Conflicting Views of Sea Turtles

How many do We Need, How Much Are they Worth?

Nat B. Frazer

University of Florida, Department of Wildlife Ecology and Conservation

SEA TURTLE CONSERVATIONISTS AND MANAGERS MUST ADDRESS THE QUESTIONS OF

‘WHAT ARE SEA TURTLES WORTH’ AND ‘HOW MANY TURTLES DO WE NEED?’ ANSWERS TO

THESE QUESTIONS REQUIRE ADDRESSING THE ECONOMIC AND OTHER VALUES WE PLACE

UPON SEA TURTLES AND THE USES WE INTEND TO MAKE OF THEM. THUS, WE MUST

CONSIDER ‘USE’ AND ‘NON-USE’ VALUES. USE VALUES INCLUDE COMSUMPTIVE USE (FOR

EXAMPLE, HARVESTING FOR MEAT OR EGGS), NON-CONSUMPTIVE USE (FOR EXAMPLE,

ECOTOURISM), AND POTENTIAL UNKNOWN FUTURE OPTIONS. NON-USE VALUES INCLUDE

THE PERCEIVED VALUE OF LIVING IN A WORLD WITH SEA TURTLES AS OPPOSED TO LIVING IN

A WORLD WITHOUT THEM, AND THE VALUE WE PLACE UPON BEQUEATHING TO OUR

CHILDREN A WORLD WITH OR WITHOUT SEA TURTLES. THE DETERMINATION OF HOW MANY

TURTLES WE NEED DEPENDS UPON THE ARENA IN WHICH WE HOPE TO ACHIEVE

SUSTAINABILITY - - WHETHER IN AN ECONOMIC, ECOLOGICAL, LONG-TERM EVOLUTIONARY,

OR SHORT-TERM CONSERVATION CONTEXT.

Introduction

The value imparted to sea turtles and their parts as commodities (for example, eggs, meat,

shells, calipee, oil) is an important part of ‘use value’ often referred to as ‘consumption

value.’ Eggs, meat, and calipee are consumed directly, whereas shells may be sold as

souvenirs or carved into jewelry or other objects. The oils have many uses, from

waterproofing small boats to medicinal purposes. The use of sea turtles as objects of

ecotourism activities or turtle watches is one of several examples of their ‘nonconsumptive value.’ And because sea turtles may have future uses as yet unknown to us,

some people may seek to ensure the survival of these species for possible future use, thus

recognizing their ‘option value.’

Of course, sea turtles also have value other than their direct value to humans for

immediate or future subsistence, artistic, manufacturing, or commercial purposes. Their

‘non-use value’ includes the ecological services they provide to both the marine and

terrestrial ecosystems, which I refer to as their ‘ecological value’ in Figure 1. Also

included in the ‘non-use value’ of sea turtles is their ‘existence value.’ Many humans

apparently feel that sea turtles provide us with some value by our simple knowledge that

they exist, whether or not we ever view them in the wild or in captivity. Included in the

‘existence value’ is the concept of ‘bequest value.’ Some people apparently feel it is

important and valuable to bequeath to their heirs a planet that still contains sea turtles.

And many people feel that all living creatures, particularly large and charismatic species

like sea turtles (Wilson and Peter 1988) have ‘intrinsic value.’ In addition, the

incalculable cultural value that sea turtles have in many parts of the world also are a

reflection of their ‘existence value.’
FIGURE 1 GOES HERE

In 1978, during my first experience working for sea turtle conservation, a

gentleman participating in our turtle watch beach walk asked me a question I shall never

forget. I was explaining how we intercepted each turtle as she laid her eggs, removed the

eggs from the nest, and placed them in a hatchery to save them from predation by the

many raccoons (Procyon lotor) and feral pigs (Sus scrofa) on the island. He looked at me

thoughtfully and asked, ‘How many sea turtles do we need?’ Now, a quarter of a century

later, I am still trying to answer that question.

Obviously, the question of how many sea turtles we need depends upon the need

we are trying to satisfy with our management or conservation issues. In the discussion

below, I point out some of the difficulties in trying to answer the question: ‘How many

sea turtles do we need?’ by focusing on three aspects: (1) the economic viewpoint,

including their value for both consumptive and non-consumptive uses, as well as some

features of their existence value; (2) the ecological viewpoint, speculating on the

ecological value of their role in marine ecosystems; and (3) the conservation viewpoint,

(which encompasses all aspects of their total value. In terms of their conservation, I

discuss only the difficulty in trying to determine how many we need to ensure sufficient

genetic diversity for their continued long-term existence. My assessment focuses mainly

on the Wider Caribbean area, but also includes some information from other localities.

Numbers Needed to Sustain Economic Value

Consumptive Value

The pages of the Marine Turtle Newsletter are replete with scattered reports of the value

of turtles and their parts. Woody (1986) reported that the average price paid to fishermen

for a landed ridley sea turtle (Lepidochelys olivacea) in Puerto Angel (Mexico) was US$

8.42 and that the turtle was worth $25.26 to the processor as meat, bone meal, and

leather. He also mentioned that poachers received about $13.26 for a clutch of eggs. He

estimated that the annual value of the Pacific olive ridley harvest in Oaxaca (Mexico)

exceeded US$1 million, not counting direct and indirect employment related to the sale

of final products such as boots and other leather goods. Higginson (1989) stated that the

price paid to harvesters for a dozen sea turtle eggs on the Pacific coast of Guatemala rose

from US$ 0.10 in the 1960’s to US$ 1.00-4.00 in the late 1980’s. Cambers and Lima

(1990) reported that oil from leatherback turtles (Dermochelys coriacea) sold for

medicinal purposes or as an aphrodisiac brought US$20-40 per 40-ounce bottle in the

British Virgin Islands. Woodworth (1992) found that sea turtle meat sold for as little as

US$ 0.60 in the Comoros Islands (Indian Ocean), and Stam and Stam (1992) reported

illegal sale under-sized stuffed and live hawksbills (Eretmochelys imbricata) being sold

in the Dominican Republic for as much as US$ 300 and US$ 150 each, respectively.

Betz and Welch (2001) found leatherback (D. coriacea) eggs wholesaling at US$ 0.05

each and retailing at up to $0.50 each in Iryan Jaya, Indonesia.

The consumptive use of sea turtles and their parts has been reviewed many times,

with much discussion of the collapse of commercial endeavors due to over-harvesting

(Parsons 1962; Rebel 1974; Bjorndal 1995; Thorbjarnarson et al. 2000). Despite much
discussion of whether harvest of sea turtles is theoretically sustainable or not (for

example, (Mrosovsky 2000; Pritchard 2000), no sound determinations have been made of

the minimum numbers of sea turtles needed to sustain harvests.

Some of the most intensive analyses of consumptive use of sea turtles have been

accomplished for populations nesting or feeding in Central America. Campbell (1998)

and Hope (2000) provided socioeconomic analyses of olive ridley (L. olivacea) egg

harvesting programs, focusing on the nesting beach at Ostional on the Pacific coast of

Costa Rica. Although their analyses did not include determining the specific number of

turtles needed to sustain an economically viable harvest, both Campbell (1998) and Hope

(2000) recognized that egg harvests were not likely to be sustainable in the face of human

induced mortality at other life stages (for example, mortality of adults and juveniles being

taken intentionally or incidental to other fisheries).

Lagueux (1998) provided detailed assessment of the green turtle (Chelonia.

mydas) fishery on the Caribbean coast of Nicaragua. C. L. Campbell (2003) modeled the

same population and suggested that the current harvest of 11,000 large juvenile and adult

turtles a year might have to be reduced by more than 90% in order to achieve

sustainability. But no one knows whether or not a much smaller harvest would be

sustainable economically. Until biologists and economists work more closely together,

we may never know how many turtles we need to sustain the consumptive use of sea

turtles and their parts The interdisciplinary research necessary to achieve this aim will

be both extraordinarily challenging and extremely rewarding (L. M. Campbell 2003).

Non-consumptive Value

The majority of the economic aspects the non-consumptive value of sea turtles center on

their being objects of wildlife viewing in ecotourism or ancillary to other nature-based

tourist activities on beaches. One example of the potential value of sea turtles in nonconsumptive endeavors comes from the prices charged by EARTHWATCH for

participating in their expeditions, during which the public may participate in ongoing

scientific research on sea turtles. A recent visit to their internet web page

(http://www.earthwatch.org) revealed the following costs for participating in their 2004

programs (airfare to the project site is not included in the cost of the expedition): US$

1,860 to work with C. mydas in Costa Rica; US $ 1,995 to work with D. coriacea nesting

on St. Croix (US Virgin Islands); US $ 2,010 to work with E. imbricata in Barbados.

Clearly, the opportunity for non-scientists to work with sea turtles is highly valued by

certain sectors of the public. This certainly represents a substantial non-consumptive use

value, but also may reflect a high non-use existence value for sea turtles perceived by

those who pay to join the expeditions.

Gutic (1994) reported that based on the annual gross income derived from

leatherback turtles (D. coriacea) in the area around Guanacaste National Park (Pacific

coast of Costa Rica), individual leatherback turtles nesting on the beaches represented a

capitalized value of US$ 34,910, with the capitalized value of the entire leatherback

population being set at US$ 26,181,411.

There is no doubt that Tisdell and Wilson (2001a, 2001b, 2002; Wilson and

Tisdell 2001) have provided the most thorough analysis available to date on the socioeconomics of sea turtle ecotourism through their studies of the nesting beach at Mon

Repos, Australia. They found that sea turtle based ecotourism activities provide an
annual input to the local economy of approximately US$ 450,000 (Tisdell and Wilson

2001b). Furthermore, they have developed models that depict (a) the relationship

between the numbers of nesting turtles visiting the beach during the season and the

number of visits for turtle watching by tourists, and (b) the abundance (population

density) of the species being viewed and the cost/benefit to a tourist attempting to view

the species. They concluded (Tisdell and Wilson 2002) that 200 nesting sea turtles/km

might be near the minimum threshold necessary to support current levels of tourism at

Mon Repos. This is the only study of which I am aware that attempts to estimate the

number of sea turtles necessary to sustain non-consumptive economic value for a human

community.

In a study that is perhaps more indicative of non-use existence value, Whitehead

(1993) found that residents of North Carolina (USA) survey were willing to pay US$

11/year if they knew that their expenditures would ensure the continued existence of

loggerhead sea turtles (Caretta caretta) for at least another 25 years.

Numbers Needed to Sustain or Restore Ecological Value

It is generally accepted as fact that there are now far fewer sea turtles than there were

prior to the European colonization of the New World (Parsons 1962; Rebel 1974;

Bjorndal 1995; Thorbjarnarson et al. 2000). Karen Bjorndal and her colleagues have

provided the most reasoned and substantiated estimates of pre-Columbian population

levels of green (C. mydas) and hawksbill (E. imbricata) sea turtles in the Caribbean

(Bjorndal et al.2000; Bjorndal and Jackson 2003; Jackson 1997). They estimate

conservatively that there were 33-39 million adult green turtles prior to the European

arrival (Jackson 1997; Bjorndal et al. 2000). These millions of adults undoubtedly had a

major influence on both marine and terrestrial ecosystems in the region.

For example, in an excellent analysis of nests deposited in Florida, Bouchard and

Bjorndal (2000) demonstrated that nesting loggerheads (C. caretta) are an important link

in transporting nutrients and energy from the marine ecosystems onto beaches. Using

their figures for energy and nutrient transport for loggerheads, we can obtain a rough

estimate of the linkages that green turtles and hawksbills provided between the marine

and terrestrial environments prior to the arrival of Europeans in the Caribbean (Table 1).

TABLE 1 GOES HERE

The estimates in Table 1 for green turtles are based on the mid-range of the

Jackson’s (1997) estimate for the number of adult green turtles (36,000,000), assuming a

1:1 sex ratio (that is, 18,000,000 adult females), divided by a 3-yr female breeding cycle

(that is, an average of 6,000,000 females breeding in any given year) and an average of

4.2 nests for females reproducing in a given season (that is, 25,200,000 nests). The

estimates for hawksbills are based on Bjorndal and Jackson’s (2003) conservative

estimate of 540,000 adult hawksbills, assuming a 1:1 sex ratio (that is, 270,000 adult

females), an average breeding cycle of 2.54 years (that is, an average of 106,299 females

breeding in any given year) and a mode of five nests per female breeding in any given

season (Richardson et al. 1999), for an average of 531,496 nests in a typical year.
But in addition to their effects on terrestrial systems, green turtles and hawksbills

also must have affected marine ecosystems. Bjorndal and Jackson (2003) estimated

conservatively that a total pre-exploitation green turtle population of 100 million (adults

and juveniles) consumed 6.2 X 10

9

kg of sea grasses annually (mainly Thalassia

testudinum), while 540,000 adult hawksbills consumed 200-400 million kg of sponges

(wet mass) per year. If so, there can be little doubt that these two sea turtle species were

major architects of marine ecosystem structure and function.

These estimates are impressive, particularly given Bjorndal and Jackson’s (2003)

suggestion that the true numbers of sea turtles may have been as much as 10 to 20 times

greater than their conservative estimates. And rarely do we consider the important roles

that must have been played by the uncountable millions of hatchlings entering the sea

each year, and the ecosystem services that young green, hawksbill, leatherback, ridley,

and loggerhead sea turtles must have provided – as prey for both terrestrial and marine

predators and as predators or herbivores themselves. Obviously, the restoration of former

levels of ecosystem services provided by sea turtles would require hundreds and hundreds

of millions of sea turtles. And it also would require restoring sufficient foraging and

nesting habitat to support such unimaginable number of turtles and their young. Given

the propensity of humans to reproduce and spread themselves across the globe, it seems

unlikely that we ever will be willing to curtail our own influence on ecosystems in order

to restore turtles to perform their former important influence on marine and terrestrial

ecosystems. The ultimate answer to the question of ‘How many sea turtles do we need to

sustain or restore ecosystem function?’ completely depends upon the degree to which we

are willing to have their former levels of influence restored – in other words, it depends

upon how willing we are to restrict or curtain our own current level of influence on

marine and terrestrial systems.

Numbers Needed to Ensure Long-term Conservation

When population numbers are low, conservation geneticists become concerned that the

species in question may not retain sufficient genetic variability to meet environmental

challenges. The problem can be exacerbated by the fact that not all adults in a real

population will breed every year. The ‘effective population size’ refers to those

individuals actually breeding (Roughgardern 1979). This number refers only to adults,

and is typically smaller than the total size of the adult population for several reasons. If

breeding is non-random, the genetic contribution of some individuals to the genetic

make-up of the next generation will be greater than that of others who breed less

frequently. Some adults may not breed at all. And in populations with unequal sex

ratios, the effective population size will be reduced by the rarer sex.

Franklin (1980) and Soulé (1980) suggested that an effective population size of

500 breeding adults was sufficient to maintain genetic variability for conservation

programs long term. However, Lande (1995) determined that an effective population size

of at least 5000 might be necessary to ensure the degree of genetic variability required to

meet the long term adaptive and evolutionary needs of a species. He further suggested

that an effective population of 5000 breeding adults in some cases might require average

actual population sizes of wild species to be much more numerous. And when one
recognizes that populations are not just composed of adults, the total population size

requirements may be in the tens or hundreds of thousands.

In the case of sea turtles, it is difficult to determine effective population size.

Nesting beach studies may eventually yield sufficient data on the proportion of adults

breeding each year, but we also need information on the sex ratio of adults, on the

proportion of males that are actively breeding, whether or not breeding is random, the

presence and degree of multiple paternity, and other information related to the calculation

or effective population size. We also need information on what exactly constitutes the

population, and the amount of genetic material that may be exchanged with other

populations.

Research on sea turtle mitochondrial DNA suggests that a nesting aggregation

may be genetically isolated from other rookeries due to female philopatry to their natal

beaches (Bowen 1997, Francisco 2001). If male turtles born to mothers from a particular

nesting beach breed only with female turtles from that same beach, then we may be able

to define populations geographically. Some mitochondrial studies show that male green

turtles also display philopatry (FitzSimmons et al. 1997a). However, nuclear DNA

studies on both green turtles (FitzSimmons et al 1997b) and loggerheads (Francisco

2001) show that males also may be important vectors moving genes between nesting

aggregations as they breed with females passing by during migrations to other nesting

beaches, or in areas where turtles from several different rookeries congregate to feed.

This male mediated gene flow will make it more difficult to determine the effective

population size for a given local population.

In addition, Sugg and Chesser (1994) showed that multiple paternity may increase

a breeding population’s effective size, and recent studies have shown that multiple

paternity occurs in clutches of sea turtle eggs (Bollmer et al. 1999; Moore et al. 2002;

Hoekert et al. 2002). Thus, the calculation or estimation of effective population sizes

cannot be accomplished without detailed knowledge of the degree of multiple paternity

for a given breeding population.

The maintenance of sufficient genetic variability in wild sea turtle populations

necessary to ensure their long-term adaptability almost certainly will require effective

breeding population numbering many thousands of adults. This in turn will require that

total population sizes be numbered in the hundreds of thousands, if not millions, when we

consider all age classes. As indicated in the previous section on restoration of ecosystem

services, it is unlikely that sufficient habitat remains to support sea turtle populations of

the size required to ensure natural levels of genetic variability in more than but a few sea

turtle populations.

Concluding Thoughts

In order to do the best possible job of conserving and managing sea turtles will

undoubtedly take an interdisciplinary approach, involving economists and other social

scientists as well as biologists and ecologists (L. M. Campbell 2003). But the

economists and other social scientists who study the human dimension of conservation

are unlikely to be able to help us determine whether our biologically-based sea turtle
conservation and management plans are feasible or affordable until we provide them with

a clear idea of just what our objectives are (Metrick and Weitzman 1998).

If our objectives are to have sufficient numbers of sea turtles necessary to (1)

fulfill their ecological roles (Bjorndal and Jackson 2003), or (2) to ensure sufficient

genetic diversity for their long term survival, and/or (3) satisfy human needs and desires

related to their use and non-use values, how will we know when we have saved enough

turtles? And assuming that we are able to determine the number of turtles we think we

need for a given purpose, what sacrifices are we willing to make (or to ask others to

make) to reach and sustain that number of turtles?

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Table 1. Amount of Nutrients and Energy Transported from the Marine to the Terrestrial

Environment by Green Sea Turtles (Chelonia mydas) and Hawksbill Sea Turtles

(Eretmochelys imbricata) Nesting on Caribbean Beaches Prior to European

Colonization.

Chelonia Eretmochelys Total

Organics (kg) 17 337 600 365 669 17 703 269

Nitrogen (kg) 1 814 400 38 268 1 852 668

Phosphorus (kg) 163 800 3 455 167 255

Energy (kJ) 471 844 800 000 9 952 000 000 481 796 800 000
Figure 1. Components of the Value of Sea Turtles.

Total

Value

Use

Value

Consumptive

Value

Non-consumptive

Value

Option

Value

Existence

Value

Bequest

Value

Ecological

Value

Non-use

Value

Intrinsic

Value