied, although abundances were highest at the restored sites and at the N2 reference site (Fig. 1). Fyke nets and emigrant traps captured 13,201 individuals in 2003 and </p><p>emigrant traps captured 2198 individuals in 2004. Four amphibian families representing 3 </p><p>frog and 3 salamander species were captured at the 6 study sites. </p><p>Species abundances of amphibians varied </p><p>among the study sites (Fig. 1). Red-legged frog (Rana aurora) tadpole abundances were signif- icantly higher in N2 than in N1, 01, and 02 </p><p>(Kruskal-Wallis single factor analysis of vari- </p><p>5- C 4 </p><p>3- E </p><p>2-Z </p><p>N2 Ri St2 /V 12 0 02 Site </p><p>FIGURE 1. Catch-per-unit-effort (CPUE, number/ net/24-h trapping period) of amphibian species cap- tured at 2 restored wetlands (R1 and R2), 2 reference wetlands (N1 and N2), and 2 oxbow habitats (01 and </p><p>02). RC = bullfrog, RA = red-legged frog, AG = northwestern salamander, TG = rough-skinned newt. Adult and tadpole or larval life stages were combined for all species except RA for which only the adult CPUE's are shown. RA tadpole CPUE's (N2 = 605, R1 = 141, R2 = 120, and N1, 01, and 02 </p></li><li><p>212 NORTHWESTERN NATURALIST 87(3) </p><p>TABLE 1. The number of individuals per species captured in 1-way emigrant traps at oxbow habitats (01 and 02) and restored wetlands (R1 and R2) in the Chehalis River floodplain, Washington, during 2003 and 2004. Note: 02 had flooding and was the earliest site to desiccate, reducing trap nights in 2003. </p><p>01 02 R1 R2 R1 R2 Species 2003 2003 2003 2003 2004 2004 </p><p>Ambystoma gracile larvae and adults 0 0 62 10 10 52 Ambystoma macrodactylum adults 0 0 1 0 3 3 Taricha granulosa larvae and adults 0 1 243 4 281 72 Rana aurora adults 0 2 245 22 21 52 Rana aurora tadpoles 0 0 1414 1635 743 58 Pseudacris regilla adults 0 0 4 11 1 0 Rana catesbeiana adults 1 0 1 21 4 72 Rana catesbeiana tadpoles 2 1 7 640 9 621 Total amphibians 3 4 1977 2343 1072 930 Total trap nights 32 16 34 35 28 32 Number/trap night 0.09 0.25 58.1 66.9 38.3 29.1 </p><p>tured at the reference sites (2 at N1; 10 at N2) and at oxbow habitat 02 (1 frog). </p><p>Species richness ranged from 2 to 5 species per study site and the rough-skinned newt was the only species captured at all sites (Fig. 1). Restored and reference wetlands had similar </p><p>species richness (4 to 5 species). 02 had a spe- cies richness of 5, and 01 had a species richness of 2. </p><p>The 1-way emigrant trap results showed that a considerably higher number of amphibians emigrated from the restored sites than from the oxbow sites. Also, the rate of amphibian emi- </p><p>gration (measured as the number of individu- als captured per trap night) from the restored sites was higher in 2003 than in 2004 (Table 1). </p><p>Differences in hydroperiod were identified </p><p>among the study sites. The restored sites had intermediate hydroperiods with &gt;7 mo of in- undation. Although the restored sites were drawn down in the spring, they each contained a small (</p></li><li><p>WINTER 2006 HENNING AND SCHIRATO: AMPHIBIANS IN FLOODPLAINS 213 </p><p>emergent vegetation ha...</p></li></ul>

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