er 1983.Kallemeyn1983.Cochnauer et al.1985, Ro-
chard et al.1990,Moyle et al.^1 ).
Five of theNorth American sturgeons arelisted
as endangered orthreatened bymanagement au-
thorities:shortnosesturgeon(Dadswell et al.1984),
green sturgeon (Moyle et al.^1 ), pallid sturgeon
(Keenlyne & Jenkins 1993). Alabama sturgeon
(Williams el al.1989). andGulfsturgeon,Acipenser
oxyrinchusdesotoi(Mason &Clugston1993), which
is a subspecies ofAtlantic sturgeon. Although not
officiallylisted asendangered or threatened, three
otherspecies of North Americansturgeons and
paddlefish havebeenreduced tosuch low densities
at some point inthiscentury that fisheryclosures
were instituted.Harvesting oflake sturgeon in the
LakeWinnebagosystem,Wisconsin, wasprohibit-
ed from191.5 t o1931 d u e t o aconcernover thedrop
in abundance (Folz &Meyers1985).Harvest of
white sturgeon in theSnakeRiver wasterminated
after1983 due to adecline inabundance, and a total
fisheryclosure wasrecommended forsections of
the river (Cochnauer et al. 198.5). In Wisconsin and
Iowa, non-fishing zonesbelownavigation dams
were adopted to protectshovelnose sturgeonfrom
overfishing(Becker1983). Athree-year moratori-
um on commercial harvest ofpaddlefish was initi-
ated inLouisiana in1986 and therecreational creel
limit wasreduced to onefish per daybecause of de-
clines in stock levels(Reed et al.1992).
Although draconian fishing restrictions have
beeninstituted formany of theNorth American
chondrosteans, demand for thespecies has not di-
minished.Since themiddle1800s,NorthAmerican
sturgeons havebeen thetarget of intensivefisher-
ies,primarily forcaviar and also for their meat
(fresh,smoked, ortinned);angling forsport isalso
growingmore popular,especially for white andlake
sturgeons (Rochard et al.1990).Whensturgeons
becameunavailable for thelucrative caviarmarket,
somefisheries switched to paddlefish(Carlson &
Boinislawsky 1981,Reed et al.1992).
In thispaper, Iexamine thesensitivity ofNorth
Americansturgeons andpaddlefish to fishing and
earlylifemortality.Specifically, Ipresent theimpact
of fishingmortality on reproductive potential for
several representative sturgeon and paddlefish
populations, and examinewhether adjustments to
fishingmortality could beused to offsetreductions
in reproductive potential caused byothersources of
mortality dueto humanactivities. I alsocompare
the chondrosteans tootherfishspeciescurrently
supportingintensive fisheries inNorth America
(stripedbass in theHudsonRiver, NewYork, win-
ter flounder inCape CodBay,Massachusetts, and
bluefishalong theAtlanticcoast ofNorth America)
to demonstrate how life history characteristics
make the chondrosteansmoresensitive to fishing
mortality.MethodsEffects of fishing mortality on reproductive potentialFor purposes ofthispaper, Idefinereproductive
potential as the potentiallifetime eggproduction of
an age 1 female (eggs-per-recruit,EPR).Thismea-
sure is the sum of thenumber ofeggs she is likely to
produce at each agetimes the probabilitythat she
willsurvive tothat age(Boreman et al.1993):(1)
whereρiis the proportion offemalesmature at age
i, is the average fecundity of an age-ifemale,Fjis
the instantaneous rate offishingmortality during
periodj,Mjis the instantaneousrate ofnatural mor-
talityduring periodj, andnis the oldest spawning
age. Themaximumvalue forpotentiallifetime egg
production (EPRmax) is achieved when no fishing
mortality occurs (Fj = 0 for all j). As F is increased,
EPRwilldecline due to the lessened probability
that an age 1 femalewillsurvive to thenext age, giv-
en the increasedrisk offishingmortality alongwith
the risk ofnaturalmortality she also mustendure.
Relativesensitivity ofreproductivepotential to a
Specificrate offishingmortality is theratio of the
EPR-value calculated forthatrate to EPRmax.(^1) Moyle,P.B..R.M.Yoshiyama,J.E.Williams &E.D.Wikrama-
nayake. 1996 Fish species of special concern inCalifornia(sec-
ond edition).Prepared for theState ofCalifornia, The Re-
sources Agency, Dept. Fish and Game Int Fish. Div., Rancho
Cordova,California (in press).