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American Eel Supply to an Estuary and Its Tributaries: Spatial Variation in Barnegat Bay, New Jersey
Kenneth W. Able, Jennifer M. Smith, and Jamie F. Caridad

Northeastern Naturalist, Volume 22, Issue 1 (2015): 53–68

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Northeastern Naturalist Vol. 22, No. 1 K.W. Able, J.M. Smith, J.F. Caridad 2015 53 2015 NORTHEASTERN NATURALIST 22(1):53–68 American Eel Supply to an Estuary and Its Tributaries: Spatial Variation in Barnegat Bay, New Jersey Kenneth W. Able1,*, Jennifer M. Smith1, and Jamie F. Caridad1 Abstract - We evaluated the spatial variation in the supply of Anguilla rostrata (American Eel) glass eels and elvers to a Mid-Atlantic Bight estuary (Barnegat Bay, NJ) by sampling over two years at multiple inlets, thoroughfares to adjacent estuaries and tributaries. Both inlets and all three thoroughfares provided sources of glass eels to Barnegat Bay. However, the level of supply to individual tributaries was markedly different, although size and pigmentation stage was consistent. The difference between tributaries might reflect distance from inlet supply and local human disturbance (a large lagoon-front housing development in one tributary). These pronounced differences imply that glass eel and elver supply to tributaries should be taken into consideration before mitigation or restoration is attempted in response to the decline of this species in North America. Introduction There is spatial variation in the decline of Anguilla rostrata (Lesueur) (American Eel). Populations in the northern part of the range are clearly declining, especially in Canadian waters (Casselman 2003, Casselman and Cairns 2003, Rickhaus and Whalen 2000), while those along the central east coast of the US do not appear to be declining based on earlier analysis of the supply of pre-juvenile larval eels (commonly referred to as “glass eels” due to their transparent bodies and also as “elvers” when referring to the young eels migrating up a river from the sea) (e.g., Able and Fahay 2010, Sullivan et al. 2006). There is less known about spatial variation at the estuarine watershed scale. Spatial variation in seasonal habitat use by glass eels and elvers appears to be in response to seasonal variation in the 10–12 °C isotherm (Sullivan et al. 2009). Other factors that may influence dispersal in estuaries include a combination of abiotic (temperature, river flow, tidal stage; Edeline et al. 2005, Martin 1995 ) or biotic (predation; Musumeci et al. 2013) variables. Habitat restoration is especially important because the decline in American Eel populations (Bonhommeau et al. 2008, Casselman 2003, Casselman and Cairns 2003, Haro et al . 2000) has prompted numerous studies attempting to understand the basis for this pattern. As a result, several potential mechanisms have been invoked including: oceanic effects such as changes in the strength/position of major current systems and thus larval supply to estuaries (Castonguay et al. 1994a, b; Wirth and Bernatchez 2003); impacts on estuaries including over-fishing of prespawning stages (McCleave 1996); reduced access to freshwater habitat, especially 1Marine Field Station, Rutgers, the State University of New Jersey, 800 c/o 132 Great Bay Boulevard, Tuckerton, NJ 08087. *Corresponding author - able@marine.rutgers.edu. Manuscript Editor: Jay Stauffer Northeastern Naturalist 54 K.W. Able, J.M. Smith, J.F. Caridad 2015 Vol. 22, No. 1 due to dams (Busch et al. 1998, Greene et al. 2009); and parasitism by an introduced nematode (Barse and Secor 1999, Barse et al. 2001, Morrison and Secor 2003, Sures and Knopf 2004). In an attempt to further resolve the factors responsible for the spatial variation in the supply and distribution of early life-history stages in and between estuaries, we studied the patterns of abundance, length, and stage of the glass eels and elvers across inlets, thoroughfares between estuaries, and tributaries to Barnegat Bay, NJ. Such an enhanced perspective can help to understand spatial variation and its importance relative to habitat restoration. Field Site Description Barnegat Bay is a shallow (average depth < 2 m, range = 1–6 m), lagoonal estuary with a surface area of 279 km2 that extends along the coast of New Jersey for approximately 70 km (Fig. 1; Kennish 2001). This estuary is connected to the Atlantic Ocean at Little Egg and Barnegat inlets, where the tides are semidiurnal with highest velocities at Barnegat (>1 m/s) and Little Egg (> 2 m/s) inlets (Kennish 2001). An area of exchange for northern Barnegat Bay occurs via the Pt. Pleasant Canal between Barnegat Bay and the Manasquan River estuary. In addition, exchanges between southern Barnegat Bay (Little Egg Harbor) and Great Bay occur at several thoroughfares (Jimmy’s Creek, Little Thoroughfare) which connect these two estuaries (Fig.1). Within Barnegat Bay, the water column is well mixed, although two-layer flow may be evident in the deeper waters near the inlets and in the larger river tributaries (Carpenter 1963, Chizmadia et al. 1984). The flushing time for the bay varies seasonally and is reported to range from 27 to 71 days, with the longest times during the summer (Guo et al. 1997). Freshwater flow into Barnegat Bay comes from tributaries along the western shore of the bay with the largest tributaries feeding into the bay north of Barnegat Inlet (Kennish 2001). Total surface inflow of freshwater into the bay represents about 2–3% of the tidal prism, with other substantial contributions coming from groundwater. Mean salinity in the bay ranges from 18 to 25 ppt (range = 8–32 ppt) with the highest salinities near the two inlets (Kennish 2001). Salinity is lowest (less than 15 ppt) off Toms River and to the north until the vicinity of the Pt. Pleasant Canal where values are higher. Subtidal circulation in the bay is driven primarily by coastal pumping (Chant 2001). Water temperature ranges from -1.4 °C to nearly 30 °C with highest temperatures at the mouth of Oyster Creek due to thermal discharges from the Oyster Creek Nuclear Generating Station (Kennish 2001). The juveniles of American Eel are a common component of the fauna in the system (Able and Fahay 2010, Jivoff and Able 2001, Tatham et al. 1984). Materials and Methods Sampling techniques We sampled for glass eels and elvers at multiple inlets, thoroughfares, and tributaries utilizing two techniques: plankton nets and eels collectors. We used plankton Northeastern Naturalist Vol. 22, No. 1 K.W. Able, J.M. Smith, J.F. Caridad 2015 55 Figure 1. Barnegat Bay study sampling sites/gears including at inlets (Little Egg, Barnegat), thoroughfares between adjacent estuaries (Jimmy’s Creek and Little Thoroughfare with Great Bay, Pt. Pleasant Canal with Manasquan River), and tributaries with dams (Tuckerton Creek, Mill Creek, Kettle Creek). Northeastern Naturalist 56 K.W. Able, J.M. Smith, J.F. Caridad 2015 Vol. 22, No. 1 nets to determine the timing and abundance of glass eels as they entered estuary inlets from the Atlantic Ocean. Collections behind Little Egg Inlet, where Atlantic Ocean water flows into the estuary, followed a weekly, ongoing sampling program for early stage, estuarine-dependent fishes from the bridge over Little Sheepshead Creek during winter and spring 2011 and 2012 (Fig. 1; Able and Fahay 1998, Witting et al. 1999). This site has been previously sampled to detect long-term trends in glass eel timing and abundance (Sullivan et al. 2006, 2009) and collection of live eels for assessing swimming capabilities of American Eel and Conger oceanicus (Mitchill) (Conger Eel) (Wuenschel and Able 2008). For the present study, weekly sampling at this inlet and Barnegat Inlet occurred over two winter/spring periods during 2011 and 2012 (Table 1). We also used plankton nets to sample glass eels in thoroughfares between estuaries to determine other potential sources to tributaries (Table 1). Collections at Little Sheepshead Creek, Jimmy’s Creek, and Little Thoroughfare also served to measure movement between Great Bay and Barnegat Bay, while collections at Point Pleasant Canal measured movements from the Manasquan River into northern Barnegat Bay (Fig. 1). Simultaneous sampling at each thoroughfare occurred during night flood tides. Three 30-minute tows per creek occurred in February and April of 2011 at Jimmy’s Creek and Little Thoroughfare and the same months at Point Pleasant Canal in 2012. Mean values of density, length, and stage were based on combined Table 1. Sampling location and effort for Anguilla rostrata glass eels and elvers into and in Barnegat Bay, NJ, during 2011 and 2012. The Little Egg Inlet sampling occurred at Little Sheepshead Creek. See Figure 1 for further details of location of sampling sites. BI = Barnegat Inlet, LEI = Little Egg Inlet, PPC = Point Pleasant Canal, JC = Jimmy’s Creek, LT = Little Thoroughfare, TC = Tuckerton Creek, MC = Mill Creek, and KC = Kettle Creek. # = number of samples. Median and range provided for temperature and salinity data. Sampling Location Gear Period Frequency # Temp (°C) Salinity (ppt) Inlets BI Plankton net Feb, Apr 2012 Bi-Monthly 2 8.5, 6.4–10.5 32.0, 31.1–33.0 LEI Plankton net Jan–May 2011, Weekly 37 7.0, 1.5–16.0 28.0, 25.0–32.0 Jan–May 2012 Thoroughfares PPC Plankton net Feb, Apr 2012 Bi Monthly 2 11.5, 6.6–16.4 20.3, 16.5–24.0 JC Plankton net Feb, Apr 2011 Bi-Monthly 2 14.5, 2.1–26 27.1, 23.4–31.9 LT Plankton net Feb, Apr 2011 Bi-Monthly 2 16.7, 1.7–26.6 29.4, 14.8–30.6 Tributaries TC Collector March–July 2011, Bi-Weekly 150 12.2, 3.6–24.7 8.3, 0.04–26.6 Jan–Apr 2012 MC Collector March–July 2011, Bi-Weekly 154 12.3, 5.3–25.9 0.1, 0.01–0.1 Jan–Apr 2012 KC Collector March–July 2011, Bi-Weekly 132 5.0, 4.4–27.1 0.1, 0.1– 0.1 Jan–Apr 2012 Northeastern Naturalist Vol. 22, No. 1 K.W. Able, J.M. Smith, J.F. Caridad 2015 57 values for each of the 3 tows on a given date. All glass eels and elvers collected were brought back to the laboratory, preserved in 95% ETOH, and measured for total length. We assumed that all of the eels from Little Egg Inlet, while not staged individually, were stage 1–2 based on prior examination of numerous samples over multiple years (Sullivan et al. 2006, 2009). Collections at Point Pleasant Canal, a thoroughfare between the Manasquan River and Barnegat Bay, occurred in February and April 2012. We determined availability of glass eels and elvers to tributaries with eel collectors, originally developed for sampling early stages of New Zealand and Australian Anguilla spp. (Table 1; Silberschneider et al. 2001). Collectors are passive habitats constructed out of buoyant tufts of unraveled polyethylene rope fiber attached to a polyvinyl chloride (PVC) and terra cotta base (300 mm diameter). Individual collectors represented a standardized sampling replicate (Silberschneider et al. 2001) consisting of equal numbers of fiber tufts (15) unfurled from equal lengths of rope (500 mm). We seasoned new collectors in seawater for 2 weeks to reduce artificial odors and to encourage the development of biofilms prior to deployment, as we have done in the past (Sullivan et al. 2006, 2009). Site selection in tributaries was limited to easily accessible locations below dams. At these sites, we deployed collector arrays on top of homogenous mud or sand substrata along banks of shallow creeks immediately downstream (less than 20 m) from a dam spillway (Tables 1, 2). We selected sites with minimal tidal ranges such that collectors were never completely exposed at low tide and never more than 1–2 m below the surface at high tide. Arrays of collectors (3) were deployed on the bottom, retrieved 24 hours after deployment, and were inverted and submerged 30 times into a plastic tub filled with water to remove eels. We repeated this process twice for each collector or until no eels were detected, and then poured the contents of the tub through a 1-mm-mesh sieve. We counted the eels and transferred them to a holding bucket. Collectors were fished simultaneously at all sites. We sampled the 3 sites in Barnegat Bay bi-weekly from February to July 2011, and January to April 2012 (Table 1). For all sites, we recorded physical variables at deployment and retrieval of sampling gear. In most instances, a YSI was used to record temperature (°C) and salinity (ppt). A random sub-sample of 10% or a maximum of 40 American Eels per collector were anaesthetized using MS-222 and then measured and assessed for length and Table 2. Characteristics of the tributary sampling sites below dams for glass eels and elvers in Barnegat Bay, NJ, during 2011 and 2012. See Figure 1 for further details of location of sampling sites. Distance from dam face to Distance of Depth Little Egg Inlet/ collectors range Barnegat Inlet/ Barnegat from dam Tidal at below Location Point Pleasant Canal (km) Bay (km) face (m) dam dam (m) Tuckerton Creek 12.8/ 27.6/ 57.7 4.9 24.0 Yes 1–2 Mill Creek 23.2/ 15.6/ 44.8 7.1 6.3 No less than 1 Kettle Creek 63.2/ 31.7/ 8.3 5.0 3.0 No less than 1 Northeastern Naturalist 58 K.W. Able, J.M. Smith, J.F. Caridad 2015 Vol. 22, No. 1 stage of development as per Haro and Krueger (1988) such that: Stage 1– indicates no pigment on any part of the body between dorsal and anal fin origins; Stage 2 – pigment is along the base of the dorsal fin, but not extending below apices of dorsal posterior cone myosepta; Stage 3 – pigment extends ventrally along myosepta approximately halfway to the lateral line; Stage 4 – pigment extends to the lateral line, which is now distinctly pigmented, and intermyoseptal pigment is usually present dorsolaterally; Stage 5 – pigment extends ventrally to midway between the lateral line and apices of ventral posterior cone myosepta, and the intermyoseptal pigment is always present dorsolaterally, but pigment is more intense along myosepta; Stage 6 – pigment extends further ventrally along myosepta, forming irregular ventral margin, dorsolateral surfaces are uniformly pigmented, intermyoseptal pigment is usually present below the lateral line, but myosepta are more distinctly pigmented, and the pigment on the base of the dorsal fin may be present or absent; Stage 7 – previously pigmented areas are now all uniformly pigmented, obscuring myoseptal pigmentation, ventral margin or pigment is a distinct line, the base of the dorsal fin is usually pigmented, and the base of the anal fin is either pig mented or not. Data analysis We used General Oceanics flowmeters to determine water volume sampled and standardize abundance of species caught with plankton nets at each inlet and thoroughfare. This information, along with abundance data, was converted into eel densities (individuals/1000 m3) combined across all three plankton tows. Similarly, we based estimates of eel abundance (catch-per-unit-effort, CPUE) from collectors on total number from all 3 collectors combined at each site. Results Environmental characteristics Temperature and salinity during 2011 and 2012 varied between inlet, thoroughfare, and tributary sites, but the former two overlapped between these locations while the latter was distinctly different for salinity (Figs. 2, 3). Temperatures ranged from 1.5 to 24.5 °C for inlet sites (Little Egg Inlet, Barnegat Inlet), 1.7–26.6 °C for thoroughfares (Point Pleasant Canal, Jimmy’s Creek, Little Thoroughfare), and 3.6–27.1 °C for tributaries (Tuckerton, Mill, and Kettle creeks). The wide values in temperature occurred because they were collected from winter into spring months at all sites (December–June; Table 1). Salinities ranged from 25–33 ppt for inlet sites, 14.8–31.9 ppt for thoroughfares, and 0.01–26.6 ppt for tributaries. Variation in supply to inlets, thoroughfares, and tributaries Glass eels and elvers were collected at every site sampled in Barnegat Bay including 2 inlets, 3 thoroughfares, and 3 tributaries over 2011 and 2012 (Table 1; Figs. 2, 3). The timing of occurrence of eels was similar across inlets, thoroughfares, and tributaries in 2011 and 2012. If we combine the sampling periods across both years, the composite occurrence began with collections in December 2011 (at Little Egg Inlet) and extended to May 2012. The peak in abundance at Little Egg Northeastern Naturalist Vol. 22, No. 1 K.W. Able, J.M. Smith, J.F. Caridad 2015 59 Inlet occurred in April in 2011 and February in 2012, but the values were similar from February through April in both years. The peak in occurrence at the site with the most-abundant collections (Tuckerton Creek tributary) was in March in both years; the peak at Kettle Creek was in April in 2011 and February in 2012. The number of glass eels and elvers collected varied among the inlets, thoroughfares, and tributaries during 2011 and 2012 in part due to the different collecting techniques, timing of collection, and degree of effort. The number of individuals per collection was always greatest at Tuckerton Creek (2011 n = 4813; 2012 n = 23,913) with eel collectors and much lower at Little Egg Inlet (2011 n = 153; 2012 n = 192) with the plankton net and at the Kettle Creek (2011 n = 912; 2012 n = 1130) and Mill Creek (2011 n = 0; 2012 n = 11) tributaries with eel collectors. Barnegat Inlet, with much fewer collections, was lower in 2012 (n = 3). The thoroughfares had variable values at Point Pleasant Canal (from the Manasquan River; 2012 n = 17), Jimmy’s Creek (2010 n = 2; 2011 n = 30), and Little Thoroughfare (between Great Bay and Little Egg Harbor: 2010 n = 0; 2011 n = 15). Among the inlets, during synoptic sampling, the density of glass eels at Little Egg Inlet (18.9 individuals/1000 m3 for February and April 2012 only) was nearly double that at Barnegat Inlet (9.6 individuals/1000 m3 for February and April 2012) when collections were made on the same nights. Among the thoroughfares, the values ranged from the highest, Pt. Pleasant Canal (223.1 individuals/1000 m3), at the northern limit of the bay to those at Jimmy’s Creek (25.5 ind/1000 m3) and Little Thoroughfare (5.5 individuals/1000 m3) at the southern limit of the bay, although these were from similar months but different years. Among the frequently collected tributaries on the western side of the bay, the composite abundance was an order Figure 2. Spatial and seasonal average monthly eel abundance at Little Egg Inlet (density) during 2011–2012. Northeastern Naturalist 60 K.W. Able, J.M. Smith, J.F. Caridad 2015 Vol. 22, No. 1 of magnitude greater in both years at Tuckerton Creek (187.8 individuals/collector/ day) than Kettle Creek (13.3 indidivduals/collector/day) and both of these were much greater than at Mill Creek (0.062 individuals/collector/day) with the same collecting technique (Fig. 3). These patterns were consistent across all synoptic sampling periods. The collections at Mill Creek were uniquely low with no eels collected in 2011 and only 11 collected in 2012 when we enhanced our sampling Figure 3. Spatial and seasonal average monthly eel abundance at Barnegat Bay tributaries during 2011–2012: CPUE with different scales at (A) Tuckerton and (B) Mill and Kettle creeks. Northeastern Naturalist Vol. 22, No. 1 K.W. Able, J.M. Smith, J.F. Caridad 2015 61 effort by increasing the number of collectors and locations along the creek in which we sampled (5 locations and 15 collectors). Variation in length and stage In winter of 2011 and in winter through spring of 2012, when the collections across the period of eel supply were most complete, the stage of eels changed over time (Fig. 4) but length did not change markedly. The mean length of eels was similar regardless of whether they were collected at inlets (54.2 mm, range = 46.9–60.4 mm) or thoroughfares (53.7 mm, range = 44.3– 63.9 mm) (sample size for inlets and thoroughfares = 170 glass eels). However, mean lengths were slightly greater at tributaries (57.5 mm, range = 51.5–69.8 mm) (Tuckerton, Mill, and Kettle creeks; sample size = 30,957 glass eels). A few glass eels also occurred at Tuckerton Creek and Kettle Creek tributaries during January, but subsequently there was an increasing number of later stages such that by March–April, stages 3–6 were the most prominent even though a few glass eels were collected at the same time. Only glass eels (stages 1–2) and stages 3–4 occurred in the very few eels collected at Mill Creek. Figure 4. Seasonal and spatial changes in average stage of glass eels and elvers for 3 tributaries (Tuckerton, Mill, and Kettle creeks) and Little Egg Inlet during the winter and spring 2012. Northeastern Naturalist 62 K.W. Able, J.M. Smith, J.F. Caridad 2015 Vol. 22, No. 1 Discussion Supply to inlets, thoroughfares, and tributaries While the variation in sampling gears (plankton nets, eel collectors) across habitat types (inlets, thoroughfares, tributaries) and at different intervals makes quantitative comparisons difficult (Ogden and Forward 2012), the composite collections across all these habitats provides, for the first time anywhere, a useful spatial perspective on glass eel and elver supply to a lagoon estuary. A similar approach in 2 other New Jersey drowned river valley estuaries provides a basis for comparison (Sullivan et al. 2009). In all 3 systems, whether they are lagoon type or drowned river valleys, the period of ingress at the inlets was long, from December through May at this latitude. Based on the data collected in this study, American Eels in Barnegat Bay come from multiple sources, including from the ocean and from adjacent estuaries. In both years, glass eels were evident from Little Egg and Barnegat inlets, as well as from thoroughfares between Barnegat Bay and Great Bay to the south and Manasquan River to the north. These multiple sources help to ensure a glass eel/ elver supply to lower salinity tributaries but also make it difficult to determine the relative contribution of the different sources. The eels in collectors below the dam in Tuckerton Creek could have come primarily through Little Egg Inlet either via lower Barnegat Bay (Little Egg Harbor) or from thoroughfares (Jimmy’s Creek, Little Thoroughfare) from Great Bay. Similarly, the eels in collectors at Kettle Creek may have come from Barnegat Inlet or through the Point Pleasant Canal from the Manasquan River or both. The relative lack of American Eels at Mill Creek is surprising given its location midway between Barnegat and Little Egg inlets and relatively near the thoroughfares behind Little Egg Inlet (Fig. 1). Prior studies in adjacent drowned river valley estuaries in New Jersey have suggested that movement upstream from inlets to tributaries does not occur until temperatures reach 10–12 °C (Sullivan et al. 2009) or 10–15 °C (Overton and Rulifson 2009) in the spring. However, in the present study some peaks in abundance at the Tuckerton and Kettle creek tributaries to Barnegat Bay occurred at temperatures of 5–6 °C. At Tuckerton Creek, which was sampled in an earlier study with the same techniques (Sullivan et al. 2009), the arrival time started and showed peaks in abundance earlier. Further, at Kettle Creek, all of the obvious peaks in abundance occurred before the 10–15 °C threshold was reached. This difference in arrival times could be due to earlier arrival at inlets in 2012, where glass eels were detected as early as December. This observation is consistent with the warmer water temperatures during this winter (K.W. Able, Rutgers University Marine Field Station, Tuckerton, NJ, pers. observ.). The effect of temperature has been considered to have an important effect on the upstream migration of other species of Anguilla as well (August and Hicks 2008, Bureau du Columbier et al. 2011). Others have noted annual variation in the upstream migration of glass eels and elvers in the Roanoke River, NC (Overton and Rulifson 2009). Still others have noted a difference in salinity preference among different contingents of Anguilla anguilla (L.) (European Eel) (Edeline 2007, Edeline et al. 2005). This difference Northeastern Naturalist Vol. 22, No. 1 K.W. Able, J.M. Smith, J.F. Caridad 2015 63 could compound our understanding if it occurs in the American Eel, as has been suggested (Arai and Chino 2012, Daverat et al. 2006, Lamson et al. 2006, Sola and Tongiorgi 1996, Sullivan et al. 2006). While many have suggested that freshwaters are the cue for some of these upstream movements, others have indicated the scent of decaying leaf detritus, aquatic plants, and migratory Alosa pseudoharengus (Wilson) (Alewife) were the actual attractants (Sorenson 1986) or migration was influenced by an individual’s energy status (Bureau du Colombier et al. 2009, 2011; Edeline 2007). When upstream migration does occur, it is often associated with changes in pigmentation, as in this and other studies of American Eel (Haro and Kreuger 1988, Luers et al. 2011, Sullivan et al. 2009) and A. anguilla (Briand et al. 2005, Iglesias et al. 2010). The results from Barnegat Bay tributaries indicate that the stages observed there are similar to those attained, with similar collecting techniques in the adjacent Mullica River–Great Bay estuary and Great Egg Harbor estuary (Sullivan et al. 2009). Variation in supply to tributaries The patterns of distribution and abundance of eels was most variable among tributaries. All tributaries were within similar minimum distances of a source of eels: Little Egg Inlet for Tuckerton Creek (12.8 km), Barnegat Inlet for Mill Creek (15.6 km), or Point Pleasant Canal for Kettle Creek (8.3 km). Thus, the differences observed were not likely a function of distance from a source. However, the exchange of waters from the ocean at the larger Little Egg Inlet is much greater relative to Barnegat Inlet and even greater than at the Point Pleasant Canal (Chant 2001, Kennish 2001). This difference may account for the larger number of eels collected at Tuckerton Creek, which is near Little Egg Inlet. Also, the much greater abundance at Tuckerton Creek may have been the result of the close proximity of estuarine salinity to a clear freshwater source at this location, thus the change between saltwater and freshwater was most obvious and may have been more detectable by the eels. The near absence of eels at Mill Creek in both years, despite enhanced sampling in 2012, implies that there was a reduced source of eels for this site, even though there were two nearby inlets from the ocean (Barnegat and Little Egg inlets). Because all the tributary sites were similar distances from Barnegat Bay, that factor should not have influenced eel abundance in the collectors. Also, both Kettle and Mill creeks were above tidal influence and were entirely freshwater, so those variables did not likely contribute to the reduced abundance at Mill Creek. Because the collections of eels in Mill Creek were absent or very low during both years, we transected the creek with kayaks and by wading to determine if there were obstructions that prevented eels from swimming upstream. No obstructions were found over 3 days (11 hours) of searching, but we noted the large lagoon development (Beach Haven West: 2.2 mi2 [569.8 ha] in area with 104 dead-end canals) downstream of the collecting site. These dead-end canals are known to create less-than-optimal conditions elsewhere in Barnegat Bay because they cause hypoxia/anoxia (not a problem in the winter; Sugihara et al. 1979). In other estuaries, similar dead-end canals have produced similar low dissolved oxygen conditions as well as increased Northeastern Naturalist 64 K.W. Able, J.M. Smith, J.F. Caridad 2015 Vol. 22, No. 1 production of hydrogen sulfide (Luther et al. 2004, Ma et al. 2006), all of which can cause a negative response by many organisms (Bargarinao and Lantin-Olaguer 1999, Bagarinao and Vetter 1989, Seliger et al. 1985, Theede 1973). The proliferation of these dead-end, artificial waterways is increasing on all continents (Waltham and Connolly 2011) and may result in the decline in habitat quality and, as a result, in the decline of Anguilla spp. In conclusion, the occurrence of glass eels and elvers at the inlets, thoroughfares, and tributaries indicates that there are multiple sources to Barnegat Bay and its tributaries, which is probably true for other topographically complex estuaries as well. The great differences in occurrence and abundance at each of the 3 tributaries sampled synoptically with identical collectors over 2 years indicates that if there is an attempt to mitigate for and provide passage over dams or other obstructions that may be contributing to the decline of eels (Gollock et al. 2011, Kemp and O’Hanley 2010, O’Hanley and Tomberlin 2005, Righton et al. 2012), there should first be an attempt to evaluate supply to individual tributaries. As an example, attempts to provide passage over the dam at Mill Creek would have been unproductive because so few eels reached the dam. Alternatively, providing eel passage at Tuckerton Creek would be optimal because large numbers of glass eels and elvers accumulated at this dam site in both years of this study and in previous ones (Sullivan et al. 2009). Thus, providing eels passage at this dam would result in many more eels introduced into the freshwaters above the dam. Acknowledgments We would like to thank numerous technicians at Rutgers University Marine Field Station, especially T. Malatesta, R. Hagan, J. Rackovan, and C. Denisevich, and the Jacques Cousteau National Estuarine Research Reserve volunteers P. Filardi, S. Zeck, T. Siciliano, T. Bonovolanta, and E. Lesher. The Barnegat Bay Partnership, Corporate Wetlands Restoration Partnership, and Research Internships in Ocean Sciences (RIOS) National Science Foundation-Research Experiences for Undergraduates (via an internship to J. Cullen) provided funding. This paper is Rutgers University Institute of Marine and Coastal Sciences Contribution Number 2015-1. Literature Cited Able, K.W, and M.P. Fahay. 1998. The First Year in the Life of Estuarine Fishes in the Middle Atlantic Bight. Rutgers University Press, New Brunswick, NJ. 342 pp. Able, K.W., and M.P. Fahay. 2010. Ecology of Estuarine Fishes: Temperate Waters of the Western North Atlantic. 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