L''' NATURAL HISTORY of TWO-LINE EELPOUTS (BOTHROCARA BRUNNEUM, FAMILY ZOARCIDAE)
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l''' ~JO~JG tJ\I;JL)!h]Q! t ; I' F 0 Eo: / ~~~J NATURAL HISTORY OF TWO-LINE EELPOUTS (BOTHROCARA BRUNNEUM, FAMILY ZOARCIDAE) A thesis submitted to the faculty of San Francisco State University in partial fulfillment of the requirements for the degree Master of Science in Marine Science by Lara Annette Ferry San Francisco, California June, 1994 NATURAL HISTORY OF TWO-LINE EELPOUTS (BOTHROCARA BRUNNEUM, FAMILY ZOARCIDAE) Lara Annette Ferry San Francisco State University 1994 Two-line eelpouts were collected from two deep-sea sites in the Eastern North Pacific in order to study feeding habits and morphology, age and growth, and reproduction and demography. Two-line eelpouts eat primarily shrimp-like crustaceans, and secondarily, juvenile zoarcids, probably of the same species. Significant differences in diet between the two sites were found at the most general and the most specific levels of taxonomic characterization (!-test on PSI matrix; t = 26.6 and 14.5, tu=oos(2) = 1.96). Two-line eelpouts collected were a maximum of 14 years of age. A logistic growth model was the best fit to the data and predicts an asymptotic length of 690 mm total length. Instantaneous mortality estimates (z) ranged from 0.20 to 0.32 depending on considerations of variations in longevity. Two-line eelpouts have a relatively low fecundity of 215- 339 eggs per female, and appear to reproduce only once or, at the most, a few ·, times in their life. Age of first reproduction is relatively late in life, 11 years in females and B years in males. Best demographic estmates indicate this population is at or just exceeding a stable equilibrium with a long generation time of 10.13 to 14.60 years. ACKNOWLEDGMENTS I would like to thank the Earl H. Myers and Ethel M. Myers Oceanographic and Marine Biology Trust for partial funding of this project, and the David Packard foundation for travel support. Funding was also received through a US Navy grant to San Jose State University (Navy CLEAN Contract No. N6247 4-88-0-5086). I would also like to thank David Griffith and Russ Vetter from the National Marine Fisheries Service (Southwest Fisheries Science Center, La Jolla, CA), Bob Lauth and the late Paul Raymore also of NMFS (Alaska Fisheries Science Center, Seattle, WA), and Danny Heilprin of Scientific Applications International Corporation, for allowing me to participate in research cruises and/or obtain specimens, and for providing data ne~ded for analysis in this project. In addition, I am grateful to Bob Leos and Jerry Spratt at California Department of Fish and Game for their assistance in trying to obtain specimens from commercial fishermen. I would like to extend special thanks to Anne Summers and Lisa Smith Beasley of Moss Landing Marine Labs who helped to identify prey items; Allen Andrews, Jocelyn Nowicki, and Kenneth Coale also of Moss Landing Marine Labs for guidance with the radiochemistry attempts; and Mary Yoklavich of Pacific Fisheries Environmental Group, and Guillermo Moreno from the University of Sydney, Australia, for guidance in ageing the otoliths. Thanks to Michael Foster and James Harvey who offered constant and much needed advice on statistics and experimental design, as well as Ross Clark, Matt Edwards, James Downing, and Erica Burton (who cut up more than her share of IV dead fish). I would also like to thank M. Eric Anderson from the J.L.B. Smith Institute, Grahamstown, South Africa for his advice on zoarcids and guidance throughout my pilot study and thesis project Lastly I owe a huge debt of gratitude to my advisor, Greg Cailliet, and my committee members, Ralph Larson, and Waldo Wakefield. Also to Lisa Weetman who is responsible for getting me involved in this project from the beginning. I am ever grateful for the continued support of my parents, David and Darleen Ferry, and also Michael Graham, who challenged me to ask the most difficult questions and inspired me to always find the answer. v TABLE OF CONTENTS List of Tables vii List of Figures viii List of Appendices IX Introduction 1 Materials and Methods Collection of Specimens 4 Feeding & Morphology 5 Age & Gro\1/lh 9 Reproduction & Demography 12 Results Feeding & Morphology 15 Age & Gro\1/lh 19 Reproduction & Demography 21 Discussion Feeding & Morphology 23 Age & Grov.tth 26 Reproduction & Demography 29 Literature Cited 35 VI LIST OF TABLES Table Page 1. Summary of trawl effort 43 2. Prey items found in guts 44 3. Potential prey at study sites 45 4. Life table for constant mortality 47 5, Life table for type I and type Ill mortality 53 vii LIST OF FIGURES Figure Page 1. Map of study site 57 2. Otolith diagram 58 3. Total length frequency histogram 59 4. Fish size trends with depth 60 5. Length frequency histogram for fish used in feeding study 61 6. Cumulative prey curves 62 7. General Index of Relative Importance (IRI) 63 8. Specific IRI .. 64 9. Jaw morphology and relative prey sizes 65 10. Gut morphology 66 11. Length frequency histogram for fish aged in otolith analysis 67 12. Plots of otolith length, otolith width, and otolith weight versus total length 66 13. Growth curves \ 69 14. Male maturity plots 70 15. Female maturity plots 71 16. Egg diameters and total fecundity 72 17. Cumulative maturity plot 74 18. Catch curve 75 19. Survivorship curves 76 viii LIST OF APPENDICES Appendix Page A. Trawl information 77 B. Otolith length and weight data 82 ix INTRODUCTION Technological advances in deep sea research have provided scientists greater opportunities for studying the unique creatures that live there and their interactions with this environment. Because the deep sea has been difficult to study, little is known regarding fish inhabiting this zone (Marshall 1979, Moyle and Cech 1988). Many generalizations have been used to describe deep-sea fish and their survival mechanisms, without much evidence other than morphological inference. Eelpouts (Family Zoarcidae) are abundant and widespread residents of North America's Pacific coast. The family has many members in the midwater, deep-sea, and continental slope environments (Miller and Lea 1972, Eschmeyer and Herald 1983). By studying the species that inhabit the continental slope, it is possible to understand how species adapt to this transitional environment between the "true deep sea" and more shallow marine environments. Two-line eel pouts (Bothrocara brunneum) are common to this region, and are the largest of the deep-sea eel pouts (Bayliff 1954, Bayliff 1959, Miller and Lea 1972, Hart 1980), making them a prime candidate for studies to increase our understanding of ecology of fishes ofthis habitat. They are caught frequently in research trawls on the continental slope and as by-catch in several commercial fisheries (Eschmeyer and Herald 1983; Wakefield 1990). They are common at depths of 200 to 1500 m off California, and have been recorded as deep as 1800 m off Oregon (Miller and Lea 1972, Hart 1980, Eschmeyer and Herald 1983). In spite of their relative abundance, few ecological studies of two-line eel pouts have been conducted. 1 Information regarding the diet of two-line eelpouts is scarce. Few researchers have studied the diet of any eelpout species, but many have reported gut contents associated with other descriptive work. These observations indicated eel pouts may consume a variety of benthic invertebrates (Andriiashev 1954, Kliever 1976, Anderson 1980, McAllister et al. 1981, Anderson 1982, Livingston and Gainey 1983, Mauchline and Gordon 1984, Houston and Headrich 1986, Keats et al. 1987). Because prey is presumed scarce in the deep sea, fish living there are typically assumed to employ a generalist feeding strategy (Mayle and Cech 1988). Fitch and Lavenberg (1968) and Gotshall and Dyer (1987) suggested that two-line eelpouts eat almost any organism they encounter that will fit into their mouths. Life span and growth rate of two-line eelpouts are unknown. Fitch' and Lavenberg (1968) claimed that age could not be determined from otoliths of two line eelpouts, although they admitted information may be obtained using new techniques. Age and growth estimates determined from whole otoliths are available for only a few eelpout species. Other eelpouts appear to grow rapidly and, for species studied, may reach a maximum age of only five to eight years (Levings 1967, blackbelly eelpout, Lycodopsis pacifica; Kliever 1976, persimmon eelpout, Eucryphycus (=Maynea) californicus; Anderson 1980, pallid eelpout, Lycodapus mandibularis; Lancraft 1982, midwater eelpout, Melanostiqma pammelas). These researchers, however, did not validate age estimates. Therefore, one can only speculate regarding age and growth of other eel pouts species. Reproduction in two-line eelpouts has not been investigated. Studies of 2 other species indicate that eel pouts produce a few large eggs per female (Gotshall 1971, Anderson 1980, La ncr aft 1982). Whether egg production is semi-annual, annual, or less frequent is debated among researchers (Levings 1967, Anderson 1980, Lancraft 1982). In benthic species, eggs may be laid in shallow burrows in sediment (Kendall et al. 1983, Silverberg et al. 1987), or in an eggmass guarded by the parents (Matarese et al. 1989). Because they are rarely collected in plankton nels, it is assumed larvae may become demersal or semi-demersal soon after hatching (Matarese el al. 1989). Consequently, larvae of only four species of this diverse family have been described (Kendall el al. 1983, Matarese et al. 1989). Larvae, presumably two-line eelpout, were found in an egg cluster extracted from sediment cores (Kendall el al. 1983). Such observations indicate this species may have a reproductive strategy similar to other eel pouts. With such a lack of information regarding an abundant species, it was apparent that study of the two-line eel pout was necessary to learn more about how fish species have adapted to survive in the deep sea.