Progress 09/01/11 to 08/31/14
Outputs
Target Audience: Water and resource managers and others including academics involved in the eradication and control of quagga and zebra mussels, and aquatic invasive species more broadly. We reached these groups through verbal and written efforts, including face-to-face meetings, presentations at community group meetings and professional conferences, written correspondence and abstracts. We expect to continue extending this information through these means. Changes/Problems: Two problems were encountered when conducting this research. First, our initial planktivorous biocontrol agent – the threadfin shad – did not do well when placed within our enclosures. While our replacement species, the bluegill sunfish, proved to be a quite promising biological control agent, this issue demonstrated that not all species will be acceptable candidates for site-specific application requiring the use of enclosures. Second, we were unable to collect enough redear sunfish to run the experiment at several locations. This illustrated a limitation to this method; fish of the right type and size need to be present in adequate numbers where the method will be applied. What opportunities for training and professional development has the project provided? This project provided both training and professional development activities for several people. First, PIs worked side-by-side with a laboratory assistant who was trained in experimental design, field and laboratory techniques and data management and analysis. The laboratory assistant also was mentored in writing scientific papers, developing a poster for a professional conference and presenting results of the project through a poster session. This person has since gone onto graduate school and is utilizing skills obtained during this project. Three other volunteer laboratory assistants also gained experience with field and/or laboratory work associated with this project. We also engaged four local volunteers in field work, training them in experimental field techniques and exposing them to concepts of aquatic invasive species management. How have the results been disseminated to communities of interest? Thus far, results have been disseminated primarily through scientific conferences. We developed and presented both a poster describing the laboratory results and a presentation on the planktivorous fish field experiments. A handout was developed to educate the public about our work with redear sunfish. Results continue to be disseminated through various means, including educational talks to boaters, lake managers and the public about control of quagga mussels, scientific manuscripts and an upcoming book on IPM for aquatic invasive species. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Our study results have contributed substantially to knowledge regarding management of aquatic invasive species that could help reduce costs and impacts from these pests. First, results from this study have provided new information about a potential means for controlling a top aquatic invasive species – the quagga mussel, and potentially its close relative, the zebra mussel -- thereby providing savings of up to several millions of dollars that currently are spent annually to control these species nationwide. We have identified a fish – the bluegill sunfish -- that significantly reduces mussel densities by consuming both the larval mussel before it attaches to substrates and the juvenile mussel right after its attaches. While this fish is itself a non-native species and therefore should not be introduced to areas where it does not occur, it is a prized sportfish that was stocked long ago and now is resident in many western region lakes and reservoirs where mussels occur and where options for mussel control are limited because the water bodies serve as water sources for local communities. Using a fish that already is present in these systems provides a more environmentally safe alternative to mussel control. Through this project we also have illustrated how another fish species initially believed by many to be a good biological control agent candidate – the redear sunfish – may have limited ability to control mussels due to feeding constraints associated with its feeding behavior, consumption rates and prey (mussel) size. Second, this project supports the idea that applying biological controls to specific sites may be a more efficient and effective way to utilize biological controls. Typically, biological controls are released into a system in densities that are believed to maintain control of the pest throughout the system. Here we have illustrated that containing the control agent (fish) in a specific area can help reduce mussels in that area even if fish don’t normally feed there. Applying this and other control techniques in such a site-specific manner, is likely to help reduce mussel densities in ‘hot-spots’ where mussels often aggregate but where mussel predators may not be abundant, thereby potentially providing a more effective and efficient way to control mussels within a system. Taken together, project results have provided information that likely will increase the use of integrated pest management (IPM) in aquatic habitats, something that has been little applied despite the great benefits of IPM in terrestrial systems. Application of this approach will undoubtedly help reduce costs of control and impacts associated with aquatic invasive species. Objective #1: Planktivorous fish as biological control agents To evaluate whether bluegill sunfish reduce the number of mussels settling on experimental substrates of various orientations at a single water depth, we deployed five paired (treatment/control) 1m3 enclosures with four substrates (two horizontal, two vertical) at a mussel-infested reservoir. Treatment enclosures received either 20 or 35 fish averaging 8.3 cm total length (TL). Percent cover of mussels on substrates was determined using point contact analysis, with average percent cover on replicate substrates compared for treatment and controls. Substantially higher percent cover of mussels occurred on the control substrates as compared to the treatment substrates, with higher cover of mussels on the bottom horizontal substrates as compared to the top horizontal or vertical substrates. Mussel cover was generally lowest in the enclosures with higher densities of fish. A second trial was conducted to determine whether bluegill would be effective biological control agents throughout the water column, not just at a single water depth. For this trial there were 4 treatment and 4 control enclosures that were much larger (1m x 1m x 9m) and had substrates at three depths (4m, 6m, and 8m). Treatment enclosures received 50, 40 or 30 fish averaging 9.0 cmTL. Percent cover of mussels was determined using point contact analysis, with average percent cover on substrates compared for treatment and controls. Significantly higher percent cover of mussels occurred on the control substrates as compared to the treatment substrates at all three depths, with more mussels covering the bottom horizontal substrates than the top horizontal or vertical substrates. In fish larger than 11 cm TL, fragments of mussel shells were found in the stomach and/or intestine indicating that a few of these larger bluegill also were acting as molluscivores, and not just as planktivores. This finding suggests that using bluegill sunfish of various sizes may be highly effective for reducing mussel populations by controlling both the larval and early juvenile mussel stages. Objective #2: Molluscivore fish as biological control agents An experiment similar to our first trial was conducted to evaluate whether molluscivorous fish reduce the number of mussels on experimental substrates of various orientations at a single water depth, but we used redear sunfish and we provided 2 substrates (1 horizontal, 1 vertical) with mussels attached and 2 substrates (1 horizontal, 1 vertical) without mussels. Six paired treatment/control 1m3 enclosures were deployed with two redear sunfish averaging 27.2 cm TL and 375 g added to each treatment enclosure. Percent mussel cover was determined and used to calculate the change in mussel cover for each substrate during the experiment. Redear sunfish reduced juvenile and adult mussel densities, but consumption varied among individuals and with substrate orientation. Percent cover of mussels was substantially reduced on the top surface of the horizontal substrates when fish were present, but increased when fish were absent. In contrast, percent cover of mussels increased on the bottom surface of the horizontal substrates in both the presence and absence of fish. Percent cover of mussels on vertical substrates changed little no matter whether fish were present or not. These results indicate that redear were primarily feeding on mussels attached to the top of the horizontal substrates. To complement this field experiment we conducted a laboratory experiment evaluating the functional response of redear to quagga mussels. Fish ranging from 14.3cm to 24.4 cm TL and 38.21 to 223.6 g were placed in individual aquaria containing an experimental substrate (20x20cm) on the bottom of the tank having one of several densities of mussels (1, 2, 4, 12, 16, 20, 24, 28 mussels per aquaria). Two replicate trials were conducted, with the health of each sunfish and the amount of mussels consumed recorded once per day for two days. The functional response of redear sunfish showed a significant linear increase in the number of quagga mussels consumed per predator over increasing densities of prey (r2=0.998, p<0.001); virtually all mussels were consumed regardless of the density of mussels provided. While these results indicate that the rate of consumption may be proportional to prey density without any satiation, it is inevitable that at some point redears will become satiated and stop eating for a period of time. Additional observations suggest that redear sunfish may satiate at prey densities of 30-40 mussels per day. Taken together, our field and laboratory results indicate that redear sunfish may serve as a potential biological control agent for quagga mussels, particularly if they can be enclosed in areas where other prey items are scarce. However, because they feed most effectively by assuming a downward facing posture removing prey from the top surfaces of horizontal substrates, their use for control of mussels would seem to be limited to benthic areas and top surfaces of pipelines or other structures, not the underneath, bottom surfaces of structures such as docks, floating restrooms, and pump barges.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Culver, C., A. Brooks, S. Ginther, D. Daft and L. Johnson. 2014. Fish As Biocontrol Agents: An Integrated Pest Management Tactic Worth Considering for Quagga Mussels? American Fisheries Society Annual Conference. Quebec City, Canada. August 17-22, 2014.
https://afs.confex.com/afs/2014/webprogram/Paper16262.html
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Ginther, S., C. Culver and A. Brooks. 2013. Potential biocontrol agents for an invasive freshwater mussel.
http://westsocnat.com/yahoo_site_admin/assets/docs/WSN_2013_Long_Program_-_Final.56184040.pdf
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Progress 09/01/11 to 08/31/12
Outputs
OUTPUTS: During this reporting period we devoted our time to three main activities: 1) collaborating with California Department of Fish and Game personnel to identify sources and best methods for collecting fishes, 2) designing, testing, constructing and deploying experimental cages as part of a pilot field experiment, and 3) conducting a series of laboratory experiments aimed at estimating the functional response of fishes feeding on quagga mussels. Fish Collections (Activity 1): With the help of the California Department of Fish and Game and the City of San Diego Water Department we collected both threadfin shad, Dorosoma petenense, and redear sunfish, Lepomis microlophus, for laboratory and field studies. The threadfin shad were collected for a pilot field test. The redear sunfish were used for laboratory studies. Experimental Cages (Activity 2): We designed two types of cages to assess whether fish predators will reduce mussel infestations on substrates that mimic water delivery infrastructure. Two cage types are necessary for achieving the project objectives of 1) mussel control over time and 2) mussel control throughout the water column. The first cage type constructed of hard plastic, vexar mesh (volume = 1m3), was developed to investigate whether fish predators can control mussels populations over periods as long as several months. The hard surface of this cage allows the cage to be cleaned of fouling (algae) and facilitates the longer immersion times required for this experiment. We constructed 10 of these cages. The second cage, composed of a series of collapsible rings (1 m2 in area) surrounded by a soft nylon mesh net 10m in length, will be used to evaluate whether predatory fishes can control mussel populations throughout the upper portion of the water column. The soft mesh fabric and collapsible nature of these cages allows easier handling than would be possible with a vexar cage. Unfortunately, our second cage type cannot be used for periods greater than one month, as it is not rigid enough to withstand the continual cleaning required to prevent algal fouling. Several prototypes of the nylon mesh cages were constructed and tested to ensure safe and efficient handling of the large cage from the side of a small boat. We have settled on a final design and have constructed two nets for further field-testing. Experiments (Activity 3): Two laboratory studies were conducted using redear sunfish. In each experiment, we used two sizes of sunfish and ten different densities of mussels per fish size class. By identifying the maximum number of mussels eaten per day, and the variability in consumption among fishes, we will be better able to determine the densities of fish that may be required to control mussel populations given the level of infestation on the target infrastructure. We also conducted a pilot field experiment using threadfin shad as a biocontrol agent. Fish were collected and placed into the vexar cages that had been deployed in El Capitan Reservoir. Survivorship of fishes and settlement of quagga mussels was assessed after two weeks. PARTICIPANTS: Several collaborators have assisted us with various activities. The City of San Diego Water Department has provided access to field sites, space for laboratory experiments and assistance with field and laboratory work. The California Department of Fish and Game has assisted us with fish collections, including identifying sources and best methods for collection of various fish species and collection of fish. The Metropolitan Water District and the US Bureau of Reclamation have provided input on site selection and cage designs. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Our research efforts during the first year resulted in three outcomes. Firstly, we expanded knowledge about the use of different cage types for field studies of fish biocontrol agents. While the vexar cage is a standard cage style used in aquatic research, with similar designs used by others, we found them to be too rigid for the threadfin shad (see next paragraph). In addition, our other cage - the nylon, collapsible ring cage - is to the best of our knowledge a new design for field research, although it is based upon the design of lantern nets that are used by aquaculturists. The collapsible nature of the cage makes it easier to store and deploy, and the lightweight materials make handling of the large cage easier than hard rigid cages. Secondly, we advanced the knowledge about using select fish biocontrol agents for site specific control of aquatic pests. Specifically, during our pilot field study we found threadfin shad were not conducive for caging, at least in our rigid (vexar) cage design. This was largely due to their escape response behavior that resulted in numerous encounters with the sides of the rigid cages. As our project goal is to evaluate the use of site specific application of fish biocontrol agents for control of quagga mussels, the fish agents must be able to tolerate being caged. Further investigation into appropriate cage types will be necessary to continue evaluations of threadfin shad as a biocontrol agent. With this in mind, we are exploring the use of other filter feeding fishes as potential biocontrol agents. Lastly, we obtained preliminary data useful for understanding the potential effectiveness of redear sunfish as a biocontrol agent for quagga mussels. Through our laboratory experiments, we found that redear sunfish predation on mussels is quite variable, ranging from 0-15 mussels consumed per day. While some fish ate many mussels, others ate none. This variability in mussel predation by redear sunfish has major implications for their use as a biocontrol agent. More fish will be needed, if the consumption of mussels is truly variable among individual fish. However, transport and laboratory conditions may have stressed some fish. Additional studies are planned to explore whether handling or holding stress may have inhibited feeding by some fish.
Publications
- No publications reported this period
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