Spot, continued 



Fecundity : Fecundity ranges from 20,900 eggs in a 

 female with a standard length (SL) of 136 mm to 

 51 4,400 eggs in a 1 78 mm SL female (Sheridan et al. 

 1984). The spot appears to be a fractional spawner 

 capable of several spawning events during a single 

 season (Killam et al. 1992). 



Growth and Development 



Egg Size and Embryonic Development : Egg sizes 

 range from 0.72 to 0.87 mm (Lippson and Moran 1 974, 

 Johnson 1978, Ditty and Shaw 1994). 



Age and Size of Larvae : Larvae hatch in about 48 

 hours at 20°C at a size of 1 .6 to 1 .7 mm SL (Ditty and 

 Shaw 1 994). Fruge and Truesdale (1 978) collected 86 

 larval spot in coastal waters of Louisiana, ranging in 

 size from 1 .6 to 1 0.7 mm SL. Larvae can grow from 1 .6 

 mm SL to 17-19 mm in 90 days (Warlen and Chester 

 1985). In North Carolina's Cape Fear River estuary, 

 daily growth rates for larvae are 0.14 to 0.16 mm/day 

 (Weinstein and Walters 1 981 ). Increases in the rate of 

 daily growth have been demonstrated when high den- 

 sities of microzooplankton are present, particularly 

 when larvae and food are concentrated in waters that 

 are hydrographically discontinuous (Govonietal. 1985). 



Juvenile Size Range : Transformation to the juvenile 

 stage occurs at about 1 5 mm TL (Ditty and Shaw 1 994). 

 Growth rate varies with location, environmental factors 

 (Johnson 1978), and possibly age (Warren 1981). 

 Juveniles from the Gulf of Mexico grow at about 7-1 8.6 

 mm/month (Parker 1971, Ruebsamen 1972, Warren 

 1981, Warren and Sutter 1982). Spot grow rapidly in 

 their first year growing as much as 90 to 140 mm TL. 

 .Growth is slower during the second year, proceeding at 

 only 5.5 mm/month. 



Age and Size of Adults : Maturation occurs at the end of 

 the second year or early in the third year on the Atlantic 

 coast. In the Gulf of Mexico, some spot mature at age 

 I; males at 123 mm SL and females at 127 mm SL 

 (Sheridan et al. 1984). Spot are one of the smallest 

 members of the drum family (Shipp 1 986). In the Gulf 

 of Mexico it can grow up to 250 mm TL (Hoese and 

 Moore 1977), although it can reach up to 340 mm SL 

 in the northern parts of its range (Johnson 1978). 

 There is a pronounced sexual dimorphism in growth 

 rate with females growing more rapidly. Females also 

 become proportionally more abundant in the popula- 

 tion at a later age, and live longer than males. Overall, 

 this is a short-lived species that rarely attains a maxi- 

 mum age of 5 years, but usually only lives 2 to 3 years 

 (Hales and Van Den Avyle 1989, Mercer 1989). 



Food and Feeding 



Trophic Mode : The spot can be both an opportunistic 

 generalist or a selective predator depending on its 



developmental stage and food availability (Hales and 

 Van Den Avyle 1989, Killam et al. 1992). Larval and 

 postlarval spot are size-selective planktivores 

 (Livingston 1984, Mercer 1989, Govoni and Chester 

 1 990). Juveniles and adults are nocturnal, opportunis- 

 tic bottom feeders utilizing infaunal and epibenthic 

 invertebrates (Hales and Van Den Avyle 1989, Killam 

 et al. 1992). Feeding by juveniles appears to tidally 

 influenced, with most feeding occuring in marsh inter- 

 tidal zones during high tide when they can presumably 

 take advantage of the greater concentration of prey 

 items that occur there (Archambault and Feller 1 991 , 

 Killam et al. 1 992). Prey items within 2 to 3 mm of the 

 substrate surface are most susceptible to feeding 

 activities by juvenile spot. Adults feed on benthic fauna 

 by scooping and straining sediments through their gill 

 rakers to remove prey items and spitting out unwanted 

 material (Killam et al. 1992). 



Food Items : Food habits of the spot change with its 

 growth and development (Currin et al. 1984). Larvae 

 feed on zooplankton such as tintinnids, fish and inver- 

 tebrate eggs, bivalve veligers, copepod nauplii, and 

 postlarvae feed predominantly on copepods (Livingston 

 1 984, Mercer 1 989, Govoni and Chester 1 990). Feed- 

 ing appears to be influenced by visibility, size, and 

 motility of potential prey items (Govoni et al. 1985, 

 Govoni and Chester 1 990). Juveniles feed primarily on 

 crustaceans (especially copepods), molluscs, nema- 

 todes, and polychaete worms (Ruebsamen 1972, 

 Sheridan 1979, Levine 1980, Livingston 1984). In a 

 portion of Florida's Apalachicola Bay complex, the diet 

 of spot fell into two feeding patterns (Sheridan 1979). 

 Food items from shallow, low salinity, nearshore areas 

 consisted mostly of insect larvae, bivalves, and detri- 

 tus, while in deeper, higher salinity areas, it was 

 primarily polychaetes and harpacticoid copepods. 

 Adults most frequently consume polychaetes, amphi- 

 pods, bivalve and gastropod molluscs, cumaceans, 

 nematodes, mysids, and copepods (Hales and Van 

 Den Avyle 1989). Although some studies show that 

 spot will forage regardless of substrate type, evidence 

 suggests that muddy substrates are preferred over 

 sandy ones (Killam et al. 1992). The ability of spot to 

 sieve coarser sediment through their gill rakers may be 

 a limiting factor. 



Biological Interactions 



Predation : A study in the Cape Fear River estuary in 

 North Carolina found that silversides (Menidia sp.) and 

 killifish (Fundulus sp.) prey on larval and early juvenile 

 stage spot (Weinstein and Walters 1981). Other re- 

 ported piscine predators of spot from the U.S. Atlantic 

 coast include sand bar shark, silky shark, longnose 

 gar, striped bass, bluef ish, different species of seatrout, 

 king mackerel, and flounders (Dawson 1958, DeVane 

 1 978, Medved and Marshall 1 981 , Rozas and Hackney 



272 



