tài liệu tham khảo cực hay

Tap chi Khoa hoc va Cong nghe biin T9 (2009). So 4. Tr 6 3 - 7 5

NGUON LOI THAN MEM HAI MANH VO 6 VUNG BIEN BINH THUAN
TRONG MOI QUAN HE VOfI HIEN TlTONG N U 6 c TROI
VO SI TUAN, HlTA THAI TUYEN
Tom tdt: Kit qud nghien cicu cua nhieu de tdi khdc nhau trang thai ky 1990 - 2005 cha
phep khdng dinh viing bien ven bd Binh Thudn la viing phdn bo vai mat do cao cua nhiiu loai
thdn mem hai mdnh sdng a viing dual trieu, diin hinh Id: Diep qugt (Chlamys nobilis), Sd
ldng (Anadara antiquata), Ddm ndu (Modiolus phllippinarum), Nghiu lua (Paphia undulata)
vd Bdn mai (Pinna sp.). Sic giau cd vdt chdt him ca do ddng trdi mgnh vd hiiu img true tlip su phong phii thirc vdt phii du (vd cd thi cd qud trtnh chuyin ddi vdt chdt sau thai ky trdi
mgnh) Id nhiing yiu to thudn lai cha su phdt trien thudn lai cita cdc dong vgt thdn mim hai
mdnh an loc ndy. Tiiy thudc vao dgc tinh sinh thdi qudn thi md muc dd lien quan den hieu ung
sinh thdi cua viing trdi mgnh cd thi khdc nhau giica cdc lodl Diep qugt la loai phu thudc
nhiiu nhdt, sau do Id Ddm ndu. Sd long vd Nghiu lua cd mdi quan hi din cdc yiu td liin quan
nuac troi vd vdt chdt lua dia tdi ra trong mua mua. Cd thi cho rdng su thay ddi cuang dd vd
vi tri tdm ciia viing trdi mgnh cd the chi phdi cdc qud trinh sinh hoc vd tic dd gdy nin su bien
ddng sinh khdi ciia cdc qudn the thdn mim hai mdnh vd trong vung biin Binh Thudn.

I. MOf DAU
Binh Thuan la mdt tinh duyen hai Nam Trang bg cd chieu dai bd bien 192 km, dien
tich mat nudc bien khoang 52.000 km^. Viing bien nay dugc coi la ngu tradng ldn cho
nghe khai thac thuy san. Dac biet, viing bien ven bd Binh Thuan la noi sinh s6ng ciia mgt
s6 loai than mem hai manh vo co gia tri'kinh te cao nhu diep quat, sd ldng, ban mai, ngheu
lua... San lugng khai thac cac d6i tugng nay dat tit 20.000 - 40.000 tan m6i nam, gdp
phan lam tang gia tri san xuat thuy san ciia tinh, giai quyet cdng an viec lam cho mgt so
lugng ldn ngu dan ven bien, gdp phan tang thu nhap cho nhan dan va tang thu ngan sach
cho dia phuang.
Cac nghien cim chung ve ngudn lgi than mem (Vd ST Tuan, 1997b; Nguyen Hilu
Phung va cs, 2001) cho rang viing bien Binh Thuan la noi dac biet phong phii ciia than
mem hai manh vd sdng d vimg dudi trieu. De phuc vu cho quan ly khai thac ben vung
ngudn lgi, nhieu de tai khoa hgc cap tinh da dugc tiln hanh va cung cip nhilu dan lieu vl

phan bl, sinh san, sinh tradng va biln dgng nguIn lgi cdng nhu dl xuit cac giai phap khai
thac hgp ly. Tuy nhien, viec he thdng hda tu lieu nhim nit ra nhiing nhan dinh mang tinh

63


khoa hgc ve quan he giiia dieu kien mdi tradng va tinh dgc dao cua nguIn lgi than mem
hai manh vd chi mdi dugc tien hanh gin day. Mdt dilu cin phai luu y la viing giau co
nguon lgi nay nam d khu vuc chiu anh hudng manh ciia hien tugng nudc trdi trong miia
gid tay-nam. Viec nghien ciiu quan he giiia dieu kien moi tradng ndi chung va anh hudng
ciia hien tugng nudc trdi ndi rieng vdi ngudn lgi than mem chi mdi quan tam budc dau d6i
vdi vai ddi tugng nhu Diep quat va Sd long (Vd ST Tuan, 1997a; Biii Hdng Long & Vd ST
Tuin, 1997).
H. PHI/ONG PHAP NGHIEN CLTU
1. Tong quan tai lieu thv cap
Trong giai doan 1991 - 1994 mdt sd de tai nghien ciiu lien quan den ngu6n lgi than
mim hai manh vd da dugc tien hanh d Binh Thuan, bao gdm "Nghien cim ve sinh hgc,
kha nang khai thac, di gidng va bien phap sii dung ngudn lgi Diep Chlamys nobilis a vimg
bien Thuan Hai", "Nghien cim mdt sd dac diem sinh hgc ciia Dom nau Modiolus
philippinarum", "Dieu tra ngudn lgi va dac tinh sinh hgc cua Sd long Anadara antiquata".
Trong khudn khd de tai cap Nha nudc KT. 0305 do PGS TS Vd Van Lanh lam chu nhiem
(Vd Van Lanh, 1995), tac ddng sinh thai cua dong trdi manh ddi vdi nguIn lgi than mim
hai manh vd d tinh Binh Thuan ciing da budc dau dugc xem xet. Ket qua da cdng b6 lien
quan den quan he ciia sinh vat ngudn lgi vdi dieu kien mdi tradng (Vd ST Tuin, 1997a, b;
Biii Hdng Long & Vd ST Tuin, 1997; Pham Van Thom & Vd ST Tuin, 1998) trong khuon
khd cac de tai ndi tren dugc sii dung cho viec he thdng hda tu lieu.
2. Nghien ciru bo sung
Trong giai doan 2002 - 2004, de tai ""Nghien ciiu cac qui luat sinh hgc, phan b6, di
chuyen va du bao bien dgng ngu6n lgi cua mgt s6 loai than mem hai manh vd tai virng
bien Binh Thuan" da cho phep tien hanh khao sat ddng thdi tat ca cac ngudn Igi dgng vat

than mem hai manh vd quan trgng, bao gdm Diep quat {Chlamys nobilis). So 16ng
{Anadara antiquata), Ddm nau {Modiolus phllippinarum), Ngheu lua {Paphia undulata)
va Ban mai {Pinna sp.). D I tai da tiln hanh ba chuyen khao sat vao cac thang 5 va 10/
2003 va thang 5/ 2004. Mau smh hgc va mdi tradng dugc thu thap tren 21 tram tit do sau
25 m trd vao bd. Ciing trong khudn khd de tai, cac th6ng tin v l biln dgng san lugng khai
thac dugc thu thap qua tham vin vdi cac co quan chite nang ciia dia phuong va cdng ding.
Cac ket qua nghien cuu lien quan den phan bd, sinh trudng va mdi trudng song cua cac
loai noi tren trong khudn kh6 de tai nay dugc phan tich nham tim hieu m6i quan he giiia
sinh hgc ngudn lgi vdi cac dac tnmg mdi tradng vimg bien, chii trgng din hien tugng

64


nude trdi. Ngoai ra, cac tac gia da tim hilu phan b l ciia cac loai tren trong nhiing khao sat
thuoc cac dl tai khae trong thdi gian gin day.
III. KET QUA VA THAO LUAN
1. Thanh phan, phan bl
Tdng hpp cac ket qua nghien cim cho phep khang dinh viing bien ven bd Binh
Thuan la vung phan bd vdi mat dp eao eiia nhieu loai than mem hai manh s6ng d vimg
dudi trieu. Cac loai co y nghTa quan trpng ve san lugng va gia tri bao gdm: Diep quat
{Chlamys nobilis), Sd 16ng {Anadara antiquata), Dom nau {Modiolus phllippinarum),
Ngheu lua {Paphia undulata) va Ban mai {Pinna sp.). Dieu can luu y tat ca cac loai nay
deu la sinh vat s6ng vui hoac bam tren nen day d vimg dudi trieu va co tap tinh an Igc thuc
vat phii du d tang day va vat chat hUu co trong tram tich hoac d tang sat day. Ket qua
nghien cim ciia de tai KT 0308 ve cac loai dac san ciia viing bien ven bd Viet Nam da
nhan dinh rang cac dgng vat than mem hai manh nay dac biet phong phu d viing bien tir
Binh Thuan den Vdng Tau trong khi cae loai dgng vat than mem hai manh s6ng d vimg
trieu lai phan bd tap trung d vimg ven bien mien Bac va Nam bd (Nguyen Hiru Phung &
cs, 2001). Nghien ciiu cua Pham Van Thom & Vo ST Tuan (1998) da budc dau khang dinh
ty le C/N (hiiu co) trong tram tfch la yeu td tao nen su khac biet cua viing bien ven bd

Binh Thuan. Ty le C/N trung binh trong nghien ciiu d Binh Thuan vao nam 1993 cd gia tri
xap xi 11, phan anh mdt hdn hgp ciia thuc vat phii du (cd ti sd C/N vao khoang 7) va vat
chat hiru co co ngudn gdc luc nguyen (ti so C/N rat ldn). Dac diem tram tich cua viing
bien Binh Thuan khac biet vdi tram tich cua vimg cita s6ng Me K6ng noi uu the ciia vat
chat CO ngudn gdc luc nguyen (ti s6 C/N eiia 33 mau phan tich d Tra Vinh len den 22,31 s6 lieu chua c6ng b6 ciia de tai KT 0308) va phong phii cac than mem hai manh vimg trieu
nhu Ngheu {Meretrix lyrata) va Sd huyet {Anadara granosa).
Vdi phan tich tren cd the cho rang phan b6 ciia eac than mem hai manh vo d vimg
bien Binh Thuan lien quan chat che den ngudn thiic an la thuc vat phii du ma su phong
phii ciia chiing lien quan chat che den hieu ilng sinh thai ciia hien tugng nudc tr6i . Khao
sat ve thuc vat phu du trong khu6n khd de tai KT 0305 (Nguyen Nggc Lam 1997), da ket
luan sinh lugng ciia thuc vat phii du d viing tam nudc trdi tuong ddi thap, nhung kha cao d
vimg phia Nam tam nudc trdi, vdi dinh cao nhat vao thang 7, trimg vdi thdi ky cd dong
tr6i manh nhat. So do phan bd xay dung bdi nghien ciiu tren cho thay vimg ven bien Binh
Thuan la khu vuc cd mat do cua thuc vat phu du rat cao, dac biet viing ven biln huyen Tuy
Phong cd gia tri mat do Ien tren 10x10^ tl bao/m^ hoac thi tich 30ml/ml Nhu vay, co thi

65


cho ring sinh kh6i thuc vat phii du tao ra tir hieu ling nudc trdi la mdt yeu to quan trgng
dii vdi su giau cd cua ngu6n lgi than mem mem hai manh vo d viing bien Binh Thuan.
Cac nghien cim trong nhilu nam qua cho phep xay dung so d6 phan b6 chi tiet ciia
cac loai nhu dugc thi hien tren cac hinh 1, 2, 3, 4 va 5 sau day. Cac so do nay khang dinh
tinh phan bl tap trang ciia cac loai d vimg bien ven bd Binh Thuan d6ng thdi cdng chi ra
dac dilm rieng vl phan bd cua cac loai do su khac nhau ve dac diem sinh thai ciia sinh vat,
va tinh khdng ddng nhit va biln dgng vl dieu kien mdi tradng. Quan he giira phan b6 va
moi tradng la vin dl phiic tap va ddi hdi nhiing nghien ciiu chuyen sau. Cac nghien cim
eho den nay chi cho phep neu len mgt s6 nhan dinh ve quan he giiia phan b6 va dieu kien
m6i tradng, chu trgng den hieu img ciia hien tugng nude trdi.

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Hinh 1: So do phan b6 cua Diep quat
(theo Vd ST Tuan, 1997b; viing dam la viing phan b6 tap trang)

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Hinh 2: So do phan bd ciia Sd 16ng (khao Hinh 3: So do phan bo ciia Ddm nau (khao
sat nam 2003 - 2004, thang mat do: sat nam 2003 - 2004, thang mat dp:
con/l.OOOm^)
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Hinh 4: So do phan b6 cua Ban mai (khao
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Hinh 5: So dl phan bl ciia Ngheu lua
(khao sat nam 2003 - 2004, thang mat dp:
con/l .000 m^)

D6i vdi Diep quat, mdt sd nghien ciiu trade day (Vo ST Tuin, 1994, 1997b) da tim
hieu tinh phan bd ciia loai nay trong mdi quan he vdi cac yeu td moi trudng va cho ring
viing phan bd cua Diep quat dugc gidi han hi Ca Na din Nam Binh Thuan (keo dai tren
100 km dgc bd) nhu la vimg giao thoa ciia hai yeu td bao gIm do sau phii hgp va nhiet do

nudc bien thap (vao mua ddng do ludi nudc lanh ep sat bd, vuon tdi Ham Tan va thip vao
mua he do hieu ling cua hien tugng nudc trdi). Tuy nhien, Diep quat kh6ng phan bl diu
va viing phan bo cd the thay ddi theo 3 thdi ky khac nhau diu, gida va cuoi nam nhd tap
tinh "bay trong nudc". Vao thdi ky nudc trdi, diep thudng tap trang d cac bai phan bl
chfnh (hinh 1). Trong chuyen khao sat thang 5/ 2003, mat do dat cao nhit d vimg Bic
Phan Thiet (287ca the/100 m^). Dudng nhu su hdi tu nay cd lien quan din tap tinh sinh

67


san ciia quan the diep. Hon niia, trong thdi ky nudc trdi boat dgng manh ddng chay tang
day hinh thanh cac xoay quan cue bg co kha nang tao nen nhiing vimg lang dpng tram tich
(Bui Hdng Long & Vo ST Tuan, 1997) lam hpi tu ngu6n thitc an ciia diep).
So 16ng khdng c6 kha nang di chuyen nhu Diep quat va vung phan b6 ciia chiing phu
thupc chu yeu vao che dp ddng chay vao thdi ky phat tan au the. Do miia sinh san chinh
vao thang 4 - 5 (Traong ST Ky, 1994), su hinh thanh cac bai sd lien quan den che dp dong
chay trong thdi ky thang 5 - 6 . Nghien citu sau d vinh Phan Ri (Biii Hdng Long & Vo ST
Tuin, 1997) cho ring day la thdi ky ma dong chay do dong trieu quyet dinh va tao nen cac
viing ddng luc chii ylu gay ling dpng tram tfch d phfa Ddng va Tay dong trieu dang nit.
Au thi sd, vi vay, se tap trang d hai phia vinh. Nghien ciiu quan he vdi tram tich (Pham
Van Tham & Vo ST Tuin, 1998) con chi ra ring thanh phan chat hilu co (the hien qua chi
s6 C/N), ty le cap hat bun set va dp chpn lpc cua tram tich co the la nhiing yeu t6 chinh
anh hudng den phan bd cua Sd 16ng. Nhu vay, c6 the coi hai yeu to chinh quyet dinh phan
b6 cue bp cua Sd long la dong chay trudc miia nudc trdi va chat day, cdn hieu img nudc
tr6i chii yeu eung cap dinh dudng cho sinh trudng cua quan the. Mgt dieu can luu y la So
long con CO the phan b6 vdi sinh kh6i ldn vao den vimg bien Binh Chau (Ba Ria - Viing
Tau) trong mdt s6 nam (Vd ST Tuan, 1998). Neu chap nhan quan diem ve moi quan he
giira nudc trdi - thuc vat phii du - ti le C/N hila co trong tram tfch nhu da thao luan d tren,
cd the ggi y rang hieu ilng sinh thai cua vimg trdi manh Nam Trang bd cd the anh hudng
vao den viing bien Binh Chau trong mdt sd thdi ky nhat dinh.

Ddm nau phan b6 rai rac tit vung bien Tuy Phong cho den Ham Tan nhung vimg
tap trang chinh van la Phan Ri va Phan Thiet. Chiing thudng co mat do thua va dugc khai
thac chung vdi cac ddi tugng khac nhu so long, ngheu lua, diep quat. Ngheu lua phan bo
tit Phan Rf Cita keo dai den khu vuc Ham Tan. Do sau phan bo tir 5 - 24 m sau. Chat day
ciia-vung phan b6 so bg dugc xae dinh la cat, cat bim, eat min va ca d nhiing noi cat co
pha vd sinh vat cimg miin ba hdu eo. D6i tugng nay song vui trong nen day, cd khi den do
sau 1 0 - 1 5 em. C) mgt sd khu vuc, Ngheu lua phan bd lan vdi cac ddi tugng khac nhu So
16ng, Ban mai, Ddm nau, Diep quat nhung ciing co mgt vai khu vuc chung phan b6 dgc
lap tao nen mat do cao nhu d mdt vai diem ngoai ven bd vimg Phan Thiet va Ham Tan.
Ban mai phan bd rai rac khap vimg ven bd Binh Thuan vdi mat do kh6ng cao. Noi dat mat
do cao nhat la 139 ca the/ 100 m^ (khu vuc Phii Hai) vao thang 5/ 2004. Co the nhan thay
la vung phan bd cua 3 loai nay kha rong, ngoai trir kh6ng ra phfa Bac den vinh Ca Na nhu
phan b6 cua Diep quat. Rieng Ddm nau tuong d6i ngheo d vung phia Nam (Ham Tan).
Quan he gida tinh chat phan bd cua chiing vdi dac trung mdi trudng vung bien chua dugc
nghien ciiu chi tiet.

68


Trong ba loai noi tren, Ddm nau hau nhu khdng gap d cac vimg bien ven bd khac cua
Viet Nam; So 16ng dugc ghi nhan d nhieu vimg bien nhung kh6ng d dau ed sinh kh6i ldn nhu
d Binh Thuan (ehu y rang vimg bien ven bd Kien Giang ciing nhieu Sd long nhung la loai A.
subcrenata). Rieng Ngheu lua con cd mgt vimg phan b6 vdi sinh kh6i ldn d vimg bien Ba Lua
(Kien Giang). Ban mai ciing dugc ghi nhan d nhieu vimg bien ngoai Binh Thuan. Co the cho
rang su phan b6 tap tnmg cua Dom nau d Binh Thuan cd lien quan true tiep den hieu ling sinh
thai ve phia Nam ciia vung trdi manh. D6i vdi So long, Ngheu lua va Ban mai, vimg tr6i manh
Cling c6 hieu img tfch cue cho su phan bd tap trung eua chimg.
2. Dac diem sinh hoc trong moi quan he vdi dieu kien moi trudng
Vo ST Tuan (1997a) va Bui H6ng Long & Vo ST Tuan (1997) da bude dau nghien
cim quan he giiia dac diem sinh hgc cua Diep quat va So long vdi dieu kien m6i trudng d

vimg bien Binh Thuan. Mgt ket luan quan trgng la nhiet do thap trong thdi ky nudc tr6i co
vai tro quyet dinh hinh thanh mua sinh san chinh ciia diep vao thang 7 - 8 vdi sire sinh san
cao gap hai lan mua sinh san phu (thang 1 - 2). Dieu nay chimg to Diep quat la sinh vat co
ngu6n g6c 6n ddi va sinh san vao mua nhiet do thap. Theo quan diem kinh dien trong sinh
thai hgc quan the (nhiet do quyet dinh mua sinh san va thuc an quyet dinh sire sinh san),
CO the cho rang hieu img nude trdi co vai tro rat quan trgng cho su phong phu eua quan the
Diep quat d Binh Thuan. Ve sinh trudng, nghien cim nay da tinh toan chi s6 do beo - mgt
chi s6 phan anh mile do thuan lgi ciia dieu kien mdi trudng d6i vdi sinh vat. So sanh he s6
do beo (K) cua Diep quat va So long theo cac thang cho thay cac loai nay sinh trudng
thuan lgi nhat trong thdi ky tu thang 7 den thang 10. Diep quat dat do beo eao nhat vao
thang 7 trong khi Sd long co chi s6 K cao nhat vao thang 9. Nghien cim b6 sung tit 2002 2004, khang dinh lai dinh cao do beo ciia Sd 16ng tu thang 8 - 1 0 (hinh 6) va cung cap dan
lieu ve bien thien he s6 K eiia 2 loai Dom nau va Ngheu lua (hinh 7, 8). C6 the nhan thay
gia tri do beo cao nhat eua Ddm nau la vao thang 10 - 11, trong khi cua Ngheu lua la tir
thang 8 den thang 10 (triing vdi bien thien do beo cua So long).
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Hinh 8: Bien thien he s6 do beo (K) cua Ngheu lua

Xu the bien thien do beo ciia cac loai ndi tren cho mgt ggi y de thao luan vl miic do
lien quan giira ngu6n cung cap dinh dudng tit hieu ung eua vimg trii manh va sinh tradng
cua cac than mem hai manh nay nhu sau: Su phong phii cua thuc vat phii du la hieu img
sinh thai true tiep ddi vdi vung bien phia Nam ciia tam trdi manh. Diep quat - than mim
hai manh vo song bam tren nen day, co thi di chuyin va cd thilc an chu ylu la thuc vat
phu dii (Dao Tan Hd, chua c6ng bl) - dugc hudng lgi hieu ilng true tiep noi tren va nhd
vay CO dieu kien thuan lgi de dat do beo cao ngay tit thang 7. Sd 16ng va Ngheu lua la cac
than mem hai manh sdng viii trong nen day va ft cd kha nang di chuyin. Co le thiic an uu
the ciia chiing thien ve vat chat hdu co trong nin day va lo limg d ting sat day - nhiing san
pham ciia qua trinh ehuyen d6i vat chit tu tam trii manh vl phia Nam, bao gIm ca ling
dgng xae sinh vat phu du. Do vay, hieu img cua tam trdi manh doi vdi hai loai nay cham
hon ddi vdi Diep quat khoang 1 - 2 thang. Thdi ky sinh trudng thuan lgi eiia Dom nau

muon hon nhieu (do beo cao vao thang 10 - 11) so vdi Diep quat va Sd 16ng. Day la than
men hai manh vd sdng vui va bam vao eac gia the trong nin day va dinh dudng cua chiing
cd le lien quan nhieu hon din vat chit hiiu co trong trim tich. Mpt dilu khac cin luu y la
mua mua d Binh Thuan dien ra tit thang 7 - 10 va co thi ddng vai trd nhit dinh trong cung
cap vat chat hiiu co cho than mem hai manh vo an lpc, nhit la d viing cd lugng mua ldn
phia Nam (Phan Thilt va Ham Tan). So dl phan b l cua Sd huylt va Ngheu lua vdi viing
mat do cao d Phan Thilt va Ham Tan (hinh 2 va 5) ggi y ring vat chit tu dit liin chic
chan se d6ng gop mdt vai trd nhit dinh cho sinh tradng phat triln ciia quin thi hai loai So
long va Ngheu lua. Mdt dilu ehua thi dugc giai thich la vi sao Ddm nau phan b l mat do
cao chu yeu d Phan Ri va Bic Phan Thilt ma tuong dii ngheo d phia Nam (hinh 3) noi co

70


lugng mua nhieu hon han so vdi phfa Bac. Phai chang thiic an cua Dom nau phu thupc
vao vat chat hilu ca cua thdi ky hau nudc troi.
2. San luong khai thac va bien dong nguon loi
Theo cac ket qua nghien citu da c6ng bd san lugng khai thac cac loai than mem hai
manh vo d vimg bien Binh Thuan bien thien kha ldn; tir 100 den 15.000 tan d6i vdi Diep
quat, 3.500 - 4.000 tin dii vdi Ddm nau (Vo Si Tuan & Nguyen Huu Phung, 1998); tu
dudi 1.000 den 25.000 tan d6i vdi Sd 16ng (Vo ST Tuan, 1998). Th6ng tin tit dia phuong
ciing cho thay san lugng Ban mai trong giai doan 1995 - 1999 dat tdi 20.000 tan/nam.
Theo thdng tin chua cdng b6 cua Chi cue Bao ve Ngu6n lgi Thuy san Binh Thuan, Ngheu
lua bat dau dugc khai thac tir nam 2000 vdi san lugng thap, sau do san lupng tang dan va
dat 42.000 tan vao nam 2004. Cac dan lieu nay chiing minh mpt thuc te la vung bien Binh
Thuan rat giau cd ngu6n lpi than mem hai manh vo nhung san lugng khai thac lai bien
dpng qua ldn, nhieu khi trd nen bat thudng. Viec giai thfch nguyen nhan bien dgng san
lugng khai thac kho cd the thue hien do th6ng s6 nay phu thudc vao nhieu bien s6, bao
gom: trii lugng ngu6n lgi, nhu cau khai thac, thi trudng tieu thu, ky thuat khai thac, lgi
nhuan. Mat khae, sd lieu th6ng ke nhieu khi kh6ng phan anh thuc te khai thac cua ngu dan

va tieu thu tren thi trudng.
Tuy nhien, cac nghien ciiu mat do quan the trong nhiing nam qua cho thay co su
bien dgng kha ldn ve trii lugng quan the ciia cac loai nay. Nhu mgi ngudi deu biet trir
lugng ciia quan the phu thudc vao nhieu yeu to khac nhu: ty le sinh san, ty le chet, toe do
tang trudng, su canh tranh cimg loai, khac loai (ngu6n thuc an, quan he vat dii - con m6i),
cac yeu t6 m6i tradng va mite chet do khai thac.
Vdi cac dan lieu lich sit ve khai thac ngu6n lgi Diep quat trong thdi ky 1982 - 1992
va cac phan tich ve sinh thai quan the dua tren nhieu nghien cim chuyen sau (Shokita,
1977; Ito, 1990; Vo ST Tuan, 1994), mgt nghien eiiu ve bien dgng nguon lgi da dugc tien
hanh (Vo ST Tuan, 1997a). Trong nghien ciiu nay, trd lugng quan the duge qui d6i tu san
lugng khai thac vdi he sd khai thac bang 0,7 sau khi danh gia tinh hgp ly cua hoat dgng
khai thac ciia cac giai doan khac nhau va ngu6n bo sung tir nam trudc dugc udc tfnh. Ket
qua phan tfch va tfnh toan cho thay trd lugng cua mdt nam nao day (Nj) se phu thuge vao
dieu kien m6i tradng cua nam trudc do (Nj.i) cd thuan lgi vdi su sinh san, phat trien cua iu
triing va cua ngay nam do d6i vdi sinh trudng, tdn tai cua diep trudng th^nh hay khong.
M6i lien quan gida trii lugng udc tinh (Y) cua nam Nj vdi mpt s l thdng sl m6i trudng da
dugc xem xet, bao gdm: lugng mua cua nam Nj; lugng mua vao thang 7 - 1 0 , nam Nj.i;
nhiet do nudc trung binh thang 7 - 8, nam Nj va nam Nj.i; nguIn diep b l sung tir nam
trade; van toe gio thang 8, nam nam Nj.i; hudng gid thinh hanh thang 8, nam Nj.i. Ham

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tuong quan nhieu bien da duge thiet lap, trong dd trd lugng (S) c6 quan he ham mii vdi
eac biln (LnS cd quan he tuyen tinh vdi cac bien). Dang ham nay cho phep giai thfch sir
bung nd dot nggt so lugng quan the trong nhirng nam eo dilu kien cue thuan hay giam bat
thudng trong nhiing nam bat lgi (Sviregiev, 1988). He so cua cac bien duge tinh toan cho
thiy cac ylu t l lien quan den ddng trdi manh nhu nhiet do va gid chiem ty le khoang 45%
trong ting nguyen nhan gay bien dgng ngu6n lgi. Che do mua eung eo vai trd quan trgng,.
chilm khoang 36,6%. Nhu vay, nguyen nhan quan trgng nhat gay nen su bien dgng nguon

lgi Diep quat la su thay dii cac yeu td lien quan den dong troi manh.
Nghien eiiu su biln dgng ngudn lgi cua cac loai con lai ciing da dugc dat ra, nhung
chua dat dugc mong muln, trudc hit la do khdng co day s6 lieu lich su nhieu nam ve san
lugng khai thae. Hon niia, sinh thai quan the cua cac loai nay ciing ehua dupc hieu biet
diy du. Tuy nhien, nhu da phan tfch d tren, sinh trudng cua cac loai nay deu ft nhieu lien
quan din vat chit do nudc trdi cung cip. Co the cho rang su thay d6i cudng dp va vi tri
tam cua viing trdi manh cd the lien quan den bien doi lupng vat chat hiiu eo eung cap cho
thuy vuc va thay d6i cac ddng cue bp chi phoi qua trinh lang cua au the. Nhiing yeu to nay
gop phin quan trpng gay nen sir bien dpng sinh kh6i cua cac quan the than mem hai manh
vd trong vung bien Binh Thuan, ke ca nhirng bien dgng dot bien nhu bung n6 so lugng
quan the hay hau nhu bien mat ngu6n lpi trong nhiing nam nao day.
IV. KET LUAN
Su phan b6 tap trang cua cac dpng vat than mem hai manh vo s6ng d vimg duoi
trieu trong khu vuc chiu hieu img sinh thai eua vung trdi manh Nam Trung bd kh6ng phai
la hien tugng ngau nhien. Su giau cd vat chat hiru co do ddng trdi manh va hieu img true
tiep - su phong phu thuc vat phii du (va cd the ca qua trinh chuyen ddi vat chat sau thdi ky
trdi man) la nhiing yeu td thuan lgi cho su phat trien thuan lgi cua cac ddng vat than mem
hai manh an Igc.
Trong cac dgng vat than mem hai manh d Binh Thuan, Diep quat la sinh vat gan bo
chat che nhat vdi hien tuong nudc tr6i: Sinh san chu yeu vao thdi ky tr6i manh nhat (nhiet
do thap), su dung thue vat phii du trong mua trdi nhu la thiic an uu the, au the dugc phat
tan va lang dgng trong mdi lien quan den cac xoay quan cue bg trong thdi ky nudc troi.
Tinh phan b6 dac tnmg cua Dom nau d Binh Thuan ggi y mdi quan he chat che vdi hien
tugng nudc tr6i, tuy chua co nhieu dan lieu de giai thich mgt cac rd rang. Cac than mem
hai manh vo khac nhu So long, Ngheu lua. Ban mai deu tang trudng thuan lgi trong va sau
thdi ky troi manh. Theo nguyen ly sinh thai hgc, sinh trudng thuan lgi la mgt trong nhiing
dieu kien de quan the dat sinh kh6i ldn va cung cap trii lugng eao cho khai thac nguIn lgi.

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Dan lieu ciing cho thay vai trd cua vat chat tir sdng cd the tuong ddi quan trgng d6i vdi So
ldng va Ngheu Iua. Tu lieu hien cd chua du de thao luan ve m6i quan he giira hieu img
cua vung trdi manh ddi vdi Ban mai.
Ket qua thao luan ve dac diem phan bd va sinh hgc ngudn lgi cho thay hieu img cua
nudc tr6i co the khong chi hien hiiu trong thdi ky trdi manh ma con co the keo dai lau hon
hoac rong hon thdng qua chu trinh chuyen d6i vat chat san sinh do ddng tr6i. Day la van
de can dugc nghien ciiu vdi su tham gia cua cac chuyen gia thudc cac ITnh vuc khac nhau.
Sir bien dgng vdi pham vi rong ve trir lugng cua dgng vat than mem hai manh vo d
viing bien Binh Thuan la mgt thuc te ma nguyen nhan chinh co the la do su bien doi cua
dieu kien m6i trudng. Ddi vdi Diep quat, day la quan he theo ham mii va cac yeu to lien
quan hien tugng nudc troi (nhiet do, gid) ddng vai tro kha ldn. Vdi thao luan nay, eiing cd
the cho rang su thay ddi cudng do, vi tri cua tam tr6i manh se chi phdi bien dgng trir lugng
cua cac quan the dgng vat than mem hai manh vo d vung nay. Van de nay can dugc quan
tam nghien ciiu nhieu hon trade khi dua ra nhiing ket luan thuyet phuc.
Viec xem xet hieu ling sinh thai cua ddng trdi manh d6i vdi dgng vat than mem hai
manh vd can dugc thuc hien theo quan diem toan dien, kh6ng tach biet anh hudng cua cac
yeu td m6i tradng khac, nhu che do mua. Dac biet, can chu y den hoat dgng khai thac
(mua vu, kich thudc, san lugng khai thac) - yeu t6 lien quan chat che d6i vdi ngu6n bo
sung quan the sinh vat va chi ph6i trd lugng ngudn lgi. Khai thac hgp ly ngu6n lgi se cho
phep duy tri mgt san lugng khai thac nhat dinh trong nhieu giai doan, khi ma dieu kien
m6i trudng khdng cue thuan hoac qua bat lgi.
TAI LIEU THAM KHAO
1.

Bui Hong Long & Vd SI Tuan, 1997. Dat van de nghien ciiu anh hudng cua cac
dieu kien thuy van dgng luc ddi vdi mgt sd sinh vat bien. T/t Hgi nghi Sinh hgc bien
toan quIc lin nhit. Nha Trang. NXB Khoa hgc KT thuat. Ha Ngi: 240-247.

2.

Ito H., 1990. Some espects of offshore spat collection of Japanese Scallop. In:
Marine farming and Enhancement. Albert K. Spacks (ed). NOAA Technical Report
NMF 85: 35-48.

3.

Nguyen Hiru Phung, Vo SI Tuan & Nguyen Huy Yet, 2001. Phan b l va nguIn lgi
dgng vat than mem kinh te thuge ldp Chan bung (Gastropoda) va ldp Hai manh vd
(Bivalvia) d ven bien Viet Nam. Tuyen tap Hdi thao Quoc gia vl Ddng vat Than
mem lin I, Nha Trang 25-27/3/1999. NXB Ndng nghiep, tp. Ho Chi Minh: 27-60.

4.

Nguyen Ngoc Lam, Thanh phan loai va sinh vat lugng thuc vat phu du vung nudc

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tr6i manh Nam Trang bd. Tuyln tap cac kit qua nghien cim vung trii manh Nam
Trung bg. NXB Khoa hgc Ky thuat. Ha Ngi: 131-142.
5.

Pham Van Tho'm & Vo SI Tuan, 1998. Ve dac dilm m6i tradng vimg biln ven bd
Ca Na-Ham Tan va m6i quan he cd the giiia chung vdi su phan b6 cua So long.
Tuyen tap Nghien ciiu Bien. Vlll: 66-71.

6.

Shokita S., 1977. Biology and artificial propagation of Japanese Scallop (general

review). Proceeding of the Seceond Soviet - Japan Joint Symposium on
Aquaculture. Nov., 1973. Moscow: 75-114.

7.

Truong Si Ky, 1994. Sinh hgc sinh san cua So long Anadara antiquata d viing bien
Binh Thuan. Bao cao chuyen de thudc de tai "Dieu tra ngu6n lgi va dac tinh sinh hoc
ciia Sd long Anadara antiquata. Vien Hai duong hge.

8.

Vo Van Lanh, 1995. Bao cao tong ket de tai KT 0305. Vien Hai duong hgc.

9.

Vo Si Tuan & Nguyen Huu Phung, 1998. Status of Bivalve exploitation and
farming in the coastal waters of South Vietnam. Proceeding of 8th workshop of
TMMP. Phuket Marine Biological Center Special Publication, 18(1): 171-176.

10.

Vo SI Tuan, 1994. Mgt s6 ket qua nghien cim ve sinh hgc sinh san cua Diep quat
Chlamys nobilis (Reeve) d vung bien Binh Thuan. Tuyen tap Nghien ciiu Bien, V:
73-81.

11.

Vo SI Tuan, 1997a. Gop phan nghien ciiu su bien dgng cua ngudn lgi Diep Chlamys
nobilis (Reeve) d tinh Binh Thuan. Tap chi Sinh hgc. III: 56-64.

12.

Vo SI Tuan, 1997b. Mgt s6 dan lieu ve tac dgng sinh thai cua vung tr6i manh doi
vdi ngudn lgi than mem hai manh vo d Binh Thuan. Tuyen tap cac ket qua nghien
ciru vung troi manh Nam Trang bg. NXB Khoa hge Ky thuat. Ha Ngi: 181-191.

13.

Vo SI Tuan, 1998. Vai net ve van de su dumg lau ben ngu6n lgi sinh vat d vimg
bien Ba Ria - Viing Tau. T/c Th6ng tin Khoa hgc KT thuat Ba Ria - Viing Tau: 12-14.
BIVALVE RESOURCES IN THE COASTAL WATERS OF BINH THUAN
PROVINCE (VIET NAM) AND THEIR RELATIONSHIP
WITH THE STRONG UPWELLING
VO SI TUAN, HUA THAI TUYEN
Summary: Based on analysis of the published papers and data obtained by different
projects implemented during 1990 - 2005, it is highlighted that the coastal waters of Binh
Thuan Province (South Viet Nam) are characterised by the abundant distribution afsublitaral

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bivalves, including inter alia: Chlamys nobilis, Anadara antiquata. Modiolus phllippinarum,
Paphia undulata and Pinna sp. The richness of nutrients provided by the strong upwelling and
its direct ecological effect - abundance of phytoplankton (and possible material
transformation following strong upwelling) are considered as favourable factors for growth
and high biomass of these bivalves. Levels of the relation with ecological effects of the strong
upwelling change among species due to differences on population ecology of the species. The
Scallop C nobilis depends on the strong upwelling at the highest level and seconded by
mussel M. phllippinarum. The clams A. antiquata and P. undulata are Influenced by factors
caused by upwelling and river discharge. It is able to wrap up that changes in position and

intensity of the strong upwelling would control biological processes and as a result,
fluctuation of population biomass of these species in the coastal waters of Binh Thuan
Province.

Ngdy nhgn bdi: 29 - 10 - 2009

Dia chi: Vien Hai duong hgc

Nguoi nhgn xet: PGS.TSKH. Nguyin Tac An

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