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sp. from Chaenobryttus gulosus and Lepomis cyanellus; Pelichnibothrium
sp. from Salmo gairdnerii Richardson. Acanfhocepha/a: Rhadinorhynchus
sp. from Salmo gairdnerii.

A key to 23 species in the genus Lepocreadium is given.


To date there lias been only one major study concerned with endo-
parasites of freshwater fishes of California. Haderlie (1953) sum-
marized investigations up to that year and conducted a general survey
of the monogenetic and digenetic trematodes, cestodes, nematodes,
acanthocephalans, copepods, and hirudinians of fishes of northern
California. From 2,010 fishes representing 36 species in 11 families,
examined over a three-year period, he obtained a total of 59 species
of helminths, copepods, and hirudinians.

Other investigations include those of Wales (1958), m'Iio described
two new blood flukes, one infecting trout in southern Oregon, the other
common in northern California hatcheries and rivers. Colley and Olsen
(1963) studied the metacercaria of Posfhodiplosfomnm minimum (Mac-
Callum, 1921) Dubois, 1936 in fishes of Lower Otay Keservoir, San
Diego County.

The primary purpose of the current investigation was to gain some
knowledge of the species of endoparasites of fishes of the Sacramento-
San Joaquin Delta. Two hundred and thirty-six fishes representing
26 species were examined between March 1966 and June 1967. This
has resulted in the recovery of three metacercariae, three adult digenea,
several adult, immature and larval cestodes, one acanthocephalan, and

'^ Accepted for publication July 196S.

= Present address : Department of Zoology, University of Kansas, Lawrence, Kansas.

( 247 )


several species of nematodes. Not iiieludcd in this pjipcr ;ii-c the iicina-
todes and the caryopliyllaeid cestodes; the hitter group is represented
hy ])()(trly ])r()cessed specimens.

The major site of collection was tlie tisli conci-tiii-j- facility of the
U. S. Bureau of Reclamation at its Tracy Puiiii)iim- IMant. Other col-
lecting sites included various locations in Middle, Old, Sacramento,
San Joaquin, and Calaveras Rivers in the Delta.

Trematodes and small cestodes -were fixed in alcohol-formal in-acetic
acid (AFA) inider slight cover slip pressure. Large cestodes were
allowed to relax and extend in chloretono or in 1he refrigerator for
several hours before AFA fixation. The single acanthoccphalan was
placed in fresh water in the refrigerator overnight until the proboscis
became fully extended. All worms were stained with Semichon's car-
mine, dehydrated in successive and increasing concentrations of alcohol,
cleared in methyl salicylate, and mounted in Kleermount.

All drawings and their scales were made by microprojoction. with
details filled in from microscopic examination. Measurements are in
mm except for eggs, which are given in \l. Sucker ratios for trematodes
were calculated by taking the average of the length and width of each,
the oral sucker being expressed as one. A new host record is indicated
by an asterisk.


Class Trematoda

PosfJiodiplostomum minimum ccntrarchi (MacCallum, 1921 ; Dubois,
1936) Hoffman, 1958

Hosts: *Archoplites interruptus (Girard)
Chaenodriiftvs fjtilosiis Cuvier
Lcpomis cjjancUus Rafinesque
Lcpomis macrochiriis Rafin(»s(iue

Site : Encysted in the liver and on the heart

Ncascus sp.

Figure lA

Host : Hysterocarpus trasJ{i i-fraskii Gibbons

Site : Encysted on the heart

These metacercariae are described separately because of the possi-
bility that they may represent a new species. The host is a member
of tlie family Embiotocidae, which is not known to harbor the meta-
cercaria of PostJwdiplosfominn minimum. A certain host specificity is
believed to exist in this group of larval trematodes (jMiller. 1953;
Hoffman, 1960, 1967). IMeasurements based on a typical worm: body
elongate; forebody 1.200 long by 0.480 wide; hindbody 0.480 long by
0.360 wide. Oral sucker 0.053 in diameter, terminal ; pharynx 0.044
long by 0.031 wide ; ventral sucker equatorial with respect to total
body length, 0.077 long by 0.083 wide; holdfast organ considerably
posterior to ventral sucker, 0.181 long by 0.165 wide; holdfast gland
distinct, at posterior border of holdfast organ. Ceca extend past pri-
mordial gonads in hindbody. Gonadal primordia confined to central



FIGURE 1— A, Neoscus sp. from Hysterocarpus fraski /zzfrosfe/i Gibbons, ventral view; B, Neoscus
sp. from Lepomis cyanelius Rafmesque, ventral view; lepc:hroc/ium californianum sp. n., paratype,
ventral view; D, L ca//7ornJanum sp. n. from Roccus saxatills (Walbaum), holotype, ventral view.


region of tlie liiiidbody; bursa copulatrix subtermiiuil. O.IOT long by
0.1(35 wide. Reserve Ijladdci- llu'dimlidut I'orcbody. l)i-;iiichiiig and

Neascus sp.

Figure IB

Host : Lcponiis cyanclhis Rafinesque

Site : Uneneysted in tlie vitreous humor of the eye

la one gfcen sunfish, metacercariae were found luicucssti'd in the
eye. Due to the unique site of the infection, and the morphological
variation in the holdfast gland and holdfast organ, it is believed that
this Avonu may represent a species different from those given earlier.
])eserii)tion ;ind measurements based on one typical si)ecim('n : body
spatulate, 1.080 long; forebody 0.816 long by 0.445 wide; hindbody
0.264 long by 0.354 wide. Oral sucker subterminal, 0.044 long by 0.048
wide; pluirynx 0.036 long; ventr;d sucker equatorial witli i-csjx'e't to
total body length, 0.060 long by 0.067 wide; holdfast organ with ser-
rated margin, 0.132 long by 0.107 wide; holdfast gland indistinct at
posterior border of holdfast organ. Ceca extend to level of (•(iiisli'ictioii.
Gonadal ])riin(»Tdin confined to hindbody; bursa (•()])uhi1i-ix oval, sub-
terminal, 0.071 long by 0.108 wide. Reserve bladder confined to fore-
body, composed of branching and anastomosing tubules.

Pisciamphisfoma sfiinl-ardi (IIoll, 1929) Yanuiguli. 1954

Synonym: Paramphistomum sinnlxardi IIoll, 1929

Hosts: Chocnohryttus gulosus Cuvier

Lcpojiiist (jihhosMs Linneaus

Site : Posterior region of intestine

Deposited specimen : U.S. National Museum No. 70959

This s])ecies was first described by IIoll (1929) as ParaniphisftDnion
stKuhardi. Yamaguti (1954) placed this species in the genus Plscia))i-
phistoma, which he distinguished from Paramphistomum by the pres-
ence of an esophageal bulb. In his original descrii)tion, IIoll (1929)
reports finding it in the ])Uini)kinseed, Lepomis (jihb()s)is, and in the
warmoulh, Chaciiohrijtfus qkIosks, in Dnrham, North Carolina. Bang-
ham (1940, 1941) and Bangham and X'cnard (1942) reported a A^ery
low rate of infection b}' this Avorin in centrarchid and silui-id fishes of
Florida, Ohio, and Tennessee. Ilach'rlie (1950, 1953) found it in 4 out
of 69 black crappie, Pomoxis nigromaculatus. It is of interest to note
that our material Avas also found in the ])iim])kinseed and Avarmouth,
the hosts from \\hich I'Iscldiii pli istoma stiinJxardi Avas originally recov-
ered. Both fishes Avere introduced into California from the easlcrn
Ignited States.

Alloglossidium. corti (Lamont, 1921) Mueller, 1930

Synonyms: PJagiorchis corti Lamont, 1921

Phigiorchis nmcinrcnsis IMcCoy, 1928
Alloglnsaidium l^niti Simer. 1929


Host: Ictalurus catus (Linneaus)

Site : Posterior region of intestine

Deposited specimen : U.S. National Museum No. 70960

Six specimens were recovered from the above host and are referred
to this species on the basis of topography of gonads, extent of viteHaria,
cirrus sac, and uterus. Tliese specimens, however, are somewhat hirger
(1.70-2.00 X 0.370-0.430), the eggs a little wider (28-36 x 15-21 \i) ,
and perhaps of greater significance is the indistinct lobation on the
anterior margin of the pharynx, observed in all specimens.

Lcpocrcadvmn calif ornianiim sp. n.
Figures IC, ID
Host: Boccus saxatiUs (Walbaum)
Site : Intestine
Holotype : U.S. National Museum No. 70961

Description (based on three specimens, one sectioned frontallv) : bodv
oval to pyriform, 1.248-1.536 long by 0.576-0.648 wide at the level of
the ventral sucker. Cuticular spines extending to posterior end of body.
Eye spot pigments present. Oral sucker 0.156-0.173 long by 0.165 wide,
subterminal ; ventral sucker at posterior end of anterior third of body,
0.115-0.119 in diameter; sucker ratio 1:0.70-0.72. Prepharvnx 0.027-
0.040 long ; pharynx 0.065-0.083 long by 0.073-0.081 wide ;" esophagus
0.042-0.071 long ; ceca narrow, long, extending to posterior end of body.

Testes two, oblique, triangular to irregular in outline ; anterior testis
right of midline in posterior half of bodv, 0.165-0.206 long bv 0.198-
0.239 wide; posterior testis 0.198-0.272 long by 0.198-0.247 wide;
cirrus sac well developed, extending left of acetabulum in two speci-
mens, right in the third, slightly posterior to ventral sucker, enclosing
spherical internal seminal vesicle 0.038-0.066 long by 0.036-0.041 wide,
well-developed prostate vesicle, prostate glands, and muscular cirrus
0.206-0.263 long; external seminal vesicle saccate to tubular 0.123-0.222
long by 0.049-0.066 wide.

Ovary pretesticular, equatorial to left of midline, 0.082-0.107 long
by 0.091-0.132 wide, nmrgin entire or slightly irregular; seminal re-
ceptacle spherical to ovoid. 0.090-0.156 long by 0.041-0.107 wide; uterus
short, pretesticular ; metraterm well developed to right of ventral
sucker. Genital pore median or submedian at level of intestinal bifurca-
tion. Eggs few. maximum number four; opaque ones 112-128 bv
51-72 ^i.

Vitelline follicles large, mostly extracecal. extending from level of
pharynx to posterior end of bodv. confluent posterior to testes. Excre-
tory vesicle tubular, extending to anterior margin of left testis; pore

Levocreadinm calif orniamim sp. n. is to be compared with and dis-
tinguished from those snecies of Tj^vocrcadium with large eggs. These
include L. archosargi Pearse 1949 (esfgs 140 x 60), L. micropogoni
Pearse, 1949 (eggs 130 x 60). and L. cahallcroi Sogandares-Bernal
and Hutton, 1960 (eggs 108-112x48). L. ovale Manter, 1931, L. seti-


fcroidis Miiiiiii, 1988, L. tridlafurmc Linton, 11)10. ;\m\ L. dongdinm
(Nao:aty. 1042) also have large eggs, though somcwliat smaller than
those of 1li(' first three species.

Lepocreadmm calif ornianiDi) s]i. n. differs from all of the above-men-
tioned species in the reversed position of the gonads. The ovary is
sinistral and close to the left cecum, and the right, rather than tlie
left, testis is more anterior. From L. archosargi it dilTers in lacking two
ani ; tli(» vitellaria extend less anteriorly; there is a smaller ratio of
egg length to ventral sucker diameter; and a greater posterior extent
of spination. L. rnicropogoni was considered species inquerenda by
Sogandares-Bernal and Ilutton (1960). Pearse's drawing (Pearse,
1949) shows a small cirrus sac, mostly preacetabular. Other distinguish-
ing features include a less posterior extension of spines and a greater
egg length-ventral sucker ratio in L. micropngoni. From L. cahallcroi,
L. calif ornianum sp. n. differs in body shape, greater anterior extent of
vitellaria, and in having an entire rather than a bilobed ovary; from
L. ovale in having larger but fewer eggs ; from L. setiferoidcs in body
shape and better-developed prostate complex; from Tj. fruUaformc in
having more oblique testes, fewer and larger eggs, and in lacking con-
fluent vitellaria dorsal to the intestinal bifurcation; from L. clongaium
in body shape, lesser posterior extent of the cirrus sac, more tubular
external seminal vesicle, and in having an entire rather than a four
or five lobed ovary.

Lepocreadinm calif ornianum sp. n. is the first member in this genus
to be reported from a fish in fresh water. The host, a striped bass,
Roccus saxafilis. was obtained from the Tracy fish collecting facility.
The water in this area is characterized as fresh according to the 1958
Venice Hydrobiological Nomenclature. The host, 5 inches in length,
was approximately 1 year old. A fish of this size could have migrated
to the Tracy fish collecting facility from a downstream mnriiic cmiron-

Manter (1962. 1963), in discussing zoogeogra]ihical relationships of
trematodes. indicates that members of the family Le]iocreadiidae ar(>
primarily parasites of marine fishes, the ITomalometroninae being the
only subfamily with members parasitizing fishes in salt, brackish, and
freshwater environments. In the latter paper IManter states "fresh-
water fishes with parasites of this subfamil}^ usually have marine con-
nections of some kind".

The genus Lepocrradium is a member of the subfamily Lepo-
creadiinae. members of which are strictly marine. Therefore, recovery
of L. California num sp. n. from a fish in a freshM^ater environment Avas
unexpected. In all likelihood this Avas a recent infection in the host
during a temporary residence in a marine environment.

Of the 31 species placed to date in the genus Lepocreadinm, the au-
thors recognize 24 species as valid members of the genus; twenty-three
species including L. calif ornianum sp. n. are compared in the following
key and one, L. pegorchis (Stossich, 1901) Stossich, 1903, is not in-
cluded because its description is not available to us. The other seven
species should be retained as members of the closely related genera
Lepidapedon, Opechona, and Pscudocreadiiim.


Key to the Species of Lepocreadium Stossich, 1903

la. Vitellaria extend anteriorly to level of ventral sucker or below;
testes tandem 2

lb. Vitellaria extend to intestinal bifurcation or more anteriorly;

testes tandem or oblique 4

2a. Body elongate ; ovary entire 3

2b. Body pyriform; ovary lobed

L. truncatum Nahhas and Cable, 1964

3a. Cirrus spiny ; cirrus sac extends posterior to ventral sucker, almost
half way to ovary L. pyriforme (Linton, 1900) Linton, 1940

3b. Cirrus not spiny; cirrus sac does not extend posterior to ventral

sucker L. hiniarinum, Manter, 1940

4a. Eggs as large as or larger than diameter of ventral sucker 5
4b. Eggs smaller than diameter of ventral sucker 9

5a. Testes tandem; eggs small, 45-55 x 30-37 [i

L. hcmiramphi Nahhas and Cable, 1964

5b. Testes oblique ; eggs large, usually more than 100 [x in length 6

6a. Right testis anterior L. calif ornianum sp. n.

6b. Left testis anterior 7

7a. Ani (2) present; vitellaria extend anteriorly to level of oral sucker
L. archosargi, Pearse, 1949

7b. Ani absent; vitellaria do not reach oral sucker 8

8a. Vitellaria extend anteriorly to level of pharynx ; cirrus sac

does not extend posterior to midacetabular level

L. micropogoni Pearse, 1949

8b. Vitellaria extend anteriorly to cecal bifurcation ; cirrus sac

extends half way between acetabulum and anterior testis

L. cahalleroi Sogandares-Bernal and Hutton, 1960

8c. Vitellaria to pharyngeal level; cirrus sac extends slightly
posterior to acetabulum L. sctiferoidcs Martin, 1938

9a. Ovary entire 10

9b. Ovary lobed 13

10a. Testes tandem, lobed

L. alhum (Stossich, 1890) Stossich, 1903

10b. Testes tandem, entire L. hravoae Lamothe, 1964

10c. Testes oblique, smooth 11

11a. Vitellaria confluent dorsallv at level of intestinal bifurcation and

posterior testis; eggs 84-88 x 40-44

L. trnUaforme Linton, 1940

lib. Vitellaria not confluent as above 12

12a. Eggs 96 x 56 L. ovale Manter, 1931

12b. Eggs 54-72 X 33-38

L. opsanusi Sogandares-Bernal and Hutton, 1930

13a. Cirrus sac does not extend posterior to ventral sucker 14

13b. Cirrus sac extends posteriorly some distance between ventral

sucker and gonads 18

14a. Pharynx with lobed anterior border 15

14b. Pharynx simple 16


15a. Body oval; testes entire; external seminal vesicle ru(liin(Mitary__
L. cxiguum iManter, 1963

15b. Body Iruiicate jiostcrioi'ly ; testes deeply Idbed; external seminal

vesiele long and narrow L. incisum Hanson. 11)55

l(i;i. Vilcllaria extend anteriorly to and overlappin<r oral sucker;
pharynx smaller than ventral sucker; external seminal vesicle

small and spherical

L.vitcIIosum (Oz.iki. 10.36) Manter, llUfi

IGb. Yitellaria extend anteiMorl.N to level of ])harynx; ])harynx
about same size as ventral sucker or slightly larger; external

seminal vesicle elongate 17

17a. Body truiu-ate posteriorly; genital pore to right of midline, near

the ])osterior border of the pharvnx

L. mnris (Caballero, 1957) Manter, 1963

17b. Body oval to elongate ; genital pore just behind intestinal bifur-
cation, somewhat sinistral to nndline

L. clavatum (Ozaki, 1932) Yamaguti, 1938

18a. Testes tandem 19

18b. Testes oblique 20

19a. Pliarynx massive, larger than ventral sucker; cirrus spiny

L. hrevoortiae Nahhas and Short, 1965

iDb. I'harynx sinaller than ventral suekef; eii-mis not spiny

L. jloruJaniini Sogandares-Bernal and ITutton. 1950

20;i. Body truncate posteriorly; ovary tbree-lobed; external semi-
nal vesicle tubular or elongate; genital pore median or sub-
median, near intestinal bifurcation

L. trulla (Linton, 1907) Linton, 1910

20b. Body elongate ; ovary four- or five-lobed ; external seminal
vesicle spherical or ovoid; gmiital pore midway between

acetabulum and intestinal birurcation, sinistral

L. elomjatum (Nagati, 1942) Manter, 104(i

Class Cestoda
CoraUobotlniiiiii uifiaiih imt Essex, 1927
Host: Jcldlin-iis coius (Tiinuaeus)
Site : Intestine

CorallohotliriKni jiinhridlKin Essex, 1927

Hosts: Ictalurus catus (Linnaeus)
I. pimctatus Bafinesque

Site : Anterior third of intestine

Prof coccplml IIS sp.
Host: IctaJunis cafiif! fljinnaeus)
Site : Intestine

Eight larval and immature ]-)roteoce]->halids were recovered. These
cestodes possess four simple suckers but no apical organ is evident.


Two other larval proteocephalids were found in the liver of Lepomis
gihbosns Linnaeus. The scolex possesses four simple suckers and a non-
muscular apical organ.

BofJiriocephalus sp.

Hosts: Chacnohri/ttiis gnlosus Cuvier
Lepomis cyancUiis Rafinesque

Site : Intestine

Four immature worms were collected. Members of this genus possess
a characteristic scolex composed of two longitudinally elongated bothria
and apical disc having indented edges.

Pelichnihothrinm sp.

Host : Sahno gairdnerii Richardson

Site : Intestine

Identification of the three larval tapeworms is based on the presence
of four nonserrated sessile bothridia, each terminating anteriorly in
an accessory sucker, and a fifth apical sucker. The latter characteristic
distinguishes this genus from FluiUohothrium. Iladerlie (1053) errone-
ously placed similar larvae obtained from Oncorhynclms tshawytscha
in Phyllohothrium, but his drawings and description clearly indicate
the presence of a fifth apical sucker.


EhadinorhyncJms sp.

Host : Salmo gairdnerii Richardson

Site : Intestine

A single femnle specimen was found and is referred to this genus on
the basis of trunk spination. Members of this genus are characteristi-
cally marine. Shaw (1947) reported Fhadinorhynchus sp. from the
same host in Oregon.


The authors wish to express sincere aiiprociation to A. T>. Lyons,
Joseph Silva, and other employees of the fish collecting facility of
the U.S. Bureau of Reclamation at its Tracy Pumping Plant for making
tlie facility available for the acquisition of fish ; to Tliomas Rodella and
Eric B. Guinther of the Department of Biological Sciences of the Uni-
versity of the Pacific, for their assistance in collecting fisli ; and to the
personnel of the California Department of Fish and Game, Delta Study,
who added much information concerning the life histories and habits
of the local fishes.


Bangham, R. V. 1040. Parasites of fresh-water fish of southern Florida. Proc. Fla.

Acad. Sci., 5 : 289-307.
. 1941. Parasites from fish of Buckeye Lake, Ohio. Ohio Jour. Sci.. 41 : 441-

Bangham. R. Y., and C. E. Yenard. 1942. Studies on parasites of Reelfoot Lake fish.

lY. Distriliution studies and checklist of parasites. Jour. Tenn. Acad. Sci.,

17 : 22-38.


('nllf\. 1''. ("., mill A. ( ". < iIm'ii, .1 r. l',)(i!>. I'usl limliiihishihiii m iii ill i mil iii ( Ti rinnl i"la :
Diplostomidao) in lislics nl' I.dwci' i)|.i\ Kcsci'\ nir. S;iii Uicun ('uiiiily. ( '.•I'ifdinin.
Jour. Piirnsitol.. 4!» : 14S.

Ilndcrlic, !■]. (". l!t.">0. I';ir;isit('s of llic ficsli-wjilcr lislics of iiorilu-ni (';rifi)riii;i.
I'liiv. (";ilif., Berkclty. rii.j>. Dissertation.

. ]!>r)8. I'arasilcs of ilir fri'sli water fislios of iiortlioni California. T'ni\. r.-iMf.

Publ. Zool.. r>7:a(».S-41((.

Iloffiiiaii, (i. L. llKiO. S.viiopsis of Striseoidca (Tromatoda) of (islifs and llicir life
cycle.s. r.S. Fish and Wildl. Sorv.. Fish. Bull., GO (175) : 4:W-4(;!t.

. in()7. Parasites of Noiih .\nierican freshwater fi.shes. t'ni\. Calif. I'res.s,

Berkeley and Los Auiiclcs. ISC) p.

IIoll, F. J. 1920. A paraniiihistonie from lishes. Jour. I'ara.'iitol. li) : •i~>-li~.

Manter, H. W. 1!H>2. Notes on th<' (axononiy of eertaiii di.t;eneti<- treniatodes of

South AniericaTi frcshwalcr lishes. I'l'oe. Ilelinintli. Soc. >\'asli.. 4!> : '.17 102.
. 100.'?. The zoolnnical alliiiilies of I reinal odrs of Soiilli .Vniciacan f icshwaler

fishes. Syst. /<<(.!. 12:4.1-70.

Miller, .1. \l. lOf).'! Studies on the life history of I'DsllioiliplonloiinDn niiiiiinuiii
CNIacCalluni. 1021). Jour. Parasitol. 80:255-270.

I'earse, A. S. 1040. Observations on flatworms and nenienines euUecied al Beau-
fort, N.C. Proc. U.S. Natl. Mus., 100 (3255) : 25-38.

Shaw. J. N. 1947. Some iiarasites of Oregon wild life. Oregon Agric. Exper. Sta.,
Sta. Tech. Bull. 11 : 3-15.

Sofi-andares-Bei-ual, F., and R. F. Tint (on. lOOO. The status of some marine s])ecies
of Lcpocicadiuiu Stossich. 1004 (Tremafoda: Lepoci'eadiidae) from Ihe North
American Atlantic. In Sohretiro del lihro homenaje al Doctor Kduardo Cahalh'vo
y Calallero. Mexico, D.F.

\\'a!es. J. II. 105S. Two new blood fluke iiarasites of ti'oiil. Ca'if. Fish and (^ame,
44: 125-130.

Yamrs"'!- '^- 1054. S.xslema Helmiiitlnim. Part I. I >i.i;-eiiet:c trem.-itodcs of fishes.
Maru/.eu ( "o.. Tokyo. 4(15 p.

Calif. Fish and Game, 54(4) : 257-2G9. 19GS.



Marine Resources Operations

California Department of Fish and Game

A stratified two-stage research vessel survey was designed to estimate
the relative abundance of ocean shrimp, Pandalus jordani, in the Klamath
River-Redding Rock bed. Otter trawl hauls at randomly selected points
were the first-stage units and a random subsample of the catch from
each haul constituted the second stage. Formulas are given for unbiased
estimators of relative abundance and for associated variances. Several
allocations of sampling effort are discussed and applied to data from
the Fall, 1965 Survey. Proportional allocation at the first stage coupled
with a constant sample size at the second stage are recommended for
use because this combination is operationally the most feasible.


Estimates of year-class relative abundance derived from statistically
designed research vessel cruises possess certain advantages over similar
determinations based on commercial fisheries data. Principal among the
advantages are internally generated estimates of precision as well as
unbiased estimates of the abundance parameters. These are not gen-
erally obtainable from commercial data, since the behavior of the fishing
fleet cannot be controlled. Only precarious assumptions on tlie random-
ness of fishing or of the fished population allow one to claim these
desirable properties for statistics derived from commercial fishing. A
statistically designed survey also can eliminate problems associated
with a lack of fishing in areal strata and with the use of biased ratio-
type estimates. An extensive discussion of other problems and considera-
tions which are involved in making relative abundance estimates from
commercial fishing data is contained in the report of a symposium on
the measurement of abundance of fish stocks (Gulland, 1964).

High cost is the main disadvantage of research vessel surveys. How-
ever, a high cost is certainly justified if the relative abundance esti-
mates are to be incorporated into a mathematical population model for

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