BRUNUAGE and MEADOWS: ATLANTIC STURGEON IN DELAWARE RIVER ESTUARY 



only 10% of those from Delaware Bay and 22% of 

 those taken in the upper tidal river. 



Length data were available for 97 Atlantic 

 sturgeon. Reported fork length (FL) for 1 1 speci- 

 mens were converted to total length (TL) with 

 the relationship FL = 0.878 TL -6.551, r =0.999, 

 calculated from measurements of 19 specimens. 

 Total length ranged from 457 to 2,000 mm (X = 

 885 mm; n = 45) for specimens taken in Delaware 

 Bay, from 128 to 1,431 mm (X= 863 mm; n = 48) 

 in the lower tidal river, and from 157 to 196 mm 

 (X= 176 mm; n = 4) in the upper tidal river (Fig. 

 3). Based on age-length data for the Hudson 

 River estuary (Dovel 1979), the probable age of 

 specimens taken in Delaware Bay ranged from 

 0+ to ca. 20+ and from 0+ to ca. 14+ in the lower 

 tidal river. Only age 0+ specimens were taken in 

 the upper tidal river. No individuals in spawning 

 condition were reported. 



5 r 



CE 

 UJ 



m 



Z> 



Figure 3. — Length-frequency distributions of Atlantic 

 sturgeon captured in three regions of the Delaware River 

 estuary, 1958-80. 



DISCUSSION 



Despite the limitations imposed by reliance on 

 incidental catch records, a number of generali- 

 zations regarding the Atlantic sturgeon in the 

 Delaware River estuary can be made. The data 

 strongly indicate that there is a viable population 

 of Atlantic sturgeon in the Delaware system 

 which utilizes different regions of the estuary to 

 varying degrees depending on season and life 

 stage. A definite pattern of seasonal movement 



within the estuary can be inferred. In early 

 spring substantial numbers of juvenile Atlantic 

 sturgeon occurred in the shallow waters of 

 Delware Bay; later in spring, abundance 

 increased in the lower tidal river and this 

 upstream movement continued through early 

 summer. This is similar to the pattern described 

 by Dovel (1979) for the Hudson River, i.e., 

 juvenile Atlantic sturgeon overwinter in the 

 deeper waters of the lower estuary and move up- 

 stream and inshore in spring in response to in- 

 creasing water temperature. However, in the 

 Delaware River estuary, juvenile Atlantic 

 sturgeon ranged to the the fall line at Trenton, 

 whereas in the Hudson River they were found 

 only to river km 145 (Kingston, N.Y.), some 100 

 km below the limit of tidal intrusion. 



During summer, Atlantic sturgeon were most 

 abundant in the lower tidal portion of the Dela- 

 ware River and probably use this region as a 

 foraging ground. Numbers in this reach de- 

 creased somewhat during August, the month of 

 maximum water temperature. Dovel (1979) 

 reported that Hudson River Atlantic sturgeon 

 seek cooler waters during summer and may 

 move south before water temperature peaks. In 

 the present study, however, no such movement to 

 Delaware Bay during August was evident, 

 although numbers in the bay increased slightly 

 in September. 



Abundance in the Delaware system decreased 

 in the upper and lower tidal river in September 

 and increased somewhat in Delaware Bay 

 during September through November, suggest- 

 ing a return to overwintering areas. Some indi- 

 viduals may have left the estuary at that time to 

 overwinter in the nearshore ocean. Interviews 

 conducted in 1978 and 1979 with commercial 

 trawl fishermen operating out of Ocean City, 

 Md., indicate that Atlantic sturgeon are 

 commonly taken near the mouth of Delaware 

 Bay in fall. Most of these fish are small, ranging 

 from 0.6 to 1.5 m long, with occasional captures 

 of larger individuals of 2.5-3.5 m. 



Evidence on occurrence of older juveniles in 

 the Delaware system disagrees with reports 

 from other systems. Murawski and Pacheco 

 (1977) reported that these fish emigrate from the 

 estuary when they reach 760-915 mm long and do 

 not return for a number of years until mature. 

 Dovel (1979) found that Atlantic sturgeon be- 

 tween about 800 mm (ca. age 5) and 1,300 mm TL 

 (ca. age 12) were rare in the Hudson River 

 estuarv and inferred that these individuals re- 



341 



