Gizzard shad, continued 



Table 5.19. Relative abundance of gizzard shad in 

 31 Gulf of Mexico estuaries (Nelson et al. 1992, 



Relative abundance: 



Highly abundant 



® Abundant 



O Common 



V Rare 



blank Not present 



na No data available 



Life stage: 



A - Adults 

 S - Spawning 

 J - Juveniles 

 L - Larvae 

 E - Eggs 



Life Mode 



This is generally a pelagic fish occurring at or near the 

 surface of shallow, quiet waters for all life stages (Miller 

 1 960). Young-of-the-year gizzard shad form compact 

 schools, but in subsequent years aggregations occur 

 with no true schooling. An upstream spring "run" 

 occurs in rivers prior to the spawning season (Swift et 

 al. 1977). 



Habitat 



Type : The gizzard shad is nektonic in fresh to polyhaline 

 waters. It prefers areas with warm water and high 

 phytoplankton production, and occurs in the littoral and 

 limnetic regions of lakes and reservoirs, and in rivers, 

 canals and coastal bays. This species commonly 

 enters brackish and occasionally marine waters (Lee 

 etal. 1980). 



Substrate : This species is widely distributed over mud 

 bottoms, but also occurs over hard bottom lake shores. 

 It is taken over mud, vegetation, rubble, sand, gravel, 

 boulders, and bedrock (Nash 1950). 



Physical/Chemical Characteristics 

 Temperature: This species is not considered hardy, 

 and is susceptible to changes in temperature and low 

 dissolved oxygen (Manooch 1984). Juveniles and 

 adults have been collected from 5.0° to 34.9°C and 

 suffer high mortality rates when temperatures fall to 

 2.2°C. Northern populations are susceptible to cold- 

 induced winter kills (Bodola 1 966, Perret 1 971 , Jester 

 and Jensen 1 972, Juneau 1 975, Pineda 1 975, Tarver 

 andSavoie 1976). 



Salinity: Eggs, larvae and small juveniles are limited to 

 freshwater. Juveniles less than 40 mm are found in 

 1.1 %o or less (Renfro 1960, Swingle 1971). Larger 

 juveniles, usually greater than 70 mm TL, begin to 

 enter brackish and more saline waters with one being 

 collected at 41.3%o (Renfro 1960, Dunham 1972). 

 Although adults are euryhaline (2-33.7%=,), they are 

 rare in "pure saltwater" (Gunter 1942, Gunter 1945, 

 Perret 1 971 , Pineda 1 975). They prefer oligohaline to 

 mesohaline salinities with the greater abundance oc- 

 curring below 1 5%o. One study reported captures from 

 4 to 20%o (Wagner 1973). 



Dissolved Oxygen: The lowest reported dissolved oxy- 

 gen (DO) concentration where this species has been 

 collected is 4.6 parts per million (ppm) (Chambers and 

 Sparks 1959). 



Movements and Migrations As larvae, there is a gen- 

 eral movement from surface to midwater as size in- 

 creases. Juveniles slowly make their way to more 

 saline waters with age, but do not enter until about 70 

 mm TL. Adults are concentrated in deeper water 



149 



