51813_Sturgeon biodioversity an.PDF

taggingexperiments inorder toassess (using the

Jolly-Sebermethod) thesize of thestockwhich en-

ters the GirondeEstuary in summer (Rochard

1992). We used aspeciallydesigned tie-on tag made

of a stainlesssteelwire with avinyltube marker

(HallprintPty.Ltd.)placedthrough themuscle an-

terior to the dorsal fin (Castelnaud1988). Trawling

has been performedsince1986 toenhance our sam-

plingeffort(Castelnaud et al.1991).

By the early 1970s, A. sturio was no longer an eco-
nomicallyimportantresource and itbecameclear
that itssurvivalwouldrequire alongtermprogram
encompassingprotection of both thespecies and its
habitats, improvement ofbiological and ecological
knowledge, and probably, restocking. It was shown
in the former USSR (Barannikova 1987, Khodorev-
skaya et al. 1997 this volume)thatrestocking not
only improvedsturgeoncatches in the Caspian and
Azovseas, but alsosaved the beluga,Huso huso,
population in the Caspian Seafromextinction.
Most individuals of H. huso in the Caspian Sea are
now of hatcheryorigin.
We started ourinvestigations on thewildA. stu-
rio in the Girondesystemduring the late1970s. Ba-
sic lifehistoryinformation onthispopulation is
summarized in Figure 1. In the early1980s, we per-
formedstudies ofartificialreproduction onSiber-
ian sturgeon, A. baerii, using it as a biological model
to avoidadditionalimpact on indigenouspopula-
tions ofA. sturio.The availabilityduring the1980s
of Siberiansturgeonalso allowed us toinitiatestud-
ies on nutrition and onmethods ofearly sexdeter-
mination.
Thispaperpresents information onA. sturioin-
cluding thestatus ofwildpopulations,characteris-
tics ofavailable broodfish, results ofexperiments
on artificialbreeding andrearing of larvae, and ad-
aptation ofjuveniles tofarmconditions. Wealso
present themain directions of ourproposed resto-
ration program.

Age determination

We modified(Rochard &Jatteau1991) t h eaging

method for sturgeon(Classen1944,Cuerrier1951,

Magnin 1959a) toavoidadditionalmortality on this

endangeredspecies asalreadyreported byKohl-

horst(1979).Only asmall piece of the first ray of a

pectoral fin wasused(Cochnauer et al.1985). We

used theWalfordgraph and the VonBertalanffy

growth function(Rochard &Jatteau1991) t oestab-

lish seasonal age-growth relationship (Rochard

1992).

Location ofspawninggrounds

We established an inventory ofpotentialspawning

grounds in thelowerpart of the Garonne and Dor-

dognerivers(Trouvery1980) usingechosounding

equipment and information obtained fromexperi-

encedfishermen.

Materials andmethods

Capture-mark-recapture

Our taggingprogramfocusing onlarge juveniles,

whichenter thelowerGirondeEstuary for summer

feeding (Magnin1962),started in1981.Fishing op-

erations are conductedwith thecollaboration of lo-

cal fishermenusingdriftingtrammelnets. Fisher-

men are compensated on thebasis of themean ex-

pectedloss of income. Thefish are measured,

weighed, and tagged(Petersendisc) t odelineate

the distribution and migrationpattern ofthis pop-

ulation (Trouvery et al. 1984). In 1985, we modified

Artificialreproduction

Eachyear before theexpected spawningmigration,

we askedfishermen(via the localnewspaper) to

contact Cemagref in case of accidental catches of A.

sturioduring the lamprey andshadfishingseason.

The only way we canobtainwildbroodfish is to pay

a highprice forthem(despite the factthatsturgeon

fishing is illegal). Fishwere transportedcarefully to

the hatchery formeasurement (totallength, T L and

body weight, W) andimmediate determination of

sex, asmost do not exhibitexternalcharacteristics

of gender. Abdominalmassage maylead to sperm