Secor et al.; Dispersal and growth of Aapensei oxynnchus 



805 



three most upstream sites (rkm 50, 36, and 24) showed a 

 significant pattern of downriver displacement (P<0.01) at 

 average ground speeds of 0.4 ±0.08 SE, 0.1 1 ±0.04 SE, and 

 0.08 ±0.02 SE km/day. respectively (Fig. 4). Fish released 

 at rkm 13 did not show a consistent up or downriver move- 

 ment (P>0.9). There were also significant differences in 

 dispersal patterns between fish released at different dates 

 within the same section. For instance, fish released 22 

 July at rkm 36, and 12 August at rkm 24 did not show a 

 consistent downriver dispersal pattern. 



The average probability of relocation tended to be higher 

 in the middle section of the river (0.46 ±0.071 SE) than 

 in the lower and upper sections, where average probabili- 

 ties of relocation were 0.30 ±0.06.5 SE and 0.28 ±0.064 SE, 

 respectively. However, such probabilities were not signifi- 

 cantly different from each other, as indicated by logistic 

 regression analysis {P=0.13). No significant correlations 

 were found between dissolved oxygen, water temperature 

 or salinity, and proportion of total relocations occurring 

 within a given section (P>0.11). Although no significant 

 correlation occurred between salinity and distribution of 

 fish relocations, most fish had left freshwater areas (0 to 

 1 ppt) within one week of being released. More than 90'7f 

 of later relocations occurred in the range 1 to 7 ppt. All 

 attempts to capture sturgeon where position of fish was 

 triangulated through biotelemetry were unsuccessful. In 

 25 bottom trawls and five gillnet deployments, only two 

 cultured juveniles were physically captured, one in a gill 

 net on 26 July (24 cm TL) and the other in an otter trawl 

 on 24 October (43 cm TL). 



During fall and winter (earliest capture 1 November 

 1996), fishermen captured juveniles as an incidental catch 

 in the mainstem of the Chesapeake Bay. Location of cap- 

 tures varied seasonally (Fig. 5). During fall and winter 

 months (November-March) most captures occurred in the 

 vicinity of the mouth of the Nanticoke River and north of 

 the Nanticoke River in the mainstem of Chesapeake Bay. 

 As winter progi'essed, sturgeon captures were concentrated 

 at upper Bay mainstem sites. The distribution of captures 

 tended to spread toward the lower Chesapeake Bay and 

 into tributaries dunng late winter (March) and spring 

 months, where several sturgeon were captured high up in 

 major tributaries (Patuxent, Potomac, Rappahannock, and 

 James rivers). Much of the shift in captures during spring 

 and summer may have been an artifact of delayed imple- 

 mentation of a reward program in Virginia (initiated Feb- 

 ruary 1997) and seasonal changes in fishing effort (see 

 "Discussion" section). In March 1997. two individuals were 

 captured outside of Chesapeake Bay in the Chowan River 

 (Albemarle-Roanoke estuary. North Carolina). 



The majority of juvenile sturgeon (60"^^ captured by 

 commercial fishermen were ensnared in drift or anchored 

 gill nets set for striped bass, white perch [Morone ameri- 

 cana). and catfish ^Ictalur-us pi/nctatiis. Ameiiiriis catusK 

 40% of the captures were from pound nets principally 

 set for menhaden [Brevoortia tyrannus). Gillnet captures 

 occurred most often between January and early March, 

 with a mean capture length (TL) of 61 cm ±5.6 SE. Pound- 

 net captures v/ere concentrated between April and late 

 June. Mean length for poundnet captures was 66 cm TL 



10 20 30 40 50 60 



Days after release 



Figure 4 



Relocation site (river kilometer) and mean trajectories 

 for fish fitted with ultrasonic devices and released at 

 different locations in the Nanticoke River. (A) release 

 site 1 (rkm 50), (B) release site 2 (rkm 36-38), (C) 

 release site 3 (rkm 24), and (D) release site 4 (rkm 13). 

 Star icons indicate release site. Other icons within a 

 graph indicate individual fish. Note that mean trajec- 

 tories have been corrected for autocorrelation within 

 individuals. 



±5.7 SE. Captured yearlings were kept for up to 2 days by 

 fishermen, prior to inspection by USFWS agents, by hold- 

 ing sturgeon in pens and tanks, or by tying them (by the 

 mouth or tail) to fixed structures in the water Juveniles 

 inspected by agents were all judged to be in good condition 

 and released without apparent harm to the fish. 



Overall, 89^ of stocked juveniles were taken incidentally. 

 Sixteen Floy-tagged juveniles (size class II) were multiple 



