51813_Sturgeon biodioversity an.PDF

Restrictingfishingmortality tooffset lossesfrom the Hudson River has aminimumsize limit of 152
othersources cm (Kahnle et al^3 ). I did not attempt todivide fish-
ing mortalityintosport orcommercial. Forshort-
Fisherymanagershave theoption ofregulating nosesturgeon andpaddlefish, I assumedthat all ag-
fishingmortality to offset impacts of mortalityfrom es 1 and olderwould beequallyvulnerable to any
unknown orlargelyuncontrollablesources, such as increase in mortality beyondthatalreadyincorpo-
changes in riverflows andcontaminanttoxicity, rated into thenaturalmortalityrates.
which usually occur in fishstocksduring thefirst Values for life history parameters offemale
year oflife. To maintain stationary population striped bass in the Hudson River are from
abundance,i.e.,population abundancethat isnei- Goodyear(1988). Thevalues are for thepopulation
therincreasing nordecliningover generations, the prior toclosure of thefishery in theriver in1976 due
survivalrate of afemale egg to age 1 (S 0 ) must be tochemicalcontamination, and represent a period
equal to twotimes the reciprocal of theEPR-value when coastal landings ofstripedbassfrom the Hud-
(assuming the sexratio of depositedeggs is50:50), sonRiver and elsewherealong theAtlanticcoast of
so that: NorthAmericawere attheir peak (Boreman &
Austin1985).Boreman et al.(1993)listparameter
values forfemale winterflounder inCape CodBay,
and parametervalues forfemalebluefish along the
Atlanticcoast aregiven inMAFMC^4.

(2)

If survivalrateduring age 0 declines, thepopulation
abundance can be maintained if EPR is increased to
a levelthatkeeps the product of age 0 survival and
EPRequal to two,assumingthat the population has
sufficientcompensatory capabilities to maintain
stationarity under all mortalityconditions.

Results anddiscussion

Effects of fishing mortality on reproductive potential

To preventharvesting of spawners below the re-

Data sources placementlevel oftheirprogeny,Goodyear(1993)

recommendsmaintaininglevels of spawningstock

Sufficientinformationexists inavailable publica- biomass perrecruitthat are atleast 20% of the max-

tions toestimateEPRvalues forthreesturgeon imum(whenF= 0), unlessevidenceexists for ex-

populations and one paddlefish population in ceptionallystrong density-dependence in the pop-

North America:whitesturgeon in theColumbia ulation.Boreman et al.(1984)used a higherlevel of

RiverbelowBonneville Dam(Tracy & Wall 1993, 50% ofmaximum spawning stock biomass per

DeVore et al.1996);Atlantic sturgeon in the Hud- recruit as atarget forrebuilding(rather thanmain-

son River (Kahnle et al.1992,Kahnleunpublished taining)populations of shortnose sturgeonalong

data);paddlefish inLake Ponchartrain,Louisiana theAtlanticcoast. Ifspawningstockbiomass and

(Reed et al.1992); andshortnose sturgeon in the egg production arelinearlyrelated(fecundity is

lower ConnecticutRiver(Boreman^2 ). The fishery typically alinearfunction of female body weight),

for whitesturgeon in thelower ColumbiaRiver cur- then thesame 20% and 50%targetlevelsshould

rently has minimumsize limit of 112 cm and a maxi-

mum size limit of 168 cm(DeVore personal commu-

nication), and thefishery forAtlantic sturgeon in^3 Kahnle, A , , K.Hattala & K.McKown. 1992.Proposed New

YorkState Atlantic sturgeon regulations.Prepared for the At-

lanticStatesMarine Fisheries Commission, Atlantic Sturgeon

Plan Review Team. 14 pp.

(^4) MAFMC(Mid-Atlantic Fishery ManagementCouncil).1990.
Fisherymanagementplan for thebluefish fishery. Mid-Atlantic
FisheryManagementCouncil,Dover, Delaware. 79 pp.
(^2) Boreman, J .1992.Impact ofaddedmortality on thereproduc-
tive success ofshortnose sturgeon in thelower Connecticut Riv-
er. Report prepared for the Northeast RegionalOffice,National
Marine Fisheries Service. 14 pp.

EPR.S 0 = 2.