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<br />Southwestern Fishes and the
<br />Enigma of "Endangered Species"
<br />Man's invasion of deserts creates problems for
<br />native animals, especially for freshwater fishes.
<br />W. L. Minckley and~atnes E, Deacon
<br />Increasing public interest in man's
<br />pressure on the world's biota is evident
<br />from the number of agencies now ac-
<br />tively involved in attempts to conserve
<br />what remains. These range from small,
<br />private conservation clubs to large
<br />established groups such as The Nature
<br />Conservancy and the International
<br />Union for the Conservation of Nature
<br />and Natural Resources. Activities of
<br />some organizations have been comple-
<br />mented by action oa-the part of some
<br />state and federal departments. For ex-
<br />ample, in January 1967 the Nevada
<br />Game -and Fish Commission accepted
<br />responsibility for preserving the unique,
<br />endemic fishes of that state, and acted
<br />to protect habitats of a number of
<br />forms, and in December 1967 Cali-
<br />fornia initiated similar action (1). The
<br />U.S. Bureau of Sport Fisheries and
<br />Wildlife has defined rare and endan-
<br />gered species, and has begun to catalog
<br />them (2). A laboratory for studying and
<br />preserving such organisms is established
<br />at the Bureau's Patuxent Wildlife Cen-
<br />ter in Maryland.
<br />Concern for natural environments
<br />has therefore spread from individuals
<br />through state, local, and federal govern-
<br />ments, to become international in scope;
<br />with such a diversity of interest, it is not
<br />surprising that there are some problems.
<br />Emotion and lack of understanding
<br />often obscure the picture, and these fac-
<br />tors, coupled with gross lack of basic
<br />biological information on many species,
<br />promote confusion and conflict. In this
<br />article we outline some of otJr ideas on
<br />the problem of "endangered species,"
<br />discussing certain freshwater fishes of
<br />Dr. I~finckler is assistant professor in the de-
<br />nartmen[ of zoology, Arizona Stale Universit}•,
<br />Tempe; Dr. Deacon is associate professor in the
<br />den<runent of biological sciences and a start
<br />member of the Desert Research Inui[um, Ne-
<br />vada Southern university, Las Vegas.
<br />the Southwest as examples. We do not
<br />aspire to solve problems or smooth con-
<br />flicts-perhaps we shall confuse the
<br />issues for some. If so, we hope the con-
<br />fusion leads to constructive inquiry.
<br />Kinds of Species
<br />In considering "endangered species"
<br />one is immediately confronted with a
<br />need to understand, and to be able to
<br />explain, diverse abundances and degrees
<br />of dispersion, Except for- domesticated
<br />animals, not considered here, the only
<br />objective definition of "endangered"
<br />must be one given in terms of an or-
<br />ganism's ability to maintain its popula-
<br />tions in nature. If the organism is to
<br />accomplish this, suitable habitat must
<br />be continuously available.
<br />Recognizing some subjectivity and
<br />overlap, we divide organisms into four
<br />broad categories with respect to habitat
<br />needs:
<br />1) Species having habitats produced
<br />by or changed by man, which have re-
<br />sponded to man's influence by extending
<br />their range and abundance.
<br />2) Organisms which have not re-
<br />sponded to man's influence and which
<br />inhabit large geographic areas and aze
<br />at present common.
<br />3) Animals which require large, spe-
<br />cial habitats.
<br />4) Species living in small, unique
<br />habitats as re]icts or isolated endemics.
<br />Category 1 is irrelevent to our discus-
<br />sion, except where introduced or invad-
<br />ing forms are detrimental to indigenous
<br />species.
<br />Category 2 likewise needs little dis-
<br />cussion. This category includes animals,
<br />tolerant of environmental extremes,
<br />which occupy broad spectra of available
<br />habitats in their native ranges. Influ-
<br />1424
<br />ences of man on animals of category 2
<br />are fairly direct, and decreases in gross
<br />abundance (as opposed to decreases is
<br />°number per unit area of suitable hab.
<br />itat) must already have occurred in tnosl
<br />species. However, because of the wide
<br />ecological tolerances of these species,
<br />modifications of habitat must be exte4.
<br />live to extirpate them. Even if Itlc~
<br />decimation occurs, their broad, general
<br />distributions insure against extinctioa,
<br />There may in the future be cause for
<br />concern for animals o~ ~.~is eategory~
<br />but at present those of other categories
<br />bear far greater pressure. ~
<br />Animals of category 3 are intimately
<br />dependent on some major fc:tture or
<br />features of their environment. Tttis de.
<br />pendence automatically places them ip
<br />an untenable position if the feature they
<br />need is also needed by, or modifJed by,
<br />man. A familiar example is the Amer-
<br />ican bison, which man actively elimi-
<br />nated in the natural state, converting its
<br />grasslands for agriculture and for graz-
<br />ing herds of domestic meat-producing
<br />animals. Bison now are essentially do-
<br />mesticated and are common, but for a
<br />few years they were certainly endan-
<br />gered. Anumber of other spectacular
<br />species are known, even by laymen, tp
<br />be endangered. Large amounts of
<br />money and hundreds of hours of time
<br />are spent is perpetuating these forms,
<br />especially if they are of commercial,
<br />sporting, or esthetic importance.
<br />Many fishes are included in category
<br />3. In fresh- waters, those kinds that de-
<br />pend on, or move through, large,
<br />strongly flowing rivers are especially
<br />noteworthy. No species of Pacific salm-
<br />on (genus Oncorhynchus) is immedi-
<br />ately endangered, yet certain runs of
<br />these fishes have declined or disap-
<br />peared because of man-made obstruo-
<br />tion of rivers or modifications of
<br />spawning grounds; such phenomena are
<br />well documented. Similar effects are
<br />known, but less well substantiated, in a
<br />number of "big-river" fishes of North
<br />America, More subtle, but perhaps even
<br />more important, aze changes in the
<br />quality of water, induced by impound-
<br />ment. Siltation behind dams, concomi-
<br />tant reductions in silt loads of rivers,
<br />increased penetration of light, changes
<br />in temperature relations-all contribute
<br />to form anew habitat, which elicits
<br />faunal change. The channelization of
<br />rivers often has opposite effects and
<br />modifies riparian habitats drastically (3).
<br />In the American Southwest, complete
<br />drying of streams or of riparian habitats
<br />may destroy whole faunas (4}, Io all
<br />instances, faunal shifts that occur must,
<br />SCIEtiCE, VOL. 159
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