Species Description: Leiostomus xanthurus is a moderately deep-bodied, compressed fish with an elevated back. Body color is typically bluish-gray dorsally, fading to golden yellow or yellow-tan ventrally. A set of 12-15 dark streaks run obliquely from the dorsal surface down the sides to about mid-body. These tend to fade with age. Fins are typically pale yellow in color. The head is short, with a small, inferior mouth. The maxilla extends to approximately the middle of the eye. The dorsal fin is continuous, with a notch separating the spinous portion from the soft rays. There are 9-11 dorsal spines, and 29-35 soft rays. The anal fin has 2 spines and 12-13 rays. The caudal peduncle is moderately deep, and the caudal fin is notched. A large black spot is set above the upper edge of the gill cover. There are 72-77 lateral line scales (Johnson 1978).
Potentially Misidentified Species: Adults are not typically mistaken for other Sciaenids due to the prominent spot and faint oblique stripes. However, juveniles resemble a number of related species including the Atlantic croaker, Micropogonias undulatus and the silver perch, Bairdiella chrysoura. The Atlantic croaker is differentiated from the spot by having barbells on the lower jaw and a serrate preopercule. The silver perch is differentiated by its rounded caudal fin and well developed teeth.
Regional Occurrence: Leiostomus xanthurus is common along the Atlantic coast from Cape Cod south to the Bay of Campeche, Mexico. It occurs irregularly in south Florida and the Florida Keys, and north of Cape Cod, Massachusetts (Bigelow and Schroeder 1953; Chao 1978).
IRL Distribution: Spot are common throughout the Indian River Lagoon, especially around Brevard and Indian River Counties.
Age, Size, Lifespan: Leiostomus xanthurus grows to approximately 11 inches total length (TL). In the first year it may reach 5.9 inches; in the second year, 8.7 inches; and in the third year 11 inches (Townsend 1956; Welsh and Breder, 1923; McRae et al. 1997). The lifespan may be as long as 5 years (DeVries 1982).
Growth rates in spot show both seasonal and annual variation. In young juveniles, growth rates are fastest in late spring and early summer, with high estuarine water temperatures in late summer and early fall tending to reduce feeding and retarding growth (Weinstein and Walters, 1981). Both juvenile and adult spot grow more slowly during winter (Dawson, 1958).
Abundance: Leiostomus xanthurus is one of the most common demersal fishes in coastal and estuarine waters of the Atlantic, and has both commercial and recreational importance. In some areas, the recreational catch often exceeds the commercial harvest (Hales and Van Den Avyle 1989).
Locomotion: Larval spot have limited swimming abilities measured at 0.25 - 1.0 m/s for brief periods (Lewis and Judy 1983). Adult spot have significantly slower swimming speeds than other estuarine species (Hettler 1979), with a typical speed of approximately 0.7 m/s (Rulifson 1977).
Small spot (less than 2.7 cm SL) are unable to orient in currents exceeding 15 cm/s. Larger spot, (to 5 cm SL) cannot maintain orientation when currents exceed 30 cm/sec (Hales and Van Den Avyle 1989).
Reproduction: Spot typically migrate offshore and spawn in the relatively deep water of the outer continental shelf, though some evidently spawn in both nearshore waters and estuaries (Dawson 1958; Lewis and Judy 1983). Ripe adults aggregate off beaches in fall and begin migration offshore, possibly migrating to more southern waters in the process (Pearson 1932). Spot may spawn repeatedly over several weeks (Hildebrand and Cable 1930), with some individuals remaining offshore after spawning (Pearson 1932; Wenner et al. 1979, 1980).
In the south Atlantic region of the U.S., spawning occurs from October through March, peaking in December and January (Townsend 1956; Lewis and Judy 1983; Warlen and Chester 1985). This is later than in mid-Atlantic waters and earlier than in the Gulf of Mexico, where spawning begins in December and peaks in January and February (Nelson 1969).
Most spot reach sexual maturity in the second year, but some require 3 years (Hales and Van Den Avyle 1989). Dawson (1958) and Music (1974) reported that spot measuring 170 -175 mm total length (TL) showed ripened gonads. However, other research (Hildebrand and Cable 1930; Gunter 1945; Townsend 1956) suggests sexual maturity is attained at somewhat larger size, between 185 - 210 mm TL. Music (1974) reported that males may reach maturity at slightly smaller sizes than do females, 170 mm TL for males vs. 205 mm TL for females.
Dawson (1958) estimated fecundity for spot at approximately 77,000 - 84,000 eggs per season.
Embryology: Eggs are pelagic and buoyant. Under laboratory conditions, eggs hatched at 20°C within 24 hours. Larvae absorb the yolk sac and oil globule within 5 days of hatching (Powell and Gordy 1980). Larvae are initially found in surface waters but become more demersal as they grow (Hildebrand and Cable 1930; Lewis and Judy 1983). Due to the limited swimming ability of larvae, it is believed that passive mechanisms (wind, Ekman transport, tides) are the primary transporters of larvae to the nursery habitats of estuaries and bays.
Larvae arrive at estuaries when they are approximately 10 - 24 mm standard length (SL) and 40 - 47 days old (Warlen and Chester 1985), typically in January (Hildebrand and Cable 1983; Lewis and Judy 1983), with recruitment peaking in February and March (Hildebrand and Cable 1983). Larvae continue to enter estuaries through June.
Postlarvae and smaller juveniles tend to congregate in shallow water areas of tidal creeks in estuaries for 3-6 months (Weinstein and Walters 1981). Thereafter, they tend to migrate to other estuarine habitats, and often migrate to deeper waters (Weinstein 1983; Weinstein and Brooks 1983; Rojas and Hackney 1984).
Warlen and Chester (1985) examined growth characteristics of larvae and juveniles and found that initial growth is rapid while larvae remain in offshore waters, presumably due to the abundance of plankton available. Growth then slows in the early period of estuarine residency, until approximately April. After metamorphosis to the juvenile stage, growth is again accelerated.
Temperature: Mass mortality of spot was observed at water temperatures of 5 - 10 °C, but larvae and postlarvae may be more tolerant of widely ranging temperatures than are older fish (Hildebrand and Cable 1930; Hodson et al. 1981a).
Under laboratory conditions (Hettler and Powell 1981) reported spawning occurred at 17-25°C. Spot embryos do not develop at temperatures below 14°C; however, larvae can tolerate temperatures as low as 5 °C. (Hettler and Clements 1978). Burton (1979) reported symptoms of cold stress in juveniles held at 5°C.
Upper thermal tolerance for postlarvae and juvenile spot is approx 35 °C, depending on the size and general condition of fish, as well as the temperature to which they have been acclimated. Generally, as acclimation temperatures increase, the critical thermal maximum also increases (Hodson et al. 1981a).
Salinity: Low salinity does not appear to be necessary for proper development and metamorphosis to the juvenile stage; however, it may affect survivorship of larvae (Powell and Gordy 1980). Perez (1969) found that spot tended to be more active under lab conditions when salinity changed quickly, suggesting that they may actively try to avoid areas where salinity levels change rapidly.
Dissolved Oxygen: Postlarval and juvenile spot have intermediate tolerance to hypoxic conditions compared to other estuarine species (Burton et al 1980). Exposure of 90 mm TL spot to 0.8mg/L for 96 hours resulted in 5% mortality; however, lowering the concentration to 0.6 mg/L resulted in 95% mortality.
Trophic Mode: Leiostomus xanthurus show two distinct feeding modes. Larvae are selective plankton feeders, while juveniles and adults are partly olfactory-dependent, benthic feeders that prey on infaunal and epibenthic invertebrates.
Preferred larval foods include ciliates, invertebrate eggs, and copepod nauplii. Individuals up to 25 mm SL feed primarily on copepods and ostracods (Hildebrand and Cable 1930). Upon metamorphosis, the diet changes to include insect larvae, polychaetes, harpacticoid copepods and other crustaceans (Hildebrand and Cable 1930; Townsend 1956; Hodson et al. 1981b); however, the juvenile diet can be flexible and often is reflective of prey availability in specific areas (Hales and Van Den Avyle 1989).
Chao and Musick (1977) reported that in Chesapeake Bay, prey for adult spot includes zooplankton and benthic infauna, with polychaetes most frequently observed in gut contents. Other prey types included amohipods, cumaceans, gastropods, nematodes, mysids, and copepods.
After growth to 10 - 15mm SL, larvae of all sizes feed diurnally (Govoni et al. 1983).
Competitors: Spot likely compete with other estuarine species; however little research has been undertaken in this area.
Habitats: Spot are common in coastal waters during the spawning season, and in estuaries and nearshore waters during other parts of the year. They are typically found over sandy or muddy bottoms in waters up to approximately 60 m deep.
Activity Time: Postlarvae feed most actively during daylight hours, with peaks in late morning (Kjelson et al. 1975). Juveniles switch to nocturnal feeding after metamorphosis, perhaps as a predator avoidance mechanism, or to avoid high daytime temperatures in shallow marshes (Hodson et al. 1981b). Adults tend to be nocturnal.
Predators: Predators of spot include silversides (Menidia spp.), which may affect postlarval distribution in estuaries (Weinstein and Walters 1981). Juveniles and adult spot are also preyed upon by many fishes, including striped bass, sharks, seatrout, bluefish, mackerels, gars, and flounders (Hollis 1952; Rozas and Hackney 1984).
Parasites: Parasites of spot include copepods of the genera Lernaeenicus and Ergasilus, as well as a marine leech, Myzobdella lugubris (Sawyer et al. 1975). Internal parasites include trematodes, microsporideans, and acanthocephalans (Sprague and Hussey 1980; Govoni 1983).
Fisheries Importance: In 2001, statewide landings in Florida were 352,786 pounds. Of this, approximately 90% of the statewide landings were made on the Atlantic coast of Florida; with the recreational fishery for spot accounting for 86% of the total (Murphy 2003). Commercial landings on the Atlantic are generally concentrated around Brevard, Indian River and Martin counties.
Before 1995, the commercial fishery for spot relied almost exclusively on gill nets. The ban on entangling nets enacted in late 1995 prompted a shift toward smaller gear such as cast nets and haul seines. As reflected in the reduced commercial landings since the rule went into effect, Florida's abolition of entangling gear use in July 1995 almost eliminated the traditional commercial fishery for spot. Reduced fishing pressure could result in higher and more stable recruitment in the future (McRae 1997b).
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