Donna Marie Bilkovic1, H. Ward Slacum, Jr., Kirk J. Havens1, 

Danielle Zaveta2, Christopher F. G. Jeffrey3, Andrew M. Scheld1, 

David Stanhope1, Kory Angstadt1, John D. Evans4

Ecological and Economic Effects of Derelict 

Fishing Gear in the Chesapeake Bay

2015/2016 Final Assessment Report

Revision 2, Oct. 7, 2016

Prepared for

Marine Debris Program

Office of Response and Restoration

National Oceanic and Atmospheric Administration

Contract DG133E-10-CQ-0034, Task Order 007

Derelict crab pot removal in the Chesapeake Bay (Photo credit: Matt Stewart)

1Virginia Institute of Marine Science 2Versar, Inc. 3CSS-Dynamac, Inc. 4Global Science & Technology, Inc.
Contents i

Ecological and Economic Effects of Derelict Fishing Gear in 

the Chesapeake Bay (2015/2016)

Final Assessment Report (Revision 2) – Oct. 7, 2016

Table of Contents

1. Introduction.....................................................................................................................................3

1.1 Background..............................................................................................................................3

1.2 Approach .................................................................................................................................7

2. Bay-wide Distribution and Densities of Derelict Crab Pots...............................................................8

2.1 Chesapeake Bay Biogeographic Framework .............................................................................8

2.2 Key Variables/Data Acquisition and Preparation ......................................................................9

2.2.1 Blue crab fishery spatial patterns...................................................................................9

2.2.2 Bathymetry................................................................................................................. 11

2.2.3 Recreational boat traffic activity ................................................................................. 11

2.2.4 Status of derelict crab pots from removal efforts ......................................................... 13

2.2.5 Vessel traffic data (AIS data)...................................................................................... 14

2.3 Geographically Weighted Regression (GWR) Model.............................................................. 15

2.4 Quantitative Findings from the GWR Model .......................................................................... 21

2.5 Model Sensitivity ................................................................................................................... 22

2.6 Uncertainties and unknowns................................................................................................... 23

3. Ecological and Economic Effects Assessment................................................................................ 24

3.1 Ecological Effects.................................................................................................................. 24

3.1.1 Ecological modeling framework and key variables...................................................... 24

3.1.2 Bycatch Analysis........................................................................................................ 24

3.1.3 Habitat impact analysis............................................................................................... 27

3.2 Economic Effects................................................................................................................... 31

3.2.1 Quantitative findings .................................................................................................. 32

3.2.2 Sensitivity analysis ..................................................................................................... 34

3.2.3 Uncertainties and unknowns ....................................................................................... 35

4. Management Scenarios – Mitigation Alternatives .......................................................................... 36

4.1 Introduction ........................................................................................................................... 36

4.2 Accidental and Intentional Loss.............................................................................................. 36

4.3 Reduction of Derelict Pot Effects ........................................................................................... 36

4.3.1 Pot removal ................................................................................................................ 36

4.3.2 Pot modifications........................................................................................................ 37

4.4 Management Scenarios........................................................................................................... 39

5. Future Directions........................................................................................................................... 40

6. Conclusions................................................................................................................................... 41

Appendix A. Blue Crab Pot Loss Rates................................................................................................A-1

Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots.....................................B-1

Appendix C. Data Requirements, Inventory, Compilation, and Preparation ..........................................C-1

Appendix D. Blue Crab Management in Virginia and Maryland...........................................................D-1

Appendix E. Derelict Fishing Gear Outreach Activities and Presentations............................................ E-1

Appendix F. Questions Used for Watermen Conversations in Maryland................................................F-1

Appendix G. The Dilemma of Derelict Gear........................................................................................G-1
ii Contents

List of Figures

Figure 1-1. Marine Debris Items Recovered from Virginia Tidal Waters Over Four Winters..................3

Figure 1-2. Commercial Crabbing Effort in Maryland and Virginia. ......................................................4

Figure 1-3. Derelict Blue Crab Pot. .......................................................................................................5

Figure 1-4. Total Derelict Pot Catch Composition for Fish and Blue Crab in the Chesapeake 

Bay, excluding Bait Effects. ................................................................................................6

Figure 2-1. Map Showing Spatial Framework used to Characterize Chesapeake Bay Derelict 

Crab Pot Spatial Patterns.....................................................................................................8

Figure 2-2. Spatial Patterns of Blue Crab Fishery Effort in the Chesapeake Bay. ................................. 10

Figure 2-3. Chesapeake Bay bathymetry.............................................................................................. 11

Figure 2-4. Chesapeake Bay Recreational Boating Activity. ................................................................ 12

Figure 2-5. Spatial Distribution of Crab Pots identified as Lost or Abandoned during Retrieval 

Projects in Maryland and Virginia. .................................................................................... 13

Figure 2-6. Vessel Density Aggregated from AIS Data........................................................................ 14

Figure 2-7. Locations of Known or Estimated Derelict Crab Pots in the Chesapeake Bay..................... 16

Figure 2-8. Spatial Mapping of Locally Weighted Coefficient of Determination (R2) between 

GWR Observed and Fitted Values..................................................................................... 18

Figure 2-9. Spatial mapping of locally estimated coefficients. ............................................................. 19

Figure 2-10. Positive impacts of Effort, Recreational Boating, and Commercial Vessel Traffic 

on Derelict Pot Abundance................................................................................................ 20

Figure 2-11. Predicted derelict crab pot densities and spatial distribution. .............................................. 21

Figure 2-12. Bivariate scatterplot showing the strength of correlation and confidence interval 

ellipses between fishery effort and GWR predicted pot densities for the 

Chesapeake Bay. ............................................................................................................... 23

Figure 3-1. Estimated Annual Blue Crab Catch (left) and Blue Crab Mortality (right) from 

derelict crab pots............................................................................................................... 25

Figure 3-2. Estimated Annual Bycatch of White Perch (left) and Atlantic Croaker (right) from 

derelict crab pots............................................................................................................... 26

Figure 3-3. Potential spatial overlap between derelict crab pots and SAV habitats within the 

Chesapeake Bay. ............................................................................................................... 29

Figure 3-4. Potential spatial overlap between derelict crab pots and mapped oyster reefs within 

the Chesapeake Bay. ......................................................................................................... 30

Figure 3-5. Potential Economic Costs of Derelict Fishing Gear............................................................ 31

Figure 3-6. 95% Confidence Region of Chesapeake Bay Blue Crab Harvests with (Blue) and 

without (Red) Derelict Gear Removals. ............................................................................. 33

Figure 3-7. Increase in Blue Crab Harvest Resulting from Removal of Derelict Blue Crab Pots. .......... 33

Figure 4-1. Derelict peeler pot recovered from the Chesapeake Bay with diamondback terrapin 

and blue crab bycatch........................................................................................................ 38

Figure A-1. Watermen removal of derelict blue crab pots...................................................................A-5

Figure A-2. Ten Tidal Creeks in Virginia Where Derelict Pot Surveys and Removals were 

Conducted in 2014 and 2015. ..........................................................................................A-6

Figure B-1. Blue Crab Pot schematic (modified from Kennedy et al. 2007). .......................................B-1

Figure B-2. Mesocosm outfitted with cameras....................................................................................B-3

Figure B-3. Blue crab marked for mesocosm experiment. ..................................................................B-3

Figure B-4. Mean Crab Bycatch/Pot/Day for Four Locations..............................................................B-5

Figure B-5. Cumulative Blue Crab Mortality......................................................................................B-6

Figure C-1. Draft conceptual Framework of the distribution, densities, and effects of derelict 

crab pots in the Chesapeake Bay and how this framework can be used to inform a 

Derelict Fishing Gear Management Framework...............................................................C-2
Contents iii

List of Tables

Table 2-1. Predictors of Derelict Crab Pot Distributions in the Chesapeake Bay. ..................................9

Table 2-2. Geographic Weighted Regression (GWR) Results for Predicting Derelict Crab 

Pots in the Chesapeake Bay............................................................................................... 17

Table 2-3. Estimated Amount of Derelict Pots in Selected Regions of the Chesapeake Bay 

with the Extent of the Associated Areas Where Crabbing Occurs. ..................................... 22

Table 3-1. Annual Measured Rates for All Blue Crabs Captured and Killed in Pots during the 

Simulation Studies ............................................................................................................ 25

Table 3-2. Annual Capture Rates for White Perch and Atlantic Croaker in Simulated Derelict 

Crab Pots. ......................................................................................................................... 26

Table 3-3. Presence-absence contingency table showing counts of 1 km x 1 km grid cells 

containing submerged aquatic vegetation (SAV) and predicted derelict pots...................... 28

Table 3-4. Presence-absence Contingency Table Showing Counts of 1 km x 1 km Grid Cells 

with Oyster Reefs and Predicted Derelict Pots................................................................... 30

Table 3-5. Results from Different Models used to Evaluate the Economic Effects of Derelict 

Gear Removals.................................................................................................................. 32

Table 3.6. Average harvest/pot during years of removals in areas with and without removals............. 34

Table 3.7. Average harvest/pot before and after the first year of removals in areas with and 

without removals............................................................................................................... 34

Table 4-1. Species Recorded from Derelict Blue Crab Pots. ............................................................... 38

Table A-1. Activities Contributing to Pot Loss with Potential Mitigation Options. ............................A-1

Table A-2. Percent Pot loss in creek systems, main tributaries, and Chesapeake Bay. ........................A-4

Table A-3. Survey Areas and Number of Derelict Pots Removed. .....................................................A-4

Table A-4. Derelict Pot Removal and Loss Rates for Sarah Creek, VA..............................................A-5

Table A-5. Docks, Ramps, and Marinas Per Creek. ...........................................................................A-5

Table B-1. Capture Rates of Blue Crabs within Derelict Pots. ...........................................................B-2

Table B-2. Blue Crab Capture Rates in Virginia................................................................................B-4

Table B-3. Blue Crab Escape Rates from 1 and 2 Year Old Pots. ......................................................B-5

Table B-4. Time to Mortality of Blue Crabs in Derelict Pots in the Laboratory..................................B-6

Table B-5. Blue Crab Escape Rates from Derelict Pots. ....................................................................B-7

Table B-6. Blue Crab Mortality Rates for Derelict Pots.....................................................................B-7

Table C-1. Variables Associated with the Distribution, Densities, and Effects of derelict crab 

pots in the Chesapeake Bay. ............................................................................................C-1

Table C-2. Data types used to evaluate the ecological and economic effects of derelict crab 

pots in the Chesapeake Bay. ............................................................................................C-2

Table D-1. Regulations Governing the Maryland Blue Crab Fishery in 2008-2015............................D-4
Executive Summary 1

Executive Summary

Derelict fishing gear represents a major challenge to marine resource management: whether through 

deliberate abandonment or through accidental loss, derelict traps in particular have significant negative 

effects both economic (e.g., reduced fishery harvest from ghost fishing and gear competition that leads to 

the reduced efficiency of active gear) and ecological (e.g., degraded habitats and marine food webs and 

crab and bycatch mortality). Throughout the Chesapeake Bay, commercial harvest of hard-shelled blue 

crabs is a major fishing activity: every year sees the deployment of several hundred thousand blue crab 

traps (known locally as crab “pots”) across the Bay, of which an estimated 12-20% are lost each year. 

This report focuses on these derelict crab pots, drawing on many direct or remote observations and other 

data to quantify their abundance and spatial distribution across the Chesapeake Bay, and their resulting 

ecological and economic effects.

The study used a unified geostatistical framework to integrate disparate spatial datasets to predict the 

distribution and abundance of derelict crab pots in Chesapeake Bay and to evaluate their adverse effects 

on sensitive habitats and bay species. Predictor variables that likely affect the distribution and abundance 

of derelict crab pots that were evaluated included fishing effort, recreational boating activity, marine 

traffic patterns, and water depth. Using all of these data inputs, as well as derelict pot removal data and 

derelict pot field surveys, a geographically weighted regression (GWR) model successfully predicted and 

mapped the densities of derelict pots throughout the Chesapeake Bay, and estimated over 145,000 derelict 

pots Bay-wide; about 58,000 in Maryland and 87,000 in Virginia. 

An inventory of data available from many different sources identified several crucial but unknown 

variables necessary to evaluate ecological impacts of derelict crab pots baywide, such as pot loss rates, 

fishing practices affecting pot loss, and escape and mortality rates for crabs and bycatch (non-crab 

species) caught in derelict crab pots. These “data gaps” were filled through fieldwork (inspection and 

removal of derelict crab pots), controlled laboratory observations of crabs in and near pots, and structured 

conversations with watermen. The predicted geographic distribution of these pots served to pinpoint areas 

with significant ecological impacts: by combining the numbers and distribution of derelict pots from this 

model with annual blue crab catch and mortality rates, we estimate that each year, derelict pots catch over 

6 million crabs, and kill over 3.3 million — 4.5% of the 73 million crabs harvested in 2014. The effects 

on bycatch are also significant: for example, our model estimates that each year, derelict pots entrap over 

3.5 million white perch and nearly 3.6 million Atlantic croaker across the Bay. The effects of derelict pots 

on marine habitats appear to be less significant: only 16% of predicted derelict pots are in areas with 

submerged aquatic vegetation; and only 2% are in oyster beds. However, derelict pot removal programs 

required the avoidance of sensitive habitats including SAV and oyster reefs; therefore the impact on 

habitats may be greater.

Next, a spatially explicit harvest model was used to predict the economic effect of pot removal efforts on 

commercial blue crab harvests, by comparing actual harvests (with the derelict pot removals that occurred 

from 2008-2014) against those one would have expected in a counterfactual scenario of zero derelict pot 

removals. Model results suggest that pot removals increased harvests by over 30 million lbs in Virginia 

(27.2%, valued at $22.6 million) and over 8 million lbs in Maryland (16.3%, valued at $10.9 million); for 

a Bay-wide total of over 38 million lbs (23.8%, valued at $33.5 million) over the 6 year period. The 

model also suggested that over the derelict pot removal period, pot removals increased the efficiency of 

active pots by 0.43 lbs/pot in Chesapeake Bay; so on average, for each pot removed, harvests increased by 

868 lbs. Finally, the removal of derelict pots from high intensity potting areas (hotspots) can produce 

significant economic benefit beyond reducing mortality. For example, removing as little as 10% of the 

derelict pots from the 10 most heavily fished sites (5 sites in Virginia; 5 in Maryland) could increase blue 

crab harvest in the Chesapeake Bay by 22 million pounds or approximately 14%.
2 Executive Summary

These findings suggest several spatially-explicit management actions likely to reduce derelict crab pot 

accumulations and their harmful effects in the Chesapeake Bay. Minimizing spatial conflicts between 

crabbing and recreational and commercial boating traffic, and educating vessel operators on pot 

avoidance, would greatly reduce pot loss. Targeted pot removals in heavily-fished areas would be a 

highly cost-effective way to increase catch efficiency and reduce bycatch mortality. The number and 

impact of derelict pots would also be reduced by incentives to accelerate the removal of abandoned pots 

and to modify crab pots with biodegradable escape panels. We can already quantify the effects of some of 

these mitigation measures: for example, biodegradable escape panels would likely reduce crab mortality 

in derelict pots from over 3.3 million per year (4.5% of the harvest) to under 440,000 (0.6%).

The report discusses the sensitivity of these findings to the various inputs; as well as the confidence and 

precision levels attainable with current data; and charts ways to further refine these results to inform a 

generalized framework for determining ecological and economic effects of derelict fishing gear that can 

be used in similar fisheries in the United States and elsewhere.

Appendices to the report - some of which are full research reports in their own right - provide crucial 

detail and context. Appendix A documents the fieldwork, analysis, and findings related to loss rates of 

blue crab pots. Appendix B records the laboratory (mesocosm) study of capture, escape, and mortality 

rates for crabs in derelict pots. Other appendices detail the data used in the study; the complex and 

changing regulatory context for blue crab management across the Bay; the team’s outreach activities over 

the course of the project; the template for conversations with watermen; and a published article detailing 

the economic effects analysis.
Introduction 3

1. Introduction

1.1 Background

Marine debris, also known as marine litter, includes “any persistent solid material that is manufactured or 

processed and directly or indirectly, intentionally or unintentionally, disposed of or abandoned into the 

marine environment or the Great Lakes.” (Marine Debris Research, Prevention, and Reduction Act - 33 

U.S.C. 1951-1958 (2006)). Marine debris comes from both land-based and ocean-based sources and is 

frequently comprised of synthetic materials such as plastics and metal. Synthetics, like plastics, in recent 

decades have become a common material for consumer waste (e.g., bags, balloons, bottles), industrial 

products, and derelict fishing gear. While the majority of marine debris is land-based (Sheavly and 

Register 2007), derelict fishing gear can make up a significant proportion of the ocean-based marine 

debris in coastal areas (National Research Council 2008). Derelict fishing gear includes nets, lines, traps, 

and other recreational or commercial fishing equipment that has been lost, abandoned, or otherwise 

discarded (UNEP, 2005). The availability of synthetic materials in modern times has increased the 

efficiency, durability, and lifespan of gear for numerous fisheries. Derelict gear is of concern because it 

can damage sensitive habitats, trap and kill target and non-target species, cause economic impacts from 

the loss of recreational and commercial harvest of valuable species, and pose a safety hazard to human 

navigation (e.g., Guillory, 1993; Matsuoka et al. 2005; Bilkovic et al. 2014; Scheld et al. 2016).

The Chesapeake Bay supports several important commercial finfish and shellfish fisheries that utilize a 

wide array of fishing gear, including oyster hand tong, crab pots, eel pots, ordinary clam tong, various 

types of gill nets, conch dredge, fyke nets, and purse seines (Kirkley, 1997). However, blue crab traps, 

known locally as crab “pots,” are the prevailing derelict fishing gear found in the Chesapeake Bay

(Figure 1-1) because of the large number of pots deployed, their relatively high loss rates (~12-20%), and 

the long fishing season (Apr-Nov). 

Figure 1-1. 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 included tires, appliances, oyster 

aquaculture cages, buckets, chairs, and balloons. From Bilkovic et al. 2014.
4 Introduction

Numbers fluctuate; but, in recent years, estimated summer deployment of crab pots Bay-wide has 

exceeded 350,000 (Slacum et al. 2011a; Slacum et al. 2012; Figure 1-2).

The distribution, abundance, 

and persistence of derelict 

gear are strongly related to 

fishery activity and management. For example, the 

spatial extent of areas with 

concentrated fishing effort or 

no-fishing zones will largely 

dictate the boundaries of 

expected lost gear. Characterizing the fishery is an

important first step to assessing derelict fishing gear 

effects.

The Chesapeake Bay has 

always been a prominent 

source of blue crab, making 

up 50% of the national 

market by mid-century. 

However, the blue crab 

population has also 

experienced significant 

declines over the past few 

decades and only recently 

begun to rebound. Currently, 

the Chesapeake Bay blue 

crabs are not considered to be 

overfished, although large 

population fluctuations still 

occur. For the Chesapeake 

Bay, the target population is 

215 million and the target 

exploitation factor for female 

crabs is 25% of the stock 

(CBSAC 2014).

While blue crabs have been a noted food item in the Chesapeake Bay since before colonial times, the 

invention of the Chesapeake Bay crab pot and advances in crabmeat processing in the early 20th Century 

resulted in significant increases in hard crab harvests (Kennedy 2007). Since the mid-20th century, the 

primary gear used to capture blue crabs in the Chesapeake Bay is the rigid square-shaped wire pot with 

dimensions of approximately 2 ft. x 2 ft. x 2 ft (Figure 1-3).

Figure 1-2. Commercial Crabbing Effort in Maryland and Virginia.

Density estimates derived from an independent survey of crabbing effort 

conducted in 2010. From Slacum et al. 2011a.
Introduction 5

The Chesapeake Bay blue crab fishery is 

managed jointly by the States of Maryland and 

Virginia and the Potomac River Fisheries 

Commission. The three jurisdictions collaborate 

on Bay-wide annual harvest goals, but each 

jurisdiction implements its own unique set of 

regulations to manage the harvest from their 

waters. Virginia and Maryland have implemented a number of blue crab management actions,

including expansion of the spawning sanctuary, 

closure of the winter dredge fishery, establishment of daily individual and vessel harvest and 

possession limits, and establishment of crab and 

peeler pot tending requirements, as well as many 

other actions (Blue Crab Management in 

Virginia and Maryland, 2014; Maryland 

regulations from 2008 to 2015).

The crabbing season dedicated to potting generally runs from April through November with a closed 

winter season. In Virginia, the number of commercial crab pot licenses has gradually declined because of 

management actions and diminishing numbers of active watermen since the early 1990s (~1,800 licenses) 

to the present (~1,100 licenses). Similar reductions in licensed crabbers have occurred in Maryland over

the past decade due to a State-initiated license buy-back program and general attrition. Though it is 

unclear how the number of active watermen relates to the numbers of crab pots, the number of pots has 

decreased over this time as well. The allowable number of crab pots fished on the basis of licenses in 

Virginia likewise has declined from about 440,000 to 270,000 during the same time frame (1994-2014).

Key management actions potentially influencing derelict pot distribution are 1) Maryland regulations 

prohibit commercial crabbing in tributaries with pots, whereas this is allowed and practiced in Virginia; 2) 

a no-crabbing sanctuary (928 square miles) during the crab spawning season covering the mainstem and 

portions of the lower Chesapeake Bay to protect the spawning females; and 3) effort restrictions.

Blue crab fishery management actions are partially linked to the complex life cycle of the blue crab,

which involves multiple horizontal and vertical migrations across state boundaries and dependencies on 

high salinity areas in the lower Chesapeake Bay, Virginia for spawning, larval development, and overwintering. Generally, in the spring and summer blue crabs inhabit shallow low salinity waters of 

tributaries and creeks (Van Engel, 1958). Following insemination, females will migrate to the more saline 

deeper areas near the mouth of the Chesapeake Bay for egg brooding and hatching (Van Engel, 1958; 

Turner et al. 2003; Aguilar et al. 2005); when temperatures drop below 9°C, crabs aggregate in deeper 

water and bury in muddy sediments (Jensen et al. 2005; Jensen & Miller, 2005; Smith & Chang, 2007).

Independent surveys of crab pot efforts have documented that spatial patterns of fishing effort follow the 

spatial movement and migration of blue crab. The majority of crab pots are deployed in shallow waters 

less than 10m in the tributaries and mainstem in Virginia and only in the mainstem in Maryland (Slacum 

et al. 2011a; Slacum et al. 2012; Figure 1-2). Within Virginia, crab pots are fished singly; however, in 

Maryland, watermen are able to deploy pots singly or multiple pots can be attached to a single long line.

Blue crab pot loss in the Chesapeake Bay is often the result of the buoy line being separated from the pot 

(e.g., by vessel propellers, faulty buoy lines, or vandalism). Pots are also lost due to storm events that pull 

the buoy below the surface. Within Virginia, pot abandonment can be as high as 41% of derelict gear 

(Bilkovic et al. 2014). Once lost, pots pose threats to the natural environment due to their ability to 

continue to capture marine organisms. A derelict crab pot can persist from months to several years, 

Figure 1-3. Derelict Blue Crab Pot.
6 Introduction

depending on its construction; in the Chesapeake Bay, for example, derelict crab pots were estimated to 

persist from 1-7 years (Arthur et al. 2014). Organisms caught in derelict gear often face starvation, 

exposure to low dissolved oxygen, cannibalism, and disease, which can lead to death (Guillory et al.

1993). Over forty species have been documented in derelict crab pots in the Chesapeake Bay (Bilkovic et 

al. 2014, Slacum et al. 2009) (Figure 1-4). A species known to be at high risk to mortality from active 

and lost crab pots is diamondback terrapin Malaclemys terrapin, the only entirely estuarine turtle species 

in Chesapeake Bay. Recent studies have attributed terrapin population declines and changes in sex ratios 

directly to bycatch mortality in commercial crab pots (Roosenburg et al. 1997; Dorcas et al. 2007; Grosse 

et al. 2009). Lost crab pots represent an unknown source of mortality for terrapins- even though high 

numbers of terrapins, some in various stages of decay, have been reported in derelict pots suggesting that 

lost pots continue to capture and kill terrapin (Bishop, 1983; Roosenburg, 1991). 

Maryland

Dominant species observed: blue crab, 

white perch, oyster toadfish, spot. 

Other species: pumpkinseed, Atlantic 

menhaden, Atlantic croaker, American 

eel, sheepshead, black sea bass. 

(From Slacum et al. 2009)

Virginia

Dominant species observed: blue crab, oyster 

toadfish, black sea bass, Atlantic croaker. 

Other species: American eel, white perch, 

catfish, spot, flounder, tautog.

(From Bilkovic et al. 2014)

Figure 1-4. Total Derelict Pot Catch Composition for Fish and Blue Crab in the Chesapeake Bay, 

excluding Bait Effects.

Research addressing various aspects of derelict pots in the Chesapeake Bay has occurred for nearly a 

decade. The majority of this work is comprised of studies conducted independently in the waters of 

Maryland and Virginia. Research conducted in Maryland waters was co-led by representatives of Versar, 

Inc. and the NOAA Chesapeake Bay Office with support from the MD Department of Natural Resources, 

and commercial watermen from Maryland. Research in Virginia waters was led by representatives of the 

Virginia Institute of Marine Science (VIMS) with support from the Virginia Marine Resource 

Commission (VMRC), and commercial watermen from Virginia.

Original work conducted by Havens et al. 2008 and Slacum et al. 2009 evaluated the distributions of 

derelict pots and derelict pot bycatch in various Chesapeake Bay habitats. Later work included modeling 

the distribution of derelict pots in Maryland (Slacum et al. 2011b), and the implementation of several 

large-scale derelict pot retrieval projects in Maryland (Slacum et al. 2011b and 2013), and Virginia 

(Havens et al. 2011, Bilkovic et al. 2014). Information about derelict pot distributions, condition, and 

bycatch was collected from retrieval efforts providing additional insights into how pots become derelict, 

the lifecycle of a pot, and their effects on biota.

While Chesapeake Bay studies improved our knowledge of many characteristics of derelict pots, the 

ecological and socioeconomic effects across the Chesapeake Bay are still poorly understood. Fortunately, 

much of the derelict pot data in the Chesapeake Bay are well documented. There are many other data 
Introduction 7

sources from ongoing Bay research that includes variables likely to influence derelict pot effects, and 

there is good information on the dynamics of the blue crab fisheries. These factors provide the NOAA 

Marine Debris Program with a unique opportunity to evaluate the effects of a specific type of derelict 

fishing gear and use this case study as a pathway to develop the framework to evaluate the effects of 

derelict fishing gear in other regions of the United States.

1.2 Approach

The socioeconomic and ecological effects of derelict crab pots will vary depending on structural and 

functional components of the Chesapeake Bay ecosystem. To approach this complex question a project 

team was assembled that included representatives with expertise in derelict crab pot research from 

Maryland and Virginia, fishery economics, spatial modeling, and data integration. The Chesapeake Bay 

blue crab fishery was selected as a model because of its high applicability to other fisheries in many 

locations. Due to the high numbers of pots set in the Chesapeake Bay and the high loss rates of pots, there 

is a critical need to assess the potential effects of derelict blue crab pots on both the ecology and 

socioeconomics of the Chesapeake Bay.

The goal of this project was to conduct a regional impact assessment of derelict fishing gear in the 

Chesapeake Bay, focused on derelict blue crab pots, as a basis for a more general Derelict Fishing Gear 

Assessment Framework.

Six objectives are being employed to accomplish the study goal:

1. Identify and evaluate characteristics of the Chesapeake Bay blue crab pot fishery that contribute to the 

distribution and densities of derelict crab pots.

2. Inventory available data related to variables determined in objective one with consideration to data 

that would likely be available in other U.S. regions.

3. Identify data gaps and design surveys and experiments to provide those data.

4. Develop a spatial model framework to evaluate factors influencing the distribution and densities of 

derelict crab pots.

5. Quantify the ecological and economic effects of derelict crab pots in the Chesapeake Bay.

6. Develop a framework for assessing derelict fishing gear that can be used for similar fisheries in the 

United States and elsewhere.

A critical first step to assess the ecological and economic effects of derelict pots is to identify and 

evaluate all the factors expected to contribute to pot loss and determine the amount of influence that each 

factor contributes to the overall effects of derelict pots. A conceptual framework was initially developed 

to capture both structural and functional variables. (See Figure C-1 in Appendix C.) Specifically, an 

integrated biogeographic approach using expert opinion to determine key contributing variables was used 

to characterize spatial patterns in the densities and distribution of derelict crab pots as well as to infer 

spatial variability in the potential ecological effects within the Chesapeake Bay. A common spatial 

framework was used to integrate disparate datasets of derelict crab pot locations through the Maryland 

and Virginia portions of the Chesapeake Bay and explored the spatial inter-relationships among several 

variables hypothesized to affect the distribution and densities of derelict crab pots. 

Furthermore, we used a geographically weighted regression model to account for spatially varying 

influences of the various variables and to predict and map the densities of derelict crab pots throughout 

the Bay. Model predictions of derelict crab pots were then used to map hotspots of derelict crab pots, 

identify areas of high potential ecological impacts, and recommend spatially-explicit actions that could 

reduce derelict crab pots.
8 Bay-wide Distribution and Densities of Derelict Crab Pots

2. Bay-wide Distribution and Densities of Derelict 

Crab Pots

2.1 Chesapeake Bay Biogeographic Framework

A spatial framework was created in a geographic information system (GIS) to aid in the integration and 

interpretation of compiled data sets. Locational data on derelict crab pots and potential independent 

variables that may be used to predict derelict pot distribution and abundance within the Chesapeake Bay 

were compiled from VIMS and Versar (see Appendix C) and integrated into a 1 km by 1 km polygon 

grid (Figure 2-1). The 1 km x 1 km grid was selected as the highest spatial resolution for spatial 

modeling based on previous analyses done by Versar and VIMS. Spatially-explicit response variables 

(density of derelict crab pots) and predictor variables (e.g., fishery effort, bathymetry and other derived 

variables) were derived through geostatistical resampling of raw data.

Figure 2-1. Map Showing Spatial 

Framework used to Characterize 

Chesapeake Bay Derelict Crab 

Pot Spatial Patterns.

The spatial grid extent covers areas 

in the Chesapeake Bay where 

crabbing occurs. Grid cells are 1km 

x 1km.
Bay-wide Distribution and Densities of Derelict Crab Pots 9

2.2 Key Variables/Data Acquisition and Preparation

Guided by expert local knowledge and review of historical work on derelict crab pots in the Chesapeake 

Bay, a list of variables expected to contribute to the distribution and effects of derelict crab pots was 

compiled. Variables were integrated into an ecological and economic conceptual framework to map their 

interactions and connectivity to one another. (See Figure C-1 in Appendix C.) All variables were 

evaluated based on their relative contribution to the distributions, densities, and effects of derelict crab 

pots. Data availability for key variables was also assessed, and additional research was implemented to 

collect additional information when data gaps were identified. (See Appendices A and B for additional 

research.) A description of methods, a list of all variables and sources that were identified and evaluated 

is presented in Appendix C (Versar and VIMS supplied the derelict crab pot data used in this evaluation 

and are referred to as the data source owner in this report).

The compiled data sets were in different file formats ranging from excel spreadsheets to ESRI coverages 

that included raster grids point, line, and polygon shapefiles. Each dataset was processed in Statistical 

Analysis Systems (SAS, Version 9.4) to ensure that data and field names were in consistent and 

standardized formats. For all compiled data sets, we conducted a thorough review of their metadata to 

understand the purpose and intent for which the data were collected, the methods used, and any associated 

biases. Data were also evaluated to ensure either they met specific criteria for spatial modeling, including 

assumptions normality, stationarity of mean and variance, and statistically significant spatial 

autocorrelation or that the data could be transformed to remove non-random trends. Excel files were 

converted to ESRI point shapefiles and were visualized in ESRI ArcGIS to determine the spatial extent of 

dataset coverage and any obvious spatial patterns.

Table 2-1. Predictors of Derelict Crab Pot Distributions in the Chesapeake Bay.

Variable Source

Blue crab fishery spatial patterns Versar

Bathymetry NOAA

Recreational boating hotspots Versar, VIMS, VMRC

Vessel traffic spatial patterns Marine Cadastre

MD derelict crab pot locations documented with SSS Versar

VA derelict crab pot locations from retrievals VIMS

Several predictors of derelict crab pot distribution were identified for integration into the biogeographic 

modeling framework (Table 2-1). These predictors were integrated and used to model the spatial 

distribution and densities of derelict crab pots, and were used along with additional variables to determine 

the spatial distribution of ecological effects throughout the Chesapeake Bay. These data were integrated 

with the 1 km x 1 km polygon grid through spatial overlays. 

Below we provide detailed descriptions of the predictors along with maps showing their distributions 

throughout the Chesapeake Bay.

2.2.1 Blue crab fishery spatial patterns

Day to day commercial fishing operations can influence the amount of fishing gear that becomes derelict. 

Therefore, it is important to understand the spatial patterns of the fishery and to attain as much 

information about when, where, and how intense a fishery operates. Versar conducted several fisheries 

independent surveys across Maryland and Virginia. The surveys were stratified based on known fishing 

efforts and consisted of transects where number of crab pot floats were counted as a measure of fishing 

effort. Inverse distance weighting was used to interpolate transects to estimate fishing effort (# pots/km2) 
10 Bay-wide Distribution and Densities of Derelict Crab Pots

across the Chesapeake Bay (Figure 2-2). Areas where crabbing does not occur, such as the Maryland 

tributaries and the deep channel or “deep trough” of the Chesapeake Bay, were removed from the 

interpolation. Data used in this project included data from surveys conducted in Maryland during the 2007 

to 2011 crabbing seasons, and from Virginia during the 2010 crabbing season. (See Appendix C for 

survey metadata.)

Figure 2-2. Spatial Patterns of 

Blue Crab Fishery Effort in the 

Chesapeake Bay.
Bay-wide Distribution and Densities of Derelict Crab Pots 11

2.2.2 Bathymetry

Derelict crab pots have been documented in all depths where the commercial fishery is active, but the 

distribution and densities of derelict pots within certain depth intervals can vary with depth (Slacum et al.

2009). Bathymetry data were obtained from NOAA National Centers for Environmental Information

(Bathymetry for Chesapeake Bay was derived from two hundred ninety-seven surveys containing 

3,178,509 depth soundings collected between 1859 to 1993 (source: 

http://estuarinebathymetry.noaa.gov/bathy_htmls/M130.html). The hydrographic data were used to 

develop a rasterized (30-meter) digital elevation model for the Chesapeake Bay, from which depth were 

extracted with the 1 km x 1 km grid (Figure 2-3).

2.2.3 Recreational boat traffic activity

The intensity of recreational boating activity in the Chesapeake Bay represents a contributing factor to 

occurrence of derelict fishing gear in that area. Typically, watermen set their pots with a line attached to a 

marker buoy or 'float'. The float identifies ownership and facilitates retrieval of the pots. High intensity of 

Figure 2-3. Chesapeake Bay 

bathymetry.
12 Bay-wide Distribution and Densities of Derelict Crab Pots

recreational boat use increases the likelihood that marker buoy and pot float lines will inadvertently 

interact with boat propellers. Crab pots can then become 'derelict' after their float line is severed by vessel 

propellers, chafed through due to wave action, or tangled up on the pot itself as it is rolled by strong 

currents and waves. Without floats, watermen are unable to find their pots to retrieve them and harvest the 

contents. Areas with relatively high recreational fishing activity were mapped in Maryland and Virginia

using local expert knowledge. For the Maryland portion of the Chesapeake Bay, representatives 

participating in the fishery independent survey of commercial crabbing effort delineated areas of 

relatively high recreational boating activity. For the Virginia portion of the Bay, high intensity 

recreational boating areas were determined using local knowledge of VIMS experts, Virginia Marine 

Resources Commission officers, and watermen, in combination with the locations of artificial reefs 

(which typically are heavily visited by recreational fishers). This participatory mapping exercise provided 

local expert knowledge on the locations of heavily used recreational boating areas and filled gaps in in the 

spatial coverage of that data. For this study, areas denoted by these local experts as high boat use areas 

were used as a proxy for increased derelict crab pots and were assumed to have higher likelihood of 

derelict gear occurrence (Figure 2-4).

Figure 2-4. Chesapeake Bay 

Recreational Boating Activity.
Bay-wide Distribution and Densities of Derelict Crab Pots 13

2.2.4 Status of derelict crab pots from removal efforts

Derelict Fishing Gear Status refers to whether a crab pot was abandoned or accidentally lost. VIMS and 

Versar conducted derelict crab pot retrieval studies throughout the Chesapeake Bay and it is estimated 

that 12% to 20% of deployed pots are lost annually (Appendix A). In Virginia, as part of these studies, 

whether a pot had a buoy or line attached was noted. For this study, each pot was assigned a status of 

‘abandoned’ only if the pot had a buoy attached or ‘lost’ otherwise. The assumption is that the presence of 

a buoy suggested that watermen deliberately abandoned rather than retrieved the crab pot, whereas the 

absence of a buoy suggested that the pot was accidentally lost. The Maryland studies did not distinguish 

between ‘abandoned’ and ‘lost’. Based on these data, we mapped the spatial occurrence of abandoned and 

lost pots in Virginia and lost pots only in Maryland (Figure 2-5). In addition, while not displayed here, 

4,146 derelict pots were also removed from Virginia’s seaside eastern shore, of which 81% were 

considered abandoned (Bilkovic et al. 2014). Abandoned pots in the Virginia portion of the Chesapeake 

Bay accounted for 8,392 (~28%) of 29,840 mapped derelict pots.

 

Figure 2-5. Spatial Distribution of Crab Pots identified as Lost or Abandoned during Retrieval Projects in 

Maryland and Virginia.

(Abandoned pots are shown only for Virginia: the Maryland studies did not distinguish ‘abandoned’ vs. ‘lost’ pots.)
14 Bay-wide Distribution and Densities of Derelict Crab Pots

2.2.5 Vessel traffic data (AIS data)

The Chesapeake Bay is a major route for shipping, transportation, and cruise industries along the eastern 

seaboard. For example, Baltimore is ranked 9th for total dollar value of cargo and 13th for cargo tonnage 

for all U.S. ports (Maryland Manual, http://msa.maryland.gov/msa/mdmanual/01glance/html/port.html). 

In 2015, the total international cargo (imports and exports) moving through the Port of Baltimore was 

32.4 million tons with a total cargo of around $51 billion. The Port of Baltimore serves over 50 ocean 

carriers that average around 1,800 visits each year. 

The combination of commercial 

shipping and recreational boating 

is a constant source of vessel 

traffic along the mainstem, 

rivers, and tributaries of the 

Chesapeake Bay which could 

affect fishing activity and 

occurrence of derelict fishing 

gear in the Chesapeake Bay. 

Data on vessel traffic within the 

Chesapeake Bay were obtained 

from the Marine Cadastre 

(http://marinecadastre.gov/ais/) 

and used to map ship traffic 

patterns for calendar years 2009 

through 2014. Data on Vessel 

traffic were collected by the U.S. 

Coast Guard through an 

Automatic Identification System 

(AIS). AIS is an onboard 

navigation safety device that 

transmits and monitors the 

location and characteristics of 

large vessels in U.S. and 

international waters in real time. 

The Marine Cadastre provides 

AIS data filtered and 

summarized into one-minute 

intervals, with each record 

representing a ship’s location 

every minute. Specific AIS 

information obtained included 

vessel location, time, ship type, 

speed, length, beam, and draught. 

For this project, we calculated monthly densities of vessel traffic for each 1 km x 1 km grid cell within the 

Chesapeake Bay study region as the summation of the number of one-minute vessel records with 

instantaneous speeds greater than zero for each calendar month between January 2009 and December 

2014. Monthly densities were calculated for all ships as well as only for fishing vessels (Figure 2-6).

Figure 2-6. Vessel Density Aggregated from AIS Data.
Bay-wide Distribution and Densities of Derelict Crab Pots 15

2.3 Geographically Weighted Regression (GWR) Model

Previous work has shown that derelict crab pots vary spatially across the Chesapeake Bay and there are 

known factors that contribute to their distribution and densities. The five variables described in section 

2.2 represent a portion of those factors, but were variables for which data could be attained. The influence 

of each factor on the presence of derelict crab pots was not known, but was expected to vary by location.

A geographically weighted regression (GWR) modeling technique was chosen to estimate the distribution 

and densities of derelict crab pots in the Chesapeake Bay. The use of a GWR model has proved successful 

in estimating other marine ecological distributions (e.g. Windle et al. 2010) and a previous study of 

derelict crab pot hotspots in Maryland (Slacum et al. 2011b, 2013).

A two-step process was used to develop a predictive model of derelict crab pot distributions in the 

Chesapeake Bay. The overall method included a global regression to assess important parameters and 

then the development of a spatially explicit regression model. GWR is a local spatial statistical technique 

that expresses spatial variation relationships between variables.

To setup a GWR design, a global ordinary least squares (OLS) model was run in ArcGIS and identified 

significant variables within the variable pool for estimating known abundance of derelict pots. The 

general form of the OLS equation is as follows:

 

 

where yi is the estimated dependent variable at observation i, β0 is the intercept, βj is the parameter 

estimate for variable j, is the value of the j

th variable for i, and 

is the error term.

GWR modifies the global regression by including geographic coordinates for each prediction location. To 

do this, GWR generates a separate regression for each observation. The addition of geographic 

coordinates to each observation creates the following equation:

 

 

 β (  ) β (  ) 

 

 

 

where is the intercept estimated at each coordinate  , is the parameter estimate for variable j

at each coordinate (Fotheringham et al. 1998). This spatially explicit model then sets independent weights 

for parameter estimates that are dependent on geographic location (Brunsdon et al. 1998).

Within the GWR framework is the assumption that closely located observations have greater influence on 

neighbor’s parameter estimations. The GWR weights observations using a distance decay function that 

can be tailored in a variety of ways to best suit the dataset. Various methods in modifying the decay 

function include manipulating the bandwidth or the distance of influence of one observation to another.

Bandwidth can be set as a “fixed” value or “adaptive.” Fixed bandwidth allows one to control how 

localized parameters are estimated across the entire spatial dataset while adaptive allows the bandwidth to 

expand in areas where observations are few and contract in areas with a high density of observations.

To assess the effects of these decay function manipulations, a set of candidate models were developed and 

evaluated using Akaike information criterion adjusted for small sample sizes (AICc). AICc values were 

used to rank models based on fit and performance. Smaller AICc values within the set of candidate 

models indicate better performance. AICc values were compared using Akaike differences (Δmodel), 

which determines the relative difference in AICc value for each model from the model with the lowest 

AICc value (Burnham and Anderson 1998). The most parsimonious model was selected using criteria for 

model confidence, where a Δmodel value < 2, indicates substantial support.
16 Bay-wide Distribution and Densities of Derelict Crab Pots

For model development, a calibration dataset was used with observed densities of derelict crab pots and 

related variables at specific locations. This dataset was used to explore variable significance and 

subsequently to train the GWR model. For additional independent variable review, the GWR provides 

local parameter coefficient estimation for each grid cell. This gives the ability to map spatial distributions 

of local R2. The final output was then interpolated into a raster (power = 2, variable search radius, number 

of points = 4).

The training dataset of known and 

estimated derelict crab pot densities 

was compiled using a combination 

of survey data collected in Maryland and Virginia. The resulting 

data set consisted of 836 training 

data points. The Maryland portion 

of the data set included 286 

locations of known derelict pots 

collected during a side-scan-sonar 

survey conducted in 2007 (see 

Appendix C for metadata). The 

Virginia portion of the data 

consisted of 550 points from the 

Virginia derelict crab pot cleanup 

efforts from 2009 to 2012 (Figure 

2-7). The Virginia dataset was 

comprised of random points 

selected from the interpolation of 

Virginia pot retrieval data. The 

points were only selected in areas 

where crabbing occurs with 15% of 

the points selected from high 

densities of recovered derelict pots.

Estimates of each potential 

predictor variable were appended to 

each derelict crab pot density point 

and were analyzed with OLS model 

to indicate independent variable 

significance. The initial OLS global 

regression model indicated that 

independent fishing effort, depth, 

recreational boating traffic, and 

AIS data were significant variables 

in predicting the density of derelict 

crab pots.

For GWR development and derelict crab pot predictions, the data were first reformatted for use in the 

ArcGIS modeling toolbox by converting the 1 km grid into a point grid where the centroid of the grid cell 

was the coordinate for the grid point. To aid in model efficiency, the “deep trough” portion of the bay 

where crabbing does not occur was excluded from the analysis.

Figure 2-7. Locations of Known or Estimated Derelict Crab Pots in the 

Chesapeake Bay.

These data were used as a training data set to develop the geographically 

weighted regression model (GWR) for the Chesapeake Bay. Color scale 

indicates the density of derelict pots per km2.
Bay-wide Distribution and Densities of Derelict Crab Pots 17

The GWR model explained 34% of the variation in derelict pot density and distribution. Independent 

fishing effort, water depth, recreational boating traffic, and AIS vessel traffic data were significant 

variables in predicting the density of derelict crab pots. (Table 2-2)

Table 2-2. Geographic Weighted Regression (GWR) Results for Predicting Derelict Crab Pots in the 

Chesapeake Bay.

Parameter Minimum 25% quartile 50% quartile 75% quartile Maximum

Intercept -1.59 20.44 31.49 46.42 68.32

Blue crab fishing effort -0.06 0.03 0.06 0.09 0.33

Depth -6.97 -4.40 -3.20 -1.58 4.23

Recreational boating -0.12 11.39 17.34 27.22 67.02

AIS -0.05 0.00 0.02 0.06 0.25

Condition Number 3.20 3.93 4.82 5.52 7.56

Adjusted R2

0.34

AICc 8,704.60

This value attests to the difficulty in estimating derelict pot occurrence over a large spatial region that 

encompasses dynamic systems. The adjusted R2value here is similar to the previous study in Maryland 

(Slacum et al. 2013) which found the hotspots predicted by a similar model to be very consistent to 

estimates derived from recovery efforts. Multicollinearity was not a serious issue within the model as all 

condition number values were substantially less than 30. 

To examine how well the GWR model predicted the local derelict pot density from the training data, a 

map of the locally weighted R2between the observed and the estimated values was created (Figure 2-8). 

Local R2 was not homogeneously distributed across the Chesapeake Bay, with weakest fits occurring in 

the Maryland portion of Tangier Sound, the mainstem of the bay outside of the Choptank River, and 

eastern Virginia Pocomoke Sound. The poorer fit in these regions may imply the need for additional 

covariates to explain derelict pot distribution.
18 Bay-wide Distribution and Densities of Derelict Crab Pots

In addition, parameter coefficients were mapped for each independent variable where the significance was 

greater than 90% using the calculated pseudo t value (Figure 2-9). All parameters showed heterogeneous 

patterns of pseudo t values across the Chesapeake Bay with depth having the lowest significance of the

independent parameters.

Figure 2-8. Spatial Mapping of 

Locally Weighted Coefficient of 

Determination (R2) between 

GWR Observed and Fitted 

Values.
Bay-wide Distribution and Densities of Derelict Crab Pots 19

Figure 2-9. Spatial mapping of locally estimated coefficients.

Locally estimated coefficients include [A] independently measured fishing effort (Effort), [B] depth, 

[C] recreational boating traffic, and [D] automatic identification system vessel tracking data (AIS). 

Color shade denotes significance, with lighter shades for (p< 0.1) and darker shades for (p< 0.05).
20 Bay-wide Distribution and Densities of Derelict Crab Pots

Examining positive relationships between variables that can be manipulated (i.e. fishing effort and vessel 

traffic) indicated that higher fishing effort and greater recreational and commercial traffic occurred in 

most areas of higher derelict pot density (Figure 2-10) except in the mid-section of the Maryland portion 

of the Chesapeake Bay near the Choptank River. 

Figure 2-10. Positive impacts of Effort, Recreational Boating, and Commercial Vessel Traffic on Derelict Pot 

Abundance.

(A) Effort and Recreational Boating impact; (B) Effort and AIS impact. (dot = 90 derelict pots/km2)

We used contingency analysis to test the hypothesis whether or not there was spatial overlap between 

predicted presence of derelict crab pots and recreational boating activity. Results indicated that only 11% 

(770) of grid cells had both predicted derelict crab pots and recreational boating activity whereas 80% 

(5,743 out of 7,216) of grid cells predicted to contain derelict crab pots did not overlap with recreational 

boating activity. This result indicates very low agreement and overlap occurred between derelict crab pots 

and recreational boating (Kappa = -0.01148782 SE= 0.003257692; p<0.063). Conversely, the absence of 

spatial overlap in the co-occurrence of derelict crab pots and recreational boating was significantly high 

(Chi-Square=5392.8, p<0.0001). Although this analysis suggested a lack of significant overlap between 

recreational boating and predicted presence of derelict crab pots, the result was possibly biased by the 

relatively small coverage of the recreational boating activity data for the Chesapeake Bay region. For 

example we did not have data on recreational boating activity for many grid cells where derelict pots were 

predicted to be present. Spatially-specific baywide data on recreational boating are needed to refine 

predictions of derelict pot occurrence.
Bay-wide Distribution and Densities of Derelict Crab Pots 21

2.4 Quantitative Findings from the GWR Model

Overall, the total number of derelict pots in the Chesapeake Bay was estimated at 145,233 derelict pots 

with 58,185 derelict pots estimated in Maryland and 87,048 in Virginia. Figure 2-11 shows the spatial 

distribution of predicted derelict pots across the Bay. 

Figure 2-11. Predicted 

derelict crab pot densities 

and spatial distribution.

In addition to Bay-wide estimates, derelict pot abundance in specific regions can also be extracted from 

the model output: Table 2-3 shows example numbers for several major tributaries, sounds, and mouths of 

tributaries.
22 Bay-wide Distribution and Densities of Derelict Crab Pots

Table 2-3. Estimated Amount of Derelict Pots in Selected Regions of the Chesapeake Bay with the 

Extent of the Associated Areas Where Crabbing Occurs.

Chesapeake Bay Region Approximate

Area (km2)

Estimated

Derelict Pots

Choptank Mouth 61.8 3,242

Little Choptank Mouth 60.3 2,391

Patuxent River Mouth 26.8 1,206

Eastern Bay 63.3 3,459

South River Mouth 15.8 1,438

Severn River Mouth 15.0 1,587

Magothy River Mouth 13.8 1,552

Chester River Mouth 45.8 3,059

Patapsco River Mouth 26.5 3,043

Gunpowder River Mouth 22.5 1,987

Rappahannock River 243.0 2,658

Mobjack Bay and Tribs 137.3 4,221

James River (with Elizabeth River) 414.5 7,882

Tangier Sound (MD) 192.0 7,359

Tangier Sound (VA) 99.0 3,573

Pocomoke Sound (VA) 281.0 10,209

2.5 Model Sensitivity

The goal of this predictive modeling analysis was to use known or estimated counts of derived from field 

surveys to predict the spatial abundance and distribution of derelict crab pots throughout the Chesapeake 

Bay. Through the use of co-variable datasets with extensive spatial coverage, our GWR model 

successfully used 856 derelict crab locations to predict the presence, absence, and mean densities and 

standard errors of derelict crab pots for 7,216 1 km grid cells within the Chesapeake Bay with global 

mean of 35.4±0.26 crab pots per grid cell. Several model performance criteria including Akaike 

Information Criterion (AIC), adjusted R2, and parameter Condition number indicated that the GWR model 

performed adequately, although it only explained 34% of the overall variance in the estimates of the 

derelict crab pot density. However, locally adjusted R2 which measures how well the model fit the 

available data ranged from 0.03 to as high as 0.77 for some locations. This large range in density estimate 

of derelict crab pots largely reflects spatial variability in the input variables. Figure 2-12 shows a 

bivariate plot of predicted (from GWR) vs. observed crab pots from field surveys, with Confidence 

Interval ellipses. While there is an observable positive correlation between observed and predicted crab 

pots, this plot suggest that above a certain threshold (e.g., fishery effort of 400 crab pots per grid cell), 

predicted estimates of crab pots could vary widely. Nevertheless, the GWR model seems fairly robust 

based on the performance criteria reviewed here. 
Bay-wide Distribution and Densities of Derelict Crab Pots 23

Figure 2-12. Bivariate scatterplot showing the strength of correlation and confidence interval 

ellipses between fishery effort and GWR predicted pot densities for the Chesapeake Bay.

2.6 Uncertainties and unknowns

Input data used for the GWR model and for quantifying potential impacts to benthic habitats were 

obtained from a variety of sources, were of different types (continuous and categorical), and were 

collected through various methods, technologies, and at a variety of spatial scales. Our spatial framework 

provided a useful approach for data integration, characterizing broad-scale spatial patterns in the 

distribution of derelict crab pots within the Chesapeake Bay, and identifying bay-wide interactions with 

sensitive habitats. However, it is unclear, whether these spatial patterns will hold for smaller locales. For 

example, because we used a grid-based approach for spatial analyses, point locations and their attributes 

were aggregated to 1 km2 which could have overestimated coverages and spatial overlap between derelict 

crab pots and sensitive habitats. Conversely, most of the existing data on fishing effort and derelict crab 

pot loss are based primarily on commercial fishing, however recreational crabbing can also contribute to 

crab pot loss. As such our GWR predictions could underestimate abundance of blue crab pots within the 

Chesapeake Bay.
24 Ecological and Economic Effects Assessment

3. Ecological and Economic Effects Assessment

3.1 Ecological Effects

3.1.1 Ecological modeling framework and key variables

The effects of Chesapeake Bay derelict crab pots on blue crab, bycatch, sensitive habitats, and the fishery 

is dependent upon complex spatial and temporal interactions among these variables. Using GWR to 

predict the spatial patterns of Chesapeake Bay derelict crab pots was a key first step toward quantifying 

their ecological and economic effects. The distribution map not only provided the base for quantifying 

effects, but also provided useful guidance for exploratory analyses of several co-variables to evaluate 

their relevance. For example, direct effects of derelict crab pots could not be assumed if the modeled 

spatial distribution did not overlap with a particular species or habitat.

Two major ecological effects of derelict crab pots were examined: (i) capture and mortality of blue crab 

and prevalent bycatch fish species; and (ii) interaction with sensitive habitats. Ecological effects of 

derelict pots on blue crab and bycatch were quantified by applying observed blue crab and bycatch 

capture and mortality rates to predicted derelict pot density and distribution outputs provided by the GWR 

model (Section 2.3). To determine the potential adverse effect of derelict crab pots on Bay habitats, the 

spatial overlap of derelict pots with oyster reefs and submerged aquatic vegetation was quantified.

Other variables such as temperature, salinity, and dissolved oxygen vary spatially and are important 

environmental determinants of blue crab abundance and population demography, and indirectly affect the 

spatial distribution of fishing effort and derelict pot locations. The EPA Chesapeake Bay Program 

monitors water quality parameters throughout the Chesapeake Bay and its surrounding watershed. 

However, water quality variables were not included in this study because of large differences in spatial 

resolution and a lack of spatial overlap between water quality and derelict pot data sets within the Bay.

3.1.2 Bycatch Analysis

3.1.2.1 Estimating bycatch and mortality rates

Estimates of bycatch due to derelict crab pots were derived from field experiments conducted in 

Maryland and Virginia. With the Chesapeake Bay encompassing a wide range of salinity gradients, it was 

important to simulate derelict crab pots at field sites in both the northern low salinity and southern high 

salinity portions of the bay. The Maryland study was 14-month simulated study conducted by Versar and 

the NOAA Chesapeake Bay office between 2006 and 2008 (for additional details refer to Slacum et al.

2009). This Maryland study was used as a guide in developing the Virginia field experiments conducted 

during the 2015 crabbing season (for additional details refer to Appendix B).

In reviewing species that were commonly observed as bycatch in derelict crab pots, it was decided to 

focus on the impacts to blue crab, white perch (Morone americana), and Atlantic croaker (Micropogonias 

undulates). These species are common bycatch in both the Maryland and Virginia experimental derelict 

crab pot studies and are important commercial fisheries to the Chesapeake Bay region making their 

inclusion critical for a holistic bay wide assessment.

Prior to applying these estimated per pot rates to the estimated number of pots from the GWR model, 

several comparisons were made to review data compatibility. After comparing these baselines between 

the two studies, it was decided to apply the estimations derived from the field work to the Chesapeake 

Bay assessment for each respective state.
Ecological and Economic Effects Assessment 25

In addition to the catch and mortality rates, Maryland Department of Natural Resources (MDDNR) and 

Virginia Marine Resources Commission (VMRC) harvest data was used to guide the spatial extent of fish 

species distributions. By using these data as a spatial reference, we can then avoid predicting bycatch 

where these species do not frequently occur in the Chesapeake Bay. 

3.1.2.2 Bycatch findings: blue crab

Annual blue crab catch and mortality rates from the Maryland and Virginia experimental derelict pot 

studies (Table 3-1) were applied to the estimated numbers of derelict pots from the GWR model to derive 

bay wide total of over 6 million crabs entrapped and over 3.3 million crabs killed annually which were 

mapped to review crab bycatch distribution (Figure 3-1). This results in an annual mortality of 

approximately 4.5% of the 2014 harvest (which was 35 million lbs @ 2.1 crabs/lb = 73 million crabs).

Table 3-1. Annual Measured Rates for All Blue Crabs Captured and Killed in 

Pots during the Simulation Studies

Crabs per pot per year Mean Standard Error

Maryland Catch 21 1.32

Mortality 20 3.5

Virginia Catch 65 11.5

Mortality 25 4.4

Chesapeake Bay Catch 43

Mortality 23

 

Figure 3-1. Estimated Annual Blue Crab Catch (left) and Blue Crab Mortality (right) from derelict crab pots.

Inferred from catch and mortality rates (43 & 23 crabs/pot/year) seen in simulation studies (Table 3-1).
26 Ecological and Economic Effects Assessment

3.1.2.3 Bycatch findings: finfish

In addition to blue crab catch estimation, annual white perch and Atlantic croaker catch per pot were

estimated from derelict pot experimental studies (Table 3-2, Chambers et al. unpublished data, Havens et 

al. 2008, Slacum et al. 2009). From these data and modeled numbers of derelict pots, it is estimated that 

derelict pots catch over 3.5 million white perch and nearly 3.6 million Atlantic croaker each year. Figure 

3-2 depicts the predicted spatial distribution of white perch and Atlantic croaker bycatch across the Bay.

Table 3-2. Annual Capture Rates for White Perch and Atlantic Croaker 

in Simulated Derelict Crab Pots.

State Species

Fish per Pot per Year Total fish 

Mean Standard Error Pots per year

Maryland

White Perch 22.4 2.98

58,185

1,303,344

Atlantic Croaker 0.89 0.45 51,785

Virginia White Perch 25.6 3.65 87,048 2,228,429

Atlantic Croaker 40.7 11.7 3,542,854

Chesapeake White Perch 24.3 145,233 3,531,773

Atlantic Croaker 24.8 3,594,638

Figure 3-2. Estimated Annual Bycatch of White Perch (left) and Atlantic Croaker (right) from derelict crab pots.

Inferred from capture rates for Maryland and Virginia seen in simulation studies (Table 3-2).
Ecological and Economic Effects Assessment 27

3.1.2.4 Bycatch Sensitivity Analysis; Uncertainties and Unknowns

To estimate annual bycatch for derelict pots, experiments that simulate derelict pot bycatch capture and 

mortality over multiple seasons and in different regions are essential. Slight differences in the 

experimental design of derelict pot simulation studies can influence bycatch estimates. Ideally, 

individuals captured would be marked and tracked over time without disturbing the pot, in an effort to 

most closely simulate a derelict pot. These pots will be more likely to attract additional bycatch by either 

acting as bait or attracting female blue crabs for mating and could help extend life expectancy within the 

pot as captured and killed animals may be a food source. However, this requires rigorous and time 

intensive field work, including divers, which may be difficult and expensive to conduct in the field for 

large sample sizes. Valuable information can be obtained from studies included in this assessment that 

periodically pull pots and do not remove animals or do not track specific individuals over time, and 

instead release animals with each retrieval, with an understanding that estimates derived from these 

approaches may be conservative.

Although there is incidental bycatch data from the pot retrieval programs, we were unable to extract fish 

mortality data with any confidence because data collection occurred in the winter and watermen were 

inconsistent with reporting of mortality. Moreover, annual catch and mortality estimates for derelict pots 

cannot be readily derived from incidental bycatch because of potential seasonal and spatial variability. In 

addition to direct mortality, delayed mortality resulting from derelict pots (injury, stress, infection, 

fatigue) is considered a significant issue and could result in increased mortality rates over time (Guillory 

1993, Guillory 2001, Uhlmann & Broadhurst 2015). Mortality estimates presented in this report do not 

include any possible delayed mortality; therefore, these values may be underestimating total mortality.

3.1.3 Habitat impact analysis

3.1.3.1 Estimating interactions with sensitive benthic habitats

Research assessing the ecological impacts of marine debris suggest that derelict pots can damage the 

seafloor as well as sensitive shoreline and benthic habitats (Sheridan et al. 2005; Uhrin et al. 2005; Uhrin 

and Schellinger, 2011; Clark et al. 2012; Arthur et al. 2014). For a more comprehensive review of 

potential marine debris impacts on coastal and benthic habitats please refer to a recent report from the 

NOAA Marine Debris Program (2016; https://marinedebris.noaa.gov/reports/marine-debris-impactscoastal-and-benthic-habitats).

Derelict crab pots can have physical damaging impacts on sensitive benthic habitats. The Chesapeake Bay

comprises a variety of benthic habitats; submerged aquatic vegetation (SAV), marshes, turtle nesting 

beaches, and oyster reefs are considered important and sensitive habitats. Based on available data, the 

spatial coverages of these habitats seem relatively small (SAV~4%, Oyster reefs ~ 7% of mapped area), 

but they are actively protected and restored by federal state, and local agencies, along with industry, 

academic institutions, and nonprofit groups. 

Given their widespread occurrence within the Chesapeake Bay tidal waters, it is possible that derelict crab 

pots can have interactions with sensitive habitats, and that their removal can aid in recovery and 

conservation of those habitats. June and Antonelis (2009) and Uhrin et al. (2005) respectively reported a 

30% increase in (eelgrass) recovery in Puget Sound and full recovery of Spartina alterniflora (smooth 

cordgrass) in North Carolina tidal marsh after removal of crab pots. Benthic habitat data compiled by the 

NOAA Chesapeake Bay Office Benthic Habitat Integration Program indicate that SAV occupies ~512 

km2and natural oyster reefs cover ~907 km2of the Chesapeake Bay. A typical crab pot has a footprint of 

0.36 m2; so assuming a summer deployment of 350,000 crab pots and an estimated 12-20% loss rate, lost 

crab pots could potentially physically disturb between 0.015 km2and 0.025 km2of the Chesapeake Bay 
28 Ecological and Economic Effects Assessment

seafloor annually. However, it is likely that the disturbance area is greater than this because of derelict pot 

movement across the seafloor.

For this study we mapped the locations of SAV and oyster reefs throughout the Chesapeake Bay for 

comparison with observed and predicted distributions derelict crab pots. Shapefiles showing the spatial 

coverage of SAV for the Chesapeake Bay region were obtained from VIMS (http://web.vims.edu/bi 

/sav/gis_data.html). VIMS mapped the coverage and density of SAV based on aerial photography 

collected at a scale of 1:24,000 for various regions of the Bay. For this analysis, composited annual SAV 

surveys covering the years 2003-2012 were used to be representative of potential SAV coverage in recent 

years. Natural oyster reef distribution was represented using the “Chesapeake_Bay_habitat” shapefile 

developed by the Maryland Department of Natural Resources Fisheries Division (Greenhawk 2005). This 

shapefile combines historic oyster reef surveys from Maryland and Virginia.

3.1.3.2 Habitat findings: submerged aquatic vegetation

To test the potential for spatial overlap between derelict crab pots and SAV occurrence within the 

Chesapeake Bay, derelict pots predictions from the GWR model were spatially intersected with the SAV 

map. Polygon grid cells with predicted derelict crab pot counts > 0 were recoded as 1 (indicating

presence), whereas grid cells with predicted derelict pots counts = 0 were considered lacking derelict crab 

pots. Similar coding was done for the SAV map. This yielded a dataset with 7,216 grid cells each 

attributed with either presence or absence of predicted derelict crab pots and SAV (Table 3-3). A twoway contingency analysis was used to measure the degree of agreement (i.e. spatial overlap) between the 

occurrence of derelict crab pots predicted from the GWR model and SAV. Results indicated that only 

15% (1, 39) of grid cells had both predicted derelict crab pots and SAV coded ‘present’ whereas 76% 

(5,460 out of 7,216) of grid cells predicted to contain derelict crab pots were mapped as SAV absent 

(Table 3-3). Of the 1,053 grid cells with spatial overlap between derelict pots and SAV, 490 were in 

Maryland and 563 were in Virginia (Figure 3-3). This result indicates very low agreement and overlap 

occurred between derelict crab pots and SAV (Kappa = 0.00506 ± 0.0031; p<0.063). Conversely, the 

absence of spatial overlap (i.e. disagreement) in the co-occurrence of derelict crab pots and SAV was 

significantly high (Chi-Square=5,172, p<0.001). Given that derelict pot presence is highly correlated with 

fishing effort, these results suggest that blue crab operators generally may have avoided crabbing in SAV 

habitats. An important caveat however, is that National Environmental Policy Act requirements restricted 

derelict pot removal activity in sensitive habitats such as SAV and that the model for predicted derelict

crab pot occurrence was based, in part, on data from retrieval programs that avoided pot removal from 

these habitats. To what degree these data negatively biased the amount of spatial overlap between derelict 

crab pots and SAV habitats is unknown and may require further investigation.

Table 3-3. Presence-absence contingency table showing counts of 1 km x 1 km grid 

cells containing submerged aquatic vegetation (SAV) and predicted derelict pots

Predicted Derelict Pots SAV Count Expected Percent

Present Present 1,053 1,039 15

Present Absent 5,460 5,474 76

Absent Present 98 112 1

Absent Absent 605 591 8

Total 7216 7216 100
Ecological and Economic Effects Assessment 29

Figure 3-3. Potential spatial 

overlap between derelict crab 

pots and SAV habitats within the 

Chesapeake Bay.

3.1.3.3 Habitat findings: oyster reefs

The degree of spatial overlap between the occurrence of derelict crab pots and locations of oyster reefs 

was similarly tested with a two-way contingency analysis. Results showed that there was very little 

spatial overlap in the occurrence of derelict crab pots and oyster reefs within the Chesapeake Bay (Kappa 

= -0.0018 ± 0.0043; p<0.037). Only about 21 % (1,486 out of 7,216) of grid cells had both predicted 

derelict crab pots and oyster reefs whereas 70% (5,027 out of 7,216) of grid cells had predicted derelict 

crab pots but were not mapped as oyster reefs (Table 3-4). The areas of spatial overlap were well 

distributed throughout the Chesapeake Bay, but lower for Maryland (568 grid cells) than for Virginia 

which has 918 grid cells were derelict pots and oyster reefs overlap (Figure 3-4). Conversely, the absence 

of spatial overlap (i.e. disagreement) in the co-occurrence of derelict crab pots and oyster reefs was 

significantly high (Chi-Square=4479, p<0.001). Given that derelict pot presence is highly correlated with 

fishing effort, the absence of high spatial overlap between derelict pots and oyster reefs suggest that blue 

crab operators may be targeting non-oyster reef habitats.
30 Ecological and Economic Effects Assessment

Table 3-4. Presence-absence Contingency Table Showing Counts of 1 km x 1 km Grid Cells with 

Oyster Reefs and Predicted Derelict Pots

Predicted Derelict Pots Oyster Reef Count Expected Percent of Total

Present Present 1,486 1,515 21

Present Absent 5,027 4,999 70

Absent Present 192 164 3

Absent Absent 511 540 7

Total 7,216 7,216 100

Figure 3-4. Potential spatial 

overlap between derelict crab pots 

and mapped oyster reefs within 

the Chesapeake Bay.
Ecological and Economic Effects Assessment 31

3.2 Economic Effects

There can be both direct and unexpected, indirect economic costs from derelict fishing gear, such as crab 

pots. Direct mortality of target and bycatch species is considered an ecological loss, though economic 

costs might be imposed if these animals would have contributed to commercial harvests or recreational 

fisheries, or hold significant non-use value. Derelict gear may also decrease harvests and recreational 

catch by attracting target and bycatch species, reducing the efficiency of actively fished gear and 

imposing a cost entirely independent of any economic losses associated with increased mortality. Other 

economic costs imposed by derelict fishing gear include damage to sensitive habitats, hazards to 

navigation, and replacement gear costs (Figure 3-5). 

Harvest Loss from derelict crab pots – Though mortality of target and bycatch species may be significant 

(Slacum et al. 2009, Bilkovic et al. 2014, Section 2 of this report), due to the nature of the target species 

fishery, lost harvests arising from competition between active and derelict gear were also thought to be 

substantial. These economic costs—commercial harvests of the target species lost as a result of inefficient 

and underproductive gear—can be determined by assessing the effects of derelict pot removals on 

harvests. This modeling approach requires temporally and spatially resolved data on 1) retrieved derelict 

pots, 2) effort, 3) harvest, and 4) stock abundance. Annual price data are required to infer changes in 

revenues from predicted harvest changes. The inclusion of stock abundance is necessary to account for 

variations in natural factors or management actions that may contribute to shifts in stock recruitment 

and/or survival. Evaluating changes in harvest while controlling for abundance of the target species 

removes any harvest increases resulting from reduced mortality due to fewer derelict pots. 

Figure 3-5. Potential Economic Costs of Derelict Fishing Gear. 

Decreased harvests were modeled for the Chesapeake Bay using spatially resolved data on retrieved derelict pots, 

effort, harvest, and stock abundance.
32 Ecological and Economic Effects Assessment

3.2.1 Quantitative findings

Baywide economic benefits to subsequent blue crab harvest resulting from derelict pot removals were 

estimated using temporally and spatially resolved data on 1) retrieved derelict pots in Maryland (2010 and 

2012) and Virginia (2008-2014), 2) effort (VMRC, MDDNR), 3) harvest (VMRC, MDDNR), and 4) 

stock abundance (Chesapeake Bay Stock Assessment Committee 2014; not spatially resolved). A 

spatially explicit harvest model was used to predict commercial blue crab harvests in the Chesapeake Bay 

under two scenarios: actual derelict pot removals and a counterfactual of zero derelict pot removals (i.e., 

what would have been harvested had no derelict pots been removed during 2008-2014 in Virginia and 

2010 and 2012 in Maryland). The difference in these predictions provided a robust assessment of the 

removal programs’ effect on harvests (Appendix G. Scheld et al. 2016).

Baywide – Model results indicate that the 43,968 removals in both VA (34,408 removals, 2008-2014) and 

MD (9,560 removals, 2010 and 2012) increased harvests by 38.17 million lbs (SE = 6.31), or a 23.8% 

increase above that which might have resulted had no removals occurred (Table 3-5, model RE VA-MD;

Figure 3-6). These gains are estimated to be valued at $33.5 million in revenues (2014 dollars).

Table 3-5. Results from Different Models used to Evaluate the Economic Effects of Derelict Gear Removals.

Model: RE VA-MD FE VA-MD RE VA FE VA RE MD FE MD

VA-MD Δ Harvest 

(millions of lbs)

38.17

(6.31)

27.45

(5.25) — — — —

VA Δ Harvest 

(millions of lbs)

30.09

(3.78)

20.83

(2.81)

29.71

(3.74)

19.88

(2.70) — —

MD Δ Harvest 

(millions of lbs)

8.08

(4.41)

6.62

(4.09) — —

2.83

(7.94)

-0.06

(7.68)

Δ Harvest / Pot Removed 

(VA-MD) (lbs)

868

(144)

624

(119) — — — —

Δ Harvest / Pot Removed 

(VA, 2009-2014) (lbs)

875

(110)

605

(82)

864

(109)

578

(78) — —

Δ Harvest / Pot Removed 

(VA, 2013 & 2014) (lbs)

2,270

(461)

1,032

(366)

2,053

(450)

854

(354) — —

Δ Harvest / Pot Removed 

(MD, 2010 & 2012) (lbs)

845

(462)

693

(427) — —

296

(830)

-7

(803)

Δ Harvest / Pot Fished

(VA-MD) (lbs)

0.43

(0.07)

0.31

(0.06) — — — —

Δ Harvest / Pot Fished

(VA, 2009-2014) (lbs)

0.48

(0.06)

0.33

(0.04)

0.48

(0.06)

0.32

(0.04) — —

Δ Harvest / Pot Fished

(MD, 2010 & 2012) (lbs)

0.31

(0.17)

0.25

(0.16) — —

0.11

(0.30)

-0.002

(0.29)

Notes on Table 3-5:

 All models used a translog Schaefer harvest specification allowing for area specific catchabilities.

 Random effects (RE) and fixed effects (FE) models were estimated using Virginia (VA) and Maryland (MD) data 

alone as well as jointly (VA-MD).

 VA-MD models allowed harvest elasticity parameters to differ by state due to differences in commercial fishery 

regulations, data collection, and removal programs. FE models were fit after removing group (area) means from 

all variables.

 Standard errors are presented in parentheses beneath average effects; they were constructed using a semiparametric (residual) bootstrap of parameters in the harvest model. 

 Estimates not significant at a 95% level of confidence are in italics.

Harvest improvements came from increases in the efficiency of actively fished gear, which averaged 0.43 

lbs/pot (Table 3-5, model RE VA-MD). This amounts to nearly an additional crab every time a pot was 
Ecological and Economic Effects Assessment 33

pulled in a year following removals (1 blue crab ≈ .475 lbs). Harvest increases per pot removed were 

also substantial, averaging 868 lbs. Benefits from removals were spatially heterogeneous and tended to be 

concentrated in high effort areas near the main-stem of the bay (Figure 3-7). 

Figure 3-6. 95% Confidence Region of 

Chesapeake Bay Blue Crab Harvests with 

(Blue) and without (Red) Derelict Gear 

Removals.

Figure 3-7. Increase in Blue Crab Harvest 

Resulting from Removal of Derelict Blue 

Crab Pots.

Increased harvests were modeled for 

Chesapeake Bay using spatially resolved data 

on retrieved derelict pots, effort, harvest, and 

stock abundance. The hatched area in the 

mainstem of the Bay represents the no-take 

blue crab sanctuary.

The effect of removals on commercial harvests was more difficult to assess in Maryland due to the 

limited spatial resolution of the data (9 management areas as opposed to 54 in Virginia) and fewer 

removal observations. A significant implication of these findings is that derelict gear recovery programs 

can yield substantial net economic benefits.
34 Ecological and Economic Effects Assessment

Harvests per pot were observed to be greater in areas with removals both during the removals program 

and when compared to harvests prior to removals (Table 3.6, Table 3.7).

Table 3.6. Average harvest/pot during years of 

removals in areas with and without removals

No Removals Removals 

VA 2009 – 2014 1.45 (0.50) 2.17 (0.62) 

MD 2010 & 2012 1.88 (0.60) 2.18 (0.61) 

Notes on Table 3-6:

 Standard deviations are shown in parentheses. 

 Italics indicate average harvest/pot not statistically different at a 95% level of confidence between areas with and 

without removals.

 Sample sizes varied depending on the size and number of management areas in each state, years of removals, and 

the number of areas which experienced removals in a given year (VA No Removals, n=110; VA Removals, 

n=190; MD No Removals, n=8; MD Removals, n=10). 

Table 3.7. Average harvest/pot before and after the first year of removals in 

areas with and without removals.

Before (2008) After (VA – 2009; MD – 2010)

Removals (VA, n=38) 1.84 (0.48) 2.06 (0.68) 

No Removals (VA, n=12) 1.56 (0.70) 1.50 (0.52) 

Removals (MD, n=5) 1.95 (0.66) 2.58 (0.51) 

No Removals (MD, n=3) 2.15 (0.47) 2.22 (0.46) 

Notes on Table 3-7:

 Standard deviations are shown in parentheses. 

 Italics indicate average harvest/pot not statistically different at a 95% level of confidence before and after the first 

year of removals.

Virginia model results indicate that the removal program increased harvests by 30.09 million lbs (SE 

=3.78), or 27.2%. These gains are valued at $22.6 million in dockside revenues (2014 dollars). Efficiency 

gains for active gear averaged 0.48 lbs/pot; average harvest increases per pot removed were estimated at 

875 lbs (Table 3-5, model RE VA-MD). Targeted removals from derelict gear hotspots in 2013 and 2014 

were found to be highly effective. During this time, harvest increases per pot removed grew considerably, 

averaging 2,270 lbs. All estimated removal effects in Virginia are significant at a 99% confidence level.

Maryland model results indicate that the removal program increased harvests by 8.08 million lbs (SE = 

4.41), or 16.3%. Maryland harvest gains are valued at $10.9 million (2014 dollars; note that blue crab 

prices are frequently 30-50% higher in Maryland). Active gear efficiency is estimated to have increased 

by 0.31 lbs/pot; average harvest increases per pot removed were estimated at 845 lbs (Table 3-5, model 

RE VA-MD). Removal effects in Maryland were not statistically significant at a 95% confidence level.

3.2.2 Sensitivity analysis

Semi-parametric (residual) bootstraps were used in quantitative economic modeling to incorporate 

uncertainty in parameter estimates and model results. During the bootstrap procedure residuals were 

resampled and used to construct synthetic observations before re-estimating the statistical harvest model.
Ecological and Economic Effects Assessment 35

All standard errors presented, as well as those shown in Table 3-5, were calculated based on 10,000 

bootstrap draws of the parameter vector.

Data quality concerns regarding effort reporting accuracy were handled through sensitivity analyses. A 

resampling procedure was used to evaluate the impact of variable effort misreporting. Three scenarios 

were considered: 1) half of all observations underreport actual effort by 50%; 2) three-quarters of all 

observations underreport actual effort by 50%; and 3) one-quarter of all observations underreport effort 

by 50% while one-quarter of all observations over-report effort by 50% (note that, for Maryland, the 

scenarios considered represented effort misreporting in addition to what had already been assumed and 

corrected for). After adjusting effort (number of pots) for a random sample of observations, which 

corresponded, to the specific misreporting scenario being evaluated, models and removal effects were reestimated. This process was repeated 10,000 times for each misreporting scenario. (For a detailed 

description as applied to Virginia data, see Scheld et al. 2016, and Supplementary Information at 

http://www.nature.com/article-assets/npg/srep/2016/160121/srep19671/extref/srep19671-s1.pdf.)

The effects of variable effort misreporting were found to be fairly minimal. Estimated average harvest 

increases ranged from 31.5 (scenario 3) to 35.7 (scenario 2) million lbs, or roughly 82-93% of the harvest 

increases estimated under the null model. None of the three effort misreporting scenarios tested yielded 

results that were statistically different at a 95% confidence level from those estimated by the null model. 

This sensitivity analysis indicates that even in instances of substantial, and variable, misreporting of 

effort, derelict gear removal is still found to have large and positive commercial harvest effects. General 

results should therefore be viewed as considerably robust to misreporting of effort. 

3.2.3 Uncertainties and unknowns

Commercial fisheries in each state operate differently and are managed by separate agencies (though 

cooperation in data collection and stock assessment does exist through the annual winter dredge survey 

and the Chesapeake Bay Stock Assessment Committee). As such, fishery data are collected under 

different processes and protocols, varying in terms of their spatial resolution, and perhaps, their degree of 

accuracy. Parameters were included in the statistical harvest model to capture state-by-state differences in 

underlying relationships, however large disparities in spatial resolutions among the two states and 

potential differences in data quality present challenges to a comprehensive and integrative assessment.

The modeling approach aimed to isolate effects of derelict gear removals by controlling for other factors 

influencing harvests. The final model controlled for both observed variables (effort, stock) and 

unobserved spatiotemporal effects. Still, the potential for confounding bias can never be entirely ruled 

out. If unobserved deterministic factors were correlated with removals (spatially and in magnitude) then 

the model may yield inconsistent estimates. Fortunately, there is little reason to expect this is the case.
36 Management Scenarios – Mitigation Alternatives

4. Management Scenarios – Mitigation 

Alternatives

4.1 Introduction

Policies and management actions to reduce the loss of derelict fishing gear and its effect once lost are 

vital for any successful strategy to address the issue of derelict blue crab pots. Several different 

management and policy actions have been suggested for reducing the amount and impact of derelict pots. 

The loss of crab pots in the Chesapeake Bay, estimated between 12 – 20%, can be categorized as 

accidental or intentional (Arthur et al. 2014) while reduction of derelict pot effects can be divided into pot

removal, pot modifications, and policy changes (Slacum et al. 2009, Havens et al. 2011).

4.2 Accidental and Intentional Loss

Accidental loss can result from improper equipment, or equipment failure, such as breakage at the 

line/buoy or line/pot attachment point, insufficient weighting of pot, insufficient line length, entanglement 

of pot trotlines, or line to dock breakage in the recreational fishery. Storm events and abnormal water 

currents and tides also contribute to pot loss. In 1999, over 100,000 crab pots were reported lost due to

Hurricanes Dennis and Floyd (NCDMF 2013). Storms or strong currents can tumble pots wrapping the 

line around the pot and pulling the buoy underwater, move pots into deeper water where the buoy line no 

longer reaches the surface, or cause pot ‘pile-up’ and line entanglement. In some cases, pots are stored in 

advance of storms or in the closed season on estuarine islands or marshes. Such storage of pots on 

marshes can be problematic, affecting marsh vegetation, trapping terrestrial animals, and can become 

particularly troublesome when storms wash pots into adjacent waters (Lee 2009, Uhrin and Schellinger 

2011, Voss et al. 2015).

Resource user conflicts between commercial crabbers, recreational users, and commercial shipping 

activities can result in pot loss due to propeller or keel entanglement (Breen et al. 1990). Reducing spatial 

conflicts between crab pots in the water and other uses may minimize pot loss. In the Chesapeake Bay a 

relationship between high shipping and recreational boat traffic and pot loss exists – though the modeled 

overlap is slightly more than 10% which may be an artifact of limited spatially explicit information on 

recreational boating activity. Restricting commercial vessel traffic to channels and keeping pots out of 

channels can reduce pot loss. Education of recreational boaters on the consequences of lost pots, how to 

avoid pots, and what to do should their vessel become entangled in a pot should be an ongoing program 

(i.e. Coast Guard auxiliary, boater safety classes). The use of reflective tape on pot buoys has been shown 

to reduce pot loss rates from 17% to 7% in some areas (Hassell 2 7). In addition, the use of “line 

cutters” (cf. http://www.spursmarine.com/shaft-main.html) on propellers in areas where potting activity 

occurs can be problematic and lead to additional unnecessary pot loss. 

4.3 Reduction of Derelict Pot Effects

4.3.1 Pot removal

In some instances, pots are intentionally discarded, vandalized, or left in the water as part of periodic pot 

replacement. Abandoned pots (pots that still had the line and buoy attached) have been observed in 

Maryland (W. Slacum per. communication) and made up 41% of the recovered pots in the four year 

Virginia removal program (Bilkovic et al. 2014). In addition to the marker buoy, identification of pot
Management Scenarios – Mitigation Alternatives 37

ownership with a tag on the pot itself that is replaced annually with the purchase of the commercial 

license has been suggested as a mechanism to reduce intentionally discarded pots (Lee 2009) and is 

required by the Potomac River Fisheries Commission in the Potomac River of the Chesapeake Bay. 

Adequate allocation of resources to state marine resource agencies to enforce the removal of illegal pots 

during the closed season could alleviate a large source of derelict pots. 

In many states, legal restrictions prohibit the removal of derelict pots except by authorized agents. 

Allowing citizens to remove derelict pots during the closed season would empower local communities to 

police their own waterways, but could be problematic in the Chesapeake Bay where some pot fisheries 

remain active during the blue crab closed season and could be mistaken for abandoned pots (i.e eel pots). 

In addition, allowing disposal of pots in landfills at no charge would incentivize proper disposal of pots 

(NCDMF 2013). 

In the Chesapeake Bay, direct mortality of blue crabs from derelict pots is estimated to be 4.5% of the 

blue crab harvest. Derelict pots removed during the winter months in the Virginia and Maryland removal 

programs had different percentages of entrapped mature females, 60% and 36%, respectively (Bilkovic et 

al. 2014, Slacum et al. 2013) which is indicative of blue crab distribution in the Chesapeake Bay. The 

60% mature female catch ratio in Virginia is similar to the ratio of females versus males (67% vs. 33%) 

found in a study of blue crab catch during the regular season in Virginia (Bilkovic et al. 2012) and this 

study (56%) which suggests a potential impact of derelict pots on the blue crab breeding population 

(Havens et al. 2011) similar to the derelict pot effect reported for red king crab (Long et al. 2014) . The 

removal of derelict pots from high intensity potting areas (hotspots) can produce significant economic 

benefit beyond reducing mortality (Scheld et al. 2016). For example, removing just 10% of derelict pots 

(approximately 4,400) from the five most heavily fished sites in each of Virginia and Maryland could 

increase blue crab harvest in the Chesapeake Bay by 22 million pounds or approximately 14%.

4.3.2 Pot modifications

Blue crab pots capture numerous species of animals besides blue crabs including diamondback terrapin 

and even Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus, (Mangold et al. 2007). Animals recorded 

captured by derelict pots in the Chesapeake Bay are listed in Table 4-1 and the incorporation of 

biodegradable escape panels in crab pots has been recommended as a mechanism to reduce bycatch 

mortality (Guillory 1993, McKenna and Camp 1993, Guillory 2001, Lee 2009, Havens et al. 2011, 

Wagner 2013, NCDMF 2013, Arthur et al. 2014, Bourgeois et al. 2014, Voss et al. 2015, Perry et al. 

2015). In Virginia, watermen tested biodegradable panels in blue crab pots and found no difference in 

blue crab catch (Bilkovic et al. 2012). Additional studies found that pots with biodegradable escape 

panels reduced the capture of crabs by 87% as compared to standard pots and 47% of those retained in the 

pots with biodegradable panels were either shedding or mating (resulting in a baywide mortality of 3 

crabs/pot/yr versus 23 crabs/pot/yr, respectively). Pots with biodegradable escape panels had no captures 

of terrapins as compared to standard pots that captured an average of 0.18 terrapins per pot per day 

(Chambers et al. unpublished data). In a study of Dungeness crabs, Antonelis and others (2011) found 

that the incorporation of biodegradable components on Dungeness crab pots increased escape by 86 

percent. Other work with Dungeness crab pots showed that escape mechanisms that relied on detachment 

and buoyancy and gravity to work rather than complete biodegradation often failed due to biofouling and 

the subsequent encrustation holding the device in place (Maselko et al. 2013). The use of bycatch 

reduction devices on those crab pots fished in terrapin habitat (e.g., tidal creeks, shallows near marshes or 

nesting beach habitat) should also minimize terrapin mortality if those pots become derelict (Upperman et 

al. 2014) . 
38 Management Scenarios – Mitigation Alternatives

Peeler crabs are crabs preparing to shed (or “peel” 

off their hard shell) to become soft-shelled crabs, 

a highly prized cuisine product. Specialized pots 

are used to capture peeler crabs which are 

different from regular commercial-style pots in 

that they have a smaller mesh size and are not 

required to have escape or “cull” rings for smaller 

sized crabs or the cull ring is a smaller size than 

for regular hard crab pots (i.e. Potomac River 

Fisheries Commission). Peelers will often enter 

pots in an apparent search for shelter before 

shedding. The smaller mesh size, with no escape 

or cull rings, results in increased mortality of both 

the target species and by-catch species in derelict 

pots (NCDMF 2013) (Figure 4-1). Peeler pots 

made up 11.4% of recovered derelict pots in 

Virginia and 13.2% in Maryland (Slacum et al.

2013). Derelict peeler pots had proportional similar amounts of crabs as derelict hard crab pots but had a 

higher proportional percent fish bycatch capture of black seabass (31.2%), Atlantic croaker (10.2%), and 

white perch (7.5%) than hard crab pots, (5.8%; 7.3%, 3.5%; respectively) (Virginia Marine Debris 

Location and Removal Program 2009-2012). In Virginia, watermen tested biodegradable panels in peeler 

pots and found no difference in blue crab catch (NFWF 2015). Positioning the bottom of the 

biodegradable escape panel level with the upper chamber floor can increase the likelihood of escape by 39 

times once the panel has biodegraded (Havens et al. 2009, NFWF 2009). However, derelict pots have 

been shown to provide attractive structure for oysters, Crassostrea virginica, and other marine animals 

and can have a neutral or positive impact if the pots can be ‘disarmed’ from continuing to capture animals 

(Slacum et al. 2009, Havens et al. 2008, Havens et al. 2011, Bilkovic et al. 2014, Anderson and Alford 

2014, Voss et al. 2015). 

Table 4-1. Species Recorded from Derelict Blue Crab Pots.

Species Scientific name Species Scientific name

Atlantic croaker Micropogonias undulatus Mullet spp Mugil spp

Atlantic menhaden Brevoortia tyrannus Muskrat Ondatra ziberthicus

Atlantic spadefish Chaetodipterus faber Oyster toadfish Opsanus tau

American eel Anguilla rostrata Pigfish Orthopristis chrysoptera

American lobster Homarus americanus Pinfish Lagodon rhomboides

Black drum Pogonias cromis Porgy spp Sparidae

Black sea bass Centropristis striata Pufferfish spp Tetraodontidae

Blue crab Callinectes sapidus Pumpkinseed Lepomis gibbosus

Bluefish Pomatomus saltatrix Red drum Sciaenops ocellatus

Bowfin Amia calva Scup Stenotomus chrysops

Butterfish Peprilus triacanthus Shad Alosa or Dorosoma spp

Cancer crab Cancer spp. Sheepshead Archosargus probatocephalus

Catfish spp Ictaluridae Spider crab Libinia emarginata

Channeled whelk Busycotypus canaliculatus Spot Leiostomus xanthurus

Cunner Tautogolabrus adspersus Stargazer Astroscopus guttatus

Figure 4-1. Derelict peeler pot recovered from the 

Chesapeake Bay with diamondback terrapin and blue 

crab bycatch.
Management Scenarios – Mitigation Alternatives 39

Table 4-1. Species Recorded from Derelict Blue Crab Pots.

Diamondback terrapin Malaclemys terrapin Striped bass Morone saxatilis

Duck Duck spp. Striped burrfish Chilomycterus schoepfii

Flounder spp Paralichthyidae Tautog Tautoga onitis

Hogchoker Trinectes maculatus Turtle Turtle spp.

Horseshoe crab Limulus polyphemus Rappa whelk Rapana venosa

Knobbed whelk Busycon carica White perch Morone americana

Merganser (diving duck) Merganser spp.

4.4 Management Scenarios

Three main management scenarios are recommended for consideration: (1) avoidance of resource user 

conflict, (2) removal of derelict pots from ‘hot spots’, and (3) pot modification.

1. Avoidance of resource user conflict

A. Reducing recreational boating/commercial shipping and commercial crabbing spatial overlap 

could reduce the input of derelict pots to the Chesapeake Bay.

2. Removal of derelict pots from hotspots.

A. Focusing removal effort on just the most heavily fished areas (hotspots) can be a cost effective 

strategy to increase blue crab harvest baywide.

B. Providing adequate resource agency support for enforcing the removal of abandoned pots (pots 

that still have the line and marker buoy attached) can remove thousands of derelict pots from the 

Chesapeake Bay annually.

3. Pot modification.

A. Incentivize the incorporation of biodegradable escape panels in crab pots (both peeler and standard 

pots). Utilizing biodegradable escape panels in crab pots can reduce blue crab mortality in derelict 

pots from over 3.3 million marketable crabs/year (4.5% of the harvest) to under 440,000 crabs/year 

(˂ 1% of the harvest) and reduce or eliminate mortality of other animals.

B. Cutting the wire mesh on pots where cull rings are fastened will allow proper function of the cull 

ring for release of sublegal crabs and smaller animals should the pot be lost.
40 Future directions

5. Future Directions

This study represents the first Chesapeake baywide assessment of ecological and economic effects of 

derelict crab pots. The framework for this assessment allowed for the incorporation of new and evolving 

data on derelict pots in the Bay. When evaluating data on variables that may influence crab pot loss and 

synthesizing data into a common spatial format, several important data gaps were revealed. Filling these 

gaps would enable more refined predictions of derelict pot distribution, which would make management 

activities more effective. This would require spatially-explicit data on the following variables:

Recreational and commercial boating traffic: Recreational and boating activity likely have a greater 

effect on pot loss than was evident in the assessment due to the lack of spatially and temporally explicit 

information on boating intensity throughout the Bay.

Recreational blue crab fishery: Information on the recreational blue crab fishery in the Chesapeake Bay 

is lacking resulting in little information of the impact of recreational derelict crab pots. Anecdotal 

information suggests that recreational pots are lost though many are tied to private piers. However, in 

some cases recreational pots tied to piers are left unchecked in the water for extended periods acting as a 

de facto derelict pot; and because most recreational potting activity takes place near terrapin habitat, they 

can disproportionately impact terrapins. Spatially explicit information on the recreational blue crab 

fishery would be useful in completing the picture of blue crab pot loss and impact in the Chesapeake Bay. 

Diamondback terrapin: Unfortunately, baywide delineations of diamondback terrapin distributions or 

suitable habitat do not exist which precluded the quantification of overlap between terrapin habitat and 

derelict pots. While state-specific data do exist, the differences in data collection and output do not make 

these readily comparable. In Virginia, observations of terrapin at representative sites were used to create a 

map of suitable terrapin habitat (Isdell et al. 2015). In Maryland, a beach survey during the summer 2002 

nesting season covered a wide-geographic range of beaches to map terrapin observations (USGS Patuxent 

Wildlife Research Center 2002; http://www.pwrc.usgs.gov/terrapin/). More complete delineation of

potential and/or realized terrapin habitat (including feeding and nesting habitats - marshes, beaches, 

shallows) are needed to fully assess potential terrapin mortality risk from derelict pots in Chesapeake Bay.

Potomac River blue crab fishery: In assessing the impacts of derelict pots on the resources of the 

Chesapeake Bay, commercial blue crab data were obtained primarily from Maryland and Virginia 

regulatory agencies. The blue crab in the Potomac River is regulated by a separate agency, the Potomac 

River Fisheries Commission. The Potomac River blue crab fishery represents about 5% of the total 

Chesapeake Bay harvest and the derelict pot removal effort in the Potomac River was limited in scope 

with only about 2% of the total derelict pots removed coming from the Potomac River. While a more 

robust removal program coupled with spatially explicit data on fishing effort and harvest would allow a 

specific assessment for the Potomac River, it is reasonable to assume that the impacts determined for the 

Chesapeake Bay and other main tributaries are similar for the Potomac River system. 

Abandoned pots: In derelict pot removal activities, collecting data on pot location, bycatch, and pot 

condition (i.e. presence or absence of attached buoy and/or line) is extremely helpful. In this report, data 

on the presence of a buoy and line from each state’s derelict pot removal program was recorded for 

Virginia but not for Maryland. From the Virginia data, it was shown that a large percentage of pots still 

had their marker buoy attached and were thus considered abandoned. Similar data from Maryland would 

have been useful, but anecdotal information from Maryland suggests a similar pattern and specific 

management strategies can be targeted for abandoned pots.

Derelict pot capture efficiency over time: It is well established that blue crab pots can continue to 

capture and kill bycatch after they are lost for several years but information is lacking on a lost pot’s 

capture efficiency past a couple years. The time period for this project (two years) restricted the ability to 

gather data on capture rates and subsequent mortality for pots lasting more than two years. Accordingly, 

calculations of effects over time in this report utilized a conservative pot life span of two years.
Conclusions 41

6. Conclusions

It is estimated that between 12% to 20% of blue crab pots deployed annually in Chesapeake Bay waters

are lost or abandoned and at any given time, there are on average 145,000 derelict crab pots Bay-wide, 

representing a non-depreciated replacement gear value between $3.6 and $5 million ($25 to $35 per pot, 

depending on material type and additions such as zincs, rebar, etc). These derelict pots capture and kill 

millions of blue crabs per year, amounting to nearly 5% of the commercial harvest as well as many other 

species including commercially important white perch and Atlantic croaker. Fishing effort, water depth, 

and recreational and commercial boating traffic were all found to be significant predictors of the density 

of derelict crab pots.

The lack of significant overlap of derelict pots and sensitive bay habitats suggest that commercial blue 

crab potting generally may avoid submerged aquatic vegetation and oyster reef habitats. An important 

caveat however, is that National Environmental Policy Act requirements restricted derelict pot removal 

activity in sensitive habitats and the model for predicted derelict crab pot occurrence was based, in part, 

on data from retrieval programs that avoided pot removal from these habitats.

Derelict gear may impose a variety of economic costs (see Figure 3-5). The costs of decreased harvests 

due to ghost fishing can be further separated into those which are caused by stock reductions (i.e., due to 

mortality and/or reduced recruitment) and those that result from increased gear competition, and thus the 

reduced efficiency of active gear. In fisheries with large amounts of effort and gear loss, such as blue crab 

fisheries in the Chesapeake Bay, the economic costs of inefficient gear may be significant. In this report it 

was noted that the 43,968 removals which occurred in Maryland and Virginia from 2008-2014 are 

thought to have resulted in an additional 38.17 million lbs of harvest valued at $33.5 million. Though 

measured and discussed here as harvest and revenue losses, these costs may equally be thought of in 

terms of additional time and effort. Increased gear competition means fishers must exert more effort and 

resources in procuring harvest. Chesapeake Bay blue crab fishers might therefore obtain crab at a much 

lower cost, were it not for derelict gear. 

Several management strategies are highly likely to reduce derelict crab pot abundance and associated 

adverse ecological and economic effects. These include targeted derelict pot removal in high density 

areas, enforcement of the removal of abandoned pots, education of recreational boaters to minimize useconflict, and pot modifications that include a biodegradable escape mechanism.

 Removing derelict pots from high intensity potting areas (hotspots) can produce significant economic 

benefit beyond reducing mortality. For example, removing just 10% of derelict pots (approximately 

4,400) from the five most heavily fished sites in each of Virginia and Maryland could increase blue 

crab harvest in the Chesapeake Bay by 22 million pounds or approximately 14%.

 Recreational and commercial boating traffic are significant predictors of the distribution and 

abundance of derelict crab pots. Reducing the overlap between recreational and commercial boating 

and commercial potting activities can reduce the input of derelict pots to the Chesapeake Bay and 

boater education should highlight this issue in appropriate training or instruction venues.

 Biodegradable escape panels in crab pots can reduce blue crab mortality in derelict pots from over 3.3 

million to under 440,000 market crabs/year and reduce or eliminate mortality of other animals.

Developing a fine scale biogeographical framework that can be matched to fishery management needs (in 

this case NOAA codes) enhances the utility of the information and provides a platform from which to 

adaptively manage impacts of derelict crab pots, as well as other similar derelict gear, in fisheries both 

nationally and worldwide. More generally, beyond providing a quantitative assessment of derelict fishing 

gear in the Chesapeake Bay, this study also validates a broader assessment framework for derelict fishing 

gear – a generic, structured analytical process applicable to other regions and other fisheries.
42 References

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Acknowledgments 45

Acknowledgments

We would like to thank a number of individuals and organizations that helped with this report:

 Capt. Jamie Green (Virginia Marine Resources Commission)

 Sgt. Chris Miller (Virginia Marine Resources Commission)

 Mr. Rob O’Reilly (Chief of Fisheries, Virginia Marine Resources Commission)

 Commissioner John Bull (Virginia Marine Resources Commission)

 All the Virginia and Maryland watermen that assisted in derelict pot removal and data collection –

especially Mr. Billy Bonniville, Mr. Richard Green, Mr. Clay Justis, Mr. Earl Kellum, and Mr. Don 

Miles.

 The NOAA Chesapeake Bay Office (NCBO) for funding support and staff time in support of the 

many Chesapeake Bay studies. Especially Steve Giordano, Jay Lazar, and David Bruce for their 

contributions to this body of work.

 The hundreds of Maryland watermen who participated in derelict crab pot removal and data 

collection efforts.

 The Maryland Department of Natural Resources for supporting derelict crab pot studies and retrieval 

project in Maryland, and for providing data in support of this project.

This study also benefited from interactions with the NOAA Marine Debris Program, the National Marine 

Fisheries Service, the National Fish and Wildlife Foundation, and the Virginia Office of the Secretary of 

Natural Resources.

GST is grateful for the depth of insight, unflagging perseverance, and unparalleled esprit de corps of the 

expert study team that conducted this research and assembled this report:

 H. Ward Slacum, Jr.;

 Donna Marie Bilkovic, Kirk Havens, Andrew Scheld, David Stanhope, and Kory Angstadt of the 

Virginia Institute of Marine Science at the College of William & Mary;

 Chris Jeffrey, Angela Orthmeyer, and Matt Poti of CSS-Dynamac, Inc. ; and

 Danielle Zaveta of Versar, Inc.

We are particularly grateful to the NOAA Marine Debris Division for their oversight and support to this 

work, which was performed under NOAA SciTech contract # DG133E-10-CQ-0034, Task Order 007.

Appendix A. Blue Crab Pot Loss rates A-1

Appendix A. Blue Crab Pot Loss Rates

Introduction

Humans have been using various trap or pot designs to capture fish and shellfish for thousands of years. 

In more modern times plastic, wire, and plastic coated wire for pot construction have replaced less 

durable material such as bamboo, reed, and wood. The substitution of more durable pot material has 

exacerbated the issue of lost or abandoned pots, allowing them to remain intact and continue to capture 

and kill marine life (Havens et al. 2008; Bilkovic et al. 2014; Uhlmann and Broadhurst 2015) and act as 

an attractant ultimately impacting harvests (Eggleston et al. 1998; Sturdivant and Clark, 2011, Scheld et 

al. 2016). 

Blue crab pots are approximately 0.6m x 0.6m x 0.6m generally galvanized or vinyl-coated twochambered wire traps designed to be deployed and recovered by a line and buoy system. Typically, pots 

become lost when buoy lines are severed by vessel propellers, lines break because of age, pots are 

abandoned or are vandalized, or storms roll the pots, pulling the buoy below the surface (Guillory, 1993) 

(Table A-1). It is estimated around 20% of deployed blue crab pots are lost annually in Virginia waters 

(Havens et al. 2008; Bilkovic et al. 2014) while North Carolina estimates pot loss rates of 14% – 21% 

(McKenna and Camp 1992; Hassell 2007; Lee 2009) though pot loss rates can vary among different pot 

fisheries (Morison and Murphy, 2009; Arthur et al. 2014). Lost or abandoned blue crab pots can continue 

to capture crabs, fish, and other organisms for multiple years (Guillory, 2001; Havens et al. 2008, 

Bilkovic et al. 2014, Arthur et al. 2014) and can affect blue crab harvest (Scheld et al. 2016).

Estimates of annual blue crab pot loss have been reported for Virginia as 10% to 30% (Havens et al.

2008) and later refined to 20% (Bilkovic et al. 2014). However, these estimates were derived from 

information gathered mostly from large tributaries or the mainstem of the bay. Limited information is 

available regarding annual pot loss from small to medium-sized tidal creeks (< 10 km

2

) where potting also 

occurs (Havens et al. 2008).

Table A-1. Activities Contributing to Pot Loss with Potential Mitigation Options.

Factors Affecting Pot Loss

Accidental Loss

Boat Traffic

Recreational - propeller entanglement

Commercial – propeller entanglement, barge interception

Equipment Failure

Buoy & line detachment

Line & pot detachment

Current driven movement

Insufficient weighting

Biofouling causing drag and movement

Insufficient line length and pot ‘walking’

Entanglement of multiple pot trotlines

Line to dock detachment (recreational)

Storms

Movement of pot to deeper water

Pot ‘pile up’ and line entanglement

Exacerbate equipment failure

Intentional Loss

Discarded

End of pot life

Out of business
A-2 Appendix A. Blue Crab Pot Loss rates

Table A-1. Activities Contributing to Pot Loss with Potential Mitigation Options.

Periodic pot replacement

One time pot use (i.e. peeler pots)

Vandalism

Theft

Mitigation Options

Reduction of Effects

Removal

From high intensity fishing areas

From high pot loss areas

From sensitive habitats

Pot Modifications

Biodegradable escape mechanisms

Policies 

Enforcement of closed seasons

Enforcement of shipping lanes

Enforcement of pot prohibition in marked channels

Incentives for proper pot disposal

Incentives for use of biodegradable components in pots

State funding for participants

Extended fishing season for participants

Enhanced product pricing for participants

Methodology

Watermen Estimated Blue Crab Pot Losses in Virginia- Five commercial fishers were employed to 

remove all derelict crab pots from ten tidal creeks (5 paired creeks with low and high crabbing effort in 5 

regions of Virginia) during the winter of 2014 (Figure A-2). During the fishing season they periodically 

surveyed the number of active pots in these creek systems. In the winter of 2015 they returned to the 

creeks for and again removed all derelict pots.

Participants were provided a Humminbird 1197SI side-imaging unit and trained in its use. In addition, 

each participant was provided with data sheets for cataloging bycatch. Participants outfitted their own 

vessels with a removable transducer mount and were instructed to place the GPS directly above the side 

imaging transducer. Units were preprogrammed to scan using 75 ft swaths and acquire GPS points 

(survey tracks) with a 30 s ping rate. Participants were instructed to maintain preset functions for 

consistency. Proper survey procedures (i.e. scanning an area in a grid pattern with some overlap, speeds 

_6.0 kt) were explained and all participants were experienced surveyors having being in the Virginia 

Marine Debris Location and Removal Program (Havens et al. 2011). Participants were instructed in the 

proper retrieval techniques to reduce bottom disturbance using grappling devices raised slightly above the 

bottom surface or lines embedded with bent nails) (Figure A-1). These retrieval methods combined with 

the Global Positioning System of the side-imaging unit allowed for targeted removal of derelict crab pots. 

Vessel track lines were recorded to calculate the area surveyed. Mean blue crab pot loss rates per creek 

were calculated as number of derelict pots per active pot per month and averaged across the season.

Previous loss estimates were obtained from watermen participating in the Virginia Marine Debris 

Location and Removal program where they reported loss rates of 20% for three consecutive years (2009–

2011) (Havens et al. 2011) with the bulk of the their potting activity taking place in the mainstem bay or 

tributaries. In addition, a five-year (2005-2009) field survey using side scan sonar to locate and remove 

derelict pots in one tidal creek (Sarah Creek) was conducted from 2005 – 2009 showed annual pot loss 

rates of 26.2% of fished pots on average over the five year period (Table A-4).
Appendix A. Blue Crab Pot Loss rates A-3

Watermen Estimated Blue Crab Pot Losses in Maryland – The portion of active crab pots lost annually in 

Maryland is unknown. In 2014 and 2015 we spoke with active Maryland watermen to gather information 

about annual pot losses. These conversations used a template tailored to characterize where the watermen

actively fished, the percent of their crab pots lost annually, and their opinion on the cases of pot losses 

(See questionnaire in Appendix F). We sought to collect information from watermen that covered a range 

of fishing activity (from full time to part time), and with representative coverage throughout the extent of 

crabbing area in Maryland. These interactions provided background information on Maryland fishing 

practices by region including average loss rate of crab pots per waterman, the total number of derelict pots 

removed by watermen, and the total number of crab pots present. This information served in groundtruthing the modeling efforts and in comparing the Maryland and Virginia fisheries. These conversations 

also give insight to the potential sources of derelict pots in different geographic regions of the Chesapeake 

Bay; in particular they suggest that an average pot loss for watermen ranges between 1.5% and 10% of 

total gear in the summer and fall. 90% of the watermen we spoke with indicated that recreational boater 

traffic was the chief cause of pot loss, with theft as the number two cause. The template for these 

conversations may be found in Appendix F.

The information collected through interactions with watermen was unfortunately considered of limited 

value due to several influencing factors. The first factor was the limited sample size. The Paperwork 

Reduction Act which required information gathering on a one-on-one basis rather than through a broad 

mailing questionnaire. The second factor was the perception by watermen we spoke with that these 

conversations would result in new regulations. Many watermen believe they would be required to add 

escape panels if pot loss was determined to be high; it was assumed their responses were very 

conservative because of this fear. Therefore these conversations could only acknowledge that pot losses 

occur, but could not determine the loss rate for crab pots in Maryland.

Results & Discussion

In Virginia, the total area surveyed for derelict pots was 31.8 km

2

in 2015 and 31.6 km

2

in 2016 (Table 

A-3). Mean active blue crab potting ranged from 0 (no crabbing) in the Pagan to 498 pots in 

Occohannock. The number of recovered derelict pots after the 2015 fishing season ranged from 2 in 

Timberneck to 35 in Guilford. In Sarah Creek, the five-year study showed a mean loss rate of 26.2%. The 

pot loss rate ranged from 5.2 to 26.2% (not considering the Pagan but including Sarah) with a mean 

across all creeks of 12.7% (SE 2.6) (Table A-2).

A review of the number of docks, ramps (both private and public), and marinas suggests that areas with 

higher boating activity, near marinas and public ramps, could result in higher pot losses (Table A-5).

Blue crab pot loss rates measured in creeks in the Virginia portion of the Chesapeake Bay was 12.7% in 

the creeks sampled in this study, including a five-year study of one creek in Virginia that showed an 

average loss rate of 26%. Fishers in the Virginia Marine Debris Location and Removal program reported 

loss rates over three years, averaging 19.7% in main tributaries and the Bay. These rates are similar to 

those reported by Bilkovic et al. (2014) and Arthur et al. (2014).

To calculate a Virginia bay-wide estimate, the creek and tributary/mainstem loss rates were weighted 

based on the relative fishing pressure. The 32,000 derelict pots recovered in the first four years of the 

Virginia Marine Debris Location and Removal Program were used to determine the relative portion of 

potting activity in the creeks versus the mainstem of the bay and tributaries. Virginia bay-wide annual pot 

loss rate was weighted using the creek (31%) versus river/bay (69%) proportion and the loss rate 

weighted mean was calculated using the following equation.
A-4 Appendix A. Blue Crab Pot Loss rates

 

 

 

Where = weighted mean, = proportion (weight), and = loss rate.

The mean annual pot loss rate for the Virginia portion of the Chesapeake Bay is estimated at 17.5%. 

While no direct measurements of pot losses were made in Maryland, it’s reasonable to assume that 

portion of active pots lost in Maryland is similar to the range of lost pots documented in Virginia. Fishing 

practices and effort are similar in both States and the factors affecting pot loss have also been proven to 

be similar. Therefore, these data suggest an annual pot loss estimate of 12% to 20% in the Chesapeake 

Bay depending on the location (creek or main tributary/bay), though it could be higher in areas where 

high potting activity is coupled with high boating activity.

Table A-2. Percent Pot loss in creek systems, main tributaries, and Chesapeake Bay.

Creek 2015 

Derelict Pots

2016 

Derelict Pots

Mean Number of 

Active Pots

Mean Percent Loss ± 

(SE)

Perrin 7 11 52 23.7% ± 3.8

Guilford 26 35 428 21.2% ± 13.2

Timberneck 3 2 16 13.5% ± 2.0

Queens 4 4 46 12.6% ± 3.9

Warwick 7 8 153 6.6% ± 1.9

Occohannock 1 24 498 6.5% ± 1.9

Old Plantation 1 2 87 6.3% ± 2.1

Cherrystone 23 7 232 5.2% ± 1.5

Back 0 3 59 5.2% ± 0.4

Pagan 0 0 0 NA

Sarah (mean loss rate 2005-2009) 26.2% ± 4.2

Mean across all creeks 12.7% ± 2.6

Mainstem and main tributaries* (mean loss rate 2010-2012) 19.7% ± 1.2

Chesapeake Bay wide loss rate 12 - 20%

*Bilkovic et al. 2014

Table A-3. Survey Areas and Number of Derelict Pots Removed.

Creek

Area Surveyed 

2015 (km

2

)

Derelict Pots 

Removed 2015

Area Surveyed 

2016 (km

2

)

Derelict Pots 

Removed 2016

Guilford (Eastern Shore) 4.7 26 6.5 35

Occohannock (Eastern Shore) 5.5 1 5.5 24

Old Plantation (Eastern Shore) 3.0 1 3.9 2

Cherrystone (Eastern Shore) 4.9 23 5.5 7

Pagan (Western Shore – James River) 2.1 NA 2.1* NA

Warwick (Western Shore – James River) 7.9 7 4.6 8

Queens (Western Shore – York River) 0.92 4 0.98 4

Timberneck (Western Shore – York River) 1.1 3 0.83 2

Perrin (Western Shore) 0.4 7 0.4 11

Back (Western Shore) 1.3 0 1.3* 3

* Track line anomalies. 2015 track lines substituted.
Appendix A. Blue Crab Pot Loss rates A-5

Table A-4. Derelict Pot Removal and Loss Rates for Sarah Creek, VA.

Year Active Pots Derelict Pots Percent Loss Rate

2005 40 8* 20.0

2006 54 12 22.2

2007 51 11 21.6

2008 53 13 24.5

2009 54 23 42.6

Mean loss rate 2005 – 2009 (± SE) 26.2 ± 4.17

*16 pots were removed but assumed a two year accumulation.

Table A-5. Docks, Ramps, and Marinas Per Creek.

Creek Docks

Public 

Ramps

Private 

Ramps Marina

Marina 

< 50 slips

Marina 

>50 slips

Avg % 

loss

1 Sarah 92 3 3 2 26.2

Perrin 38 0 10 4 23.7

Guilford 8 2 1 21.2

Timberneck 31 0 3 1 13.5

Queens creek 21 3 1 12.6

Warwick 203 1 10 6.6

Occohannock 140 2 5 1 6.5

Old plantation 25 0 5 6.3

Back 88 2 8 2 5.2

Cherrystone 21 0 7 1 5.2

2 Pagan 70 0 3 2 4 NA

1 Five year average.

2 No active pots in 2015 or 2016. It was noted that due to the boating activity in the area, watermen have recently 

ceased fishing the Pagan with pots (per. comm. R. Green).

Figure A-1. Watermen removal of derelict blue crab pots.
A-6 Appendix A. Blue Crab Pot Loss rates

Figure A-2. Ten Tidal Creeks in Virginia Where Derelict Pot Surveys and Removals were Conducted in 2014 

and 2015. 

Counts of active pots were conducted during the 2015 fishing season.
Appendix A. Blue Crab Pot Loss rates A-7

References for Appendix A

Arthur, C., Sutton-Grier, A., Murphy, P., Bamford, H. 2014. Out of sight but not out of mind: Harmful 

effects of derelict traps in selected U.S. coastal waters. Mar. Pollut. Bull. 86, 19-18.

Bilkovic, D.M., Havens, K., Stanhope, D., Angstadt, K., 2014. Derelict fishing gear in Chesapeake Bay, 

Virginia: spatial patterns and implications for marine fauna. Mar. Pollut. Bull. 80, 114–123.

Eggleston, D. B., Etherington, L. L. & Elis, W. E. Organism response to habitat patchiness: species and 

habitat-dependent recruitment of decapod crustaceans. J. Experi. Mar. Biol. Ecol. 223, 111–132 (1998).

Guillory, V., 1993. Ghost fishing by blue crab traps. North Am. J. Fish. Mgmt. 13, 459–466.

Guillory, V., McMillen-Jackson, A., Hartman, L., Perry, H., Floyd, T., Wagner, T., Graham, G., 2001. 

Blue crab derelict traps and trap removal programs (Report). Gulf States Marine Fisheries Commission, 

Ocean Springs, MS, p. 14.

Hassell, J. 2007. Minimizing pot loss and retrieval of lost pots. North Carolina Sea Grant. Blue Crab 

Research Program. Report 06-ECON-03. Raleigh, NC. 14p.

Havens, K.J., Bilkovic, D.M., Stanhope, D., Angstadt, K., Hershner, C., 2008. The effects of derelict blue 

crab traps on marine organisms in the lower York River, Virginia. North Am. J. Fish. Mgmt. 28 (4), 

1194–1200.

Havens, K.J., Bilkovic, D., Stanhope, D., Angstadt, K., 2011. Fishery failure, unemployed commercial 

fishers, and lost blue crab pots: an unexpected success story. Environ. Sci. Policy 14 (4), 445–450.

Lee, D.S. 2009. North Carolina derelict crab pots 101: shallow water efforts, in Morison, S. and P. 

Murphy (eds). 2009. Proceedings of the NOAA Submerged Derelict Trap Methodology Detection 

Workshop, June 2-4, 2009. NOAA Technical Memorandum NOS-OR&R-32.

McKenna, S., Camp, J.T. 1992. An examination of the blue crab fishery in the Pamlico River estuary. 

Albemarle-Pamlico Estuarine Study Report: 92-08. 101p.

Morison S, P. Murphy (Eds.), Proceedings of the NOAA Submerged Derelict Trap Methodology 

Detection Workshop, June 2–4, 2009 (2009) NOAA Technical Memorandum NOS-OR&R-32

Scheld, A. M., Bilkovic, D, Havens, K.J., 2016. The dilemma of derelict Gear. Sci. Rep. 6, 19671; doi: 

10.1038/srep19671.

Sturdivant, S. K. & Clark, K. L. An evaluation of the effects of blue crab (Callinectes sapidus) behavior 

on the efficacy of crab pots as a tool for estimating population abundance. Fish. Bull. 109, 48–55 (2011).

Uhlmann, S. S., Broadhurst, M. K. 2015. Mitigating unaccounted fishing mortality from gillnets and 

traps. Fish and Fisheries 16 (2): 183–229.

Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots B-1

Appendix B. Capture, Escape, and Mortality 

Rates in Derelict Blue Crab Pots

Introduction

Since the 1950s, one of the primary methods for capturing blue crabs is the wire-mesh crab pots (Stagg 

and Whilden 1997). Typical crab pots are cube-shaped and measure approximately 2ft x 2ft x 2ft. They 

are generally made of wire, either galvanized or vinyl-coated, and designed with a lower bait chamber and 

an upper trap chamber. The lower and upper chambers are separated by a v-shaped wire mesh with two 

opens at the top of the “v” (Kennedy et al. 2007). Two to four entrance funnels are located in the lower 

chamber and crabs enter through the funnels to access the bait that is usually held in a finer mesh wire 

cylinder. Circular ‘cull’ rings that permit the escape of sublegal crabs are incorporated on the side panels 

of the pot (Figure B-1). 

Figure B-1. Blue Crab Pot schematic (modified from Kennedy et al. 2007).

Peeler pots, which are designed to catch premolt crabs for the soft shell market, generally have smaller 

mesh size without cull rings resulting in a greater potential of ghost fishing mortality than hard crab pots 

(NCDMF 2013).

Lost or abandoned (derelict) crab pots present safety, nuisance, and environmental effects in estuarine 

waters. Blue crabs and fish that are entrapped and die in derelict pots can act as an attractant to crabs and 

other marine life, resulting in a self or auto-baiting effect (Havens et al. 2008; Slacum et al. 2009; 

Bilkovic et al. 2014). Crabs and other marine life retained in pots are subject to increased mortality due to 

the cannibalistic and aggressive nature of crabs (Eldridge et al. 1979; Savoie and Casanova 1982, Smith 

and Hines 1991; McKenna and Camp 1992). When a derelict pot is recovered, any bycatch present 

represents an instantaneous catch rate, meaning at that instance those animals were caught. However, it is 

well known that catch rates vary across season and multiple sampling over time is necessary to accurately 

estimate a seasonal or yearly catch rate. 

A number of behavioral activities beyond feeding may attract crabs to derelict pots. Blue crabs have been 

shown to prefer structured habitat (Everette and Ruiz 1993) and may enter pots as refuge rather than to 

feed (Sturvidant et al. 2011). Sturvidant and others (2011) also suggest that, as further evidence that blue 

crabs may enter pots in response to their value as structure, crabs have been captured in unbaited pots 
B-2 Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots

(Guillory, 1993). This is further supported by studies on unbaited pots in the Chesapeake Bay (Havens et 

al. 2008; Slacum et al. 2009). In addition, fishers regularly use unbaited pots (or pots baited with a large 

male crab) to capture pubertal-molt females (peelers) (Christian et al. 1987). In Virginia it has been 

reported that pots baited with a large male crab may catch 100 female peelers per day during the 

approximate two week spring period when males and females are pairing (Kennedy et al. 2007).

Derelict crab pots have the potential to be a significant source of unaccounted fishing mortality (Van 

Engel 1982, Guillory et al. 2001, Haddon 2005, Havens et al. 2008, Slacum et al. 2009, Sturdivant et al.

2011, Bilkovic et al. 2014). The mortality caused by derelict pots is related to the durability of the pot and 

its retention capability. The use of vinyl-coated wire in pot construction has increased the life of crab pots 

(Guillory et al. 2001, Lee 2009, Uhlmann and Broadhurst 2015) resulting in multiple years of blue crab 

and other bycatch capture and mortality. For blue crabs, estimates of annual capture rates by derelict pots 

have been variable across ecosystems (Gulf of Mexico, 47.7 crabs/pot/year, Guillory 1993; North 

Carolina Pamlico River, 32 crabs/pot/year, NCDMF 2013; North Carolina, 40 crabs/pot/year, NCDMF 

2013; Lower Chesapeake Bay, 50.6 crabs/pot for April-November, Havens et al. 2008; Upper 

Chesapeake Bay 21 crabs/pot/year, Slacum et al. 2009) though Havens and others (2008) found that 

simulating self-baiting doubled the catch rate to 100 crabs/pot/season (Table B-1).

Table B-1. Capture Rates of Blue Crabs within Derelict Pots.

Capture

# crabs/ pot/yr # of crabs/pot/day Reference

48 0.14 Guillory 1993

50.61(1002) 0.24 (0.143) Havens et al. 2008 (simulated self-baiting)

21 0.06 Slacum et al. 2009

40 0.11 NCDMF 2013

40.8 0.244(0.115) Whitaker 1979

65 0.178 This Report Virginia

43.8 0.12 This Report6 Chesapeake Bay-wide

1 April – November.

2 Simulated self-baiting. 

3 Extrapolated to one year.

4 168 days. 

5 Extrapolated to one year. 

6Average of capture numbers from Slacum et al. 2009 (0.06) and this report (0.18).

Blue crab escapement studies, however, suggest that blue crabs may escape derelict pots at a rate of 34% 

(Guillory 1993) and 56% (Arcement and Guillory 1993) in the Gulf region and 14% in the upper 

Chesapeake Bay (Slacum et al. 2009). Sturdivant and others (2011) reported escape rates from blue crab 

pots in field and mesocosm experiments in the upper Chesapeake Bay of 41% and 85%, respectively and, 

while they note that crabs regularly moved in and out of the pots lower chamber, they report only a 2% 

escape rate of blue crabs once entrapped in the upper chamber. Underwater video has shown a consistent 

pattern in blue crab behavior in pots. Blue crabs rarely swim within the confines of a pot and once in the 

upper chamber spend most of their time crawling along the upper chamber floor (Havens et al. 2009). 

Once entrapped, crabs are believed to suffer mortality at annual rates ranging from 20-60 crabs/pot in 

South Carolina (Whitaker 1979), to 25.8 crabs/pot in coastal Louisiana (Guillory 1993), to 20 crabs/pot in 

upper Chesapeake Bay (Slacum et al. 2009) to 26 crabs/pot in lower Chesapeake Bay (Bilkovic et al.

2014), and 53.8 crabs/pot averaged across several ecosystems (Poon 2005). Mortality is usually a result of 

starvation, cannibalism, infection, disease, and prolonged exposure to poor water quality (i.e. low 

dissolved oxygen) and the longer a crab is retained within a pot, the more likely it will be injured or killed 

by larger conspecifics (Rudershausen and Hightower 2016). 
Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots B-3

This study investigated capture, escape, and mortality rates of blue crabs to more precisely estimate the 

impact of derelict blue crab pots.

Methods

To investigate derelict pot capture rates, we had five commercial watermen deploy and fish 1 “lost” pots 

and 10 regular pots as part of their typical fishing season. The watermen fished the “lost” pots 1 week per 

month for the crabbing season (March – December 2015) and recorded number and sex of crabs, other 

bycatch and location of animals in the pots (upper or lower chamber). The waterman conducted the work 

in the following locations: York River, James River, Southern Eastern Shore, Northern Eastern Shore.

To investigate escape and mortality rates, the 43,000 square foot Virginia Institute of Marine Science 

Seawater Research Laboratory (SRL) was used to set up a mesocosm experiment. The SLR provides 800 

gallons per minute of treated seawater and a 5,700 gal tank was used to run experiments. Standard, vinylcoated pots were deployed in the tank. Video surveillance was conducted as well as interval monitoring to 

record blue crab movement within the mesocosm (Figure B-2). For video surveillance, four (one over 

each crab pot) DefenderTM Ultra resolution (6 TVL) outdoor night vision (36 IR LEDs) security 

cameras (model #21006) connected to a DVR that was connected to the network to allow videos to be 

saved directly to backed up share drives. Crabs were numbered using a white or silver permanent paint 

marker (The PumperTM) (Figure B-3). 

Figure B-2. Mesocosm outfitted with cameras. Figure B-3. Blue crab marked for mesocosm 

experiment.

Escape Experiment

Mesocosm 1

Crabs were released into the mesocosm and allowed to acclimate for 48 hrs after which any dead crabs 

were removed and four standard, unbaited, vinyl-coated pots were deployed. The experiment was 

conducted in the summer (n=48) and fall (n=24). Crab movement was monitored continuously for 4 hrs.

Mesocosm 2

Crabs were released into the mesocosm and allowed to acclimate for 48 hrs after which any dead crabs 

were removed and four standard, unbaited, vinyl-coated pots were deployed. The experiment was 

conducted over spring (n=23), summer (n=48), and fall (n=24), though a harmful algal bloom (red tide) 
B-4 Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots

event in August / September required a one-month pause in the experiment. Crab movement was 

monitored continuously over 53 hrs. 

Mesocosm 3

Twelve standard (6 less than 1 yr old, 6 2 yr old), unbaited, vinyl-coated pots were deployed with 6 

randomly selected crabs (n=72) (size range: males 12.7-15.2 cm; females 12.3-15.6 cm) in the lower 

chamber of each pot. Six pots were less than one year old and 6 pots were 2 years old. Crabs were tagged 

and tracked for 7 days. Position in the pot (lower or upper chamber) was recorded daily. This experiment 

was replicated with a new set of crabs (size range: 11.4-15.5 cm; females 11.9-16.4 cm).

Mortality Experiment

Blue crabs from mesocosm experiment 1 were tracked for 7 days. In a second experiment, crabs were 

placed in the tank to acclimate for 48 hrs and any dead crabs were removed. Crabs were then tracked 

daily for 25 days. Mortality was estimated for each experiment.

Results

Capture Rates

Annual capture rates (crabs/pot/yr) in Virginia varied from 0.12 to 0.39 with an average annual rate of 

0.178 (65 crabs) (Table B-2 and Figure B-4).

Table B-2. Blue Crab Capture Rates in Virginia.

Catch of blue crabs in Virginia

Location

Average of crab 

catch in pot/day (SD)

Average annual 

crab catch pot/day

Number of 

crabs/pot/annual

James River 10.271± (0.24) 0.13 47.5

N. Eastern Shore 20.662± (0.37) 0.39 142.4

S. Eastern Shore 10.371± (0.29) 0.19 69.4

York River20.282± (0.09) 0.16 58.4

Total30.413± (0.31) 0.22 ± (0.06) 80.3

Guthrie Creek (York River) 4,6 0.264,6 ± (0.22) 0.15 54.8

Cedar Creek (York River) 4,6 0.274,6 ± (0..22) 0.16 58.4

Sarah Creek (York River) 4,6 0.204,6 ± (0.15) 0.12 43.8

York River 4,6 0.214,6 ± (0.24) 0.12 43.8

Total 4,6 0.244,6 ± (0.20) 0.14 ± (0.01) 51.1

Grand Total 50.325± (0.15) 0.178 ± (0.03) 65

Number of days: 1 183, 2 214, 3 199, 4 211, 5 205 in season. 6 Havens et al. 2008.
Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots B-5

Figure B-4. Mean Crab Bycatch/Pot/Day for Four Locations.

Each error bar is constructed using 1 standard deviation from the mean.

Escape Rates

Mesocosm 1

The summer escape rate over the 4 hour continuous observation from the lower chamber was 22.5% and 

from the upper chamber 0% (n=12). The fall escape rate from the lower chamber was 31% and from the 

upper chamber 8.3% (n=15). The mean across all seasons was lower chamber 26.8% and upper chamber 

4.1%.

Mesocosm 2

After 53 hours of observation, in the spring, 87% of the crabs ended up in pots with a 10% escape rate. In 

the summer 54% of the crabs ended up in pots with a 7.7% escape rate. In the fall 83% of crabs ended up 

in pots with a 15% escape rate. Mean escape rate across all seasons was 11%. All escapes were from the 

lower chamber.

Mesocosm 3

After 7 days, the average escape from the lower chamber of 1 year old pots was 40.3% and from the 

upper chamber 4.7%. Average escape from pots was 40.3%. The average escape from the lower chamber 

of 2 year old pots was 72.2% and from the upper chamber 8.3%. Average escape from pots was 68.05. 

The overall average escape from the lower chamber, upper chamber, and total pot was 56.2%, 6.1%, and 

54.2%, respectively (Table B-3).

Table B-3. Blue Crab Escape Rates from 1 and 2 Year Old Pots.

Escape Lower chamber Upper chamber Total pot

Experiment 1

˂ 1 yr pots 38.9% 6.7% 36.1%

2 yr pots 75.0% 8.3% 61.1%
B-6 Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots

Table B-3. Blue Crab Escape Rates from 1 and 2 Year Old Pots.

Average 57.0% 7.2% 44.5%

Experiment 2

˂ 1 yr pots 41.2% 2.3% 44.5%

2 yr pots 64.9% 16.7% 75.0%

Average 61.1% 10.0% 59.7%

Total ˂ 1 yr pots 40.3% 4.7% 40.3%

Total 2 yr pots 72.2% 8.3% 68.0%

Grand Total 56.2% 6.1% 54.2%

Mortality

Mesocosm 4 

In experiment 1 over 82% of the crabs were dead after 168 hrs (7 days) (Table B-4). It is important to 

note that the laboratory experiment crabs were obtained from a commercial crabbing operation and, while 

they were harvested the morning of the experiment, they had been handled prior to the start of the 

experiment at noon the same day.

In experiment 2, 63% of crabs were dead within 7 days (Figure B-5), which compares with Guillory 

(1993) who found approximately 40% of blue crabs died after 1 week, 70% after 2 weeks, and 90% after 

4 weeks.

Table B-4. Time to Mortality of Blue Crabs in Derelict Pots in the Laboratory.

Experiment N (alive) Days (hrs) N (dead) Percent

Laboratory 1 72 7 58 80.6

Laboratory 2 72 7 61 84.8

Average 82.7

Figure B-5. Cumulative Blue Crab Mortality.
Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots B-7

Discussion

The blue crab capture rate per derelict pot per day for Virginia was 0.18 and when averaged with the 

Maryland rate of 0.06 (Slacum et al. 2009) results in a Chesapeake Bay-wide value of 0.12.

Escape rates are variable over time and season and appear in increase over time, particularly escapement 

from the lower chamber (Table B-5). It is important to note that in our 7 day escape experiment, six crabs 

were placed in the lower chamber at the beginning of the experiment potentially artificially setting up an 

intraspecies conflict scenario, resulting in crabs more actively seeking movement out of the pots. This 

follows the pattern identified by Guillory (1993) who found higher escape rates in pots with more than 4 

crabs (33.3%) than in pots with less than 2 crabs (16.7%). In the shorter time frame experiments, crabs 

were allowed to seek and independently enter pots and their movement was tracked from that point on. In 

these cases, the number of crabs in a pot or chamber at any one time was reduced. The laboratory escape 

rate of 54.2% was averaged with the Maryland field escape rate of 14% (Slacum et al. 2009) for an 

overall Chesapeake Bay-wide escape rate of 34.1%.

Table B-5. Blue Crab Escape Rates from Derelict Pots.

Escape

Percent escape of blue 

crabs from pots Experiment Type Reference

45% Field Guillory 1993

56% Field Arcement and Guillory 1993

14% Field Slacum et al. 2009

41% Field Sturvidant et al. 2011

85% Mesocosm Sturvidant et al. 2011

2% (upper chamber only) Mesocosm Sturvidant et al. 2011

64% Field NCDMF 2013 (referencing NCDMF 1993)

55% Field NCDMF 2008

54.2% Mesocosm This Report

34.1%

1 Combined field/mesocosm Chesapeake Bay-wide

1 Average this report and Slacum et al. 2009.

Table B-6. Blue Crab Mortality Rates for Derelict Pots.

Mortality

Crabs per pot over time Percent Reference

20 95% (annual) Slacum et al. 2009 (Maryland)

26 55% (annual) Guillory 1993

26 37% (instantaneous) Bilkovic et al. 2014

31.81 NA Poon 2005

12236% (annual) NCDMF 2013

19 44% (annual) NCDMF 2013

253 82.7% (annual) This Report (Virginia)

234annual This Report Chesapeake Bay-wide

1 Extrapolated from data from Arcement and Guillory (1993).

2 Defined as “legal crabs.”

3 Capture rate 0.178 (65 crabs) x escape rate 54.2% (30.1 crabs retained) x mortality 82.7%.

4 Average of MD mortality (20) and VA mortality (25).
B-8 Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots

The Virginia mortality of 25 crabs per pot per day was averaged with the Maryland mortality rate of 20 

crabs per pot per day (Slacum et al. 2009) for a Chesapeake Bay-wide an average annual mortality of 23 

crabs per derelict pot (Table B-6).

References for Appendix B

Arcement, G., V. Guillory. 1993. Ghost fishing in vented and unvented blue crab traps. Proc. Louisiana 

Acad. Sci. 56: 1-7.

Bilkovic, D.M., K. Havens, D.A. Stanhope, K. Angstadt. 2014. Derelict fishing gear in Chesapeake Bay, 

Virginia: spatial patterns and implications for marine fauna. Mar. Pollut. Bull. 80, 114–123.

Casey, J.F., A.E. Wesche. 1977. A short report on ghost pot fishing. Maryland Department of Natural 

Resources Report. 

Christian, P.A., M.V. Rawson, Jr., T.D. Shierling. 1987. Effectiveness of six trap types and other factors 

for harvesting premolt blue crabs (Callinectes sapidus) in a Georgia tidal creek. N. Am. J. Fish. Mgmt. 7: 

63-70.

Eldridge, P.J., V.G. Burrell, Jr., G. Steele. 1979. Development of a self-culling blue crab pot. Mar. Fish. 

Rev. 41(1): 21-27.

Everett, R. A., G. M. Ruiz. 1993. Coarse woody debris as a refuge from predation in aquatic 

communities: an experimental test. Oecologia 93:475–486.

Guillory, V. 1993. Ghost fishing in blue crab traps. North American Journal of Fisheries Management 

13:459–466.

Guillory, V. 2001. A review of incidental fishing mortalities of blue crabs. Pages 28–41 in V. Guillory, H. 

M. Perry, and S. Vanderkooy, editors. Proceedings of the blue crab mortality symposium. Gulf States 

Marine Fisheries Commission, Ocean Springs, Mississippi.

Guillory, V., A. McMillen-Jackson, L. Hartman, H. Perry, T. Floyd, T. Wagner, and G. Graham. 2001. 

Blue crab derelict traps and trap removal programs. Gulf States Marine Fisheries Commission, Ocean 

Springs, Mississippi.

Haddon, M. 2005. Review of the Chesapeake Bay blue crab (Callinectes sapidus) 2005 stock assessment.

National Oceanic and Atmospheric Administration, Chesapeake Bay Office, Annapolis, Maryland.

Havens, K. J., D.M. Bilkovic, D. Stanhope, K. Angstadt, C. Hershner. 2008. The effects of derelict blue 

crab traps on marine organisms in the lower York River, Virginia. North American Journal of Fisheries 

Management 28:1194–1200.

Kennedy, V. S., M. Oesterling, W. A. Van Engel. 2007. History of blue crab fisheries on the U.S. Atlantic 

and Gulf coasts. Pages 655–709 in V. Kennedy and L. Cronin, editors. The Blue crab: Callinectes 

sapidus. Maryland Sea Grant College, College Park.

McKenna, S., J.T. Camp. 1992. An examination of the blue crab fishery in the Pamlico River estuary. 

Albemarle-Pamlico Estuarine Study Report: 92-08. 101p.

NCDMF. 2008. North Carolina oyster fishery management plan. North Carolina Department of 

Environment and Natural Resources. North Carolina Division of Marine Fisheries. Morehead City, NC. 

282 p.
Appendix B. Capture, Escape, and Mortality Rates in Derelict Blue Crab Pots B-9

NCDMF. 2013. North Carolina oyster fishery management plan. North Carolina Department of 

Environment and Natural Resources. North Carolina Division of Marine Fisheries. Morehead City, NC. 

488 p.

Poon, A. 2005. Haunted waters: an estimate of ghost fishing of crabs and lobsters by traps. Master’s 

thesis. University of British Columbia, Canada.

Rudershausen, P.J., J.E. Hightower. 2016. Retention probability varies with cull ring size in traps fished 

for blue crab. North American Journal of Fisheries Management 36 (1): 122-130.

Savoie, L.B., K.L. Casanova. 1982. A study of areal and seasonal abundance of American eel (Anguilla 

rostrate) at selected sites in southeast coastal Louisiana. Louisiana Department of Wildlife and Fisheries. 

Tech. Bull. 34.

Slacum H.W., Jr., S. Giordano, J. Lazar, D. Bruce, C. Little, D. Levin, H. J. Dew-Baxter, L. Methratta, D. 

Wong, R. Corbin. 2009. Quantifying the effects of derelict fishing gear in the Maryland portion of 

Chesapeake Bay. Prepared for the NOAA Marine Debris Program. July 2009.

Smith, L.D., A.H. Hines. 1991. Autotomy in blue crab (Callinectes sapidus Rathbun) populations: 

geographic, temporal, and ontogenetic variation. Biol. Bull. 180:416-431.

Stagg, C., M. Whilden. 1997. The h stor of Chesapeake Ba ’s bl e crab (Callinectes sapidus): fisheries 

and management. Investigaciones Marinas Universidad Catolica de Valparaı ́so 25:93–104.

Sturdivant, K.S., K.L. Clark. 2011. An evaluation of the effects of blue crab (Callinectes sapidus) 

behavior on the efficacy of crab pots as a tool for estimating population abundance. Fish. Bull. 109: 48-

55.

Uhlmann, S. S., Broadhurst, M. K. 2015. Mitigating unaccounted fishing mortality from gillnets and 

traps. Fish and Fisheries 16: 183–229.

Van Engel, W. A. 1982. Blue crab mortalities associated with pesticides, herbicides, temperature, salinity, 

and dissolved oxygen. Pages 187–194 in H. M. Perry and W. A. Van Engel, editors. Proceedings blue 

crab colloquium. Gulf States Marine Fisheries Commission, Publication 7, Ocean Springs, Mississippi.

Whitaker, D. 1979. Abandoned crab trap study. South Carolina Wildlife and Marine Resources Report, 

Columbia.

Appendix C. Data Requirements, Inventory, Compilation, and Preparation C-1

Appendix C. Data Requirements, Inventory, 

Compilation, and Preparation

C.1 Data Requirements

The effects of derelict crab pots on blue crab, other bycatch, and habitats will vary depending on the 

distribution and densities of pots throughout the Chesapeake Bay. Research on derelict pots in both the 

Maryland and Virginia portions of the Bay suggests a number of factors contribute to derelict pot

distribution and densities (Bilkovic et al. 2014; Slacum et al. 2009). The interaction between crabbing 

effort and boating activity are two of the factors suspected to contribute to pot loss; however other 

variables such as location and storm events will also modify the distribution and densities of derelict pots.

A critical first step to assess the ecological and economic effects of derelict pots is to identify and 

evaluate all the factors expected to contribute to pot loss and determine the amount of influence that each 

factor contributes to the effects of derelict pots. A list of variables expected to contribute to the 

distribution, densities, and effects of derelict pots was developed through a review of derelict pot research 

in the Chesapeake Bay, other literature, and expert opinion (Table C-1). Variables listed in Table C-1

were also assumed to be common factors influencing derelict pot distribution, densities, and effects in 

other regions outside of the Chesapeake Bay. A conceptual model depicting these variables is presented in 

Figure C-1.

Table C-1. Variables Associated with the Distribution, Densities, and Effects of 

derelict crab pots in the Chesapeake Bay. 

Response variables are metrics describing the distribution, densities, and effects of derelict 

pots. Covariates are variables that influence the magnitude of the response variables.

Variable Type Variable

Response variable

Distribution of derelict crab pots (#/km2)

Blue crab catch (kg/km2)

Other bycatch species (kg/km2)

Commercial blue crab harvest

Covariate

Boating activity

Commercial crabbing effort

Commercial harvest of finfish

# of licensed fishers

Geographic location

Depth

Time (year, month, season)

Storm events

Submerged Aquatic Vegetation
C-2 Appendix C. Data Requirements, Inventory, Compilation, and Preparation

Figure C-1. Draft conceptual Framework of the distribution, densities, and effects of derelict crab pots in the 

Chesapeake Bay and how this framework can be used to inform a Derelict Fishing Gear Management 

Framework. 

C.2 Data Inventory 

An inventory of data was conducted to identify data sets that were readily available and to determine if 

data gaps existed for data considered crucial to complete the ecological and economic impact analysis.

The inventory process also considered whether data were specific to the Chesapeake Bay or if the data 

were common to other regions and would be helpful for developing the generalized framework. Important 

factors considered for the data inventory were:

 Do data exist for each variable, 

 What is the spatial extent of existing data, 

 Where do the data reside, 

 What data do exist, 

 Are there data gaps and can those data be generated?

A description of each data type is listed below; while all presented inventoried data were considered for 

the assessment, some data had spatial limitations or other incompatibilities that precluded their synthesis 

into the final assessment. Table C-2 highlights key data used in the final assessment.

Table C-2. Data types used to evaluate the ecological and economic effects of derelict crab pots in the 

Chesapeake Bay. 

Data Type

Assessment 

Category

File 

Type Source

Metadata 

Location

Crab pot distribution in MD Derelict crab pot

Distribution

GIS Versar GST 

Crab pot distribution in VA GIS Versar, VIMS GST 
Appendix C. Data Requirements, Inventory, Compilation, and Preparation C-3

Table C-2. Data types used to evaluate the ecological and economic effects of derelict crab pots in the 

Chesapeake Bay. 

Derelict crab pot distribution: MD GIS Versar GST

Derelict crab pot distribution: VA GIS VIMS GST

Effects of derelict crab pots to blue 

crab and bycatch

Target and nontarget Bycatch GIS VIMS, Versar GST

Effect of derelict crab pots on 

commercial blue crab harvest Harvest GIS VIMS GST

Bay-wide SAV distribution 

(nursery habitats for economically 

important fisheries)

Habitat GIS VIMS website

Chesapeake Bay Bathymetry Derelict crab pot 

Distribution GIS Chesapeake Bay Program website

Recreational and commercial vessel 

activity

Derelict crab pot 

Distribution

(Vari

ous)

VIMS, VMRC, 

Versar; AIS from 

Bureau of Ocean 

Energy Mgmt. 

(BOEM), NOAA.

GST

Fisheries catch / landings data for 

Croaker, White Perch Bycatch GIS VMRC, MDNR GST

Dredge survey data for MD and VA 

(to obtain spawning female crab 

density estimates)

Bycatch Database Chesapeake Bay Pgm. report

Oyster beds Habitat GIS MDNR GST

Note: Metadata files maintained by GST may be accessed via https://goo.gl/u6ykoA.

C.2.1 Chesapeake Bay Derelict Crab Pot Data

Distribution of Derelict Crab Pots in Maryland- The densities and distribution of derelict crab pots in 

Maryland were estimated based on a stratified random transect sonar survey conducted by Versar and the 

NOAA Chesapeake Bay office in 2007. Instantaneous derelict pot densities (pots/km2) were calculated 

based on counts of derelict pots identified in side-scan sonar imagery. Derelict pot densities and 

distribution were evaluated for several habitat variables. Additional information on the condition, 

location, depth, buoy status, and bycatch was also documented through ground-truthing.

Distribution of Derelict Crab Pots in Virginia- The densities and distribution of derelict crab pots in 

Virginia were estimated based on temporal and spatial data provided by four years of derelict pot surveys 

and removal efforts which provided data on (1) mean annual survey area covered, (2) mean annual 

number of crab pots retrieved per km2, and number of crab pots retrieved in shallow (≤2m) and deep 

(>2m) waters. NOAA bathymetric depth contours were used to quantify the number of crab pots within 

the different contour depths. Additional information on the condition, location, buoy status, functionality,

and bycatch for every pot recovered (~34,000) was documented.

Effects of Derelict Crab Pots in Mesohaline portion of Chesapeake Bay- The effect of derelict crab 

pots on blue crab and other by-catch was determined through and 14-month simulated study conducted by 

Versar and the NOAA Chesapeake Bay office between 2006 and 2008. Study results provided data on the 

types and amount of species caught and killed in derelict pots. In addition, this study provided 

information on seasonal fluctuations in catch rates for derelict pots as well as escapement rates and pot

degradation.
C-4 Appendix C. Data Requirements, Inventory, Compilation, and Preparation

Effects of Derelict Crab Pots in Lower portion of the Chesapeake Bay- The effect of derelict crab 

pots on blue crab and other by-catch was determined from catch data obtained from the 6 year pot

removal effort (2008-2014) and simulated derelict pot studies conducted from 2005 – 2007 and 2010. The 

results of the studies provided data on the types and amounts of species caught and killed in derelict pots 

as well as escapement rates and pot degradation. Because derelict pots were recovered during cold winter 

months in Virginia in the 6 year pot removal project, the number and abundance of species captured and 

reported from that project are likely underestimates of the annual loss of marine fauna to derelict pots. To 

provide additional information on seasonal variability of catch, five commercial watermen recorded

species captured in simulated derelict pots for comparison in catch to their regular fishing activities 

throughout the fishing season 2015 (Appendix B).

Observed Blue Crab Escapement Rates in Derelict Crab Pots- When a derelict pot is recovered any 

bycatch present represents an instantaneous catch rate, meaning that instance those animals were caught. 

However, some animals may move in and out of pots while others will perish. A mesocosm study was 

conducted in 2015 using the VIMS state-of-the-art seawater laboratory to allow for replicate sampling and 

observation of crab movement within pots and likelihood of escape estimates (Appendix B).

Distribution of Derelict Pot Hotspots in Virginia Portion of the Chesapeake Bay – Using four years 

of derelict pot removal data in Virginia, high and low density areas of derelict crab pots were determined 

with a kernel density estimator in conjunction with ArcGIS 9.3 to spatially display the data on the basis of 

equal interval quantiles (excluding zeroes) to depict relatively high and low density values. The area of 

the highest densities (hotspots) of pots was calculated from density data in the uppermost quantile of the 

distribution. High density (15–311 pots/km2) clusters of pots were identified from the kernel density 

analysis over 562 km2of Virginia waters (18% of the area surveyed). The locations within geographic 

regions with the strongest concentration (hotspots) of crab pots were surrounding Tangier Island, Little 

Wicomico River, lower York River, Mobjack Bay, Eastern Shore and Seaside tidal creeks, and Pocomoke 

Sound.

Distribution of Derelict Pot Hot-Spots in Maryland Portion of the Chesapeake Bay- This dataset is 

comprised of information collected during 48 marine debris clean up events that occurred in 2010 and 

2012. Clean up events were conducted by Maryland watermen in the locations predicted to have high 

densities of derelict pots throughout the Maryland portion of the Chesapeake Bay. Data includes general 

locations of all marine debris (including derelict pots), type of debris, condition of debris, bycatch 

associated with derelict pots, and other variables.

Watermen Estimated Blue Crab Pot Losses in Virginia- Watermen reports (watermen participants (n = 

56) for three consecutive years (2009–2011) and a 5-year (2005-2009) field survey in one tidal creek 

suggest that annual pot loss rates are 20% of fished pots on average. To augment these data, five 

watermen conducted removal efforts in ten tidal creeks (5 paired creeks with low and high crabbing effort 

in 5 regions of Virginia) during the winter of 2014. During the fishing season they periodically surveyed 

the number of active pots in these creek systems. In the winter of 2015 they returned to the creeks for an 

additional removal effort to help refine the pot loss rate estimates. A map of field work locations is

located in Appendix A.

Watermen Estimated Blue Crab Pot Losses in Maryland- Conversations with Maryland watermen in 

the winter and spring of 2015 provided background information on Maryland fishing practices by region 

including average loss rate of crab pots per waterman, the total number of derelict pots removed by 

watermen, and the total number of crab pots present. This information served in ground-truthing the 

modeling efforts and in comparing the Maryland and Virginia fisheries. These conversations also give 

insight to the potential sources of derelict pots in different geographic regions of the Chesapeake Bay; in 

particular they suggest that an average pot loss for watermen ranges between 1.5% and 10% of total gear 

in the summer and fall. 90% of the watermen participating in these conversations indicated that 
Appendix C. Data Requirements, Inventory, Compilation, and Preparation C-5

recreational boater traffic was the chief cause of pot loss, with theft as the number two cause. The 

template for these conversations may be found in Appendix F.

C.2.2 Chesapeake Bay Commercial Blue Crab Fishery

Distribution of Commercial Blue Crab Effort in Maryland- A multiyear (2007-2012) stratified 

random transect survey of commercial crabbing effort was conducted by Versar in Maryland to provide 

spatially explicit counts of actively fishing blue crab pots that is used to estimate blue crab fishing effort 

in the Maryland portion of the Chesapeake Bay.

Distribution of Commercial Blue Crab Effort in Virginia- A one year (2010) survey of commercial 

crabbing effort was conducted by Versar in Virginia to provide spatially explicit counts of actively fishing 

blue crab pots that is used to estimate blue crab fishing effort in the Virginia portion of the Chesapeake 

Bay.

Reported Blue Crab Harvest Details in Virginia- Reported commercial crabbing effort and harvest for 

the timeframe between 1994 and 2014 were provided by the Virginia Marine Resources Commission. The 

Virginia Marine Resources Commission (VMRC) requires fishermen to submit weekly reports that

specify total pots (and other gear) fished, their location, and pounds of blue crab harvested. From these 

weekly reports, aggregate annual data on area-specific harvest and potting effort from 1994-2014 for 43 

unique management areas and 11 area-aggregates were obtained. 

Reported Blue Crab Harvest Details in Maryland- Reported commercial crabbing effort and harvest 

for the timeframe between 1994 and 2014 were provided by the Maryland Department of Natural 

Resources (DNR) Fisheries Division. The MD DNR Fisheries Division requires fishermen to submit 

monthly reports that specify total pots (and other gear) fished, their location, and pounds of blue crab 

harvested. From these monthly reports, aggregate annual data on area-specific harvest and crab potting 

effort from 1994-2014 were obtained. 

C.2.3 Chesapeake Bay Commercial and Recreational Vessel Traffic

Distribution of Piers and Boat Ramps in the Chesapeake Bay- Chesapeake Bay shoreline inventory 

data were provided by CCRM-VIMS. These data include spatially-explicit information on shoreline 

structures (riprap, bulkhead, piers, boat ramps, marinas), riparian land use, and bank condition for the 

tidal shorelines of the Chesapeake Bay. Virginia data date from June 2014 and include updated county 

shorelines in VA that were inventoried recently. This shoreline is always being updated and corrected 

when possible, but is currently the most up to date. Maryland inventories were primarily conducted in 

2002-2003. These inventories are a baseline dataset used in the Environmental Sensitivity Index (ESI) 

used by the state.

Recreational boating hotspots - The locations of shoreline structures provided some ability to predict 

recreational boating density; but for a more reliable picture of recreational boating patterns we used two 

maps showing areas of high recreational boating activity: one for Maryland from a previous study, and 

the other compiled in collaboration with the VMRC Patrol Officers. Both of these are qualitative / binary 

maps (“high traffic” vs. “not”) based on local knowledge of Chesapeake recreational boating traffic 

patterns.

US Coast Guard Automated Identification System (AIS) data for commercial vessels - A year’s 

worth of “pings” from transponder-equipped vessels provided a detailed picture of larger commercial 

vessels traveling through the Bay. We filtered these to include only vehicles in motion; and aggregated 

them by computing their density in each 1x1km grid cell of our modeling framework.
C-6 Appendix C. Data Requirements, Inventory, Compilation, and Preparation

C.2.4 Bycatch Species

Distribution and Abundance of Terrapin Turtles in Virginia-Terrapin distribution in Virginia was 

determined using field surveys and occupancy modeling approach. Repeat surveys were conducted at 165 

sites 3 times over the course of the summers of 2012 and 2013. Key terrestrial and aquatic variables 

identified that explaining heterogeneity in terrapin occupancy were agriculture, low-urban development, 

shoreline armoring, derelict crab pot density, active crabbing pressure, and marsh area. These variables 

were used in a spatially applied model that predicted terrapin distribution throughout Virginia. Data 

outputs include the terrapin presence locations, and maps of the probability of occupancy throughout 

Virginia. 

Distribution and Abundance of Terrapin Turtles in Maryland-This survey by USGS Patuxent 

Wildlife Research Center was conducted to assess the distribution of terrapins in Maryland, Chesapeake 

Bay, based on evidence related to nesting. They conducted a survey of the beaches during the nesting 

season in the summer of 2002. They walked along the shoreline of over 1,350 beach segments looking for 

evidence signifying the presence of terrapins based on nesting activity. These results represent a singleseason snapshot of conditions during the surveys and at the locations visited during that season; it should 

not be assumed that this is representative of terrapin nest locations and numbers today. 

Reported Commercial Finfish Harvest Details - Reported commercial fishing effort and harvest for the 

timeframe between 1994 and 2014 were obtained from the Maryland Department of Natural Resources 

Fisheries Division and the Virginia Marine Resource Commission. Data set variables included the 

location and pounds of species-specific harvest. We requested aggregate annual data on area-specific 

harvest for MD DNR management areas in Maryland, and for VMRC management areas in Virginia. 

Bycatch species of interest included Atlantic croaker and white perch.

C.2.5 Habitat

Chesapeake Bay Bathymetry- This dataset was created as a byproduct of the Chesapeake Bay Program's 

submerged aquatic vegetation (SAV) restoration goals. The bathymetric soundings were interpolated to 

support the development of the SAV Tier goals. The resulting interpolation was used to create the one 

meter low water contours for the mainstem of the Chesapeake Bay. NOAA NOS produced the dataset.

Submerged Aquatic Vegetation Distribution-Chesapeake Bay SAV data were mapped annually from 

aerial photography, primarily at a scale of 1:24,000 (methodology is described in each annual report - e.g. 

see Orth et al. 2013; http://web.vims.edu/bio/sav/sav13). Data were collected by the Virginia Institute of 

Marine Science. A ten-year composite SAV dataset covering the years 2003-2012 was created by CCRMVIMS. These data were used to evaluate the overlap of sensitive habitats with derelict gear.

Distribution of Natural Oyster Bars- This data layer consists of compilation of several historic habitat 

datasets in Maryland and Virginia with some modifications. For Maryland, these historic layers include 

the Yates Survey, the Maryland Bay Bottom Survey, DNR repletion sites, Maryland leased bars, and 

sanctuaries and reserves. For Virginia, these layers included Virginia leased bars and sites identified as 

potential areas for oyster restoration. Details on how these layers were compiled are given by Greenhawk 

(2005). The cultch area data set was created for use by DNR scientists, managers, and modelers involved 

in work related to the preparation of an environmental impact statement entitled ‘Development of an 

Environmental Impact Statement for Introducing Non-Native Oyster Species into the Chesapeake Bay, 

Including an Evaluation of Native Oyster Restoration Alternatives. 

Greenhawk, K. 2005. Development of a Potential Habitat Layer for Maryland Oyster Bottom, 

Chesapeake_Bay_habitat. Maryland Department of Natural Resources, Fisheries Division.
Appendix C. Data Requirements, Inventory, Compilation, and Preparation C-7

C.2.6 Storm Events

Some anecdotal evidence exists, indicating pots loss due to high winds, storm surges, or increased debris 

(H. Ward Slacum personal communication). However, conversations with watermen (see Appendix F) 

indicated little to no pot loss by storms.

C.3 Data Compilation

A comprehensive set of metadata was developed for all data sets originating from project team members.

The metadata format was standardized to include a set of common descriptors used to describe the source 

of each data set, methods used to derive or collect data, data creation date, data type, and file types.

Additional data details were provided in abstracts included in the metadata file. Existing metadata from 

requested datasets and data sets without metadata were reformatted into the established project metadata 

format. All project data files and metadata were stored at a centralized GST ftp site for common access by 

project team collaborators. 

Among these datasets include a variety of geospatial files that were compiled into an ESRI ArcGIS file 

geodatabase for assessment purposes. This includes data compiled from derelict pot research previously 

conducted within the Chesapeake Bay.

C.4 Data Evaluation and Standardization

Many of the variables required for the derelict crab pot ecologic and economic evaluation consisted of 

data collected during different time periods and in different habitats throughout the Chesapeake Bay.

Previous work to evaluate derelict crab pots in Maryland and Virginia had similar goals, but often 

employed different survey approaches or methods, or covered different timeframes. Other source data had 

similar mismatches. In addition, all compiled data sets were in different file formats ranging from Excel 

spreadsheets to raster grids to Geographic Information System (GIS) point, line, and polygon shapefiles. 

Therefore, a thorough metadata review of all compiled data sets was conducted to determine the 

objectives of data collection, the methods that were used, and the types of variables (data) that were 

derived. The goal of the review was to evaluate the overall use of each data set, its connectivity to other 

data sets, and determine if any limitations existed for the use of each data set in future analysis.

Appendix D. Blue Crab Management in Virginia and Maryland D-1

Appendix D. Blue Crab Management in Virginia 

and Maryland

D.1 Virginia’s 21-Point Blue Crab Management Plan 

October 1994, the Commission established the following 7-point blue crab management plan:

• Expanded the spawning sanctuary (146 sq. mi.) establish in 1942 by 75 sq. mi., with no crab 

harvest allowed from June 1 through September 15.

• Established a 14,500-acre winter-dredge sanctuary in Hampton Roads.

• Shortened the crab pot season to April 1 through November 30.

• Required two cull (escape) rings in each commercial and recreational crab pot.

• Required four cull rings in each peeler pound that allows escapement of small peeler crabs.

• Capped the number of peeler pots per license to prevent expansion of the fishery.

• Limited the crab dredge size to 8 feet to prevent increases in effort.

The Commission reinforced the 7-point management plan in January 1996.

• Prohibited the possession of dark-colored (brown through black) sponge crabs (adult female hard 

crab which had extruded her eggs on her abdomen), with a 10-sponge crab per bushel tolerance.

• Limited license sales of hard crab licenses, based on previous eligibility or exemption 

requirements.

• Established a 300-hard crab pot limit for all Virginia tributaries of the mainstem Chesapeake Bay. 

Other Virginia harvest areas were limited to a 500-hard crab pot limit.

• Established a 3 1/2-inch minimum possession size limit for all soft shell crabs.

Concerns over excess effort in the fisheries and a persistent trend of low spawning stock biomass 

during most of the 1990s led to additional crab conservation measures in 1999 and 2000.

• Lowered the maximum limit on peeler pots from 400 to 300 pots in 1999. Harvest by this gear 

type increased by 90%, from 1994 through 1998, while the overall harvest remained relatively 

static.

• Initiated a moratorium on additional commercial licenses for all commercial crabbing gear. This 

moratorium became effective May 26, 1999 and continued until May 26, 2004.

• Established (in 2000) a Virginia Bay-wide Blue Crab Spawning Sanctuary, in effect June 1 

through September 15. This additional sanctuary (435 sq. mil) allows for increased spawning 

potential.

A cooperative Bay-wide agreement (October 2000) to reduce harvest 15% by 2003 led to new 

measures.

• Enacted an 8-hour workday for commercial crabbers (2002) that replaced Wednesday closures of 

2001.

• Established a 3-inch minimum size limit for peeler crabs (2002).

• Reduced peeler pot limits from 400 to 300 pots (for 2001).

• Reduced the winter dredge fishery limit from 20 to 17 barrels (2001).

• Augmented (2002) the Virginia Blue Crab Sanctuary by 272 sq. mi. (total sanctuary area = 928 

sq. mi.).

• Reduced unlicensed recreational harvester limits to 1 bushel of hard crabs, 2 dozen peelers 

(2002).
D-2 Appendix D. Blue Crab Management in Virginia and Maryland

• Reduced licensed recreational harvester limits to 1 bushel of hard crabs, 2 dozen peelers, with 

vessel limit equal to number of crabbers on board multiplied by personal limits (2001).

2008

• Larger cull ring (2-5/16”) required to be open at all times in all tidal VA waters to promote 

additional increases in escapement.

• Peeler crab minimum size limit increased from 3” to 3 1⁄4” (through July 15) and to 3 1⁄2” (as of 

July 16).

• Use of agents modified to prevent license “stacking” and to curtail use of agents.

• Winter dredge fishery capped at 53 licensees (from previous 225 licensees), all being active 

harvesters in previous two winter seasons.

• Adopted an extended closure (May 1 - September 15) of blue crab spawning sanctuary, to protect 

spawning females, except for the historical sanctuary (146 square miles) managed by law.

• Established a fall closure for female harvest (October 27 – November 30).

• Implemented a 15% reduction in pots per individual for 2008 crab pot fishery and a 30% 

reduction for 2009 crab pot and peeler pot fishery.

• Closed 2008/09 winter dredge fishery season.

• Required use of two 3/8” cull rings for all areas (except Seaside of Eastern Shore) effective July 

1.

• Eliminated 5-crab pot recreational license.

• Revamped revocation procedures, to allow a hearing after just two crab violations in a 12-month 

period.

• In an attempt to address the latent effort, the Commission placed crab pot and peeler pot 

fishermen who had been inactive (no harvest) for a 4-year period (2004-07) on a waiting list until 

the abundance determined from the Bay-wide Winter Dredge Survey of age-1+ crabs exceeds the 

interim target of 200 million.

2009

• Shortened closed season for female crabs to November 21 - November 30.

• Closed 2009/10 winter dredge fishery season.

• Lowered percentage reduction of crab pots from 30% (2008) to 15% (2009).

• Reestablished 5-pot recreational crab pot license but prohibited harvest on Sunday and from Sept 

16 - May 31.

• Right to hold revocation hearing for crab licensee after two crab violations by authorized agent 

(agents cannot be licensed for any crab fishing gear).

• Regulation tolerance of 10 per bushel (Previously March 17 – July 15).

2010

• Made it unlawful (from March 17 - June 30) to possess dark sponge crabs exceeding regulation 

tolerance of 10 per bushel (Previously March 17 – July 15).

• Made it lawful (indefinitely) that commercial licenses (crab/peeler pot, scrape, trap, 

ordinary/patent trot line, dip net) shall be sold only to commercial fishermen eligible in 2010, 

except those placed on the waiting list established in November 2007.

• Closed 2010/11 winter dredging fishery season.

2011

• Changed closed season on harvest from Virginia Blue Crab Sanctuaries from May 16 to May 1.

• Changed boundary line of Blue Crab Sanctuary in upper Bay near Smith Point Light.
Appendix D. Blue Crab Management in Virginia and Maryland D-3

• Closed 2011/12 winter dredging fishery season.

• Established 5-day maximum tending requirement for crab pots and peeler pots.

2012

• Closed 2012/13 winter dredge fishery season.

• Funded the Winter Dredge Gear Study using Marine Fishing Improvement Funds.

• Extended the 2012 season until December 15, 2012 for both male and female crabs and applied 

conservation equivalent bushel limits to the 2013 crab pot season by gear license categories as 

follows:

o For up to 85 crab pots a maximum limit of 27 bushels.

o For up to 127 crab pots a maximum limit of 32 bushels.

o For up to 170 crab pots a maximum limit of 38 bushels.

o For up to 255 crab pots a maximum limit of 45 bushels.

o For up to 425 crab pots a maximum limit of 55 bushels.

o Restricted crabbing in the Virginia portion of the Albermarle and Currituck watersheds to 

crab pots and peeler pots only.

2013

• Established a vessel harvest and possession limit equal to only one of the largest legal bushel 

limits on board any vessel.

• Limited the use of agents in the hard pot fishery to 168, with priority going to those licensees who 

received approval for agent use in 2012.

• Established daily individual and vessel harvest and possession limits for the 2013 season.

• Closed 2013/14 winter dredge fishery season.

• Results of the Winter Dredge Mortality Project were presented.

• Extended the 2013 season until December 15, 2013 for both male and female crabs and applied 

conservation equivalent bushel limits to the 2013 season extension and the 2014 crab pot season 

by gear license categories as follows:

o For up to 85 crab pots a maximum limit of 16 bushels.

o For up to 127 crab pots a maximum limit of 21 bushels.

o For up to 170 crab pots a maximum limit of 27 bushels.

o For up to 255 crab pots a maximum limit of 43 bushels.

o For up to 425 crab pots a maximum limit of 55 bushels.

• Established the 2014 crab pot season as March 17 through November 30, 2014 for both male and 

female blue crabs.

• Established a declaration date for agent use requirements in the crab pot fishery for the 2014 

season.

2014

• Closed the 2014/15 winter dredge fishery season.

• Enacted management reductions in response to the current scientific determination that the 

Chesapeake Bay blue crab abundance of spawning-age female crabs is depleted. The basis for 

this 10 percent reduction, which equals a potential savings of 1,316,726 pounds of female blue 

crab, is to augment spawning in summer 2014 and spring 2015 and help reverse the depleted 

stock condition of blue crab.

• From July 5, 2014 through November 15, 2014 and April 1, 2015 through July 4, 2015

o 10 bushels, or 3 barrels and 1 bushel, of crabs, if licensed for up to 85 crab pots.

o 14 bushels, or 4 barrels and 2 bushels, of crabs, if licensed for up to 127 crab pots.
D-4 Appendix D. Blue Crab Management in Virginia and Maryland

o 18 bushels, or 6 barrels, of crabs, if licensed for up to 170 crab pots.

o 29 bushels, or 9 barrels and 2 bushels, of crabs, if licensed for up to 255 crab pots.

o 47 bushels, or 15 barrels and 2 bushels, of crabs, if licensed for up to 425 crab pots.

• From November 16, 2014 through November 30, 2014 and March 17, 2015 through March 31, 

2015.

o 8 bushels, or 2 barrels and 2 bushels, of crabs, if licensed for up to 85 crab pots.

o 10 bushels, or 3 barrels and 1 bushel, of crabs, if licensed for up to 127 crab pots.

o 13 bushels, or 4 barrels and 1 bushel, of crabs, if licensed for up to 170 crab pots.

o 21 bushels, or 7 barrels of crabs, if licensed for up to 255 crab pots.

o 27 bushels, or 9 barrels of crabs, if licensed for up to 425 crab pots.

• The lawful season for the commercial harvest of blue crabs by all other commercial gears shall be 

March 17, 2014 through September 15, 2014 and May 1, 2015 through November 30, 2015. It 

shall be unlawful to place, set, fish or leave any lawful commercial gear used to harvest crabs, 

except crab pots, in any tidal waters of Virginia from September 16, 2014 through April 30, 2015.

2015 

• Maintained and modified measures to conserve and allow rebuilding of the Blue Crab Resource 

Maintained previous crab management season and bushel limits. 

• Adjusted closure dates for non-crab pot gear season, closing September 26 and reopening April 

21.

• Made it unlawful for any vessel to act as both a crab harvester and a crab buyer on the same trip.

• Made it unlawful for any person to possess dark sponge crabs from March 17 through June 15.

• Redefined Virginia Blue Crab Sanctuary Area 1 as Virginia Blue Crab Sanctuary Area 1A and 

Blue Crab Sanctuary Area 1B and implement separate closure dates for Blue Crab Sanctuary 

Areas 1A, 1B and Areas 2 through 4.

• Closed the winter crab dredge fishery season from December 1, 2015 through March 31, 2016. 

D.2 Significant Regulatory Changes in Maryland Blue Crab 

Fishery between 2008 and 2015

Table D-1 below lists the regulations imposed on the Maryland blue crab fishery in 2008-2015. This 

information was modified from a table included in Slacum et al. 2012 and information posted on the 

Maryland Department of Natural Resources website. Additional details are still being gathered.

Table D-1. Regulations Governing the Maryland Blue Crab Fishery in 2008-2015.

Year Regulations Implemented to Reduce Female Harvest

2008

 Restricted participation in the fall female fishery to only those waterman with history in 

this portion of the fishery since 2004

 Those participants permitted to harvest females during the fall were given daily bushel 

limits based on their harvest history. Bushel limits ranged from 5 to 50 per day

 Closed to female harvest on 10/23 (Formerly 12/15)

 Banned recreational harvest of females

2009  Replaced limited access to fall female fishery with daily bushel limits spanning the entire 

crabbing season.
Appendix D. Blue Crab Management in Virginia and Maryland D-5

Table D-1. Regulations Governing the Maryland Blue Crab Fishery in 2008-2015.

 Implemented periodic closures to commercial female harvest

 Closures: 6/01-6/15, 9/29-10/04, Closed to female harvest on 11/10

 Daily bushel limits ranged from 2 to 45 depending on date and license type

2010  Implemented periodic closures to commercial female harvest

 Closures: 6/01-6/15, Closed to female harvest on 11/10

2011

 Implemented periodic closures to commercial female harvest

 Closures: Closed to female harvest 6/01-6/14, Closed to female harvest on 11/11

 Daily bushel limits ranged from 2 to 54 depending on date and license type

2013  Female limits provided by public notice.

2014  Female limits provided by public notice.

2015  Female limits provided by public notice.

Appendix E. Derelict Fishing Gear Outreach Activities and Presentations E-1

Appendix E. Derelict Fishing Gear Outreach 

Activities and Presentations

2014

November 7th– Crestwood Elementary School (Richmond, VA), VIMS presentation.

November 14th– VIMS briefing for Virginia Secretary of Commerce and Trade Maurice Jones.

November 17th– Smithsonian Estuarine Research Center watermen meeting (Virginia/Maryland).

2015

January 14th– Association of General Contractors, VIMS presentation.

January 16th– VIMS briefing for US Congressman Wittman.

January 28th– VIMS/W&M 75th Anniversary, VIMS presentation.

March 20th– VIMS briefing for Virginia Marine Resources Commissioner John Bull and VMRC 

Fisheries Chief Rob O’Reilly.

March 23rd- VIMS participation in Virginia Marine Debris Reduction Plan meeting (Richmond, VA).

March 31st- Point O’ View Elementary School (Virginia Beach, VA), VIMS presentation.

April 16th– Longwood University (Farmville, VA), VIMS presentation.

April 19th- NC Coastal Federation meeting (Manteo, NC), VIMS presentation.

May 13th– Science Under Sail Event (Yorktown, VA), VIMS presentation.

May 22nd– North American Association of Fisheries Economists 8th Biennial Forum, VIMS presentation.

May 30th– Marine Science Day (Virginia Institute of Marine Science), VIMS presentation.

June 23rd– 25th– NOAA Marine Debris Reduction Plan Workshop, VIMS presentation.

July 15th– Aqua KidsTM, VIMS presentation.

July 22nd- Passage Middle School (Newport News, VA), VIMS presentation.

August 5th- Middle Peninsula Governor’s School (Middlesex, VA), VIMS presentation.

September 10th–Virginia House of Delegates Subcommittee on Natural Resources, Agriculture, 

Chesapeake Bay, VIMS presentation.

September 14th- VIMS briefing NOAA Marine Debris Chief Scientist Amy Uhrin.

September 15th- RILL Lifelong Learning, VIMS presentation.

October 8th– VIMS briefing for Preston Bryant (former Virginia Secretary of Natural Resources) and Jeff 

Corbin (Senior Advisor to the EPA Administrator for the Chesapeake Bay).

October 13th– A Healthy Bay for Healthy Kids: Cooking with the First Lady event. First Lady Dorothy 

McAuliffe, VIMS presentation.

October 18th– Historic Rosewell Event (Rosewell, VA), VIMS presentation.

November 3rd– Guest lecture in undergraduate marine science course at the College of William & Mary, 

VIMS presentation.
E-2 Appendix E. Derelict Fishing Gear Outreach Activities and Presentations

November 6th– 5

th grade Crestwood Elementary, VIMS presentation

2016

January 7th– Chesapeake Bay Commission, STAC/VIMS presentation.

February 9th– Radio interview, St. John’s Fisheries Broadcast, VIMS.

February 18th– Guest lecture in undergraduate remote sensing course at the College of William & Mary, 

VIMS presentation.

March 7th-9

th

– Virginia Marine Debris Summit, VIMS presentation.

March 22nd– Center for Natural Resource Economics & Policy Conference, VIMS presentation.

April 8th– Virginia Environmental Health Association, VIMS presentation.

April 11th– Abingdon Ruritan Club, VIMS presentation.

April 14th– College of William & Mary Center for Geospatial Analysis, VIMS presentation

May 6th– VIMS 75th Gala Event, VIMS presentation.

May 21st– Marine Science Day, VIMS presentation.

June 13th– Indian Creek Yacht Club, VIMS presentation.

July 8th- US Department of State, Washington DC Foreign Press Center, journalists from Chile, Congo, 

Czech Republic, Germany, Romania, Slovakia, Ukraine, Vietnam, Europe, VIMS presentation.
Appendix F. Questions used for Watermen Conversations in Maryland F-1

Appendix F. Questions Used for Watermen 

Conversations in Maryland

Q1 Did you obtain a pot license last crabbing season? A: Yes B: No

Did you fish crab pots last crabbing season? A: Yes B: No

Q2 Where did you crab in the most last crabbing season?

(Please choose one area from map) A B C D E F G

Q3 Do you use single pot buoys or use flagged buoys (multiple crab pots 

attached to a line with flagged buoys on each end)?

A: Single pot buoys only

B: Mix of both

C: Only flagged buoys

If you use a mix of both, what percentage of your pots use flagged 

buoys? (Please choose the closest response)

A: Around 25%

B: Around 50%

C: Around 75%

Q4 Do you fish with hard crab pots, peeler pots, or both?

A: Hard crab pots only

B: Peeler pots only

C: Both

If both, what is the proportion of peeler pots to total pots? (Please choose 

the closest response)

A: Around 25%

B: Around 50%

C: Around 75%

Q5 What was the maximum number of pots you had in the water during the 

spring (March, April, and May)?

A: None

B: 1-50

C: 51-100

D: 101-200

E: 201-300

G: 401-500

H: 501-600

I: 601-700

J: 701-800

K: 801-900
F-2 Appendix F. Questions used for Watermen Conversations in Maryland

F: 301-400 L: 901+

What percentage of your pots was lost last? (Please write in) %

Q6 What was the maximum number of pots you had in the water during the 

summer (June, July, and August)?

A: None

B: 1-50

C: 51-100

D: 101-200

E: 201-300

F: 301-400

G: 401-500

H: 501-600

I: 601-700

J: 701-800

K: 801-900

L: 901+

What percentage of your pots was lost? (Please write in) %

Q7 What was the maximum number of pots you had in the water during the 

fall (September, October, and November)?

A: None

B: 1-50

C: 51-100

D: 101-200

E: 201-300

F: 301-400

G: 401-500

H: 501-600

I: 601-700

J: 701-800

K: 801-900

L: 901+

What percentage of your pots was lost? (Please write in) %

Q8 What practices do you use to reduce pot loss?

Q9 What are your thoughts on pot loss?

Q10 How do you prepare annually for pot loss?

Q11 Are there any specific days or events when pot loss is greater? This 

might include holidays or particular weekdays.

Q12 How do you prepare for high pot loss events such as boat traffic or storm 

events?

Q13 Where do you get information about potential high pot loss events?

Q14 In your fishing area what contributes to the greatest pot loss?

A: Recreational boat traffic

B: Shipping traffic

C: Storm events

D: Debris

E: Vandalism

F: Other (please fill in)

Q15 Do you avoid fishing in areas with lots of lost pots?

Q16 What would you suggest to reduce pot loss?

(Please write in)

Q17 Did you retrieve any lost pots last year? A: Yes

B: No

If you did retrieve lost pots, approximately how many did you bring in?

A: Between 1-5

B: Between 5-10

C: Between 10-20

D: Between 20-30

E: Between 30-50

F: Over 50

If you did retrieve lost pots, what method did you use to retrieve lost 

pots?

A: Grapples

B: Hooks on a line

C: Modified crab dredges

D: Other (please write in)

If you did retrieve lost pots, were there any animals in the pot? A: Yes

B: No

Were any alive? A: Yes

B: No
Appendix G. The Dilemma of Derelict Gear (reprinted from Scientific Reports 6, 19671) G-1

Appendix G. The Dilemma of Derelict Gear 
G-2 Appendix G. The Dilemma of Derelict Gear (reprinted from Scientific Reports 6, 19671)
Appendix G. The Dilemma of Derelict Gear (reprinted from Scientific Reports 6, 19671) G-3
G-4 Appendix G. The Dilemma of Derelict Gear (reprinted from Scientific Reports 6, 19671)
Appendix G. The Dilemma of Derelict Gear (reprinted from Scientific Reports 6, 19671) G-5
G-6 Appendix G. The Dilemma of Derelict Gear (reprinted from Scientific Reports 6, 19671)
Appendix G. The Dilemma of Derelict Gear (reprinted from Scientific Reports 6, 19671) G-7