Feeding Oflarval Sprat(Sprattus Spratius L.) Ami Sardine

Home , Sardine, Sprat

., '-ejJt< ...... -.~ .' International Council for the C.M. I9911L: 76 Exploration of the Sea Biological Oceanography Committee. Theme Session v

Feeding oflarval sprat (Sprattus spratiUs L.) ami sardine (Sardina pilchardus 'Valbaum)

D.V.P. Conwayl, P.R.G. Tranteri, M.L. Femandez de Puelles2 and s.il. Coombs1•

1 Natural Erivironment Research Council, Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PLI 3DH, Devon, England 2 Centro OceanogrMico de BaIeares, Instituto Espaiiol de Oceanogrilfia, Muelle de Poniente s/n, Ap:irtado 291, Palma de Mallorca, Mallorca; Spain.

ABSTRACf • Ai; a contributiori towards the Sardine Arichovy Recruitrrient Projeci (SARP) a study was carried out on the food of larval sprat in the Irish Sea and Geiman Bight of the North Sea. and hlrval sardine offthc north coast ofSpain. The specificobjectives of the work were to determirie the dietafy range and prey size preferences of the larvae in order to allow microzooplankton analysis to be focussed on the organisms of rdevance in the diet. In common with other su-aight-gutted speeies ahigh proportion of larvae had empty guts due to evacuation during sampling. Similar to the diet of most marine fish larvae, those of sprat and sardine fed predominantly on. the developmeniaI stages of copepods (on average 85% of the diet). As jaw gape increased with length of larvae the maXimum prey size also increased, aIthough the parallel increase in minimum prey size was less marked. Diurnal changes in feeding incidence were less ob'Vious in larvae

The Sardine Anchovy Recruitment Project (SARP) is an integrated study to determine the factors dunng the clupeid, larVal phase which deterrriine recniitment levels (IOC, 1989). Central to the study is the hypothesis that unfavourable oceanographic conditioris (eg offshore transport) are ainong the principal determinants of larVal survival. Food availabiIiiy is considered to be one of the main links between oceanography and larval survival (eg Hunter. 1976; BaHey arid Houde, 1989).

Tbe preseni work fomis part of a European SARP programme on larval sprat (Sprattus sprattus L.) in the Gerrrian Bight (North Sea), sardirie (Sardina pilchardus Walbaum) off the north coast of Spain and änchovy (Engraulis ellcrasicolus (L.)) off Portugal. Also included are results from a complenientary progranime on sprat in the Irish Sea. The ------I ~ ...• ~

specific objectives of the work reported here were to determine the dieiary range and prey size preferences of the larvae so that analysis .of microzooplankton sampIes to gauge temporal and spatial differences in food availability could be tailoroo to the feeding requirements of the larvae. i

" . , '. "'." ; . , ..' ; " .\ (' Microzooplankton was. sampled concurrently wlth the larvae. Samphng was by. nets of 53pm mesh aperture·. either attached to the MAFF sainpler. äs small fcimed (20cm diameter) bongo riets. or by means of direct filtnitiori of water through a 53prri gauze. On the basis of the size and range of organisms on which hlrVae. werc~ feeding the microzooplankton sampIes were analysed for copepod eggst nauplii und copepodile stages by dissecting microscope. In this study, for cOInparative purposes. the results of the microzooplankton arialysis was arranged by sire ~ groups: eggs

2 •• >

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. , RESULTS .'

Feeding ofsprat in the Irlsh Sea i987 • 1991

A total of 403 sprat larVae were examinoo from five cruises in the Irish Sea (Table 1), 58% of which had food in their guts. The scope of the diet and feedirig incidence for three , length rimges of larvae are given in Table 2. There was an increasing mean number of 'food hems laken with increasirig size of larvae. The main focid items for the sinallest hirvae «lOmm in length) were copepod näuplii, ,which decreasect in importance with increase in size of larvae until the main items in the diet of the hirgest larvae (>15mm in length) were calanoid eopepodite stages and eopepodite stages of the smaller cyc1opoid copepod, Oiihona spp.

Diet varied sÜghtiy.between eruises, retlecting the inierozooplai1kton spedes present in the plankton. This influence was also seen in larvae from the more inshore stations where a wider variety of food organisms were also taken in the planktori. arie larVae in the central I~sh Sea had fed on four C()sciliodiscUs sp., the,only phytoplankton species observed. However in sampIes taken off the north eoast of ,\Vales, gutS of,larvae, especially of the smaller specimens, contained green unidentifiable inaterial whieh had no, recognisable strUeture; at this time there was a bloori-i of Phaeocystis sp. in the area. Only one rotifer was foimct in all of the guts exainiried, although they were present iri significtlnt riumbers in surfaee microzooplankton sampies.

Feeding ofsprat in the Germa" Bighl 1989· 1991

Of the 499 sprat larvae examined from the six emises in the German Hight eTables 1 and 3) 58% had been feeding (the sameperceniage as in the Irish Sea). Copepod nauplii and copepodite stages agäin predominated in the diet. Ca/anus spp. eggs, whieh are liberated free into. the sea, riumerically forrned a signifieant proportion of the diet of the larger larvae. Duririg the May!lune 1991 cruise many srriall hirvae (3.3 - 4.6mm in length) were sarnpled, of whieh a high proportion still had remains of yolk sacs, but norie had any food iri their guts.

The mimber offood items per feeding larvae was simiJar to the Irish Sea, being generally higher for larger larvae. As in the Irish Sea larger food items were taken with increase in size of die larvrie (i.e. fewer eopepod nauj>lii imd more eopepodite stages). SmalJer larVae had the greatest proportiori of unidentifiable material in their guts. This may have been of phytoplankton or faeeal pellet origin, but any eolour may have bleaehed out during preservatiori. Identifiable phytoplankton was agairi an insignificant pan of the diet.

Fee'ding ör sardine offthc north coast of Spain 1991.

181 sardine)arVae were examined from the north eoast of Spain (Table 4) ofwhieh 28% had been feedirig . This is a lower percentage than for sprat larvae from the Irish Sea or German Bight. Mean number of items in the guts was similar for aiI iength ranges ami lower than for sprat in the Irish Sea or German Bight. Tbe range of organisms laken was

3 ..

more limited than iri the other two areas, but this may rehite. to the fewer larvae examined. Devclopmental stages of copepods again predominated, the larger larvae laking more copepod copepodite stages than smaJler larVae. Copepod nauplii were an importllnt component in the diet of alJ sizes of larvae. Tintinnids (Tintinnopsis sp.) were found in

the guts of a few of the smaJler larvae. I

Diel variation iri fe~dirig incidence. ., _ The diel vanaiion in feeding iflcidence for" the three sire ranges of iarväe shows higher :feeding inciderice in sprat larvae compared to: sardine (Fig. 2). For ,all species. lowest . feeding incidence was duririg the. dark. betweeri 2000 and 0400 GMT. Larval sprat arid sardine <10rrim in length showed the least change in feeding incidence over the diel period. vafying betweeeri,17% and 48% and iridicating JittJe diurnal effeet; larvae >15mrri showed the most change. Sardine larvae >15Il'llli. .had the lowest feeding incidence (0-50%). From the digestive condition of foOd in the guts of both sprat and sardine it was ciear that some feeding was takirig plnce throughout the 24 hour penod, as reJaÜvely undigested remains were found at all times. Observations 'on the degree of digestion of items in the • guts of sprat larvae in thc Irish Sea, indicated, that at least in this area, there was a dusk and dawn increase in feedirig, which is paraJleloo to some extent in the feeding incidence plot of Fig. 2. '

, Larger larvae tended to have more food items in their guts (Fig. 3); as many as 30 items in one gut, with the exception of sardine larvae >15rriiri in length which had a low feeding incidence. The mean number of items in the gutS of different lengths of laivae over thc diel period was very variable. For sprat there was a suggestion of a dawn and dusk increase in numher of food partic](';s taken. The smaJlest diel chariges in riumber of fooÜ iiems laken were in larvae <10min of both sprat and sardine. ; , Diet compared with microzooplankton abundance I a)Sprat larvae: ,..,.,... Feeding iricidence' between the Irish Sea and German Bight (fables 2 and 3) waS simiJar for all lengths oe larVae. There waS also JittJe :difference in the mean riumber of eggs, nauplii arid copepOditc stages of copepods in the' gutS (Fig. 4). 111e number of copepodites laken was slightly lower in the, Germari Bight but this was compensated hy a higher number of copepod eggs. Numbers of the different, copepod developmental stages in microzooplankton sampIes was also generally simiJar in theIrish Seil arid Gcrman Bight (Fig. 5). However then~ were somewhat higher ilurribers of copepodites in the German Bight which was not reflected in the observed diet. The results suggests some selection of nauplii in preference to copepodites. .

b) Sardine larvae: Sardine larvae off the north coast of Spain were sampled at three 24 hour stations (Fig. 1). Concentrations of potential food iteros wece half the values in the Irish Sea or German Bight (Fig. 7. cf Fig. 5). Feeding incidence between the three sites was similar (fable 5) but larvae at Station 1 (Off Cape Ortegal) had on average twice aS many particles in their guts. Nmiplii were most numerous iri the guts of larvae at Station 1 and leaSt numerous at Station 3, while copepodites showoo the reverse, trend (Fig. 6) . Only at Station 2 were ,I

4 J :,' t . , .

eggs taken. Coniparison with the microzoopIankton at the same stations (Fig. 7) shows a similar pattern, with diet generally reflecting the composition of the plankton. There was little difference between the three stations in the coinposition of other organisms in the guts, except fortintinnids (Tbitinnopsis sp.) being identified from hirvae at station 1 arid

OithOlia spp. at stäiiciii 3. !. •

Prey length relative to larval ierigth in sprat and sardine.

\Vith. iricrease in larval jaw gape~ larger prey can 1,e ingested (Figs. 8 and 9). The regression lines plotted against the minimum arid maximum prey length from gUt contents were similar for sprat and saroine. Maximum prey length doubled for a similar increase in larvai length , although there was only a small increase in minimum prey lerigth.

DISCUSSION

The diet of larave of sprat and sardine was similar to that taken by most marine fish " .. larirae (Turner, 1984), und reflects the items of a suitablesize most commonly available in the planktcin, viz the deveIopmental stages of copepods. These comprised on average 85% • of the food taken. In comrnon with other studies (Last, 1980; MeridioIa, 1974) there was :i general increase in maximum size and numbei- of prey items laken as larval length increased, due to iricreasing jaw gape (Figs. 8 arid 9) and also possibly due to greater feeding ability. Only traces of phytophinkton were fourid in the preserit study, although it is found in the diet of a wide range of fish larVae (Ulst; 1980), usually in the smalIer larVae but often in low abundance. Cod lai-vae have been showri to actlvely feCd cin phytoplankton (Meeren, 1991). .

A large proportion of the guts of both sprat and sardine 'were empty which is a common observation with clupeid and other straight-gutted species (Dekhnik; 1974; Last, 1980; Hay, 1981) as a fesult of regurgitation or defaecation in the net. Evidence thai food was being defaecated in both sprat and sardine is provided by observations that in the inajoi-ity of cases where food was observed in the gut Ü was located in the very hind part, just antenor to the anus and sometimes protruding from it. On only iwo occasions was food found anterior to ihe short oesophagus, in the long narrow thin-wallCd fore-gut region. This suggests. that food either passes through this area ver; quickly (Schumann, 1965) or that it is easily expelled fröm here. Arthur (1976) exarilined over 13,000 clupeid larvae (Sardina siJgax, and Engrau/is mordax) and found no food in the fore-gut. No larvae with remains of yolk sac were found to be feedirig, which accords with the observations of ATthur(1976) for other eIupeid species, although Last (1980) repoTted, that in twenty larval fish species examined, inCluding clupeids, alllarvae found in the yolk sac stage had begun to feed on dinoflagellates.

Because there are diurnal changes in feeding activity for both sprat and sardine (Fig., 2 and 3), average feeding iriciderice v:lIues can be unrepresentative if there is any day/night bias in sampling. Diurnal variation in feeding incidence was most marked between 2000 rind 0400hrs GMT, in commonwith most other fish larval species (Last, 1980), related to the fact that they are visual feeders. Surprisingly the smallest l:iIvae «lOmm) showed the least diurnal effect, maintaining almost the same feeding incidence day and night in both

5 , \ '. spedes, in contrast to other obserVatioris (eg AIthur,1976) that clupeid larvae did not feed ai night

Whiie Last (1980) noted that in sprat larvae from the Norih Sea there was an increasing percenuige feeding with increase in h~ngth, in the present stüdy sprat arid especially sardine larvae >15mm often had a feduced feeding ineidenee eompared with smaller larvae. Arthur (1976) reviewed five studies on feeding in CIupeid larvae arid all showed high initial feeding incidence which dropped drainatically by the time the larvae were 7-8min in length and remained quite low over the sire range of larger larVae in this stlldY. before increasing • .'. '. Reasons suggested by Aitllllr (1976) for reduced feeding iricidenee, sueh as faster digestion rate, do not adequately resolve why some gutS were compleiety empty. The low incidence of food in sprat arid sardine >15mm'may be due to äri iricreasing tendency to .evacuate fooo. '

Relaiing larval feeding to food availabiÜty iri the plankton is complex, due to small seale temporal and spatial patchiness in distribution of larvae and prey (McKenzie et cl/., 1990), and larVal feeding behaviom . A companson ofthe maiß dietary hems. in the guts demonstrates a general similarity between the Irish Sea • Germari Bight and Spanish coast. Differenees in gUt eontents between areas are mostly a refleetiori of differences in • availability of organisms in the plankton. Ca/anus spp. eggs formed a greater propoition of the diet in the Gerinan Hight compared to ~e Irish sea. an iridiCation of the greater abllndance of adultS of this species in the North Sea. Oithona spp. which, iri the diet of larVal fish are often an important iriteririediate sire of food item between miuplii and copepodites. were inore,COmnlori in the diet of larvae from the Irish Seä arid off Spain. again iridicating availability in the plalIkton. ' .. i The resultS from the present investigations giv~ 'a gerieral descrlption of the diet of sprat ... '.' .", .,."..- ." and sardine but, In common Wlth other studles based on gut contents analysIs. cannot give iriformation on absolute feeding levels. However, in the coniext of the requirements of a SARP progrärrirrie in which foOd availability is considered an important deteririinant of larval surVival. the main aims of the study have been accomplished. The sire and preferred composition of larval diet has been identified. allowing microzooplarikton arialysis to be foeussed only on those orgariisms of relevance. In practical terms the generalized reliarice of both sprat arid sardine larvae on eopepod nau'pHi arid copepodites iri their diet allows a simple. rapid arid non-specific analysis of microzooplankton to broad sire categories in order to gauge food availability. i

I. ACKNOWLEDGEMENTS

This work forrris pari of the programme of Laboratory Project 2 of the Plymouth Marine Laboratory (PML) a component. institute of 'the UK Natural Environment Research Council. Finance has been provided iri part by ihe UK Ministry of Agneulture Fisheries arid Food (MAFF) under contraci GCA1O. and by the EC under contraet MA.l.96.

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REFERENCES ,Arthur. D.K. (1976). Food and feeding of larvae of three fis~es occurring in the Califomia current. Sardinops sagax. Engraulis mordax. and Trachurus symmerricus. Fish. BuH ., ..' . US .• 74. 517-530. Bailey. K.M.• Houde E.D. (1989). Predation on eggs and larvae of marine fishes and the recruitment problen:t. Ad~. mar Biol.. 25 • 1-83. , Dekhnik. T.V~ (1974). Comments on the articles by V. Ye. Zaika and N.A. Ostrovskaya entitled 'Indicators of the availability of food to larval fish'. J. Icthyol. 14. 804-808. (Translation from Vopr. Ikhtiol). Hay. D.E. (1981). Effects of capture and fixation on gut contents and body size of Pacifie herring larvae. Rapp. P.-v. Reun. Cons. Int. Explor. Mer. 178; 395-400. • Hunter. J.R. (1976).. Report of a colloquium on larval fish morcility studies and their relation to fisheries research. January 1975. NOAA Tech. R~p.• NMFS eire. 395: 5pp. IOC (1989). IOC workshop report of the expert consultation on the Sardine/Anchovy Recniitment Programme (SARP). IOC Workshop Rep. 66. Intergovemmental Oceanographie Commission~ UNESCO. Paris. 64pp. Last. J.M. (1980). The food of twenty species of fish larvae in the w'est-central North Sea. Fish. Res. Teeh. Rep~ MAFF Direct. Fish. Res.: Lowestoft, 60, 44pp. MacKenzie. B.R., Leggett. W.C.• Peters, R.H. (1990). Estimatirig larval fish ingestion rates: can laboratory derived values be reliably extrapolated to the wild? Mar. Ecol. Prog. Sero 67. 209-225. Meeren. T. van der (1991). Algae as first food for eod larvae. Gadus morhua L.: filter feedirig or ingestion by aecident? J. Fish Biol.. 39, 225-237. Mendiola. B.R. de (1974). Food of the larval anchoveta Engrau/is ringens J. In: The Early Life History of Fish. pp277-285. Ed. by J.H.S. Blaxter. Berlin. Springer Verlag. Milligan. S.P.• Riches. B.F. (1983). The new MAFF/Guildline high speed plankton . . . sampIers. International Council for the Exploration of the Sea. (C.M. Papers and Reports), L:7, 6pp. (mirneo). Schumann, G.O. (1965). Some aspects of behavior in clupeid larvae. CaUf. Coop. Oceanic Fish. Invest. Rep.• JO.71-78. Turner. J.T. (1984). The feeding ecology of some zooplanktefs thai are important prey items oflarval fish. NOAA Tech. Rep., NMFS 7. 28pp.

7 Table 1. Cruise dates and details of Clupeid larvae examined for gut contents.

Numberof Number Size range %w1lb sampIes oflarwe (mm) rood examlned Irish Sea (sprat) RV Cirolana 26 May -7 lune 1987 27 117 3.3 - 24.1 32 RV Prince Madog 27 ·30 luly 1987 6 20 10.4 - 23.1 32 RV Cirolana 10 - 21 April 1988 13 102 3.2 - 16.0 38 RRS Challenger 21 May - llune 1988 14 55 2.8 - 21.8 45 RV Cirolana 14 - 29 April 1989 24 109 4.4 - 18.6 49

German Bigbt (sprat) FS Victor Hensen 4 - 9lune 1989 13 53 6.4 - 24.4 38 RRS Challenger 9 -22lune 1989 19 102 2.9 -22.2 44 RV Cirolana 10 ·24 April 1990 42 158 5.2 - 18.6 57 RRS Challenger 30 April - 1 May 1990 2 12 7.7 - 16.5 75 FS Victor Hensen 6 • 12 May 1991 9 28 3.4 - 14.4 21 FS Victor Hensen 27 May - llune 1991 21 146 3.2·17.2 28

North coast of Spain (Sardine) Comide de Saavedra 15 April- 13 May 42 254 3.7 - 21.9 28 • 1991

Table 2. Sprattus sprattus. Percentage composition ofthe gut contents of feeding larvae from the Irish Sea. 1987 - 1989. .-~' Lengtb ranges (rom)

Food organisms <10 10 -15 >15 i

ParalPseudocalanus spp. 2 6 22 Acartia spp. 1 16 Te11Wra longicornis 5 2 Cenrropages spp. 1 Oithona spp. 14 12 Harpacticoid copepods 1 1 Unidentified copepods 6 5 1 Copepod nauplii 76 63 6 Calanus spp. eggs 1 Other copepod eggs 1 1 9 Cirripede nauplii 9 Lamellibranch larvae 2 2 15 Rotifers 1 Coscinodiscus spp. 4 Faecal pellets 1 Unidentified remains 11 2 6

Totallarvae examined 178 169 56 Feeding incidence (%) 37 48 41 Mean no. items/feeding larva 1.7 2.7 4.7 Table 3. Spratlus spral/us. Percentage composition of the gut contents of feeding larvae from the German Bighl, 1989 - 1991. (+ symbol indicates values less than 0.5%)

Length ranges (mm)

Food organisms <10 10-15 >15

Calanus spp. 1 1 ParalPseudocalanus 1 4 32 Temora longicornis 2 7 6 Acartia spp. 2 3 3 Oithona spp. 1 1 Corycaeus spp. + 2 Unidentified copepods 4 9 12 Copepod nauplii 64 54 28 Calanus spp. eggs 11 10 Other copepod eggs 3 4 Lamellibranch larvae 2 5 2 Gastropod larvae 1 Coscinodiscus sp. + Dinoflagellate sp. + • Sphaerosoma sp. 1 Unidentified remains 22 1 4

Totallarvae examined 223 201 75 Feeding incidence (%) 34 51 43 Mean no. items/feeding larva 1.5 3.8 3.5

Table 4. Sardina pilchardus. Percentage composition of the gut contents of feeding larvae from the north coast of Spain. Length ranges (mm)

Food orgaoisms <10 10 ·15 >15

ParalPseudocalanus spp. 1 2 21 Acartia spp. 5 7 Oithona spp. 6 2 7 Unidentified copepods 2 12 Copepod nauplii 58 77 43 Copepod eggs 1 14 Tintinnopsis sp. 25 Unidentified remains 6 2 7

Totallarvae examined 120 91 43 Feeding incidence (%) 32 27 16 Mean no. items/feeding larva 2.1 1.7 2.0

Table 5. Sardina pilchardus. Comparison between feeding at the three 24 hour stations off the north coast of Spain. Sto.l Sto.2 Sto.3

Totallarvae examined 59 74 48 Feeding incidence (%) 24 24 33 Mean no. items/feeding larva 3.2 1.4 1.4 Size range of feeding larvae (mm) 4.2 - 18.8 4.7·21.9 4.5 - 16.7 ...

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FRANCE

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Fig. 1. Sampling areas in the lrish Sea, Gennan Bight and off the north coast of Spain. The three 24 hour station positions off Spain are also shown. •

200

IRISH SEA 160

120

o 0000-0400 0400-0800 0800-1200 1200-1600 1600-2000 2000-2400

200 GERMAN BIGHT

160

120

o 0000-0400 0400-0800 0800·1200 1200-1600 1600-2000 2000-2400

200 NORTH COAST OF SPAIN

160

120

o 0000-0400 0400-0800 0800·1200 1200-1600 1600-2000 2000-2400 TIME (GMT)

Fig. 2. Diel variation in feeding incidence for three length groups of sprat larvae in the Irish Sea and German Bight and for sardine larvae off the north coast of Spain; all are plotted as cumulative percentage of feeding Iarvae. •

IRISH SEA 1989-1990

o 0000-0400 0400-0800 0800-1200 1200-1600 1600-2000 2000-2400

GERMAN BIGHT 1989-1991 • 6

•

IE] 10-15mm 4 o >l5mm

o 0000-0400 0400-0800 0800-1200 1200-1600 1600-2000 2000-2400

NORTH COAST OF SPAIN 1991 6

o 0000-0400 0400-0800 0800-1200 1200-1600 1600-2000 2000·2400 TIME (GMT)

Fig. 3. Mean number of food items per feeding larvae for three length groups, for sprat in the Irish Sea and German Bight and for sardine larvae off the north coast of Spain by four-hourly time intervals...... ;..

1.6

1.2

MEAN No/ 08 GUT .

0.4

IRISH GERMAN SEA BIGHT

Im COPEPODITE D NAUPUI o EGGS

Fig. 4. Sprattus sprattus. Mean number of food items (eggs <0.2mrn, nauplü <0.45mm and copepodite <0.7mm) per feeding larva for all larvae sampled in the Irish Sea and German Bight.

NO/I

IRISH GERMAN SEA BIGHT

mJ COPEPODITE 0 NAUPUI o EGGS

Fig. 5. Sprattus sprattus. Numbers per litre of copepod developmental stages (eggs <0.2mm, nauplii <0.45mm and copepodites <0.7mm) in microzooplankton sampIes taken in the Irish Sea and German Bight , averaged for all cruises. .. .

1.5

MEAN No/ 1 GUT

0.5

0'+---+----+----+ STN 1 STN 2 STH 3

t§ COPEPODITES 0 NAUPUI o EGGS

Fig. 6. Sardina pilchardus. Mean number of food items (eggs

No/I 2

STN 1 STN 2 8TH 3

mCOPEPODITES 0 NAUPUI o EGGS

Fig. 7. Sardina pilchardus. Numbers per Iitre of copepod developmental stages (eggs

0.8

PREY LENGTH 0.6 (mm)

0.4

0.2 • MIN. PREY ~----~. 0 • • • 0 5 10 15 20 25 LENGTH OF LARVAE (mm)

Fig. 8. The relationship between prey size (cephalothorax length for copepods, total length for nauplii) against length of larvae, for sprat larvae from the Gennan Bighl Regression lines are shown for the two sets of solid data points, for minimum and maximum pIey size.

1.2 Sardina pilchardus n=113 1 • MAX. PREY 0.8

PREY LENGTH 0.6 (mm)

0.4

0.2 MIN. PREY

0 0 5 10 15 20 25

LENGTH OF LARVAE (mm)

Fig. 9. The relationship between prey size (cephalothorax length for copepods, total length for nauplii) against length of larvae, for sardine larvae from off the coast of Spain. Regression lines are shown for the two sets of solid data points, for minimum and maximum pIey size.