Aspects of the Life History of California's Two Cowshark Species, Notorynchus Cepedianus and Hexanchus Griseus

Home , Big skate, Hexanchus, Leopard shark, Notorynchus

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 determination 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.

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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 patterns along the California coast.

7 l1ATERIALS AND METHODS

Collection Techniques

Sevengill and sixgill shark data were obtained either

from field samples or from reference collections. Most

sevengill data were obtained from field collections made in

Humboldt Bay (lat. 40° 52' N), San Francisco Bay (lat. 37°

42' N), and Monterey Bay (lat. 36° 50' N). Sampling in San

Francisco Bay was conducted bev~een the Richmond-San Rafael

Bridge and San Mateo Bridge (Figure 1). The majority of

sampling .in these bays was dependent on the cooperation of

comrrerical fishermen. A limite~ amount of data on sixgill

sharks were obtained from field collections in the ~~nterey

Bay area. Additional sevengill and most sixgill sharks

were obtained from the California Academy of Sciences, Los

Angeles County Museum of Natural History, Hoss Landing

Marine Laboratories, and the Tiburon Center for Environ- n:ental Studies.

Shark san:ples were collected by several methods,

including gill net (3.1 m x 275 m x20 em), harpoon, long \ line (6 to 335, l2/0 hooks per set), and rod and reel (one

12/0 hook per pole). Sevengills in Humboldt Bay were cap-

,, tured using a gill net or harpoon during minus tides in the T spring and su.rrnrer. Shark fishing in San Francisco Bay was

4 I 5 conducted year-round using long-line and rod and reel. I Gill nets were used in San Francisco Bay only during winter "f months, Measurerrents of shark alternate length (AL), girth (G),

precaudal length (PCL), and total length (TL) in millimeters,

and weight (kilograms) were recorded (Figure 2). t.Jeights

were not always taken because scales of sufficient capacity

were not always available.

Miscellaneous elasmobranchs that were caught in San

Francisco Bay were noted during the study. Data were re

corded monthly on all species and used to provide a rough

estimate of the species composition. Catch per unit effort

(CPUE), using catch per hook-hour, was calculated for long

line and rod and reel. Gill net CPUE was calculated by

catch\ per hour.

Reproductive Biology l The reproductive tracts of individuals of both sexes I were examined to determine maturation. Hale sharks were

categorized according to their maturation status as either juvenile or adult (Holden and Raitt 1974). Several methods

were employed to determine maturity in male sharks: 1) the

inner clasper length was rreasured and plotted against total I length. As the male sevengill approaches maturity, the 6

claspers lengthen and stiffen. A sharp increase in clasper

length versus total length indicates maturity (Chen and Mizue I! 1973 and Clark and von Schmidt 1965); 2) with the onset of

maturity development of the siphon sac mechanism can be

observed along the claspers of cowsharks; 3) the presence

of a straight versus coiled wolffian duct. Hith the onset

of maturation the wolffian ducts enlarge and coil (Cailliet

et al. 1981 and Hischnitzer 1972); 4) sperm smears were

taken by applying pressure along the posterior end of Ehe

wolffian duct. In mature sharks this forced sperm out of

the genital papilla (Chen and l1izue 1973 and Kauffman 1950).

The sperm was collected and smeared on glass slides. These

slides were air dried and stained (Pratt 1979). A compound microscope was used to determine the presence of sperm; and

5) a field test for the presence of sperm was made by cross-

sectioning the kidney and examining the wolffian duct (Pratt I 1979), a test which indicated maturation in individual blue

sharks (Pri·onace· glauca). Length-weight relationships were

plotted and combined with the information above to indicate

approximate size at maturity. A curve was fitted to the

data using a polynomial regression (Zar 1974).

Sexual maturity of female sharks could only be determined by internal examination. Females were categorized as

juvenile, adolescent, or adult. The developmental stage 7 was determined by the condition of the ovaries (Holden and

Raitt 1974}. Females were considered adults when the ovaries contained large yellow eggs, 22 to 75 mm in diameter.

Pregnant females were those with eggs or embryos in the oviduct (Jones and Geen 1977). The number and size of eggs

( > 18 rmn in diameter) or embryos per female were recorded

to determine fecundity and size at parturition. A graph depicting the length-weight relationship of females was plotted and combined with the information above to indicate approximate size at maturity. A polynomial regression (Zar

1974) also was fitted to these data.

During the course of this -investigation several sevengills were observed to bear scar and tooth marks that had been inflicted by other sharks. Shark length (TL), sex, and location of those wounds were recorded.

Food Habits

Stomachs were dissected and the contents identified.

Food items not identified in the field were preserved in

10% formalin and returned to the laboratory. Empty stomachs • or those containing only bait (squid or mackerel) were noted and discarded. Food items other than bait were I identified to the lowest possible taxa. Three measurements of importance were used to rank sevengi 11 prey items. They were numerical importance (%N) , volume (%V), and frequency ' 8 of occurrence (%FO). These measurements were combined into a single index of relative importance for ranking prey items

(Pinkas et al. 1971).

Age Determination

Vertebral sections were collected from some specimens and returned to the laboratory for use in age determination.

Vertebrae were removed from an area just posterior to the head region. Ageing techniques currently in use for elasmo branch studies at Moss Landing Marine Laboratories (Cailliet et al. 1981, 1983 a, b) were tested. These techniques in cluded the use of silver nitrate impregnation and ultra violet light, x-ray spectrometry, and histology.· All these techniques can enhance calcified rings that are present on the centra (Cailliet et al. 1981, 1983 a). However, the centra in hexanchids can only be recognized by the presence of a transverse septum of fibrocartilage (Hidewood 1921).

Therefore, since hexanchids do not possess true centra, vertebrae were cross-sectioned and examined for calcified rings.

Miscellahe·ous· Hexahchid Observati-ons

During this study I observed a di,stinct difference in backgroLID.d coloration of the dorsal region of sevengills from different geographic regions. Observations were made

' 9

throughout the study to document the extent of this color

ation, and to describe these color patterns. Extensive observations were made in both Humboldt Bay and San Francisco

Bay.

Sixgill and sevengill sharks were also grossly examined

for parasites. Parasite samples were collected and pre served in 10% formalin for later identification.

Sorre sharks were tagged in order to obtain movement information and growth data. These tags (FD-67, manufac tured by Flay Tag Company, Seattle, Washington), were inserted in the dorsal fin. Capture and release location,

date, ·species, and size were recorded.

7 RESULTS

General Elasmobranch Observations

Using all gear combined, a total of 441 sharks and rays was caught in San Francisco Bay (from November 1981 through May 1983) representing seven elasmobranch species.

Elasmobranchs other than sevengills caught in San Francisco

Bay, included the leopard shark (Triakis semifasciata), spiny dogfish (Squalus acanthias); brown smoothhomd shark

(Mustelus henlei), soupfin shark (Galeorhinus zyopterus), bat ray (Myliobatus californica)~ and the big skate (Raja binoculata). No sixgill sharks were caught inside San

Francisco Bay. The type of fishing gear employed in San Francisco Bay was dependent on co1!1llErcial fishermen who found rod and reel was the easiest and most effective method (Table 1). Long line gear was too time consuming and expensive (bait) for the low number of elasmobranchs caught (Table l). One fisherman who long-lined exclusively, was financially forced to suspend operation. Winter storms limited my use of the gill net to only six sets (Table l). \ I found the most productive fishing months for all species in Humboldt Bay and San Francisco Bay were ~uring the spring and sUJI1llEr (May ,through mid-June). The only

10 11 ~ I ' sevengills caught in Humboldt Bay were taken in May and June 1983 using harpoon and gill net. No additional fishing

effort occurred in other months. The most productive fish

ing months using rod and reel in San Francisco Bay for all

elasmobranch species were May through October 1982, and May

1983 (Table 2). There was no fishing effort reported for

February through April 1982, and February and April 1983

(Table 2). Fishing effort during these months was pre

cluded by inclem=nt weather.

Leopard sharks were the most abundant elasmobranch

species caught in San Francisco Bay and represented 40%

of the rod and reel catch (Table' 3). Sevengill sharks

represented 8"lo of the elasmobranchs caught on rod and reel. The soupfin shark was the least abundant species caught,

representing 1%.

The ro,d and reel catch categorized according to sex,

revealed that the sevengill was the only elasmobranch

species caught in which males outnumbered females. The

sevengill shark and big skate were caught at a 1:1 sex •' ··--·-- ' ratio. Females dominated in the remaining elasmobranch

species catch, with sex ratios ranging from 1:2 for leopard

sharks to 1:4. 5 for bat rays. \ SEVENGILL SHARK

General Information on 128 sevengill sharks (Notorynchus cepedianus) was gathered during a 20 month period, from November 1981 through June 1983. Of this total, 96 sevengills were taken by my field collections. The majority of sevengills caught (84) were from San Francisco Bay, while the remainder were taken from Humboldt Bay (11) and Monterey Bay (l). Additionally, information on 32 seven gills was obtained from several California institutions.

Reproductive Biology

Size at sexual maturity for male sevengill sharks was determined by analysis of 71 specimens that ranged from 44 to 242 em TL. Eighteen of 71 specimens were mature.

The smallest mature sevengill had a total length of 132 em, while the largest immature specimen examined was 150 em TL.

The clasper length increased abruptly at 150 em TL (Figure ia 3) and with development of the siphon sac mechanism this ~~ size represented the onset of sexual maturity.

Examinations for the presence of',spermwere negative, - except in those male sevengills with a fully coiled and enlarged wolffian duct ( > 150 em TL). Coiling of the

-12 13 wolffian ducts in males occurred at approximately 130 to

150 em TL. Sperm smears taken at the genital papilla dis-

closed that sharks were fully mature when the sperm could

be expelled. Sperm smears collected at the genital papilla proved to be an easier method for determining maturity in

18 sevengills than taking a cross-section through the kidney.

Cross-sectioning the kidney and taking sperm smears in eight

mature speci!D2ns provided the sarre results as those s!D2ars taken at the genital papilla.

Accurate weights were obtained for 22 male specimens

ranging between 45 em (0. 5 kg) and 242 em TL (79. 5 kg).

The length-weight curve for male sevengills began to more

rapidly increase in weight at 150 em TL .(Figure 4)_. Hale

sevengills of 153 em TL and weighing 13.6 kg were fully mature.

Examination of the reproductive system of 57 female sevengills, ranging between 78 em and 290.7 em TL, revealed

that 48 were juveniles, three· were maturing (adolescents),

and six were adults. Those in the juvenile stag~_ had ovaries --····--···---··. ~ that were small and contained no eggs or follicles. Juvenile ::::!!!

sevengills were recorded up to 186.5 em TL. TWo of the three

adolescent female sevengills examined contained approximately .. ";;. --- -- 100 eggs per ovary, ranging from 0. 5 to 18 rom in diameter.

The third was smaller (164 em TL) and contained only 75 eggs 14 per ovary, ranging from 0. 5 to 10 m in diameter. The smallest mature female caught was 268 ern TL and weighed 12 7. 3 kg.

Fecundity in sevengills varied from 82 to 95 large yellow eggs per female. The number of eggs per ovary in mature sevengills ranged from 39 to 55, with numerous smaller eggs ( < 18 rnrn in diameter) present. The left ovary always contained 2 to 16 more eggs. Only one specimen contained 82 near-term embryos. One embryo was measured (a male) and found to be 45 ern TL.

A sharp increase in the weight of female sevengills occurred after 200 em TL as they reach adulthood, a bit larger than males (Figure 5). The largest female sevengill recorded was 290.7 em TL and weighed in excess of 182 kg.

There was no scale available of sufficient capacity to weigh this specimen.--

Two adult and two adolescent female sevengills were scarred. Both adults had three types of wounds that appeared specific to certain_a:reas_:::of _the "body (Figure 6). Fresh .lB Ul tooth slashes were observed on both of the adult sevengills and appeared as parallel straight or curved cuts. They were superfical and:"-confined--to- the dorsum, anterior to the _jjj "-n! dorsal fin. Fresh semicircular jaw iu;p:::·:ssions showing continous tooth ·marks were observed on both paired fins of one specimen. The other adult'female sevengill had only a v;

healed semi-circular jaw impression on its left pectoral

fin. Single, straight, deep tooth cuts were observed

laterally between both paired fins. I examined fresh tooth

cuts on one female with large (75 mm diameter) eggs, while

another specimen with smaller (22 to 40 mm diameter) eggs

had only healed tooth cuts. Hhen healed these cuts appear

as white patches of scarred tissue. Adolescent female

sevengills had tooth slash marks similar to those seen in

the adults, but no marks of any kind were observed on

juveniles.

Six mature male sevengills were observed to have slashes

and tooth cuts laterally between the dorsal and tail fins

(Figure 6). Occasionally, slashes were observed more ante ·riorly toward the head region. Parts of the dorsal and

caudal fins were occasionally missing.

Food Habits

Of the 106 sevengill stomachs examined, 61 were empty,

38 contained prey items, and seven had only bait. Food

items in sevengill stomachs included representatives of

four groups, Chondrichthyes (cartilaginous fish), Osteich

thyes (bony fish), Mammalia, and Crustacea (decapod). The . I cartilaginous and bony fishes were the two majo-rprey grouPs :~ 1 ~.-"'~"~ eaten by sevengills, with their index of relative importance

(I. R. I.) values being 6822.2 and 5577.6, respectively. ' 16

Chondrichthyans were the most ab1.mdant prey group by percent number and frequency of occurrence (Figure 7). lfammals and decapods, although representing the highest percent volUire fo1.md in sevengill stomachs, had low I. R. I.

values of 783.3 and 245.8, respectively (Figure 7).

Five species of elasmobranch were :'onnd in sevengill

stomachs (Table 4), four of which were important ~rey items

(Figure 8). The brown smoothho1.md shark represented the

single most important prey species in the sevengill's diet;

bat rays also ranked high (Figure 8). Osteichthyes as a

group were important in the sevengill' s diet, but most were

partially digested and could not be identified to species;

two were identified to species, two-others to genus, and~ fifth to family (Table 4). The only sevengill fonnd to have ingested an invertebrate, the market crab (Cancer

magister), was a 44 em Ti; specirren._ Larger sevengills

consumed harbor seals (Phoca vituliha) on three separate

occasions.

Age Determination

None of the methods tested to age sixgill and seven

gill sharks by using t-qe:i,_E_ :vr=_I:t:~b,r_aep_:r;oved successful. Of the vertebrae that had beE;.n· cros's-:..sectioned, no recog.;

nizable calcified rings were present. The vertebrae were very pliable and tended to sh-r:-ivel up during preparation. 17

Miscellaneous Sevengill Observations

The dorsal background color of sevengills collected from Humboldt bay typically ranged from a pale silvery gray to reddish brown. These colors were consistence and were observed in both sexes. Although no observations were made on small specimens ( < 210 em TL), coloration did not appear to be related to size. Sevengills collected in San Francisco Bay had a dorsal background color ranging from olive brown to muddy gray. These colors also did not appear to be related to size or sex. With one exception, these colors were consistent for all specimens examined from San Francisco Bay. The exception was a piebald sevengill, caught on 16

June 1983, off Hunter's Point, San Francisco Bay. It was ' a 117 em TL immature male and was caught by rod and reel at a depth cif l?:m,_ _:l.lS:i.ng--Pacific ~ackerel (Trachurus i ·-·- -- -· ·----·--·-:--- -- 1 symmetricus) bait. This sevengill had a white background color dorsally, with exceptionally large dark spots (from 3. to 18 mm fn aiameter)~ Spotting on the extreme dor~um_-·;_;~ was clumped, while spotting on the sides was irregular; spots extended ~mto both the paired and unpaired fins. Laterally, this s-p-E_!ci'rreh'hacl the same 'olive brown color- __ ,_-~. . - --~· ~;--·-·- ...:.:::~=-'~~ ation as that of a normal San Francisco Bay sevengill.

Internal examination of this specimen revealed no apparent

7 difference from other sevengills of a comparable size. 18

Three species of parasites were observed on sevengills.

The isopod, Lironeca vulgaris (Cymothoidae) was observed in

the gills of three sevengills. The copepod, Pandarus

bicolor (Pandaridae), was observed on 56 sevengill sharks

and were found predominantly on both the paired and unpaired

fins, but soue were observed on the dorsal and ventral

body surfaces. The leech, Branchellion lobata (Piscolidae),

was observed twice: one in the oral cavity of a 160 em TL

female sevengill, and another on the pelvic fins near the

cloacal opening of a 268 em TL female specimen.

Five sevengills were tagged and released in San

Francisco Bay during the study (Table 5). No tag returns

were recovered during the study period.

----

•I

j ',;~~=-.:.:.:..;·:o__o~ I ---_:s.s;~~-::::..a~~

-~---=----""--='-"-''-"~- '"--' I SIXGILL SHARK

----General Information on 24 sixgill sharks (Hexanchus griseus) was obtained concurrently with the sevengill shark study period (November 1981 through June 1983). Seven sixgill sharks were taken by my field collections. Six of these came from Nonterey Bay, and one from off Lopez Point (lat.

36" 00' N). Information on the remaining 17 sixgill sharks was obtained from museum specimens.

Reproductive Biology

Only three male sixgill sharks, ranging from 110 em to 170 em TL, were examined and none were mature. All females recorded were"i!llll18:fure, with the exception

421 em TL specimen caught 30 Hay 1975 off Church Rock,. San

Luis Obispo County, California at a depth of 160 m (L. A. C. M. ace. no .. 34~65-1) ~;, Thi~: spe:~nen e~ntained 5~ nea~:,;~·~;~;: embryos that ranged from 68 to 73.6 em TL.

Using a combination of lengths and weights from field

-~- H ~-- __;;__- _,_, \ caught and mU.seumspeCimens, · th~~w~~ght of female· siJC~:;;;=:;~:;· rapidly increases as they reach maturity at approximately

421 em TL (Figure 9).

19 20

Food Habits

Prey items were found in five of the eleven sixgill stomachs examined. All prey items observed occurred only once, and the sample size was insufficient to calculate an index of relative irr:portance. The prey items observed were whale blubber, the rat fish (Hydrolagus colliei) , the hake

(Merluccius productus), and two t.midentified bony fish.

Parasites

Two parasite species were examined on sixgills. Otodi- stomum veliporu.m (Azygiidae) was fot.md in the stomachs of

two speciuens and Pandarus bicolor (Pandaridae) was found externally on the paired and unpaired fins,· and head region of four specimens.

7 DISCUSSION

General Elasmobranch Observations

11y data indicate that the present dominance of leopard sharks in San Francisco Bay suggests that a shift may have occurred in the elasmobranch assemblage. Hy data show that the brown smoothhound shark represented only 23% of the elasmobranchs caught (Table 3). The leopard shark accounted for 40% of the elasmobranchs caught. De Wit (1975) and

Herald (1953) both reported the brown smoothhound shark as being the most abundant elasmobranch species in the Bay, over 4li, of the recorded catch. De Wit (1975) reported the brown smoothhound as being most numerous in the catches

from June through September 1972, while I found them to be

dominate in the catch only during August and October 1982

(Table 2). Obviously rrrJ data represent_ onl:y a rough estimate ______~ l .~:r;;:'F'!":-~~i'F~.~·. e '1P7¥J of the elasmobranch assemblage in San Francisco Bay, ·and

any observed differences may reflect a bias in the v4rious.~!~;.,~;_;:,.;:;::;

sampling methods e~loyed. However, the corrnnon denominator

in de Wit (1975), Herald (1953), and rrrJ own sampling methods

was that the fishing gear (gill nets ,I. iong-Iine, and; rod "-"~'';c;•"~·'i~

and reel) employed was specifically targeted toward elasmo

branchs. Furthermore, although de Wit (1975) conducted his

study south of the San Mateo' Bridge, his results compared 21 22 favorably to those of Herald ( 195 3) whose sample area was similar to my own (Figure 1). The sex ratios I found for sorre species were different from that reported by Russo and Herald (1968) who based their estimate on a shark mortality that occurred along the east Bay. I found the male-female sex ratio for brown srnoothhounds to be 1:2. 2. Russo and Herald (9168) reported that the brown srnoothhound had a sex ratio of 1:4.5 (males to females). Sus an Smith (National Narine Fishery Service,

Tiburon, California, pers. comm.) found a 4:1 male-female sex ratio for brown smoothhounds from a long-line study conducted near Hunter's Point in September 1979. Herald and Ripley (1951) noted a similar reyersal in the sex ratios of sevengills between 1943 and 1950, but could offer no explanation. I also, found a difference in the sex ratio of leap ard sharks ( l: 2, male- female) and bat rays ( l: 4. 5, male female), comparJi~,d ,to w:hat Russo and Herald (1968) reported - _,._ - -~·~:-,,----" ~-- ' which was 1:1 for both species. I recorded a 1:1.6 male- female sex ratio for leopard sharks at a San Francisco Bay shark derby held in September 1983. Therefore, these diffei- ences between Russo and Herald (1968), Susan Smith (pers. comm.), and ~~o~~,d~ta may not be signHicant due to the difference in owr sampling methods.

' 23

There may be a general population decline of several elasmobranch species occurring in San Francisco Bay. Partie- ularly evident was the low abundance of soupfin sharks when corrpared to that reported by Herald (1953) and Russo and

Herald (1968). The reasons for this apparent change are unclear, but may be related to: 1) a combination of lower salinities in San Francisco Bay from large amounts of rain- fall (Reilly and Hoare 1982) and unusually warmer open coastal waters (Smith 1983) that caused sharks to seek a cooler, more suitable habitat, and/or (2) overexploitation.

An increased fishing pressure was evident in San Francisco

Bay during the mid to late 1970's (L. J. V. Cornpagno, pers. comm.) and although the California Department of Fish and

Game obtains commercial shark catch data, the principal take of elasmobranchs is by recreational fishermen. Catch data are not available for this type of fishing. Due to time constraints I was unable to measure size frequency, but it appeared that most sharks caught w&e at-;e;tl:\~~~

. ·. . --.· 1l.. ~ . -- : ~-ill~' =:: ~ . . size for maturity. The soup fin shark fishery · collapsed previously from overfishing (Ripley 1946). ·Holden (1974) cites other .instances where overexPloite"d'~elasmi:J.branch fisheries have collapsed. If the reduction in shark numbers in San Francisco Bay is due to reduced sa'Einity:::O=-:a:rm;;;;;;;,, -1.:: ______,_ ------. --0"-~- water then the decline may be temporary .. However, if the l; - - ~--·'-' ,.,-.. -":.:."'·"''"""'~=.;..~-<~ft- -~

! I c""-.;,.--: '·- decline is due to overexploitation this may have long,_~,..~~...._.,,.,.,..,.-,..__ term··

eSC \&.f% ,. - i1 uJ : 35 1 24 effects and a manageuent program will have to be imple- uented to sustain this fishery.

J ·~

- -~--~--.-·. -·

-"'.:e·- c''~c.:.-~"-zMr .. ~- ~ifi

~;.':T',..a'Z"'t;,~-::-:"i",: ~;a.. & _____ -~---~

1 SEVENGILL SHARK

General

All hexanchids, except for Notorynchus cepedianus, are known to occur to depths exceeding 200 rreters (Castro 1983).

The sevengill has been captured at a depth of 136 m (Stead

1963). I examined several specirrens that had been captured

outside bays in water less than 50 m. Along with Stead

(1963) I have also observed the sevengill on the surface.

Though data are scant it appears that sevengills occupy a

relatively shallow open coastal habitat. In northern California, sevengill sharks commonly- inhabit shallow bays

(Gotshall et al. 1980, Jordan and Evermann 1896, and Roedel

and Ripley 1950). Therefore, my eriphasis on field collec

tions of sevengill sharks was focused in Humboldt Bay and

San. Francis co Bay. ·J .... -·~ . -~~~~:::-;:""--:'_:~~--- -s,- ~J The occurrence of sevengill sharks in H~gldt ~anif"'S'IDf'cc-~ :;~.

Francisco Bays during the spring and sulllllEr ~ppears. to ......

suggest a .seasonality. Sorre sevengills are d.aughti~~%,;;:--~-~ _T ______~-_,_,.~-"'-'?!"' round, however, the numbers caught in Humboldt and San I Francisco Bays were higher during the spring; through,~·-.e.il:rclL_~.- ~- fall months. This ubs~::--"-·ation is further S·i!E..~I,!iz~~T ~-~n: ,...,, rrercial fisherrren in Humboldt Bay who concerit:iate''tf'l'e1'r· """¥¥--~

efforts on seVe:ngills during the spring and ,su=r 1' 25 ' 26 due to their abundance at this time (Ken Bates, commercial fisherman, Eureka, California, pers. comrn.). Only a relatively small number of elasmobranchs, predominantly the spiny dogfish, were caught during the winter period despite the use of several types of fishing gear. De Wit (1975) also reported the predominance of spiny dogfish during the winter months in San Francisco Bay.

The seasonal occurrence of sevengills follows the appear ance of other elasrnobranch species in these bays suggesting a possible migration sequence. According to commercial shark fishermen in both Humboldt and San Francisco Bays, with eleven years combined fishing.experience, sevengills becarne prominent in the overall catch during the spring after several other elasmobranch species have apl)eared.

The sevengill catch also decreased prior to a reduction in the catch of other elasmobranchs during the late su.rrmer, ' early fall periods (K. Bates, and Dennis Kittredge, commercial fisheruen, San Francisco, California, pers. co~:y_::'~"-=~Jlli!l

Since evidence for a possible migratory sequence of elasrno-

1 ·- . . .·. •·•·••••· branchs into bays is based on catch records this inforib.tio~~~~ ~ --- .: --~1'r,'_-_,_ ·-~""£\--"" may not be significant. Additional information as to seven gill movement patterns into and outside 1 of bays will have

to rely on tag and recapture or telemetry studies. l" -~:::.:.~~-ng···- .. TE-j "4- .. -.:;;~"¥?-,~ __ ---~t!

1L" H Reproductive Biology

My results from five indices inclicate that all male sevengills over 150 em TL and weighing 13.6 kg are mature

(Figures 3 and 4). Internally, coiling of the wolffian duct and expulsion of sperm through the genital papilla are conclusive indicators of maturity. The expulsion of sperm has been observed in several species of shark (Chen and Mlzue 1973, Kauffman 1950, and Springer 1960). The wolffian ducts of mature sevengills collected at various tines of the year all contained viable sperm. A consistently unimodal distribution of egg size in individual specimens suggests that qnly one group of eggs

develop at a tine. Further evidence for this cane from a

female examined during May that contained 82 near-term embryos but no large eggs in the ovary. This is plausible

since female sevengills carry between 82 and 95 eggs or

embryos at a tin:e and the size at parturition is quite

large (approximately 45 em TL). My data indicate that--egg

size in adult females is approximately 75 mm in dian:eter

prior to fertilization. Female sevengills with. large.~_eggs J (55 to 75 nnn dian:eter) present in their ova;~~~:-b~~'-i~~kingl any embryos were caught during May and early June. These ' specinens also bore severe mating scars_ (see below). Eggs

from another female sevengill examined during-June were small (22 to 41 mrn diarreter) and based on egg size, partu-

" -~----- ·-:::-, -_---- ~- 28 rition had already occurred in this specimen. Therefore, it appears the next generation does not initiate develop ment until after parturition.

Based on the above information a schematic diagram of the developmental stages and their proposed timing for the sevengill is presented in figure 10. Sevengills (both males and females) do enter bays during the spring and females with developing eggs or embryos have been observed during this time. The length of time for large yellow eggs

(approximately 75 mm in diameter) to development is uncer tain. However, assuming Herald and Ripley's (1951) specu

lation that sevengills enter San Francisco Bay for breeding

is correct, then the time from parturition to fertilization

may be from 6 to 12 months. Additionally, based on Holden's

(1974) calcula~ions for !!_. griaeus, the time from fertil

ization to parturition (gestation) would extend another

·. -· . . . ~· . '·" . --p·. rR ;;:,,.:.=- year •.. _Therefore,. after first parturition adult female ~ -..:·'@ "'1""'.::;-:::;:_*"!@ll sevengills would give birth every 18 to 24 months.

It i_s still tm.clear whether fertilization and parturi- ·-··--- · ___ :-~--.. .c-,__.-:,-o;J~.. "-.. •·.·'·-.·--~,.:._-_:--;,:·~-- 1..:!: -~- ""- - ....____., -- - 1.~: --- -;.:.,;~sr""n'i tiori-Tns·evengills actually occurs in bays as suggestedr;by '<-··""•······· ... ·.. Herald and Ripley (1951). Males are capable of reproducing I throughout the year, but females may have ·an annual or

The reproductive habits :kif n sevengills outside of bays is 1mknown. Therefore, whether ----- ' I~; breedin,g·oc£,m;:s _seasonally or ]ear-round is uncertain. Tr ll 29

As with many ela.smobranch species, female sevengills

mature at a considerably larger size than males (Hourms

1977). The smallest fully mature female sevengill (264 em

TL) was reported by Herald (1968). All of the adult females

I examined were larger than Herald's (1968). Based on the

largest adolescent female I examined, maturation probably

occurs at a size in excess of 220 em TL. Furthermore,

based on egg size, and from data presented in figure 5,

females reach maturity at a size of about 250 em TL and a

weight in excess of 91 kg.

The maximum size attained by sevengills is uncertain.

The largest reported sevengill is a 288 em TL specimen

caught in New Zealand (.Phillips 1935). A 290.7 em TL

female weighing in excess of 182 kg was caught in San

Francisco Bay in July 1981. I am uncertain as to the exact cause and nature of

tooth slashes on sevengills. Baldridge and \.Jilliams (1969)

>.;_ reported similar tooth slashes on the head of a dusky shark,·· -!-" Carcharinus obsclirus, were from another shark, but they could offer no explanation for these scars.

Fresh. tooth cuts and semi-circular jaw inpressio.ns on

-· gravid female sevengills caught in Fumboldt Bay and San Francisco Bay during the spring and early summer s"::;gest a

possible breeding season. Breeding seas on ali ty has be~~ observed in several shark species (Jones and Geen 1977,

-_·-~-~ 30

Olsen 1954, and Parsons 1983) and it is "C.Jell known that male

sharks often bite their mates during copulation (Gilbert

1981). Also, adult females that presumably had recently

given birth lacked fresh wounds suggesting these cuts are

inflicted only when the female is ripe. Healed wounds were

observed on these specimens. However, it must be noted that no mature female sevengills were captured during other

seasons for comparison.

Since there were no observations of the copulatory

behavior of sevengills, the cause and nature of s earring on

males is uncertain. It is possible that these cuts are due

to a precopulatory behavior as suggested for blue sharks

(Stevens 1974). My observations of_ sevengills suggest their

bodies are limber enough to assume a coiled position during

copulation. Clark (1963) however, suggested that large

sharks cannot assume a coiled position as do smaller sharks

(Wourms 1977) due to their less flexible bodies. Sevengills

are a m::>re limber shark than the stout bodied lemon shark,

Negaprion brevirostris observed by Clark (1963).

Food Hab:i:iffic_

Sevengills appear to be top predators in the bay eco-

system, since elasiOCJbranchs and bony fish were major prey

items. Marine mammal remains in sevengill guts also are not -N-~~.,.,:;,::;,,"1",?~~~-- - • ' . -·-

--'tmUS'U'a·l~o"rding to fishermen (K. Bates and D. Kittredge,_ '

-- 31 pers. CO!Iilll.). It is 1.mknown whether the marine •nammals were dead or alive before being ingested. Other prey items reported found in sevengills include dolphin, human remains, jack srrelt, and rats (Castro 1983, and K. Bates and L. J. V.

Compagno, pers. comm.).

Age Determination

The use of vertebral rings to age sevengills was not possible due to lack of calcification in the vertebrae (Bass et al. 1975, Ridewood 1921, Springer and Garrick 1964, and

Springer and Waller 1969). The use of other hard parts for ageing hexanchids seems unlikely since elasmobranchs cont~n ually replace teeth and scales tend to be variable (Applegate

1967). Unless new techniques are developed, the ageing o~ both the sixgill and sevengill shark may be dependent on tag and recapture studies.

}:!iscellaneous Se\rehgill Observations I I observed the copepod, p·andarus bic.olor, to be the 1 most abundant parasite on the sevengill shark. Russo (1975) also noted the abundance of P _. b.i.color. on sevengills, pattic l ularly on the trailing edges of the fins. The leech, Branch- ellion lobata, was reported by Russo (19,75) on the claspers, fins, ~~d buccal cavity of the sevengill shark, while Moser

~-:::.i,;.--,_.:~ and Anderson {lgzj~"~~~;~~::~~;~-that B. lobata had infectecfl - . '--=~/~'''~-'~".:: "'"'if::i •. • • •·c '""''~' ••.. :C - I the embryos of a Pacific angel 'shark, Sqtiatina: californica. - . l ~2~G~~· J J J 32

One species uf parasite not ul2ntioded by Russo (1975) the isopod, Li rt?!l-ec_?.:_ yulg_aris , is a gi 11 parasite coiill!1only fol.rrld on many species of marine teleosts (Morris et al. 1980).

The occur; ence of !o· Yl~l_g_

Since no tag retutns were recieved during this study, tagging information will be retained on file at Moss Landing

Marine Laboratories and at the Steinhart Aquarium. SIXGILL SHARK

C-eneral

Field collections for the sixgill shark were difficult

because unlike the sevengill, they do not commonly frequent

bays. The occasional occurrence of sixgills in San Francisco Bay (Herald and Ripley 1951) is most likely due to its depth

near the entrance. Sixgills do not inhabit shallow bays

. such as Humboldt Bay; but they do occur outside this bay in

deeper water (K. Bates, pers. comm.). Sixgill sharks along

the California coast have been reported to depths of 291 m

(Hiller and Lea 1972). Therefore, because the sixgill shark

is a deep water species, no information was obtained on its

moveuent patterns.

Reproductive Biology

The 421 em TL Church Rock specimen is believed to be

the only reported mature sixgill from the eastern North

Pacific. Springer and Haller (1969) reported that no mature

sixgill, male or female, had been reported from the eastern

I I North Pacific. This specimen also appears to be the smallest

reported mature female world wide, based on Springer and

Waller's (1969) estimate of maturity at 450 em TL. Appar- I , ently, there are no catch records for mature male sixgill

33 34 sharks, and none are reporc.er!. in the literature. Springer and Haller (1969) reported a male sixgill that was immature at 348 em TL.

The 421 em TL speciTIEn ·was noted to be giving birth. while being brought on board ship, and it is likely that several may have spontaneously aborted during capture.

Therefore, the actual number of young in this specirren was uncertain. The tendency of near-term females to abort their young upon being captured may account for the wide discrep- ancy reported for sixgill fecundity (Springer and Waller

1969).

Sixgill embryos reach a much larger size prior to parturition than do sevengill embryos. The size range of

term embryos (68 to 73.6 em TL) taken tram the 421 em TL specimen was consistent with that reported by Vaillant (1901).

Desbrosses (1938) reported juvenile sixgills smaller than

67 em TL had been taken in the Hediterranean Sea, but

Springer and Waller (1969) thought these specimms may have been H. vitulus, a considerably smaller shark. However, the occurrence of H. vitulus has not been confir=d in the

~diterranean Sea (Springer and Haller 1969). I Female sixgills showed a sharp increase in weight at

about the onset of sexual maturity (Figure 9). This growth pattern is similar to that seen for female sevengills

(Figure 5). The largest reported sixgill shark is 482 em TL ,, 35

(Castro 191;3).

Food Habits

Based on my findings and that reported in the literature

(Backus 1957, Bigelow and Schroeder 1948, Hart 1973, Spi-inger and Waller 1969, and Wheeler 1975) the diet of sixgills consists mainly of cartilaginous and bony fishes. The con sumption of marine mammals has also been reported by Wheeler

(1975). Invertebrates have been reported in the guts of six gills by several authors (Backus 195 7, Bigelow and Schroeder

1948, and Hart 19 73).

Parasites

Due to the considerable tiJJ:E lapse (several hours to several days) from capture to examination, parasite data for the sixgill shark is rather incomplete. Unlike the seven gill, no freshly caught sixgills were examined. CONCLUSION

Sixgill and sevengill sharks apparently each occupy .. a ·~, distinct, but not mutually exclusive, habitat along the

California coast. Sevengill sharks are seasonally abundant,

and poorly illlderstood, apex predators in several northern

California bay ecosystems. The seasonal occurrence of seven-

gills in these bays appears to correspond with their repro

ductive cycle, since adult females caught during the spring

and surnrrer had large eggs or embryos and mating scars.

Sevengills appear to be top predators in bays feeding primar ily on cartilaginous and bony fishes·. The importance of sevengills to the bay environment and their activity outside of bays is for the most part illlknown and considerably more information is still needed to confirm suspected movement patterns within and outside of bays. Sixgills apparently

do not coilllllOnly frequent bays, but instead prefer a deep water habitat along the open coast. Sixgills do not appear

to be abillldant anywhere and their occurrence along the deep

coastal waters of California is for the most part unknown:. I Since both these species, particularly the sevengill, are being actively fished, i.lte necessary life history information

to understand such a fishery remains unanswered.

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Table 1. -- Elasmobranch catch and effort data, according to gear type, from San Francis co Bay.

C-ear ,!:~ No. hooks No. sets Hours fished Catch CPUE --·,-:.; ~.; Set line 1736 10 63 44 0.0004 (range 6- 335 hooks per set)

Gill net 6 32 8 0.25

Rod/reel 158 57 125 389 0.02 (one 12/0 hook per pole)

Totals 1894 73 220 441 0.2704

' Tabla 2. •• Jtod an4 nal catc.h/o!!ort data by a:onth of dl etumobr&ncb apocLoo in Sa:a FuncLaco Day, from Mowailer 1941 throuah May 1983,

Hourt Ho. s • H h ~.b. Total fhha4 hook a IUCort cat~ cpua CAt I¢cpua cot~uo cat~ua catc:~ cpua cat~ c:pua c .. t Cf\Tr:p Ull cat c:h / c:p \Jil Yo &r/IDOflth 1981/Hov. 5.5 33.0 0 l/0.03 2/0,06 0 0 0 0 l/0.09 Dec. 6.25 •6 lB. 7 2/0.11 3/0. 16 1/0,05 0 0 0 0 6/0.32 1982/Jao. 5.67 ll 17.0 0 0 0 0 0 0 0 0 Fa b. Ho Ert'on: Har. Ko· Effort Apr. Ho l!forc Hay II 16 10/0.17 20/0,:14 0 15/0.25 2/0,03 2/0.03 0 4910.82 J~m. 16.08 16 "·'45.4 2/0.04 27/0.6 8/0,lJ 14/0,24 0 0 0 51/1.12 J.U... 6.1l a 11.5 l/0. 0& 4/0.ll 19/1.09 l/0.17 0 0 l/0.06 21/l.' •.n l u.a 5/0.U 3/0.U 1.0/0.)\ WfO. 3'\ a 0 • 1&/1.0$ """"Sop. 1.0.7 22 43.4 5/0.ll l\/0. 7l 0 20/0.46 0 16/l. a 0 11/\.1.4> ' Oct. 2. 17 4 8, 6 l/0.12 2/0.ll 7{0,81 16/l. 84 0 l/0.5 0 27/).0 Nov. 3.42 4 6.1 0 0 0 0 0 0 0 0 Dec. 12.98 19 :14.0 0 1/0,03 ll/0.32' 0 0 0 l/0.09 15/0.44 1983/JM. 4.16 a a. 3 0 0 0 0 0 0 0 0 Fa b. Ko Eltort Har. 1.92 2L 20.4 0 3/0.15 0 0 0 0 1/0' 05 4/0.2 Apr. ldo tffort Hay 19.59 31 41.0 6/0.15 61/1.49 10/0,24 11/0,27 0 14/0.34 4/0,1 106/2. 5I 45

Table 3. -- Number, percent, and sex of seven elasmobranch species caught in San Francisco Bay on rod and reel from November 1981 through Hay 1983.

Males Females Total Species No. % No. % No. % Triakis semifasciata

leopard shark 53 34 103 66 156 40.1 Mustelus henlei

brown smoothhound shark 28 31 61 69 89 23

Sgualus acanthi as

spiny dogfish 17 25 51 75 68 18 Notorynchus cepedianus

sevengi 11 shark 17 53 15 47 32 8 l!Jyliobatis californica

bat ray 6 18 27 82 33 8 Raj a- binoculata

big skate 4 44 5 56 9 2 Galeorhinus zyopterus

soup fin shark 0 0 2 100 2 1

7 Table 4. ~- The percent number, volume, frequency of occurrence, and index of relative importance values for 38 sevengill shark stomachs that contained prey items.

Prey item No. %N "/oV %FO I. R.I. Rank

Unidentified bony fish 11 26.8 95.5 26.8 3288.4 1 Mustelus henlei 9 22.0 91. 7 22.0 2501.4 2 l1yliobatis californica 6 14.6 95.8 14.6 1611.8 3 Phoca vi tulina 3 7.3 100.0 7.3 783.3 4

., Sgualus acanthi as 2 4.9 100.0 4.9 514.0 6 Triakis semifas ciata 2 4.9 100.0 4.9 514.0 6 Sebastes sp. 2 4:9 100.0 4.9 514.0 6 · Acipenser sp. 1 2.4 100.0 2.4 245. 8 10

Roccus saxatilis 1 2.4 100.0 2.4 245.8 10

Porichthys notatus 1 2.4 100.0 2.4 245.8 10 Gottidae 1 2.4 100.0 2.4 245.8 10

CanceE magister 1 2.4 100.0 2.4 245. 8 10 r;:· Notorynchus cepedianus 1 2.4 20.0 2.4 53.8 . 13 .,.. "' 47

Table 5. -- Tagging records for five sevengill sharks.

;,~

Date tagged Tag Sex T. L. (em) Tagging location

5 Jun 1982 Aq00872 F 105 Candlestick Pt.

28 Aug 1982 Aq00869 M 81 Candlestick Pt. 28 Aug 1982 Aq00868 M 95 Candlestick Pt.

28 Aug 1982 Aq00867 F 78 Candlestick Pt.

11 May 1983 Aq00865 M 193 Roundabout (Steinhart Aquarium)

·.

I r-~~------·-··------....,

1 :r:;::-r -,----, 6 m I r 1 1 1 rn = 10 km R = ROD and REEL L = LONG-LINE G =GILL NET NUMBERS INDICATE NUMBER OF TIMES FISHED

,.. Hunters Point '~).'""'-Ill> R3 L3 Candlestick Point R14 L1:

Oyster Point R1 G1 Ll

·. South San Francisco Bay

0 R3

Figure 1. - Hap of San Francisco Bay showing gear type. and the areas fished. 49

------TL ------lll'-l

~------PCL

TL: TOTAL LENGTH PCL: PRECAUDAL LENGTH AL: ALTERNATE LENGTH G: GIRTH

Figure 2. - External rreasurerrents recorded for hexanchid sharks along the California coast. 225-r------~------~_t-A

200 Notorynchus cepedianus N= 60 •- Juvenile 175 A= Adult E E 150 ~ .c -Olc: 125 ell ..J

~ ell a. (1) 100 ro ()

~ Q) c: 75 ' .5

50 Au.. eA ' ..Olli

J .-:J"" 25 ...... e .. ct.. • • 6 Ill

0 500 1000 1500 2000 2500 Total Length Males (mm)

Figure 3. - The inner clasper length versus length for 60 sevengill Ll1 .' 0 sharks collected from November 1981 through June 1983. 200~~------~

Notorynchu• cepedianus 175 N= 22 y = -3.39+(1.23x10-')(x.)+(-1.58 X 1 o-") IX:l+(1.01x10-") (x,") • = Juvenile A= Adult 150 @= O.nolea two specimens

~ .:s.Cl -en 125 Q) co :i: .c .21- 100 Q) 3: co -0 75 ' 1-

25 ONE WAS MATURE ONE WAS IMMATURE ' 0 1- 0 500 1000 1500 2000 2500 3000

Total Length Males (mm) Figure 4. - Total length versus weight for 22 male sevengill sharks collected from November 1981 through June 1983. --~,.,_ .. ___, ______

200-r------~~------~

Notorynchus cepedianus 175 N= 17 I y = -59+ (0.14)(x.)+ (-1 .1 x10"')(X:l+ (3.08 X 1 O"") (x,") I • =Juvenile 0= Adolescent I Jt..= Adult l

~ I 01 I .:.: 125 -en

)

0 500 1000 1500 2000 2500 3000

Total Length Females (mm) '-" N Figure 5. - Total length versus weight for 17 female sevengill sharks collected from November 1981 through June 1983. Tooth slashes Deep tooth cuts 53

ADULT FEMALE SEVENGILL

ADOLESCENT FEMALE SEVENGILL

Tooth slashes and cuts ' -""~.' ~:~;-~~ '-' Parts of the unpaired fins missing

ADULT MALE SEVENGILL

Figure 6. - Scarring patterns observed on se·vet.gill sharks.

' 54 ------Chondrichthyes ---- Osteichthyes Mammalia Crustacea 50

40 N= 38

20 30

40 g 50 UJ ~ 60 :J ..J §! 70

100

FREQUENCY OF OCCURRENCE (%) I I I I I I 0 50

Figure 7. - Index of relative importan~e for the prey groups taken from thE. stomachs of 38 sevengill sharks collected from November 1981 through June 1983. M. henlol M. calHomle

FREQUENCY OF OCCURRENCE (%) N= 38 I I I I I 0 10 20 30 \J1 \J1 Figure 8. - Index of relative importance graph for the prey items found in the stomachs of 38 sevengill sharks collected from November 1981 thfough June 1983.

·---·----- 600

550 Haxanchus grisaus N- 14 2 0 500 y = -37 ,5+ (6.64X1 0- ) (x,) +(-3.11 X1 o-•) (x~) + (1 X1 0- ) (X~) " =Immature 450 A= Mature * Literature

~ Cl ,:,(. 400 ~

100 •

0 0 1000 2000 3000 4000 5000

Total Length Females (mm)

Figure 9. - Total length versus weight for 12 sixgill sharks recorded .from November 1981 through June 1983. 57

Newborn sevengill ~ 45-53 em TL

... :~~:.;·... --...:::c ,..·· :-;...·,_.:.--._.;3.,----=>-

Adult: Age at reproductive / / maturity unknown/ I I I I -- Some evidence of time proposed Small white eggs t -- No evidence of time proposed < 18mm diameter O

Development of eggs to Ovulation to birth fertilization 6 to 12 months 12 months

Fertilization: Large yellow ( ~ 75mm diameter) highly vascularized eggs. 40 to 55 eggs per ovary

Figure 10. - A schematic diagram of the developrrental stages and their proposed timing in the sevengill shark (Notorynchus cepedianus). Length of lines are not proportional to tirres proposed.

\ I. I I MOSS UIHDIHG MARINE LAB liBRARY POST OFFICE BOX 450 MOSS LANDING, CALIF. 95039