The shovelnose guitarfish (Pseudobatos productus) is a ray in the family Rhinobatidae. P. productus was first described by ichthyologist William Orville Ayre in 1854 as Rhinobatos productus, with the genus derived from the Greek word rhinos, meaning nose, and the Latin word batis, meaning ray. It was later placed in the genus Pseudobatos following reconsideration of many species placed in Rhinobatos. As its common name suggests, this species possesses a pointed shovel-shaped snout and a body similar to that of a guitar with a larger head and long, slender body. The shovelnose is considered to be a primitively developed ray, with many features of both sharks and rays. The shovelnose guitarfish was first considered to be a shark because of its dorsal fins' shape. Fossils of P. productus ancestors have been recovered, dating back over 100 million years.
Description
The coloration of this species ranges from olive to sandy brown which aids in the species' ability to camouflage in the sand. Other identifying features of Pseudobatos productus include a depressed body shape with a dorsoventrally flattened opaque snout, no gap between the pectoral and pelvic fins, and protruding eyes. This species also has two dorsal fins which are closer to the posterior end of its body and caudal fin. Shovelnose guitarfish have around 102 to 112 small round teeth. Sexual maturity is reached in females at an estimated age of 8 years and 7 years in males.
This species exhibits sexual dimorphism in which females tend to be larger than males. Males are between 90–100 cm (35–39 in) long, while females are around 99 cm (39 in) at that age. The average size of shovelnose guitarfish is still not well known as many studies have seen fluctuations in the total length they can reach. The ray can live up to 11 years, and full-grown sizes are around 120 cm (47 in) for males, and females reach 137 cm (54 in). The bowmouth guitarfish is found in waters of the Indo-West Pacific and has a more rounded snout than the shovelnose, and larger dorsal fins which can reach lengths up to cm (about 9.68 ft).
Distribution and geographical range
Pseudobatos productus inhabits shallow estuaries and bays of the Mexican Pacific ranging from San Francisco, California to Guerrero, Mexico. Additionally, they are widely distributed in the Gulf of California. Research suggests that La Jolla, California is the preferred residency of adult shovelnose guitarfish. Members of this species are not commonly found in open water and tend to remain in coastal ecosystems such as bays, estuaries as well as seagrass beds at depths of less than 40 feet. There have been sightings of shovelnose guitarfish reaching depths of up to 91 meters, but this is uncommon for the species. Rhinobatos productus has magnetic particles in its vestibular receptors, and the magnetic particles are believed to be exogenous in origin. The magnetic particles' spatial arrangement may aid in the sensitivity of the receptors to movements.
Physiological characteristics
Shovelnose guitarfish possess spiracles found behind their eyes which are used to pump water over to gills to absorb oxygen. Because their gills are on the underside of these rays, this allows the species to continue to breathe while remaining on the seafloor.
Feeding and hunting
thumb|Ventral view of P. productus|left|310x310pxShovelnose guitarfish feed on benthic invertebrates including worms, mollusks, crustaceans, cephalopods, and small fish. Much of their diet consists of decapods such as crabs and shrimps. As bottom-feeders, their mouth is on the underside of their body to easily capture food on the ocean floor. Smaller P. productus specimens tend to be more specialized predators, only feeding on crustaceans. Larger specimens have a more generalized diet but still maintain a diet dominated by crustaceans. When prey is visible, the fish will quickly ambush and trap its prey beneath its body, immobilizing it while creating a suction with the mouth to chew and ingest. Shovelnose guitarfish are not efficient at capturing fast-moving prey and therefore must maintain a diet of slow-moving organisms.
P. productus plays an important ecological role in their ecosystem by being both a prey and predatory species in coastal marine areas. They consume fish and mollusks, both second-order consumers, and are prey to coastal sharks, large predatory birds and California sea lions. The water temperature is also a factor, as more activity is recorded in the species at warmer temperatures between 20°C and 24.58°C. Temperature preference is similar in both males and females of this species. There is also evidence that shovelnose guitarfish regulate their metabolic rate by feeding in warmer waters and resting in cooler waters.
Female shovelnose guitarfish are aplacental viviparous and give birth to live young, but do not develop a placenta. Pregnant females generally carry an average of 5 embryos at a time with a maximum of 10. Embryos begin their development in late March and birth occurs 4 to 5 months after from June to October. At birth, the length and weight of P. productus is on average 175mm (about 6.89 in) and 2.7 grams. The gestation period of females is about 12 months. Shovelnose guitarfish are monogamous and will only mate once a year.
Conservation
Shovelnose guitarfish were listed as "near threatened" in the Red List of the International Union for Conservation of Nature (IUCN) in 2014. This was an effort to reduce capture of this species but also maintain fishing in the area. Pseudobatos productus, like many other species of rays, experiences late maturity, slow growth, and a small reproductive rate. This species is harvested through artisanal fisheries during the summer months for their high value. Adults are primarily caught consisting of mostly pregnant females.
As food
In national markets, shovelnose guitarfish is sold fresh, dried, and as salted filets.