HOI NGH! KHOA HOC TOAN QUOC V£ SINH THAI VA TAI NGUYEN SINH VAT Li,N THLf BA MQT SO YEU TO TAC DQNG DEN KHA NANG BAO TON NGUON GIONG T\f NHIEN VUNG TRIEU CLTA SONG BACH DANG TRAN MANH HA, NGUYEN TH| T[.]
Trang 1M Q T SO YEU TO TAC DQNG D E N KHA NANG BAO TON
NGUON GIONG T\f NHIEN VUNG TRIEU CLTA SONG BACH DANG
TRAN MANH HA, NGUYEN TH| THU
Vi^n Tdi nguyen vd Moi truang Bien, Hdi Phong
Viing cua sdng dugc danh gii la mdt trong nhtimg hf sinh thii ddc dao va phirc tap nhung rit giau cd ve tii nguyen thifn nhien Vifc khai thic cic dang tai nguyen thien nhien tmdc diy chi dimg lai d miic dg su dyng cac phuong tifn khai thic thd so Tuy nhien thdi gian gin day do siic
ep cua sy gia ting dan sd v i do nhu cau sir dyng ngiy cing cao cic dang tii nguyen thien nhien thi vifc khai thic tii nguyen lai cing chen ra manh me Nhieu boat dgng dien ra ty phit, mgt so phuong phip danh bit mang tinh buy dift, khdng cd quy hoach da dan tdi buy hoai nghiem trgng mdi truomg sinh thii v i ngudn lgi sinh vat vimg trieu cua sdng
Nam trong tam giic phit trien kinh te H i Ngi - Hii Phdng - Quang Ninh, viing cira sdng Bach Dang Ii noi dien ra cic boat dgng kinh te quan trgng nhu giao thdng van tii bien, xiy dyng cac cang bien v i phit trien cic khu cdng nghifp ciing nhu cac boat dgng nudi frdng va danh bit hii sin, du lich dich vy v i cic boat dgng bao tdn bien Bdi vay vifc nghien ciru dinh gii tiem ning ngudn gidng v i xac dinh dugc cic tic dgng de doa den ngudn gidng ty nhien phyc v\i cho vifc phit trien hgp Iy nghe nudi v i bao tdn hifu qua ngudn gidng ty nhien la vifc lam can thiet v i hiru ich
L TAI LIEU VA PHUONG PHAP NGHIEN CLTU
Bii bio niy dugc hinh thinh tren co sd sd lifu thu dugc qua cic dgt khao sit trong hai miia
mua va miia khd trong 2 nim 2005 v i 2006 cua de tai "Nghien cuu, danh gid nguon giong torn
cua cd viing trieu vd vung cua song Each Huyen (Bgch Dang) phuc vu phdt trien nghe nuoi thiiy sdn vd bdo ve nguon lai", ngoai ra cdn tham khio mgt so tai lieu ve ngudn gidng tdm cua vimg
bien tu Hii Phdng den Quing Ninh, cic bio cio quan trie chat lucjmg mdi trudng nude ciia tram quan trie quoc gia vi sir dyng so lifu dieu tra tinh hinh kinh te xa hgi trong khudn khd de tai Cac tic ddng den ngudn giong dugc dilu tra theo cic phuong phap: Dilu tra khio sit ngoai thyc dia, phdng van cic cip chinh quyen xa Phii Long v i huyfn Cit Hii, phdng van cic hg dan nudi trdng va dinh bit thuy sai ven bd khu vyc cira Bach Dang Cac sd lifu dugc xir Iy bing phuong phap thdng ke
n KET QUA NGHIEN CLTU VA THAO LUAN
1 Dieu kifn tu nhien viing trieu cira sdng Bach Dang
Ket qui do dac qua cac dgt khao sat cho thay: Cac thdng sd mdi trudng khu vyc cira Bach Ding phan anh tinh chat man lg ciia thuy v\rc Do muoi tmng binh vio miia mua khoang 1-19%o
va vao miia khd tir 21-30%o Gia fri trung binh nim dat 21%o pH trong nim dao ddng tir 7,42-8,30, gii frj trung binh dat 8,05 Nhift do nude trung binh nim dao dgng trong khoing 18,3-32,7
°C v i dat gia tri trung binh 25,2 °C Gii tri dxy hoa tan dao dgng trong khoang 5,2-6,7 mg/l va dat gia tri frung binh nam 6,1 mg/l
Cic yeu td mdi trudng cua viing cira sdng Bach Ding deu nam trong khoang gidi ban tdt cho
Trang 2HQI NGH! KHOA HOC T O A N Q U O C V £ SINH THAI VA TAI N G U Y £ N SINH VAT lAvN THLf BA
2 Sy suy giam nguon giong tdm, ca viing trieu ciia sdng Bach Dang
Theo cic sd lifu khio sit tir 2005-2006 va qua thdng ke cac tai lifu da cd ve nguon gidng vimg cira sdng Bach Ding cho thay, sau khoang 20 nim thanh phan loai ci lcin viing nude cira Bach Ding thu dugc giam gin 50%) trong khi thinh phan ca bgt giam gan 30% Cd the thay sy ving mat ciia nhieu loai thudc cac hg ci trich (Clupeidae), ci trdng (Engraulidae), ci uc (Ariidae), c i dua (Muraenesocidae), c i trie (Priacanthidae) va ca nuc (Carangidae^, ci suot (Atherinidae) v Day Ii cic loai cho sin lugng khai thic vi gii tri kinh te lcin cho nghe c i vimg nude cira sdng niy trudc diy (hinh 1)
90
80
70
60
50
40
30
20
10
0
1 1 S^ taxoQ ci h^X, ck con
- 2 S 6 l 0 3 i c a l 6 n So loal ca lo'n
150
140
120
100
80
60
40
20
4 0
C;ufl L?ich Huy?n - B^ch DSng b> Ket qua thu tai dia Lach Htjy?n tru6c 1994 2005-2006
KIi\n')ic
Hinh 1: Bien dfng thinh phan nguon giong ca vi ci Ion viing cira Bach Dang
Ngoii sy bien ddi vl thanh phin loii thi mat dg nguon giong ci trong viing nude cung cd sy biln ddng theo thdi gian (hinh 2)
Nam 1982 N4m 2000 NSm 2006
Thirl gian (nam)
Hinh 2: Bien dfng so luyng nguon giong ca vimg cu-a song Bach Dang
Qua hinh 2, ta thay su biln dgng manh vl sd lugng ngudn giong trong khoing thdi^gian 30 nim Sd luong trung binh giim din tir 744 con/lOOm^ (1970) xudng gin 600 con/lOOm (1982), tilp din nim 2000 sd lugng giam cdn 485 con/100m\ trong cac chuyen khio sit^vio cac nim 2005-2006 thi mat dg ngudn giong c i da giam rd rft chi cdn khoang 200 con/100m
Trang 3HOI NGHI KHOA HOC T O A N Q U O C V f SINH THAI V A TAI N G U Y £ N SINH VAT L^N THLf BA
Ngudn gidng tdm trong cac thuy "vyc nude ciing da dugc quan tam tir lau nhung cac nghien ciiu vin cdn mang tinh nhd le va rai ric (Pham Dinh Trgng, 1985, 1993) Cac ket qua khio sit ngoii hifn trudng tir 2005-2006 ket hgp vdi thong ke cic nghien ciru da cd ve ngudn giong tdm cho thiy sy biln ddi cua ngudn gidng tdm tai khu vyc cira Bach Dang (hinh 3)
y.y
-5
M
Tring cat Bfii triAu BAI tridu Bfii Tri^ Bfii Iridu BBi triAu Bfii Ih^u Bfii tridu Bfil triiu
1976 OlnnVQ Dkih VO Uim Nhi Hoing Tan cfra Van ciraTliai NgMa Hi/ng L«ch Huy«n 19S9 2006 Mac 1989 1969 Uc 2001 Binh 2001 (Nam Dinh 2006
D|a akm thM gian 2002)
FTmh 3: Bien dfng mat dp nguon giong torn tren mgt so bSi trieu cira song phia Bac
Phan tich cic sd lifu thu dugc theo chuoi thdi gian, nhan thay mat do ngudn gidng tdm fren cic bai trieu cd phan suy giam sau khoang 10 den 30 nim (1976-2006), tuy nhien mirc dg suy giam khdng nhieu Khi so sinh mat dg ngudn gidng cua cac khu vyc nim phia ciia Nam Trifu la Dam nha Mac nim 1989, bai trieu Hoang Tan 1989 vdi mat do tdm gidng thu tai Dinh Via 2006 (cira Nam Trifu) va bai trilu Phii Long (cira Lach Huyfn) thay mat dg tdm gidng fren mgt don
vj difn tich bai frifu khdng suy giam dang ke sau gin 30 nim
Mat khic, nguon gidng tdm t ^ khu vyc cira Bach Dang cd phan thap hem so vdi cic khu vyc khic nhu cira Vin Uc, ciia Thai Binh-noi cd bai trifu bim rgng lcin va tham RNM dugc trdng trong nhirng nam 2001 dang phit trien
Nhu vay, cd the thay sy phan bo so lugng giong tdm tren bai trieu phu thugc vao die tinh tram tich bai, vj tri so vdi cira sdng va yeu to dgng lyc sdng - bien tai khu vyc dd Hon nua, thiy ring mat dg ngudn giong tdm con (giong day) tuy cd sy suy giam theo thdi gian song khdng dang ke nhu ngudn gidng ci
3 Cac tac dgng de do^ tdi kha nSng bao ton nguon giong viing ciia song Bach Dang 3.1 Hifn trang khai thac nguon Igi thuy san va nguon giong viing cua Bach Dang Nim 2003, d xa Phu Long, chi cdn 65 hg, mdi hg chi cd mgt thuyen danh ca nhd 1 -2 tan lip may
6-8CV Nghi khai thac chii dao la lucii 3 minh vcii sin hsgng khai thac nam 2004 dat 1000 tin trong
dd, mgt phan lcin dugc dua vao che biln nude mim vdi cdng suit 1000 lit Chi cd 5 hg lip miy 12-15CV de frang bi dan den dinh myc d khu vyc Cat Bi Ngoai ra, cdn cd dgi tau thu mua khoing 20 tiu cd frgng tai 10 tan de thu mua hai san Sin lugng thu mua khoang 500 tan ca/nim diing de phoi khd bin ra thi tmdng (Biii Dmh Chung, 2(X)3) Kit qua dilu tra tra thyc dia ket hgp vcii so lifu thdng
ke thi cac loai nghe khai thac chinh cua x i Phii Long dugc cy the nhu sau:
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Ca cau nghe khai thac hai san ciia xa Phu Long, Cat Hai
Loai nghe
Ludi ghe
Ludi myc
Xim
Cau
Loai lu'di
Re froi
Re 3 ldp
Co dinh Cau ludi
So lirgTig
29
18
23
5
So vang ludi
44
43
49
Ty If (%)
37,2 23,0 33,3
6,5
Nghi xim diy va ludi ghe chiem ty trgng Icin hon ca trong co ciu nghi khai thic hii sin cua khu vyc cua sdng Bach Ding Khu "vyc dinh bit ciia nghe niy thudng d cac lach, bii bdi, ven khu rimg ngap man va sin phim dinh bat theo con nude hang ngiy thucmg Ii cic loai ca, tdm, cua song d day Hinh thirc danh bit niy dang cd xu the bi thu hep do lam cin trd hoat ddng c;iia cic tau ldm v i phuong thirc dinh bit huy dift ngudn lgi nen chinh quyen dia phuong di ra cac bifn phap ban chi hoac khdng khuyen khich phit trien
Cho tdi cuoi 2006, khu vyc cua sdng Bach Ding cdn 3 hang diy phia trong phi Phii Long vdi hon 10 mifng ludi chilm difn tich rat rgng, khai thic hiu het cic nhdm tdm, cua, c i di ra vi
di vio qua cira Bach Ding Ngoii ra, cdn mgt sd hing ding quay quanh cic bai frong rimg ngip min Hifn nay, sin lugng nudi trong thiiy sin (tdm, cua ci) cing ngay (:hilm ty trgng cao hon trong tdng sin lugng ciia nganh: tir 37,43% nim 2000 len tdi 59,42% tdng sin lugng thuy sin Tuy nhien, sin lugng danh bit cd xu thi suy giim va chiem ty trgng thip hon so vcii nudi trong trong tdng sin lugng cua nginh: tir 62,57% nim 2000, it dao dgng trong khoing 52-53% trong cic nam 2001 va 2002 nhung tyt xuong cdn 40,58% tdng sin lugng thiiy sin ciia nam 2003 Theo kit qui dilu tra nhin din vi dya tren so lifu thdng ke cua Tmng tam Phit trien ndng thdn nim 2001, d xa Phii Long trong vdng 20 nim trd lai day, ning suit khai thic da giim di 15 lin, tir 30kg/ngudi/ngay nim 1980 xuong chi cdn 2kg/ngudi/ngay Mit khic, do thieu kinh nghifm dinh ci xa bd cho nen ngay c i khi dugc Nhi nude cho vay vdn dl ddng dugc tau Icin cung boat ddng khdng cd hifu qui dan tdi lim in thua lo va frd vl nghi khai thac ci ven bd Doi vdi cic hg din tir cic dia phuang khic (chii ylu tu huyfn Thiiy Nguyen) thucmg chuyen doi nghi theo miia vdi hai nghi chinh la ludi gia va ding diy Hg cd so tau thuyin khoing 15 thuyin lip miy 15CV di thanh timg dgi 3 thuyin Ddi tugng khai thic chu ylu Ii ci diy, tdm sit, sd gao sin lugng khai thic frung binh Ii 10kg cic loai/dem vdi gii tri quy thinh tien khoing 100-170 ngan dong Thdi gian khai thic nghi gii khu vyc Bach Ding vi Cit Bi Ii cic thing 2, 3 vi 4 sau dd hg quay vl lam nghi ding diy d khu vyc Phi Rimg, sin lugng tmng bmh khoing 15kg ca cic loai
Theo cic so lifu thu dugc tii dilu fra nhin dan, mgt sd loai hai sin tai khu vyc cira Bach Ding gin nhu khdng cdn cho san lugng khai thic Vi dy: ci mdi dudng, sd gao frong vdng 5 nim trudc cd thi khai thic dugc vii trim kg/thuyln/dem d khu vyc phao den nhung tdi nay thi hiu nhu cdn rat it, 6 c buong trong vdng 5 nim trd vl trudc d khu vyc Bach Ding cdn tuong ddi nhilu vdi ning suit khai thac khoing 40-50kg/thuyln/dem nhung cho tdi nay thi nguon lgi nay gin nhu khdng cdn
Hifn trang khai thac ngu6n giong tdm, ci bing nghi xim diy Ii tiiyc t l dang luu y d khu vyc cira Bach Ding Kit qua phin tich mau tir cic hing ludi diy tren cira Bach Dang trong cac
Trang 5HOI NGHI KHOA HQC T O A N Q U O C V ^ SINH THAI V A TAI N G U Y £ N SINH VAT L^N THLf BA
dgt khio sit thing 7/2005 va thing 9/2006 cho thay hau hit cac loai thu dugc deu cd kich thudc nhd, la ngudn gidng cac loai tdm, ca (bang 2)
Bdng 2
Thanh phan, so lugng va kich cd ca khai thac ciia nghe ludi day
STT
1
2
3
4
5
6
Ten h9
Hg ca trdng (Engraulidae)
Hg ca dii (Sciaenidae)
Hg ca lift (Leiognathidae)
Hp ca nuc (Carangidae)
Hg ca chai (Platycephalidae)
Cac hg khac
Tong cfng
•* So lugng ca the (0,5 kg san pham tir ludi) Thing 7/2005
104
28
16
7
8
163
Thing 9/2006
223
3
10
253
Ty if (»/.)
63,8 17,2 9,82
17
4,29
4,91
100
Kich Cff ca the trung binh (cm)
4,34-7,4 3,5 3,3
5,07 3,3-5
Ket qua lay mau ngau nhien cua nghe ludi diy trong cac thing 7/2005 v i thing 9/2006 cho thiy, trong mgt me ludi keo diy, hg c i trdng (Engraulidae) cd so lugng c i the Icin nhit, 104 ci the chiem ty If 63,8%) tdng sd ci the cd trong me ludi Tiep dd Ii cic hg ca dii (Sciaenidae) 28
ci the (17,2%o), ca lift (Leiognathidae) 16 c i the (9,82%)) v i hg c i chai (Platycephalidae) 7 ca the (4,29%o); cac hg khic chi gdm 8 c i the chiem 4,91%)
Tuong ty thinh phan vi so lugng, kich cd cic loii tdm thu dugc trong me ludi diy trong thing 9/2006 dugc trinh bay frong bang 3
Bdng 3 Thanh phan, so lugng \k kich cd torn khai thac ciia nghe ludi day
STT
1
2
3
4
5
6
7
8
Ten loai
Acetes japonicus Alpheus sp
Alpheus sp
Majidae
Metapenaeus ensis Metapenaeus joyneri
Metapenaeus moyebi
Palaemon sp
Tong cfng
So lugng
(0,5 kg sin pham tir ludi)
16
5
3
2
38
6
42
2
114
Tyl?
(%)
14
4
3
2
33
5
37
2
Kich thirdc (mm)
35-85
62 30-87
Ket qua cho thay cd hon 100 con tdm cic loai trong 0,5 kg sin pham thu dugc tii hing lucii
diy cira Bach Dang trong do cd tdi gan 40% la tdm rio gidng (Metapenaeus ensis), 40%o cdn lai
Trang 6HOI NGH! KHOA HQC T O A N Q U O C Vg SINH THAI VA TAI N G U Y £ N SINH VAT LAN THU BA
la cac loai tdm vang vi tdm sit diu Ii cic loai nguon Igi viing cua sdng Hiu hit chung cd kich cd nhd, Ii con non
Tir cic thdng ke^ thiy ring, phin I'cin nhdm tdm, ci khai thac cd kich thudc gidng trong khoang tir 3-5cm, dilu nay cd nghTa Ii viec khai thic bing nghi ludi day thi hifn tinh huy dift°
Da sd ci torn thu dugc cdn trong giai doan con non do dd mdt lugng nguon gidng rit Idn da khong thi tham gia vio tii tao nguon lgi cho viing nude Kit qua tren day khi phii hgp vdi kit qua nghien ciru ciia Le Vin Mien (2000) khi nghien cim quin dan giong bj dinh bit bdi cac hing diy d phi Tam Giang
3.2 Cac de dga doi vdi nguon giong viing cira sdng Bach Ding
- De dog tir moi trudng tu nhien
Mdi trudng ty nhien tic dgng din nguon gidng thdng qua sy thay ddi ciia die tinh vi chit lui^ng ciia khdi nude, nen diy vi cac loai sinh cinh m i trong dd nguon gidng sinh vat ton tai vi phit trien, cd the tdm tit cic tic dgng ciia ty nhien din ngudn giong nhu sau:
+ Sy thay ddi tuong tic sdng bien vi ddng chay ven bd:
Cimg vdi lu lyt dau ngudn da giy ra sy ling dgng trim tich qui ldn d noi nay song lai gay xdi Id cic vimg bai khic Nhtrng qui trinh niy deu lim inh hudng tieu cyc den sy phin bo ciia cac loai thuy hai sin d giai doan con non Viing cua sdng Bach Ding trong dd cd cira Bach Ding cd xu the bj bien lan vi nim trong qui trinh xdi Id ty nhien ciia toin bd vimg bien ven bd phia Bic Vift Nam keo theo dd Ii sy thu h?p bai frieu ty nhien, vung bd Cit Hii mit di 4-8m chieu ngang bai moi nim Tuy nhien tdc dg xdi Id tir nim 1965 -1990 da giim 30% so vdi tir nim 1930-1965 (Tran Vin Difn, 2002)
+ Sy ndng len cua khi h^u va cic hifn tugng thdi tiet bat thuomg:
Theo ket qui quan trie cua hf thong dai tram quoc gia, nhiet dg nude ven bd Vift Nam ting xip xi 2°C 'tir 1995-1998 do cic nhieu dgng khi hiu nhift ddi khu vyc cd lien quan den hifn tugng EI - Nino vi sy am len ciia khi hau toan cau Nhift dg nude bien ting cimg vdi cic hifn tugng thdi tiet bat thuomg lam biing phit cac dgt thuy trieu dd vdi tan suit cao, tic dgng tryc tiep tdi sy ton tai vi phit trien ciia cic loai thuy hii sin trudng thanh cung nhu d giai doan con non Dong thdi Ii sy bimg nd vl sd lugng cua quin xa sira do sy bien ddi khi hiu cDng gdp phan lam suy giim sd lugng ngudn gidng thuy san thdng qua khi ning in sinh vat phii du, trong dd
cd iu triing tdm, cua, ci (Nguyen Thj Thu va nnk, 2007)
- Cdc de dog tit cdc hogt dpng phdt trien kinh te xd hpi
Nim trong tam giac phit triln kinh tl H i Ngi-Hii Phdng-Quing Ninh, vung ciia sdng Bach Ding la noi diln ra cac boat dgng kinh tl quan trgng nhu giao thdng van tii bien, xay dyng cic cing bien vi phat frien cic khu cdng nghifp ciing nhu cic boat dgng nudi frdng va danh bit hii sin, du Ijch dich vy va cic hoat dgng bio tdn bien Tat c i cic boat dgng tren da tryc tiep hay gian tilp lim suy giim nguon Igi ven bd ndi chung va ngudn giong tdm, ca ndi rieng
+ Md rgng cic khu cdng nghifp:
Theo cic so lifu thdng ke, vimg cua sdng Bach Ding cd hang trim nha miy, xi nghifp cdng nghifp dgc bd sdng gom nhi may ddng tiu, nhi may xi ming, nhi miy hoi chat, chiem hon 80% difn tich bai trilu cao da vi dang xi thii dgc hai ben ha luu sdng va ra bai frilu phia cira Bach Ding, bai trilu phia ddng nam dio Dinh Vu Trong dd hon 80% Ii nude thii chua qua xu h' da gay d nhilm vi lim inh hudng din sy ton tai va phit friln ciia cac loai thuy hii sin ndi chung cung nhu ngudn gidng trong vimg
Trang 7HQI NGHI KHOA HOC T O A N Q U O C Vfe SINH THAI V A TAI N G U Y £ N SINH VAT LAN THQ- BA
+ Canh tic ndng nghifp:
Mdt trong nhtmg tic dgng de doa tdi nguon gidng thuy sin viing trieu ciia sdng Bach Ding ciing nhu cic viing nude ven bd khic la thudc trir sau (TTS) v i cic loai hoa chat bao vf thyc vat khac dugc sir dyng trong canh tic ndng nghifp
Khu vyc bien ven bd tir Ha Long din cira Bach Ding, nong do thudc trir sau vd co Cio ting cao vao miia mua va giam thip vio miia khd Ndng do d miic tmng binh vdi 0,108 - 0,110 pg/1 trong miia khd den 0,236 - 0,216pg/l frong miia mua He sd nii ro trung bmh cua TTS trong viing nude bien ven bd phia Bic da dugc Luu Vin Difu khuyin cao vdi tdng DDT la 48,3 Cd the thay mirc riii ro cua cac hgp chat TTS trong nude so vdi tieu chuan ciia Indonesia va Malaysia Ii khi cao Mirc do nay da cd bilu hifn -vorgt qua gicii ban cho phep ddi vdi nude bien ven bd cho nudi trdng thuy sin
+ Md rdng difn tich dam nudi thuy sin:
Difn tich dam NTTS ting nhanh frong 10-15 nam trd lai day, da lim giam 50 - 70 % dien tich bai frilu vi mit di vai nghin ha RNM Rieng khu vyc Cat Ba, RNM da giam tir 5000ha xudng cdn 1200ha sau hom 10 nim Nhu vay, mdi nim tai khu vyc nghien ciiai, difn tich RNM
da bi giam hon 300ha Khu vyc bai trilu Bach Ding chu ylu thudc xa PhiiLong cd hom 300Qha bai frieu Vifc xay dyng dim d i chilm hon 1500ha v i din nay chi cdn gan lOOha bai trifu cd RNM Diy chinh Ii sy mit di bai cu tni cho nhilu loai ngudn giong thuy sin Sy mit di ciia RNM ben cic bai trieu cdn giin tiep lam ting nguy co xdi Id bai vi lai tiep tuc lim mit di nai ling tru cua cic loai au trimg tdm c i vi ngudn thirc in Ii mim ba htm co cho chiing
Cung vdi cic tic ddng tren mat rgng, vifc ting cudng cic boat dgng khai thic theo cich dip dam nudi tren vimg trieu cdn lim ting cac nguy co gay suy thoii chat lugng mdi trudng frim tich Sy suy giam chat lugng mdi trudng trim tich do cic boat dgng khai thic viing cira sdng Ii hit sire nghiem frgng va dl lai h^u qua rit lau dii (Nguyen Diic Cy, 1998)
+ Md rdng quy md cing va xay dyng cic ciu cang mdi:
Trong khoang 15 nim trd lai day, boat dgng van chuyin hang hoa tang nhanh cimg vdi difn tich cing ngay cing md rgng Tdng lugmg hing hoi ting tir 7,5 trifu tin tdi 14,3 trifu tin nam
2004 Rieng cang cdng nghifp Dmh Vu da dugc xay dyng tren 85ha difn tich von Ii bai frilu ven ciia sdng
Cic boat dgng kinh te cing da lim ting dg dye cua nude, lam thay ddi ddng chay, roi loan HST diy mem, giy ra sy di cu cua cic loii thuy sinh, giy d nhiem chit hiru co trong khu vyc cing Ngoii ra cic chat d nhiem vdn tich ty trong dit nay bi khuylch tan va lan tmyIn sang cic khu vyc l|rt can Tuy nhien nguy co trin diu vi hoi chit tir cac boat ddng ciia cang la tic ddng gay d nhiem lcin nhit ddi vcii ngudn Igi thuy sin, ngudn giong sinh vat va cic hoat ddng nudi trdng thuy sin
Theo kit qui quan trie frong hf thong fram quoc gia, thay cac loai HCBVTV co d o da vugt ngudng TELs Dd la 4,4 DDE 2, 39 lin, DDD 1,7-4, 3 lin, 4, 4 DDT vugt 2,7-24,5 lin, tham chi vugt nguomg PELs (4,4 DDT -6, 1 lan), Ndng dd diu trong frim tich khu vyc bai trilu gin cing ting 2,4 lin (Nguyen Diic Cy, 2003)
Cac ket qui nghien ciiu cho thiy •vimg cira sdng Bach Ding cd him lugng diu trong nude cao nhit khi so sinh vcii toin vimg biln ven bd Vift Nam Theo Luu Van Difu (2004), viing nude cua sdng Bach Ding vi Vinh Cua Lyc Ii hai khoi nude lien quan fryc tilp tdi khu vyc nghien cim cd ndng dg (dau trong nude kha cao, tdi l,5mg/I va hf so nii ro d nhiem do diu ting hon 2 lan ke tir 1995 den 2001 Hf sd riii ro tmng binh cua dau trong viing nude bien ven bd phia Bic ting tii 0,8 don vj nim 1995 din 2,2 don vj nam 2001 Ciing cd thi thiy viing nude
Trang 8Cira Luc - Cira Bach Ding da va dang chiu sy de doa tu d nhiem dau lcin nhit trong dii ven bd phia bac Hon niira, theo ke hoach phit trien cho nhirng nam 2010 - 2020, khi khu kinh tl Dinh
Vu - Cit Hai vi Cang Bach Dang di vio khai thac manh, nguy co tran diu se cdn la de doa tic dgng va gay tdn that nhieu hon nira cho ngudn Igi hii sin
+ Cac hoat dgng khai thic va dinh bit buy dift:
Sy cd ging cao ciia chinh quyen cic cap khu vyc cira Bach Ding da gin nhu han chi tdi da dugc nan dinh c i bing min tai Bach Dang Hon niia, da tuyen tmyen vi khuyen khich chuyen nginh nghe cho nhieu hg khai thic nhd ven bd sang nudi ong, nudi de vi dinh bat xa bd Song cho tdi cuoi 2006 van tdn tai hon 5 hang diy vdi mdi hing diy gdm 5-7 mifng ludi, mdi mifng ludi thu 10kg ci, tdm con theo ddng nude ra hoic vao sdng trong mdi miia Khio sit gin diy nhit vao thing 12/2007, cho thiy cic hang diy nay da dugc giii toi Tuy nhien lai xuat hifn huih thirc danh bit mdi la loai bay ldng dugc chin ngang ducmg xudng tir cic bai trieu de bit tdm, ci khi trieu nit xudng Day ciing Ii nghe cin xem xet vi tinh huy dift vdi ngudn gidng Dong thdi vin cdn mdt sd tiu su dyng nghe te difn len liit hoat ddng
Trong 5 nhdm nguyen nhin gay suy giim ngudn gidng thiy cd 2 nhdm nguyen nhin dau Ii
hf qua cua cic qui trinh ty nhien hay cic dien bien sinh thii toin ciu nen khd khic phuc, cdn 3 nhdm nguyen nhin sau lien quan nhieu den cic hoat dgng kinh te xa hdi Cac nhdm nguyen nhan tic dgng niy cd the dugc khic phyc de giim thieu mirc dg tic dgng neu cd kip thai cic chiln luge, chinh sich, giai phap quin Iy tdng hgp hucing tdi sir dyng ben vtrng viing trieu cira sdng vi ven bd
HI KET LUAN
1 Nguon giong viing cira Bach Ding chju tic dgng Idn ciia c;ic cac yeu to ty nhien cung nhu cac hoat ddng kinh te xa hdi ciia con ngudi Hifn nay, nguon gidng da suy giim tren 50% so vdi thdi gian 30 nim trudc
2 Cic tic nhin gay suy giim nguon giong dugc tap hgp trong 5 nhdm tic dgng gom: Thay ddi vl cic ylu to mdi trucmg song; bj canh tranh bdi djch hai va vit dir; d nhiem mdi tmdng; khai thic qui mirc, buy dift, va mat noi cu tni
" 3 Mgt so nguyen nhan khd khic phyc do la hf qui ciia qui trinh sinh thai toan ciu, cic nguyen nhan khic cd thi khic phyc nlu cd kjp thdi cic chinh sich va giii phap quin ly tdng hgp nhim su dyng bin vtrng ngudn Igi vimg cira sdng
TAI LIEU THAM KHAO
1 Biii Dinh Chung, Nguyen Thj Hai, 2003: Tic dgng ciia khu bao ton nguon lgi Phu Long tdi hoat dgng nudi trdng v i danh bit Ky ylu hgi thao "Nhin lai hai nam thyc hifn dy in BVNLVB dya vao cgng dong" Trang 8-15
2 Nguyen Dire C\f, 1998: Sy biln ddi die dilm dia hoi trim tich ciia vimg cua sdng Bach
Ding dudi tic ddng con ngudi va dl xuit giii phip phyc hoi mdi tmdng Tuyen tap Tai nguyen va Mdi trucmg bien Tip V
3 Luu Van Difu, 2007.' Hifn trang va xu thi biln dgng chit jugng nude vimg bien ven bd phia Bic Vift Nam Tuyln tip Tii nguyen vi Mdi trudng biln Tip XII
' 4 Le Quang Dung, Nguyen Dire Cy, Nguyen Manh Cudng, 2007: Thir nghifm dgc tinh cip cua cyanua, ddng, kem ddi vdi 4 loai sinh vat tai tram bien Dd Son, Hai Phong Tuyln tap Tii nguyen vi Mdi trudng bien Tip XII
Trang 9HOl NGHI KHOA HQC T O A N Q U O C Vfe SINH THAI V A TAI N G U Y £ N SINH VAT LAN THU BA
5 English S, C Wilkinson, V Baker, 1997: Siuvey manual for fropical marine resources
Ausfralian Institute of Marine Science, Townsvile, Chapter Seagrass communuty, pp
163-264
6 Haywood M D E et al., 1998: Marine Ecology Progress Series, 162: 201-214
7 Janekarn Vudhichai, 1986: "Composition and occurrence of fish larvae in mangrove
areas along the east coast gf Phuket Island, Western Peninsular, Thai Land" Reseach bulletin (44) Published by Phuket Marine Biological Center
8 Laegdsgaard Pia, Craig R Johnson, 1995: Marine Ecology Progress Series, 126:
67-81
9 Vu Trung Tang, 1994: Cac hf sinh thii cua sdng Vift Nam NXB KH & KT, Ha Ndi lO.Nguyen Thj Thu, 1998: Nghien ciiu, dinh ^ia sy bien ddi ciia cac nhdm sinh vat diy va
ngudn gidng khu vyc cua sdng Cam sau dap dap Dinh Vii, de tii cap co sd, luu trir tai Vifn Tii nguyen v i Mdi tmcmg bien
11.Cao Thu Trang, 2006: Kiem ke cic van de mdi trudng cang Hai Phdng Bio cio Hgi
thio de tai Mdi frudng Cing
12.Pham Dinh Trgng, Lang Van Ken, 1985: Ngudn lgi torn gidng va hifn trang ciia nd d
dao Dinh Vu va Ian can Bio cao luu trir tai Vifn Tai nguyen va Mdi trudng bien
13.Pham Dinh Trgng, Nguyen Thj Thu, Le Thj Thuy, 1993: Ngudn gidng tdm, cua, ci
vimg bien ddng nam Cit Bi, Bio cao chuyen de de tai Nghien ciiai co sd khoa hgc thiet lip khu bio tdn bien ddng nam Cit Ba Tii lifu luu trii tai thu vifn Phan Vifn Hii duong hgc tai Hai Phdng
FACTORS AFFECTING THE NATURAL LARVAE SOURCES IN LITTORAL
AREAS OF BACH DANG ESTUARY
TRAN MANH HA, NGUYEN THI THU
SUMMARY The composition and abundance of aquatic larvae sources have decreased in the last 20 years due to natural processes and human impacts The aim of this study is to determine the effects on the diversity of larvae sources in Bach Dang Esmary Information was accumulated based on field samples and interviews with local authorities and local fisherman and reports statistics Main effects on larvae sources are changing the environment parameters, predator competition, environment pollution, overfishing, and lost of habitat The solutions, strategies and policies for integrate management coastal zone need to be put forward