The University of Southern Mississippi

AN ANALYSIS OF SEA TURTLE STRANDINGS IN LOUISIANA

by

Jessica L. DeJean

A Thesis

Submitted to the Honors Collegeof The University of Southern Mississippi

in Partial Fulfillmentof the Requirements for the Degree of

Bachelor of Sciencein the Department of Biological Sciences

March 2010

Approved by

________________________________Patricia M. Biesiot

Associate Professor of Biological Sciences

________________________________Frank R. Moore, Chair

Department of Biological Sciences

________________________________David R. Davies, Dean

Honors College

TABLE OF CONTENTS

Abstract……………………………………………………….……………………….XX

Introduction……………………………………………………….……………………XX

Materials and Methods…………………………………………….…………………...XX

Results………………………………………………………………….………………XX

Discussion………………………………………………………………….…………..XX

Summary……………………………………………………………………….………XX

Acknowledgements……………………………………………………………….……XX

Literature Cited…………………………………………………………………………XX

LIST OF TABLES

Table Page

1. Shrimp Trawling Season Opening and Closing Dates

A. Zone 1……………………………………………………………………….XX

B. Zone 2…………………………………………………………….…………XX

C. Zone 3………………………....…………………………………………….XX

2. Sea Turtle Strandings……………………………………………………………..…XX

3. Sea Turtle Strandings with Strike Marks……………………………………………XX

4. Chi Square Test of Association

A. All Zones Combined………………………………………………………..XX

B. Zone 1…………………………………………………………………….....XX

C. Zone 2…………………………………………………………………….....XX

D. Zone 3…………………………………………………………………….....XX

LIST OF FIGURES

Figure Page

1. Louisiana Shrimp Management Zones………………………………...…………….XX

2. STSSN Stranding Form

A. Front…………………………………………………………………….…..XX

B. Back……………………………………………………………………..…..XX

3. Google Earth Maps of Strandings

A. 2002…………..……………………………………………………………..XX

B. 2003…………..……………………………………………………………..XX

C. 2004…………..……………………………………………………………..XX

D. 2005…………..……………………………………………………………..XX

E. 2006…………..……………………………………………………………..XX

F. 2007…………..……………………………………………………………..XX

G. 2008…………..……………………………………………………………..XX

H. 2009…………..……………………………………………………………..XX

5. Alive and Dead Strandings

A. Alive Strandings…………………………………………………………….XX

B. Dead Strandings…………………………………...…………………...........XX

6. Scatter Plots of Sea Strandings

A. Zone 1…………………………………….…………………………………XX

B. Zone 2……………………………………………………………...………..XX

C. Zone 3…………………………………………………………………….....XX

ABSTRACT

The Audubon Aquarium of the Americas (AAOA) in New Orleans has been

collecting and archiving observations about strandings of marine mammals and sea

turtles along the Louisiana coast. For the present study, we collated and mapped the data

for 163 sea turtles (5 different species) archived over the past eight years. Recorded

strandings are concentrated primarily in the Lake Charles area and along Grande Isle and

Grand Terre. The strandings peak around the end of April through the beginning of June

and again at the beginning of October through mid-November. About 23% of the sea

turtles had obvious strike marks. The areas with high stranding concentrations are heavily

used by sport and commercial fishermen. The stranding dates overlap with periods of

warm weather recreational boating and with open fisheries seasons for menhaden and

shrimp. We examined the association between strandings and open fisheries seasons

using a chi-squared test. Most strandings occurred during open menhaden season except

in 2002 and 2007 where most occurred when both menhaden and shrimp seasons were

open. Although there was a statistically significant association between sea turtle

strandings and open fisheries seasons, this does not imply that fishing caused the

observed morbidity and mortality.

INTRODUCTION

There are seven identified species of sea turtles, including the leatherback turtle

(Dermochelys coriace), Kemp’s ridley turtle (Lepidochelys kempii), olive ridley turtle

(Lepidochelys olivacea), green turtle (Chelonia mydas), hawksbill turtle (Eretmochelys

imbricate), loggerhead turtle (Caretta caretta), and flatback turtle (Natator depressus)

(Castro and Huber, 2007). With the exception of the flatback turtle, which is found only

in Australia, all other species can be found in the waters of the United States, and five of

these six species are currently found in the Gulf of Mexico (Department of Commerce,

2003). The Endangered Species Act of 1973 classified the Kemp’s ridley, leatherback,

loggerhead, hawksbill and green sea turtles as endangered species. The loggerhead and

the green turtles were also classified as threatened at that time.

Over the past 20 to 25 years sea turtle populations have struggled to exist around

the world (Lewison and Crowder, 2007). Various natural factors contribute to sea turtles

dying daily, but determination of the cause of death can be problematic in the marine

environment (Crowder et al., 1995). When sea turtles start to decompose, their bodies fill

with gases, and they float on the surface of the water (Crowder et al., 1995). Some wash

onto shores (referred to as strandings), but many are broken apart, eaten, and may sink

without ever being seen. The strandings washed onto shores can therefore only account

for a small number of dead and injured turtles in a region. These strandings may provide

evidence of the current human impact on sea turtle populations.

The adverse conditions under which sea turtles live can be quite problematic for

their survival. Humans have impacted sea turtle populations in the past with interference

on beaches, by cleaning, artificial lighting, or sand mining. In addition, oil contamination

and other types of pollution in waters inhabited by sea turtles have the potential cause

even more declines in sea turtle populations (Lewison and Crowder, 2007). Incidental

capture by fishing gear has been the focus of sea turtle strandings in the past (Lewison

and Crowder, 2007; Wallace et al., 2008). One of the reasons that incidental capture has

such a negative affect on sea turtle populations is because it has a tendency to cause

higher mortality rates in sea turtles of reproductive maturity, decreasing the number of

possible reproductive offspring in the following generations.

When an organism like a sea turtle is incidentally captured, it is commonly

referred to as bycatch. Bycatch becomes a concern when it involves a threatened species

such as a sea bird, marine mammal or sea turtle (Moore et al., 2009). Many countries

including the United States are currently working to protect the threatened species that

are more susceptible to becoming incidentally captured in fisheries practices. Even if

greater efforts are put into other conservation strategies like nest protection for sea turtles,

the populations will not be able to recover without reduction of their bycatch worldwide

(Zydelis et al., 2009).

Managed by the National Oceanic and Atmosheric Administraiton (NOAA),

fisheries activities in the United States are under surveillance to reduce bycatch of species

in recovery (Moore et al., 2009). Surveillance by actual observers on vessels is one way

that NOAA can monitor the bycatch of threatened species. Under the direction of the

Magnuson-Stevens Fishery Conservation and Management Act (MSA) NOAA Fisheries

is sanctioned to place observers on vessels, however these observers are not required, and

the NOAA’s sanctions cannot control fisheries on the state level. Not only is the state

fishery difficult to control, generally very little funding is allocated to cover the expenses

for on vessel observers. According to Moore et al. (2009), this is very problematic

because state fisheries are commonly a source of the bycatch of sea turtles.

Various studies state that evidence of bycatch in fisheries can be seen in the form

of strandings (Lewison et al., 2003; Cox et al., 2007). Strandings in this case are defined

as turtles that have washed up on shores dead (Cox et al., 2007) or at times injured.

Lewison et al. (2003) determined that a study of the reduction of sea turtle bycatch could

be carried out by analyzing frequencies of sea turtle strandings and in turn the

effectiveness of various bycatch reduction devices.

Shrimp fisheries are considered the top contributor in the bycatch and stranding of

sea turtles (Lutz and Musick 1997; Lewison et al, 2003; Cox et al, 2007; Casale et al,

2007). In the Gulf of Mexico, the shrimp fishery is dominated by two species, the white

shrimp, Litopenaeus setiferus, and the brown shrimp, Farfantepenaeus aztecus (LDWF,

2006). The coastline of Louisiana is divided geographically into three separate shrimping

zones (Fig. 1). Each zone has its own opening and closing dates for shrimp seasons that

can be tracked by LDWF. The targeted species of shrimp are caught during the open

season using funnel shaped trawl nets that are pulled through the water by a fishing

vessel in a process called trawling. Observing increases in sea turtle strandings during

shrimp trawling seasons can provide evidence that this human interaction is contributing

to more sea turtle mortality (Lewison et al., 2003; Cox et al., 2007).

During the early 1970s, the first instances of shrimp trawler interactions with sea

turtles were indentified (Crowder et al,. 1995). In 1997 Lutz and Musick stated that the

incidental capture of sea turtles in shrimp trawls has caused more sea turtle deaths than

any other human interaction combined, and it has been estimated by NOAA that 62,000

loggerhead turtles and 2,300 leatherback turtles have been killed due to interactions with

shrimp trawls (Department of Commerce, 2003).

Over the past 20 years, over 150 bycatch reduction devices have been tested to

establish one that is consistently reliable (Manjarrés et al., 2008). Turtle excluder devices

(TEDs) are the most common bycatch reduction device in shrimp trawling. In order for a

TED to be approved by the National Marine and Fisheries Service (NMFS), it must be

proven to be at least 97% effective during testing (Department of Commerce, 2003).

Approved TEDs have been implemented in the southeastern United States surrounding

the Gulf of Mexico in an attempt to reduce bycatch (Spotila, 2004), and some have been

quite successful, reducing bycatch numbers by up to 50% (Lewison and Crowder, 2005).

Originally met with high opposition, TEDs requirements were challenged in at least ten

different court cases until passing in 1991 (Lewison, et al., 2003). Even though TEDs

have been highly effective in decreasing in incidental sea turtle mortality (Spotila, 2004);

there is evidence that suggests that after the initial two to three years of decreases in

strandings after 1991, turtle strandings in the Gulf of Mexico began to increase once

again (Lewison et al., 2003). Under the regulations of the National Oceanic and

Atmospheric Administration, shrimp and flounder trawlers operating in the southeastern

United States are now required to use National Marine Fisheries Service (NMFS)

approved TEDs. But even with federal law requiring the use of TEDs and trawls,

Louisiana continues to refuse to enforce the laws and regulations (LDWF, 2006).

The use of these bycatch reduction devices has been most effective in smaller sea

turtles, including the Kemp’s ridley, but the effectiveness of these devices on the larger

sea turtles remains a concern. In recent studies, there is evidence that 33-47 % of

stranded loggerheads and 1-7 % of stranded green turtles are too large to fit through

TEDs. In addition, 75 % of the Loggerhead turtles in the Gulf of Mexico are too large to

escape through the openings in the devices (Department of Commerce, 2003).

In other parts of the world, TEDs have proven to be highly effective. Since their

implementation in Australia, turtle bycatch has decreased by at least an estimated 90%

(Department of Commerce, 2003). In a field study by Cox et al. (2007), vessels trawled

next to each other, one with a TED and one without; the use of the TED proved to

decrease the bycatch rate by 97%. This proves that it is possible for TEDs to be highly

effective in the reduction of bycatch. However, shrimp trawl TEDs have little

effectiveness if very low compliance exists in using the devices, especially when on

vessel observers are not present (Moore et al., 2009). When states are unwilling to

enforce federal regulations like Louisiana has in the past, there is very little hope for the

device to work to the best of its ability. After decades of federally required TED use, the

success of the device is still greatly determined by how well and accurately it is used not

how long the requirements have been in place (Lewison et al., 2003). The lack of

compliance with TED use in the Gulf of Mexico is a direct contributor to the high

numbers of strandings (Cox et al, 2007).

Another important fishery in the Gulf of Mexico is the purse-seine fishery of Gulf

menhaden, Brevoortia patronus (Smith et al., 2002; Anderson, 2007; Vaughan et al.,

2007). With a history as far back as the 1800s, menhaden fishing is today of the most

valuable fisheries in the United States with the largest tonnage (Vaughan et al., 2007).

Since 1995 when most commercial fishing equipment was banned in Florida (Vaughan et

al., 2007), Louisiana has been the leader in the menhaden industry (Smith et al., 2002).

Louisiana is currently responsible for 92% of the menhaden catch annually (Vaughan et

al, 2007).

Menhaden fishing involves the use of two boast and a purse seine net to catch

entire schools of menhaden at a one time (de Silva and Condrey, 1997; Rester and

Condrey, 1999; VanderKooy and Smith, 2002). Once a school of menhaden is spotted,

the two boats encircle it with the net. The net is pulled closed and the contents are

brought on board the mother ship. A flexible hose is used to pump the catch into the

refrigerated hold. This entire process usually lasts no longer than one hour. Though

bycatch numbers are much lower for the menhaden industry compared to shrimp

trawling, the bycatch of large fishes and sharks in these devices is still seen as a major

issue.

As far back as the 1950s, efforts have been made by menhaden fisheries to reduce

incidental bycatch (Rester and Condrey, 1999). Two types of bycatch reduction devices

have been established and are commonly used: hose cages and large fish excluders. Hose

cages are used to prevent larger fishes from getting pumped into the refrigerated hold on

deck and large fish excluders are made of thick bars, also preventing larger fishes from

passing into the holds. In a study by Rester and Condrey (1999) it was determined that

the hose cages needed substantial improvements in order to work effectively as bycatch

excluder devices. The cages allowed the passage of menhaden as well as the fins, heads,

and tails of larger fishes. Less than 28% of the bycatch that encountered the menhaden

fishery survived in the observations. Through the observations of Rester and Condrey

(1999), it was determined that the best way to decrease the mortality of the bycatch is to

make alterations to the hose cages.

Another study of bycatch in the menhaden fishery by de Silva and Condrey

(1998), determined that the best way to eliminate bycatch of different species was to

pinpoint what they referred to as “hot spots” in the Gulf of Mexico. These spots included

the waters east of the Mississippi River from April to August. In these areas during these

few months, large numbers of incidental catches of fin fishes, shrimp and sharks were

found in purse-seine nets. De Silva and Condrey (1998) also determined that one of the

best ways to decrease the mortality of the bycatch was to make modifications to the

purse-seine nets.

Though there is no record of sea turtle capture in purse-seine nets thus far, sea

turtles have recently been capture incidentally in gillnets (Carretta et al, 2003). Over

seven years, 132 sea turtles were captured as bycatch in the gillnets that are very similar

to the nets used in purse-seine fisheries like menhaden. Entanglement and drowning in

these nets is the generally what leads to sea turtle mortality, and with no current standards

for bycatch reduction set in the menhaden fishery bycatch of various large species is

inevitable (Rester and Condrey, 1999).

The conservation effort of sea turtles is problematic because it interferes with a

market of high economic value. Fishermen profits can be compromised in the effort to

save a species that they do not find essential to their business. Increases in the

convenience of these devices and possibly some economic benefit could encourage more

fishers to become more accepting of safer materials and practices (Gilman et al., 2006).

Various other coutries have set up incentive programs for their citizens in order to protect

endangered sea turtle (Ferraro and Gjertsen, 2009). These simple and inexpensive

payments to the environmentally conscious have already begun to show increases in the

success of juvenile and adult sea turtles. Cox et al. (2007) suggested that TED use for

reduction of bycatch to targeted levels simply will not occur until some sort of incentive

program is established. By implementing small yet effective techniques to decrease sea

turtle bycatch, improvements in survival among sea turtle populations can be made in the

Gulf of Mexico.

MATERIALS AND METHODS

Records of sea turtle strandings in Louisiana from 2002-2009 were reported to the

AAOA. The observer of each stranding filled out a document (Fig. 2) produced by the

Sea Turtle Stranding and Salvage Network (STSSN). The form included the observer’s

name, address, and phone number. The details of each stranding included but were not

limited to date found, number found (if more than one found in one day), species and sex

(if identifiable), condition (i.e. level of decomposition), and geographic location. The

observer made notes on the final state of the carcass (buried, painted, etc.) to insure the

stranding would not be surveyed more than once. Details of injury could also be noted

on an included diagram. Many of these forms were complete and detailed, but others

included only basic information. When possible, photographs were taken and sent via

email. Some species were recorded as unidentified under specific conditions. Some sea

turtles were not complete specimens due to decomposition. In some, only a small portion

of the turtle was found and could not be properly identified. Some sea turtles were found

and referred to “hybrids.” These sea turtles displayed recognition characteristics for

more than one species and could not be properly placed into one species category.

However, these strandings cannot be technically classified as hybrids without proper

DNA analysis (James et al., 2004). Many stranding reports noted instances of obvious

boat strikes and propeller marks that were later noted. Few observers included

measurements, and tagging information was usually not available. The documents were

either faxed or emailed to AAOA.

The eight years of sea turtle strandings were collated and entered into Excel

spreadsheets, noting the details of each stranding. The geographic coordinates were also

plotted on maps using Google Earth in order to pin point their location along the

Louisiana coastline. The strandings were categorized by the week of the year that they

occurred.

The Louisiana Department of Wildlife and Fisheries (LDWF) was consulted

regarding the dates for the opening and closing of shrimp seasons each year. The zoning

for shrimp trawling was geographically defined, and the individual strandings were

located within one of the three shrimp trawling zones (Fig. 1). The opening and closing

dates were recorded for each of the three zones set by LDWF (Table 1). The opening and

closing dates were also defined by the week of the year that they occurred. The opening

and closing dates for menhaden fishing season were also obtained from LDWF. The

menhaden dates were also defined by the weeks of the year that they occurred.

My null hypothesis for this study was that open shrimp and menhaden fishing

seasons have no effect on the frequency of sea turtle strandings in Louisiana. A chi

square test of association was performed for the stranding data.

RESULTS

The sea turtle strandings in Louisiana from 2002-2009 included 163 turtles as

follows: 102 Kemp’s ridleys, 27 loggerheads, 20 unidentified, 8 green sea turtles, 4

leatherback sea turtles, and 2 hawksbill sea turtles (Table 2). Strandings were

concentrated in Lake Charles (Zone 3) and Grand Isle/Grand Terre (Zone 2) (Fig. 3). On

average, 87.8% of stranding in all zones between 2002 and 2009 involved dead rather

than live sea turtles (Fig. 4).

After the strandings were divided by zone, each was plotted on a scatter plot by

week they occurred during the year (Fig. 5). The weeks of open shrimp season only, open

menhaden season only, and both open shrimp and menhaden fishing seasons were

indicated by shading present in figure 5. Most strandings occurred during open

menhaden season except in 2002 and 2007 where most occurred when both menhaden

and shrimp seasons were open. The strandings peak around the end of April through the

beginning of June and again at the beginning of October through mid-November. About

23% of the sea turtles had obvious strike marks (Table 3) from what was assumed to be

boats and boat propellers.

The chi square test of association demonstrated a positive association between

open fishing seasons and the frequency of sea turtle strandings in Louisiana (Table 4).

The null hypothesis was rejected, and it was determined that open shrimp and menhaden

fishing season have an effect on the frequency of sea turtle strandings in Louisiana.

DISCUSSION

In the present study, it was determined that sea turtle strandings in Louisiana were

influenced by the shrimp and menhaden seasons. The strandings seemed to be

concentrated in two main areas: the Lake Charles area and Grand Isle/Grand Terre.

These areas are heavily used by sport and commercial fishermen. If the strandings were

fairly evenly dispersed then it could be assumed that the chance of incidental bycatch is

evenly spread over Louisiana waters. However, this clustering suggests that sea turtle

bycatch is more likely to be encountered in these particular fishing areas (Lewison et al.,

2009).

The stranding dates frequently seen in the data overlap with periods of warm

weather recreational boating and with open fisheries seasons for menhaden and shrimp.

However, the impact of recreation boating on sea turtle strandings was not reviewed in

this study. It is possible that many of the propeller marks on stranded turtles occurred

from these types of activities.

Although there was a statistically significant association between sea turtle

strandings and open fisheries seasons, this does not imply that all sea turtle strandings

were caused by shrimp trawling and menhaden fishing. There are many other factors that

could have influenced the sea turtle strandings throughout the eight years in this study.

Many other human interactions have caused sea turtle mortality in the past, and it is

possible that any of these could have been the cause of some of the strandings. It is also

possible that some of the strandings could have died of natural causes and then washed

up on the Louisiana shores.

All factors must be considered when determining the cause of sea turtle

strandings. While taking all of these factors into consideration, the results of this study

still agree with various prior studies, stating that there are obvious patterns between sea

turtle strandings and trawling fisheries (Crowder et al., 1995; TEWG, 2000; Lewison et

al., 2003). However, necropsies of the strandings were never taken, eliminating almost

all possibility of determining the cause of death.

SUMMARY

The strandings in this study were concentrated Lake Charles (Zone 3) and Grand

Isle/Grand Terre (Zone 2). Both are major areas for commercial and recreational fishing

as well as for recreational boating activities. On average, 87.8% of stranding between

2002 and 2009 involved dead rather than live sea turtles. The chi square test

demonstrated a positive association between open fishing seasons and the frequency of

sea turtle strandings in Louisiana. However, we did not investigate the impact of

recreational fishing and boating on strandings. Other factors that may have contributed to

sea turtle strandings are seasonal migrations between feeding areas and spawning areas as

well as migrations based on water temperature changes (Crowder et al., 1995).

There is always room for improvement in the reduction of incidental bycatch in

sea turtles, but as long as budgetary and organizational constraints are affecting fisheries

practices, sea turtles will continue to strand (Moore et al., 2009). Without Louisiana’s

enforcement of federal TED laws, sea turtle strandings will continue in Louisiana.

ACKNOWLEGEDMENTS

First and foremost, special thanks go to Dr. Patricia Biesiot for her assistance

throughout the development of this study. Thank you to the Audubon Aquarium of the

Americas and stranding coordinator, Michele Kelley for access to the data used. Special

thanks for their help and expertise go to Paul Cook, Mandy Courville and Keith Ibos at

the Louisiana Department of Wildlife and Fisheries for their assistance with dates of the

shrimp fishing season. Also, thanks to Joseph Smith at the National Oceanic and

Atmostpheric Administration for his help regarding the menhaden fishing industry.

Thank you to Dr. Carl Qualls at The University of Southern Mississippi for his assistance

in statistical analysis of this study.

I would also like to thank the USM Department of Biological Sciences and USM

Honors College for their financial support of this study.

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