NOAA Technical Memorandum NMFS-PIFSC-10

July 2007

Chemoreception in Loggerhead Sea Turtles: An 

Assessment of the Feasibility of Using Chemical 

Deterrents to Prevent Sea Turtle Interactions 

with Longline Fishing Gear 

Amanda Southwood, Benjamin Higgins, 

Richard Brill, and Yonat Swimmer 

Pacific Islands Fisheries Science Center 

National Marine Fisheries Service 

National Oceanic and Atmospheric Administration 

U.S. Department of Commerce
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Pacific Islands Fisheries Science Center 

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Chemoreception in Loggerhead Sea Turtles: An 

Assessment of the Feasibility of Using Chemical 

Deterrents to Prevent Sea Turtle Interactions with 

Longline Fishing Gear 

Amanda Southwood,1 Benjamin Higgins,2 

Richard Brill,3 and Yonat Swimmer4 

1

Joint Institute for Marine and Atmospheric Research 

University of Hawaii 

2570 Dole Street, Honolulu, Hawaii 96822-2396 

2

NOAA Fisheries Sea Turtle Facility 

4700 Avenue U 

Galveston, Texas 77551 

3

Virginia Institute of Marine Science 

P.O. Box 1346, Gloucester Point, Virginia 23062 

4

Pacific Islands Fisheries Science Center 

National Marine Fisheries Service 

2570 Dole Street, Honolulu, Hawaii 96822-2396 

NOAA Technical Memorandum NMFS-PIFSC-10

 July 2007

 iii 

ABSTRACT 

The mechanisms by which sea turtles are attracted to and become hooked and 

entangled in commercial fishing gear are not well understood. Identification of sensory 

attractants and repellants may prove useful in developing gear and bait modifications to 

reduce sea turtle bycatch in commercial fisheries. We conducted experiments to investigate 

the ability of loggerhead turtles (Caretta caretta, Linnaeus 1758) to use chemical and flow 

cues to successfully locate squid bait and also tested to see if chemical modification of squid 

bait would reduce the turtles’ ability and/or willingness to track and locate bait. Captivereared juvenile loggerhead turtles were placed in a seawater-filled flume tank with a current 

of 3–5 cm·sec-1. A nylon bag containing either nylon (control), squid, or squid that had been 

marinated in 2-phenylethanol or shark-derived compounds was placed in the current upstream 

from the turtle. Trials were conducted in darkness, and the behavior of turtles was monitored 

and recorded using an IR-sensitive video surveillance system. The presence of squid bait in 

the tank elicited feeding and searching behavior; however, turtles showed limited ability to 

locate squid bait in the absence of visual cues. Only 25–33% of turtles located and ate the 

squid bait during the 10-minute trial period. These results indicate that visual cues are 

important for foraging success in loggerhead turtles, and chemoreception likely plays a 

secondary role. Treatment of squid with 2-phenylethanol or shark-derived compounds did not 

prevent turtles from eating squid bait. There was no significant difference in the number of 

turtles that located and ate bait between control, squid, and chemically modified squid trials. 

An effective chemical deterrent for sea turtles has yet to be identified. 

 Keywords: behavior, bycatch, fisheries, olfaction, sea turtle 
 
INTRODUCTION 

The incidental capture of sea turtles in commercial longline fishing gear is an issue of 

growing concern for fishers, fisheries management agencies, and environmental groups. 

Bycatch of sea turtles in longline gear designed to capture pelagic fish species is a source of 

mortality for endangered leatherback turtles (Dermochelys coriacea, Vandelli 1761), 

loggerhead turtles (Caretta caretta, Linnaeus 1758), green turtles (Chelonia mydas), and olive 

ridley turtles (Lepidochelys olivacea, Eschscholtz 1829) in the North Pacific Ocean (Balazs 

and Pooley, 1994). To help speed the recovery of sea turtle populations, the National Marine 

Fisheries Service (NMFS; NOAA Fisheries) has enacted numerous mitigation measures to 

reduce or prevent the incidental capture of sea turtles by U.S. longline fleets in all oceans 

(www.nmfs.noaa.gov/pr/PR3/regulations.html). Regulations currently required in all U.S. 

longline fishing operations, such as use of large circle hooks and fish bait, may not be viable 

options in all foreign fisheries, which account for a much larger fishing effort than the U.S. 

longline fleets (Lewison et al., 2004.) Accordingly, alternative methods to minimize or 

prevent sea turtle bycatch in longline gear are being investigated. 

 

Sea turtles and pelagic fishes are evolutionarily distinct groups of animals with 

differences in sensory biology that may influence the ways in which they interact with fishing 

gear. The factors that attract sea turtles and target fish species to longline gear and bait are 

not well understood, but numerous sensory cues may be involved. In 2000, a 

multidisciplinary interagency collaborative effort was initiated by NOAA Fisheries scientists 

to investigate the visual, auditory, and chemosensory abilities of sea turtles and pelagic fishes 

to identify differences in sensory abilities that may be exploited to develop gear and bait 

attractive to fish but undetectable or unattractive to sea turtles. This paper presents results 

from a series of studies designed and conducted to assess the chemosensory abilities of 

loggerhead turtles and explores the feasibility of using chemical deterrents to prevent sea 

turtles from interacting with longline fishing gear. 

 

The term “chemoreception” refers to an organism’s ability to detect and differentiate 

chemical cues in its environment by taste (gustation) or smell (olfaction). Chemical cues may 

be used for prey detection and location (Zimmer and Butman, 2000), orientation during long 

distance migrations (Atema et al., 2002; Doving and Stabell, 2003), or intraspecific 

communication related to reproduction and predator avoidance (Weldon, 1990; Hara, 1993; 

Wisenden, 2003 and references therein). The role of chemoreception in the ecology of marine 

invertebrates and fishes has been well-studied, but relatively little information is available on 

the ecological importance of chemoreception for marine reptiles. 

 

We were primarily interested in determining the role of chemoreception in the 

foraging and avoidance behaviors of loggerhead turtles. Although sea turtles are generally 

considered to be visual predators, other sensory cues (tactile, flow, chemical) may also 
 2 

contribute to foraging success. There is compelling evidence that chemoreception is an 

important factor in food recognition by post-hatchling and juvenile sea turtles (Grassman and 

Owens, 1982; Constantino and Salmon, 2003), but the ability of sea turtles to use chemical 

cues to effectively track and locate prey has not been studied. If sea turtles use 

chemoreception to detect and find food sources in their aquatic environment, then chemicals 

emanating from squid and mackerel bait may play a role in attracting sea turtles to longline 

fishing gear. Chemical modifications that make bait less appealing or more difficult for sea 

turtles to detect may help deter sea turtles from interacting with fishing gear. 

 

The ability of aquatic organisms to use chemical cues to locate prey can be affected by 

numerous factors. Results from studies of chemical tracking behavior in marine invertebrates 

and fishes show that flow patterns, in particular, play a critical role in the successful location 

of prey in a dynamic and complex environment. Orientation into flow (rheotaxis) is a 

common component of searching strategies, as the most likely source of an odor would be 

upstream (Hodgson and Mathewson, 1978; Weissburg and Zimmer-Faust, 1994; ZimmerFaust et al., 1995; Vickers, 2000; Carton and Montgomery, 2003; Kanter and Coombs, 2003). 

We designed a flume tank in which squid bait was presented to loggerhead turtles under 

unidirectional flow conditions to assess the ability of loggerhead turtles to use chemical cues 

in combination with flow cues to locate a food source in the absence of visual cues. These 

experiments were designed to gauge the relative importance of chemoreception for successful 

prey location. The flume tank was also used to investigate behavioral responses of 

loggerhead turtles to bait that had been chemically modified. We presented loggerheads with 

squid that had been treated with a chemical odor-masking agent, 2-phenylethanol. Loggerhead 

turtles are capable of detecting 2-phenylethanol, although in previous studies they showed no 

sign of attraction to this chemical and are unlikely to identify it with a food source at first 

exposure (Manton et al. 1972; Southwood et al., 2005). We also presented loggerhead turtles 

with squid that had been treated with skin secretions of tiger sharks (Galeocerdo cuvier, 

Lesueur 1822), a known predator of sea turtles. Several species of reptile display avoidance 

and defensive behavior when presented with skin extracts and rinses from predators (Dial, 

1990; Weldon, 1990), and we were interested in assessing the potential for using predatorderived compounds to elicit avoidance behavior in sea turtles. We hypothesized that 

loggerhead turtles presented with chemically modified squid would exhibit a lower rate of 

success in locating bait compared with turtles presented with untreated squid. 

MATERIALS AND METHODS 

Test Animals 

All experiments were conducted with 2-year-old loggerhead sea turtles at the NOAA 

Fisheries Sea Turtle Facility (NOAA-STF) in Galveston, Texas, U.S.A. during a 3-week 

period in September – October 2004. Loggerhead turtles at this facility originate from 

hatchlings collected from Florida nesting beaches and are captive reared until 3 years of age, 

at which time they are released off the Florida coast. Details of animal husbandry at the 

NOAA-STF are described by Higgins (2003). Briefly, yearling turtles were housed 
 3 

individually in 76 cm diameter (45 cm depth) circular plastic containers with mesh flooring. 

Containers were suspended in rectangular fiberglass raceways (6.5 x 2.0 x 0.6 m) filled with 

6435 L of seawater at 29 °C–30 °C. The raceways were drained and new seawater pumped in 

every other day. Ambient air temperature in the facility was regulated at 30 °C. Skylights in 

the facility roof exposed the turtles to a natural light photoperiod that varied with season. At 

the time of our experiments, local sunrise and sunset were at approximately 0630 and 1730, 

respectively. Fluorescent lights above the tanks were used to supplement natural sunlight and 

were on from 0730 to 1600. Turtles were fed a ration of two squid (approximately 150–200 

grams) three times a week when experiments were not being conducted. The average mass of 

turtles used in this study was 8.35 ± 0.14 (S.E.M.) kg and average straight carapace length was 

42.08 ± 0.23 (S.E.M.) cm. 

Experiment Tank 

 A fiberglass rectangular tank was used to assess the behavior and tracking abilities of 

juvenile loggerhead turtles presented with untreated squid bait and chemically modified squid 

bait under steady, semi-turbulent flow conditions. The working section of the tank consisted 

of a 0.9 x 0.9 m start chamber separated from a larger (2.1 x 0.9 m) main chamber by a gate 

attached to a pulley system (Fig. 1). The tank was filled to a depth of 26 cm with seawater at 

29 °C. A series of three plastic honeycomb baffles (Specialized Metals, Coral Springs, FL) 

were located on the side of the main chamber opposite the start chamber and gate. During 

trials, seawater was pumped through these baffles at a volume flow rate of 275 l⋅min-1 and 

drained out of the tank through a drain grate on the floor of the start chamber. A Marsh 

McBirney electromagnetic flowmeter (Model 2000) was used to generate flow profiles of the 

tank under trial conditions. Flow speed was 3–5 cm⋅sec

-1 in the central portion of the flume 

and tapered off to < 1 cm⋅sec

-1 along the tank walls. 

 

Treatments 

Seventeen turtles were randomly selected and assigned to either the 2-phenylethanol 

(2-PEA) or tiger shark skin extract (TIGER) treatment group. Each turtle in the 2-PEA (N = 

8) and TIGER (N = 9) treatment groups was subjected to three trials; an untreated squid trial, 

a chemically modified squid trial, and a control trial. For the untreated squid trial, a nylon 

bag containing ~ 20–25 g of chopped squid was secured onto the side of the baffle facing into 

the main chamber. The nylon bag was positioned 12 cm below the water surface along the 

midline of the tank. For the chemically modified squid trial, a nylon bag filled with ~ 20–25 

g chopped squid marinated overnight in either 0.1 M 2-phenylethanol (2-PEA treatment 

group) or skin secretions obtained from live, wild-caught tiger sharks (TIGER treatment 

group) was secured to the baffle. The third type of trial was a control trial in which the nylon 

bag was simply filled with more nylon and secured to the baffle (i.e., no squid, untreated or 

chemically modified, was presented to the turtle). We conducted the nylon-only control trials 

to see if flow cues alone could induce the same behaviors that we observed for chemical trials. 

Trial order was randomized for each treatment group. 
 4 

All chemicals used for these experiments were approved by the NOAA Fisheries Sea 

Turtle Facility staff veterinarian. 

Trial Protocol and Analysis 

Turtles were fasted for 36–44 hours prior to trials and all trials were conducted 

between 0800 and 1600. A trial was initiated by placing a turtle in the start chamber with the 

gate closed. The turtle was left in the start chamber for a 20-minute acclimation period in 

static water, and then seawater flow through the tank was initiated. Seawater flowed through 

the baffles and the nylon bag, effectively pushing a plume of chemical towards the start 

chamber. Two minutes after flow began, the gate separating the start chamber from the main 

chamber was lifted, and the turtle was free to explore both chambers for 10 minutes. All trials 

were conducted in complete darkness. During the exploration period, the turtle’s behavior 

was monitored and recorded using a system of infrared (IR) spotlights and IR-sensitive 

cameras interfaced with a digital video recorder (DVR) (A-1 Services Unlimited Inc., 

Bradenton, Florida). 

 

We were primarily interested in whether or not turtles could use a combination of flow 

and chemical cues to successfully locate squid bait in the absence of visual cues, and if 

chemical manipulation of squid bait would reduce the turtles’ ability and/or willingness to 

track and locate bait. Trial videos were analyzed to assess successful location of bait, as 

indicated by the turtle striking and attempting to consume the nylon secured to the baffle, and 

the length of time necessary for turtles to locate bait. The amount of trial time spent in the 

main chamber where the chemical plume originated was also recorded. 

During trials, turtles frequently displayed a behavior in which they suddenly stopped 

swimming, put their nostrils to the tank floor, raised their front flippers to the side of their 

head, and used rear flippers to paddle backwards or spin in circles around the same spot. This 

searching behavior is typical of captive turtles feeding in tanks, and we refer to it as “backup” 

behavior. The frequency with which backups were displayed during trials was recorded. 

 

Within each treatment group, a logistic regression for binomial data (S-Plus, 

Insightful Corporation, Seattle, WA) was used to analyze differences in the number of turtles 

that located bait between control, untreated squid, and chemically modified squid trials. If 

data met assumptions for parametric tests, we used one-way repeated measures analysis of 

variance between groups (ANOVA) to assess differences between trials in backup frequency 

and the amount of time spent in the main chamber of the tank where the chemical plume 

originated. If data did not meet assumptions of normal distribution and equal variance, then a 

non-parametric repeated measures ANOVA on ranks (Friedman rank test) was used to look 

for statistical differences between trials. 
 5 

RESULTS 

 Turtles showed limited ability to locate squid bait in complete darkness under the flow 

conditions created in our experiment tank (Fig. 2). During trials in which untreated squid was 

presented to turtles, only 25–33% of turtles successfully located squid within the 10-minute 

trial period for the 2-PEA and TIGER treatment groups. Logistic regression showed that 

chemical modification of squid did not alter the ability of turtles to find bait: there was no 

significant difference in the number of turtles that found bait in untreated squid, chemically 

modified squid, and control trials for the 2-PEA (X2

 = 3.632, df = 2, P = 0.163) or TIGER (X2

= 4.270, df = 2, P = 0.118) treatment groups. 

 Because so few turtles actually located the bait, we could not make any meaningful 

statistical comparison of the length of time necessary for turtles to locate bait during squid, 

chemically modified squid, and control trials. Table 1 shows a summary of the time taken by 

turtles to locate bait for each trial type in the 2-PEA and TIGER treatment groups. No 

consistent trend was obvious. For the 2-PEA treatment group, turtles found chemically 

modified squid bait 2–3 times faster than they found untreated squid bait. In the TIGER 

treatment group, only one turtle successfully located the chemically modified squid bait, and 

its recorded time was about twice as long as the average time taken for turtles to locate bait in 

the untreated squid and control trials. 

 Despite their limited ability to actually locate squid bait using chemical cues, turtles 

showed alterations in behavior when squid was present in the experiment tank. In the TIGER 

treatment group, turtles displayed characteristic feeding behavior (i.e., “backup” behavior) 

with significantly greater frequency during untreated squid and chemically modified squid 

trials compared with control trials (X2

 = 12.514, df = 2, P < 0.001) (Fig. 3). There was, 

however, no difference in backup frequency between untreated squid and chemically 

modified squid trials, so treating squid bait with extracts from a natural predator (tiger shark) 

did not alter feeding behavior in captive loggerhead turtles. Likewise, we found no 

significant difference in backup frequency between untreated squid, chemically modified 

squid, and control trials for the 2-PEA treatment group (F = 2.063, df = 2, P = 0.164) (Fig. 3). 

 There was no significant difference in the amount of time that turtles spent in the 

section of the tank where the chemical plume was generated (i.e., the main chamber) between 

trials in the 2-PEA (F = 1.951, df = 2, P = 0.179) or TIGER (F = 0.346, df = 2, P = 0.713) 

treatment groups (Fig. 4). 

DISCUSSION 

Given the difficulties of studying the oceanic stage of juvenile loggerhead turtles in 

their pelagic environment, our understanding of their foraging behavior and how their 

foraging behavior might lead them to interact with fishing gear is rather limited. A recent 
 6 

extensive survey of gut contents of loggerhead turtles captured in the North Pacific high-seas 

driftnet fishery showed that a variety of prey items are consumed, with surface-dwelling 

pelagic snails, crabs, jellyfish, and tunicates comprising the majority of gut contents (Parker et 

al., 2005). Non-neustonic prey items that occur at depths up to 100 m are also represented in 

gut contents but are less common. Patchy prey distribution in the oceanic habitat likely 

fosters opportunistic feeding behavior in juvenile loggerhead turtles (Tomas et al., 2001; 

Parker et al., 2005), and it is hard to imagine that turtles would pass up a “free meal” of 

longline squid bait should they come across it in their oceanic wanderings. Both sea turtles 

and other large pelagic predators, such as the target fish species of commercial longline 

fisheries, are attracted to oceanographic features such as seamounts and convergent fronts 

where prey are concentrated (Polovina et al., 2000) increasing the chances that turtles will 

come into close proximity to fishing operations and making them susceptible to interactions 

with longline fishing gear. Indeed, satellite-tracking studies have demonstrated that in the 

North Pacific Ocean juvenile loggerhead turtles congregate at the Emperor Seamounts and 

along convergent fronts characterized by strong gradients in sea surface temperatures and 

chlorophyll—areas also exploited by longline fishing fleets (Polovina et al., 2000; Parker et 

al., 2003; Polovina et al., 2005). 

 

The sensory cues used by juvenile sea turtles for orientation and prey-seeking in the 

open ocean are not fully understood. Association with oceanic fronts, where prey is more 

readily available, may be maintained by using temperature and current cues (Polovina et al., 

2004). Loggerhead turtles are generally considered to be visual predators, but it is possible 

that chemical cues associated with high concentrations of prey items in frontal zones 

contribute to the turtles’ ability to detect and locate food in the open ocean. Use of chemical 

and flow cues in open-ocean orientation and migration has been demonstrated in salmon 

(Doving, 1990; Doving and Stabell, 2003), but has yet to be demonstrated for marine turtles. 

Results from our laboratory study of chemical orientation in juvenile loggerhead turtles do not 

provide strong evidence that turtles are effective at using only chemical and flow cues to 

locate a food source. Flow conditions in our flume tank were necessarily different from what 

turtles experience in the pelagic environment; however, we attempted to create uncomplicated 

flow conditions that would be conducive for tracking a turtle’s response to prey treatments, 

i.e., a unidirectional current of low-to-moderate speed with a food source located upstream. 

Only 20–33% of turtles found squid bait presented under these simple flow conditions in the 

absence of visual cues. Flow conditions in the loggerhead turtle’s pelagic habitat are 

undoubtedly more complex and dynamic than those we could create in the laboratory. The 

ability of turtles to use additional cues provided by currents and oceanographic gradients to 

orient towards a source of attractant chemicals in the oceanic environment is unknown and 

warrants further investigation. 

Constantino and Salmon (2003) reported that post-hatchling leatherback turtles 

showed a rheotactic response when food homogenate was introduced into a test chamber 

through an underwater filter outflow, but we observed no strong rheotactic response to the 

current created in our flume tank. Behavior during trials was characterized by turtles moving 

back and forth between the start chamber and the main chamber along the sides of the tank, 

with occasional swims down the center of the tank, both facing into and away from the 

current. We found that the presence of food chemicals resulted in an increase in backup 
 7 

behavior, wherein turtles searched the tank floor for the source of food odors, rather than a 

rheotactic response in which turtles searched “upstream”. Backup behavior is an artifact of 

captive rearing; the tank floor is the most likely place loggerhead turtles will encounter food 

in their holding tanks. This obviously is not true for wild loggerhead turtles in the open 

ocean. Further experiments with turtles acclimatized to feeding under more natural flow 

conditions may help clarify the role of flow cues in feeding behavior. In addition to chemical 

and flow cues, tactile cues may also play a role in bait striking behavior of loggerhead turtles. 

Five of the nine turtles in the TIGER treatment group bit the nylon bait bag even when there 

was no squid inside (Fig. 2). 

Although chemical cues elicit feeding behavior in loggerhead, green, and leatherback 

turtles (Grassman and Owens, 1982; Owens et al., 1982; Steele et al., 1989; Constantino and 

Salmon, 2003), most experimental evidence suggests that visual cues are of primary 

importance in foraging success. Constantino and Salmon (2003) found that when visual and 

chemical cues associated with jellyfish, a primary prey of leatherback turtles, were 

simultaneously presented to leatherback post-hatchlings, the turtles ignored the current 

created by chemical delivery and oriented towards the visual stimuli instead. When tested 

separately, visual stimuli evoked a more robust feeding response than chemical stimuli 

(Constantino and Salmon, 2003). Our experiments support the idea that sea turtles are 

primarily visual predators, as juvenile loggerhead turtles showed a low success rate locating 

food in the absence of visual cues (Fig. 2). For this reason, it seems likely that use of a visual 

deterrent, rather than a chemical deterrent, would be a more effective means of preventing sea 

turtle interactions with longline gear. Researchers with the NOAA Sensory Biology Working 

Group are currently investigating visual capabilities of sea turtles and pelagic fishes in an 

attempt to identify visual attractants and repellents (Fritsches et al., 2005; Wang et al., 2005). 

Even if an effective visual deterrent is identified and implemented in longline fisheries, 

however, bait chemicals in the vicinity of fishing operations may alert turtles to the presence 

of food and induce a heightened awareness of prey leading to alteration of searching behavior. 

The effectiveness of a visual deterrent will depend largely on whether or not the turtle’s 

aversion response overrides the heightened feeding response, which is fueled in part by 

chemical cues. Studies investigating the efficacy of various methods for repelling birds show 

that a combination of both visual and chemical deterrents is more effective than either on its 

own (Mason and Clark, 1996). 

Unfortunately, an effective chemical deterrent has yet to be identified for sea turtles. 

Previous studies have shown that loggerhead turtles readily consumed squid that had been 

soaked in lactic acid, urea, quinine hydrochloride, capsaicin, wasabi oil, and natural toxins 

(ink from Aplysia spp.) (J.B. Swimmer, personal communication). One approach we took for 

the current study was to assess the feasibility of disguising the odor of longline bait with a 

novel chemical, such as 2-phenylethanol, as a means to prevent loggerhead turtles from biting 

squid bait. Treatment of squid bait with 2-phenylethanol did not significantly alter the 

behavior of loggerhead turtles during trials, so the odor-masking approach using this 

particular chemical was ineffectual. Although wash-off in the current could have decreased 

the concentration of 2-phenylethanol over the course of the 10-minute trial, it is unlikely that 

this affected the results, as turtles located and bit squid bait marinated in 2-phenylethanol in 

less time that it took them to locate untreated squid bait (Table 1). 
 8 

We were also interested in assessing the behavior of loggerhead turtles in response to 

chemical compounds derived from sharks, the main natural predators of juvenile and adult sea 

turtles. Higgins et al. (2005) demonstrated that captive-reared juvenile loggerhead turtles in 

nearshore holding pens show defensive behavior upon encountering a shark-shaped decoy and 

subsequently avoid the section of the pen where the decoy is present, providing experimental 

evidence that visual recognition plays a strong role in predator avoidance. The role of 

chemical recognition in predator avoidance has not previously been investigated for sea 

turtles. Terrestrial reptiles and amphibians display avoidance and defensive behavior when 

presented with skin extracts and rinses from predatory snake species or when placed in 

environments that have been “conditioned” by predator presence (Dial, 1990; Weldon, 1990); 

however, we found no significant difference in behavior of loggerhead turtles between 

untreated squid trials and trials in which squid had been treated with skin secretions from live 

wild-caught tiger sharks. If association of a predator’s scent with a threat is learned rather 

than innate, then this may explain why shark-derived chemicals did not alter the behavior of 

captive-reared loggerhead turtles -- with no previous exposure to tiger shark scent -- during 

bait-tracking trials. Behavioral responses to predator-derived chemicals may be more 

pronounced in wild-caught sea turtles. 

CONCLUSIONS 

In conclusion, we found that although loggerhead turtles detect and respond 

behaviorally to the presence of food chemicals in their aquatic environment, they have limited 

success in tracking and locating a food source using only chemical and flow cues. Visual 

cues are likely of primary importance to foraging success in loggerheads, with the chemical 

senses playing a secondary role. Further research is necessary to identify sensory deterrents 

and evaluate the feasibility of using sensory deterrents to reduce or prevent sea turtle bycatch 

in longline fisheries. 

ACKNOWLEDGMENTS 

We thank R. Zimmerman, T. Fontaine, and T. Minello for allowing us to use their 

facilities for this research project. The staff and volunteers in the Protected Species Branch of 

the Galveston Laboratory provided invaluable assistance with animal care and with behavior 

trials. L. Mc

Naughton helped coordinate logistics. R. Vogt, S. Moein-Bartol, I. Bartol, K. 

Lohmann, K. Fritsches, E. Warrant. Permits to conduct this study were granted by the 

University of Hawaii Institutional Animal Care and Use Committee (03-042) and the Florida 

Fish and Wildlife Conservation Commission (TP #015). Research was funded by a NOAA 

Fisheries Oceanography grant (#658329). 
 9 

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Table 1.--Length of time necessary for loggerhead turtles to locate and strike untreated squid, 

chemically-modified squid, and control bait in the 2-phenylethanol (2-PEA) and tiger shark 

extract (TIGER) treatment groups. 

TREATMENT 

& trial type

Time to locate bait 

(min)* Number of turtles that located bait 

 

2-PEA 

squid 2.57 ± 0.94 2 

2-PEA 7.48 ± 0.02 2 

control n/a 0 

 

TIGER 

squid 4.71 ± 1.00 3 

tiger 9.83 1 

control 5.80 ± 1.27 5 

 

*Results presented as arithmetic mean ± standard error of the mean (S.E.M). 
 14 

Figure 1.--Diagram of tank used in experiments to assess chemical tracking abilities and 

 behavior of 2-year-old loggerhead turtles at the NOAA Fisheries Sea Turtle 

 Facility in Galveston, Texas. 

start 

chamber gate 

uni-directional flow 

(~3-5 cm⋅sec-1)

bait 

baffles main 

chamber 
 15 

squid 2PEA control

# of turtles

0

2

4

6

8

10

located bait

(A)

squid tiger control

# of turtles

0

2

4

6

8

10

located bait

(B)

Figure 2.--Number of 2-year-old loggerhead turtles that successfully located bait during 

 untreated squid, chemically modified squid, and control trials for the (A) 2-PEA 

 and (B) TIGER treatment groups. White bars represent the total number of 

 turtles used in trials (N). Black bars represent the number of those 

 turtles that found bait.
 16 

squid 2-PEA control

number of backups

0

2

4

6

8

10

(A)

squid tiger control

number of backups

0

2

4

6

8

10

(B)

*

Figure 3.--Frequency with which backup behavior was exhibited by loggerhead turtles 

 presented with untreated squid, chemically modified squid, and control bait 

 for the (A) 2-PEA (N = 8) and (B) TIGER (N = 9) treatment groups. Turtles 

 in the TIGER treatment group displayed backup behavior significantly more 

 often during untreated squid and chemically modified squid trails compared 

 with control trials (X2 = 12.514, df = 2, P < 0.001).
 17 

 

squid 2-PEA control

% trial time in main chamber

0

20

40

60

80

100

(A)

squid tiger control

% trial time in main chamber

0

20

40

60

80

100

(B)

 

Figure 4.--Amount of time turtles spent in the main chamber of the experiment tank, 

 where the chemical plume originated, during untreated squid, chemically modified 

 squid and control trials for (A) 2-PEA (N = 8) and (B) TIGER (N = 9) treatment 

 groups. In both treatment groups, there was no significant difference in time spent 

 in the main chamber between the three trial types. 

 

Availability of NOAA Technical Memorandum NMFS 

Copies of this and other documents in the NOAA Technical Memorandum NMFS series issued 

by the Pacific Islands Fisheries Science Center are available online at the PIFSC Web site 

http://www.pifsc.noaa.gov in PDF format. In addition, this series and a wide range of other 

NOAA documents are available in various formats from the National Technical Information 

Service, 5285 Port Royal Road, Springfield, VA 22161, U.S.A. [Tel: (703)-605-6000]; URL: 

http://www.ntis.gov. A fee may be charged. 

Recent issues of NOAA Technical Memorandum NMFS–PIFSC are listed below: 

NOAA-TM-NMFS-PIFSC-4 Evaluation of time-area closures to reduce incidental 

 sea turtle take in the Hawaii-based longline fishery: 

 generalized additive model (GAM) development and 

 restrospective examination. 

 D. R. KOBAYASHI and J. J. POLOVINA 

 (March 2005) 

 5 The Hawaiian monk seal in the Northwestern 

 Hawaiian Islands, 2002. 

 T. C. JOHANOS and J. D. BAKER (comps. and eds.) 

 (July 2005) 

 6 A sociocultural assessment of Filipino crew members 

 working in the Hawaii-based longline fleet. 

 S. D. ALLEN and A. GOUGH 

 (October 2006) 

 7 Sea turtle and pelagic fish sensory biology: developing 

 techniques to reduce sea turtle bycatch in longline fisheries. 

 Y. SWIMMER and R. BRILL 

 (December 2006) 

 8 Hawaii longline fishermen’s experiences with the observer 

 program. 

 S. STEWART and A. GOUGH 

 (February 2007) 

 

 9 The Hawaiian monk seal in the Northwestern Hawaiian 

 Islands, 2003. 

 T. C. JOHANOS and J. D. BAKER (comps. and eds.) 

 (March 2007)