Estimated Loggerhead and Unidentified 

Hard-shelled Turtle Interactions 

in Mid-Atlantic Gillnet Gear, 2007-2011 

US DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Northeast Fisheries Science Center 

Woods Hole, Massachusetts 

May 2013

NOAA Technical Memorandum NMFS-NE-225 
Estimated Loggerhead and Unidentified 

Hard-shelled Turtle Interactions in Mid-Atlantic 

Gillnet Gear, 2007-2011 

Kimberly T. Murray 

National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543 

 

US DEPARTMENT OF COMMERCE 

Penny Pritzker, Secretary 

National Oceanic and Atmospheric Administration 

Kathryn Sullivan, Acting NOAA Administrator 

National Marine Fisheries Service 

Samuel D. Rauch III, Acting Assistant Administrator for Fisheries 

Northeast Fisheries Science Center 

Woods Hole, Massachusetts 

May 2013

NOAA Technical Memorandum NMFS-NE-225 

This series represents a secondary level of scientific publishing. All issues employ thorough internal 

scientific review; some issues employ external scientific review. Reviews are transparent collegial 

reviews, not anonymous peer reviews. All issues may be cited in formal scientific communications. 
Editorial Notes 

Information Quality Act Compliance: In accordance with section 515 of Public Law 106-554, the 

Northeast Fisheries Science Center completed both technical and policy reviews for this report. 

These predissemination reviews are on file at the NEFSC Editorial Office. 

Species Names: The NEFSC Editorial Office’s policy on the use of species names in all 

technical communications is generally to follow the American Fisheries Society’s lists of 

scientific and common names for fishes, mollusks, and decapod crustaceans and to follow the 

Society for Marine Mammalogy's guidance on scientific and common names for marine 

mammals. Exceptions to this policy occur when there are subsequent compelling revisions in the 

classifications of species, resulting in changes in the names of species. 

Statistical Terms: The NEFSC Editorial Office’s policy on the use of statistical terms in all 

technical communications is generally to follow the International Standards Organization’s 

handbook of statistical methods. 

Internet Availability: This issue of the NOAA Technical Memorandum NMFS-NE series is 

being as a paper and Web document in HTML (and thus searchable) and PDF formats and can be 

accessed at: http://www.nefsc.noaa.gov/nefsc/publications/. 
iii 

TABLE OF CONTENTS 

Abstract ........................................................................................................................................... 1 

Introduction ..................................................................................................................................... 1 

Methods........................................................................................................................................... 2 

Overview of Analysis .................................................................................................................. 2 

Study Region ............................................................................................................................... 2 

Data Sources ................................................................................................................................ 2 

Sea Turtle Interaction Rate Models ............................................................................................. 4 

Total Estimated Interactions/Mortality ....................................................................................... 5 

Estimated Adult Equivalent Interactions ..................................................................................... 6

Estimated Interactions by Managed Fish Species Landed .......................................................... 6 

Results ............................................................................................................................................. 7 

Characteristics of Fisheries Interactions ..................................................................................... 7 

Sea Turtle Interaction Rate Model .............................................................................................. 8 

Total Annual Estimated Interactions, Adult Equivalent Interactions, and Mortalities ............... 8 

Discussion ....................................................................................................................................... 9 

References Cited ........................................................................................................................... 11 
1 

ABSTRACT 

The total number of interactions between loggerhead and hard-shelled (loggerheads plus 

unidentified hard-shelled) turtles and commercial gillnet gear in the Mid-Atlantic from 2007-

2011 was estimated by using data collected by Northeast Fisheries Observer Program (NEFOP) 

observers and at-sea monitors (ASM). A generalized additive model (GAM) was used to 

estimate interaction rates (defined as the number of turtles per ton of fish landed), which were 

then applied to commercial Vessel Trip Report (VTR) data to estimate the total number of 

interactions. From 2007-2011, an annual average of 95 hard-shelled turtles (CV = 0.21, 95% CI 

over all years: 60-138) and 89 loggerheads (equivalent to 9 adults) were estimated to have 

interacted with gillnet gear. An estimated 52 annual loggerhead interactions (equivalent to 5 

adults) were considered to result in mortality. Gillnet trips landing monkfish had the highest 

estimated number of loggerhead and hard-shelled turtle interactions during 2007-2011. 

Estimated rates and interactions have decreased relative to those from 1996-2006. 

INTRODUCTION 

Interactions between turtles and commercial fishing gear are considered a threat to the 

recovery of several species of turtles, including loggerheads (Caretta caretta), greens (Chelonia 

mydas), Kemp’s ridleys (Lepidochelys kempii), and leatherbacks (Dermochelys coriacea). All of 

these species are protected under the US Endangered Species Act (ESA) of 1973, which aims to 

reduce or eliminate threats to the species to aid in their recovery. Here an “interaction” is defined 

as synonymous with the definition of a “take” under the ESA – i.e., to “harass, harm, pursue, 

hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct” 

(ESA 1973). 

Several hundred interactions between loggerheads and gillnet gear were estimated to 

occur each year during 1995-2006 (Murray 2009a). Historically, interaction rates between 

loggerheads and several types of commercial fishing gear have been higher in the southern MidAtlantic (i.e., waters off of Maryland to North Carolina) when surface water temperatures are 

warm (Murray and Orphanides 2013), and interactions with gillnets tend to be highest in large 

mesh nets (≥7 in stretched mesh). Conservation measures have been implemented in the southern 

Mid-Atlantic to reduce the likelihood of commercial interactions with sea turtles. For instance, 

fishers are prohibited from using gillnets with mesh sizes ≥7 in during times and areas that 

overlap with the seasonal occurrence of loggerheads (US Department of Commerce 2002, 2006). 

Despite these conservation measures, fisheries observers continue to document interactions 

between sea turtles and gillnet gear in the Mid-Atlantic during times and areas outside of the 

large mesh closure restrictions or in mesh sizes smaller than 7 in. 

This report describes characteristics of observed gillnet fisheries interactions with sea 

turtles from 2007-2011 and estimates the total number of loggerhead and hard-shelled turtle 

interactions, adult equivalent (AE) loggerhead interactions, and the number of mortalities from 

the interactions during this time frame. The estimate of hard-shelled turtle interactions include 

loggerheads plus unidentified hard-shelled species (i.e., a non-leatherback turtle that was 

observed in a gillnet but was not able to be identified to species). Adult equivalence considers a 

turtle’s reproductive value (RV), defined as the contribution of an individual in an age-class to 

current and future reproduction (Fisher 1930), and is an important metric for understanding 

population-level impacts of fisheries interactions (Haas 2010). Total interactions are reported for 
2 

the entire gear type and also are apportioned by managed fish species landed (Murray 2009b) to 

aid in ESA Section 7 evaluations of management actions targeting specific fisheries. 

METHODS 

Overview of Analysis 

Data collected year-round by Northeast Fisheries Observer Program (NEFOP) observers 

and at-sea monitors (ASM) aboard commercial gillnet vessels from 2000-2011 were pooled to 

model interaction rates of loggerhead and hard-shelled turtles. It was necessary to pool before 

2007 to have a sufficient level of observed interactions to derive model-based estimates. Total 

interactions between leatherbacks and gillnet gear were not estimated because the low number of 

observations did not support a robust modeling approach, even with the larger pooled dataset. 

Moreover, estimates for Kemp’s ridley and green turtles are not provided because interactions 

with these species occurred exclusively within internal North Carolina waters, and bycatch 

estimates for these species in this area are reported by the North Carolina Division of Marine 

Fisheries (NCDMF 2013). 

Predicted rates were applied only to 2007-2011 commercial Vessel Trip Report (VTR) 

data because estimates of loggerhead rates and interactions from 1995-2006 are reported in 

Murray (2009a). Observer data prior to 2000 were not used to model rates because several new 

Fishery Management Plans (FMPs) were implemented that year, as well as an initial rule-making 

for large mesh closures (US Department of Commerce 2000), which significantly altered the 

magnitude and characteristics of current (2007-2011) fishing effort. 

Study Region 

The northern extent of the study region was defined by the boundaries of the MidAtlantic Ecological Production Unit (EPU), characterized by distinct patterns in oceanographic 

properties, fish distributions, and primary production (Ecosystems Assessment Report 2012). 

The study region extended eastward from the continental coastline (including bays and internal 

North Carolina waters) to the Exclusive Economic Zone (EEZ) and southward to the southern 

extent of NEFOP data collection (~34°N) (Figure 1a). 

Data Sources 

NEFOP and ASM observer effort 

A total of 2,658 trips (12,787 hauls) were observed by NEFOP observers from 2007-2011 

in Mid-Atlantic region gillnet fisheries (Table 1, Figure 1a). Gillnets were either anchored to the 

bottom (65% of hauls), unanchored but fishing on the ocean bottom (32% of hauls), or 

drift/floating (3% of hauls). 

Almost all NEFOP trips (96%) were considered “standard” observer trips, where 

observers are on board commercial vessels recording information about kept and discarded 

catch, fishing practices, and protected species interactions. An alternative platform observer 

program was employed from 2007-2009 because of the prevalence of gillnet fisheries prosecuted 

from small vessels (<7.3 m) that cannot easily accommodate observers (Kolkmeyer et al. 2009). 

This program used a separate vessel, with a NEFOP-certified fisheries observer on board, that 

approached fishing vessels on the water to conduct observations. Roughly 4% of NEFOP trips 
3 

used in this analysis were collected via the alternative platform program in coastal areas of the 

southern Mid-Atlantic. 

The ASM program began 1 May 2010 in response to Amendment 16 of the Northeast 

(NE) Multispecies Fishery Management Plan1

. At-sea monitors are deployed on vessels that have 

been issued a limited access NE multispecies permit fishing under NE multispecies days-at-sea 

(DAS) (including monkfish (Lophius americanus), skate (Leucoraja and Raja spp.), and spiny 

dogfish (Squalus acanthias) trips that used a groundfish DAS). At-sea monitors collect data on 

catch, area fished, and protected species interactions. However, at-sea monitors collect less 

information than NEFOP observers do on fishing activity (such as depth and sea surface 

temperature[SST] at the fishing location), and they do not collect biological samples from 

protected species. In this analysis, a total of 209 trips (1,085 hauls) observed by at-sea monitors 

from May 2010 – December 2011 were pooled with the NEFOP data. As most of the ASM trips 

occur in the Gulf of Maine, only a small portion (9%) of ASM data was used in this analysis, and 

all trips were north of 39.5°N (Table 1, Figure 1b). 

Commercial Data 

The primary data used in estimating total bycatch were VTR data because most VTRs 

contained the necessary information on fishing location and characteristics (e.g., mesh size) to 

derive total bycatch in this analysis. However, not all gillnet trips are recorded in the VTR 

database. A comparison of VTR landings with the Northeast regional (NER) dealer and North 

Carolina Department of Marine Fisheries (NCDMF) landings from the same state and federal 

waters revealed that about 30% of the commercial gillnet landings were not reflected in the VTR 

database. Therefore, VTR landings were adjusted upwards to equal the landings reported in the 

NER dealer database for all states except North Carolina, where landings were adjusted upwards 

based on the NCDMF data. 

To adjust VTR data to match the magnitude of landings in the fishery landings databases 

(either the NER dealer or NCDMF data, depending on location), the VTR and fishery landings 

were first totaled by state and year strata (i). Next, an adjustment factor (AF) for each stratum 

was calculated as: 

AFi = ∑ Dealer landingsi (1) 

∑ VTR landingsi

where i = year and state in which catch was landed. For each VTR trip in stratum i, the landed 

catch was multiplied by the AF for stratum i. These VTR data were considered to be an adequate 

representation of total fishing effort, based on previous explorations of the representativeness of 

VTR data (Murray 2009a). 

Trips from Delaware and Maryland had the highest adjustment factors (AF > 25 in 2007 

and 2009), though these trips accounted for only 0.2% of total gillnet fishing effort in the MidAtlantic. Excluding these outliers, adjustment factors ranged between 1-7.8 (median AF = 1.2). 

Sea Surface Temperature (SST) data 

At-sea monitors and VTR logbooks do not record SST on their fishing trips. Instead, SST 

data were obtained from satellite sources, which varied depending on the year. For VTR trips 

 

1

 NOAA Fisheries 2011, 15 CFR Part 902, 50 CFR Part 648 
4 

during 2007-2009, SST data were obtained from either 5 day composites derived from Advanced 

Very High Resolution Radiometer (AVHRR) Pathfinder Version 52, Moderate Resolution 

Imaging Spectoradiometer (Modis) Aqua, Modis Terra, or Geostationary Operational 

Environmental Satellite (GOES) satellites, or 5 day climatology images downloaded from 

NASA’s Jet Propulsion Laboratory, following methods in Murray (2009a). For VTR trips 

operating in North Carolina, where satellite-derived SST is biased warm (Murray 2009a), SST 

was predicted from observer-recorded temperatures based on statistical area and month 

(R2

=0.88). 

For 2010 and 2011, SST data were obtained from either a global high resolution Global 

1km Sea Surface Temperature (G1SST) data source (Chao et al. 2009) or a multi-scale ultra-high 

resolution (MUR) data source (both downloaded from NASA’s Jet Propulsion Laboratory) 

because the same SST sources used for 2007-2009 were not available. The sources used for 2010 

and 2011 blend SST data from multiple sensors. These were the only sources used for at-sea 

monitor trips, which began in 2010. The preferred satellite source in the Mid-Atlantic was 

chosen depending on calendar quarter (MUR for April-June, and the G1SST for July-Dec), based 

on a comparison between satellite values and observer-recorded values at the same location. The 

relationships between the G1SST or MUR sources and observer-recorded SST were weak 

(R2<0.30) in January, February, and March, so for these months SST was predicted from 

observer-recorded temperatures based on statistical area and month (R2=0.88). 

Sea Turtle Interaction Rate Models 

The interaction rate (R) on each haul was defined as: 

R = Number of observed turtles 

Ton of fish landed (2) 

A Generalized Additive Model (GAM) with a Poisson distribution (GAM function, SPLUS 7.0) was used to create two models: one model of the expected loggerhead interaction rate 

and the other of the expected hard-shelled turtle (loggerhead plus unidentified hard-shelled 

turtle) interaction rate. The form of the GAM can be written as: 

    ( [ ]) log( ) ( )

1

n

i

j j i i j Log E y tonslanded f x (3) 

where 

yj = the number of turtles observed on the jth haul 

log(tons landedj) is an offset term for the unit of effort (tons landed) on the jth haul 

α = a constant intercept term 

fi = a series of smoothing splines for each predictor variable 

xij = environmental or gear characteristics at the beginning of each haul 

 = unexplained error 

 

2

 Reference to any specific commercial products, process, or service by trade name, trademark, manufacturer, or 

otherwise, does not constitute or imply its endorsement, recommendation, or favoring by the United States 

Government. 
5 

Loggerhead interaction rates with gillnet gear in the Mid-Atlantic have previously been 

modeled as a function of SST, mesh size, and latitude, and rates did not differ significantly each 

year during 1995-2006 (Murray 2009a). Therefore, a model describing interaction rates as a 

function of SST, mesh size, and latitude was used as a baseline candidate model to estimate 

loggerhead interaction rates with 2000-2011 data. Several additional variables were also tested, 

the models were evaluated with respect to Akaike’s Information Criterion (AIC), and the percent 

of additional deviance explained was compared to the baseline model. These additional variables 

included: data source (ASM vs. NEFOP), inside/outside internal North Carolina waters, year, 

soak duration, depth, and trip type. Data source was tested because the ASM data only reflect 

characteristics of vessels fishing under NE multispecies DAS, and those vessels may fish 

differently than other gillnet vessels sampled by NEFOP observers. Any differences between 

NEFOP and ASM trips (beyond differences in variables already tested, such as mesh, soak 

duration, and year) would be captured by this variable. Trip type refers to the observer’s 

sampling priorities on the trip, which could have an effect on whether a turtle interaction is 

witnessed as the haul is brought on board. All of the candidate variables were chosen based on a 

priori knowledge that they may influence loggerhead interaction rates. Because AIC evaluations 

tend to favor complex models for large datasets (Maunder and Punt 2004), variables were 

retained only if they increased the percent deviance explained by >5% (Warden 2011a; Murray 

2009a). 

The final model was checked for overdispersion, measured by calculating the dispersion 

parameter (Φ) defined as: 

Φ = 

residual df

y  i   i  i ( ˆ ) / ˆ 2

 (4) 

Finally, estimated hard-shelled interaction rates were modeled as a function of the same 

variables in the preferred loggerhead model by using loggerheads plus unidentified hard-shelled 

turtles as the response. A model with different covariates was not explored because loggerheads 

composed most of the response in the hard-shelled turtle model. 

Total Estimated Interactions/Mortality 

The loggerhead and hard-shelled models were each applied to adjusted VTR landings 

data from 2007-2011 to derive both an estimated loggerhead and hard-shelled interaction rate for 

each VTR trip and an estimated number of loggerheads and hard-shelled turtles caught on each 

VTR trip. The total of annual estimated interactions was the sum of the predicted number of 

turtles captured over all trips in a year. Total loggerhead interactions were estimated from the 

loggerhead model, plus a portion of the estimated hard-shelled interactions that were over and 

above the amount estimated from the loggerhead model. This additional portion of “presumed” 

loggerheads was based on the observed loggerhead proportion (84%) that occurred outside 

internal North Carolina waters (where all the unidentified interactions occurred). The number of 

mortalities was estimated by applying the mortality rate for gillnet gear (58%, Upite et al. 2013) 

to the total estimated interactions. The mortality rate does not differentiate between turtle species 

or life stages. 

Bootstrap resampling was used to derive coefficient of variations (CVs) and confidence 

intervals (CIs) around total model-estimated interactions. Bootstrap replicates were generated by 

first resampling hauls with replacement 1000 times from the original observer dataset and then 
6 

computing total interactions by applying each replicate to VTR data. The 95% CI for total 

estimated bycatch was computed from the upper 97.5% and lower 2.5% quartiles of the bootstrap 

replicates. 

Estimated Adult Equivalent Interactions 

An adult equivalent loggerhead is the RV of the turtle scaled to adults, where the RV for 

adults is equal to 1 (Wallace et al. 2008). Adult equivalent loggerhead interactions from 2007-

2011 were estimated based on the methods in Murray (2011). Observed loggerheads were 

grouped into size classes based on the 6 loggerhead life stages (TEWG 2009), and RVs were 

assigned to each respective stage class based on Wallace (2008). These stage classes (RV values) 

were as follows: Stage 1 (0.002); Stage II (0.008); Stage III (0.040); Stage IVa (0.124); Stage 

IVb (0.547); and Stage V (1.0). Because the life stages overlap (TEWG 2009), size classes were 

truncated at the intersection of each life stage to create discrete size classes; stage IV was 

subdivided into 2 stages because RVs vary widely in this stage (Murray 2011). 

The number of estimated adult equivalent (AE) loggerhead interactions over all 6 life 

stages and all 5 years was calculated as: 

 AE = i

i

j i

j

T *P *RV

6

1

5

1

  

 (5) 

where T = total estimated loggerhead interactions in gillnet gear in year j, plus the portion of 

 total estimated hard-shelled interactions presumed to be loggerheads 

 P = the proportion of loggerheads observed in life stage i

 RVi = the reproductive value for life stage i

Because of the limited number of measured loggerheads from 2000-2011, P was based on 

NEFOP data collected from 1995-2011 (n = 14 measured loggerheads). 

Estimated Interactions by Managed Fish Species Landed 

When multiple species are landed, the estimated loggerhead interactions per trip are 

allocated to a managed fish species based on the proportion (by weight) of the species landed on 

the trip (Warden 2011b; Murray 2009b). Total loggerhead and hard-shelled interactions for 

managed fish species j on trip i (Tji) are multiplied by the proportion of reported landings of 

species j caught on trip i: 

 Tji = Ti * Lji/Li (6) 

where Lji is the amount of tons landed of species j on trip i, and 

 Li is the amount of tons landed on trip i. 

Total estimated loggerhead and hard-shelled interactions for species j over all gillnet trips (N) 

from 2007-2011 is then: 
7 

 Tj = 

N

i 1

Tji (7) 

Bootstrap resampling was used to derive CVs and CIs around the estimated interactions 

by managed species landed. Bycatch rate replicates in each stratum were applied to each VTR 

trip in that stratum to derive the estimated interactions, which were then apportioned across the 

managed species landed on that trip. For each replicate, estimates for the managed species were 

summed over all VTR trips, and the 95% CI was then computed from the upper 97.5% and lower 

2.5% quartiles of the distribution. 

For each managed fish species, a portion of the estimated hard-shelled turtles was 

presumed to be loggerheads by using the same approach as that used for the gear-wide estimate. 

RESULTS 

Characteristics of Fisheries Interactions 

NEFOP observers reported a total of 7 loggerheads, 5 Kemp’s ridleys, 12 greens, 1 

leatherback, and 3 unidentified hard-shell species in Mid-Atlantic gillnet gear from 2007-2011, 

Figure 1a). In addition, at-sea monitors reported a total of 6 loggerheads, 1 leatherback, and 1 

unidentified hard-shelled species during May 2010-2011 in the Mid-Atlantic, as well as 1 

loggerhead in the western Gulf of Maine (which was excluded from the model as it was outside 

the spatial extent of the analysis) (Figure 1b). Turtles that were not positively identified to 

species had fallen from the gear before the observer was able to examine the turtle closely or 

take a photograph. 

Temporal and Spatial Distribution 

With the exception of the loggerhead that was captured north of 42°N in August, hardshelled turtles were observed south of 41.5°N in waters ranging from 4-141m deep. All of the 

green and Kemp’s ridley interactions, and 5 (71%) of the loggerhead interactions, occurred 

inside the barrier islands of Core Sound off North Carolina during 2009 and were observed via 

the alternative platform observer program. Hard-shelled turtles were observed in June, July, and 

August with SST ranging from 16.1–28.7°C. Leatherbacks were observed around 41°N and 

35°N, in waters 13 and 46 m deep. Both leatherbacks were observed in October. 

Fishing Method 

Loggerheads were captured in gillnet mesh sizes ranging from 5.5–12 in; soaking from 

12-48 hours; and catching predominately monkfish (n = 5), skates (n = 2), southern flounder 

(Paralichthys lethostigma) (n = 4), bluefish (Pomatomus saltatrix) (n = 1), and sandbar shark 

(Carcharhinus plumbeus) (n = 1). Greens and Kemp’s ridleys were captured in gillnets with 

mesh sizes ranging from 5.5–5.75 in, soaking from 12-21 hours, and catching southern flounder. 

Unidentified hard-shelled species were captured in gillnets with mesh sizes that were 12 in, 

soaking 72-216 hours, and catching predominately monkfish (n = 2) or skate (n = 2). 

Leatherbacks were captured in gillnets with mesh sizes of 3.6 or 12 in, soaking 2 or 72 hours, 

and catching Spanish mackerel (Scomberomorus maculatus) or monkfish, respectively. 

When recorded (in NEFOP hauls only), the hang ratio of nets with turtle bycatch was 

almost always 0.50 (with the exception of one observed loggerhead in a net with a hang ratio of 
8 

0.33). All nets catching monkfish and skates that had observed bycatch were using tie-downs. No 

acoustic deterrent devices were on any nets with observed turtle bycatch. 

Animal Condition and Entanglement Situation 

Observers recorded turtles captured alive with or without injuries (7 loggerheads, 7 

greens, 4 Kemp’s ridleys, 1 leatherback, and 2 unidentified hard-shelled turtles), dead (4 

loggerhead, 4 greens, and 1 leatherback), or of unknown condition (3 loggerheads, 1 green, 1 

Kemp’s ridley, and 2 unidentified hard-shelled turtles). Turtles were mainly entangled by their 

head or flippers in the net mesh, free of the floatlines or lead lines. 

Turtle Sizes 

The length (curved carapace length [CCL] from notch to tip) and width (curved width 

measured at widest part of carapace) of NEFOP-observed turtles were as follows: loggerheads (n 

= 2) were 60.6 and 75.0cm CCL and 60.0 and 72.0cm wide; greens (n = 7) were 27.6-34.3 cm 

CCL and 23.6 33.7 wide; Kemp’s ridleys (n = 2) were 28.0 and 29.6 cm CCL and 28.2 and 30 

cm wide; leatherback and unidentified hard-shell species sizes were not measured. Many turtles 

could not be measured if they fell from the net before they could be brought on board. Size 

measurements are also not recorded by at-sea monitors. 

For the purpose of computing AEs, which used observed loggerhead measurements from 

1995-2011, loggerheads were Stage II (n = 7, or 50%), Stage III (n = 5, or 36%), and Stage IVb 

(n = 2, or 14%). 

Sea Turtle Interaction Rate Model 

The baseline candidate model from Murray (2009a) was found to be the best-fitting 

model of loggerhead interaction rates in the Mid-Atlantic gillnet fishery from 2000-2011. 

Interaction rates were modeled as a function of latitude, SST, and mesh size (Table 2); 

cumulatively, these three variables explained 39% of the variation in observed interaction rates. 

Variables indicating observer data source; inside/outside internal North Carolina waters; year, 

soak duration, depth, and trip type were not included in the model as they each explained <5% 

additional deviance over that explained by the baseline model. Estimated dispersion value of the 

final model was 0.80, indicating that the model was not overdispersed. 

Estimated bycatch rates increased with decreasing latitude, increasing SST, and 

increasing mesh sizes (Figure 2). Estimated rates in large mesh (>7 in) gear in warm (>15°C) 

waters of the southern Mid-Atlantic have generally declined relative to those during 1996-2006, 

while those in the northern Mid-Atlantic have stayed relatively the same (Figure 3). 

Total Annual Estimated Interactions, Adult Equivalent 

Interactions, and Mortalities 

From 2007-2011, an annual average of 95 hard-shelled turtles (CV = 0.21, 95% CI = 60-

138) were estimated to have interacted with gillnet gear, and an annual average of 89 

loggerheads (equivalent to 9 adults) (Figure 4). Of these 89, 54 (CV = 0.26, 95% CI=29-82) 

were estimated from positively identified loggerheads, and another 35 were hard-shelled turtles 

presumed to be loggerheads. An estimated 52 annual loggerhead interactions (equivalent to 5 

adults) were considered to result in mortality. 
9 

VTR trips landing monkfish had the highest estimated number of loggerhead and hardshelled turtle interactions during 2007-2011 (Table 3). 

DISCUSSION 

With 5 years of additional monitoring data, loggerhead interaction rates in Mid-Atlantic 

gillnet gear continue to be associated with latitude, sea surface temperature, and mesh size. High 

interaction rates are estimated in the southern Mid-Atlantic, in warm surface temperature water, 

and in large mesh nets, and these findings are consistent with those in Murray (2009a). Average 

estimated interaction rates in large (>7 in) mesh gear in warm, southern Mid-Atlantic waters 

have declined in the last 5 years relative to those from 1996-2006, as did the total commercial 

fishing effort. On the other hand, large mesh commercial effort increased in the northern MidAtlantic, particularly after 2010, though the impact to turtles was relatively small because 

estimated rates in that region are low. The reduction in commercial effort in the southern MidAtlantic, combined with lower estimated interaction rates, contributed to fewer estimated turtle 

interactions in the last 5 years. From 2007-2011, roughly 89 estimated loggerhead interactions 

occurred each year, compared to an annual average of 288 estimated interactions from 2002-

2006 (Murray 2009b). 

Expressing interactions in terms of adult equivalents allows managers to compare 

different fishing activities under a “common currency” of expected reproductive output (Wallace 

et al. 2008). A larger number of adult equivalent interactions implies a greater impact on the 

population. Other types of fishing gear interact with loggerheads in the Mid-Atlantic, such as 

bottom otter trawls and scallop dredges. Annual estimated adult equivalent loggerhead 

interactions are higher in trawl gear (Warden 2011a) than in scallop dredge (Murray 2011) or 

gillnet gear (this analysis) because of a larger magnitude of total interactions and a higher 

proportion of larger turtles taken in the fishery. 

In this analysis, a portion of the estimated hard-shelled turtles were added to the modelbased estimates of loggerheads because otherwise the model-based estimates would have only 

reflected a minimum estimate. The portion of estimated hard-shelled turtles presumed to be 

loggerheads was based on the observed proportion (84%) of loggerheads outside internal North 

Carolina waters, where all the unidentified interactions occurred. This presumed loggerhead 

portion was also applied to the estimated hard-shelled turtles for each managed fish species. 

While this portion may differ for each managed fish species depending on the spatial distribution 

of both the fish and turtle species, there were too few interactions, and little or no observer 

coverage in some fisheries, to tailor the “loggerhead portion” to each managed fish species. 

Estimated turtle interactions are assigned to individual managed fish species to support 

ESA Section 7 consultations for various Fishery Management Plans (FMPs). The approach 

explicitly recognizes that gear and environmental factors affect interaction rates on individual 

fishing trips, rather than the fish species caught or targeted. While this approach is consistent 

with the interaction rate models, the estimates will reflect the composition of catch as reported in 

VTR data. If non-federally regulated fish species are sold, and the vessel does not possess a 

permit for a federally regulated species, a VTR logbook record is not required to be filed. If this 

or other factors result in some species being underrepresented in the VTR data, estimated takes 

will be underestimated in these fisheries, and possibly overestimated in other fisheries. 

Landings data were used as the measure of fishing effort in this analysis because landings 

data are generally recorded and available for the entire fishery, and this unit of effort is 
10 

consistent with historic bycatch analyses of loggerheads in the Mid-Atlantic (Murray 2009a). An 

alternative unit of effort which reflected the amount of time and gear fished (expressed as soak 

time * net length) could not be explored because of limitations in the VTR data. To evaluate the 

quality of effort information recorded on VTR trips, over 3,000 VTR logbooks from 2007-2011 

were matched to logbooks recorded by observers for the same trip. On average, the quantity of 

gear recorded on VTR logbooks was three times larger than the information recorded by 

observers on the same trip. Applying estimated rates (modeled by using observer data) to inflated 

VTR effort would have overestimated the total number of loggerhead interactions. Therefore, a 

decision was made not to use soak time * net length (which is calculated from the quantity of 

gear recorded on the log) as a unit of effort. 

An alternative approach to estimate interactions was investigated to determine that the 

model-based estimates were robust. The alternative approach used stratified ratio estimators to 

estimate hard-shell species and loggerhead interactions by using observer and ASM data from 

only the more recent years, 2007-2011. In this approach data were stratified by time period (pre 

and post ASM monitoring), region (Mid-Atlantic vs. Gulf of Maine), season (summer [16 May – 

31 Oct] vs. winter [1 Nov – 15 May]), and mesh size (>7 in mesh vs. ≤7 in mesh). Observed 

loggerhead and hard-shelled turtle interaction rates (expressed as number of turtles per ton of fish 

landed) were computed in each stratum and applied to adjusted VTR data to derive total 

estimated interactions. The model-based estimates of both loggerhead and hard-shelled turtles 

reported here were within the 95% confidence intervals for those estimated with stratified ratio 

estimators, and the model-based estimates had lower CVs. Thus, pooling data from 2000-2011 

does not appear to have biased estimated interaction rates from 2007-2011, and pooling led to 

more precise estimates. 
11 

REFERENCES CITED 

Ecosystem Assessment Report. 2012. Ecosystem status report for the northeast shelf large 

marine ecosystem - 2011. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 12-07; 32 

p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, 

MA 02543-1026, or online at http://nefsc.noaa.gov/publications/ 

ESA (Endangered Species Act of 1973), 1973. 16 USC Secs. 1531–1544 (available online at 

http://frwebgate.access.gpo.gov/cgibin/usc.cgi?action=browse&title=16uscc35&pdfs=yes). 

Chao Y, Li Z, Farrara JD, Hung P. 2009. Blending sea surface temperatures from multiple 

satellites and in situ observations for coastal oceans. J of Atmos Oceanic Tech 26:1415-

1426. 

Fisher, RA. 1930. The genetical theory of natural selection. Oxford University Press, London, 

UK. 318p. 

Haas H. 2010. Using observed interactions between sea turtles and commercial bottom-trawling 

vessels to evaluate the conservation value of trawl gear modifications. Coastal Mar Fish: 

Dyn Manage Ecosyst Sci 2: 249-262. 

Kolkmeyer T, Guthrie B, Byrd BL, Hohn AA. 2009. Report on the alternative platform observer 

program in North Carolina: January 2007 to May 2009. NOAA Technical Memorandum 

NMFS-SEFSC-592. 31 p. 

Maunder MN Punt AE. 2004. Standardizing catch and effort data: a review of recent approaches. 

Fish Res 70:141-159. 

Murray KT. 2009a. Characteristics and magnitude of sea turtle bycatch in US mid-atlantic gillnet 

gear. Endang Species Res 8:211-224. 

Murray KT. 2009b. Proration of estimated bycatch of loggerhead sea turtles in US mid-Atlantic 

sink gillnet gear to vessel trip report landed catch, 2002-2006. US Dept Commer, 

Northeast Fish Sci Cent Ref Doc. 09-19; 7 p. 

http://www.nefsc.noaa.gov/publications/crd/crd0919/ 

Murray K.T. 2011. Interactions between sea turtles and dredge gear in the US sea scallop 

(Placopecten magellanicus) fishery, 2001-2008. Fish Res 107:137-146. 

Murray KT, Orphanides CD. 2013. Estimtating risk of loggerhead turtle (Caretta caretta) bycatch 

in the US mid-Atlantic using fishery –independent and –dependent data. Mar Ecol Prog 

Ser 477:259-270 
12 

NCDMF. 2013. Application for an individual incidental take permit under the Endangered 

Species Act of 1973. North Carolina Division of Marine Fisheries, Morehead City, NC. 

Available at: 

www.nmfs.noaa.gov/pr/pdfs/permits/ncdmf_seaturtle_itp_application_updated2013.pdf 

Turtle Expert Working Group (TEWG) 2009. As assessment of the loggerhead turtle population 

in the Western North Atlantic ocean. NOAA Technical Memorandum NMFS-SEFSC575, 131p. Available from: www.sefsc.noaa.gov 

Upite CM, Murray KT, Stacy BA, Weeks SE, Williams CR. 2013. Serious injury and mortality 

and determinations for sea turtles in US Northeast and Mid-Atlantic fishing gear, 2006-

2010. NOAA Technical Memorandum, NMFS-NE-222, 25p. 

US Department of Commerce. 2000. Sea turtle conservation: restrictions to fishing activities. 

Fed Regist 65: 31500-31503. 

US Department of Commerce. 2002. Sea turtle conservation: restrictions to fishing activities. 

Fed Regist 67:71895-71899. 

US Department of Commerce (2006). Sea turtle conservation: restrictions to fishing activities. 

Fed Regist 71:24776-24797. 

Wallace BP, Heppell SS, Lewison RL, Kelez S, Crowder LB. 2008. Impacts of fisheries bycatch 

on loggerhead turtles worldwide inferred from reproductive value analyses. J Appl Ecol 

45:1076-1085. 

Warden ML. 2011a. Modeling loggerhead sea turtle (caretta caretta) interactions with US MidAtlantic bottom trawl gear for fish and scallops, 2005-2008. Biol Conserv 144:2202-2212 

WardenML. 2011b. Proration of loggerhead sea turtle (Caretta caretta) interactions in U.S. MidAtlantic bottom otter trawls for fish and scallops, 2005–2008, by managed species 

landed. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 11-04; 8 p. 
13 

Table 1. Annual Northeast Fisheries Observer Program (NEFOP) and at-sea monitors (ASM) 

observer effort and observed turtles in Mid-Atlantic gillnet fisheries from 2007-2011. 

AVTR=Adjusted Vessel Trip Report Landings; OC = Observer Coverage, expressed as: (NEFOP 

tons + ASM tons)/AVTR tons * 100. Obs = observed, Cc = Loggerhead (Caretta caretta); Dc = 

Leatherback (Dermochelys coriacea); Cm = Green (Chelonia mydas); Lk = Kemp’s ridley 

(Lepidochelys kempii); Unid = Unidentified hard-shelled turtles. Information prior to 2007 is 

reported in Murray (2009a). 

Year NEFOP 

Trips 

NEFOP 

Tons 

Landed 

ASM 

Trips 

ASM 

Tons 

Landed 

AVTR 

Tons 

Landed 

OC Obs 

Cc 

Obs 

Dc 

Obs 

Cm 

Obs 

Lk 

Obs 

Unid 

2007 814 756 0 0 20725 4% 0 1 0 0 0

2008 556 445 0 0 19375 2% 1 0 0 0 0

2009 455 423 0 0 21631 2% 6 0 12 5 2

2010 506 520 52 217 17044 4% 4 0 0 0 1

2011 327 349 157 390 24062 3% 2 1 0 0 1

Total 2658 2493 209 607 102839 3% 13 2 12 5 4

 
14 

Table 2. Variables examined in analysis of factors affecting estimated interaction rates of loggerhead turtles (Caretta caredegrees of freedom, AIC = Akaike’s Information Criterion, k = number of parameters. The “baseline” model is shaded in g

model in Murray (2009a), as well as this analysis. 

Model structure Residual df Residual 

deviance 

Cumulative % of 

deviance 

explained 

% deviance 

explained by 

additional 

variable 

AIC ΔAIC (relative to 

baseline model) 

Null model 33209.0 428.9 430.9 Null + latitude + s(sst) + s(mesh) 33200.1 260.9 0.39 280.7 0 Null + latitude + s(sst) + s(mesh) + observer data source 

33199.1 256.4 0.40 0.01 278.2 2.5 

Null + latitude + s(sst) + s(mesh) + (in/out NC sounds) 

33199.1 257.0 0.40 0.01 280.8 -0.1 

Null + latitude + s(sst) + s(mesh) + s(year) 

33196.2 254.2 0.41 0.01 281.8 -1.1 

Null + latitude + s(sst) + s(mesh) + (year) 

33189.1 241.9 0.44 0.04 278.2 2.5 

Null + latitude + s(sst) + s(mesh) + s(soak duration) 

33196.2 250.6 0.42 0.02 278.2 2.5 

Null + latitude + s(sst) + s(mesh) + s(depth) 

33196.2 254.9 0.41 0.01 282.5 -1.8 

Null + latitude + s(sst) + s(mesh) + trip type 

33198.1 260.8 0.39 0.0 284.6 -6.4 
15 

Table 3. Annual and average estimates of loggerhead (Caretta caretta) and hard-shelled turtle interactions by managed spgillnet gear, 2007-2011. Estimated loggerheads include those estimated by the model, plus the portion of estimated hard-sloggerheads. Confidence intervals are around the mean estimates in each time period. Only those managed species with are reported. ATOL = Average Tons Observed Landed, NEFOP = Northeast Fisheries Observer Program, ASM= at-sea mon

variation, CI = Confidence interval. Columns might not sum to reported totals because of rounding of numbers. Managed Species3

ATOL (NEFOP and ASM) 

Estimated Loggerheads Non-Loggerhead Estimated Hard-Shelled T

 2007 2008 2009 2010 2011 Mean CV 95% 

CI 

2007 2008 2009 2010 2011 Me

Monkfish 196 23 44 7 23 39 27 0.28 16-41 2 3 0 1 3 Skates 218 6 10 6 30 30 16 0.30 9-23 0 1 0 2 2 Spiny dogfish 

43 2 2 4 7 11 5 0.37 2-8 0 0 0 1 1 

Smooth dogfish 

18 9 11 14 23 26 17 0.54 6-32 0 1 2 2 2 

Bluefish 49 14 7 22 22 7 14 0.46 6-26 1 0 2 2 1 Summer flounder 

2 0 0 0 0 1 0 0.38 0-0 0 0 0 0 0 

Croaker 55 18 3 2 2 4 6 0.43 2-10 1 0 0 1 0 Spanish mackerel 

5 0 0 1 1 1 1 0.73 0-1 0 0 0 0 0 

King mackerel 

1 1 0 0 1 1 1 0.53 0-1 0 0 0 0 0 

Sandbar shark 

0 1 1 0 0 0 0 0.65 0-1 0 0 0 0 0 

Blacktipped shark 0 1 2 0 1 0 1 0.41 0-1 0 0 0 0 0 Thresher shark 

0 0 0 0 1 0 0 0.48 0-0 0 0 0 0 0 

Sharpnose shark 

0 0 1 0 1 0 0 0.43 0-1 0 0 0 0 0 

Black drum 0 0 1 0 1 0 0 0.54 0-1 0 0 0 0 0 Total 75 82 55 113 120 89 4 5 4 9 9 3 Scientific names for the managed species are as follows: monkfish (Lophius americanus); skates (Leucoraja and Raja spp.); spiny dogfish (Sq

(Mustelus canis); bluefish (Pomatomus saltatrix); summer flounder (Paralichthys dentatus); croaker (Micropogonias undulatus); Spanish macke

King mackerel (Scomberomorus cavella); sandbar shark (Carcharhinus plumbeus); black-tipped shark (Carcharhinus limbatus); thresher shark (Rhizoprionodon terraenovae); black drum (Pogonias cromis) 
16 

Figure 1a. Northeast Fisheries Observer Program (NEFOP) observed gillnet hauls and turtle 

interactions, 2007-2011. This analysis encompasses the region south and west of the solid black 

line, depicting the boundary of the Mid-Atlantic Ecological Production Unit (Ecosystems 

Assessment Report 2012). Cc = Loggerhead (Caretta caretta), Cm = Green (Chelonia mydas), Dc = 

Leatherback (Dermochelys coriacea), Lk = Kemp’s ridley (Lepidochelys kempii), and 

Unk=Unidentified hard-shelled species. 
17 

Figure 1b. At-sea monitor (ASM) observed gillnet hauls and turtle interactions, May 2010-2011. 

Data from the region south and west of the solid black line were used in this analysis. Cc = 

Loggerhead (Caretta caretta), Dc = Leatherback (Dermochelys coriacea), and Unk=Unidentified 

hard-shelled species 
18 

Figure 2. Generalized additive model smoothers depicting partial effects of latitude, sea surface 

temperature (SST), and mesh size on loggerhead (Caretta caretta) interaction rates. 

 
19 

Figure 3. Estimated loggerhead (Caretta caretta) interaction rates (turtles per metric ton landed) 

and vessel trip report (VTR) tons landed from 1996-2011 on VTR trips fishing a, c) south of 37°N, in 

waters >15°C, with large (>7 in) gillnet mesh, and b, d) north of 37°N, in waters >15°C, with large 

(>7 in) gillnet mesh. Rates prior to 2007 are from Murray (2009a). Note the different y-axis scales.

a) 

 

c) 

b) 

d) 
20 

Figure 4. Total estimated hard-shelled and loggerhead (Caretta caretta) turtle interactions in gillnet 

gear during 2007-2011, including adult equivalent loggerhead interactions in parens. Estimated 

loggerhead interactions include those estimated from the loggerhead model, plus a portion of 

estimated hard-shelled turtles presumed to be loggerheads. 
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