CalCOFI Reports, Vol. 11, 1967 - California Cooperative Oceanic ...

18 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIOSSof northern anchovy, Pacific sardine, and Pacificmackerel. Many hundreds of individuals of thesemluable commercial species were reared from theireggs to the juvenile stage in the laboratory. At thesame time approximately 18 other species of marinefish were successfully carried from hatching throughmetaniorpliosis to the juvenile form.Success in rearing may have resulted from thecombination of a suitable environment and a goodfood supply. Observations on newly-hatched larvaeindicated tlie need for large volumes of sea waterbecause of its stability of temperature, salinity, andbiotic factors. Large aquaria provide room for swimmingwithout frequent contact of walls, one of themajor causes of mortality of laboratory-rrarrd fishes.,4t first feeding, sardine and anchovy larrae requirehigh densities of food in tllrir immediate environment.Live plankton has been provided, which lias beenobtained by filtering large volumes of sea water toobtain sufficient numbers of minute plankton organismsof sizes that can be ingested by newly-feedinglarrae (organisms no largcr than 0.08 mni in diameter).As the larvae grew, larger food organisms weresupplied in high densities.Sardine and anchovy larvae, at first feeding, ciinswim only limited distances. Their swimniing abilityrequires that the entire volume of a 500-gallonaquarium must contain uniform distribution of foodorganisms at a density not less than 4 per cubic centimeterof water, regardless of whether only one larvaeor a thousand are being cultured. This problem wassolred by restricting the space for the larrae withuse of thin-walled plastic bags floated in the aquarium.The thin plastic permitted gas exchange to take placebrtween the wxtrrs inside and outside of tlie bag, whilethe soft material offered very little resistance whenstruck by a swimming larva. When larvae becomeable to hunt food over greater distances, the bags weresilt open and the growing fish allowed the freedom ofthe larger container.Life History Studies of Rockfish. A major goal ofthe Life History and Taxonomy program is to preparecomplete descriptions of the life history stages of thefishes that contribute eggs and larvae to the planktonof the California Current region. A4 major study isbeing made of rockfishes (Xebastodes spp.).The large number of rockfish species (more than50) pose an immense problem in attempting to identifyrockfish larvae collected in plankton. The problemis simplified by the fact that rockfish are live bearersthat retain their young to the larval stage. Such earlylarvae of 17 species haw been obtained from identifiedfemales and have served as a means for identifyingthe later larval stages in our collections.The complete series of derrloprnrntal stages fromthe developing embryo to the adult, have been describedfor Xebastodes pnzrci.spiiai.s. It was found thatyoung of this rockfish species spend the first severalinoiiths of their life as epipelagic larvae and transforminto juveniles at 30 mni length. Juveniles arefound in shallow coastal waters over rocky bottom3in association with Agile (Macrocystis, Laminarin, andEgrcgia) or over sand bottom in association with eelgrass (Zostera). Juveniles remain in vaters shallowerthan 20 meters during their first year of life, thenmove into deeper water. Most of the adults collectedwere found in depths of 80 to 300 meters during theinvestigation.Plartkton Dynamics. Since the start of the work onquantitative sampling of fish eggs and larvae in 1939.the California Current Resources Laboratory has beeninvolved in problems of quality control of planktoncollection. In 1963 the diverse plankton-samplingstudies were united under one program. The work ofthe Plankton Uynaliiics program is divided into fourareas : plankton sampler design and operation, planktonbchavior, riiicrodistributioll, and measures ofamount of zooplankton (biomass).It was our judgment in starting the plankton programthat two major problems were inhibiting theimprovement of precision and accuracy in quantitativezooplankton sampling. One problem area was thatof plankton behavior, of the responses of organismsto sampling gear. The other was an inadequate understandingof the operation of plankton sampling gear.As anticipated, the description of the performance ofsampling gear has proceeded at a faster pace than thestudy of the biological problems.Comprehensive tests of hydrodynamics of planktonsampling devices were carried out at the David TaylorModel Basin near Washington, D.C. Eighteen personsparticipated in or were actively associated with thesetests, including personnel from five BCF laboratoriesand from several university and industry groups.The tests showed that in “clean” water at the modelbasin, the amount of effective straining area ratherthan the size of the mesh apertures was the predominantconsideration. As long as the ratio of mesh aperturearea to mouth area was it least 4 to 1, littlediff erence was observed in filtering efficiencies of fineor coarse-meshed Nites nets in “clean” water attowing speeds of 13 to 3 knots. All had filtering efficienciesof 90 percmt or more when new (less if thenet previously had been used at sea).The tests also showed that bridles and tow cablescause major accelerations and turbulence in the waterahead of ncts. Although thew disturbances have littleeRrct iipon the actual filtering efficiencies of largenets, they provide cues to which animals may respondto avoid capture.Following the studies of plankton net performanceunder controlled model basin conditions, the nets weretaken to sea, in order to study the effects of cloggingon plankton net performance. The telenietering flowmeasuring devices used for the model basin tests wereadapted for use at sea. Clogging was monitored insrreral phytoplankton rich areas, usually near shore.as well as in clear waters, 250 miles seaward of Pt.Conception. The rate of clogging wvas found to bemarkedly dependent upon tlie composition of theplankton community. When a series of nets meretested in plankton-rich waters at the same locality.the rate of clogging was found to be affected by meshaperture size, mesh aperture amount and net form