Grant and Olney: Spawning of Morone saxatilis in Virginia rivers 



191 



10 20 30 10 



APRIL MAY 



Figure 8 



Spatial and temporal abundance (numbers/100 m :i ) 

 of striped bass eggs and larvae in the Rappahan- 

 nock River, 1982. River miles are nautical miles 

 above the river mouth. 



Peak larvai densities were recorded on the Rappa- 

 hannock River in 1982 during late April and early May 

 (Fig. 8). These densities were the highest observed in 

 our 3-year study of Virginia rivers. Modal lengths of 

 larvae were 5-6 mm NL until mid-May; all larvae from 

 21 May to the conclusion of sampling in June were at 

 least 8mm in length. In 1983, larvae from the early 

 May surveys were all less than 8 mm in length and at- 

 tained a maximum density of 103 larvae/100 m 3 . 



Discussion 



Tresselt (1952), Rinaldo (1971), McGovern and Olney 

 (1988), and this study constitute the only direct obser- 

 vations on striped bass eggs and larvae in major Vir- 

 ginia rivers. Striped bass spawning in Virginia rivers 

 occurred from early April through the first week or two 

 in May 1980-83, and within the first 40 km of tidal 

 freshwater, generally confirming earlier observations 

 of Tresselt (1952) and Rinaldo (1971). 



Tresselt (1952) observed spawning on the two major 

 rivers of the York River system, the Pamunkey River 

 (4-13 April 1950) and the Mattaponi River (13-30 April 

 1950). He found largest numbers of eggs 27 km above 

 the mouth of the Pamunkey and 14 km above the mouth 

 of the Mattaponi. Historic centers of successful spring 

 fishing for striped bass were in these tidal freshwater 

 rivers. Spawning in the Pamunkey River in 1966 oc- 

 curred 8-48km above West Point during 24 April-13 



May 1966 (Rinaldo 1971). Surveys of Virginia striped 

 bass spawning grounds in 1950 (Tresselt 1952) were 

 inadvertently somewhat late in the Chickahominy and 

 James rivers, but provide the only direct documenta- 

 tion of striped bass spawning prior to the present 

 study. He found only three eggs in 30 collections in the 

 Chickahominy River, 5-8 May 1950, and 57 eggs in 38 

 collections from the James River during 9-10 May. No 

 direct observations on striped bass larvae were made 

 prior to the present study. Use of the Rappahannock 

 River as a spawning site by striped bass was also 

 documented by Tresselt (1952), although his limited 

 survey (four sampling dates in May 1950) yielded only 

 five eggs. 



Temporal occurrence of striped bass spawning is 

 similar throughout Chesapeake Bay. In Virginia rivers, 

 peaks in spawning were sharp and of limited duration. 

 They occurred in the fourth week of April in York River 

 tributaries in both surveyed years (1980 and 1983) and 

 in the Rappahannock River in 1983; peak spawning was 

 a week earlier in the Rappahannock River in 1982. 

 Spawning in the James River was somewhat later, 

 peaking in the first week of May in both 1981 and 1983. 

 Peak spawning in this time-period is also typical for 

 the Potomac River (Setzler-Hamilton et al. 1981) and 

 in the upper Chesapeake Bay and Chesapeake and 

 Delaware Canal (Johnson and Koo 1975, Kernehan et 

 al. 1981). Although striped bass eggs were found in a 

 wide range of temperatures (8.0-21.2 c C), peak den- 

 sities were limited to rapidly rising temperatures in the 

 range 13.7-19.5°C and nearly always to freshwater. 

 Annual differences in time of spawning within a given 

 river system are most likely a result of differences in 

 temperature and the rate of vernal warming. 



Areas of peak spawning and the spatial extent of the 

 spawn are remarkably similar among years and river 

 systems, but differences can occur in years of drought. 

 The present data from the James River contrasted a 

 year of severe drought (1981) with one of near-average 

 rainfall (1983). The estimated streamflow from the 

 James River system into Chesapeake Bay during 

 March, April, and May averaged only 69,000cfs in 1981 

 compared with 180,000 cfs in 1983 (monthly summary 

 reports of estimated streamflows entering Chesapeake 

 Bay, 12/30/81 and 12/30/83, U.S. Geol. Surv., Towson, 

 MD). Peak egg production was displaced 15 km upriver 

 in 1981, in advance of encroaching saltwater, whereas 

 interannual differences in location of peak spawning 

 in the other river systems where drought was not a fac- 

 tor were insignificant (<2km). 



The tidal freshwaters of the Rappahannock River 

 were surveyed for striped bass eggs and larvae in the 

 spring of 1982, during production of what later was 

 determined to be the strongest year-class measured in 

 Virginia during the period 1971-82 (Colvocoresses 



