CHITTENDEN: PRESENT SPAWNING GROUNDS OF SHAD 



Table 1. — Summary of catch size in) and total lengths (mm) 

 of young American shad collected during July and August 1966. 



'Thie listed n v*/as estimated as about tialfttie total catch; large amounts of 

 detritus were mixed with the East Branch, Hancock catch, small fish were 

 hard to find and measurements were not taken. 



ripe female was captured as early as 15 May. The 

 gonads of some dead fish collected near Marcus 

 Hook on 21 and 23 May 1965 were nearly ripe. 

 Three females seined at Skinners Falls, N.Y., on 

 3 June 1964 had partially spawned. In the East 

 Branch near Hancock, I observed much spawning 

 from 10 to 17 June 1964; a few adults moved into 

 a spawning area there after dark on 1 July 1965, 

 suggesting that some spawning occurred then. 

 Most spawning probably occurred before late 

 June, however, because there was a great mortal- 

 ity of adults by then (Chittenden 1976). 



Spawning ended at a later date upstream than 

 it did downstream based upon the minimum sizes 

 of young captured (Table 1). Assuming a month 

 between hatching and transformation at about 25 

 mm (Walburg and Nichols 1967), spawning in 

 1966 ended about 7 June near Scudders Falls and 

 about 25 June near Riegelsvllle. At Belvidere, 

 spawning occurred at least until early June and 

 at Dingmans Ferry until 1 July. Spawning ended 

 near Tusten from 1 to 15 July and at Lordville 

 from 15 July to 1 August. Length frequencies of 

 young in July and August 1966 (Chittenden 1969) 

 also show that spawning ended later upstream 

 than it did downstream. However, the spawning 

 period probably varies slightly between years and 



at different locations depending upon spawning 

 stimuli. 



The spawning period is apparently prolonged 

 for individual fish. The ovaries of females cap- 

 tured near Hancock during June 1964 varied in 

 size, many ovaries being about one-third or two- 

 thirds the size of those from prespawning fish cap- 

 tured at Lambertville. This suggests prolonged 

 spawning of individuals as Lehman (1953) con- 

 cluded from egg diameter measurements. 



BEHAVIOR DURING 

 THE SPAWNING PERIOD 



During the day, behavior depended upon the 

 habitat occupied. The nontidal Delaware consists 

 of a sequential arrangement of shallow swift 

 riffles and slow-moving deep pools. Shad prefer- 

 red pools but were frequently observed in riffles 

 about 0.3 m deep. Schools offish circled slowly in 

 the pools but often formed a V in riffles. The point 

 of the V headed upstream or in the direction of 

 travel and left a readily observed wake. When the 

 school was stationary and facing upstream, the 

 fish at the point of the V moved to the rear after 

 about 30 s. The fish immediately behind these 

 leaders then moved to the point. This behavior 

 spreads energy expenditure among all members 

 of the school and may conserve energy as would 

 the preference for pools. Both may be important 

 to survival. Weight loss during the spawning 

 migration is high (Leggett 1972; Chittenden 

 1976), and starvation causes a large mortality on 

 the Delaware River spawning grounds (Chitten- 

 den 1976). 



Adults were observed after dark in the shal- 

 lows by using a pole to suspend a lantern high in 

 the air. The large schools typical of the day seem 

 to disperse during the evening spawning period, 

 because only one to three fish were usually ob- 

 served. Several times a behavior was observed 

 which may have been the spawning act: a smaller 

 fish (male?) lined up on either side of a larger fish 

 (female?) bringing their vents in close proximity 

 while swimming; a brief splashing coincident 

 with a rattling sound occurred at or near the sur- 

 face; and the fish separated after a few seconds. 

 Splashing and rattling noises were continually 

 heard outside the lighted area. This behavior was 

 only witnessed after dark, and it occurred in 

 water as shallow as about 150 mm. Plankton nets 

 were not available to collect fresh eggs to confirm 



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