Investigations of juvenile shortnose and Atlantic sturgeons in the lower tidal Delaware River.
KEY WORDS: juvenile Acipenser brevirostrum; juvenile Acipenser oxyrinchus oxyrinchus; Delaware River
Shortnose sturgeon (Acipenser brevirostrum) and Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) co-occur in large rivers and estuaries along the east coast of North America from southern Canada to Florida. The Delaware River historically supported populations of both species (Cope, 1883; Bean, 1893; and Cobb, 1900) and, in the 19th century, was the location of the largest and most profitable Atlantic sturgeon fishery on the East Coast (Ryder, 1888). The abundance of both sturgeons declined in the Delaware River and throughout their ranges in the late 19th and early 20th centuries as a result of overexploitation, water pollution, and habitat modification. The shortnose sturgeon was placed on the Endangered Species List in 1967 and is currently protected under the Endangered Species Act of 1973, as amended. The harvest of Atlantic sturgeon is prohibited in all U.S. waters (Spear, 2007) and the species is being considered for listing under the Endangered Species Act (Atlantic Sturgeon Status Review Team, 2007).
Sturgeon research in the Delaware River, while considerable, has focused primarily on adult (total length (TL) > 55 cm; Bain, 1997) shortnose sturgeon (Brundage and Meadows, 1982a; Brundage, 1986; Hastings et al., 1987; O'Herron et al., 1993; ERC, 2006a, b) and subadult (i.e., older juvenile, 50-149 cm TL; Bain, 1997) Atlantic sturgeon (Brundage and Meadows, 1982b; Lazzari et al., 1986; Shirey et al., 1997). The purpose here is to fill a gap in our understanding of juvenile sturgeons in the Delaware River. The specific objectives here are to present the results of 1) a netting survey to determine the occurrence and relative abundance of juvenile sturgeon in the lower tidal Delaware River and 2) an investigation of the movements of juvenile sturgeon using acoustic telemetry.
The tidal Delaware River extends from the fall line at Trenton, NJ (river km 214.5) (river kilometer references based on DRBC, 1969) to the head of Delaware Bay (river km 77.6) (Fig. 1). The river above Philadelphia, PA is fresh water (salinities of 0-0.5 [per thousand]) year round. Below Philadelphia the river evidences an oligohaline to mesohaline gradient (salinities of 0.5-18 [per thousand]), where salinity varies on seasonal and daily scales with freshwater inflow, tidal stage, and local meteorological conditions (Cronin et al., 1962). Water temperature within the tidal river varies annually from 0[degrees]C in mid-winter to over 30[degrees]C in summer (Pulis et al., 1973). Tides in the Delaware River are semidiurnal with a period of 12.42 hours and average amplitude of about 1.9 m. Maximum tidal currents typically reach speeds of 1.0-1.3 m/sec (Pulis et al., 1973). A dredged navigation channel extends from Trenton seaward through the tidal river. Bottom substrate throughout most of the tidal river is fine-grained (silt, sand, and clay), although larger substrates ranging from gravel to bedrock outcrops occur in some areas (Sommerfield and Madsen, 2003). The landscape adjacent to the tidal Delaware River is mostly urbanized and industrialized.
Monthly sampling for juvenile sturgeon was performed with anchored gill nets and trammel nets during May 2005 through December 2006 as part of environmental studies for a proposed riverside facility in Logan Township, NJ. The gill nets were 100 m long and 1.8 m deep, consisting of 33-m panels of 2.5-, 5.1-, and 7.6-cm stretch monofilament nylon mesh. The trammel nets were 50 m long and 1.8 m deep, consisting of two outer panels of 60.8-cm stretch multifilament nylon mesh and an inner panel of 2.5-cm stretch multifilament nylon mesh. Nets were set at three stations on the New Jersey side of the river between river km 119-126. Three nominal depth ranges were sampled at each station; "shallow" (<3.0 m at mean low water), "intermediate" (3.0-6.1 m), and "deep" (>6.1 m). A gill net and a trammel net were set at each of the sampled depth ranges. Supplemental gill net sampling, specifically to collect sturgeon for acoustic tagging, was performed in May, June, and September-November 2006.
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Water depth during net deployment was measured with a Techsonic Industries Hummingbird 100SX digital depth finder. Surface and bottom water temperature, dissolved oxygen concentration, specific conductance, and salinity were measured for each gill net-trammel net pair using a Yellow Springs Instrument Company (YSI) Model 85 handheld meter.
Sturgeons were removed from the nets and placed in an out-board live car or an on-board tank containing river water at ambient temperature and dissolved oxygen levels. Sturgeon were measured for fork length (FL) and total length (TL) to the nearest millimeter, weighed to the nearest gram, and tagged with a numbered T-bar tag (Floy Tag and Manufacturing, Inc.) and/or a Passive Integrated Transponder (PIT) tag. The PIT tags were Destron 14 mm tags activated at a frequency of 125 kHz. Non-target fish collected in the nets were identified and enumerated, and a random sample of up to 10 individuals per species per collection were measured for total length.
All sampling and handling of sturgeon followed established protocols (Moser et al., 2000) and were performed in accordance with Permit to Take Endangered Species No. 1486, issued by the National Marine Fisheries Service (NMFS).
An acoustic transmitter was surgically implanted in the abdomen of selected juvenile sturgeon collected during May-December 2006. Transmitters of two sizes manufactured by VEMCO (Shad Bay, Nova Scotia) were used in this study: models V9-6L (length-20 mm; diameter-13 mm; weight in air-3.3 g) and V13P-1H (length-44 mm; diameter-13 mm; weight in air-12.4 g). Transmitter weight comprised 0.63-1.34% of the recipient sturgeon's body weight. Sturgeon for acoustic tag implantation were anesthetized using MS-222 (dose 50 mg/L) and then held upside down in a cradle where the gills were perfused with aerated flowing water. A sterile scalpel was used to make a small longitudinal abdominal incision and a transmitter was inserted into the body cavity. The incision was closed with interrupted sutures of 3-0 polydioxanone (PDS) and treated with povidone iodine (10 percent solution) to prevent infection. Post surgery fish were held in an aerated holding tank and released upon recovery from anesthesia. The surgical procedure required approximately five minutes to complete, with a total holding time (surgery plus recovery) of 15 minutes or less per individual.
Each acoustic transmitter was coded with a unique pulse series/ tag number and pulsed at 69.0 kHz. The tags were programmed to transmit at random intervals ranging from 20-60 seconds. Calculated battery life was 55 days for the V9-6L tags and 120 days for the V13P-1H tags, although actual tag life proved to be longer. The V13P-1H tags telemetered depth (0.3 m resolution) in addition to their identification codes. The transmission ranges of the V9-6L and V13P-1H tags were approximately 300 and 600 m, respectively.
The movements of acoustically tagged sturgeon were monitored using a network of 54 VEMCO VR2 single-channel receivers, deployed on U.S. Coast Guard aids to navigation from the upper tidal Delaware River at Trenton to the mouth of Delaware Bay, in the eastern Chesapeake and Delaware (C&D) Canal, and in the Elk River, MD near the western terminus of the C&D Canal (Fig. 1). The receiver network was established and cooperatively maintained by Environmental Research and Consulting, Inc. (ERC) and Delaware State University (DSU).
Acoustic transmissions were decoded by the receiver and stored in its flash memory, which had a capacity of 300,000 detections. The data stored by the receiver included receiver identification number, transmitter identification number, date/time of signal detection, and the number of detections received during the period the sturgeon was present. Data from the V13P-1H sensor tags also included the depth of the tag. Records of the occurrence of each tagged sturgeon were extracted using the "pinger search" data processing option of the VR2 receiver software. Extracted data were then compiled in EXCEL spreadsheets for further analysis. Data extraction was conducted at a time scale of hours for location and minutes for depth.
A total of 209 gill net (894.2 net-hours) and 186 trammel net (786.8 net hours) collections were made in the Marcus Hook, PA to Wilmington, DE reach of the Delaware River during May 2005 through December 2006. Ten juvenile shortnose sturgeon and six juvenile Atlantic sturgeon were captured (Table 1). Relative to the total catch of 6,223 specimens of 29 fish species, juvenile shortnose sturgeon ranked 18th (0.16%) and juvenile Atlantic sturgeon ranked 21st (0.10%).
Juvenile Shortnose Sturgeon
Juvenile shortnose sturgeon were collected in all months except February, March, and April. Seven of the shortnose sturgeon were taken by gill net and three were collected by trammel net. Shortnose sturgeon ranged from 311-566 mm in total length, 267-483 mm in fork length, and 120-960 g in weight. All of the shortnose sturgeon were collected in "deep" sets at depths of 8.1-15.2 m. Shortnose sturgeon were collected at water temperatures ranging from 3.9-28.7[degrees]C, dissolved oxygen concentrations ranging from 4.9-13.2 mg/L, specific conductances ranging from 98-161 [micro]S/cm, and salinities ranging from 0.0-0.1[per thousand] (Table I).
Four juvenile shortnose sturgeon were tagged with acoustic transmitters (Table II). These fish were detected over 25-141 km of the river ([bar.x] = 62.0 km) during periods ranging from 100-185 days ([bar.x] = 136.8 days). Mean daily movement ranged from 4.1-7.3 km and maximum daily movement ranged from 14-40 km. Acoustically tagged shortnose sturgeon evidenced short distance roving behavior, probably indicative of foraging, as well as longer-distance directed movements suggestive of seasonal migration. Shortnose sturgeon 2951, whose tag was active during late spring and summer, utilized a 29 km reach of the lower tidal river between Chester, PA (river km 134) and Deepwater, NJ (river km 105) (Fig. 2a). The three shortnose sturgeon whose tags were active during some or all of the winter evidenced different patterns of movement. Shortnose sturgeon 171 spent the fall and most of the winter between Deepwater and upper Delaware Bay (river km 70). In mid-March this fish moved upriver and ranged between Marcus Hook and Philadelphia (river km 123-154). In late March it moved rapidly to the upper tidal river and was last detected in early April by the most upriver receiver (river km 211) at Trenton (Fig. 2b). Shortnose sturgeon 171 was tagged with a depth-sensing transmitter. Depths recorded for this fish (n=1,979 measurements) ranged from 2.6-19.1 m and averaged 10.8 m (Fig. 3). Shortnose sturgeon 2950 evidenced a more localized movement pattern and spent the fall and early winter within a 25 km reach of the river between Deepwater and Marcus Hook (Fig. 2c). Shortnose sturgeon 2953 spent mid-December through mid-January in the Philadelphia area between river km 154-163. It then moved downriver to the Marcus Hook area, remaining there until early April. During early April through early May, this fish made several rapid upstream-downstream movements between Philadelphia and Wilmington (Fig. 2d).
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Juvenile Atlantic Sturgeon
Juvenile Atlantic sturgeon were collected in July, August, and September (Table I). All were taken by gill net. Atlantic sturgeon ranged from 555-712 mm in total length, 474-610 mm in fork length, and 740-1,660 g in weight. Five of the Atlantic sturgeon were taken in "deep" sets (10.7-14.5 m) and one was collected in the "intermediate" depth stratum (4.6 m). Atlantic sturgeon were collected at water temperatures ranging from 20.6-29.1[degrees]C, dissolved oxygen concentrations ranging from 4.8-5.8 mg/l, specific conductances ranging from 102-163 [micro]S/cm, and a salinity of 0.0[per thousand] (Table I).
Atlantic sturgeon 170 was tagged with a depth-sensing transmitter in late September that was detected through November (46 days). This fish moved an average of 7.7 km/day and a maximum of 52.0 km/day (Table II). It utilized a 111 km reach of the estuary between Marcus Hook and lower Delaware Bay, and spent most of its time in the vicinity of Artificial Island (river km 83). In early November, this sturgeon moved rapidly from the lower tidal river (river km 110) to lower Delaware Bay (river km 19), where it was last detected (Fig. 4). It was briefly detected in the eastern end of the C&D Canal just before it moved down bay. Depths recorded for this sturgeon (n=589 measurements) ranged from 2.6-16.0 m and averaged 11.7 m (Fig. 5).
Two of the juvenile Atlantic sturgeon collected in this study were subsequently recaptured in eastern Long Island Sound, more than 560 km from their original capture location (Thomas Savoy, Connecticut Department of Environmental Protection, personal communication). One of these was tagged on September 23, 2005 and recaptured on June 27, 2007, having been at large for 642 days, grown 335 mm in total length, and gained 3,060 g. The other was tagged on August 17, 2005 and recaptured on September 23, 2008. It had been at large for 1,133 days, grown 419 mm in total length, and gained 4,290 g.
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This study suggests juvenile Atlantic and shortnose sturgeons in the Delaware River do not segregate on the basis of salinity, at least not within the sampled zone of the lower tidal river. All of the juvenile Atlantic and shortnose sturgeon in this study were captured in fresh water. Hatin et al. (2007) found juvenile Atlantic sturgeon in fresh or very low salinity water close to the salt wedge boundary. In contrast, Haley et al. (1996) found juvenile Atlantic sturgeon predominantly in mesohaline waters (3-16 [per thousand]) on the downstream side of the salt wedge, while juvenile shortnose sturgeon occurred upstream in fresh water. Dadswell (1979) reported similar segregation on the basis of salinity in the St. John River, with juvenile Atlantic sturgeon being most abundant in higher salinity (<3 [per thousand]) waters.
Juvenile Shortnose Sturgeon
This study found juvenile shortnose sturgeon occurring in the Wilmington to Marcus Hook (approximately river km 110-130) reach of the lower tidal Delaware River year-round. During summer, higher salinity below Wilmington and lower dissolved oxygen concentrations (<3 mg/L) in the Philadelphia area may bound the region of the lower river that can be utilized by juvenile shortnose sturgeon. Laboratory studies indicate that juvenile shortnose sturgeon are sensitive to low dissolved oxygen concentrations (Campbell and Goodman, 2004) and higher salinities (Jarvis et al., 2001). Collins et al. (2002) reported that the tolerance of juvenile shortnose sturgeon to higher salinity decreased as water temperature increased.
The observed movements of acoustically tagged individuals in this study suggest that juvenile shortnose sturgeon broaden their distribution in fall and winter, and may use the entire lower tidal Delaware River from Philadelphia to below Artificial Island for overwintering. None of the juvenile shortnose sturgeon reported herein utilized the primary adult overwintering area located in the upper tidal river between Newbold Island and Trenton (O'Herron et al., 1993). Present-study data suggest that the juvenile shortnose sturgeon in the Delaware River overwinter in a dispersed fashion and not in the dense aggregations typical of adults (O'Herron et al., 1993).
Hastings (1983), who conducted targeted sturgeon sampling in the Delaware River from Philadelphia to Trenton, reported the capture of 34 juvenile shortnose sturgeon, mostly from the upper tidal river near Bordentown. More recent records include incidental collections of single juvenile shortnose sturgeon near the mouth of Oldmans Creek, NJ (river km 123.9) in August 2004 and at the mouth of Crosswicks Creek, NJ (river km 205.9) in September 2005 (Mark Boriek, NJ Division of Fish and Wildlife, personal communication). These records combined with the results of this study indicate that juvenile shortnose sturgeon may occur over a large portion of the tidal Delaware River. This is consistent with studies in the St. John (Dadswell, 1979), Connecticut (Kynard, 1997), and Hudson (Bain, 1997) Rivers reporting that juvenile shortnose sturgeon disperse widely through the tidal freshwater and seasonally brackish river zones.
Most of the shortnose sturgeon collected in the present study may have been from the same year class. Based on the length-at-age relationships for juvenile shortnose sturgeon developed by Hastings (1983), the shortnose sturgeon collected during June 2005 through January 2006 (267-343 mm FL) were likely age 1 or 2, while four of the five specimens collected during May through December 2006 (391-410 mm FL) were probably age 2 or 3. A recent study in the Hudson River (Woodland and Secor, 2007) showed that shortnose sturgeon year class strength is very variable and that a few successful year classes may account for a substantial portion of the population.
The largest shortnose sturgeon collected in this study (483 mm FL) was probably age 4. This fish (acoustic tag code 171) evidenced rapid and directed movement to the upper reach of the tidal river in early spring 2007, a movement pattern typical of spawning adults (ERC, 2006a). This sturgeon was within the length-at-maturity range (45-55 cm FL) given by Dadswell et al. (1984), although maturing gonads were not evident when the acoustic tag was surgically implanted in October 2006.
All of the shortnose sturgeon captured during this study were from the "deep" depth stratum, where nets were set in the deepest water available. This is consistent with other river systems, where juveniles are generally associated with deep channel habitats (Pottle and Dadswell, 1979; Haley et al., 1996; Bain, 1997; Kynard, 1997). The telemetry data for shortnose sturgeon 171 also indicated a preference for deeper water, although depths as shallow as 2.6 m were recorded. It cannot be determined from the telemetry data whether this fish was actually in shallow water or was swimming in the upper water column. McCleave et al. (1977) reported that telemetered adult shortnose sturgeon in Montsweag Bay, ME frequently occurred in shallow water and often swam across deeper channels at depths of <2 m.
Juvenile Atlantic Sturgeon
The juvenile life stage of Atlantic sturgeon is protracted and includes an initial riverine (estuarine) phase and a later marine phase (Bain, 1997). Bain (1997) defined three intervals for Atlantic sturgeon juveniles in the Hudson River. Early juveniles are approximately 2-44 cm FL and 0.08-2 years old, intermediate juveniles are 45-63 cm FL and 3-6 years old, and late juveniles are 64-134 cm FL and 6-11 years old. Based on Bain's classification five of the Atlantic sturgeon captured during this study were intermediate juveniles and one other was a late juvenile. Burton et al. (2005) captured a 34.2 cm FL early juvenile Atlantic sturgeon by gill net in the Marcus Hook area in February 2005 while none were captured during this study. The absence of early juveniles in present-study collections may simply reflect the very low abundance of this life stage. Atlantic sturgeon stocks are reported to be near historically low levels throughout their range (Atlantic Sturgeon Status Review Team, 2007).
The use of anchored gill and trammel nets, which are passive fishing methods, may have affected sampling of early juvenile Atlantic sturgeon. Two recent studies suggest that active fishing methods, such as trawling (Hatin et al., 2007) or drift gill netting (McCord et al., 2007), may be more effective in capturing early juveniles than passive methods. In contrast, Haley et al. (1996) and Sweka et al. (2007) were successful in collecting early juveniles using anchored gill nets. Given these contradictory reports, it is uncertain whether early juvenile Atlantic sturgeon were effectively sampled in the present study. From a practical perspective, the use of active bottom fishing techniques in the study area would likely have been ineffective because of the numerous snags.
Juvenile Atlantic sturgeon were captured only during summer and fall, and the acoustically tagged Atlantic sturgeon evidenced directed movement from the lower tidal river to lower Delaware Bay in early November. This is consistent with the generalized pattern of upstream movement of juvenile Atlantic sturgeon into the seasonally brackish and tidal freshwater regions of the river in spring-summer and downstream movement to overwintering areas in the lower estuary or near shore ocean in fall-winter inferred from other studies in the Delaware estuary (Brundage and Meadows, 1982b; Lazzari et al., 1986; Shirey et al., 1997) and the Hudson River (Dovel and Berggren, 1983; Bain, 1997). A component of the juvenile Atlantic sturgeon population in the Delaware River may overwinter in tidal fresh water, as evidenced by the collection of an early juvenile in the lower tidal river in February by Burton et al. (2005) and the capture of multiple juveniles in the upper tidal river during December through February by Lazzari et al. (1986) and O'Herron (unpublished data). Based on the lengths-at-age presented in Dovel and Berggren (1983), Lazzari et al. (1986), and Shirey (1996), the Atlantic sturgeon collected in this study were probably ages 2-6. Dovel and Berggren (1983) reported that Atlantic sturgeon are resident in the Hudson River for up to 6 years, but may leave the estuary as young as age 2.
Five of the juvenile Atlantic sturgeon taken in the present study were collected from the "deep" depth stratum and one was collected from the "intermediate" depth stratum. The data from the acoustically tagged Atlantic sturgeon also reflected a preference for deeper water, although depths as shallow as 2.6 m were recorded for this fish. The apparent affinity of juvenile Atlantic sturgeon for deeper water is consistent with earlier reports for the Delaware River (Lazzari et al., 1986; Shirey, 1996) and other rivers (Pottle and Dadswell, 1979; Haley et al., 1996; Bain, 1997; Sweka et al., 2007). Hatin et al. (2007) reported that age 2 Atlantic sturgeon in the St. Lawrence estuary used deeper water (6-10 m) close to a channel, but did not use the deepest water available. Moser and Ross (1995) reported that juvenile Atlantic sturgeon in the lower Cape Fear River, NC typically preferred water >30 m deep, although some telemetered individuals swam within 2 m of the surface.
This study provides preliminary data on the seasonal and spatial utilization of the lower tidal Delaware River by juvenile shortnose and Atlantic sturgeons. It also demonstrates that acoustic telemetry can provide insights into sturgeon movements which could not feasibly be obtained using traditional collection methods. It is recommended that further studies using acoustic telemetry be performed to refine understanding of the occurrence, movements, and specific habitat associations of juvenile sturgeons in the Delaware River. It is especially urgent that such study not be delayed in the instance of the Delaware River estuary Atlantic sturgeon stock whose young are few and their habitat use poorly known.
Aspects of this study were funded by the National Marine Fisheries Service (NMFS), Protected Resources Division, and the NJ Division of Fish and Wildlife, Bureau of Freshwater Fisheries. The authors thank Mary Colligan, Julie Crocker, and Dana Hartley of NMFS; and Mark Boriek, Lisa Barno, and Jeanette Bowers-Altman of the NJ Division of Fish and Wildlife for their interest in, and support of, this research. We thank Dave Blaha, Carol Young, and Jason Willey of Environmental Resources Management for technical assistance; and Dewayne Fox, Phil Simpson, and Naeem Willet of Delaware State University for their cooperation in maintaining the acoustic receiver network. Finally, we thank two anonymous reviewers for their constructive comments on the manuscript.
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HAROLD M. BRUNDAGE, III AND JOHN C. O'HERRON, II
ENVIRONMENTAL RESEARCH AND CONSULTING, INC., KENNETT SQUARE, PA 19348, HBRUND1124@AOL.COM AMITRONE O'HERRON, INCORPORATED, CORNWALL, PA 17016
Table I. Juvenile Sturgeon Collected in the Lower Tidal Delaware River, May 2005-December 2006. DATE LOCATION RIVER GEAR (a) DEPTH KILOMETER (M) Shortnose Sturgeon 6/24/2005 Marcus Hook anchorage 125.7 GN 11.6 7/22/2005 Wilmington 119.5 TN 9.4 8/24/2005 Marcus Hook anchorage 125.7 GN 15.2 9/22/2005 Marcus Hook anchorage 125.7 TN 12.8 11/12/2005 Wilmington 119.5 TN 8.1 1/8/2006 Marcus Hook anchorage 129.8 GN 14.9 5/17/2006 Marcus Hook anchorage 129.8 GN 14.6 10/2/2006 Wilmington 114.8 GN 9.4 10/12/2006 Marcus Hook anchorage 125.7 GN 14.2 12/11/2006 Marcus Hook anchorage 129.8 GN 14.5 Atlantic Sturgeon 7/22/2005 Wilmington 119.5 GN 10.7 8/17/2005 Marcus Hook anchorage 129.8 GN 14.0 9/23/2005 Marcus Hook anchorage 129.8 GN 13.9 9/23/2005 Marcus Hook anchorage 129.8 GN 13.9 8/8/2006 Wilmington 119.5 GN 4.6 9/21/2006 Marcus Hook anchorage 129.0 GN 14.5 Mean 11.9 TOTAL FORK WE1GHT WATER DISSOLVED LENGTH LENGTH (G) TEMP. OXYGEN (MM) (MM) ([degrees]C) (MG/L) Shortnose Sturgeon 6/24/2005 311 268 200 24.5 6.5 7/22/2005 327 286 125 28.7 5.3 8/24/2005 367 311 180 27.7 5.0 9/22/2005 311 267 120 25.9 4.9 11/12/2005 386 343 260 11.9 8.7 1/8/2006 391 338 240 3.9 13.2 5/17/2006 454 391 460 17.6 6.8 10/2/2006 566 483 960 20.1 7.3 10/12/2006 463 398 420 18.7 6.9 12/11/2006 491 410 520 8.0 10.4 406.7 349.5 348.5 18.7 7.5 Atlantic Sturgeon 7/22/2005 677 574 1650 28.7 5.3 8/17/2005 631 543 1210 29.1 4.8 9/23/2005 555 474 740 25.9 5.3 9/23/2005 564 517 1000 25.9 5.3 8/8/2006 679 574 1540 28.9 5.7 9/21/2006 712 610 1660 20.6 5.8 636.3 548.7 1300.0 26.5 5.4 SPECIFIC SALINITY ACOUSTIC CONDUCTANCE (960) TAG ([micro]S/CM) NO. Shortnose Sturgeon 6/24/2005 123 0.1 -- 7/22/2005 154 0.1 -- 8/24/2005 154 0.1 -- 9/22/2005 161 0.1 -- 11/12/2005 120 0.1 -- 1/8/2006 101 0.1 -- 5/17/2006 104 0.1 2951 10/2/2006 134 0.1 171 10/12/2006 108 0.1 2950 12/11/2006 98 0.0 2953 125.7 0.1 Atlantic Sturgeon 7/22/2005 154 0.1 -- 8/17/2005 127 0.1 -- 9/23/2005 163 0.1 -- 9/23/2005 163 0.1 -- 8/8/2006 108 0.1 -- 9/21/2006 102 0.1 170 136.2 0.1 (a) Gear GN=gill net TN=trammel net Table II. Data for Acoustically Tagged Juvenile Sturgeon in the Lower Tidal Delaware River, May, 2006-May 2007. ACOUSTIC TAG DATE OF DATE OF DETECTION TAG NO. TYPE FIRST LAST PERIOD DETECTION DETECTION (DAYS) Shortnose Sturgeon 2951 V9-6L 5/17/2006 8/24/2006 100 171 V13P4H 10/2/2006 4/4/2007 185 2950 V9-6L 10/12/2006 2/2/2007 114 2953 V9-6L 12/11/2006 5/7/2007 148 Atlantic Sturgeon 170 V13P-1H 9/21/2006 11/5/2006 46 DAILY MOVEMENT ACOUSTIC RANGE OF (KM/DAY) TAG NO. RIVER TRAVERSED MEAN MAX (KM) Shortnose Sturgeon 2951 29 5.0 25.0 171 141 7.3 31.0 2950 25 4.1 14.0 2953 53 4.1 40.0 Atlantic Sturgeon 170 111 7.7 52.0
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|Author:||Brundage, Harold M., III; O'Herron, John C., II|
|Publication:||Bulletin of the New Jersey Academy of Science|
|Date:||Jun 22, 2009|
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