The NW of
more often
the shelf
sardine in
Spain is influenced by episodic upwelling which occurs
between March and October. The consequent enrichment of
waters is the origin of a very important fishery for
the area.
Eggs and larval survival is directly related to the oceanograph¡c
conditions between the date of birth and recruitment. Laryal
survival seems to be related essentially to weak upwelling
conditions since they favour the non-dispersion of eggs (larvae)
and allow growth of medium sized phytoplankters as suitable food.
On the other hand, strpng upwelling causes dispersion of eggs
(larvae) and favours growth of very large phytoplankton specles,
mainly diatoms, that are thought to be un-suitable food for
larvae. However, strong upwelling conditions are favorable for
sardine adults, since the large phytoplankters growing during
these upwelling events were found to be the main food supply, as
shown by the study of stomach contents

Cabanas-López, J.M. (José Manuel)

Porteiro-Lago, C. (Carmen)

Varela-Rodríguez, M. (Manuel)

English

Repositorio Institucional Digital del IEO

International Council forthe Exploration of the SeaCM 1989/H:18 Ref. C+LPelagic Fish CommitteeRef. Hydrog./ Biol. Ocean. ComoA POSSIBLE RELATION BETWEEN SARDINE FISHERIES ANDOCEANOGRAPHIC CONDITIONS IN NW SPANISH COASTAL WATERSJ.M. Cabanas (1), C. Porteiro (1), and M. Varela (2)Instituto Español de Oceanografia(1) Centro Costero de vigo. Apdo. 1552, 36280 vigo, Spain(2) Centro Costero de La Coruña. Apdo. 130, 15080 La Coruña, SpainABSTRACTThe NW ofmore oftenthe shelfsardine inSpain is influenced by episodic upwelling which occursbetween March and October. The consequent enrichment ofwaters is the origin of a very important fishery forthe area.Eggs and larval survival is directly related to the oceanograph¡cconditions between the date of birth and recruitment. Laryalsurvival seems to be related essentially to weak upwellingconditions since they favour the non-dispersion of eggs (larvae)and allow growth of medium sized phytoplankters as suitable food.On the other hand, strpng upwelling causes dispersion of eggs(larvae) and favours growth of very large phytoplankton specles,mainly diatoms, that are thought to be un-suitable food forlarvae. However, strong upwelling conditions are favorable forsardine adults, since the large phytoplankters growing duringthese upwelling events were found to be the main food supply, asshown by the study of stomach contents.RESUMELe NW de Espagne est influencée par afleurements épisodiques deteau que se montre le plus fréquemment dans la periode entre Marset Octobre. Cet enrichement deau cotiere est ~origine d~neimportant pecherie des sardines.La survivance des oeufs (larves) estroceanographie chez la date de nalssancedirectement reliée avecet le recrutement. Lasurvivance des larves parait etre reliée avec un afleurementfaible puisqu~l favorise la non dispersion des oeufs Clarves) etpermets la croissance du fitoplancton de dimension moyen queconstitue un nourrissement bon a manger.Au contraire, fort afleurisement cause dispersion des oeufs(larves) et favorise la croissance des especes fitoplanctoniquesgrandes, la majorité diatomées, que constituen une faiblenourrissement pour les larves. Cependant, des conditionsdafleurement fort son favorables pour les sardines adultespuisque, le fitoplancton grand qui grandi pendant ces épisodesd~fleurement, constitue le plus grande source de nourrisement,comme se trouve quand on analise le contenue des estomacs.INTROOUCTIONForecasting recruitment to mature or exploitable stocks has longbeen a central problem in fishery research. Stock-recruitmentmodels have dominated this field. These models are basedexclusively on biological interactions and integrate the entirelife history into a single prerecruit class. There is an unknownerror in the parent stock size, and they ignore potentiallyimportant abiotic influences on recruitment processes.In coastal systems, short-term and long-term variations in thedistribution, abundance and production of a variety of organismshave been related to the effects of abiotic factors, and to theimpact of large-scale meteorological influences on the oceanenvironment CLasker, 1978).In the last 10 years, the oceanography of the west coast of theIberian peninsula has been investigated CFraga, 1981; Blanton etal, 1984). In this area, between April and September, there is awind induced seasonal upwelling. This is the most northerly partof the north-east Atlantic upwelling system which extends betweenthe Gulf of Guinea and the northem Iberian Peninsula CWooster,1976).¡he relation b~twQQn upwelling and biological production ist 11 1987; oickson et al, 1988). There are twostrong, CBlanton e a , f rface coastal watercoastal waters, the transport o su .effects on of nutrients to the phOtlC layer,to the open sea, and the supply . .f h· h b ologlcal potential. In the pre-which produce areas .0 .. lg 1 ·n the coastal upwellingrecruit period, most lndlvld~als are 1areas, where the food supply lS guaranteed.l·S a maJ·or component of the diet of sardines inPhytoplankton 1 1 1988) Inupwelling areas CBlaxter and Hunter, 1982; Varela e a, 11:11· periods or in areas not affected by upwe lng,non upwe lng . ' t of stomach contents of adu1tzoop1ankton is the maln componensardines.In this area we do not have historical data serles ofphytoplankton to try to establish a relationship between thedistribution of phytoplankton and sardine recruitment. We onlyhave data from two cruises carried out on the Galician continentalshelf in 1984 (Varela et al, 1987a,b), and one cruise in 1985. Wealso have information during the sardine spawning season in April1987 (Sarp-area cruise). However, the available information allowsus to speculate about the type and size of phytoplankton thatmight serve as food for both larva and adult sardines, and theenvironmental conditions necessary for the growth of such kinds ofphytoplankton.FISHERY ANO BIOLOGY OF IBERIAN SAROINEThe Iberian sardine (Sardina pilchardus, Walb.) lS the target ofan important fishery on the Atlantic Coast of the IberianPeninsula, where most of the landing ports are located. The catchand its economical and social implications make it one of the mostimportant fisheries of this area. Most of the catch is taken insummer and autumn. The period of maximum landings coincides withthe main recruitment periodoAt present, only one stock is considered in the assessment of thissardine, distributed from France to Gibraltar. Since 1979 thisstock is evaluated by the W.G. on the assessment of pelagicstocks in divisions Vlllc and IXa of ICES.Recruitment estimates using Virtual Population Analysis, showvariability in the period 1976-1988. The 1983 year class was thestrongest (34 514 * 10A_6) and that of 1986 was the weakest(7 998 * 10A_6). Table l.Acoustic surveys carried out in Spanish waters during March(spawning season) (Pastor et al 1986 a; Anon., 1989), found amajor concentration of sardines ln Cantabrian waters. Theseresults are in agreement with the egg distribution found onichthyoplankton surveys carried out in the same area (Sola, 1985;Garcia, 1988). On the other hand, cruises in August, during theupwelling season, show major concentrations, of adult and juvenilesardines in Atlantic waters, where more suitable food is presentdue to upwelling (Pastor et al, 1985, 1986 b).The Iberian sardine has two maln spawning areas, the northernPortuguese coast (spawn Oec-Jan) (Cunha, 1988), and the CantabrianSea (spawn March-April) (Sola, 1985). The recruits are mainlydistributed on the west coast of the Iberian Peninsula. Year classI is concentrated in Portuguese waters and moves north as itgrows. Year class 5 and higher are located in the Cantabrian Sea(Porteiro et al, 1988; Anon., 1988).BIOTOPE CHARACTERISTICSIn the coastal waters of this area, we found three layers notalways well defined CFraga, 1982, 1985).-The surface layer, limited by the thermocline C20 m), withTemperature CT) and Salinity (S) conditions varying according withmeteorology.-A mixed water layer between the thermocline and 60 m in thewest CGalicia) or 250 m in the north CCantabrian Sea), withhomogeneous T, S, and nutrients. It is formed in winter by themixing of surface water with NACW, and in summer on the west coastit disappears due to upwelling.-NACW CNorth Atlantic Central Water),Cll.5-13QC, 35.5-35.7%.,5-10 pM NO;/l), between 60 Cor 250) and 450 m, composed of twowater bodies, one of which penetrates Biscay Bay from the NW andmoves to the SW as far as Cape Finisterre, and another comes whichfrom the south along the Portuguese coast to Cape Finisterre.Where they meet there is a poorly defined front. This water massupwells on the west coast between April and September, and reachesthe surface on the shelf and in the Rias.The mass transport trends found in the 0-100 m layer are afunction of the water mass characteristics and their dynamics, andare dominated by the winds CBakun and Nelson, 1975). By Ekman'stheory, the total integrated mass transport of pure drift currentslS glven as:where:.-.Ve the total mass transport resulting from an applied localwind stress.f the Coriolis parameter.k the unit vector directed vertically upward.T local wind stress.In the northern hemisphere this transport is directed 90Q to theright of the wind stress.According to this and knowing the wind stress, we can estimatetransport across the shelf. We calculated the transport in theEast-West direction at three points along the northern coast. Thewind stress was obtained from the pressure field show on dailymeteorological maps C3 maps/day). Fig. 1 gives the average monthlywind induced transport for the period studied.For the nearshore circulation, a simple numerical model of thewind driven component was developed by McClain et al (1986). Whitha wind stress of about 3 dy/cm2 from N and NW, they found acoastal jet to the west CCantabrian) and south CGalicia) near thecoast CO-10 Km), with progressive pycnocline elevation Cupwelling)and an offshore poleward flow. The order of magnitude of thesecurrents is 5-10 cm/s in the north and 3-7 cm/s in the west, witha transverse current due to upwelling < 2 cm/s Csupposing anupwel1ing of about 500 m3/Cs*Km), and a thermocline layer about 30m deep).PHYTOPLANKTON ANO LARVAL OISTRIBUTION.Nutrients enrichment of the photic layer during upwelling causesan important increase of production and phytoplankton biomass.However, the changes in the community are not only quantitativebut qualitative CVarela and Costas, 1987). In non upwellingperiods, phytoplankton biomass is very low. Small formsCnanoplankton, essentially microflagellates), are predominant. Onthe contrary, when upwelling occurs, there is a predominance oflarger forms Cnetplankton), dominated by colony-forming diatoms.In fig. 2 we show the importance of both phytoplankton fractions:nanoplankton Cless than 10 pm) and netplankton Cbigger than 10pm), in the two main types of stations we consider in Galiciancontinental shelf in relation to upwelling. Oceanic stations arethose not affected by upwelling events. Upwelling stations arethose affected by upwelled water. In fig. 3 the size classesdistribution of phytoplankton in the two types of stationspreviously described is presented.In the oceanic areas, the phytoplankton biomass is low, and mostof it lies in the smallest size classes considered: 3 pm of meanspherical diameter. This size is too small to serve as food forboth larval and adult sardines. In upwelling areas, the increaseof biomass coincides with a sift to larger size classes. In thiscase, an important percentage of phytoplankton biomass will beavailable as food for larva and adult sardines.For sardine feeding, both larval and adult, the total amount oforganic matter present in the water lS no critical, but thedistribution of that organic matter in the appropriate size rangeis very important. The size of the first food of the Iberiansardine is not known, but may be between 40 and 80 pm CP. Smith,pers. comm.). For adults, the minimum size is around 45 pmCAndreu, 1969), which coincides well with our own observations ofstomach contents. Roughly, we can consider that the classes 35-70pm would be available as food for larvae, and the classes largerthan 45 pm for sardine adults.Fig. 4 shows the distribution of less and bigger than 35 p'mphytoplankton fraction, in oceanic and upwelling stations. Only lnupwelling stations an important phytoplankton biomass would beavailable for larvae feeding.When we compare the distribution of larvae and the distribution ofchlorophyll Ccorresponding to phytoplankton, 40-80 pm size), thecorrelation is positive but too small CR=0.25) to drawconclusions. It may be that, besides phytoplankton, a significantamount of microzooplankton biomass exist, mainly planktonicciliates, as observed during phytoplankton counting. Thisabundance has not been evaluated, but might greatly contribute tolarval feeding.On the other hand, the 40-80 pm range size is probably effectiveonly for first feeding. Eventually, larvae probably feed on largerprey, such as copepod nauplii (Lasker, 1978), or even onmacrozooplankton. This would explain the positive and significantrelation (R=0.40) between macrozooplankton and larvae found onSARP-area crUlses. Then, the relations between the 40-80 pmfraction and young larvae must be studied, as well as relationsbetween the fractions larger than 80 pm and older larvae.RELATION BETWEEN UPWELLING AND SARDINE RECRUITMENTUsing the upwelling index (Iw) as an indicator of mass transportand food availability in surface waters, and relating this to theyear's recruitment (YC), we can try to analyze how oceanographicconditions affect recruitment.For the period 1976-1988,correlation analysis.we study the possible relation uSlngThe variables considered are:YC - annual year class strength (recruitment).Iw - Upwelling index, calculated for a point 150 Kmwest of Cape Finisterre.Initially we correlated YC with Iw for all months; ln the monthsFebruary (IwF), May (IwMy), and the average of April and May(IwAMy) and of April and September (IwAS) the correlations aresignificant. Table 1, fig.5; for the others months the correlationare poor, but the ,Iw for March and April (IwM, IwA) are consideredtoo because it is the spawning periodoFrom the monthly correlation coefficients between Iw and YC we maydeduce:In February and March, (R positive, Iw negative); a higher inabsolute value of Iw corresponds to a minor value of YC. This maybe due to the fact that west winds disperse the larvae from thewinter spawning (Dec~JanJ on the west coast.In May (R negative, Iw positive); north winds intensify thecirculation towards the west in the Cantabrian Sea, and maydisperse the larvae from the spring Cantabrian spawning area inthe corner of the Iberian Peninsula; only the larvae nearest thecoast drift south and survive.•.••..•..The correlation with IwAMy is negative; this may indicate thatdispersion predomites over the other upwelling induced phenomena(such as suitable food) that favour the success of spawning.DISCUSSIONThe distribution and behavior of the Iberian sardine seem torespond to the upwelling regime in the area. Thus the timing anddistribution of spawning are during non-upwelling conditionsCMarch-May in Cantabrian Sea, November-December on the northernPortuguese coast) to avoid wind induced turbulence, which isgreather during upwelling. These two spawning periods also seem tobe related to water temperature, which reaches 13.5-14QC earlierCDecember-January) on the Atlantic coast than in the CantabrianSea, where this temperature is reached in March-April.Transport conditions in the upper water layer of the shelf arevery important for recruitment because the spawning areas are indifferent places. Eggs spawned in Cantabria drift to Galicianwaters if the surface currents are favorable, and reach theupwelling area in May, where suitable food for larvae andprerecruits exists. This general circulation feature is verycritical near Cape Finisterre, where under certain conditionsCstrong north winds) intense upwelling is produced, which caninterrupted the nearshore ~irculation along the west coast anddisperse offshore all matter that reaches the cape CChesney andAlonso, 1988).The results of the relationship between recruitment and themonthly upwelling indices show that for the March spawning in theCantabrian Sea, the April-May period is critical for larvalsurvival. Moderate upwelling on the Atlantic coast in this periodproduces good recruitment. If upwelling is intense the larvae aredispersed and recruitment is weak.Thus upwelling seems to be related to recruitment of pelagic fish.If it is moderate at the beginning of the season CApril-May), itfavours transport from the spawning to the pre-recruit areas, doesnot disperse the larvae, and produces suitable phytoplankton thatserve as food for larvae. After this period CJune-Oct.) the larvaeare older and remain in the upwelling area with abundant food.REFERENCESANDREU B. 1969.- Las branquispinas en la caracterizacion de laspoblaciones de Sardina pilchardus. Inv. Pesq. 33(2), 1-25.ANONIMO 1988.- Report of the Planning Group for Acoustic Survey inICES sub-areas VIII and IX, 9-12 Feb. 1988. ICES Doc. C.M.1988/H:2BAKUN A., C. NELSON 1975.- Climatology of upwelling related pro-cesses of Baja California. CALCOFI Rep. vol. XIX, 107-127.BLANTON J.O., L.P. ATKINSON, F.F. CASTILLEJO, A. LAVIN 1984.-Coastal upwelling off the Rias Bajas, Galicia, NW Spain.I.- Hydrographys studies. J. Rapp. et Proc.-Verb. Reun.Cons. int. Exp. Mer 183, 79-90

A possible relation between sardine fisheries and oceanographic conditions in NW Spanish  coastal waters

Cabanas-López, José Manuel

Porteiro-Lago, Carmen

Varela-Rodríguez, Manuel

Digital.CSIC

http://www.repositorio.ieo.es/e-ieo/bitstream/10508/1622/1/ICES%20CM%201989%20H18%20A%20possible%20relation.pdf

A possible relation between sardine fisheries and oceanographic conditions in NW Spanish coastal waters

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