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Leopard shark mating observed off La Jolla, California

Authors:
  • Seiurus Biological Consulting
CALIFORNIA FISH AND GAME
128
California Fish and Game 91(1):128-135 2005
128
LEOPARD SHARK MATING OBSERVED
OFF LA JOLLA, CALIFORNIA
SUSAN E. SMITH
Southwest Fisheries Science Center
8604 La Jolla Shores Drive
La Jolla, CA 92037
susan.smith@noaa.gov
INTRODUCTION
On 4 August 2003, mating behavior was observed in an aggregation of leopard
sharks, Triakis semifasciata, in shallow water near the surf zone along a sandy ocean
beach in La Jolla, California, approximately 21.6 km north of the entrance to San Diego
Bay. The following account provides the first documented observations of leopard
shark mating in the wild.
The leopard shark is an inshore coastal, largely benthic shark that is distributed from
southern Oregon south to Baja California, Mexico, including the upper Gulf of California
(Eschmeyer et al. 1983). Although it is reportedly common in enclosed muddy bays,
other habitats include flat sandy areas, mud flats, and bottoms strewn with rocks near
rocky reefs or kelp beds (Eschmeyer et al. 1983; Compagno 1984; Love 1991; PFMC
19981; Ebert 2003). It feeds mostly on small fishes and benthic invertebrates (Russo
1975; Smith 2001). The population is thought to be composed of various regional
subpopulations with limited exchange among them (Smith and Abramson 1990),
although no range-wide stock study has been undertaken to date. Because of their
restricted geographical range, shallow water distribution, and assumed limited exchange
among regional stocks, leopard sharks near large population centers may be vulnerable
to heavy localized fishing pressure and habitat disturbance. Stocks in California are
at least partially protected by commercial fishing area closures in inshore waters, a
recreational and commercial minimum size limit (91 cm total length (TL)) since 1992 and
1994, respectively, and a recreational bag limit of three fish since 1992.
Mating areas, behavior, and seasonality have not been documented for this
species, nor has critical habitat for reproduction been described. The occurrence of
large leopard shark aggregations, some of them numbering in the hundreds, is not
unusual for certain mud flat and sandy beach locations in California, including the La
Jolla study area (e.g., Eschmeyer et al. 1983; Ackerman et al. 2000, Anonymous 2000
a, b; Huard 2002; Ebert 2003). But little documentation exists concerning specific
behavior associated with these shoals. Some are presumed to be for the purposes of
foraging on organisms made accessible during periods of high tides (Ackerman et al.
1Pacific Fisheries Management Council (PFMC). 1998. Groundfish Essential Fish Habitat
Appendix. June 15, 1998. Prepared by Groundfish Core Team Casillas, E., L. Crockett, Y.
deReynier, J. Glock, M. Helvey, B. Meyer, C. Schmitt, and M. Yoklavich. NMFS
Northwest Region, Seattle, WA.
LEOPARD SHARK MATING OBSERVED OFF LA JOLLA, CALIFORNIA 129
2000), others may represent females gathering in pupping areas. For example, there is
one documented report of dozens of pregnant females gathering in the shallow flats
in Catalina Harbor, giving birth to pups (Smith 2001). Neonate-sized pups are also
abundant seasonally along many protected southern California beaches and bays,
such as Santa Monica Bay, where they were once harvested for the aquarium trade
(Smith 2001).
Since 1991, the author has observed in the general study area numerous leopard
shark aggregations composed of large juveniles and adults numbering from 25 to 180
individuals, but with no obvious pupping, courting or mating behavior taking place2.
According to Kusher et al. (1992), females reach sexual maturity at approximately 105
cm TL; males at about 100 cm TL. The aggregations have been observed mainly during
midsummer through fall (July through November), with one observation of over a
hundred individuals in February 1996. Because viewing conditions must be optimum
(clear water, calm sea state, favorable light angle) to see the sharks from the cliff top,
and divers tend to disrupt the sharks’ normal activity and cause them to move away,
it has been difficult to observe detailed behavior to confirm whether mating, pupping
or feeding activity is taking place when the sharks form these aggregations. Also, it
is not known whether the peak in summer and early fall sightings is due to an actual
increase in this behavior or because viewing conditions are more favorable during this
period than during the stormy winter-spring period, when rain runoff reduces water
clarity and windier conditions disturb the sea surface. The probability of human
encounters with these groupings increases during the warmer months, when more
people frequent the beaches.
The purpose of this note is to document observed group mating activity and
associated habitat, as part of ongoing efforts to identify areas that may be important
for reproduction in this species.
METHODS AND STUDY AREA
Observations were made from a cliff-top vantage point overlooking the ocean
approximately 68 m above the southern end of Black’s Beach in La Jolla, California (Fig.
1). The leopard shark aggregation was viewed with the naked eye and with Leica 8X32
binoculars. All observations were made from the ocean-facing, 2nd floor walkway of the
National Marine Fisheries Service’s Southwest Fisheries Science Center at 8604 La Jolla
Shores Drive, La Jolla, CA. This area is located approximately 21.6 km north of the
entrance to San Diego Bay, and is adjacent to the head of Scripps Canyon, which comes
to within 305 m of shore at this location (Munk and Traylor 1947) (Fig. 1). The coastal
ocean off this beach is part of the Marine Life Refuge of the San Diego-La Jolla
Underwater Park system, the bottom consists of smooth sand, with a small reef of
sedimentary rock immediately adjacent to the south, which extends out from the beach.
The area is usually characterized by calmer sea conditions than beach areas 1 km to the
2S. E. Smith, unpublished data, NMFS, Southwest Fisheries Science Center, La Jolla, CA.
CALIFORNIA FISH AND GAME
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north (Black’s Beach surfing area) and immediately to the south (Scripps Institution
of Oceanography pier south to 32E51’48"N latitude) (Munk and Traylor 1947).
Figure 1. Map of the La Jolla, California area and location where leopard shark mating activity
was observed, showing proximity to Scripps Canyon.
LEOPARD SHARK MATING OBSERVED OFF LA JOLLA, CALIFORNIA 131
RESULTS
The shark aggregation was observed at approximately 1400-1430 h (PDT) on 4
August 2003 off northern La Jolla Shores, San Diego, California (approx. 32E52'19.1"N,
117E15'14.8"W, Fig. 1). It was composed of a small group of nine leopard sharks located
approximately 20 m offshore, swimming in water 1-3 m deep. Judging from the size of
nearby Western Gulls (Larus occidentalis) resting on the surface nearby, individuals
in the aggregation appeared to be between 122-152 cm TL long. The sharks were milling
about in a relatively tightly spaced, almost circular-shaped group (Fig. 2). Most
members of the group were closer than a body length from each other, although once
a single individual strayed out of the circle a few meters, before immediately returning.
Physical measures taken at nearby Scripps Pier at 1416 h PDT were as follows: sea
bottom temperature, 17.4EC; sea level pressure, 1013.72 mb; wind speed, 11.4 km per
h; wind direction, WNW 285E; tide height, 1.60 m (high at 1504 h); sunlight intensity,
72%; moon phase, one-quarter.3 The data buoy at nearby Point La Jolla at 1400 hr PDST
recorded a sea surface temperature of 21.5EC, wave height of 0.85 m, peak and average
wave period of 14.29 and 6.87 seconds respectively, and mean wave direction from the
SSW (204E).4
For the first few minutes of observation, the sharks appeared to be milling randomly,
although intermittently an individual would tilt its body and briefly roll over, flashing
the white of its under belly before re-orienting itself in a normal swimming position.
Because of the distance and vantage point, it was not possible to distinguish sex
(presence or absence of claspers) of individuals in the group. The animals milled
smoothly, exhibiting mild agitation only when banking abruptly to maintain the group’s
cohesive, roughly circular shape. The frequent belly flashing appeared passive, and
not associated with avoidance of another aggressive individual in the group. Several
individuals, at least two simultaneously, were seen exhibiting this belly-flash behavior.
When the milling aggregation strayed laterally in any direction, it moved generally as
a unit, the individuals moving together but without parallel orientation. At one point,
in the center of the circular aggregation, a smaller-sized shark (presumably male, referred
to as shark No. 1), began to follow close behind another larger shark (presumably female,
shark No. 2). It then quickly moved forward and parallel to shark No. 2 and wrapped
its body around it (Fig.2). The two sharks then rolled together entwined, a slight forward
momentum still carrying them slowly in the direction they had originally been swimming,
then both appeared to rest on the bottom. They remained thus entwined for a period
estimated to be not more than 15 seconds, before separating. At the instant of
3Scripps Institution of Oceanography (SIO) Pier Weather. 2004. Data from 1916 to today. Pier
5-minute data archive. Scripps Institution of Oceanography, La Jolla, California. http://
meteora.ucsd.edu/wx_pages/scripps.html (Accessed January 29, 2004).
4Scripps Institution of Oceanography (SIO) Coastal Data Information Program (CDIP). 2004.
Station Description for Point La Jolla, CA 095. Scripps Institution of Oceanography, La
Jolla, California. http://cdip.ucsd.edu/tmp/stream_frame08853.html (Accessed January 29,
2004).
CALIFORNIA FISH AND GAME
132
separation, just as the female broke away, a milky cloud (presumably seminal fluid),
billowed to the surface above their location. Others in the group did not appear to
interact with the pair during the brief copulation, but stayed in close proximity,
becoming less closely spaced after the pair had separated. The group remained
together for about 15 additional minutes, gradually spreading out over time, eventually
dispersing randomly and disappearing out of view. Total viewing time was approximately
30 minutes. No additional pairings or copulations were observed, although one animal
was seen to briefly roll and show the white of its belly before the group dispersed. No
obvious aggressive behavior or fin nipping was observed in any shark within the group.
However, when the two sharks were entwined, fin biting and holding may have
occurred. The head of shark No. 1 during coitus was positioned directly over shark No.
2’s right pectoral fin, and the entwining shark could have been holding the fin in its
mouth to gain purchase on shark No. 2.
Figure 2. Progression of courtship and copulation behaviors observed in a small group of leopard
sharks off La Jolla, CA, August 4, 2003, showing a) the milling group with pivot and belly flash
behavior; b) parallel swimming, and c) copulation at the center of the group.
LEOPARD SHARK MATING OBSERVED OFF LA JOLLA, CALIFORNIA 133
DISCUSSION
Just as muddy bays, estuaries and sloughs serve as important habitat for this
species north of Point Conception, shallow, surf-protected areas along southern
California sandy beaches and coves may be similarly important to southern California
leopard sharks for feeding, pupping, and mating. Certainly the study area, and the La
Jolla Shores area to the south, are important leopard shark aggregating locations in San
Diego County, based on these and past observations and anecdotal accounts in this
same general area.
It has previously been assumed, but not confirmed, that mating takes place
sometime in summer after spring parturition (Smith and Abramson 1990). The mating
activity reported here, although brief in duration and viewed from a distance, provides
documentation that mating in the San Diego area occurs in summer, and can occur at
midday along sandy beaches in shallow water. In all elasmobranchs, copulation
requires the insertion of one or both claspers into the cloaca and oviduct or oviducts
of the female (Pratt and Carrier 2001). While it was impossible to observe this type of
detail from the distance observed, the presence of what appeared to be seminal fluid
in the water immediately after separation of the entwined pair, suggests that copulation,
however brief, took place.
Fin biting was not observed, but might have been obscured by the distance and
viewing angle (generally from above). Fin biting and holding have been reported for
courting leopard sharks in captivity (Manny Ezcurra and Kevin Lewand, Monterey Bay
Aquarium, pers. comm., 10/2003) and in other species of sharks in captivity and in the
wild (e.g., Klimley 1980; Castro et al. 1988; Pratt and Carrier 2001). In most elasmobranchs
in which mating behavior has been observed, the male bites and often holds the female,
apparently as a precopulatory releasing mechanism to invoke female acquiescence
during courtship, to facilitate insertion of the clasper, and to maintain proper position
and proximity until sperm transfer is complete (Pratt and Carrier 2001). Observations
of body wrapping are consistent with that reported for mating leopard sharks in
captivity (Ackerman citing Herald5; Manny Ezcurra and Kevin Lewand, pers. comm. 10/
2003) and mating in other slender, flexible sharks, in which there is a tendency for the
male to wrap its body around the female (Dempster and Herald 1961; Dral 1980). But
no group courtship or mating behavior has been reported for leopard sharks in
captivity.
Unfortunately, the gender of individuals in the group observed in the wild at La Jolla
could not be determined directly, but based on the wrapping behavior and presence
of what appeared to be a sperm cloud, the central pair was likely male and female. It is
uncertain whether the group was polygynous (one male with several females),
polyandrous (one female with several males), or promiscuous.
5Ackerman, L. T. 1971. Contributions to the biology of the leopard shark, Triakis semifasciata
(Girard) in Elkhorn Slough, Monterey Bay, California. M.A. Thesis, Sacramento State
College, Sacramento, California, USA.
CALIFORNIA FISH AND GAME
134
Pratt and Carrier (2001), in their review of elasmobranch reproductive behavior,
present a case study of mating behavior in the nurse shark Ginglymostoma cirratum,
a species that also mates in extremely shallow water. They suggest that females seek
out the shallows as a refuge from pursuing males from deeper water, but the males
nonetheless follow them there, where they encircle them in groups of 1 to 4 males per
female, often with much persistence. In the present case, members of the group milled
together smoothly, with no obvious indication of aggressiveness or male pursuit
behavior until the moment of abrupt parallel swimming and copulation exhibited by the
one pair. Also, the belly flashing observed here appeared to be more passive than the
tilt and roll behavior described by Pratt and Carrier (2001) as a female male-avoidance
response.
This group of leopard sharks differed in size, cohesiveness, and behavior from other
daytime leopard shark aggregations the author has observed in the same area in the
past. Only nine individuals were observed, and these formed a tightly knit group, whose
members appeared to interact and display to each other with body tilts and belly flashes.
They remained together in a cohesive unit, before, during, and immediately after the
central pair copulated. Large aggregations previously seen by the author in the same
area (e.g., > 100 individuals) did not exhibit ‘close-following,’ ‘belly-flashing,’ or
copulatory behavior, and the only interaction occurred when a shark swam to one side
to avoid colliding with another. It is possible that these large, more diffuse daytime
aggregations are for the purposes of feeding (or preparing to feed later at night), while
mating aggregations tend to be smaller and more closely knit. Nonetheless, one cannot
entirely rule out that even these larger groupings, especially those seen during spring
and summer, may be gatherings preparatory to reproductive activity such as pupping
or mating. Additional and closer observation is needed by divers careful not to disturb
the sharks, or with unobtrusive, remotely operated vehicles or cameras.
ACKNOWLEDGMENTS
G. Cailliet, C. Dawson, M. Ezcurra, D. Holts, K. Lewand, W. Pratt, and D. Ramon,
made comments or provided information that led to improvements and clarifications in
early drafts of this work. I also thank C. Lane, D. Parker, and an anonymous reviewer
for helpful comments on the final draft. Roy Allen prepared the figures from my rough
sketches during a time that was especially busy for him. Special thanks to Manny
Ezcurra and Kevin Lewand (Monterey Bay Aquarium) for providing information on
leopard shark mating behavior in captivity.
LITERATURE CITED
Ackerman, J.T., M.C. Kondratieff, S.A. Matern, and J.J. Cech, Jr. 2000. Tidal influence on
spacial dynamics of leopard sharks, Triakis semifasciata, in Tomales Bay, California.
Environmental Biology of Fishes 58: 33-43.
Anonymous. 2000a. Leopard sharks, by the hundreds, are back. San Diego Union Tribune Jul
29 2000, p. B.5.
LEOPARD SHARK MATING OBSERVED OFF LA JOLLA, CALIFORNIA 135
Anonymous. 2000b. Sharks by the shore. San Diego Union Tribune Sep 13, 2000, p. A1.
Castro, J.I., P.M. Bubucis, and N.A. Overstrong. 1988. The reproductive biology of the chain
dogfish, Scyliorhinus retifer. Copeia 1988 (3), pp. 740-746.
Compagno, L.J.V. 1984. FAO Species Catalogue Volume 4, Sharks of the World, Part 2.
Carcharhiniformes. FAO Fish Synopsis 125: 251-655.
Dempster, R.P. and E.S. Herald. 1961. Notes on the horn shark, Heterodontis francisci, with
observations on mating activities. Occasional Papers California Academy of Sciences 33: 1-
7.
Dral, A.J. 1980. Reproduction en aquarium du requin de fond tropical, Chiloscyllium griseum
Müll. et Henle (Oretolobidés). Revue francais Aquariologie 7: 99-104.
Ebert, D. A. 2003. Sharks, rays and chimeras of California. California Natural History Guides
No. 71, University of California Press, Berkeley and Los Angeles, California, U.S.A.
Eschmeyer, W.N., E.S. Herald, and H. Hammann. 1983. A field guide to Pacific Coast fishes
of North America from the Gulf of Alaska to Baja California. Houghton Mifflin Company,
Boston, Massachusetts, U.S.A.
Huard, R. 2002. Swim with the sharks. San Diego Union Tribune. Aug 12 2002, p. B1.
Klimley, A. P. 1980. Observations of courtship and copulation in the nurse shark Ginglymostoma
cirratum. Copeia 1980 (4), pp. 878-882.
Love, M.S. 1991. Probably more than you want to know about the fishes of the Pacific Coast.
Really Big Press, Santa Barbara, California, U.S.A.
Munk, W.H. and M. A. Traylor. 1947. Refraction of ocean waves: a process linking underwater
topography to beach erosion. Journal of Geology 55(1):1-26.
Pratt, H. L. Jr., and J. C. Carrier. 2001. A review of elasmobranch reproductive behavior with
a case study of the nurse shark, Ginglymostoma cirratum. Environmental Biology of Fishes
60, 157-188.
Russo, R.A. 1975. Observations on the food habits of leopard sharks (Triakis semifasciata)
and brown smoothhounds (Muselus henlei). California Fish and Game 61:95-103.
Smith, S.E. 2001. Leopard shark, p. 252-254. In (W.S. Leet, C.M. Dewees, R. Klingbiel, and
E. J. Larson, eds), California’s Living Marine Resources: A Status Report. California
Department of Fish and Game. University of California Agriculture and Natural Resources.
Sea Grant Publication SG01-11.
Smith, S.E. and N. Abramson. 1990. Leopard shark Triakis semifasciata distribution, mortality
rate, yield, and stock replenishment estimates based on a tagging study in San Francisco Bay.
Fishery Bulletin, U.S. 88(2):371-381.
Received: 18 April 2004
Accepted: 9 August 2004
... one of the most researched elasmobranchs along the Pacific Coast of North America with several aspects of its biology well defined (Ackerman 1971;Russo 1975Russo , 2013Russo , 2015Russo , 2018Russo , 2019Talent 1976Talent , 1985Smith 1984Smith , 2001Smith , 2005Smith and Abramson 1990;Cailliet 1992;Kusher et al. 1992;Au and Smith 1997;Smith et al. 2003;Hight and Lowe 2007;Lewallen et al. 2007;Starr 2009, 2010;Nosal et al. 2013aNosal et al. ,b, 2014Launer 2014;Barker et al. 2015). Various reproductive studies have occurred for leopard sharks (Ackerman 1971;Talent 1985;Ebert and Ebert 2005;Smith 2005;Nosal et al. 2013aNosal et al. , b, 2014Launer 2014;Russo 2015Russo , 2018Russo , 2019. ...
... one of the most researched elasmobranchs along the Pacific Coast of North America with several aspects of its biology well defined (Ackerman 1971;Russo 1975Russo , 2013Russo , 2015Russo , 2018Russo , 2019Talent 1976Talent , 1985Smith 1984Smith , 2001Smith , 2005Smith and Abramson 1990;Cailliet 1992;Kusher et al. 1992;Au and Smith 1997;Smith et al. 2003;Hight and Lowe 2007;Lewallen et al. 2007;Starr 2009, 2010;Nosal et al. 2013aNosal et al. ,b, 2014Launer 2014;Barker et al. 2015). Various reproductive studies have occurred for leopard sharks (Ackerman 1971;Talent 1985;Ebert and Ebert 2005;Smith 2005;Nosal et al. 2013aNosal et al. , b, 2014Launer 2014;Russo 2015Russo , 2018Russo , 2019. Although these studies have found sexual segregation the specifics of male sexual maturity remain unknown. ...
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... In central and northern California, parturition appears to occur from March through September, with a peak in April and May (Ackerman 1971, Talent 1985, Smith and Abramson 1990, Ebert and Ebert 2005. In southern California pupping is believed to occur around May and June, although it has been reported to occur as late as September in San Diego Bay (Eigenmann 1891, Smith 2005. Mating is believed to occur shortly after pupping (Ackerman 1971, Talent 1985, Ebert 2003 and has only been observed once in the wild, in the shallow surf zone in La Jolla (Smith 2005). ...
... In southern California pupping is believed to occur around May and June, although it has been reported to occur as late as September in San Diego Bay (Eigenmann 1891, Smith 2005. Mating is believed to occur shortly after pupping (Ackerman 1971, Talent 1985, Ebert 2003 and has only been observed once in the wild, in the shallow surf zone in La Jolla (Smith 2005). Females may mate with multiple males with as many as 36% of litters having multiple paternity (Nosal et al. 2013b). ...
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... It may be that these sharks mate at a different time of year and store sperm in the shell gland, as has been reported for the blue shark, Prionace glauca (Pratt 1979). Smith (2005) observed mating in T. semifasciata in La Jolla Cove, San Diego, California, in August 2001. If the timing of Smith's observation, late summer, is indicative of the time of year mating takes place in T. semifasciata this would be 2-3 months after parturition. ...
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