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Against Oversimplifying the Issues on Relocating Turtle Eggs

Nicholas Mrosovsky

Published online: 5 February 2008

Springer Science+Business Media, LLC 2008

Abstract Translocating sea turtle eggs at risk from high

tides to safer places is one of the most widely undertakenconservation measures on behalf of these species. Recent

research work has shown that individual female turtles

differ in their nest-site preferences. If more of the nests

saved by translocation come from turtles with tendencies to

lay near the water, might this perhaps interfere with natural

selection? This possibility adds to the controversy already

surrounding relocation of turtle nests.

Keywords Individual differences Nest-site selection

Relocating eggs Sea turtle Stabilizing selection

Introduction

This exchange of views (Mrosovsky 2006, Pike 2007)

concerns the conservation practice of translocating turtle

eggs liable to be destroyed by high tides to safer places. My

earlier article (Mrosovsky 2006) was aimed at biologic, not

social or economic, ramifications. Of course, nonbiologic

considerations must be taken into account in conservation.

I do not dispute with Pike that the public relations aspects

of hands-on conservation may energize local communities

(and perhaps facilitate fund increasing). However, I cannot

agree that opportunities to do this, such as translocating

eggs, should proceed regardless of the true biologic

importance of the conservation practice. Indeed, feel-

good conservation carries the danger that if an increasingly

sophisticated and environmentally knowledgeable publicdiscover that their actions had little positive biologic

impact, they might feel less good, disillusioned, and put

upon. For some of the most egregious examples of public

relationsoriented conservation with turtles, see my book

(Mrosovsky 1983a).

With regard to my proposal that eggs from nests at high

risk of destruction be sold and eaten, with the proceeds

used to support conservation, rather than being translocated

and put back into the gene pool, Pike argues that any such

practice is bound to send a negative conservation message

by commercializing a precious and legally protected

resource. For what, or for whom, one wonders, is this a

resource? However, this is not the place to get into the

black hole of debate between preservationist and sus-

tainable-use approaches. Some may find Pikes absolute

certainty on such matters naive. To see that there are

arguments on both sides, he need look no further than the

Northern Territories of Australia and the status of the salty

crocodile, a reptile that, like sea turtles, produces many

eggs, most of which do not become adults.

Turning to the biologic aspects, Pike again oversimpli-

fies: he divides female turtles into good nesters, which

always lay in areas where eggs hatch, and poor nesters,

which always lay in areas where eggs do not hatch. That is

not how I conceptualized the situation. I started by asking

why turtles might swim for hundred of kilometers and then

fail to crawl a few meters further up to lay their eggs in a

safe location. With opposing pressures against nesting too

near the water, as well as against nesting too far up on the

beach, nest-site choice is probably the outcome of stabi-

lizing selection but with the important caveat that the

beachscape is unpredictable. Some years, the seas come

unusually high up on the beach; other years, the dangers of

N. Mrosovsky (&)

Department of Ecology and Evolutionary Biology,

University of Toronto, 25 Willcocks Street,

M5S 3B2 Toronto, Ontario, Canada

e-mail: mro@zoo.utoronto.ca

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nesting too high on the beach may predominate (e.g.,

abundance of terrestrial predators, difficulties for hatch-

lings in reaching the sea expeditiously). Therefore, it is not

a case of female turtles being either good or poor nesters.

In some years, certain female turtles do better; in other

years, other female turtles do better.

It was never claimed that some turtles consistently

always nest in certain areas. To show this would requireinformation about nest sites of animals throughout their

reproductive lives. What the data showed was a tendency

for certain female turtles to move higher up the beach than

others (Kamel & Mrosovsky 2004, 2005). However, run-

ning alongside such tendencies for particular individuals to

nest more often in particular places, there was still some

scatter in nest-site selection by any given female turtle.

Nevertheless, with high repeatability values for the

hawksbill turtles studied, it was plausible to think that

genetic factors might have accounted for some of the

variability in behavior. With that in mind, it seemed of

interest to explore what might be the implications if onemade the assumption there was some genetic contribution.

In particular, what might be the consequences of moving

eggs and thereby altering the chances of survival? What

might be the consequences of interfering with the com-

plicated balances and adaptations of nest-site choice in an

unpredictable environment?

Given that the moving and reburying of turtle clutches

thought to be doomed, or even at some risk, is a widespread

practice, I welcome Pikes interest and views; these things

merit discussion. However, such a discussion must be

based on an accurate appreciation of the facts and the

inferences made from those facts. I end here by listing

some miscellaneous errors, or misconceptions, in Pikes

commentary:

1. Our data do not show any qualitative differences

between leatherback and hawksbill turtles. Individual

differences were significant in both species (Kamel &

Mrosovsky 2004, 2005). It was a quantitative matter of

how pronounced individual differences were, with

higher repeatability values in the hawksbill turtles.

2. Hawksbill turtles do sometimes nest so close to the sea

that their nests are inundated (Fig. 5 in Kamel &

Mrosovsky 2005). I did indeed write that few hawks-bill turtle nests are deposited lower than the high tide

line, but I went on to indicate that with the small

numbers currently nesting at many hawksbill turtle

rookeries, the more relevant figure is the percent of

nests laid that are at risk. In any case, the important

point is not how many hawksbill turtle nests are laid

too near the water but that there are individual

differences among female turtles in their nest-site

selection.

3. I did not say translocation should not be undertaken. I

said it depends on the circumstances. If a population is

seriously depleted, the relocation of eggs seems

reasonable. I also recommended that if it is done, then

it be undertaken after more discussion, regulation,

monitoring, and documentation than has sometimes

been the case.

4. Campbell and Smith (2006) surveyed volunteers whowere not engaged in helping moving eggs, so citing

them in support of using relocation to inspire volun-

teers is inappropriate. The study by Lee and Snepenger

(1992) is also irrelevant; it does not concern or even

mention relocation. In contrast, articles bearing on this

matter, not entirely supportive of Pikes views, go

unmentioned (e.g., Almeida and Mendes 2007).

5. Pike seems to think survival of translocated eggs is too

low to make much difference; in his example, 0.03%

of eggs hatch and survive to adulthood. However, we

need to compare this value with the survival rate of

eggs left in situ. Evolution can work with smalldifferences over long time periods. Therefore, saving

tidally doomed eggs might perhaps alter gene pools in

favor of promoting turtles with tendencies to lay eggs

in unsafe places.

6. Pike stated, Unless hundreds of sea turtle nests are

relocated annually, the probability that any relocated

eggs will result in adult turtles is extremely low. I

am unsure about the absolute numbers, but on some

beaches the proportion of relocated nests has been

high. In North Carolina from 1998 to 2002, approx-

imately 30% to 55% of nests were relocated each

year (Godfrey & Cluse in press, personal commu-

nication 2007). In Broward County, FL, in 1989, 82%

of nests were moved (Mattison and others 1990). The

reason for relocation was not always risk of flooding.

However, whatever the rationale, these are major

interventions, and there are many other places where

relocation of some nests is common and likely to

continue to be so. Pikes dismissal of potential

downsides to translocation, on the grounds that few

eggs will ever produce adults, seems premature or

uninformed.

7. Pike says: Before discussing drastic changes to

current conservation practices, the feasibility of alter-

native programs should be evaluated. I say: Before

assuming current practices are the best available, they

should be evaluated to determine whether we need to

change course. The question of what, if anything, to do

with doomed eggs has been with us for a long time

(e.g., Mrosovsky 1983b, Schulz 1975). Little guidance

was available because of the scarcity of information

about nest-site selection and whether a turtle that laid

in an unpropitious place was liable to do so again,

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more so than a turtle that had nested in a suitable place

previously. But now we have some new data. These

are limited to a few beaches and species, but at least

we have some data, i.e., those tenaciously collected by

Kamel and colleagues. The essential finding was that

individual turtles, nesting multiple times in a season,

differed in their choice of nest sites. It would be remiss

not to discuss this and to learn if it has any bearing onwhat may well be the most common conservation

intervention on behalf of sea turtles.

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