steps needed to plan for sturgeon and paddlefish terns have certainly influenced the biogeography of
conservation (e.g. Rochard et al. 1990). Our review Acipenseriformes although at present, we can do
has several explicit purposes. little more than catalogue them, because no one un-
First, although Acipenseriformes has long been derstands the genetic bases or adaptive significance
regarded as a biogeographically interesting group, of these patterns. An important but still neglected
the phylogeny necessary to study this question has approach to studying the evolution of different life
yet to be assembled. Comprehensive phylogenetic history patterns of Acipenseriformes are ideas of Ba-
undertanding, particularly concerning relation- Ion (I990 and references therein) that emphasize
ships within the genus Acipenser,still eludesus. the importance of altricialorprecocial patterns of
Complicating factors include high levels of ontoge- development. This is likely to prove a productive
netic and individual variation, hybridization, and approach, for size and yolk content differences are
extirpation of many populations withinthe historic known for different species of sturgeons, though
ranges of certain species (Bemis et al. 1997b this vol- they have not yet been correlated with different
ume) Some key intergeneric relationships are patterns of life history.
equally problematic. Results from karyological and Fourth, we want to introduce the remaining pa-
molecular phylogenetic approaches (Birstein & pers in the status part of this collection (Bemis et al
DeSalle 1997) place the two species ofHusowithin 1997a), which detail aspects of life history and bio-
Acipenser(as sister taxa toA. ruthenus) whereas os- geography for many of the extant species of Aci-
teological data placeHusoas the sister taxon of all penseriformes. One need that emerges immediate-
other sturgeons (Findeis 1997 this volume). Future lyis for more detailed river surveys and life history
updating of our interpretations is inevitable as our studies of virtually all species of sturgeons, partic-
phylogenetic insight into Acipenseriformes im- ularly those from geographically remote regions in
proves. Asia and northern North America. These surveys
Second, a detailed understanding of the geo- need to be done with the most advanced technol-
graphic distribution of acipenseriforms is compli- ogies available, including in particular telemetry of
cated by the wide ranges historically reported for individuals to determine life history patterns (Ky-
adults of certain species, so that a more restrictive nard 1997 this volume) and molecular based identi-
and useful definition of species ranges is required. fication of populations within and between river
We explicitly propose the concept that rivers in systems (Wirgin et al. 1997 this volume).
which spawning occurs should be the central unit of
analysis for interpreting the biogeographic ranges
of acipenseriform species (and other groups con-
taining anadromous species). We provide a global
summary of these rivers, but given the scope of the
question (i.e., identify all rivers in the world in
which sturgeons or paddlefish historically We begin with three general biogeographic obser-
spawned) it is certain that more exhaustive analyses vations:
will yield additional rivers. It may also be necessary 1. With the exception of the Pearl River in China,
to find nore restrictive ways to define our concept all spawning rivers used by Acipenseriformes lie
of spawning rivers, and perhaps we will succeed in entirely within the north temperate zone of Asia,
provoking such a response. Europe or North America, although individual
Third, Acipenseriformes exhibit a broad array of adults have been taken at sea south of the Tropic
spawning and feeding migratory patterns, with of Cancer. All known fossil Acipenseriformes
some species utilizing fresh water exclusively, arealso from north temperate localities (Grande
others fresh water and estuarine environments, & Bemis 1991, Jin 1995, Bemis et al. 1996 this vol-
while others span the rangefromfresh water to fully ume, Grande & Bemis 1997). The absence of
marine environments. Different life history pat- Acipenseriformes from tropical rivers is proba-
Basic backgroundBiogeographic observations