An Evaluation of Boat Basin Dredging Effects: Response of Fishes and Crabs in a New Jersey Estuary

Transcription

1 North American Journal of Fisheries Management 30: , 2010 Ó Copyright by the American Fisheries Society 2010 DOI: /M [Article] An Evaluation of Boat Basin Dredging Effects: Response of Fishes and Crabs in a New Jersey Estuary KENNETH W. ABLE* AND JOSEPH DOBARRO Marine Field Station, Institute of Marine and Coastal Sciences, Rutgers University, 800 c/o 132 Great Bay Boulevard, Tuckerton, New Jersey 08087, USA ANGELA M. MUZENI-CORINO New Jersey Department of Environmental Protection, Division of Water Supply, Bureau of Safe Drinking Water Technical Assistance, 401 East State Street, Post Office Box 426, Trenton, New Jersey , USA Abstract. Dredging is one of the most common human modifications of estuaries and although its effects have often been studied, there has been little effort in evaluating the effects on mobile macrofauna, such as fishes and crabs. We evaluated the response of fishes and crabs to 4 d of dredging in a small boat basin within a polyhaline marsh creek of a New Jersey estuary. We used several measures, including fish and crab species composition, abundance, and size from trap collections and movements of marked mummichogs Fundulus heteroclitus before, during, and after dredging. In general, the fauna changed little during the 4 d of dredging relative to the 1.5-month sampling period. Species composition variations that did occur may have been due to seasonal changes that are typically observed during the fall based on annual sampling at this site. The movement of tagged mummichogs was minimal, with most recaptures taking place in the boat basin. Individuals that left the boat basin moved into pools in an adjacent marsh for the winter. These results suggest that the short-term effect of this low-sediment-volume dredging project was negligible for the benthic fishes and crabs studied, which we believe are representative of the high-salinity portions of estuaries in the northeastern United States. Dredging is one of the most common forms of human activity in estuaries in the USA and other countries (Kennish 1992, 1998; Wilber and Clarke 2001; Elliott and Hemingway 2002; Schoellhamer 2002; Ponti et al. 2009). While numerous state and federal regulations are designed to limit negative effects of dredging, the interpretation of these effects is still controversial, especially relative to ambient natural influences during seasonal turnover and episodic events, such as storms. Much of our current understanding of dredging effects is based on the deposition of suspended sediments as a result of dredging in navigation channels (Wilber and Clarke 2001; Ireland 2007). Most attention has been focused on the effects of sediment concentration and exposure duration in laboratory settings as opposed to actual field evaluations. Further, there has been relatively little attention on mobile fauna, such as fishes and crabs (Wilber and Clarke 2001), and there have seldom been attempts to determine their movements in response to dredging. However, a small boat basin adjacent to Great Bay in New Jersey has been the focus of long-term, detailed studies of the fish and crab fauna * Corresponding author: able@marine.rutgers.edu Received November 17, 2009; accepted May 23, 2010 Published online August 25, 2010 (Able and Fahay 1998, 2010), particularly the movements of the mummichog Fundulus heteroclitus, an important prey species for many economically and ecologically important fish and birds (Able and Fahay 2010). Thus, this boat basin provides an excellent site for evaluating the effects of dredging. In the present study, we evaluate the response of fishes and crabs to dredging of the aforementioned small boat basin. Attention is focused on responses inside the boat basin by comparisons of fish and crab species composition, size, and abundance and especially the movements of tagged mummichogs before, during, and after 4 d of dredging. Over the same periods, several environmental variables (temperature, salinity, dissolved oxygen, and turbidity) were monitored inside and outside the basin to provide perspective into the changes associated with dredging. Study Area The study was conducted in a small boat basin adjacent to Great Bay, part of the Jacques Cousteau National Estuarine Research Reserve (JCNERR) at Mullica River Great Bay in southern New Jersey (Figure 1). Great Bay is a temperate, polyhaline estuary with a broad seasonal temperature range ( 0.18C to 25.28C), a relatively stable salinity range ( %), and a moderate tidal range (1.1 m; Able et 1001

2 1002 ABLE ET AL. FIGURE 1. Sampling sites for a dredging effects study in Great Bay, southern New Jersey: (A) locations of the study area, the salinity and turbidity sensors at buoys 126 and 139, and the meteorological station at Nacote Creek; (B) locations of specific sampling sites adjacent to the Rutgers University Marine Field Station (RUMFS) boat basin; and (C) detailed view of the boat basin, including placement of deep and shallow traps (see panel B also) and one trap equipped with a camera. al. 1992; Able and Fahay 1998; Kennish and O Donnell 2002). Compared with other estuaries along the northeastern Atlantic seaboard, Great Bay is relatively pristine due to a mostly undeveloped and protected watershed (Psuty et al. 1993; Kennish 2004). The study area was a small embayment that serves as the Rutgers University Marine Field Station (RUMFS) boat basin and was comprised of a basin (;200 m wide) and an access channel (200 m long; Figure 1). The basin is connected to Schooner Creek, a subtidal creek (maximum depth to 2 m), and Shooting Thorofare, a channel (maximum depth to 11 m) leading from Little Egg Harbor into Great Bay. The basin was previously dredged in 1974, 1988, 1991, and Methods Dredging operations. Dredging operations were conducted on ebbing tides during November 10 18, 2003, with 4 d of actual dredging. Approximately 7,646 m 3 of sediment were removed with a hydraulic dredge equipped with a 35.8-cm-wide cutterhead. Average depth increased from 0.5 to 1.5 m in the basin and from 0.2 to 1.6 m in the access channel based on detailed hydrographic surveys conducted 9 d before and 1 d after completion of dredging. Environmental parameters. A YSI 6000 Series datasonde (Yellow Springs Instruments) was deployed in the center of the boat basin before, during, and after dredging in order to monitor water quality (Figure 1). The datasonde was housed in a short section of polyvinyl chloride pipe that was mounted in the center of a steel cage ( m); both the pipe and the cage protected the data logger from damage by the dredging equipment. The following parameters were measured at 30-min intervals: temperature, salinity, conductivity, dissolved oxygen percent saturation, dissolved oxygen concentration, ph, depth, and turbidity. The same type of datasonde was also deployed at two locations (Buoy 126 and Buoy 139) in Great Bay (Figure 1A) as part of regular sampling by the JCNERR System Wide Monitoring Program (Kennish and O Donnell 2002). Fish and crab sampling. Sampling for fishes and crabs was conducted in six habitats, including basin deep, basin shallow, subtidal creek, intertidal creek, marsh pool, and marsh perimeter (Figure 1B, C). The basin deep sites were in the central portion of the basin and were slated for dredging along with a site located in the access channel leading into the basin. The basin shallow sites were in the basin periphery, an area not to be dredged. To observe any potential movements of

3 BOAT BASIN DREDGING EFFECTS 1003 TABLE 1. Sampling effort (number of trap sets) for the mark recapture study used to evaluate fish and crab responses to dredging in the Rutgers University Marine Field Station boat basin (see Figure 1) in Basin deep refers to traps set in areas that were subject to dredging, including existing long-term trap sampling sites, traps set at the boat basin mouth, and the camera trap. Basin shallow refers to traps set in shallower areas of the boat basin that were not subject to dredging. Note that not all sites were sampled during dredging operations. Number of trap sets Period Dates Number of days sampled Basin deep Basin shallow Subtidal creek Intertidal creek Marsh pool Marsh perimeter Total Before dredging Oct 22 Nov During dredging Nov 11 Nov After dredging Nov 20 Dec Total fish from the boat basin, additional sampling was conducted at two subtidal sites located within Schooner Creek (a natural tidal creek adjacent to the dredging site) and at a single intertidal site located in a small creek that branched off the main channel of Schooner Creek. Sampling also took place within a single pool in an adjacent natural marsh and at an additional site located on the marsh perimeter outside of the boat basin. These provided reference points for comparison with the sampling in the boat basin. Unbaited, wire-mesh traps (45-cm length, 23-cm diameter, 20-mm opening, 6-mm mesh) were placed at the above-mentioned locations in the boat basin and the natural sites nearby (Figure 1; Table 1). Within the boat basin, the same traps from our long-term sampling protocol there (Able and Hales 1997; Able et al. 2006; Able and Fahay 2010) were utilized in order to compare these data across years. The long-term sampling protocol consisted of two traps in deeper areas off each of three docks. Since these traps were in areas slated for dredging and would have to be moved, we added six traps in shallower areas that were not slated for dredging to provide continuous sampling (Figure 1C). In addition, two traps were set at each of the additional sites outside of the basin. The traps were set out on the first day of each week of the sampling protocol (normally Monday). On the subsequent days, the traps were fished daily (;every 24 h) until the end of the week (Friday). Sampling was conducted during October 22 through December 5, 2003, with a total of 11 sampling days before dredging, 4 sampling days during dredging, and 10 sampling days after dredging. During actual dredging, traps were not set at the mouth of the boat basin or the marsh perimeter because of limited access to these sites at this time. For each trap sample, fish and selected crab species were identified and enumerated, and 20 random individuals of each species were measured to the nearest millimeter total length (TL) or fork length for fishes and the nearest millimeter carapace width for crabs. A separate count was maintained for all mark recaptures (see below). All individuals, including recaptures, were then immediately released at the capture site. Fish behavior. We utilized a wire-mesh minnow trap outfitted with a camera to better understand factors influencing fish catches and behavior. The camera (Multi-SeaCam 1050; DeepSea Power & Light, Inc.) was mounted in the opening on one side of the trap. This camera was connected to a monitor located in the RUMFS office of the first author so that real-time and recorded observations were possible. Prior to the collection of fish from this trap, the monitor was observed for 10 min and behavior was recorded. These observations included the number and species of fish in the trap, behavior within the trap, and activity outside the trap. When there were numerous fish in the trap, we recorded the species present, an approximate count of each species, and the types of behaviors observed (i.e., feeding, aggression, exit or entry, and swimming behavior [slow versus active]). Observations outside of the trap included whether or not a predator (e.g., a crab) was present, interaction between fish inside the trap and a predator or other fish outside of the trap, and the presence or absence of fish outside of the trap. In instances when recording the number of interactions was difficult because the fish were too numerous, each interaction type was only noted as being observed. Mark recapture. In an attempt to determine whether dredging influenced residency and movements, we marked a number of species, including the sheepshead minnow Cyprinodon variegatus and cunner Tautogolabrus adspersus (September 29 November 7). In addition, we targeted mummichogs for a 3-d period (September 29 October 1). All of these fish were collected from the boat basin (from various locations, both deep and shallow) using unbaited, wiremesh traps identical to those used for sampling fish and crabs. Fish were marked subcutaneously with injected acrylic paint on the dorsal surface of the body (Lotrich and Meredith 1974; Thresher and Gronell 1978) and

4 1004 ABLE ET AL. were released immediately back into the boat basin in a central location (Figure 1). It was assumed that marking mortality would be low because prior analyses indicated little effect of acrylic marking on mortality, growth, and mark retention for individuals of similar size (Smith and Able 1994; Chitty and Able 2004; Able et al. 2005). Data analyses. Catch per unit effort (CPUE) and recaptures per unit effort (RPUE) were calculated to standardize unequal effort across years and sampling areas. Repeated-measures analysis of variance was performed to test for differences among environmental variables, total species composition, CPUE, RPUE, and species abundance during various dredging periods and sampling areas. Results Environmental Characteristics Some environmental characteristics appeared to change briefly as a result of dredging, while others did not (Figure 2). Salinity values within the boat basin were not affected by the dredging operations. Salinity values were missing for a portion of the sampling period, but the salinity values measured shortly after dredging operations were consistent with those measured before dredging. Temperature decreased significantly (F ¼ 3,075.52; df ¼ 2; P, ) during dredging. Dissolved oxygen in the boat basin decreased significantly (F ¼ ; df ¼ 2; P, ) at the beginning of dredging to a low of 2.2 mg/l and then rebounded to predredging levels throughout the 4-d dredging period and beyond. Water clarity in the basin was measured as nephelometric turbidity units (NTU). Turbidity rose significantly (F ¼ ; df ¼ 2; P, ) to average levels of 138 NTU about halfway through the dredging operations and then settled back to predredging levels shortly after the end of dredging. The period of dredging coincided with a storm that may have confounded some of the measures in the boat basin. On November 13 and 14, storm effects were evident based on increased wind speeds at a JCNERR meteorological station at Nacote Creek (Figures 1A, 3). During the same period, salinity decreased and turbidity increased at two buoys in adjacent Great Bay. Thus, the increased turbidity in the boat basin may have been due in part to storm effects. Similar effects of other storms were evident after the period of dredging. Fish and Crab Species Composition From October 22 to December 5, 49,016 fish representing 16 species and 191 crabs representing 4 species were collected, with most individuals (25,830 fish [16 species] and 38 crabs [4 species]) collected before dredging, when the sampling effort was longer (Table 2). Fewer species and fewer individuals were collected during dredging (7,707 fish [10 species] and 45 crabs [3 species]). After dredging, the same number of species but more individuals (15,479 fish [10 species] and 108 crabs [2 species]) relative to the dredging period were collected. Overall, the CPUE for all species was significantly different before dredging versus after dredging (F ¼ 10.24; df ¼ 2; P, ). However, the response to dredging did vary by individual species. The most abundant species throughout the sampling period was the mummichog (n ¼ 48,074). This species was the most frequently occurring in traps before (94.4%), during (100%), and after dredging (94.1%) and also had the highest CPUE before (93.8 individuals/trap), during (97.1 individuals/trap), and after (63.9 individuals/trap) dredging. This variance in CPUE was significant (F ¼ 18.98; df ¼ 2; P, ). Sheepshead minnow declined over the sampling period, with the frequency of occurrence decreasing from 27.5% before dredging to lower levels during (15.4%) and after (13.1%) dredging. During the same period, CPUE of sheepshead minnow declined from 0.94 individuals/trap before dredging to similar levels during (0.36 individuals/trap) and after (0.31 individuals/trap) dredging. For Atlantic silversides, frequency of occurrence increased over the sampling period from 15.6% before dredging to 23.1% during dredging and 33.5% after dredging, while CPUE followed the same pattern (before dredging: 0.36 individuals/trap; during: 0.77 individuals/trap; after: 1.09 individuals/trap). However, changes in CPUE for sheepshead minnow (n ¼ 353) and Atlantic silversides (n ¼ 426) were not significantly different (Table 2). Another relatively abundant species, the cunner (n ¼ 51), decreased in frequency of occurrence from 10.8% before dredging and 11.5% during dredging to 0.8% after dredging. Similarly, cunner CPUE was 0.13 individuals/trap before dredging and 0.19 individuals/trap during dredging but fell to 0.01 individuals/trap after dredging. Other, lessabundant fish species (with at least one period in which CPUE. 0.1) increased slightly during dredging (fourspine stickleback and striped killifish), did not change (oyster toadfish), or decreased during dredging and then were absent after dredging (winter flounder). Among crab species, only the green crab was collected during all three sampling periods; its abundance peaked during dredging and remained high after dredging (Table 2). Size composition of mummichogs, the most abundant species, did not change significantly over the sampling period. Prior to dredging, the average size of mummichogs was 58.7 mm TL (range ¼ mm);

5 BOAT BASIN DREDGING EFFECTS 1005 FIGURE 2. Average daily temperature (8C), salinity (%), dissolved oxygen (mg/l), and turbidity (nephelometric turbidity units [NTU]) at the Rutgers University Marine Field Station boat basin during Data are from a data logger placed at end of the center dock (see Figure 1C). Gray area indicates the period during which dredging of the boat basin occurred. after dredging, the average size was 53.4 mm TL (range ¼ mm). To further evaluate the response to dredging, the seasonal abundance of mummichogs observed during the study period was compared with the same period in the boat basin in other years (Figure 4). We separated abundance into estimates from deep (where dredging occurred, ;1 m) and shallow (immediately adjacent to dredged areas,,1 m) trap depths to provide more detailed examination of the response during The

6 1006 ABLE ET AL. FIGURE 3. Salinity, turbidity, wind speed, and wind direction as indicators of storm activity in Great Bay, New Jersey, during the fall and early winter of 2003 (see Figure 1A for monitoring site locations). Gray area indicates the period during which dredging of the boat basin occurred. abundance in deep traps did not decline during dredging but was significantly lower after dredging (F ¼ 11.85; df ¼ 1; P, ) and then increased again at the time of the last sample collection. The abundance in shallow traps decreased significantly during dredging (F ¼ 10.7; df ¼ 1; P, ) but then reached the highest levels before declining over the last 2 weeks of sampling. In other years, the response of mummichogs during this period of declining temperatures (Able and Hales 1997; Able et al. 2005), as in 2003 (Figure 2), varied by year. Often, abundance increased over the sampling period, especially in , with greater abundance by week 52 in all prior years (Figure 4). Thus, the response of mummichogs to dredging must be interpreted in that seasonal context. In a further attempt to evaluate how changes in mummichog abundance might be influenced by dredging, we examined patterns relative to habitats in the boat basin (basin deep, basin shallow) and in

7 BOAT BASIN DREDGING EFFECTS 1007 TABLE 2. Abundance (Abun.), percent frequency of occurrence (Freq.), and mean (SE) catch per unit effort (CPUE; individuals/trap) for fish and crab species collected before, during, and after dredging operations at the Rutgers University Marine Field Station boat basin in See Figure 1C for sampling locations (basin shallow, basin deep). Asterisks indicate species that were observed in the camera trap during each period. Before During After Species Abun. Freq. CPUE Abun. Freq. CPUE Abun. Freq. CPUE Fourspine stickleback Apeltes quadracus (0.01) 12* (0.05) (0.01) Blue crab Callinectes sapidus ,0.01 (,0.01) (0.01) 0 Green crab Carcinus maenas (0.03) (0.14) (0.06) Black sea bass Centropristis striata 3* (0.01) (0.03) 0 Conger eel Conger oceanicus (0.01) (0.01) 0 Sheepshead minnow Cyprinodon variegatus (0.18) (0.11) (0.09) Smallmouth flounder Etropus microstomus ,0.01 (,0.01) 0 0 Mummichog Fundulus heteroclitus 25,383* (3.75) 7,574* (5.71) 15,117* (3.89) Striped killifish Fundulus majalis (0.02) (0.04) (0.02) Naked goby Gobiosoma bosc (0.01) 0 0 Asian shore crab Hemigrapsus sanguineus (0.04) (0.03) Inland silverside Menidia beryllina ,0.01 (,0.01) Atlantic silverside Menidia menidia 109* (0.08) (0.27) 257* (0.18) Oyster toadfish Opsanus tau 12* (0.01) (0.03) (0.01) Lady crab Ovalipes ocellatus (0.01) 0 0 Summer flounder Paralichthys dentatus ,0.01 (,0.01) Winter flounder Pseudopleuronectes americanus (0.01) (0.02) 0 Northern pipefish Syngnathus fuscus ,0.01 (,0.01) 0 0 Tautog Tautoga onitis ,0.01 (,0.01) ,0.01 (,0.01) Cunner Tautogolabrus adspersus 34* (0.02) (0.08) (0.01) Grand total 25,868 7,752 15,587 adjacent habitats (the subtidal creek sites, intertidal creek site, marsh pool, and marsh perimeter; Figures 1, 5). In most habitats, there was a general yet insignificant decline in abundance over the sampling period. This also occurred at sites outside the boat basin, including the intertidal creek and marsh pool sites. On this basis, the magnitude of change in fish abundance in the basin deep and basin shallow sites during the dredging period was similar to the magnitude of change at the adjacent undredged sites (Figure 5). Fish Behavior The behavior of fish in the camera trap did not indicate any obvious response to the dredging, although visibility was somewhat limited during dredging. Throughout the sampling period (before, during, and after dredging), several species were observed (Table 2). There were no marked qualitative differences in the behaviors (i.e., feeding, aggression, exit or entry, swimming behavior) for mummichogs, the dominant species (.98%) observed during each period. In addition, no mortality was observed, and there were no obvious signs of stress or unusual behaviors. Qualitative observations indicate that there was less feeding after dredging, but this could also be due to the lower water temperatures (on colder days, the fish appeared sluggish and less active). Feeding was still observed, however; for instance, on November 21 (only 2 d after dredging activities were completed), a mummichog was observed to be feeding on a shrimp Palaemonetes sp., and other mummichogs were chasing it in an attempt to steal the shrimp. Residency and Movements In an additional attempt to define the response of common fish species to dredging, we sought to evaluate residency and movements of several species. Three of the four marked species were not recaptured after dredging, but the number tagged was small: 120

8 1008 ABLE ET AL. FIGURE 4. Weekly average abundance (catch per unit effort [CPUE]) for all mummichogs collected across trap sampling sites in the boat basin (shallow ¼ traps at the margin of the boat basin [see Figure 1B, C]; deep ¼ traps that correspond in location to long-term sampling sites). Data for are from long-term boat basin trapping; data for 2003 are from the current dredging effects study. Gray area indicates the period during which boat basin dredging occurred in 2003.

9 BOAT BASIN DREDGING EFFECTS 1009 FIGURE 5. Daily average abundance (catch per unit effort [CPUE]) for mummichog at separate sampling sites (Figure 1B, C) during the dredging effects study in Basin deep traps include the existing boat basin traps, the camera trap, and the mouth of the boat basin. Gray area indicates the period in which boat basin dredging occurred.

10 1010 ABLE ET AL. FIGURE 6. Daily average mummichog recaptures per unit effort (RPUE) in the boat basin and adjacent sites (Figure 1B, C) during the dredging effects study. Basin deep traps include the existing boat basin traps, the camera trap, and the mouth of the boat basin. Gray area indicates the period in which boat basin dredging occurred. sheepshead minnow, 87 cunners, and 27 winter flounder. Mummichogs were also marked (2,085 individuals: mean TL ¼ 54.2 mm; range ¼ mm), and sufficient recaptures were obtained for this species. The size ranges of mummichogs marked before (mean TL ¼ 58.7 mm; range ¼ mm), during (mean TL ¼ 57.3 mm; range ¼ mm), and after (mean TL ¼ 53.4 mm; range ¼ mm) dredging operations were not significantly different (v 2 ¼ , P ). The total number of mummichogs recaptured varied from before (n ¼ 1,289), during (n ¼ 271), and after (n ¼ 406) dredging,

11 BOAT BASIN DREDGING EFFECTS 1011 FIGURE 7. Days at liberty for marked and recaptured mummichogs that were initially marked at the boat basin during September 29 October 1, with a significant decline (F ¼ 26.52; df ¼ 2; P, ) in RPUE as the study progressed and as recaptured individuals were removed from the study site (Figure 6). These recaptures occurred with declining numbers throughout the study period and up to a maximum period at liberty of 67 d before the termination of the experiment (Figure 7). The recaptures occurred throughout the study area, including basin deep and basin shallow locations, where recaptures were always the highest (Figure 8). Thus, there was considerable site fidelity to the habitats in which tagging occurred, including the deep and shallow areas of the boat basin. Mummichogs tagged in the boat basin were also recaptured in all adjacent habitats (including the nearby marsh pool, the intertidal creek site, and the two subtidal creek sites) before, during, and after dredging. Thus, the movements from the tagging and release site did not seem to differ in response to dredging. This RPUE pattern (Figure 8) was similar to the mummichog CPUE pattern (Figure 9) before, during, and after dredging at all habitats. Discussion Environmental Characteristics The environmental response during the dredging period varied: several characteristics changed (temperature, dissolved oxygen, and turbidity), while others did not (salinity). The cooling temperatures during dredging were probably a response to the deepening of the boat basin and the access channel, which provided more water exchange with the adjacent deeper, cooler waters of Shooting Thorofare (Figure 1). In addition, the storm that occurred during the dredging period could have contributed to the temperature change. The decline in dissolved oxygen, which was limited to the initial days of dredging, was probably in response to increased biological oxygen demand during dredging. Turbidity changed during dredging, reaching the highest value about halfway through the dredging period. Both of these measures were highly variable and were affected by other outside factors, such as boat movements unrelated to dredging (docking vessels stirring up bottom sediments in the basin). Furthermore, turbidity values may have been influenced by a storm that occurred in the region during the dredging operations. Thus, it is difficult to separate these multiple potential effects. However, most values returned to predredging levels shortly after dredging ended. Fish and Crab Species Composition and Behavior The fishes and crabs collected in the RUMFS boat basin are characteristic of fauna found in shallow, benthic areas elsewhere in the Great Bay estuary at polyhaline salinities during the fall (Able et al. 1996; Able and Fahay 1998; Able 1999), including adjacent portions of Little Egg Harbor and Barnegat Bay (Wilson and Able 1996; Jivoff and Able 2001). The obvious exceptions are pelagic species that are not susceptible to collection by traps (e.g., Atlantic herring Clupea harengus, bluefish Pomatomus saltatrix, etc.) but do occur in inshore estuarine areas, such as the

12 1012 ABLE ET AL. FIGURE 8. Overall percentage of mummichog recaptures at the boat basin and adjacent sites (Figure 1B, C) before (n ¼ 1,289 recaptures), during (n ¼ 271), and after (n ¼ 406) boat basin dredging. Basin deep includes long-term traps, camera trap, and traps at the mouth of the boat basin. RUMFS boat basin (Hagan and Able 2003, 2008). Other species-specific studies conducted in the same basin have provided details of the early life history (Able et al. 1996) and site fidelity of some of the same species collected in the present study: the black sea bass (Able and Hales 1997), spotfin butterflyfish Chaetodon ocellatus (McBride and Able 1998), cunner, and tautog (Able et al. 2005). Thus, the findings here may apply to other estuaries in the northeastern USA. With respect to the crabs collected, the occurrence of the blue crab, lady crab, and green crab is to be expected (Jivoff and Able 2001), although the green crab is an invasive species from Europe that has been long established on the East Coast of the United States. Another species, the Asian shore crab, is a recent invader on the East Coast, including New Jersey (McDermott 2000). It was difficult to discern any major effects of dredging on the composition, abundance, and behavior of the fish and crab fauna. This may have occurred for several reasons. First, there were no indications of mortality or stress due to the dredging. This was most

13 BOAT BASIN DREDGING EFFECTS 1013 FIGURE 9. Mummichog catch per unit effort at the boat basin and adjacent sites (Figure 1B, C) before, during, and after boat basin dredging. Basin deep includes the long-term traps, traps at the mouth of the boat basin, and the camera trap. evident in the camera trap and for a variety of species that were captured in traps in the immediate vicinity of dredging. Second, there were no obvious declines in species richness or abundance. The possible exception is for the several less-abundant species that did decline (e.g., the sheepshead minnow, cunner, and winter flounder) at the same time as regular seasonal changes for these species (Able and Fahay 1998). Thus, it is not possible to absolutely separate dredging effects from seasonal effects. Further evidence of seasonal changes

14 1014 ABLE ET AL. includes those species that increased over the study period, apparently aggregating lower in the Great Bay estuary in anticipation of offshore movements (e.g., Atlantic silverside; Rountree and Able 1992, 1993) or those species that typically increase in abundance in the boat basin during the winter (striped killifish; Able and Fahay 1998). The decline of sheepshead minnow, however, may have been due to dredging because these fish typically increase in abundance by November (Able and Fahay 1998). Residency and Movements of Mummichogs The response of marked mummichogs suggested little effect of dredging on this species. The abundance of mummichogs remained high throughout the study period, and there was no change in fish size. In addition, there was a very high number of mummichog recaptures (.40%) before, during, and after dredging. These values are among the highest recapture rates for any fish species in a marine or estuarine environment and are even higher than those for other species (tautog: 31%; cunner: 23%; black sea bass: 21 31%; spotfin butterflyfish: 35%) tagged in the same boat basin when undisturbed by dredging (Able and Hales 1997; McBride and Able 1998; Able et al. 2005). The high rate of recaptures for mummichogs may be due to site fidelity, which has been reported in the same marsh watershed (K. W. Able, personal observation), the same estuary (Able et al. 2006), and other natural marsh watersheds (Teo and Able 2003; Able et al. 2005). Although some individual mummichogs did move into other habitats (intertidal creek, subtidal creek, and marsh pool) during the study period, such movements occurred before, during, and after dredging and thus were not necessarily in response to dredging. We suspect that the movements out of the boat basin and into other marsh habitats (e.g., the marsh pool) were associated with cooling temperatures in the fall, as has been reported for mummichogs in this marsh (Smith and Able 1994) and in other marshes (Fritz et al. 1975; Raposa 2003). In summary, there were no obvious negative responses in fish and crab species composition, abundance, size, or behavior before, during, or after dredging. In addition, the movements of marked mummichogs indicate that most remained in the basin over the study period, further suggesting no obvious response to dredging. The benthic fishes and crabs general lack of response to dredging in this study of a small, estuarine boast basin might be due to their tolerance of the turbidity and episodic conditions typical of shallow estuaries. One such example is the storm that occurred during the period of dredging. It is of interest that the peak turbidity in the boat basin during dredging (mean ¼ 160 NTU) was intermediate to the peak values measured during the storm at the two buoys (mean ¼ 133 and 184 NTU at Buoys 126 and 139, respectively) in the adjacent estuary. This suggests that some natural storm events cause turbidity levels of similar magnitude to those produced by this small dredging project. Another interpretation of the fish and crab response is that the lack of a response (i.e., movement away) by some species might be the result of their high degree of site fidelity based on our prior studies; this might especially apply to mummichogs because of their small home ranges, at least during the summer. Thus, both fishes and crabs might have been inclined to remain despite the disturbance. Further, it is well known that the mummichog is especially tolerant of a wide variety of conditions (Collette and Klein-MacPhee 2002), including suspended sediments (Wilber and Clarke 2001), but this is true of other estuarine species, including some of those represented in this study. Regardless of the above interpretations, this shortduration, small-volume dredging project in an estuary seemed to have little impact on the fishes and crabs based on a number of measures. Acknowledgments Numerous individuals at the RUMFS assisted in the field and laboratory components of this study. Gregg Sakowicz, Steve Evert, and JCNERR personnel were especially helpful in monitoring water quality and meteorological conditions during this study. Thomas Grothues provided helpful comments on an earlier draft. Jackie Toth assisted with the statistical analysis, and Carol Van Pelt provided editorial assistance. Funding for this project was provided by RUMFS. 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