The gray smooth-hound (also spelled as smoothhound) (Mustelus californicus) is a houndshark of the family 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 of the subtropical eastern Pacific. Its range extends from northern California to the Gulf of California (between latitudes 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.enCompagno, Dando, & Fowler, Sharks, Collins Gem, HarperCollins, London (2006) 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 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 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 is relatively small.Compagno, L. J. V. (Ed.). (2001). FAO species catalogue for fishery purposes. 1,2: Bullhead, macherel and carpet sharks, (Heterodontiformes, Lamniformesand Orectolobiformes). https://www.iucnssg.org/uploads/5/4/1/2/54120303/fao_species_catalogue_for_fishery_purposes_-_1984_-_sharks_of_the_world_-_an_annotated_and_illustrated_catalogue_of_shark_species_known_to_date_-_part_2_-_carcharhiniformes.pdfGill, T. (1864). Second Contribution to the Selachology of California. Proceedings of the National Academy of Sciences of Philadelphia, 16(3), 147–151. https://www.jstor.org/stable/4623921
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 (M. 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 (M. albipinnis) has white margins on its fins, which the gray smooth-hound lacks. The sharptooth smooth-hound (M. 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 and Baja California, ranging from Cape Mendocino, California to Mazatlán, Mexico. 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 continental shelves as well as shallow muddy estuaries and bays 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 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 coastal predator and mostly feeds on crustaceans. Specifically, they are known to feed on crabs (Cancrids and Grapsids), shrimps, scallops, 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) have been found in gray smooth-hound stomachs.
Reproduction The gray smooth-hound is a viviparous (live-bearing) shark. When the embryo is developing, the 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). There is a positive linear relationship between litter size and mother total-length, where longer females have larger litters.