Report of the

Workshop on Marine Turtle Longline

Post-Interaction Mortality

Bethesda, Maryland, USA

15-16 January 2004

Cheryl E. Ryder

Therese A. Conant

Barbara A. Schroeder

U.S. Department of Commerce

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

NOAA Technical Memorandum NMFS-OPR-29

January 2006
Report of the

Workshop on Marine Turtle Longline

Post-Interaction Mortality 

Cheryl E. Ryder

Therese A. Conant

Barbara A. Schroeder

NOAA Technical Memorandum NMFS-OPR-29

January 2006

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary

National Oceanic and Atmospheric Administration

Vice Admiral Conrad C. Lautenbacher, Jr., USN (Ret.)

Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service

William T. Hogarth, Assistant Administrator for Fisheries
Literature citation should read as follows: 

Ryder, C.E., T.A. Conant, and B. A. Schroeder. 2006. Report of the Workshop on Marine Turtle

Longline Post-Interaction Mortality. U.S. Dep. Commerce, NOAA Technical Memorandum

NMFS-F/OPR-29, 36 p. 

Additional copies may be obtained from:

National Marine Fisheries Service

Office of Protected Resources

1315 East West Highway, 13th Floor

Silver Spring, MD 20910

301-713-2322

This document can also be downloaded from the NMFS website: 

http://www.nmfs.noaa.gov/pr/publications
TABLE OF CONTENTS

EXECUTIVE SUMMARY ............................................................................................................1

PART I: OBJECTIVES AND OVERVIEW .................................................................................2

PART II: SUMMARIES OF FORMAL PRESENTATIONS ......................................................3

PART III: MODERATED DISCUSSIONS ...............................................................................11

PART IV: FEEDBACK INSTRUMENT ....................................................................................19

PART V: REVISION OF FEBRUARY 2001 CRITERIA ..........................................................25

APPENDIX 1: PEER REVIEW OF REVISED CRITERIA .......................................................27

APPENDIX 2: PARTICIPANT LIST .........................................................................................29

APPENDIX 3: AGENDA ...........................................................................................................30

APPENDIX 4: PARTICIPANT FEEDBACK INSTRUMENT .................................................32

APPENDIX 5: LIST OF BACKGROUND DOCUMENTS .......................................................34

1

EXECUTIVE SUMMARY

The National Marine Fisheries Service (NMFS), Office of Protected Resources (OPR), was

charged with conducting a review of the NMFS post-hooking mortality criteria, established in

February 2001, and determining whether, and if so, how, those criteria should be modified. As

part of this review, OPR convened a Workshop on Marine Turtle Longline Post-Interaction

Mortality (Workshop) in Bethesda, Maryland on 15-16 January 2004. Seventeen experts in the

areas of sea turtle biology, sea turtle anatomy/physiology, sea turtle veterinary medicine, sea

turtle satellite telemetry, and longline gear deployment participated in the workshop. 

Consideration of the workshop discussion, along with a comprehensive review of all of the

information available on the issue, led OPR to establish revised post-hooking interaction

mortality criteria. Despite the refinement of the criteria, knowledge of the effects of sea turtle

interactions with longline gear remains limited and is unlikely to be elucidated further in ways

that will be particularly relevant to sea turtle recovery. What is certain is that reducing sea turtle

interactions with longline gear is necessary for the long-term survival and recovery of these

highly migratory species. A summary of the key changes to the 2001 criteria follows.

Categories: The February 2001 injury categories have been expanded to better describe the

specific nature of the interaction. The February 2001 criteria described two categories for

mouth hooking: (1) hook does not penetrate internal mouth structure, and (2) mouth hooked

(penetrates) or ingested hook. The revised criteria (Appendix 1) divide internal hooking events

into three categories that reflect the severity of the injury and account for the probable

improvement in survivorship resulting from removal of gear, where appropriate, for each injury. 

The new criteria also separates external hooking from mouth hooking, eliminates the ‘no injury’

category, and adds a new category for comatose/resuscitated turtles.

Probable Improvement in Survivorship When Gear is Removed: The new criteria recognize

that in most cases removal of all or some of the gear (except deeply ingested hooks) may improve

the probability of survival. The categories for gear removal are: (1) released with hook and with

line that is greater than or equal to half the length of the carapace; (2) released with hook and

with line that is less than or equal to half the length of the carapace; and (3) released with all gear

removed. Turtles that have all or most of the gear removed, depending on the nature of the

interaction, are expected to have, on average, a higher probability of survival.

Species Difference: Species differences between hard-shelled turtles and leatherbacks likely

play a role in post-interaction survivorship. The new criteria takes this into consideration and

assigns slightly higher rates of post-interaction mortality for leatherback turtles.
2

PART I. OBJECTIVES AND OVERVIEW

Workshop Objectives

The objective of the Workshop was to bring together a group of relevant experts to present recent

information on post-interaction mortality of marine turtles incidentally captured in longline

fisheries, review the best scientific information available on the topic, and receive individual,

technical input from invited participants on whether, and how, NMFS should modify the

February 2001 criteria for estimating post-hooking mortality. The Workshop goal was not to

reach consensus, but to share information that could be used by OPR to revise, if appropriate, the

February 2001 criteria. 

Workshop Introduction and Overview

The two day Workshop was convened by NMFS-OPR with the assistance of facilitators Dr. Scott

McCreary and Dr. Eric Poncelet, from Concur, Inc. Participants were invited based on their

expertise in five specific fields: sea turtle veterinary medicine, sea turtle anatomy/physiology, sea

turtle biology, sea turtle satellite telemetry, and longline fishing technical operations (Appendix

2). A packet of information materials, including the Workshop Agenda and Background

Information Documents, was provided to each participant in advance of the Workshop

(Appendices 3 and 5). NMFS asked participants to provide individual input based on their

expertise in these respective areas. The Workshop was also open to observers. Participants were

informed that the focus of the Workshop was narrowly defined to the objective above and was

not convened to include discussions on fishery closures, gear modifications, research to

investigate gear modifications, development of gear research plans, status of turtle populations,

determining bycatch rates, or the jeopardy standard pursuant to the Endangered Species Act. 

The first day of the workshop and the morning of the second day were dedicated to reviewing

background material on the best available scientific information relating to post-interaction

mortality, through both formal presentations and moderated, topic-driven discussion. 

Participants spent the afternoon of the second day individually responding to a structured

feedback instrument. A review and compilation of the feedback instruments indicated that there

was no unified assessment on whether the February 2001 criteria should be amended, and if so,

how NMFS should do this. However, for those individuals who felt that modifications were

necessary, there was convergence around a number of important issues including expansion of

the injury categories, improvement in survival probabilities when gear is removed, and

recognition of differences in survival probabilities between hardshelled turtles and leatherbacks.
3

PART II: SUMMARIES OF FORMAL PRESENTATIONS

Current NMFS Marine Turtle Post-Hooking Mortality Criteria – Background Presentation

Barbara Schroeder, NMFS Office of Protected Resources

The process by which the February 2001 criteria were developed was summarized. In December

2000, NMFS-OPR was tasked with reviewing existing information and preparing a

recommendation on evaluating post-hooking mortality of marine turtles. During January 2001,

OPR sought input on the topic from agency, academic, and industry experts. OPR took the

responses under advisement and issued a memorandum in February 2001 recommending the

adoption of post-interaction mortality criteria and providing supporting documentation for the

proposed criteria. The Office of Sustainable Fisheries (OSF) subsequently suggested revised

criteria. In mid-February, the Directors of OPR, OSF, and Science and Technology met to

discuss the various recommendations and produced a Decision Memorandum (February 16,

2001) establishing guidelines for estimating post-interaction mortality. These criteria established

four categories for determining post-hooking mortality and attributed mortality risk to each of

these categories as follows:

1. No hooking, no injury, disentangled completely 0%

2. Hooked externally or entangled, line left on animal 

(hook does not penetrate internal mouth structure, e.g., lip hook) 27%

3. Mouth hooked (penetrates) or ingested 42%

4. Dead 100%

Following the background presentation, four presentations were made on recent research on

marine turtle post-interaction mortality. The presentations and the group discussions that

followed are summarized below.

Post-Hooking Dive Behavior and Movement Patterns of Oceanic Stage Loggerhead Turtles

Alan B. Bolten, Brian Riewald, and Karen A. Bjorndal (Presented by Alan Bolten) 

Data were presented from a study using satellite telemetry to assess post-hooking mortality of

loggerhead turtles captured in the Azores longline fishery. The study involved 6 turtles that had

ingested J hooks and 12 hand captured control animals not related to the longline fishery but

captured in the same area and of the same size classes. The treatment animals were released with

the hook in place and approximately 18" of the leader attached to the eye of the hook. 
4

Key points from the presentation included the following:

Post-Hooking Behavior

• Composite dive depth and dive duration histograms indicated that the hooked turtles

made more shallow and longer dives than the control animals. Deep dives were rare in

the hooked animals. Additionally, the hooked turtles used only a fraction of the water

column; they spent the vast majority of their time just below the surface (2-5 meter depth

range). Hooked turtles were absent from 40-150 meters where they would normally be

expected to forage.

• The hooked turtles appeared to stop orienting and all moved in nearly the same direction,

away from the location where they were hooked. It was assumed that these animals were

floating with the current, since the direction of travel was consistent with the direction of

movement of the main Azorean current. Conversely, the control animals continued to

orient in the area where they were released, presumably to remain in rich foraging areas.

• Hooked turtles moved with greater “straightness” suggesting that they were floating with

the prevailing current.

Sublethal Effects of Hooking

Data were presented showing that half of the hooked turtles in the study began to show

movement and dive patterns characteristic of orientation approximately 8-10 months after they

were released, indicating that some turtles may take many months to recover from a hooking

incident. Although these later movements and behavior were more consistent with that of the

control turtles, there are likely sublethal effects resulting from the loss of or reduction of foraging

for 8-10 months of the oceanic juvenile stage. Changes in location and nutrition may decrease

growth and productivity during these periods, potentially resulting in longer term reproduction

impacts at the population level. Although this study provides the first direct evidence of

sublethal effects, the effects cannot be quantified at this time.

PARTICIPANT DISCUSSION KEY POINTS:

• The surface layer is a dynamic environment, as are the layers beneath the surface. It is

possible that water temperature factored into the behaviors exhibited by treatment

animals. However, since the control animals were released into the same waters, this

alone would not account for the subsequent difference in behavior. In reference to water

temperature, it was also noted that reptiles tend to seek out warmth when they are

injured and that this may be a choice to fight infection.

• It would be normal to see diving in the range the treatment turtles were avoiding. Several

participants noted that deeper portions of the water column were required for foraging

and that these animals could not have survived for 8-10 months without feeding.

• It was suggested that the straight movements of the treatment animals might actually be

directed, rather than passive travel, and that turtles were orienting their travel based on
5

currents, SST fronts, or bathymetry. However, in this study, non-hooked turtles have not

exhibited straight movements as observed in the treatment group.

• On the long, inactive dives, treatment animals may exist a few meters down in a less

traumatic medium and float in a healing mode. It was noted that there was no predation

on these animals; thus, they may not be acting like prey due to their inactive behavior.

• In this study, the recorded satellite data immediately showed anomalies that could be

interpreted as impacts from the hooking event. One of the physiologists noted that this

could be due to either altered behavior or a physical inability to dive.

• It can be difficult to discern behavioral differences between hooked and control turtles

brought on board. Hooked turtles often show no visible signs of stress at the time, but

may be experiencing undetected injuries. In this study, the turtles appeared strong and

robust and there was no immediate apparent difference between the treatment and

control groups on deck. This contrasts with the findings of different diving behavior and

movements between the two groups after release. It was noted that the history of the

interaction may be a factor in understanding these behaviors. Even though the animals

can get to the surface, physiological impacts may happen during the time that the animal

is still on the hook, and this could be compounded by acute injury. The real trauma may

have already occurred. Lactic acid sampling of boarded animals might provide

additional information on this issue. 

• Transmitter failure and attachment failure are two different potential sources of error in

this and other telemetry studies. There was some discussion of keeling and compression

relative to attachment failure and of ghost hits. Frequent ghost hits can be due to dying

batteries or failing tags and ghost hits can be received from transmitters that have

expired or are no longer in existence. This can confound data interpretation.

Post-hooking Mortality - Atlantic Pilot Study

Sheryan Epperly, Christopher Sasso, Eric Prince, Alan Bolten, and Carlos Rivero (Presented by

Sheryan Epperly)

Data were presented from a pilot study directed at assessing post-hooking mortality of

loggerhead turtles captured in the pelagic longline fisheries. The study was conducted from

2001-2003 in the Northeast Distant (NED) statistical reporting area. It involved 4 entangled, 5

flipper hooked, 10 mouth hooked, and 10 ingested hook treatment animals, as well as 10 control

animals dipnetted in the NED. In addition, the study also involved 4 free floating tags (not

attached to turtles) deployed in the Azores. All gear, except swallowed hooks, was removed

from the treatment animals. All turtle were fitted with PAT2 or PAT3 pop-up archival

transmitting (PAT) satellite tags.
6

Key points from the presentation included the following:

• The results of the study are preliminary, since tags are still deployed and researchers are

still working on interpreting data received to date.

• A key issue is the duration of the study. A short study (< one year) could fail to detect

longer term post-hooking mortality. A study that is too long has the potential for

confounding results due to natural mortality. Consequently, researchers decided to

conduct a year long study, which would also allow for analyzing seasonal effects.

Confounding effects due to the long study duration are accounted for by also conducting

a study of control turtles for comparison. The decision to conduct a long-term study

dictated the type of PAT tag used.

• Preliminary findings suggest that the location of the hook on the turtle is a factor in posthooking survival. The satellite tags on deeply hooked turtles failed to transmit more

often than tags on turtles that were externally hooked or hooked in the mouth. 

• The data showed similar dive patterns for deeply hooked turtles and turtles externally or

mouth hooked.

• Performance of PAT tags has been a significant hurdle in this study. Performance of

PAT 3 tags was superior to that of PAT 2 tags.

• There are numerous potential sources of error including: tagging induced mortality (not

likely to be significant and accounted for in the comparison with control turtles), tag

shedding (see study mentioned below), tag failure, and data interpretation. The

researchers are currently in the process of evaluating the tag attachment, tether, and pin

over the course of a year on captive turtles to evaluate the probability of tag shedding.

They are also working with Wildlife Computers to improve tag performance and to

improve the ability to interpret the transmitted data.

PARTICIPANT DISCUSSION KEY POINTS:

• Some turtles continue to swallow hooks when they are on deck. Therefore, it is

important to process and sample the turtles as soon as possible. There was some

discussion on whether turtles should be processed right-side up or upside-down. The

physiologists supported working up the turtles right-side up (carapace up) for optimal

ventilation. This is not currently the practice in the NED experiment.

• Based on information presented from both the Azores and NED studies, there was

preliminary discussion about expanding the mouth hooked category to differentiate the

lower jaw from the upper jaw and roof of the mouth. A number of participants felt the

need to better understand how hooks behave in the mouth of a turtle and the resultant

damage from different hook types. Participants suggested approaching the issue
7

anatomically, considering the location of the injury instead of focusing on hook type. It

should be possible to categorize injuries without focusing on gear type, since gear type is

reflected in the description of the injury. The afternoon session commenced with a gear

demonstration and characterization and a description of the anatomy of the mouth and

jaw. 

Modeling Post-release Mortality of Pelagic Loggerhead Sea Turtles Exposed to the HawaiiBased Pelagic Longline Fishery 

Milani Chaloupka, Denise Parker, and George Balazs (Presented by Milani Chaloupka)

Findings were presented from analyses of an existing data set of 40 marine turtles captured in the

Hawaii-based pelagic longline fishery and outfitted with satellite tags prior to release. This

project re-analyzed data from a study that lacked rigorous scientific design. The objectives of the

project were to evaluate post-hooking mortality using satellite telemetry data from turtles

captured by the Hawaii-based longline fishery, applying nonparametric survival probability and

hazard rate modeling with left, right, and interval censored data. This study looked exclusively at

location data since no dive data were collected.

Key findings and major points from the research and analysis include the following:

• In the Hawaii study, there were significant differences in transmission time between light

and deeply hooked turtles within the first 90 days post-hooking. There was no difference

in transmission time between these two hooking classes for turtles that transmitted

beyond the first 90 days post-hooking.

• The survival function is the probability of the ARGOS network recording a signal from

the transmitter at least to time (t) for any specified time (t) post-release. The hazard

function results, presenting risk of failure at any point in time, showed a bathtub or “U”

shape, suggesting an early failure period followed by a more constant failure period and

then an accelerating period of failure. It was concluded that early failures were most

likely due to defects or poor attachment while later failures were more likely due to dying

batteries.

• The Hawaii-based study included only 40 tags. While this is a relatively small number of

tags, this remains the largest study of its kind in the world. Additional studies with much

larger data sets are needed, since enough tags have not yet been deployed to draw

conclusions with any degree of certainty.

• Study design issues that are unavoidable in the analysis of this (and other) studies

included the following:

< Inference of death is extremely problematic.

< When death is inferred, it is difficult to determine from these types of data

whether mortality is due to natural causes or longline hooking. 
8

< It is not possible from this or other similar studies to infer post-release mortality

unless the cause of each transmitter failure is known with certainty. Various

modes of transmitter failure exist. Ultimately, these types of satellite telemetry

projects provide data on time until transmitter failure, not survivorship of turtles.

< Biases introduced by observer assignment of tags to turtles have not yet been fully

evaluated. 

< Study results were confounded by using different duty cycles that were changed in

the middle of the experiment.

< Study results were confounded by year effects, since the data were not collected

during the same period.

< If the study is longer than 90 days, the effects of natural mortality and longline

related mortality may be confounded. This requires a well reasoned control group

to overcome.

< At present, no unequivocal studies on post-hooking mortality of marine turtles

exist. The current studies are most useful as stepping stones toward conducting

better studies.

PARTICIPANT DISCUSSION KEY POINTS:

• Participants with veterinary expertise generally felt that the majority of turtles released

alive with lethal injuries would likely die within 90 days post-release. It was noted that

recovery from non-lethal injuries may encompass a longer term period (e.g., over many

months or even years). However, this long term recovery is a best case scenario with

veterinary treatment. It was also noted that recovery from comparable trauma proceeds

more slowly in reptiles than in warm blooded animals. 

• There was considerable discussion over the selection of a 90 day time limit within which

hooking induced mortality could be distinguished from other mortality: what it means and

what it was based on. A number of participants felt that a 90 day time frame would

underestimate mortality in the Hawaii study, since mortality likely exists after that, even

if it is not possible to detect. Others felt that the 90 day benchmark should apply only to

the Hawaii study - with its inherent design and technology issues - rather than to limit

how future studies are conducted. Other studies could look beyond 90 days, using other

methods for determining death, or if there is an appropriate control group. It was also

noted that drawing inferences is complicated by the fact that natural mortality may vary

seasonally. In concluding this part of the discussion, it was noted that distinguishing

between natural and fisheries mortality will continue to be a problem that will need to be

addressed. 

• It was noted that experimental controls to date for post-hooking studies have been “quasicontrols” rather than true controls. Controls only serve as true controls when all of the
9

turtles in both the control and test sets remain in the same habitat (e.g., in the Azores, the

control group went off to a totally different habitat). Better control studies are needed to

help differentiate between natural mortality and hooking-induced mortality, but these

controlled studies are very difficult to conduct. However, it is possible to have control

groups for certain behaviors (e.g., movements) and it was reiterated that what is needed

for these studies is not true “classic” controls, but controls that characterize normal

behavior in the wild. The problems associated with the non-randomized and biased

treatment groups were also identified. Generally, participants felt that the current studies

provide stepping stones to better studies, but until we can design better studies we need to

be circumspect in our conclusions.

Survivorship and Movements of Sea Turtles After Their Release from Longline Fishing

Gear in the Pacific 

Yonat Swimmer, Randall Arauz, Lianne McNaughton, Mike Musyl, Rich Brill, and Anders

Neilson (Presented by Christofer Boggs)

Research findings were presented from a pop-up archival satellite tag (PSAT) study conducted in

cooperation with local fishermen off the Pacific coast of Costa Rica from November 2001

through June 2003. The objectives of the study were to examine diving behavior and

survivorship following interactions with longline gear. Pop-up satellite tags were deployed on 9

olive ridley turtles and one green turtle captured on longline fishing gear and an additional 5

control animals (olive ridleys) captured by hand while free swimming. Turtles were hooked

either externally or in the mouth and all gear was removed with the exception of one deeply

throat hooked olive ridley where the hook remained in place. The satellite tags were set to

release at a pre-set pop-up date. The tags were also set to release if they stayed at a constant

depth for 4 days or exceeded 1,500 meters in depth (both events suggest death of the turtle, as

these parameters exceed the range expected in live turtles). Behavior (movements and

survivorship) of longline captured and control turtles were compared. 

Key findings and major points included the following:

• In this study, short term survival appeared high. PSATs remained on control and longline

captured turtles for an average of 61 and 54 days, respectively (range 26 to 115 days) and

on the green turtle for 26 days. 

• The high incidence of premature tag shedding indicates that refinements are needed in the

attachment method.

• The researchers felt that they conclusively verified the death of one of the control turtles

that sank 66 days after being tagged.

• Both treatment and control olive ridleys spent nearly all of their recorded time within the

top 60 m, with very few dives exceeding 100 m.

• Olive ridleys spent over 90% of their recorded time in water temperatures of 22-28° C

and horizontal movements appeared to correlate with oceanographic variables. 
10

• There were few clear differences between the behavior of longline captured and control

turtles.

PARTICIPANT DISCUSSION KEY POINTS:

• It would be helpful to evaluate post-hooking behavior along with other behaviors that

might not appear in a control set, such as reproductive behavior.

• Olive ridleys in this experimental area are there to mate, not forage and dive. Hence,

they cannot be readily compared to animals that are feeding in the Azores.

• Several participants noted that a slide of an olive ridley showing purported hooking scars

from previous longline gear interactions may have been mating-related scars.
11

PART III: MODERATED DISCUSSIONS

Topic Area 1: Marine Turtle Veterinary Medicine, Physiology, and Anatomy

The objective of this moderated discussion was to seek input on how injuries resulting from

longline hooking or entanglement may alter behavior and/or lead to infection, resulting in

mortality or reduced fitness. The discussion would help to inform post-hooking mortality

estimates, address problems in distinguishing lethal and sublethal injuries, and contribute to our

understanding of the potential for recovery in the wild. Participants discussed the following four

questions:

Question 1: What injuries may occur from forced submergence, hook ingestion, external

hooking, entanglement, and hook removal that may result in mortality?

Participants with expertise in veterinary medicine, sea turtle anatomy, and sea turtle physiology

suggested categorizing injuries according to the mortality risk level to help direct the discussion. 

They suggested the following list of ideas for turtle bycatch injuries that may result in immediate

or future mortality. The list was considered as a gradient of risk and was based on their

experience with necropsy findings, knowledge of sea turtle anatomy and vulnerable structures,

and consideration of issues such as soft palate injuries, esophageal separation, vascular function,

hemorrhage, laceration of trachea, esophageal abscess, forced submergence effects, sepsis, and

hooking. The anatomy of sea turtles and the proximity of the hook to certain anatomical

structures was considered very important in developing the list. This preliminary working

exercise did not take into account whether the gear was removed. 

Higher Risk:

1. Comatose and resuscitated

2. Hook embedded at or below the level of the heart (i.e., hook not visible through

mouth

3. Cervical esophagus hooking (this category was added during discussion)

4. Released with external entanglement

5. Hook in glottis and/or jaw joint hooking (very sensitive structures in turtles)

6. Hook in soft palate (e.g., coming out of eye)

7. Line trailing at greater than half the carapace length

Lower Risk:

8. Line trailing at less than half the carapace length

9. Hook in lower jaw (not jaw joint) or adnexa other than glottis

10. Any external hook with no line attached

11. No hooking, no injury, disentangled completely

It was emphasized that the jaw joint is a very sensitive structure in turtles and there could be

residual edema, joint injury, or arthritis even if the hook were removed. The veterinarians
12

generally thought the likelihood of a hook entering the brain cavity was low. Three of the

categories - “release with external entanglement,” “line trailing at greater than half the carapace

length,” and “line trailing at less than half the carapace length” - are qualitatively different from

the other categories. While the other categories indicate injury resulting from gear interaction,

these three categories pertain to the state of the turtle as it is released from the boat. Thus, they

serve more as compounding factors to the existing injuries.

Role of gear removal: Several participants noted that when gear can be removed without

inducing further injury, removing hooks and other gear could have a significant positive effect on

the recovery of an individual turtle. However, one participant noted that removing gear would

not have equal effect for each of the listed injuries and that equal “benefits” could not be

assumed across the gradient of injuries. It was also emphasized that surgical removal under

laboratory conditions is a much different scenario from de-hooker removal on-board a vessel. 

Under on-board conditions, the potential for future infection and other complications would also

be expected to be higher. While hook removal was advocated for most hooks, several

participants identified that additional injury can result from the act of removing hooks from

certain locations (e.g., deeply ingested hooks). Additionally, several participants opined that

sufficient information does not exist to quantitatively determine the decrease in risk of mortality

associated with hook/gear removal. 

Other post-interaction injuries: Participants also discussed other potential post-interaction

injuries not captured in the list above. These included: osteoarthritis, penetration of skin, soft

tissue injury, eye puncture, line strangulation of limbs and subsequent infection/amputation or

fused joints, and water inhalation leading to lung infection. Forced submergence and the

incidence of asphyxiation and hypoxia were also discussed, but it was acknowledged that given

the current tools, there is no way to assess this on board a vessel.

Uncertainties are inherent in forecasting: Participants noted that sea turtles tend to be inherently

robust animals; when subjected to severe stress, mechanical damage, and risk of infection they

will become survival-oriented in their behavior and physiology. The effect that this may have on

the outcome of a post-hooking injury is unknown. 

Question 2: What sublethal effects may occur from forced submergence, hook ingestion,

external hooking, entanglement, and hook removal?

Participants discussed potential sublethal effects that might have an impact on sea turtles. These

included: loss of growth, delayed development, diminished productivity, and delayed time to

maturity. Any significant amount of trailing line can always present the risk of later effects. 

Sublethal impacts were documented in the Azores study and this is the best available research to

reference on this issue. Participants generally agreed that sublethal effects were an important

consideration, but they remain very difficult to quantify with the information currently available. 

Several participants noted that it can be difficult to distinguish between lethal and sublethal

injuries, as an injury can cause a pathology that later leads to death. One participant noted that

sublethal effects may outweigh lethal effects due to impacts at the population level. Some

participants noted a need for additional studies in this area. 
13

Question 3: Are there inherent physiological differences among marine turtle species relevant

to their response to: forced submergence, hook ingestion, external hooking, entanglement,

and hook removal?

Participants felt that species (in particular, hard-shelled versus leatherback turtles), size, and sex

were most relevant to physiological differences in response to trauma associated with longline

interaction events.

Leatherbacks versus hard-shelled turtles - Participants noted and discussed the following relative

to the differences between leatherbacks and hard-shelled turtles and how those differences may

affect their respective risk for post-interaction mortality:

• Field and laboratory observations indicate that loggerheads and olive ridleys appear to be

less susceptible to trauma than leatherbacks, which have more friable skin and softer

bones. One participant felt that a leatherback brought along side a vessel would sustain

greater external damage than a hard-shelled turtle. 

• Necropsy findings indicate that internal hooks inflict greater damage in leatherbacks due

to the fragility of both soft and hard tissue structures.

• In reference to the above observations, circle hooks in the mouth/throat may be more

damaging to leatherbacks. 

• In the U.S. northeast distant shallow set swordfish fishery, loggerheads should be able to

get to the surface when hooked, if they are not entangled. Since leatherbacks are more

likely to be entangled, they will be less likely to be able to get to the surface to breathe. 

Lab studies also suggest that leatherbacks may take longer to recover from acidosis. 

• Based on experience with three live leatherbacks entangled in gillnet gear in the Atlantic,

one participant observed that leatherbacks may be more vulnerable to the ecological

impact associated with displacement from their normal foraging area; higher rates of

travel and a longer time period to resume normal dive behavior were documented.

Size of turtles - Participants discussed the following differences between larger and smaller

turtles that might influence their susceptibility to injury and mortality:

• Larger turtles have greater lung capacity than smaller turtles.

• The bigger the turtle, the greater chance it has of reaching the surface after being hooked

or entangled.

• Larger turtles are more susceptible to injury if dropped on deck or when coming into

contact with the vessel while in the water.

Sex of turtles - Participants generally noted that it is very difficult to evaluate sex differences

relative to mortality rates, since it is impossible for observers to determine the sex of immature

turtles. It was noted that in the Pacific studies to date, virtually all of the olive ridleys and green

turtles that have been caught have been females, suggesting either a skewed sex ratio or the gear

taking a disproportionate number of females due to the location and timing of the fishery.
14

Question 4: For marine turtles that are moderately or severely injured, over what time period

would you anticipate effects from the injury to persist?

After reviewing the most recent information presented, participants generally agreed that an

injured turtle can die relatively quickly (a matter of hours) to over nine months or more following

the injury. Turtles may take a long time to recover from forced submergence.

Topic Area 2: Gear Materials

The objective of this moderated discussion was to seek individual input how (and if) different

materials used for longline hooks might affect mortality, since different materials corrode at

different rates. Participants briefly discussed the effect of gear materials on post-interaction

mortality. Key discussion points included the following:

• Current regulations already stipulate the use of corrodible hooks. It was noted that carbon

steel hooks are still legal and they are as enduring as the prohibited stainless steel hooks. 

• Corrodible hooks generally corrode very slowly. Corrosion has toxic effects, but these

corrosion materials are typically not that toxic to sea turtle gastrointestinal tracts. 

Therefore, the gradual rusting process shouldn’t be a significant concern for sea turtles. 

• Corrosion can also cause inflammation that may increase hook expulsion.

• Little research on this topic has been conducted with sea turtles. More research is being

done on fish and this could have some application to sea turtles.

Topic Area 3: Satellite Telemetry

The objective of this moderated discussion was to seek individual input on the potential for

satellite telemetry to inform the issue of post-interaction mortality and to discuss some of the

problems and limitations inherent to satellite telemetry studies relative to post-interaction

mortality. Participants discussed the following four questions:

Question 1: What types of data do satellite tags provide?

Participants listed the following categories of data that, depending on manufacturer and

configuration, can be provided by conventional (standard Argos-linked satellite tags, periodically

sending data via Argos) and pop-up archival satellite tags (configured to store data and transmit

once the tag releases from the turtle): location, dive duration, dive profile, deepest dive, surface

time (dry time), sea temperature profile, and sea temperature at depth. Conventional tags provide

higher resolution location data, whereas pop-up tags provide less finely resolved location data. 

Conventional tags report the above data according to a prescribed duty cycle (which can be near 

real time), while pop-up tags report only after the tag has been released and floats to the surface. 

Pop-up tags have the capability to report premature release, since the release function can be
15

programmed for a set time. Several participants noted that the data reported by the two primary

tag technologies are both important in addressing the issue of post-interaction survivorship.

Question 2: What are the advantages and disadvantages of the different types of satellite tags?

Participants discussed the following respective advantages and disadvantages of conventional

and pop-up satellite tags:

Conventional Tags

Key advantages:

• Duty cycle permits regular data transmission

• Higher resolution geolocation data

Key disadvantages

• Difficult to determine mortality

Pop-Up Tags

Key advantages: 

• Can potentially report data on turtle mortality, though not yet fully operational

• Can be designed to release under various conditions (e.g., when the preset pop-up

date is reached, when the tag is at constant depth for 4 days, when the tag is at

1,500 m depth)

Key disadvantages:

• Delay in receiving data

• Less reliable attachment to date

• Less reliable geolocation

• Difficulties receiving all stored data through the Argos link if tag is not recovered

• Extremely high failure rates to date

Some disadvantages apply to both tag types:

• Satellite coverage diminishes at lower latitudes

• Hardware problems

• Expensive technology

Question 3: What post-deployment transmission characteristics may be used as a proxy for

mortality? 

Participants suggested the following as proxies that may indicate mortality and commented that

studies with large sample sizes are most reliable:
16

Conventional Satellite Tags

• Complete transmission failure post-release. 

• Cessation of transmissions, coupled with an understanding of previous transmissions,

diving profiles, or other sensor data.

Pop-Up Satellite Tags

• Aberrant deep dive or tag depth followed by activation of release mechanism due to

exceeding of pre-set maximum depth point.

• Constant depth for several days followed by activation of release mechanism per pre-set

parameters. 

• Participants also noted that while uncertainty will still exist, it may also be helpful to look

for patterns of consistency (e.g., of battery power). However, this requires larger sample

sizes. 

Participants reinforced that they are still investigating their ability to interpret these data and

discussed the need to explore alternative methods other than relying on interpreting location and

dive data as a means of determining marine turtle mortality. Although constant depth may be

indicative of a dead turtle, this also involves some speculation. There is also the problem of

correctly interpreting tags that release prior to the programmed release date. Cessation of

transmissions cannot simply be assigned as tag failure. Subsequent fisheries interactions,

predator encounters, or other acute events unrelated to the original longline hooking event can

confound interpretation of the data. Participants who have been involved with post-interaction

telemetry studies agreed that at this stage, very few conclusions can be drawn with confidence. 

Question #4: What can be learned from existing satellite telemetry data?

Satellite telemetry technology has greatly improved in recent years. Transmitters can be built

with more data sensors and data resolution has improved for certain types and models of tags. 

Marine turtle scientists have taken advantage of these advances and our knowledge of

movements, behavior, and ecology have improved. However, applying this technology to

address post-interaction mortality still presents numerous challenges. Participants generally

agreed that the satellite telemetry data that exist are insufficient for drawing clear conclusions or

implications for post-interaction mortality. Simply put: it is still difficult to figure out what a

turtle is doing and relate that behavior to a specific event. There is a lot of variability among

tags. Too many unknown variables prevent robust statistical treatment of the data. Participants

noted that at present only limited conclusions can be drawn from recent studies. These included

the following:

1) Evidence of a difference in behavior between hooked and non-hooked turtles (Azores

study results). However, when examining dive data to distinguish post-interaction
17

impacts, autocorrelation is a concern, since dive patterns are not necessarily independent

events. 

2) A pattern of early tag failure for deeply hooked turtles (Hawaii-based and northeast

distant area Atlantic study results).

Several participants recommended that post-release studies performed to date be viewed as “pilot

studies” that suffer from small sample sizes, presumed high failure rates of pop-up tags, and

variation among tag manufacturers and tag batches. Pop-up tags in particular have a wide range

of performance and there were significant differences of opinion regarding their reliability. It

was agreed that hundreds of tags would need to be deployed to achieve the sample sizes

necessary to attempt to resolve mortality events and to investigate patterns. Several participants

opined that a summary report on all of the pop-up tags that have been deployed to date is

desperately needed to help us to better understand the performance and utility of these tags.

Telemetry experts at the Workshop agreed that we need to work with telemetry companies to

develop next generation tags that might provide more useful data to inform the question of posthooking effects. Further, data from these tags need to be more directly comparable among

studies. In the future it would also be beneficial to build information on the condition of the

instrument into the tag itself. In spite of the potential advancements, it was noted that there are

still significant obstacles to overcome and this will continue to be an issue. 

Topic Area 4: Current NMFS Post-Hooking Mortality Criteria

The objective of this moderated discussion was to seek individual input regarding the February

2001 post-hooking mortality criteria. The discussion would help inform NMFS whether

modifications to the current criteria are needed , and if so, how such modifications might be

structured. Key comments on the existing criteria included the following:

• Restatement of criteria - While the current criteria are titled “Post-Hooking Mortality

Criteria,”several participants noted that “Post-Interaction Mortality Criteria” would be

more accurate, since this broader designation could include factors other than hooking

and would also extend to sublethal effects. 

• Revised categorizations - Participants suggested a variety of alternative ways to revise

the injury categories in the existing post-hooking mortality criteria. Most suggestions

were directed at re-defining the types of injuries listed within categories, or to dividing

the existing four categories into a greater number of sub-categories. Several participants

specifically mentioned adopting the categories discussed during the moderated discussion

under Topic Area 1. Several participants offering this suggestion also proposed adding

the category “hooked in cervical esophagus” to the high risk category.

• Comments on Existing Category 1 - No hooking, no injury, disentangled completely. 

Nearly all of the participants expressed support for the view that any fisheries interaction

with sea turtles results in a greater than zero probability for risk of mortality in the future. 

However, most agreed that the mortality risk would be small - likely less than 1%.
18

• Comments on Existing Category 2 - Hooked externally or entangled, line left on animal

(line does not penetrate internal mouth structure, e.g., external beak hook). Several

participants suggested that 27% is probably high for the injuries now included in that

category.

• Comments on Existing Category 3 - Mouth hooked (penetrates) or ingested. 

Participants generally felt that mouth hooking should not be in the same category as

ingested hooks and they viewed lower jaw hooking as having a lesser relative risk than a

hook in the roof of the mouth (soft palate) or an ingested hook. Several participants

recommended that this category be broken down to distinguish between lower jaw, roof

of mouth (soft palate), and ingested hooks.

• Comments on Existing Category 4 - Dead. Several participants noted that the dead

category was not really needed, since it is clear that dead animals constitute a 100%

mortality rate.

Additional topics of discussion included the following:

• Absolute versus relative risk - While most participants felt comfortable stating that

some injuries are relatively worse (or less worse) than others, they also opined that

assigning specific risk percentages to different gear interaction possibilities is difficult

without better data. Many participants, while acknowledging NMFS’ requirement to

develop quantitative criteria, felt more comfortable ascribing relative risk (e.g., low,

moderate, high), rather than absolute risk (i.e., quantifying risk in percentage terms).

• Effects of gear removal - Participants recommended that NMFS modify the criteria to

allow for reduced risk in cases where gear is safely removed. However, it was also noted

that there are cases when removing the gear can worsen the magnitude of the injury (e.g.,

hooks in the cervical esophagus at or below the level of the heart). There were divergent

opinions on when it is appropriate to attempt removing hooks from certain locations. 

However, there was general agreement that if the insertion point is not visible when

viewed through the mouth, the hook should not be removed. 

• Precision of assigned mortality rates - Many participants noted that given the limited

and uncertain data available, post-interaction mortality rates should not reflect a precision

that does not exist. For example, instead of assigning rates like 27% or 42%, rates should

be in increments of 5% or 10%.

• Species differences - Participants generally agreed that the current criteria apply more

readily to hard-shelled turtles than to leatherbacks, which were viewed as more

vulnerable because of their friable skin, softer tissue, bone structure, and increased

susceptibility to both entanglement and anoxia. Participants felt that the risk for most

injury categories would be greater for leatherbacks. 
19

PART IV: FEEDBACK INSTRUMENT 

To provide an opportunity for participants to organize their thoughts and input, the workshop

conveners prepared a feedback instrument (Appendix 4). The instrument was organized around a

series of eight questions, all of which provided the opportunity for open-ended, qualitative

response, and did not force answers into a quantitative scale. On the afternoon of the second day,

participants were asked to provide individual input using the feedback instrument as a guide. A

summary of the responses to the feedback instrument is provided below. 

Participants made a serious effort to engage in the material presented and this was reflected in

their responses. Although some respondents provided more detail and rationale for their

feedback than others, a number of general comments summarized:

• For most questions there was a range of responses, as well as a notable degree of

convergence. Specifically, the majority of the respondents supported expanding and

refining the number of injury criteria categories. However, respondents were mixed in

their ability to assign quantitative mortality rates to the revised categories. 

• Respondents conveyed varying degrees of willingness to draw inferences based on the

existing data that are available on this issue. Some respondents were willing to be

normative and prescriptive, while others were uncomfortable making recommendations.

• On question 8, which asked for additional comments and recommendations, several

respondents noted the difficulty of accurately assessing the effects of post-interaction

effects and several respondents called for additional studies focused on this issue.

Summary of Feedback Instrument Responses

Question 1) When a trained fishery observer is present to record and characterize an

interaction what information relative to the gear should be considered in

determining post-hooking mortality?

a. Location of hook

b. Fate of hook (removed or left intact)

c. Nature of line entanglement (for example: number of appendages

involved, number of wraps, etc.)

d. Fate of line (completely removed, partially removed, or left intact)

e. Length of line and/or leader left on turtle 

f. Hook material (corrosiveness/degradability)

g. Other (describe)

• Participants showed strong support for recording and characterizing information on:

location of the hook, fate of the hook, nature of line entanglement, fate of line, and length

of line and/or leader left on turtle. Participants placed less importance on hook material,
20

since little information exists on the relative rates of decay for various hook materials

currently used. 

Question 2) Which of the following non-gear parameters do you believe would make a

meaningful difference in the probability of mortality?

a. Size of turtle

b. Species

c. Nature or extent of visible injuries (for example: extensive tissue damage,

minor abrasions, etc.)

d. Behavior (while on deck, in the water, and/or post-release

e. Oceanographic factors (for example: water temperature, currents)

f. Other (describe)

• The two non-gear parameters that received nearly unanimous support for consideration

were: species and nature or extent of visible injuries. 

• A strong majority of respondents stated that behavior would make a meaningful

difference in the probability of mortality. However, it was noted that the behavior of

turtles on deck can be deceiving and may not be indicative of the true condition of the

animal.

• A majority of respondents also stated that the size of the turtle would make a meaningful

difference in the probability of mortality, since larger turtles are at greater risk of injury

during boarding or when handled on or adjacent to a vessel. 

• A few respondents felt that oceanographic factors would be relevant. Supporters noted

that water temperature can affect healing rates and appetite, while one opponent noted

that temperature is unlikely to make a difference if the turtle is taken and released in the

same water temperature.

Question 3) Considering the existing conventional and pop-up archival satellite telemetry

studies, do you believe that quantitative or qualitative assessments of posthooking mortality can be made?

• Most participants noted that there have been some improvements since 2001 in the

quality of data available to inform post-interaction mortality determinations. Some

participants were willing to make inferences from the most recent data, while others were

not. At the same time, participants widely acknowledged that substantive improvements

in the quality of data are still needed.

• Approximately ten respondents expressed the view that some qualitative or quantitative

assessment of post-hooking mortality could be determined based on satellite telemetry

studies that have been conducted to date. However, these respondents noted that any

quantitative assessments that could be made would be limited. Seven respondents did not
21

believe that satellite telemetry studies could produce definitive answers regarding postinteraction mortality. When examining the same data sets, participants had differing

interpretations on the ability to draw meaningful inferences or conclusions.

Question 4) Are there sublethal effects (e.g., reduced fitness or delayed maturation due to

depressed growth rates) that should be factored into an assessment of posthooking mortality?

• Approximately half of the respondents stated that sublethal effects should be factored into

an assessment of post-hooking mortality, but most of these respondents noted that they

had no clear idea of how this could be done. Several respondents noted that there is very

little data to support factoring sublethal effects into post-hooking mortality assessment.

Question 5) Based on available information from archival and/or conventional satellite

telemetry, what behavioral factors, if any, should be considered and evaluated as

an indicator of altered or compromised post-release behavior?

a. Diving patterns

b. Movement patterns

c. Other

• Nearly all respondents expressed the view that both diving and movement patterns should

be considered and evaluated as an indicator of compromised post-release behavior. Of

these two factors, dive patterns were seen as more critical. Several respondents noted that

the quality of this information is dependent on the presence of good controls (a feature 

that has been lacking in a number of studies to date). It was also noted that when

assessing diving behavior, autocorrelation is a real concern. Several respondents were

unclear as to how these behavioral factors could be applied to the issue.

Question 6) In considering how to evaluate post-release mortality, how would you recommend

expanding or contracting current post-hooking criteria categories of interaction?

• Many respondents noted that there are multiple sub-categories that could be separated out

from the current injury categories to better characterize the risk associated with specific

injuries. Conversely, two respondents stated that there was insufficient new data to

warrant changing the existing four criteria categories and that there were benefits to

keeping the same categories. 

• Approximately two-thirds of respondents proposed expanding or refining the existing

criteria categories. Respondents recommended a variety of approaches, generally

recognizing that the categories need to be practical for NMFS to use. Many expressed

support for using the high/low risk list of injuries presented during the Workshop to
22

expand the existing categories. Few of the respondents proposed altering the relative

ordering of the list of injuries as initially discussed during the Workshop. However,

respondents differed in their approach as to how these injuries should be grouped. Some

respondents felt that all eleven injuries could be grouped under as few as two or three

broad strata, while others suggested as many as six categories. Still others suggested that

rather than adjusting the number of categories, a preferable course would be to add

precision to the types of injuries and group them into three broad categories of high,

medium, and low risk (plus the 100% dead category). Among the specific revisions

suggested were:

1. Disaggregate the existing “mouth hooked or ingested hook” category into

subcategories (e.g., lower jaw, upper jaw (soft palate), hook embedded in

esophagus at or below heart). 

2. Create a specific category called “comatose and resuscitated”. 

3. Subdivide categories by considering whether the hook/line was removed. 

This could include adding detail to length of attached line (one-half the

carapace length was suggested).

4. Subdivide categories further by considering species (leatherback versus

hard-shelled turtles).

Several respondents suggested retaining the existing categories based on the following rationale:

• Given existing data, expanding categories might be premature.

• The existing categories are simple and adequately match the mouth/external and deephooked categories already used in most existing studies, further expansion would be

uninformative.

Based on the injury categories discussed during the Workshop, a number of respondents ranked

the different injury categories relative to other classes of injury. Generally these ranking schemes

closely paralleled the ranking scheme discussed during the Workshop, originally suggested by

the participating veterinarians. Many of the respondents noted that their perceptions of mortality

probabilities are affected by other compounding factors. Some of these involved the condition of

the turtle at release. Key among these were: 

• Whether hooks/line are removed

• The length of line remaining on the turtle

• Whether removal of gear caused additional injuries

Other additional compounding factors unrelated to gear included: 1) whether the turtle was

injured while being brought or handled on board; and 2) whether the turtle was experiencing

stress due to severe entanglement.
23

Respondents viewed several of the injuries as posing approximately equivalent risks and grouped

these together for assigning post-injury mortality rates by category. This provided input on how

injury categories might be grouped differently from the February 2001 criteria. Observations

from this exercise included the following: 

• No respondents viewed the categories of “Dead/comatose and not resuscitated”

and “Comatose and resuscitated” as equivalent.

• Seven respondents viewed the categories of “comatose and resuscitated” and

“hook embedded at or below level of heart” as somewhat equivalent. Three

respondents placed them at different levels of risk.

• Approximately two-thirds of respondents viewed the categories of “hook

embedded at or below level of heart” and “hooked in cervical esophagus” as

approximately equivalent. 

• Approximately half of respondents viewed “hooked in cervical esophagus” as

approximately equivalent to “hook in glottis/jaw hinge.” Several (2-3)

participants saw these as significantly different.

• Slightly more than half of 11 respondents viewed “hook in glottis/jaw hinge” as

equivalent in risk to “hook in soft palate.”

• Approximately two-thirds of respondents viewed “hook in soft palate” as a higher

degree of risk than “hook in lower jaw.” Approximately 3 respondents viewed

these two categories as similar risks of mortality.

• Approximately half of the respondents viewed “hook in lower jaw” as nearly

equivalent to “external hook with no line attached.” Approximately 6 respondents

viewed these categories as qualitatively different risks.

(Note that the term “approximately” as used above relates to situations where there was some

question regarding how a respondent interpreted and responded to a particular question). 

Question 7) Please provide a post-hooking mortality rate or range or ranking for each

proposed category you identified in Question 6 above and provide an explanation

of your rationale for assigning either a quantitative rate or a qualitative rate.

Five respondents stated that they could see merit in qualitatively ranking risks of mortality by

sources of injury, but preferred not to, or could not, assign quantitative percentiles. Nine

respondents recommended revising the criteria and offered specific, quantitative suggestions on

how to do this. Most of the respondents who suggested quantified mortality rates appear to have

based their percentages, at least in part, on the numbers presented in the February 2001 criteria. 

Within this last grouping, key considerations included the following:
24

• The current “No hooking, no injury, disentangled completely - 0%” category should be

revised upward to a percentage greater than 0. Suggestions for modifying this ranged

from .05 - 5%.

• Hook/gear removal, consistent with NMFS guidance, should be treated as lowering the

risk of mortality. 

• Mortality rates presented in multiples of 5% or 10% are more appropriate than absolute

numbers that imply precision.

• There is merit to having relatively fewer groupings of injuries (3-5) for ease of

administration.

• Leatherbacks are at greater risk in all categories of injury and 5-10% should be added to

the mortality rate for leatherbacks for each category of injury.

• Sublethal effects are a factor, but given the lack of knowledge in this area it is not

possible to address this quantitatively.

• Suggestions for the appropriate mortality rate for high risk injuries ranged from 40-70%,

with a cluster of responses in the 40-50% range. 

Question 8) Please provide any additional comments and recommendations.

Participants emphasized the need to conduct additional research specifically targeting this issue. 

Suggestions in this area included:

• Research on species differences

• Research on the physiological effects of hooking 

• Improved experimental design with larger sample sizes

• Continuing work on tag development that will better enable the confirmation of

mortality versus tag or attachment failure 

The need to disseminate clear handling and release protocols to longline fishermen was also

reinforced. 
25

PART V: REVISION OF FEBRUARY 2001 CRITERIA

Following the Workshop, OPR reviewed the information presented formally and during directed

discussions, the feedback instruments completed by participants, and all of the available

information relevant to the issue. Based on this detailed review, OPR concluded that changes to

the existing criteria were appropriate and necessary. The revised criteria (Table 1) reflect the

information presented at the Workshop, the detailed discussions among expert participants, the

expert feedback received from individual participants at the Workshop, peer reviewer comments

(Appendix I), and OPR’s review of all other relevant information. 

Summary of Recommended Changes

Categories: The February 2001 injury categories have been expanded to better describe the

specific nature of the interaction. The February 2001 criteria described two categories for mouth

hooking: (1) hook does not penetrate internal mouth structure, and (2) mouth hooked (penetrates)

or ingested hook. The new criteria divide the mouth hooking event into three components to

reflect the severity of the injury and to account for the probable improvement in survivorship

resulting from removal of gear, where appropriate, for each injury. The new criteria also

separate external hooking from mouth hooking, eliminate the ‘no injury’ category, and add a new

category for comatose/resuscitated turtles,

Probable Improvement in Survivorship When Gear is Removed: The new criteria recognize that

in most cases removal of all or some of the gear (except deeply ingested hooks) is likely to

improve the probability of survival. The “release condition” of turtles interacting with longline

gear are divided into four categories: (1) released with hook and with trailing line greater than or

equal to half the length of the carapace (line is trailing, turtle is not entangled); (2) released with

hook and with trailing line that is less than or equal to half the length of the carapace (line is

trailing, turtles is not entangled); (3) released with hook and entangled; and (4) released with all

gear removed. Turtles that have all or most of the gear removed are expected to have, on

average, a higher probability of survival. 

Species Difference: Species differences between hard-shelled turtles and leatherbacks likely play

a role in post-interaction survivorship. The new criteria take this into consideration and assign

slightly higher rates of post-interaction mortality for leatherback turtles.
26

Table 1: Criteria for assessing marine turtle post-interaction mortality after release from longline gear. Percentages are shown for hardshelled

turtles (i.e., loggerhead, Kemp’s ridley, olive ridley, hawksbill, and green turtle), followed by percentages for leatherbacks (in parentheses).

Injury Category

Release Condition

Released with hook and

with trailing line greater

than or equal to half the

length of the carapace (line

is trailing, turtle is not

entangled)

Released with hook

and with trailing line

less than half the

length of the carapace

(line is trailing, turtle is

not entangled)

Released with hook

and entangled (line is

not trailing, turtle is

entangled )

1

Released with all

gear removed

Hardshell (Leatherback) Hardshell (Leatherback) Hardshell

(Leatherback)

Hardshell

(Leatherback)

I Hooked externally with or without entanglement. 20 (30) 10 (15) 55 (65) 5 (10)

II Hooked in upper or lower jaw with or without

entanglement. Includes ramphotheca, but not

any other jaw/mouth tissue parts (see Category

III).

30 (40) 20 (30) 65 (75) 10 (15)

III Hooked in cervical esophagus, glottis, jaw joint,

soft palate, tongue, and/or other jaw/mouth tissue

parts not categorized elsewhere, with or without

entanglement. Includes all events where the

insertion point of the hook is visible when

viewed through the mouth.

45 (55) 35 (45) 75 (85) 25 (35)

IV Hooked in esophagus at or below level of the

heart with or without entanglement. Includes all

events where the insertion point of the hook is

not visible when viewed through the mouth.

60 (70) 50 (60) 85 (95) n/a2

V Entangled only, no hook involved. Released Entangled

50 (60)

Fully Disentangled

1 (2)

VI Comatose/resuscitated. n/a 70 (80) n/a 60 (70) 3 3

 Length of line is not relevant as turtle remains entangled at release. 1

 Per veterinary recommendation hooks would not be removed if the insertion point of the hook is not visible when viewed through the open mouth. 2 

Assumes that a resuscitated turtle will always have the line cut to a length less than half the length of the carapace, even if the hook remains. 3 
27

APPENDIX 1: PEER REVIEW OF REVISED CRITERIA

Upon completion of the Report of the Workshop and the draft revised criteria, the Office of

Protected Resources contacted three external reviewers with expertise in the areas of marine

turtle veterinary medicine, pathology, and epidemiology and requested their independent review

of the revised criteria for assessing post-interaction mortality. While the Workshop Report

provided the necessary background on the issues, workshop discussions, and participant

feedback, reviewers were asked to comment specifically on the revised criteria. 

The reviewers were:

Dr. Robert A. Morris MS, DVM who has had a private veterinary practice - The Makai Animal

Clinic in Kailua, HI for 27 years, is a graduate of Cornell University. Dr. Morris served as a

contract veterinarian for the NMFS monk seal program and has been under contract with the

NMFS Pacific Islands Fisheries Science Center sea turtle program for the past 11 years,

evaluating all live sea turtle strandings in Hawaii. To date, he has observed and evaluated over

500 sea turtles.

Dr. Charles Manire, DVM, a veterinarian and research scientist who focuses specifically on

marine veterinary medicine and is a graduate of Texas A&M University. Dr. Manire is the Chief

Veterinarian and a Staff Scientist at Mote Marine Laboratory and Aquarium in Sarasota, Florida. 

He oversees the Sea Turtle Rehabilitation Hospital and the Dolphin and Whale Hospital at Mote

Marine Laboratory and has been involved in sea turtle rehabilitation for over 13 years. 

Dr. Elliott Jacobson , Ph.D., DVM, has extensive research experience in health assessment of

reptiles, reptile immunology, and infectious and noninfectious diseases of reptiles. A graduate of

both the Veterinary and Zoological Medicine programs at the University of Missouri,

Dr.Jacobson has been a professor of Wildlife and Zoological Medicine with the College of

Veterinary Medicine at the University of Florida since 1990 and has extensive experience with

sea turtle health and disease issues.

Comments on the Revised Criteria

The reviewers generally felt that the revised criteria did a good job of defining the post-hooking

injury categories as well as the possible release conditions. One of the reviewers felt that NMFS

did not have sufficient data to accurately estimate the mortality rates associated with the various

injury categories, but that our best capability at this time is to determine the relative mortality of

each category compared to the other categories. However, he did feel that the revised criteria

accurately reflects and estimates that relative mortality. Another reviewer also expressed

reservations about whether there is adequate data to have confidence in the actual percentages

assigned to injury categories and indicated that he would feel more comfortable assigning a range

(e.g., 0-20%) rather than an actual percentage (e.g., 10%) to each category. However, he noted
28

that if there is a need for an actual number for calculation purposes then each number in the table

probably falls near the middle of the expected range for each category. A third reviewer also felt

that the mortality figures would make more sense if presented as a range, since this would better

reflect our imperfect knowledge. As noted above, the post-interaction mortality estimates

presented in the revised criteria are necessary for mortality calculation and represent the best

estimate of actual mortality based on all of the available information. This reviewer also felt that

the mortality percentages might have been high in some cases. He also emphasized that both

entangling and ingested lines can cause serious injuries (flipper fractures, amputations and

intussusceptions), implying that perhaps these mortality criteria categories underestimated

post-interaction mortality. We believe that the revised criteria have adequately estimated the

severity of injuries caused by lines. One reviewer suggested modifying the category heading for

the nature of the interaction to a more simplified term: “Injury Category.” This term has been

changed in the revised criteria. It was also suggested that the comatose/resuscitated category

should be listed as a subcategory under each injury category. We note however, that the creation

of this category as a stand alone category does take into account all of the other injury categories,

and the associated estimated mortality rate reflects the serious nature of this condition. 

In addition to the specific comments on the revised criteria, each of the reviewers identified other

issues that mirrored some of the discussions that occurred during the workshop and are captured

in the Workshop Report, most notably, the difficulty in assessing post-interaction mortality given

the current state of knowledge. While these points are important, we believe they were

adequately considered and addressed during the development of the criteria. 

Suggestions for Further Research

The reviewers had a number of constructive suggestions for additional research and improved

studies that could help to better inform the issue of post-hooking mortality. One reviewer

suggested that a comprehensive survey of sea turtle rehabilitation facilities be conducted to

review the available medical records on hooked sea turtles to establish how many turtles with

hooks removed survived, how many died despite treatment and, for the ones that died, how long

after arrival at the facility they died. Another reviewer noted a recently developed technique to

estimate mortalities in various categories from tag/recapture data. He felt that this approach,

initially used for sharks, might be applicable to sea turtles, although the need for a large number

of recaptures may preclude its use. 

Another reviewer highlighted the need to establish criteria to enable inference of death of sea

turtles via post-hooking telemetry studies. He suggested that all hooked turtles that die in

rehabilitation facilities be fully necropsied to obtain data on the pathological consequences of

hooking. This same reviewer suggested that an epidemiologist could help design an improved

study to determine post-interaction mortality and that there may be some epidemiological models

that can be applied to this issue. While developing new studies or improving on studies

conducted to date was not an objective of the Workshop, these recommendations may help guide

future efforts directed toward these questions.
29

APPENDIX 2: PARTICIPANT LIST

Workshop Facilitators - CONCUR, Inc.

Dr. Scott McCreary

Dr. Eric Poncelet

Workshop Participants

Mr. Nelson Beideman - Blue Water Fisherman’s Association

Dr. Christofer Boggs - NMFS Pacific Islands Fisheries Science Center

Dr. Alan Bolten - University of Florida

Dr. Milani Chaloupka - University of Queensland

Dr. Scott Eckert - Duke University Marine Laboratory

Ms. Sheryan Epperly - NMFS Southeast Fisheries Science Center

Dr. Joe Flanagan - Houston Zoo

Dr. Craig Harms - College of Veterinary Medicine, North Carolina State University

Mr. Mike James - Dalhousie University

Mr. John LaGrange - Hawaii Longline Association

Dr. Molly Lutcavage - University of New Hampshire

Dr. Peter Lutz - Florida Atlantic University

Dr. David Owens - College of Charleston

Mr. Earl Possardt - U.S. Fish and Wildlife Service

Ms. Barbara Schroeder - NMFS Office of Protected Resources

Dr. Thierry Work - U.S. Geological Survey

Dr. Jeanette Wyneken - Florida Atlantic University

Workshop Rapporteurs

Therese Conant - NMFS Office of Protected Resources

Kristy Long - NMFS Office of Protected Resources

Cheryl Ryder - NMFS Office of Protected Resources

Workshop Observers

Marydele Donnelly - The Ocean Conservancy

Rachael Littman - Oceana 

George Mannina - O’Connor & Hannan

Chris Sasso - NMFS Southeast Fisheries Science Center

Sierra Weaver - The Ocean Conservancy
30

APPENDIX 3: AGENDA

AGENDA

Workshop on Marine Turtle Longline Post-Interaction Mortality

Convened by NMFS - Office of Protected Resources

January 15-16, 2004

Bethesda Hyatt Regency, Lalique Room

Bethesda, MD

Day 1: January 15, 2004

9:00 Welcome, Purpose of Workshop, Ground Rules and Logistics

9:15 Introduction of Participants

9:45 Introductory/Background Presentation on Current NMFS Sea Turtle Post-Hooking

Mortality Criteria - Barbara Schroeder

10:30 BREAK

10:45 Presentations (each presentation includes 15 minutes for clarifying questions)

10:45 Post-Hooking Dive Behavior and Movement Patterns of Oceanic-stage

Loggerhead Turtles - Alan B. Bolten, Brian Riewald, and Karen A. Bjorndal

11:25 Post-Hooking Mortality - Atlantic Pilot Study - Sheryan Epperly, Eric Prince,

Chris Sasso, Alan B. Bolten

12:15 LUNCH

1:30 Presentations ((each presentation includes 15 minutes for clarifying questions)

1:30 Modeling Post-Release Mortality of Pelagic Loggerhead Sea Turtles Exposed to

the Hawaii-Based Pelagic Longline Fishery - Milani Chaloupka, Denise Parker,

George Balazs

2:20 Survivorship and Movements of Sea Turtles after their Release from Longline

Fishing Gear in the Pacific Ocean - Yonat Swimmer, Randall Arauz, Lianne

McNaughton, Mike Musyl, Rich Brill, Anders Neilson 

(presented by Chris Boggs)
31

APPENDIX 3 (continued)

3:15 BREAK

3:30 Moderated Discussion - Veterinary Medicine/Physiology

• What sublethal effects may occur from forced submergence, hook ingestion,

external hooking, entanglement and hook removal?

• What injuries may occur from forced submergence, hook ingestion, external

hooking, entanglement and hook removal that may result in mortality?

• Are there inherent physiological differences among marine turtle species

relevant to their response to: forced submergence, hook ingestion, external

hooking, entanglement and hook removal?

• For marine turtles that are moderately or severely injured, over what time

period would you anticipate effects from the injury to persist?

5:00 Moderated Discussion - Day 1 Topics

6:00 Adjourn

Day 2: January 16, 2004

9:00 Recap and Questions

9:15 Moderated Discussion - Satellite Telemetry

• Is satellite telemetry a viable method for assessing post-interaction mortality?

• What factors (e.g. transmitter manufacturer, transmitter model) are relevant to

the question of evaluating post-interaction mortality via satellite telemetry

studies?

• What post-deployment transmission life should be used, if any, as a proxy for

mortality?

• Can satellite telemetry studies elucidate any sublethal effects of sea

turtle/longline interactions?

10:30 Break

10:45 Moderated Discussion - Current NMFS post-hooking mortality criteria

12:00 Feedback Instrument Walk-Through

12:30 Lunch

2:00 Participants Complete Feedback Instrument

4:00 Adjourn
32

APPENDIX 4: PARTICIPANT FEEDBACK INSTRUMENT

1. When a trained fisheries observer is present to record and characterize an interaction, what

information relative to the gear should be considered in determining post-interaction mortality

(underline and expand on all that apply)

 1. Location of hook

2. Fate of hook (removed or left intact)

3. Nature of line entanglement (for example: number of appendages involved, 

number of wraps, etc.)

4. Fate of line (completely removed, partially removed, or left intact)

5. Length of line and/or leader left on turtle 

6. Hook material (corrosiveness/degradability)

7. Other (describe):

For each item selected above, please provide additional written comments supporting your

selection(s):

2. Which of the following non-gear parameters do you believe would make a meaningful

difference in the probability of mortality? (underline and expand on all that apply)

1. Size of turtle

2. Species

3. Nature or extent of visible injuries (for example: extensive tissue damage, minor

abrasions, etc.)

4. Behavior (while on deck, in the water, and/or post-release

5. Oceanographic factors (for example: water temperature, currents)

6. Other (describe):

(A) For each item selected above, please provide additional written comments supporting your

selection(s):

(B) For each item selected above, please discuss whether data exist to either quantify or qualify*

in a meaningful way, the effect(s) that these non-gear parameters may have on the probability of

mortality:

*{Quantify for example would be: likely to increase (or decrease) mortality by X%) and qualify

would be: highly likely to increase (or decrease) mortality, somewhat likely to increase (or

decrease) mortality}
33

APPENDIX 4 (continued)

3. Considering existing conventional and archival satellite telemetry studies, do you believe that 

quantitative or qualitative assessments of post-interaction mortality can be made? Please

describe:

4. Are there sublethal effects (for example: reduced fitness, delayed maturation due to depressed

growth rates, etc.) that should be factored in to an assessment of post-interaction mortality? If

so, how would you incorporate sublethal effects into the post-interaction mortality criteria?

5. Based on available information from archival and/or conventional satellite telemetry what

behavioral factors, if any, should be considered and evaluated as an indicator of altered or

compromised post-interaction behavior? 

1. Diving patterns

2. Movement patterns

3. Other (describe):

Please provide additional written comments supporting your above response:

6. In considering how to evaluate post-interaction mortality, how would you recommend

expanding or contracting the current post-hooking criteria categories of interaction? (see

February 16, 2001 memo for current criteria)

7. Please provide a post-hooking mortality rate (or range) or ranking for each proposed category

you identified in #3 above and provide an explanation of your rationale for assigning either a

quantitative rate (for example: X% or X-Y%) or a qualitative ranking (for example: high

probability of mortality, moderate probability of mortality, low probability of mortality):

8. Please provide any additional comments or recommendations you may have relative to the

issue of post-interaction mortality.
34

APPENDIX 5: BACKGROUND DOCUMENTS PROVIDED TO PARTICIPANTS

NMFS Documents on Post-Interaction Mortality Criteria

1. January 4, 2001 Knowles Memorandum to Powers: F/PR recommended criteria for posthooking mortality including comments received on strawman

2. February 8, 2001 Knowles Memorandum to Hogarth: F/PR response to internal

comments and associated documents

3. February 16, 2001 Fox/Knowles/Morehead Memorandum to Hogarth: Decision

memorandum establishing post-hooking criteria

Additional Background/Information Documents

Aguilar, R., J. Mas, and X. Pastor. 1992. Impact of Spanish swordfish longline fisheries on the

loggerhead sea turtle Caretta caretta population in the western Mediterranean. In: J.I.

Richardson and T.H. Richardson (compilers). Proceedings of the Twelfth Annual

Workshop on Sea Turtle Biology and Conservation. NOAA Tech. Memo. NMFSSEFSC-361, pp 1-6.. AND Eric Hawk electronic mail to B. Schroeder et al, January 31,

2001. “Conversation with Aguilar and Pont.” [e-mail clarifies several issues in the 1992

study].

Balazs, G.H. 1994. Satellite Monitoring: A potential method for evaluating post-release survival

of hooked sea turtles in pelagic habitats. In: Research Plan to Assess Marine Turtle

Hooking Mortality: Results of an Expert Workshop held in Honolulu Hawaii, November

16-18, 1993. NOAA-Tech. Memo. NMFS-SWFSC-201.

Balazs, G.H., D.R. Kobayashi, D.M. Parker, J.J. Polovina, and P.H. Dutton. 2000. Evidence for

counter-current movement of pelagic loggerhead turtles in the north Pacific Ocean based

on real-time satellite tracking and satellite altimetry. In: H.Kalb and T. Wibbels

(compilers) Proceedings of the Nineteenth Annual Symposium on Sea Turtle

Conservation and Biology. NOAA Tech. Memo. NMFS-SEFSC-443, p 21.

Bjorndal, K.A., A.B. Bolten, and B. Riewald. 1999. Development and use of satellite telemetry

to estimate post-hooking mortality of marine turtles in the pelagic longline fisheries. 

NOAA Fisheries Southwest Fisheries Science Center H-99-03C.

Chaloupka, M., D. Parker, and G. Balazs. Modeling post-release mortality of pelagic loggerhead

sea turtles exposed to the Hawaii-based longline fishery. Submitted to Fishery Bulletin. 
35

APPENDIX 5 (continued)

Eckert, S.A. 1994. Evaluating the post-release mortality of sea turtles incidentally caught in 

pelagic longline fisheries. In: Research Plan to Assess Marine Turtle Hooking Mortality:

Results of an Expert Workshop held in Honolulu Hawaii, November 16-18, 1993. 

NOAA-Tech. Memo. NMFS-SWFSC -201.

Jacobson, E. 1995. Veterinary experiences with hooked sea turtles. Edited transcript of verbal

presentation. In: Guidelines for Handling Marine Turtles Hooked or Entangled in the

Hawaii Longline Fishery: Results of an Expert Workshop Held in Honolulu, Hawaii,

March 15-17, 1995. NOAA Tech. Memo. NMFS-SWFSC-222

Parker, D.M., G.H. Balazs, S.K.K. Murakawa, and J.J. Polovina. 2005. Post-hooking survival of

sea turtles taken by pelagic longline fishing in the north Pacific. In: M.S. Coyne and R.D.

Clark (compilers) Proceedings of the Twenty-first Annual Symposium on Sea Turtle

Biology and Conservation. NOAA Tech. Memo. NMFS-SEFSC-528, pp 50-52.

Parker, D.M., G.H. Balazs, and J.J. Polovina. 2001. Estimation and Comparison of time spent

on surface for pelagic sea turtles using the Telonics ST10/18 surface-time-counter

function. NOAA Fisheries Southwest Fisheries Science Center.

Riewald, B., A.B. Bolten, and K.A. Bjorndal. 2000. Use of satellite telemetry to estimate posthooking behavior and mortality of loggerhead sea turtles in the pelagic longline fishery in

the Azores. Final Contract Report to National Marine Fisheries Service, Honolulu

Laboratory.

Swimmer, Y., R. Brill, and M. Musyl. 2002. Use of pop-up satellite archival tags to quantify

mortality of marine turtles incidentally captured in longline fishing gear. Marine Turtle

Newsletter 97:3-7.

Work, T.M., and G.H. Balazs. 2002. Necropsy findings in sea turtles taken as bycatch in the

north Pacific longline fishery. Fish. Bull. 100: 876-880.