Methods

NLA data were obtained from US Environmental Protection Agency National Aquatic Resource Surveys website (https://www.epa.gov/national-aquatic-resource-surveys/data-national-aquatic-resource-surveys). We incorporated the NLAs definition of human-made lakes, lakes that did not exist prior to European settlement and resulted from impoundment, as reservoirs in our analysis. From this database, we identified geographically co-located lake and reservoir pairs. Pairs were defined as lakes and reservoirs within a 50 km radius of one another. We developed pairings using the near proximity analysis tool for Geographic Information Systems (ArcGIS 10.1). If more than one lake was found within 50 km of a reservoir, the closest lake was chosen for the analysis. We identified 66 lake-reservoir pairs and for each lake or reservoir, we consolidated its catchment and water body attributes from the NLA data onto our data spreadsheet.
Laboratory and field methods for the NLA data are reported by the US Environmental Protection Agency (https://www.epa.gov/national-aquatic-resource-surveys/national-lakes-assessment-2007-results). We used the NLA data directly to collect basic geographic and morphometric parameters (elevation, catchment area, lake area, lake perimeter, maximum depth) and physical parameters (Secchi disk depth, turbidity, chlorophyll, surface water temperature, bottom water temperature). Mean residence times were provided by Renée Brooks (pers. communication) and were estimated using stable isotopes of hydrogen and oxygen as described in Brooks et al. (2014). If more than one parameter was collected for a site, then the average among the values was used in the analysis. From these parameters, we also calculated the ratio of catchment area to surface area (CA:SA) and depth-corrected difference in temperature between the surface and bottom waters.

Methods

Experimental designThe experiment was conducted from 16 to 26 June 2008. In the first treatment, oxygen was added to the hypolimnion. In the second, nutrients were added to the epilimnion. The third treatment simulated a mixing event (overturn). There also was a control enclosure with no treatment and sampling of the ambient lake water. Throughout this manuscript, we refer to these as Oxygen, Nutrient, Mix, Control and Ambient.Twelve limnocorrals were constructed as enclosures for the experiment. Each limnocorral was cylindrical and extended vertically from the surface of the lake to the sediment (approximately 4 m). The total volume was approximately 5050 l. Details of limnocorral construction are provided in online Supporting Information.The limnocorrals were deployed on 15 June 2008 to allow the sediment and water column to stabilize before treatment on 16 June 2008. The limnocorrals were deployed in a random spatial arrangement throughout the lake, at a maximum depth of 3.25 to 3.5 m. Replicates from each treatment were instrumented with a chain of HOBO temperature sensors (Onset), and one replicate from each had a self-logging DO sonde (Yellow Springs Incorporated) in the hypolimnion (3 m depth). More thermistors were deployed in the Oxygen and Mix treatments because thermal stratification was important for evaluating success of these treatments.For the Mix treatment, a 60 cm flat disk was raised and lowered between 3.5 m depth and the lake surface. Holes were drilled through the disk surface to increase turbulence (Sanford, 1997; Regel et al., 2004). A brick was tied underneath the disk to maintain stability. We manually oscillated the disk every 10 min for 1 h and then, after a 1 h break, continued for an additional hour. Temperature and DO profiles were monitored within the limnocorral with a hand-held probe to track mixing progress.The goal of the Oxygen treatment was to aerate the hypolimnion water without allowing it to mix with the epilimnion. This treatment was achieved by pumping hypolimnion water from the bottom of the limnocorral into an external cooler where the water was aerated with bubble diffusers, and then returned to the bottom of the limnocorral (Fig. S1). Valves on a compressed air cylinder were used to control the delivery of air to the coolers. One cooler was maintained for each replicate limnocorral. Thermally insulated tubing was used to transport water. A thermistor was deployed in each cooler to ensure ambient hypolimnion temperature was maintained. The water was removed and returned using two linear diffusers that were 0.6 m in length, spanning a depth range of approximately 2.5–3.1 m within the hypolimnion. The diffusers faced inward with 0.5 m fixed distance between them, retained by a plastic divider. This treatment was applied continuously over 3 h, until DO concentrations increased.The Nutrient treatment was achieved by adding ammonium chloride (NH4Cl) and potassium phosphate monobasic (KH2PO4) as N and P sources. These compounds were chosen because they are commonly bioavailable sources of nutrients. P was added to the epilimnion to achieve a final concentration of 3 micro g P l−1, which was approximately the average concentration expected in the mixed water column. This value was based on nutrient analyses from integrated water collected on 9 June 2008 in North Sparkling Bog, a week prior to experiment start. Similarly, N was added to achieve a final concentration of 70 µg N l−1. The limnocorral s epilimnion volume (0–2 m integrated depth) was calculated to be 2520 l, and we used the molar mass to determine the amount of each nutrient added to the epilimnion to achieve the expected mixed concentration. Dry chemicals were dissolved into to 500 ml of surface water from each limnocorral, and then added into each separately. Rationale for directly manipulating only one layer in the Oxygen and Nutrient treatments is given in the online Supporting Information.The Control limnocorrals were left undisturbed. To prevent mixing during equipment removal, all tubing was left inside the limnocorrals until the experiment ended.

Methods

Rainbow smelt were sampled from Crystal Lake to obtain age and growth estimates. Samples were taken using vertical gillnets and beach seines during late July and early August of 2009. Annual growth was estimated using sectioned sagittal otoliths from 25 individuals spanning the observed length range (31–164 mm). Otoliths were mounted in epoxy and a transverse section was removed using a low-speed saw. Annual growth estimates were measured along a radius from the origin to the edge oriented perpendicular to annual growth rings. Age-specific length was estimated using the biological intercept method of back-calculation. The biological intercept was calculated by applying the average rainbow smelt otolith radius at time of hatch, to our observed linear relationship of natural-log-transformed total otolith radius and total fish length. Of the 25 individuals aged using otoliths, 5 were YOYs. As a result, annual growth was only back-calculated using the 20 older individuals. Weight at age was determined from back-calculated lengths using a weight–length relationship derived from 100 individuals captured during late July and early August of 2009.

Methods

A total of 183 yellow perch from 43 study lakes with approximate length of 150 mm were analyzed

Methods

As part of the Landscape Position Project, yellow perch were collected for mercury and isotope analysis by a combination of angling, beach seining, vertical gill net, fyke net and electrofishing in the summers of 1998 and 1999. A total of 86 yellow perch from 25 lakes were analyzed. Scales were used to determine age and length at ages 1 to 3 years. The nitrogen stable isotope signature indicates the relative food-web position of the fish relative to cladocerans collected from the same lake. The N_SIGNATURE value divided by 3.2 gives trophic position relative to cladoceran Sampling Frequency: one survey on each lake in late June through late July of 1998 or 1999 Number of sites: 25

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

In 2001 - 2004 littoral habitat, fish and macrophyte surveys were performed at eight sites within each of the 55 lakes. The sites were chosen by randomly selecting two points per compass quadrant of each lake. Each year littoral habitat surveys were conducted in June, fish surveys in July and macrophyte surveys in August.Littoral habitat (substrate and coarse woody habitat) was measured along a 50 m transect parallel to shore along the 0.5 meter depth contour at each site. The two Littoral CWH variables (number of logs km-1 greater than 5 cm diameter, and number greater than 10 cm) were transformed by log of (1+number) to normalize the variables.