Marine Pollution Bulletin xxx (2014) xxx–xxx

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Marine Pollution Bulletin

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Derelict fishing gear in Chesapeake Bay, Virginia: Spatial patternsand implications for marine fauna

0025-326X/$ - see front matter � 2014 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.marpolbul.2014.01.034

⇑ Corresponding author. Tel.: +1 804 684 7331; fax: +1 804 684 7179.E-mail address: donnab@vims.edu (D.M. Bilkovic).

Please cite this article in press as: Bilkovic, D.M., et al. Derelict fishing gear in Chesapeake Bay, Virginia: Spatial patterns and implications for marineMar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.01.034

Donna Marie Bilkovic ⇑, Kirk Havens, David Stanhope, Kory AngstadtVirginia Institute of Marine Science, College of William & Mary, P.O. Box 1346, Gloucester Point, VA 23062, United States

a r t i c l e i n f o a b s t r a c t

Keywords:Blue crabBycatchDerelict fishing gearDiamondback terrapinEastern oysterMarine debris

Derelict fishing gear is a source of mortality for target and non-target marine species. A program employ-ing commercial watermen to remove marine debris provided a novel opportunity to collect extensivespatially-explicit information for four consecutive winters (2008–2012) on the type, distribution, andabundance of derelict fishing gear and bycatch in Virginia waters of Chesapeake Bay. The most abundantform of derelict gear recovered was blue crab pots with almost 32,000 recovered. Derelict pots werewidely distributed, but with notable hotspot areas, capturing 40 species and over 31,000 marine organ-isms. The target species, blue crab, experienced the highest mortality from lost pots with an estimated900,000 animals killed each year, a potential annual economic loss to the fishery of $300,000. Importantfishery species were captured and killed in derelict pots including Atlantic croaker and black sea bass.While some causes of gear loss are unavoidable, others can be managed to minimize loss.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Humans have been fishing the world’s estuaries and oceans forthousands of years, but the availability of synthetic materials inmodern times has increased the efficiency, durability, and lifespanof gear for numerous fisheries. An unfortunate result of theseimprovements and intensified fishing effort has been an increasein the quantity and persistence of derelict fishing gear in the mar-ine environment (Carr and Harris, 1997; Macfadyen et al., 2009).Derelict fishing gear includes nets, lines, traps, and other recrea-tional or commercial fishing equipment that has been lost, aban-doned, or otherwise discarded (UNEP, 2005). Derelict gear is ofconcern because it can damage sensitive habitats, trap and killtarget and non-target species, cause economic impacts from theloss of commercially valuable species, and pose a safety hazardto human navigation (e.g., Guillory, 1993; Matsuoka et al., 2005;Bilkovic et al., 2012). Captured animals in derelict fishing gear,including invertebrates, finfish, turtles, birds, and mammals, canstarve, cannibalize each other, drown, develop infections, andbecome injured or diseased (Guillory, 1993; Matsuoka et al.,2005; Hart and Crowder, 2011).

Chesapeake Bay supports several important commercial finfishand shellfish fisheries that utilize a wide array of fishing gearincluding oyster hand tong, crab pots, eel pots, ordinary clam tong,various types of gill nets, conch dredge, fyke nets, and purse seines(Kirkley, 1997). In Virginia, purse seines (targeting Atlantic

menhaden Brevoortia tyrannus) or the offshore scallop dredge typ-ically account for the highest landed value with blue crab (Callinec-tes sapidus) pots providing the third highest landed value (Kirkley,1997). In Maryland, by landed value in 2011, blue crabs (primarilycaught with pots) far exceed other species fished in the Bay, withstriped bass Morone saxatilis (primarily caught with gill nets) sec-ond in value (Maryland Manual Online – Seafood Production,2013). Chesapeake Bay is one of the nation’s largest sources of bluecrabs (Fogarty and Lipcius, 2007) and crab pots are the most com-mon gear used to capture them. Baywide, crab pots targeting hardcrabs or peelers (crabs preparing to shed or ‘‘peel’’ off their hardshell to become soft-shelled crabs which are considered a delicacy)account for roughly 70% of all crabs harvested commercially (62%in MD and 81% in VA) (Kennedy et al., 2007). Pots in ChesapeakeBay are rigid, cube-shaped structures that usually measure 0.6� 0.6 � 0.6 m and are constructed of either 18-guage double-gal-vanized or vinyl-coated wire with 1.5 in. hexagonal or squaremeshes (Kennedy et al., 2007). The pots are designed to be de-ployed and recovered by a line and buoy system. By number, crabpots far exceed any other gear type in Chesapeake Bay. There areclose to 800,000 commercial crab pots licensed in the Bay and thatnumber does not include an unknown but significant recreationalfishery (Bilkovic et al., 2012). By comparison, in 2011, 15 purseseine licenses were purchased in Virginia (Maryland has prohibitedpurse seining since 1931) and 4441 gill net licenses were pur-chased baywide (Virginia Marine Resources Commission http://mrc.virginia.gov/commlicensesales.pdf; Maryland Department ofNatural Resources http://www.dnr.state.md.us/fisheries/commer-cial/stripedbass/index.asp).

fauna.

2 D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

In addition to inducing mortality for the target species bluecrabs, derelict crab pots pose a threat to non-target species. Forexample, in North Carolina, the annual mortality from derelict potswas estimated to be 1.9 million blue crabs and 249,000 finfish(NCDENR, 2011). A non-target species known to be at high risk tomortality from lost crab pots is diamondback terrapin Malaclemysterrapin, the only entirely estuarine turtle species in ChesapeakeBay and a keystone species for its influence on community structureof intertidal marshes (Silliman and Bertness, 2002). Terrapins exhi-bit strong habitat fidelity (Roosenburg et al., 1999; Gibbons et al.,2001), nest site fidelity (Mitro, 2003), and have relatively smallhome ranges (typically <2 km: Sheridan et al., 2010), so that sub-populations tend to be spatially discrete. Recent studies have attrib-uted terrapin population declines and changes in sex ratios directlyto bycatch mortality in commercial crab pots (Roosenburg et al.,1997; Dorcas et al., 2007; Grosse et al., 2009). In Virginia waters,the blue crab fishery has exerted sufficient selection pressure onthe terrapin bycatch to affect the growth rate and average size of fe-male terrapins (Wolak et al., 2010). The outcome of both chronicand acute mortality events from crab pots on terrapin populationshas been dramatic, with observed declines in population size tooutright local extinction of terrapins (Roosenburg, 2004). Mortalityof terrapins in pots is dependent on pot location (water depth, dis-tance from shore), water temperature, season, and terrapin size(Hart and Crowder, 2011). Lost crab pots represent an unknownsource of mortality for terrapins. Though high numbers of terrapins,some in various stages of decay, have been reported in derelict potssuggesting that lost pots continue to capture and kill terrapin(Bishop, 1983; Roosenburg, 1991).

In response to the declaration of a commercial blue crab fisheryfailure in Chesapeake Bay by the US Department of Commerce in2008, the Virginia Marine Resources Commission (the state agencywith regulatory oversight) developed a Blue Crab Fishery ResourceDisaster Relief Plan (VMRC, 2009). One component of the plan, theMarine Debris Location and Removal Program, involved theemployment of commercial watermen to locate and remove lostor derelict fishing gear from Virginia waters. This program pro-vided a novel opportunity to collect extensive spatially-explicitinformation for multiple, consecutive years on the type, distribu-tion, and abundance of derelict fishing gear in the Virginia watersof Chesapeake Bay. These data can provide crucial baseline infor-mation on spatial and temporal trends in gear loss as well as spe-cies interactions with lost gear. Distribution of derelict gear willdictate the species at risk to injury or mortality from capture. Forinstance, diamondback terrapin will be most susceptible to com-mercial crab pots within shallow waters because this is where theytypically reside (Harden and Willard, 2012). Ultimately, data de-rived from removal programs such as this one can be used to facil-itate management solutions to reduce the loss and impact ofderelict fishing gear.

Our objectives were to (1) describe the spatial and temporalpatterns of derelict gear distribution in the lower ChesapeakeBay, (2) document the diversity and abundance of marine faunain recovered derelict crab pots, and (3) identify regional hotspotsof derelict gear and bycatch.

2. Methods

2.1. Marine Debris Location and Removal

Virginia’s Marine Debris Location and Removal Program em-ployed commercial watermen to locate and remove derelict fishinggear, particularly blue crab pots, during the winter months(December–March) when the crab pot fishery is closed. Abbrevi-ated methods are presented herein, for more detailed methodology

Please cite this article in press as: Bilkovic, D.M., et al. Derelict fishing gear in ChMar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.01.034

refer to Havens et al. (2011). The program completed four consec-utive years (2008–2012). In the first program year, 58 watermenparticipated. In year two, all the existing participants elected to re-turn and the program was expanded to include 7 additional com-mercial watermen for a total of 65 participants. Years 3 and 4, 5more watermen were added for a total of 70 participants. Each par-ticipant was restricted to 49 days of on-the-water work for years1–3 and 24 days during year 4 which was abbreviated due to lim-ited funds. In the first year, the program ran from December 15,2008 – March 30, 2009. For all other years, retrieval activities be-gan on December 1 and ceased on March 15. Henceforth, for sim-plicity, program year 1 will be referred to as ‘2009’, program year 2will be referred to as ‘2010’, and so forth.

We previously determined that side-imaging technology waseffective at locating and identifying marine debris, particularly der-elict blue crab pots (Havens et al., 2008). Crab pots are distinctivein imagery and can be differentiated from other debris based onthe shape (square and may have an acoustic shadow distal to thenadir) and dimensions (side 1 m or less). The availability of rela-tively inexpensive (�$2500) side-imaging units (fish-finders), al-lowed for the possibility of employing a large number of peoplewith varying backgrounds to locate and remove debris. Prior toprogram initiation, the Humminbird™ 1197SI side imaging unit(dual frequency 455–800 kHz) was compared with known technol-ogy (Marine Sonics Sea Scan; 600-kHz transducer) in terms of im-age resolution, ease of use, and data extraction capability.Identification of marine debris was similar between both units,and the Humminbird™ unit required minimal post-processingwith an easily understood interface. It also has the ability to beprogrammed for quality control by recording track lines and mark-ing and saving a screen shot image of each marked object. Wedetermined that Humminbird units were viable options for useby individuals for surveying and trained participants on equipmentuse and survey protocols.

We provided each participant with a side imaging unit, water-proof digital camera for cataloging recovered debris items and der-elict gear bycatch, maps of sensitive habitat areas (oyster reefs andsubmerged aquatic vegetation), and datasheets to fill out for eachretrieved item. Participants outfitted their own vessels with aremovable transducer mount and were instructed to place theGPS directly above the side imaging transducer. Units were prepro-grammed to scan using 23 m (75 ft) swaths and acquire GPS points(survey tracks) every 30 s. On the basis of anticipated derelict potabundance, travel time, and other logistical considerations, we as-signed broad areas to individuals to avoid excessive overlap, andmade efforts to ensure surveys were conducted in most Virginia ti-dal water regions. We showed examples of imagery with positivelyidentified bottom features, such as crab pots, sunken vessels, nets,gravel bars, and fish schools, during training to help participantsdifferentiate debris from other underwater elements. During sur-veys, participants marked potential marine debris observed onthe side imager and Global Positioning System (GPS) coordinatesand an image of the scanned object were stored. Once an itemwas marked and coordinates saved on the side-imaging unit, the‘‘goto’’ feature on the Humminbird could be used to return to theexact location for item retrieval. Protocols for debris removal, datacollection, and debris disposal were coordinated with the NOAAMarine Debris Program personnel. We instructed participants inthe proper retrieval techniques to reduce bottom disturbance.

2.2. Data collection and summary

During this program, once an item was retrieved, it was photo-graphed, and date, time, location (waypoint), and item descriptorswere documented. If the item was a crab pot, a series of descriptorswas recorded, including presence of a visible surface buoy,

esapeake Bay, Virginia: Spatial patterns and implications for marine fauna.

D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx 3

functionality (fishable condition), and pot material (vinyl or metal).To differentiate abandoned versus unintentionally lost (e.g., cut/tangled buoy lines from storms or boat traffic) derelict pots, wecategorized pots with the presence of a visible surface buoy asabandoned by the waterman, and pots with no buoy or a sub-merged buoy as lost. If the item was a net, the type (gill or seine)and size (0–100 ft or >100 ft) were recorded. Other retrieved mar-ine debris (e.g., tire, appliance) was simply described. Informationon bycatch from any derelict fishing gear was reported as the num-ber, sex and status (live or dead) of blue crabs, fish species abun-dance, and number and type of other organisms captured (e.g.,diamondback terrapin, ducks). All live bycatch was released.During the first year, participants reported numerous derelict crabpots containing live oysters, so we modified their datasheets to in-clude a categorization of the number of live oysters associated witheach pot which was then recorded in years 2–4. For larger quanti-ties of oysters on a given pot, watermen reported the abundance innumber of bushels. To estimate number of oysters on a pot, weconsidered a bushel to be 100 oysters.

Every other week, we downloaded GPS marked coordinates(geographic coordinate system WGS 1984), sonar images ofmarked items, and vessel track line data from side-imaging unitsusing SD memory cards. We used participant vessel track linesfor auditing and accountability purposes, as well as quantificationof the areal extent surveyed. We also downloaded digital photo-graphs of derelict gear from participant cameras and stored in adigital library. We scanned and transcribed datasheets to digitaldatabases for further analyses. For three program years (2009–2012), we surveyed participants for information on the numberof crab pots they fished during the crabbing season and the num-ber they lost to obtain average annual pot loss rates.

2.3. Data analyses

We summarized the abundance of types of derelict gear re-trieved, the number of individuals of blue crab, fish, and terrapincaptured, the number of blue crab reported dead, and the inverte-brate taxa associated with pots including eastern oyster Crassostreavirginica for the entire survey area. To characterize patterns of mar-ine debris distribution and associated bycatch, we aggregated thewatershed boundaries in the Chesapeake Bay Program (CBP) Seg-mentation Scheme (USEPA, 2004) to create 10 reporting regionsof Virginia tidal waters that generally corresponded to fishingzones. Virginia regions comprised Tangier Island, Eastern Shore,Seaside, Upper Bay, Western Shore, Southside, and the four majortributaries Potomac, Rappahannock, York, and James rivers. Wecreated spatial databases in ArcGIS with marine debris locationsand all associated attributes and bycatch abundance. We extractedthe abundance of each marine debris type and bycatch for each re-gion and program year. The vast majority (n = 31,813) of derelictpots had information on the condition of the pot at the time of re-trieval, and we were able to summarize and compare across seg-ments and years several descriptors of derelict crab potsincluding pot material (vinyl/metal), actively capturing animalsversus non-functioning, and lost versus abandoned (buoy intact).

We investigated temporal and spatial patterns of the data byestimating for each region and the entire study area (1) mean an-nual survey area covered by participants, (2) mean annual numberof crab pots retrieved per km2, and (3) number of crab pots re-trieved in shallow (62 m) and deep (>2 m) waters. To determinedensity of derelict crab traps (the most abundant form of marinedebris) per region, we extracted the survey area within each regionfrom composited vessel tracklines of all participants for each yeardownloaded from side-imaging units. We merged and dissolvedtrackline polygons to create a composite area surveyed for eachyear. We extracted bathymetric depth contours from National

Please cite this article in press as: Bilkovic, D.M., et al. Derelict fishing gear in ChMar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.01.034

Oceanic and Atmospheric Administration (NOAA) HydrographicSurvey Data and quantified the number of crab pots within the62 m, 2–6 m, and >6 m depth contours. We extracted average dailywater temperature data for the duration of recovery activities fromthe Virginia Estuarine and Coastal Observing System (VECOS)Gloucester Point Continuous Monitoring Station (YRK005.40), lo-cated at the mouth of the York River to relate to blue crab bycatchabundance.

We quantified spatial patterns of the density of crab pots, abun-dant bycatch species such as blue crab and Atlantic croaker, andassociated species of importance (diamondback terrapin, oysters)using a kernel density estimator. The kernel density estimator cal-culates density within a circular surface around a point on the ba-sis of a selected search radius in this case 1 km2. The resultingraster coverage was in a 30 m grid that was converted to polygonsso that area could be calculated (ArcGIS 9.3). We spatially dis-played data on the basis of equal interval quantiles (excludingzeros) to depict relatively high and low density values. We calcu-lated the area of the highest densities (hotspots) of pots or bycatchfrom density data in the uppermost quantile of the distribution.We projected all spatial databases to the Universal Transverse Mer-cator (UTM, Zone 18N; WGS 1984).

3. Results

3.1. Spatial and temporal patterns of marine debris

Over four program years, 34,080 marine debris items were re-trieved from Virginia tidal waters. Of these, there were 31,952(93.8%) blue crab pots, 467 (1.4%) eel pots, 161 (0.5%) nets, and1472 (4.3%) miscellaneous debris (e.g., oyster aquaculture cages)(Fig. 1). In addition 25 sunken vessels were identified. Similar num-bers of items were collected during each of the first 3 years of theprogram (2009–2011) which consisted of 48–49 days of retrievaleffort, with slight increases in the second (�1000 more items)and third (�1500 more items) years attributable to the retrievalfrom the additional participants in those years. The final programyear (2012) was abbreviated to 24 days and corresponding to thereduced effort the retrieved items amounted to about half of whatwas retrieved in previous years. In total, the participants surveyedapproximately 3300 km2 of bay bottom.

Over 90% of the crab pots were collected in 7 respective regions:Tangier Island, Seaside, Eastern Shore, York River, Upper Bay, Poto-mac and James River (Table 1). Approximately 95% of eel pots werecollected in 7 respective regions: York River, Tangier Island, East-ern Shore, Seaside, James River, Upper Bay, and Rappahannock Riv-er. The mean density of crab pots retrieved over the entiresurveyed area was 5.3 ± 4.2 (SD) pots/km2 with the highest densityof pots in Seaside, Potomac River, York River, and Tangier Island re-gions (Fig. 2). A relatively small area (90 km2) of the Potomac Riverwas surveyed by a single efficient participant contributing to thehigh observed pot density. High density (15–311 pots/km2) clus-ters of pots were identified from the kernel density analysis over562 km2 of Virginia waters (18% of the area surveyed). The loca-tions within geographic regions with the strongest concentration(hotspots) of crab pots were surrounding Tangier Island, LittleWicomico River, lower York River, Mobjack Bay, Eastern Shoreand Seaside tidal creeks, and Pocomoke Sound.

In total, 41% of recovered pots were likely abandoned (intactbuoy) by watermen with a high variability among geographic re-gions (range: 9–81%). Seaside, Western shore, and Eastern shorehad the highest mean annual percentage of pots abandoned(83 ± 5, 62 ± 19, 61 ± 8, respectively), while the lowest mean an-nual percentage of abandoned pots (620%) occurred within YorkRiver, Tangier Island, and Potomac River regions (Fig. 3). These

esapeake Bay, Virginia: Spatial patterns and implications for marine fauna.

Fig. 1. Number of marine debris items recovered from Virginia tidal waters over four winters. Blue crab pots were the dominant form of marine debris retrieved in each year.Additional fishing gear retrieved were eel pots and nets (seine, gill). Other marine debris items included tires, appliances, oyster aquaculture cages, buckets, chairs, andballoons.

4 D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

areas had high (P80%) percentages of unintentionally lost potswhich are typically the result of cut/tangled buoy lines fromstorms or boat traffic. Annually, the overall proportion of recoveredpots that were abandoned was remarkably consistent ranging from37% to 46%. In total, 35% of recovered pots were able to actively fishor continue to capture organisms, with a regional range of between25% and 41% (Table 1, Fig. 3). Annually, the proportion of recoveredpots actively fishing ranged between 28% and 38%. A large percent-age of derelict pots (45%, 14,535 pots) were retrieved in shallowwaters (62 m depth) and 52% of the pots (16,570) were retrievedin waters between 2 and 6 m depth.

3.2. Bycatch in derelict fishing gear

We documented 31,546 marine organisms and 40 species cap-tured in derelict fishing gear (nets, crab and eel pots) over thecourse of four years of removal activities in Virginia waters. Thisincludes organisms that were large enough to be captured in thederelict gear: fish (n = 5111), blue crabs (25,317), diamondbackterrapin (n = 47), whelks (n = 1061), lobster (n = 2), birds (n = 3),and mammals (n = 4). Other invertebrates that may be associatedwith the derelict gear but not necessarily captured were not in-cluded in this number (e.g., oysters). The vast majority of capturedorganisms (97%) were observed in derelict blue crab pots.

3.3. Bycatch in derelict crab pots

3.3.1. Blue crabsIndividual derelict pots contained between 0 and 46 blue crabs

(mean = 1.0). Of the 25,043 blue crabs documented in crab pots,37% (n = 9160) were dead. The mortality estimate was relativelyconsistent among years (2009 = 32%, 2010 = 33%, 2011 = 44%, and2012 (abbreviated year) = 25%). More than 90% of the blue crab by-catch was observed in Tangier Island, Seaside, Eastern Shore, UpperBay, York River, and James River, respectively (Table 1). The highestdensity (upper quartile) of blue crab catch in derelict pots was be-tween 18 and 389 crabs/km2 (total range 0–389 crabs/km2). Highcrab density occurred over 332 km2 (11% of the area surveyed).The locations with the strongest concentration (hotspots) of crabbycatch corresponded to high crab pot density locations (Fig. 2).Forty percent of the blue crabs in derelict crab pots were reportedin the first 2 weeks of December when water temperatures were

Please cite this article in press as: Bilkovic, D.M., et al. Derelict fishing gear in ChMar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.01.034

still relatively high (10 �C on average) (Fig. 4). The catch did not in-crease as water temperatures warmed in the early spring. Annualcrab and fish bycatch amounts were highest in program years 2and 3 (Fig. 5). Bycatch abundance was noticeably lower in theabbreviated year 2012 and in the first year because retrieval activ-ities began 2 weeks later than all other years missing the relativelywarm temperatures in early December.

3.3.2. FishIndividual derelict pots contained between 0 and 50 fish

(mean = 0.2). Thirty-three different fish species were reported inderelict crab pots and over 95% of the catch was comprised of 9 pri-marily demersal (bottom-dwelling) species including oyster toad-fish Opsanus tau, Atlantic croaker Micropogonias undulatus, blacksea bass Centropristis striata, American eel Anguilla rostrata, whiteperch Morone americana, and catfish Ictaluridae spp. (Table 2).Although participants were not explicitly asked to record whetherfish were alive or dead upon retrieval, many participants did reportthis information. When reported upon, oyster toadfish were oftennoted alive with the smaller animals likely using the pots as habi-tat (49% of gear was reported upon, 62% oyster toadfish alive).Other fish species were often reported dead including Atlanticcroaker (15% of gear was reported upon, 83% croaker dead), andblack sea bass (27% of gear was reported upon, 63% sea bass dead).The highest density (upper quartile) of total fish catch in derelictpots was between 57 and 76 fish/km2 (total range 0–76.0 fish/km2). High total fish density occurred over 1.7 km2 (0.1% of thearea surveyed). The locations with the highest concentration (hot-spots) of fish bycatch were primarily dispersed within the York andJames rivers and the Seaside. Oyster toadfish had a widespread dis-tribution with high densities (3.9–76.0 oyster toadfish/km2) inMobjack Bay, York and James rivers, and the Eastern Shore(Fig. 6a). High densities of Atlantic croaker (1.4–12.9 croaker/km2) and black sea bass (1.7–35.1 sea bass/km2) bycatch were re-ported near Tangier Island (Fig. 6b and c). Catfish and white perchbycatch were observed primarily in brackish reaches of the tribu-taries (Fig. 6d).

3.3.3. Diamondback terrapinIndividual derelict pots contained between 0 and 7 terrapin.

Terrapin were predominantly captured in pots on the seaside ofVirginia (60%) with the highest captures in 2008 and 2009. The vast

esapeake Bay, Virginia: Spatial patterns and implications for marine fauna.

Table 1Summary of four years of marine debris removal program results by Chesapeake Bay region. Fig. 2 illustrates the location of each region. Mean survey area represents the annualaverage area covered by participants. Total number of watermen indicates the total number of participants surveying within the region over the course of the four years. Meanannual number of crab pots retrieved per km2 surveyed were obtained by dividing annual pot retrieval totals with mean area surveyed in each region. A vast majority of derelictpots (n = 31,813) had information on the fishing condition of the pot at the time of retrieval. Percent abandoned pots represents the proportion of total retrieved pots that retaineda buoy. Percent active represents the proportion of total retrieved pots that were actively capturing organisms on the basis of presence of bycatch and/or reported condition ofpot. Total blue crab, fish, and terrapin are reported catch for all years in all derelict gear. The number of oysters recorded on pots is an estimate on the basis of reported abundance,which was either exact counts or for larger numbers as bushels, for example a bushel was considered to be 100 oysters.

Region Meansurvey area(km2)

Total numberof watermen

Totalcrabpots

Totaleelpots

Meanpots(km2)

Abandonedpots (%)

Pots stillfishing(%)

Totalbluecrab

Totalfish

Terrapin No. oysters onderelict gear

% of totalcrab pots

York 244 22 6996 182 7.1 22 25 3930 1842 9 13,875 21.9Tangier 248 20 5891 16 6.0 20 41 8066 318 2 510 18.4Eastern Shore 329 29 5683 42 4.4 60 32 4588 645 5 675 17.8Seaside 169 12 4575 15 7.8 81 34 3031 166 28 749 14.3James 192 11 2962 100 3.9 49 34 1702 1170 0 2820 9.3Upper Bay 164 31 2269 42 3.7 28 39 2360 273 2 123 7.1Rappahannock 137 11 1659 47 3.3 26 40 655 518 1 119 5.2Potomac 34 3 1410 19 15.4 9 42 678 63 0 5 4.4Western Shore 88 19 269 3 0.8 70 25 123 37 0 5 0.8Southside 57 8 238 1 1.1 23 40 184 79 0 27 0.7

All Regions 1664 70 31,952 467 5.3 41 35 25,317 5111 47 18,908 100

D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx 5

majority of terrapin (83%, n = 39) were captured in pots in shallowwaters (62 m depth). There was no association with water temper-atures; terrapin were reported in derelict pots retrieved whenwaters were 2.5–12.4 �C. All terrapin were dead in the pots exceptfor one captured on January 7th 2009 on the seaside in 6.8 �Cwater.

3.3.4. Other bycatchDucks (diving) and muskrats (Ondatra zibethicus) were also ob-

served in a small number of derelict crab pots. Ducks (n = 3) werecaptured on the seaside and the York River and muskrats (n = 4)were captured on the seaside, and York and Potomac rivers.

3.4. Invertebrates associated with derelict crab pots

3.4.1. OystersA total of 17,446 oysters were estimated to be attached to 868

derelict blue crab pots. Individual derelict pots contained between0 and 800 oysters. The highest density (upper quartile) of oysterson derelict pots was between 47 and 1320 oysters/km2 (total range0–1320 oysters/km2). High oyster density occurred over 80.2 km2

(2.6% of the area surveyed). There was high variability among geo-graphic regions with relatively high abundance in the York (lowerYork River, Mobjack and Poquoson bays) and James River and lowabundance in the Potomac River, Southside, and Western Shore(Table 1, Fig. 7).

3.4.2. Other invertebrate speciesA number of invertebrate species were documented in and on

derelict crab pots over the 4 years. Because watermen were notexplicitly asked to identify every species of invertebrate present,the number of species and taxa present on derelict pots is likelyan underestimate. Invertebrate taxa reported included whelks(Busycon carica, Busycotypus canaliculatus), crabs (Panopeus herbstii,Cancer spp., Pagurus spp. and Libinia spp.), American lobster Hom-arus americanus, sea urchins, sponges, tunicates, barnacles, andclams and mussels. The non-native veined rapa whelk Rapana ven-osa was positively identified in three derelict pots (6 animals) nearthe Bay mouth (in the Southside Region and two tributaries of theJames River, Nansemond and Elizabeth rivers) within the knowndistribution of rapa whelks in the Chesapeake Bay (Harding et al.,2005).

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4. Discussion

The recovery of thousands of derelict pots for four consecutiveyears suggests that lost blue crab pots are a significant and ongoingsource of marine debris in Chesapeake Bay. The number of animalsand species captured or killed in the pots represent only those ani-mals that have not decomposed and are present and active in thecooler winter months. Therefore, the observed bycatch in recov-ered pots likely underestimates the annual mortality induced bya lost pot that continues to trap. Blue crabs and terrapins becomedormant in the winter months burrowing in mud and remaininginactive for extended time periods (Haramis et al., 2011; Hardenand Willard, 2012). During summer months in shallow water areasof Chesapeake Bay, terrapin capture rates were reported to be0.17 terrapins/pot/day (Roosenburg et al., 1997), suggesting thatthe low number of terrapin (n = 39) captured in the shallows dur-ing the winter months is not representative of annual capture ratesof terrapin. Similarly, an average capture rate of 50 blue crabs/der-elict pot was estimated during the crabbing season in the lowerChesapeake Bay (Havens et al., 2008). Instantaneous observationsof catch during recovery (mean = 1 crab/pot) did not convey thesum total of capture or mortality that blue crabs experience duringthe lifespan of a derelict pot. Several fish species that are suscepti-ble to capture in crab pots move offshore seasonally and are pri-marily absent from Bay waters in the winter, including summerflounder Paralichthys dentatus, bluefish Pomatomus saltatrix, stripedbass Morone saxatilis, and alosine species (shads and river her-rings), which suggests that their abundance in recovered derelictpots underestimates annual bycatch rates. In contrast, Atlanticcroaker and spot Leiostomus xanthurus spawn offshore in wintermoving into the estuary in the late spring while young fish over-winter in the estuary. Their high abundance in recovered pots islikely attributed to their presence in the estuary in the winterand early spring as well as the fact they are demersal fish. How-ever, Atlantic croaker accounted for the highest proportion(29.7%) of the finfish catch in experimental derelict pots that werefished over a year in the lower York River, and the average summer(May–August) catch rate was 14 croaker/pot (Havens et al., 2008).This suggests that Atlantic croaker may experience relatively highlevels of capture in derelict pots year-round.

Mortality from derelict pots can be roughly estimated for bluecrabs from derelict gear recovery data. The maximum allowablecommercial crab pots in Virginia waters currently is approximately385,000. The annual loss rates of pots have been previouslyestimated to be 10–30% of fished gear (Bilkovic et al., 2012). On

esapeake Bay, Virginia: Spatial patterns and implications for marine fauna.

Fig. 2. Spatial distribution of the density of recovered derelict crab pots and associated blue crab bycatch in Virginia tidal waters.

Fig. 3. Abandoned and actively fishing derelict crab pots in relation to the annualaverage of recovered derelict pots during the three full program years 2009–2011.

Fig. 4. Blue crab bycatch in relation to mean water temperature. The largestnumber of blue crabs captured in derelict pots occurred during early Decemberwhen waters were relatively warm and not all crabs may have burrowed in the mudfor hibernation which is triggered around 9 �C. By March, waters are warming tocomparable levels as early December (in excess of 9 �C), but crabs may not haveemerged from hibernation.

6 D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

average, watermen participants (n = 56) reported they had a 20%annual loss rate (SD range 12–16) for three consecutive years(2009–2011). Each derelict pot has been previously estimated tocapture 50 crabs per year in Virginia (Havens et al., 2008).

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Considering that the recovery data suggest that on average 37%of crabs captured in derelict pots were dead, approximately 18crabs/pot/yr are estimated to be killed in derelict pots in Virginia.This mortality estimate is similar to values reported for the Gulfof Mexico (26 crabs/pot/yr, Guillory, 1993) and Maryland(20 crabs/pot/yr, Giordano et al., 2011). By conservatively assum-ing that 250,000 traps are fished and 20% are lost annually, we esti-mate that approximately 50,000 derelict traps are introduced toVirginia waters every year and 900,000 blue crabs are killed annu-ally by derelict pots with a $300,000 value (6.6 crab/kg, $2.20/kg)potentially lost.

esapeake Bay, Virginia: Spatial patterns and implications for marine fauna.

Fig. 5. Comparison of the annual abundance of blue crab and fish bycatch inrecovered derelict crab pots.

D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx 7

Some of the invertebrate species reported were bycatch includ-ing lobster, whelks, and horseshoe crab, while other species weremerely associated with derelict gear as biofoulers including theimportant fishery species eastern oyster. Oysters were not uni-formly distributed on derelict pots throughout Virginia waters.There were notable regions with high densities of oysters includingthe lower York River, Mobjack Bay region that were in close prox-imity to existing oyster bars previously characterized as sources(North et al., 2008). The recovery data may provide ancillary infor-mation on oyster dispersal and settlement in the Bay to supportrestoration activities. In general, oysters are found in salinities >5and depths <10 m throughout the Chesapeake Bay and tributaries(Kennedy, 1991). Dispersal of the planktonic larvae of oysters isinfluenced by swimming behavior and hydrodynamics with an

Table 2Mean abundance (SD) of fish species bycatch among years (2008–2012). Nine species com

Fish species Scientific name

Oyster toadfish Opsanus tauBlack sea bass Centropristis striataAtlantic croaker Micropogonias undulatusAmerican eel Anguilla rostrataWhite perch Morone americanaCatfish spp. IctaluridaeSpot Leiostomus xanthurusFlounder spp. ParalichthyidaeTautog Tautoga onitisMinnow spp. CyprinidaeUnknown spp.Sheepshead Archosargus probatocephalusStriped bass Morone saxatilisPigfish Orthopristis chrysopteraAtlantic spadefish Chaetodipterus faberRed drum Sciaenops ocellatusStargazer Astroscopus guttatusMullet spp. Mugil spp.Pufferfish spp. TetraodontidaeButterfish Peprilus triacanthusAtlantic menhaden Brevoortia tyrannusHogchoker Trinectes maculatusBlack drum Pogonias cromisStriped burrfish Chilomycterus schoepfiiBowfin Amia calvaCunner Tautogolabrus adspersusPorgy spp. SparidaeScup Stenotomus chrysopsBluefish Pomatomus saltatrixPinfish Lagodon rhomboidesShad Alosa or Dorosoma spp.Feather blenny Hypsoblennius hentzStriped killifish Fundulus majalis

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estimated median dispersal distance of oyster larvae in the Bayof 9.0 km (North et al., 2008). Thus, the observations of oystergrowth on geo-referenced derelict pots can be related to larvalsource areas and be indicative of potential suitable habitat whichhas implications in oyster reef restoration efforts. The crab potsare likely attractive as settlement habitat because they are elevatedfrom the bottom, minimizing siltation effects, act as hard substrate,and the interior chambers and central bait box serve as protectionfrom predators.

Derelict crab pots were widely distributed throughout Virginiatidal waters. Many watermen in Virginia will move their crab potsto follow blue crab seasonal movements. In the spring and summermonths, blue crabs inhabit shallow low salinity waters of tributar-ies and creeks (Van Engel, 1958). Following insemination femaleswill migrate to the more saline deeper areas near the mouth ofthe Chesapeake Bay for egg brooding and hatching (Van Engel,1958; Turner et al., 2003; Aguilar et al., 2005), and when temper-atures drop below 9 �C crabs aggregate in deeper water and buryin muddy sediments (Jensen et al., 2005; Jensen and Miller,2005; Smith and Chang, 2007). As the crabbing season begins inearly spring, watermen focus potting activity in deeper waters,the mainstem of the Bay, and near the mouths of tributaries. Dur-ing the later spring and summer months, watermen follow crabs asthey move into less saline and shallower waters of tributaries andcreeks where they typically mate. This seasonal movement of gear,in combination with the large numbers of pots that are fishedannually, account for the observed widespread distribution of der-elict pots.

Fishing gear can become derelict through a variety of mecha-nisms including the severing of buoy lines by vessel propellers, linebreakage because of age, pots are abandoned or vandalized, orstorms roll the pots, pulling the buoy below the surface (Guillory,1993). Approximately 60% of the recovered crab pots were without

prised greater than 95% of the catch.

Abundance Cumulative % of catch

837 (171) 66.8104 (96) 75.178 (74) 81.346 (18) 85.044 (9) 88.543 (40) 91.923 (13) 93.713 (13) 94.813 (6) 95.812 (21) 96.711 (8) 97.67 (8) 98.26 (1) 98.75 (6) 99.02 (2) 99.22 (1) 99.31 (2) 99.41 (2) 99.51 (2) 99.61 (1) 99.61 (1) 99.71 (1) 99.71 (1) 99.71 (1) 99.8<1 99.8<1 99.9<1 99.9<1 99.9<1 99.9<1 100.0<1 100.0<1 100.0<1 100.0

esapeake Bay, Virginia: Spatial patterns and implications for marine fauna.

Fig. 6. Spatial distribution of the density of fish in derelict crab pots for abundant bycatch species (a) oyster toadfish, (b) Atlantic croaker, (c) black sea bass, and (d) whiteperch and catfish.

8 D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

buoys and likely had lines severed through vessel propellers orvandalism. The largest proportion of derelict pots reported withsevered lines was in Tangier Island and York River (78%) regions.The proportion of lost gear caused by severed buoy lines from rec-reational and commercial vessel traffic is expected to be highest inareas with significant boating activity. Surrogate measures of ves-sel traffic can include the number of boats registered in an area,

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and presence of marinas and/or ramps and docks. The York Riverdoes have a high number of registered vessels (13,749) in compar-ison to the other crabbing regions combined (average of �85,000registered vessels from 1997 to 2012; VDGIF, 2013), which maybe related to the large number of pots recovered with severed lines(5452). But this is not the case for Tangier Island, which has a rel-atively low number of vessels registered (n = 4375) and the second

esapeake Bay, Virginia: Spatial patterns and implications for marine fauna.

Fig. 7. Spatial distribution of the density of eastern oysters associated with derelictcrab pots. The highest densities of oysters (47–1320 km2) were observed in thelower York River, Mobjack Bay and select areas of the James River and EasternShore.

D.M. Bilkovic et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx 9

highest number of pots with severed lines (n = 4611) reported.Tangier Island is accessible only by boat or airplane and most ofthe residents make their living as commercial watermen. Boatscarring of the bottom within seagrass beds on the eastern shoreof the Bay was most prevalent in the grassbeds near Tangier Island(Orth et al., 2001) suggesting high vessel traffic in the area. In com-bination, the high crabbing effort and vessel traffic near the islandmay account for high pot loss in this region. Further investigationinto the relationship between commercial and recreational vesseltraffic patterns and crab pot loss could help formulate more effec-tive preventive measures for pot loss.

Several different management and policy actions can be eluci-dated from the recovery program information on derelict gearcharacteristics, distribution, and bycatch. While derelict gear losscan never be completely eliminated, some causes of gear loss canbe prevented. Consistently, approximately 40% of traps recoveredfrom watermen retained their buoy. Though, a small percentageof these pots were moved during storm events and lost to thewaterman, most were abandoned for a variety of reasons includingillness or advanced age of pots. Economic measures may be imple-mented that discourage illegal abandonment and encourage prop-er disposal of traps, such as the enforcement of the closed season(no pots legally allowed in the water). A grace period may be givenfollowed by fines for abandoned pots. Recovery data can be used toidentify specific regions with significant numbers of abandonedpots for easy removal in the off-season and regulatory action. En-hanced education and outreach to recreational boaters is recom-mended to reduce the number of pots lost by severing of buoylines. Beyond preventative measures, for those pots or fishing gearthat are unavoidably lost, management and policy options includethe continued removal of lost gear in targeted hotspots and theapplication of innovative approaches to disarm derelict gear toreduce mortality. One possibility is the use of a biodegradable

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component on a pot such as a panel that will dissolve once a potis lost to allow escape of captured animals (Bilkovic et al., 2012).

In summary, the most abundant form of derelict fishing gear inChesapeake Bay, Virginia is blue crab pots with almost 32,000 potsrecovered from 3300 km2 of Bay bottom during four consecutivewinters. Derelict pots were widely distributed in Virginia tidalwaters and captured 40 target and non-target species and almost32,000 marine organisms. High density clusters of derelict crabpots and blue crab bycatch were observed in several key regions:Tangier Island, York River (particularly the lower York and MobjackBay), and Eastern Shore and Seaside tidal creeks. Because derelictgear was recovered during cold winter months, the number andabundance of species captured is likely an underestimate of the an-nual loss of marine fauna to derelict gear. The target species, bluecrab, experienced the highest mortality from lost pots with an esti-mated 900,000 animals killed each year, a potential annual eco-nomic loss to the fishery of $300,000. In addition to the targetspecies, important fishery species were captured and killed in der-elict pots including Atlantic croaker, black sea bass, American eel,white perch, and catfish. The amount of derelict gear recoveredwas similar among years indicating that each year a consistentproportion of fishing gear in the Bay becomes derelict. While somecauses of gear loss are unavoidable, others can be managed to min-imize loss. Management options include implementing disincen-tives for illegal abandonment of gear, targeted removal ofderelict gear in hotspot locations, and education for vessel opera-tors on derelict gear impacts and gear avoidance techniques. Inno-vative modifications to fishing gear that will effectively disarm lostgear should be investigated and implemented. Once ‘disarmed’derelict pots could provide some beneficial habitat for oystersand other structure-orientated animals.

Acknowledgments

The project benefited tremendously from support from VirginiaMarine Resources Commission including J. Travelstead, J. McCros-key, R. O’Reilly, T. Short, D. Sparks, L. Gillingham, and J. Grist. Manythanks to K. Duhring, J. Kidwell, L. Ott, and J. Herman for contribu-tions to data collection, entry, and quality assurance. A specialthank you to the 70 commercial watermen. Communication andadvice from NOAA’s Marine Debris Program was invaluable. Theproject was funded through NOAA Grant NA09NMF4520027. Thispaper is Contribution No. 3344 of the Virginia Institute of MarineScience, The College of William and Mary.

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