Dedicated To Tribal Aquaculture Programs
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December 1993 ~ Volume 6 | |
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Topics of Interest:
Intensive Culture Techniques For Lake Whitefish
Intensive Culture Techniques For Lake Whitefish
By: Steve Mortensen and John Ringle, Leech Lake Reservation Tribal Hatchery, Division of Resources Management
The interest in intensive culture of lake whitefish for stocking and as an aquaculture species has increased dramatically over the last 10 years. This interest, along with some prodding from MTAN, has resulted in the following outline of the techniques we use to rear whitefish in our hatchery. The lake whitefish is not a particularly easy species to rear, and when we started almost 10 years ago our success was rather dismal. Refinements in rearing techniques, proper rearing conditions and better feed now make it possible to rear these fish on almost a routine basis.
Egg collection
All of our eggs are collected from wild broodstock. Gametes from enough broodstock (400) should be used to insure genetic variation. The timing of egg collection varies considerably from location to location, dependent on water temperature and possibly strain differences. Temperatures in the 4-6 C range seem to generate the most ripe fish. Our earliest fish spawn in late October and the latest ones, in a lake only 15 miles away, spawn about 2 weeks later. We get our eggs from commercial fishermen, which is a very easy and cost-effective means of gathering them. This also gives our fishermen an opportunity to be directly involved in the stocking effort.
Using this method of egg collection we routinely get 60-70% eye up. This percentage can only be achieved using live fish. Early in the run when water temperatures are still warm and many of the gill netted fish dead, percentages will be lower. We have achieved eye up rates of 93% using fish that hatchery personnel caught, but this was at considerable effort and cost.
Eggs are stripped using a dry method of spawning. Eggs from several females are stripped into a dry pan, milt from 3-4 males is added and thoroughly mixed before lake water is added to activate the milt. The eggs are left in milt and water for several minutes and stirred occasionally before being rinsed in a screen box and allowed to water harden in the lake. Eggs are placed in a large cooler filled with water and transported back to the hatchery.
Egg Incubation
Upon arrival at the hatchery the eggs are tempered to hatchery water. Eggs are incubated in Big Redd incubators, but not hatched in them. We can adjust the temperature to get the eggs to hatch whenever needed. The range of temperatures that will give you high percent hatch is from 4-7.5 C. There is an excellent paper on the effects of temperature on whitefish hatch by L. T. Brooke in Trans. Am. Fish. Soc., 1975, No.3, pp 555-559. Our normal temperature regime starts out by maintaining the same temperature as the falling lake temperature until all our eggs are collected. We then set the temperature to about 50 C and incubate for about a month. We then start increasing the temperature to time the hatch of the eggs for after January 1. Our total incubation time is about 70 days, and the total daily temperature units (DTUS) is about 650.
Eggs are treated with formalin (1:600) at 3-day intervals to prevent fungus problems. Dead eggs are siphoned off as needed throughout incubation. Once the eggs are ready to hatch we remove them from the Big Redds, measure out the quantity of eggs we want to hatch, plus about 10% to make up for eggs that don't hatch, into each rearing tank. The eggs are then placed in a conventional McDonald jar that is placed directly into the rearing tank.
By hatching in this manner we have a fairly accurate idea of how many fry are in each rearing tank, and we never have to handle the fry, thus greatly reducing handling mortality. Hatching can also be enhanced by increasing the water temperature several degrees once the eggs are ready to hatch.
Rearing
Whitefish are reared in circular tanks initially at a rate of about 100 fry per gallon. Initial water exchange rate is about 2 (tank) per hour. Fry do not have to be fed right after hatch, because they are absorbing their yolk sack. We start feeding about 1 week post-hatch. Water temperature is set at 12-13 C to stimulate the fry to start feeding. Fry are started on BioKyowa B-400gm larval fish feed. This is a very high-quality, and expensive feed, but it is the only feed we have been able to attain a high percentage fish survival with. Don't waste your time trying to feed brine shrimp nauplii. The larval feed is fed at a rate of about 10% of body weight (BW) at half hour intervals 24 hours a day. Tanks are illuminated 24 hours a day. Larval feed is fed until the fry go through metamorphosis (they get silvery sides at this stage) at a length of about 18mm. This usually takes about 20-30 days, depending on temperature. Once the fish have gone through metamorphosis they can be gradually switched to a high-quality salmon starter feed. We feed this at about 6% BW. Fish are switched to larger sizes of feed as they grow and percent of BW fed is decreased.
Tank water exchange rates are increased as the fish grow to maintain a dissolved oxygen level of 6 ppm or greater in the tank drain standpipe. We have reared fish at densities as high as 7 lbs. per cubic foot using an oxygen injection system, but do not recommend going over 3 lbs. per cubic foot for fingerlings. Tanks must be cleaned every day to maintain high quality rearing conditions for the fish. This also greatly reduces the chance of disease problems. Salt baths at 2% to 1.0% can be used to reduce stress and as a pretreatment.
The only disease problem we have ever had is bacterial gill disease. We treated the fish with Chloramine-T at 6.5 ppm for 1 hour. Nitrogen gas (N2) appears to be a real problem for whitefish so you need to maintain it below 100% saturation. Packed columns, vacuum degassing or oxygen injection is usually a must when using ground water.
At water temperatures of 13-14 C whitefish will grow almost an inch a month, and we usually grow them up to 3-4 inches by June 1 when they are stocked into lakes. We have also reared them to 6-7 inches. They have been reared to market sizes in other aquaculture facilities. Barring any disasters, we will get a survival rate of about 75% from feeding fry to stocked fish. We transport fish in water with a salt concentration of 0.5%.
The information provided above is only a general outline of procedures we use to rear lake whitefish at our facility, but changes and improvements are made almost every year. Please feel free to contact us if you have any questions or need further information.
Alternative Methods For Anesthetizing Fish During Fin Clipping Operations
By: Michael Donofrio Keweenaw Bay Biologist Keweenaw Bay Fish Hatchery
The Great Lakes Fishery Commission recommends that all lake trout which are stocked into Lake Superior, must have at least one fin clipped. At the Keweenaw Bay Indian Fish Hatchery, we will stock lake trout in November and May. During normal inquiries about the availability of MS-222 to anesthetize our fish (during fin clipping), we were told that MS-222 could not be permitted without an EPA discharge permit. Since EPA permits often take a long time to obtain, we felt a need to pursue the availability and use of other fish anesthetics. Some hatcheries in Wisconsin and possibly other fisheries professionals, have experimented with the use of seltzer water as a fish anesthetic.
During our work with Jeff Slade (Fishery Biologist for the U.S. Fish and Wildlife Service), in the summer and fall of 1993, we became acquainted with seltzer water as an anesthetic. Frank Stone (USFWS) provided us with a Wisconsin DNR memo on the experimental use of non-MS-222 anesthetics on fish. After consultation with Frank and review of local availability, we decided to use Seltzer water without sodium to anesthetize our fish for fin clipping before stocking into Lake Superior.
We planned on anesthetizing approximately 6,700 lake trout (30 fish/lb. or 5 inch fish) over a 2-3 day period with two people. The trout were in a 1,600 gallon fiberglass tank inside our hatchery building. We use unfiltered well water with packed columns for aeration. The water temperature is 7.5 C and pH is approximately 7.5 units. We purchased Canfield's Seltzer water from local grocery stores. The ingredients of this water were only triple filtered carbonated water. There are several kinds of seltzer water on the shelf, but all others had artificial flavors, colors, and/or preservatives. We also purchased two 10 gallon tubs to serve as anesthetizing and recovery tanks. We used two 2"x4" boards across the tanks as a temporary work station. This work station would hold our 10 gallon tubs, data sheets, dip net, scissors, stop watch and anesthetizing tub. We then added 1 liter of seltzer water to create an approximate 1:20 solution. Groups of lake trout (60-300) were netted and placed in the anesthetic tub, the induction time was recorded. Then each fish was clipped and moved to a recovery tub. We placed a cover on the anesthetic tub to prevent the fish from jumping out prior to the induction time. To better monitor the effects of the test, we waited until each group of fish were clipped before transferring them from the recovery tub back into the main rearing tank.
The initial induction time for each group of fish was 2 minutes, the 2nd group was 2.5 minutes, and the third from 3 to 3.5 minutes. We could usually clip four groups of fish for each anesthetic solution. The last group would usually take 4 minutes for induction. The induction time was variable for each group and depended on the number of fish in the tank and the time interval since the seltzer solution was made. Most fish recovered from the anesthetic within 3 minutes. We tried to make sure the fin clipping procedure lasted no more than 15 minutes, (from initial netting, until final placement into the rearing tank).
We clipped approximately 1,600 fish the first day, 2,500 the 2nd, and 2,600 the third day. During the fin clipping process, a few fish, (< 10%) were seen to exhibit hemorrhaging at the base of the ventral fins. We were concerned that maybe there was too much stress in the anesthetic tank or too high a concentration of carbon dioxide in the water. However, after fin clipping all of the fish, we only recorded 3 dead fish after the first day, 1 dead fish after two days, and 0 mortality after three days.
We used 13 bottles of seltzer water to anesthetize these fish at a cost of $0.70/ bottle or $9.10. A bottle of carbon dioxide gas would be considerably cheaper as long as there was a simple formula to follow for adding the right amount of gas to a given amount of water. We will consult with other fishery professionals to decide on anesthetic use for our Spring clipping of 45,000 lake trout. We will definitely hire temporary help to aid in the clipping process.
The Keweenaw Bay fisheries program will soon begin to investigate the possibility of inserting a coded wire identification tag into each fish we stock from the hatchery. Since other state, federal, and provincial hatcheries are stocking lake trout into Lake Superior, we would like to evaluate the survival of the fish we stock. All Keweenaw Bay Indian Community stocked lake trout will go into lower Keweenaw Bay. Survival of the fish will be monitored through sampling of commercial catch and summer small mesh assessments commencing in 1995.
Eggs, Apples and Fish
By: Tim Goeman, Minnesota Department of Natural Resources
Thanks to the watchful eye of Mike Gallinat (Fisheries Biologist for the Red Cliff Indian Reservation), the following article was submitted for our MTAN readers. The article was composed by Tim Goeman (MNDNR) and was taken from a recent issue of the Mainstream newsletter. Mr. Gallinat is concerned that as natural resource managers, we all need to remember the number of fish we may stock is NOT as important as determining whether they need to be stocked in the first place. Mr. Gallintat was also concerned that natural resource managers not be pressured to stock out large numbers of small, poor quality fish, in lakes that already have good natural reproduction. This may lead the sports angler to believe that tribally speared, or commercially netted lakes, may need a fish stocking program.
The fisheries manager watches the irate resort owner drive away from his office. The last two hours have not been pleasant. The resorter wanted walleye stocked in his lake. The manager's best efforts at explaining adequate natural reproduction, exploitation, harvest, year class variability, and recruitment seemed to fall on deaf ears. Finally, the resorter stormed out with a threat of going to the Governor. The manager wondered at the lack of progress fisheries professionals have made in communicating sound fisheries principles to the fishing public.
Meanwhile, in a separate building only 100 yards away, the assistant fisheries manager has begun his fourth hatchery tour of the afternoon for school children. The batteries of eggs always intrigue the wide-eyed youngsters. The egg-take has been good this year. The hatchery is running at near-full capacity. Soon, millions of fry will emerge.
These scenarios are guaranteed to continue until fisheries professionals begin realistically assessing the long-term costs of the way we do business. What has the fisheries manager really communicated to his clientele when the most significant public relations effort of the year is the hatchery tour? The message conveyed is:
1) That fish come from hatcheries.
2) That habitat degradation is so severe that naturally spawning populations are inadequate or no longer exist.
3) That the long-term health of the fishery resource depends on hatchery technology.
Fisheries professionals are quick to pontificate about the value of habitat protection , watershed management, and preserving genetic integrity of fish stocks.
But when was the last time a school group was guided on a tour that emphasized habitat and the importance of this ecological component?
It's so easy to give a hatchery tour. It's convenient for everyone. It always gets rave reviews and it helps give a fisheries program some visibility. The long-term costs, however, reach far beyond the mere dollars and cents of a cost-benefit analysis. I am convinced the real cost shows up years later when the child has taken ownership of his parents' resort, a poor year of fishing starts cutting into his profits, and he remembers his third-grade field trip of years earlier. Is it really so amazing that the resorter will not believe the fishery manager's reasoning for not stocking fish?
Well-managed hatchery and stocking programs do have a place in fisheries management, but only as they fit within a sound ecological plan that has fully considered the long-term integrity of the resource. Hatchery and stocking programs are not an excuse for habitat loss and poor fisheries management. Such programs merely serve as treatments for symptoms rather than remedies for the real problems.
At least three times during my short fisheries career of about 15 years, Aldo Leopold's land ethic has emerged in an effort to give new life to natural resource management. One reason his thoughts are still valid today is that most people are urban dwellers with little practical appreciation for natural and wild processes. The fact is, for most people, eggs come from the dairy case, apples from the produce aisle, and fish from the hatchery. The fisheries manager can change some of this thinking, if we change the way we do business.
Applications for Synthetic Liners in Fish Hatchery Rearing Ponds
BY: Timothy A. Duhe Construction Industry, DuPont Polymers DuPont Bldg. 5066-3, Wilmington, DE 19898 302-773-2206
ABSTRACT
In this paper I will present information on synthetic liners that are on the market today. An increasing number of fish hatcheries are including flexible membrane liners based on HYPALON Synthetic Rubber in their hatchery rehabilitation program. We will review some of the technical reasons why this trend exists.
Introduction
Accessing technology is always a challenge for our engineering and designing disciplines. Successfully applying that technology can be one of the most intensive experiences one might have, especially if that technology is new. We are fortunate today because a large number of major companies have made major commitments to take existing technology to new industries. This is the case with synthetic liners in the Aquaculture Industry.
In 1930, Wallace Carothers, a young chemist working at Du Pont, invented the first synthetic rubber, Neoprene. Over half a century later you can see Neoprene in over 1500 products and the next 100 applications are right around the corner. Since Neoprene, a large number of other rubbers and plastics have been introduced to a variety of industries. Several of these are raw materials for synthetic liners. Synthetic liners have served industries for over 20 years in applications from radioactive waste to fish rearing ponds. In most cases you would not use the same liner for both applications. An evaluation of the expected performance will often help engineers "design by function". There is no one single liner material that will satisfy all applications.
Brief History Of Liners
One of the earliest applications of impervious linings is reported to have occurred over 3,200 years ago in the construction of the Tigris River embankment lining at Assur. Since then, natural materials have been used in a variety of engineering applications, but today most countries in the world are using synthetic flexible membrane liners. Flexible membrane liners have achieved the status of "Best Available Technology". Natural materials are being used less frequently as the sole protector of the environment.
Natural soils or clays generally have a permeability value in the range of 1 x 10-7 cm/sec. and only retard the flow of liquids. Synthetic liners on the other hand are considered to be impermeable because they have permeability values approaching infinity. (1 x 10-11 cm/sec.)
Synthetic Flexible Membrane Liners
A flexible membrane liner or pond liner can be defined as a continuous plastic or rubber sheeting used to cover the bottom of ponds, pits, and lagoons with the purpose of containing liquids and preventing seepage. Flexible membrane liners are the leading technology for long lasting economical barriers for such applications.
A wide variety of liner materials are being manufactured and marketed today. These materials vary considerably in physical and chemical properties, methods of installation, cost and interaction with various chemicals. The base "polymers" used make the variations even greater because of differences due to compounding, manufacturing seaming and installation techniques of suppliers. Choosing a flexible membrane liner material is no easy task today for many industries, especially those in the waste containment business.
One of the first things to remember is to "design by function". Project requirements will determine the proper liner material. Rarely will the lowest priced material be the "best" liner for the job. Compromises are usually made if price is the major factor rather than performance. Price should only be a factor when more than one material meets all your project requirements. Some of the applications where synthetic liners are being used in the fish hatcheries include:
Rearing ponds and race ways.
Intensive culturing facilities.
Relining concrete and asphalt ponds.
Wastewater treatment ponds and settling basins.
Why Use A Synthetic Liner
The use of synthetic liners in fish hatcheries has been rapidly increasing for several reasons. These include:
Prevention of Water Loss. By preventing the loss of water, hatchery managers have found pH control to be much more consistent. Temperature control and oxygen balance are also more manageable when the water level in the rearing ponds are maintained.
Disease Control. Some early experiences indicate that control of diseases is much easier to attain in a synthetically lined pond. Effective bacteria treatment has been attributed to the elimination of contaminated soils. A soil layer on the bottom is not necessary and is counter productive to parasite elimination. We hope to see further research on this subject in the near future.
Automation. Several fish hatcheries have reported 40-60% cost reductions in harvesting of small fry and fingerlings because of the elimination of the soil bottom. These synthetic liners are designed to drain into the kettle area. The slopes are engineered to insure against "puddling" thus making dipping and seining obsolete. A synthetically lined pond that is left exposed to the weather (no soil cover) can be harvested with a minimal amount of labor.
Choosing A Synthetic Liner
Recognizing that there are numerous types of synthetic lining materials on the market today, let's take a look at the most widely used materials for lining rearing ponds and similar applications. Without trying to go down a line and list every liner on the market, let's take a look at it from a generic approach, a polymer approach. Every material on the market will fit into one of four generic categories. Each of these generic categories has strengths and weaknesses and by understanding these you will be better able to match a liner material with your specific project needs.
What's A Polymer
Polymers include such chemically different compounds such as plastics, rubbers and even some of the proteins. The word "polymer" means repetition of structural chemical units, such as linear chains. These polymer chains can align themselves in different ways. In some cases they intertwine like strands of spaghetti-amorphous structures. In other situations, they align themselves in parallel crystalline structures. So called crystalline polymers are semi crystalline only, for amorphous portions invariably persist which fill the intervening space between the crystalline chains. The level of crystallinity or "semi crystallinity" has a marked effect on physical properties. (An amorphous polymer may be a very viscous liquid in the extreme state while a highly crystalline polymer may be very hard or rigid). This level of crystallinity is what physical properties of lining materials ultimately relate back to.
Four Classifications Of Polymers Used In The Liner Industry
As previously mentioned, all liners on the market today can be categorized in one of the following generic classifications:
1) Rubber/thermosets (Neoprene, EPDM, Butyl)
2) Compounded plastics (PVC, CPE)
3) Crystalline plastics (HDPE)
4) Thermoplastics elastomers (HYPALON)
The types of liner listed next to the classification are just a handful of lining materials that are on the market, however, these are the materials that you would most likely see in water containment applications. Let's take a look at each of the generic classifications! Each of these has strengths and weaknesses and please remember that there is no single material that will work in every project. You should become familiar with these advantages and disadvantages and make your liner decision on which is the best material based on the technical requirements of a specific project.
Synthetic Rubber/Thermosets
Neoprene, butyl and ethylene propylenediene monomer, EPDM thermosets were the first generation of liner materials. By definition rubbers/elastomers are materials which at room temperature can be stretched to twice its original length and upon immediate release will return with force to it's original length. Due to difficulty in producing good seams with cured materials, thermosets are not generally used today in containment applications.
Compounded Plastics - Polyvinyl chloride (PVC) and Chlorinated polyethylene (CPE):
By definition, thermoplastics are heat formed products that gain their strength from their crystalline structure. Polyvinyl chloride is a versatile thermoplastic which can be compounded with materials such as plasticizers and other modifiers to produce a flexible membrane. You may be familiar with PVC in its more rigid form such as plastic pipe and siding, however, compounding plasticizers into the material will produce a very flexible rubber-like material. There is a wide choice of plasticizers (both the traditional liquids and polymerics) that can be used in PVC sheeting, depending upon the application and service conditions under which the PVC membrane will be used.
Carbon black is added to prevent ultraviolet attack of the PVC polymer. The carbon black causes the absorption of solar energy when left exposed, raising the temperature to a high level to cause migration of the plasticizer making the PVC less flexible. Plasticizer loss during service is the key source of PVC degradation. The effects of plasticizer in fish ponds is not known. A soil or other suitable cover material used to bury the liner protects it from ultraviolet exposure and reduces the rate of plasticizer loss.
Newer PVC formulations are designed to retard the loss of plasticizer for longer exposures. CO polymer alloys and nitrile butadiene are two examples of improved plasticizers. PVC's are generally lower in price and have good seaming characteristics. PVC is the most widely used compounded plastic on the market today. Life span is limited and the added expense of a dirt cover makes PVC less attractive for rearing ponds. Plasticizer migration is the major concern.
Seaming and Repairing PVC
PVC is prefabricated into large panels and then delivered to the site for field seaming. Prefabricating the panels provides better quality control and reduces the amount of field seaming. PVC can be heat welded or solvent welded in the field. Any repairs that are to be made to a PVC liner can be done in a similar manner following the manufacturers instructions.
Crystalline Plastic - High density polyethylene (HDPE):
Polyethylene is widely used for liners because of its good resistance to chemicals and was needed for extremely hazardous waste disposal sites in spite of other mechanical and physical problems. The properties of polyethylene are largely dependent upon its crystallinity and its density. In fact, it is this crystallinity which accounts for almost all of its recognized problems today. HDPE has a high coefficient of thermal expansion, causing stress in the seam areas. The polyethylene being used today in the liner market is generally a medium density polyethylene, but many producers still refer to it as "HDPE".
HDPE polymers do exhibit good resistance to oils, solvents and permeation by water. Unprotected clear polyethylene degrades readily on outdoor exposure but the addition of 2-3% of carbon black can produce improved protection from ultraviolet attack. Polyethylenes for the most part are free of additives such as plasticizers.
Polyethylene membrane liners are made by sheet extrusion processes. The width of the sheet can be as much as 22 to 34 feet. Thickness is usually between 40 to 100 mils. These thicker sheets are very stiff in comparison to the other membranes described in this paper. Thinner sheets are more difficult to field seam due to temperature sensitivity and are also punctured easily under impact such as when rocks are dropped on the liner. {A Note from MTAN} You may want to fence your ponds in to ensure deer will not puncture holes into the liner.
Seaming and Repairing HDPE
HDPE is supplied to the job site in rolls that are the same width as it is produced. Because of the stiffness of the HDPE it would be very difficult to prefabricate panels and then fold them as is done with other flexible membranes, i.e. HYPALON and PVC. The rolls of HPDE are unrolled at the job site and each sheet is seamed to the adjacent one using either an extrusion welding technique or some other type of heat seaming such as a heated wedge, double wedge etc. Seam integrity is very dependent on operator skill.
If using the extrusion welding process, the beaded extrudate used to cap the overlapping sheets must be of the same resin type as the original sheeting to assume a homogeneous seam. HDPE cannot be solvent welded.
Polyethylene is more difficult to seam, although it appears easy if you watch the process in the field. If you inspect the seams, most will look good and you'll walk away satisfied. What you don't see is that the act of melting the polyethylene during any of the processes has caused a realignment of the crystals, in effect producing a polymer having different properties along the seam area than found in the center of the sheet. This melting and cooling process builds in stresses which can produce cracks in the liner with time. Also, if repairs are needed on a HDPE liner after the installation crew has left the site, then all the heavy seaming equipment must be brought back. Various suppliers of HDPE have placed heavy emphasis on improving seam methodology, which undoubtedly is to the benefit of the reservoir owner.
HDPE is more subject to environmental stress cracking. We will discuss environmental stress cracking in the "physical properties" section of this paper.
In summary, a strict (QA/QC) Quality Assurance/Quality Control program is highly recommended.
Thermoplastic Elastomer - HYPALON / Chlorosulfonated Polyethylene:
HYPALON is made from high density polyethylene but with some important differences to address previously discussed problems of straight HDPE. To solve the problems associated with the crystallinity of HDPE, the chlorine in HYPALON interrupts or reduces the crystallinity and produces an amorphous, rubbery product. Since the crystallinity is the source of strength to HDPE, the addition of chlorine has reduced this inherent strength. A small amount of sulfur is then added to get back to a stronger but much more flexible liner material. HYPALON is characterized by ozone resistance, ultraviolet stability, heat resistance and excellent weatherability. Compounded HYPALON has achieved wide recognition as a sheet membrane for roofs due to its excellent performance as an exposed membrane.
Since 1958, HYPALON has been used in protective applications such as wire and cable, HYPALON coated fabric such as the Good Year Blimp and many other demanding applications where weatherability and durability are major criteria. Membranes based on HYPALON are available in a variety of colors other than black. Potable water reservoirs use the colorability of HYPALON to enhance aesthetics while providing the environmental protection to our drinking water. Compounded HYPALON has no plasticizer and so has good resistance to growth of mold, mildew, fungus and bacteria.
Flexible membranes liners based on HYPALON are available in industrial and potable grades. The potable grade of HYPALON is approved by the American Water Works Association for storage of drinking water. Flexible membrane based on HYPALON are produced by calendaring a coating of HYPALON on both sides of a polyester scrim. The HYPALON encases the scrim by bonding to itself through the openings between the fibers. This double encapsulation avoids possible pinholes that can occur in unreinforced films. The scrim reinforces the HYPALON and provides dimensional stability, increases tensile and tear strength and improves properties at elevated temperatures. The most commonly used scrim is a 10x10x1000D which has 10 counts per inch in both directions. A membrane with a single ply of scrim is generally used with a total thickness of 36 mils.
Scrim reinforced HYPALON is produced in five foot wide rolls. The rolls are fabricated "in house" under controlled conditions (without the typical field variables of air temperature, air velocity, relative humidity, equipment speed, etc.) into larger panels custom sized to specific site specifications, drastically reducing the number of necessary field seams.
Seaming and Repairing Hypalon
HYPALON is seamed with solvent cements or with heat. Any field seaming is usually done with a bodied solvent consisting of 10% HYPALON compound dissolved in a solvent, which evaporates after bonding leaving the composition of the seam to be the same as the remainder of the membrane.
Any repairs that are to be made to a HYPALON liner can be made using the manufacturer's instructions with only scissors, brushes, bodied solvent and a hand roller.
Designing With Synthetic Liners - Physical Properties
The design process should include full consideration of all aspects of expected performance. Designing is much more than specifying a liner based on thickness as is being done more often than not today.
A full evaluation of physical performance is recommended to obtain the most appropriate liner for your individual site. It is not an easy task to compare reinforced membranes to unreinforced membranes.
The following is a review of some physical test data that can help you specify your liner requirements.
A. Strength in Tension - Strength in tension measured in one direction:
HDPE produces a curve with a yield point in the range of 15 to 20 percent elongation. At the yield point it starts to "neck-down" in a localized area until the polymer chains are highly oriented and they resist further elongation. As the tensile test continues the adjoining areas start to neck-down until they are also highly oriented. This process continues until the test specimen breaks.
This performance seems impressive, but the stress-strain curve does not adequately describe what is happening to the HDPE as it is being stretched. The high strength indicated by the stress-strain curve is realized only in the direction the specimen is being stretched. The strength in any other direction is very poor. For this reason, tear strength and puncture resistance are also very poor after the HDPE starts to neck-down. This can be demonstrated by taking a stretched test specimen, placing it on a soft surface and pushing a ballpoint pen into the surface of the specimen. It will easily penetrate completely through the membrane where it has been stretched. After it has been punctured, it can be torn very easily.
Scrim-reinforced HYPALON provides a stress-strain curve with a sharp yield point at about 20 percent elongation when the longitudinal scrim fibers break. The membrane still provides a continuous barrier of HYPALON, but the longitudinal strength is now much lower than it was. The useful part of the stress-strain curve is primarily the part before the fabric break.
To compare the strength of HDPE membrane with that of a scrim-reinforced membrane of HYPALON, the strip tensile method of ASTM D751 was used. This test uses a 1 inch strip pulled at 12 inches/min. The maximum strength at yield or a fabric break was measured for each membrane material.
At room temperature scrim-reinforced 36 mil HYPALON is stronger than 60-mil HDPE and is almost as strong as 80-mil HDPE. At 158 F HYPALON is equivalent to 60-mil HDPE.
When elongated at 2 in./min, the 36-mil scrim-reinforced HYPALON has higher strength than 60-mil HDPE. HYPALON also has significantly higher elongation at yield compared to HPDE at any thickness. Similar stress-strain tests were run at a much slower strain rate (.02 in/min) to simulate the very slow strain rate that occurs when differential settling is encountered in a pond or landfill. At this slow strain rate, all materials have lower tensile strength but that of HYPALON is slightly better than 80-mil HPDE.
B. Biaxial Strength - Strength in tension measured in two directions at the same time:
Stress imposed on flexible membrane liners in actual service is often in two directions rather than the one measured by typical stress-strain test. Special testing equipment is required to obtain this type of stress-strain data and only limited study has been conducted in this area. However, in June 1984, Steffen reported the results of his work with a number of commercial membrane liners (International Conference on Geomembrane in Denver). He found that HDPE fails at relatively low elongations when stressed in two directions. He also found that the elongation at failure was dependent on the thickness of the membrane. Steffen expressed the belief that there was further evidence supporting the need for a minimum thickness requirement for HDPE membrane liners of 2.O mm (79 mils).
Scrim reinforced HYPALON was not included in the original work, but has since been tested on the same equipment and by the same test procedure. HYPALON was found to have a failure elongation of 30.3 percent, which is 3 times greater than 60 mil HDPE. The higher elongation provided by HYPALON is very meaningful for liners for ponds or landfills. The stress applied to the liner by the tons of liquids or solids it supports would far exceed the strength of any liner if it were not supported by the soil underneath. To avoid rupture and failure of the liner, it must be able to accommodate the movement caused by any differential settling of the soil without exceeding the failure elongation of the liner. The high elongation of scrim reinforced HYPALON provides a big safety factor compared to HPDE.
C. Environmental Stress Cracking:
Crystalline and semi-crystalline polymers, such as HDPE, can develop stress cracks when exposed to certain conditions while under stress. Some of these conditions include chemicals that only attacked these polymers when they are under stress. This problem is generally labeled as environmental stress cracking.
HDPE is known to be sensitive to a variety of chemicals of which the most common types are soaps and detergents. Environmental stress cracking is receiving a great deal of attention. Several organizations are researching and trying to explain the cause of this phenomenon.
D. Coefficient Of Thermal Expansion:
The amount of expansion or contraction that occurs when a membrane is heated or cooled is expressed as its coefficient of linear thermal expansion. It is determined by accurately measuring the dimensions of a test section at two different temperatures and calculating the percent change/degree F or C. HDPE has a very high coefficient of thermal expansion (.018%/ C). This means that a liner on a 500 foot berm will expand more than 6 feet on a day when the temperature starts at 32 F and the black liner gets up to 158 F in the early afternoon sun. To accommodate this much expansion, the liner develops large undulations or waves on the berms and exposed side slopes. Besides providing a poor appearance, this results in severe stress in the region between the exposed membrane and the membrane that is below the liquid level which expands very little. This high linear expansion also placed limitations on when seaming can be done. Seaming on hot sunny days can result in split seams or the liner lifting away from the corners at the top of the side slopes as the liner contracts during cooling in the evening.
Scrim reinforced HYPALON has a coefficient of linear thermal expansion of .006%/ C (1/3 that of HDPE). With the greater flexibility of the HYPALON liner, it can easily accommodate this much expansion without causing problems. A high coefficient of linear thermal expansion will add tension to the seam areas causing failed seams.
Private Sector
As the demand for fish as a major food source continues to increase, intensive culturing is becoming more necessary. Extended life of ponds as well as water quality are becoming factors that are critical to the success of fish farming. The ability to control the factors that influence the health of the fish is being achieved by utilizing the latest available technology, flexible membrane liners. Flexible membrane liners have also contributed to the elimination of "off taste" fish. A phenomenon that has cost some fish farms as much as 80% of their harvest to go to second quality at second quality prices.
Sport Fish Restoration Program
Thanks to programs such as the sport fish restoration program, utilizing the latest available technology has become attainable. The state wildlife and fisheries organizations have been successful in qualifying fish hatchery rehabilitation as a sport fish restoration program, thus utilizing the federal funds that are available. Each state has a federal aid contact that handles compliance to this program. Handbooks are also available from the U. S. Fish and Wildlife Service that better define the program requirements.
Conclusions
While there are many liner materials to choose from, only the requirements of the individual project should dictate which material is the best choice. In buried applications the choice for a liner material varies greatly. In applications where the liner will be left exposed to the sun in order to enhance drainage and harvesting then the choices are fewer. Each material's strengths and weaknesses should be considered. Flexible membrane liners based on HYPALON synthetic rubber have demonstrated decades of proven performance. Approval by the American Water Works Association combined with its excellent weathering properties have made the potable grade of HYPALON synthetic liners the "best available technology".
Plastic Pond Liners at Lac dU Flambeau
By: Larry Wawronowicz, Fish and Game Director, Lac Du Flambeau Band, Lac Du Flambeau, WI
The Lac du Flambeau Fish Culture Program has purchased and installed 135,746 square feet of plastic liners for six 1/2 acre ponds located on Highway 47 North and Longs Point Lane. The liners were purchased from Yunker Plastics of Lake Geneva, Wisconsin.
Over the past several years, seepage in ponds one through six started to become a problem which was having an negative effect on walleye fingerling production. The fertilization program was becoming unpredictable and pumping costs were increasing. Since clay is a very rare commodity in Lac du Flambeau, Wisconsin, plastic liners were chosen to seal the ponds. The Lac du Flambeau Fish Culture Program purchased the plastic liners from Yunker Plastics because they provided an excellent product within budget and friendly service. The program is always conscious about supporting businesses located in Wisconsin.
The plastic material purchased is described as AW 1616-16A Black HDPE/LDP woven. Physical characteristics include coating, color, weight, total thickness, flex abrasion, low temperature bend, tear strength, bursting strength, tensile strength, hydrostatic resistance, dimensional stability and carbon black. The plastic material includes carbon black to provide some UV stabilization, is approximately 20 mils thick, and has 16 x 16 counts per inch which makes the material strong yet flexible at cold and warm temperatures. The material reminds me of black strapping tape with strapping going in both directions or perpendicular to each other.
Installation of the liners was easier than anticipated. One major advantage was that they are in one piece. No in pond seams have to be welded. Ponds were prepared by removing vegetation, rocks, sticks and other sharp objects from the pond bottoms and levees. A trench was dug around the perimeter of each pond with a "witch-ditch" and attachment sites for the liners around the water supply lines and drain lines were installed.
The pond liners, which are folded like an accordion, were rolled out along the crown of the long levee with a tractor. Approximately 20 people lined up and grabbed the free end of the liner with sticks and on count, ran down the levee, across the pond bottom, and up the opposite levee. The air trapped under the liner makes the liner float over the pond causing the liner to be installed in one quick and easy coordinated motion. If the installers became uncoordinated and the liner hit the bottom of the pond before everyone is on the opposite levee, or if the liner had to be repositioned, air had to be pumped under the liner by simulating the "stadium wave". After the liner is properly positioned, the ends of the liner are inserted in the trench in a "J" configuration and dirt from the ditch returned to lock the liner to the levee. Holes are cut into the liners to accommodate the water supply and drain lines and then sealed.
For more information on the material, its physical characteristics, or installation procedures,
please call Mr. Brian Yunker of Yunker Plastics (Yunker Plastics 200 Sheridan Springs Road,
Lake Geneva, WI 53147, Phone 414-249-5233).
Wisconsin Aquaculture Advisory Council
By: Larry Wawronowicz, Fish and Game Director, Lac Du Flambeau Band Lac Du Flambeau, WI
Many of our Wisconsin readers may not know Wisconsin has an Aquaculture Industry Advisory Council (WAIAC). The purpose of the WAIAC is to:
Assist in implementing the Wisconsin Aquaculture Plan.
Advise legislators and other interested agencies on how aquaculture is going to develop in Wisconsin.
The Council is chaired by Mr. Bud Sholts and consists of 12 voting council member and non-voting ex-Officio council members. All council members are industry representatives and ex-Officio members are representatives from the Department of Natural Resources, the University system and Department of Agriculture, Trade and Consumer Protection.
Currently, the member tribes of the Great Lakes Inter Tribal Council are being represented by Mr. Dick Hartmann (715-349-2195) of St. Croix and Mr. Larry Wawronowicz (715-588-3303) of Lac du Flambeau. If your tribe has any ideas, comments, suggestions, information, or problems in dealing with aquaculture, feel free to contact Mr. Hartmann or Mr. Wawronowicz. Your tribe's input would be greatly appreciated and required in order to represent your tribe accurately. WAIAC meetings are held on a quarterly basis. The meetings are open, so feel free to attend.
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Product and company names mentioned in this publication are for informational purposes only. It does not imply endorsement by the MTAN or the U.S. Government.
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