RESULTS OF THE EXPLORATORY CRUISES OF THE ALEJANDRO DE HUMBOLDT IN THE GULF OF CALIFORNIA"

Transcription

1 RESULTS OF THE EXPLORATORY CRUISES OF THE ALEJANDRO DE HUMBOLDT IN THE GULF OF CALIFORNIA" ABSTRACT During th yar April 1971March 1972, R/V ALEJANDRO DE HUMBOLDT opratd by th Mxico/FAO Rsarch and Dvlopmnt Projct of th Unitd Nations Dvlopmnt Program, carrid out prliminary cruiss in th Gulf of California to valuat th potntial fishry rsourcs. A stock of hak, Mrluccius sp., found principally north of Isla Tiburon and along th ast coast of th Gulf as far south as Guaymas was survyd in thr cruiss btwn Jun 1971 and March Th abundanc was gratst in Fbruary and March, with a total stimatd biomass in th northrn Gulf at that tim of 28 mtric tons. Langostino or squat lobstr, Pluroncods planips, was found to b widly distributd in th Gulf south of Isla Tiburon, with th major part of th population north of Guaymas. South of th latitud of Bahia d Yavaros th trawls brought up sampls of sdimnts and othr matrial with vidnc of activ anarobic dcay. Th dpth at which this occurrd dcrasd southward to th mouth of th Gulf, and th gratst dpth yild CA C. P. MATHEWS ', J. 1. GRANADOS and J. ARVIZU FAO/UNDP and lnstituto Nacional d Psca ORRIENTES O I ' I I I ' I ' I ' 11 15' Figur 1. Map of Gulf of California. ing apprciabl amounts of groundfish dcrasd in th sam way. Masurmnts of dissolvd oxygn indicatd that ths conditions prvaild whr th sa floor was within th oxygn minimum layr. This is not ncssarily th viw of FAO. b Prsnt addrss : Dpartmnt of Fishris Ocanography Unidad d Cincias Marinas. UABC Apartado Postal 453 Ensnada, Baja California ITh currntly accptd nam for P. planips appars to b langostilla. Apartada M1778, Mxico (1). D.F., Mxico In spit of this limitation of spac availabl to groundfish, a potntial annual yild to a fishry was stimatd to li btwn about 7 and 19 mtric tons. Th total annual bycatch in th shrimp fishry was found by calculation to li within this rang. INTRODUCTION During th yar April 1971March 1972 th R/V ALEJANDRO DE HUMBOLDT, opratd by th Mxico/FAO Rsarch and Dvlopmnt Projct of th Unitd Nations Dvlopmnt Programm, carrid out xtnsiv xploratory and prospctiv cruiss in th Gulf of California. Th chronology and aras covrd ar shown in Tabl 1 and Figur 1. Th arly cruiss, April through Jun 1971, attaind thr main objctivs : xploratory fishing throughout th Gulf, shaking down th ship, and ducating th crw and scintists in conducting oprations. Aftr this priod th crw and scintists could handl th fishing gar as dp as 1 m, th limit imposd by th quipmnt availabl. Subsquntly bcaus of mchanical difficultis fishing was confind to dpths lss than 6 m. Prliminary study of th rsults ld to stting up svral long trm objctivs : concntrating ffort on th astrn shlf and slop which is mor favorabl for trawling than th narrow and rocky wstrn TABLE 1 Chronology of oprations by R/V ALEJANDRO DE HUMBOLDT undr th Mxico/FAO Rsarch and Dvlopmnt Projct of th Unitd Nations Dvlopmnt Program from April 1971Octobr 1972 Dat 1971 April, May Mazatl%n to Yavaros, coast of Sinaloa, and La Paz May, Jun Yavaros to R. Colorado, coast of Sonora and northp gulf.^^_.^.^_^.^_..^. 3, 9 July I. Angl d la Guarda to C. San Lucas, coast of B. California ~ 3 CAB SAN LIJCAS/ MAZATLAJ4' July MzatlLn to C. Corrints, coast of Nayarit ISLAS TRES MARIASA. August Northrn Gulf, north of I. Tihur6n...._. 4 PTA RAZA I. Tibur6n to Guaymas, coast of Sonora.. 4, 1 August Sptmbr Novmbr Nov, Dc Dcmbr 1972 Fb, March Octobr 1 All aras shown in figur 1. Ara of oprations Northrn Gulf, north of I. Tibur6n Transcts across shlf, Mazatlan to C. Corrints.. Transcts across shlf, Mazatlan to Yavaros Transcts across shlf, nar I. San Pdro Nolasco... Shown in igurs' Northrn Gulf, to I. San Pdro Nolasco. 5, 12 Pacific coast of Baja California._. shlf; invstigating th population of larg hak, Mrluccius sp., in th northrn Gulf; invstigating th stock of langostino, or squat lobstr, Pluroncods plaizips, in th ara btwn Isla Tiburon and Bahia d Yavaros; and obtaining additional data on th

2 12 CALIFORNIA COOPERATIVE OCIUNIC FISHERIES INVESTIGATIONS xtnt and ffcts on fish of oxygndficincy and anarobic conditions in th dpr watrs and floor of th Gulf. No othr ground fish stock smd SIX&? cintly larg or important to justify any spcial invstigation, but som fishing ffort was xpndd on th mixd groundfish stock in th cours of othr work. As a rsult a considrabl volum of data on ths stocks was obtaind. Mthods and Equipmnt Th ALEJANDRO DE HUMBOLDT is a 45 gross ton strn trawlr, providd with biological and hydrographic laboratoris. Th fishing quipmnt usd during this study was an ottr trawl, providd with ottr boards to kp th nt mouth opn. Figur 2 shows a schmatic rprsntation of th fishing quipmnt usd. Th msh siz of th wings was fairly small (<1. cm) whil that of th codnd varid : until Jun 1971 a matrial of 5.5 cm msh was usd, whil from July onwards a 4.5 cm msh codnd was substitutd. Th ratio of warp out to dpth was usually 3.:l to 3.5:l; this was incrasd to around 5.:l in Fbruary For dpths gratr than 5 m, lowr ratios wr usd. Th spd at which th nt was hauld along th bottom varid from 2. knots at dpths ovr 45 m to 4. knots in vry shallow watrs, but most hauls wr carrid out at from 3. to 3.5 knots. Figur 2. Schmatic drawing of th ottr trawl usd, not b scal. During th whol yar s obsrvations only thr ottr trawl nts wr availabl; by th nd of this priod ths nts had suffrd vry considrabl distortion, and th vrtical distanc sparating footlin from hadlin may hav bn as littl as 23 m, whn it should hav bn 34 m. Such distortion of th quipmnt is likly to rsult in lowr than normal catchs bing obtaind and, if no corrction is mad, calculatd abundancs would b likly to rr on th low sid, particularly in FbruaryMarch, Th dpth during ach trawl was monitord continuously by mans of an chosoundr, and whnvr possibl th ship s cours was adjustd so as to kp trawling at a constant dpth. If a considrabl chang in dpth was unavoidabl (>lo% of th initial dpth) th haul was usually ndd; for most hauls dpth did not vary by mor than 23%. Th ship s spd was rcordd at th bginning and th nd of ach trawl. Th swpt ara tchniqu was usd for convrsion of th catch in kilograms to abundanc in kilograms pr hctar (kg/ha), and th following assumptions wr mad: (i) that th ottr boards and danlinos wr ffctiv in startling fish and so mad all fish btwn th ottr boards accssibl to th nt; (ii) that th ottr boards wr 6 mtrs apart during trawling (this was basd on masurmnts of a simpl scal modl) ; (iii) that, bcaus of scapmnt around and through th nt, only 5% of th accssibl fin fish wr caught; (iv) that no adjustmnt owing to scapmnt was ncssary for Pluroncods planips. Th catch pr unit ara, C,, is calculatd from th masurd catch C as follows. C, = C/K kilograms pr hctar (kg/ha) whr K is th ara swpt. K = 6o 1853 Vt = 11 X Vt hctars 1 ~... whr 6 is th distanc btwn th ottr boards in mtrs 1853 is th numbr of mtrs in a nautical mil V is th avrag ship s spd during th haul in knots is th duration of th haul in hours 1 is th numbr of squar mtrs in a hctar Th abundanc of fin fish, that is, th total biomass living on unit ara, assuming 5% scapmnt, is stimatd as, A = 2c, Th abundanc of langostino is stimatd as A = Ca. Th hydrographic work was carrid out with a BisstBrman Salinity/Dpth/Tmpratur Rcordr (STD), modl 96, which was calibratd from tim to tim. Nansn bottls and rvrsibl thrmomtrs wr usd to obtain sampls for oxygn and salinity dtrmination and for chcking STD obsrvations. Th mthods usd wr thos standardizd by th U. S. Hydrographic Offic (U.S. Naval Ocanographic Offic, 197). RESULTS 1. HAKE (Mrluccius sp.) Hak wr first caught in quantity in Jun. Figur 3 shows th locations of hauls and th calculatd abundancs. Mor than half (6) of th 15 xploratory hauls wr mad on th shlf or dlta sdimnts whr th dpth to th safloor was lss than 18 m (1 fm), and 52 of ths hauls caught no hak or only ngligibl quantitis. Out of th 45 hauls at gratr dpths, th catchs in twlv hauls wr quiv

3 REPORTS VOLUME XVII, 1 JULY 1971 TO 3 JUNE alnt to abundancs btwn and 2 kg/ha and in fiv hauls to abundancs btwn 2 and 1 kg/ha. All but four of ths productiv hauls wr north of Isla Tibur6n and Isla Angl d la Guarda. Th rmaining four wr on th slop nar Isla San Pdro Nolasco and Guaymas. Figur 6 shows that whil hak wr takn at all dpths from 15 m (at night) or 16 m (daytim) to 54 m, th bulk of th fish wr caught btwn about 18 and 4 m. Figur 3. location of hauls and abundanc of hak in th northrn Gulf of Californio, Jun a 22 Y 21 m m. *?a %. 6..*. \ 8 *no m 99 5

4 14 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONS o m :. r" 5. 1 IO sa.oo,oo rang as in prvious months, and corrspondd to a considrably highr avrag abundanc. During othr cruiss, hak wr caught as far south as Bahia d Yavaros off th Sonora coast and Isla dl Carmn off th Baja California coast, but in abundancs nvr gratr than 4 kg/ha. Tabl 2 summarizs th hauls and corrsponding abundancs of hak in th northrn Gulf. On th sa floor at dpths blow 18 m, th man abundanc was considrably highr in FbruaryMarch 1972 than during th prcding summr. Mathws (in prparation) proposs a migration pattrn consistnt with this fact. Tabl 3, showing th catch rats (kg/h) for larg hak (mor than 45 cm in total lngth) during this xploratory fishing, suggsts that during FbruaryMarch it might support a commrcial fishry. TABLE 3 Catch of hak mor than 45 cm in total lngth Catch rat (kilograms pr hour) Maximum lngth (cntimtrs) Abundanc lvl (kilograms pr hctar) Jun 1971 Jun 1971 liminating 6 hauls at Augustlss than Sptmbr 181x Fbruary March 1972 Total I 15 I 45 I 6 I 63 Th total biomass of hak in th northrn Gulf during ach cruis priod can b stimatd by multiplying th man abundanc in ach dpth zon by th ara of sa floor in that zon. Tabl 4 shows th rsults of such a calculation. Sinc th man abundanc as shown abov is highst at dpths btwn about 18 and 37 m, most of th hak biomass in th northrn Gulf appars to occur btwn ths dpths. Howvr, rviwing th whol body of data whil writing this papr, and noting that in Fbruary March out of tn hauls mad at or abov 18 m, ight yildd abundancs of.22 kg/ha, it sms possibl FIGURE 8. Dpth of hauls and abundanc of hak in th northrn Gulf of California, FbruaryMarch 1972.

5 that furthr tsting of th productivity of th shallow portions of th shlf is warrantd. Estimats of mortality basd on approximatly 9 pairs of otoliths takn btwn Jun 1971 and March 1972 indicat that natural mortality (M) is about.29 Dpth (mtrs) _ _ TABLE 4 Estimatd biomass of hak north of Isla Tibur6n and Isla Angl d la Guarda I I I Man abundanc (kilograms pr hctar) Aug Jun Spt Fb Mar 1972 ~ REPORTS VOLUME XVII, 1 JULY 1971 TO 3 JUNE Ara (thousands of hctars) I Biomass (mtric tons) ,2 3, ,2 8 2,1 ~ ~ _. 8,9 4, 28,1 Figur 1. Location of hauls and abundanc of langostino btwn lsla Tibur6n and Guaymas, August for fmals and.47 for mals. Assuming that harvsting would occur mainly in th sason of maximum biomass (FbruaryMarch, Tabl 4) and that th maximum yild would b obtaind whn th fishing mortality is adjustd to qual th natural mortality (Gulland 197, p. 2) thn th maximum would b btwn :.29 x.5 x 28 = 46 mtric tons. and.47 x.5 x 28 = 658 mtric tons. Th man of about 5 tons is th bst availabl stimat pnding furthr study of th stock. 2. LANGOSTINO (Pluroncods planips) Langostino was widly distributd in th Gulf south of Isla Tiburbn, but has not bn found north of th island. Th highst concntrations wr found off th coast of Sonora btwn Isla San Pdro Mbrtir and Guaymas (Figurs 912). From Guaymas to Bahia d Topolobampo catchs wr smallr. From Bahia d Topolobampo to Mazatlbn, usually lss than 5 individuals wr obtaind in a catch and south of Mazatlhn, catchs wr vry low. Figurs 13 and 14 show th distribution in SprilMay and Novmbr rspctivly from Bahia d Yavaros to Mazatlbn. Abundanc of Lmgoitino (Kglhal mor lhon 1 Figur 9. Location of hauls and abundanc of langostino btwn lsla Tibur6n and Guaymas, Jun Figur 11. Location of hauls and abundanc of langostino nar Guaymas, Dcmbr Figur 12. Location of hauls and abundanc of langostino btwn lsla Tibur6n and Guaymas, FbruaryMarch Tabl 5 shows th calculatd abundancs corrssponding to catchs mad at diffrnt dpths in ach of th sasonal cruiss in th ara btwn Isla Tibur6n and Bahia d Yavaros. Th largst numbr of catchs yilding larg abundancs wr mad in Dcmbr and Jun. In Dcmbr and Jun, 1 catchs wr mad (out of a total of 14 productiv hauls) yilding abundancs gratr than 7 kg/ha. No catch was mad in any othr month yilding an abundanc gratr than 27 kg/ha. Only in Dcmbr did th catchs suggst larg populations at dpths gratr than 37 m. On catch (abundanc btwn 1 and 5 kg/ha) in Dcmbr was mad at mor than 7 m. In January 1972 a singl catch in shallow watr (75 m) corrspondd to an abundanc of mor than 4 kg/ha. Furthr work is ncssary to dfin th dpth distribution of langostino. In th ara south of Bahia d Yavaros only four catchs wr mad

6 16 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONS corrsponding to abundancs gratr than 1 kg/ha. All wr at dpths lss than 37 m (Figurs 13 and 14). In Figurs 13 and 14, positions ar also plottd at which th trawl brought up solid matrial or objcts, TABLE 5 Numbrs of catchs and abundancs of langostino btwn lsla Tiburln and Bahia d Topolobampo at diffrnt dpths and sasons such as sdimnt, watrloggd and dcaying wood and dcaying bons accompanid by radily vidnt hydrogn sulfid. Figurs 15, 16 and 17 show hydrographic data, including tmpratur, salinity, and dissolvd oxygn concntration in Dcmbr along a sction northwst of Isla San Pdro Nolasco (Figur Dpth (mtrs) Jun 1971 (36 hauls) Sptmbr 1971 (7 hauls) 18 18Q MEXICO Abundanc of &go lkg/hal L L YJ1 AbUndaMd of Othr Groundfish IKglhol 22 x 21 A 12 Dpth (mtrs) For locations s Figurs 9,1,11 and s Figur 14. Location of hauls and abundanc of mixd groundfish and langostino, Bahia d Yovaros to Mazatlbn, NovmbrDcmbr ). Btwn th surfac and th sa floor at 5 m th tmpratur dcrass a grat dal, and th rat of dcras is spcially rapid btwn about 5 and 1 mtrs, showing that vrtical mixing at this lvl is slow. Partly as a rsult, th dissolvd oxygn concntration blow 3 m is vry low, lss than.5 ml pr litr of sa watr. Th numbrs along th sa floor ar rlatd to th abundanc of langostino IO I,...,I.I.,.I 1s.1 ~.. ll..l Figur 13. Location of hauls and abundanc of mixd groundfish and langostino, Bahia d Yavoros to Mazatlbn, April and May Figur 15. Tmpratur (cntigrad) in a sction northwst of lsla San Pdro Nolasco (s Figur 11) Dcmbr 1971.

7 I REPORTS VOLUME XVII, 1 JULY 1971 TO 3 JUNE z,.. a. 'yo: 8 Figur 16. Salinity (parts pr thousand) in a sction northwst of lsla Son Pdro Nolasca (s Figur 11) Dcmbr Y ) o 1 : Y 2 p.o m * IW.. I I PO 3.m Figur 17. Dissolvd oxygn (millilitrs pr litr) in a sction northwst of lsla Son Pdro Nolasco (s Figur 11) Dcmbr Numbrs on th sa floor show abundanc of langostina, kg/h. drivd from thos catchs. Th abundancs in this st of catchs ar largst at intrmdiat dpths and oxygn concntrations. Th rang of salinitis is small and unlikly to b critical. Th tmpratur rang is larg and th tmpratur at both th last and th gratst dpths may b unfavorabl and may thrfor in part control th dpth distribution of langostino. It is also natural to rgard th vry low oxygn concntrations as limiting. Howvr, as Figurs 13 and 17, and Tabl 5 show, catchs of langostino wr mad at dpths gratr than 37 m in th southrn Gulf (s also Figurs 9, 11, and 12). Oxygn concntrations as low as.1 ml pr litr hav bn obsrvd in a considrabl body of watr btwn 4 and 8 m btwn th latituds of Bahia d Yavaros and Guaymas (Rodn 1964, Mathws and Granados, in prparation). This is discussd furthr blow. It sms possibl that langostino tolrats oxygn concntrations much lowr than do many othr organisms.

8 18 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONS TABLE 6 Estimatd biomass of groundfish othr than hak and Iangostino north of lsla Tibur6n. Jun 1971 TABLE 9 Estimatd biomass of groundfish othr than hak and langostino in th Gulf of California Dpth (mtrs) Man abundanc Ara (kilograms (thousands pr of hctar) hctars) ~~ 23 3, _._ Biomass (mtric tons) 74,5 1,8 2,3 87,1 Man abundanc Ara (kilograms (thousands Biomass Numbr pr of (mtric of hauls hctar) hctars) tons) 33.8 I 3,; 1 1, , ,31 Total 1 56 I 1 I 92,9 Ara Isla Tibur6n to Guaymas Guaymas to Bay of Yavaros Topolobampo shlf Topolobampo shlf to C. Comnts Bay of La Pas Man abundanc (kilograms Dpth pr (mtrs) hctar) Total biomass (mtric tons) in various dpths: 183 m m m 6 Total Ara thousands of hctars) , Biomass (mtric tons) 9,6 2,1 4 13, ,2 28,1 1,4 No data ar prsntly availabl for stimating any of th population paramtrs of th mixd ground &h stock; in th absnc of such data it is suggstd that th sustainabl yild is unlikly to b lss than.2 or mor than.5 of th biomass. Using ths Figur 2. Location of hauls and abundanc of groundfish, Mazatlhn to Cab Corrints, July Dpth (mtrs) Man abundanc Ara (kilograms (thousands Biomass Numbr pr of (mtric of hauls hctar) hctars) tons) *.t'&> YLYYYYLLYUYYLLYIY L u m A 1 Assuming that th abundanc at 78 m qualld that at m. Figur 21. Location of hauls and abundanc of groundfish, Bahh d La Paz, April 1971.

9 REPORTS VOLUME XVII, 1 JULY 1971 TO 3 JUNE lar YI' PP 22 x 21 n 12 mor tho" 2 Y hydrogn sulfid ME XlCO fishry in th Gulf of California. As a rsult of this study, Chhvz (prsonal communication) suggsts that th bst stimat of th ratio of th bycatch to th shrimp catch is 5:l by wight. In 1971, statistics providd by th Scrtaria d Industria y Comrcio show that shrimp landings in Baja California and Sonora totalld 83 mt and landings in Sinaloa and Nayarit totalld 153 mt. Using Chhvz's ratio, th corrsponding bycatchs ar shown in Tabl ' Figur 22. Location of hauls and abundanc of groundfish, Mazatl6n to Cabo Corrints, Novmbr figurs, it is possibl to stimat th yild from th Gulf of California groundfish. It is assumd that any fishry would b concntratd on ths stocks during th priod of highst abundanc. It is furthr assumd that an stimatd yild of lss than 1 mt would b of no commrcial intrst; this assumption holds if th groundfish ar principally intndd for rduction, but may rquir rvision if a substantial fraction of th fish caught could b dstind for human consumption. Tabl 1 shows that th total yild is likly to li btwn 73 and 186 mt. Of this narly 9% would b obtaind from th ara' north of Isla Tibur6n. TABLE 1 Estimatd potntial yild of th Gulf of California groundfish othr than hak and langostino (mtric tons pr yar) North of Isla Tibur6n Biomass abov 183 m. 314,1 Minimum stimatd yild 62. Maximum stimatd yild_ 157, Minimum stimat for th whol Gulf _. Maximum stimat for th whol Gulf Isla Tibur6o to Guaymas 9,61 1,9 4, , Guaymas to Yavaros 13,7: 2,7 6,9 _ 1 Sason of maximum biomass (Fbruary to March) from Tabl 8. 2 From Tabl 9. Topolobampo Shlf 6, ,1 Topolobampo to Cabo Corrints 28,1* 5,6 14, It is instructiv to compar th figurs givn in Tabl 1 with th commrcial production of groundfish in th Gulf of California. Attntion is drawn to th largst componnt, i.. to th bycatch. An xtnsiv study of th bycatch of th Gulf of California shrimp fishry (Anon) is availabl basd on 1117 trawls carrid out in th months of July and August. Of ths trawls 8% wr carrid out from 36 mtrs and th rst from 369 mtrs; only a vry fw wr carrid out blow 73 mtrs, which may b rgardd as th usual limit for th commrcial shrimp Calculatd bycatchs B. Calif. and Sonora 41,5 Sinaloa and Nayarit 76, Total (roundd) 117, Estimatd potntial yilds ~ _ minimum mazimum North of Yavaros 66,6 169, Topolobampo and south 6.W 17,1 Sampl dpth (mtrs) , 186, Th calculatd bycatch for th whol Gulf is wll within th rang of th stimatd yilds. Howvr th ratio of th bycatchs sparatly calculatd from th shrimp landings in th northrn and southrn Gulf stats dos not compar wll with th stimatd potntial yilds in th northrn and southrn Gulf (Tabl 11). This disparity suggsts that a considrabl fraction of th landings in southrn parts may hav bn takn in th northrn Gulf, or altrnativly altogthr outsid of th Gulf. DISCUSS ION As prviously notd, in th southrn sction of th Gulf, many hauls brought up from th sa floor dcaying organic mattr smlling of hydrogn sulfid. Hydrographic sampls from dp watr had low concntrations of dissolvd oxygn. Tabl 12 shows in a TABLE 12 Abundanc of groundfish, prsnc of hydrogn sulfid in sdimnts, and oxygn contnt of watr at diffrnt dpths (sampls takn along sction V in Figurs 23 and 24) Soundings (mtrs) Hydrogn sulfid in sdimnts + Abundanc )f groundfish (kilograms pr hctar) 1.5 Oxygn concntration I millilitrs pr litr _ ~ <.3 <.3 <.3 + prsnt. absnt. sction off Pta. Raza (s sction V in Figur 22) that at 4 mtrs th oxygn concntration was 2.6 ml/litr and at 14 mtrs and blow, it was not mor than.3 ml/litr (th lowst valu that could b

10 11 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONS rad with th availabl quipmnt). Figur 23 shows that th oxygn concntration dcrasd sharply from abov 4. mlflitr at 2 to 4 mtrs to lss than 1. ml/litr at 7 to 8 mtrs. Figur 24 shows on of th hydrographic faturs rlatd to this distribution, namly a tmpratur dcras of 1 C in th uppr 67 mtrs. Sinc th salinity changd only.4% in this layr, th tmpratur drop was ncssarily accompanid by a grat incras in dnsity with North of Isla Tibur6n... Jun 1971 North of Isla Tihur6n... AugSpt 1971 North of Isla Tibur6n... FbMar 1972 Isla Tihur6n to Guaymas.._. Jun 1971 Isla Tibur6n to Guaymas... Spt 1971 Isla Tibur6n to Guaymas.... FbMar 1972 Guaymas to Bahh d Yavaros... Bahfa d Yavaros... Topolobampo shlf... Altata to MasatlLn... Pta. Piaxtla to Pta. Rasa... MazatlLn to Cabo Corrints..... Bshh d La Pas... TABLE 13 Gratst dpths at which groundfish wr tokn in localitis from north to south in th Gulf of California Maximum dpth Locality 1 Dat (mtrs) May 1971 May 1971 May 1971 April 1971 Nov 1971 July 1971 April 1971 not lss than' 4 not lss than 55 not lss than 4 not lss than 4 not lss than 3 not lss than 4 not lss than 45 not lss than 2 not lss than 1 not lss than 2 not lss than 1 not lss than 82 not lss than 1,Go *? Figur 23. Dissolvd oxygn (millilitrs pr litr) in a sction off Pta. Roza (sction V in Figur 22). Th numbr and dot on th sa floor indicat th abundanc (kg/ha) of groundfish found at that dpth. Th othr labls indicat th prsnc of hydrogn sulfid in matrial from th sa floor. Figur 24. Tmpratur (cntigrad) in a sction off Pta. Raza (sction V in Figur 22). dpth, and hnc by vry slow vrtical mixing. Th othr important hydrographic fatur is th watr in th dpths of th southrn Gulf, which is part of a grat body of such cool and oxygnpoor watr in th astrn tropical Pacific (Rodn 1964, Wyrtki 1966). Tabl 12 and Figur 23 show at 57 m a modst catch of groundfish, with ngligibl catchs blow, whil at ach of th gratr dpths th trawl brough up mattr smlling of hydrogn sulfid. Absnc of fish, low oxygn concntrations in th watr, and anarobic dcay in th sdimnts (producing hydrogn sulfid) ar corrlatd throughout th Gulf. Tabl 13 shows th gratst dpths at which hauls for groundfish wr succssful in localitis survyd, from th ara north of Isla Tibur6n to th ara btwn Mazatlhn and Cab Corrints. Procding from north "Not lss than" mans that catchs wr mad down to this dpth, hut no dpr hauls wr attmptd. In all othr cass, hauls wr mad at gratr dpths but catchs wr ngligibl. 2 Catchs wr ngligibl btwn 2 and 7 mtrs. Modrat catchs wr mad at 7 and 8 mtrs, and a haul at 1 mtrs was unprcductlv. to south th trnd is upwards, that is fish ar takn only in shallowr and shallowr watr. This trnd also appars in Tabl 9 whr th abundancs of groundfish dcras to th south, spcially blow 183 mtrs, Whil during th Novmbr and Dcmbr cruiss thr was som troubl in masuring low oxygn concntrations aboard ship, th rsults wr consistnt with information on th distribution of dissolvd oxygn in th Gulf availabl from othr sourcs (Rodn 1964, Scripps Institution 1965). Tabl 14 summarizs a prtinnt aspct of this distribution as obsrvd during four months in It is clar that th uppr limit (dfind as <1. ml pr litr, Wyrtki, 1966) of th layr of oxygnpoor watr slops upward toward th mouth of th Gulf. During th cruiss of th ALEJANDRO DE HUMBOLDT it was obsrvd that in no cas whr th watr clos to th sa floor was found to hav an oxygn contnt significantly highr than.3 millilitr pr litr was hydrogn sulfid dtctd in a trawl in th sam locality." As shown by Rodn (1964) and th 1957 cruiss by Scripps ships (Scripps Institution 1965) in th southrn Gulf ovr a considrabl ara, a layr svral hundrd mtrs thick,.g., btwn th dpths of 4 and 8 m) contains lss than.1 millilitr pr litr of oxygn. Blow this, slightly highr concntrations ar found. Whil langostino can prhaps tolrat conditions within th layr, and thr wr obsrvd in th prsnt survys two small to modrat catchs of groundfish at 7 and 8 m (Tabl 13), for fishs valud commrcially at th prsnt tim, th dpr watrs of th southrn Gulf do not appar promising. a Sinc writing this papr on of us (CPM) has participatd in a cruis on th R/V ALEXANDER AGASSIZ during which 1 trawls wr carrid out with a small ottr trawl nt, th foot rop of which was 11 ft (3.35 m) long. Hsdrocasts wr takn at som localitis whr trawls wr carrid out. Th rsults obtaind confirmd th rorrlation htwn low 9 concntrations and vry low or zro fish catchs. Sdimnt sampls wr takn with a box cor by Mr. A. Soutar, and showd that H2S did not arjpar in th sdimnts abov dpths of c 335 cm, nor did it appar outsid of th zon whr th 2 minimum intrsctd th bottom.

11 REPORTS VOLUME XVII, 1 JULY 1971 TO 3 JUNE TABLE 14 last dpth at which dissolvd oxygn was lss than 1. ml/litr Scripps Institution of Ocanography cruiss 1957 Numbr April 574 Jun 576 August x2 x8 X5 _ X25 _ XlOoO X2613 X17 X X225Ob X38 _ _ Ths columns show th numbr of stations occupid on that lin in that month. Whn thr was mor than on station occupid in a lin, th two numbrs show th shallowst and dpst obsrvations. Thr was a tndncy for th surfac of th layr of low oxygn contnt to b shallowr on th ast sid of th Gulf, so that th numbr on th lft usually charactrizs th ara trawld. b Th X indicats that at all dpths down to th gratst dpth (or dpths) sampld, as shown, th oxygn contnt was gratr than 1.O millilitr pr litr. ACKNOWLEDGEMENTS W ar particularly gratful to Mr. R. C. Lockrman of th U.S. National Ocanographic Data Cntr of N.O.A.A., for his advic and assistanc; w ar also vry gratful to Mr. B. C. Bdford, Fishris Laboratory, Lowstoft, for much advic and invaluabl assistanc during work both at sa and in th laboratory. Biol. H. Chbvz has also bn vry hlpful to us. Of cours w ar rsponsibl for any rrors this work may contain. Of th many othrs who hlpd us carry out our work w wish to singl out Captain F. Hrnbndz Ascncio of th R/V ALEJANDRO DE HUMBOLDT, and Ingniro Adolfo Torrs May of th Suprintndncia d Buqus in Mazatlbn. Without thir invaluabl support most of what w did would not hav bn don. W also wish to acknowldg th assistanc of Dr. G. L. Kstvn, thn Projct Managr, and Dr. M. Ruivo, Fishris Division at FA in Rom, whos fforts mad it possibl to carry out this work. REFERENCES Anon Inform d dsarrollo d trabajo. Inst. Nut. Inv. Biol. Psq., (2). Programa d Fauna d Acompafiaminto d Camar6n. Gulland, J. A In J. A. Gulland (d.) Th fish rsourcs of th ocan. FA Fish. Tch. Pap., (97). Food and Agricultur Organization of th Unitd Nations, Rom. Rodn, Gunnar I Ocanographic aspcts of Gulf of California, p In T. H. van Andl and G. G. Shor, Jr. (ds.) Marin gology of th Gulf of California. Am. Ass. Ptrol. Gol., Mmoir, (3): 148. Scripps Institution of Ocanography of th Univrsity of California Ocanic obsrvations of th Pacific: Univ. Calif. Prss, Brkly. U.S. Naval Ocanographic Offic Instruction manual for obtaining ocanographic data. 3rd d Govt. Print. Off., Wash., D.C. v.p. Wyrtki, Klaus Ocanography of th astrn quatorial Pacific Ocan, p In Harold Barns (d.) Ocanoggraphy and marin biology : an annual rviw, 4. Gorg Alln & Unwin Ltd., London.