JOURNAL OF SHELLFISH RESEARCH VOLUME 25, NUMBER 1 APRIL 2006 The Journal ofShellfish Research (formerly Proceedings ofthe National Shellfisheries Association) is the official publication of the National Shellfisheries Association EDITOR Sandra E. Shumway University ofConnecticut EDITORIAL BOARD Standish K. Allen, Virginia Institute ofMarine Science, USA (2006) USA Shirley Baker, University ofFlorida, (2006) Bruce Barber, Eckerd College, USA (2007) Brian Beal, Universin' ofMaine. USA (2006) Norman Blake, University ofSouth Florida, USA (2006) Neil Bourne, Department ofFisheries and Oceans. Canada (2007) Susan Bower. Department ofFisheries and Oceans, Canada (2007) Andrew R. Brand, University ofLiverpool. UK (2007) Eugene Burreson, Virginia Institute ofMarine Science. USA (2007) Peter Cook, Austral Marine Senices, Australia (2006) UK Simon Cragg, University ofPortsmouth, (2006) Leroy Creswell, University ofFlorida. USA (2007) Louis D'Abramo, Mississippi State University, USA (2006) USA Christopher V. Davis, Pemaquid Oyster Company. (2006) Ralph Elston, Aqua Technics, Washington. USA (2007) Susan E. Ford. Rutgers University. USA (2006) Raymond Grizzle, Jackson Estuarine Laboratory. USA (2007) Karolyn Mueller Hansen, University ofDayton Research Institute. USA (2006) Juliana Harding, Virginia Institute ofMarine Science. USA (2007) Ellen Kenchington, Bedford Institute ofOceanography, Canada (2007) Maureen K. Krause. Hofstra University, USA (2007) Jerome LaPeyre, Louisiana State University. USA (2007) Mark Luckenbach, Virginia Institute ofMarine Science, USA (2007) Bruce MacDonald. University ofNew Brun.swick. Canada (2006) Roger Mann, Virginia Institute ofMarine Science, USA (2006) Islay D. Marsden, University ofCanterbury. New Zealand (2006) Sharon McGladdery. Department ofFisheries and Oceans. Canada (2007) G. Jay Parsons, Fisheries and Oceans Canada. Canada (2007) Martin Posey, University ofNorth Carolina. USA (2007) Laura Rogers-Bennett, University ofCalifornia , USA (2007) Tom SONIAT, Nicholls State University, USA (2006) Elisabeth von Brand, Universidad Catolica del Norte, Chile (2007) Randal Walker, University ofGeorgia. USA (2006) J. Evan Ward, Universits- ofConnecticut. USA (2006) Gary Wikfors, NOAA/NMFS. USA (2006) Robert B. Whitlatch. University ofConnecticut. USA (2007) Correspondence: Dr. Sandra E. Shumway, Department ofMarine Sciences, University ofConnecticut. 1080 Shennecossett Road, Groton. CT 06340; Ph: 860 405 9282; FAX: 860 405 9153; email: sandra-shumwaye"uconn.edu Instructions to authors located on back page ofJournal and at www.shellfish.org/pubs/jsr.htm Journal ofShellfish Research Volume 25, Number 1 ISSN: 0730-8000 2006 April MBLWHOI Library Jaiinial ofSlwllfish Researcli. Vol. 25. No. 1. I-1.\ 2000. THE WHELK DREDGE FISHERY OF DELAWARE MAY 1 2 2006 WOODS HOLE DAVID GARClA BRUCE* Massachusetts 02543 Division of Fish and Wildlife. DcUiwtirc Dcpcutincm of Natural Resoarccs and Enviroiuiwiiial Connol. Little Creek Fisheries Luhoratorx. P.O. Bo\ .^30. Little Creek. Delaware IW6I ,ABSTR.ACT The statusofthe Delaware whelk dredge fishery was assessed fromstate landingsreports andfromdatacollectedby an onboardobserver. Mean annual whelk landings for 1994to2000 were 18.5 mtofmeats and increasedto241.6mtforthe period 2001 to2004. Annual landings for2001 to 2003 were 88% to 119% ofthe sum ofdredgeand trawl fishery landingsreportedbythe remaining stateson the United States Atlanticcoast. Althoughknobbedwhelks,Busyconcarica,are landedthroughouttheyear, 88% ofpooled monthly landingsfor 1994to2004 were taken between March andJune inclusive. Elevenobservercruises wereconducted March to June 2004. Total estimated daily take of legal (length >I27 mm| knobbed whelks ranged from to 197-3,710 organisms. E.\pectedcatch rateswereestimated at 83.2 legal knobbed whelksperhourpermeterofdredge width. Dredgesweregenerallytowed paralleltobathymetriccontoursandadjacenttoshoal featuresin2-20mdepths.Estimatesoftheareaofbottomdredgedoneachcrui.se rangedfrom4.9-14.2ha.Attimes,multipleboatswereobserveddredgingthesamebottom,suggestingacooperativefishingtechnique. Seventy-ninepercentofdredgetowsoccurredonbottomcomprisedofmudandsand, and mean numbersofknobbed whelks in0.04 m' samplesweregreatestfrom mud/sandhabitats.Twenty-onetaxonomicgroupsoforganismswere observedin samplestakenfrom dredges. Knobbed whelk and horseshoe crabs, Limtiltis polyphennts. dominated dredge catch by number. Whelks collected in the AtlanticOceanweresignificantlylargerthanthosecollectedintheDelawareBay.MeanlengthsofwhelkscollectedintheBayin2004 were significantly less than lengths ofBay whelks collected in 1994 prior to the inception ofthe minimum length regulation. Shifts in sizedistributionandthecyclical natureofotherwhelk fisheriessuggestthattheelevatedlandingsexperiencedduring 2001 to2004 are not sustainable. KEY WORDS: knobbedwhelk,Biisyctmcancel, whelk landmgs.fisheryobserverinvestigation,essential fishhabitat, DelawareBay INTRODUCTION 1948,Gendron 1992.Castagna& Kraeuter 1994,Power& Keegan 2001, Avise et al. 2004). In addition to having longer shells than Knobbed whelks, Busycim carica (Gnieliii, 1791) and chan- males (Magalhaes 1948, Anderson et al. 1985, DiCosimo & Du- neled whelks, Biisyeonpus canaliciilatiis (Linnaeus, 1758), are Paul 1985, Walker 1988), female knobbed whelks are wider and large gastropods that occupy estuarine and shelf habitats from heavier than males (Anderson et al. 1989). Observations of inter- CStaapteesC(oEddwtaorCdsap&e HCaarnaasveevrvaylchon19t8h8e).AtBlaontthicspCeocaisets oocfctuhpeyUsnaintdeyd tsiudcaclesmsaftuilnlgyapcrtoivdiutcyeinedgigcatsetrtihnagtss(mPaollweerrmeatleals,a2n0d02l)a.rgeLafregmealfees- habitats and prey on bivalve mollusks (Magalhaes 1948, Carriker inales, variable and skewed sex ratios (Anderson et al. 1985), and 1951, Davis 1981, Peterson 1982). Colloquially known as conchs, the presence of male characters in females in at least 12 Buc- tShteatetswoAtslpaentciicescohaasvteastulpepaosrttseidncmeultthiepl1e93fnisshe(rMieascKoennztiheeU1n9i9t7e)d. cinidae genera (Power & Keegan 2001) has lead tothe hypothesis that knobbed whelks may be protandric hermaphrodites that ini- Cgwehhaearrnen(aeEslveekrdsnoowlbheeble&kdsAwnahdreeelrkhssaornavre1es9t8me4od,stpDraivvmuialsrnie&lryaSbwilisetshotnopod1tr98eo8dr,getWraoalrpktegreraawrel,t tliaarlgleyrmsaitzteisre(Wasalmkaelres19a8n8d).thReenceunntdeDrNgoAfuanncatlyisoinsa,lhsoewxerveevre,rsainldia-t al. 2003. Logothetis & Beresoff 2004). cates that knobbed whelks aregenetically dioecious, having main- Mark and recapture studies have demonstrated that knobbed malian-like sex chromosomes (Avise et al, 2004); observed phe- whelk growth is generally slow (Anderson et al. 1985, Kraeuteret notypic sex reversal orpseudohermaphroditism, may result from a al, 1989). Short-term negative growth has been observed (Magal- variety ofenvironmental factors (Jenner 1979). haes 1948, Anderson et al, 1985), and there are examples of pe- Whelks have been landed as by-catch or from directed dredge r1i9o8d9i)c.rAa\peirdaggreogwrtohwt(hDiiCnolseinmgtoh&ofD1u0P4amualrk1e9d85w,heKlrkaesutinereaesttearln. o(rNOtrAawAl Ffiisshheerriieess f2r0o04m;alhlttUpS://Awtwlwa.nstti.cnmsftsa.tgesov)e.xceCpotasFtl-owriiddea aVli.rg1i9n8i9a).thaKtneoxbhbiebidtewdhpeolskitlievenggtrhowatthagweasha3s.2bmeemn/yrrec(oKrrdaeedutferroemt l1a0n5d.i2ngiTsitforfommeadlrsedigne1a9n5d0,twrahwelnfFieshdeerriaels rheacvoerdiinngcrbeeagsaend,ftrooma captive specimens and from examination ofannual growth marks highof 1913.5 mt in 1994. .'Mthough total landingshavedecreased identified on opercula. Average length (/( = 20) of 10-y-old cap- to 549.8 ml in 2003, ex-vessel price has remained high, as total tive eastern Virginia whelks was 144 mm (Castagna & Kraeuter landings \aluc was $1.55 million in 2003 relati\e to$1.79 million 1994). Eastern Virginia whelks 158 mm long were predicted to be in 1994 (NOAA Fisheries 2004). Whelk meats are generally re- 10y from operculum agedata(age = -10.99+ 1.33(length); ii = moved from shells locally and then shipped on ice to northern 45. r2 = 0.50 P = 0.0001; Kraeuter et al. 1989), United States metropolitan areas for canning or fresh retail sale; Age or size at reproductive maturity in knobbed whelks has they are also frozen and shipped to East Asia(Eversole & Ander- been difficult to determine because gender ontogeny has not been son 1984, Kaplan & Boyer 1992). well understood, Phenotypic gender differentiation in whelks is In Delaware, an expanding dredge fishery has raised concern determined by the presence or absence of a penis (Magalhaes over the long-term sustainability of whelk stocks. Additional at- tentionhasfocusedonby-catchconsiderationsandpotential physi- cal effects ofdredging activity on ecologically significant benthic *Corresponding author. E-mail: da\[email protected] habitats, particularly the structures created b> the colonial poly- Bruce chaetesSabeUaria vulgaris (Verrill. 1873)andHydroidesdiamhus i^uu - (Verrill. 1873). Because ofthe general lack ofpublished infomia- tion on mid-Atlantic whelk fisheries, this study presents updated landingsinformationandtheresultsofanonboardfisheryobserver 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 obser- vations document previously unknown attributes such as gear types, spatial and temporal variation in catch and effort, by-catch coinposition. 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 LandingsAnalyses 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 re- quired to submit monthly catch reports that are archived by the Division ofFish and Wildlife. The information recorded includes number oftrips, general location dredged, gear type, the monthly take ofknobbed and channeled whelks and whether take was by- catch from other fisheries or from directed whelk fisheries. In additiontorequiringmonthly logbookreporting. Delaware fishery regulationsincludethepossessionofacommercial license,a 127.0 mm minimum length limit forknobbed whelks, a l.'i2.4 mm mini- mum length limit forchanneled whelks and a prohibition ofnight- time dredging. Whelk landings are published in biannual summaries ofstate- wide shellfish harvest and fishery status that date back to 1994 (Whitmore & Greco 2005). Cuirent whelk landings information compiled by the state of Delaware were compared with federally reportedcoast-widedredge andtraw1 fishery landingstoassessthe relative magnitude of the Delaware fishery. Coast-wide landings dataprovidedby NOAAFisheries(http://www.st.nmfs.gov)donot differentiate knobbed and channeled whelks; therefore for com- parative purposes, Delaware landings data used here include both taxa. Delaware landings are reported as total weight including the shell, whereascoast wide landingsarereportedas weightofedible meats; toallow comparison in equivalent units. Delaware landings were divided by a factor of3 (Whitmore & Greco 2005). Fishery seasonality was assessed from mean monthly landings and catch- per-unit-effort (CPUE) from Delaware harvest reports 1994 to 2004. CPUEwascalculatedbydividingmonthly harvestinweight by the number of trips reported by each fishery participant. OnboardFishery Observation Elevenobservercruiseswereconductedonthreevesselsduring March toJune 2004to obtain fishery information notcontained in monthly reports. Dredge type, width, ring and mesh size were recordedatthebeginningofeachcruise. Foreachdredgetow. start andendtimeswererecordedtodetermine tow durationandfishing effort. Total daily take, in volume of legal knobbed whelks, was recorded at the end ofeach cruise. Landed volume was converted to numbers with a conversion factor of 64.37 legal whelks per 0.04 nv' (1.0 bushel). Estimated number of legal whelks was con- vertedtoweightwithcruise-specific lengthfrequencydistributions and a length-weight relationship derived during the cruises (Fig. Delaware Whelk Dredge Fishery uhclk lengths(ProcGLM.SAS 2002); lengthdatawere log^.traiis- only 3% of 3,031 reported directed trips that landed knobbed Icimicd to satisfy least squares assumptions. whelks occurred in the Atlantic Ocean. Knobbed whelk landings showed distinct seasonal patterns. RESULTS Landings from the directed dredge fishery were reported from all months of the 1994 to 2004 period, but the greatest mean total Fishery Ijindings 1994to2004 monthly landings occurred from March to June (Fig. 3). For the directed fishery, mean landings ofwhelk meats for March toJune In addition to the dredge fishery. Delaware has a smaller but ranged from 12.9—10.2 mt. whereas mean landings forthe remain- significant pot fishery (Table 1). Whelk kaidings were not re- ing months ranged from 0.2 mt to 2.7 mt. Mean monthly whelk corded by the State until 1994 when legislation was passed regu- by-catch landings from the Delaware Bay winter blue crab Calli- lating all whelk fisheries. Analysis of monthly reports for the nectes sapidus (Rathbun, 1896) dredge fishery ranged from 0.1- period 1994 to 2004 reveal that participation and landings have 2.9 mt. Higher CPUE during March to May suggested seasonally increased in recent years. The number oflicense holders that par- increased vulnerability todredge gearratherthan increaseddredg- ticipated inthedirecteddredge fishery was 1 1 in 1994, declinedto ing effort (Fig. 3). 2 in 1997, and increased to 19 in 2003. Sixteen license holders Fishery Observations 2004 participated in the 2004 directed fishery (Whitmore & Greco 20051. Landingsofpooled knobbedandchannel whelks wererela- Catch Between March 15 andJune 24, 2004eleven observer tively low for 1994 to 2000 and then increased to high levels in cruises were conducted on three dredge vessels. Two vessels op- 2001 to2004(Fig.2).Themeanannual landingofwhelkmeatsfor erated from Bowers Beach, DE. and the other from Lewes, DE. 101)4 to 2000 was 18.5 mt and for 2001 to 2004 the mean annual Two used single scallop dredges deployed from the stern of landing was 241.6 mt (Whitmore & Greco 2005). Except for the deadrise workboats, the other used a motorized bay schooner with bluecrabfishery,whelksprovidethegreatestex-vessel valueofall paired toothbar crab dredges deployed from the sides. Scallop Delaware commercial fisheries. Dockside ex-vessel value of dredges were 2.62 m and 3.44 m in diameter; bag rings ranged dredged knobbed and channeled whelks was $ 574,645 in 2004. from63.5 mm to88.9 mm indiameter;bagmeshrangedfrom 50.8 Mean annual whelk landings from the Delaware dredge fishery mmto 127.0 mm bar measure. Toothbardredgeswere2.3 m wide, 2001 to 200.^ were 96.4% of mean landings for all dredge and rings were 49.0 mm in diameter, and mesh was 127.0 mm bar trawl whelk landings 2001 to 2003 from the remaining Atlantic measure. Fishing effort was directed at whelks on all cruises, but states (NOAA Fisheries 2004; Fig. 2). Although Federal coastal horseshoecrab,Linudiispolyphemus(Muller, 1785),andbluecrab fisheries statistics do not differentiate channeled and knobbed by-catch was retained on Cruise 1 and 3, hard clam Mercenaria whelk landings. State reports indicate that for 1994 to 2004, meicenaria (Linnaeus, 1758) by-catch was retained on Cruise 2. knobbed whelks comprised between 78.8% and 99.9% of total Whelkdredging beganatdaylightandendedbetween 1500and annual landings by weight in the Delaware dredge fishery. Most 1700 h. The general dredge-fishing consisted of towing the gear fishery effort occurred in the Delaware Bay during 1994 to 2004, for approximately 15 min. retrieving the gear, making a 180° turn TABLE I. Coastal .Atlantic whelk landings from directed and by-catch llsheries for 2003. Knobbed and channeled whelk landings are pooled. Delaware landings comefrom monthly logbook reports, whereas landings forthe remainingstates were reported by NOAAFisheries. Landings Itonnes meats) Blue Minimum Total Conch Crab Clam Other Crab Fish Other Conch Crab Lobster Fish Other Legal State Landings Dredge Dredge Dredge Dredge' Trawl Trawl Trawl" Pot Pot Pot Pot Pot' Size (mm)^ Connecticut Bruce 1000 CO Delaware Whelk Dredge Fishery TABLE 2. Dredge gear, effort, and landings oflegal knobbed whelk (>127 niml on 11 <ibser>er cruises in the Delaware Bay March toJune 20114. Horseshoe crab and blue crab were retained on Cruises 1 and .1, and hard clams were retained on Cruise2. Bruce Cumulative catch from Cruises 10 and 11 illustrates why the Bay between Bowers Beach and Cape Henlopen. DE, and Cruises fishery ceases in late June. On Cruises that occuired prior to 9 8 and 1 I were located just off-shore, in the Atlantic Ocean, south June, catch rates remained similar throughout the day (Fig. 4). On ofCape Henlopen. Fishery activity occuired adjacent to the beach Cruises 10 and 11, initial catch rates were similar to previous in the ocean and on the slopes ofthe numerous shoals that define cruises, but declined after approximately two hours offishing ef- Delaware Bay bottom topography. Dredge tracks were generally fort (Fig. 4. inset). Low catch rates and declined efficiency, pre- oriented parallel tobathymetriccontours (Fig. 6). Depthsrecorded sumably elicited by increased light levels, prompted both coop- during dredge deployment and retrieval ranged from 2 to 20 m. erators to cease fishing for the season. June 9 was the last day of The area ofvirgin bottom impacted by scallop dredges, estimated dredging for vessel B and June 24 was the last day for vessel C from dredge trackline distance and dredge width, ranged from 4.9 (Table 2); no other boats were observed fishing on either dates. ha on Cruise 1 1-14.2 ha on Cruise 4 (Table 2). Fishery Location Bentliic Habitat Types Dredge-boat cruises occuned in the Delaware Bay and in the Bottom type was recorded from 212 of 274 total dredge tows. Atlantic Ocean (Fig. 5). Cruises 1-7, 9 and 10 were located in the Bottom material observed in dredges included mud, clay, sand. Cape May, NJ Cape LEGEND • Location of tows (drecJge m 3.3 Contour m 9.8 Contour -/^ Shoreline 2.5 5 10 15 Kilometers Delaware Whelk Dredge Fishery (mean = 1; /; = 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% ofclassified tows. Tube casings of the colonial "reef building polychaetes S. vul- garis and H. diamluis were observed infrequently, but were gen- erallyassociated withhard substratessuchasrockandoystershell. Catch Composition Proportions ofknobbed whelks relative to numbers ofby-catch organisms observed in volumetric samples were highly variable. Mean percent knobbed whelk by number was less than 50% on Depth four of the eleven cruises, but ranged up to 88.1% on Cruise 9 (metersMLLW) (Table 2). Twenty-one ta.xonomic groups were enumerated from ^ 149 samples taken from dredge contents. The most abundant spe- -8 cies in the samples were knobbed whelk and horseshoe crabs -15 (Table 3). Proportions of pooled knobbed whelk by number ex- -22 Dredgetracklines amined ranged from 31.7% on Cruise 11-88.4% on Cruise 9: for Figure 6. Locations ofdredge tracklines relative to hathynietric fea- horseshoe crabs proportions range from 1.0% on Cruise 9^1.0% tures at Lower Middle Shoal in the Delaware Ba>. (;PS coordinates onCruise 8.Thehighestproportionsofhorseshoecrabsby number wererecordedatthebeginningandendofdredgetows.Tracklinesare were observed in samples from ocean Cruises 8 and 11. Knobbed interpolated and assume a straight line between wajpoints. whelks were observed in 98.6% ofall dredge tows and horseshoe crabs were observed in 85.2% ofall tows (Table 3). Windowpane oyster shell, and rock. Less dense material, such as mud. silt and flounder Scophthalnuis aqiiosa (Mitchill. 1815) and unidentified shell fragments may have been washed away during dredge re- skates were the most evenly distributed taxonomic groups as they trieval, and dredges were occasionally rinsed to remove fine sedi- were observed in all cruises in similar proportions. Channeled ments, which resulted in potentially ambiguous distinction be- whelk occurred in only 22.2% of the dredge tows sampled and tween Mud/Sand and Sand categories (Fig. 7). Six of the seven comprised only 1% of organisms observed in samples (Table 3). bottom categories werecharacterizedby mudorsandcomponents. Proportions of channeled whelk in pooled volumetric samples Knobbed whelks were most frequently associated with mud and ranged from 2.9% in Cruise 8% to 0% on Cruise 11; both cruises sand bottoms. The greatest number of whelks enumerated from occurred in the Atlantic Ocean. Although not enumerated in 0.04 m' samples came from bottoms classed as mud/sund/shell samples, the shells of dead knobbed whelks generally were the hash (mean = 24.1: standard error = 3.7. /; = 8): the lowest most abundant nonliving material observed in dredges, and fre- numberofwhelks in samples, came from rock/worm tube bottoms quently were more abundant than li\ing whelks. lau -[ #>° ,»^° S»<^^ ,e* ^6*^.^\3H VN^'.61*' i^^' ,6**^" S»^ ,«^" v^^'i^'^' Bruce TABLE 3. Composition oforganisms obserxcd in (1.04 ni' samples taken from \vhell< dredge contents. Counts Here pooled from single samples from 149 dredge tows on 11 vessel cruises. Frequency ofoccurrence is the proportion ofsamples containing the specific taxon. Percent Frequency Common Number of ofOccur- Name LatinName Observed Total rence (%I Knobbedwhelk Busycon curku 2SI3 63.96 9S.66 Horseshoecrab Umuliispnlxplwnms S()2 IS.24 S5.23 Skate Rajidac ISI 4.11 51.68 Wiiidowpane Scophfluibniis {ii/iiiiMis 120 2.73 43.62 tlounder Hardclam Mercenaria 10? 2.39 12.08 mercenaria Spidercrab Libinia spp. 102 2.32 22.82 Rockcrab Cancel-iiToratus 87 1.98 23.49 Blue crab Calliiieaes.miHcliLs 5S 1.32 24.16 Channeled Biisyconrns 44 1.00 22.15 whelk canaliciiliirK.s Summer Piiraliclnlnsilcnmiiis 37 0.S4 14.77 flounder Bluemussel MytiluseduHs 5 Starfish Asteriidae Mudcrab Panopeus spp. Oystertoadfish Opsiiiuiskilt Hogchoker Trineclcsmaculatiis Striped searobin Prionotiisevolaiis Atlantic Poliniccsdupliciitiis moonsail Dogfish ElasmobranctiHimorphi Northern Sphoei'oidesimiciiUiliis pufferfish Squid Teuthoidea 1 0.02 0.67 Total observed = 4398