ASPECTS OF THE LIFE HISTORY OF CALIFORNIA'S TWO COWSHARK SPECIES, NOTORYNCHUS CEPEDIANUS AND HEXANCHUS GRISEUS A Thesis Presented to The Faculty of the Department of Biology San Jose State University In Partial Fulfillment of the P~quirernents for the Degree Master of Arts By David A. Ebert August , 19 84 ABSTRACT Life history information was gathered on 128 sevengill sharks (Notorynchus cepedianus) and 24 sixgill sharks (Hexanchus griseus) from the coastal waters of California during a 20 month period from November 1981 through June 1983. The majority of sevengill sharks (96) were collected during the spring and summer in Humboldt and San Francisco Bays, while most sixgills (6) were collected from Honterey Bay. Year- round sampling in San Francisco B~y indicated peak shark catches in the spring and surrnner. Leopard sharks (Triakis semifasciata) dominated these catches suggesting a shift may have occurred in the species composition of elasmobranchs. Gonad character­ istics and scarring in adult male and female sevengills captured in bays during the spring and summer suggest a possible breeding season. Cartilaginous and bony fishes were the major prey items of sevengills captured in bays. A distinct back­ ground color was observed for sevengills from different geographic regions. Only a limited amount of life history information was collected on the sixgill shark. The only \ mature sixgill recorded was a female (420 em TL) containing 51 near-term embryos, ranging in size from 68 to 73 em TL. Prey items were found in five of eleven sixgill stomachs iii examined with each occurring only once. Several age deter- mination techniques using vertebrae from both species were tested but proved unsuccessful. The ecosystem of several northern-California bays play an important role in the life h~story of sevengill sharks, while sixgills prefer· a deep water coastal habitat. ,. ; ; - . ' ~ . iv TABLE OF CONTENTS Page ABSTRACT ... iii LIST OF TABLES vii LIST OF FIGURES ........•........... viii ACKNOWLEDGEMENTS x INTRODUCTION . 1 METHODS AND l-i..ATERIALS Collection Techniques 4 General Elasmobranch Observations 5 Reproductive Biology 5 Food Habits . 7 Age Determination 8 Miscellaneous Hexanchid Observations . 8 RESULTS ·General Elasmobranch Observations . 10 Sevengill Shark General . .. .. , . .. 12 Reproductive Biology ..........•..•.• 12 Food Habits . , 15 Age Determination 16 Miscellaneous Sevengill Observations . •. 17 v ' Sixgill Shark General . .. .. .. .. .. .. .. .. 19 Reproductive Biology . • . • . 19 Food Habits 20 Parasites 20 DISCUSSION General Elasmobranch Observations . 21 Sevengill Shark General . .. .. .. .. .. .. .. .. .. .. .. .. 25 Reproductive Biology ................ 27 Food Habits . 30 Age Determination .. 31 Sixgill Shark General 33 Reproductive Biology ................ 33 Food Habits 35 Parasites 35 CONCLUSION 36 LITERATURE CITED 37 TABLES .. 43 FIGURES . • . • . • 48 vi f I ! LIST OF TABLES Table Page 1. Elasrnobranch catch and effort data, according to gear type, from San Francis co Bay. 43 2. Rod and reel catch/effort data by month of all elasmobranch species in San Francisco Bay, from November 1981 through May 1983. 44 3. Nurrber, percent, and sex of seven elasmobranch species caught in San Francisco Bay on rod and reel from November ·1981 through Hay 1983. 45 4. The percent number, volume,_ frequency of occurrence, and index of relative irrportance values for 38 sevengill shark stomachs that contained prey items. 46 5. Tagging records for five sevengill sharks. 47 I ' \ Vii LIST OF FIGURES Figure Page 1. Map of San Francisco Bay showing gear type and the areas fishes. 48 2. External measurements recorded for hexanchid sharks along the California coast. 49 3. The inner clasper length versus length for 60 sevengill sharks collected from November 1981 through June 1983. 50 4. Total length versus weight" for 22 male sevengill sharks collected from November 1981 through June 1983. 51 5. Total length versus weight for 17 female sevengill sharks collected from November 1981 through June 1983. 52 6. Scarring patterns observed on sevengi11 sharks. 53 7. Index of relative importance for the prey groups taken from the stomachs of 38 sevengill sharks collected from November 1981 through June 1983. 54 80 Index of relative importance graph for the prey items found in the stomachs of 38 sevengill sharks collected from November 1981 through June 19830 55 90 Total length versus 1o1eight for 12 sixgill sharks recorded from November 1981 through June 19830 0 0 o 0 0 o 0 0 0 0 0 0 56 100 A schematic diagram of the developmental stages and their proposed timing in the sev-engill shark (Notorynchus cepedianus) 0 57 ix ACKN OWLE DGEHENTS I would like to thank the following people for their time and consideration throughout this research. Ken Bates, Dennis Kittredge, and Bret Van Gorp for their fishing efforts in providing the numerous sevengills I examined. The following people provided additional specimens from their respective institutions, Leonard Campagna of the Tiburon Center for Enviromrental Studies, Robert Lavenberg and Jeffery Seigel of The Los Angeles County Museum of Natural History, and John McCosker of The California Academy of Sciences. The members of my thesis corrnnittee Greg Cailliet, Mike Foster, and John HcCosker for their helpful suggestions and comments in review- ing this manuscript. Leonard Campagna, Earl Ebert, Robert Lea, and Susan Smith provided many helpful ideas and suggestions. Mike Moser for identifing the parasites, Matt Kittredge for his fine work in illustrating the figures. General assistance in various portions of this study was given generously by Thomas Ebert, N. J. Haas, Kent Hauge, Kevin Lohman, Feney Matthews, Lisa .Natanson, and Steve Willis. George and Patricia Schmidt and Bill and Joanne Willis for the gracious hospitality they extended me on my numerous journeys to the bay area. I would like to express sincere appreciation to my parents, Earl and Peggy Ebert, for their constant support and encour­ agel!Ent in helping me to achieve my educational goals. X I INTRODUCTION Interest in elasmobranchs as a food resource has in- creased in California (Cailliet and Bedford 1983 and Pleschner 1983). Among the more commonly marketed species are the sixgill shark, Hexanchus griseus (Bonnaterre 1788), and the sevengill shark, Notorynchus cepedianus Peron 1807 (Frey 1971). Both these sharks are known to frequent bays (Miller and Lea 1972), including San Francisco Bay (Herald and Ripley 1951), where they support a small fishery and are a popular target species of sportfishermen (Cuanang 1981). Unfortnnately, the elasmobranch assernb 1age of San Francisco Bay is poorly understood and the importance of larger sharks, like the sixgill and sevengill, to the bay environment is not well dnown. Therefore, additional ; infoootion is needed to assess the shark populations and i their fisheries in San Francisco Bay. I The sixgill and sevengill sharks are members of the family Hexanchidae (cowsharks), which Compagno (1973, 1977, 1981) lists as having three genera and four living species. There are several nominal species of Notdrynchus, however, they all appear referable to N. cepedianus. The two most commonly referred to species N. maculatus Ayres 1855 and N. cepedianus are synonymous (L. J. V. Compagno, Tiburon Center I . 1 1-·.·. 2 t.;; for Environrrental Studies, pers. comm.). In the ·eastern North Pacific both species range from southeast Alaska, southward to central Baja California (Clemens and Hilby 1946, 1961, Knaggs, Sun ada, and Lea 1975, Miller and Lea 1972, and •{;I Roedel and Ripley 1950). Their distribution is notable because both occur in temperate regions, while the only other two members of the family; Heptranchias pe:do and H. vitulus, are tropical and subtropical (Bass et al. 1975, Bigelow and Schroeder 1948, Castro 1983, Garrick and Paul 1971, Pequeno 1979, Roedel and Ripley 1950, and Springer and Haller 1969). Since many elasmobranch species including sixgill and sevengill sharks are mobile ·and reach a relatively large size, life history studies have been difficult (Holden 1974). Members of the Hexanchidae are ovoviviparous (Breder and Rosen 1966 and Gilbert 1981), but further information on I their reproductive biology is limited. Springer and Haller (1969), based on the examination of a few large specimens, estimated that female H.· griseus reach maturity at 450 em total length. Herald and Ripley (1951) examined a number ·of sevengill sharks between 54 and 228 ern TL cought at shark derbies, and reported that all se\rengills examined were sexually immature. Herald (.1961) estimated that se"Vengills reached maturity at a length ·of 306 ern TL. ·However, Herald 7 3 (1968) revised this estimate after examination of a male (197.4 em TL) and female (264 em TL) sevengill that were both mature. Information on the feeding habits of the sixgill and sevengill is rather incomplete. Hart (1973) reported that sixgills ingest a wide variety of fishes and crustaceans, and noted that the sevengill' s diet included smaller sharks. Herald and Rip ley (l951) examined a few sevengill stomachs and found them to be either empty or to contain only bait. The objectives of this research were to investigate the elasmobranch assemblage in San Francisco Bay and the life history of the sixgill and sevengill sharks in California. Life history aspects include the reproductive biology, length-weight relationships, food habits, examination of possible age determination techniques, color variation, parasites, and moverrent