Methods

We sampled largemouth bass between June and August of 2006 primarily via electrofishing along the lake perimeter. Fish were collected via angling when lake conductivity was not suitable for electrofishing. Thirty fish were collected from each lake to determine size-specific growth rates. Fish length (total length; mm) was recorded, and 5 to 10 scales were collected from each fish from the area posterior to a depressed pectoral fin. We removed young-of-the-year fish from the analysis owing to the lack of annuli, and as a result, sample size varied between lakes. Scales from yearling fish and older were sonicated and pressed between two slides. Nonregenerated scales were read into a digital imaging system. Annual growth rates (mm per year)1) were determined using Fraser-Lee’s method of back calculation with Carlander’s recommended constant of 20 mm for largemouth bass. It is possible that LRD could have changed during the lifetimes of the longer-lived bass in our study, especially because LRD boomed during the 1990s but slowed substantially during the 2000s. To eliminate any potential effects of changing LRD levels, only the annual growth estimates from 2001 to 2005 were included as repeated measures of annual growth for each fish.

Methods

We chose five lakes with high density of houses and five lakes with a low density of houses based on the lakes and housing quintiles developed by Anna Marburg. In each lake, we chose three sites with no wood and three sites with high wood based on the CLC surveys. We took two benthos samples at each site and for the sites with CWH, we took two wood samples. Macroinvertebrates were identified to the lowest possible taxonomic level. Number of sites: 60 Sampling Frequency: once per siteTo characterise the littoral benthic invertebrate community in each lake, invertebrates were collected using an underwater airlift sampler within a 0.25m2 quadrat (see the study by Butkas, Vadeboncoeur & Vander Zanden, 2011, for details about the airlift). This method samples the overall macroinvertebrate community (both epi- and in-faunal species). Samples were collected at a depth of 1 m in triplicate for both sand and cobble habitat in a 500 um mesh bag at the top of the airlift. Samples were transported on ice and hand-sorted within 4 h of collection. Picked specimens were fixed in 70 % ethanol and identified to genus. For statistical analysis, we pooled macroinvertebrate numbers into broad taxonomic groups, namely Tricoptera, Ephemeroptera, Diptera, Amphipoda, Isopoda and Mollusca, because of large among-lake variability in presence at the genus level. Nilsson E, Solomon CT, Wilson KA, Willis TV, Larget B, Vander Zanden MJ. 2012. Effects of an invasive crayfish on benthic invertebrate abundance, fish benthivory and trophic position. Freshwater Biology. 57:10–23

Methods

Wisconsin Net samplesLower the Wisconsin net to the bottom sample depth ( top of the net should be one meter above the bottom). Pull it up slowly at a rate of about 3 seconds per meter. A slow haul prevents the net from pushing water and plankton away from the mouth of the net. To drain the cup swirl it until the water level is below the lower mesh window, then pour contents into the sample jar. Avoid inverting the cup while swirling, as you will lose the sample into the net. Rinse the inside of the cup with 95percent ETOH several times adding the rinse to the sample jar. Wait until the chemistry crew member is finished taking Temp or D.O. profile before taking the Wisconsin net sample, so as not to stir up the sediments. Take replicate sample.

Methods

Macrophyte surveys were conducted on Sparkling Lake, Vilas County, Wisconsin in mid-July of the years 2001 to 2009. Eight sites were chosen that corresponded to trap survey sites for rusty crayfish and represented the range of macrophyte communities in the lake. These sites corresponded to trap survey sites 1, 4, 10, 16, 20, 23, 27, and 35. At each site, we swam a transect perpendicular to shore from 0 to 4 m depths. A tape measure extended from shore to the 4 m depth contour, and buoys were placed at the 1, 2, 3, and 4 m depth contours. We visually estimated the percent cover of each macrophyte species within a 0.24 meter squared quadrat. Quadrats were placed along each transect at 1 m intervals. Thus, we used fewer quadrats on transects with a steeper slope. At site 23, we only found a macrophyte on one event: Vallisneria sp. in 2004.Transect: corresponds to trap survey site number.Quadrat: occur at 1 m intervals starting from shore (0) and going until you reach the 4 m depth contour (highest number).Substrate: substrate within the quadrat categorized as muck, sand, gravel, cobble, logs, leaves, or any combination of these.Abundance: percent cover of each species within the quadrat determined by visual estimation. The percent covers of all species within a quadrat do NOT necessarily add to 100.Depth Interval: depth interval that each quadrat was in. Quadrats between 0 and 1 m deep are in depth interval 1, those between 1 and 2 m deep are in depth interval 2, etc.

Methods

Fish were collected by beach seining, hook and line angling, and minnow traps. Commonly captured species were largemouth bass, bluegill, yellow perch, rock bass, and black crappie. Population Estimates: Chapman-modified continuous Schnabel mark-recapture population estimates were conducted on each basin of Little Rock and Camp lakes annually. Adult population estimates for largemouth bass, yellow perch, rock bass, and black crappie were calculated for Little Rock Lake during 2001-2006. All fish were captured by hook and line angling, minnow traps, and beach seining. Adult population estimates for largemouth bass and bluegill were calculated for Camp Lake during 2002-2006. All fish were captured by hook and line angling and beach seining. Fish Length/Weight Tag data: Length, weight, and mark data was recorded for all fish used to collect diet information. Diet information was collected from up to 15 individuals of each species biweekly May-September using gastric lavage. Diet information was collected from largemouth bass, yellow perch, rock bass, and black crappie in Little Rock Lake from 2001-2005 and 2007 - 2009. Diet information was collected from largemouth bass and yellow perch in Camp Lake from 2002-2005. Fish Length Tag data: Length and mark data was recorded for all fish used to calculate the mark-recapture population estimates. Length and the mark were recorded from all fish captured in Little Rock and Camp lakes from 2001-2006. Length and mark data exists for all fishes collected in Little Rock Lake from 2001-2006 and 2007 - 2009. Fish species from Little Rock include largemouth bass, yellow perch, rock bass, and black crappie. Length and mark data exists for all fishes collected in Camp Lake from 2002-2006. Fish species from Camp Lake include largemouth bass, yellow perch, and bluegill. All fish were captured by beach seining, hook and line angling, and minnow traps. Minnow trap CPUE: Minnow traps were the most effective gear for capturing yellow perch on Little Rock Lake. Standardized minnow trapping was conducted on both basins of Little Rock Lake in 2003-2005. In 2003, 10 minnow traps in each basin were deployed biweekly and picked twice per week. In 2004-2005, 20 minnow traps in each basin were deployed biweekly and picked twice per week. Catch per unit effort was calculated as catch of yellow perch per trap. Age Growth Rates: Growth rates were calculated for a subset of fish collected from Little Rock Lake (2001-2004) and Camp Lake (2002-2005). Back-calculated growth rates from five fish from every 10 mm size increment were examined. In the process, age was determined from scale samples and length at each annulus was back-calculated. Size-specific growth rates were calculated based on the relationship between fish length at age and ln transformed growth rate at age. Back-calculated growth information was assessed from largemouth bass, yellow perch, rock bass, and black crappie in Little Rock Lake. Back-calculated growth information was assessed from largemouth bass and bluegill in Camp Lake.

Methods

Two approaches for trapping were used in the initial phase of this study: removal trapping and "standardized surveys". Traps set for removal of rusty crayfish were concentrated in areas of the lake to maximize catch rates. In 2001, removals began on 14 August 2001 and traps were emptied daily during the last 2 weeks of August. From 2002 on, crayfish are trapped and removed from mid to late June through late August. Traps are wire mesh minnow traps with openings widened to 3.5-cm diameter. (In 2001, other traps and trapping methods were also evaluated.) Traps are baited with 4- 5 dead smelt.Removal traps were set in arrays of 10 at 10-m intervals along the 1-m depth contour, and were emptied daily during during 2001 - 2003 and every 1 to 4 days starting in 2004. Removal traps were concentrated on the southern and western shorelines of the lake where catch rates are highest from 2001-2004. From 2005-2008, traps were set around the entire perimeter of the lake. From 2001 to 2004 the sex of each crayfish in a trap was recorded, and a randomly selected subsample of the daily crayfish catch was used to estimate mean size. From 2005-2008, the number of crayfish in each trap was recorded, and a randomly selected subsample of 50 individuals was measured and their sex was determined.To assess the environmental predictors of rusty crayfish catch rates, "standardized surveys" were conducted prior to harvest in 2001 through 2006. Standardized surveys were comprised of perimeter trapping and depth trapping. Although perimeter trapping occurred every year, depth trapping only took place in 2001 and 2003. For perimeter trapping, 43 traps were baited with 120 g of beef liver and set for 24 hours at 1-m depths at 100-m intervals along the shoreline. Perimeter traps were set on 6 dates in June through August. Three days after the June and July perimeter trapping events, 14 depth transects were set around the perimeter of the lake. Depth transects were spaced 300-m apart and along the transect, traps were set at 0.5, 3, 5, 8 and 12-m depths. Perimeter trapping at the 43 sites, but not the associated depth transect trapping, was done on four dates in 2002 and continued to be done for three to five dates annually through 2006.Trap_id: During removal trapping, from 2001-2004 10 traps were set at each of the standard trapping sites. For years 2001- 2004, the trap_id of removal traps includes additional information about the spatial location of the trap. The first number of the trap_id indicates the trap site (1 to 43) and the number after the dash identifies which trap of 10 was pulled from the site as you move clockwise around the lake. For example, trap 12-1 is at the flagpost of site 12, trap 12-5 is approximately halfway between sites 12 and 13, and trap 12-10 is just before you arrive at site 13.Starting in 2005, the removal traps are distributed equally around the lake starting at trap site 1 and proceeding in a clockwise direction. These traps are given trap_ids of sequential numbers as they are lifted. These trap_ids do not relate directly to the trap site. However, you can calculate the approximate trap site for each trap by knowing the total number of traps set over the 43 standard trap sites. In 2005, a total of 277 traps were initially set. In 2006, 220 traps were set over the 43 sites. During the initial retrieval in 2006, data were grouped for each of the 22 sets of 10 traps. To make these data comparable to the rest of the removal trap data, the crayfish represented in the grouped data were assigned randomly to individual traps within the 10 trap set. In 2007, the maximim trap_id was 269. In 2008, the maximum trap_id was 289.Removal: Traps set annually at 43 sites around the lake and fished through the trapping season. In 2002, additional single traps were set near logs and other likely places which were not in close proximity to other traps. These traps have -MIN appended to the trap number in TRAP field.Perimeter: Traps set annually (through 2006) on standard arrays at 43 sites around the lake at 1 m deep for a limited number of days. The last year perimeter traps were used was 2006.Depth Transect: Traps set on standard arrays that ranged from 0.5 to 12 m deep. Depth transects were set in 2001 and 2003 only.Lead: Traps were set at the ends of a “lead” made of aluminum flashing and staked to the bottom of the lake in 2001 only. Experiment was to see if the flashing would be a barrier to the crayfish, and would lead crayfish into small minnow traps. Traps were set at different depths. Leads were set at survey sites: 7, 15, and 26. (Site is indicated in the TRAP field for these traps). Traps were set at each end of the lead and along the middle, as indicated by the depth they were set.Minnow: Minnow traps set in 2001.Commercial: Experimental large box traps used only in 2001.Wik: Traps designed by Don Wik and used in 2002 only. These were square traps with trapezoid-shaped ends, and an entrance on the top of the trap.References:Hein, Catherine L., Brian M. Roth, Anthony R. Ives, and M. Jake Vander Zanden. 2006. Fish predation and trapping for rusty crayfish (Orconectes rusticus) control: a whole lake experiment. Canadian Journal of Fisheries and Aquatic Sciences: 63 383-393Hein, Catherine L., M. J. Vander Zanden, John J. Magnuson. 2007. Invasive trapping and increased fish predation cause massive population decline of an invasive crayfish. Freshwater Biology:
Update 2021
Table biocom_crayfish_daily_station was extened by summarising 2001-2006 data from biocom_crayfish_individual. New data are added for 2011-2019

Methods

Setting NetsSet nets in areas of high catch first, moving clockwise around the lake.GPS location of netRecord dates in that locationNumber nets consecutively from first net set. (Nets do not need to be pulled in order they were set.) If a net is moved, keep the same number and add an a, b, c, etc after.Sketch net location on a map with the net number (keep with In-Boat data sheets)Pulling NetsTake lake map with net numbers and In-Boat data sheetRecord date, time, collectors namesAt each net, record net number, number of bags and any comments (note anything unusual)For a zero catch… note if the net was fishing (tipped over, twisted, etc). If there were no problems write NORMAL SET.Try to set the net in exactly the same location. (Over burlap if applicable)Data CollectionIf there is not enough time, please follow this order for priority of data collection.Daily CatchUse Daily Catch sheetRecord date, net number, bag number, number of bags from that netWeigh bags in kilograms. Record.Note if fish were kept for sex determination, length – weight or scales and the number kept.Sex ratioUse Sex sheetRandomly select 2 nets. Sample 50 fish from each net.Record date and net numberWeigh two empty buckets and record weight.Separate fish by sex. Try not to squeeze out eggs/sperm.Count number of males and females. Record.Weigh buckets with males or females in them. Record.Length WeightUse Length Weight sheetSelect a random net and sample 30 fish from itRecord date, net number, if fish were frozenRecord length, weight and sex.Compare to scale sheet. Collect scale sample if category is not filled. Pull scales from behind the dorsal fin. Note on data sheet that scales were taken. Scale envelopes should have date, length, weight, net number and sex of fish on them.

Methods

Riparian samplingPREPARATIONDatasheet packets:Each lake has 8 survey sites.One packet per site:3 10m x 10m riparian zone plot data sheets1 Sapling plot or General Site Info data sheetFor 2 of the 8 sites, packets will need to include 2 riparian subzone data sheets.Weather can be highly variable. Data sheets should be printed on write in rain paper.Survey site selections:8 Sites per lake will be selected using GIS software.Subzones: To look at the effects of wind, sun, and fetch; select 2 of the 8 sites for additional subzone surveys. One site must be located in the NW quarter of the lake and the other in the SE. Within each of these 2 chosen sites, randomly select a 10m x 10m subzone plot in zone 2 and another 10m x 10m subzone plot in zone 3. (See figure 1).Sapling plots: At each site, two 5m x 5m sapling plots should be randomly selected within plots A, C, andoror E (Refer to figure 3).EQUIPMENT LISTClipboard, data sheet packets, lake and site maps, pencils, watch, compass, 50m measuring tapes, Diameter tapes (fabric and combination tapes), flagging, GPS unit,Oars, cushions and vests, motor, gas. Appropriate rain gear and boots.FIELD DATA COLLECTIONRecord the lake name, site number, plot number, date, observers, start and stop time.Collect a GPS point at the start of each of the 8 survey sites (plot A).timesIf the site has to be relocated due to denied permissions, mark new location on lake maps.Prepare Survey Plots:Each site is 30m x 50m in size. Five 10mx10m plots along shoreline are the zone 1 survey plots. Subzones are located in Zones 2 and 3. Plots should never overlap.Set up plots (A, C, E)Facing the selected site location (looking from the water towards shore), plot A is on the left, C and E are to the right of A respectively.Mark the sites starting point (with a flag and a GPS point). Using a meter tape to place flags at 10m increments along the shorelines ordinary high water mark (0m, 10m, 20m, 30m, 40m, 50m).For each 10x10 plot, determine the shoreline aspect, then use a compass and meter tape to place corner flags back 10 meters from shore so that each plot is square.Record the slope and aspect (perpendicular to shore) for the start of plots A, C, and E. This will represent the hills steepness and direction.Recording Data:General site info:Site information must be recorded for all 5 plots (A, B, C, D, and E)Record ownership (public or private).List the number of docks and buildings –count them only once if they cross into 2 plots.Presenceorabsence information – Using the list provided, check anything that is present, or list it as other. Record what is dominant. There are 2 parts to the General site info list:Qualitative assessment of habitat (forest stands, herbaceous, wetlands, etc).Human development andoror disturbance.FOR PLOTS A, C, and E:Live Trees:Record the species and diameter at breast height (DBH) for every living tree that is larger or equal to 5cm DBH (other woody plants having a greater than or equal to 5cm DBH should also be recorded).Diameter at breast height: Since trees are swelled at the base, measurements are made 4.5 feet (1.37 meters) above the ground in order to give an average diameter estimate.Trees on plot edge: Sometimes trees will be questionable as to whether they are in or out of the plot. Good rule of thumb is a 50percent cut off. If the tree is more than 50percent within the plot, count it. Do not count 1 tree in more than one plot!Standing snags: A snag is a (or part of a) dead standing tree taller than 1.37 meters (DBH). If a snag is greater than or equal to 10cm DBH then record type (snag), type of break (natural, un-natural, beaver), species (if known), DBH, and branchiness (0-3).Stumps: A stump is dead tree cut or broken off below 1.37 meters (DBH). Record stumps that are greater than or equal to 10cm in diameter. Take the diameter at the base of the stump but above the root mass. Record type (stump), type of break (natural, un-natural, beaver), species (if known), and diameter at base. Branchiness is assumed to be 0.Coarse Woody Debris (CWD) in Riparian zone:For this study, CWD is considered any logs greater than or equal to 10cm in diameter and greater than or equal to 150cm in length.Record type (log) and type of break (natural, un-natural, beaver, unknown). Record the species type (species, conifer, hardwood, or unknown), the diameter at base, and log length from base to longest branch tip.Record Branchiness (0-3). Where 0 is no branches, 1 is few, 2 is moderate, and 3 is many branches.Record Decay (0-5). Where 0 is a live tree touching the ground at two or more points, 1 is recent downwood (e.g. lacking litter or moss cover), 2 is downwood with litterorhumus or moss cover; bark sound, 3 is bark sloughing from wood; wood still sound, 4 is downwood mostly barkless; staubs loosening; wood beginning to decay; logs becoming oval and in contact with the ground along most of their length, and 5 is decay advanced; pieces of wood blocky and softened; logs becoming elliptically compressed. timestimes NOTE: paper birch retains its bark long after the wood has rotted, score logs of this species by the softness of the wood, not the presenceorabsence of bark. timestimesAdditional parameters:If a log extends out of a plot, record its entire length and measure diameter at the base regardless of whether the base is inside or outside of the plot.If a log crosses into more than one plot, record the entire length and measure diameter at the base, but record log only in the plot where the base is (if the base is outside of the site, then record in the plot closest to the base).Paper birch: often are broken into many small parts. If segments are still in line (no more than ~5 cm separating them), then you can count breaks as a single log.Logs that extend over the water are measured only from the base to the shoreline and listed in notes as measured to water.For each site, Two 5m x 5m sapling plots are randomly selected in plots A, C, andoror E. Use the numbering scheme depicted in graphic.Use compass and meter tape to setup and mark square plots using the original plot aspect.For each sapling plot, count and record all tree saplings greater than 30 centimeters in height but having less than a 5 cm DBH.Subzones:Subzone plot data are recorded the same as plot data.Refer to figure 1 to set up random subplots at 2 of the 8 sites at a lake. Use compass and meter tape to setup and mark square subplots. Use the original plot aspect when possible.For each square 10m x 10m subplot (one in zone 2 and one in zone 3) record slope and aspect.Record all live trees that have greater than or equal to 5cm DBH. Record all stumps greater than or equal to 10cm DBH and snags greater than or equal to 10cm diameter at base. Record logs greater than or equal to 10cm in diameter and greater than or equal to 150cm in length.

Methods

Lower the Secchi into the water on the shady side of the boat. Lower the disk until you cannot see it; record this depth as the down reading. Raise the disk until you can again see it; record this depth as the up reading.

Methods

Study Lakes We selected 60 northern temperate lake sites in Vilas County, Wisconsin lake district. Methods for lake choice and sampling are given in greater detail in Marburg et al. (2005) Each lake was sampled once between 2001 and 2004, in June, July, or August (15 different lakes each summer). We chose stratified lakes deeper than 4 m to insure that all the lakes contained a diverse fish community. With two exceptions (chains of lakes), lakes were chosen to be in separate watersheds. Lakes were chosen based on two criteria landscape position, using historical DNR water conductivity data as a proxy of position, and riparian housing development, measured in buildings km-1 shoreline (Marburg et al. 2005). Landscape position refers to the location of a lake along the hydrological gradient. The gradient ranges from the top of a drainage system, where seepage lakes are fed mainly by rainwater, through lakes which receive water from groundwater and have surface outflows, to lakes further down in the drainage system, which receive water from both ground and surface flow (Kratz et al. 1997).Landscape position affects lake water chemistry, because as water flows across the surface and through soil, it picks up carbonates and other ions which increase the waters electrical conductivity (specific conductance, a temperature-independent measure of salinity), alkalinity, and its ability to support algal and macrophyte production. In addition, aspects of lake morphology correlate with landscape position. Most obviously, larger lakes tend to occur lower in drainage systems (Riera et al. 2000).The riparian (near-shore terrestrial) zone around northern Wisconsin lakes is being rapidly developed for use as both summer and permanent housing (Peterson et al., 2003). Concurrent with housing development, humans often directly and indirectly remove logs (Kratz et al. 2002) and aquatic vegetation (Radomski and Goeman 2001) from the littoral zone (near shore shallow water area), resulting in reduced littoral zone complexity. The slowly-decaying logs of fallen trees create physical structure (coarse woody habitat CWH) in the littoral zone of lakes that provides habitat and refuge for aquatic organisms (Christensen et al. 1996). Fish, including plankton-eating species (planktivores), reproduce and develop in shallow water (Becker 1983). Because planktivorous fish affect zooplankton community structure through size-selective predation (Brooks and Dodson 1965), there is the potential for indirect effects of housing development on zooplankton.Lakes ranged in size from 24 to 654 ha. In 2001, 2002 and 2004 we chose lakes from the extreme ends of the conductivity and housing density gradients and in 2003 lakes were chosen to fill in the gap in the middle of the ranges. The study lakes range from oligotrophic to mesotrophic (Kratz et al. 1997 Magnuson et al. 2005).At each lake we sampled zooplankton, water chemistry, riparian and littoral vegetation, fish, crayfish, and macrophytes. Each lake was sampled only once, but given the large number of lakes sampled in this area, we expect to see relationships between variables within lakes and at a landscape scale. A snapshot sampling design maximizes sites that can be visited, and is sufficient for a general characterization of zooplankton communities (Stemberger et al. greater than 001).