Life History of Hickory Shad in the St. Johns River, Florida

Abstract

Hickory shad Alosa mediocris spawn in rivers from Maryland to Florida, but little research has been published regarding their life history. We collected hickory shad in the St. Johns River, Florida, during five consecutive spawning years from 2000 to 2005. Hickory shad migrated upstream by December and remained in the river and its tributaries until March. Females were larger than males and accounted for 17.7% of the adults collected. All but one female examined were mature and contained yolked oocytes. No females had hydrated oocytes, but four had fresh postovulatory follicles (POFs , 24 h old), indicating a batch spawning pattern. Females with fresh POFs were collected from Shad Alley and the Wekiva and Econlockhatchee rivers, but otherwise the spawning grounds could not be delineated. Fish constituted over 97% of the diet by weight and were found in 11.5% of the stomachs examined. Scale and otolith ages produced the same age range, from 1 to 7 years. A test of symmetry did not detect systematic age differences between the two methods, although exact agreement was only 57%. Spawning marks on scales indicated that mature hickory shad ranged in age from 2 to 7 years and that most spawning individuals were age 3 or 4. Hickory shad are iteroparous, and fewer than 50% showed evidence of previous spawning. Our estimates of sex ratio, age distribution, and age at maturity differed from values measured in the 1970s by Williams et al. (1975). We are uncertain whether the later age at maturity in the early 2000s relative to the 1970s was due to a biological change or a difference in sampling methods between the two studies. There is an apparent latitudinal pattern in the timing of the spawning migration for hickory shad; individuals in more northerly rivers spawned later in the season than those in southern systems.

Population demographics of Hickory Shad (Alosa mediocris) during a period of population growth

“…The 57% agreement between scale and otolith ages in our study in the Albemarle Sound-Roanoke River watershed is similar to results reported by Harris et al (2007), who found a 57.3% agreement for fi sh from St. Johns River; 96% of the ages were in agreement of one year. Our study found no more than 2 years disagreement for any given fi sh.…”

“…However, we observed Hickory Shad in the Roanoke River (during this study) and Neuse River (Murauskas and Rulifson, 2011) with full stomachs, and Harris et al (2007) found similar trends in the St. Johns River population. To determine whether feeding or fat reserves were more important during the phase of inland spawning migration, we removed mesentery fat from the viscera and weighed it to the nearest 0.01 g. Food items removed from the stomach and intestine were identifi ed to the lowest practical taxon, enumerated, and weighed to the nearest 0.01 g. T-tests were used to test for signifi cant differences in mesentery fat between males and females and between fi sh collected in Albemarle Sound and fi sh collected in the Roanoke River.…”

“…The few literature references available on this topic indicate that Hickory Shad usually do not feed during the spring spawning migration (White and Curtis 17 ; Curtis 18 ; Perkins and Dahlberg, 1971;Pate, 1972;Harris et al, 2007). However, we observed Hickory Shad in the Roanoke River (during this study) and Neuse River (Murauskas and Rulifson, 2011) with full stomachs, and Harris et al (2007) found similar trends in the St. Johns River population.…”

“…Therefore, otoliths should be used whenever possible for aging Hickory Shad. The few published studies on age composition of Hickory Shad and other Alosa species generally show 1-3 dominant year classes (Street and Adams 15 ; Pate, 1972;Street et al 4 ; Kornegay, 1977;Winslow 19,20 ; NCDMF 21 ; Harris et al, 2007). In our study, ages 3 and 4 were the dominant age classes, with male Hickory Shad contributing the majority of the younger age classes (ages 2 and 3) and female Hickory Shad contributing the majority of the older age classes (ages 4-7) (Table 2).…”

“…Hickory Shad appear to be iteroparous south of Cape Hatteras as indicated by repeat spawners in the Neuse River (Pate, 1972;Hawkins 8 ), Altamaha River (Street, 1970), and St. Johns River (Harris et al, 2007). Because of the short life spans and limited number of spawning events (i.e., repeat spawning) exhibited by Hickory Shad and other Alosa species, successive years of poor recruitment could result in relatively quick population declines.…”