CALIFORNIA STATE UNIVERSITY, NORTHRIDGE AGE, GROWTH AND GENETIC DIVERSITY OF GIANT SEA BASS, STEREOLEPIS GIGAS A thesis submitted in partial fulfillment of the requirements For the degree of Master of Science in Biology By Holly A. Hawk August 2013 The thesis of Holly Hawk is approved: Dr. Virginia M. Oberholzer Vandergon Date Dr. Cindy S. Malone Date Dr. Michael P. Franklin Date Dr. Larry G. Allen, Chair Date California State University, Northridge ii TABLE OF CONTENTS Signature Page ii Acknowledgements iv List of Tables v List of Figures vi Abstract vii Introduction 1 Methods and Materials 6 Results 11 Discussion 13 Literature Cited 25 Appendix I: Haplotype Summary Table 31 Appendix II: Images of Selected Otoliths 32 iii ACKNOWLEDGMENTS This study would not have been possible without the help and support of many people. Dr. Larry Allen gave me the opportunity to pursue a master’s degree. He has supported me and taught me to grow a thick skin. I would like to thank Dr. Gini Vandergon for agreeing to serve on my committee and for nourishing my love of science education. I also thank her for giving me countless opportunities to educate others. I appreciate the support and guidance of my other committee members, Drs. Michael Franklin and Cindy Malone. Dr. Franklin spent many hours answering many questions. Dr. Malone has not only had invaluable input but has been incredibly supportive and always makes me laugh. Of course, none of this would have been possible without the love and support of my friends and family. I am so incredibly lucky to be surrounded by such wonderful people. iv LIST OF TABLES Table 1. Mitochondrial control region universal primers for Stereolepis gigas………………………………………...…………………...…………..19 Table 2. Results of the AMOVA among sampling locations of Stereolepis gigas..19 Table 3. FST values of Stereolepis gigas ………...…………………….…………..19 Table 4. ANCOVA for age and length relationships between Stereolepis gigas collected in California and Mexico............................................................20 Table 5. Sample size of Stereolepis gigas at individual collection sites in the Southern California Bight..........................................................................20 v LIST OF FIGURES Figure 1. Sampling locations of Stereolepis gigas in California and Mexico.......…21 Figure 2. Haplotype Network of California and Mexico Stereolepis gigas .……....22 Figure 3. Transverse cross section of left sagittal otlolith of oldest verified Stereolepis gigas........................................................................................22 Figure 4. Age at length frequencies and growth rate of Stereolepis gigas …...……23 Figure 5. Haplotype distribution of Stereolepis gigas within five-year age bins demonstrating the distribution of rare haplotypes among age classes.......23 Figure 6. Standard lengths and age frequencies between Stereolepis gigas in California and Mexico...............................................................................24 vi ABSTRACT AGE, GROWTH AND GENETIC DIVERSITY OF GIANT SEA BASS, STEREOLEPIS GIGAS By Holly Hawk Master of Science in Biology The giant sea bass, Stereolepis gigas, is a large predatory fish that inhabits the southern California kelp forest community. S. gigas is a critically endangered species, yet little is known about its life history. A more complete knowledge of the life history of this once commercially viable fish is necessary before an effective management strategy can be proposed. Giant sea bass were collected through collaborative efforts with commercial fish landings, scientific gill-netting, and through catch-and-release methods employed by recreational fisherman. A total of 59 samples were used for both mitochondrial DNA and age-and-growth analysis. Genetic analysis of the mitochondrial control region indicated gene flow among all sampling sites, no phylogeographic structure, as well as low haplotype (h) and nucleotide diversity (π). Sagittal otoliths were cross sectioned and analyzed with digital microscopy techniques, resulting in the verification that S. gigas is a long–lived species growing to at least 76 years of age. The -0.041(t+0.839) calculated von Bertalanffy growth function (lt= 2048.4(1-e ) for S. gigas was also characteristic of a slow growing, apex predator. Long-lived species that are slow to reach maturity often have a low resilience to over-fishing, therefore it is of paramount vii importance that we continue to collect essential life history data on this species in order to more effectively protect and manage the S. gigas population. viii INTRODUCTION Fisheries provide a valuable food commodity, with over 80 million tons of fish caught commercially every year (Watson and Pauly, 2003). However, global catches began declining in the 1980s (Pauly et al., 2002) including the decline of large predatory species which have been suggested to have been fished down to only 10 % of their pre- industrialized fishing biomass (Myers and Worm, 2003). As larger predatory species decline, smaller fish species and invertebrates are often targeted in a practice known as “fishing down the foodweb” (Pauly et al., 1998). The decline of large predators can result in fisheries targeting progressively smaller species of fish in a trophic system, thus decreasing the overall abundance of several species within an ecosystem. Exploitation of a single fishery threatens not only the targeted species but the biodiversity of the marine ecosystem that species inhabits (Molloy et al., 2009). The removal of apex predators has profound effects on ecosystems through top-down effects, where the lack of a large carnivore or keystone predator elicits population explosions of herbivores resulting in kelp deforestation in temperate climates (Steneck et al., 2002). Tropical ecosystems also benefit from biodiversity as coral reef habitats are shown to be more resilient to major disturbances and have decreased coral disease when fish biodiversity is high (Raymundo et al., 2009). Lack of biodiversity is associated with decreased productivity in marine systems and decreased ability to recover from abiotic and biotic perturbations (Worm et al., 2006). These perturbations include but are not limited to resource exploitation such as overfishing, habitat destruction and loss, pollution and effects on marine ecosystems from global climate change (Worm et al., 2006). 1 Management and conservation of marine fisheries requires the consideration of many factors and consequent comprehensive data collection. Such factors may include, but are not limited to, age and growth data (Cailliet et al., 1996), interspecific interactions (Jackson et al., 2001), stock structure and genetic variation (Rhodes et al., 2003) and species-specific life history traits (Pinsky et al., 2011). Large marine fish that are long- lived are particularly susceptible to over-exploitation (Reynolds et al., 2005) and recovery of a population after a decline can take well over a decade to even several decades, if at all (Hutchings, 2000; Russ and Alcala, 2004). The resilience of any population of fish and its subsequent recovery depends on a suite of variables, many of which will be species specific such as the longevity and growth rate of individuals, fecundity, larval duration and age at maturation. Russ and Alcala (2004) suggest that it may take 15 to 40 years for a predatory fish population protected by marine reserves to recover fully. The giant sea bass is the largest teleost megacarnivore found in the southern California kelp forest community, and was recently verified to reach at least 62 years of age (Allen and Andrews, 2012). Historically, giant sea bass are distributed from Humboldt Bay into southern Baja California and the Sea of Cortez. Populations are concentrated south of Point Conception in shallow rocky reefs along the southern California coast and offshore islands. Giant sea bass were commercially and recreationally sought after for most of the 20th century. Commercial fishers first attained giant sea bass by hand line then switched to gill netting, significantly decreasing their numbers in California. Commercial landings in California peaked at 115 metric tons in 1932 and then drastically declined. Mexican commercial landings remained higher as 2 California stocks declined, but fell below 200,000 pounds in 1964 (Domeier, 2001). Commercial and recreational fishing depleted giant sea bass stocks to the point that a moratorium was declared in 1982. Although they are restricted from being targeted, commercial vessels are allowed to retain and sell one individual per trip as incidental catch. Giant sea bass caught in Mexican waters are allowed to be landed and sold in California markets, however the limit is two fish per trip per angler. There are no commercial or recreational restrictions on giant sea bass in Mexico today (Baldwin and Keiser, 2008). In 1994, gill netting was banned within three miles of mainland California and one mile from the Channel Islands. Following the commercial and recreational restrictions placed on giant sea bass and the closure of near-shore gill nets, recent reports indicate that S. gigas are returning to the Southern California Bight (Crooke, 1992; Pondella and Allen, 2008). Very little verifiable data has been collected on the life history traits of giant sea bass. Gaffney et al. (2007) suggest sex ratios of S. gigas are approximately 1:1, indicating that giant sea bass are not sequential hermaphrodites. A previous study on two widespread species also in the wreck