CALIFORNIA STATE UNIVERSITY, NORTHRIDGE DIRECT AND INDIRECT IMPACTS OF FISHING ON THE TROPHIC STRUCTURE OF KELP FOREST FISHES OFF SOUTHERN CALIFORNIA A thesis submitted in partial fulfillment of the requirements for the degree of Masters of Science in Biology By Parker Henry House May 2015 ! ! The thesis of Parker H. House is approved by: __________________________________________ ___________________ Maria S. Adreani, Ph.D. Date __________________________________________ ___________________ Peter J. Edmunds, Ph.D. Date __________________________________________ ___________________ Mark A. Steele, Ph.D. Date __________________________________________ ___________________ Larry G. Allen, Ph.D., Chair Date California State University, Northridge ! ii ACKNOWLEDGEMENTS I would like to express my gratitude to the following people for making this research possible. First and foremost, I would like to thank my advisor and mentor Dr. Larry “Gandalf” Allen for accepting a guy who was pulling seine nets in the Louisiana bayou and teaching me all things related to the fishes of the northeastern Pacific. I could not have done this project without your enthusiasm for research, continual support, friendship, and knowledge. Thank you to Dr. Mark Steele and Dr. Mia Adreani for their invaluable input, insight, and reviewing of this thesis. I would also like to thank Dr. Peter Edmunds for his valued discussions, support, edits to this thesis, and always asking “so where’s the Ecology manuscript?” My upmost gratitude goes to those who helped me in the field. Thank you to Jennifer “JSmo” Smolenski for selflessly, continuously, and saintly helping me throughout my first field season, even after hour long surface swims off La Jolla, long cold days at Anacapa Island, and throughout the summer putting up with consistently eating peanut butter and pop-tarts for lunch. Thank you to Michael “Abalone” Abernathy for guidance and help at Anacapa Island and for teaching me the skills necessary to operate a boat. I would especially like to thank J.R. Clark for his immeasurable help researching giant sea bass, being an exceptional field assistant and lab mate, but even more so a great friend. I am very grateful to Juan Aguilar and the staff at the USC Wrigley Institute for Environmental Studies for field assistance and allowing me to do research from out of the one and only Big Fisherman Cove. Upmost thanks to Dr. Jack Engle and Dr. Ed Parnell for their proficient advice and input to this study, and to Dr. Steve Dudgeon for being a iii! ! fellow night owl and letting me stalk and ask questions on statistical analyses late at night in Magnolia Hall. I would also like to thank Myron Hawthorne and the highly skilled CSUN Science Shop team for constructing the laser outfitted DPVs for giant sea bass, as well as the “zombie killer.” Many thanks to the Allen Ichthyology Lab, fellow friends/graduate students at CSUN, and particularly Nick Evensen, Edwin “Yoda” Leung, and Barbara “Babs” Sanchez for all their help. I would like to give a very special thank you to Kelcie “Chiquita” Chiquillo for countless discussions about this project, unwavering and continual encouragement and support, and for hundreds of opaleye grandbabies. This research was funded by the CSUN Graduate Thesis Support Program, Nearshore Marine Fish Research Program, Sigma Xi Grants in Aid of Research, Southern California Academy of Sciences, and the USC Wrigley Summer Fellowship Program. ! iv ! DEDICATION This work is dedicated to my loving mother and father, Debbie and Randy House, who have always supported my brothers and myself to pursue our passions in life as long as we work hard doing it. ! v TABLE OF CONTENTS Signature Page ii Acknowledgements iii Dedication v Abstract vii Chapter 1 Differences in trophic and community structure of kelp forest fishes inside and outside of three long-standing MPAs in the Southern California Bight Introduction 1 Materials and Methods 15 Results 24 Discussion 29 Table 39 Figures 48 Chapter 2 Stock biomass, numerical densities, population characteristics, and community presence of giant sea bass (Stereolepis gigas) off Santa Catalina Island, California Introduction 60 Materials and Methods 65 Results 67 Discussion 69 Table 75 Figures 76 References 85 vi Abstract Direct and Indirect Impacts of Fishing on the Trophic Structure of Kelp Forest Fishes off Southern California By Parker H. House Masters of Science in Biology In many marine ecosystems worldwide, overfishing is a prominent cause in removing large predatory fishes from ecological communities. Fluctuation in the abundance of higher trophic level species can transform an ecosystem’s structure and function by altering trophic interactions through density-mediated top-down control. Accordingly, understanding the extent to which humans indirectly influence a community through altering predator abundance is of critical importance. Thus, during the summer of 2013 and 2014 the impacts of fishing on the trophic structure and community assemblage of kelp forest fishes were examined within the Southern California Bight. In 2013, I tested whether decreased abundance through fishing for higher trophic level predators relieves predation pressure on lower trophic level prey. Using a combination of underwater survey techniques, density (no. fish/100 m2) and biomass (g/100 m2) of conspicuous fish species were sampled inside and outside of three long- standing Marine Protected Areas (MPAs) off La Jolla, Santa Catalina Island, and Anacapa Island, California. I found that secondary carnivore and herbivore/omnivore trophic levels significantly decreased outside of MPAs. Inversely, the primary carnivore trophic level biomass increased outside of MPAs. Species-level results revealed a lower ! vii abundance outside MPAs of large kelp bass (> 25 cm) and higher densities of its prey, kelp perch. My results show overall fish trophic level changes due to fishing pressure, and provide support for a weakening of top-down control on the kelp perch population through the removal of predatory fishes outside MPAs. To investigate the possible return of the historically overfished apex predator of the kelp forest fish community, I censused the giant sea bass (Stereolepis gigas) population at eight sites off Santa Catalina Island from mid-June through mid-August, 2014. Three possible spawning aggregations were identified at the sites Twin/Goat, The V’s, and Little Harbor. The giant sea bass population at these sites primarily consisted of individuals 1.2 - 1.3 m long (total length, TL) with small and probably newly mature fish (estimated to be 10 - 11 years old) observed in aggregations. However, larger individuals 1.8 - 1.9 m TL accounted for the majority of the population biomass. Overall, mean spawning stock biomass of giant sea bass was 36.3 kg/1000 m2. Providing a general comparison of mean biomass among the trophic levels of kelp forest fishes off Santa Catalina Island revealed a nearly top-heavy biomass pyramid. The relatively high abundance of giant sea bass provides evidence that this species is recovering at kelp forests off Santa Catalina Island, and possibly throughout the Southern California Bight. The removal or recovery of predators can greatly influence an ecosystem. As more recent studies suggest that indirect community effects of fishing and protection can take up to decades to detect, it is necessary to document the continued changes on the structure, function, and dynamics of the kelp forests and rocky reefs off southern California. ! viii Chapter 1 Differences in trophic and community structure of kelp forest fishes inside and outside of three long-standing MPAs in the Southern California Bight Introduction The partitioning of food resources among different species in a community determines the trophic structure of an ecosystem. Fluctuations in species abundance within various trophic levels can alter the composition and function of a community by means of bottom-up and top-down influences. Bottom-up processes are fundamental to the foundation of an ecosystem by altering community composition through variation in abiotic influences and primary production. On the other hand, top-down control regulates how fixed carbon resources are distributed throughout a community (Estes et al. 2001). Neither bottom-up nor top-down processes are mutually exclusive, functioning together to influence the abundance and diversity of organisms within an ecosystem. Due to recent declines in abundance of large carnivores globally (Estes et al. 2011), there have been a growing number of studies focused on understanding the effects of top-down pressures on ecological interactions within communities. However, measuring the effects of declines in predator abundance on a community can be problematic, as there are small amounts of historical baseline data for comparing current community structure (Dayton et al. 1998). Although impacts of top-down control can be difficult to detect, there has been a considerable number of studies documenting predator effects on communities. From the regulation of zebras by lions in the Serengeti (Grange and Duncan 2006), recovery of aspen trees after wolf reestablishment in Yellowstone National Park (Ripple and Beschta 1! ! 2007b), fluctuations of plankton abundance due to experimental manipulations of lake fishes in Wisconsin (Carpenter and Kitchell 1988), to the decimation of Alaskan kelp forests after decreases in sea otter populations (Estes and Palmisano 1974), many ecosystems are subject to a release in