The whelk dredge fishery of Delaware.

ABSTRACT The status of the Delaware whelk dredge fishery was assessed from state landings reports and from data collected by an onboard observer. Mean annual whelk landings for 1994 to 2000 were 18.5 mt of meats and increased to 241.6 mt for the period 2001 to 2004. Annual landings for 2001 to 2003 were 88% to 119% of the sum of dredge and trawl fishery landings reported by the remaining states on the United States Atlantic coast. Although knobbed whelks, Busycon carica, are landed throughout the year, 88% of pooled monthly landings for 1994 to 2004 were taken between March and June inclusive. Eleven observer cruises were conducted March to June 2004. Total estimated daily take of legal (length [greater than or equal to] 127 mm) knobbed whelks ranged from to 197-3,710 organisms. Expected catch rates were estimated at 83.2 legal knobbed whelks per hour per meter of dredge width. Dredges were generally towed parallel to bathymetric contours and adjacent to shoal features in 2-20 m depths. Estimates of the area of bottom dredged on each cruise ranged from 4.9-14.2 ha. At times, multiple boats were observed dredging the same bottom, suggesting a cooperative fishing technique. Seventy-nine percent of dredge tows occurred on bottom comprised of mud and sand, and mean numbers of knobbed whelks in 0.04 [m.sup.3] samples were greatest from mud/sand habitats. Twenty-one taxonomic groups of organisms were observed in samples taken from dredges. Knobbed whelk and horseshoe crabs, Limulus polyphemus, dominated dredge catch by number. Whelks collected in the Atlantic Ocean were significantly larger than those collected in the Delaware Bay. Mean lengths of whelks collected in the Bay in 2004 were significantly less than lengths of Bay whelks collected in 1994 prior to the inception of the minimum length regulation. Shifts in size distribution and the cyclical nature of other whelk fisheries suggest that the elevated landings experienced during 2001 to 2004 are not sustainable.

KEY WORDS: knobbed whelk, Busycon carica, whelk landings, fishery observer investigation, essential fish habitat, Delaware Bay

INTRODUCTION

Knobbed whelks, Busycon carica (Gmelin, 1791) and channeled whelks, Busycotypus canaliculatus (Linnaeus, 1758), are large gastropods that occupy estuarine and shelf habitats from Cape Cod to Cape Canaveral on the Atlantic Coast of the United States (Edwards & Harasewych 1988). Both species occupy sandy habitats and prey on bivalve mollusks (Magalhaes 1948, Carriker 1951, Davis 1981, Peterson 1982). Colloquially known as conchs, the two species have supported multiple fisheries on the United States Atlantic coast at least since the 1930s (MacKenzie 1997). Channeled whelks are harvested primarily with pot or trap gear, whereas knobbed whelks are most vulnerable to dredge or trawl gear (Eversole & Anderson 1984, Davis & Sisson 1988, Walker et al. 2003, Logothetis & Beresoff 2004).

Mark and recapture studies have demonstrated that knobbed whelk growth is generally slow (Anderson et al. 1985, Kraeuter et al. 1989). Short-term negative growth has been observed (Magalhaes 1948, Anderson et al. 1985), and there are examples of periodic rapid growth (DiCosimo & DuPaul 1985, Kraeuter et al. 1989). Average growth in length of 104 marked whelks in eastern Virginia that exhibited positive growth was 3.2 mm/yr (Kraeuter et al. 1989). Knobbed whelk length at age has been recorded from captive specimens and from examination of annual growth marks identified on opercula. Average length (n = 20) of 10-y-old captive eastern Virginia whelks was 144 mm (Castagna & Kraeuter 1994). Eastern Virginia whelks 158 mm long were predicted to be 10 y from operculum age data (age = -10.99 + 1.33(length); n = 45, r2 = 0.50 P = 0.0001; Kraeuter et al. 1989).

Age or size at reproductive maturity in knobbed whelks has been difficult to determine because gender ontogeny has not been well understood. Phenotypic gender differentiation in whelks is determined by the presence or absence of a penis (Magalhaes 1948, Gendron 1992, Castagna & Kraeuter 1994, Power & Keegan 2001, Avise et al. 2004). In addition to having longer shells than males (Magalhaes 1948, Anderson et al. 1985, DiCosimo & DuPaul 1985, Walker 1988), female knobbed whelks are wider and heavier than males (Anderson et al. 1989). Observations of inter-tidal mating activity indicate that smaller males and large females successfully produce egg strings (Power et al. 2002). Large females, variable and skewed sex ratios (Anderson et al. 1985), and the presence of male characters in females in at least 12 Buccinidae genera (Power & Keegan 2001) has lead to the hypothesis that knobbed whelks may be protandric hermaphrodites that initially mature as males and then undergo functional sex reversal at larger sizes (Walker 1988). Recent DNA analysis, however, indicates that knobbed whelks are genetically dioecious, having mammalian-like sex chromosomes (Avise et al. 2004); observed phenotypic sex reversal or pseudohermaphroditism, may result from a variety of environmental factors (Jenner 1979).

Whelks have been landed as by-catch or from directed dredge or trawl fisheries from all US Atlantic states except Florida (NOAA Fisheries 2004: http://www.st.nmfs.gov). Coast-wide landings from dredge and trawl fisheries have increased from 105.2 mt of meats in 1950, when Federal recording began, to a high of 1913.5 mt in 1994. Although total landings have decreased to 549.8 mt in 2003, ex-vessel price has remained high, as total landings value was $1.55 million in 2003 relative to $1.79 million in 1994 (NOAA Fisheries 2004). Whelk meats are generally removed from shells locally and then shipped on ice to northern United States metropolitan areas for canning or fresh retail sale; they are also frozen and shipped to East Asia (Eversole & Anderson 1984, Kaplan & Boyer 1992).

In Delaware, an expanding dredge fishery has raised concern over the long-term sustainability of whelk stocks. Additional attention has focused on by-catch considerations and potential physical effects of dredging activity on ecologically significant benthic habitats, particularly the structures created by the colonial polychaetes Sabellaria vulgaris (Verrill, 1873) and Hydroides dianthus (Verrill, 1873). Because of the general lack of published information on mid-Atlantic whelk fisheries, this study presents updated landings information and the results of an onboard fishery observer investigation. Temporal and spatial variation in Delaware landings are described and compared with coastwide landings trends to assess the relative magnitude of the fishery. Direct fishery observations document previously unknown attributes such as gear types, spatial and temporal variation in catch and effort, by-catch composition, and variation in the size structure of Delaware knobbed whelk populations. This work focuses on Delaware's dredge fishery, but contextual comparisons are made with dredge, trawl and pot fisheries in other Atlantic States.

METHODS

Landings Analyses

Landings from the Delaware whelk dredge fishery for 1994 to 2004 were summarized from reports by fishery participants. By statute, Delaware commercial dredging license holders are required to submit monthly catch reports that are archived by the Division of Fish and Wildlife. The information recorded includes number of trips, general location dredged, gear type, the monthly take of knobbed and channeled whelks and whether take was by-catch from other fisheries or from directed whelk fisheries. In addition to requiring monthly logbook reporting, Delaware fishery regulations include the possession of a commercial license, a 127.0 mm minimum length limit for knobbed whelks, a 152.4 mm minimum length limit for channeled whelks and a prohibition of nighttime dredging.

Whelk landings are published in biannual summaries of statewide shellfish harvest and fishery status that date back to 1994 (Whitmore & Greco 2005). Current whelk landings information compiled by the state of Delaware were compared with federally reported coast-wide dredge and trawl fishery landings to assess the relative magnitude of the Delaware fishery. Coast-wide landings data provided by NOAA Fisheries (http://www.st.nmfs.gov) do not differentiate knobbed and channeled whelks; therefore for comparative purposes, Delaware landings data used here include both taxa. Delaware landings are reported as total weight including the shell, whereas coast wide landings are reported as weight of edible meats; to allow comparison in equivalent units, Delaware landings were divided by a factor of 3 (Whitmore & Greco 2005). Fishery seasonality was assessed from mean monthly landings and catch-per-unit-effort (CPUE) from Delaware harvest reports 1994 to 2004. CPUE was calculated by dividing monthly harvest in weight by the number of trips reported by each fishery participant.

Onboard Fishery Observation

Eleven observer cruises were conducted on three vessels during March to June 2004 to obtain fishery information not contained in monthly reports. Dredge type, width, ring and mesh size were recorded at the beginning of each cruise. For each dredge tow, start and end times were recorded to determine tow duration and fishing effort. Total daily take, in volume of legal knobbed whelks, was recorded at the end of each cruise. Landed volume was converted to numbers with a conversion factor of 64.37 legal whelks per 0.04 [m.sup.3] (1.0 bushel). Estimated number of legal whelks was converted to weight with cruise-specific length frequency distributions and a length-weight relationship derived

during the cruises (Fig. 1). The presence of other vessels fishing in the same location was also noted throughout each cruise.

[FIGURE 1 OMITTED]

Cumulative catch was recorded at random intervals throughout the latter seven cruises, and was used to estimate catch rates for legal knobbed whelk. To describe catch relative to time fished, catch volume was divided by the total dredge width, thus standardizing gear differences among cruises. A general catch rate estimate was derived with a linear regression model fitted to cumulative catch data from cruises five through nine (PROC REG, SAS 2002).

GPS coordinates were recorded at the beginning and end of each dredge tow. Waypoints were then plotted with Geographic Information Systems (GIS) to identify spatial distribution of fishing activity. Straight tracklines, interpolated from waypoints, were used to represent the path of the dredges. Dredge tracklines were layered upon bathymetry to identify relationships between fishing activity and seabed topography. GIS tools were also used to estimate the area dredged. Buffer polygons were created around intersecting tracklines with a diameter equal to the dredge width, and the total dredge footprint or virgin area dredged on each cruise was estimated from the area of the polygons. Spatial data from Cruises 2, 6, 9 and 10 were not included in areal estimates because the vessel's course frequently did not follow a straight line between waypoints.

At the end of each tow the dredge was brought aboard and contents were dumped on deck. A 0.04 [m.sup.3] sample of dredge contents was collected before legal-sized whelks were removed. Seabed composition was documented from sample contents and from material attached to dredge gear. All organisms in samples were enumerated to quantify by-catch composition. Knobbed whelk shell lengths were recorded to assess potential spatio-temporal variation in the size structure of the population. Length distributions from Delaware Bay cruises were pooled and compared with lengths from the Atlantic Ocean. Size distribution data collected in the Delaware Bay during 2004 were compared with fishery-dependent data collected in November 1993 and March-April 1994 prior to when the 127.0 mm length limit was imposed. Significant differences in length distributions were identified with the Kolmogorov-Smirnov (KS) test (Proc NPAR1WAY, SAS 2002). Analysis of variance and Tukey tests were used to compare mean whelk lengths (Proc GLM, SAS 2002); length data were [log.sub.e] transformed to satisfy least squares assumptions.

RESULTS

Fishery Landings 1994 to 2004

In addition to the dredge fishery, Delaware has a smaller but significant pot fishery (Table 1). Whelk landings were not recorded by the State until 1994 when legislation was passed regulating all whelk fisheries. Analysis of monthly reports for the period 1994 to 2004 reveal that participation and landings have increased in recent years. The number of license holders that participated in the directed dredge fishery was 11 in 1994, declined to 2 in 1997, and increased to 19 in 2003. Sixteen license holders participated in the 2004 directed fishery (Whitmore & Greco 2005). Landings of pooled knobbed and channel whelks were relatively low for 1994 to 2000 and then increased to high levels in 2001 to 2004 (Fig. 2). The mean annual landing of whelk meats for 1994 to 2000 was 18.5 mt and for 2001 to 2004 the mean annual landing was 241.6 mt (Whitmore & Greco 2005). Except for the blue crab fishery, whelks provide the greatest ex-vessel value of all Delaware commercial fisheries. Dockside ex-vessel value of dredged knobbed and channeled whelks was $ 574,645 in 2004. Mean annual whelk landings from the Delaware dredge fishery 2001 to 2003 were 96.4% of mean landings for all dredge and trawl whelk landings 2001 to 2003 from the remaining Atlantic states (NOAA Fisheries 2004; Fig. 2). Although Federal coastal fisheries statistics do not differentiate channeled and knobbed whelk landings, State reports indicate that for 1994 to 2004, knobbed whelks comprised between 78.8% and 99.9% of total annual landings by weight in the Delaware dredge fishery. Most fishery effort occurred in the Delaware Bay during 1994 to 2004, only 3% of 3,031 reported directed trips that landed knobbed whelks occurred in the Atlantic Ocean.

[FIGURE 2 OMITTED]

Knobbed whelk landings showed distinct seasonal patterns. Landings from the directed dredge fishery were reported from all months of the 1994 to 2004 period, but the greatest mean total monthly landings occurred from March to June (Fig. 3). For the directed fishery, mean landings of whelk meats for March to June ranged from 12.9-40.2 mt, whereas mean landings for the remaining months ranged from 0.2 mt to 2.7 mt. Mean monthly whelk by-catch landings from the Delaware Bay winter blue crab Callinectes sapidus (Rathbun, 1896) dredge fishery ranged from 0.1-2.9 mt. Higher CPUE during March to May suggested seasonally increased vulnerability to dredge gear rather than increased dredging effort (Fig. 3).

[FIGURE 3 OMITTED]

Fishery Observations 2004

Catch Between March 15 and June 24, 2004 eleven observer cruises were conducted on three dredge vessels. Two vessels operated from Bowers Beach, DE, and the other from Lewes, DE. Two used single scallop dredges deployed from the stern of deadrise workboats, the other used a motorized bay schooner with paired toothbar crab dredges deployed from the sides. Scallop dredges were 2.62 m and 3.44 m in diameter; bag rings ranged from 63.5 mm to 88.9 mm in diameter; bag mesh ranged from 50.8 mm to 127.0 mm bar measure. Toothbar dredges were 2.3 m wide, rings were 49.0 mm in diameter, and mesh was 127.0 mm bar measure. Fishing effort was directed at whelks on all cruises, but horseshoe crab, Limulus polyphemus (Muller, 1785), and blue crab by-catch was retained on Cruise 1 and 3, hard clam Mercenaria mercenaria (Linnaeus, 1758) by-catch was retained on Cruise 2.

Whelk dredging began at daylight and ended between 1500 and 1700 h. The general dredge-fishing consisted of towing the gear for approximately 15 min, retrieving the gear, making a 180[degrees] turn and releasing the gear again. Dredge tows were oriented in the same direction and intersected. Vessel speed during dredging was between 3.5 and 5.2 kts. Except for Cruises 10 and 11, the total number of dredge tows per cruise ranged between 16 and 38 (Table 2). Whelk catch and effort varied among cooperators. Maximum take of legal knobbed whelk occurred on Cruise 4 and was estimated at 2.03 [m.sup.3], 1304.1 kg, and 3677 organisms (Table 2). Higher whelk landings were associated with additional vessels dredging the same area. Catch-per-unit-effort (CPUE) for scallop dredges was 0.009-0.083 [m.sup.3]/m dredge width/hour, mean = 0.04; and for toothbar dredges CPUE was 0.012-0.039 [m.sup.3]/m dredge width/hour, mean = 0.026 (Table 2). The expected hourly catch rate derived from Cruises 5-9 (Fig. 4) was 0.05 [m.sup.3] legal whelks/m dredge width. The model used to estimate catch rate was ([m.sup.3] catch/m dredge width) = -0.03 + 0.05 x hours; P < 0.0001; [R.sup.2] = 0.90; n = 49.

[FIGURE 4 OMITTED]

Cumulative catch from Cruises 10 and 11 illustrates why the fishery ceases in late June. On Cruises that occurred prior to 9 June, catch rates remained similar throughout the day (Fig. 4). On Cruises 10 and 11, initial catch rates were similar to previous cruises, but declined after approximately two hours of fishing effort (Fig. 4, inset). Low catch rates and declined efficiency, presumably elicited by increased light levels, prompted both cooperators to cease fishing for the season. June 9 was the last day of dredging for vessel B and June 24 was the last day for vessel C (Table 2); no other boats were observed fishing on either dates.

Fishery Location

Dredge-boat cruises occurred in the Delaware Bay and in the Atlantic Ocean (Fig. 5). Cruises 1-7, 9 and 10 were located in the Bay between Bowers Beach and Cape Henlopen, DE, and Cruises 8 and 11 were located just off-shore, in the Atlantic Ocean, south of Cape Henlopen. Fishery activity occurred adjacent to the beach in the ocean and on the slopes of the numerous shoals that define Delaware Bay bottom topography. Dredge tracks were generally oriented parallel to bathymetric contours (Fig. 6). Depths recorded during dredge deployment and retrieval ranged from 2 to 20 m. The area of virgin bottom impacted by scallop dredges, estimated from dredge trackline distance and dredge width, ranged from 4.9 ha on Cruise 11-14.2 ha on Cruise 4 (Table 2).

[FIGURES 5-6 OMITTED]

Benthic Habitat Types

Bottom type was recorded from 212 of 274 total dredge tows. Bottom material observed in dredges included mud, clay, sand, oyster shell, and rock. Less dense material, such as mud, silt and shell fragments may have been washed away during dredge retrieval, and dredges were occasionally rinsed to remove fine sediments, which resulted in potentially ambiguous distinction between Mud/Sand and Sand categories (Fig. 7). Six of the seven bottom categories were characterized by mud or sand components. Knobbed whelks were most frequently associated with mud and sand bottoms. The greatest number of whelks enumerated from 0.04 [m.sup.3] samples came from bottoms classed as mud/sand/shell hash (mean = 24.1; standard error = 3.7, n = 8); the lowest number of whelks in samples, came from rock/worm tube bottoms (mean = 1; n = 1; Fig. 7). The most frequently recorded bottom category was mud/sand, at 79% of classified tows, and the least frequent was oyster shell/worm tubes at 0.9% of classified tows. Tube casings of the colonial "reef" building polychaetes S. vulgaris and H. dianthus were observed infrequently, but were generally associated with hard substrates such as rock and oyster shell.

[FIGURE 7 OMITTED]

Catch Composition

Proportions of knobbed whelks relative to numbers of by-catch organisms observed in volumetric samples were highly variable. Mean percent knobbed whelk by number was less than 50% on four of the eleven cruises, but ranged up to 88.1% on Cruise 9 (Table 2). Twenty-one taxonomic groups were enumerated from 149 samples taken from dredge contents. The most abundant species in the samples were knobbed whelk and horseshoe crabs (Table 3). Proportions of pooled knobbed whelk by number examined ranged from 31.7% on Cruise 11-88.4% on Cruise 9; for horseshoe crabs proportions range from 1.0% on Cruise 9-41.0% on Cruise 8. The highest proportions of horseshoe crabs by number were observed in samples from ocean Cruises 8 and 11. Knobbed whelks were observed in 98.6% of all dredge tows and horseshoe crabs were observed in 85.2% of all tows (Table 3). Windowpane flounder Scophthalmus aquosa (Mitchill, 1815) and unidentified skates were the most evenly distributed taxonomic groups as they were observed in all cruises in similar proportions. Channeled whelk occurred in only 22.2% of the dredge tows sampled and comprised only 1% of organisms observed in samples (Table 3). Proportions of channeled whelk in pooled volumetric samples ranged from 2.9% in Cruise 8% to 0% on Cruise 11; both cruises occurred in the Atlantic Ocean. Although not enumerated in samples, the shells of dead knobbed whelks generally were the most abundant nonliving material observed in dredges, and frequently were more abundant than living whelks.

Size Distributions of Knobbed Whelk

Shell lengths of knobbed whelk taken from volumetric samples ranged from 66-243 mm (Table 4). Mean lengths ranged from 132.5 mm on Cruise 1-185.9 mm on Cruise ll. Although there were significant differences in loge transformed mean length among the cruises (P < 0.0001), considering spatial and gear differences among cruises, comparison of means indicate whelks had similar lengths on 7 of the 11 cruises (Table 4). Transformed mean length on Cruise 1 was significantly less than all the other cruises ([alpha] = 0.05; Tukey's Studentized Range Test). Mean length on Cruise 11 was significantly greater than all the other cruises except Cruise 8, and Cruise 8 mean length was not significantly different from Cruise 5 means ([alpha] = 0.05; Tukey Studentized Range Test; Table 4). Mean lengths from Cruises 2-4, 6-7 and 9-10 were not significantly different ([alpha] = 0.05; Tukey's Studentized Range Test). The observed variation in whelk size among cruises may be explained by location, as the two cruises with the largest mean whelk length, Cruises 11 and 8 (Table 4), occurred in the ocean.

Because of length differences observed among individual Bay and Ocean cruises, whelk length data from the Bay were pooled and compared with Ocean length distributions. The 2004 length distribution of knobbed whelks collected in the Bay was generally mound shaped (mean = 148.2, median = 147, standard error = 0.54, n = 2198), whereas the length distribution from the Ocean was multimodal and skewed towards greater proportions of larger whelks (mean = 179.4, median = 183, standard error = 2.03, n = 247; Fig. 8). Bay and ocean length distributions were significantly different (KS test, P < 0.0001). Loge transformed mean lengths of whelks collected in the Ocean in 2004 were significantly greater than Bay whelks collected in 2004 (P < 0.0001).

[FIGURE 8 OMITTED]

The relative frequency distribution derived from fishery dependent length data collected from the Bay dredge fishery in November 1993 and May and April 1994 (Michael Greco, Delaware Department of Fish and Wildlife, Little Creek, DE 19961; unpublished data), prior to the inception of the 127.0 mm minimum length limit, was compared with the 2004 Bay distribution (Fig. 8). The two distributions were significantly different (KS test, P < 0.0001). Delaware Bay knobbed whelk lengths measured in 1993-1994 (mean = 158.8 mm, median = 147, standard error = 0.64, n = 1567) was intermediate between 2004 Bay lengths and 2004 Ocean lengths. Loge transformed lengths were significantly greater than 2004 Bay mean length, but less than 2004 Ocean mean length (Tukey's Studentized Range Test, [alpha] < 0.05). Length variation suggests a temporal shift toward smaller whelks over the last decade (Fig. 8). The proportion of Bay whelks >175 mm declined from 29.4% of the sample in 1993 to 1994 to 17.2% of the sample in 2004.

DISCUSSION

Whelk Fishery Landings

In addition to dredge gear, whelks are landed with trawls, pots, and traps (Table 1). In 2003, pooled landings of knobbed and channeled whelks from all Atlantic dredge/trawl fisheries were 561.3 mt meats, and landings from trap/pot fisheries were 570.1 mt meats (NOAA Fisheries 2004: http://www.st.nmfs.gov). The greatest landings from trap/pot fisheries were 224.5 and 91.4 mt meats from the states of Virginia and Delaware respectively; and the greatest landings from dredge fisheries were 262.5 and 163.0 mt meats from the states of Delaware and New Jersey respectively (Table 1).

Over the last decade, landings and effort from the Delaware whelk dredge fishery have exhibited a general increasing trend, but during this period landings from dredge and trawl fisheries the other Atlantic states have declined. Aside from the states of Delaware and New Jersey, the top producing states, Georgia, Maryland, Massachusetts, South Carolina, and Virginia (NOAA Fisheries 2004), are currently experiencing periods of reduced landings (Fig. 9). Whelk landings time series, from 1958 to 2003, indicate that dredge and trawl fisheries generally exhibit abbreviated periods of increased landings followed by longer periods of reduced landings, and that the intervals of reduced harvest may last 1-2 decades (Fig. 9). Because coast-wide landings of knobbed and channeled whelks are pooled, and directed and by-catch fisheries are not differentiated, it is difficult to identify the factors that influence landings cycles. For example, peak landings in Virginia during 1974 to 1975 (Fig. 9) resulted from large landings of channeled whelk by-catch from the surf clam dredge fishery, that coincided with peak surf clam landings (DiCosimo & DuPaul 1985).

[FIGURE 9 OMITTED]

Landings variability in whelk dredge and trawl fisheries is determined by a combination of supply, demand, economic costs, or regulatory constraints. In New Jersey, whelks can be harvested as by-catch from the blue crab dredge fishery, and as with any other type of fishery, whelk landings are largely determined by abundance and market conditions (Jeffrey Normant, New Jersey Bureau of Marine Fisheries, Port Republic, NJ 08241; pers. comm.). In Georgia, landings are dependent on whelk abundance, operational costs, and success of the previous shrimp season. The Georgia whelk trawl fishery offers off-season income to the shrimp fleet, and annual shrimp and whelk landings are often inversely related (James Page, Georgia Marine Resources Division, Brunswick, GA 21520; pers. comm.). Similar to the Georgia fishery, landings in South Carolina provide supplemental income to the shrimp fleet during the off-season and fishing effort is dependent on a combination of market value, cost of fuel, and whelk abundance (William Anderson, South Carolina Marine Resources Division, Charleston, SC 29422; per. comm.).

Among the top whelk producing states in the mid and south Atlantic (Fig. 9), Delaware's is the only directed dredge or trawl fishery that has no seasonal restrictions. Maryland has no whelk season closure, but trawl landings are by-catch from a groundfish trawl fishery (Steven Doctor; Maryland Department of Natural Resources, Matapeake, MD 21666; pers. comm.). In New Jersey, whelks can be landed throughout the year with pot gear, and can be landed as by-catch from the winter blue crab dredge fishery that occurs from mid-November through mid-April (http:// www.state.nj.us/dep/fgw/saltwater). In Virginia knobbed whelks are landed as by-catch from the blue crab dredge fishery that occurs between December and March in the Chesapeake Bay. Virginia also allows a directed fishery in distinct inshore and offshore management zones with varying seasonal restrictions (http:// www.mrc.state.va.us/commercialcrabbingrules). The South Carolina directed trawl fishery occurs between the shrimp fishery closure in January and the reopening in April, and landings are usually highest in the months of March to April. South Carolina whelk seasons may close prematurely if fishery-dependent information identifies low whelk abundance or presence of sea turtles (William Anderson; pers. comm.). The Georgia trawl fishery also occurs during a January to April shrimp closure; premature closure of the whelk season may be influenced by market forces or triggered by the onset of knobbed whelk reproduction identified by the occurrence of egg strings in fishery independent surveys (James Page; pers. comm.).

There is a strong seasonal pattern in landings from the Delaware whelk dredge fishery. Whelks are retained as by-catch from the blue crab dredge fishery that runs from mid-December through March, and are landed by a directed fishery that is open year-round. The highest mean monthly landings, however, occur March to June. High CPUE demonstrates that seasonality in landings may be related to increased whelk vulnerability to dredge gear during March to June. Behavioral information is largely derived from observations of intertidal whelks, but generalizations may be drawn to explain seasonality in CPUE of the subtidal fishery. Intertidal whelks in Georgia were most active during spring and fall (Walker et al. 2004). Released whelks were buried and inactive at 9[degrees]C water temperature (January) and were on the surface or partially buried at 13[degrees]C water temperature (March); whelks released in the summer initially burrowed up to 14.4 cm into the substrate and then migrated to subtidal areas (Walker et al. 2004). In North Carolina intertidal whelks released in the summer immediately burrowed into sediments and remained so for several days; burrowing behavior was so prevalent that it was termed a vertical migration (Magalhaes 1948).

Whelk activity appears negatively associated with ambient light intensity; during the summer, intertidal whelks were most active at night, during crepuscular periods, or on overcast days (Magalhaes 1948). During December to February subtidal whelks may be sufficiently buried to be less vulnerable to dredge gear (Fig. 3). Although whelks are active in the summer, negative phototaxis may explain intermediate summer CPUE levels. Commercial dredgers in New Jersey report that both knobbed and channeled whelk burrow during the day and capture success is greatest at night or on days with heavy cloud cover (Dobarro 1993). Negative phototaxis during the summer may explain why catch rates on Cruises 10 and 11 declined after approximately 2 hours of dredging (inset Fig. 4), and resulted in a cessation of fishing activity for the season. High CPUE during March-May may result from sediment emergence and increased diurnal activity mediated by increased temperature relative to winter months, and presumably lower light intensity and shorter photoperiod relative to summer months. Although nothing is published on the seasonality in the spatial distribution of subtidal whelks in Delaware, high springtime CPUE may also be related to high densities resulting from affinities to specific over-winter habitats or from premating aggregations.

Gear and Benthic Habitats

Whelk burrowing behavior may explain fishery tactics and the use of specific gear types. Toothbar dredges are the most frequently used gear in Delaware, and are the traditional gear of the winter blue crab fishery. Currently, only three fishermen use scallop dredges, but use of this gear is likely to increase in the future. Unlike toothbar dredges that have 15 cm teeth, scallop dredges use heavy tickle chains to disturb the substrate ahead of the bag. Although catch data was collected from only one toothbar dredger, CPUE (Table 2) and cumulative catch plots (Fig. 4) suggest that scallop dredges are at least as efficient as toothed dredges for harvesting knobbed whelks. Gears used in other whelk dredge/ trawl fisheries include modified shrimp trawls (Anderson et al. 1985, Walker 1988), groundfish trawls and assorted dredges used to collect clams, sea urchins, mussels and oysters (NOAA Fisheries 2003). Dredgers on the New Jersey side of the Delaware Bay are permitted to use toothed crab dredges, dredges with a toothless bar, or a chain in place of the toothed bar (Paul Scarlett, New Jersey Bureau of Marine Fisheries, Port Republic, NJ 08241; pers. comm.). The spatial pattern of dredge deployment in the Delaware fishery is typified by multiple tows over the same area by single or multiple boats. Presumably, dredge track overlap and cooperative dredging enhance catch rates because whelks are at least partially embedded in the sediment and are not easily dislodged on the first pass. The use of toothbar dredges and scallop dredges with heavy tickle chains also indicate that whelks must be dug from the substrate. In South Carolina, otter trawls are modified with cables and tickler chains that dig whelks from the sediment, and chaffing gear is added to minimize damage to codend webbing (William Anderson; pers. comm.). Because otter trawls must penetrate into the sediment, gear and boat damage is a major economic consideration for entry into the Georgia fishery (James Page; pers. comm.).

Considerable focus has been given to the effect of mobile fishing gear on benthic habitats (National Research Council 2002). Essential Fish Habitat (EFH) considerations relative to ecologically significant habitats were included in recent fisheries legislation (Benaka 1999). So- called "worm reefs" (structure created by the tube dwelling polychaetes S. vulgaris and H. dianthus), occur in the Delaware Bay (Wells 1970, Haines & Maurer 1980), and have been attributed to having EFH value (NREFHSC 2002, Miller 2001). Increased effort in the whelk dredge fishery over the last decade has raised concern over potential negative effects on Delaware Bay benthic habitats. H. dianthus creates a calcareous casing (Haines 1978) and was only observed from dredge tows that contained rock and oyster shell. S. vulgaris creates casings of sand grains (Wells 1970) and when observed in dredges, was attached to a variety of hard materials including the shells of living whelks and horseshoe crabs. Material considered to be representative of worm-reef habitat was only observed in seven of 22 analyzed tows on Cruise 2. Cruise 2 was an anomaly relative to the other cruises, because the vessel targeted hard clams in addition to whelks and the captain wanted to demonstrate the spatial distribution and variability of benthic materials to the observer. Because H. dianthus and S. vulgaris only colonize hard substrates (Wells 1970, Curtis 1975, Tinsman & Hense 2004), worm-reef habitat is generally not dredged by the whelk fishery because of the difficulty of culling relatively few whelks from heavy nonliving material and potential damage to gear. Because most fishery effort and whelk catch comes from mud and sand habitats, it appears that the dredge fishery has a negligible effect on worm reef habitats. The cumulative effect of dredge fishery activity on mud and sand habitats, however, is unknown.

Catch Composition

A variety of organisms were observed in whelk dredge samples and ratios of whelks to by-catch varied within and among observer cruises. Temporal, spatial, and gear variability presumably contributed to differences in catch composition. The highest variability on the proportion of knobbed whelks to by-catch was observed during Cruise 2 (Table 2), and is demonstrated by high proportions of hard clams and horseshoe crabs, and by fishing effort expended on a variety of bottom types, such as tube worm habitat, that held relatively few whelks. Ninety-three percent of all hard clams and 19% of horseshoe crabs enumerated in Delaware Bay samples came from Cruise 2. Variability in Cruise 2 catch composition occurred because hard clams were targeted in addition to whelks, and the captain chose to dredge a variety of bottom types. Proportions of knobbed whelks in samples were also low on cruises that were conducted in the Ocean. Lower numbers in volumetric samples from Cruises 8 and 11 may be explained by larger size of ocean whelks (Fig. 8) and by high levels of horseshoe crab by-catch. Taxa observed as by-catch in whelk trawl fisheries include Atlantic croaker Micropogonias undulatus (Linnaeus, 1766), sting rays Dasyatis spp., horseshoe crabs, blue crabs and spotted seatrout Cynoscion nebulosus (Cuvier, 1830) in South Carolina (William Anderson; pers. comm.); and fringed flounder Etropus crossotus (Jordan & Gilbert, 1882), Atlantic stingray Dasyatis sabina (Lesueur, 1824), star drum Stellifer lanceolatus (Holbrook, 1855), southern stingray Dasyatis americana (Hildebrand & Schroeder, 1928), and southern kingfish Menticirrhus americanus (Linnaeus, 1758) in Georgia (James Page, pers. comm.).

The scarcity of channeled whelks in dredge samples is congruent with the observations of others that knobbed whelk dominate landings from dredge and trawl fisheries (Anderson et al. 1985, Davis & Sisson 1988) and channeled whelks dominate landings from pot or trap fisheries (Davis & Sisson 1988, Walker et al. 2003, Logothetis & Beresoff 2004). The absence of knobbed whelks in pots may be explained by a preference for live bivalves rather than bait and carrion, and potentially a reduced ability to enter traps because of a heavier shell than the thinner-shelled and more active channeled whelk (Davis 1981, Sisson & Wood 1988, Dobarro 1993, Walker et al. 2003, Logothetis & Beresoff 2004). Channel whelks have been documented as being less diurnally active than the knobbed whelk (Magalhaes 1948). During daylight, channel whelks may be sufficiently buried to be invulnerable to dredge gear.

Size Distributions

Analysis of knobbed whelk size distributions from 2004 revealed that mean lengths were relatively similar among cruises in the Bay, but whelks from the Ocean were larger than those from the Bay. Delaware landings reports for 1994 to 2004 reported that only 3% of 3,031 dredging trips occurred in the Ocean. Log-book reports from 2004 indicate that 5% of 478 trips occurred in the Ocean. Lower levels of fishing effort and exploitation in the Ocean may explain spatial differences in size distributions. Observed differences between whelks collected in 2004 and whelks collected in 1993 to 1994, when there was no minimum legal length, suggest that the size distribution in the Bay has shifted to smaller individuals over that last decade. Length data from 2004 were recorded on-board prior to culling, whereas 1993 to 1994 data were recorded from landed whelks. Although there was no minimum legal length in 1993 to 1994, it is possible that smaller whelks were collected, but were culled and not landed. Regardless, the mode at 190 mm observed in the 1993 to 1994 distribution (Fig. 8) was absent in the 2004 length distribution. Increased exploitation (Fig. 2) may explain shifts in Bay size distributions over the last decade.

There is evidence that declines in annual whelk landings may result from over-harvest. Declines in catch and size of pot-caught channeled whelk in New England has been attributed to increased fishing pressure (Davis & Sisson 1988). The South Carolina trawl fishery experienced record landings in 1982 followed by precipitous declines in 1983 to 1984 (Fig. 9). Landings declines were attributed to high and sustained levels of fishing effort by South Carolina trawlers, coupled with low growth rates and confined home ranges of knobbed whelk determined from mark and recapture studies (Anderson et al. 1985). Presently, the United States South Atlantic whelk fishery is considered to be over-fished and overall annual landings are expected to remain low (Burrell 1997).

Landings from Delaware and New Jersey dredge fisheries are the highest on the Atlantic Coast (Figs. 2 and 9). In Delaware more whelks are landed from the Delaware Bay than from the Atlantic Ocean. Although whelks are also dredged from New Jersey's coastal bays, a good portion of the whelks harvested by dredge that are landed in New Jersey come from the Delaware Bay (Jeffrey Normant; pers. comm.). Because of the magnitude of fishery activity in the Delaware Bay, it appears that whelk productivity in the Bay has been relatively high. The presence of sublegal whelks in commercial gear (Fig. 8) indicates that successful recruitment occurs. Despite increased fishery activity, whelk densities may remain elevated in some locations. For example, during Cruise 4, an estimated 3,677 legal whelks were taken from an approximately 14.2 ha area. If all 13 boats observed fishing the same bottom that day (Table 2) maintained an equivalent catch rate, the estimated density would be 3,354 legal whelk per ha or approximately 1 whelk per 3 [m.sup.2].

Landings time series among the top-producing dredge and trawl fisheries in the Atlantic states reveal a general pattern of years of large landings followed by multiyear periods of smaller annual landings (Fig. 9). Delaware landings data (Fig. 2) suggest that the fishery is at a peak in the cycle as landings and effort have been consistently high over the last four years relative to the 1994 to 2000 period. Demand for domestic whelk meats appears to be consistently high and is partially driven by depletion of global whelk fisheries (Kaplan & Boyer 1992); thus current effort levels in the Delaware fishery will continue until profitability declines. Given the experiences of other states and an apparent inability of whelk populations to sustain elevated exploitation for extended periods, the Delaware dredge fishery should expect reduced landings in the future.

ACKNOWLEDGMENTS

The author thanks the captains and crews of cooperating dredge vessels for accommodating an observer and allowing this work to be done; Craig Shirey, Roy Miller, Rick Cole and anonymous reviewers for comments on various manuscript drafts and William Anderson, Steven Doctor, Jeffrey Normant, James Page and Paul Scarlett for providing information on other whelk fisheries.

LITERATURE CITED

Anderson, W. D., A. G. Eversole & B. A. Anderson. 1985. A biological evaluation of the knobbed whelk fishery in South Carolina. South Carolina Wildlife and Marine Resources Department. Completion Report 2-392-R.

Anderson, B. A., A. G. Eversole & W. D. Anderson. 1989. Variations in shell and radula morphologies of knobbed whelks. J. Shellfish Res. 8:213-218.

Arise, J. C., A. J. Power & D. Walker. 2004. Genetic sex determination, gender identification, and pseudohermaphroditism in the knobbed whelk, Busycon carica (Mollusca: Melongenidae). Proc. R.-Soc. Lond. [Biol]. 271:641-646.

Benaka, L., editor. 1999 Fish habitat: essential fish habitat and rehabilitation. American Fisheries Society, Symposium 22, Bethesda, Maryland.

Burrell, V. G. 1997. Molluscan fisheries of the South Atlantic region of the United States. In: C. L. MacKenzie, Jr., V. G. Burrell, Jr., A. Rosenfield & W. L. Hobart, editors. The history, present condition, and future of the molluscan fisheries of the North and Central America and Europe, Vol. 1. Atlantic and Gulf Coasts. US Dept. Commerce, NOAA Tech. Report 127.

Castagna, M. C. & J. N. Kraeuter. 1994. Age, growth, sexual dimorphism and fecundity of knobbed whelk, Busycon carica, in a western mid-Atlantic lagoon system, Virginia. J. Shellfish Res. 13:581-585.

Carriker, M. R. 1951. Observations on the penetration of the tightly closing bivalves by Busycon and other predators. Ecology 32:73-83.

Curtis, L. A. 1975. Distribution of Sabellaria vulgaris Verrill (Polychaeta: Sabellariidae) on a sandflat in Delaware Bay. Chesapeake Sci. 16:14-19.

Davis, J. P. 1981. Observations of prey preference and predatory behavior in Busycon carica and B. canaliculatum (Linn.). Biol. Bull. 161:338-339.

Davis, J. P. & R. T. Sisson. 1988. Aspects of the biology relating to the fisheries management of New England populations of the whelks, Busycotypus canaliculatus and Busycon carica. J. Shellfish Res. 7:453-460.

DiCosimo, J. & W. D. DuPaul. 1985. Preliminary observations of the Busycon fishery of Virginia. J. Shellfish Res. 5:34.

Dobarro, J. 1993. A summary of the life histories for two commercially important Busyconine whelks: the knobbed whelk, Busycon carica and the channeled whelk, Busycotypus canaliculatum, with a discussion of the fishery in New Jersey. New Jersey Bureau of Shellfisheries. pp. 18-19.

Edwards, A. L. & M. G. Harasewych. 1988. Biology of recent species of the subfamily Busyconinae. J. Shellfish Res. 7:467-472.

Eversole, A. G. & W. D. Anderson. 1984. Whelk fishery in the South Atlantic Bight: preliminary observations. Am. Malacol. Bull. 39:102.

Gendron, L. 1992. Determination of the size at sexual maturity of the waved whelk Buceinium undatum Linnaeus, 1758. in the Gulf of St. Lawrence, as a basis for the establishment of a minimum catchable size. J. Shellfish Res. 11: 1-7.

Haines, J. L. 1978. The Hydroides dianthus assemblage and its structural complexity. College of Marine Studies. Masters Thesis. University of Delaware, Newark, DE.

Haines, J. L. & D. Maurer. 1980. Quantitative faunal associates of the serpulid polychaete Hydroides dianthus. Mar. Biol. 56:43-47.

Jenner, M. G. 1979. Pseudohermaphroditism in Ilyanassa obsoleta. Science 205:1407-1409.

Kraeuter, J. N., M. Castagna & R. Bisker. 1989. Growth rate estimates for Busycon carica (Gmelin, 1791) in Virginia. J. Shellfish Res. 8:219-225.

Kaplan, I. M. & B. C. Boyer. 1992. Monitoring marine resources: ecological and policy implications affecting the scientific collecting and commercial value of New England Conch (Busycon). Biol. Bull. 183:379-380.

Logothetis, E. A. & D. A. Beresoff. 2004. Viability of a conch pot fishery in Southeast North Carolina. North Carolina Sea Grant Project no. 02-FEG-17.64 pp.

Magalhaes, H. 1948. An ecological study of snails of the genus Busycon at Beaufort, North Carolina. Ecol. Monographs. 18:378-409.

MacKenzie, C. L. 1997. The United States molluscan fisheries from Massachusetts Bay through Raritan Bay, New York and New Jersey. In: C. L. MacKenzie, Jr., V. G. Burrell, Jr., A. Rosenfield & W. L. Hobart, editors, The history, present condition, and future of the molluscan fisheries of the North and Central America and Europe, Vol. 1. Atlantic and Gulf Coasts. US Dept. Commer., NOAA Tech. Rep. 127.

Miller, D. C. 200l. Pre-construction Sabellaria vulgaris monitoring at Broadkill Beach sand placement site, Sussex County, Delaware. US Army Corps of Engineers, Philadelphia District. Contract no. DACW61-01-P-0291.

National Research Council. 2002. Effects of trawling and dredging on seafloor habitat. Washington, DC: National Academy Press.

Northeast Region Essential Fish Habitat Steering Committee. 2002. Workshop on the effects of fishing gear on marine habitats off the North-Eastern United States. NOAA Northeast Fisheries Science Center reference document 02-01.

Peterson, C. H. 1982. Clam predation by whelks (Busycon spp.): experimental tests of the importance of prey size, prey density, and sea grass cover. Mar. Biol. 66:159-170.

Power, A. J. & B. F. Keegan. 2001. Seasonal patterns in the reproductive activity of the red whelk, Neptunea antiqua (Mollusca: prosobrachia) in the Irish Sea. J. Mar. Biol. Assoc. UK 81:243-250.

Power, A. J., E. Covington, T. Recicar, R. Walker & N. Eller. 2002. Observations on the egg capsules and hatchlings of the knobbed whelk, Busycon carica (Gmelin, 1791) in coastal Georgia. J. Shellfish Res. 21:769-775.

SAS. 2002. SAS Institute Inc., Cary, NC, USA.

Sisson, R. T. & R. S. Wood. 1988. Observations on some life history aspects of a commercially exploited population of Busycon canaliculatum (Linne) in Narragansett Bay, Rhode Island. J. Shellfish Res. 7:176.

Tinsman, J. C. & Z. Hense. 2004. Macrobenthic communities of Delaware artificial reef sites. Status report for the Delaware Artificial Reef project. Delaware Division of Fish and Wildlife.

Walker, R. L. 1988. Observations on intertidal whelk (Busycon and Busycotypus) populations in Wassaw Sound, Georgia. J. Shellfish Res. 7: 473-478.

Walker, R. L., T. Recicar & A. J. Power. 2003. Quantitative comparison between the Chesapeake Bay conch pot and the standard crab trap for harvesting whelks in Wassaw Sound, Georgia. University of Georgia Mar. Ext. Bull. no. 26.

Walker, R. L., J. H. Smith & A. J. Power. 2004. Movement and behavior patterns of whelks on intertidal flats in Wassaw Sound, Georgia. University of Georgia Mar. Ext. Bull. no. 29.

Wells, H. W. 1970. Sabellaria reef masses in Delaware Bay. Chesapeake Sci. 11:258-260.

Whitmore, W. H. & M. J. Greco. 2005. Delaware commercial shellfish harvest and status of the fisheries 2003-2004. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

DAVID GARCIA BRUCE *

Division of Fish and Wildlife, Delaware Department of Natural Resources and Environmental Control, Little Creek Fisheries Laboratory, P.O. Box 330, Little Creek, Delaware 19961

* Corresponding author. E-mail: [e-mail]

TABLE 1.

Coastal Atlantic whelk landings from directed and by-catch fisheries
for 2003. Knobbed and channeled whelk landings are pooled. Delaware
landings come from monthly logbook reports, whereas landings for the
remaining states were reported by NOAA Fisheries.

                            Landings (tonnes meats)

                    Total      Conch      Crab       Clam
    State         Landings     Dredge    Dredge     Dredge

Connecticut          12.6
Delaware            353.9     157.0      105.5
Georgia              40.9
Maryland             91.2                            <0.1
Massachusetts       110.0       0.2                   0.1
New Jersey          196.7                163.0        1.3
New York             30.7
North Carolina        3.5
Rhode Island          2.9
South Carolina        1.4
Virginia            287.5      31.7        9.0        0.1
Total              1131.5     188.8      277.5        1.5

                            Landings (tonnes meats)

                    Other       Crab       Fish      Other
    State         Dredge (1)   Trawl      Trawl     Trawl (2)

Connecticut                                1.0
Delaware
Georgia                        39.7
Maryland                                  10.6       <0.1
Massachusetts       <0.1                  17.4
New Jersey           0.3                   2.1
New York                                   3.1
North Carolina                  0.1        0.1        2.4
Rhode Island                               0.7
South Carolina                  0.3
Virginia                                  15.6       <0.1
Total                0.3       40.1       50.6        2.5

                         Landings (tonnes meats)

                              Blue
                    Conch     Crab       Lobster    Fish
    State            Pot      Pot        Pot        Pot

Connecticut         10.8                 0.7        <0.1
Delaware            91.4
Georgia                       1.2
Maryland            80.0                 0.4         0.2
Massachusetts        0.6                 0.8        <0.1
New Jersey          24.6      5.4                   <0.1
New York            25.9                 1.6         0.1
North Carolina                0.9
Rhode Island         1.6                 0.1         0.5
South Carolina                1.1
Virginia           224.5      6.6
Total              459.4     15.2        3.7         0.8

                  Landings (tonnes meats)

                                Minimum
                  Other          Legal
    State         Pot (3)     Size (mm) (4)

Connecticut                       None
Delaware                       127/152 (5)
Georgia                           None
Maryland                        152/152
Massachusetts     90.9          70/70 (6)
New Jersey                      127/127
New York          <0.1            None
North Carolina                    None
Rhode Island                      None
South Carolina                  102/102
Virginia          <0.1          None/140
Total             91.0

(1) Sea scallop and undefined dredge fisheries

(2) Sea scallop and undefined trawl fisheries

(3) Eel, undefined crab, and undefined pot fisheries

(4) Length unless otherwise noted

(5) Knobbed whelk/channeled whelk

(6) Width

TABLE 2.

Dredge gear, effort, and landings of legal knobbed whelk
([greater than or equal to] 127 mm) on 11 observer cruises in the
Delaware Bay March to June 2004. Horseshoe crab and blue crab were
retained on Cruises 1 and 3, and hard clams were retained on Cruise 2.

              Date    Dredge     Total     Tow      Dredged
Cruise (1)    (m/d)    Type      Tows     Time     Area (ha)

[1.sup.A]     3/15    Scallop      36      10.8       11.9
[2.sup.B]     3/25    Toothed      31       9.1        --
[3.sup.C]     4/2     Scallop      20       7.5        9.2
[4.sup.A]     4/14    Scallop      33       9.3       14.2
[5.sup.C]     4/20    Scallop      17       7.4       12.5
[6.sup.B]     4/30    Toothed      37       9.0        --
[7.sup.A]     5/7     Scallop      38      10.3        9.9
[8.sup.C]     5/19    Scallop      16       7.3       12.9
[9.sup.B]     5/27    Toothed      25       8.1        --
[10.sup.B]    6/9     Toothed      11       3.7        --
[11.sup.C]    6/24    Scallop      10       3.1        4.9

                       Whelk Landed

                 Volume                                    No.
Cruise (1)    ([m.sup.3])    No.      kg     CPUE (2)   Vessels (3)

[1.sup.A]         1.30      2364     681.4     0.046         0
[2.sup.B]         0.60      1391     446.2     0.014         0
[3.sup.C]         0.58       652     199.2     0.023         0
[4.sup.A]         2.03      3677    1304.1     0.083        3-12
[5.sup.C]         0.98      1773     869.5     0.038         0
[6.sup.B]         1.60      3710    1157.8     0.039        0-6
[7.sup.A]         1.52      2758     869.9     0.057        0-4
[8.sup.C]         0.79      1445     853.3     0.032         0
[9.sup.B]         1.40      3246    1110.4     0.038        1-3
[10.sup.B]        0.20       464     163.4     0.012         0
[11.sup.C]        0.10       197     119.5     0.009         0

                     % Knobbed Whelk in
                   Volumetric Grab Samples
                      (0.04 [m.sup.3])

                     Geometric      Coefficient
Cruise (1)    n         Mean       of Variation

[1.sup.A]     17        71.6            0.65
[2.sup.B]     20         7.8           60.24
[3.sup.C]     13        58.3            0.84
[4.sup.A]      8        74.5            0.24
[5.sup.C]     14        47.7            0.68
[6.sup.B]     12        66.0            0.73
[7.sup.A]     17        53.5            0.85
[8.sup.C]     14        42.9            0.75
[9.sup.B]     19        88.1            0.11
[10.sup.B]     6        74.0            0.23
[11.sup.C]     9        23.6            3.13

(1) Common subscript indicates same vessel.

(2) CPUE = volume ([m.sup.3]) landed/m dredge width/hour dredged.

(3) Number of additional vessels dredging same area.

TABLE 3.

Composition of organisms observed in 0.04 [m.sup.3] samples taken from
whelk dredge contents. Counts were pooled from single samples
from 149 dredge tows on 11 vessel cruises. Frequency of occurrence
is the proportion of samples containing the specific taxon.

                                                    Percent   Frequency
     Common                               Number      of      of Occur-
      Name               Latin Name      Observed   Total     rence (%)

Knobbed whelk      Busycon carica          2813      63.96      98.66
Horseshoe crab     Limulus polyphemus       802      18.24      85.23
Skate              Rajidae                  181       4.11      51.68
Windowpane         Scophthalmus             120       2.73      43.62
  flounder           aquosus
Hard clam          Mercenaria               105       2.39      12.08
                     mercenaria
Spider crab        Libinia spp.             102       2.32      22.82
Rock crab          Cancer irroratus          87       1.98      23.49
Blue crab          Callinectes sapidus       58       1.32      24.16
Channeled          Busycotypus               44       1.00      22.15
  whelk              canalicidatus
Summer             Paralichthys              37       0.84      14.77
  flounder           dentatus
Blue mussel        Mvtilus edulis            15       0.34       2.68
Starfish           Asteriidae                 9       0.20       4.69
Mud crab           Panopeus spp.              8       0.18       4.03
Oyster toadfish    Opsanus tau                7       0.16       4.03
Hogchoker          Trinectes maculatus        3       0.17       2.01
Striped searobin   Prionotus evolans          2       0.05       1.34
Atlantic           Polinices duplicatus       2       0.05       1.34
  moonsail
Dogfish            Elasmobranchiomorphi       1       0.02       0.67
Northern           Sphoeroides                1       0.02       0.67
  pufferfish         maculatus
Squid              Teuthoidea                 1       0.02       0.67
                   Total observed =        4398

TABLE 4.

Knobbed whelk length statistics recorded from dredge fishery
observer cruises conducted in the Delaware Bay and in the Atlantic
Ocean 2004.

                           Knobbed Whelk Length (mm)

            Loca-                    Standard
Cruise      tion    Mean    Median   Deviation   Min.   Max.

  1         Bay     132.5     128       22.3      87     192
  2         Bay     145.9     151       22.2      88     187
  3         Bay     145.7     142       22.5      93     211
  4         Bay     146.4     145       28.5      84     221
  5         Bay     173.2     174       27.8     113     223
  6         Bay     149.5     149       19.9      96     204
  7         Bay     147.7     144       22.2      98     209
  8         Ocean   176.7     181       33.8      66     243
  9         Bay     150.0     149       24.1      91     223
 10         Bay     151.6     153       24.9      91     211
 11         Ocean   185.9     193       25.9     107     222

            Similar
Cruise     Means (1)     n

  1            A        298
  2            B        185
  3            B        211
  4            B        185
  5            C        193
  6            B        267
  7            B        360
  8            CD       175
  9            B        394
 10            B        105
 11            D         72

(1) Equivalent letters indicate that means of [log.sub.e] transformed
lengths were not significantly different (Tukey test, [alpha] = 0.05).