Spot (Leiostomus xanthurus)

Description

Spot (Leiostomus xanthurus) are short, broad fish with spines along the dorsal fin and a blunt snout caused by protrusion of the upper jaw (Phillips et al 1989). Spot can grow to 34 centimeters in length (Grosslein and Azarovitz 1982), and the different life stages have distinct morphological features. Larval spot have twelve distinctive anal rays that distinguish them from other larval sciaenids, and the larvae (7 to 15 millimeters in length) have no pigmentation. Juveniles have a broad, truncate tail while adults have a concave tail. Spot also have an inferior mouth, and all premaxillary and dentary teeth present in juveniles are absent in individuals larger than 100 millimeters in length. Adult spot are bluish gray in color with gold and silver iridescence. They have yellow tinged bars along their sides, a large yellow-black spot on the shoulder, and pale yellow fins (Phillips et al. 1989; Weiss 1995). Spot are schooling fish, and as members of family Sciaenidae, males can produce a characteristic drumming sound.

Background

Distribution. Spot range along the Atlantic and Gulf coasts from Massachusetts to Mexico, with the greatest abundance between the Chesapeake Bay and North Carolina (Grosslein and Azarovitz 1982). In summer, spot live in sounds, bays, and estuaries, migrating offshore in autumn. In winter, they are mostly found south of Cape Hatteras, North Carolina (Grosslein and Azarovitz 1982). Spot are found in small numbers in Raritan Bay (MacKenzie 1992).

Feeding. Larval spot (1 to 10 millimeters) feed on plankton, specifically pteropods, larval pelecypods, and copepods. At 11 to 20 millimeters, larvae eat copepods, mysids, and amphipods (Phillips et al. 1989). Juveniles are termed "nonterritorial, benthic, grazing generalists that forage effectively regardless of substrate type" (Phillips et al. 1989). Adults prey on bivalves and tube-building polychaetes, often nipping bivalve siphons and polychaete tails. Additionally, adult spot feed on small crustaceans, small fish, and plant material (Grosslein and Azarovitz 1982). They eat by grabbing a mouthful of sediment, chewing, and then spitting out unwanted matter.

Fishery. The largest portion of the spot fishery is from recreational fishing, rather than commercial. In the early 1900s, spot were extremely abundant in the NY Bight. In fact, the Brooklyn Edison Company had to shut down its generator to remove spot from the pumps in 1925 (Grosslein and Azarovitz 1982). Commercial landings dropped drastically in the NY Bight region during the 1940s through the 1960s, and then began to increase in the 1970s. Landings in the New York/New Jersey fisheries have been low compared to U.S. totals and recovery in the 1970s and 1980s was minimal (NMFS 1999). Spot populations have declined substantially in Raritan Bay over the past few decades, and overharvesting from both fisheries is presumed to be a major contributing factor (MacKenzie 1990). Spot occur more frequently in the Chesapeake Bay area and coastal North Carolina than in the NY/NJ Harbor area (Grosslein and Azarovitz 1982, Phillips et al. 1989, NMFS 1999).

Life Cycle

Spot reach sexual maturity in their second or third year, usually at approximately 20 centimeters in length (Phillips et al. 1989). Adults migrate in late fall toward offshore spawning grounds over the continental shelf. Spawning occurs through early spring, with larger fish spawning earlier. Spawning has been induced in aquaria at temperatures ranging from 18 to 25 degrees Celsius and in 8 hours of daylight (Phillips et al. 1989). Laboratory females produce 30,000 to 60,000 eggs, which are 0.7 to 0.9 millimeters in diameter, and incubation lasts approximately 48 hours. Eggs are buoyant and larvae measure 1.5 to 1.7 millimeters in length at hatching. They begin feeding at 3 days, and larvae grow at a rate of approximately 7 percent of body length per day, which decreases to 1.5 percent of body length when they enter inshore waters with the ebb tide or bottom currents (Phillip et al. 1989). Larvae live in the mid to deep waters during the day and migrate to the surface at night. Larval spot enter inlets and bays in April at a length of 15 to 20 millimeters and inhabit estuarine and fresh water nursery areas. By the end of their first year, juveniles average 8 to 18 centimeters and grow to 28 to 34 centimeters by age three (Phillips et al. 1989). In the fall, spot migrate offshore and return to bays and estuaries in the spring. Typically, these fish do not live beyond three years of age (Grosslein and Azarovitz 1982).

Environmental Influences

Salinity and Temperature. Spot are euryhaline and can tolerate a wide range of salinities. Typically, they are more abundant in tributaries with lower salinities, but experiments show that varying salinity does not affect distributions (Phillips et al. 1989). Spot, especially juveniles, are susceptible to changes in temperature. Their seasonal migration patterns reflect their responses to temperature changes (Grosslein and Azarovitz 1982).

Predation. Spot are an important prey of striped bass (Morone saxatilis), sea birds, and spotted sea trout (Grosslein and Azarovitz 1982, Phillips et al. 1989). Chaetognaths are a predator of larval spot, but they also compete for food resources.

Pollution. As young spot move into estuaries and freshwater environments, they are more susceptible to pollution. Experimental analysis has demonstrated that spot experience reduced survivorship when exposed to chlorine-producing oxidants and copper, especially in warmer temperatures (Phillips et al. 1989).

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