THE DISTRIBUTION, ABUNDANCE, AND FEEDING ECOLOGY OF FOUR SPECIES OF FLATFISH IN THE VICINITY OF ELKHORN SLOUGH, CALIFORNIA
LIBRARY MOSS LANDING MARINE LABORATORIES P 0. Box 450 Moss Landing, California 95039
A Thesis
Presented to the Faculty of the Department of Biology
San Jose State University
ln Partial Fulfillment
of the Requirements for the Degree
Master of Arts
By
David Anthony Ambrose
December, 1976 TABLE OF CONTENTS
Page
LIST OF TABLES • • v
LIST OF FIGURES. • • vii
ACI INTRODUCTION • • • • • • • • • 1 ' HATERIALS AND HETHODS. • • • • 5 f Field and Laboratory Procedure. • • 5 Statistical Analysis Procedure. . • • • • • 13 RESULTS. . • • . • • . . . • . • • 16 Distribution and Abundance, • • • • • 17 Horphological Relationships • • 20 Cumulative Prey Analysis. . • • • 22 Variation of Diet with Size and Season. • • • • • 22 Feeding Frequency • • • • • • • • • • • • • 23 Feeding Habits·and Hajor Prey Groupings • 24 Dietary Variations Be tHe en Localities • • • 26 Trophic Diversity • • • • • • • • . 33 Dietary OverlaP • • • • • • • 35 Electivity, • • • • • • 36 DISCUSS ION . . . • • • • 41 Distribution and Abundance. 41 Horphometric RelationshiPs. • • • • 43 Cumulative Prey Analysis. • • • • 46 Dietary Variation '"i th Size and Season. 47 Feeding Frequency .• . . ' . • 48 Feeding within a Location 4g iii Feeding Strategies ••...... 49 " Flatfish Feeding Habits with Resoect to Prey Natural History ...... • . • . . 50 Troohic Diversity: Generalists vs. Specialists. 55 Dietary Overlap • • • • • 58 Electivity. • • • • 59" APPENDIX. • • • 109 LITERATURE CITED. • • • • • • • • • • • • • • • • • • 115 iv LIST OF TABLES Table Page 1. Seasonal percent abundance and mean number per otter trawl .tow of the major flatfish species by locality. • • • • 61 2, Fish collection locations, methods, and times ...... • • • • 62 3. Mean ratios, X, and standard deviation values, SD, for the standard length to the length of the maxillary on the ocular side • • , •• . . . . • • • 63 4. Mean ratios, X, and standard deviation values, SD, of the standard length and stomach lengths to the length of the entire gastrointestinal tract • • • • • . . 64 5. Kendall tau rank correlation coefficients of Index of Relative Importance values of prey categories betHeen different size classes within a flatfish species by station and season . . . . • • • • • 65 6. Mean Kendall rank correlation of Index of Relative Importance values of prey categories among seasons by soecies • • 66 7. Percent similarity indices for the combined prey of all individuals of each flatfish category between adjacent stations. • • • 67 v 8. Percentage of unique prey categories between adjacent localities by flatfish grouping , •• . . • • • • • • • 68 9, Trophic diversity summary, • • • • • • • 69 10. Index of ·overlap, __ CA• between flatfish categories within a locality •••••• , • 70 vi LIST OF FIGURES Figure Page 1. Map of study area • • , • • • • • • • • • • 71 2. Length frequency histograms for Platichthys stellatus by season and locality. , , , • • • • • • • • • • • 73 3, Length frequency histograms for Parophrys vetulus by season and locality...... • . . , • • • • • • • 75 4. Length frequency histograms· for Citharichthys stigmaeus by season and locality. • •• • • • • • • 77 s. Length frequency histor~ams for Psettichthys melanostictus by season and locality. • • • • • • • • • 79 6. Linear regression of the maxillary length to the standard length by species • ••••• o • o •• • • • • • 81 7. Linear regression of the gastrointestinal tract length to the standard length by species. . . • . . . • . • • • • • • • 83 8. Linear regression of the gastrointestinal tract length to the stomach length by species. • • • • • • • • • • • • • • • 85 9, The cumulative number of prey categories from the pooled number of fish for each vii flatfish category at the Kirby Park and Dairy stations, • • • • • • • 0 • • • • • 87 10. The cumulative number of prey categories from the pooled number of fish for each flatfish category at the Bridge and Ocean stations. • • • • • • • • • • • • • 89 11. The numerical percent composition of the major prey groupings for Platichthys stellatus, Parophrys vetulus, and Citharichthys stigmaeus by station. • • • • • 91 12. Percent composition in.number (% N), volume (% V), -and frequency of occurrence (% F.o.) of prey categories with Index of Relative Importance values ~50 for Platichthys stellatus, Parophrys vetulus, and Citharichthys stigmaeus by station. • • • • • • • • • • • • 93 13. Percent composition in number (% N); volume:(% V), and frequency of occurrence (% F,O,) of prey categories with Index of Relative Importance values ;;:.. 50 for Psettichthys melanostictus at the Ocean station. • 0 • • • 95 14. Frequency histograms of individual trophic diversity for Platichthys stellatus, Parophrys vetulus, and Citharichthvs stigmaeus by statron. • • • • • viii 15, Frequency histogram of individual trophic diversity for Psettichthys melanostictus at the Ocean station...... 99 16, The relationships betl~een the mean evenness component (J) and the mean richness component (H) of individual trophic diversity for each flatfish category at the Kirby Park and Dairy stations, • , • , , , 101 17. The relationships between the mean . evenness component (J) and the .. mean richness component (H) of individual trophic diversity for each flatfish category at the Bridge and Ocean stations, • • 103 18, .Diagram of the relative abundance of the 10 most numerous items in the environment as measured by benthic cores (% P), the relative abundance of the 10 most numerous prey items in the diets of each flatfish category (% R), Electivity (E), and the Percent Similarity Index value (% SI) between the relative composition of all items in the benthic cores and in the diets of each flatfish category for Platichthys stellatus, Paroohrys vetulus, and Citharichthys stigmaeus at each station. , ..• 105 ix 19. Diagram of the relative abundance of the 10 most numerous items in the environment as measured by benthic cores -(% P), the relative abundance of the 10 most numerous. prey items in the diets of each flatfish category(% R), Electivity (E), and the Percent Similarity Index value (% Sl) between the relative composition of all the· items in .the benthic cores and in the diets of each flatfish category for Psettichthys melanostictus at the Ocean station. • ...... 101 X ACKNOWLEDGEMENTS I wish to express my sincere thanks to those who generously contributed assistance and advice during the course of this study. Dr, Gregor Cailliet provided valuable guidance, constructive criticism and encouragement during all stages of the research and writing. .All the members of my master's committee have contributed valuable sugges tions. The field work could not have been accomplished - -without·-many hours of capable-assistance ·by- Brooke Antrim and many other.students at Moss Landing Marine Laboratories, I am greatly indebted to Chris Jong, Peter Slattery, and John Oliver for their expert identifications of many invertebrate prey items and also for providing the benthic invertebrate availability data, This investigation Has funded by a grant from the Pacific Gas and Electric Company. xi INTRODUCTION Estuaries and coastal embayments are extremely pro ductive and have a major nursery function in that young marine fish often aggregate in these bodies of water (Orcutt, 1950; Ketchen, 1956: Gunter, 1957; Haertel and Osterberg, 1967); therefore, they should be studied more intently. Man's activities·are increasing the stress on these delicate environments, making it imperative that more be learned about the ecological. processes involved . in-order-to better evaluate .the_effects that man's. in fringements are having on these unique·areas. The fish fauna inhabiting Elkhorn Slough and the Monterey Bay area have been well documented (Browning ~ al, 19721 Ku_kowski, 1972) and the majority of the teleost fish inhabiting the slough are in the families Engraulidae, Atherinidae, Embiotocidae, Gobiidae, Cottidae, Bothidae, and Pleuronectidae. The flatfish (Bothidae and Pleuronectidae) were selected for this study since they are abundant, easily captured (Allen, 1960) 1 and appear to form an important ecological assemblage associated with the bottom. The species investigated starry flounder, Platichthys stellatus ~allas 181ij; English sole, Parophrys vetulus Girard 1854; sand sole, Psettich thys melanostictus Girard 1854; and speckled sanddab, Citharichthys stigmaeus Jordan and Gilbert 1882 -- have been the subject of many previous papers ·and much is known . 1 2 about the life history of these species. Starry flounders are among the most abundant pleuronectid flatfishes from Santa Barbara, California to Arctic Alaska and the Sea of Japan in waters less than 275 m (Miller and Lea, 1972). Males and females generally-become mature during their secorid and third years respectively and spawn in shallow water in Monterey Bay from November through February with the peak season in December and January (Orcutt; 1950). They are euryhaline and the young are known to occur in rivers in salinities as low as .02 parts per thousand. · - (Hubbs 1 -~ 1947 1 Haerte 1 ·and 0s terbet-g;c 1966), ":: The--feeding habits -of: this species in Monterey Bay were qualitatively described by Orcutt (1950). Starry flounders appear to feed primarily during the day (Miller, 1967), English sole are also very abundant pleuronectid flatfish from San Cristobal Bay in Baja California, to Unimak Island in western Alaska, between the surface and -about 550 m of water (Forrester, 1969), Male and female English sole mature in their second and third or fourth years respectively (Ketchen, 1956) and the spawning period in-Monterey Bay is similar to the January to March spaiYning season in British Columbia (Taylor, 1946). Spawning grounds are usually in relatively sheltered water at a depth of approximately 60 to 80 m where the bottom is soft mud (Ketchen, 1956). Sand sole are common pleuronectids in water less than 183 m over sandy bottoms from southern California to the 3 Bering Sea.(Hart, 1973). The spawning period for these fish is variable, since they have been reported to spawn as early as January in Puget Sound (Smith, 1936) and as late as July in Sydney Inlet (Manzer, 1947). The feeding .habits of adult sand sole in Puget Sound were investigated by-Miller (1967).and he found that. this species is a diurnal feeder • .Speckled sanddabs are.·small bothids that are abundant from.Magdalena Bay in Baja California to southern Alaska (Miller and Lea, 1972). Their.normal bathymetric range ··extends ·from a: depth of·-less .than ·.1- m-.to'-about. 90 m. ·.·This -species .. is- probably the most abundant--demersal· fish inhab iting the shallow, sandy bottoms along the California coast. Speckled sanddabs become ripe in their second year of life and spawn in the· spring and summer months along the California coast (Ford, 1965). Ford also found that these fish also feed mainly during daylight hours. The feeding behavior of'flatfish has long been a subject of investigation (Bateson, 1890: Stevens, 1930; Bregnballe, 1961; Pearcy, 1962; de Groot, 1969; Olla, Wicklund and Wilk, -1969; Frame, 1974; Levings, 1974); however, until this time, no attempt has been made to deal with the trophic interactions of young members of these four species in a quantitative, ecological study. Huch of the literature dealing with trophic ecology has not concerned fish as subjects, but most of the concepts discussed, such as trophic diversity or resource breadth (Hurtubia, 1973) and food overlap (Horn, 1966), are • equally applicable to fish studies. 4 The objectives of this study Here to provide information on the distribution, abundance, and feeding habits of the four.major species of flatfish inhabiting Elkhorn Slough and the shallow sandy shelf of Monterey Bay near the mouth of the slough. The relationships betHeen morphology, trophic diversity, the degree of specialization, niche overlap, and interspecific competition among these fish were investigated. The feeding habits were also rela·ted to the availability of prey organisms in the environment in an effort to obtain information on the selectivity of feeding by each species. l'fATERIALS AND METHODS Field and Laboratory Procedures Elkhorn Slough lies approximately halfway between Monterey and Santa Cruz, California (Figure 1), and extends inland approximately 4 kilometers (km), with an axial len~th of about 10 km. The main channel-is approximately 10 meters (m) wide and has a depth of from 3 to 5 m (Smith, 1973), The drainage basin for Elkhorn Slough is only 585 km2 (W~ng, 1970). Sampling was conducted at three stations witqin the slough• Kirby Park, Dairy, and Bridge (Figure 1), and one (the "Ocean") just outside the slough in Monterey Bay, The Ocean sampling station was on the clean sandy s~elf on both sides of the entrance to the Hoss Landing Harbor aporoximately 200 m offshore between depths of 5 to 10 m. The Bridge station extended from the bridge at High~.ray 1 approximately 1 km into the slough and was up to 5 m.deep. The Dairy station was located 2 to 3 km into the slough with a water depth of about 4 m, The most inland station, Kirby Park, extended from 5.5 to 6,5 km into the slough ~ere the water was approximately 3 m deep. The main sampling technique emoloyed in this study was a small experimental otter_trawl (4.8 m head rope and 5,8 m foot rope,-with 38.1 mm stretch mesh in the body and 31.7 mm stretch mesh with a 12.7 mm stretch mesh liner in the codend), The trawl was pulled approximately 37 m behind a Boston Whaler 6 equipoed with a 40 horseoower Johnson outboard motor. Tows were made into the flow of the current at an estimated net speed of 1 kilometer per hour. Tows of five minute duration were made from August through mid-December 1974. The decrease in fish abundance during the winter months necessitated lengthening the dur- ation of the tows to 10 minutes so that a sufficient number of fish could be obtained for gastrointestinal tract content analysis. The 10 minute towing period was maintained for the remainder of the study (through October, 1975), A large . beach, seine. (approximately 80 m.. long. with 25,4-mrn_stretch -mesh in the body and 12.7 mm stretch mesh in the purse) was occasionally employed at each of the stations, The number of fish taken during five minute tows was doubled in order to standardize the results to a ten minute towing period, The percent abundance (% A) was calculated as the percentage that a species composed of the total flat- fish catch during a particular season at a particular station. The mean number of flatfish per 10 minute tow (N/T) was cal- culated for each soecies at each season and station (Table 1). Each station was sampled at least monthly (Table 2). Stations with lower abundance often had to be sampled more often in order to obtain an adequate number of fish for gut content analysis. Water temperature was taken before each tow with a bucket thermometer accurate to + 0,50 C. Salinity was measured by means of a Goldberg temperature compensated refractometer accurate to z 0.5 parts per thousand. The majority of the sampling was done between 7 0800 and 1600 hours and occurred at all tidal periods; however, several tows with the otte~ trawl were made at night.at various times of the year (Table 2), The fish that were captured were measured to the nearest mnL(standard length) and weighed to the nearest 0.1 gram (gm), Live flatfish captured in excess of the number required for gut content analysis were tagged with Floy internal anchor spaghetti tags and released. All the ·remaining fish were preserved in 1~~ formalin. No regurgi tation.was observed. The body cavities of these fish were ··injected· with· 10% ·formalin by. means 'of a· pressurized syringe (Congdon ~ _ll• .1:975) 1 . in order-. to ·ensure preservation of the gut contents. In the case of large specimens, the entire gastrointestinal tract and the gonads were removed and pre served in formalin. After fixation, the·smaller fish and the separated gastrointestinal tracts were soaked in water and transferred to 5~~ isopropyl alcohol before the gut contents were analyzed. The gut was surgically extracted by cutting at the eso phagus and.at the rectum. The connective tissue was removed and the stomach length and total gastrointestinal tract length was measured to the nearest millimeter, The gastro intestinal tracts were cut longitudinally and with the con tents intact, the fullness of the stomach was subjectively scored ass 0= empty; 1= 25%; 2= 5~~; 3= 75%; and 4= 1007. full (c.f. Tyler, 1970; DeWitt and Cailliet, 1972). State of digestion was scored as1 1= very finely digested, nothing 8 ·recognizable·; 2= medium· digestion, some recognizable parts; 3= some digestion, some undigested material; and 4= undi- ·gested, whole animals (c.f, Tyler, 1970). Prey organisms were located, identified to the lowest possible taxon, measured to :t 0,1 1\lffi and counted using a Nikon dissecting microscope equipped with an ocular micrometer.·· The contents on each gut were considered, as unity, and the percent volume contribution of each prey category was estimated by eye (c.f.-McHugh, 1940; Bray and.Ebeling, 1975). It was necessary to analyze the food material found along the entire gastrointestinal- tract due to the varying amounts of decomposition among the different·prey items. In many cases, prey items of all cate~ories (polychaeta, mollusca, and crustacea) could be identified even in the posterior regions of the intestine. The undigestible material ingested by these bottom feeding fish could be better esti mated by examtning the entire gut length. Sand sole and speckled sanddabs appeared to digest the majority of their food in their stomachs whereas in English. sole and starry flounders most of the digestion occurred in the intestine. Thus it was decided that the most equitable estimates of number and prey types eaten by all flatfish species would be achieved by analysis of the entire gastrointestinal tract. Fish were found with empty stomachs but their intestines were relatively-full of prey in recognizable condition, These fish were definitely not starving and it would have been misleading to classify them as having empty stomachs. 9 The large number of prey categories in varying states of decomposition and the large amounts of inorganic. debris consumed by some of the flatfish while feeding made any gravimetric or displacement estimates of prey category volume impractical. Since only one person assigned.all the estimates of prey volume, the subjective bias inherent in this method was at least consistent. The problems '~ith this procedure were further minimized by having a large number of estimates over a long time period. ·· The prey .were often fragmented, so counts had to be standardized. Each bivalve siphon was counted as an indi vidual (c.f. Bregnballe, 1961) and bivalve shells were counted by attached hinges. Polychaetes and crustaceans were counted by the heads. This standardization probably resulted in a rather conservative estimate of the actual number of prey. Voucher specimens of the prey items from each fish '~ere placed in a vial or jar and labeled inside and out with the code for the station, collection number, and number.for the individual fish, to be used for future reference if needed. Food items about which initial identification was uncertain were placed in separ~tely labeled containers for identifi cation by experienced invertebrate t_axonomists, A_random sample of the fish from each station and season was retained for further morphometric analysis_of the size, position, and shape of teeth; the number, size and shape of the gill rakers; and the size of the maxillary in relation to -the standard length of the fish. 10 Since different size classes of many species of fish have been shown to feed on different types of prey (Allen, 1942; Orcutt, 1950; Frame, 1974; Levings, 1974), the starry flounders (Platichthvs stellatus) were separated into three size classes for analysis of feeding habits: small (fish less than or -equal to.'99 mm sta.ndal'd length), medium (100 :. ·199 mm), and large ( 200 - 299 rnm), A fe'~ individuals larger than 300 mm were included in the 200- 299 mm category at the Ocean station due to the low abundance of this species and the l!;eneral··absence of· smaller starry flounders at that station. These size classes were selected-on the basis of the roughly quantitative study. by Orcutt (1950)·,-· which suggested that these groupings ·might have d:lfferent·•feeding habits. ·The speckled sanddab (Githarichthvs stigmaeus) were divided up into two size classes: small (fish less than or equal to 79 mm in standard length) and large (those-80 mm or greater). These size categories were chosen because Ford (1965) suggested that adults might eat some,vhat different foods than did juveniles, The English sole (Paroohrys vetulus) were similarly divided at 80 mm. Th:ls division was selected in order to better compare the feedi~g habits between the same size groupings of English sole and speckled sanddabs. The sand sole (Psettichthys melanostictus) were separated into·~ 150 mm and > 150 mm s:lze ~>;roupings for-dietary analysis. For the purposes of statistical analysis the data from the trawl collections and the gut content examina~ions were 11 grouped seasonally (November-January, February-April, May July, and August-October). These groupings were chosen because they corresponded \~ell with the changes in abundance and distribution patterns of the fish species, and·since these groupings roughly approximated the normal·climatic seasonality of the study area. The August-October 1974 and August-October 1975 seasons demonstrated similar patterns in the distribution and feeding habits of the fish;· therefore, fish from this season in both years were combined. In.order tO'determine if the number of gastrointestinal • ·-tracts-~examinedo·was sufficient--to--represent the---majority· of prey categories that \vere available to the fish in the . environment, the gut contents from each fish category at each station were randomly pooled and plotted against the cumulative number of prey categories. To compare the feeding habits of the flatfish in a general manner, the prey were divided up into 16 major groupingsz echiuroidea, polychaeta, miscellaneous annelida, copepoda, gammaridea, caprellidea, mysidacea, miscellaneous crustacea, bivalve siphons > 10 mm, bivalve siphons£:. 10 mm, ·bivalvia, decapoda, ostracoda, gastropoda,.fish, and mis- cellaneous. The numerical percent composition of each major prey grouping was calculated for all flatfish in each size category at each station, The prey availability data for the slough were taken from benthic cores that were taken at all stations along 30 m transects at approximately the -0.5 tide level (Nybakken, 12 1976). _-_The mean number of organisms per core at the Bridge station was based upon 52 stanpard size cores (height= 17 em; area= ,018 m2) taken at approximately bimonthly intervals from July 1974 through August 1975. The mean number of individuals per core at the Dairy station was derived from 12 standard.size cores taken in August 1975 and November 1975, The Kirby Park station had large amounts of organic debris which necessitated the use of smaller sized cores (height= 17 c~, area= ,OOS m2), The mean number of prey items .per--core- from this station was based on data. from 49 -_7e·small--size-.-cores _-,taken· at-approxima tely~b-imonthly- -int:e~vals from July~l974--ehrough August 1975. The prey availability data for the Ocean station-were derived from the mean number·of individuals per core for the- 25- most--numerous species based up(m 278 standard sized cores made at depths from 9-18 m from June 1971 through June 1975 (Oliver~ al, 1976). l3 Statistical Analysis Procedure 'The· Index of Relative Importance (IRI) of each prey ·category was calculated for food-containing fish as a· combination of its numerical and volumetric importance and frequency of occurrence (c,f. Pinkas ~ al, 1971), The numerical importance ·(%N) of a particular item was the percentage ratio of its abundance to the total abun- dance of all'items in the contents, The volumetric im- portance (%V)-was its average percent estimated volume, The percent frequency of occurrence was the percentage of ' ·. f-ish-ocontaining at -least- one- individual .. of a. par.ticular -·prey category. The IRI was calculated-by summing the numerical and volumetric percentage values and multiplying by the percentage frequency of occurrence: IRI = (%N + %V) %FO The Kendall coefficient of rank correlation, tau, (Kendall, 1962) was employed to compare the .ranks of IRI values for prey of different size classes of fish within a species, The means of tau values of prey category rankings .for the various flatfish groupings between seasons within a locality were also calculated, The Brillouin equation for diversity (H) was used to measure the trophic diversity found in individual fish of the various flatfish categories: where N is the total number of prey individuals and N1 is the number of individuals in the 1th prey category (Brillouin, 1960), The contents of each gut were treated 14 as a finite collection because the patchiness of available prey and the feeding selectivity of the fish made it im- . possible to obtain random samples of the available prey population (Hurtubia, 1973). The evenness component of diversity (J), .which measures total numbers of prey individuals (N) distributed among the prey categories (S), was calculated• J = H/Hmax where and r = N-S * (Pielou, 1966), The Percent Similarity Index, %SI (Silver, 1975), was calculated· in an effort to.measure:the similarity-of,prey types for a species of fish between adjacent stations and to describe the re~ationships between the proportion by number that all prey categories composed, both in the diet of the fish and in the environment. This index was simply the sum ~f the smaller value of the pair of proportions in a comparison of two arrays of prey categories. A value of zero indicates no similarity and a value of 100 indicates perfect agreement. The percentage of unique prey categories between adjacent localities was also calculated and consid- ered to be high if L. 35% and low if < 35%. The trophic overlap measure of Horisita (1959) as modified by Horn (1966) was employed to show the overlap in exploitation of alternative food sources from within the same locality 15 where Pix was the proportion that the ith prey category composed of the sum of the IRI values for fish grouping x and Piy was the proportion that the ith prey category composed of the sum of the IRI values for fish grouping y. The overlap coefficient, C), , varies from 0 when the samples are completely distinct.(containing no food categories in common) to 1 when the samples are identical with respect to proportional importance of food.category composition. The index of dietary overlap values were divided up into three categories for the purpose of analysisz high, Cx >.70; ·-.intermediate; _C_>.=:::_.10; and lm-r,_C.>.< .10. The relationships between c.the -availability of the prey in the environment and the proportions of the types of prey in the fish's diet were expressed using the Electivity Index, E (Ivlev, 1961). E = (Ri-Pi)/(Ri+Pi) where Ri or 1-R was the relative content of any ingredient in the ration of the fish expressed .as a percent by number of the individuals in that particular prey category to the total number of individual prey items. Pi or %P was the relative value of the same ingredient in the food complex of the environment as measured by the proport.ion of the total mean number of organisms per core, Electivity values range from +1 to -1, with positive values indicating pre ference and negative values indicating "avoidance"·. A value of zero means that the item t-ras consumed in exact proportion to its relative abundance in the prey community, RESULTS During the course of this study, 146 otter tra,•l and 7 beach seine samples, made from August 1974 through October 1975 resulted in the capture of 369 Platichthys stellatus (starry flounder), 655 Paroohrys vetulus (English sole), 692 Citharichthys stigmaeus (speckled sanddab), and 75 Psettichthys melanostictus (sand sole). A detailed description of the study area was provided from a SCUBA diving survey of the slough from May to June, 1975 (Nybakken et-- al, 1976) and sediment size frequency analysis at each station in February, 1976 (J• Oakden, unpubl. .data). The bottom at the Bridge station. was- com- posed of muddy sand (mean grain size 2,35 microns), shells, rocks and broken pilings. At the Dairy station the bottom was softer silty clay (mean particle size 1.81 microns) with many shell fragments in the sediment. The bottom at the Kirby Park station was deeP, soft mud (mean-partic.le size 0,36 microns) with hard debris such as rocks and cement blocks scattered about. Water turbidity was always high at Kirby Park; visibility usually being much less than 1,0 m (secchi disc). Visibility varied considerably with the season and the stage of the tide at the other two slough stations; but the secchi"disc measurement usually ranged between 1,5 and 4.5 m (Nybakken ~ al, 1976). The water throughout the year was generally clearer at the Ocean station than it was in the slough. 16 17 Distribution and Abundance Definite seasonal patterns were apparent in the distri bution of the several species of flatfish (Table 1). In general, the abundance of Platichthys stellatus (starry flounder) did not change very much throughout the year within a locality, Starry flounders were abundant at the most inland station, Kirby Park, throughout the year and they numerically dominated the catch at this station in every season except May;_July. The starry flounders '"ere less abundant jat the Dairy station: however, they were still .the mos~ abundant flatfish taken at the Dairy in the November- January and February-April seasons. The number of starry flounders taken per tow at the Bridge station was higher than at any other station throughout the year, but the other species of flatfish were also more abundant there and the starry flounders were never the most abundant flatfish at this station at any season during this study. Fewer-.e starry flounders were caught per tow at the Ocean than at any other locality in all seasons and this species never was the most abundant flatfish taken at this station in any season. Parophrys vetulus (English sole) demonstrated the most dramatic seasonality in distribution of all the flatfish studied (Table 1). _ English sole were not taken from a:ny locality during the November-January season, Their numbers increased steadily at all stations during the February-April season and by the Hay-July season they were the most abundant flatfish caught at every station except the Bridge, In Hay- 18 July,--the English sole were particularly numerous at Kirby Park. The tendency -for English sole --to be concentrated in the inland portions of the slough during the May-July season was dramatically reversed in the August-October -season when the majority of these fish were collected at the more sea ward locations in the_ slough. There were no English sole taken in any of the 12 otter trawls made during the August October season at Kirby Park in two --consecutive years, and fewer•-' English sole were taken per tow at the Ocean station than from any other slough-locality for eachseason. --The--most striking--feature of--'-the -distribution,_of Ci:tharichthys _stigmaeus (speckled __ sandda:b) was their virtual absence in all seasons from the most inland station, Kirby Park (Table 1), They w-ere also not very numerous at the Dairy station with the exception of the August-October season. The center of abundance for this species was at the Bridge station where it numerically-dominated the flatfish catch in all seasons. The number of sanddabs caught per tow decreased at the Ocean station from what it was at the Bridge station; however, this species was still one of the most --abundant - flatfish caught at the Ocean station throughout the year. Psettichthys melanostictus (sand sole) were caught exclusively at the Ocean station, never having been taken in any of the 99 otter trawls or 5 beach seine sets made in the slough. The largest number of sand sole per tot> were taken during the August-October season and the fetvest 19 during November-January (Table 1). In. the February-April and May-July seasons, the catch tvas stable at about 1. 2 sandsole per ten-~inute tow, rhis species made up the largest percentage of the flatfish catch only during the August-October season. --The distribution of the starry flounders varied .with the size of the fish (Figure 2). Starry flounders less than 80 rom were taken-infrequently and only from Kirby Park and starry flounders less than 200 rom in standa~d length were also concentrated-at this locality. The mean standard lengths ..:of "this species were· significantlycsma:tler -(t-test, p= <.001) -at ·Kirby Park than at any of the other stations throughout the year. The majority of the starry flounders caught at the other slough stations were about 235 rom and still immature, probably in their first and second years (Orcutt, 1950), Mature flounders , greater than 300 rom (Orcutt, 1950)i were most often captured at the Bridge station, The average sizes of the starry flounders taken at the Ocean and Bridge stations ''ere similar; however, the Ocean station had fewer starry flounders shorter than 200 rom standard length. English sole utilized the slough from February through October, during the first year of their lives (Smith and Nitsos, 1969) •.. They. appeared to concentrate in the most inland portions of the slough during the Hay-July season when their average size was about 76 mm (Figure 3). Very few Englis-h sole larger than 100 mm were ever taken at Kirby 20 Park. In the August-October season,·the average size of this species was about 102 mm and they were concentrated in· the most seaward regions of the slough, ·while none were taken at Kirby Park. No English sole larger than 140 mm were ever caught in the slough. English s.ole larger than 250 rom were takenat the Ocean station during the February-April and August-October seasons. The size frequency distribution of the speckled sanddabs did not change very.much during the year at any station (Figure 4). Immature fish,.less than about 78 mm in standard ~-1-Emgth--(-Ford ,---1965), ·composed t:he--majority-of- -the catch- at the.Dairy.and Bridge stations. _Larger, more mature fish.were more frequently caught at the Ocean station, Sand sole were taken at the Ocean station throughout the year (Figure 5). Recently metamorphosed individuals '~ere caught early in the August-October season. The majority of the sand sole caught were less than 250 mm and immature (Manzer, 1947) , Morphological Relationships A comparison of the morphological relationships among the flatfish revealed that each species was variously adapted ·to exploit different food resources. The ratio of standard length to length of ocular side maxillary was significantly unique (t-test, p =<.001) among all species of flatfish (Table 3), The 26 sand sole measured had proportionately 21 the- largest-mouths, with the 32 speckled sanddabs being second largest, The measurements of the 26 English sole -and 25-starry flounders indicated their mouths were smaller proportionately than. those of the starry flounders, The sizes of the mouths of the starry flounders and English sole were closer to each other than to either of the other t\-10 flatfish species, Gastrointestinal tract length also varied significantly (t-test, p=_.<.OOl) -between each-pair of the flatfish studied (Table- 4), -The starry flounders had by far the longest gastrointestinal tract, __ equalling about 13cr/. of the standard length. -The English sole and speckled sanddabs had. inter mediate gastrointestinal tract lengths, respectively 94% and 86% of their standard lengths, The sand sole had the shortest gut, equal to only 75% of the standard length, Stomach length as a proportion of total gastrointestinal tract length was also significantly different (t-test, p= .001) for each of the flatfish species (Table 4). The length of the stomach in all of the flatfish was inversely correlated with the length of the gastrointestinal tract, that is, those fish that had the longest gastrointestinal tract had propor tionately the smallest stomach and vice versa, _ The least squares linear regression and correlation coefficients for the relationships between the maxillary length and standard length (Figure 6), the gastrointestinal tract length and standard length (Figure 7), and the gastro intestinal tract length to stomach length (Figure 8) demon- 22 strated that in all species the morphological relationships were strongly linearly correlated. Cumulative Prey Analysis The-leveling off of the number of cumulative prey categories for all the species and size groupings of flat fish taken from the slough stations, with the exception of the .starry flounders.599 nun at Kirby Park (Figures· 9 and 10) indicated that the majority of the utilizable prey categories '"ere adequately sampled by the number of fish guts examined. The Ocean station's potentially.utilizable prey were probably not sufficiently well represented for the English sole, the large starry flounder, and the sand sole > 150 nun. A suf ficiently large number of these fish was sampled 1 hmvever 1 to demonstrate the feeding relationships among the flatfish caught at-this station. In general, the number of potential prey categories utilized by the fish increased from Kirby Park to the ocean and the number of fish guts that were re quired to give a good estimate of all the types of prey eaten also increased in the same manner. Variation of Diet with Size and Season The Kendall rank correlation comparison of prey Index of Relative Importance values demonstrated that dietary changes with size were more pronounced in some of the flatfish than in others (Table 5) 1 and that there was no significant 23 change in the relative importance of the prey categories for any of the fish groupings at any location throughout the year (Table 6). The starry flounder size classes 100- 199 mm and 200-299 mm and the sand sole ~ 150 mm and > 150 mm were the only flatfish species to have prey rankings which were. clearly different at the .05 probability level, The ~ 99 mm size class and the 100-199 mm size class starry flounders were only marginally similar at the ,OS level; therefore, they were also separted for feeding habit analysis. The diets of the English sole and the speckled sanddabs did not change significantly. as ·-the -fi-sh grew, so. all- size classes of these two-species were ·lumped together in_the feeding habit study. Feeding Frequency There were few empty gastrointestinal tracts for any of the species throughout the year. Six percent of the 272 starry flounders' guts were empty and 5 percent of the 357 speckled sanddabs' gastrointestinal tracts were empty. Only 1% of the 259 English sole and ~k of the sand sole's guts examined were empty, The only large difference in the per centages of empty guts bet,veen localities was that for the speckled sanddabsz 1%-of the 245 fish taken from the slough stations had empty gastrointestinal tracts, while 14% of the 113 fish from the Ocean station had empty gastrointestinal tracts, There were, however, differences in the fullness and 24 amount of digestion of the food among the flatfish cate gories. The small and medium-sized starry flounders, English sole and speckled sanddabs taken during the day aooear to feed continually on small prey since 8~h of the 743 guts of these species examined were half full and had a state of digestion of 3 or higher indicating recently eaten prey, The large starry flounders and the sand sole seem to feed more sporadically since only 21% of the 163 guts examined were more than half full and contained re cently eaten prey. Feeding Habits and Major Prey .Groupings Distinct trends were recognizable in the feeding habits of the various flatfish categories when the numerical per cent composition of the major prey categories were analyzed (Figure ·11), Small starry flounders ( <99 mm) were captured in limited numbers and only from the Kirby Park station. Polychaetes composed over half of the diet by number (53.~h). Small bivalve siphons less than 10 mm in length and 3 mm in diameter were numerically next important (23,6%), Gammarid amphipods composed about 10.4% of the prey, The medium sized starry flounders (100-199 mm) also were .more common at the inland portions of the slough where. polv chaetes were of less importance for this size class than for the smaller sized starry flounders (Figure 11). Whole bi valves and the small bivalve siphons increased in numerical importance. Gammarid amphipods, particularly at Kirby Park, 25 composed a larger portion of the diet of the 100-199 mm P. stellatus (23.5%) than they did for the ~99 mm size class. Large starry flounders (200-299 mm) had the center of their distribution at the seaward stations of the slough and offshore. Polychaetes were less important in the diet of the large starry flounders than they were in the diet of the medium-sized starry flounders (Figure 11). Large bivalve s i?hons longer than 10 tnm and wider. than about 3 mm became important in the diet and the smaller siphons were numer ically insignificant for the large starry flounders. Whole bivalves continued to increase in numerical importance as the starry flounders grew. Echiuroids were a numerically important food source, particularly at the Bridge station. Crabs increased in importance for the large starry flounders particularly at the Ocean station. Gammarid amphipods were not numerically significant in the diets of large starry flounders. Parophrys vetulus (English sole) were seasonal inhabitants of various areas of the slough and at times utilized the entire slough. Similar to the medium-sized starry flounders, English sole preyed upon annelids, whole bivalves and small bivalve siphons to a large degree (Figure 11), Crustaceans other than decapods were generally more numerically important to the English sole than they were to the starry flounders. Decapods were not an important food source for the English sole. Ostracods were somewhat numerically important at the Ocean station. 26 Citharichthys stigmaeus (speckled sanddabs) utilized onlY the seaward stations of the slough and the most impor tant prey grouoing for the speckled sanddabs normally were t:he crustaceans, particularly - amphipods and mysids (Figure 11). Polychaetes were numerically most important to the sanddabs only at the Bridge station. When this species fed in the slough, the small bivalve siphons were also consumed. Whole bivalves were n~numerically important in the diet of speckled sanddabs, ·oecapods and to a lesser extent fish were also eaten. Like the English sole, the speckled sand dabs also fed to some extent on ostracods at·-,the Ocean ·station. The numerical importance of the major prey groupings for Psettichthys melanostictus (sand sole) was not graphically presented due to the extreme trophic specialization demon strated by this species. Fish composed numerically 62% of the diet of the large sand sole ( > 150 mm in standard length). The only other numerically important major prey grouping was the decapod crustaceans (19.8%). Mysidacea was the only imoortant major prey grouping for the small sand sole (~150 mm), comprising numerically 86,4% of the diet. Dietary Variation Between Localities The relationshio between the percent number, percent volume, and percent frequency of occurrence of the prey categories with Index of Relative Importance (IRI) values greater than or equal to SO for each flatfish category at each station helped to demonstrate the differencesand 27 similarities of the feeding habits of the flatfish among the different localities (Fi~1res 12 and 13), The number oi fish guts examined which contained food, the numerical values for the percent number, percent volume, percent frequency of occurrence, and the ranking of the IRI values for all prey categories by flatfish species are included for each station in Appendix Tables B-E, The flatfish taken at Kirby Park fed primarily on small polychaetes, one species of amphtpod, and small bivalve siphons (Figure 12). The polychaete Streblospio benedicti was the most important -identifiable prey category in the diets of both the small starry flounders and the English sole. Another polychaete·, Capitella capitata, was an important prey category for all the flatfish taken at Kirby Park. Gammarid amphipods of the genus Corophium were eaten frequently and were dietarily important for all the flatfish caught at this station, especially for both size classes of ~he starry flounders, The cumacean Cyclasois sp. was fre quently important only in the diet of the English sole. Small bivalve siphons (probably Macoma spp.) had, excluding digested material, the highest IRI rank for the medium-sized starry flounders and the second highest ranks in the diets of both the small starry flounders and the English sole. Medium sized starry flounders were the only flatfish at Kirby Park that fed importantly on whole bivalves. Gemma gemma was the pelecypod most frequently eaten by the flounders at this station. 28 Starry flounders caught at the Dairy station revealed changes in prey category importance when compared with the flounders taken at Kirby Park (Figure 12), A polychaete, Armandia brevis, which was not important to the medium-sized starry flounders at Kirby Park, was,· excluding digested material, the second most important. prey category eaten by these flatfish at the Dairy station. Streblospio was eaten .less frequently by these fish at the Dairy station than they were at Kirby Park •. Another species of amphipod, Aoroides columbiae, replaced Corophium spp. in the dietary importance for the medium-sized starry flounders taken at the Dairy station, The small Macoma-Iike bivalve siphons·.were about equally important to the medium-sized starry flounders at the Dairy and Kirby Park stations. Macoma spp. replaced Gemma gemma as the most important whole bivalve fed upon by this fish at the Dairy station, Changes in the diet of the English sole taken at the Dairy station and Kirby Park were similar in many respects 'to the changes noted for the medium-sized starry flounders (Figure 12). Streblospio was less important and_Armandia was eaten more frequently by the English sole at the Dairy station, compared to Kirby Park. The dietary increase in importance of Armandia from Kirby Park to the Dairy station was not as great for the English sole as it was for the medium-sized starry flounders. Aoroides replaced Coroohium as the most important amphipod at the Dairy station, Macoma spp. were consumed in low numbers but over 10 times more 29 frequently by the English sole taken from the Dairy station than from Kirby Park. The diets of the speckled sanddabs from the Dairy station contained fewer prey categories with IRI values greater than 50 than did any other flatfish category taken at that station. Aoroides was overwhelmingly the most important prey category fed upon by the speckled sanddabs at this station (Figure 12)J and was consumed in higher numbers, more frequently, and made up a larger volumetric portion of the diet in the speckled sanddabs than in the diets of any of the.other flatfish, Juvenile mysids were eaten on only a··few occasions by the sanddabs 1·but in sufficientlyclarge·numbers to be considered dietarily important at the Dairy station, Speckled sanddabs consumed the small.Macoma-like bivalve siphons more frequently than any other prey category, but the numerical and volu metric importance was far less than for the amphipods, There was not a large change in the ordering of the most important prey items for.the medium-sized starry flounders between the Dairy' and Bridge stations (Figure 12), Armandia was even more important in the diets of these fish.at the Bridge station than it was at the Dairy station, Capitella was dietarily important for the medium-sized starry flounders at the Bridge station but not at the Dairy station, whereas the opposite was true with Streblospio. Aoroides was very much less important to these fish at the Bridge station than it was at the Dairy station. The Macoma-like siphons were also still very important for the medium-sized starry flounders- at the Bridge locality, -The major change in the diet of the large starry floun ders between the Dairy and the Bridge stations was the com plete dominance of the diet by Urechis caupo at the Bridge relative to the insignificant role itplayed in their diet at the Dairy station (Figure 12). ··Armandia was ·eaten infre quently but in large numbers at both stations. The mud crab, Hemigrapsis oregonensis, was also relatively important in the diets of the large starry flounders at both the Bridge and Dairy stations, Tresus nuttallii siphons were. ··-much--mere important-to--the -large starry .f-lounders--at. the Bridge station than at the Dairy~station. :_-Saxidomus nuttallii siphons were numerically abundant for these fish caught at Dairy station but not for the ones taken at the Bridge station. There were a few changes in the categories of prey im~ortant to the English sole between the Bridge and Dairy stations. Armandia was much more important and Streblospio was less important for these fish at the Bridge than the Dairy station. Another polychaete, Notomastus tenuis, was imoortant in the diet of the English sole at the Bridge station but not at the Dairy station, Aoroides was eaten at about the same frequency at both stations, but this amphipod was consumed in lower numbers at the Bridge station. The small Macoma-like bivalve siphons were still the most dominant prey category for the English sole at the Bridge station, although the siphons' numerical abundance was 31 somewhat decreased at this station with respect to the Dairy· station, _The change in the importance of prey categories for the speckled sanddabs between the Bridge and Dairy stations was very noticeable, but the sanddabs at the Bridge station continued to have a fewer number of prey categories with IRI values greater than 50 than did any other flatfish category taken at this locality (Figure 12). Armandia was more important in number, volume, and frequency of occurrence in the sanddabs taken at the Bridge than at the. Dairy.. station •..The ..opposite trend was noticed for Streblospio 1 since it was very important in the-diets of speckled sanddabs at the Dairy but not at the Bridge station, Aoroides was also very much less important for these fish at the Bridge station, Caprellid amphipods were dietarily important only to the sanddabs at the Bridge ·station. The majority of the prey categories eaten by all the flatfish at the Ocean station (Figures 12 and 13) were different from the prey categories eaten by the flatfish caught within the slough. The large starry flounder and the speckled sanddabs taken at the Ocean station had no major prey categories in common with the same two species· of fish captured at any other station in the slough. The starry flounders at the Ocean station ate mostly large polychaetes (Nothria elegans), crabs (Pinnixa franciscana and Cancer magister), whole bivalves (Siligua spp.), and 32 sand dollars. The speckled sanddabs concentrated their feeding on mysids (Acanthomysis davisii), amphipods (Atylus tridens} and the pea crab (Scleroplax granulata). The English sole taken at the Ocean station had consumed only 3 major prey categories that were also. eaten by_these fish at any station in the slough (Armandia, Capitella, and small bivalve siphons). The order of importance of these 3 prey items was very different between the Ocean and slough stations, English sole at the Ocean consumed mostly the polychaetes (Prionospio pygmaeus, ~rmandia, and Capitella),: the -amphipods (Synchelidum spp. and Monocu- · loides .spp.) , __ and c.the ostracod_ (Euphilomedes carcharodonta). The sand sole were··caught only at the Ocean station and there was no overlap in the major prey categories between the sand sole and any of the flatfish caught in the slough. Small sand sole consumed primarily the mysids (Acanthomysis davisii, Metamysidopsis elongata and Neomysis kadiakensis) 1 and the shrimp (Crangon spp.) (Figure 13), Large sand sole, greater than 150 mm, ate more fish (Engraulis mordax and Psettichthys melanostictus). The Percent Similarity Index (%Sl) for the combined prey of all individuals of each flatfish category between adjacent stations (Table 7) indicated the following rela tionships• prey at the-Dairy and Bridge stations were most similar, the Kirby Park and Dairy stations were nex-t, and prey categories eaten by the flatfish at the Ocean and Bridge stations were most dissimilar. All the flatfish 33 had a high percentage of prey unique to Kirby Park ( > 35%) and a low percentap,e of prey unique to the Dairy station ( < 35%) when these two stations were compared. Prey unique- ness was high for the large starry flounders, the English sole, and the speckled sanddabs at the Bridge station.and low at the Dairy station. The medium-sized starry flounders were the exception to this trend, having a high percentage of their prey unique Dairy station and a low number of their orey unique to the Bridge station. All the flatfish taken at the Bridge and Ocean stations had high percent unique prey c<'ltegories at the Ocean station and a comparatively low percent prey uniqueness at the Bridge station. Trophic Diversity ·The distribution of the trophic diversity in individual guts was somewhat skewed for several of the flatfish (Figures 14 and 15), but values of trophic diversity were similar to the median values in almost all'cases (Table 9). The majority of the results of this analysis will be considered from the mean individual trophic diversity standpoint. The mean individual trophic diversity value (H) was more variable among· the species than the mean evenness comoonent of individual dietary diversity (}) (Figures 16 and 17). H contributed more to the trophic diversitv differences among the species than did J. English sole had the highest H value of all flatfish at all localities, ranging around .86 at the slough stations 34 and increasing to 1.00 at the Ocean station (Table 9). J for this species was about .75 at Kirby Park and the Dairy stations, but decreased to about ,64 at the Bridge and Ocean stations. Speckled sanddabs had the second highest trophic diversity in individual guts at all localities where they occurred. The H value (,51) for the sanddabs at the Ocean station should be higher than the value for the large ,: . starry flounders since the skewed distribution of the trophic diversity values in the flounders made the H value ---misleadingly-high at -.53 -(Figure 14). --:The median value of ,38 was probably a better estimate of-the trophic diversity for individual starry flounders at the Ocean station, • Sanddabs had their highest H value at the Bridge station ' (,75), and their values at the Dairy and Ocean stations were similar to each other at- .53 and ,51 respectively. The evenness component of diversity for the diet of the speckled sanddab increased progressively toward the Ocean station (Table 9), The medium-sized starry flounders (100-199 mm) had one of the lowest overall individual trophic diversities at all of the slough stations (Table 9). H values for this species decreased progressively away from Kirby Park. The mean evenness component of diversity fluctuated between ,55 and .65 within the slough, The large starry flounders also had H values which were less than those of the English sole or speckled sand- 35 dabs at all locations, The individual trophic diversity values for this species were essentially the same at all localities: Dairy, H= ,37; Bridge, H= ,36; and Ocean, median H= ,38, The evenness in individual diets of large starry flounders was higher at the slough stations than it was at the Ocean station (Table 9), Both size classes of sand sole ( <150 mm and >150 mm) had H values which were lower than any other flatfish from any locality and J values which were among the highest of any of the flat fish (Table 9), Dietary Overlap The small starry flounders at Kirby Park had a high C~ value ( >. 70) with the English sole and intermediate dietary overlap value c;:::...1o) with the medium-sized starry flounders at this locality (Table 10). The overlap between the diets of the medium-sized starry flounders and the English sole was high at all slough stations and increased progressively from Kirby Park to the Bridge statio~. Speckled sanddabs had only intermediate values of overlap with all other flatfish categories at the Dairy station, but at the Bridge locality the overlap of the sanddabs with the English sole and medium-sized starry flounders almost doubled resulting in high CA values. The diets of the large starry flounders showed very little overlap (CA =S.10) with any other flat fish at every locality where they were taken, The only significant overlap between any of the flatfish at the Ocean 36 station was between the speckled sanddabs and the small sand sole. This high overlap was due almost exclusi'Tely to the_lar~e extent both of these fish fed upon one species of mysid, Acanthomysis davisii. Electivity The results of Ivlev's Index of Electivity (E) and the Percent Similarity Index (% SI) help to indicate whether differences in the types of prey items eaten by the flatfish at the various locations were due to preference or avail abili~y. Prey items such as bivalve siphons, large biYalves, harnacticoid copepods, Urechis cauno, various species of mysids, active amphipods, and large polychaetes were impor tant in the diets of the flatfish but were not well repre sented in the benthic cores. Organisms such as oligochaetes, nhoronids, and nemertean worms that were very numerous in the cores taken in the slough, and several species of amphi- nods and polychaetes that were numerically very imoortant in the cores from the Ocean station were not found abundantly in any of the flatfish (Figures 18 and 19), The small starry flounders, medium-sized starry flounders, and English sole sampled the available prey in a more similar way to the benthic cores than did the large starry flounders, speckled sanddabs, or sand soles, The benthic cores taken at Kirby Park caught Streblosoio benedicti, Oligochaetes, Corophium spp., Cyclasnis sp., and Gemma gemma in large numbers (Figure 18). The small starry I 37 flounders at this locality selected positively for Streblosoio, Caoitella caoitata, and the small bivalve siphons, while they fed upon the Oligochaetes, Corophium, Cyclaspis, and Gemma in lesser prooortions than were taken with the cores, The medium-sized starry flounders showed a preference for Capitella, small bivalve siphons and '~hole bivalves, but consumed Streblosoio, Oligochaetes, Coroohiurn, Cyclaspis and Gemma in fewer numbers than weresampled with the cores. The English sole had positive electivity values for Armandia brevis, Caoitella, harpacticoid copepods, and :·small-bivalve--siphons. -English so-le -showed-no preference for Streblosoio or.Exogone lourei, by feeding on them in the same proportions as they were taken by the cores. These fish had negative electivity values for Oligochaetes, Coroohium, Cyclaspis and Gemma, indicating avoidance. The cores at the Dairy station were numerically dominated by Oligochaetes and Streblospio, and Capitella and Coroohium were present in lesser numbers (Figure 18). The medium-sized starry flounders had positive E values for Armandia, unident ifiable polychaetes, Aoroides columbiae, bivalve siphons and whole bivalves, Notomastus tenuis and Macoma nasuta had E values close to zero, indicating feeding by this fish on these prey in proportion to the prey's abundance in the cores. The medium-sized starry flounders avoided Streblosoio, Caoitella, Oligochaetes, and Coroohium at this station. The large starry flounders selected positively for Armandia, Urechis caupo, Hemigraosis oregonensis, and numerous types 38 of large bivalve siphons and 'mole bivalves, The majority of the ~prey. items .taken by the cores at this station '"ere avoided by these fish. The English sole had positive E values for Aoroides, Cvclasois, haroacticoid copepods, small bivalve siphons and Macoma. These fish had nearly neutral' E values for Capitella, Armandia,. and Coroohium; and Oligochaetes and Streblospio were avoided, The speckled sanddabs overwhelmingly selected for Aoroides, but other amphipods, mysids and crabs were also positively selected. Sanddabs fed upon Capitella, Armandia, and Corophium in about the same proportions as they were taken by the cores at this station. Streblospio, Oli!';ochaetes, and Macoma were avoided by these-fish at the Dairy station. Armandia, Caoitella, Notomastus, Phoronids, Oligochaetes, and Cyclaspis were numerically very abundant in the cores made at the Bridge station (Figure 18). The medium-sized starry flounders at this station had positive E values for G·lycera, unidentifiable polychaetes, Aoroides, crabs, small _bivalve siphons and whole bivalves, These fish consumed Armandia and Macoma in nearly neutral proportions. Medium sized starry flounders avoided Capitella, Notomastus, Phoronids, Oligochaetes, and Cyclaspis. The large starry flounders at _the Brid!>;e station fed preferentially on Urechis cauPo, Glycera, large bivalve siphons and whole bivalves. These fish fed neutrally on Notomastus, ·mactrids, and Hacoma. The large starry flounders had a negative E • value for Armandia and this fish avoided the same type of ~9 ?rey as did the medium-sized starry flounders at this station, En~lish sole had ?Ositive E values for Aoroides, harpacticoid copepods, and small bivalve siphons. These fish ate Stre blospio and Macoma in essentially the same ?roportions as these prey .were taken in the cores at this. s.tation. Armandia, Capitella, Phoronids, Oligochaetes,·and Gyclaspis were avoided by the English sole. The S?eckled sanddabs had positive selection for the same types of prey at the Bridge station as .. they did at _the Dairy station, .i.e,, Aoroides, other amphipods, .and small bivalve siphons, These fish had negtrtive· E value· .for Armandia ,·:.Notomastus, Capitella, Phoro nids, Ol-igochaetes, _and·cvclaspis. In spite of the large number of benthic cores made at the Ocean station (278), the food in the guts of the flat fish was not well represented by the cores at this locality (Figures 18 and 19). The large starry flounders consumed primarily crabs and large bivalves at this station, whereas the cores sampled primarily sma_ll crustaceans and polychaetes. The English sole at this station had positive E values for Polydora sp., Armandia, Streblospio, bivalves, and crabs. These fish had neutral electivity values for Prionosoio pvgmaeus and Euphilomedes carcharodonta, and avoided the majority of the items taken in the cores. The speckled sanddabs selected for mysids, crabs, and other crustaceans and avoided nearly all the organisms collected by the cores. Large sand sole fed preferentially on fish and the small sand sole on mysids, There was no overlap at all between 40 the types of organisms taken by the cores and the major prey categories eaten by both size groupings of sand sole. DISCUSSION Distribution and Abundance Distributions and mi~rations of flatfish may be influenced by many factors, including the search for adequate food, changing physiological requirements during life history, purposeful movements made without regard to the environment, the avoidance of predators, the type of substrate, and changes in the physical para meters of the environment such as temperature, salinity, turbidity, oxygen content, nutrient levels and changes in photoperiod (Fleming and Laevastu, 1956), The distri bution of the flatfish throughout the study area varied with respect to the season, the size classes, and the species; however, why these patterns exist is very difficult to explain. The concentration of the small starry flounders at the more inland portions of the slough and the larger flounders closer to the ocean throughout the year is similar to the distribution pattern of this species in the Columbia River estuary (Haertel and Osterberg, 1967), The availability of food might be one of the major factors which is responsible for this distribution of starry flounders in Elkhorn Slou!';h. The large bivalves and llrechis cauoo which are very important food sources for the lar~e starrY flounders are not found abundantly at the most inland station, Kirby Park. Coronhium son., small polychaetes, and small bivalves that are the 41 42 staoles iri the diets of the smaller size starry flounders are quite abundant at the lower portions of the slough. Elkhorn Slough appears to function as a nursery and feeding ground for young English sole, since no individuals larger than 150 mm were ever taken inside the slough. The absence of the English sole from the study area during the winter did not appear to be induced by a decrease in the availability of food or by marked changes in temperature, salinity, or nutrient content of the water (Smith, 1974). A decrease in the photoperiod might have some influence on this distribution pattern; however, this does not explain whv the English sole are not found in the most inland regions of the slough but are abundant near the Bridge station from August through October. Similar patterns of the young English sole moving into deeper waters during the winter have been observed in British Columbia (Ketchen, 1956), Oregon (Westrheim, 1955), and Humboldt Bay, Cali fornia (Misitano, 1976). Speckled sanddabs are limited in their distribution to the outer regions of the slough and offshore areas. During much of the year, the water temperature, salinity, oxygen content, and the other hydrographic parameters do not appear to differ enough between the inland stations and the more seaward stations to form barriers to the use of the entire slough by these fish (Smith, 1974). The types of food at Kirby Park also do not seem to be a limiting factor in their distribution. The primary limiting factors are more likely 43 the substrate type and the turbidity of the water. The bottom sediment becomes softer and the transoarency of the water ~>;enerally decreases progressi,lely inland from the ocean. The speckled sanddabs rely on sight for feeding and they pick their food from the bottom without consumin~ much extraneous material (Ford, 1965). The poor visibility in the wa.ter at Kirby Park and the silty sediment might make it difficult for these fish to feed effectively. Of all the flatfish studied, the sand sole were the most limited in their distribution, being restricted to the Ocean station ·throughout the year. The muddy substrate -of the s laugh might not be suitable _for the sand sole. These fish also appear to feed by sight (Miller, 1967) and probably require fairly clear water in order to capture their active prey. There must also be sufficient food (fish and mysids) available, to· them in the offshore waters. Morphometric Relationships The results of the morphological measurements and the feeding habits of the flatfish species in this study agree with many of the findings in previous studies on the rela tionships between morphology and trophic ecology. Alexander (1970) stated that fish with larger mouths can better feed on active prey and grasp prey from the side, whereas fish with smaller mouths can better suck in their prey. The sand sole, which feed on active mysids and fish, and the soeckled sanddabs, which primarily eat active crustaceans, 44 have the largest relative mouth sizes. Starry flounders and English sole have smaller mouths and concentrate their feeding on the less active polychaetes and bivalves. Hatanaka et al (1954) found that the teeth of annelid eating flatfish are more numerous and better developed on the blind side than on the eyed side of the flatfish, and s_uch was the case with the English sole and starry flounders. They also contended that the pharyngeal teeth are usually not well-developed for annelid-feeders hut often form grinding plates for flatfish that eat molluscs, The annelid-eating English sole and small starry flounders had very weak 1Jharyngeal teeth, but the large starry floun ders, which frequently eat whole bivalves, have pharyngeal teeth that form strong grinding plates, The speckled sand dabs and sand sole have canine teeth on both dorsal and ventral jaws for piercing and holding their active prev. Hatanaka et al (1954) also found this to be the case with other species of flatfish that feed on mysids and fish. The structure of ~he gill rakers also gives an. indi cation of the type of food consumed, since the·space between gill rakers controls the minimum size of the prey that can be eaten, especially for active prey. De Groot 0971) found that polychaete-mollusc feeders usually lack large gill rakers and crustacean-feeders have long, more developed gill rakers. This is also true for the starry flounder, which have stubby gill rakers, and for the speckled sanddab and sand sole, whose gill rakers are long and well 45 developed, However, the English sole have relatively large gill rakers, contrary to what should be expected according to de Groot. This observation helps to confirm Yasuda's (1960) finding that stronger correlations exist bet,veen mouth sizeo and food types than between gill raker length and food types, especially for flatfish. The relative proportions of parts of the alimentary canal are also useful in the study of feeding habits. Flatfish that feed on annelids and molluscs have long intestines, whereas the intestines of flatfish that eat fish and crustaceans are quite short (Hatanaka et al, 1954). This is definitely true for the starry flounders with very long guts, and the sand sole and speckled sanddabs with relatively short guts. The English sole again have somewhat of an intermediate gut length, longer than those of the sand sole and sanddabs, but much shorter than the starry flounders' guts. De Groot (1971) correlated flatfish that ate small prey continuously with relatively long guts, and correlated others that eat large prey sporadically with ~hart guts, Starry flounders and English sole have relatively long guts, but small stomachs where very little digestion occurs. Large starry flounders, contrary to de Groot's findings, often feed sporadically on large.prey such as_Urechis or large bivalves, but the medium and small-sized starry flounders and the English sole appear to feed continually during the day on small prey, Sand sole and speckled sanddabs have relatively short guts but large stomachs in Which most of 46 the digestion takes place. Sanddabs also appear to feed contrary to the finding of de Groot, since they feed on relatively small prey continuously during the day. Sand sole, however, do seem to feed on large prey more sporad ically. This comparison of feeding frequency among the flatfish is possible because the various species of flatfish appear to have similar gastric emptying rates. Different prey categories are digested at different rates under different conditions (Windell, 1967); but, in general, complete digestion and gastrointestinal tract evacuation for small fish takes less than 14 hours (Ford, 1965; Tyler,_1970). Immature European flounders (Pleuronectis flesus), which resemble the starry flounders in morphology and general biology, clear the entire alimentary tract of food in 19 hours (Arndt and Nehls, 1964). Cumulative Prey Analysis It has long been believed that in estuarine systems the number of invertebrate prey species available to the fish should decrease from the ocean to the more inland portions of the environment (Hedgpeth, 1937; Frolander, 1964). The cumulative number of prey categories from the pooled number of fish (Figures 9 and 10) shows this to be true in Elkhorn Slough, but also that the number of fish that have to be sampled in order to obtain an adequate estimate of avail- 47 able ~rey also decreased from the ocean to the more inland portions of the environment. Dietary Variation with Size and Season The diet of some fish has been shown sometimes to vary with the size of the fish and/or the season (Orcutt, 1950: Bregnballe, 1961: Haertel and Osterberg, 1966; Miller, 1967: Levings, 1974). The changes in the diet of the starry flounders and the sand sole seem to agree with the findinp;s of other researchers who found that fish normally eat the largest prey that they can unless small prey are abundant and densely concentrated, or if large prey are unavailable (Hall~ al, 1970). As starry flounder and sand sole grow, they feed on different types of larger prey categories, even thoup;h the prey types that. they ate when they Here smaller still remain abundant. These changes in diet t size could not be observed in the English sole and speckled sanddabs since all the individuals examined were small and had fewer prey types that were potentially available to them. The lack of seasonal variation of the feeding habits of the flatfish in this study is not surprising since the major prey items of the fish were abundant throughout the year (Nybakken --et •1. 1976). Hatanaka --et al (1954) also found no seasonal variation in the diets of the flatfish in Japanese waters. 48 FeedinF, Frequency Miller (lq67) indicated that adult female starry floun ders stop feeding during the winter in Puget Sound, but that the sand sole feed throughout the year. Very few of the guts of any of the flatfish taken during this study were empty. This might be because the majority of the fish examined were immature, since according to Schaeperclause (1933), younger fish have higher energy requirements t~an do older fish and have to eat more frequently; therefore, the probability of finding young fish with empty stomachs is less than for finding older fish with empty stomachs. Feeding Within a Location The type and abundance of prey species eaten by flatfish mav vary from one locality to another (Hertling, 1928; Blegvad, 1930), but in order for these patterns to become distinct, the fish must feed within a locality for a rela tively long period of time, to prevent overlap of prey< The Percent Similarity Index values for the prey of each flat fish category between adjacent stations (Table 7) and percen tage unique prey categories between adjacent stations (Table 8) indicate that those fish examined must have been feeding within each locality lonF, enough for distinct patterns to occur. The time required would probably be somewhat less than the 12-19 hours required for complete alimentary tract evacuation by these small flatfish. 49 Tagging and recapture experiments with the starry flounders within the study areas also indicated that this species has a relatively small home range at least during part of its life (Nybakken ~ al, 1976). Manzer (1952) also found that starry flounders in British Columbia usu ally had small home ranges. Feeding Strategies Speckled sanddabs and sand sole appear to employ dif ferent feeding strategies than starry flounders and English sole. Sanddabs and sand sole localize their prey by sight (Ford, 1965; Miller, 1967). Starry flounders and English sole, particularly in very turbid waters of the inland regions of the slough, probably rely more on olfaction than on visual cues, Plaice (Pleuronectes ulatessa), which closely resemble English sole in feeding habits, morphology, and general biology, and European flounders also have a highly develoued olfactory sense (de Groot, 1971). De Groot also found that plaice and European flounders are able to detect a small jet of water more easily than dab (Limanda limanda), which are quite similar to the speckled sanddabs. Perhaps English sole and starry flounders in the natural environment are attracted by the small waterflow of these siphons as well as by visual stimuli; whereas, speckled sanddabs have to rely almost entirely on visual input. This might partially explain why English sole and starry flounders so consume more bivalve siphons than do sanddabs. The large amounts of extraneous debris in the guts of English sole and starry flounders indicate that these fish are capable of feeding by plowing through the substrate. The large size of some of the starry flounders within the study area permits them .to forage deeper into the sediment than the English sole can reach. Speckled sanddabs and English sole are readily attracted by sediment disturbances or by the vibration created by.digging small holes in the substrate (L. Hulberg, pers. ·comm.). The disturbances of the bottom--by -larger fish-,--Such-.as .starry flounders or Mylio batus californicus (MacGinitie, .1935), are probably of bene fit to speckled sanddabs and English sole by dislodging pre viously unavailable food organisms from the sediment, Flatfish Feeding Habits tvith Respect to Prey Natural History The natural history of prey can often provide clues as to hotv and where the fish are feeding. Streblospio benedicti, and Capitella capitata are small, surface, tube-dwelling polychaetes that would primarily be available to fish that feed by foraging through the sediment like English sole and starry flounders. These polychaetes would normally be available to speckled sanddabs only after the sediment was disturbed by one of the grubbing-type feeders. The abundance of Streblospio in the benthic core decreased seaward from Kirby Park (Nybakkert, 1976). At the Ocean station it was replaced completely by Priospio sp. CaPitella was most 51 abundant at the upper regions of the slough and it could also be found at the head of the Monterey Submarine Canyon offshore. Armandia brevis is more active than the previous species and it is known to swim up into the water column (Hermans, 1966). This polychaete is eaten whole by all the flatfish, but its small size causes it primarily to be con- sumed by the smaller fish. Armandia was quite numerous at the Bridge station, Its abundance decreased progressively inland from this station and offshore. Magelona sacculata is a small polychaete eaten only by the fish taken offshore. Large, deep dwelling polychaetes, such_as Glycera sp. were available only to the large starry flounders. English sole and speckled sanddabs are most likely to nip the tentacles of the tube dwelling terebellid polychaetes but not fatally damaging this potentially renewable food resource. Oli~o- chaetes were quite numerous throughout the slough, but they were not found commonly in the guts of the flatfish, Either the fish could effectively avoid eating them, or, these quite delicate annelids were consumed but rendered unidentifiable extremely quickly in the fish's digestive process. The flat fish often did not feed upon the whole polychaete and the uneaten portion might, in many instances, be able to regen- erate itseif (Dales, 1970). The large starry flounders Here the only flatfish that consistently ate the deep, tube-dwelling Urechis cauno. Urechis have been observed to come partially out of their burro,~, but the large starry flounders were probably capable 52 of burrowing deep into the sediment in order to feed upon these worms. This was evidenced by one individual having eaten a Urechis, a commensal pea crab (Scleroplax granu- lata), the commensal polychaete (Hesperone adventor), a ~ commensal fish (Clevelandia ios) and a considerable amount of detritus, all at the same time. Urechis was most abun- dant at the upper portions of the slough but it was not found offshore at all. This worm is also heavily preyed upon by the leopard sharks, Triakis semifasciata in the slough (Talent, 1973). The major crustaceans in the slough were• the amphi- pods (Corophium spp., Aoroides columbiae, and Caprella spp.), a cumacean (Cyclasois sp.), and the mud crab (Hemi- graosus oregonensis). Coroohium and Aoroides are small, slow-moving, surface, tube-dwelling amphipods that all the flatfish are capable of eating whole. Speckled sanddabs feed most on Aoroides at the Dairy station •..Coroohium was quite abundant in cores from Kirby Park, and Aoroides ,.,.as numerous only in cores from the Dairy and Bridge stations. Caorella was eaten only by speckled sanddabs at the Bridge station. This amphipod is known to be associated with hydroids and. swims up into the water column (Rickets and Calvin, 1968). Cyclaspis is a small epibenthic cumacean found throughout the slough. This cumacean was significantly fed uoon by only the English sole and small starry flounders. Large starr~flounders probably consume Cyclasnis as well as the harpacticoid 53 copepods only incidentally with the debris consumed while foraging for larger Prey items. Offshore, the fish fed upon different species of crus taceans. The fast swimming amphipod Atylus tridens· and the slower swimming epibenthic amphipods Monoculoides spp. and Synchelidium spp, were fed upon primarily only by the speckled sanddabs, As previously mentioned, the fast swimming mysids are also extremely important in the diets of speckled sanddabs and small sand sole. Lamprops sp. and several other epibenthic cumaceans are more important in the diet of the English sole than in any other flatfish. An active swimming ostracod, Euphilomedes sp,, was quite abundant at the Ocean station and was eaten frequently by on~y the English sole and speckled sanddabs, Small sand nestling juvenile Cancer magister and a crab that is commensal in crab burrows (Pinnixa franciscana)~e eaten more numerously by the starry flounders than by any other flatfish, Although the sand sole is physically capable of eating crabs, it was the only flatfish taken offshore which never contained this abundant prey item, The large starry flounders often had fragments of Dendraster ex .. - centricus in its guts, along with crab exoskeletons, These fish might possi91Y have eaten sand dollars secondarily while trying to feed on the crabs that hide in the Den draster beds for safety. Several bivalves were consumed in large numbers by the flatfish in the slough• Gemma gemma, Macoma spp., Saxidomus 54 n1ltta lli and Tresus nlltta llii. Gemma is an introduced, small, soft-shelled clam that was found primarily at Kirby Park where it was fed upon by English sole and starry flounders. Macoma nasuta was by far the most numerous small bivalve throughout the remainder of the slough. This soft-shelled bivalve usually remains in soft mud about 200 mm below the surface and extends its incurrent siphon to the surface. MacGinitie and MacGinitie (1949) observed that Macoma may project the tip of its siphon as far as 20 mm above the mud and wave it back and forth while feeding. This motion quit~ probably attracts the attention of the flatfish. The flatfish are quite prudent predators (Slobodkin, 1968) in feeding heavily upon these siphons since the clams are able to regenrate the siphon tips and live to feed a flatfish in the future. Whole Macoma were occa sionally eaten by the starry flounders and English sole, but not nearly as frequently as the siphon tips were cropped. The large size of the Saxidornus and Tresus siphons·usually prevented all the flatfish, except the large starry flounders, from feeding on them. Offshore, the hard-shelled Clinocardium nuttallii, that lives in coarse, moving sand, was swallowed whole by large starry flounders. Siligua sp. was also consumed occasionally by these fish, probably when these fast burrowing bivalves were momentarily dislodged from their burrows by a large wave or strong.current. 55 Fish are the staples of the large sand sole's diet. Sand sole feed uoon many active fast·swimming fish, such as Engraulis mordax. In order to capture these prey, the sand sole probably has to lie camouflaged on the bottom and ambush the faster fish as they pass, These fish are also cannibalistic. When feeding on its young it could actively search for the food and swim after and overtake the slower fish, In spite of the high abundance of speckled sanddabs offshore, sand sole fed very little on these fish; perhaps the reason for this was the sanddabs are quite alert fish and are able to successfully avoid the larger sand sole. Trophic Diversity: Generalists Vs. Specialists Springer (1960) and Keast (1970) found that the trophic diversity may be greater for larger fish, This conclusion might appear to be valid since large fish are potentially capable of consuming a greater range of prey sizes than are smaller flatfish, In this study, however, several of the smaller flatfish had mean individual-•trophic diversity values that were higher than those of larger flatfish (Table 9), This apparent contradiction is due to the higher number of small orey categories in the environment than larger prey categories. McNaughton and Wolf (1970) state that the most numer icallY abundant or dominant species usually have the highest 56 niche breadth and the trend in this study follows, with the English sole and speckled sanddabs being numerically the dominant flatfish at the majority of the stations and also having the hi~hest mean individual trophic diversity values, The starry flounders were only numerically.dominant at the Kirby Park station, but at this locality these fish had their highest individual trophic diversity values. The sand sole were among the least abundant of all the flatfish studied and they had the lowest mean individual trophic diversity values. Animals may be classified as trophic generalists or specialists based upon the breadth of food types consumed and by the size of the repertoire of feeding behavior (Schoener, 1971), English sole are the most generalized feeders of all the flatfish studied, since they not only had the highest mean individual trophic diversity (Table 9), but are able to feed throughout the study area. English sole are also generalized morphologically in that their morphological characteristics are intermediate between the crustacean-fish feeders such as the sand sole and speckled sanddabs, and the polychaete-mollusc feeders such as the starry flounders. The speckled sanddabs are also trophic generalists since they have high individual trophic diversity values, but are more dependent in feeding on crustaceans and appear to require better water visi bility when feeding than do English sole, The starry flounders should probably be considered as generalists 57 in spite of their comparatively low mean individual trophic diversity values because they eat a wide range of prey types and are able to feed under a '~ide variety of environ mental conditions. Sand sole are specialists since they have a very low individual trophic diversity and appear to be restricted to sandy areas with relatively good water visibility. In areas like the slough where food is abundant and fluctuations of its abundance occur in either time or soace, trophic generalists are,favored. The majority of the fish in the slough appear to be generalized enough in their feeding repertoire to enable them to "switch" somewhat their mode of feeding in order to utilize the various prey items at different localities. At the Ocean station, where the food resources are less abundant, greater specialization on particular kinds of food appears to be important. Flatfish feed more heavily within a major prey grouping, such as polychaetea, mollusca or crustacea at the Ocean station (Figure 11), in spite of the overall increase in the number of prey categories eaten at this locality. Crustaceans dominate the diet of the speckled sanddabs at the Ocean station much more than any other single major prey taxon did at the slough stations. Similarly, the English sole's diet is much more specialized for poly chaetes at the Ocean station than in the slough. 58 Dietary Overlap One theory is that fish have overlapping food niches only when food resources are superabundant and discrete niches when abundance of orey is reduced (Keast, 1965: Nilsson, 1967: Zaret and Rand, 1971). This is consistent with my findings, since the niche overlap values are gen erally much higher between fish in the slough than from the Ocean station (Table 10). The apportionment of food resources among the flatfish species appears to be much more distinct at the Ocean station than at the slough stations. The only exception to this trend is the high overlap in the diets of the speckled sanddabs and the small sand sole, indicating ontogenetic competition. The high overlap is exclusively due to feeding on one species of mysid, Acanthomysis davisii. This mysid is known to swim in schools close to the bottom and this aggregation could possible explain why it is consumed in such large numbers by these two flatfish. The trophic overlap value was high at the Bridge station for English sole and speckled sanddabs than at any other locality. The clarity of the water and the sandy texture of the substrate at the bridge are more conducive to the visual, picking-type of feeding by the sanddabs than are the con ditions further into the slough, thus allowing it to compete more strongly with the English sole for the quite abundant polychaete and bivalve resources at this station, The 59 medium-sized starry flounders also had .their highest value of trophic overlap at the Bridge station, but it was less abundant numerically at this station than at any other in the slough. The high competition and low abundance of the medium-sized starry flounders could possibly suggest that these fish are being competitively excluded from the use of the resources in the seaward regions of the slough. Electivity The traditional attitude about northern demersal fish is that they are generalists (Ogilvie, 1927). More recent studies show that these fish are not indiscriminate feeders (Jones, 1952; Richards, 1963; and Rae, 1969). Problems with patchiness of prey, avoidance of the sampling device by the prey, and the distribution of large prey outside the depth range of the coring device all prevented the making of complete estimates of the availability of all types of prey to the flatfish. These inadequacies are reflected in the lot.; percent similarity index value:; for the food eaten by the fish and the organisms taken with the benthic cores. Nevertheless, the availability esti mates were sufficient to demonstrate that the different fish selectively feed uoon different prey categories and that the electivity is not as finely develooed in the starry flounders. English sole, or speckled sanddabs as it is in the sand sole. 60 MacArthur (1958) stated that different species eat differ~ent food for only three reasons1 1) they feed in different places or different times of day; 2) they feed in such a manner as to find different food; and 3) they select different kinds of food from among those to which they are exposed, A combination of these reasons is sufficient to explain why the flatfish, despite their propensity for opportunistic feeding, are able to appor tion the resources of the study area in a manner that minimizes competition, except in areas where the resources are superabundant. 61 Table L Seasonal percent abundance (%A) and mean number per 10 minute otter tra,.;l to,., (N/T) of the major flatfish soecies by locality Nov,' 74 Feb. '75 May '75 +Aug-Oct' 74 -Jan. '75 -Apr. '75 -July'75 Aug-Oct'75 %A N/T %A N/T %A N/T %A N/T KIRBY PARK P. stellatus 100 3,4 63 3.4 8 5.4 98 5.9 P. vetulus 0 0 37 2.4 91 58.4 0 0 c. stigmaeus 0 0 0 0 1 0.2 2 0.1 Number of fish 32 33 309 59 DAIRY P. s.tellatus 68 1.6 72 2.0 24 3.3 10 1.4 P. vetulus 0 0 17 1.0 65 7.6 20 3,0 c. stigmaeus 32 1.3 11 0.6 11 1.3 70 6.3 Number of fish 28 47 82 129 BRIDGE P. stellatus 14 3. 8 30 14. 7 22 5.5 7 7 .o P. vetulus 0 0 9 2.8 34 8.5 38 31.0 C. stigmaeus 85 30.2 61 11.8 44 11.0 55 57.0 Number of fish 118 153 100 384 OCEAN P. Stellatus 11 0.4 17 1.7 8 0.7 8 O,R P. vetulus 0 0 8 0.7 63 0.2 17 1.5 c. stigmaeus 78 2.0 61 5,9 17 1.4 35 2.8 P, melanostictus 11 0.3 14 1.4 12 1.0 40 3.2 Number of fish 18 89 84 129 62 Table 2, Fish collection locations, methods,and times Kirby Park Dairv Bridge Ocean Month O.T, B.S. O.T. B.S. o.T. B.S. O.T. B.S. 1974 August 1* 2* 1* September 2* 1* 1* October 2* 1* 1* 4* November 1* 2 2*+(1 )* (1 )* 3*+(1 )* December 4*+2 3*+2 1*+1 3* 1975 January 4+(2) 4 2+(1) 4 2 February· 2 2 1 3 4 March 1 2 2 2 4 Aoril 2 4 4 2 May 1 2 1 3 June 2 2. (1) 2 4 July 3 3 1 3 August 2 2. 1 4 September 2+(1) 1+(1) 1 4 October 2 1+~1 ~ l 4 36 -2- 38 -1- 25 2 47 2 Totals O.T. (Otter Trawl) = 146 Seine) B.S. (Beach = m7 * = 5 minute tows. All other tows 10 minute duration, ( ) = Night tows 63 Table 3. ~ean ratios, X, and standard deviation values, SD, for the standard len~th to the length of the maxillary on the ocular side. * ~ the ratio for that species is si~nif icantly different from the ratio of any other species at p = .001; t-test. Species Number Size Standard length(mm~ Examined Range(mm) Maxillary on ocular side(mm) X SD Platichthvs stellatus 25 R0-325 14.41 (.9R)* Paroohrys vetulus 26 40-142 16.3R (.7fl)* Citharichthys stigmaeus 32 37-125 11.43 (.73)* Psettichthys melanostictus 26 3R-252 10.1R (.39)* 64 Table 4. Mean ratios, X, and standard deviation values, SD, for the standard len~th and stomach lengths to the length of the entire gastrointestinal tract. * = signif icance levels same as in Table 3; Soecies Number Standard length Storoach length Examined Gl_tract length Gl tract length X SD X SD Platichthys stellatus 126 .77 (,09)* .15 (.02)* Paroohrys vetulus 112 1.06 ( .17)* .23 (.04)* Citharichthys stigmaeus 126 1.16 ( .17)* .33 (.03)* Psettichthys melanostictus 40 1. 34 (.15)* .35 (.04)* 65 Table 5, Kendall tau rank correlation coefficients of Index of Relative Importance values of prey categories, IRI, between different size classes within a flatfish species by station and season. N = the number of fish examined. NS = the IRI rankings were not significantly similar at ,05 probability level. Species (N) Station Season Tau Significance at Probability levels A(l5 )xB ( 11) Kirby Park May-July '75 .35 .05 B(7)xC(8) Dairy May-July '75 .28 NS B(9)xG(l5) Bridge Feb. -Apr. 4 75 .21 NS D(25)xE(l4) Kirby Park May-July '75 .54 .001 F(l9)xG(15) Ocean Aug. -Oct. '75 .45 • 01 H(31)xi(6) Ocean Aug.-Oct. '75 .14 NS A = Platichthys stellatus ~99 rnm B = Platichthys stellatus 100-199 mm" c = Platichthys stellatus 200-299 mm D = ParoJ2hrys vetulus sao mm E = Paro12hrys vetulus >80 mm F = Citharichthys stigmaeus <80 mm G = Citharichthys stigmaeus )80 mm H = Psettichthys melanostictus ~150 mm I = Psettichthys melanostictus >150 mm 66 Table 6_, Mean Kendall rank correlation (Kendall, 1962) of Index of Relative Importance values of prey categories among seasons for each flatfish grouping at each locality. X =No fish, Probability levels: * = ,05; ** = ,01; and *** = ,001. Species Kirby Park Dairy Bridge Ocean Platichthys . stellatus (1 00-199 mm) .41*** .34** .43* X i Platichthys -s-t-ellatus (200-299 mm) X .• 33* .31* .• 34** Paro2hrys vetulus .48*** .56*** .SO*** ,53*** Citharichthys stigmaeus X .52*** .42** ,49*** 67 Table 7. Percent similarity indices for the combined prey of all individuals of each flatfish category between adjacent stations. X =No fish. Species Kirby Park-Dairy Dairy-Bridge Bridr,e-Ocean Platichthys stellatus (100-199 nun) 41.7 50.3 X Platichthys stellatus (200-299 nnn) X 52.9 12.9 ParoQhrys vetulus 45.8 52,3 32•0 Citharichthys stigrnaeus X 35.8 26.4 68 Table~ 8. Percentage of unique prey categories bet1veen adjacent localities by flatfish grouping. X = No fish. KP =Kirby Park, D = Dairy, B =Bridge, and 0 =Ocean. Species KPxD DxKP DxB BxD BxO OxB Platichthys stellatus (1 00-199 mm) 38"/. 24% 51% 15% X X Platichthys stellatus (200-299 mm) X X 21% 35% 31% 45% Paro2hrys~ vetulus 42'7'. 23% 11"/. 43% 29% 41% Citharichthys stigmaeus X X 15% 46% 28% 42% All values in these paired comparisons refer to the first location listed, For example, in P. stellatus (100- 199 mm) 38% of the prey categories eaten at Kirby Park were unique when compared with the Dairy station. while 24% of the prey categories at the Dairy did not occur-. in this flatfish taken at Kirby Park. Table 9. Troohic diversity summary. N = the total number of individual prey items. S = the total number .Qf prey categories. F = the number of guts ana lY7.ed which contained food, H (SD) = the mean Brillouin trophic diversity in individual ~uts and (one standard deviation), M.H. =the median trophic diversity it1 individual guts, J (SD) = the mean evenness component of. trophic diversity i1:1 individual guts and (one standard deviation) Station Species N s F H(SD) MH J(SD) Natural bels KIRBY PARK P.stellatus ( ~99mm) 355 11 15 .59(.355) .64 .63(.233) P. stellatus (1 00-1 99mm) 3751 39 R3 ,56(,356) .57 .65(.274) P.vetulus 105R 31 50 ,87(.396) .95 .76(.189) DAIRY P.stellatus (1 00-1 99rrun) 2933 31 32 .49(,371) .44 .55(.269) P.stellatus (200-299mm) 396 25 27 .37(.357) .49 .71(.294) P.vetulus 1392 43 52 ,89(,466) .86 .75(.189) c.stigmaeus 1931 37 65 .53(.347) .53 .58(.231) BRIDGE P.stellatus (1 00-199mm) 228 17 17 .43(.387) .35 .60(.340) P.stellatus (200-299mm) 2598 31 53 .36(.376) .32 .79(.284) P.vetulus 5455 67 112 • 85 (. 431) .89 .66(.230) c.stigmaeus 4281 60 177 .75(.434) .84 • 72(. 233) OCEAN P.stellatus (200+mm) 434 39 28 .53(.435) .38 .65(.204) P.vetulus 3863 81 43 1.00( .455) 1.10 .61(.229) C.stigmaeus 1188 74 97 .51(.408) .56 .80(.194) P.melanostictus (5.150mm) 502 16 39 ,30(.310) .34 .79(.198) P.melanostictus ( > 150mm) 70 13 16 .12(.196) .10 .86(.317) en "' 70 Table-10. Index of overlap, c,~ , between flatfish categories within a locality. P.stel.= Platichthys stellatus, P.vet.= Paroohrvs vetulus, C. stip.;.= Citharichthys stigrnaeus, P.mel.= Psettichthys melanostictus. X= No fish P.stel. P.stel. P.stel. P.vet, C.stig. < 99mm 100-199 200-299 P. stel. $. 99mm .54 X .88 X K ~ I P, s tel. X X .72 X R 100-199 B - ~ ly P.stel. X • 09 X X 200-299 p ~- - ·-·- A X R P.vet. ' X ,84 • 03 - -~ K C.stig. X .48 .06 .47 ~- DAIRY P.stel;_ P.stel. P.vet. C.stig. P .mel. -p .mel. 200+ mm 100-199 <-150 > 150 . P.stel .11 .11 .04 X X 200+ mm i~ P,stel. X .93 • 95 X X 100-199 - ~ B P.vet. .11 X • 85 X X R ~ I D C.stig. ,03 X .07 X X G - ~ E P.mel. :::;- 150 0 X 0 .91 ~ X P.mel > 150 0 X 0 0 0 --- ~ 71 Figure 1. Map of study area. Regular sampling areas are hatched. 72 - ·.. . - -~ .·- .... - . - .- -.- ·.·: ...... - . OCEAN 73 Figure 2, Length frequency histograms for Platichthys stellatus by season and locality. N = the number of starry flounder caught. SL = the mean standard length + one standard deviation. NOV. '74- JAN.'75 FEB.- APR.'75 MAY- JUL.'75 AUG.- OCT.'74 AUG.- OCT. '75 %N eo N•32 N• 2.1 N •27 N •58 · KIRBY 60 S.L.=\39± 2 9.3 5Lal69±14.8 S.L.-\09 ± 42.8 S.La\25± 21.8 PARK 40 - 20 0 %N eo N•l9 N•34 N•20 N•l3 SL.• 217±62.5 D,l'\\RY 60 SI..=214±56.o S.L.•236±55.7 SL.=22\ ±5\.5 40 20 0 ,.. %N eo N•l7 N•45 N•22. N•26 SI..=213±83.7 BRlDGE 60 SI..=237± 55.4 S.L.=2.69±52..9 S.L.=2.72± 56.5 40 20 0 %N eo . N=2 N=l5 N=7 N•ll 60 . S.L.=282±38.0 SI.=231±44.3 S.L.=2.70±34.7 • SL.• 2.36 ±33.95 OCEAN .--.-- 40 • r- 20 1- 0 . cdl,, h + + + + + + + + + '+ + + + + + + + + .frn tnOtnOtnO!!> U)Ol!>OiilOI!'l t.n 0 - LfJ to C\1 tO 0> N V'OJ---C\lC\JC\lf() IllVCO---••• o - Ill ro ~.. IllC'IJC\1{0 a> '" 75 Figure 3, Length frequency histograms for Parophrys vetulus by-season-and-locality. N =the number of English sole caught. SL-= the mean standard length+ one standard deviation. FEa-APR. '75 MAY-JUL.'75 AUG.-OCT. '74 AUG.-OCT. '75 %N BO 60 KIRBY N=l2 N=2BI N=O PARK 40 S.L.=41±9.3 S.L.=72±13.4 20 0 %N so 87 60 - DAIRY N•B N•53 r-~26 40 S.L.=57±B.O S.L.=B3±14.3 S.L.•IOI±I1.2 20 0 n %N BO 60 BRIDGE N=l4 N=34 N=l45 40 S.L.=30±5.7 . S.L•73±16.1 S.L.=I03±13.9 20 0 / %N BO 60 OCEAN N=7 •5:3 N•22 40 SI..•I07±140.1 SI..=I02±17. 5 S.L.=134± 67.2 20 0 +++++++++ JbD +++++++++ ~++++++++ oll)ol/loltlel(l;? oll)ol/loll)omo o 100 1!)0 toOl!) o C\Jr"lt{) Figure 4, Length frequency histograms for-Citharichthys stigmaeus by season and locality. N = the number of speckled sanddab caught. SL = the mean standard length + one standard deviation. . - NOV. '74-JAN.'75 FEB.-A?R.'75 MAY- JUL.'75 AUG.- OCT'74 AUG.-OCT. '75. (':J N so l.>o 60 N=9 N=5 N•9 N•90 DA!RY S.L.=66±19.6 S.L.=53± 18.5 S.L.•66±9.2 S.L.=72±5.6 40 20 r-1 lr-lrl[h nf 0 I 0 ~N 8o - 60 - N•IOI N2 94 N= 44 • N•213 BRIDGE S.L.=70±12.5 · S. L.= 48± 10.9 S.L.=60± 14.1 ,s.L.•70± 6.8 40 - - 20 0 r h "''NJ,l 8o 60 N=l4 . N•55 N=14 N•44 OCEAN Sl.•64±11.1 SI..•77±21.3 S1..=49±22.9 lf.l..•76±22.7 40 ril if. + + + .n~~~ _n 2: JJ]++ !r+++++++++ ++++++++++ + + + + + + + + + + l~ ~ oo oo . 00 oooooooooC\l oooooooooC\l oooooooooC\l oooooooo8~ C\lt0<:tU'"JlDt--COOl-;- C\l t0 <:t U') tO t-- co Ol - - C\lt0<:ttOlDt--COOl-- C\lt()<:j-tl'.llOt--OJOl-- STAI'\DARD LENGTH (m.m.) 79 Figure 5. Length frequency histograms for Psettichthys ~-mel:anostictus--by -season ~and locality. N = the. number of sand sole caught. SL = the~mean standard length~~ one standard deviation, 80 OCEAN NOV. '7~·~ JAN.'75 - - N=2 S. L.= 94±31.1 40 2 FEB.= APR.'=f5 N=l2 4 S.L.=221 ± 90.7 %N 20 - 0 MAY-JUL.'75 N=IO S.L= 18 + 9.4 40 6 6 %N 20 0 AUG.~ OCT. '75 N=51 40 S.L.=99±62.0 %N 20 0 0 I o-=:L- VJ + + + + + + +. + STANDARD LENGTH (i!l.ril.) 81 Figure 6. Linear regression of the maxillary length to the--standard ·length-by -s·pec·ies. c·r =-correlation coefficient. 82 20.0 I 0 I 0.0 • -E 16.0 0 • E 14.0 / - 0 I 2.0 b. e3 ~:j I 0.0 0 0 6 8.0 0 ~C <~ 6.0 Ol c (9 ' r= .99 _j P. melanosticfus c. 4.0 C. stiqmaeus = 0 r= .98 P. stellatus = 0 r= .97 P. vetu/us = 0 r= .95 2.0 0 200 24·0 0 40 80 120 160 (m.m.) Standard Lenath;;J 83 Figure 7. Linear regression of the gastrointestinal tract length to the standard length by species. r = correlation coefficient. 84 400 0 360 0 320 ~ 0 E; 280 ...... ,.E .I::. -c- 240 l:J) 0 c (!) _J -c-200 (.) c ""'" Fl60 -(!) 120 80 = 0 r= .97 0 r= .95 40 = r= .93 Pmelanoslictus = eo r= .96 0 . 40 80 120 160 200 240 280 Standard Length -~(rn.m.) 85 Figure 8, Linear regression of the gastrointestinal tract -length to -the stomach -length. by- species, r = correlation coefficient. '" 86 400 I 0 l 360 ~ ~320 ~ E -280 F"" 0 ~--<-- C)) ; 6 240 0 _J 0 I --u 200 0 ~ - 160 <.::> 0 120 D./ 80 = 0 r= .94 P.vetu/us = 0 r =.94 40 C. stigmaeus = 0 r= .95 P. me/anostictus = 6 r= .98 0 20 40 60 80 Stomach Length (m.nt) 87 Figure 9. The cumulative number of prey categories from the. ,pooled number_ of. fish. for each flatfish category at the -Ki-rby Park and ·nairy statiotis. 88 l 30 - 20 P. ve tu Ius = L; P.stel/otus (100-199 m.m.)= o 10 P.sfe//otus Cs99m.m.)= o 0 DAIRY ,..r-~- 40 ~~l:!i _,....,.--o-o- J 0 30 ~~/o~ 0 20 ~ P. vetu/us = "' C.stigmoeus = o 10 r 0 4·0 ru > ·- 30 ' 20 P. stellatus (I 00-199 m.m.)=o P.stel/otus (200-299m.m.)= o 10 0 0 I 0 2 0 3 0 4 0 5o 6 0 70 8 0 9 0 Pooled Number of Fish ' I ' ' '~ ..... 89 Figure 10. The cumulative number of prey categories from the pooled number of fish for each flatfish category at .the BrLdge_and Ocean- stations, 90 8RlDGE -~ 80 6_,-r-6- 60 6~ or--o-o- ~ -o_.....-o...... -' 40 6r o_,....-- _6~ P. vetulus ·- 6 ~ C. stigmaeus o 20 0 = P. stellatus (200-2~9 m.mJ= o 0 OCEAN 80 t::r / o/o--- 60 6 0 / P.vefulus = 6 __..,-/ C. stigmoeus = o 40 0 c/ P.stellatus (200+m.mJ = o, -~ P. melanoslicfus (>I 50 m.m) = o 20 P.melanosfictus (sl5 0 m.m.) = c. 0 . 0 20 . 40 GO .80 100. 120 lt;·O . 130 100 Poo~~cl Nurnber of Fish 91 Figure 111• The numerical percent composition of the major prey groupings for Platichthys stellatus, .. Parophrys vetmlus, and Citharichthys stigrnaeus by station. 92 60 KIRBY PARK so DAIRY so 40 P. s/e/Jcius (I00-1~9m.m.) N•32 40 30 0 P. .J.'r:!l!aTJ:r (200-2S"9IT'-'f0 30 20 N• 2.7 P.. :SiiJIJa!us (:5 99 mm.) :.~ 0 20 N :JS 10 ~ ·.c"' 10 ·a ~~ E 40 :;J 0 z 30 30 P.sN/Jolus (100-199mml I! ~IUu/us r. N •S3 N • 52 -c 20 20 "'0 10 ~ r Q_"' 0 P. velulus N•-50 OCEAN 50 BRIDGE 40 P.llcllalus 40 P. slt;/lulu~ U00-199m.mJ 30 N •17 (2.00+mmJ 30 0 20 P.s/~1/cfus (2.00-2.9Sm..m} N•2B N •53 20 G 10 - 0 ~ 10 I\ I"····· ll 50 .c"' a I< D E4o 40 :;J P.Yelutus Z3o 30 f! YfifU/1,/S H=112 20 N•43 "E 2.0 Q) 0 10 10 ~ Q_"' 0 0 40 40 C. sligmaeus 30 30 C. slijmaaus N ~177 N .. 97 20 20 Major Prey Groupings Major Prey Groupings 93 Figure 12. Percent composition in number (%N), volume (%V) •~-and_ frequency of occurrence (%F .o. Y of- prey-categories- -with- _~Index- of~ Relative Importance values-> 50 for Platichthys stellatus, Parophrys vetulus, and Citharichthys stigmaeus, by station, See Appendix Table A for list of prey category codes. 94 KIRBY PARK DAIRY Pr')' C!:lli!~iary Cc~~ Prey Cate~ory Code ~ I-bn. kd Sl;on N, Mcc i:li. Tn{Sl A'J Sn(S ~ "• %N ""'I %N 1 '" ..--""l.C.-1 I I I I fl~'t.ffi '%F.O. f . "0 I i 10 P. s/~1/o/us (IOO-I99m.m.l %V '" %V ~ ~. %N 'oo 0 0 L • I 10 :~ - R stella/us (200-2.99m.m.} I %V • %N "%0 I 10 lT - %F.O. 0 ------1--~· 00 :'''"'k~~ %V P. 3/e//atus ( :S 99 m.m.J :: "kF.O. <0 ·~~- __ju __ -[ ;( 00 10 P. t't!lulus %V •o IL,_,Cc___.J "'',_.,-.-_,_,_,__,.;..,_._-;--+-+-;--+-+-+--+-+-+--+-+--<-< 30- Dig %N ~: %N of---I 10 f! t'elu/us c.s/igmaeus %V ::\------' %V t--1 .. 2 0 '"I• F.Q. BRIDGE OCEAN Pfro 5!& %0"' %N "' %V P. .st~llatus ( 100-199 m.m.l %V {200+.m.m.l " %H ·:::::1-".:___.,i. \'\'\ 'liP~~ __ %F.O. %N %V l:r - r ~ P. stel/alt..•s (2C0-2S9m.rn.) %V %.14 "10 ' ------;t.F.O. %N "/.V - 1 95 ! ~ ' Il l Figure 13, Percent composition,in number (%N), volume (%V), and ·frequency of occurrence (%F ,Q,) of--prey categories with Index of Relative Importance values I >50 for Psettichthys melanostictus at the Ocean station. See Appendix Table A for list of prey category codes. I 96 OCEAN Prey Category Code 70 . Adav Melo ·-Nkad Dig Gran 60-t------__:_I ____ ..., 50 %N 40- 30- 20 10 Q. -- %F.O. 10 20 30 P.melonostictus ( :5150 m.m.) ·%v 4 50 60r------~ l l I I I Pisc Em or Pmel Dig 201.__!_J-~~ I I I %N 10 ' 0 -% F.O. %V 10 }---L_~.J----L-1 20 P. melanostictus ( > 150 r:u.l.) 1---:--+-7--r'-!-~:-:-11---1--:~:--:--} ; I . 1--1 =20%F.O. 97 Figure 14. Frequency histogr~ms of individual trophic diversity for Platichthys stellatus, Parophrys vetulus, and_Citharichthys stigmaeus_bystation. 98 DAIRY P. s/~1/alu:s {IOO-t99m.rn..l N•32 D H"'.49·±.37t P. stellatus {2:00-2S9m.. :n) N•27 II] .H=.ar ±.357 P. veJulus N= 52. H= .as± .466 r-- -~~ C.sligmoeu s 1--: N= 65· ii·.53' ± .347 - ·11-, ~ ~ + + + + + + + + 0 .2.0 .40 .SO .80 LOO 1.20 l40 1.60 I.BO 40 40 OCEAN P. slella/us (200 +m.mJ · 30 BRIDGE 30 P.llellolutt (I00-t99m.ml N= 28 H•l7 D H:.s 3 ± .435 20 H•.43 ±.3s7 20 rn P. stella/us {200-299rn.mJ -:::s-, 0 (.!) N•53 D .... H.• .36±.376 0 0 ~ 30 20~·· P..efulus ' .c"' N=43 E ::l 20 z N::lf2 1:~455 H.:~.BS±-431 <= - 10 0 "'~ 30 C. stigmoeus Q_ 0 "' N,97 20 C. stigmat!us H=.st ± .4oa 20 N= 177 tO H"'.75±A34 10 oL-L-L-L-l-l-~i------ + + + + + + + + + + oL-L-L-l-l-~~~J=~--- 0 .20 :40 _60 .80 LOO l20 l40 L60 lBO ++++++++++ 0 .20 .40 .60 .BO 1.00 L20 1.40 L60 LBO Trophic Diversity in a Single Gut (H) Trophic Diversity in a Single GL~ (H) 99 Figure 15. Frequency histograms of individual trophic diversity for Psettichthys melanostictus at the-Ocean station. N = the number of fish examined which-contained food. H = the mean Brillouin trophic diversity in 1 individual guts ~ one standard deviatio~. 100 OCEAN- 70,_ P me!anostictus ( :5150 m.m.) (/') 6 -¢=- 0 ::J N=39 D (!) - H= .30 ± .310 "-."- 0 0 5 !.- i @ P.1me!anostictus (>150 m.m.> _Q 4 0- - E - - N::iJ6 :::J -H= .12 ± .196 z 3 0- """""r;;. Q) :~~tJ (.) i:::;:;::~ b. 2 0- (9 Q_ 10,_ 0 + + + + + + 0 .20 .40 .60 .80 1.00 Trophic DiversHy in a SinQie Gu7 (H) 101 Figure 16. The relationships bet,~een the mean evenness ·component· (J) and· the-·mean richness component (H) of trophic diversity for each flatfish category at the Kirby Park and Dairy stations. The bars indicate one standard deviation. ·.;·.,, 1.00 102 I KIRBY PAR~{ .80 IT J ll .60 r~ .40 P. stellatus ( =:: 9 9 m.m.) = o .20 P. stellatus (I00-199 m.m.) = 6 P. velulus = o 0 ~--~----~----~----~----~----~--~ 1.00 - I DAIRY .80 .• TT -, .• I J • .6 • --{>I • • l ' 1 61 . . .40 P. stellatus (I00-199 m.m.) = 6 P. stellatus (200-299rn.m.) = o .20 P.vetulus = 0 C stigmaeus = e:. 0 ~---.-----.----~------~----~----· .20 .40 .60 .80 1.00 1.20 1.40 H 103 Figure 17. The relationships between the mean evenness component (J) and the mean .richness component (H) of individual trophic diversity_for each flatfish category at the Bridge and Ocean stations. The bars indicate one standard deviation. 104 1.00- BRIDGE .80- I • f-- - t;.- I J 0 • .60- 6 1 l I 1 .40- P. stellatus (I00-199m.m.) = e; P stellatus ( 200-299m.m.) = o .20- P.vetulus = 0 C. stigmaeus = c. 0 I I I I I I 1.00 I OCEAN If] j, .80 II 1 • J I I if~ .60 1 1 "I '1 .4 P stellatus (200+ m.m.) = €9 Pvetulus = 0 .20 C. stigmoeus = A P. melanostictus ( ~ 150 m.m.) = 0 L-----.-----.-~P._.~m~e~m~n~o~st~i~ctru~s __(~>-+!5~0~m~.m~.~) ___=__ o _ 0 11 0 .20 .40 .60 .80 1.0 0 I. 20 1.40 H 105 Figure 18, Diagram of the relative abundance of the 10 most numerous items ·i:n the environment as measured by benthic cores (% P), the relative abundance of the 10 most numerous prey items in the diets of each flatfish category(% R), Electivity (E), and the Percent Similarity Index value (% SI) bet,veen the relative composition of all the items in the benthic cores and in the diets of each flatfish category for Platichthys stellatus, Parouhrys vetulus and Citharichthys stigmaeus at each station. See Apuendix A for list of prey category codes. DAIRY C. 1!l~ma,;1 P. rstulus KIRBY PARK P.sflll/otus {I00-199m.m.) P. stllllolus (200-2.99) %51•12. P, VIIIU/US %81•17 P stsllolus (IOO~I99mml "loSI•IS •,.!.51•3 %P '"loR P. $/II/lOIIlS ( :S m.m.l 0/r..P 0/r..R 99 "/a5[•33 •t,p %R 0 %51•39 '/. p 60 20 %51•2.7 %P %A .,,--"-'" ""' •;.p %R ,, '"0 llllp -'i •;..P %R 0 --"If"- Sn\51-'-ft-L- I eolp B1lp "" Hcop " I 1'•00 "'~ ~" Poly !l•l~" " !hip Ho" Toll ~· Ma~ ' I ,.. SnlSl j!,biC Abit ... Ada. Tn(!;) ' I Abfl '""' Copr Myld '"" "' c~ap ,.., "' Han Ill•.' \ ""' "'"t./ftOI ) Eta~ Acal '"ccap '" ,,. A~ol Tn~t ' J ) Sbln Sbo~ "" ... / Crcl "''Tc~a~ Abfl Abrl 1/ ~~fl ,.. Pool '"' "'",~, COlO I ( I '"' Coro Cara Nttn'"' c~ap Pool ' I I Co ·~·Goma ·~·0\1; ~~0~~(/ "" '"" ~.: ""j!,ono I Pilo i Noml ( Goma\ J>.ono.~· -,.-W--,.--;: ,,. 0 U>O 01!~'~'-r-~--r~ •J.OO EM~ E >00 •1.00 0 -1.00 0 "0 E OIIQ ct_,-~,-~ E 0 1.00 ·1.00 0 t.OO E ·1.00 E E E OCEAN C.sNgmtMIJ$ P. vetullls BRIDGE P.ilsllofus (200+m.m.l %51• 9 C.stlgmaous P.v111ulus •JaSI• 2.5 R Sllllla/US (200-299m.m.) %51•16 %51• 8 'kP "'o)\_o P,.!f/11/(J/US (1QQ-[99m.m) "/.51• 29 "'oP "faA 0 "!o51•2.4 •kP %R '?_ "!oS\•41 ... p %R %P %R 0 0 "' %R zo 0 w Adn %P EO ~0ZO Pt.>lyd I •,<,p '/. R )lCop ro 40 z• BllP'-It-1-/P- 0 Euph I" ,,,o 4 ''"Cmm; ~ ~"'-~ ··~Tnui Ur• Ceo! Mopl 5olp 4 1"4 EgQI Cryp I 5~10 E991 SlhO I EDn? '""'Sn(Sl "'~ ... "''Glyt Cirri ""'! PiM IIi• \1 ,,. Pl!o ) Alrl ... Qom """ !hie Glyl I Abll ,~, Sbln Sill I !loip '"'Cap\ PpfQ Plro Di• ""At a\ Pho I ~COl Poly Cron Sblft J sl\! Hill SQIO Aco\ ldaot ~·· ·:_) Noll Pno ),I nOI Mact ,. Sb•n N1l1 """ I• ,...,• I Tmod ( .. ).lOCI Eabl r A~o~~~...... l Abrt ( Cr.cp / '"'I'IPI ~I "'"'Nlon Cytl ~.. ( Me<~l( Mocl \ '"""Abll ~ .. ( Nt•n Tmod J ··~ Sbon 1 ••• Cytl """ '"' I .. ,... I .... ""Sbtn "'", ... 141rTII Ceo~ Phto" ·~·Pl(ll l I t.~ooc , 0 Hlml 1 j "" ,.. . L 0'\ ~or/ t.~oct Ecol Ctd \ CJCI .... ~ >.00 d i I -1.00 0 9 I'Owb ' 100 '"" ! ' """ ,;,, .....+ ' ""'.. ~ ,), ,__..!: E 0 . . 0 ''"I •IDO f't,"' ' r' . ,ooO"•C!O 0 "'•CI 1.00 Pdob I ' rl'1 0' •.bo Qll 9 ~f&l0 ' 0 "' "·ibo ' ., E ·L E -~.ooo -.be '" E E E E 107 Figure 19, Diagram of the relative abundance of the 10 most numerous i terns in the environment -as --measured by benthic .. cores (% P), the relative abundance of the 10 most numerous prey items in the diets of each flatfish category (% R), Electivity (E), and the Percent Similarity Index value (%S.I,) between the relative composition of all the items in the benthic cores and in the diets of each flatfish category for Psettichthys melanostictus at the Ocean station. See Appendix A for list of prey category codes. j 108 P.melanostictus (> 150m.m.) P.melonosticlus (~ 150 m.m.) %SI=O %SI=O %P %R %P %R 20 0 20 20 0 20 60 Pisc Adav I Em or Melo '----r---'o-lj ' i Pmel Nkad i Gran Aeon· i Pvet Gran i Aeon Cnut i Begg Cane i Cnig Poly i Bath Atri i Ophi Aseu Nele • .------Nele •....----- ~----· 1 . I Eear j Eear j Ppyg j Ppyg j Meal j Meal j Pepi j Pepi i Esen j Esen j T~odj Tmodj Msae j Msae j Eobl j Eobl j Pdub • Pdub • ,-----'L--.,---'---r-~ .--'---1---'---r--. -1.00 0 1.00 -1.00 0 1.00 E E 1• APPENDIX 109 l 110 Table A. List of prey category codes used in Figures 12-13 l and 18-19. Prey Cat~cories Hioher Ta:xon Aang Allorchestes angusta c Mact Mactridae M Ab.:c At:"or. .on Ta becc~r i i Pr Mel a Metamysidapsis elongata C Abre Ar~ndl9 brevis p "Mnas Macoma nasuta M Acan Acanthomysis sp. c Mono Monoculaides sp. C Acol Aoroides columbiae c Msac Megelona saccu lata P Adav Acanthcmysls davisii c Mspi Manoculoides spinipes C AI g Algae Myid Myidae M Ascu AcanthO""ysis sculpta c Mysi Mysidae C Atri Atylus tridens c Nele Nothri a e I egan s P Bath Bath~edon sp. c Neme Nemertlne.':l Begg Brachiuran eggs c Nlo>d Neorr.ysis kadiakensis C Biv Bivalvia M Nten Not~astus tenuis P Brae B;.achiopoda c Nvir Neanthes virens P Bsip Bivalve siphons H Ollg Ollgochae~a Cane Cancer sp. c On up Onuphidae P Capi Capitellidae p Ophi · Ophiuroidca Ed Gapr Capretta sp. c Pbic Platynereis biCa.ndliculata P Ccal CapreJia callfornica c Pdab ParaphoJ<:us dabOius C Ccap Capite! ra capitata p Pegg Pisces eggs Pi Cirr Cirripedia cirri c Pepi Paraphoxus epist~us C Dnag Cancer mag ish:r. c Pfra Pinnixa franciscana C Cnig Crangon nigro~aculata c Phor Phoronidea Cnut -CI inocardium nuttall i i H Pisc Pisces Pi Core Corophium Si). c Pinn Pinnixa sp. C Cran Crangon :sp. c PI ig PolyC:ora I igni P Cryp Cryptor:~ya ca f i fern ica H Pmt!l Psettichthys melanostic-fus PI Cycl Cyclaspis sp. c Pobt Paraphox~s obtusidense C Cypr Cirripedia cypris larvae c Poly Polychaeta P Oexc Dendraster excentricus Ed Polyd Palydora sp. P Dig Digested material Polyn Polynoidee P Eana . Emerita ana toga C Ppau Pol ydora paucibrachiata P Ecar Euphi fomcdes carchcrodonta C Ppyg Priospio pygr.~a.;!:.JS P Eggs Crustacean eggs C Po;t Podocopid ostr=cad C Elou Exasond fourei P Pvet Parophrys vetulus Pi Emor Engraul is mordax Pi Sben Streblospio benedicti P Eobl Euphi lc::r.edes oblonga C Sgra Scleroplax granulata C Epug Epine!!al ia pugetTC!nsis C. Si I i Siliqua sp. M Esen Eohaus+orius senci !Ius C Sn(S) Saxidcrnus nuttall i siphons M Ete E7eone SiJ. p Spio Spianidee P Euoh Euphi lcr..~..!as sp. C Ssho Synch.::l idium shaer.~keri C G~ Ger.T."aric!~= C Ssic Solen sicarius M C~d Ge=n.2: g~.! M Syn Synchel idiur.~ sp. C Glyc Glyc:era sp. P Terc .., Tercbellidae P Grab Glyc~:-a robusta p Trr.cd Tell ina mode:;ta M Hcop Harpadicoid cope;:od C Tnut Tresus nutted iii M Hare Her.~igra;JSUS or:;vnensis C Tn Platlc:htn!(! stellatllS t101J-I~1 PI"'IO"""' FDf'-tnll•ra h.,l,...t,l ,_, 0.91 t.lll o.o«s 4.00 9.U ...... , •• boccarll 11,00 O.)l \l,l)- 111.11 6 ,_,. 0.011 '-"' " ],98 0.69 u.oo 6.5] "' (IFtlldh..., go.nlarl '·"' " l.ll 0.]2 2.00 ].311 " -rt-"--rt... fo.ntdent.l ,_, ,_, . o.oo o.y; e.oo ,_, Ec:llllli"'I.-. • "-"' '·"' " " Un~chll """'"' 0.01 ,_., 1.20 0.07 AnMIIda Qllgodle•ho ,_., n Pol yd'>oet• Polyc:hM-111 lo.nldent.) 16.1!6 l'6..ll 10.91 Pltytln6o<:ldae (o.nl,...t.l '·"o.n ,_,. 0.16 " " Etecn• ~- 9.61 11.18 "'-' 11.110 [f..,... 1""0" ,..l[fomtc:.o. 0.13'-"' ,_,. .[..,.Ida J.P• " ,_, " '·" " 1.6l •.oo E .... tu bil<>llah ].60 4.00 'il.•l " b.og,.....,.,.,,..., O,l5 O.ll 6.66 4.~ II 0.15 0.14 2.~ ].,1 n ].46 16.00 112.110 "7 Splcntd- (...,[dent. I 1.01 0.62 1.20 1.95 ;~ Poly Table C. Index of ~elative Imoortance (IRI) summary for the Dairy station. %N = percent num~rical composition, %V =percent volumetric composition, %F.O. = percent frequency of occurrence ,,,._.., .. _ "·"" a,f:l l.M tal .....u...-..•••-~ ,_ ... •--•- 1.~ ~ ...... ,..,,_ ;.lllo I.N l.U 0 ... U -·-..._._ ...... ~ .. 0 ... C.lt 1.~ c . .- .. _, -·-~'""' ...... t.IO Q,l< 3.1'0 0... l7 o.•• "--"' s... s.to .w -~~-go•-· l.lll l.lll J... U... Z:Z b.,. 1.~ t.U J.:tO 1:1 ""'f<"-"' ..... ,..,_ .. ,_;_,_, L:l< I.U ,1,11 111.!11 I J.I'O •••• u.u "'-10 u J ..U 1,0) ot.U to.... 1:1 J'•ll' 1... 1<... H.ll u- ... 1.1! L:ZU I.:D l... l7 [-·~~-- c.- .... .,...... ;:: ::~ !:: !::; : ;,, II•• 1.11 '·" ,.., ( ...... u ...... D,H l.lO ),~I' 1.'11 Zl l,tc o.n J... tl.U U ~.oo "·-'"' t,U ~.U ll.'l ca..,...,..,.u..,._ ·--· o.:ro a... J.Ja o.JZ 21 c._..._,,_ 1.01 LX J.Ja J.aJ JJ a.Jl G.ZII I.A 1.20 o.J ...... _ 1.... 1..10 ),lJ IT..cl Ol -...... -·~-··· h ... G.OJ 1.211 1.11 O,M :1"1 ,...... ~.,.... ,,.,., .... J.lol 0.31 1.1.2 •••• tl _,..,.. _...wfo f...... :loc D., 1.01 1.'11 J...N l!l .. _,.. 1.10 ,_.. • ... ~1-lo .... 11.11 '·" u.n u.n 11 J..JJ 1.es ''·" n.n • i.l:l 1.,. 1.11 '·" .u "''-'-l""'-···..... _. ... a,,. Lt:l :S.It 1.&:1" B 0.011 J,n I.S:Z 1.0<1 M ....u .... ,_,.,..,._...,_, __ ,.,.., D,.., I.SO l.tl:l O,t:lli 1l 11..&1 11.%1 11..3<1 ~·..n I.U J.OJ SQ.N Z11.to o '.11 o.OQ IJ ... l:t,oa a;._..,.,,_,_,_,_l 2.}1 1.-"' J... II.CI lO ,.CM J,M 1.,11 I,U 1t c ...... ,, ...... t,l!l l.J& 1... 14,)0 II -....~. a.co 1.n t.cz 1.;111 c.s U,J!I 1,)1 :W.ll llt,lC .. _, 1.11 J.JII ... u J.:rl o,.- .Q.H 1)Q',Cl 0 t.M 1.1:1 l!l.l'l U.t -·---·· I,U 1.11 11,)) J,I,H II 11,1$ G.JO l.ll 1.!11 )0 ol-hlo t.•ol-.1 '·" ~~ :m.ll Ill... o.n o.u u.u M.lt ··-···· U.ll l.ts ,,JT IIIJ.CS u.n 1.11 '"·" ..... n B.Jl U.lt l4.'11 )l)J,ZJ I 1.~ O.J.I U.Cl ICCIO.ll l >.'II t.,ZJ 3a 1-.... - ..... a,.., z.to 1.u '·" n.3Q 1o.a-. 1 t.n 2~ t.SJ 1,12 11 ··-·-··-·'-'-...,..,.,._. _..,,, .. ,_. o.:ro ).ft I.U "·" n tt.n "·" "·" 110.~ J ...... _ G.ll LD 1.1.2 l.fl B a.Jt a.fl 1.10 o.n :zu -~ o.rt o.n s... •-:t J.t ,...... ,._...... 1.0<1 J.c::~ u.,., ur.n '·" 1.!11 1.00 11,11 10 ~·-·-·-·-·_ 2.... 1,11 OI.JII UI.:U ... 1 0.!.0 O.lol 1.01 2.... "' '·" J...lf. n •.., 11o..!.D '·" '·" n.1.1 zn.JO o •·" I,IJ l... V.u U ~.:H I.U 1.31 1.11 J1 1.lll .... l,ll ·-~ 21 J.n J.U 1.... ~-<.,. 11 Sc>l-=:::....ol.,.rl I.IJ '·" J,oa 011.n n c.y,.-... __ ...,.,_,_c.l ...... Cio a.1o a.J& 1.10 1.10 zo (11...... ,_1_ -"•Uti 1..11 l.n ),II 11... II 1... •.u J.lO D.JI IS ~...._ ,,_,_.._, o.u o.n o.n '·"' lll L"' G.Gl J.U 0.011 )1.} ~!!"'""'"""·-- G."' LV 1.12 11.1 J,Jo 2., 0,61 .l<.... II a.... J.l'l I,H l,ll 11... II ...... f;l.-1-·•-"--~~ ... ·-·-~-· .. 1,... 0,00 1,01 U,U II ••I'S 0,1-0 I.JJ •.Oll I" _ 11.10 0.~1 l.l'Q 1.u n t..-.-...... - _ '·" a., t.n .,_.., '' O.lrl J.U U:.ll J . O,lrl 1.,00 1.01 1.2:1 :1"1 o.1r1 ,_., :o.= 11.n 10 0.011 a,TJ 1.00 s.a; 11 u.q "'----··· Llrl ll!.)l 1<0.1ll161.1U I a,I'Q \6.0 II ... UI'C,U I 0.0<1 l'l.ll SJ,JQ ll•J...., l 0.1'1 IJ.l-0 M.A IJ'III.tl I un tn• ..,...,-.. .. ,,.....,u,opr, .. . " "y •" - ...... ,_._. t.l ... .;..._,..,, • n • .! - I , • - ,f1; f- !.!111~ i · I ""'"""0 ,.... OJ m,~ H-!., 30JO" f!! 1 11 1 1 "0,.... ~ ' l" '· 1! Ifi I ~!!I lj!Ifffl.!l!ilii fi{fji11! I ~!!!i ff!ff!l!!If11 fffli!·~lflifi!i!l . 0 -'•CO Il '~ 1 VlO : I I dl l ,l,.. ' 1.. . ,,.~II ' I i"• ,• ,.I " ..•' I• ljill ·- ,!t,.•• ,.1-ll"lli'··-H!·.r. .•.•... 1·!' • 'I1 ,. l ~- 0 !. !. -lo::S ~ l I ~ ~~ ;. ,-;.. ·i!· i !: c· , •r if ~~ --=!lll'l... ,nH! ~ ~ :_;: g • _n ! - ,...... ' . . -1 l . - '. II " - " B· - I i ' - 'II • I ~. r 1 ' , ~E lj ~- • >c 1- -, 1 • '1- 1- -,l ! 'j- - ' -.. ' ~- l r ~ Pt • 1· c J · 1- - • ! 1-l . · - 5 Icc 0 • r i = -~i ~! ~ .-fja:: ~ ..::> "":z .....::1 d 1- Cl. 1 I . ..,~ 11 ro>< ! f PP • "0 '" 'p " oroo..,.., i ~ ~ ('} 11 ro ;o ::> ro "0 rt ~ "' ' ro OJ ii ~ "l:lrt " ' , n c: -..lo ' ro 3 < ' ,...... ,::> ro ro ~ !"!"'!" :"Pl"'P ,. ~ ,...... a:.: ;;u~ k ' ' """3"lOJ'O P t' t':"' I"PP' :" p pp p p p Pt':' PP!"P . r ~ ::! = :::;: ;::~= 1$ w:::~ :'!¥:8~ :: ~g ro o ' ' e ' .n .., t':" ;"!" '!';";" ;" !" 1":"1" c ('} ..... ::~• a; 1111 1 ~~~ ~~~~ ~ 'k ~ ::11:1 i E k roow ::> 3 ::> ' , I l:l Fl"!l :" t t' n-on ~~!: • i~ G~ ~H ~ s ' . ' , i ' Table Index of Relative Importance (IRI) summary for the Ocean station. %N = percent numerical composition, %V = percent volumetric composition, %F.O. = percent frequency of occurrence .__ ,...,._, __ , ou. .,_., :r.n '·"" .._. ... _~...... __ ...... -...... _...... ~ '·"' ...... ,.::-·--·-·-··_ ._, __ , _... . ·~ . _.... ,.._... ,_, __ , ...... _,, ._ __ .... _,... ,_._, ...... ,_.__.... ·-·-·-·-···...... __ _ .. ~ ·--· '" ~- . .. ·- ·--··-··--· ...... :::::-.._._.._.,,=-=··-·-·· ...... '" . ___ _ '·" .... s.n ,..,. n · ::::::::=.:....--- J,...... = ...... ,... _,,.., __ , ...... __...... __ ...... _ ...... J .. _,_,__,..,, ,. :::::.::-..!::!7'·' ...... ~ ::: '!:~ ·~~ ..: ..... &.M ._.. Lll =:::~:::.::---· >:LJS •·• Ln ••• • ...... :::: ...... -·-._,,_._,_... ·-·-··...... l..D • --·--· ::;; ...... ''·" ...... o.u ...... :n ..._'E-- -·-·-·"· ...... Lu o.a ..._.. ZL<> a ~"":.-·-'-·--· ...... ··- ..._, _,.,.,_.._, ~~:::t;~: ..... - __... --~-·- .... o.n o.n o.a ._., ., ~--...,, __ ,_ ..LZo ...... ::: .::!! •.t:: .. ":'' ...... -·" ·--._._.. ...a....tL uo. ""'-AS. a cr ..•-•• ..:::::::-·· .... .__, ,,... J..n ..., ...... • •• &I ...... ~·. ,...... ~!"..:::.~-· ...... ,. ...:> ..... c.-._,__ , ...... c,.,_,.._----·-··..... ,._,._ .. =-::-"- ...... __,_ ...... __ , ~~~ ...... -·- o.or oo.n o.• a ...... '::!: g.• ...... -·-:.:....";.:::..:;:;:." ...... La L • .._., ..!:!: '; ...... ~t:.!:~ !::;:-" ...... ~~- .,..., ._., Ln n ...... ~- . ,... _._ ... ,__ , ...... ~ tE ::: ..'" o.;a o.a ._ .. 10 :.:_~:::_- .. .. o.• ur z.or .._, ...... L.lt .... • ... -·-- ...... , ...... '·" ._.,__:~-=_.. __ ...... '" :.::; ::: ...... ILM..... :10...... '" ~~~-_ ::~ t-J n ...... · ~= __ .. __ ...... 1.3< ...... ---·-··=:: ::::!!-,_,.,...... ___ ._.. ._ .. Ltz LIO U :::::;-:::~ ...... --" . '·" ·~.- ...... _ ...... _._ 1..>o ...... -.,,., ., ~..=:!-::-··--__ __ ~ ::: ::: ·.:::_ : ._...... __ , :::: ::: ~ :::..... !:·'...... ::~ ::: ::: ::: ~ ...... --·=:--~·..-:::·- ._,. '·'" on.n .. .._... ..-.,_ ...... -·-·-· __ ..... gg~~fi~ ~~:~-~:...... ~-" ...... -·---"'"-_ ...... 1.10 ...... --··· :::: ~.: :::: .... ~ ...... o.ll ..,~ --·---"""...... • ...... :::: :~ :::: .::: :!·" g ...... E::~3~ ._ __ .. .. '!:': !; ...... ·~ "·' o.n Ln •-"' ""'...... •...... , -..-·-·-..... !:!: .·~ ~;: E -:::::-:: ..... -...... •n...... • ,,,_,, __ ...... ·-· L.l:O .... ::~ '·" ...... :.-:: ~-· ...... -·~: :: ·-·-·· ... ,...... :f. ::: t~ ::~ .... - 0.:1<1 .... . --=:::.-· .. - "·' ...... :::~.::::;-·' ...... _., ...... tt.n ..o.u I !:C"..:.:.:. -;;:::_, ~::... ::: ":::: ~-:::.:.:·- ...... ,_ .. , --·:::: ::..-.. ~- ...... _...... _-.. , '-".... .,_,_., ...... "·" n ...... _._ .. ,__ ,_,_ ...... -- ...... ~- LITERATURE CITED Alexander, R. MeN. 1970. 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