# Atlantic sturgeon in the Delaware River: contemporary population status and identification of spawning areas

Completion Report: Award NA05NMF4051093

Philip C. Simpson Delaware State University Department of Agriculture and Natural Resources 1200 N. Dupont Hwy. Dover, DE 19943 (302) 284-8587 philchristiansimpson@yahoo.com Dewayne A. Fox* Delaware State University Department of Agriculture and Natural Resources 1200 N. Dupont Hwy. Dover, DE 19943 (302) 857-6436 dfox@desu.edu2 Introduction The Atlantic sturgeon ( Acipenser oxyrinchus oxyrinchus ) is one of 27 species within the family Acipenseridae and one of nine species/subspecies extant in North American waters (Cech and Doroshov 2004). A tlantic sturgeon historically occupied all major river systems along the Atlantic coast between Canada (Bachus 1951) and Florida (Vladykov & Greely 1963), with the Delaware Ri ver historically s upporting the largest population (Secor and Waldman 1999). Atlantic sturgeon are anadromous with spawning in the southern portion of their range typi cally occurring in the early spring months followed by a general trend of later spawni ng times in northern rivers (Smith and Clugston 1997). The adhesive eggs are depos ited on rocky or hard-b ottom substrate and fertilized externally (Smith et al. 1980). Th e Atlantic sturgeon is a slow maturing fish (females reach sexual maturity at 16 years or older, males at least 12 years within the mid-Atlantic coast region (Van Eenennaam et al. 1996)). Fecundity of female Atlantic sturgeon is estimated to range from 4 00,000 – 8 million eggs (Smith et al. 1982, Van Eenennaam and Doroshov 1998, Dadswell 2006) w ith a spawning interval of 2-6 years (Vladykov and Greeley 1963, Van Eenennaam et al. 1996, Stevenson and Secor 1999). Larval Atlantic sturgeon emerge in roughly 4 - 6 days and begin to work their way downriver towards brackish waters (Smith et al. 1980). Juveniles may remain in brackish waters for months or years before moving out to sea, where they are known to migrate great distances (Sm ith and Clugston 1997). Humans took advantage of the migratory behavior of spawning Atlantic sturgeon to develop a fishery for Atlantic sturgeon fles h and roe (i.e. caviar). Caviar production in3 the United States did not flourish until the late 19 th century (Cobb 1900), subsequently transforming the Delaware River Atlantic st urgeon fishery from a small, flesh-driven business into the caviar capital of North America (Saffron 2002). By the late 1800’s, the Delaware River Atlantic sturgeon fishery was the largest in the United States and produced 75% of the US sturgeon harves t from 1890-1899 (Townsend 1900). Between

the collection roe from mature females fo r caviar production a nd the canning of the smoked flesh, the fishery provided a way of lif e for many people in search of post-Civil War prosperity (Saffron 2002). Delaware Ri ver landings reached a peak in 1888 with a total catch of nearly 3000 metr ic tons of Atlantic sturgeon (Smith 1894). The success of the fishery was short-lived, and by 1900 the to tal catch was less than 10% of the peak harvest totals (Ryder 1890; Cobb 1900). Given the steep decline in landings, mana gement intervention was required. In 1891 the State of New Jersey passed legisl ation to protect “mammose” (young sturgeon under 1m in length) sturgeon in the waters of Delaware River, bay, or tributaries within state jurisdiction (Cobb 1900). In 1990, the A tlantic States Marine Fisheries Commission (ASMFC) produced a Fishery Management Plan (FMP) for the Atlantic sturgeon with a stated goal of restoring the species throughout its range to allow an annual harvest of about 317 metric tons, which is approximately 10% of the peak catch totals (Smith and Clugston 1997). Following a petition to lis t the Atlantic sturgeon under the Endangered Species Act, a status review was conducted in 1998 that eventual ly determined the species did not warrant protection, although the ASMF C imposed a coastwide moratorium during the same year. In Ma y of 1999, National Marine Fisheries Service (NMFS) extended the fishing ban into federal waters (North Carolin a Division of Marine4 Fisheries 2006). Currently th ere is no allowable commercia l, recreational or tribal harvest in the United States as designated by the ASMFC (1998), however the fishing moratorium has not been in place long e nough to generate measurable recovery (Auer 2004). In 2005, the NMFS initiated another stat us review of the A tlantic sturgeon based on the conclusions of a 2003 NMFS/USFWS joint committee. The status review team released their recommendations in February 200 7 which stated three of the five distinct population segments of Atlantic sturgeon be listed as threatened under the ESA, including the Chesapeake region al population segment. Since the height of the fishery in the late 1800s, the Delaware River Atlantic sturgeon stock has not recovered. Although mo st harvest ended by the start of the 20 th century, there is little evid ence of an extant spawning popul ation. A number of factors have likely contributed to the lack of Atlantic sturgeon reco very in the Delaware River, including habitat loss primarily due to dr edging, saltwater intrusion, water quality degradation, harvest pressure and bycatch mortality (Albert 1988; Stein et al. 2004).

Estuarine and riverine habitat areas available to Atlantic sturgeon la rvae, juveniles, and adults have been degraded over the last centu ry (Albert 1988). Because Atlantic sturgeon

are anadromous and utilize a combination of ri ver, estuary and ocean habitats, damage to any of the three can have detrimental eff ects. The Delaware River became heavily industrialized throughout the latter half of the 19 th century, and the increased activity resulted in rising water pollution to the point where large sections of the river became anoxic during summer months when Atlantic sturgeon occupy the system (Albert 1988). Siltation caused by the industrial coal i ndustry drastically altered the substrate composition of the Delaware River (Albert 1988), which may have reduced available5 spawning habitat. The Delaware River has also experienced larg e-scale dredging to accommodate commercial shipping traffic, resulting in changes in substrate composition and tidal flows (Di Lorenzo et al. 1993; Walsh 2004). Within the period 1877 – 1987, the mean depth of the Delaware River increased by 1.6m and the mean cross-sectional area increased by nearly 3,000 m 2 (Walsh 2004). By 1973, the US Army Corps of Engineers (USACE) estimated that nearly 154,000,000 m 3 of material had been removed from the Delaware Estuary (Walsh 2004). The channe l deepening process increased the tidal range in the upper estuary; si multaneously, extensive water re movals and diversions were occurring within the non-tidal watershed, re sulting in saltwater intrusion in the freshwater-tidal reach of the estuary. This displacement of freshwater habitat may have negatively affected any poten tial success for the cont emporary spawning population. A serious knowledge gap exists regardi ng temporal and spatial spawning patterns of Atlantic sturgeon in most river sy stems including the Delaware. The most comprehensive information regarding Atlant ic sturgeon reproduction in the Delaware River is nearly 100 years old (Ryder 1890; Cobb 1900; Borodin 1925). Since the conclusions drawn concerning th e location and timing of Atlantic sturgeon spawning are based primarily on information collected in fi shery dependent sampling, it is possible that information on spawning locations may not be completely valid. Th e historically noted spawning areas were based on the fact that “rip e” fish were collected at these locations, where “ripe” pertains to adult Atlantic st urgeon that contained eggs ideal for caviar production rather than eggs ready for ferti lization. Ripe eggs as defined for caviar production are actually premature in a repr oductive sense. Eggs suitable for caviar typically have a higher polarization index, lighter color a nd firmer texture than eggs in6 the ovulatory stages (Van Eenennaam et al. 1996; Mohler 2003). Places such as Pea Patch Island, DE and Penn’s Grove, NJ (rk m 85-110) were noted as likely spawning areas, but such locations are currently brackish habitat unsuitable for survival of larvae. Additionally, the significance of historical informati on could increasingly lose relevance given the broad-scale environmen tal context shift caused by global climate change. Given the anthropogenic stressors already functioning within the Delaware River such as dredging and non-tidal wate rshed diversion rights combined with acknowledged climate change, the reliance of present day fisheries managers on 100- year-old fisheries dependent data becomes more problematic. By identifying where spawning activity is currently taking place, essential fish

habitat areas can be characterized for Dela ware River Atlantic sturgeon. Young-of-theyear fish (342 mm TL) have been report ed as recent as 2005 (Hal Brundage, ERC Ltd. pers. comm) supporting the existence of a remnant spawning population. Available information on the early life history of Atlantic sturgeon indicates a natal riverine/brackish water residency period for young-of-the-year (B ain 1997). Genetic evidence also supports the existence of a Dela ware River specific haplotype (Tim King, USGS, Leetown, WV. pers. comm). Because the Atlantic sturgeon is curre ntly listed as a species of concern (Department of Commerce 2004) and limited data poses challenges for fishery managers, we will hopefully provide information that will ultimately help define Atlantic sturgeon habitat utilization patterns within the Delawa re River. The primary research objectives were to 1) determine the contemporary status of Atlantic sturgeon in the Delaware River, 2) attempt to identify both the spatial and temporal extent of spawning, and 3) identify7 critical riverine habitats used during pre- and post-spaw ning movements and determine duration of fresh-water residency.

Materials and Methods Sampling Locale: The study took place in the Delaware Bay and Delaware River, ranging from the entrance of the bay near Ca pe Henlopen, DE and Ca pe May, NJ to as far upriver as Trenton, NJ (Figure 1). Collection of Specimens: Nine adult Atlantic sturgeon (FL>1.3m FL) were captured using monofilament and multifilament gill nets of varying mesh size (primary gear consisted of 30.5cm stretch-mesh monof ilament nets using 1-4, 122m panels, 6.1m height), length, and height, and by fishing a combination of drift and anchored sets. Fishing occurred primarily in the regi on around Woodland and Primehook Beaches Delaware during April, near the Artificial Island anchorage area during May, then into the Cherry Island Flats region and the Ma rcus Hook anchorage area during May and June. Although the drift method had been used successfully to capture adult Gulf sturgeon by Fox et al. (2000), th e local Delaware River fish ing contingent as well as

Delaware Natural Resources and Environm ental Control (DNREC) fishery managers suggested using anchored net techniques as well as drift. Anchored fishing modeled that of the anchored striped bass commercial harvesters, where 30.5cm stretch-mesh gillnets were moored using commercial gillnet anch ors and allowed to fish continuously, being tended at least once per day. Fishing locations were based on three vari ables: 1) advice from the local fishers and DNREC fishery managers, 2) having the capacity from a physical standpoint to allow fi shing of nets exceeding 2000m 2 in size, and 3) striped bass fishing reports provided by DNR EC that documented adult Atla ntic sturgeon as bycatch.8 Upon capture, the sturgeon were placed in a live well, approximately 680L in capacity, where water was pumped in directly from the river system, maintaining ambient temperature, salinity and dissolv ed oxygen levels. Each fish was then implanted with an ultrasonic transmitter (Vemco Ltd. (V-16, 6-H, 69.0 kHz). A reward system was also established to allow us to work with local commercial striped bass harvesters, where they were paid $300.00 for a live Atlant ic sturgeon of adult size (>1.3m FL). Each harvester involved in the program was fi rst required to obtain permission from the DNREC to handle the sp ecies beyond a normal release. Authorized local striped bass commercial harv esters were allowed to retain an adult Atlantic sturgeon whenever they encountered one as bycatch. Once the fish was secured to an anchorage point, the catch was reported to Delaware State University researchers. An immediate response was made to each reported catc h, whereupon Dewayne Fox or Phil Simpson took possession of the fish and implanted it with an ultrasonic transmitter. Tags not utilized for adult Atlantic sturge on were implanted into juvenile Atlantic sturgeon after water temperatures exceeded 25 o C, the likely threshold for spawning activity (Dovel and Beggren 1983). There is pr esently only limited research available regarding juvenile Atlantic sturgeon seasonal migrations, nursery areas, overwintering habits, and movement patterns in the Delaware River. The most recent findings (Shirey 1997), identified two import ant holding areas (near ri ver kilometers 88 and 125, respectively) utilized by juvenile Atlantic sturgeon during the sp ring and summer months in the Delaware Bay and Delaware River. Additionally, sampling reports from Shirey during the period 1991-1997 showed a decline in catch rates from a reported 32.2 fish/hr to 1.4 fish/hr. This additional juvenile information may aide future researchers by9 determining optimal sampling times and loca tions, as well as policy makers who may better identify habitat zones important to the gr owth and survival of Atlantic sturgeon.

Surgical Procedures: The ultrasonic transmitters used in this study were 90mm in length, 16mm diameter, and weighed 14g (in wate r). The transmitters were coated with Dow Corning Silastic® biological ly inert silicone elastomer in an attempt to minimize rejection rates (Fox et al. 2000). Upon capture, each fish was placed in the live well. The TL and FL (cm) and, when available, weight (kg) was measured and recorded. Any captured Atlantic sturgeon were scanned thoroughly for the presence of an existing PIT tag. If no tag was present, a 16mm Biomark® PIT tag was inserted on left side of fish at the base of the dorsal fin. A barbel sample was taken and placed in 95% etha nol for future genetic analysis. A plastictipped dart tag was inserted on the left side of the fish be low the fourth dorsal scute. Surgical implantation of the Vemco ultrasonic transmitter followed the protocol established by Fox et al. (2000).

Telemetry: Telemetered Atlantic sturgeon we re monitored once a week using the telemetry techniques described below. Riveri ne waters were surveyed weekly, weather and personnel permitting, from June until October, or until most or all of the fish had moved out of the survey range. Fixed survey stations were set at one kilometer intervals and listening occurred for at least two mi nutes using an omni-directional hydrophone. Once a tagged fish was detected, a direc tional hydrophone was used to determine the10 exact location of the fish. Th e location and depth were reco rded along with water quality parameters (temperature, salinit y, conductivity, and dissolved oxygen). A passive array of VR2 receivers was al so be established and periodically

checked to determine broad scale fish moveme nts (Figures 1-2). These receivers were

attached to the United States Coast Guar d navigational aides (F igure 3) and were distributed throughout the river and bay in or der to maximize the pot ential for monitoring upstream and downstream movements of teleme tered Atlantic sturgeon. An additional array for a separate DSU research project whic h utilized anchored re ceivers in two linear arrays was positioned between Slaughter Beach and Cape Henlopen, DE. Data sharing with the privately owned research firm Envi ronmental Research and Consulting, Inc. also utilizing Vemco VR2 receivers within the Delaware River, allowed for an overall

increase in the amount of data collected by all parties. The average detection range of the VR2 r eceivers was determined by a series of tests. Each test documented a percent of po ssible tag detections at varying distances and

directions from the VR2 receiver. Starting at the receiver, a te st transmitter similar to the ones used for this study was attached to a weighted line and deployed at a depth approximately two meters off the river bottom to mimic the presumed benthic nature of Atlantic sturgeon. Simultaneously us ing a VR100 manual hydrophone and a handheld GPS unit, the time of each transmittance wa s recorded along with the location. Deploying the tag for no less than three minut es, the number of detections recorded by the VR2 receiver was compared to the number of possible detections to produce a percent transmittance. This process was repeated at distances of 500m, 1km, and 1.5km for each north, south, east and west h eadings. Although numerous te sts have been conducted in11 prior research (Domeier 2005; Szeldlmayer a nd Schroepfer 2005) and claims made about the detection capabilities of the VR2 receivers are well documented (Miller and Sadro 2003; Simpfendorfer 2006), the detection range can vary significantly because of both physical and biological factor s (Heupel et al. 2006). Th e probable detection range, according to the available litera ture, may reach 90% in a static water setting (Clements et al. 2005) but may decline and potentially reach a maximum between 400m – 800m (Heupel and Hueter 2001; Hildebrand and H ildebrand 2004), but can also be as low as 300m (Semmens et al. 2005), or in extreme cases as low as 45m (Finstad et al. 2005). Telemetry methods and habitat characterizati on techniques were id entical for adult and juvenile Atlantic sturgeon.

Habitat Characterization: Habitat parameters such as water depth (m), temperature ( o C), dissolved oxygen (mg/L), salinity (ppt) and conductivity (mS) were measured and recorded at each capture location and relocation point. The manual telemetry relocations of Atlantic sturgeon we re plotted using ArcM ap and overlaid with sediment-type data collected by Sommerfield and Madsen (2003) to determine habitat

selection. Sommerfield and Madsen utilized sidescan sonar methods to produce a benthic map of the Delaware River from the region ju st north of Pea Patch Island (approximately river kilometer 110) upriver to approximately Bridgeport, NJ. Each relocation point was classified by sediment type based on the loca tion of the point within the benthic mosaic developed by Sommerfield and Madsen. The total area comprised of each habitat type within the region of relocations was calculat ed, and an individual Chi-square analysis was performed to determine if Atlantic stur geon are selecting hab itat based on sediment12 type. Similar methods were utilized to a ssess Atlantic sturgeon de pth preferences using

data obtained from the USACE. Additionally, overall movement of tele metered Atlantic sturgeon was crossplotted with water temperature ( o C) as well as river flow (ft 3 /s) data obtained from the United States Geological Survey gaging stati on in Philadelphia, PA to determine if a correlation exists between overall migration pa tterns of juvenile Atlantic sturgeon and

either of the two environmental variables.

Reproductive status: Gonadal biopsies were prepped using standardized histological techniques and were staged using the clas sification criteria established by Van Eenennaam and Doroshov (1998).

Egg Collection: Abrasive surface artificial substrate pads suitable for adherence of eggs have been successfully used for wh ite and Gulf sturgeon egg collection (McCabe and Beckman 1990; Marchant and Shutters 1996 ; Fox et al. 2000). Egg mats (diameter 56cm) were deployed in areas of the river wh ere spawning was believed to be occurring based on active telemetry data and substrate sampling. When rocky or gravel substrate was collected using a petite ® Ponar grab, egg mats we re deployed approximately 10- 15m from each other and checked for deposit ed eggs at a maximum of every third day (based on the hatch times established by th e Northeast Fishery Center (Mohler 2003)) until spawning fish were no longer in the area.

Results13 The 2005 sampling season began on May 10, and concluded on September 22. The 2005 fishing efforts produced only juvenile Atlantic sturgeon (Table 1). Beginning May 10, fishing efforts were directed towa rds adult Atlantic sturgeon. On June 30, efforts shifted to juvenile Atlantic stur geon as water temperatures approached 26 o C. Out of the 23 total juvenile Atla ntic sturgeon captured, 12 were implanted with transmitters (using a minimum total length 80.0cm as size criter ia) . The sizes of fish captured ranged from 65.3cm – 131.0cm (Table 2). The fishing efforts for the season concluded on September 22, 2005. During May and early June, fishing occurred primarily in the upper bay off Woodland Beach and Bombay Hook. Efforts shifted towards Artificial Island from mid-June to the end date of Septembe r 22, with some nets deployed near Cherry Island Flats (rkm 110) and Marcus H ook (rkm 125) as well (Figure 4). During 2006, netting began April 12, however the first three Atlantic sturgeon implanted with transmitters were obtained as a result of the reward system. The first of

these fish was below the adult size threshol d (FL >1.3m) and therefore was considered juvenile. The reward program ceased on May 1 as the commercial striped bass season came to a close. From May 10, under the guid ance of commercial striped bass fisherman Larry Voss, six 30.5cm stretch-mesh gillnets, ea ch 91 meters in length, were anchored in upper Delaware Bay. These nets were checked at least once per day for captured adult Atlantic sturgeon. Using these methods, a th ird Atlantic sturgeon of adult size was captured and tagged May 18. We continued to fi sh using this style of anchored sets until May 26. At this point, netting efforts were moved upriver (river kilometer (rkm) 85-90) as potentially reproductive Atlantic sturgeon were be lieved to move upriver.14 Starting May 30, we moved our fishing e fforts towards Artificial Island (river kilometer 88). Gill nets were anchored at slack tide and allowed to fish until the subsequent slack water event. A fourth adul t Atlantic sturgeon was captured June 1 and

fitted with an ultrasonic tran smitter. Sampling continued until June 18, and gradually moved upriver into the Cherry Island Flat s/Marcus Hook Bar region (rkm 110-125) as well as riverine sections appr oaching Trenton, NJ (Figure 4), using relocations of the four tagged adult Atlantic sturgeon as a guide to di rect fishing efforts (Table 3). The gonadal biopsies collected from each fish identified all four fish as males, each of them potentially of reproductive size. Histologi cal examination of the 2006 gonad samples indicated potentially two out of four i ndividuals had reached a near-term spawning maturation phase. By mid-July, tracking data indicated the telemetered adult Atlantic sturgeon had moved out of probable spawning areas and retu rned to brackish waters. Additionally, water temperatures began to exceed the reported maximum (25 o C) for spawning activity (Dovel and Berggren 1983). At this point, the focus again turned to juvenile Atlantic sturgeon. Beginning July 24, smaller mesh nets (15-20cm) were deployed near Artificial Island (rkm 88) in addition to the large mesh nets used previously. Ten more juvenile Atlantic sturgeon were tagged in th e summer of 2006 (Table 4). During 2005 and 2006 a total of 27 Atlantic sturgeon were tagged, producing 181,999 passive relocations coupled with 183 ma nual relocations (Table 5). Telemetry results point to a late spri ng/early summer inward migra tion, followed by a period of dampened movement during the warm summer m onths of August and September, then an outmigration during October and November. During the summer months juvenile15 Atlantic sturgeon displayed little movement co mpared to spring and fall months (Figure 6a – 6c). Juvenile Atlantic sturgeon concen trated in three specific areas, two of which (Artificial Island, Cherry Island Flats) had been identifie d by previous research conducted on the Delaware River (Figure 5). The previ ously unidentified area, however, is situated in the Marcus Hook anchorage zone (rkm 125). According to manual relocation data, juvenile Atlantic sturgeon ar e selecting for depth (Figure 7a) but are not selecting for substrate type (Figure 7b).

Of the four adult size Atlantic st urgeon tagged during 2006, one individual, Vemco ID #1744, migrated into freshwater-tid al reaches of the Delaware River (Figure 8), although the histological ex amination of the gonads of this fish indicated it was sexually immature. Atlantic sturgeon #1744 moved upriver to Tinicum Island (rkm 136) immediately after it was tagged, and remained there from June 4 – June 10. Initial sediment sampling was performed near the relo cation points at Tinicum Island during this time period, however by June 12; this individu al had migrated towards Trenton, NJ (rkm 211) where it remained until June 27. By July 7, Atlantic sturgeon #1744 had returned to the location where it was originally captured. Once Atlantic sturgeon #1744 entered th e upper river near Trenton, NJ, habitat characterization began through the use of a Ponar grab in order to classify the substrate as hard-bottom, and egg mats were deployed where hard-bottom, rocky substrate was prevalent (Figure 9). A total of 75 egg ma ts were deployed on June 16 between river kilometers 197 – 210 in clusters of 12-16 pads and fished until June 28, as river flow measured at Trenton, N.J. rose from 8,000 CFS to over 200,000 CFS within a 24-hour16 period. Only one-third of this gear was r ecovered following the flood event. No eggs were collected during the study. Preliminary range tests following ou r described methodology indicate that

transmitter detection success is less than 50% at distances of 500m or more. These findings stem from tests performed on nears hore receivers in depths not exceeding 8m. However, based on other analysis methods, th ere is evidence that the VR2 receivers can detect transmitters at distances of greater than 2km. There were multiple instances where two receivers deployed in close proximity to one another detected a transmitter simultaneously. The most extreme example of this scenario occurred at Tinicum Island (rkm 136 and rkm 141), where the inter-receiver distance is 5.7 km. If a transmitter is detected by both receivers, then each receiv er must have a minimu m detection range of 2.8 km. While percent transmittance values are not obtainable using this analysis method, we can get some idea as to the maximu m detection range of the receivers.

Discussion The Delaware River once supported the la rgest population of Atlantic sturgeon known to exist (Secor and Waldman 1999) a nd although our telemetry results are not conclusive, coupled with the collection of ri pe adults, and prelimin ary genetic analyses, they strongly suggest that a remnant spaw ning population exists today. The telemetry results from Atlantic sturgeon obtained dur ing 2006 provide some insights about the probable spatial and temporal ex tent of spawning behavior. Given the fact that sexually mature male Atlantic sturgeon were capture d in Delaware Bay between mid-April and June 1, our findings for the Delaware Rive r agree with those of Dovel and Beggren17 (1983) regarding Atlantic st urgeon spawning times reported for the Hudson River. Additionally, the rapid upriver migration made by Atlantic sturgeon #1744 to freshwater

habitat where hard-bottom s ubstrate is prevalent would indicate that spawning for Atlantic sturgeon may occur much further uprive r than the historical reports of “ripe fish” observations made by Cobb (1899) as well as Borodin (1925). Spawning habitat of Atlantic sturgeon may also be shared with the closely related shortnose sturgeon ( A

. brevirostrum ) in the Delaware River. These findings differ from Bain’s (1997)

conclusions for Hudson River shortnose and Atlantic sturgeon where such a spatial overlap is not thought to occur regularly. Based on our findings, it seems likely that the present day lower limit of Atlantic sturgeon spawning may be in the area of the upper limit of salt water intrusion near Tinicum Island (river kilometer 136) while the up per limit is likely at the fall line near Trenton, NJ (river kilometer 211 ). Dovel and Beggren (1983) reported that early in the season (late May), Atlantic sturgeon spawning in the Hudson River occurred near the salt wedge, and then continued upstream into June and early July. A tlantic sturgeon #1744 appeared to fit the profile for a spawning adult sturgeon (e.g. Fox et al. 2000), occupying areas around Tinicum Island (negligible salinit y) during early June then making a rapid directly movement upstream towards Trenton, wh ere it remained until late June before making a downriver migration in early July. However, the histologi cal analysis of the gonad sample obtained from Atlantic sturge on #1744 proved inclusive and indicated this fish had undifferentiated gonads. However, we hypothesize that the gonadal biopsy of this individual missed the reproductively ac tive portion of the gonad since the gonads of18 Atlantic sturgeon may exhibit different st ages of development throughout the gonadal tissue (Joel VanEenennaam, pers comm). Atlantic sturgeon #1225 migrated as far upriver as the mouth of the Schuylkill River (rkm 148) on May 31 st, 2006; however, the duration of the stay was less than 24 hours and did not appear indicative of spawning behavior. After quickly returning to the upper bay waters (rkm 80), Atlantic sturgeon #1225 returned to the area of Marcus Hook Bar (river kilometer 134) on June 28. Again, the visit was short and, within one day, the fish returned to the upper bay. Nevertheless, this migration may indi cate this fish was searching for a mate and could indicate th e presence of other spawning adult Atlantic sturgeon near the regions of Marcus Hook Bar and Tinicum Island during the month of June. Additionally, the histolog ical results from this individual indicate that it was sexually mature and ready to spawn, sugge sting that spawning may occur between Tinicum Island (rkm 136) and the mouth of the Schuylkill River (rkm 148). The discussion pertaining to the secti on of river between Marcus Hook Bar and the mouth of the Schuylkill River becomes more significant when the idea of habitat selection is introduced. Atlantic sturgeon not only require freshw ater for spawning but also hard-bottom substrate (Gilbert 1989, Smith and Clugston 1997). Based on Sommerfield and Madsen (2003), there are multiple zones of hard-bottom substrate within the Marcus Hook-Schuylki ll River area that are considered freshwater. This area has been classified as freshwater (0.0 to 0.5 ppt upstream of Marcus Hook) by the Army Corps of Engineers (1997). Sommerfield and Madsen classify much of this area as “Mixed-grained reworking” where the dominan t sediment types are “mixed gravel, sand, and mud,” or “Coarse-grained bedload” with “moderately well-sorted sand and gravel” as19 the dominant sediment types and “Non-depositio n where the dominant sediment types are

“cobble and bedrock.” Based on the findings of Sommerfiel d and Madsen (2003), the substrate composition between Marcus Hook and Tinicu m Island may represent suitable spawning habitat for Atlantic sturgeon. The major ity of the hard-botto m substrate zones, particularly the coarse-grained bedload areas, either neighbor or are within the shipping channel, indicative of suitable spawning dept hs (Smith and Clugston 1997). However, the presence of hard-bottom substrate within the shipping channel may also be a limiting factor in terms of spawning success, potentially exposing adult Atlantic sturgeon to mortality due to boatstrike. The identification of spawning areas in th e Delaware River is difficult because of

the limited data received from telemetered adult Atlantic sturgeon and the lack of fertilized egg collections. The Delaware River, between Marcus Hook (rkm 125) and Trenton (rkm 211), could be considered pot ential spawning habitat based on availability

of freshwater and hard-bottom substrate. Because males tend to be more active (Fox et al. 2000) than females during spawning events, it is difficult to apply the telemetry data to spawning habitat quantifica tion. For example, Bain described males as occupying a stretch of the Hudson River greater than 100km in length during the spawning season; however females were relegated to two con centration zones totaling about 20km in length (1997). Although telemetry of a mature female and egg collections is nearly essential to begin the quantification of pot ential spawning habitat, some assumptions can be drawn based on the telemetry of adult male Atlantic sturgeon.20 The upriver migrations made by Atla ntic sturgeons #1744 and #1225 are also significant when compared to the movement s of juveniles documented during 2005-2006. Only in a few isolated incidences were relocations of telemetered juvenile Atlantic sturgeon made above the Commodore Barry Bridge (rkm 135); the majority of

relocations occurred in the area of Marcus Hook (rkm 125) or below. This may indicate some spatial separation between adult and juvenile Atlantic sturgeon, and would be inconsistent with the findings of prior rese arch (Bain 1997; Fox et al. 2000; Hightower et al. 2002), where no spatial separation existe d between spawning adults and juveniles. Although a population assessment is not one of the specific objectives of this research, the low numbers of Atlantic stur geon collected given the effort expended is

worth some discussion. Our low CPUE is troubling considering in 1888, nearly 3.0 million kilograms of Atlantic sturgeon were harvested from the Delaware River (Secor and Waldman 1999). Ultimately, during 2005 and 2006, fishing efforts were almost completely fruitless, especially those ta rgeted at adult Atla ntic sturgeon. Although sampling restrictions (not being able to sa mple within the shipping channel) may have limited our catch rates, restrictions alone cannot account for such a low CPUE. However low the CPUE, the fact remains that sexually mature Atlantic sturgeon were captured in Delaware Bay. A problem th at is of growing con cern to the continued existence of Atlantic sturgeon in the Delaware River is mortalities of Atlantic sturgeon by

boat strikes. This is not a new problem as it has been observed anecdotally over the last few years. During each of the past two y ears approximately 5-10 adult (>1.3m) Atlantic sturgeon have been observed with blunt trauma that is indicative of being struck by a boat. Results provided through this study indicate that Atla ntic sturgeon (juveniles and21 adults) often inhabit main channel habitats (Figure 7a) The navigation depth of this channel is currently maintained at 12.2m by the USACE. Aside from being the largest free flowing river on the East Co ast, the Delaware River is also the busiest freshwater commercial port. Large commercial ships often have limited bottom clearance (<2m) when transiting the Delaware River. This f act coupled with Atlant ic sturgeon occupying main channel habitat increases the probability that a boat strike incident will occur. Our results indicate that juvenile Atlan tic sturgeon occupy specific sections of the Delaware River for prolonged periods during the summer months. Based on our telemetry results we have identified three riverine concentration areas of telemetered juvenile Atlantic sturgeon: Artificial Island (rkm 89), Cherry Island Flats (rkm 110), and Marcus Hook Anchorage (rkm 125). The lower two sites, Artificial Island and Cherry Island Flats, were previously identified and it was noted th at substrate composition may play a role as a unifying ch aracteristic for the two site s (Shirey 1997). A recent study looking at the substrate composition of th e upper two areas note that they are predominated by mixed gravel and sand sediments with areas of non-depositional substrate, however not necessarily due to th e presence of slag deposits (Sommerfield and Madsen 2003). Based on our recapture data, many juven ile Atlantic sturgeon within Delaware Bay and River likely do not stem from Dela ware River genetic stock. While a specific genetic haplotype has been identified fo r the Delaware River Atlantic sturgeon population (Tim King, pers comm.) , our netting efforts and tele metry results, as well as mark-recapture data collected by DNREC (Greg Murphy, pers comm.) indicate juvenile Atlantic sturgeon collected and or spawned in other rivers are using the Delaware River22 and Bay as a nursery habitat. In terms of management implications, the lack of a distinctive stock could significan tly alter recovery efforts. If stocking programs were ever to be implemented, such genetic considerations would come into play.

Conclusions Our telemetry results coupled with the co llection of ripe male Atlantic sturgeon although not conclusive provide strong evidence to suggest that a remnant population of spawning Atlantic sturgeon exists in the Delaware River. Although the location of spawning habitat has not been confirmed, our telemetry result s together with information on substrate and water qualit y data indicate that spawni ng may be occurring between

mid-June - late June in fr eshwater-tidal reaches between north Philadelphia, PA (rkm 176) and Trenton, NJ (rkm 211). These spawni ng areas are located much further upriver than historically reported spawning grounds (rkm 75 – 130; Ryder 1890, Cobb 1899) which may, in part, be due to increased sa ltwater intrusion. The effects of increased

saltwater intrusion on Atla ntic sturgeon in the Delaware River although not well understood, may continue to play a role in the slow recovery of this population especially with the political and socio-economic pressu re to expand dredging efforts in the river potentially furthering the saltwater intr usion and reducing av ailable habitat. Atlantic sturgeon bycatch mortality is known to occur in both the Delaware Estuary and nearby continental shelf regions (Stein et al. 2004), and undoubtedly has played a role in slowing the recovery of this population. We became aware of an additional source of mortality during the course of this study as we documented numerous reports of adult and juvenile Atlant ic sturgeon mortalities, many of which were23 likely caused by propeller strikes. The Dela ware River serves as one of the most important shipping ports in the US and is the number one east coast port for petroleum shipments. This strategic importance must be weighed against the costs to the ecological integrity of the Delaware River Estuary. At present there are numerous large-scale shipping and refining projects proposed for the Delaware Estuary. We propose that managers should apply a precautionary approach to the approval of any such projects and take into account how their pote ntial impacts can alter the re covery trajectory for what was once the largest populati on of Atlantic sturgeon.

Acknowledgements We would like to thank the following individuals for their assistance in completion of this research: Lori Brown, Collette Cairns, Naeem Willett, and Don Wujtewicz, Delaware State University; Hal Brundage, Environmental Research and Consulting, Inc; Greg Murphy and Craig Sh irey, Delaware Natural Resources and Environmental Control; Clyde Roberts, La rry and Lawrence “Limbo” Voss; Captain Thomas Flynn and Lieutenant Brian Huff, Unite d States Coast Guard; the crew of the USCGC William Tate; Russ Allen, New Jersey Department of Environmental Protection; and John Jacobs, NOAA Oxford Laboratory.24 LITERATURE CITED

ASMFC. 1996. ASMFC Breeding and Stoc king Protocol for Cultured Atlantic Sturgeon, Fishery Management Report No. 68 of the ASMFC. 20 pp.

ASMFC. 1998. Amendment 1 to the Intersta te Fishery Management Plan for Atlantic sturgeon. Fishery Management Report No. 31 of the ASMFC. 43 pp. Albert, R.C. 1988. The historical context of water quality management for the Delaware Estuary. Estuaries, 11:99-107. Auer, N.A. 2004. Conservation. Sturgeons and Paddlefish of North America , p. 252- 276. Bain, M.B. 1997. Atlantic and shortnose st urgeons of the Hudson River: common and divergent life history attributes. Environmental Biology of Fishes, 48:347-358. Bachus, R.H. 1951. New and rare records of fishers from Labrador. Copeia 1951:288- 294. Borodin, N.A. 1925. Biological observa tions on the Atla ntic sturgeon ( Acipenser sturio ). Transactions of the American Fisheries Society, 55:184-190.

Cech, J.J. and S.I. Doroshov. 2004. Envi ronmental requirements, preferences, and tolerance limits of North Am erican sturgeons. Sturgeons and Paddlefish of North America , 73-86.

Clements, S., D. Jepsen and M. Karnowski. 2005. Optimization of an acoustic telemetry array for detecting transmitter-implanted fish. North American Journal of Fisheries Management. 25:429-436.

Cobb, J.N. 1900. The sturgeon fishery of Dela ware River and Bay. Reports of United States Commission of Fish, 25:369-380.

Dadswell, M. 2006. A review of the status of Atlantic sturgeon in Canada, with comparisons to populations in the Unite d States and Europe. Fisheries 31:218- 229.

Di Lorenzo, J.L, P. Huang, M.L. Thatcher, a nd T.O. Najarian. 1993. Effects of historic dredging activities and water diversio ns on the tidal regime and salinity distribution of the Delaware Estuary. Final Report for the Delaware Estuary25 Program Preliminary Characterization a nd Research Topic 5: Long-term River Flow and Circulation Studies. 124p.

Domeier, M.L. 2005. Methods for the Deploy ment and Maintenance of an Acoustic Tag Tracking Array: An Example from California’s Channel Islands. Marine Technology Science Journal. 391:74-80.

Dovel, W.L. and T.J. Berggren. 1983. A tlantic Sturgeon of the Hudson Estuary, New York. New York Fish and Game Journal, 30(2): 140-172. Department of Commerce (National Oceanic and Atmospheric Association). 2004. Federal Register Notice, 69(73):19975-19979. Finstad, B. F. Okland, E.B. Thorstad, P.A. Bjorn and R.S. McKinley. 2005. Migration of hatchery-reared Atlantic salmon and w ild anadromous brown trout post-smolts in a Norwegian fjord system. Journal of Fish Biology. 66:86-96. Fox, D.A., Hightower, J.E., and Paruaka, F. M. 2000. Gulf sturge on spawning migration and habitat in the Choctawhatchee River sy stem, Alabama-Florida. Transactions of the American Fisher ies Society, 129:811-826.

Gilbert, C. R. 1989. Atlantic and shortnos e sturgeons. United States Department of Interior Biological Report 82: 28 pp.

Heupel, M.R. and R.E. Hueter. 2001. Use of an automated acoustic telemetry system to passively track juvenile blacktip shark movements. Electronic tagging and tracking in marine fi sheries, 217-236. Heupel, M.R., J.M Semmens and A.J. Hobda y. 2006. Automated acoustic tracking of aquatic animals: scales, design and deploym ent of listening station arrays. Marine and Freshwater Research. 57:1-13. J. E. Hightower, K. P. Zehfuss, D. A. Fox, F. M. Parauka (2002) Summer habitat use by Gulf sturgeon in the Choctawhatchee River, Florida Journal of Applied Ichthyology 18 : 595–600. King, T.L., B.A. Lubinski and A.P. Spidle . 2001. Microsatell ite DNA variation in Atlantic sturgeon ( Acipenser oxyrinchus oxyrinchus ) and cross-species amplification in the Acipenseridae. Conservation Genetics, 2(2):103-119.

Marchant, S.R. and M.K. Shutters. 1996. Artificial substrates collect Gulf sturgeon eggs. North American Journal of Fisheries Management, 16:445 447.26 McCabe, GT, Jr., and LG Beckman. 1990. Use of an artificial substrat e to collect white sturgeon eggs. California Fish and Game. 76:248-250. Miller, B.A. and S. Sadro. 2003. Residen ce time and seasonal movements of juvenile coho salmon in the ecotone and lower estuary of Winchester Creek, South Slough, Oregon. Transactions of the Ameri can Fisheries Society. 132: 546-559. Mohler, J.W. 2003. Culture Manual for the A tlantic sturgeon. United States Fish and Wildlife Service. Hadley, Massachusetts. 70p. Peterson, D.L., M.B. Bain, and N. Haley. 2000. Evidence of declin ing recruitment of Atlantic sturgeon in the Hudson River. North American Journal of Fisheries Management, 20: 231-238. Ryder, J.A. 1890. The sturgeons and sturge on industries of the eas tern coast of the United States, with an account of expe riments bearing upon sturgeon culture. Bulletin of U.S. Fish Commission, 8: 231-329. Townsend, C.H. 1900. Statistics of the fisherie s of the Middle Atlantic States. Part 26 of the Commissioner’s Report to the U.S. Commission of Fish and Fisheries: 195- 310. Saffron, I. 2002. Caviar. Broadway Books, New York, NY. 270 p. Secor, D.H. and J.R. Waldman. 1999. Hist orical abundance of Delaware Bay Atlantic sturgeon and potential rate of recovery. American Fisheries Society Symposium, 23:203-216. Semmens, B.X., K.E. Luke, P.G. Bush, C. Pattengil-Semmens, B. Johnson, C. McCoy and S. Heppel. Investigating the re productive migration an d spatial ecology of Nassau grouper ( Epinephelus striatus ) on Little Cayman Island using acoustic tags—an overview. Website: http://www.reef.org/data /GCFI_2005_GMPfinal.pdf Shirey, C. A., C. C. Martin, and E. D. St etzar. 1997. Abundance of sub-adult Atlantic sturgeon and areas of con centration within the lower Delaware River. DE Division of Fish and Wildlife, Dover, DE, USA. Smith, H.M. 1894. A statistical report on the fisheries of the Middle Atlantic States. Bulletin of the U.S. Fish Commission 14:339-467. Smith, T. I. J., D. E. Marchette and R. A. Smiley. 1982. Life history, ecology, culture and management of Atlantic sturgeon, Ac ipenser oxyrhynchus oxyrhynchus, Mitchill, in South Carolina. South Carolina Wildlife Marine Resources. Resources Department, Final Report to U.S. Fish and Wildlife Service Project AFS-9. 75 pp.27 Smith, T.I.J. and J.P. Clugston. 1997. Stat us and management of Atlantic sturgeon, Acipenser oxyrinchus , in North America. Envi ronmental Biology of Fishes, 48:335-346. Smith, T. I. J., E. K. Dingley, and E.E. Ma rchette. 1980. Induced spawning and culture of Atlantic sturgeon. Progressive Fish Culturist 42:147-151. Smith, T. I. J. 1985. The fishery, biology, and management of Atlantic sturgeon, Acipenser oxyrhynchus , in North America. Enviro nmental Biology of Fishes 14:61-72. Sommerfield, C.K. and J.A. Madsen. 2003. Se dimentological and geophysical survey of the upper Delaware Estuary. Final Re port to the Delaware River Basin Commission. 126p. Stein, A.B., K.D. Friedland, and M. Sutherla nd. 2004. Atlantic sturgeon marine bycatch and mortality on the continental shelf of the Northeast United States. North American Journal of Fish eries Management 24:171-183. Stevenson, J. T., and D. H. Secor. 1999. Age determination and growth of Hudson River Atlantic sturgeon, Acipenser oxyrinchus . Fishery Bulletin 97: 153-166. Szedlmayer, S.T. and R.L. Schroepfer. 2005. Long-term residence of red snapper on artificial reefs in the northeastern Gulf of Mexico. Transactions of the American Fisheries Society. 134:315-325. Van Eenennaam, J. P., S. I. Doroshov, G. P. Moberg, J. G. Watson, D.S. Moore, and J. Linares. 1996. Reproductive conditi ons of the Atlantic Sturgeon ( Acipenser oxyrinchus ) in the Hudson River

. Estuaries, 19(4):769-777. Van Eenennaam, J. P. and S. I. Doroshov. 1998. Effects of age and body size on gonadal development of Atlantic sturge on. Journal of Fish Biology, 53:624-637. Vladykov, V. D. and J. R. Greely. 1963. Fish es of the Western North Atlantic. 1:24-60. Waldman, J.R. and I.I. Wirgin. 1998. Stat us and restoration options for Atlantic sturgeon in North America. C onservation Biology, 12 (3):631-638. Walsh, D.R. 2004. Anthropogenic influences on the morphology of the tidal Delaware River and Estuary: 1877 – 1987. Masters Thesis, University of Delaware. 90p.

Wigin, I.I., J.R. Waldman, J. Rosko, R. Gross, M.R. Collins, S.G. Rogers, and J. Stabile. Genetic structure of Atlantic sturge on populations based on mitochondrial DNA control region sequences. Transactions of the American Fisheries Society, 129:476–486.28 Websites: http://www.ncfisheries.net/stocks/atsturg.htm (updated 6-06)29 Figure 1. Passive receivers (Vemco VR2) used for Atla ntic sturgeon telemetry, 2005.30 Figure 2. Passive receivers (Vemco VR2) used for Atla ntic sturgeon telemetry, 2006.31 Figure 3. Schematic of VR2 deploym ent using USCG navigational aide.32 Figure 4. Atlantic sturgeon netti ng and capture locations, 2005-2006.33 Figure 5. Passive relocations for juvenile Atlantic sturgeon, 2005-06.34 Figure 6a. 2005 Atlantic sturgeon movement.

0 20 40 60 80 100 120 140 160

06/30 07/20 08/09 08/29 09/18 10/08 10/28 11/17 12/07 12/27 Dateriver kilometer

Figure 6b. 2006 Juvenile Atlantic sturgeon movement.

0 20 40 60 80 100 120 140 160

03/14 05/03 06/22 08/11 09/30 11/19 Dateriver kilometer35 Figure 6c. 2006 Adult Atlantic sturgeon movement.

0 50 100 150 200 250

04/18 05/18 06/17 07/17 08/16 09/15 10/15 Dateriver kilometer

Figure 7a. Atlantic sturgeon utilized vs. availa ble depth. Based on manual relocation data, 2005-2006.



### 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

0 - 2.00 2.01 - 4.00 4.01 - 6.00 6.01 - 8.00 8.01 - 10.00 10.01 - 12.00 12.00 - 14.00 > 14.01 

### Depth (m)Relative Frequency 

### Expected Observed36 Figure 7b. Atlantic sturgeon utilized vs. available substrate type. Based on manual relocation data, 2005-2006.

0.00 0.10 0.20 0.30 0.40 0.50 0.60

cobble/bedrock mixed gravel/sand/mud mud mud/fluid mud well sorted sand/gravel Sediment typeRelative Frequency 

## Expected Observed37 Figure 8: Summary movement patterns for ripe male adult Atlantic sturgeon which was implanted with transmitter # 1744 on June 1, 2006.38 Figure 9. Atlantic sturgeon egg pad deployment locations, 2006.39 Table 1. Catch per unit effort, 2005.

Total Net Fished (m 2 ) 115998.7 Total Hours Fished 253.3 Total Catch 23 CPUE (catch/m 2 /hr) 7.83E-07 Table 2. Length summary for captur ed and telemeterd Atlantic sturgeon, 2005.

Minimum Maximum Fork Length (cm), non-telemet ered captures 56.0 94.0 Weight (kg), non-telemetered captures 1.6 2.9 Fork Length (cm), telemetered captures 78.4 122.5 Weight (kg), telemetered captures 4.2 10.0 Table 3. Catch per unit effort, 2006. Total Net Fished (m 2 ) 73046.9 Total Hours Fished 2585.0 Total Catch 18 CPUE (catch/m 2 /hr) 7.41E-08 Table 4. Length summary for captur ed and telemeterd Atlantic sturgeon, 2006.

Minimum Maximum Fork Length (cm), non-telemet ered captures 57.4 71.2 Weight (kg), non-telemetered captures 1.5 2.1 Fork Length (cm), telemetered captures 67.8 158.0 Weight (kg), telemetered captures 2.5 28.440 Table 5. Atlantic sturge on relocation summary 2005-2006.

Fish ID Date Captured Fork Length (mm) Passive Detections Manual Detections Total Detections Date Last Relocated

1232 6/30/2005 820 761 10 771 8/18/2006 1234 6/30/2005 913 4132 5 4137 5/5/2006 1233 7/7/2005 880 1002 15 1017 11/3/2005 1229 7/7/2005 851 50754 20 50774 10/31/2006 1224 7/11/2005 784 2121 13 2134 4/25/2006 1223 7/19/2005 950 7606 8 7614 4/26/2006 1222 7/27/2005 1225 499 11 510 10/28/2005 1221 8/1/2005 940 2641 7 2648 11/25/2005 1230 8/1/2005 970 534 6 540 5/28/2006 1231 8/2/2005 1140 881 8 889 9/30/2005 1227 9/13/2005 785 5133 3 5136 11/1/2005 1235 9/22/2005 857 4900 5 4905 1/6/2006 1226 4/18/2006 1210 1770 0 1770 10/5/2006 1228 4/23/2006 1550 1436 0 1436 6/3/2006 1225 4/27/2006 1580 3169 8 3177 9/26/2006 1747 5/18/2006 1370 714 1 715 9/9/2006 1744 6/1/2006 1370 13877 15 13892 10/27/2006 1731 7/24/2006 796 15722 7 15729 10/3/2006 1732 7/24/2006 969 5604 5 5609 10/9/2006 1733 7/24/2006 782 14788 6 14794 10/8/2006 1740 7/24/2006 800 4596 7 4603 10/8/2006 1742 7/24/2006 780 14292 7 14299 10/21/2006 1746 7/24/2006 818 9459 6 9465 11/1/2006 1739 8/2/2006 722 1 1 2 8/2/2006 1741 8/2/2006 678 8720 7 8727 10/27/2006 1750 8/25/2006 808 800 0 800 8/29/2006 1734 9/6/2006 754 6087 2 6089 10/9/2006 Total Passive Detections 181999 Total Manual Detections 183 Total Detections 18218241