The gray smooth-hound (also spelled as smoothhound) (''Mustelus californicus'') is a

houndshark The Triakidae or houndsharks are a family of ground sharks, consisting of about 40 species in nine genera. In some classifications, the family is split into two subfamilies, with the genera ''Mustelus'', '' Scylliogaleus'' and '' Triakis'' in t ...

of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Triakidae. It is spotless and smooth with a narrow head and long blunted snout.Miller, D. J., & Lea, R. N. (1972). Guide to the coastal marine fishes of California. ''California Department of Fish and Game'', ''Fish Bulletin''(157). https://escholarship.org/uc/item/6s04v367 This shark is found on

continental shelves A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

of the

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones immediately to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Ge ...

eastern

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

. Its range extends from northern

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

to the

Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...

(between

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

s 40° N and 23° N), usually residing in waters less than 80 meters (262 ft 6 in) deep.IUCN. (2014). ''Mustelus californicus: Pérez-Jiménez, J., Vásquez, V.E., Chabot, C.L. & Ebert, D.A.: The IUCN Red List of Threatened Species 2015: e.T161334A80672080''. http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T161334A80672080.en Adults are between 0.5 and 1.6 meters (1 ft 8 in to 5 ft 3 in) long.Yudin, K. G., & Cailliet, G. M. (1990). Age and Growth of the Gray Smoothhound, Mustelus californicus, and the Brown Smoothhound, M. henlei, Sharks from Central California. ''Copeia'', ''1990''(1), 191. https://doi.org/10.2307/1445835 Furthermore, this shark is

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

with an egg yolk placenta.Tárula-Marín, A. O., & Saavedra-Sotelo, N. C. (2021). First record of the mating system in the grey smoothhound shark ( ''Mustelus californicus'' ). ''Marine Biology Research'', ''17''(4), 362–368. https://doi.org/10.1080/17451000.2021.1964533 Reproduction occurs annually and inland estuaries are common nursery grounds. Although there is little data on the shark’s population trends and catch quantities, the gray smooth-hound is not considered as vulnerable to overfishing. Additionally, there have been three reported sightings of

albinism Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and reddish pink or blue eyes. Individuals with the condition are referred to as albinos. Varied use and interpretation of ...

in this species, which is rare for elasmobranchs (rays and sharks).Talent, L. G. (1973). Albinism in Embryo Gray Smoothhound Sharks, Mustelus californicus, from Elkhorn Slough, Monterey Bay, California. ''Copeia'', ''1973''(3), 595. https://doi.org/10.2307/1443129Cohen, J. L. (1973). An Albino Grey Smoothhound Mustelus californicus Gill. ''California Fish and Game'', ''59''(3), 210–211

Description

The gray smooth-hound is a medium-sized spotless shark with a short narrow head.Pérez-Jiménez, J. C., & Sosa-Nishizaki, O. (2010). Determining reproductive parameters for population assessments of two smoothhounds (Mustelus californicus and Mustelus lunulatus) from the northern Gulf of California, Mexico. ''Bulletin of Marine Science'', ''86''(1), 3–13 It is morphologically similar to others of its genus with its slender body, long blunt snout, conspicuous sub-ocular ridges, and dorsolateral eyes. The gray smooth-hound is brown to dark-gray dorsally and white ventrally. The ventral caudal lobe (lower part of tail) is poorly developed and the second

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

is relatively small. The gray smooth-hound can be distinguished by the snout shape and placement of the dorsal fin. It is often confused with the brown smooth-hound (''Mustelus henlei''), though there are several characteristics that differ between these two species. In the gray smooth-hound, the midpoint of the dorsal fin is closer to the start of the pelvic fin than it is to the end of the pectoral fin (see image below). In the brown smooth-hound, the midpoint of the dorsal fin is equidistant from the pelvic and pectoral fins. Additionally, the tooth shape of these two species differs slightly: gray smooth-hounds have smooth teeth that are blunt and not cusped whereas a basal cup can be seen on the sides of the middle upper teeth in the brown smooth-hound. The sides of the mandible are concaved in the gray smooth-hound but are slightly convex in brown smooth-hounds. Moreover, the posterior side of the dorsal fins have no scales and are frayed in the brown smooth-hound, which is unlike the gray smooth-hound. Scales on the sides of the brown smooth-hound are tricuspid (three pronged), which is not seen in gray smooth-hounds. Tooth and scale differences can only be observed under magnification.Starks, E. C. (1917). On the Differential Characters between Mustelus henlei and Mustelus californicus. ''Copeia'', ''46'', 61. https://doi.org/10.2307/1435660 Additionally, another species in the genus ''Mustelus'', the sicklefin smooth-hound Gray smooth-hound and brown smooth-hound comparison

Gray smooth-hound and brown smooth-hound comparison

(''Mustelus lunulatus''), can be easily distinguished by a pointed lower lobe of the caudal fin, which is not present in the gray smooth-hound. The sicklefin smooth-hound also has a longer snout, shorter upper labial furrows, and eyes set further apart. The white-margin fin smooth-hound (''Mustelus albipinnis'') has white margins on its fins, which the gray smooth-hound lacks. The sharptooth smooth-hound (''Mustelus dorsalis'') has higher-cusped teeth as compared to the gray smooth-hound. The total length of mature gray smooth-hounds ranges from around 50–160 cm (19.7-63.0 in). Females mature at a larger size and have a larger maximum reported size than males (see biology and ecology section for more details). The size at birth is around 20–30 cm (7.9-11.8 in).

Distribution and habitat

The gray smooth-hound can be found in warm waters along the

coast of California Coastal California, also known as the California Coastline and the Golden Coast, refers to the coastal regions of the U.S. state of California. The term is not primarily geographical as it also describes an area distinguished by cultural, economic ...

and

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

, ranging from

Cape Mendocino Cape Mendocino ( Spanish: ''Cabo Mendocino'', meaning "Cape of Mendoza"), which is located approximately north of San Francisco, is located on the Lost Coast entirely within Humboldt County, California, United States. At 124° 24' 34" W longit ...

Mazatlán Mazatlán () is a city in the Mexican list of states of Mexico, state of Sinaloa. The city serves as the municipal seat for the surrounding , known as the Mazatlán Municipality. It is located on the Pacific Ocean, Pacific coast across from th ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

. In the warm waters of Mexico and Southern California, these sharks do not migrate. However, in colder northern waters, sharks will migrate to central-northern California in the summer and then return to more southern regions during the rest of the year. These sharks are bottom-dwellers, living on

as well as shallow muddy

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

and

bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a ''gulf'', ''sea'', ''sound'', or ''bight''. A ''cove'' is a small, ci ...

s along the coast and into the Gulf of California.Espinoza, M., Farrugia, T. J., & Lowe, C. G. (2011). Habitat use, movements and site fidelity of the gray smooth-hound shark (Mustelus californicus Gill 1863) in a newly restored southern California estuary. ''Journal of Experimental Marine Biology and Ecology'', ''401''(1–2), 63–74. https://doi.org/10.1016/j.jembe.2011.03.001 In California, this shark is usually found in shallow waters that are less than 12 meters (39 ft 4 in) deep, but it has been found to a maximum depth of 67 meters (219 ft 10 in). In the Gulf of California, the majority of gray smooth-hounds are found less than 80 meters (262 ft 6 in) deep but have been found up to 265 meters (869 ft 5 in) below the sea surface. Important nursery grounds for the gray smooth-hound include the Biosphere Reserve of the upper Gulf of California, the Colorado Delta, Elkhorn Slough, and Full Tidal Basin in Bolsa Chica have also been identified as nursery grounds.Freedman, R., Espinoza, M., Voss, K. M., Farrugia, T., Whitcraft, C. R., & Lowe, C. G. (2017). Does Estuary Restoration Design Alter the Fine Scale Movements of Gray Smoothhounds ( ''Mustelus californicus'' ) in Southern California? ''Bulletin, Southern California Academy of Sciences'', ''116''(2), 88–97. https://doi.org/10.3160/soca-116-02-88-97.1 In the Full Tidal Basin (after restoration efforts), gray smooth-hounds have become seasonally abundant in the summer, where the population is mostly made up of juveniles. They are most often found at the edges between eelgrass patches and muddy substrates. Eelgrass is home to many prey items of the gray smooth-hound. Additionally, most gray smooth-hounds select warmer habitats found in the middle of the basin during the day, then venture into cooler habitats where their prey is found at night. It is thought that this helps thermoregulate their body temperature. The amount of dissolved oxygen in the water is also thought to influence their movements.

Biology and ecology

Growth

Gray smooth-hounds are a relatively fast-growing shark species. It only takes 2–3 years for females to mature and 1–2 years for males. They live up to a maximum of around 9 years.

Generation time In population biology and demography Demography () is the statistical study of human populations: their size, composition (e.g., ethnic group, age), and how they change through the interplay of fertility (births), mortality (deaths), and mi ...

for this species is around a decade. At birth, females are around 23–37 cm (9.1-14.6 in) long and males are around 27-44 (10.6-17.3 in) cm long. Gray smooth-hounds are considered mature when females reach a total length of 86 cm and males reach a length of 72 cm (28.3 in). The maximum reported size is 1.632 meters (5 ft 4 in) for females and 1.16 meters (3 ft 10 in) for males.

Feeding

The gray smooth-hound is a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

coastal predator and mostly feeds on

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s. Specifically, they are known to feed on crabs ( Cancrids and Grapsids),

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

scallop Scallop () is a common name that encompasses various species of marine bivalve molluscs in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related famili ...

s, ghost shrimp ('' Callianassa spp.'').Talent, L. G. (1982). Food habits of the gray smoothhound, Mustelus californicus, the brown smoothhound, Mustelus henlei, the shovelnose guitarfish, Rhinobatos productus, and the bat ray, Myliobatis californica, in Elkhorn Slough, California. ''California Fish and Game'', ''68''(4), 224–234 The red rock crab ('' Cancer productus'') and pacific rock crab ('' Cancer antennarius'') account for most of the adult diet. Gray smooth-hounds smaller than 100 cm (39.3 in) mostly feed on the yellow shore crab ('' Hemigrapsus oregonensis''). The yellow shore crab, along with the slender crab ('' Cancer gracilis''), have been found to be more than 69% of the total food volume for these smaller sharks. Adults will also incorporate fish into their diet such as herring (specifically '' Clupea harengus pallasi)'' and toadfish ('' Porichthys notatus''). Though rare, innkeeper worms (''

Urechis caupo ''Urechis caupo'' is a species of Echiura, spoon worm in the family Urechidae, commonly known as the innkeeper echiuran, the fat innkeeper worm (because their tunnels often contain other animals), the innkeeper worm, or the penis fish. It is fou ...

'') have been found in gray smooth-hound stomachs.

Reproduction

The gray smooth-hound is a

(live-bearing) shark. When the

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

is developing, the

yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...

differentiates into a yolk sac placenta, which aids in nutrient and gas exchange between the embryo and the mother. Similar to other smooth-hound species, Gray smooth-hounds reproduce annually. The gestation period is estimated to be between 9–12 months. Reports for pups per litter vary from 3-17 pups. Due to their early age of maturity, large litter sizes, and yearly reproduction cycles, these sharks have high reproductive output. Moreover, the number of female and male sharks found per litter is about equal (1:1

sex ratio A sex ratio is the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. However, many species deviate from an even sex ratio, ei ...

). There is a positive linear relationship between litter size and mother total-length, where longer females have larger litters. Gray smooth-hounds have oviducal glands, which would allow females to store sperm from multiple matings. This suggests that females mate with multiple males (known as

polyandry Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives ...

), though this has yet to be confirmed. The first and only record of the gray smooth-hound’s mating system comes from a paper published in 2021. Tissues were collected from two small females, and their pups were genetically analyzed. They found that these two females were genetically

monogamous Monogamy ( ) is a relationship of two individuals in which they form a mutual and exclusive intimate partnership. Having only one partner at any one time, whether for life or serial monogamy, contrasts with various forms of non-monogamy (e.g. ...

(where the offspring of a female are only related to one male). One possible reason is that the females engaged in post-copulatory mechanisms (i.e.

sperm competition Sperm competition is the competitive process between Spermatozoon, spermatozoa of two or more different males to fertility, fertilize the same Egg cell, egg during sexual reproduction. Competition can occur when females have multiple potential m ...

and

cryptic female choice Cryptic female choice is a form of mate choice which occurs both in pre- and post-copulatory circumstances in which females of certain species use physical or chemical mechanisms to control a male's success of fertilizing their ova or ovum; i.e. by ...

), choosing sperm from one male and fertilize her eggs with. This would result in genetic monogamy within a polyandrous species. However, it is also possible that the small females avoided multiple mating encounters which would also result in genetic monogamy. Additionally, the females may be able to selectively abort embryos with low fitness. Other species of smooth-hounds seem to have low or moderate levels of multiple paternity (females carrying offspring from multiple males), so, if this information is confirmed, gray smooth-hounds would be unique in their genus for genetic monogamy. Since current mating system information comes from one study with a low sample size, more research is needed to fully understand whether gray smooth-hounds engage in multiple matings and whether they are genetically monogamous.

Parasites

Several parasites are known to infect the gray smooth-hound, which include ''Calicotyle californiensis,'' ''Chloromyxum ovatum,'' ''Dollfusiella litocephalus, Dollfusiella macrotrachelus, Lacistorhynchus dollfusi, Symcallio pellucidum,'' and ''Ptychogonimus megastomum''.Merlo-Serna, A. I., & García-Prieto, L. (2016). A checklist of helminth parasites of Elasmobranchii in Mexico. ''ZooKeys'', ''563'', 73–1

Albinism

True

is rare in Elasmobranchs. However, there have been three recorded instances of albinism in the gray smooth-hound. The first was an immature male (34 cm or 13.4 in long) caught on June 7, 1959. It was unclear whether this shark was a true albino as its eye color could not be determined. The second was an immature female (26.3 cm or 10.4 in long) caught on July 3, 1969. Then, on December 9, 1971, a pregnant female gillnetted in Elkhorn slough was found to have 5 albino embryos out of 10 total offspring. 3 of 6 males and 2 of 4 females were albino. 2 albino embryos were found in one ovisac, 3 from the other. These embryos were identified as truly albino—completely white with pink eyes. The pregnant female was gray and thus,

heterozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mos ...

for albinism.

Human interactions

Gray smooth-hounds are caught by recreational fishers, caught as

by-catch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

, and targeted by

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life or, more commonly, the site where such enterprise takes place ( a.k.a., fishing grounds). Commercial fisheries include wild fisheries and fish farm ...

, though this shark has low economic value. Usually, they are caught with

gillnets Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...

trawlers Trawler may refer to: Boats * Fishing trawler, used for commercial fishing * Naval trawler Naval trawlers are vessels built along the lines of a fishing trawler but fitted out for naval purposes; they were widely used during the World War I, Fir ...

, or with line and hook. Young sharks are likely able to swim through gillnets. Fishing demand is highest in the

, where as much as 500 kg (1102.3 lbs) of gray smooth-hound has been caught during a single fishing trip. A 2015 IUCN assessment categorized gray smooth-hounds as a species of least concern. This is partially because population data from Baja California Sur implies that gray smooth-hound populations are stable. Additionally, their life history traits (e.g. high reproductive output and early age of maturity, see growth and reproduction) make these sharks more resilient to fishing and allow a larger capacity to recover from overfishing as compared with other sharks. This claim is further supported by a 2017 impact assessment, which found that gray smooth-hounds were found to not be particularly vulnerable to

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

for similar reasons. However, the population trend of gray smooth-hounds is unknown, and the catch and by-catch data are incomplete. The Mexican government does regulate

elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by h ...

fisheries, but there is no information on the effectiveness of these regulations and whether they are enforced. More research is needed to fully understand the population patterns of gray smooth-hounds.

References

{{Taxonbar, from=Q2544976 gray smooth-hound Fauna of the Baja California Peninsula Fish of the Gulf of California gray smooth-hound gray smooth-hound