Developing and Evaluating Methods to 

Determine Abundance and Trends of 

Northwest Atlantic Loggerhead Turtles

Barbara A. Schroeder

Alan B. Bolten

Robert F. Hardy

Jennifer L. Keene

William L. Kendall

Ann Marie Lauritsen

Trent L. McDonald

Christopher R. Sasso

Jeffrey A. Seminoff

U.S. Department of Commerce 

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

NOAA Technical Memorandum NMFS-OPR-67 

October 2020 
 
Developing and Evaluating Methods to 

Determine Abundance and Trends of 

Northwest Atlantic Loggerhead Turtles

Barbara A. Schroeder

Alan B. Bolten

Robert F. Hardy

Jennifer L. Keene

William L. Kendall

Ann Marie Lauritsen

Trent L. McDonald

Christopher R. Sasso

Jeffrey A. Seminoff

NOAA Technical Memorandum NMFS-OPR-67 

October 2020 

U.S. Department of Commerce 

Wilbur Ross, Secretary

National Oceanic and Atmospheric Administration

Neil Jacobs, Acting Under Secretary for Oceans and Atmosphere

 

National Marine Fisheries Service

Chris Oliver, Assistant Administrator for Fisheries 
Literature citation should read as follows: 

Schroeder, B.A., A.B. Bolten, R.F. Hardy, J.L. Keene, W.L. Kendall, A.M. Lauritsen, T.L. 

McDonald, C.R. Sasso, J.A. Seminoff. 2020. Developing and Evaluating Methods to Determine 

Abundance and Trends of Northwest Atlantic Loggerhead Turtles. NOAA Technical 

Memorandum NMFS-OPR-67, 28 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: 

https://www.fisheries.noaa.gov/resources/allpublications?title=&field_category_document_value%5Btechnical_memo%5D=technical_memo

&field_species_vocab_target_id=&sort_by=created
TABLE OF CONTENTS

EXECUTIVE SUMMARY 1 

PART I:

 SUMMARY OF A WORKSHOP TO DEVELOP AND EVALUATE

 METHODS TO DETERMINE ABUNDANCE AND TRENDS OF

 NORTHWEST ATLANTIC LOGGERHEAD TURTLES 2 

PART II:

 DEVELOPING AN AERIAL SURVEY RESEARCH METHODOLOGY: 

 NEXT STEPS 15 

PART III:

 EXAMPLE OF A ROTATING PANEL AERIAL SURVEY STUDY DESIGN 16 

APPENDICES:

 APPENDIX I: PARTICIPANT LIST 20 

 APPENDIX II: WORKSHOP AGENDA 21 
1 

EXECUTIVE SUMMARY

The National Marine Fisheries Service, Office of Protected Resources, convened a Workshop 

November 15-17, 2016 with the following objective: determine whether an in-water sampling 

plan for Northwest Atlantic loggerhead sea turtles (Caretta caretta) in neritic foraging habitats 

can or cannot be practically designed and implemented to provide long-term, statistically robust 

population abundance estimates to assist in monitoring population trends over time. The 

Workshop was hosted by the United States Fish and Wildlife Service and was held at the United 

States Geological Survey St. Petersburg Coastal and Marine Science Center, 600 4th St S, St. 

Petersburg, FL 33701. Experts in sea turtle biology, sea turtle in-water and aerial survey 

monitoring techniques, and experts in assessing abundance and trends in terrestrial and non-sea 

turtle marine taxa participated in the Workshop. 

The Workshop opened with presentations and discussions on current abundance sampling 

methodologies and analytical approaches for sea turtles and other taxa. These presentations 

included line transect methodologies (aerial- and vessel-based) and capture surveys (capturemark-recapture and catch-per-unit-effort analyses). Occupancy and density modeling were also 

discussed. Biological and ecological constraints and challenges were presented and discussed for 

the various methodologies. 

Workshop participants discussed and coalesced around the development of a sea turtle-focused 

aerial survey research methodology as the most feasible approach to estimating in-water 

abundance and monitoring population trends of Northwest Atlantic loggerheads over time. 

Workshop participants discussed sampling plans and identified the most important next steps 

toward developing a robust, sea turtle-focused aerial survey research methodology. These next 

steps are intended to guide survey design development. 

 

Following the Workshop, the conveners requested additional input from Dr. Trent McDonald 

regarding his recommendations to use a rotating panel design aerial survey to provide long-term 

population trend information for the Northwest Atlantic loggerhead population. Dr. McDonald 

presented an outline for such a study design, presented in Part III of this Workshop report. 
2 

PART I: SUMMARY OF A WORKSHOP TO DEVELOP AND EVALUATE METHODS 

TO DETERMINE ABUNDANCE AND TRENDS OF NORTHWEST ATLANTIC 

LOGGERHEAD TURTLES

INTRODUCTION

The Workshop was convened by National Marine Fisheries Service Office of Protected

Resources and hosted by the United States Fish and Wildlife Service; November 15–17, 20161. 

The Workshop was held at the offices of the United States Geological Survey St. Petersburg 

Coastal and Marine Science Center, 600 4th St S, St. Petersburg, FL 33701. The Participant List 

and Workshop Agenda can be found in Appendix 1 and Appendix 2, respectively. 

The purpose of the Workshop was to determine whether an in-water sampling plan for Northwest 

Atlantic loggerhead sea turtles (Caretta caretta) in neritic foraging habitats can or cannot be 

practically designed and implemented to provide long-term, statistically robust population 

abundance estimates to assist in monitoring population trends over time. If a sampling 

methodology was determined to be feasible, the secondary objective was to outline a sampling 

plan, including sampling methodologies, location, and frequency. 

In preparation for the Workshop, NMFS convened a small Steering Committee to structure the 

agenda, identify candidate participants, and develop materials for use before and during the 

Workshop. Members of the Steering Committee are indicated on the Participant List (Appendix 

1). Background literature on abundance estimates, population monitoring, trend analysis, and 

survey methodology was provided to participants to review in advance of the Workshop. 

The Workshop began with the introduction of participants and a review of the meeting agenda 

and goals. The Workshop format provided an opportunity to explore participants’ knowledge and 

insights, gather information and brainstorm methodologies to conduct in-water surveys of the 

Northwest Atlantic loggerhead sea turtle population. The Workshop was not chartered under the 

Federal Advisory Committee Act and as such was not a consensus-seeking meeting. 

SUMMARY OF WORKSHOP PRESENTATIONS

Overview of the Workshop 

B. Schroeder summarized the Workshop background and purpose. The goal of determining longterm population abundance and trends is to meet the management need for information regarding 

population status and recovery trajectory. Robust population trend information is needed for U.S. 

Endangered Species Act of 1973 (ESA) status reviews, ESA Section 7 Consultations, ESA 

Section 10 permits, regulatory actions, and recovery action evaluations. Historically, 

standardized surveys have evaluated loggerhead abundance on nesting beaches. 

While critically important, abundance trends of nesting females are only one aspect of the overall 

1 The information included in this document (which is dated 2020) was current as of the date of the Workshop. 

 
3 

population trend (i.e., they do not directly reflect juvenile or adult male abundance/trends). 

There has been a universal call to understand the abundance and population trends of sea turtles 

away from the nesting beaches (i.e., in-water). The Recovery Plan for the Northwest Atlantic 

Population of the Loggerhead Sea Turtle includes recovery actions that recommend in-water 

sampling to assist in determining abundance and trends to aid in assessing population recovery. 

Knowledge of abundance and trends is needed to evaluate progress toward recovery as specified

in the Demographic Recovery Criteria of the Recovery Plan: 

“(2) Trends in abundance on foraging grounds: A network of in-water sites, both oceanic 

and neritic, distributed across the foraging range is established and monitoring is 

implemented to measure abundance. There is statistical confidence (95%) that a 

composite estimate of relative abundance from these sites is increasing for at least one 

generation.”

Surveys examining loggerhead abundance in neritic habitats are challenging for several reasons, 

including that the species is widespread across habitat types and ocean basins, they live in 

shallow to deep water, and there are divergent opinions on the statistical robustness of various inwater survey methodologies. The purpose of this Workshop was to determine whether an inwater sampling plan of juvenile and adult (>45cm straight carapace length, SCL) Northwest 

Atlantic loggerheads in neritic foraging habitats (including inshore and offshore continental shelf 

waters, < 200m depth) can be practically designed and implemented to provide long-term and 

statistically robust population abundance and trend data. If a survey methodology that could 

yield sufficient statistical power to detect trends was determined to be feasible, then Workshop 

participants were asked to participate in developing a sampling plan. 

Overview of the Biology and Ecology of Northwest Atlantic Loggerheads 

A. Bolten summarized the loggerhead sea turtle as a generalist species with an extensive, 

heterogeneous geographic range (Canada to Mexico), not limited to a specific habitat type (e.g., 

bays, estuaries, coastal areas, inland waterways, soft bottom, hard bottom, seagrass beds, coral 

reefs) and with a generalized diet. Loggerheads have extensive developmental and seasonal 

movement patterns, undergo extensive reproductive migrations, and have a complex life history. 

Loggerheads generally recruit into neritic habitats between 7 and 12 years of age and at a straight 

carapace length (SCL) of 45-65cm. Northwest Atlantic loggerheads reach sexual maturity at 30–

35 years, adult males and females migrate inshore during the breeding season, and females return 

to their natal beach to lay their eggs. There is some evidence of site fidelity to neritic foraging 

grounds but little is known about developmental migrations. The Northwest Atlantic loggerhead 

population consists of 8 or 9 specific haplotypes/sub-populations; however, estimating the 

abundance of these subpopulations with current technologies is not practical due to mixing of 

these subpopulations on the foraging grounds. A survey of the entire continental shelf from 

Canada to Mexico must take into consideration the generalist nature of the species, as well as 

spatial and temporal movements inherent to their complex life history.
4 

Overview Presentations on Currently Employed Sampling Methodologies and Analytical 

Methods for Sea Turtles 

Line-Transect Methodologies (aerial and vessel surveys)

L. Garrison described the methodology and potential biases of line-transect methodologies from 

aerial and vessel surveys. Line-transect surveys for sea turtle assessment are efficient and can 

include multiple species, provide broad-scale synoptic estimates of abundance, generate data to 

support spatial and temporally explicit density models, and have a well understood statistical 

basis for sampling and estimation. To obtain accurate and precise abundance estimates, these 

potential sources of bias must be minimized to the extent possible in either the design and 

execution of the survey, application of the statistical models for estimating abundance, or by 

integrating additional data collected external to the survey. Potential biases include: availability 

(the animal may be below the surface; dive behavior varies seasonally and spatially), detection 

probability / perception (the animal is on the surface but not seen), distance from the trackline 

must be measured accurately, animals may avoid the survey vessel/aircraft, in some aircraft 

observation near the trackline may be more difficult than observing to either side, small animals 

are more difficult to detect (40-45cm SCL for sea turtles is the minimum reliable size), and 

species identification can be difficult. Methodologies to increase the robustness of a Distance 

model based on line-transect data include: deploying two fully independent observer teams to 

estimate perception bias, integrating satellite tag data to characterize dive-surface behavior, 

ensuring that platform configuration provides adequate visibility near the trackline, employing 

accurate tools to measure distance from the trackline, and using experienced, well trained 

observers. Photographic or video-based data collection methods may also be useful in verifying 

species identification and potentially allowing estimation of animal size. Approximately 60 

observations are needed to fit a reliable distance detection function. Additionally, tracklines 

should be uniformly spaced with a random starting point and be oriented perpendicular to 

environmental gradients or bathymetric contours (i.e., across instead of along areas of 

particularly high or low animal density). Spatial modeling is used to integrate observation data 

with habitat variables to predict spatial and temporal variations in population density. Several 

large scale, multiple year aerial survey sampling programs have been recently completed or are 

ongoing (Atlantic Marine Assessment Program for Protected Species - AMAPPS, Deepwater 

Horizon Natural Resource Damage Assessment - NRDA, and Gulf of Mexico Marine 

Assessment Program for Protected Species - GoMMAPPS) although they are currently limited to 

two per season on the Atlantic coast and the surveys of the Gulf of Mexico are under 

development. 

Capture-Mark-Recapture Analyses (in-water capture surveys)

T. Eguchi described the main advantages, challenges, and statistical methods associated with 

capture-mark-recapture (CMR) in-water surveys for determining population trends in loggerhead 

turtles. Advantages of CMR studies include ability to directly adjust captures for detection 

probability and captured animals can be physically tagged and sampled (e.g., blood, health 

assessment, size, age). Abundance can be estimated from multiple capture occasions per time 

period, but this requires that the population in the survey area remain closed to systematic 

movements in and out of the area, or that there are enough capture periods and recaptures to 

model the movement in and out of the area. Abundance can be estimated from a single capture 

occasion per year, although with reduced precision, if survival, immigration, and emigration 
5 

across years are properly accounted for. While estimating abundance through CMR survey is 

possible at localized study areas, it is unlikely that CMR is a feasible approach for sampling the 

widespread geographic and temporal distribution of the Northwest Atlantic loggerhead 

population. Cost would be prohibitive to achieve adequate samples and to implement an 

appropriate design that would meet model assumptions for a CMR survey to estimate abundance 

of the neritic stage. 

Capture Per Unit Effort (CPUE, trawler capture surveys)

M. Arendt described the four main categories of data collected in ongoing trawl capture surveys 

covering four regions off the southeast US coast: species composition, relative abundance, 

spatial distribution, and demographics (including genetics, sex determination, and health 

assessments). In addition, trawl surveys can be used to capture animals for acoustic or satellite 

telemetry tagging. Some of the limitations associated with CPUE trawl surveys include 

incompatibility with hard-bottom habitat, infrequent captures (77% of effort results in no 

captures), and Generalized Linear Model parameters (including explanatory factors describing 

temporal and spatial variation, habitat type, prey, and environmental factors) that do not account 

for the variance in the collected data. In addition, recapture rates are low (~3%), surveys are 

expensive, and surveys can have permitting and planning requirements that may be restrictive. 

Capture Per Unit Effort (CPUE, non-trawler capture surveys: tangle nets, hand capture) 

R. Hardy reviewed non-trawler capture survey methods including set netting, strike netting, dip 

netting, hand capture and incidental capture. Drawbacks of these methods for measuring 

abundance include difficulty and expense of in-water work and their restriction to shallow water. 

Additionally, varying research objectives among non-trawler capture study designs complicate 

data collection for abundance monitoring as most projects are designed to maximize efficiency 

and focus on population hotspots. The methodology of non-trawler capture surveys is often 

tailored to specific study area conditions; i.e., changing habitat types may require a different 

capture method. 

Occupancy and Density Models

B. Kendall discussed the use of occupancy models to determine population trends. Occupancy 

estimation provides a measure of the proportion of the sample area that is occupied by 

conducting multiple independent surveys of species presence within a specific geographic area. 

If these repeated surveys across geographic areas include counts, N-mixture models can be used 

to estimate abundance, if abundance in each area can be assumed to come from a Poisson or 

negative binomial distribution and that the detection ability is the same for each survey. To 

generate occupancy or abundance estimates, detectability needs to be corrected for in the model, 

spatially and temporally. Telemetry can provide useful additional information for modeling 

dynamics of change in relative abundance among survey areas with the assumption that 

movements between areas are constant over time. Collection of covariate data of factors that 

influence detection is useful to stabilize the model results and more precisely define the 

abundance estimate generated from occupancy estimates.

Overview Presentations on Population Abundance/Trend Monitoring for Other Taxa

Manatee Surveys 

C. Fonnesbeck gave an overview of the methodology used to conduct aerial surveys to determine 
6 

a statewide estimate of the Florida manatee (Trichechus manatus) population in Florida. Some 

key points included: (1) the survey area should be stratified by habitat type and survey effort 

should focus on habitat strata that are likely to contain manatees, (2) observation and availability 

bias must be accounted for in order for aerial surveys to be relevant monitoring tools (3) 

appropriate survey design is conditional on spatial scale, habitat configuration and survey 

resources, and (4) population estimates should complement independent estimates of population 

vitality rates for conservation decision support. In an effort to estimate availability, an 

experiment using a submerged wooden manatee replica was conducted to determine the depths 

and distances at which manatees can be seen by observers.

Bird Surveys

J. Sauer reviewed the various methodologies used to conduct North American bird surveys. In 

recent years, many new approaches for population estimation have been developed, and most of 

these methods are used for bird surveys. He described the various scenarios in which design 

based surveys versus model based approaches are used. He noted that the main challenges in 

developing surveys include (1) determining spatial structuring and (2) addressing sparse 

sampling when abundance is low. Regardless of the survey methodology (ground count, aerial 

survey, transect, or roadside), models used to estimate population abundance and change need to 

either directly model detectability, or control for the effects of factors influencing detection. 

Collection of replicate counts, or of covariates such as distance data, observer data, or 

environmental conditions on counts, provide essential information needed for detectability 

estimation.

Terrestrial Species Surveys

T. McDonald focused his presentation on lesser prairie chicken (Tympanuchus pallidicinctus) 

aerial surveys, noting several parallels between loggerhead sea turtle and lesser prairie chicken 

characteristics, including: large geographic range, elusive, mobile, and cryptic. He described the 

multiscale occupancy model used in this survey, which included creating survey blocks in a 

defined area, selecting a Balanced Acceptance Sample of those blocks, flying two transects 

within each block, and using two independent observers per aircraft. He recommended 

referencing Mordecai, R.S. et al. (2011)2

 for further information on survey development to 

measure mobile species distributions.

Additional Presentations on Current Sampling Methodologies and Abundance Data for 

Sea Turtles 

Over the course of the three-day Workshop, participants offered to present the results of their 

own research to help address information gaps, point out information needs, and help the group 

to build on current efforts. Presentations included: 

L. Garrison: Loggerhead Broad Scale Abundance Data 2011-2012 

At the start of Day 2, L. Garrison presented data on loggerhead broad scale abundance data 

collected during surveys conducted as part of the Deepwater Horizon NRDA injury assessment 

by season (Winter, Spring, Summer, Fall) in the Gulf of Mexico in 2011 and 2012. Data were

2 Mordecai, R. S.; Mattsson, B. J.; Tzilkowski, C. J. and Cooper, R. J. 2011. Addressing challenges when studying 

mobile or episodic species: hierarchical Bayes estimation of occupancy and use. Journal of Applied Ecology 48: 56-

66.

 
7 

corrected for sea turtle dive and surface behavior, sighting, and encounter rates. The estimates of 

abundance are approximately 30-50% lower in the Spring and Summer. Participants responded 

that the significant drop in abundance in the Spring and Summer seems unrealistically high and 

cannot be fully accounted for by seasonal changes in dive behavior, turtle availability for 

detection, or seasonal migration. L. Garrison noted that dive behavior does not vary dramatically 

by water temperature based on a sample size of approximately 60 turtles. He also noted that as 

part of the developing Bureau of Ocean Energy Management (BOEM) funded GoMMAPPS 

program, additional aerial surveys and tagging studies are planned

R. Ahrens: Confidence Intervals and Population Trends 

At the start of Day 2, R. Ahrens lead a discussion on the impact of the coefficient of variation 

(CV) on determining the confidence in detecting a population trend. As the amount of data 

collected over time increases, the confidence of detecting a specific measure of change, 

directionality, and magnitude also increases. For conservation purposes, a 5% change or less 

with a 95% confidence interval for one generation (50 years) is the detection goal. However, to 

evaluate conservation actions, it would be beneficial to be able to detect smaller scale changes in 

a shorter time frame. The preliminary data from ongoing aerial surveys (AMAPPS and NRDA

studies) indicate that broad scale aerial survey design can yield a 0.1-0.15 CV while 

incorporating known variability (dive behavior, availability, movement, season) and random 

effects into the statistical analysis of abundance. These abundance estimates are then 

incorporated into a model to detect oscillations in the population. Additionally, there are

historical aerial survey data that could be explored for inclusion in population analysis. 

Workshop Discussions

Following the formal presentations, the Workshop format was structured into a series of 

discussion topics, each with guiding questions to facilitate robust discussion (see Agenda, 

Appendix 2). The discussions surrounding each of the topics are summarized below. Prior to the 

topical discussions, participants discussed the need to determine the desired survey precision to 

answer conservation management questions and touched on availability of funding. 

The relevant demographic recovery criterion from the Recovery Plan for the Northwest Atlantic 

Population of the Loggerhead Sea Turtle was discussed: 

“(2) Trends in Abundance on Foraging Grounds: A network of in-water sites, both 

oceanic and neritic, distributed across the foraging range is established and monitoring is 

implemented to measure abundance. There is statistical confidence (95%) that a 

composite estimate of relative abundance from these sites is increasing for at least one 

generation.” 

In order to help develop conservation management strategies and evaluate their effectiveness for 

recovery of the Northwest Atlantic loggerhead population, participants noted that it would be 

3

. These additional studies 

may shed light on the marked differences in the estimates of seasonal abundance from the 2011-

2012 surveys. 

 

3

Gulf-wide aerial surveys were conducted as part of GoMMAPS during summer 2017, winter 2018 and fall 2018. 

Additional loggerhead turtle telemetry data are also being collected as part of the GoMMAPPS study.
8 

important to be able to detect a 5% change within a 10-year period. It was noted that a 0.15 CV 

is achievable based on results from GoMMAPPs surveys, and that this CV may be further 

reduced with a modified sampling design. 

In addition to the discussion regarding survey precision, it was acknowledged that it is not 

possible to predict the amount of federal, state, or other source funding that might be available to 

study neritic loggerhead abundance over the next few years or decades. However, the 

development of sound methodology is needed to estimate survey budgets and to support efforts 

to seek, identify, and leverage federal, state, or other source funds. Sharing of existing survey 

platforms (e.g., AMAPPS, GoMMAPPS, existing marine mammal surveys) could aid in 

reducing cost.

Survey Methodologies

The Challenge: To date various survey methodologies have been implemented across the neritic 

range of the Northwest Atlantic loggerhead, and many of these surveys have generated 

count/abundance information. The types of surveys include non-capture surveys (i.e., aerial and 

boat-based line transect surveys) and capture surveys (e.g., trawler, tangle net, hand-capture). 

These various survey methodologies all have their respective pros, cons, and challenges. The 

ideal survey methodology to determine population trends will be population-scale relevant, result 

in high confidence that the derived estimates are a true representation of the population, address 

the biological and ecological constraints/challenges, and be logistically and economically 

feasible. Participants discussed the pros, cons, and challenges of the various survey types that 

have been implemented across the range of the Northwest Atlantic neritic loggerhead range. 

Aerial Surveys (With Observers):

• Altitude: Participants discussed the best altitude for conducting aerial surveys. The 

AMAPPS surveys are typically flown at an altitude of 600 feet, high enough that turtles 

are less likely to dive in response to the airplane, but low enough that observers are able 

to identify smaller turtles. NOAA’s Southwest Fisheries Science Center surveys to assess 

loggerhead abundance typically fly between 500-600 feet of altitude. 

• Aircraft Type and Availability: Participants agreed that the best aircraft to conduct aerial 

surveys is a dual-pilot high wing plane (de Havilland Twin Otter), due to low aircraft 

noise, maneuverability, safety, stability, and observer positioning. The NOAA fleet 

includes 4-5 Twin Otters but these are aging and may not be available in 10-15 years. 

Aircraft availability is an important part of ensuring the success of an aerial survey 

design. There are private fleets that contract Twin Otters with bubble windows; however, 

private contracted planes may be more expensive depending on configuration and 

location. It may be possible to schedule regular airtime in advance to ensure regular use 

of planes to guarantee a baseline level of sampling. 

• Pilot and Observer Skill and Consistency: NOAA pilots must meet detailed skill and 

safety criteria. For contracted planes and pilots, identifying pilots who are skilled at 

flying Twin Otters at low altitude is a key safety concern. Observer training and

consistency are also critical elements of a sound survey design. 
9 

• Transect Design: It was suggested that aerial surveys using zigzag lines rather than 

horizontal transect lines may result in airtime efficiency. However, zigzag lines could 

introduce other concerns. Participants agreed that alternate transect designs could be 

evaluated (modeled) for efficiency once the other elements of the sampling design are 

finalized. 

• Turtle Size and Detectability: Neritic-stage sea turtles with carapace length of 40-45cm 

and larger can likely be spotted by an observer in an airplane flying at altitude of 600 

feet. However, participants agreed that additional experimental modeling incorporating 

various sighting conditions (sea state, glare, cloud cover) could be useful to ensure that 

aerial surveys are in fact able to consistently sight sea turtles in the 40-45cm size range. 

Beaufort 0-1 pristine conditions are needed to accurately estimate turtle size from an 

aerial survey, and even under these conditions size classification can be difficult. 

• Sharing Survey Platform with Marine Mammal Surveys: Partnering with marine mammal 

aerial surveys would help to reduce costs on both sides. However, this could reduce the 

accuracy and precision of surveys as they are not designed specifically for loggerhead

turtles. 

Aerial Surveys (With High Resolution Aerial Photogrammetry)4

: 

Participants discussed the pros, cons, and challenges of using high-resolution aerial 

photogrammetry (still photography and/or videography) during aerial surveys in coordination 

with, or in place of observers to record turtle sightings. Challenges to implementing aerial 

photogrammetry studies during aerial surveys in conjunction with observers include: 1) ensuring 

high quality photographs takes away from observer survey time; and 2) an observer position on 

the aircraft is lost to a photographer. It was recommended that comparative studies be undertaken 

to determine detectability of turtles using photogrammetry vs. observers. Some pros of this 

technology are that planes could fly at an altitude of 1,000 feet, which further reduces the 

potential for impacting turtle behavior. However, if the plane is flying quickly and at high 

altitude, it is impossible to capture images of turtles underwater, although this technology is 

likely to improve over time. It was emphasized that the post-processing of videos takes time and 

because of this the cost of aerial photogrammetry is currently more expensive than that of aerial 

surveys using observers only. Machine learning and artificial intelligence technology may 

improve over the next ~5 years making the cost of analyzing photogrammetry footage more 

affordable. The machine learning that is current being used to identify manatees in Australian 

aerial surveys uses Google face algorithms to recognize this species, although error rates are still 

comparable to those of observer coverage (~80%). It was suggested that it may be worth 

collecting video footage now to analyze at a later date when the technology has advanced. The 

cost of collecting video images (both the opportunity cost if observers are displaced and the 

financial cost of the computer and video technology) needs to be considered. 

 

4 This is an active area of research and a lot has changed since the Workshop was held in 2016. For example, it is 

now relatively affordable to conduct surveys with a fixed camera and review of imagery can be conducted by 

experts via computer. Further, machine learning is increasingly being used for such endeavors (e.g., seal detection 

from aerial photography).
10

Satellite Telemetry:

Participants noted that satellite tracking of sea turtle movement is a valuable complement to 

aerial surveys, particularly when the survey designs are complementary. Satellite telemetry 

studies can collect data on dive behavior, movement, and migration (seasonality), and can help 

define critical habitat, examine site fidelity, and other factors that affect density and abundance 

estimates. Some participants noted that aerial and telemetry surveys should coordinate and 

account for availability bias due to weather conditions, time of day, and other variables. 

However, it was mentioned that some current models to estimate abundance have not benefited 

from addition of environmental conditions and it was noted that the greater number of 

parameters introduced into a model can result in unrealistic estimates. Additionally, more 

information is needed from these surveys on the accuracy of depth recording and to determine 

the maximum depth a turtle can be observed. It was emphasized that in order for satellite tagging 

data to assist the model in addressing availability bias, dive data must be both spatially and 

temporally representative within the survey area. There are a variety of capture methods for 

accessing turtles for transmitter deployment and that once the key variables for the telemetry 

survey (location, time of year, size class, and others) have been defined to be complementary to 

an aerial survey design, the cheapest method for capture can be selected.

Workshop participants also noted that satellite telemetry data could be used to develop an 

adaptive aerial survey design by identifying turtle location and selecting sampling units in areas 

of greater density in order to increase sampling precision. It was noted that the distribution of 

tagged turtles is highly dependent upon when and where they have been tagged, and that if this 

design were used, a more rigorous method of tagging would need to be put in place. It was 

suggested that AMAPPS surveys might provide information on density and distribution once the 

analysis is complete.

Trawl Capture Surveys:

Participants noted that, unlike aerial surveys, trawl surveys are able to obtain data from captured 

turtles such as size structure, sex, genetics, and health. Most trawl surveys are limited to 

relatively small survey areas, have a depth range of up to 50 feet, and are restricted from 

accessing sensitive hard bottom habitat. Participants commented that trawl surveys are limited in 

their geographic range and take far more units of effort to collect data than aerial surveys. It was

agreed that trawl surveys could potentially be used to complement other methodologies, but 

should not be pursued as the primary methodology to determine abundance and monitor trends in 

abundance for Northwest Atlantic loggerheads range wide. Avoidance of the trawl by turtles in 

the survey area is not known but may bias estimates from trawl surveys. Trawl survey catch rates 

vary and are often low. Substantial sample sizes are required to achieve relative precision

(confidence interval half-widths) that is comparable to other methods. It was also agreed that 

CPUE is not an appropriate metric to use for abundance estimates as it is a single, nonreproducible data point. 

Non-Trawl Capture Surveys (Net and Hand Capture): 

Participants noted that as compared with trawl surveys, non-trawl capture surveys can access 

diverse habitats, and are cheaper per unit effort. As compared with aerial, these surveys can 

examine characteristics including size class structure, behavior, habitat, health, etc. Each of the 

non-trawl capture survey methods cover relatively small shallow water sites and past studies 
11

have been set up to answer local questions. When asked whether it is possible to adapt this 

methodology to determine abundance trends over time, participants agreed that traditional CMR

studies could not logistically be scaled up to provide abundance data on a rangewide scale given 

the cost and time parameters of this survey. However, these studies could be used to complement 

aerial surveys if characteristics beyond abundance are needed. 

Occupancy Modeling: 

It was explained that occupancy modeling accommodates for both perception and availability 

bias, as long as site fidelity exists. Additionally, surveys tend to be less costly, because after one 

animal of the species of interest is identified (site is occupied), observers can move on to the next 

site. The mobility and migration patterns of sea turtles would be difficult to account for when 

choosing sampling units and time of year for an occupancy survey. It was noted that if there is a 

somewhat even distribution of turtles, occupancy modeling would not provide appropriate data 

for estimating abundance.

 

Some participants stated that occupancy modeling might be able to supplement long-term 

monitoring. Additionally, it was noted occupancy models could have utility in surveying inland 

bays and sounds not captured by aerial surveys due to their small size. However, participants 

agreed that these methods cannot detect the primary trends needed for long-term loggerhead 

conservation management.

Elements of a Successful Sampling Methodology 

Following discussion of the various survey methodologies, it was agreed by the Workshop 

participants that aerial surveys should be the focus for further discussion. The remainder of time 

was spent discussing and developing appropriate elements for an aerial survey. 

 Survey Geographic Scale

The Challenge: The Northwest Atlantic loggerhead population encompasses a large 

geographic region that includes diverse habitats, ranging from shallow inshore bays and 

sounds to deep continental shelf waters. Surveys to date have ranged from geographically 

small (i.e., several km2

) to large (thousands of km2). Geographically small surveys have 

primarily focused in areas where loggerhead turtles are present in sufficient numbers to 

justify sampling. 

Conveners asked participants to consider how a survey methodology might be developed that 

is small enough to be economically and logistically feasible, and yet captures the 

heterogeneity of resources and habitats so that results can be scaled up to provide a robust 

abundance estimate of the entire Northwest Atlantic loggerhead population. Participants were 

asked how large of a geographic area should be sampled to be confident that the sample 

provides an appropriate proxy of abundance, as opposed to changes in distribution. 

Participants were also asked to consider whether any areas along the Atlantic coast can be 

dismissed from the survey in order to develop an economically feasible yet robust 

determination of abundance trends over time. Participants noted that there are a variety of 

statistical approaches to optimizing a study over a large survey area.
12

• Inshore (Bays and Estuaries): Conveners asked participants whether the movement of 

loggerheads off the coast during the winter, and the lower abundance observed in inshore 

areas, eliminates the need to cover these inshore areas. Participants commented that the 

literature demonstrates that the number of turtles in the bays and estuaries is much 

smaller than that in the ocean and stated that the offshore population of turtles could be 

used as an acceptable proxy of overall population. It was mentioned that larger bays and 

sounds could be included in the larger sampling units as they are of sufficient size to fly 

track lines. It was noted that AMAPPS surveys have not covered bays and estuaries, 

which may be leaving a gap in the research. It was also noted that while loggerheads vacate 

some bays and estuaries in the winter, particularly at the northern extent of their range,

additional data are needed to validate these migratory patterns throughout their range. 

• Northern Latitudes: Participants agreed that in the winter, a large amount of the 

loggerhead population moves south of Cape Hatteras, North Carolina, so by surveying in 

the winter the northern range could be eliminated from the survey. In the spring and 

summer sightings are clustered both north and south of Cape Hatteras with fewer 

sightings in the middle of the range.

• Gulf of Mexico: L. Garrison reported that sightings in the Gulf of Mexico demonstrate a 

possible seasonal east-west migration. There was some discussion of whether the 

loggerhead population originating from Mexican waters may be migrating northward to 

influence this trend as well. Participants agreed that further research to arrive at 

meaningful abundance estimates in this area is a research priority.

 Survey Block Design 

Participants discussed the possibility of dividing the geographic area into three larger blocks 

to be surveyed at varying frequency or levels of intensity. Participants noted that a variety of 

geographic block designs could be simulated, and the impacts on management considered, 

before settling on a block design. Participants discussed a variety of ways to break up the 

geographic range, including: 

• Atlantic: 

o (1) North of Long Island; (2) Mid Atlantic Bight (MAB): Long Island to Cape 

Hatteras; (3) South Atlantic Bight (SAB): Cape Hatteras to Cape Canaveral (a 

very high-density turtle area); (4) South North Western Atlantic (SNWA). 

o (1) North Atlantic (break below Long Island); (2) Mid-Atlantic North (Cape Cod 

to Delaware); (3) Mid-Atlantic South (Delaware to Cape Hatteras); South Atlantic 

(Cape Hatteras to Cape Canaveral).

• Gulf of Mexico: Eastern, Western, and Northern 

It was noted that there is a break in loggerhead abundance just north of the tip of Long 

Island. There are occasional aerial surveys in Canadian waters where loggerhead turtles 

occur in lower densities therefore any sampling conducted here could be far less intensive. It 

was also mentioned that it might not be necessary to separate the northern blocks into 

separate regions.
13

Survey Temporal Scale

The Challenge: The Northwest Atlantic loggerhead population is highly migratory. Adult 

males and females are relatively faithful to foraging areas but in higher latitudes they may 

make seasonal migrations in response to water temperature. Additionally, both adult males 

and females undertake reproductive migrations/movements. Adult males may migrate short 

or long distances to breed or may remain resident on their foraging grounds. These 

movements may change over time. Adult females migrate to their nesting beaches, but not 

every year. These “remigration” intervals can change over an individual’s lifetime. 

Reproductive migrations result in significant changes in local abundance of adult males and 

females during the breeding season. Juvenile neritic loggerheads may make seasonal 

migrations, and may make developmental migrations among and/or between foraging areas. 

These juvenile movements are not well understood at the population level.

• Sampling Duration: Participants discussed the survey duration and frequency likely 

needed to resolve long-term abundance trends. Generation time for loggerheads can be 50 

years or more. It was stated that based on the survey designs discussed (aerial with 

contemporaneous in-water surveys, rotating panel design), it may take a minimum of 10 

years of surveying to detect trends of desired magnitude with statistical confidence.

• Preferred Sampling Season: Participants discussed which season(s) should be chosen for 

a survey to ensure accurate abundance measures. It was noted that the same time should 

be chosen every year, with a good weather window, to eliminate noise in the sampling 

data. Data presented by L. Garrison on loggerhead abundance estimates in the Gulf of 

Mexico showed that winter has the lowest CV. Some participants were concerned that (1) 

turtle availability may be lower in the winter due to longer dive times and (2) winter 

weather conditions are less predictable/favorable raising the time and expense of 

sampling. 

• Availability and Detectability Due to Seasonal/Environmental Conditions: Participants 

discussed the degree to which environmental conditions including water temperature and 

cloud cover affect dive behavior and availability. Water clarity can affect detectability, 

especially nearshore where turbidity is more common. Availability and detectability can 

also be influenced by season. 

• Winter Weather Conditions Impact on Sampling Efficiency and Accuracy: Because bad 

weather is more common in winter than in other times of the year, planes need to be 

booked for a longer window of time to ensure that the full area can be sampled, 

increasing expense. Wintertime surveys are also less efficient because flying occurs in 

more marginal weather. However, there are statistical methods to account for sea state 

and perception bias that occurs because of the season. However, it was noted that if 

surveys were done in the southern blocks in the winter, they would capture turtles from 

the northern blocks that had migrated south, possibly eliminating the need to survey the 

northern blocks. 

Habitat Suitability and Prey Abundance/Composition

Some participants suggested that maps of sea floor types could be combined with ecosystem 
14

information to develop inferences about loggerhead habitat. It was noted that BOEM and 

Army Corps of Engineers have significant habitat maps. However, it was noted that it is 

important for the abundance modeling that the survey design not be tied to a certain habitat, 

but rather that the monitoring include a full distribution of habitat types. 

Rotating Panel Sampling Design 

Participants discussed a rotating panel design that contains two components. One 

component captures frequent data on a small subset of sites (index sites) for trend 

estimation, while the other component surveys novel geographic areas less frequently to 

increase geographic coverage. 

The design suggested in Part III (below) contains rotating panels of survey effort. This

rotating panel sample design allows for 60-80% of the population to have been sampled at 

least once by year 30 of the sampling period. Assuming annual effort and that three to five 

blocks can be placed into each panel of the design, the goal would be to achieve 

approximately 80% power to detect a 5-10% change in a region over 10 years. Greater 

variation between sites than within sites is expected. 

To improve resolution of data, participants suggested coupling aerial surveys with 

contemporaneous surface surveys (e.g., AMAPPS, GoMMAPPS). It was further noted that 

the more sites that can be sampled every year, the more quickly abundance trends can be 

detected with higher levels of confidence. Prior to actual implementation, this and other 

design strategies should be simulated to identify the best survey/sampling design. 

Further Survey Design Considerations 

• Index Sites: It was suggested to select enough index sites to cover 5-10% of the 

population and also to select index sites that are buffered against seasonal influences and 

provide more robust data. However, some participants responded that it is more 

statistically robust to select panels at regular intervals (e.g., every 5 years) than it is to 

hand select index sites. To sample abundance, the design needs to include units from each 

subpopulation across the geographic area.

• Repeat Surveys: It was suggested to implement a form of repeat survey to help compare 

and select the most accurate method (e.g., conducting the same survey with broad scale 

lines and compare this to the same survey with fine scale lines). Participants noted that 

repeat surveys within a close time period (2 days in a row) under the same conditions see 

incredible variability so repeat surveys may be limited in their usefulness. However, it 

was noted that if there is variance between days, it would likely be within the 95% CI. 
15

PART II: DEVELOPING AN AERIAL SURVEY RESEARCH METHODOLOGY: NEXT 

STEPS

The third day of the Workshop was devoted to discussions regarding next steps that should be 

taken to move us forward toward developing an effective aerial survey sampling plan to monitor 

trends in abundance of Northwest Atlantic loggerhead sea turtles (Caretta caretta). The group 

recognized that while numerous aerial surveys have been conducted and some are currently 

ongoing, an aerial survey sampling plan specifically focused on determining long-term trends in 

abundance of Northwest Atlantic loggerheads does not yet exist. The following next steps were 

noted as important elements toward achieving that goal. The group recognized that securing 

long-term funding is a significant hurdle to accomplishing this goal.

• Define management needs relative to the ability of aerial surveys to detect changes in 

abundance across appropriate timeline(s). Define desired level of confidence in those 

abundance estimates. 

• Establish the optimal survey altitude for sea turtles by conducting additional experiments 

at altitudes between 500–1,000ft to examine/understand the size of turtles that can be 

seen and turtle behavior relative to the survey platform. 

• Conduct additional field testing to determine detectability of a range of turtle sizes under 

varying water clarity and sea state conditions. 

• Explore the pros and cons of high definition aerial photogrammetry and use of automatic 

pattern recognition, considering likely improvements in the next 5-10 years. Establish

whether calibration or ground-truthing is needed for aerial photogrammetry using sideby-side flights with both photogrammetry and observers. 

• Ensure relevant aspects of sea turtle life history (e.g., seasonal migrations, behavioral 

state) are considered appropriately in the development of the survey design. 

• Design and conduct an experiment to assess variability of abundance estimates through 

repeat aerial surveys.

• Explore whether existing satellite telemetry data are sufficient to assess the effects of sea 

state on surfacing behavior. 

• Refine measures of surface availability

o Take stock of satellite telemetry data and identify data gaps relative to location, 

life stage, and behavioral state (foraging, migrating, internesting). 

o Design appropriate satellite telemetry experiment(s) to fill identified data gaps. 

o Assess the value of repeated counts to inform surface availability; compare to 

satellite telemetry approach; integrate methods to improve surface availability 

estimation.

• Mine data from all relevant existing aerial surveys to inform a new survey design, 

including block identification if appropriate. Develop simulations to refine survey design. 

• Coordinate survey design and implementation with other ongoing efforts to maximize 

efficiency and reduce duplication/overlap. 

• Develop funding estimates and consider potential funding sources, including leveraging 

existing funding. Develop a plan for and approach to seek funds. 
16

PART III: EXAMPLE OF A ROTATING PANEL AERIAL SURVEY STUDY DESIGN

Following the Workshop, the conveners requested additional input/elaboration from Dr. 

Trent McDonald regarding his recommendations at the Workshop to use a rotating panel 

design aerial survey to provide long-term population trend information for Northwest 

Atlantic loggerhead sea turtles (Caretta caretta). This section provides Dr. McDonald’s 

outline of elements of such a study design. This section is intended to provide additional 

information to inform study design considerations as part of the next steps in planning for 

future surveys. 

• If possible, the most useful population to study is the entire Northwest Atlantic 

continental shelf population, from Mexico to Maine 

• The overall population should be divided into regions. Any workable definition of 

regions could be accommodated. As an example, a workable set of regions may be: 

1. West Gulf of Mexico (GoM) (TX to LA)

2. Northern GoM (LA to FL)

3. Eastern GoM (FL west coast)

4. Southern Atlantic (east coast FL to Cape Hatteras (or Chesapeake Bay))

5. Mid-Atlantic (Cape Hatteras to Long Island (or Cape Cod)) 

6. North Atlantic (Long Island to Canada)

• Grid each region into survey blocks 

1. Survey block size should be based on logistics of aerial flights, with the idea that 

two or more transects will be defined in each block. 

2. Workshop participants floated the idea of survey blocks being 40 × 40 km. 

• Randomly place two transects in each survey block 

1. The first transect should be randomly placed in one half of each block 

2. The second transect should be one-half block width from the first transect

• Draw a spatially balanced master sample (Robertson et al., 2013) of survey blocks across 

all regions. This master sample contains all survey blocks in spatially balanced order. 

• Ideally, funding levels are sufficient to survey a few blocks in every region every year. If

that level of funding is not possible, rotation among regions is workable. For example, 

sampling effort could rotate among 2 regions each year. For example, blocks in West

GoM and Northern GoM could be surveyed during year 1. Northern GoM and Eastern

GoM could receive sampling effort during year 2. Eastern GoM and Southern Atlantic 

could be sampled during year 3, and so on around the east coast.

• A rotating survey effort (rotating panel design) is recommended within regions. A 

reasonable rotating effort design defines two panels (i.e., sets) of survey blocks with
17

rotation schemes equal to “always revisit” ([1-0]) and “two occasions on, three

occasions off” ([2-3]) (Table 1). Blocks that are “always revisited” whenever survey 

efforts are in the region can be considered index blocks. Blocks that are surveyed “two 

occasions on, three occasions off” are considered rotating blocks, are important for 

increasing the geographic distribution of surveys, and inform trends estimated on 

index blocks. The rotation scheme among and within regions is flexible enough to allow

years of no sampling (e.g., when funding is low), provided the overall rotation scheme 

is followed when sampling resumes. 

• The reasons for recommending rotation of effort among blocks, rather than all index 

or all rotating blocks, are as follows: 

Trends are best estimated by revisiting previously surveyed blocks. Accuracy is 

enhanced when new unsampled blocks are surveyed. Rotating split-panel designs 

balance power to detect trends and accuracy of overall population size estimates. 

Most statisticians suggest allocating approximately 70% of annual effort to the [1-0] 

panel (index blocks) and 30% to the rotating panel [2-3]. Assuming 100 blocks can

be surveyed every time survey effort returns to a region, this recommendation

resurveys 70 blocks while thirty other blocks are surveyed twice in a row, then not 

for 3 occasions. After 5 visits to the region, a total of 70 (always revisit) plus 150 

(rotating) blocks will have been surveyed. 

• There are three options for sampling seasons:

1. Treat season (Winter, Summer) as two occasions in the panel rotation scheme. 

That is, occasion 1 occurs during winter, occasion 2 occurs during summer when 

survey efforts return to a region, and occasion 3 occurs during winter when effort 

returns to a region, and so on. 

2. When sampling in a region, sample all planned blocks during both Winter and 

Summer.

3. Augment the AMAPPS/GoMMAPPS sampling. If AMAPPS/GoMMAPPS is 

sampling inregion X during season Y, turtle surveys could sample all planned 

blocks of region X during season Y. If funding levels permit, turtle surveys could also 

sample the same region (i.e., X) during the other season of the same year.
18

Table 1: An example of the [1-0, 2-3] rotation scheme for a given survey region. An “x” 

indicates visiting all survey blocks in that panel (panel = set of survey blocks) that occasion. 

Ideally, occasions are years, but likely will be the occasion when survey efforts return to a 

region. The program allows 1 or more years of no sampling between occasions (e.g., if 

funding is low) provided the rotation scheme is followed when sampling resumes. A 

reasonable effort allocation scheme places 70% of annual sample effort in the [1-0] panel, 

and 30% of annual sample effort in each of the 5 [2-3] panels. The regional data collected 

under this rotation scheme can be analyzed using the methods of Piepho and Ogutu (2002). 

Panel (set 

of survey 

blocks) 

Sample occasion

1 2 3 4 5 6 7 8 9 10 11

1 X X X X X X X X X X X 

2 X X X X X 

3 X X X X 

4 X X X X 

5 X X X X 

6 X X X X X 

References

Amstrup, S.C., T. L. McDonald, and I. Stirling. 2001. Polar bears in the Beaufort Sea: a 30-year

mark-recapture case history. Journal of Agricultural, Biological, and Environmental Statistics, 

6(2):221–234. 

Bromaghin, J.R., T. L. McDonald, I. Stirling, A. E. Derocher, E. S. Richardson, E. V. Regehr, D. 

C. Douglas, G. M. Durner, T. Atwood, and S. C. Amstrup. 2015. Polar bear population dynamics 

in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications, 

25(3):634–651. 

Good, R.E., R. M. Nielson, H. Sawyer, and L. L. McDonald. 2007. A population estimate for 

golden eagles in the Western United States. The Journal of Wildlife Management, 71(2): 395-

402. 

McDonald, T.L. 2003. Review of environmental monitoring methods: survey designs. 

Environmental Monitoring and Assessment, 85(3):277–292. 

Nielson, R.M., L. McManus, T.Rintz, L. L. McDonald, R. K. Murphy, W. H. Howe, and R. E.

Good. 2014. Monitoring abundance of golden eagles in the western United States. Journal of 

Wildlife Management, 78(4):721– 730. 

Piepho, H.P. and J. O. Ogutu. 2002, A simple mixed model for trend analysis in wildlife 

populations. Journal of Agricultural, Biological, and Environmental Statistics, 7(3):350–360. 
19

Robertson, B.L., J. A. Brown, T. L. McDonald, and P. Jaksons. 2013. BAS: Balanced 

Acceptance Sampling of Natural Resources. Biometrics, 69(3):776–784.
20

APPENDIX I: PARTICIPANT LIST

*Barbara A. Schroeder, Workshop 

Convener

National Marine Fisheries Service (NMFS)

*Ann Marie Lauritsen, Workshop Host 

US Fish and Wildlife Service (USFWS)

Jennifer Keene, Workshop Rapporteur

National Marine Fisheries Service (NMFS)

Ocean Associates, Inc. (contractor)

Rob Ahrens, PhD 

University of Florida 

Mike Arendt, PhD 

South Carolina Department of Natural 

Resources

*Alan B. Bolten, PhD 

University of Florida 

Mark Dodd

Georgia Department of Natural Resources

Tomo Eguchi, PhD 

National Marine Fisheries Service (NMFS)

Allen Foley, PhD 

Florida Fish and Wildlife Conservation 

Commission

Chris Fonnesbeck, PhD 

Vanderbilt University 

Lance Garrison, PhD 

National Marine Fisheries Service (NMFS)

Heather Haas, PhD 

National Marine Fisheries Service (NMFS)

*Robert Hardy

Florida Fish and Wildlife Conservation 

Commission

Kristen Hart, PhD 

US Geological Survey (USGS) 

*Bill Kendall, PhD 

US Geological Survey (USGS)

Dennis Klemm

National Marine Fisheries Service (NMFS)

Trent L. McDonald, PhD 

Western EcoSystems Technology, Inc. 

Clint Moore, PhD 

US Geological Survey (USGS)

*Christopher R. Sasso, PhD 

National Marine Fisheries Service (NMFS)

John Sauer, PhD 

US Geological Survey (USGS)

*Jeffrey A. Seminoff, PhD 

National Marine Fisheries Service (NMFS)

Carrie Upite

National Marine Fisheries Service (NMFS)

The meeting was facilitated by Scott 

McCreary and Meredith Cowart

(CONCUR, Inc.)

*Steering Committee
21

APPENDIX II: WORKSHOP AGENDA

DAY 1: NOVEMBER 15, 2016 (TUESDAY)

WORKSHOP START-UP AND GENERAL OVERVIEW

8:30 Welcome - Barbara Schroeder and AnnMarie Lauritsen

8:40 Introduction of Participants, Agenda Review, Ground Rules, Logistics - CONCUR

9:00 Introductory/Background Presentation on Workshop Impetus and Purpose - Barbara 

Schroeder

9:45 Overview of the Biology and Ecology of NW Atlantic Loggerheads – Alan Bolten 

10:00 BREAK

BACKGROUND PRESENTATIONS – EXISTING TURTLE MONITORING/OTHER TAXA MONITORING 

(Each presentation includes 10-15 minutes for clarifying questions)

10:20 Overview Presentations on Currently Employed Sampling Methodologies/Analytical 

Methods for Sea Turtles (10-12 minutes each with 8-10 minutes for questions, use parking lot 

for in-depth discussions that are more appropriate later in agenda)

10:20-10:40: Line-Transect Methodologies (aerial and vessel surveys): Lance Garrison 

10:40-11:00: Capture-Mark-Recapture Analyses (in-water capture surveys): Tomo Eguchi 

11:00-11:20: CPUE (trawler capture surveys): Mike Arendt 

11:20-11:40: CPUE/SPUE/C-M-R (non-trawler capture surveys: tangle nets, hand capture): 

Robert Hardy 

11:40-12:00: Occupancy and Density Models: Bill Kendall

12:00 – 12:15 Wrap Up Morning Session

12:15 - 1:00 LUNCH
22

1:00 Overview Presentations on Population Abundance/Trend Monitoring for Other Taxa

(10-12 minutes each with 8-10 minutes for questions)

• 1:00-1:20: Manatees – Chris Fonnesbeck 

• 1:20-1:40: Birds – John Sauer

• 1:40-2:00: Terrestrial Species – Trent McDonald

BIOLOGICAL AND ECOLOGICAL CONSTRAINTS/CHALLENGES

2:00 – 4:30 Discussion Session: Biological and Ecological Constraints/Challenges

Topic 1: Survey Geographic Scale

The Challenge: The NW Atlantic loggerhead population encompasses a large geographic 

region that includes diverse habitats, ranging from shallow inshore bays and sounds to deep 

continental shelf waters. Surveys to date have ranged from geographically small (i.e., several 

km2) to large (thousands of km2). Geographically small surveys have primarily focused in areas 

where loggerhead turtles are present in sufficient numbers to justify sampling. 

Discussion Questions: 

1. How do we develop a survey methodology that is small enough to be economically and 

logistically feasible, and yet captures the heterogeneity of resources and habitats so that 

we can scale up to generate a robust estimate for the NW Atlantic loggerhead 

population?

2. How large must this geographic region be, i.e., how much of the species range should 

we aim to survey?

3. Can this be accomplished with a series of smaller survey areas that combine to produce 

the range-wide estimate?

4. If so, how would we select these smaller survey areas and are these “index sites”?

5. How large or small should these smaller survey areas be – what is optimal?

6. Are certain survey methodologies more able to address this challenge? Which ones?

7. Are these challenges present for non-turtle taxa and how are they addressed?

Topic 2: Survey Temporal Scale

The Challenge: The NW Atlantic loggerhead population is highly migratory. Adult males and 

females are relatively faithful to foraging areas but, in higher latitudes may make seasonal 

migrations in response to water temperature. Additionally both adult males and females 
23

undertake reproductive migrations/movements. Adult males may migrate short or long 

distances to breed or may remain resident on their foraging grounds. These movements may 

change over time. Adult females migrate to their nesting beaches, but not every year. These 

“remigration” intervals can change over an individual’s lifetime. Reproductive migrations 

result in significant changes in local abundance of adult males and females during the breeding 

season. Juvenile neritic loggerheads may make seasonal migrations, and may make 

developmental migrations among and/or between foraging areas. These juvenile movements 

are not well understood at the population level.

Discussion Questions:

1. How do we design a temporal sampling scheme that addresses the changes in 

abundance resulting from the reproductive movements of adults?

2. How do we design a temporal sampling scheme that addresses the changes in 

abundance resulting from juvenile migrations/movements?

3. How frequently should we conduct surveys?

4. Are certain survey methodologies more able to address this challenge? Which ones?

5. Are these challenges present for non-turtle taxa and how are they addressed?

Topic 3: Habitat Suitability and Prey Abundance/Prey Composition

The Challenge: Changes in habitat suitability can have profound effects on loggerhead 

abundance, especially at smaller geographic scales. Habitat suitability is not well understood 

nor is it currently monitored. Changes in prey abundance/prey composition likewise can have 

profound effects on loggerhead abundance, again, especially at smaller geographic scales. 

Loggerhead prey and effects of changes in prey distribution/composition is not well 

understood.

Discussion Questions:

1. How do we design a sampling program that takes into account changes in suitability of 

habitats?

2. How do we design a sampling program that takes into account changes in prey 

abundance and prey composition?

3. Are certain survey methodologies more able to address this challenge? Which ones?

4. Are these challenges present for non-turtle taxa and how are they addressed?

5:00 Day 1 Wrap-up and Overview of Day 2

5:30 Adjourn
24

DAY 2: NOVEMBER 16, 2016 (WEDNESDAY)

8:30 Review Day 2 Agenda

SURVEY METHODOLOGIES

Discussion Session: Survey Methodologies

The Challenge: To date various survey methodologies have been implemented across the 

neritic range of the NW Atlantic loggerhead, many of these surveys have generated 

count/abundance information. The types of surveys include non-capture surveys (i.e., aerial 

and boat-based line transect surveys) and capture surveys (trawler, tangle net, hand-capture). 

These various survey methodologies all have their respective pros, cons, and challenges. The 

ideal survey methodology to determine population trends will be population-scale relevant, 

result in high confidence that the derived estimates are a true representation of the population, 

address the biological and ecological constraints/challenges discussed on Day 1, and be 

logistically and economically feasible. 

8:45 – 10:00

Topic 4: Aerial Surveys 

Discussion Questions: 

1. What are the logistical requirements for aerial surveys and how do these affect results?

a. Altitude (size of turtles observable?)

b. Geographic Scale (inshore and offshore?)

c. Environmental Conditions (e.g., sea state, glare)

d. Extent of Habitat Surveyed?

2. How is detectability assessed and incorporated?

3. How are the biological constraints/challenges discussed above addressed?

4. Are habitat or prey changes incorporated?

5. Can the results be scaled up to the population?

6. What are the key pros and key cons?

7. Can the cons be overcome methodologically or analytically? If so, how?

8. Do repeat surveys generate similar results within the same survey timeframe and area?

9. Would it be feasible to structure a survey to determine if estimates of abundance 

derived are consistent/repeatable via the various methodologies? 

10:00 – 10:30 BREAK
25

10:30 – 12:00

Topic 5: Trawl Surveys

Discussion Questions:

1. What are the logistical requirements for trawl surveys and how do these affect results?

a. Geographic Scale (inshore and offshore?)

b. Extent of Habitat Surveyed?

2. How is detectability assessed and incorporated?

3. How are the biological constraints/challenges discussed above addressed?

4. Are habitat or prey changes incorporated?

5. Can the results be scaled up to the population?

6. What are the key pros and key cons?

7. Can the cons be overcome methodologically or analytically? If so, how?

8. Do repeat surveys generate similar results within the same survey timeframe and area?

9. Would it be feasible to structure a survey to determine if estimates of abundance 

derived are consistent/repeatable via the various methodologies? 

12:00 - 1:00 LUNCH

1:00 – 3:00 

Topic 6: Capture Surveys 

Tangle Set Net

Discussion Questions:

1. What are the logistical requirements for tangle net surveys and how do these affect 

results?

a. Geographic Scale (inshore and offshore?)

b. Extent of Habitat Surveyed?

c. Environmental Conditions (e.g., sea state, wind, currents)

2. How is detectability assessed and incorporated?

3. How is abundance measured/calculated (e.g., CPUE, CMR)?

4. How are the biological constraints/challenges discussed above addressed?

5. Are habitat or prey changes incorporated?

6. Can the results be scaled up to the population?

7. What are the key pros and key cons?

8. Can the cons be overcome methodologically or analytically? If so, how?

9. Do repeat surveys generate similar results within the same survey timeframe and area?
26

10. Would it be feasible to structure a survey to determine if estimates of abundance 

derived are consistent/repeatable via the various methodologies? 

Hand-Capture Surveys (including hand, dip-net, strike-net)

Discussion Questions:

1. What are the logistical requirements for hand-capture surveys and how do these affect 

results?

a. Geographic Scale (inshore and offshore?)

b. Extent of Habitat Surveyed?

c. Environmental Conditions (e.g., sea state, visibility)

2. How is detectability assessed and incorporated?

3. How is abundance measured/calculated (e.g., CPUE, CMR)?

4. How are the biological constraints/challenges discussed above addressed?

5. Are habitat or prey changes incorporated?

6. Can the results be scaled up to the population?

7. What are the key pros and key cons?

8. Can the cons be overcome methodologically or analytically? If so, how?

9. Do repeat surveys generate similar results within the same survey timeframe and area?

10. Would it be feasible to structure a survey to determine if estimates of abundance 

derived are consistent/repeatable via the various methodologies? 

3:00 – 3:30 BREAK 

3:30 – 4:30 

Topic 7: Occupancy and Density Modeling

Discussion Questions:

1. What are the input data needed for these modeling approaches?

2. Are these modeling approaches appropriate for sea turtles?

3. Can the results be scaled up to the population?

4. What are the key pros and key cons?

5. Can the cons be overcome methodologically or analytically? If so, how?

5:00 Day 2 Wrap-up and Overview of Day 3

5:30 Adjourn
27

DAY 3: NOVEMBER 17, 2016 (THURSDAY)

8:30 Review Day 3 Agenda

WHERE DO WE GO FROM HERE? 

Developing a Successful Sampling Program

The Challenge: Numerous projects sampling NW Atlantic neritic loggerheads have been 

conducted in the past or are currently ongoing. These include line-transect surveys (aerial and 

vessel-based) and capture surveys (trawl, tangle net, dipnet, hand-capture). These projects 

span various geographic and temporal scales. Not all of these projects were designed to 

measure/monitor abundance and/or contribute to an index of abundance. Questions and 

divergent views exist as to whether any/all of these ongoing surveys are or can generate/ 

contribute to long-term population trend monitoring in their current form. There is currently a 

lack of integration among/across these surveys in terms of contributing to long-term population 

trend monitoring. Given the Day 1 and Day 2 discussions regarding the various methodologies 

for sampling, our challenge is to develop a comprehensive, effective sampling program to 

monitor long-term population trends of NW Atlantic neritic loggerheads.

8:45 - 12:00 

Topic 8: Overarching Elements of a Successful Sampling Program

Discussion Questions:

1. What confidence level is needed regarding long-term population trend information to 

make effective conservation management decisions?

2. How much of the population do we need to ‘sample’ to be confident that our sample is 

an appropriate proxy?

3. How much of the neritic distribution of the population do we need to sample to be 

confident that our sample is an appropriate proxy?

• Inshore areas (bays, sounds, estuaries)

• Offshore areas (shelf waters offshore of the Atlantic/GOM coast)

4. What is the temporal frame within which we should be sampling the population to be 

confident that our sample is an appropriate proxy?
28

12:00 - 1:00 LUNCH

1:00-3:00 

Topic 9: Toward a Successful Long-term Sampling Program

Discussion Questions and Tasks:

1. Are there ongoing surveys, in their present form, that are sampling the population in an 

appropriate way to be confident that our sample is an appropriate proxy for the NW 

Atlantic loggerhead population?

2. If current efforts are not sufficient, what changes/modifications or wholly new 

approach(es) would allow us to accomplish the goal of a long-term sampling strategy to 

confidently monitor trends in abundance, considering logistics and cost and meeting the 

criteria discussed above (confidence level, proportion of population surveyed, 

geographic range, and temporal frame).

3. Outline and draft the specific elements, including methodology(ies), geographic 

sampling area, temporal sampling plan, ground-truthing, estimated costs, and all other

necessary elements to frame, in detail, a long-term sampling program for monitoring 

neritic NW Atlantic loggerhead population trends.

WRAP UP AND WORKSHOP CONCLUDES

3:00 Parking Lot Issues and Areas/Topics Requiring Further Work 

3:30 Next Steps 

4:00 Acknowledgements and Adjourn