{"Bibliographic":{ "Title":"Southwest Fisheries Center Monthly Report: September 1975", "Authors":"", "Publication date":"1975", "Publisher":"Southwest Fisheries Center (U.S.)" }, "Administrative":{ "Date created":"06-26-2025", "Language":"English", "Rights":"CC 0", "Size":"0006682749" }, "apiVersion": "2024-07-31-preview", "modelId": "prebuilt-read", "stringIndexType": "textElements", "content": "AENT\nIT OF COM\nPAR\nMERCE\nUNITED\nAMERICA\nSTATES OF\nHONOLULU\nLA JOLLA\nS\nTIBURON\nSOUTHWEST FISHERIES CENTER\nMONTHLY REPORT - SEPTEMBER 1975\nRESEARCH HIGHLIGHTS\nPAGE\nAnchovy Handling Experiments Begun at Tiburon Laboratory 2\nOCSEP/MARMAP Workshop on Quantitative Plankton Sampling Held Aboard Jordan 4\nData Requirements for Production Modeling of Northern Anchovy Fishery Reviewed 7\nNew Statistical Technique Devised for Plankton Sampling 8\nMicrodistribution of Food Organisms Important to Larval\nFish Investigated\nNMFS Charters Two Tuna Purse Seine Vessels to Test Porpoise-Saving Gear and Methods 12\n9\nFeasibility Studies in Progress for Aerial Survey of Porpoise Populations 13\nReview of Natural Mortality Rates of Tunas Completed\n14\nNew Cycle of Pen Rearing of Silver Salmon Underway\n16\nDr. Ahlstrom Selected as Recipient of 1975 AIFRB Outstanding Achievement Award 18\nInstituto Nacional de Pesca/CalCOFI Stock Assessment Working Panel Meets in La Jolla 19\nNOAA/NMFS\nSOUTHWEST FISHERIES CENTER LA JOLLA, CALIFORNIA\nHONOLULU LABORATORY LA JOLLA LABORATORY TIBURON LABORATORY\nMONTHLY REPORT - SEPTEMBER 1975\nSTATUS OF PUBLICATIONS\nPublished\nPerrin, William F. 1975. Distribution and differentiation of popu- lations of dolphins of the genus Stenella in the eastern tropi- cal Pacific. J. Fish. Res. Bd. Canada 32(7): 1059-1067.\nThere are at least two races of spotted dolphin, Stenella attenuata, in the eastern Pacific, based on length, color pattern, and skeletal differences. The coastal form is provisionally called S. attenuata graffmani. The offshore form is distinct from a third, Hawaiian race. Likewise, at least three unnamed races of spinner dolphin, S. longirostris, occur in the eastern Pacific. Length, shape of adult male, color pattern, and cranial differences are used to distinguish a Costa Rican, an eastern, and a whitebelly race. An Hawaiian race is distinct from these. A distributional break may indicate two stocks of the striped dolphin, S. coeruleoalba.\nShomura, Richard S., and Francis Williams (editors). 1975. Pro- ceedings of the International Billfish Symposium, Kailua-Kona, Hawaii, 9-12 August 1972, Part 3. Species Synopses. U.S. Dept. Commerce, NOAA Tech. Rep. NMFS SSRF-675, 159 p.\nApproved by Center Director\n\"Bathymetric distribution of Pleuroncodes planipes Stimpson (Gala- theidae, Crustacea): A new fishery off California\" by Angeles Alvariño. For publication in the Fish. Bull., U.S.\nThis report does not constitute publication and is for information only.\n2\n\"Catch-per-unit effort of albacore tuna, Thunnus alalunga (Bonnaterre), caught by U.S. jig vessels during 1961-1970\" by R. Michael Laurs, Harold B. Clemens and Larry H. Hreha. For publication in Mar. Fish. Rev.\nHONOLULU LABORATORY\nFISH ENVIRONMENT INVESTIGATIONS\nLeader of Recreational Fisheries Task Notes Activity for September\nFishery Biologist Heeny Yuen, Leader of the Recreational Fisheries task, worked on the Honolulu Laboratory's input to the program develop- ment plan for recreational fisheries being developed by Mr. Norman Abramson, Director of the Tiburon Laboratory, for the Southwest Region. Mr. Yuen also reported that he sent 100 aluminum tuna cooling devices to the Sea Grant agent in Kona for distribution there. It was noted that some of the recipients of these aluminum devices may mistakenly believe that the amount of ice used may be reduced or eliminated al- together when these instruments are used. This is not true, and mention will be made at the time of distribution.\nTUNA ASSESSMENT AND DEVELOPMENT INVESTIGATIONS\nAnchovy Handling Experiments Begun at Tiburon Laboratory\nAt the Tiburon Laboratory, Fishery Biologist Roger Green and Bio- logical Aid Stan Smith began anchovy handling experiments, the first of which was completed on September 22. These experiments are designed to provide additional information on the northern anchovy prior to resuming transport of these fish to Hawaii where they will be tested further as skipjack tuna baitfish. The Tiburon experiment involved handling the anchovy by 1) dry scooping, 2) pumping, and 3) bucketing; the highest mortality resulted with the dry-scooped bait, followed closely by pumped bait. Fish bucketed showed the best survival by far. A second experi- ment, begun September 25, was a two-way test on salinity. Anchovy held briefly (about 1 hour) in water of reduced salinity (50:50 sea water-fresh water) survived better than fish moved directly to full sea water. These conclusions are subject to further replications of the experiments.\nOn September 1, Mr. Green came under the direction of the Tiburon Laboratory. He will, nevertheless, continue to provide direction and\n3\ngeneral supervision for the anchovy work. Mr. Smith will carry out the work for the Honolulu Laboratory.\nStatus Report Preparation and North Pacific Albacore Data Analysis Progress Satisfactory\nFishery Biologist Dr. Robert Skillman at the Honolulu Laboratory worked on the stock assessment section of the status report on skipjack tuna at the request of the Laboratory Director. In response to a simi- lar request, Fishery Biologist Richard Uchida continued work on a status report for the frigate mackerel, completing a first draft. These reports are being prepared as background papers for an FAO-sponsored ad hoc com- mittee to review small tunas. The meeting is scheduled to be held in Honolulu 15-18 December 1975.\nFishery Biologist Dr. Jerry Wetherall and Mathematician Ms. Marian Yong are now working on yield-per-recruit analyses for North Pacific albacore, and Dr. Wetherall reports that the work is progressing satis- factorily. They have completed the cohort analyses for the albacore.\nThe gear shakedown portion of the NOAA research vessel, Townsend Cromwell Cruise 66 was completed on September 16. All gear and associ- ated equipment functioned satisfactorily and a cruise report is being prepared.\nHL Staff Observers Accompany Easy Rider on\nUnsuccessful Commercial Fishing Trip\nLaboratory Director Richard Shomura, and Laboratory staff members Tom Hida and Tom Kazama went to sea on the commercial fishing vessel Easy Rider September 24-27. The Easy Rider's track was 180 miles due south of Honolulu, to Kailua-Kona, and back to Honolulu. The purposes of the trip were 1) to test threadfin shad as live bait for pole-and- line fishing, 2) to see how the automatic fishing poles work, and 3) to conduct scouting in an area beyond the usual range of the commercial fleet. During the trip only one good feeding bird flock was encountered. Messrs. Shomura and Hida did the chumming and were able to bring the school to the stern of the vessel, but the skipjack tuna did not take the lures. One 3-1b aku was caught on the automatic pole. Several other unsuccessful attempts were made by Easy Rider in Kailua-Kona, where the Anela caught 11,000 1b. of extra-small fish.\nHawaiian Skipjack Tuna Fishery Catch Report for September\nThe September catch of skipjack tuna in the Hawaiian fishery reached an estimated 236.9 metric tons (MT), which was 51.8 MT below the catch in\n4\nSeptember 1974 and 162.2 MT lower than the September average for 1948-74. The catch for the first 9 months of this year was an estimated 1,965.4 MT, 1,031.8 MT below last year's catch for the same period and 1,874.2 MT below the long-term average.\nComputer Aid Ms. Lucille Tsukano reports that Government of Ameri- can Samoa employee Pulou Niuatoa recorded the lengths of 1,159 albacore from 24 vessels unloading in Pago Pago during the period August 30 to September 26. Nineteen sets of catch and effort data were collected. Utilizing data from five vessels only, an average size of 91.6 cm was determined and an albacore catch per 100 hooks of 1.69.\nLA JOLLA LABORATORY\nALBACORE FISHERIES\nIn addition to the albacore advisory services, including daily broadcasts over marine radio bands, work conducted by the Staff of the Albacore Fishery Program at the La Jolla Laboratory this past month, led by Dr. R. M. Laurs, included continued processing of data collected during the cooperative NMFS-American Fishermen's Research Foundation (AFRF) field studies that are being conducted during 1975: 1) cruise tracks and station locations have been prepared for the Cromwell cruise, 2) most of the STD data and other data collected on the Cromwell has been processed and analyzed, 3) an analysis of oceanic frontal conditions which occurred during spring and early summer has been completed, 4) all albacore catch records from AFRF charter vessels have been standardized and plotted by location of catch, and 5) most of the albacore tagging data have been summarized.\nA final report of the results of the joint NMFS-AFRF albacore stud- ies carried out during 1975 is expected to be completed in mid-November.\nECOLOGY OF THE CALIFORNIA CURRENT\nOCSEP/MARMAP Workshop on Quantitative Plankton Sampling Held Aboard Jordan\nNOAA's Outer Continental Shelf Environmental Program (OCSEP) and Marine Resources Monitoring, Assessment, and Prediction program (MARMAP) sponsored a workshop led by Dr. P. Smith, Fishery Biologist at the La Jolla Laboratory, on quantitative plankton sampling at sea, off the\n5\nsouthern California coast on board the NOAA research vessel, David Starr Jordan from September 8 to September 12, 1975.\nMessrs. James R. Thrailkill and Robert C. Counts, Fishery Biologists at NOAA's Southwest Fisheries Center's Laboratory in La Jolla, California, trained scientists in the procedures for conducting quantitative tows and calculation and quality control of data which allows quantitative apprais- al of oblique tows using standard MARMAP bongo gear.\nMr. Alfredo Cota visiting scientist from the Instituto Nacional de Pesca, Mexico and Dr. P. Smith, with the technical assistance of Lt. Roger Hewitt and Sharon Duke, have prepared a study of the range dependent loss of targets as influenced by target size and target strength. The first phase of the study is complete, showing the independent effects of target size and target strength. The interaction of these effects is now being prepared for study by automated means. First approximation shows a strong dependence of target strength and range and a perceptible but much weaker interdependence of target size and range. The study is to be a model of the analysis of the sonar mapping activities of California Fish and Game and Mexico.\nA variety of activities related to assembling CalCOFI data for auto- matic data processing for the prediction of a CalCOFI Data Management Sys- tem were undertaken this month. Among these, Mr. L. Eber, Meteorologist, continued his work on software development intended for the selective re- trieval of oceanographic variables interpolated to standard depths. Uni- form presentation of these data in the form of printed tables and computer- generated contour plots is another aim of this activity. The experience in assembling CalCOFI data so far is being used by Ms. D. Roll, Computer Pro- grammer, and Dr. Smith to design a complete system for standardized report- ing and fishery research using the files of the CalCOFI biological, fishery and oceanographic data.\nA paper on the status of fishery acoustic research was presented by Dr. Paul E. Smith to the MTS-IEEE meeting OCEAN '75 on September 24, en- titled \"Acoustics in Fishery Research - A Perspective\" at the invitation of Dr. James Joseph, Inter-American Tropical Tuna Commission, organizer of the acoustics symposium.\nDr. Smith also presented two committee reports to the FAO-Instituto Nacional de Pesca/CalCOFI anchovy workshop held at the SWFC on Friday, September 26. One report on biomass estimates of the northern anchovy, stressed the organization of the basic data, sized larva counts, and the methods of weighting the data for additive estimates in time and space.\n6\nThe second, on acoustics research, reported on a meeting with represen- tatives from Mexico and California Department of Fish and Game. The minutes of that meeting present a brief report of cooperative work in the past year and the resolution of that committee to meet again on November 24 to design standardized methods of collection of acoustic data amenable to all three ships involved, calibration of the acoustic equipment, and cooperative cruises aimed at standardized collection and reporting of quantitative acoustic data on fish schools.\nMARINE ENVIRONMENTAL ASSESSMENT\nThe identification guide to larvae of eastern Pacific scorpion- fishes (Family Scorpaenidae) is in the final stages of typing and then will be sent to outside reviewers. In the finished form it treats life histories of 7 genera and 20 species and is supplemented by 38 tables and 40 figures. The guide is primarily the work of Dr. H. G. Moser, although Dr. Ahlstrom and Ms. E. Sandknop made contributions.\nDuring the month, George Kelly, NMFS, Northeast Fisheries Center, Woods Hole, sent us 12 samples of larvae collected from full-term females of commercially landed redfish from George's Bank. These collections will be of considerable help in clarifying larval differences among Atlantic species of Sebastes.\nThe program studying the bottomfishes of Magdalena Bay, Baja California, in cooperation with Dr. C. Matthews of the University of Baja California is nearing completion. Ms. Elaine Carlin spent the summer working on the fish collection from this region and compiled an extensive set of meristics that will aid greatly in identifying larvae in plankton collections from off southern Baja California. She will prepare a manuscript summarizing these data.\nProgress was made in the life history study of the commercial lantern- fish, Lampanyctodes hectoris, from South African waters. A manuscript is being prepared by Drs. Ahlstrom and Moser to be submitted for the special publication of the Los Angeles County Museum honoring Dr. Carl L. Hubbs, Professor Emeritus of Biology, UCSD.\nWork continued in assembling materials for a CalCOFI Distributional Atlas dealing with flatfishes. The forms to be included are Glyptocephalus zachirus, Microstomus pacificus, Lyopsetta exilis, Parophrys vetulus, Paralichthys californicus, Citharichthys stigmaeus, Citharichthys spp., and Pleuronichthys spp. This Atlas will be a joint contribution of Drs. Ahlstrom and Moser.\nThe three authors (E. H. Ahlstrom, J. Butler and B. Sumida) of a manuscript dealing with pelagic stromateoid fishes extensively edited and revised the paper during September, and a revised draft is now awaiting typing, prior to submittal for outside review. Since this is a fairly large manuscript, it is hoped that it can be published as a unit, but if not, could be divided into two manuscripts.\n7\nNeuston collections made on CalCOFI Cruise 7210 are being worked up by Biological Technician Betsy Stevens. One of the interesting collec- tions made off Washington contained 14 jack mackerel larvae, 10 to 17 mm SL. This is a larger size than is usually taken in oblique plankton hauls. Although larger sized specimens of anchovy, rockfishes, Anoplopoms, ets., were taken in neuston hauls on Cruise 7205 as compared to oblique hauls, only small jack mackerel larvae were taken in neuston hauls on that cruise.\nDr. Moser attended a meeting of the resource board for the DOMES Project of ERL in Boulder, Colorado. Proposals for the benthic com- munity stuides were evaluated and principal investigators were selected.\nRECREATIONAL FISHERIES\nData Requirements for Production Modeling of Northern Anchovy Fishery Reviewed\nDr. Gary Stauffer, Fishery Biologist at the La Jolla Laboratory, reviewed the assumptions and data requirements of surplus production modeling for application to the northern anchovy fishery. The past catch and effort data from the California reduction fishery are insuf- ficient for fitting a model because past fishing effort has most likely not been the major influence on changes in abundance of the central stock. A major problem exists in specifying the unit of measure for effort for pelagic purse seine fisheries in a way that effort is pro- portional to fishing mortality. Variability in anchovy availability may also be such that the coefficient of catchability will not be a reasonable constant over time and area. An investigation into the measurement of effort is necessary. If measurement is feasible then a logbook system for California and Mexico would need to be developed to collect the effort statistics and experiments planned to compare the relative fishing power of California and Mexican purse seiners. The conclusion is that a minimum of 10 additional years of data will be necessary to estimate model parameters for the expanding anchovy fishery. A cooperative research program between California and Mexico is essential for developing standard formats for data collection and exchange.\nMembers of the Recreational Fisheries Program, Stauffer, McCall (CF&G), Squire, and Lasker, met with Mel Wilson of the Ocean Fish Protective Association to discuss the concern of southern California recreational fishermen over the sportfish-anchovy interrelationships. Wilson pointed out the interaction of anchovies with sportfish should be studied in the Los Angeles area where the major portion, the reduc- tion fishery, takes place. He was more concerned about the resident recreational species rather than the migratory game species such as\n8\nyellowtail and albacore. It was pointed out that this year as part of our CalCOFI program we have intensified our studies of the Los Angeles Bight with particular emphasis on the oceanography and larval survival of anchovies in the inshore zone. As a result of the meeting, an outline of the anchovy sportfish interaction problem and a study plan for the Los Angeles area will be developed.\nNew Statistical Technique Devised for Plankton Sampling\nThe analysis of survey data in which the observations are numbers of organisms per sample is under investigation by Mathematician James Zweifel and Fishery Biologist Paul Smith of the La Jolla Laboratory. Analyses are complicated by several biological, environmental, and operational factors such as variations in the volume of water strained through the net, extrusion, avoidance, sampling aliquots, etc. In general, the consequence of the interplay of such factors on the sampling program is to vary the \"effective size\" or efficiency of the samples.\nThe techniques under investigation are based upon the observations that 1) the log-normal and negative binomial distribution coincide for large means, and 2) in low mean conditions the negative binomial and Poisson log-normal (based on Poissonian variability around log-normal means) are virtually indistinguishable. Thus it appears that the nega- tive binomial as a discrete distribution offers promise as a general technique for an analysis of data of this kind.\nSeveral computer programs utilizing this model have been completed both for general application and more specifically for analysis of CalCOFI survey data. A draft manuscript is nearly complete with several examples of its application to a variety of statistical problems.\nSTOCK AND RECRUITMENT\nPaper Describing Maturation and Spawning of Pelagic Mackerel in Captivity Nears Completion\nMr. Roger Leong, Fishery Biologist at the La Jolla Laboratory reports that he has nearly completed a first draft of a paper entitled \"Matura- tion and spawning of Pacific mackerel in captivity.\" The paper describes the maturation of mackerel under different photoperiod-temperature con- ditions in the laboratory and the effectiveness of three hormones for inducing spawning. Mackerel matured in the laboratory under photoperiods ranging from 4 light 20 dark to 16 light 8 dark and at temperatures from 15° to 19º C. The fish matured fastest at 19º C but became unhealthy and gradually died off. Fish which were matured more slowly at 15º C were healthier. Of these some remained mature during the off spawning season\n9\nand could be spawned with gonadotrophic agents. Thus, the Pacific mackerel which is a seasonal spawner can now be spawned the year round to provide live larvae for stock and recruitment experiments. Three hormones: crude salmon pituitary extract, human chorionic gonadotropin, and gonadotropin from pregnant mare serum were all unsatisfactory for inducing spawning when used separately. Only when these are used in combination were they effective in inducing satisfactory spawnings. Two successful combinations were salmon pituitary or human chorionic gonado- tropin followed 24 hours later with gonadotropin from pregnant mare serum.\nManuscript in Preparation Describes Effect of Food Deprivation on the Histology of Early Anchovy Larvae\nDr. C. O'Connell, Fishery Biologist at the La Jolla Laboratory, reports the preparation of a manuscript this month describing the effects of food deprivation on the histology of early post yolk-sac anchovy larvae is in progress. Analysis of 12 histological variables indicates that the scores for three of them are strongly associated with food deprivation, and that another three are moderately associated. A scoring system appropriately weighted for these variables should permit reliable estimates of the condition of individual larvae on a scale of healthy, emaciated, or severely emaciated. Estimation of the weighting factors is nearly completed.\nExamination of somewhat older anchovy larvae from food deprivation experiments has recently been started. It appears that the histological criteria of condition will be much the same as for the early larvae.\nDr. J. Hunter, Fishery Biologist at the La Jolla Laboratory, reports that Harold Dorr, Biological Aid, has completed the construction of an apparatus designed to measure the effects of predation by fishes on eggs and larvae of the northern anchovy. Experiments are expected to begin next month.\nDr. Hunter and Ms. Sanchez continued studies of the ecological impli- cations of a diel rhythm in inflation of the air bladder of the northern anchovy larvae, and on the feeding ecology and predatory capacity of the Pacific mackerel. Preliminary studies on predation by Pacific mackerel indicate that the mackerel larvae develop the ability to eat 3.8 mm yolk-sac anchovy larvae by the time they reach 7 mm, and by the time they reach 15 mm they are able to feed on anchovy larvae up to 13 mm long.\nMicrodistribution of Food Organisms Important to Larval Fish Investigated\nIn an effort to describe the phenomenology and dynamics of variations on small distance and time scales of food organisms which are important to\n10\nanchovy and other fish larvae, members of the scientific party headed by Dr. Robert Owen, Oceanographer at the La Jolla Laboratory, conducted a 5-day investigation aboard the NOAA research vessel David Starr Jordan 2 miles off Cardiff-by-the-Sea, California. A current meter array was launched on September 23 to give current speed, direction, and shear in the thermocline during the 5 days of observation, after which \"short burst\" series of measurements were made using the STD, profiling pump, and microprofile sampler. Measured were plant pigments, size distri- bution and concentrations of larval fish food particles, nutrients, salinity, and temperature into the thermocline. Special attention was paid to the plant pigment maximum: samples taken 20 cm apart vertically in the chlorophyll maximum layer showed surprisingly large variations in particle and chlorophyll concentrations. Analysis of current meter re- cords and STD profiles may yield estimates of the diffusion which these layers must overcome to persist as layers for the periods observed. Addi- tionally, transects using STDs and XBTs were made across the shelf from where our own current meters were located toward shore where two other placements of current meters had been made by Dr. Terry Hendricks of the Southern California Water Research Project. Analysis of the transects and of the current records should yield a view of shelf circulation which will help understand the displacement of food and larval transport in this nearshore regime.\nStudy Continues on Histological Changes in Jack Mackerel Larvae Caused by Starvation\nMs. Gail Theilacker, Fishery Biologist at the La Jolla Laboratory, has completed a second set of rearing experiments designed to study the histological changes caused by starvation in jack mackerel larvae. A concentration of mackerel eggs was located, while aboard the David Starr Jordan, about 10 miles off San Diego in 18℃ water. The eggs were col- Tected, returned to the aquarium at the La Jolla Laboratory and the lar- vae reared at 15℃. A few mackerel larvae, also collected in the plankton hauls, were sorted and preserved aboard ship. The condition of the sea- caught larvae will be compared histologically to laboratory reared larvae (fed and starved) to determine the incidence of starvation and to evaluate whether starvation is one of the major causes of larval mortality.\nIn Ms. Theilacker's experiments, the jack mackerel larvae started feeding on day 6 (hatching = 0) and yolk and oil absorbtion were complete by the 8th and 9th day. Older larvae, which had been feeding for 5 days, were transferred to filtered sea water, deprived of food, sampled daily, and preserved. To date, a daily series of feeding larvae at three temper- atures and two feeding regimes and of starving larvae at three temperatures has been collected. A series was also frozen for otolith studies by David Kramer, Fishery Biologist.\nA manuscript on the transfer of aerosol chlorinated hydrocarbons into sea water was completed by Dr. Scura and Ms. Theilacker and is out for re- view. Work continued on a manuscript describing the transfer of chlorinated hydrocarbons in a three step marine food chain.\n11\n* * * * *\nDr. Edward Scura, Physiologist at the La Jolla Laboratory, has completed sea trials of a modified Coulter Counter Model A which was designed to continuously count flow rates of particles in the 40 to 400 um size range from sea water that is pumped onboard ship with a submersible pump. A portion of the sample stream is diverted through the Coulter Counter as the pump is lowered through the water column. Using this technique, it is possible to get a vertical profile of the relative concentration of organisms in a size range which is suitable as food for young larval fish.\nThis technique is being tested as part of a larger effort to detect patchiness of larval fish food organisms in nearshore waters off southern California. The apparatus was tested aboard the David Starr Jordan during a cruise this month headed by Dr. Robert Owen which began the study of larval food microstratification in nearshore waters. Although the equipment worked well at sea, no patches of orga- nisms were detected in the area under study. The concentration of micro- nauplii appeared to be fairly uniform at depths down to 30 m.\nA surface skimmer designed by James Alexander, Biological Technician, was also tested on this cruise but unfortunately the pump used with this apparatus cavitated and the resulting bubbles were detected by the Coulter Counter making it impossible to count particles.\nZooplankton Indicators and Predators on Fish Larvae Investigated\nDr. Angeles Alvariño, Fishery Biologist at the La Jolla Laboratory, completed a first rough draft manuscript this month which is a review of predation in the plankton realm, mainly on fish larvae. This covers the subject in several chapters :\n1) A general account of predation, focused on loss of fish larvae due to predation.\n2) Detailed information on the food of Chaetognatha, Siphonophorae, Chondrophorae, Medusae, Ctenophora, with data on other zooplankters feeding on fish larvae.\n3) A discussion on competition of zooplankton with fish larvae for food. Data on high and low abundance of predation zooplanktonic species are analyzed for certain regions and is discussed and related to the possible effect predation on fish larvae may have on subsequent year classes.\n12\nThe Schlieren System continues to be developed at the Southwest Fisheries Center by Dr. John H. Taylor of UCSD under a grant from the National Science Foundation. Significant improvements to the device have resulted from the acquisition of special high-resolution lenses for the still and motion picture cameras. These lenses permit utili- zation of the maximum film area for each format and thus serve to optimize the information content of the frames. The system is pre- sently so efficient in its use of luminous flux that very brief exposures are possible (<1 m sec) even on the slowest, highest-resolu- tion films.\nOceanic Fisheries Resources Division\nPORPOISE/TUNA\nNMFS Charters Two Tuna Purse Seine Vessels\nto Test Porpoise-Saving Gear and Methods\nAn important element in the NMFS program on tuna/porpoise interaction is the on-going research to develop fishing methods and gear technology which would reduce the incidental mortality of porpoises in the yellowfin tuna purse seine fishery. Mortality reduction research has concentrated on mechanisms for reducing mortality if and when porpoise contact the net and reducing the probability of contact through minor changes in gear and procedures. These measures include 1) a \"porpoise apron\" to improve the net backing down procedure, 2) the use of speedboats to prevent net col- lapse, 3) use of fine-mesh webbing to prevent mortality due to entangle- ment, 4) design of a new large-volume purse seine which can safely con- tain large catches of tuna and porpoise, 5) anti-torque purse line to prevent roll-ups of the net and finally, 6) a \"porpoise grabber\" to as- sist rescuers in removal of live porpoise from the net.\nGenerally, mortality reduction techniques are tested initially on commercial tuna purse seiners that are chartered by NMFS. On September 18 the NMFS entered into a contract with the tuna vessels, Eastern Pacific, and Bold Contender to test an extended porpoise apron, use of fine mesh webbing to prevent entanglement, and several versions of the porpoise grabber.\nAboard the Bold Contender are Messrs. Richard McNeely, gear expert with the NMFS Northwest Fisheries Center, James Coe, Fishery Biologist and Frank Ralston, of the La Jolla Laboratory. The Eastern Pacific,\n13\nwhich departed on September 29, has Mr. Jerry Jurkovich, Gear Expert with the Northwest Fisheries Center, Biological Technician David Holts and Dr. George Losey, a Behaviorist from the University of Hawaii aboard. Both vessels are expected to return to San Diego before December 20.\nFeasibility Studies in Progress for Aerial Survey of Porpoise Populations\nIn 1972, the NOAA Tuna/Porpoise Committee strongly recommended that an aerial survey be conducted to establish the density of porpoise popu- lations under exploitation by the tuna purse seine fishery. Subsequently, under contract, Dr. John Taylor of the University of California, San Diego, studied the theoretical feasibility of such a survey using high altitude, photographic reconnaissance techniques. In January-February 1974, a low altitude, visual recon type of survey was conducted. While coverage was limited, the results combined with estimates obtained from tuna vessels were used with the aid of line transect theory, in the recent Porpoise Progress Report.\nPresently, Dr. Eric Barham, Special Assistant for Marine Mammals at the La Jolla Laboratory, is investigating the various options and alternatives for conducting an aerial survey of pelagic porpoise popu- lations about January-March 1976. An optimum effort for an aerial sur- vey of pelagic porpoise populations would represent about 30 flights in a grid pattern covering about 90% of the historical fishery within the Commission Yellowfin Regulatory Area. Several longer flights would ex- tend about 1,000 miles offshore. A total flying time of about 300 hours would be necessary over a period of about 40 days, and about 41,000 miles would be flown.\nA more limited effort involving fewer flights at lesser distances from shore could be done by other alternatives. Dr. Barham is continu- ing to contact various agencies in NOAA to obtain information on avail- ability of suitable aircraft and estimates of cost, although at present there are no assurances that monies will be forthcoming to support an aerial survey.\nTUNA RESOURCES\nLength and Age Composition of the Atlantic Catch of Yellowfin and Skipjack Estimated\nA catch and length frequency data base for Atlantic tunas has been recently completed and used to estimate the length and age composition of skipjack and yellowfin tunas in the catch from the entire Atlantic Ocean. Mathematician Al Coan and Fishery Biologist Gary Sakagawa at\n14\nLa Jolla have used the data and estimates in two papers, 1) Length and age composition of yellowfin tuna from the Atlantic Ocean, 1966-73, and 2) Length and age composition of skipjack tuna from the Atlantic Ocean, 1968-73, which will be presented at the upcoming ICCAT ( International Commission for the Conservation of Atlantic Tunas) meeting in Madrid.\nResults from their analysis of yellowfin tuna show that the surface fishery in the Atlantic catches mostly Age 1 yellowfin and the longline fishery catches mostly Age 2 and 3 yellowfin. In the eastern Atlantic, longliners catch mostly Age 3 yellowfin, whereas in the western Atlantic they catch mostly Age 2 yellowfin. This difference appears to be caused by the presence in the eastern Atlantic of a well-developed fishery which takes great amounts of Age 2 yellowfin in competition with the longline fishery, whereas in the western Atlantic the surface fishery is not well-developed and not in strong competition with the longline fishery.\nVirtually all of the Atlantic catch of skipjack is caught by the surface fishery. Analysis of the length and age composition of the catch by Mr. Coan and Dr. Sakagawa indicates that Age 1 fish have dominated the catch in all years, and most of the catch has been from the eastern Atlantic.\nReview of Natural Mortality Rates of Tunas Completed\nAn evaluation of natural mortality rates for tunas has been com- pleted by Fishery Biologist T. Murphy at the La Jolla Laboratory. A review of the literature was made to obtain values of the rate of natural mortality (M) and growth (K, of the von Bertalanffy growth equation) for five species of tuna: albacore (Thunnus alalunga), bigeye (T. obesus), northern bluefin (T. thynnus thynnus), skipjack (Katsuwonus pelamis), and yellowfin (T. albacares). The apparent relation between K and M was analyzed by 1) assuming M increases at a constant rate with increasing K, and 2) M increases at an increasing rate with an increase in K. The limits of M from the relationships were:\nAlbacore: < . 19 < M .25 Bigeye: <. 38 ≤M . 48\nBluefin: <. 08