Predator Habitat Use in the San Joaquin River

Transcription

1 Watershed Management Experiential Learning for USDA Careers Internship Report Predator Habitat Use in the San Joaquin River A Plan to Supplement Existing Predator Studies Kyle Griffiths 7/29/2013

2 Table of Contents Acknowledgments 1 Executive Summary 2 Project Objectives 2 Project Approach 3 Project Outcomes 4 Conclusions 5 Works Cited 6

3 Acknowledgements This project was supported by Agriculture and Food Research Initiative Competitive Grant no from the USDA National Institute of Food and Agriculture. Thanks to Dr. Steve Blumenshine, my advisor, and to Julio Perez, Carl Temple, and Travis Bybee for their research assistance. 1

4 Executive Summary With the support of the Water Resources Institute s Experiential Learning for USDA Careers internship, I have developed a plan to supplement an existing San Joaquin River Restoration Program study to examine predation by introduced piscivorous fish in a complex of gravel mine pits in the San Joaquin River. The existing project is to assess which gravel mine pits harbor piscivores which present the highest risk to seaward juvenile salmon and to identify actions to mitigate the risk. The success of this strategy depends on whether predatory fish remain in one location to feed or roam throughout the river and mine pit complex. My analysis of predator habitat use through bioenergetic modeling, stable isotope analysis and multivariate statistical analysis should reveal how successful this approach is likely to be. Project Objectives The goal for my internship was to develop a plan to generate and analyze data on the diets and habitat use of assemblages of introduced predatory fish in the San Joaquin River to further the goals of the San Joaquin River Restoration Program. The restoration settlement mandated that the restoration program assess the mine pit habitat of the predatory fish and identify actions to mitigate predation on juvenile salmon. The partner agencies surveyed the area in 2012 (Predator Study 2012) and drafted a plan for further sampling. My graduate advisor and I were subcontracted to analyze the 2012 diet samples and further diet samples to be collected, and to provide a deeper analysis of diet and environmental data. The analysis of this data will also provide the material for my master s thesis (MS) at Fresno State. My research program s goal is to determine which, if any, of the mine pits can be identified as predation hot spots. My formal null hypothesis is that predatory fish in the region do not differ in their feeding habits, and in effect are feeding at random throughout the environment. If the fish exhibit random feeding behavior it may not be possible to prioritize mine pits for remediation. On the contrary, it may be possible to prioritize mine pits if fish show patterns in their feeding behavior with regard to location or other environmental factors. This kind of observational study does not involve direct manipulation of environmental factors, so the feeding behavior will be influenced by many uncontrolled variables and require sophisticated analyses. The only major deviation of my study plan from the one that I initially announced was that I have not pursued direct lines of inquiry on salmonid habitat use or foraging. Some of the 2

5 information for this study, such as temperature records, may be useful for studies on salmon. Although it will be important to study the actual behavior of salmon in the study area, the scope of research to be performed on the predators is more appropriate to my educational requirements and available resources. I have identified Fish Biologist as my career objective for my Water Resources Institute internship. I used the support of the internship to develop statistical and methodological skills that will make me much more competitive for this job, such as diet analysis, bioenergetic modeling, and multivariate analysis. Project Approach My role in the restoration program is to supplement the work of an existing research program planned and carried out by federal and state agencies. The current predator study work plan delineates six subunits in the 24 mile study region to sample monthly from January to June At each location, the sampling team took water samples and used electrofishing and trammel netting to capture fish. The fish were identified, tagged, and size data, tissue, and scales were collected, as well as diet samples on select individuals based on their size and species. The diet samples, including previously collected 2012 samples, water samples, and scale and tissue samples were transferred to me at various times during the sampling season between January and June I used the samples to create a database for our subsequent research. A portion of the first year of my internship was used to analyze predator diets to create a profile of the prey exploited by the fish. Each item in the diet sample is identified and measured and numbers of prey are estimated for items too numerous to count. Prey items of different taxa vary in their energy content, which is a function of size and energy density (cal/g). The overall inputs of energy from each type of prey will be used in a variety of analyses. In order to provide a general overview of resources exploited by each piscivorous species in the mine pit environment, I will use the diet data, along with temperature and estimates of other physiological variables to construct a bioenergetics model. Bioenergetic models allow researchers to estimate the amount of food consumed over a given period. As long as growth rates and the conditions that affect metabolism (e.g. temperature) are known for the period of interest, the model can provide rates and total consumption broken down by prey category and a value for the 3

6 proportion of maximum consumption for each fish in the simulation. The values for an individual fish can be extrapolated to the entire age class as long as an estimate of population size and demographic characteristics are available. Stable isotope analysis is another exciting analytical tool to investigate habitat use in the study area. Trophic relationships in food webs, patterns of prey exploitation, and movement through a habitat can be analyzed by comparing elemental isotope ratios in tissue with background abundances. This is possible because there are patterns of variation in environmental isotopic ratios, such as variation of environmental abundances of hydrogen and oxygen in snowmelt or groundwater versus precipitation, or because of patterns of heavy nitrogen enrichment with trophic level. Since the diet data are from multiple specimens and recorded for many prey types, multivariate analysis may be useful to uncover patterns in the data. Multivariate statistics can classify data, arranging it into groups, or perform an ordination on it, arranging it in lowerdimensional (e.g. Cartesian) coordinate space, by identifying combinations of variables (e.g. prey classes) that best discriminate amongst the samples. Constrained ordination relates the variation in the principle response data set (in this case the diets data) to a set of environmental variables (such as space and time), identifying which ones have the strongest influence, so this type of ordination is the best option for discovering risk factors for juvenile salmon. A good proportion of my effort this year has gone into researching multivariate statistics, including the appropriate environmental variables to measure and the proper way to perform the analyses. Project Outcomes Some broad trends have emerged from early data exploration. For instance, largemouth bass are by far the most numerous predators captured in the mine pits. In the 2012 sample data, 50 of 97 collected predators were largemouth bass, and in 2013, 139 of 217 samples registered at the time of writing were largemouth bass. This is important information for the planned multivariate analysis because it means information about largemouth bass will dominate the results unless they are treated to make them less influential. It is also easy to see that two categories of prey dominate the diet data from the 2012 samples: crayfish and largemouth bass. Since largemouth bass are also a dominant proportion of the 4

7 MU29SPB SI_RES SI12LMB SI20LMB SI24BBH SI26LMB SJR54BBH SJR57SPB MU28LMB SI17BBH SI21BBH SJR54BCR SI21LMB PASHSPB SI21BBASS SI24LMB SI23LMB SI15LMB MU29BKBH SI25LMB MU29LMB SI11LMB PASH_ALMB SI18LMB SI11CHC SJR54LMB SJR56LMB Prey Consumed (mg.) predators taken in samples, it is likely that cannibalism is an important source of energy for adult largemouth bass. It is also easy to see that the biomass of the diets varied widely Prey Consumption of Important Prey Items in SUCKR LMB LAMPR FISH_UNK CRAYF CHIRO BCR Specimen ID Figure 1. Consumption of principal prey classes (>0.6% of total diets by mass) by a subset of 2012 predator samples Conclusions During the period of my WRI internship, I researched methods to analyze predation by introduced piscivorous fish in the San Joaquin River and mine pit complex near Fresno. The product of my research was a plan that will supplement the work of the existing sampling plan. The existing plan will provide some information about the location and diet of the predatory fish, but only provides a snapshot. Supplementary analyses will allow us to reconstruct feeding patters over a longer period of time through bioenergetic modeling, multivariate analysis, and stable isotope analysis. During my remaining period in school, I will follow up on this plan to analyze the diet samples and the environmental data. Since I have been tentatively approved for a second round of internship funding, I am confident I will be able to carry this plan out, meet the graduation requirements for my master s program, and become even more competitive for USDA Fish Biologist positions. 5

8 Works Cited Predator Population Assesment (Preliminary Data Report): 2012 Mid-Year Technical Report. San Joaquin River Restoration Program. July