MLML/ MBARIUBRARY 8272 MOSS LANDING RD. MOSS LANDING, Gil 95039 ASPECTS OF THE LIFE HISTORY OF THE BLUE SHARK, PRIONACE GLAUCA L., IN MONTEREY BAY, CALIFORNIA A Thesis .Presented to the Faculty of the Department of Biology San Jose State University ( In Partial Fulfillment of the Requirements for the Degree Masters of Arts By James Thomas Harvey December, 1979 ABSTRACT.--Feeding habit, age structure, growth, morphology, and parasite data were collected on the seasonally abundant blue shark, Prionace glauca, in Monterey Bay, California from 1974 to 1977. Stomach content analysis of 150 blue sharks revealed a diet which was dominated by the northern anchovy (Engraulis mordax), euphausiids (mainly ~anoessa spinifera), hake (Merluccius productus), and several species of cephalopods. The ingestion of l· spinifera marks the first record of preda­ tion upon euphausiids by this species. In general, the rna- jority of prey live an epipelagic life or become epipelagic nocturnally. The blue sharks ranged in total length from 98.5 to 204.5 em (x = 155.6! 3.9 em). Females were signifi­ cantly more numerous (124 females:24 males) and of greater age than males. Vertebral ring counts of 98 blue sharks showed the estimated age of sampled sharks to be 2 to 6 years. Length frequency data tends to support the assumption of an­ nular ring formation. Aging and length frequency data es­ timate growth rates of 12.2-28.2 cm/yr, the higher growth rates occurring at the younger ages. Only the linear mea- surements associated with the head region changed significantly when compared to the total length for the 115 sharks examined for allometric growth. Liver weights, gonad weights, and parasite relationships were also discussed. l' i i i • I' i' TABLE OF CONTENTS Page ABSTRACT ... i i i LIST OF TABLES vi LIST OF FIGURES. v i i i ACKNOWLEDGEMENTS X I NT ROD UCT! ON . 1 MATERIALS AND METHODS. 8 RESULTS. 1 8 Length. 1 8 Allometric growth 21 Weights ••• 21 Reproduction. 24 Feeding habits. 26 Fish . 33 Euphausiids. 40 Cepha 1opods. 41 Age and growth. 41 Parasites 45 DISCUSSION 50 Catches 50 Lengths 52 Weights 53 Reproduction. 54 Feeding habits. 55 i v Engraul is mo rd ax 59 Merluccius ~uctus 60 Euphaus i ids. 61 Cephalopods. 65 Age and growth. 67 LITERATURE CITED 7 1 APPENDIX . 77 v LIST OF TABLES Table Page 1. Allometric growth relationships for six linear measurements on 115 blue sharks. 22 2. Prey items from 121 blue sharks collected between 1974 and 1977. Listed is the percent number (% N), percent volume (% V), percent frequency of occurrence(% FO), and index of relative importance (IRI) for each prey item. The prey are listed in decreasing order of importance, as determined by the IRI' s . 30 3. Prey items collected from 43 blue sharks in 1976. Listed is the percent number (% N), percent volume (% V), percent frequency of occurrence (% FO), and index of relative importance (IRI) for each prey item. The prey are 1 is ted in decreasing order of importance determined by the I RI. 35 4. Prey items from 58 blue sharks collected in 1977. Listed is the percent number (% N), percent val ume (% V), percent frequency of occurrence (% FO), and index of relative importance (IRI) for each prey item. Prey are listed in de- creasing order of importance as determined by the I RI. 37 vi 5. Mean total length measurements for blue sharks with assigned vertebral ring counts. Displayed are the sample sizes, one standard deviation, and 95% confidence intervals around the mean total lengths for females, males, and the total . 44 vi i LIST OF FIGURES Figure Page 1. Collection area for blue sharks in Nonterey Bay, California . 9 2. External measurements recorded for 120 blue sharks captured in Monterey Bay, California . 11 3. Example of measurements recorded for each blue shark centrum. • . 15 4. Number of blue sharks caught per hour for weekly intervals and the number of hours fished (effort) for 1976 and 1977. • . 19 5. Frequency histograms for total lengths of blue sharks caught in 1976, 1977, and all years combined ... 20 6. Body weight-total length relationship for 134 blue sharks collected in Monterey Bay. 23 7. Liver weight-body weight relationship for 106 female and 19 male blue sharks collected in Monterey Bay ... 25 8. Relation of cumulative prey items to randomly pooled numbers of blue sharks sampled in: (a) 1976, (b) 1977, and (c) all years combined 27 9. Feeding states of 121 blue sharks caught between 0700 and 1300 hours, from all years combined .. 29 vii i 10. Index of relative importance graph for the more important prey items of 121 blue sharks, from all years combined ... 32 11. Comparison of the major prey categories with regard to percent number (% N), percent volume (% V), percent frequency of occurrence(% FO), and index of relative importance (IRI), in the years sampled ..... 34 12. Index of relative importance graph for the more important prey items of 34 blue sharks collected in 1976 . • . 36 13. Index of relative importance graph for the more important prey items of 58 blue sharks collected in 1977 . 38 14. Ring radii measurements for blue sharks. 43 15. Growth curves for 16 rna le and 82 female b1 ue sharks caught in Monterey Bay .... • • 4 6 16. Comparison of growth curves from present study and that of Stevens (1975). ........• 4 7 17. Comparison of the total 1 ength histograms with lengths at a determined age for 98 blue sharks. • • . • • 48 18. Locations of observed surface swarms of euphausiids. 64 ix L ACKNOWLEDGMENTS I am grateful to many persons who contributed, in many ways, to the successful completion of this project. In par­ ticular, many helpful friends at Moss Landing Marine Labora­ tories have donated their valuable time and suggestions. Dr. G. Victor Morejohn, my major professor, provided guidance and financial support. Dr. Gregor H. Caill iet served as my advisor and gave generously of his time and support. Dr. Robert Has sur also served on my committee and helped in editing the manuscript. I extend my thanks to Roger Helm, Sara Tanner, Kon Karpov, Jim Heberle, Jerry Kashiwada, Bob Cayce, Kon Cayce, and Robert Yoklavich, to name only a few who have aided in my field collections. Lynne 0. Krasnow was a constant source of help, information, and 1 aughs throughout the research. Mary M. Yoklavich gave much of her time in data gathering, moral support, editing, and final typing of this thesis, and to her I am extremely indebted. Finally, I would like to thank my parents, who were instru- mental in my education and career and who assisted in the completion of this project. This investigation was funded by a grant from NOAA, Office of Sea Grant, Department of Commerce, #04-6-158- 44021. A portion of the i 11 ustrations were prepared by Mike Mallon. X INTRODUCTION The pelagic, marine ecosystem has become a current topic in scientific research, due to man's increasing interest and activity in the open ocean. Man's impact upon this system will be most apparent at the higher trophic levels. Pelagic sharks represent top carnivores in this complex and unex­ plored region of the ocean. They have also become a target in the development of elasmobranch fisheries (Holden, 1973; Ron s i v a 11 i , 1 97 8) . Un t i l r e c en t 1 y , the r o 1 e sharks p 1 ay in the pelagic environment and questions regarding their basic biology have not been explored. Information pertaining to the biology of these higher trophic level organisms may help to understand the intricate ecosystem to which they belong and the effects of man's activities on this system. The blue shark, Prionace glauca Linnaeus, is considered common in the warm temperate, tropical, and subtropical oceans of the world. Strasburg (1958) reported the blue shark to be the most abundant of the pelagic sharks in the central Pacific between 20°5 and 50°N latitude and 105°E and l85°W longitude. He found that the greatest abundance occurred north of 20°N latitude in the eastern part of the Pacific. Neave and Han­ avan (1950) found an extension of the distribution in the north Pacific to 57°N latitude in the Gulf of Alaska. Miller and Lea (1972) considered this species common in the eastern Pacific, from Chile to the Gulf of Alaska, but uncommon in the tropics. Blue sharks have been sighted from 0°N to 40°N latitude in the western Pacific (Suda, 1953). Bigelow and 1 L -----·---------- 2 Schroeder (1948) described the blue shark as the most plenti­ ful large oceanic shark in the Atlantic and Mediterranean Oceans. It is distributed from Africa to southern Norway in the eastern Atlantic and from Cuba to Newfoundland in the western Atlantic. In the Indian Ocean it is found from Africa to Australia, Indonesia and the Nicobar Islands between 17°N and 37°5 latitude (Gubanov and Grigor'yev, 1975). The migration of the blue shark into colder subpolar and temperate waters usually occurs during the hemispherical sum­ mer and early fall, when surface water temperatures increase. The studies of Neave and Hanavan (1960), in the Gulf of Alas­ ka, found blue sharks distributed only to 45°N during May and June, when the surface water temperature ranged from 5° C to 10° C. In August and September, however, they had increased their range to 57°N latitude, when the water warmed to approx­ • imately 15° C. They found that blue sharks were present in i water with temperatures ranging from 11 to 17° C.