51813_Sturgeon biodioversity an.PDF

tol Channel andNorth Sea(Castelnaud et al.1991).
It inhabitsshallowlittoralareas,with 83% ofcatch-
es occurringbetween 10 and 70 mdepth.From 1988
to present, thenumber ofaccidental catches on the
continentalshelfarea hasdecreasedprogressively
(Figure 3).
Declarations ofaccidentalcaptures ofA. sturio
increasedafter ourpublic awareness campaign, so
publicawareness isessential for thesuccess of our
restorationprogram.Moretaggedfishthan un-
taggedfish werereportedamongaccidental cap-
tures at sea(Figure 3).Perhapsfishermen informed
us and released thefishmoreoftenwhen a fish was
tagged.Curiously,tags used forscientificpurposes,
whichsometimes increase mortality due to tag in-
juries orothereffects: may in this case actually pre-
vent somemortality.
The population(1984–1988) in theGirondeEstu-
ary had a low number(500–2000individuals) of
youngfish(3–8years)during thesummer (Castel-
naud et al.1991,Rochard1992).During ourstudy
period(1987–1994), thelastrecorded naturalrepro-
duction (as evidenced bywintercatches ofsmall
fishapproximately25.0 cm TL) likelyoccurred in
summer1988.^1
The structure of thestockthatenters theGironde
during thesummer haschangedovertime (Figure
4). Before1990. weobserved atypicallypolymodal
structure (Castelnaud et al.1991) as aresult of year-
ly reproduction.After1990, thestructure of the
stockpresentedonly onemode,corresponding to
the 1988cohort. Nosign ofpathology hasbeen de-
tected. The age 0–5 yeargrowth of the 1988 cohort
was significantlyfaster (Rochard &Jatteau1991,
Rochard1992)than thatdeterminedpreviously by
Magnin(1962)when the stock was farlarger. The
difference is notattributableonly tomethodolog-
icaldifferencesbetweenstudies(Rochard1992) but
may be a densitydependenteffect(Therrien et al.
1988).
Thanks to the sex determinationmethods of
Cuisset(1993,developedoriginally forA. baerii)we
shall be able toobtaindata on thesex ration ofA.

sturioby measuringplasmaconcentrations of 11-ke-

totestosterone orvitellogenin.

Habitats

No new physicalobstacles to spawning migration

have beenerectedsince the construction of the

darns ofBergerac onthe DordogneRiver in 1851

and of GolfechnearAgen on theGaronneRiver in

1971 (Figure 1). In1981,gravel extractionstopped in

the DordogneRiver: only onesite is stillexploited

in the lowerpart ofthe GaronneRiver(Rochard et

al. 1990).Cadmium(mainly dissolved) in the Gi-

rondeEstuary is at concentrations 10 to 20times

higherthanthosemeasured inotherFrenchAtlan-

tic estuaries (Maurice 1994). This heavymetal

comes from old mines in theupper part of the Ga-

ronneRiver basin,whichstoppedworking in the

early1970s.

Exploitation

Acipenser sturiohas been protectedin Francesince

1982:fishing,transport, andcommerce are strictly

forbidden.Nevertheless, some sturgeonare caught

in thenear continentalshelf and in themouth of

someestuaries as by-catch ofsole andotherbottom

fishes. Atpresent,this is the maindirectanthropo-

genicimpact onthisstock.

Status of wild spawners

Of 40 catches of wild sturgeon, 75% were males and

25% females.Most ofthem(90%)were caught be-

fore1989, and thelastfemale was caught in1987.

This sex ratio is exactly the opposite (74%F –

24%M) of thatreported byMagnin(1962) for a 5

yearsamplingperiod in theGironde (n = 96) and by

Elvira et al.(1991) forcaptures in theGuadalquivir

River(SouthwesternSpain) from1932–1943. T h e

latterstudy indicatedthat theskewed sexratio was

an artefact ofselectivity ofthe nets,whichcould al-

the Girondebasin from mid-April to the end of

(^1) In the spring of 1995, Gemagref reported the first evidence of
the Girondesince1988 (editorsnote,March 1996).
naturalreproduction in1994 ofEuropeanAtlanticsturgeon in so be true in ourstudy.Ripebroodfish occurred in