Case Study: Dolphin release

Michael Williamson (
Mon, 29 Nov 1994 19:58:33

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Date: Tue, 29 Nov 1994 20:00:53 -0500 (EST)
From: Michael Williamson <>
Subject: Case Study: Dolphin release
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From:	SMTP%"MARMAM@UVVM.BITNET" 29-NOV-1994 17:51:31.49
Subj:	Considerations for Captive Release
Date:         Mon, 28 Nov 1994 17:49:59 -0800
Reply-To:     Marine Mammals Research and Conservation Discussion
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Subject:      Considerations for Captive Release
To:           Multiple recipients of list MARMAM <MARMAM@UVVM.BITNET>
Considerations for Captive Release
Don Croll, Bernie Tershy, and Kevin Starr and
     Recently there has been a flurry of discussion and debate
regarding the arrival at UC Santa Cruz Long Marine Laboratory of
two bottlenose dolphins from the U.S. Navy dolphin program.  It
has been suggested that these animals belong in the wild, not in
captivity in a cement pool and that they should be released
rather than held for research.  Indeed, a program for the release
of dolphins used in Navy programs has been initiated by a group
in Florida.  The hope is to reprogram these highly trained
animals so that they may again function as wild dolphins - able
to forage for themselves and engage in the kin-based social
organization of the wild population.  We do not know the details
of this program, nor do we wish to suggest that the individuals
undertaking the project are not doing the best job possible.  We
also do not intend to suggest that captive released animals
cannot incorporate into the social organization of a wild group
of animals.  The wild reintroduction of once captive animals is a
difficult task, and one that should be approached with much
careful planning, rigor, and methods for monitoring success well
into the future.  However, our reasons for writing extend beyond
this issue.
     Emotions surrounding the morality and ethical use of wild
animals held in captivity inevitably run high.  The debate
regarding the release of captive animals into the wild is not
new.  It is probably fair to say that discussions surrounding
release juxtapose the benefits to the captive animals of wild
release with the long-term benefits of perpetuating their
captivity.  Both sides often attempt to take a moral higher
ground - one side proclaiming that such use of wild animals is
unethical and that these animals should be released back to the
wild, the other side taking a righteous stand on the educational
or research value of wild species held in captivity.  Sick,
stranded, oiled, or otherwise incapacitated individuals from the
wild (particularly of those species our society has designated as
charismatic -otters, seals, dolphins, etc.) are also held in
rehabilitation centers for variable periods and released to the
wild.  We do not intend to take sides in discussions of the use
of wild animals for research and education or the rehabilitation
of incapacitated wild animals.  We do, however, wish to give
voice to a group that is seldom considered: the wild population
of animals into which the captive animal is released.  More
specifically, we hope to ask whether the release of captive-held
individuals is in the best interests of wild populations and
global biodiversity.
     Captive animals released into the wild can impact wild
populations in three ways: 1) competition for limited resources
such as food, shelter, water or mates; 2) deleterious
outbreeding-dilution or contamination of locally adapted genomes;
and 3) introduction of diseases which do not naturally occur in
the wild population.  Here we would like to focus on the
potential introduction of non-native diseases, and briefly
discuss the more obvious potential for deleterious outbreeding.
     This notion of disease spread may sound alarmist, but the
possibility is real.  Most animals are held in captivity in a
confined area where many individuals and perhaps species of wild
animal are in close proximity (e.g. zoos, aquaria, or
rehabilitation centers).  In spite of variable amounts of time
and care taken in the isolation and quarantine of individuals or
species, the risk of disease cross infection in such centers can
be significant.  Introduced diseases may be directly transferred
from one individual of a species to another, or it may be
transferred from one individual of a species to an entirely
different species.  If captive-held individuals were held in
captivity in perpetuity, then disease transfers would only be a
concern for animal husbandry and not for the conservation of
populations and biodiversity.  However, when individuals held in
captivity (for whatever reason) are released into the wild,
diseases may be released with them.
     To our knowledge, captive to wild disease transfers have not
been documented in marine mammals (to a large extent, this may be
due to the difficulty of studying the presence and origin of
diseases in wild marine mammals and the spread of disease in
marine animals).  We offer several examples of disease transfer
from captive held terrestrial animals to wild populations which
may illustrate that disease transfer is a real threat:
     The golden lion tamarin is a small primate which has lost
much of its Atlantic rainforest habitat in Brazil.  Because of
this it is endangered with only a few remnant wild populations.
Captive breeding programs for golden lion tamarins were
initiated, and releases were about to occur in an effort to
enhance the wild population numbers.  Just before the scheduled
release, the captive individuals started to die in significant
numbers from a viral disease, callitrichid hepatitis, which
originated in captivity.  This virus causes high mortality, and
if introduced into the wild, it would have pushed the species
closer to extinction.  Another similar captive breeding program
for orangutans almost led to the release of tuberculosis to the
wild orangutan population as well as introducing the disease to
the local human population.
     Another example of the possible damage of captive animal
release to native populations can be found with the desert
tortoise in Southern California.  The recovery of this endangered
population has been hampered by problems with habitat destruction
and the introduction of an upper respiratory tract disease which
originated in tortoises held in captivity as pets and
subsequently released into the wild.  More examples of disease
introductions and near introductions exist in a myriad of
species: heath hens, black-footed ferrets, whooping cranes,
Mauritius pink pigeons, Aral Sea sturgeon, rainbow trout,
Hawaiian crows, Arabian oryx...
     We would argue that captive breeding programs which aim to
enhance the number of individuals of a highly endangered
population (for example the California Condor) can be worthwhile.
These populations have few options for perpetuating themselves
and the possible benefits of enhancing the number of individuals
may be worth the risk of spreading disease to the wild
population.  In addition, such programs are generally careful
with the potential for disease transmission to the endangered
population.  We would also argue that release of captive animals
to the wild may not be worth the risk for less endangered or
threatened populations where introduced diseases could become
pandemic.  In other words, it is important that an analysis of
the benefit to the wild population versus the potential cost be
undertaken before captive release occurs.
     Captive release also brings with it the possibility of human
induced changes in the gene pools of wild populations.  This can
occur when individuals from populations native to one area are
released to areas where they would not normally occur.  This is
of particular concern when the same "species" of marine mammal
exists in separation in two ocean basins.  Such releases would
likely have a low probability of significantly altering wild gene
pools.  However, a risk of introducing potentially
deleterious gene combinations into the wild population exists.
In addition, such introductions (if the released animals
eventually breed) will change gene combinations in the wild
population and may alter evolutionary patterns in ways we are not
able to measure.
     Perhaps with great care and analysis, the risks of captive
release to wild populations can be minimized.  However, we
believe that the burden of proof (of no harm to wild populations)
should be placed on those individuals planning to release or re-
release animals into the wild.  At present such analyses are not
always undertaken.  We may also argue that the taking of wild
animals for captive uses should also be carefully considered, but
do not wish to address this issue here.  As biologists, our
intention is to examine the controversy surrounding the release
of captive marine mammals from a population perspective.  First
and foremost, we believe that the impacts and benefits of the
release should be examined from the viewpoint of the wild
population.  Until such analyses occur, we run the risk of doing
damage to populations in the hope of helping the individual.