Tgp chi Khoa hpc Trudng Dgi hpc Cdn Tha Phdn B: Ndng nghiip. Thiy sdn vd Cdng nghi Sinh hpc: 34 (2014): 55-6^
Tap chl Khoa hocTrLfdng Oai hoc Can ThcJ website: sj.ctu.edu.vn
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SAN L l T O N G VA ClTCJNG USC K H A I T H A C B E N V C T N G T O I D A d V U N G B I E N X A BCf B O N G N A M B O
Bill Van Tung'
' Phdn vien Nghiin cdu Hdi sdn phia Nam - Vien Nghien cuu Hdi sdn Thong tin chung:
Ngdy nhgn: 12/05/2014 Ngdy chdp nhgn: 30/10/2014 Title:
Maximum sustainable yield and fishing effort in the offshore Southeast waters of Vietnam
Tirkhda:
Cudng lire khai thdc ben vieng tdi da; sdn lugng khai thdc bin vieng tdi da; vimg bien xa bdDdng Nam Bd Keywords:
Maximum sustainable fishing effort; maximum sustainable yield; the offshore Southeast waters of Viemam
ABSTRACT
This report presented the research results of the maximum sustainable yield (MSY) and the corresponding level of fishing effort (fMsr) in the offshore Southeast waters of Vietnam. The surplus production model ofSchaef^ (1954)' was applied to estimate MSY and fusy. Results showed that the maximum sustainable fishing effort m offshore Southeast waters of Vietnam were 14.912 boats, in which the trawl were 5.010 boats, gill net (2,469 boats), purse seine (2.998 boats), hand line and longline (1,934 boats) and others (2,501 boats).
The fishing effort of trawl was higher than the maximum sustainable fishing effort around 56,3% (with 2.823 boats); the fishing effort of other fishing were lower than the maximum sustainable fishing effort. The maximum sustainable yield in the offshore Southeast waters of Vietnam were 1.146,140 tons.
TOM T A T
Bdo cdo ndy trinh bdy kit qua nghien cdu vi sdn lugng vd cudng luc khai thdc bin vieng ldi da a vimg bien xa bd Dong Nam Bg. Md hinh sdn lugng thang du cda Schaefer (1954) dugc su dung de xdc dinh sdn lugng vd cudng luc khai ihdc ben viing toi da cho viing bien. Kel qud nghien cuu cho thdy, cudng hfC khai thdc ben viing toi da d vimg bien xa bd Ddng Nam Bg Id 14.912 tau, trong do nghi ludi keo la 5.010 tdu. nghi ludi re 2.469 tdu, nghi ludi vdy 2.998 tau.
nghe cdu 1.934 lau vd nhdm nghi khdc Id 2.501 tdu. Cudng luc khai thdc ciia nghe ludi keo a vUng bien xa bd Dong Nam Bg vugt nguong cudng lifC khai^
thdc ben vieng toi da khodng 56.3%. tuang ung vdi khodng 2.823 fdu;yd^^^
cdn lgi cd cudng luc khai thdc thdp han cudng luc khai thdc bin viing toi da.
Tuang img vdi cudng lire khai thdc bin vung ldi da. sdn lugng khai thdc bin vung loi da d viing bien xa bd Ddng Nam Bg Id 1.146.140 tdn.
1 MO SAU
Hogt dpng khai thdc hdi sdn d vimg biin xa bd Ddng Nam Bp (DNB) bao gdm lau cua cac tinh Uong khu vyc vd tdu ciia cdc tinh ngoai khu vuc tham gia khai thdc. Theo kit qud diiu tra ndm 2012 - 2013, hdng ndm cd khodng 5.196 tdu ca cd cdng suit tii 20 CV trd lin cua cdc tinh mien Trung va Tdy Nam Bd tham gia khai thdc hai sdn d vimg biin xa bd Ddng Nam Bd, dieu nay dd Iam gia lang dp I\rc khai thdc trin vimg biin (Biii Vdn Tiing, 2013). Kit qud diiu Ua ciing cho thdy, du thira ndng Iuc khai thdc d vimg bien xa bd Dong Nam Bp hien nay dang diin ra rai nghiim trpng, dac biet
la ddi vdi nghe ludi keo. Vi vay, viec nghiin ciiu xdc dinh san luong va cudng luc khai thdc bin vihig toi da d vung biin xa bd Ddng Nam Bp Idm CO sd khoa hpc cho viec xay dung quy hogch va dira ra cdc giai phdp quan Iy hogt ddng khai thdc hai san Uin viing biin theo hudng bin viir^ Id cdn tbiet. Md hinh san lupng thang du cua Schaefer (1954) duac su dun^ di xac dinh sdn lupng vi cudng luc khai thac bin vOng tdi da cho vdng biin.
s i lieu sii dung cho md hinh la sd liiu phy thu$c nghe ca dupe thu tbl^j thdng qua diiu tra thu mSu nghi ca tiiuong phdm va tiiu mlu cudng l\rc kha tilde tir nam 2008 - 2012 d cdc tmh ven biin Dong
Tgp chi Khoa hgc Trudng Dgi hpc Cdn Tha Phdn B: Ndng nghiip. Thuy sdn vd Cong nghe Sinh hgc: 34 (2014): 55-63 Nam BS, dupe trich tu nguon sd liiu cua di tai cdp
Bp "N^ien deu bien dgng vdpiiAibdcieang luc khcd thdc hdi sem a vimg bien xabd Bdng Nam Bd".
2 PHU'ONG PHAP NGHIEN CUtl 2.1 T^i lieu
Tai lieu sii dimg trong bao cao dupe trich tii ngudn sd lieu dieu tra nghi cd thuong phdm d viing biin xa bd Ddng Nam Bd tii ndm 2008 - 2012.
Bang 1 the bien sd lupng mdu diiu ua duoc six dimg trong udc tinh sdn luong khai thac cua cac ddi tau.
Bang 1: So luong mau diiu tra nghi ca thutmg phim giai dogn 2008 - 2012 2008 2009 2010 LmHkio
Ludiri Ludi vay Nghe cau Nghi khac Tdng
788 85 216 38 46
661 112 212 116 ill
4.016 58 659 295 1.303
4.904 641 822 622 954
2.685 392 592 660 658 1.173
2.2 Phuong phap nghiin cuu 2.2.1 Ddi tugng vdphgm vi nghien cuu - E)di tupng nghien cihi: Tdu thuyin khai thac hdi san d viing bien xa ba Ddng Nam Bp cd tdng cdng suat mdy chinh > 50CV.
- Pham vi nghiin ciiu: Viing biin xa bd Ddng Nam Bd (vung Idng vd viing khoi).
2.2.2 Phucmgphdp nghien cuu
Sd dung md hinh san lupng thang du ciia Schaefer (1954) dh xac djnh san lupng vd cudng lire khai thac ben viing tdi da d vung biin xa bd Ddng Nam Bp. Cac nhdm nghi dupe lua chpn de danh gia gom: ludi keo, ludi re, ludi vay, cdu va nhdm nghe khdc (cdc nghi cdn Iai). Phuang phdp nay da dupe Sparre & Siebren (1992) dua ra nhdm udc tinh sdn lupng va cudng I\rc khai thac tdi da cho tiing nghi riing biet dua trin chudi sd lieu ve sdn lugmg va cucmg l^Idhal thdc cda Ioai nghi do theo thdi glaiKSah'.lupn^vatcuoi^ lire khai thdc dupe md td theo phuong trinh:
n=a*(f^ + b*(f^' (1) Vdi Yi la san lupng khai thac d ndm thii i va fi
Id cuong Iuc kh^ thdc d nam i. San lupng khai thdc bin viing tii da (MSY) vd cuong lire khm thdc bin viing tdi da tuong iing ifmr) dupe udc tinh theo cdng thiic.
fMsr = -(ct/2*b} (2) MSY=-(a'/4*b) (3) a Diiu tra sd liiu
• So lupng tau thuyin: So lieu tdu thuyin khai tilde bdi san d viing biin xa bd Ddng Nam Bp dupe thu thap tgi cdc Chi cue Khai thac va Bao ve ngudn Ipi Thuy san (Chi cyc KT&BVNLTS) d cac tinh
ven biin tir Quang Ngai din Kiin Giang, giai dogn 2008 - 2012.
Ndng suat khai thac: Ndng suat khai thdc cua cac dpi tau duoc xdc dinh dua vao ngudn sd lieu diiu tra nghi ca thuong pham cua de tdi
"Nghien cuu ca sd khoa hgc phuc vu cho viic dieu chinh ca cdu dgi tdu vd nghi nghiip khai thdc hdi sdn" tCr nam 2008 - 2010, sd liiu diiu tra cua cac Chi cyc KT&BVNLTS (Binh Thugn, Tiin Giang, Bin Tre va Sdc Trang) giai dogn 2008 - 2012 va sd lieu dieu tra cua d& tdi "Nghien cuu biin ddng vd phdn bd cudng luc khai thdc hdi sdn d vimg bien xa bdDdng Nam Bd", n3m 2012-2013.
Sd ngay khai thdc tiim ndng: Sd ngay khai thdc tiem ndng la dang sd lieu ljch sur, dupe thu thdp thdng qua phuang pbap tham vdn •^ kiin cda chuyin gia trong ITnh vuc khai thac hai san d cac Chi cue KT&BVNLTS.
He sd hogt ddng tau (BAC): Hi sd hoat ddng tau dupe xdc dinh thdng qua sd lieu dieu tra ciia cac Cbi cyc KT&BVNLTS (Bmh Thudn, Bin Tre, Tiin Giang va Sdc Trdng) tii ndra 2008 - 2012 va tbdng qua phuang phap tham van chuyin gia Uong nganh.
b. Xu ly vdphdn tich sd liiu
Viic xii Iy vd phdn tich sd lieu duoc thuc biin theo hudng dan cua FAO, cdc chi tieu dupe tinh loan nhu nang suit khai thdc uung binh (CPUE, kg/ngay/tau), he sd hoat dpng cua tau (BAC), tdng san lupng khai thac (C, tin) dupe xdc dinh theo phuong phap thdng ki md la thdng thudng.
Ndng sudt khai thdc: Ndng suat khai thac tnmg binh cua mdi dpi tau dupe udc tinh theo cdng thiic dudi day:
S.^SIAJM>- uaar .ti..jajM^
Tgp chi Khoa hgc Trudng Dgi hpc Cdn Tha
CPUE-- - S CPUE, ni=\ '
Phdn B: Nong nghiip, Thiy sdn vd Cdng nghi Sinh hgc: 34 (2014): 55-63 Robson (1966) duoc md ta trong tai lieu ciia P.
Sparre & S. C. Venema (1992). Quy chuin dpi tau (i) theo ddi tau chudn (c)
(4) Trong dd:
CPUE: la ndng suit khai tfiac h-ung binh cua dpi tau cdn tmh; n: la so mau tiiu thdp; CPUEi: la ndng sudt khai thac cua tdu thir i (mdu thur i)
Sdn lugng khai Ihdc: Cdng tiiiic udc tinh tdng sdn lupng khai thac cho timg dpi lau:
Ci=CPUEiyAxFxBAC (5) Trong do: CPUEj: Id ndng suit khai thac trung
binh cda dpi tau i (kg/ngdy/tdu); A: Sd ngdy hoat dOng khai thac tiim ndng ciia dpi tau i (ngay); F:
So tdu khai thdc hiin cd cua dpi tau i (tdu); BAC:
Hi sd hogt ddng cua ddi tdu i - Tdng san lupng khai thdc ciia nghi:
^5i^'- (6)
Trong dd:C: Tdng san lupng khai thdc cua nghi (tin); Ci: San lupng khai thac cua dpi tdu i (tin); n: Tong sd dpi tau tham gia khai thdc.
Sii dyng cdng thiic quy chuin cudng Iuc khai thdc ciJa cac dpi tau theo khd ndng khai thac cua ddi tdu chudn theo cdng thurc quy chudn cda
f=F,x=J. (7) CPUE^
Trong do: Fd : Tdng cudng Iuc khai thdc ciia dpi tau (i) da dupe quy chudn (tau); F, : Ting cudng lire khai thdc cua dpi tau (i); CPUE,: Ii nang suit khai thac thuc cua dpi tau (i); CPUE,: Id nang suit khai thdc cua dpi tdu chuan.
Dpi tau chuin duac lya chpn phdi ddp iing diiu kiin ciia md hinh ddng thdi he sd tucmg quan gifla tong cudng lyc khai thac vd nang suit khai thac ciia ddi tdu chudn phai la cao nhdt so vdi cdc d^i tdu cdn lai.
3 KET QUA VA THAO L U ^ 3.1 s i lupng tau tham gia khai thdc hai san d viing biln xa bd Dong Nam Bp
Hoat ddng khai thdc hai san d viing biin xa bet Ddng Nam Bd bao gdm dpi tau ciia cac tinh trong khu vyc Ding Nam Bd va dpi tau ciia cdc tJnh ngodi khu vyc (cac tinh ven biin miin Trung va Tay Nam Bd). Co cdu ddi tdu khai thdc hdi sdn d vimg biin xa bd DNB tir nam 2008 - 2012 dirpc trinh bay trong Bdng 2.
Bang 2: Ctf cdu dpi tdu khai thdc hai san a vung biin xa bd DNB giai doan 2008 - 2012 Nhom nghe
Luoi keo
Lir^re
Liroi vay
Nghe cau
Nghi khdc Nhom
TOnfi
i
>250 150-249 90 - 149
50-89
>250 150-249 90 - 149
50-89
>250 150 - 249
90 - 149 50-89
>250 150-249 90- 149 50-89
>250 150-249 90 - 149
50-89 2008 4.160 1.029 819 1.074 338 482 212 613 762 490 173 131 247 479 i l l 372 466 624 470 804 13.856
2009 4.811 818 712 966 346 557 214 717 751 477 180 122 261 492 110 357 508 646 508 847 14.401
NSm 2010 5.252 820 646 880 504 395 166 743 844 389 161 111 283 496 109 351 562 605 498 838 14.653
Dan vi linh: Chile 2011
5.408 884 593 805 386 608 212 847 757 479 167 101 330 520 114 320 548 646 484 733 14.944
2012 5.622 927 525 759 424 630 215 892 758 484 171 92 350 527 114 299 518 625 475 703 15.110
Tgp cbi Khoa hpc Tmang Dpi hpc Cdn Tha PhAn B: Nong nghiep. Thiiy san va Cong nghi Sinh hpc: 34 (2014): 55-63 3-2 Ning suit khai thac ciia cac d^i tau
Nang suit khai thac trung binh ciia cac dgi
tau khai thac hai san d vung bien xa ba Dong Nam Bo trong giai doan tu nam 2008 - 2012 dtrgc trinh bay trong Bang 3.
Bang 3: Nang sudt khai tbac cua cac doi tau or viiDg biSn sa b& BNB giai doan 2008 - 2012 Dan vi tinh: tan/lati/nam Nh6m nghe Nhom cong sudt (CV) -
2008 2009 2010 2011 2012
>250 150-249 90 - 149
50-89 158,0
44,9 37,5 29,3
166,2 57,5 44,4 14,1
135,5 79,9 67,1 31,4
84.2 75,5 82.6 84,5 54.3 54,4 22.7 23,6
>250 150-249 90 - 149
50-89 85,5 68,8 50,6 42,4
61,3 50,0 75,5 65,3
86,9 69,5 119,6 18.8
42,0 87,6 38,3 30,3
34,7 30,1 30,8 LmSivay
>250 150-249 90 - 149
50-89 168,8
88,1 59,4 52,7
156,9 106,3 161,6 98,4
63,9 100,9 61,4 99,4
92,4 98,2 128,1 122,9 120,4 123,3 93,0 109,8 Nghe can
>250 150-249 90-149 50-89
9,0 11,1 13,2 9,3
11,4 12,8 13,9 11,3
6,6 6,9 10,3 6,5
28,3 29,2 16,1 19,8 7,5 10,8 7,2 10,7 Nghe khac
>250 150-249 90 - 149
50-89 37,5 51,5 51,5 20,1
18,0 11,8 23,4 6,3
85,0 61,8 65,4 36,3
71,3 51,3 44,4 18,8
53,5 53,0 44,2 15,3 3.3 Chuan hda cudng lure khai thac
Nang Iuc khai thdc cda cac dpi tau trong cimg mdt nghi cd su khdc nhau, vi v^y can phdi chudn hda cuong Iuc khai thac di ddng nhll trudc khi udc tinh san lupng va cudng lyc khai thdc bin vihig toi da. Dpi tau chuan duac lua chpn phdi thda mdn diiu kien cua md hinh, ddng thdi he sd tucmg quan giiia tdng cudng Iuc khai thdc va nang sudt khai thac Id cao nhit so vdi cdc ddi lau cdn lgi.
Dpi tau chuin ciia cac nghi dupe ti-inh bay Uong Bdng 4.
Chuan hda cudng luc khzil thdc cua cdc nghi Bang 5: Cudng l^c khai thac ciia cac nghe theo dpi t
dupe thyc hiin iheo cdng thiic chuan hda cuong Iuc khai thac ciia Robson (1966) vdi cdc dpi tau chudn da dupe lira chpn trong Bang 4. Cudng Iuc khai thdc ciia cdc nghe theo dpi tau chuan dupe trinh bay trong Bang 5.
Bang 4: Danh sach cac dpi tdu chuan theo nghi TT Nhom nghi
1 Ludikecs 2 Ludi ri 3 Ludi vay 4 Nghi cau 5 Nghe khac
F> 250 CV
> 250 CV 50 - 89 CV 90-149CV 150 - 249 CV
Nhdm nghi Ludi keo
Ludi r i
^ I
>250 150-249 90-149 50-89
>250 150-249 90 - 149
50-89 2008 4.160 292 194 199 338 388 125 304
2009 4.811 283 190 82 346 454 264 765
Nam 2010 5.252 483 320 204 504 316 228 161
Danv 2011 5.408 867 382 217 386 1.267 193 611
7 linh. Chiec 2012 5.622 1.037 378 237 424 449 133 564
Teip chi Khoa hpc Tmdng Dgi hpc Cdn Tha Phin B: Ndng nghiip, Thuy sdn vd Cong nghs Sinh hpc: 34 (2014): 55-63
l.tt&\ vay
Nghe cau
Ngh£ khac Nhom
T6ng
>250 150 - 249 90 -149 50-89
>250 150-249 90-149 50-89
>250 150 - 249 90-149 50-89
2008 2.442 820 195 131 168 402 111 263 340 624 470 314 12.282
2009 1.920 1.257 188 122 214 451 110 290 773 646 1.006 449 14.619
Nam 2010
903 385 163 111 182 334 109 223 772 605 527 492 12.275
2011 752 660 216 101 1.242 1.115 114 307 762 646 418 268 15.934
2012 678 542 192 92 951 968 114 297 523 625 396 202 14.423 3.4 San lumig va cudng lyc khai thac ben
vtrng toi da dviing biin xa bfrDong Nam Bo Hoat ddng khai thdc hai san d viing bien xa bd Dong Nam Bd diin ra quanh nam ddi vdi cac nghi chinh, ddnh bat nhieu ddi tupng khac nhau, vi vay trong qua trinh xii ly sd liiu di udc tinh cudng lire va san lupng khai thac ben vilng tdi da, md hinh Schaefer (1954) duac dp dung cho tdng thi nguon Ipi Uin vung biin. Md hinh Schaefer (1954) md ta
tuang quan giiia cudng lire (sd lupng tau tham gia khai thac) vd san luong khai thac theo phucmg trinh bac 2, dinli cda parabol la san luang khai thac bin viing tdi da va dudng ke vudng gdc vdi tryc hoanh cdt dinh cua parapol id cudng Iuc khai thdc bin vung toi da. Md hinh Schaefer (1954) udc tinh sdn lugrng va cudng luc khai thdc bin viing tdi da cua nghi ludi keo d vimg bien xa bd Ddng Nam BO duac thi hiin trin Hinh 1.
^ 1.000.000 c
" 6 800.000 u 1 600.000 I 400.000 f 200.000
^ . ^ ^
^ ^ ^ ' ^ y =
y^ a=
X
•
•m. •
=-0,0345x2+ 320,99x
= 320,99; b = 0,0345
# •
il.OOO^r? 2.000 3.000 4.000 5.0(X) 6.000 Cudng Iuc khai thac (tan) San lupng khai thac thyc -Poly. (Sdn luang du doan)
Hinh 1: Md hinh Schaefer ud-c tinh san \uifag vd cudng lyc khai thac bin vihig tdi da ciia nghe ludi keo d viing biin xa bd ©dng Nam Bp
Cudng Iuc khai thdc bin viing tdi da ciia nghi ludi keo d viing biin xa bd Ddng Nam Bd theo dpi tdu chudn (dpi tdu > 250CV) la:
MSY = -(aV4*b) = -((320,99)^/(4*(-0,0345))) = 746.627 tin
FMSY = -(a/2*b) = -(320,99/(2*(-0,0345))) = 4.652 chiic tau
Sdn lupng khai thdc bin vung tdi da tuong ling la:
Md hinh Schaefer (1954) udc tinh sdn lupng vd cudng Iuc khai tiiac bin virr^ tdi da cda nghi ludi re d vung biin xa bd Ddng Nam B6 dupe thi hiin ti-in Hinh 2.
Tap chi Khoa hpc Trudng Dpi hpc Can Tha Phan B: Nong ngiaip, Thiiy san va Cong ng}.4 Sinh hpc: 34(2014): 55-63 120.000
•g. 100.000 2 80.000 1 60.000
• ; 40.000 t 20.000
I 0
'
0^^^-^^——-^
/ x'
•
y=-0,0302x2-H08,27x a = 108,27: b--0,0302
""\.
X
/
1.000 L500 2.000 2.500 Cutrng lyc khai thac (tau)
• San lupng khai thac thuc -Poly. (San Imjmg du doan)
Hinh 2: Md hinh Schaefer udc tinh san lupng vd cudng lyc khai thdc bin vung tdi da cua nghi lum re tf vung bien xa bfr Dong Nam B$
Cudng Iuc khai thdc ben vihig toi da ciia nghi ludi ri d viing biin xa bd Ddng Nam Bp theo dpi tau chuin (ddi tdu > 250CV) la:
FMSY = -(a/2*b) = -(108,27/(2*(-0,0302))) = 1.793 chiic tdu
San lupng khai thac bin viing tdi da tuong iing
MSY = -(aV4*b) = -((108,27)-/(4*(-0,0302))) = 97.040 tin
Md hinh Schaefer (1954) udc tinh san lupng va cudng luc khai thac ben viing tdi da cua nghi ludi vdy d vung biin xa bd Ddng Nam Bp dupe thi hiin trin Hinh 3.
^ 160.0 ' 140.0 ' L20.0 100.0 8O.0 6O.0
\ 4O.0 20.0
000
n •
^^•^— © ^ ^
^
%* \ .__ ^
/ /
y=-0,0154x'-l-92,298x "
a = 92.298; b = -0.0154
• - . . . . : ;
/
2.000 3.000 4.000 Ctrdng lyc kJiai thac (tan)
• San lupng khai thac thuc -Poly. (San lupng du doan)
Hioh 3: Md hinh Schaefer udc tinh san lirong va cuong luc khai thac bin vung toi da cua nghe ludi vay dviing bien xa bcrDong Nam Bp
Cudng lyc khai thdc bin viing toi da cua nghe ludi vdy d vdng biin xa bd Ddng Nam Bd theo dpi tau chuin (dpi tau 50 - 89CV) la:
FMSV = -(a/2*b) = -(92,298/(2*(-0,0154))) = 2.997 chiic tau
Sdn lupng khai thac ben viing tdi da tuang iing la:
MSY = -(a-/4*b) = -((92,298)^/(4*(-0,0I54))) = 138.294 tdn
Tap chi Khoa hpc Trudng Dgi hpc Cdn Tha Phin B: Ndng nghiip, Thiiy sdn vd Cdng nghi Sinh hpc: 34 (2014): 55-63 Md hinh Schaefer (1954) udc tinh san lupng va
cudng Iuc khai thdc bin viing ldi da cua nghi cau d
viing biin xa bd Ddng Nam Bd dupe the hiin trin Hinh 4.
•<«
u
"3
QC
-K
X
• ^ — ^
^ ^ ' • ~ ^
y=-0,0018x2+12,5 77x a = 12,577; b = -0,0018
1
O - k -
. : : : . i2.000 3.000 4.000 Cuomg lire kbai thac (tau)
• San lugng khai thac thuc -Poly. (San Itjgng dn dodn)
Hinh 4; Mo hinh Schaefer ii6c tinh san lif^g va cirtmg luc khai thac ben vilng toi da ciia nghe cau or vung bien xa btr Ddng Nam Bo
Cuong l\rc khai thac ben viing toi da cua nghe ciu a vung biln xa lid Ddng Nam Bp theo dpi tau chuin (dpi tau 90 - 149CV) la:
FMSY = -(a/2»b) = -(12,577/(2»(-0,0018))) = 3.494 chide tau
San lupng khai thac bin v&ng toi da tuong ijmg
MSY = -(a2/4*b) = -((12,577)^/(4*(-0,0018))) = 21.970 tin
Mo hmh Schaefer (1954) uoc tinh san lupng va cuong lire khai thac bdn vihig toi da cua nhdm nghd khac a viing bien xa bo Dong Nam Bd dupe the hien trdn Hinh 5.
„ 140.000
•g 120.000 u 100.000 S 80.000 I 60.000 g 40.000 M 20.000 5 0
•
«
---^— •
- ^ y = -0,023x2 + 86,559x "
a = 86,559; b = -0,023
• / -
; |
1.000 L500 2.000 2.500 Cudng lyc khai thac (tau)
• San lupi^ khai thac thuc -Poly. (Sdn lupng du dodn)
Hinh 5: Mo hinh Schaefer udc tinh san lupng ya cudng l^rc khai thdc bin vung t6i da ciia nhdm nghi khac et viing biin xa bit Ddng Nam Bg
Cudng luc khai tiiac bin vihig tdi da ciia nhdm FMSY = -(a/2*b) = -(86,559/(2*(-0,023))) = 1.882 nghe khdc d vimg biin xa bd Ddng Nam Bp theo ^^hiic tau
dpi tdu chudn (dpi tdu 150 - 249CV) Id:
Tap chi Khoa hpc Tmang Dai hpc Cdn Tha Phdn B: Ndng nghiip. Thuy sdn va Cdng nghe Sinh hpc: 34 (2014): 55-63 San lupng khai thac bdn vimg tdi da tuong
ung la:
MSY = -(aV4«b) 81.440 tin
-((86,559)2/(4*(-0,023)))
bin viing tdi da d viing bien xa bd DNB theo cac dpi tau chuin da dupe xac dinh, sir dung cdng thirc chuin hda cuong luc khai thac cua Robson (1966) n'nh ngupc lai de xac dinh cuong luc va san lupng khai thac ben viing tdi da cda cac dpi tau thuc dupe trinh bay trong Bang 6.
Trdn co so sdn luong va cuong luc khai thac
Bang 6: San l u ^ g vii cudng luc khai thac bin viing tdi da or vnng bien xa bdr Ddng Nam B$ theo cac dpi tau thurc
Nhdm nghi Nhdm cdng suat (CV) Cirdng luc khai thic bin San iwfn% khai thac ben vilng tdi da (tau) vifng tSi da (tan)
>250 150-249 90-149 50-89
3.596 593 336 485
588.841 108.625 39.564 24.827
Tdng 5.010 761.857
:250 150 - 249 90-149
50-89
484 720 246 1.019
34.778 36.868 10.923 46.292
T°ng 2.469 128.861
Lirdi vSy
>250 150-249 90 - 149
50-89
1.510 964 341 183
61.654 49.269 17.461 8.364
Tdng 2.998 136.748
Nghi Can
i250 150 - 249 90-149 50-89 Tong
525 790 171 448 1.934
11.896 11.500 851 2.147 26.394
Nghe khac
>250 150-249 90 - 149
50-89
558 674 511 758
27.635 33.037 20.911 10.697
Tone 2.501 92.280
Tdng chung 14.912
So vdi cuong lire khai thac bdn vting tdi da Ihi cuong lire khai thac hien tgi a vung bien xa bo Ddng Nam Bo (nam 2012) vupt ngudng bin vimg khoang 1,3%, Wong dng vdi klioang 198 tau. Phan tich theo tCmg nhdm nghd cho thiy nhdm nghi ludi keo cd cuong luc khai thac vugt nguong cuong lire khai thac bin vihig tdi da khoang 56,3% tuong ung vdi khoang 2.823 tiu, trong do dpi tiu cdng suat >
250CV 11 2.026 tau, dpi tiu 150 - 249CV (334 tau). dpi tau 90 - 149CV (274 tau) va dpi tau 50 - 89CV (189 tau); cdc nhdm nghe cdn lai cd cudng l\rc khai thic chua dat ddn ngudng cuong lgc khai thac bin vihig tdi da. Cd the nhan thay rang ap lire
khai thac d vung bidn xa bd Ddng Nam Bd hien nay chii ylu tap trung d ddi tiu nghi ludi keo, vi vay viec nghien cihi cic giai phap de dieu chinh giam cudng lire khai thIc cua dpi tau nghd ludi keo dl dim bio phat triln bin vQng nghi khai thac hii sin d vimg biln xa bd Ddng Nam Bp II cln thiet.
Tuong dng vdi cudng luc khai thac bin vimg tdi da, sin luong khai thac ben v&ng tdi da d viing biln xa bd Ddng Nam Bd 11 1.146.140 tan. Nhu vay, sin luong khai thac hien nay d viing bien xa bd Ddng Nam Bd thip hon so vdi sin lupng khai thac bin vihig tdi da khoing 17,4%, tuong ung vdi khoang 199.985 tin.
Tap chi Khoa hpc Trudng Dgi hpc Cdn Tha Phdn B:
4 KET LUAN VA BE XUAT 4.1 Kit luan
- Cudng Iuc khai tiiac bin viing ldi da d vung biin xa bd Ddng Nam Bd Id 14.912 tan, trong dd nghe ludi keo la 5.010 tau, nghi ludi ri 2.469 tau, n ^ i ludi vdy 2.998 tdu, nghe cdu 1.934 tdu va nhdm nghi khdc Id 2.501 tau
Cuong Iuc khai tiiac cua nghi ludi keo hiin nay d viing bien xa bd Ddng Nam Bd vupt nguong cudng luc khai tiidc bin viing tdi da khodng 56,3%, tuong ling vdi khoang 2.823 tau; cdc nghi cdn lai cd cudng Iuc khai thac thap bon cudng luc khai ihac bin viing tdi da, Uong do cudng Iuc khai thac cua nghe ludi re thap han cudng lyc khai thac ben vihig khoang 12,5%, nghi ludi vdy 49,8%, nghi cdu 33,3% vd nhdm nghi khdc la 7,2%.
Sdn lupng khai thac bin viing ldi da d vung biin xa bd Ddng Nara Bp la 1.146.140 tan va sdn Jupng khai thac hien tai tren vung biin thap hon so vdi san lupng khai thac bin viing tdi da khoang 17,4%.
4.2 De xuat
Sii dyng nguong cudng luc khai thac ben viing tdi da ciia cac nghe khai thdc hdi sdn d vimg biin xa bd Ddng Nam Bd lam diim tham chiiu phyc vu cho viec diiu chinh co can dpi tau va nghi nghiip khai thdc hai sdn Uen vung bien de phat Uiin ben viing.
nep, Thiiy sdn vd Cong nghi Sinh hgc: 34 (2014): 55-63 Can thiit phai cdt giam cudng Iuc khai thac cua nghi ludi keo hiin nay d viing bien xa bd Ddng Nam Bd. Ben canh dd, xay dung co che chinh sach phu hpp de hd trg ngu dan ldm nghi ludi keo cai hodn tau, mua sam ngu cu vd tr^g thiit bi chuyin sang cac n ^ e khai thac khdc; hoac hd trp chuyin sang cdc nghi khdc.
TAI LIEU THAM KHAO
1. Bui Van Tung (2013). Nghiin cdu biin ddng va phdn bd cudng Iuc khai thac hai san d viing bien xa bd Ddng Nam Bp. Bao cao tdng kit khoa hpc ky thu^t de ldi, Vien Nghiin ciiu Hai san.
2. Nguyen Vdn Khang (2011). Nghiin cuu CO sd khoa hpc phuc vu cho viic diiu chinh co cau ddi lau va nghe nghiep khai thdc hdi san. Bao cao ldng kit khoa hpc ky thudt di tai, Vien Nghiin cuu Hai san.
3. P. Span:e& S.C. Venema (1992).
InUoduction to tropical fish stock assessment, part I — manual, in FAO fisheries technical paper 306/1 Rev 1, Rome.
4. Constantine Slamatopoulos (2002). Sample- Based Fishery Surveys - A Technical Handbook. Food and Agriculture Organization of the United Nations, Rome.
