Fisheries

Edible Films for Preventing Lass af Quality inFrozen Fish

University of California, DavisR/F-139

1990 � 93

John M. Krochta, J. Bruce German, and Michael J. McCarthy

73

Fish products lose quality whenmoisture is lost to the environmentor oxygen diffuses into the fish fleshand enhances the oxidation oflipids. These undesirable changeslead to deterioration of texture,flavor, color, and odor. The result isa reduction of shelf life and theinability of the U.S. seafood industryto meet the growing demand forhigh-quality products.

To a great extent, frozen storageprevents or decreases undesirablechanges and maintains the qualityof fresh fish. However, although therates of dehydration and lipidoxidation are slower in frozen fishthan in fresh fish, these processesstill occur. Thus, the frozen fishindustry encounters problems insupplying quality products.

invisible, edible films made fromnatural ingredients and formed onthe surfaces of fish may be themeans of providing an ampleamount of high-quality frozen fishproducts. Edible coatings canprevent quality changes in foods byacting as barriers that controltransfer of moisture, uptake ofoxygen, and loss of volatile odorsand flavors. Edible films can bemade from proteins e.g., gelatin,soy protein, casein, whey protein,zein!, polysaccharides e.g., algi-nate, pectin, cellulose, starch!, lipids e..g., waxes, acetylated monoglyc-erides, surfactants!, or a combina-tion of these materials Kester andFennema, 1986!. Proteins have notbeen investigated as extensively asother biopolymers for the creation ofedible films Kester and Fennema,1986!. However, milk casein hasbeen used to make edible emulsionfilms that were good moisturebarriers Krochta, 1990!. The lipidmaterial in the films provided goodresistance to transfer of moisture;the casein provided good structuralcohesion, bound the films to wetsurfaces, and reduced the films'

waxy appearance. Casein-lipidemulsion films have been success-fully applied to fruit products toreduce moisture loss Krochta et al.,1990; Krochta, 1991; Avena-Bustillos et al., 1993, 1994!. Thestructure and numerous functionalgroups of proteins offer a widechoice of possible manipulations toachieve edible films with desirablemass-transfer characteristics. As aresult, several opportunities exist foruse of proteins for edible films,including on frozen fish.

Project GoalsThe overall goal of this project

was to develop films based on milkcasein, milk whey protein, and otherproteins that could be formed on thesurfaces of frozen fish as coatings toprevent quality deterioration due toloss of moisture and oxidation oflipids. This was divided into threesubgoals: �! development andtesting of stand-alone films formedfrom casein, whey protein, and soyprotein alone, or in combination withacetylated monoglycerides or otherlipids; �! preliminary testing of filmcoatings on ice and on a model gelunder freezing temperatures; and�! evaluation on fish of the mostpromising film coating.

Evaluation of Stand-Alone FilmsExcellent films were formed from

casein, whey protein, and soyprotein, either alone or in cornbina-tion with acetylated rnonoglyceridesor other lipids. The addition of lipidsto protein films in an emulsionsystem decreased the permeabilityof the films to moisture and reduced

many of the problems encounteredwhen lipids alone are used. Table 1contains data on moisture and

oxygen permeability for these films.Casein films, All forms of milk

casein formed edible films, becauseof the characteristic random coil ofthe protein and the ability to form

extensive intermolecular bonds,These films were transparent,flexible, soluble in water, and blandtasting. Edible plasticizers such asglycerin improved the flexibility of thefilm but were not necessary forhandling. When piasticizer wasadded to increase flexibility, magne-sium and calcium caseinate filmshad similar permeabilities; magne-siurn caseinate films provided thebest barrier to moisture loss Table1!. Films made from other forms ofplasticized casein micellar, rennet,sodium and potassium! had highermoisture permeabiiities than filmscontaining magnesium caseinate;films containing rennet had thehighest permeability. Unplasticizedsodium caseinate films had lowerpermeabilities than all the plasticizedcaseinate films. Treating a sodiumcaseinate film with calcium ascor-bate buffer solution at the isoelectricpoint of casein made the film in-soluble and reduced the film'smoisture permeability Table 1!.Films formed from emulsions ofsodium caseinate with C12 to C18fatty acids, fatty alcohols, paraffin,carnauba, and beeswax had signifi-cantly reduced moisture permeabil-ity; beeswax had the greatest effect Table 1!. Caseinate films were alsoexcellent barriers to oxygen Table1!.

Whey protein films. Films madefrom isolates of whey protein wereproduced by heating 8 � 12'/o solu-tions of whey protein to 75' � 100'Cto denature the proteins. These filmswere extremely brittle and requiredthe addition of plasticizer to formintact films. Films made from wheyprotein were insoluble in waterbecause of the covalent disulfidebonds formed during the heattreatment. The moisture permeabilityof these films was higher than that ofcasein films; this was attributed tothe amount of plasticizer needed tocounteract brittleness Table 1!. As

Table 1. Water Vapor and Oxygen Perrneabihty of Protein-Based Edible Films

Water Vapor Test Conditions for WaterPermeability Vapor Permeabilitymrn/rn2 d kPa Tem erature C

Relative Humidity Oxygen PermeabilityGradient '/o crn3 m/m2-d.kPaFilm Corn osition

Magnesium caseinate:glycerin �:1!bRennet casein:glycerin �:1!~Sodium caseinate'Buffer-treated sodium caseinate pH 4.6!'Sodium caseinate:lauric acid �:1! bSodium caseinate:acetylated rnonoglyceride �:4!'Calcium caseinate:beeswax �.7:1!'Sodium caseinate:sorbitol �.3:1! 'Whey protein isolate:sorbitol �,6:1!Whey protein isolate:beeswax:sorbitol �.5:1.8:1! 'Whey protein isolate:sorbitol �.3:1! 'Whey protein isolate:sorbitol �.5:1! 'Soy protein isolate:glycerin �:1!, unheatedttSo rotein isolate: I cerin 5:1, heated'

43.956,036.720.99.6

15.83.6

25252525252525

0/770/770/810/860/920/840/97

3.262,05.3

2525

one0/98

4.32.6

58.944.4

2727

0/68ono

aOxygen permeability was measured at 23 C and 50/, relative humidity.Ho, 1992; Avena-Bustillos and Krochta, 1993; McHugh et al., 1994; McHugh and Krochta, 1994a; McHugh and Krochta, 1994b;

gStucheil and Krochta, 1994Dashes = not tested.

The Effectiveness of Edible Filmsas Coatings on Frozen Salmon

The effectiveness of edible filmcoatings on frozen fish wasdetermined by using silver salmon Oncorhynchus kisutch ! coated witha casein-based emulsion and kingsalmon Oncorhynchustshayf/ytscha! coated with emulsionscontaining whey protein isolate.

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with films based on casein, thoseformed from emulsions of wheyprotein isolate and lipids had signifi-cantly lower moisture permeabilities Table 1!. Films made with wheyprotein were excellent barriers tooxygen; oxygen permeability wassimilar to that of caseinate films.

Soy protein films. Soy proteinisolate is a complex mixture ofproteins with widely different mo-lecular properties. The majority ofsoy proteins are globular storageproteins with a quarternary struc-ture. Heating the film-formingsolution denatured the proteins andallowed possible disulfide inter-change. Films made with soy proteinisolate were extremely brittle andrequired the addition of a plasticizersuch as glycerin to form intact films.Films made from Supro 620, acommercially available soy proteinisolate, were quite transparent, hada shiny surface, and were blandtasting. The moisture permeability offilms made from heated solutionswas lower than that of films madefrom unheated solutions Table 1!,suggesting a more dense arrange-ment of the protein chains in thefinished film. Treatment of the filmsolution with horseradish peroxidaseto enzymatically cross-link theprotein did not significantly improvethe ability of finished films to preventloss of moisture.

Preliminary Testing of Edible FilmCoatings

Two phases of preliminary testingof edible film coatings for use onfrozen fish were accomplished.These tests were performed todetermine the optimal formulationfor coatings used to prevent loss ofmoisture under freezing conditions.

In the first phase, dishes of icewere coated with emulsions ofcalcium caseinate Alanate 310! andacetylated rnonoglycerides Myvacet5-07, 7-00, and 9-00! to examine theeffect of �! the total amount ofsolids in the solution, �! the ratio ofacetylated rnonoglyceride to protein,and �! the type of acetylatedmonoglyceride in the emulsion. Wefound that the total amount of solidsin the emulsion played the mostimportant role in preventing loss ofmoisture. Increasing the percentageof solids in the coating resulted inreduced loss. The coating contain-ing 20'/o solids reduced moistureloss from ice by approximately 60'/.compared with uncoated ice. Theratio of protein to acetylatedmonoglyceride had a small effect onmoisture loss lower ratio of proteinto acetylated monoglyceride re-sulted in decreased moisture loss!,and the type of acetylated mono-glyceride had no significant effect.

In the second phase of prelimi-nary testing, we used a modelgeiiike surface composed of 1'/o

xanthan gum/locust bean gummixture Kelgurn! and 2'/o starch.The gel was heated and then formedinto 35-mm round by 10-mm highcylinders, which maintained theirshape under freezing and thawingconditions. The cylinders werecoated by dipping them in calciumcaseinate, sodium caseinate, wheyprotein, soy protein, and gelatinsolutions alone, or in emulsions ofthese proteins with acetylatedmonoglycerides Myvacet 9-08 and9-45!, and then were frozen to� 23 C. After freezing, some of thegels were sprayed with acetylatedmonoglycerides to form a bilayercoating. Weight loss was monitoredover a 10-week period, Resultsshowed that moisture loss with thebilayer coatings and acetylatedmonoglycerides alone was signifi-cantly lower than that with proteinand protein emulsion coatings.Among the proteins tested, wheyprotein-based coatings were thebest barriers to loss of moisture.

continued to increase throughout the10 weeks of the study. The patternof increase in peroxide values wasessentially the same for controlsamples and samples coated withemulsion. Again, this may havebeen due to the porous structure ofthe emulsion coatings. The peroxidevalues of the lipid-coated sampleswere always lower than those of theemulsion-coated samples. Theperoxide values of vacuum-pack-aged samples did not increaseduring the 10-week testing period.The thiobarbituric acid test showedsimilar trends for control, emulsion-coated and lipid-coated samples.Gas chromatography was notappropriate for this study; everycoating interfered with the estima-tion of pentane by preventingpentane evaporation from thesamples during storage.

Testing of king salmon. Qn thebasis of results of the tests withmodel gels, nine coatings wereapplied to pieces of king salmon: �!a spray of a 10'/o solution of wheyprotein isolate, �! a spray of a 10/.solution of whey protein isolatefollowed by a spray of a 5'/o solutionof antioxidant �.5'/o ascorbic acidand 2.5'/o citric acid!, �! a spray ofan emulsion containing 10'/o wheyprotein isolate and 10'/o Myvacet9-08, �! a spray of an emulsioncontaining 10/, whey protein isolateand 10'/ Myvacet 9-45, �! a sprayof a 10'/o solution of whey proteinisolate followed by a spray ofMyvacet 9-08; �! a dusting with apowder of whey protein isolatefollowed by a spray of Myvacet 9-08,

Table 2. Average Weight of Coatings Applied to Fish Samples

Weight of First Component Weight of Second ComponentTreatment

None uncoated10'/0 whey protein isolate10'/o whey protein isolate/antioxidant oversprayEmulsion of 10/. whey protein isolate and 10!. Myvacet 9-08Emulsion of 10/. whey protein isolate and 10!. Myvacet 9-4510/. whey protein isolate/Myvacet 9-08 oversprayPowder of whey protein isolate/Myvacet 9-08 oversprayPowder of whey protein isolate /Myvacet 9-45 oversprayMyvacet 9-08 overspray onlyM vacet9-45overs ra onl

NA1.613 + 0.4591.267 + 0.2003.213 + 0.4832.453 + 0.2571.270 + 0.1790.469 + 0.0670.453 + 0.0550.995 + 0.3101.780 + 0.209

NANA

0.758+ 0.174NANA

0.584+ 0.1160.988 + 0.2200.413 + 0.208

NANA

Note: Average weight of the fish samples to which coating was applied was 48 gr. NA = not applicable.

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Testing of silver salmon.Emulsions containing acetylatedmonoglycerides Myvacet 5-07! andcalcium caseinate Alanate 310! 9:1!, with 0.5/. added hydroxy-propyl methylcellulose to increaseviscosity, were used to coat piecesof silver salmon. Additional treat-rnents included no coating control!,vacuum packaging with Cryovacfilm, and coating with Myvacet 5-07alone. The fish was stored at � 23'Cfor 10 weeks and evaluated formoisture loss and oxidation of lipids.

All the coated samples lostmoisture at a reduced rate com-pared with the uncoated control,which lost 15.7'/o moisture during thestudy. The samples vacuum pack-aged in Cryovac film lost no mois-ture. Loss of moisture with the othercoatings was 2.7'/o with Myvacet5-07 alone, 12.0/o with an emulsioncontaining 20'/o total solids, and13.5'/o with an emulsion containing10'/0 total solids. The emulsioncoatings were less effective asmoisture barriers than the pure lipidalone, perhaps because ofthedevelopment of a porous structure inthe dried emulsion coatings. Thelipid coating, however, was lessflexible than the emulsion coatings,and cracks formed in it during frozenstorage.

Lipid oxidation was assayed byusing three different methods: �!determination of peroxide value, �!2-thiobarbituric acid test, and �!headspace gas chromatographicanalysis for pentane, The peroxidevalues of the control samples beganincreasing at 6 weeks of storage and

�! a dusting with a powder of wheyprotein isolate followed by a spray ofMyvacet 9-45, 8! a spray ofMyvacet 9-08 alone, and 9! a sprayof Myvacet 9-45 alone.

Table 2 gives the weight of thecoatings applied. Uncoated controlsamples were also prepared. Thesamples were stored at -23'C. Fivesamples per treatment were re-moved after 3, 5, 7, 9, and 11 weeksof storage. The samples wereweighed to determine total weightloss, and then the lipids wereextracted and tested for lipid oxida-tion. Moisture loss was calculatedfrom the weight loss of the storedsample. Lipid oxidation was deter-mined by using the peroxide value,which was the most useful methodfor estimating the degree of lipidoxidation in the silver salmontesting. We found no statisticallysignificant differences between thetwo acetylated rnonoglyceridesused, so results are reported forMyvacet 9-08 only. Moisture lossand peroxide values represent theaverage of five measurements foreach treatment.

Figure 1 shows the relativemoisture content of the fish samplesover the 11 weeks of study. Themoisture losses of samples coatedwith whey protein isolate alone orwith emulsions containing wheyprotein isolate were comparable atall sampling times to losses fromuncoated samples. We found nodifference between the spraycontaining whey protein isolatealone and the spray containing wheyprotein isolate and an antioxidant.

100

95

g90

4!

O 0!

o 85

47

iPCL

80

750 10 20 30 40 50 60 70 80

Elapsed Time days!

Figure 1. Relative moisture content of pieces of king salmon coated with variousedible films and stored at � 23'C. WPI = whey protein isolate.

Samples coated with a spray ofacetylated monoglyceride had lessmoisture loss than uncoatedsamples. During the first 3 weeks,the rate of moisture loss fromsamples coated with a powder ofwhey protein isolate followed by aspray of acetylated monoglyceridewas 0.007 g/cmz per week. Thiscompares with losses of 0.019 g/cmzper week from uncoated samplesand 0.069 g/cmz per week from pureice. In the uncoated samples, therate of moisture loss slowed to 0.007g/cm per week during the next 8weeks, indicating that the desiccatedsurface of the uncoated fish wasitself a barrier to moisture loss.During the same 8-week period, theaverage rate of loss from the coatedsamples was 0.008 g/cmz per week.

Peroxide values did not show anysignificant differences until the fifth

week of testing. Figure 2 gives theperoxide values for the differenttreatments at 5 weeks. All thecoatings reduced the peroxide valuesignificantly compared with theuncoated samples. Pieces coatedwith a powder of whey protein iso-late followed by a spray of Myvacet9-08 had the lowest peroxide value.The order of effectiveness of theother coatings was �! emulsioncontaining whey protein isolate andMyvacet, �! spray of whey proteinisolate followed by a spray ofantioxidant, �! spray of Myvacetonly, �! spray of whey proteinisolate followed by a spray ofMyvacet. The peroxide value washighest for pieces coated with aspray of whey protein isolate alone Figure 2!. At the sampling times of7, 9, and 11 weeks, differences inthe peroxide values between

uncoated samples and the coatedsamples were not as apparent, butall coated samples had lower valuesthan the uncoated controls data notshown!.

The peroxide value is a measureof the hydroperoxide content of thesample. Hydroperoxides are initialproducts of lipid oxidation, whichthen react further to form secondaryproducts. The rate of formation ofhydroperoxide greatly exceeds therate of decomposition during theearly stages of lipid oxidation andcorrelates reasonably with oxidationin fish oils Hardy, 1979!.

The rate of lipid oxidation in fattyfish such as salmon is affected by anumber of factors. The lipid contentand composition of the fish flesh canvary greatly, depending on the age,maturity, and size of the fish and theposition in the fish where the sampleis taken e.g., head to tail, back orbelly flap, dark or light meat! Ackman, 1979; Stansby and Olcott,1963!. Fish such as salmon containa wide variety of types of lipids,some very unsaturated and highlyreactive. The disposition of lipidwithin the tissue also affects the rateof oxidation; dark muscled fleshtends to oxidize more rapidly thanlight flesh Hardy, 1979!. Nonlipidcomponents, such as metals andtocopherols, can also affect the rateof lipid oxidation Hardy, 1979!.These factors contribute to thecomplexity of the data we obtained,Nonetheless, the reduction inperoxide values achieved with thecoatings tested clearly indicated asignificant reduction in lipid oxidationfor salmon.

Summary and ConclusionsEdible films were formed from

casein, whey protein, and soyprotein, either alone or in combina-tion with acetylated monoglyceridesor other lipids. The addition of lipidsto protein films in an emulsionsystem reduced permeability of thefilms to moisture, Casein and wheyprotein films were also excellentoxygen barriers. Model gels weredeveloped and used to test ediblefilm coatings under freezing condi-tions. Edible film coatings consistingof acetylated monoglycerides alone

76

�

O!

0

2

o 1

0

Treatment

or sprayed over protein coatingsreduced moisture loss when appliedto frozen salmon. Edible filmcoatings containing antioxidants oracetylated monoglycerides reducedthe peroxide value of the samplesand slowed the oxidation of the fishlipids, thus extending the storagelife of frozen fish.

Avena-Bustillos, R.J. and J.M. Krochta.1993. Water vapor permeability ofcaseinate-based films as affected bypH, calcium crosslinking and lipidcontent. J. Food Sci. 58�!:904 � 907.

Avena-Bustillos, R.J., L.A. Cisneros-Zevallos, J.M. Krochta, and M.E.Salveit. 1993. Optimization of ediblecoatings on minimally processedcarrots using response surfacemethodology. Trans. ASAE 36�!:801�805.

Avena-Bustillos, R.J., J.M. Krochta,M.E. Salveit, R.J. Rojas-Villegas, andJ.A. Sauceda-Perez.1994. Optirniza-tion of edible coating formulations onzucchini to reduce water loss. J. FoodEng. 21:197 � 214.

Hardy, R. 1979. Fish Lipids. Part 2. InAdvances in Fish Science andTechnology. J.J. Conneil, ed., FishingNews Books Ltd., London.

Kester, J.J. and O.R. Fennema. 1986.Edible films and coatings: A review.Food Tech 40�2!:47 � 59.

Krochta, J.M. 1990. Emulsion films onfood products to control mass transfer.In Food Emulsion and Foams: Theoryand Practice. P.J. Wan, ed., SeriesNo. 277 v. 86!, American Institute of

AcknowledgmentsDr. Robert J. Price, Seafood Technol-

ogy Specialist of the Sea GrantExtension Program, University ofCalifornia, Davis, has providedexcellent technical assistance in�! understanding fish preservationtechnology and �! making contactswith the seafood industry, includingobtaining fish for experiments.

Special thanks to Yvonne Stuchell forperforming much of the experimentaland analytical work on this project.

ReferencesAckman, R.G. 1979. Fish Lipids. Part 1.

In Advances in Fish Science andTechnology. J.J. Connell, ed., FishingNews Books Ltd., London.

Figure 2. Peroxide value at 5 weeks of pieces of king salmon coated with variousedible films and stored at -23'C. WPI = whey protein isolate.

Chemical Engineers, New York.Krochta, J.M. 1991. Coatings for

substrates including high moistureedible substrates. U.S. Patent No.5,01 9,403.

Krochta, J.M., A.E. Pavlath, and N.Goodman. 1990. Edible films fromcasein-lipid emulsion for lightly-processed fruits and vegetables. InEngineering and Food, Vol. 2. W.E.L.Spiess and H. Schubert, eds., ElsevierApplied Sciences, New York.

McHugh, T.H. and J.M. Krochta. 1994a.Dispersed phase particle size effectson the water vapor permeability ofwhey protein-beeswax edible emulsionfilms. J. Food Processing Preserv,18:173 � 188.

McHugh, T.H. and J.M. Krochta. 1994b.Sorbitol- versus glycerol-plasticizedwhey protein edible films: Integratedoxygen permeability and tensileproperty evaluation. J. Agric. FoodChem. 42:841 � 845.

McHugh, T.H., J.F. Aujard, and J.M.Krochta. 1994. Plasticized whey proteinedible films: Water vapor permeabilityproperties. J. Food Sci. 59:416.

Stansby, M.E., and H.S. Olcott. 1963.Composition of fish. In industrialFishery Technology. M.E. Stansby, ed.,Robert E. Krieger Publishing Co., NewYork.

PublicationsStuchell, Y.M. and J.M. Krochta. 1994.

Enzymatic treatments and thermaleffects on edible soy protein films, J.Food Sci. 59:1332 � 1 337.

Stuchell, Y.M. and J.M. Krochta. 1995.Edible coatings on frozen king salmon:Effect of whey protein isolate andacetylated monoglyceride on moistureloss and lipid oxidation. J. Food Sci.60:28 � 31.

ThesesHirasa, K. 1991. Moisture loss and lipid

oxidation in frozen fish: Effect of acasein-acetylated monoglyceride ediblecoating. M.S. thesis, University ofCalifornia, Davis.

Ho, B.P. 1992. Water vapor permeabilityand structural characteristics of caseinfilms and casein-lipid emulsion films.M.S. thesis, University of California,Davis.

Stuchell, Y.M. 1994. Characterizationand optimization of edible coatings forfrozen king salmon. M.S. thesis,University of California, Davis.

Abstracts and PresentationsHo, B.P. and J.M. Krochta. Effect of fatty

acids, fatty alcohols and waxes onwater vapor permeabilities of edible

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caseinate-based emulsion films. InBook of Abstracts, 1992 AnnualMeeting, Institute of Food Technolo-gists, Chicago, Illinois, June 1992.

Ho, B.P., R. Avena-Bustillos, and J.M.Krochta. Water vapor permeability ofcasein-based edible films. In FoodEngineering: Advances and Technolo-gies, Technical Program and ExtendedAbstracts, Conference of FoodEngineering, American Institute ofChemical Engineers, Chicago, illinois,March 1991.

Stuchell, Y.M., J.M. Krochta, and J.R.Whitaker. Effect of heat and enzymatictreatment on mechanical and barrierproperties of edible protein films. InBook of Abstracts, 1993 AnnualMeeting, Institute of Food Technolo-gists, Chicago, Illinois, July 1993.

Stuchell, Y.M. and J.M. Krochta. Theeffect of whey protein isolate andacetylated monoglyceride coatings onfrozen king salmon. In Book of Ab-stracts, 1994 Annual Meeting, Instituteof Food Technologists, Atlanta,Georgia, June 1994.

Stuchell, Y.M. and J.M. Krochta. Theeffect of heat, glycerin level andenzymatic treatment on properties ofedible soy protein films. In Book ofAbstracts, 1994 Annual Meeting,Institute of Food Technologists,Atlanta, Georgia, June 1994.

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The Importance of Transport Processes in Recruitmentof Rockfishes Genus Sebastes! to Nearshore Areas ofMonterey Bay, California

Moss Landing Marine LaboratoriesRIF-142

1991-94

Valerie l oeb, Mary Yoklavich, and Gregor Cailliet

AccomplishmentsThe 1991 � 93 study period off

central California was characterizedby a prolonged El Nino event.

79

Rockfishes Sebastes spp.!support important and heavilyexploited sport and commercialfisheries in central California; theirlarvae dominate inshoreichthyoplankton assemblages Loebet al., 1983 a, 1983b; MacGregor,1986; Wallace, 1988; Moser et al.,1993!. Factors affecting the survivalof young fishes, including hydrogra-phy, climate, densities of prey andpredator, and spawning seasonality,are critical determinants of recruit-ment. This 2-year project was basedon the hypothesis that the pro-cesses of physical transport affectthe distribution of young rockfishes,thereby influencing the strength andtiming of recruitment to nearshoreareas along the central Californiacoast. The arrival of pelagic juvenilerockfish to subtidal areas ofMonterey Bay appears to be associ-ated with upwelling events VenTresca et al., 1990!. The recurringplumes of cold water from a distinctupwelling center near Davenport Tracy, 1990; Schwing et al., 1991;Rosenfeld et al., 1994!, a relativelyunfished area to the north of

Monterey Bay, may be importantvehicles of transportation for youngrockfishes into Monterey Bay.Similarly, northward flow of waterupwelled off Pt. Sur may transportyoung rockfishes into the Bay fromthe south,

The objectives for the 1991 � 1993field seasons were to assess �! dis-tribution and potential transport ofrockfish larvae from nearshoresource areas before the upwellingseason and �! the role of upwetling-related processes in advectingpelagic juvenile rockfishes intoMonterey Bay.

Anomalously warm, low � salinitywater in nearshore areas duringmuch of our study suggested anonshore displacement of theCalifornia Current. Upwelling wasreduced and delayed relative tothat of other years, and distinctpersistent upwelling plumes werenot evident within the survey areaduring the sampling periods. How-ever, the 2 years differed in theintensity, duration, frequency anddirection of wind events that canaffect transport.

During early spring 1992, windspeed was somewhat higher thanduring the same period in f 991 Figure 1!, but wind directionreversed during February andMarch 1992, blowing predominantlynorthward for 2 � 12 days at a time Figure 2A!. Coincidentally, watertemperatures in the upper 60 mwere warmest during wind rever-sals Figure 2A!, and increased to15'C by April 2. Wind reversalsassociated with warm and lesssaline water indicate onshoreadvection of surface water, Theconductivity-temperature-depth CTD! vertical temperature profilesduring the spring surveys ofichthyoplankton off Davenport,California, in 1992 indicated anincreasingly stratified and warmwater column Figure 3!. DuringMay and June 1992, the along-shore winds were generally south-ward and more typical for this timeof year Figure 1!. However, windspeed was low relative to that ofthe previous year, persistentupwelling was not evident inAdvanced Very High ResolutionRadiometer AVHRR! satelliteimages of sea surface temperature,and calm events were frequent.Cool-water plumes occurred alongthe coast to the north and south ofthe Bay in July, which were the firstsigns of upwelling at the surface Figure 4!.

Winds during early spring 1993were variable, but unlike those in1992 they were mostly to the southand more typical of this season Figure 1!. Persistent southward-blowing wind commencing in earlyMarch 1993 resulted in cooler �0-14'C! temperatures in the upper 80m of the water column off Davenportby early April Figure 28!. This wasthe first evidence of upwelling duringeither year of the ichthyoplanktonsurveys, as indicated by the 10.0�10.5'C isotherm sloping up towardshore in the 6 April 1993 CTDvertical profile Figure 3!. Winddirection reversed in mid-May 1993 Figure 1!, again suggesting a briefperiod of potential onshore advec-tion. In June and July intense windsfavorable to upwelling resulted incold water at the surface to the northand south of the Bay; however,upwelling plumes did not persistduring the juvenile rockfish surveys.During May and June, a warmmeander developed off MontereyBay Figure 5!, possibly indicatingflow of water toward the equator onthe eastern shoreward! edge Rosenfeld et al., 1994!,

Extended El Nino conditions andabsence of persistent upwellingplumes during our study directlyaffected implementation of theproject e.g., sampling design andschedules for surveys of juvenilerockfish! and results during bothyears. Despite the absence ofdistinct thermal fronts, differences inwind regimes and related watertransport, especially during earlyspring surveys of ichthyoplankton,likely influenced rockfish recruitmentin the 2 years, We evaluatedbetween-year differences in thedistribution, abundance, growth, andspecies and size composition ofyoung rockfish, and interpretedthese in terms of recruitmentsuccess and potential source areas.

SCALE

10 mieeeDAILY BUOY WINDS - 1991 -1993

44042 - MONTEREY BAY �6.8'N 1224'W!

1991

1992

FEB MAR APR NAY JI BJAN

Figure 1. Daily-averaged wind vectors measured at buoy 46042 inMonterey Bay north is to top of page! during 1991 � 1 993.

Surveys of Larval RockfishSurveys of ichthyoplankton were

conducted aboard Moss LandingMarine Laboratories researchvessel Ricketts during daytime atfive stations along a northeast-southwest transect over depths of15, 30, 60, 100, and 200-m offDavenport, California Figure 6!.These stations were located 1, 3,7, 13, and 19 km from shore.During 1991 � 92, samples werecollected at approximately 2 weekintervals from early December toApril; less frequent samplingextended through June because ofthe absence of expected upwellingevents during the spring. Samplingbetween January and April 1993was limited by frequent storms andrough seas Table 1!.

Samples of larvae were col-lected with a 70-cm mouth diam-eter! bongo net without a closingmechanism. Both nets were madeof 0.505-mm mesh black Nitex.The volume of water filtered persample �0-465 m'! was estimatedby using calibrated mechanicalflowmeters positioned in the mouth

of each net. Tows were madeparallel to bathymetry at 1 � 3 kt for2 � 20 min depending on depth!and obliquely from near bottom tosurface at nearshore stations andfrom 200 m at the offshore station.Three replicate taws were done atmost stations, Oceanographicparameters e.g., conductivity,temperature, and pressure! weremeasured from near bottom to thesurface at each station with a cali-brated CTD profiler.

Plankton samples were pre-served at sea, one sample fromeach bongo pair in 5% formalin andthe other in 80% ethanol. Rockfishlarvae were sorted under dissectingmicroscopes from each pairedsample for all replicates per station.Formalin-preserved rockfish fromall replicates were counted forestimates of abundance. Only oneethanol-preserved replicate perstation was processed for speciesidentification, Standard length ornotochord length for preflexionlarvae! was measured to thenearest 0.1 mm for shortbellyrockfish S. jordani ! and blue

rockfish S. mystinus ! preserved inethanol, Otoliths were removed forage determination from a sub-sample of the dominant species shortbelly rockfish!; the methodsof Yoklavich and Bailey �990! wereused to determine larval age. Hatchdates were calculated by using alinear growth model to estimate agefrom lengths of all larval shortbellyrockfish and subtracting age fromdate of capture.

Seven rockfish species wereidentified: shortbelly, blue, bocaccio S. paucispinis!, greenspotted S,chlorostictus!, squarespot S.hopkinsI!, stripetail S. saxicola!,and cowcod S. levis; Table 2!. Twogroups of species were identified onthe basis of shared pigment pat-terns: The "copper complex" groupincludes copper S. caurinus!,gopher S. carnatus!, black-and-yellow S. chrysomelas!, kelp S.atrovirens!, china S. nebulosus!,quillback S. maliger!, and brown S. auriculatus! rockfish. TheSebastosomus group includesblack S, melanops!, olive S.serranoides !, yellowtail S, flavi-dus!, widow S. entomelas !, andbank S. rufus! rockfish. Identifica-tion of larval blue and coppercomplex rockfish was aided byreference to specimens reared inthe laboratory during a previouslyfunded Sea Grant research project Wold, 1991; Moreno, 1993!.

Larval abundance was comparedamong the five stations along theonshore-offshore transect. Abun-dance was calculated for eachreplicate at each station by multiply-ing the number of larvae by thedepth of tow and dividing by thevolume of water filtered per sample.Abundance was scaled by multiply-ing by 10 i,e�number of larvae per10 m'!

The 130 bongo net tows madeduring 10 surveys in 1991 � 1992contained 9389 rockfish larvae,Rockfish larvae were relativelyabundant from January to April1992, with the largest catchesoccurring in early February at all butone station Figure 7A; Table 2!.Abundance consistently washighest at the three offshore sta-tions i,e., 7, 13, 19 km!. Whileabundance declined steadily from

80

10m/ sec

40

160

200

06April

29 12January February

07March

1993

Figure 2. Daily-averaged wind vectors measured at buoy 46042 in Monterey Bay north is to top of page! and temperaturevariation with time in upper 200 rn at station �9 km! during ichthyoplankton surveys off Davenport, California. A, 2 December1991 � 2 April 1992. B, 29 January � 6 April 1993, CTD sampling dates are indicated with dashes.

81

80

E

120Q.

0

Z I�LUCL

O

02 18 09 23 06 21 12 02

December January February March April

1991 1992

DISTANCE OFFSHORE km!7

DiSTANCE OFFSHORE km!3 I 00 Ig13lg

001

I 201

ISO I

'I 313I 013130 ��1 34C

12

120

14'CI 013

~ 0- 14

SO- ~12

los

I So

Figure 3. Vertical temperature profiles along a sampling transect off Davenport, California, during January, February, and April in1992 and 1993. The five CTD stations are indicated by distance offshore. The 10.0 � 1 0.5 'C isotherm is shaded for comparatrvepurposes.

82

z ~

Q0

I gg J3

I

Figure 4. AVHRR satellite image ofsea surface temperatures off centralCalifornia coast 5 July 1992,indicating upwelling plumes havedeveloped off Pescadero Point north! and Point Sur south!. Coldwater is represented by lightestshades.

Figure 5. AVHRR satellite imageof sea surface temperature offMonterey Bay. Warmest tempera-ture is represented by darkestshade. Relatively cool wateroccurs of Pescadero Point andPoint Sur; arrow indicates a warmmeander in the California Current.

83

122 30' 122'W

Table 1. Dates of Collection and Number of Replicates TakenAlong an Onshore-Offshore Transect off Davenport, CaliforniaDuring Winter � Spring Months 1991-1993*

15m 30m 60mDate km 7 km

200 m19km

2527 26 28

1237

632

327

937

936

Stations are defined by bottom depth m! and distance from shore km!. indicates na samples were taken.!

1991-199202 December18 December09 January23 January06 February21 February12 March02 April04 May16 JuneSubtotal

199329 January12 February07 March06 AprilSubtotalTotal

3 3 3 3 3 3 3 3 3

Ql Figure 6. Monterey Bay study areaand larval fish sampling transect off

12'l' 30' Davenport, California,

d PN «c0 m o O

CC0

«D

m

O

g> I «3«D

CD 1'i CO N «D DI N COco

«A CO «0mN co

N

m co

cOcc

«9 m N «D CON N O

N «D

«0 «O

D

«IID 8 tcSs eCO 'UV !DZI O

'8 ccC

o P- +

X

- ICc,~O CO 8 e O$ Z «OCO«OCU «O«n

c <4CclQlQlc

QlQl1 Q C

7 QCh

E Q VQCIC5

C QU 0 CLC Q COCI

0 QV Q OO Vk0I- QX 0 UlC 0

R L COQ MClO

K Cl0

CV ECO

1 Q CLQ E

Z C V QlQ Ql

C� I

CV ~C5

D CQ gI- a

D, «8RZXc~uÃR

Q <g CO W «O

Q«cC&dgdN I dggO

co I I co d'

Ncodd!d I I mONCO «D

co ~ «D «O «O «O CO co~«ON«DN«9 «D

'aQCC

cc!C CLC

~ 0 cg 0. «c cl 2 ~ > Q � <Q.lc 0 D cc'E z «c a. <c 0 + > E J0 . «O .. C «C 0 A� 0! CO O Cfl Ch «fl V! 0 0 I- cL'

o<' «o «o «o co v! I cccc

«2QR 9

cc 5RGl

85

10000

1000

100

10

O Q C4Q 10000

1000

100

10

Figure 7. Larval rockfish abundance at five stations along an onshore-offshore transect, Davenport, California Each point is theaverage of one to three replicates; error bars = standard error. A, 2 December � 1 6 June 1992. B, 29 January � 6 April 1993.

86

early February through April at the7- and 13-km stations, numbers oflarvae remained relatively high atthe station farthest from shore �9km!.

Four surveys conducted in 1993included 39 bongo net tows contain-ing 3492 rockfish larvae. Similar tofindings in collections made in 1992,the highest abundance occurred inFebruary Figure 7B; Table 2!. Incontrast to the previous year, highcatches of rockfish larvae occurredonly at the two offshore stations.Abundances averaged over Januarythrough April surveys were similarbetween years �43 larvae/1 0 m' in1992; 381 larvae /10 m' in 1993!,but distribution patterns differed.Significantly greater numbers oflarvae occurred at the onshorestations �, 3, and 7 km! duringJanuary and February 1992 than inthe same months in 1993. Thisnearshore concentration of larvaeearly in 1992 is possibly the result ofwind-related onshore transport ofsurface water, as discussed in thepreceding text.

We were able to identify thespecies or group of species of 47'/oand 66'/o of the rockfish larvaecollected in 1992 and 1993, respec-tively Table 2!. Shortbelly rockfishwere the dominant species bothyears and accounted for a largerpercentage of total catch in 1993�6'/ vs. 29/.!. Shortbelly larvaeoccurred from late December toearly May, largely in the offshoresamples �3 and 19 km!, On thebasis of larval ages and collectiondates, we concluded that hatching ofshortbelly rockfish extended fromDecember to May, with a medianhatch date in mid-February bothyears Figure 8!. Growth of thisspecies did not differ among monthsor between years. In the 1992samples, larval shortbelly rockfishwere significantly larger at onshorethan at offshore stations. Thiscoincides with indications of onshoreadvection of water i,e., reversals inwind direction, warm and less salinewater!, suggesting retention oflarvae nearshore in 1992. Initiationof upwelling in March and April of1993 and fewer larvae at onshorestations suggest greater offshoretransport during these months.

Although much less numerousthan shortbelly rockfish, blue,stripetail, and squarespot rockfishlarvae also were abundant �-6'/o ofthe total!; the last two species wererelatively more abundant in 1993 Table 2!. Interestingly, squarespotrockfish are a southern Californiaspecies, rarely found north ofMonterey Bay, but they were adominant species in our larval andjuvenile surveys and abundant insamples collected near deep rockoutcrops in the Bay in the fall of1992 � 1993 M. Yoklavich, unpub-lished data!. The copper complexgroup, although representing only1-2/o of the total catch, generallycould be found in the nearshoresamples.

Surveys of Pelagic JuvenileRockfish

We collected pelagic juvenilerockfishes with a 24-m midwatertrawl deployed from the 15-m fishingvessel Good News, which was char-tered by the California Departmentof Fish and Game CDFG! for 12days in 1992 and 16 days in 1993.Fishing depth ranged from 26 m atshallow stations to 77 m; fishingtime was approximately 15 min.Sampling operations were flexibleand were based on prevailinghydrographic conditions monitoredin the field and from near real-timeAVHRR satellite images of sea sur-face temperature. Because of thisflexibility, we extended our studyperiod and sampled relatively largeaggregations of pelagic juvenilerockfishes occurring late in theseason both years.

Transect stations were located atthermal discontinuities indicated byunderway measurements of seasurface temperature or at evenlyspaced intervals off Davenport,northern Monterey Bay, southernMonterey Bay, Point Pinos, CypressPoint, and Point Lobos Figure 6!.Between two and six trawls weremade each night, and each transectgenerally included four to fivestations. A CTD cast was made ateach station. Rockfishes were roughsorted onboard and frozen. Afterfinal identification and standardmeasurements of length, rockfishwere transferred to ethanol.

In 1992 sampling was conductedduring early May, June, and July Table 3!. AVWRR satellite imagesobtained late in April indicated uni-formly warm sea surface tempera-tures in coastal waters, and warm,low-salinity waters characterized theupper water column �-30 m! in theMonterey Bay area during survey 1 May 4 � 9, Table 3!. Twenty towsyielded only one juvenile rockfish Figure 9A!. Although a satelliteimage obtained on May 23 indicatedsome coastal upwelling offPescadero Point north of Daven-port! and Point Sur south of Cy-press Point!, it was not apparent insubsurface temperature and salinityprofiles off Davenport or Montereyduring survey 2 June 2 � 6!. In fact,relatively warm, low-salinity waterprevailed in the southern part of thebay at this time Table 3!. A total of174 pelagic juvenile rockfishes werecollected in 20 tows during survey 2.The majority of these �58! werecollected at the southern transectstations off Cypress Point and PointPinos Figure 9B!. During survey 3 July 7-1 0!, decreased temperatureand increased salinity in the upperwater column reflected the influenceof upwelling off Pescadero Point andPoint Sur Figure 4!. This was mostapparent in the southern part of thebay where the average temperatureof the upper water column was1.8'C colder than the temperature inthe previous month Table 2!. Six-teen tows collected 58 pelagicjuvenile rockfishes during survey 3;nearly equal numbers were found inthe northern and southern parts Table 3; Figure 9C!.

Twelve rockfish taxa were repre-sented in the midwater trawl sam-ples in 1992 Table 4!, including 10species, the copper complex, andthe Sebastomus group. Shortbellyrockfishes were most abundant andaccounted for 131 �6/o! of the 233fish collected. Members of thecopper complex also were relativelyabundant �8/o!.

The size of the juvenile rockfish in1992 was generally 10-30 mm Figures 10A and 10B!; averagelength for most species during eachsurvey was less than 25 mm. Thesefish were small compared withjuveniles collected in previous years

87

Table 3. Pelagic Juvenile Rockfish Collected During Midwater Trawl Surveys in the North andSouth Monterey Bay Areas in 1992 and 1993

1992Survey 37 � 10 July

Total North South Total

Survey 22-6 June

South

Survey 14 � 9 May

North South Total North

16583.6

1993Survey 4 Survey 55 � 11 May 25 May � 6 June

North South Total North South

Survey 620 June-9 July

Total North South Total

20 20 12988 515 482549.4 25.8 402.1

25921.6

11.2 12.30.5 0.3

33.5 33.440.13 0. 11

2098849.4

10373.7

10373.7

13.40.6

33.120.13

10.30.4

33.480.12

Note: Mean and standard deviations of temperature T 'C! and salinity S! are derived from integrated 0- to 30-m CTD values.*Excludes three large, probably near-bottom catches made during 1993. � indicates no samples were taken.!

Shortbelty RocktlshHatchdate Distribution

30

1520

10 15

10

2060

1540

10 Figure 8. Hatch date distributions forshortbelly rockfish, estimated from ageof larvae collected from January throughApril in 1992 and 1993 and of juvenilescollected in June 1992 and May � July1993.

20

0DEC 1 JAN i FEB i MAR i APR i MAY

0 DEC I JAN! PEB I MAR I APR I MAY

88

No. TowsNo. FishNo. Fish/TowMeanTStd TMean SStds

No. TowsNo. FishNo. Fish/TowNo. Fish'No Fish/TowMeanTStd TMean SStds

10 10 20 101 0 1 16

0.1 0.0 0.1 1.613.1 13.1 13.1

0.7 0.4 0.433. 30 33.21 33.380.13 0.06 0.08

1015815. 813. 8

0.333.200. 07

20 6174 28

8,7 4.712.6

0.633.34

0.15

10303.0

12.00.5

33.380.11

325340166.977424.2

37oN

36o 30

122 W

37 iN

36' 30'

122 W122'W

Figure 9. Location of net tows and abundance of pelagic juvenile rockfishes collected in 1992. A, Survey 1 �-9 May!. B,Survey 2 � � 6 June. C, Survey 3 � � 10 July!.

89

20. 020.0

o 150

g. 10.0C

8 h 5.0

15.0

10.0

5.0

0.0 10 20 30 40 50 60 70 0.0 10 20 30 40 50 60 70A

20.0

e

20.0

~ 15.0

I'~ 10.0

15.0

10.0

g 5.0 5.0

0.0 0.010 20 30 40 50 60 70 10 20 30 40 50 60 70

C Standard Length mm! 0 Standard Length mm!

Figure 10. Length frequency distributions for shortbelly rockfish juveniles A! and other juvenile rockfishes B! collected in 1 992al1d shortbelly rockfish juveniles C! and other juvenile rockfishes D! collected in 1993.

90

during the National Marine FisheriesService NMFS! Tiburon GroundfishCommunities Investigation surveysin May and June Adams, 1992!.

The May � July 1993 study periodwas characterized by sporadic,strong winds, mostly from the south downwelling! in May and from thenorthwest upwelling! in June andJuly Figure I!. Juvenile rockfishwere collected during three pro-longed surveys spaced about 2weeks apart with several 1- to 3-dayefforts within each survey.

Survey 4 May 5 � 1 2 ! wasconducted north of Monterey Bay.Cool, relatively saline surface water Table 3! suggested the influence ofupwelling off Pescadero Point asindicated by satellite images duringApril!. Only 37 rockfish were col-lected in 11 tows Figure 11A!.Survey 5 May 25&une 6! wasconducted south of Monterey Bay.On average, the temperature in theupper water column was 3'Cwarmer and salinity was 0.36 pptlower than those north of the bayduring survey 4 Table 4!. This likelyreflected the onshore influence of a

warm-water meander off MontereyBay Figure 5!. A total of 988rockfish were collected in 17samples, with catch sizes rangingfrom 1 to 240 per tow Figure 11B!.Survey 6 June 20 � July 9! wasconducted both north and south ofthe bay. Decreased temperatureand increased salinity in thesouthern upper water column,relative to those in the previoussurvey, suggest decreased influ-ence by the meander and possiblysome influence of upwelling offPoint Sur. Relatively high salinity tothe north also indicates upwellingoff Pescadero Point, Twenty towsnorth of the bay contained 515rockfishes. A total of 4842 rock-fishes were collected in 13 towsmade to the south Figure 11C!.Taws with catches of 1480 and1774 rockfishes were made within15 m of the bottom nearshore offCypress Point �0-rn bottom depth!and Point Pinos �5-rn bottomdepth!. Another catch of 1312rockfishes was located within 25 mof the bottom at Portuguese Ledge,a shallow rock outcrop off Point

Pinos Figure 11C!. The associationbetween these three large catchesand shallow water suggests that welikely sampled near-bottom aggre-gations rather than pelagic juvenilerockfishes,

A total of 25 rockfish taxa werecollected in 1993 Table 4!. Short-belly rockfish was again the domi-nant species, accounting for 4809�5%! of the total 6382 rockfishcollected. Other relatively abundantspecies included squarespot S.hopkins! and halfbanded S.semicincftjs! rockfish. Almost alltaxa occurred more often and weremore abundant in samples collectedsouth of the Bay Table 4!. Exclud-ing the three large, probably near-bottom catches, the overall meanabundance in southern sampleswas more than double that of thenorthern samples. A similar patternoccurred in 1992 Table 5!.

In 1993 juvenile rockfishes were20 times more abundant, includedtwice as many taxa, and weresubstantially larger than in 1992 Table 4; Figures 10C, and 10D!. Agrowth model established for

36 30'

'422 W

3 7'N

36' 30'

122 W1 22'W

Figure 11. Location of net tows and abundance of pelagic juvenile rockfishes collected in 1993. A, Survey 4 � � 11 May!. B,Survey 5 �5 May � 6 June!. C, Survey 6 �0 June � 9 July!.

Table 4. Pelagic Juvenile Rockfishes Collected During Midwater Trawl Surveys in theVicinity of Monterey Bay, May-July 1992 and 1993

1993Total �4 Trawls! '/o

MeanNo./Trawl

S. jordani 13143171212

2. 340,770. 300.210.210.070.070. 050.04

56.5 480918.5 1227.35.2 1435.2 951.7 411.71.3 4930.9 35

73.981.88

2.201.460.630.027. 580. 54

75,41.9

2.21.50.60.07.70.5

S. atrovirensS. goodeiS. auriculatusS. paucispinisS. diploproaS. hopkinsiS. saxicola

13 0.200.90.04 0.20.02 0.4

0.40.02S. semicinctusS. entomelasS. mystinusS. flavidusS. serranoidesS. cramenS. pinnigerS. rastrelligerS. elongatus

S. melanopsS. levis

S. rufus

0. 02

TotalNo. taxa

233 4.16 6382 98.1812 25

Note: Copper complex includes copper S. caurinus!, gopher S. carnatus!, and black-and-yellow S. chrysomelas! rockfish. Sebastomus group includes greenspotted S. chlorostictus!, starry S. constellatus!, swordspine S. ensifer!, pink S. eos!, rosethorn S. helvomaculatus!, rosy S. rosaceous!, and greenblotched S. rosenblatti! rockfish. Sp. = species. Unid. = unidentified.Dashes = 0 collected.

92

1992Common Name Species Total �6 Trawls! '/o

MeanNo./Trawl

ShortbellyCopper complexKelpChilipepperBrownBocaccioSplitnoseSquares potStripetailSebastomus

groupSp. BSp. AHalfbandedWidowBlueYellowtailOliveDarkblotchedCanaryGrassGreenstripeUnid, 1BlackCowcodUnid,5Unid. 4BankUnid,7Unid.

463 7.1274 1.1429 0.4519 O. 299 0.149 0144 0.063 0053 0052 0.032 0.031 0.021 0.02

0,021 0.02

0.028 0.12

7.31.20.50.3O. l010.1

<0. 1<0. 1<0. 1<0. 1<0. 1<0. 1<0. 1<0. 1<0. 1

Table 5. Pelagic Juvenile Rocktishes Collected During Midwater Trawl Surveys in Southern and Northern Monterey BayAreas May& uly 1992 and 1993

South North1992

FrequencyS.D. '/o!

�0 Trawls!Total

MeanNo./Trawl

Frequency �6 Trawls! Mean '/o! Total No./TrawlTaxon S.D.

1122614119

4 2

3.730.870.470.370.300.130.130.07

7.541.821.091.050.780.430.430.25

33.030.023.013.017.010.010.0

7.0

19

17 3 13

0.730.650.120.040.12

1.40 31.01.54 27.00.42 8.00.19 4.00.32 12.0

0.19 4.00.04

0.070.030.030.030.03

0.250.180.180.180.18

7.03.03.03.03.0

0.04 0.19 4.0

2.89 46.01.10

TotalNo. taxa

50.0 457

1.730.90

18812

6.271.60

11.132.00

1993

Species �0 Trawls!Total

MeanNo./Trawl

Frequency �1 Trawls! Mean Frequency '/o! Total No./Trawl S.D. '/o!S.D.

'I 1,87

1,0324,07 58. 'I

1.33 48.4

1.390.680.100.321.970.130.030.03

2.96 45.21.45 29.00.39 6.50.82 16.13.21 67.70.42 9.70.18 3.20.18 3.2

0.03 0.18 3.2

0.03 0.18 3.2

0,100.060.03

0,53 3.20,35 3.20.18 3.2

0.18

552 17.81 28.74 96.815 3.03 1.69

TotalNo. taxa

124722

41.375.43

47.572.86

100.0

Note: Data from southern Monterey Bay f 993 do not include three extremely large, probably near-bottom catches. SD = standard deviation.Unid. = unidentified. Dashes = 0 collected.

93

ShortbellyCopper complexKelpChili pepperBrownSplitnoseBocaccioSquarespotSebastomus

groupStripetailUnid. AUnid. BUnid. damaged

ShortbellyChili pepperWidowCopper complexSquarespotBocaccioHalfbandedBrownStripetailBlueYellowtailSebastomus groupDarkblotchedOliveCanaryGreenstripeBlackUnid. 4Unid. 7BankCowcodUnid. 5GrassUnid.1SplitnoseUnidentitied

73510073666437183229281712

9 8 3 1 1 1 1 1 1

24.503.332.432.202.131.230.601.070.970.930.570.400.300.270.130.100.030.030.030.030.030.03

39.216,305.734.814.572.842.541.672.541.951.091.380.690.570.340.400.180.180.180.180.180,18

0.46

96,763.330.040.043.340.010.043.330.030.026.710.020.020.013.36.73.33.33.33.33.33,3

16.7

36832

4321

31061

411

1

321

shortbelly rockfish juveniles col-lected off central California duringthe 1983 El Nino Woodbury andRalston, 1991!, was used to esti-mate age, and hatch dates werecalculated. Surviving juvenileshortbelly rockfish were born late inthe season during both years median hatch dates, April 21, 1992and March 31, 1993; Figure 8!.Upwelling occurred coincidentallyduring March and April in 1993, butnot in 1992. Limited information,indicated high numbers of chaeto-gnaths, a potential predator col-lected in the ichthyoplanktonsamples, nearshore during peakabundance of larval rockfish inFebruary 1992 J. Bridges, unpub-lished data!. Our data indicatesubstantially higher survival andrecruitment of rockfish in 1993; wespeculate that this is due to in-creased upwelling and offshoretransport, lower predation, andpossibly better feeding conditionsduring the larval stages,

DiscussionIn accordance with the results of

our surveys, subtidal observationsalong the central coast made bybiologists of the CDFG SportfishProject indicated that few juvenilesof nearshore rockfish species settledinto rocky reef and kelp canopyareas off the Monterey Peninsuladuring May � August 1992 VenTresca, unpublished data!. Overallrockfish recruitment in 1992 was thelowest estimated over their 1990�

1993 study period. Relatively highnumbers of rockfish settled duringJune-September 1993, indicatingsuccessful recruitment of the pelagicjuveniles that we sampled earlier inthe year. Subtidal recruitment levelsin 1993 were similar to those during1990, a non � El Nino period,

The low abundance and smallsize of juvenile rockfishes off centralCalifornia during 1992 also werenoted during the May � June 1992Groundfish Communities Investiga-tion surveys Ralston, 1993! andwere characteristic of previous ElNina years Wyllie Echeverria et al,.1990!. However, the larger sizesand higher abundance of the pelagicjuveniles during the continued ElNino in May � July 1993 suggest that

poor recruitment success is not justthe consequence of an El Ninoevent but is most likely also relatedto the timing of optimal hydrographicconditions occurring during thelarval and postlarval stages.

Net onshore transport during thepeak abundance of larval rockfish inFebruary 1992 could have beenresponsible for heavy larval mortal-ity, most likely through increasedpredation relative to that in offshorewaters. Because of the relatively Iowintensity of the upwelling and thelack of offshore transport during thesubsequent months, possibleprolonged nearshore retention andelevated predation of the postlarvalstages and juveniles further reducedrecruitment success. In contrast,increased intensity of upwelling andoffshore transport during March andApril 1993 likely facilitated survivalof larval and postlarval stages byadvection from nearshore areas andby increased densities of prey.

High diversity and abundance ofjuvenile rockfish in southernMonterey Bay during 1993 mayhave been associated with the warmoffshore meander observed duringMay and June. Possible transport ofoffshore water to nearshore south-ern Monterey Bay via this hydro-graphic feature could have facili-tated recruitment and settlement.This feature could combine youngrockfishes that were transportedoffshore from northern source areaswith rockfishes from southernsource areas that were transportedonshore along the coast.

Collaboration and Disseminationof Information

Because we have taken an inter-disciplinary approach to understand-ing processes that affect recruitmentof young rockfishes to nearshoreareas in Monterey Bay, our studyincluded the efforts of physicaloceanographers and fishery scien-tists from several regional institu-tions. Personnel from the CDFGSportfish Project conducted subtidalsurveys of rockfishes to evaluatenearshore benthic recruitment intoMonterey Bay; this perspective wasimportant in evaluating our samplingprogram and results. CDFG sup-plied fisheries personnel, charter

vessel time, and equipment; ourresults are directly applicable to theirongoing subtidal recruitment studiesand are critical to the managementand monitoring of future resourcereserves.

Personnel from the NMFSTiburon Groundfish CommunitiesInvestigation have provided unpub-lished information on the abundanceof young-of-the-year rockfishescollected in and around MontereyBay during surveys in May and June1991, 1992, and 1993. This washelpful in preparation for our pelagicrockfish cruises and interpretation ofresults. They also helped confirmidentification of juvenile rockfishspecies in our samples. The NMFSPacific Fisheries EnvironmentalGroup provided timely estimates ofdaily and weekly upwelling indexand personnel for shipboard opera-tions; Frank Schwing has advised uson interpretation of the physicaloceanographic data. About 50 near-real-time AVHRR satellite imagesand appropriate software weremade available by Mike Laurs NMFS, Southwest FisheriesScience Center! to assist in locatingour May-July sampling stations.

A Consortium of Monterey BayRegional Oceanographic Studieswas established by M. Yoklavichand F. Schwing. Four informalmeetings were held and wereattended by about 20 scientists fromMoss Landing Marine Laboratories,NMFS Pacific Fisheries Environ-mental Group, NMFS TiburonGroundfish Communities Investiga-tion, Monterey Bay AquariumResearch Institute, CDFG, Univer-sity of California, Santa Cruz, andNaval Postgraduate School. Thesemeetings provided an opportunity toexchange details of sampling plansand results and encouraged collabo-ration among institutions andresearch groups with compatibleinterests in Monterey Bay.

Two workshops on identificationof larval and juvenile rockfisheswere convened by our projectpersonnel and were attended byresearchers from NMFS Tiburon,CDFG, and San Francisco StateUniversity.

94

Cooperating OrganizationsCalifornia Department of Fish and Game

Sporffish Project, MontereyMoss Landing Marine LaboratoriesNational Marine Fisheries Service,

Pacific Fisheries EnvironmentalGroup

National Marine Fisheries Service,Southwest Fisheries Science Center

National Marine Fisheries Service,Tiburon Groundfish CommunitiesInvestigation

ReferencesAdams, P.B., ed. 1992. Progress in

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