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SPECIAL SECTION: RESTORATION BENEFITS IN GULF OF MEXICO
Estimating the Benefits of Derelict Crab Trap Removal
in the Gulf of Mexico
Courtney Arthur
1
&Scott Friedman
1
&Jennifer Weaver
2
&Dan Van Nostrand
3
&James Reinhardt
4
Received: 29 November 2019 /Revised: 21 July 2020 /Accepted: 29 July 2020
#The Author(s) 2020
Abstract
Ghost fishing in derelict blue crab traps is ubiquitous and causes incidental mortality which can be reduced by trap
removal programs. In an effort to scale the benefits of such removal programs, in the context of restoring the Gulf of Mexico
after the Deepwater Horizon oil spill, this paper calculates the ecological benefits of trap removal by estimating the extent of
derelict blue crab traps across Gulf of Mexico waterbodies and combining these estimates with Gulf-specific crab and finfish
mortality rates due to ghost fishing. The highest numbers and densities of traps are found in Louisiana, with estimates ranging up
to 203,000 derelict traps across the state and up to 41 traps per square kilometer in areas such as Terrebonne Bay. Mortality rates
are estimated at 26 crabs per trap per year and 8 fish per trap per year. The results of this analysis indicate a Gulf-wide removal
program targeting 10% of derelict traps over the course of 5 years would lead to a combined benefit of more than 691,000 kg of
crabs and fish prevented from mortality in ghost fishing traps. These results emphasize the importance of ongoing derelict trap
removal programs. Future work could assess additional benefits of trap removal programs, such as fewer entanglements of
marine organisms, improved esthetics, and increases in harvestable catch. Lastly, this model could be utilized by fishery
managers to calculate the benefits of other management options designed to decrease the extent and impact of derelict fishing
gear.
Keywords Marine debris .Crab traps .Ghost fishing .Ecological restoration
Introduction
Marine debris, defined as “any persistent solid material that is
manufactured or processed and directly or indirectly, inten-
tionally or unintentionally, disposed of or abandoned in the
marine environment or Great Lakes”(33U.S.C. 1951 et seq.,
as amended), is widespread in marine and coastal environ-
ments. The effects of marine debris on wildlife have been
documented for decades (CBD 2012). For example, organ-
isms become trapped or entangled in derelict fishing gear or
ingest smaller debris fragments and particles, resulting in re-
duced health and mortality (e.g., Chiappone et al. 2002;
MacFadyen et al. 2009; Wilcox et al. 2016). Furthermore,
marine debris can scar seagrass habitats and coral reefs, en-
tangle boat engines and fishing gear, and impact beach es-
thetics (National Oceanic and Atmospheric Administration
(NOAA) 2008). Restoration projects that remove marine de-
bris, derelict fishing gear in particular, reduce incidental mor-
tality in gear and restore coastal habitats.
One of the most persistent and damaging types of marine
debris is derelict fishing gear because it physically impacts
habitats, entangles larger organisms, and continues to catch
fish and invertebrates in a process known as “ghost fishing”
(Butler and Matthews 2015; MacFadyen et al. 2009; Scheld
et al. 2016). Gear that is capable of ghost fishing may capture
target and non-target species and be a cause of mortality to
those species, because, once lost, the gear is no longer re-
trieved regularly by fishers. Derelict fishing gear includes gill
nets,trawlnets,longlines,andtraps.Trapfisheriesare
Communicated by Mark S. Peterson
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s12237-020-00812-2) contains supplementary
material, which is available to authorized users.
*Courtney Arthur
carthur@indecon.com
1
Industrial Economics, Inc., Cambridge, MA 02140, USA
2
Research Planning, Inc., Columbia, SC 29201, USA
3
NOAA Restoration Center, Mobile, AL 36608, USA
4
NOAA Restoration Center, Silver Spring, MD 20910, USA
https://doi.org/10.1007/s12237-020-00812-2
/ Published online: 6 August 2020
Estuaries and Coasts (2020) 43:1821–1835
especially susceptible to gear loss because they span large
areas, require high densities of gear to remain productive,
and are not continuously monitored (Breen 1990). Causes of
trap loss include storms, currents, siltation, deterioration, van-
dalism, abandonment, and buoy lines severed by vessels in
transit (Clark et al. 2012;Guilloryetal.2001b; Lewis et al.
2009; Shively 1997; Uhrin and Fonseca 2005). For example,
success in blue crab (Callinectes sapidus) fisheries depends on
fishers deploying a high number of traps over a large area and
continuously replacing lost traps, creating the potential for
high densities of derelict traps. Trap loss rates are difficult to
estimate (personal communication, LA Sea Grant), in part
because many traps are unmarked and fishers infrequently
report the number of traps fished as well as trap losses.
Abandoned traps are hypothesized to be a source of derelict
traps due to temporary fishers leaving the fishery (Guillory
et al. 2001b). Preliminary estimates of annual trap loss rates
range from 20 to 100% of the total traps fished (GSMFC
2015). The high estimate of 100% is considered a result of
intentional abandonment by fishers in advance of major storm
systems or to avoid paying disposal fees (Guillory et al.
2001b).
In addition to being susceptible to loss, traps are designed
to withstand harsh conditions for extended periods of time and
thus continue to capture and kill fish and invertebrates (Arthur
et al. 2014; Butler and Matthews 2015; MacFadyen et al.
2009). Blue crab traps, such as those used in the Gulf of
Mexico and Chesapeake Bay, are made of galvanized metal
or vinyl-coated wire, which is more effective at withstanding
the corrosive nature of high salinity environments (Carr and
Harris 1997;Guilloryetal.2001a). The degradation time of
abandoned traps is estimated to be greater than 2 years
(Giordano et al. 2010; Guillory et al. 2001b;Shively1997;
Stanhope et al. 2011). As such, derelict traps may continue to
ghost fish for more than 1 year after loss or abandonment, and
in Louisiana, the life expectancy has been estimated at 3 years
(LDFW and LA Sea Grant, personal communication; Shively
1997;Vossetal.2011).
The prevalence of ghost fishing and damage to benthic
habitats, together with high rates of trap loss and longevity
of trap function, leads to a perfect storm that makes derelict
fishing traps one of the most damaging types of marine debris.
Derelict traps can continue to catch and kill biota, even after
the bait has disintegrated or been eaten, and may be a signif-
icant source of unaccounted blue crab and finfish mortality
(Arthur et al. 2014;Guilloryetal.2001b). However, the im-
pacts of derelict fishing traps can be prevented through robust
programs to find and remove them from impacted
waterbodies. Trap removal programs are a promising ecolog-
ical restoration approach with a suite of benefits, such as re-
duction of the number of fish and invertebrates killed annually
due to ghost fishing, reduction of entanglement hazards for
wildlife and boaters, increased esthetics, reduction of habitat
impacts such as smothering seagrasses or coral reefs, and po-
tentially increases harvestable catch (see, e.g., Arthur et al.
2014;Scheldetal.2016; Matthews and Uhrin 2009).
Estuarine crabs and fishes injured due to the Deepwater
Horizon oil spill may benefit from restoration projects that
remove derelict traps in the Gulf of Mexico, and funding for
removal programs may be available as part of ongoing resto-
ration efforts (DOJ 2016; Trustees 2016). Here, we build upon
published data, state-based fishery surveys, and natural re-
source management approaches to quantify the benefits of
removing derelict blue crab traps in the Gulf of Mexico. We
utilize the concepts of resource equivalency analysis (REA), a
scaling method often employed in natural resource damage
assessment that uses biological metrics as the unit of measure
(e.g., number of organisms or lost biomass). As Baker et al.
(2020) describe, through REA natural resource injuries and
the estimated restoration benefits needed to replace what
was lost are easily replicated through use of transparent pa-
rameters and a stepwise replacement model. Here, the model
parameters estimate the restoration benefit of a derelict trap
removal project. We report restoration benefits in units of crab
and finfish biomass not killed due to ghost fishing per
waterbody per year, in order to allow resource managers to
compare proposed removal efforts in a common currency.
Methods
The analysis presented in this paper estimates the avoided
mortality expected from the removal of derelict fishing traps
(i.e., the biomass of fish and invertebrates not killed in traps
that are removed), based on the number of derelict traps per
waterbody, the mortality rate per derelict trap, and the scale of
the removal program. In addition, the analysis accounts for the
gain in the number of organisms in the previous year (i.e., it is
assumed that benefits accrue for 2 years, or the assumed du-
ration over which traps may continue to ghost fish, except in
Texas and Florida due to regulations for biodegradable com-
ponents), the percent of traps that are ghost fishing, and the
average crab and fish biomass. The derivation of each of these
analytical parameters is described in the following sections.
Derelict Traps per Waterbody
The number of derelict crabtraps in the fishery is a function of
the number of traps deployed each year and the rate at which
traps are lost. The number of traps deployed each year is
dependent on the number of commercial and recreational fish-
ers and their effort.
This analysis relied on state licensure data, estimates of
inactive licenses (i.e., “latent”licenses), and state-specific reg-
ulatory limits on the number of traps allowed per license to
estimate the number of commercial fishers and the
1822 Estuaries and Coasts (2020) 43:1821–1835
corresponding number of traps in each state. The number of
commercial licenses was obtained from Texas, Louisiana,
Mississippi, and Alabama for years 2002–2013 and from
Florida for years 2009–2013. As reported in the Louisiana
blue crab fishery management plan, the number of license
holders that report landings is approximately half of the total
number of license holders (Bourgeois et al. 2014). To the best
of our knowledge, estimates of the magnitude of
underreported landings in the GoM for the blue crab fishery
are not available. However, in the most recent blue crab stock
assessment, VanderKooy (2013) considered the magnitude of
underreporting to be small because the bulk of the fishery
consists of large-scale entities that would be detected if
underreporting occurred, and included a parameter estimating
catch measurement error at 5%. Thus, in Louisiana, this anal-
ysis adjusted the estimate of commercial fishers to reflect ac-
tive license holders plus a percentage of total license holders
that may fish but do not officially report landings (5%). The
assumption of 5% may underestimate the total underreporting
for the region. Similar information was presented in the most
recent Gulf of Mexico blue crab management plan (GSMFC
2015), and this analysis assumed 50% of license holders in
Texas, Mississippi, Alabama, and Florida do not participate in
the blue crab fishery each year.
Each type of commercial license is permitted to fish a cer-
tain number of blue crab traps (Table 1). In Florida, the aver-
age number of traps per license was determined by weighting
the number of each license type sold within the state by the
number of traps permitted by that license, and then determin-
ing a weighted average. Alabama, Mississippi, and Louisiana
do not limit the number of traps used by commercial fishers.
Therefore, we utilized responses to a survey of commercial
fishers in Louisiana, conducted by Louisiana Sea Grant to
estimate the number of traps used by Louisiana fishers (per-
sonal communication, Dr. J. Anderson Lively, LA Sea Grant).
In the absence of survey data or information on the level of
fishing effort in Alabama and Mississippi, we applied the
average number of traps used per fisher in Louisiana to
Alabama and Mississippi. We calculate the number of com-
mercial traps in each state per year by estimating the number
of license holders (reduced by 50% to account for latent
licenses) then multiplying by the number of traps permitted
per license.
Commercial TrapsC;T¼LicenseC;T0:50 Traps
LicenseC
C= commercial blue crab fishery per state; T=year
The recreational fishing sector is also a source of derelict
traps. However, the level of information that states collect on
the number of recreational blue crab traps is uneven
(VanderKooy 2013). Recreational licensure data for
Louisiana and Mississippi were obtained from state fishery
managers for years 2002–2013 and are used in this analysis.
According to state regulations, each recreational license hold-
er is permitted 10 traps in Louisiana and 6 traps in Mississippi.
Recreational traps were estimated by multiplying the number
of recreational blue crab fishing licenses by the number of
traps permitted per license in Louisiana and Mississippi.
Recreational TrapsR;TLA;MSðÞ
¼LicenseR;T
Traps
LicenseR
R= recreational blue crab fishery per state; T=year
Recreational license data were not available from Texas,
Alabama, and Florida. Based on the most recent blue crab
stock assessment in the GoM, the recreational effort in
Texas, Alabama, and Florida was assumed to be 5% of com-
mercial effort (e.g., recreational traps are estimated as 5% of
commercial traps in Texas, Alabama, and Florida;
VanderKooy 2013).
Recreational TrapsR;TFL;AL;TXðÞ¼5%ðÞTrapsC;T
R= recreational blue crab fishery per state; T=year; C=
commercial blue crab fishery per state
Commercial and recreational traps were summed per
state per year. Parameters are summarized in Table 1.
The spatial distribution of derelict traps is calculated as a
number of derelict traps per waterbody. Juvenile and adult
crabs use a wide range of estuarine habitat from freshwa-
ter to fully saline conditions and are primarily fished in
large shallow and intertidal areas at depths less than 20 m
(Anderson 2014). Thus, it was assumed that the majority
of each estuarine waterbody, including mud and vegetated
benthos, represent potential crab habitat (GSMFC 2015;
VanderKooy 2013). Waterbodies were chosen by identify-
ing locations that had reported blue crab landings for mul-
tiple years. Landings per waterbody were compared with
state-wide landings to develop a proportional fishing effort
for each waterbody in each year with available data.
Louisiana, Alabama, and Mississippi had sufficient data
to interpret landings from 2002 to 2013. Texas had land-
ings data available from 2007 to 2013. Florida had license
data available at the waterbody level from 2009 to 2013
and this analysis used those data to estimate a number of
blue crab traps used in Florida waterbodies.
EffortW;T¼LandingsW;T
LandingsS;T
W= waterbody level, T=year,S=statelevel
The proportional fishing effort was used to apportion the
total number of traps (derived at the state level) to the 28
waterbodies for each year with available data. Data were av-
eraged across years, and the average number of traps per
1823Estuaries and Coasts (2020) 43:1821–1835
waterbody was used in subsequent analyses. In the absence of
additional information, this approach inherently assumes that
trap efficiency and catchability do not vary across
waterbodies, and may underestimate the number of traps used
in some waterbodies with smaller landings estimates.
TrapsW;T¼EffortW;T
TrapsCþR
Annual TrapsW¼∑TrapsW;T
n
W= waterbody level, T=year, C=commercial traps, R=
recreational traps, n=numberof years
Numbers of derelict traps were estimated by multiplying a
trap loss rate, informed by a literature review, by the number
of traps per waterbody. Based on information in white papers
and published literature, the rate at which blue crab traps are
lost was assumed to be 25% of traps used in the fishery
(Guillory et al. 2001b). To compare numbers of traps across
waterbodies of varying sizes, trap density was calculated
using the number of derelict traps per waterbody and the esti-
mated available blue crab habitat (i.e., mud and vegetated
benthos) in each waterbody. As a general rule, we assigned
waterbodies that spanned multiple states to the state that re-
ported landings for that particular waterbody. To estimate the
available blue crab habitat per waterbody, we used ESRI geo-
graphical information system (GIS) software to subtract nav-
igation channels from the available habitat (generally, the
estuary bounds as delineated by Nelson and U.S. DOC
2015) to account for regulations that prohibit setting traps
within navigable waterways.
Derelict TrapsW¼TrapsWLoss Rate
AreaW
W= waterbody level
This analysis resulted in an estimate of the density of der-
elict traps (in traps per square kilometer) in each of the 28
waterbodies. The data were imported into GIS to create maps
that delineate the extent of each waterbody and the density of
derelict traps.
Mortality in Derelict Traps
We estimated the number of organisms (crab and fish) killed
per derelict trap per year by reviewing available data from in
situ studies of capture and mortality rates in crab traps (e.g.,
Antonelis et al. 2011; Bilkovic et al. 2014; Bilkovic et al.
2016; Butler and Matthews 2015;Havensetal.2008).
While per-trap estimates of the number of crabs killed were
directly available, per-trap estimates of finfish killed were not
available. As such, for finfish, we estimated a number per trap
killed as a function of an estimated catch rate and an assumed
mortality rate.
Table 1 Parameters used to estimate the number of derelict traps in 28 Gulf of Mexico waterbodies
Parameter (units) Source Value
TX LA MS AL FL
Commercial licenses
a
State Agencies 214 2240 203 201 200
Recreational licenses
b
State Agencies –5115 485 ––
Number of permitted commercial traps
c
State Legislation 200 No limit No limit No limit Varies by License
Number of permitted recreational traps
b
State Legislation 6 10 6 5 5
Latency (%)
d
Literature (GSMFC 2015)50
Commercial landings per waterbody (lbs.) State Agencies Varies By Waterbody See Supplementary Material
Rate of trap loss (%) Literature (Guillory et al. 2001b)25
Area of waterbody (km
2
) NODC, Census Varies See Supplementary Material
a
The estimates of commercial licenses are averages using multiple years of available licensure data. In Florida, this includes only the fishing commu-
nities reporting landings north of Tampa to the state border with Alabama. In Louisiana, we use the number of licenses reporting sales and add an estimate
of the number of non-reporting fishers (5%)
b
Recreational licensure data were unavailable in Texas, Alabama, and Florida. For those states, we estimate the number of recreational licenses and the
number of permitted traps by assuming recreational fishing represents 5% of the commercial fishery, the same approach taken in the recent blue crab
stock assessment (Vanderkooy 2013)
c
The number of traps permitted by a commercial license is regulated in Texas and Florida. In Florida, the limits vary by the type of commercial trap, and
we determined a weighted average based type of license and its regulation (n= 535). In cases where the state does not impose a limit on the number of
traps utilized, we determined an average number of traps reported by commercial fishers in a survey conducted by Louisiana Sea Grant (n=369)and
applied this average to LA, MS, and AL waterbodies
d
Latency, as described here, refers to the number of non-reporting and non-participating fishers. We estimate that 50% commercial licenses are latent,
after GSMFC (2015)
1824 Estuaries and Coasts (2020) 43:1821–1835
Crab Mortality
Guillory (1993) reported the number of crabs killed per trap;
thus, there is no need to utilize capture rates to estimate the
number killed per trap. Our analysis assumed the crab mortal-
ity rate from Guillory (1993), 55% (equivalent to 25.8 crabs
per trap per year), reflects conditions across the GoM, and
used this rate in subsequent analyses for all 28 GoM
waterbodies. Mortality rates were converted to biomass by
multiplying the number killed by the average weight of a blue
crab (VanderKooy 2013;Westetal.2016). Average crab
weight was based on the average carapace width of adult crabs
in the western Gulf of Mexico (146 mm) and is equivalent to
163 g (VanderKooy 2013;Westetal.2016)(Table2).
Fish Mortality
Few studies attempt to estimate fish mortality rates in ghost-
fishing crab traps due to concerns that all estimates under-
represent mortality caused by predation and natural decompo-
sition (e.g., Guillory 1993;Havensetal.2008). Due to a lack
of finfish mortality rates reported in the literature, this analysis
used the results of an 18-month in situ study conducted during
2013–2014 by LDWF to estimate a finfish capture rate, then
applied professional judgment to estimate a percentage of
captured organisms that are killed in derelict traps. LDWF
set traps in various regions and allowed them to soak for a
specified amount of time (LDWF 2014). The authors returned
to the traps at intervals and recorded the number of non-target
organisms captured (e.g., estuarine fish), in addition to the
species and length of each individual captured in the trap.
Data on the number of species captured per unit time and
the mean size of each species were sorted by location (e.g.,
five waterbodies in Louisiana). We then derived a catch per
unit effort (CPUE) for each month of the survey by dividing
the number of captured organisms by the number of traps
utilized in the survey and by the estimated soak time. The
average annual CPUE estimate was used as the annual fish
capture rate for each waterbody. The mean capture rate de-
rived across Louisiana waterbodies was applied to Texas,
Alabama, Mississippi, and Florida in subsequent calculations
(Table 2).
Similar to Guillory (1993) and Havens et al. (2008), Butler
and Matthews (2015) recorded finfish capture rates and dead
finfish but made no attempt to estimate mortality because the
time between observations was considered to exceed the time
required for a fish carcass to decay or otherwise disappear.
Matthews and Donahue (1997) reported a daily mortality rate
in spiny lobster traps (0.0009–0.0064 organisms per trap per
day) for all organisms, including finfish, but note the estimate
did not account for fish that might have decayed or been
consumed prior to observation. Based on a literature review
of relevant studies, blue crab capture and mortality rates in
Timbalier Bay, Louisiana, and the Chesapeake Bay were com-
pared, and a ratio of organisms killed to organisms captured
was calculated for both studies (Guillory 1993;Havensetal.
2008). The lower ratio (30%) was applied to the average fin-
fish capture rates in this study to estimate finfish mortality per
trap per year.
For each of the five waterbodies in Louisiana, fish biomass
was calculated using the number of organisms captured and
themeansizeofthoseorganisms (e.g., standard length;
LDWF 2014). The species-specific lengths were converted
to weight through predictable length-weight relationships that
were estimated using FishBase, which pulls from the under-
lying primary literature (Froese and Pauly 2017). For each
waterbody, the mean biomass of species captured in traps
was calculated as a weighted average using the species weight
Table 2 Parameters used to estimate crab and finfish mortality rates in the Gulf of Mexico
Parameter Source Value (units)
Crab mortality rate Literature (Guillory 1993) 26 (crabs trap
−1
year
−1
)
Individual crab biomass Literature (VanderKooy 2013) 163 (g)
Mean finfish capture rate
a
Derived in this study from data in LDWF 2014 26 (fish trap
−1
year
−1
)
Proportion of captured finfish killed in traps
b
Literature (Havens et al. 2008; Antonelis et al. 2011)30(%)
Mean finfish biomass
c
LDWF (unpublished data) 357 (g)
a
In Louisiana, average annual finfish capture rates (fish captured per trap per year) were estimated for Pontchartrain (n= 7.4), Barataria (n= 34.0),
Terrebonne (n= 61.6), Vermillion-Teche (n= 17.2), and Sabine (n=9.1) waterbodies. The average capture rate was applied to TX, MS, AL, and FL
waterbodies in the absence of data from site-specific bycatch studies
b
The proportion of captured finfish that are killed in traps has not been directly measured, either in the LDWF study or in the broader literature on this
topic. Based on information related to blue crab capture and mortality rates, here we assume that 30% of captured fish are killed, which is likely an
underestimate of the quick biological turnover within derelict traps (e.g., Antonelis et al. 2011;Bilkovicetal.2012,2016; Havens et al. 2008,2011)
c
In Louisiana, average captured finfish biomass was estimated for Pontchartrain (348 g), Barataria (406 g), Terrebonne (369 g), Vermillion-Teche
(265 g), and Sabine (380 g). The average biomass was applied to TX, MS, and AL waterbodies. Average biomass, accounting for only species found in
Florida, was estimated at 345 g
1825Estuaries and Coasts (2020) 43:1821–1835
and the number of that species captured. Therefore, the esti-
mates calculated for each waterbody in Louisiana reflect the
frequency of capture of certain species at that location
(Table 2). A single weighted average was derived using data
from all five waterbodies and was used in benefit calculations
for Texas, Alabama, and Mississippi (Table 2). Given the dif-
ferent species distributions expected in Florida, a separate
weighted average was derived using only those species ex-
pected to naturally occur along the Florida Gulf coast
(Table 2).
Benefit Calculations
The benefit calculations combine all parameters to estimate
the number and weight of crabs and fish that would not be
killed through a derelict crab trap removal program in 28 GoM
waterbodies (i.e., the mass of organisms that would be killed
in derelict traps if the program did not occur). To reflect the
potential scale of a removal program, we reviewed available
information and consulted with fisheries managers to deter-
mine the percentage of traps that could realistically be re-
moved. This analysis assumed that a removal program would
target 10% of the derelict traps in a given waterbody, and of
the derelict traps targeted, 30% would be ghost fishing based
on the findings of trap removal programs (e.g., Arthur et al.
2014;Giordanoetal.2010;Havensetal.2008). These as-
sumptions were based on values in the peer-reviewed litera-
ture, conversations with fishery managers, and professional
judgment (e.g., Havens et al. 2011; personal communication,
LA Sea Grant). Due to the number of analytical assumptions
that are based on point estimates (e.g., the targeted percent of
derelict traps removed per waterbody) as opposed to data col-
lected or modeled with an underlying distribution, we report
our findings as point estimates and then review the analytical
parameters.
Results
Based on this analysis, a total of 223,000 derelict traps are lost
annually across all waterbodies in the Gulf of Mexico
(Table 3). Notably, Terrebonne Bay and Lake Pontchartrain
account for 51,000 and 49,000 traps, respectively. Derelict
trap density ranges across the GoM from fewer than one to
41 derelict traps per square kilometer and is highest in
Louisiana’s Terrebonne and Barataria Bays (Table 3).
In addition, the analysis yields a number and biomass of
crabs and fish gained for each year of the removal program, in
each of the 28 waterbodies (Table 4). Maps depicting the
benefits of derelict trap removal programs are presented for
waterbodies in Texas (Fig. 1), Louisiana (Fig. 2), Mississippi
and Alabama (Fig. 3), and Florida (Fig. 4). A removal pro-
gram targeting 10% of the derelict traps generated each year in
the GoM would result in more than 78,000 kg of crabs and
finfish not killed. On a waterbody scale, the benefits of a 1-
year project targeting 10% of derelict traps ranges from 9 to
10,700 kg of crab and 6 to 17,500 kg of fish (Table 4). The
minimum benefits for both crabs and fish are derived in Lower
Laguna Madre, Texas, and maximum benefits are derived in
Terrebonne Bay, Louisiana. The benefits of a 5-year removal
program (Table 5) account for additional benefits in the sec-
ond year for Alabama, Mississippi, and Louisiana (i.e., in
states that do not require a degradable component), due to
the assumption that ghost fishing occurs over the course of
2 years before a trap degrades, and follow the same geograph-
ical trends of a 1-year project. A 5-year program results in a
benefit of 391,000 kg of crab and 300,000 kg of finfish not
killed due to ghost fishing, for a combined benefit of
691,000 kg across the GoM (Table 5).
Discussion
This analysis combined site-specific fisheries data with a trap
loss rate to estimate the number of derelict traps that are added
annually to the Gulf of Mexico. This allowed an estimation of
the likely geographic distribution of derelict crab traps and
development of a resource equivalency analysis model to
quantify the benefits of a removal program for blue crabs
and finfish. By varying the inputs related to the scale of the
program, the proposed analysis can be used by natural re-
source managers to quantify the avoided mortality of crabs
and fish and focus restoration efforts on the most effective
locations. Such a derelict blue crab trap removal program
could replace crabs and fish that were injured as a result of
the Deepwater Horizon oil spill as part of a suite of projects to
restore fish and water column invertebrates (Trustees 2016).
Review of Analytical Parameters
The parameters that drive this analysis of the benefits of trap
removal programs are the number of licenses, latency, the
number of traps used, the rate of trap loss, and mortality rates
in derelict traps. The trap estimates calculated in this paper are
based on more than 10 years of fisheries licensure data and are
robust to fluctuations over time. Fifty percent of license
holders were estimated to be latent, which may underestimate
the number of active blue crab fishers in the GoM but accounts
for the fact that not all commercial license holders are full-time
fishers.
The best available information was used to estimate the
number of traps used by commercial fishers in Louisiana,
Alabama, and Mississippi. These states do not limit the num-
ber of traps for commercial fishers and thus this analysis uses
responses to a fisher survey conducted in Louisiana to deter-
mine an average number of traps. Personal communications
1826 Estuaries and Coasts (2020) 43:1821–1835
with fishery managers and stakeholders indicate that the num-
ber of traps used by fishers may shift over time and with
personal preferences. For example, in Louisiana, some fishers
may use 800 to 1000 traps, while others use 200 to 300.
Further, determining location-specific estimates of fishing ef-
fort is challenging due to privacy laws, and so additional
sources of data that could delineate fishing effort at a more
refined spatial scale are not obtainable. Thus, the average
number of traps used in this analysis may overestimate or
underestimate fishing effort in some waterbodies.
The trap loss rate, set at 25%, may overestimate lost traps in
recreational fisheries and underestimate traps lost in commer-
cial fisheries. For example, it could be easier for recreational
fishers to find and retrieve traps set close to shore or a pier,
although it may also be more convenient to retrieve only the
traps that are easily accessible and allow the others to become
derelict. Awide range of commercial trap loss rates is reported
in the literature, and given the many factors that may lead to
gear loss, it is likely the rate used in this analysis (25% of
actively fished traps) does not overestimate trap loss over
time. For example, severe storms may cause up to 100% loss
and some years may disproportionately contribute to the over-
all loss rate (Guillory et al. 2001b).
The capture and mortality rates derived in this analysis are
quite similar to those calculated in similar studies. For exam-
ple, research in the Chesapeake Bay has determined between
18 and 20 crabs killed per trap per year, with a total of 51 crabs
captured per trap per year (Arthur et al. 2014;Havensetal.
2008). Similarly, in Puget Sound, research studies calculated
mortality and capture rates of 21 and 49 Dungeness crabs per
trap per year, respectively (Antonelis et al. 2011). These esti-
mates align well with the crab mortality rate used in this anal-
ysis (26 crabs per trap per year; Guillory 1993).
In this analysis, the capture rates of finfish varied by an
order of magnitude depending on the location within
Louisiana. This indicates that site-specific estimates of ghost
Table 3 The number of traps used in the fishery, by waterbody, compared with the estimated derelict traps
State Waterbody Traps in fishery Derelict traps
AL Bon Secour Bay/Little Lagoon, Perdido System 2152 538
Mississippi Sound-Mobile 7846 1961
Mobile Bay 23,815 5954
FL Choctawhatchee Bay 3539 885
Pensacola Bay/East Bay/Escambia Bay 5618 1404
Perdido Bay 449 112
St. Andrew Bay/West Bay/North Bay 5618 1404
St. Joseph Bay 955 239
St. Josephs Sound 3202 800
St. Vincent Sound/Apalachicola Bay/East Bay/St George Sound 18,032 4508
Tampa Bay 18,706 4677
LA Atchafalaya, Vermillion, Teche Rivers 131,908 32,977
Barataria Bay 135,279 33,820
Calcasieu, Sabine, Mermentau Rivers 48,234 12,058
Lake Pontchartrain 194,508 48,627
Mississippi River 37,136 9284
Terrebonne Bay 205,058 51,265
MS Hancock Co. 5917 1479
Harrison Co. 3134 784
Jackson Co. 9585 2396
Lake Borgne 3209 802
TX Aransas Bay/Copano Bay 5087 1272
Corpus Christi Bay/Nueces Bay 458 115
Galveston Bay/Trinity Bay 9277 2319
Lower Laguna Madre 294 73
Matagorda Bay/Lavaca Bay 2744 686
Sabine Lake 4450 1113
San Antonio Bay 4833 1208
Gulf of Mexico (combined) 891,042 222,761
1827Estuaries and Coasts (2020) 43:1821–1835
fishing, conducted in each waterbody, may yield different re-
sults than the mean capture and mortality rates derived in
Louisiana and transferred to the other states. Few studies have
estimated the impact of ghost fishing on non-target fish spe-
cies. Research in the Chesapeake Bay has shown 13.6 Atlantic
croakers are caught per trap per season (Havens et al. 2008),
which is comparable with the ghost fishing estimates present-
ed in this paper. Guillory (1993) documented 8.6 fish captured
per trap per year, although escapement and mortality were not
assessed because of the quick degradation and predation on
fish by other organisms within the traps. Thus, the fish capture
rates used in this analysis are comparable with other estimates.
Ultimately, this analysis utilizes available datasets that re-
flect the site-specific ghost fishing impacts in Louisiana,
which is the largest market for the blue crab fishery and ac-
counts for almost 80% of blue crab fishing effort (i.e., traps
used) as well as 78% of blue crab landings across the GoM
(NMFS 2018). Furthermore, this study was designed to utilize
conservative estimates for less certain parameters, which may
therefore underestimate the ecological benefits of trap removal
programs.
Impact of Removal Program
The geographic distribution of derelict traps is an important
consideration when building sustainable removal programs.
Trap density can be usedby state and federal fishery managers
as well as conservation organizations to prioritize trap removal
efforts in easily accessible locations with higher densities of
derelict traps. Implementing a trap removal program in areas
with higher trap densities may lead to greater success in re-
moval operations and thus a greater ecological benefit (Scheld
et al. 2016). Focusing on areas with high trap densities lends a
more efficient cost structure due to decreased time necessary
to remove the targeted numberof traps. Louisiana accounts for
approximately 188,000 derelict traps or 84% of the total der-
elict traps across the GoM. As the Louisiana blue crab fishery
accounts for approximately 78% of the Gulf of Mexico’sblue
Table 4 Benefits of a 1-year derelict trap removal project
State Waterbody Blue crab (kg) Finfish (kg) Biomass (kg) Total biomass (kg)
AL Bon Secour Bay/Little Lagoon, Perdido System 112 74 186 2927
Mississippi Sound-Mobile 408 271 679
Mobile Bay 1239 823 2061
FL Choctawhatchee Bay 110 71 181 2875
Pensacola Bay/East Bay/Escambia Bay 175 113 288
Perdido Bay 14 9 23
St. Andrew Bay/West Bay/North Bay 175 113 288
St. Joseph Bay 30 19 49
St. Josephs Sound 100 64 164
St. Vincent Sound/Apalachicola Bay/East Bay/St George Sound 563 361 924
Tampa Bay 584 375 958
LA Atchafalaya, Vermillion, Teche Rivers 6861 2268 9129 69,663
Barataria Bay 7037 7003 14,039
Calcasieu, Sabine, Mermentau Rivers 2509 605 3114
Lake Pontchartrain 10,118 1904 12,021
Mississippi River 1932 1283 3214
Terrebonne Bay 10,666 17,479 28,145
MS
a
Hancock Co. 308 204 512 1891
Harrison Co. 163 108 271
Jackson Co. 499 331 830
Lake Borgne 167 111 278
TX Aransas Bay/Copano Bay 159 105 264 1410
Corpus Christi Bay/Nueces Bay 14 9 24
Galveston Bay/Trinity Bay 290 192 482
Lower Laguna Madre 9 6 15
Matagorda Bay/Lavaca Bay 86 57 142
Sabine Lake 139 92 231
San Antonio Bay 151 100 251
a
Although Lake Borgne is located in Louisiana waters, landings were reported only by Mississippi
1828 Estuaries and Coasts (2020) 43:1821–1835
crab landings (e.g., 18.2 of 23.3 million kilograms in 2016), it
is not surprising that the majority of effort in the GoM blue
crab fishery is distributed across Louisiana or that derelict
traps are concentrated there (NMFS 2018; NOAA 2014).
Blue crab landings revenue across the Gulf of Mexico in-
creased from approximately $46 million in 2007 to $64 mil-
lion in 2016, though landings decreased during that time pe-
riod from 57.9 to 51.3 million pounds (NMFS 2018). The
decrease in landings may explain the increase in price per
pound over time and indicate that fishers could be increasing
fishing effort to meet demand, which could lead to an increase
in derelict fishing traps over time.
The localized trap densities calculated in this paper indicate
a need for ongoing removal programs, particularly focused in
Louisiana waterbodies. Through LDWF, Louisiana runs an
annual derelict crab trap removal program that utilizes volun-
teer support to find and retrieve gear during annual crab fish-
ery closures. In 2018, volunteers removed 4061 traps over 68
boat days, which is a significant investment but does not ap-
proach the 10% figure used in this paper to scale the derelict
trap removal program (i.e., more than 18,000 traps per year).
Funding for the LDWF program is provided in part by the sale
of crab fishing licenses, though further information on costs is
not provided to the public. The Lake Pontchartrain Basin
Foundation, a nonprofit that implements crab trap removal
projects in Louisiana, estimates a cost of between $9 and
$18 per trap removed, focusing on traps that are visible (i.e.,
traps left in the water during the closed season, with an at-
tached float). Based on knowledge of local removal efforts,
the Foundation estimates the Louisiana coastal zone may have
up to 133,000 visible derelict traps and more that are not
visible from the surface, which reinforces our estimate of more
than 188,000 derelict traps across Louisiana (Butcher et al.
2019).
Other derelict trap removal programs have been effectively
implemented at scale, such as the $4.2 million program con-
ducted over 6 years that removed more than 34,000 traps from
the Chesapeake Bay and led to an increase in harvestable
catch valued at more than $20 million (Scheld et al. 2016).
More site-specific information is needed to assess program
Fig. 1 Estimated benefits (kg biomass) of a trap removal program in Texas (derelict crab trap density in parentheses)
1829Estuaries and Coasts (2020) 43:1821–1835
costs in the Gulf of Mexico, as well as the potential impact on
harvestable catch. Based on this analysis, the benefit of a 5-
year removal program in Louisiana translates to more than
352,000 kg of blue crab not killed in derelict traps; if all crabs
were harvestable, this biomass would be valued at more than
$978,000 in 2016 prices. We provide this information for con-
text, as benefit cost analysis was not a stated goal of this study
and our model does not estimate the impact on the value of
harvestable catch.
Future Work to Address Derelict Fishing Traps
This analysis provides quantitative information about the val-
ue of derelict trap removal programs, and could easily act as a
springboard for developing a benefit cost model that targets a
specific program size and location in the Gulf of Mexico, as
well as calculating the benefits of removal programs targeting
other trap fisheries, the ancillary benefits of blue crab trap
removal programs, and the benefits of potential management
measures to reduce the number and impact of derelict traps in
the Gulf of Mexico.
The blue crab fishery is ubiquitous across the GoM and
touches dozens of communities that depend on fisheries as a
way of life. The landings data utilized in this analysis closely
match a recent evaluation of fishing communities. The NOAA
Fisheries Southeast Regional Office published an online tool
of key indicators of fishing communities, including demo-
graphics and dependence on fisheries (NOAA SERO 2017).
Blue crab landings were common throughout all major fishing
communities designated by NOAA. The blue crab fishery is
especially clustered in fishing communities in Louisiana, such
as Terrebonne and Barataria Bays, which have a high density
of derelict traps. In addition to the blue crab fishery, traps are
allowable gear for commercial and recreational fishing in
smaller-scale fisheries across the GoM, including the stone
crab (Menippe mercenaria and M. adina), golden crab
(Geryon fenneri), spiny lobster (Panulirus argus), and octo-
pus (e.g., Octopus vulgaris) fisheries (GMFMC 2010). This
analysis provides a model framework that could be applied to
Fig. 2 Estimated benefits (kg biomass) of a trap removal program in Louisiana (derelict crab trap density in parentheses)
1830 Estuaries and Coasts (2020) 43:1821–1835
other trap fisheries in the GoM to determine the benefits of
additional trap removal programs.
Much of the peer-reviewed and gray literature has focused
on method development for finding and retrieving traps as
well as determining the density of traps in coastal areas across
the USA, as opposed to quantifying the ecological benefits
afforded by habitat restoration through derelict trap removal
programs (e.g., Morison and Murphy 2009; Havens et al.
2008; Maselko et al. 2013;Vossetal.2011). Studies have
published the species captured in traps, usually determined
as part of intermittent volunteer-based trap removal efforts.
Studies of volunteer trap removal efforts (Anderson and
Alford 2014; personal communication, Dr. J. Anderson
Lively, LA Sea Grant) provide information on the ecological
losses associated with ghost fishing inderelict traps. However,
it is not possible to determine realistic catch or mortality rates
solely from data collected during trap removal programs. The
LDWF study is one of the most comprehensive ghost fishing
assessments available, though it is important to note that the
ghost fishing estimates are reflective of a single point in time
when the traps were removed and the ghost fishing was
assessed (LDWF 2014). Without underwater observation of
the traps, accurate estimates of both capture and mortality of
bycatch are elusive and a derived ghost-fishing rate will not
fully represent mortality due to the quick turnover of organism
remains in traps through degradation and consumption by
other captured individuals (see, e.g., Guillory 1993). While
this paper relies on the best available information to derive
the benefits of removal programs, there is a scarcity of in situ
measurements to corroborate the assumptions across the
GoM. For example, restoration-focused studies could further
investigate the role of location, ghost fishing duration, mortal-
ity rates for bycatch species, and how environmental factors
affect trap functionality.
Traps lost or abandoned in one location may be transported
across state boundaries and reach inshore and offshore habi-
tats far from the initial point of loss. More information from
field surveys is needed to create probability distributions for
derelict gear aggregations across the GoM. Future in situ stud-
ies could investigate the range of physical and chemical
Fig. 3 Estimated benefits (kg biomass) of a trap removal program in Mississippi and Alabama (derelict crab trap density in parentheses)
1831Estuaries and Coasts (2020) 43:1821–1835
oceanographic parameters that affect trap loss, movement, and
degradation; for example, depth, water clarity, suspended
solids, dissolved oxygen, microbial activity, siltation, benthic
cover (i.e., softbottom versus hard bottom or reef habitat), and
remaining buoy attachments likely play a role in how quickly
traps degrade or are made ineffective through burial and re-
moval (Butler and Matthews 2015; Lewis et al. 2009; Uhrin
et al. 2014). Future field studies and/or restoration pilot pro-
jects in the GoM could ground-truth our benefit estimates.
The number of derelict traps targeted in a removal program
has a large impact on the benefit of that program, such that
doubling the number of removed traps doubles the expected
benefit. Consistent with the findings and recommendations of
Scheld et al. (2016), focusing removal efforts on waterbodies
with the highest densities of derelict traps is the best strategy
to maximize the benefits and minimize the cost of the removal
program. Scheld et al. (2016) found that the difference be-
tween average benefits and costs per pot removed was highest
when derelict gear hotspots were targeted. Resource managers
can utilize the model developed in this analysis to determine
the relative GoM hotspots where derelict crab traps are gen-
erated, and therefore the locations that possess the greatest
benefits for concentrated removal programs. Side-scan sonar
may be used to estimate the number and density of derelict
traps in GoM waterbodies. Better-informed loss rates could be
determined through fisher surveys or estimates of crab trap
sales. Additional in situ restoration monitoring studies may
be conducted in tandem with trap removal programs to inves-
tigate site-specific differences in the species impacted and
therefore the ecological benefits derived from a removal
project.
However, even with additional field studies and more effi-
cient removal programs, a significant amount of gear is likely
to be lost or abandoned. In fact, as noted in Martens and
Huntington (2012), it is likely that the in situ debris supply
exceeds potential removal efforts. As such, sustained and ad-
equately funded removal programs are necessary to mitigate
the continued impacts and continuous resupply of derelict
traps (GSMFC 2015). In the absence of management options
that limit the impact of derelict traps, such as degradable
Fig. 4 Estimated benefits (kg biomass) of a trap removal program on the west coast of Florida (derelict crab trap density in parentheses)
1832 Estuaries and Coasts (2020) 43:1821–1835
panels that allow trapped organisms to escape unharmed, der-
elict traps will continue to have the same impact over time.
Some states have legislated measures such as cull rings and
degradable panels, though the impact of these devices on the
ghost fishing capability of a derelict trap has not been studied
in the GoM. Assuming additional supporting data become
available, the model developed here could be used to assess
the benefits of such management measures.
Likewise, future assessments could investigate the eco-
nomic impacts of derelict traps on GoM fishing communities
to provide added support and/or direction to derelict trap re-
moval programs. A reduction in the number of derelict blue
crab traps would lead to increases in crab and finfish biomass,
economic benefits to fishing communities, and ancillary ben-
efits such as reduced interaction with marine mammals, sea
turtles, and boating traffic. Calculating the economic impact
of restoration benefits is a logical extension of this paper, and
would create a more complete understanding of the benefits
and costs of derelict trap removal programs.
Acknowledgments We thank Drs. Julie Anderson Lively and Joan
Browder for assistance in gathering data and discussing rationale behind
certain model parameters, Amy Uhrin for reviewing this manuscript and
providing valuable feedback, and Meredith Amend and Ellen Plane for
assistance with mapping. We also thank two anonymous reviewers for
their careful review and considered feedback.
Funding Information Funding of this study and production of this pub-
lication was provided by the Federal and State Natural Resource
Agencies’(Trustees’) Natural Resource Damage Assessment (NRDA)
for the Deepwater Horizon (DWH) oil spill through the National
Oceanic and Atmospheric Administration (NOAA) Damage
Assessment, Remediation and Restoration Program (DARRP) (NOAA
Contract No. AB133C-11-CQ-0050).
Compliance with Ethical Standards
Conflict of Interest The authors declare that they have no conflict of
interest.
Disclaimer The scientific results and conclusion of this publication, as
well as any views or opinions expressed herein, are those of the authors
and do not necessarily represent the view of NOAA or any other natural
Table 5 Benefits of a 5-year derelict trap removal project
State Waterbody Blue crab (kg) Finfish (kg) Biomass (kg) Total biomass (kg)
AL Bon Secour Bay/Little Lagoon, Perdido System 1008 669 1677 26,340
Mississippi Sound-Mobile 3673 2439 6112
Mobile Bay 11,149 7403 18,552
FL Choctawhatchee Bay 552 354 907 14,377
Pensacola Bay/East Bay/Escambia Bay 877 563 1439
Perdido Bay 70 45 115
St. Andrew Bay/West Bay/North Bay 877 563 1439
St. Joseph Bay 149 96 245
St. Josephs Sound 500 321 820
St. Vincent Sound/Apalachicola Bay/East Bay/St George Sound 2814 1806 4620
Tampa Bay 2919 1873 4792
LA Atchafalaya, Vermillion, Teche Rivers 61,752 20,410 82,162 626,968
Barataria Bay 63,330 63,024 126,354
Calcasieu, Sabine, Mermentau Rivers 22,580 5444 28,024
Lake Pontchartrain 91,058 17,134 108,191
Mississippi River 17,385 11,544 28,929
Terrebonne Bay 95,997 157,311 253,307
MS Hancock Co. 2770 1839 4609 17,017
Harrison Co. 1467 974 2442
Jackson Co. 4487 2980 7467
Lake Borgne 1502 997 2500
TX Aransas Bay/Copano Bay 794 527 1321 7048
Corpus Christi Bay/Nueces Bay 71 47 119
Galveston Bay/Trinity Bay 1448 961 2409
Lower Laguna Madre 46 30 76
Matagorda Bay/Lavaca Bay 428 284 712
Sabine Lake 694 461 1156
San Antonio Bay 754 501 1255
1833Estuaries and Coasts (2020) 43:1821–1835
resource Trustee for the BP/Deepwater Horizon NRDA. Any use oftrade,
firm, or product names is for descriptive purposes only and does not
imply endorsement by the U.S. Government. This publication does not
constitute an endorsement of any commercial product or intend to be an
opinion beyond scientific or other results obtained by NOAA.
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