NOAA Technical Report NMFS 84 December 1989

Results of Abundance Surveys of

Juvenile Atlantic and Gulf Menhaden,

Brevoortia tyrannus and B. patronus

Dean W. Ahrenholz

James F. Guthrie

Charles W. Krouse

U.S. Department of Commerce
NOAA TECHNICAL REPORT NMFS

The major responsibilities of the National Marine Fisheries Service (NMFS) are to monitor and assess the abundance and geographic distribution of fishery resources, to

understand and predict fluctuations in the quantity and distribution of these resources, and to establish levels for their optimum use. NMFS is also charged with the development

and implementation of policies for managing national fishing grounds, development and enforcement of domestic fisheries regulations, surveillance of foreign fishing off United

States coastal waters, and the development and enforcement of international fishery agreements and policies. NMFS also assists the fishing industry through marketing service

and economic analysis programs, and mortgage insurance and vessel construction subsidies. It collects, analyzes, and publishes statistics on various phases of the industry.

The NOAA Technical Report NMFS series was established in 1983 to replace two subcategories of the Technical Reports series: "Special Scientific Report-Fisheries" and

"Circular." The series contains the following types of reports: Scientific investigations that document long-term continuing programs of NMFS; intensive scientific reports on

studies of restricted scope; papers on applied fishery problems; technical reports of general interest intended to aid conservation and management; reports that review in considerable detail and at a high technical level certain broad areas of research; and technical papers originating in economics studies and from management investigations. Since

this is a formal series, all submined papers receive peer review and those accepted receive professional editing before publication.

Copies of NOAA Technical Reports NMFS are available free in limited numbers to governmental agencies, both Federal and State. They are also available in exchange for

other scientific and technical publications in the marine sciences. Individual copies may be obtained from: U.S. Department of Commerce, National Technical Information Service,

5285 Port Royal Road, Springfield, VA 22161. Although the contents have not been copyrighted and may be reprinted entirely, reference to source is appreciated.

48. Widow rockfish: Proceedings of a workshop, Tiburon, California, December

11-12,1980, by William H. Lenarz and Donald R. Gunderson (editors). January 1987,

57 p.

49. Reproduction, movements, and population dynamics of the southern kingfish,

Memicirrhus amerieanus, in the northwestern Gulfof Mexico, by Stephen M. Harding

and Mark E. Chittenden, Jr. March 1987, 21 p.

50. Preparation of acetate peels of valves from the ocean quahog, Areriea is/antJiea,

for age determinations, by John W. Ropes. March 1987, 5 p.

51. Status, biology, and ecology of fur seals: Proceedings of an international

workshop, Cambridge, England, 23-27 April 1984, by John P. Croxall and Roger

L. Gentry (editors). June 1987,212 p.

52. Limited access alternatives for the Pacific groundfish fishery, by Daniel D.

Huppert (editor). May 1987,45 p.

53. Ecology of east Florida sea turtles: Proceedings of the Cape Canaveral, Florida,

sea turtle workshop, Miami. Florida, February 26-27, 1985, by Wayne N. Witzell

(convener and editor). May 1987,80 p.

54. Proximate and fany acid compoSition of 40 southeastern U.S. finfish species,

by Janet A. Gooch. Malcolm B. Hale, Thomas Brown, Jr., James C. Bonnet, Cheryl

G. Brand, and Lloyd W. Reiger. June 1987, 23 p.

55. Proximate composition, energy, fatty acid, sodium, and cholesterol content of

tinfish, ~hellfish, and their products, by Judith Krzynowek and Jenny Murphy. July

1987.53 p.

56. Some as!'<lcts of the ecology of the leatherback turtle Dermoche/ys eoriaeea at

Laguna Jolova. Costa Rica, by Harold F. Hirth and Larry H. Ogren. July 1987, 14 p.

~7. Food habits and dietary variability of pelagic nekton off Oregon and Washington,

1979-1984, by Richard D. Brodeur, Harriet V. Lorz, and William G. Pearcy. July

1987. 32 p.

58. Stock assessment of the Gulf menhaden, Brevoortia paJronus, fishery. by Douglas

S. Vaughan. September 1987, 18 p.

59. Atlantic menhaden, Brevoortia ryrannus, purse seine fishery, 1972-84, with a

brief discussion of age and size cumposition of the landings, by Joseph W. Smith,

William R. Nicholson. Douglas S. Vaughan, Donnie L. Dudley, and Ethel A. Hall.

September 1987, 23 p.

tJO. Gulf menhaden, Brevoortia parronus, purse seine fishery, 1974-85, with a brief

discussion of age and size composition of the landings, by Joseph W. Smith, Eldon

J. Levi, Douglas S. Vaughan, and Ethen A. Hall. December 1987, 8 p.

61. Manual for starch gel electrophoresis: A method for the detection of genetic variation, by Paul B. AebeT>old. Gary A. Winans, David J. Teel, George B. Milner, and

Fred M. Uner. December 1987. \CI p.

62. Fishery publication index, 1980-85; Technical memoradum index, 1972-85, by

Cynthia S. Martin, Shelley E. Arenas, Jacki A. Guffey, and Joni M. Packard.

December 1987, 149 p.

63. Stock assessment of the Atlantic menhaden, Brevoortia ryrannus, fishery, by

Douglas S. Vaughan and Joseph W. Smith. January 1988, 18 p.

64. llIustrated key to penaeoid shrimps of commerce in the Americas, by Isabel Perez

Farfante. April 1988, 32 p.

65. History of whaling in and near North Carolina, by Randall R. Reeves and Edward

Mitchell. March 1988, 28 p.

66. Atlas and zoogeography of common fishes in the Bering Sea and northeastern

Pacific, by M. James Allen and Gary B. Smith. April 1988, 151 p.

67. Index numbers and productivity measurement in multispecies fisheries: An

application to the Pacific coast trawl fleet, by Dale Squires. July 1988, 34 p.

68. Annotated bibliography II of the hard clam Mereenaria mereenaria, by J.L.

McHugh and Marjorie W. Sumner. September 1988, 59 p.

69. Environmental quality and aquaculture systems: Proceedings of the thirteenth

U.S.-Japan meeting on aquaculture, Mie, Japan, October 24-25, 1984, edited by Carl

J. Sindermann. October 1988, 50 p.

70. New and innovative advances in biology/engineering with potential for use in

aquaculture: Proceedings of the fourteenth U.S.-Japan meeting on aquaculture, Woods

Hole, Massachusetts, October 16-17, 1985, edited by Albert K. Sparks. November

1988, 69 p.

71. Greenland turbot Reinhard/ius hippog/ossoides of the eastern Bering Sea and

Aleutian Islands region, by Miles S. Alton, Richard G. Bakkala, Gary E. Walters,

and Peter T. Munro. December 1988, 31 p.

72. Age determination methods for northwest Atlantic species, edited by Judy Pennila

and Louise M. Dery. December 1988, 135 p.

73. Marine flora and fauna of the Eastern United States. Mollusca: Cephalopoda.

by Michael Vecchione, Clyde F.E. Roper, and Michael J. Sweeney. February 1989.

23 p.

74. Proximate composition and fany acid and cholesterol content of 22 species of

northwest Atlantic finfish, by Judith Krzynowek, Jenny Murphy, Richard S. Maney.

and Laurie J. Panunzio. May 1989, 35 p.

75. Codend selection of winter flounder Pseudop/euroneeres amerieanus, by David

G. Simpson. March 1989, 10 p.

76. Analysis of fish diversion efficiency and survivorship in the fish return system

at San Onofre Nuclear Generating Station, by Milton S. Love, Meenu Sandhu,

Jeffrey Stein, Kevin T. Herbinson, Robert H. Moore, Michael Mullin, and John S.

Stephens, Jr. April 1989, 16 p.

77. Illustrated key to the genera of free-living marine nematodes of the order

Enoplida, by Edwin J. Keppner and Armen C. Tarjan. July 1989,26 p.

78. Survey of fishes and water properties of south San Francisco Bay, California,

1973-82, by Donald E. Pearson. August 1989, 21 p.

79. Species composition, distribution, and relative abundance of fishes in lhe coastal

habitat off the southeastern United States, by Charles A. Wenner and George R.

Sedberry. July 1989,49 p.

80. Laboratory guide to early life history stages of northeast Pacific fishes, by Ann

C. Matarese, Arthur W. Kendall, Jr., Deborah M. Blood, and Beverly M. Vinler.

October 1989, 651 p.
NOAA Technical Report NMFS 84

Results of Abundance Surveys of

Juvenile Atlantic and Gulf Menhaden,

Brevoortia tyrannus and B. patronus

Dean W. Ahrenholz

James F. Guthrie

Charles W. Krouse

December 1989

u.s. DEPARTMENT OF COMMERCE

Robert Mosbacher, Secretary

National Oceanic and Atmospheric Administration

John A. Knauss, Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service

James Brennan, Assistant Administrator for Fisheries
The National Marine Fisheries Service (NMFS) does not approve, recommend or endorse any proprietary product or proprietary material mentioned

in this publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which would

indicate or imply that NMFS approves, recommends or endorses any proprietary product or proprietary material mentioned herein, or which has as

its purpose an intent to cause directly or indirectly the advertised product to

be used or purchased bec,use of this NMFS publication.

ii
CONTENTS

Acknowledgments iv

Abstract 1

Introduction 1

Exploratory-developmental period 2

Trial-implementation period 3

Verification analysis 5

Estimation of relative abundance 5

Correlation tests of survey means with year-class strength estimates 7

Trends in regional abundance 8

Critical conditions and assumptions 8

Inherent relationship between juveniles and recruits 8

Representative nature of trawl catches 9

Timing of the survey 10

Proportional representation of regional stream densities 11

Uniform format of survey 11

Suitability of independent estimates of year-class strength 12

General discussion and conclusions 12

Citations 13

Appendix 14

iii
Acknowledgments _

We are indebted to numerous individuals who made various contributions to the continuation of the surveys over a long period of time. Many helpful analytical suggestions were

provided by Alexander J. Chester, David R. Colby, and Rodney L. Reish. During various

stages of report preparation, excellent reviews were given by Alexander J. Chester, Sheryan

P. Epperly, Charles S. Manooch, III, Walter R. Nelson, Allyn B. Powell, John V. Merriner, and Douglas S. Vaughan. The manuscript has benefitted from discussions with

William R. Turner and George N. Johnson, as well as from comments by anonymous

reviewers. We thank Herbert R. Gordy for figure preparation. Beverly W. Harvey for

word processing, and Curtis W. Lewis for the two-boat trawling illustration.

iv
Results of Abundance

Surveys of Juvenile Atlantic

and Gulf Menhaden,

BrevoonUa ~rannus

and B. patronus

DEAN W. AHRENHOLZ

JAMES F. GUTHRIE

CHARLES W. KROUSE

Beaufort Laboratory

Southeast Fisheries Center

National Marine Fisheries Service, NOM

Beaufort, North Carolina 28516-9722

ABSTRACT

The estuarine populations of juvenile Atlantic and gulf menhaden (Brevoortia tyrannus and B. patronus) were sampled

during two-boat, surface-trawl, abundance surveys extensively conducted in the 1970s. Juvenile Atlantic menhaden were

sampled in 39 estuarine streams along the U.S. Atlantic coast

from northern Florida into Massachusetts. Juvenile gulf

menhaden were sampled in 29 estuarine streams along the Gulf

of Mexico from southeast Texas into western Florida. A

stratified, two-stage, cluster sampling design was used. Annual

estimates of relative juvenile abundance for each species of

menhaden were obtained from catch-effort data from the

surveys. There were no significant correlations, for either

species, between the relative juvenile abundance estimates and

fishery-dependent estimates of year-class strength. From 1972

to 1975, the relative abundance of juvenile Atlantic menhaden

in north Atlantic estuaries decreased to near zero.

Introduction _

Fishery managers entrusted with determining population

status, or more critically, the permissible level of harvest

for fisheries with variable levels of recruitment, would be

aided considerably by estimates of prerecruit year-class

strength. With an additional knowledge of recruitment patterns, recommendations could ultimately be made that would

maximize yield while reducing risk for a particular fishery

resource. Biologists can use a variety offishery-independent

sampling techniques, such as sampling-gear catch-effort indices, hydroacoustic and sonar surveys, or mark-recapture

programs, for obtaining estimates of prerecruit year-class

strength.

The U.S. Fish and Wildlife Service, Bureau ofCommercial Fisheries, 1 expanded their menhaden research program

in 1955 to determine whether seasonal fluctuations in commercial purse-seine landings of Atlantic menhaden (Brevoortia tyrannus) could be forecasted. This research received

additional impetus in the 1960s as landings by the commercial purse-seine fleet steadily declined from the record highs

ofthe mid-1950s (Ahrenholz et al. 1987). One approach used

to pursue this objective was to estimate the relative abundance of prerecruit juvenile (young-of-the-year) Atlantic

menhaden (Henry 1971, Turner 1973). In addition to the

juvenile Atlantic menhaden sampling, which began in 1956,

sampling for juvenile gulf menhaden (B. patronus) was

started in 1964. In the early 1970s, sampling activities

culminated in extensive Atlantic and gulfjuvenile-abundance

trawl surveys that were conducted through 1978. After 1978,

the surveys were discontinued because preliminary analyses

revealed that the objective of forecasting year-class strength

with the survey data could probably not be attained (Ahrenholz et al. 1979). Results of subsequent analyses (presented

here) with completed data sets confirmed the earlier finding.

The objectives of this report are to 1) present aspects of

estuarine sampling that should be considered when attempting to estimate juvenile abundance, especially of a marine

migrant species; 2) demonstrate the need, as well as the large

time requirement for verifying juvenile survey results; and

3) document these menhaden surveys, since a large amount

of ecological and biological information on menhaden were

obtained from these studies.

In this report we first discuss the chronology and salient

aspects of what we have termed the exploratory-developmental period of juvenile menhaden abundance sampling.

During this period, biologists examined the results for several

sampling techniques. We then discuss the trial-implementation period, when extensive, systematic trawl surveys were

conducted. We then conduct verification analyses of the

survey data. Finally, we examine some initial assumptions

relating to geographical and temporal aspects ofthe sampling

design, and suggest some additional directions for the

enumeration attempts.

'Presently the National Marine Fisheries Service, NOAA, U.S. Dept.

of Commerce.
\

FL.

+- . STEINHATCHEE RIVER

__________ CARRABELLE RIVER

--- BLACK CREEK

..--------- BAYOU CHICO

DOG RIVER

/" ~MARYWALKER BAYOU

BERNARD BAYOU

BAYOU LA CROIX

~4\ DOUBLE BAYOU

l-""~-------DICKINSONBAYOU

--COLORADO RIVER

NUECES RIVER

~~ ./J(ARROYO COLORADO RIVER

~\

BAYOU BONFOUCA

RIVER AUX CHENES

BAYOU DUPONT

BAYOU POINTE AU CHIEN

BAYOU JEAN LACROIX

BAYOU BLUE

BAYOU BARRE

:::::::.------ BAYOU TERREBONNE

~~~~=====- BAYOU PETIT CAILLOU ..: ---BAYOU GRAND CAILLOU

((j - __BAYOU DU LARGE

WEEKS BAYOU

""/--------BAYOU TIGRE

r-------VERMILION RIVER

i-------- L1TTLE PECAN BAYOU

JOHNSON BAYOU

TX.

LA.

Figure 1

Juvenile gulf menhaden survey streams, 1971-78.

Exploratory-developmental

period _

Research emphasis for estimating year-class strength focused

on the obligatory estuarine phase of the Atlantic menhaden's

life history, following suggestions made by Massmann (1953)

and Massmann et al. (1954). Because menhaden occupy

relatively small estuarine streams during their late-larval and

juvenile stages, each developing year-class appeared to be

readily available for sampling. Furthermore, earlier workers

believed this would result in more accurate estimates than

those from larvae that occur in the ocean (Turner 1973).

Sampling began in 1956 and consisted of mark-recapture

studies conducted in an estuarine tributary of Indian River,

Delaware (Pacheco and Grant 1966). The program expanded

into other areas and employed additional sampling techniques. By 1961, abundances ofjuvenile menhaden inhabiting

four coastal estuarine streams (Broad Creek, North Carolina;

Felgate Creek, Virginia; White Creek, Delaware; and Childs

River, Massachusetts) were estimated using mark-recapture

methods and catch-effort data from heach seining and surface trawling. These sampling methods were used in an increasing number of estuaries along the Atlantic coast through

1966. Although the results of all three were similar, Turner

(1973) concluded that the surface trawl was the most expedient and widely applicable method. Trawling became the

only estuarine sampling method retained. The number of

streams sampled by surface trawl increased from 10 in 1962

to 65 in 1968. Trawl sampling for juvenile Atlantic menhaden

was not conducted during 1970 or 1971.

2
PA.

NY.

.....

r,,,J ','1

:f ,. \,

"\ ! \

\ "L

t

--(\ ~I"'~ ... - I '.

--' I VT I .. i .( \

\ • , dCHLDS RIVER i.. {NH.\ PAWCATUCK RIVER

... \ THAMES RIVER

" 1----- EIGHT MLE RIVER ':--MA. OLD FERRY CREEK

: ---"AI LEUTENANT RIVER

__ -..-". \\,CT.· .~~.-~- SAUGATUCK RIVER

...,>- .' '5i~===----PECONICRIVER

{

CHICAMACOMICO RIVER ..\~----------

ONANCOCK CREEK TUCKERTON CREEK

BEARDS CREEK

MACHADOX CREEK _ ,- - STOW CREEK

MATTOX CREEK V -' LEIPSIC RIVER

BALL CREEK '

QUEENS CREEK t---=:::::::!!~~ ~7r------- __ WHITE CREEK

FELGATE CREEK FOLLY CREEK

WARWICK RIVE;nR+=====~~:" _ GRAYS CREEK J'- /."".j'~

"/.~----T------'- ~~~~~~i::EK ","" NC. BLOUNTS CREEK

,/ HANCOCK CREEK

(- ----.,,\.---- NEWPORT RIVER

__ .L---('- :;;- --==== WHITE OAK RIVER

-.-, NANCYS CREEK

\, \"" SC. CALABASH CREEK

\"'" '-"_ TURKEY CREEK

GA. "''\'' COOPER RIVER " -,E=============== MEGGETTS CREEK .. STORE CREEK

,\ LITTLE BACK RIVER

( WHITE CHIMNEY CREEK

1. DUNBAR CREEK

-----\._. .,j LANCEFORD CREEK

Figure 2

Juvenile Atlantic menhaden survey streams, 1972-78.

In 1964, the program was expanded to estimate the relative

abundance of juvenile gulf menhaden along the U. S. coast

ofthe Gulf of Mexico (Turner et al. 1974). Since the general

life history of this species is similar to that of the Atlantic

menhaden, the same basic strategy of sampling was employed. Surface trawling was the only sampling method used.

In addition to the sampling methods discussed, an aerial

survey was initiated in 1962 on both the Atlantic and Gulf

coasts to estimate the fish-school surface area of juveniles

migrating from coastal estuarine streams into coastal waters.

3

Plagued by several operational and interpretational problems,

the aerial surveys were discontinued after 1971 (Ahrenholz

et al. 1979).

Trial-implementation period _

Surface-trawl surveys were conducted with nearly constant

sampling effort from 1971 along the U.S. Gulf of Mexico

coast and from 1972 along the U.S. Atlantic coast, through
Figure 3

Operation of surface trawl for juvenile Atlantic and gulf menhaden surveys.

(Drawing courtesy of Curtis Lewis, Beaufort Lab., Natl. Mar. Fish. Serv.)

1978. These surveys represented an application of knowledge

acquired during the earlier feasibility sampling. Data from

the 1970s were comparable and were used to estimate yearclass strength and, thus, the efficacy of the survey design.

Estuarine streams selected as sampling areas for each coast

appeared to be representative of other streams in the respective surrounding areas. These streams were, for the most

part, drawn from the larger set of estuarine streams that had

been sampled during the earlier exploratory-developmental

period ofthe program. Selection of a stream during the earlier

portion of the program, or the final inclusion into the survey

itself, was not purely random. Selection required that each

stream be accessible with a launching ramp for trailered

boats. Secondly, the streams would have at one time or

another been shown to contain menhaden. Estuarine locations ranged from eastern Texas into western Florida on the

Gulf of Mexico (Fig. 1), and from northern Florida into

Massachusetts along the Atlantic coast (Fig. 2).

Each stream was sampled by a series of tows evenly

distributed along the length of the stream. Sites generally

ranged from an upstream limit, where the stream was just

large enough to deploy sampling gear, to the stream mouth.

Each stream would normally have a salinity gradient along

its length, which usually ranged from somewhere near fYJ/oo

to 10 or 2fYJ/oo. The actual number of tow sites per stream

varied, ranging on the Gulf coast from 3 to 11, and on the

Atlantic from 3 to 8.

4

Because of the large number of estuaries and vast area involved, each estuary was sampled only once during a single

annual survey. The Gulf of Mexico estuaries were surveyed

in June, Atlantic estuaries from Florida to New Jersey in

June and July, and the estuaries north of New Jersey in

September.

Since juvenile menhaden are not effectively sampled in

daylight hours when the water is relatively clear, those

streams which normally had relatively clear water were

sampled at night. Night sampling was, however, impractical

to adopt for all streams. On the Gulf coast, streams east of

the Mississippi River delta were surveyed at night. On the

Atlantic coast, several individual streams from Florida to

New Jersey, as well as all streams north of New Jersey, were

sampled at night.

Each tow site was sampled by a 5-minute surface-trawl

haul. A standardized surface trawl was pulled between two

outboard-motor boats (Fig. 3). The trawl was modified after

one reported by Massmann et al. (1952) (Fig. 4). Variables

recorded for each tow site were surface salinity, secchi depth,

temperature, and number of juvenile menhaden captured.

Relatively small catches were saved in their entirety, while

large catches were subsampled. Samples were preserved in

formaldehyde solution. The juvenile menhaden were counted

and measured (fork length) in the laboratory.
'"o

...

1mm::.1inch

200

Figure 4

Standard surface trawl used in juvenile Atlantic and gulf menhaden

surveys. Head rope 7.S m, foot rope 6.7 m, length 6.1 m, and height

0.9 m. Constructed of 6 mm bar-length multifilament knotted nylon

netting.

Verification analysis _

Catch-per-tow (CPT) values calculated from trawl samples

are measures of relative juvenile menhaden abundance, not

actual (or absolute) population size. A series of consistently

derived, annual estimates of relative juvenile abundance can

be functionally compared (e.g., by regression analysis) with

a second, independently derived estimate of absolute population size, and thus "calibrated" (see Eberhardt 1978). The

estimates of absolute population (year-class) size for this

study were derived from commercial-fishery catch statistics.

If a significant, positive relationship exists, the results of the

survey have been verified, i.e., there is a high probability

that the survey is providing the type of information it was

designed to provide.

Estimation of relative abundance

Sampling activities can be described by a stratified two-stage

cluster sampling design. Each coast was divided into several

regions (strata). Individual streams were the primary sampling units, and individual tows were taken as secondary units.

For analysis, the Gulf coast was divided into three geographic

regions: Texas, Louisiana, and the eastern Gulf (Mississippi,

Alabama, and the Gulf coast of Florida) (Fig. 1). The Atlantic

coast was divided into four regions: South Atlantic, Chesapeake Bay, middle Atlantic, and north Atlantic (after June

and Reintjes 1959) (Fig. 2). The total numbers of streams

and tow sites by region planned for the Atlantic and Gulf

coast are given in Tables I and 2. Weighting factors for

regional means were obtained from estimates of relevant

5

Table 1

Planned distribution ofsampling effort by region

and estuarine stream for juvenile Atlantic menhaden survey, 1972-78.

Number of Number of

Region streams tows

North Atlantic 8 32

Middle Atlantic 5 27

Chesapeake Bay 10 50

South Atlantic 16 91 - -

Totals 39 200

Table 2

Planned distribution of sampling effort by region

and estuarine stream for juvenile gulf menhaden

survey, 1971-78.

Number of Number of

Region streams tows

Texas 5 38

Louisiana 16 III

Eastern gulf 8 45 - - Totals 29 194

habitat area given in the literature (USFWS 1970) (Tables

3 and 4). Estimates of estuarine area were retained as acre

units (as opposed to hectares) for convenience in calculation, as each tow of the trawl sampled approximately one

surface acre. Hence, each acre of potential estuarine habitat

represents a potential secondary sampling unit for purposes

of the computations.

The weighted-mean CPT (estimate of relative abundance)

and confidence intervals for each coast and year were then

calculated using formulae from Cochran (1963) (Appendix).

Regardless of size, all fish captured by the trawl were assigned equal weight to estimate the mean. Results for this

series of calculations, done with arithmetic (nontransformed)

data, are given in Tables 5 and 6 for the Atlantic and Gulf

surveys. Results for computations with loge(Y+ 1) transformations are presented as antilogarithms minus one in Tables

7 and 8. Since the antilogarithms of the means (minus one)

of the transformed data closely approximate geometric

means, they are referred to as such here.

Because of the fixed (nonrandom) nature of the particular

streams and tow sites, these estimates of relative abundance

are biased. This is not a serious problem, however. With

respect to within-years, the only real violation ofthe random

assumption is that the tows are arranged more or less systematically along the length of each estuarine stream. This

characteristic increases the probability that the entire range

of fish densities in a stream is sampled. With respect to

among-year comparisons, it was assumed that differences

(variance) in CPT associated with stream and local site factors

would be minimized among-years by using the same sites.
Table 5

Actual sampling effort, annual stratified arithmetic mean catch/tow,

and 95% confidence intervals (CI) for juvenile Atlantic menhaden

survey, 1972-78.

Table 6

Actual sampling effort, annual stratified arithmetic mean catch/tow,

and 95% confidence intervals (CI) for juvenile gulf menhaden survey,

1971-78.

Year No. of No. of

class streams tows y" 95% CI

1971 29 194 10,517.2 5,716.3-15,318.1

1972 29 191 3,448.4 1,790.3- 5,106.5

1973 29 194 7,439.9 2,031.4-12,848.4

1974 27 186 7,363.8 2,752.9-11,974.7

1975 27 183 2,580.8 520.4- 4,641.2

1976 29 191 6,927.1 2,864.5-10,989.7

1977 29 194 3,626.8 1,457.5- 5,796.1

1978 29 194 8,732.9 4,146.1-13,319.7

Table 7

Actual sampling effort, annual stratified geometric mean catch/tow,

and 95% confidence intervals (CI) for juvenile Atlantic menhaden

survey, 1972-78.

Table 3

Estimated habitat of Atlantic menhaden in V.S.

Atlantic estuarine areas, adjusted for losses to

dredge and fill operations, and used to obtain

regional weights for juvenile abundance estimates.

Region and state Acres'

North Atlantic

Massachusetts 29,000

Rhode Island 13,800

Connecticut 18,200

New York 112,700

Total 173,700

Middle Atlantic

and Chesapeake Bay2

New Jersey 357,400

Delaware 143,900

Maryland 375,300

Virginia3 425,700

Total 1,302,300

South Atlantic

North Carolina 785,700

South Carolina 265,100

Georgia 124,200

Florida4 73,650 ---- Total 1,248,650

'USFWS (1970)

2Virginia and Maryland acreage was divided between

middle Atlantic (0.15) and Chesapeake Bay (0.85).

3Middle Atlantic acreage totaled 621 ,450 and Chesapeake Bay totaled 680,850.

4This value represents 10% of all Florida's estuaries

and is assumed to represent that portion ofthe state's

estuaries within the coastal range of Atlantic menhaden.

Table 4

Estimated habitat of gulf menhaden in V.S.

Gulf of Mexico estuarine areas, adjusted for

losses to dredge and fill operations, and

used to obtain regional weights for juvenile

abundance estimates.

Region Acres'

Texas 260,000

Louisiana 2,011,500

Eastern Gulf

Mississippi 74,600

Alabama 130,800

Florida2 184,125

Total 389,525

'USFWS (1970)

225 % of Florida acres were considered to be

within the range of gulf menhaden.

6

Year

class

1972

1973

1974

1975

1976

1977

1978

Year

class

1972

1973

1974

1975

1976

1977

1978

No. of

streams

39

39

39

39

39

36

39

No. of

streams

39

39

39

39

39

36

39

No. of

tows

200

200

200

200

200

183

200

No. of

tows

200

200

200

200

200

183

200

y"

3215.8

1578.2

1417.4

653.3

2753.5

5248.5

1850.4

y"

86.7

88.9

52.7

27.2

70.8

135.6

59.1

95% CI

<0.0-6738.8

639.8-2516.6

741.4-2093.4

392.4- 914.2

830.7-4676.3

951.4-9545.6

442.8-3258.0

95% CI

28.0-264.7

39.8-197.0

21.5-127.3

11.3- 63.4

29.0-171.5

28.0-633.3

24.6-141.2
Table 8 10

Actual sampling effort, annual stratified geometric mean catch/tow, N'

and 95% confidence intervals (el) for juvenile gulf menhaden survey,

1971-78. 8

Year No. of No. of 076

class streams tows y" 95% CI on

6 0'"

0"

1971 29 194 950.1 421.5-2145.2 '" 1972 29 191 212.7 88.3- 510.6 c 5

1973 29 194 497.5 167.6-1474.1 :0

g 4 0"

1974 27 186 622.6 277.0-1399.1 072

1975 27 183 245.3 105.4- 564.3 3

1976 29 191 490.0 237.4-1010.2

1977 29 194 352.3 137.0- 903.5

1978 29 194 407.0 128.3-1287.4

00 15 30 45 80 75 90 105 120 135 150 185

STRATIFIED GEOMETRIC MEAN CATCH PER TOW

10

9

8

075

Figure 6

Stratified geometric mean catch-per-tow ofjuvenile Atlantic menhaden

in relation to subsequent recruitment at age 0.5.

0"

00 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

STRATIFIED ARITHMETIC MEAN CATCH PER TOW

(in thousands)

Figure 5

Stratified arithmetic mean catch-per-tow of juvenile Atlantic menhaden

in relation to subsequent recruitment at age 0.5.

0,"

07>

8 9 10 11

073

0"

0"

4 5 6

072

3

075

40 077

36

32

0

w 28

«

t-<n 24 « c

I-g

z:-:=

w.o 20 :;; c 1-':':;

5

a: 16 0

w

a:

12

8

4 0

077

072

078

073

0"

"' ci

w 6

«~

!;( g 5

~~:;; c 4 t-;:;

5

a:

(J 3 w

a:

STRATIFIED ARITHMETIC MEAN CATCH PER TOW

(in thousands)

Correlation tests of survey means with

year-class strength estimates

Virtual population analysis (VPA) year-class size estimates

for Atlantic menhaden from the 1972-78 year-classes were

obtained from Ahrenholz et al. (1987), and for gulf menhaden

from the 1971-78 year-classes from Vaughan (1987). Correlation analyses of the arithmetic and geometric weightedmean CPT estimates with appropriate recruitment estimates

were performed. Resultant correlation coefficients were not

significant (p>O.lO). Any apparent relationships are too

weak to be useful for forecasting year-class strength (Figs.

5-8).

Figure 7

Stratified arithmetic mean catch-per-tow ofjuvenile gulf menhaden in

relation to subsequent recruitment at age 1.0.

7
STRATIFIED GEOMETRIC MEAN CATCH PER TOW

40!;-,1*00;;-"'5i201;;0,....,3;!;0"0---:;:401;;0,......,5;d0;n0--;;6*'00.,...-,7~0:r:0--;;8*'00;;--".!90~0~1.doo

40 017

36

078

32

C! 078

0----0 Long Island, NY to MA

.---Southern NC to FL

0-0Overall Mean

6

o

Ia:

wQ.

:I:

U

le(

U

Z

e(

W

u

a:

Iw

o

w

C!JCD

C!J

o

....l

071

074

073

07'

072

8

12

l!l 28

<

~~ 24

!Z~ w.<>

::::;: c 20

.... '" 5

5 16 w

II:

Figure 8

Stratified geometric mean catch-per-tow of juven' gulf menhaden in

relation to subsequent recruitment at 1e 1.0.

YEAR

Figure 9

Loge of the geometric mean catch-per-tow of juvenile Atlantic

menhaden in the north Atlantic area, in the southern portion of the

south Atlantic area, and in all areas combined.

Trends in regional abundance

Although combined regional estimates of abundance appear

to be insensitive to the degree of fluctuations actually observed in year-class strength, some regional trends in reproductive success were documented by the survey. In the north

Atlantic area during 1972-75, numbers ofjuveniles caught

per tow fell from a geometric mean of about 200 to near 1,

and did not recover during the remaining years of the survey

(through 1978) (Fig. 9). Based on field observations associated with other studies, recovery had not occurred through

the 1985 year-class.

A similar but less extreme reduction in reproductive success has occurred in the more southerly portion of the south

Atlantic area (from Calabash Creek, North Carolina, to

northern Florida). Fluctuations in abundance for the remainder of the south Atlantic area and the remaining two

regions more or less parallel total abundance estimates.

Critical conditions

and assumptions _

3 The annual survey was conducted at a time when juvenile

populations in the estuarine streams are reasonably stable,

comprising individuals that will compose the bulk of the

recruited year-class, and are of a size that makes them

vulnerable to the trawl ('''35-60 mm).

4 Regional stream densities are a constant proportion of the

population in that general area each year. Stream densities

could have a degree of bias, higher or lower than surrounding estuarine waters (bays, sounds, and rivers), as long as

the bias is consistent among years.

5 The survey is conducted in a uniform manner each year

(e.g.. same gear. fished the same).

6 A suitable, reasonably accurate (or consistently biased)

and precise estimate of recruited year-class strength is used.

Since a poor correlation exists between survey values and

independent fishery estimates of abundance, any or all of

the above conditions are suspect.

Although many minor factors can affect the relationship of

relative abundance estimates and estimates of year-class

strength, a strong correlation would be expected ifthe following major conditions were met:

1 A strong functional relationship exists between the true

number of juveniles alive at the time of the survey and the

number that are subsequently recruited into the fishery.

2 Catches per 5-minute trawl sample reflect what is actually

in the stream. (A consistent bias is acceptable here.)

Inherent relationship

between juveniles and recruits

A fundamental but apparently tacit assumption of all the

juvenile sampling activity was that year-class strength was

established by (or was very early into) the juvenile stage.

This notion is generally accepted for most fishes (Savoy and

Crecco 1988). A significant relationship between the relative

abundance estimates and VPA year-class strength estimates

could have provided direct evidence for this assumption.

8
20,000

18,000 Atlantic Menhaden - Mean Length

at Age Zero of Fish Landed During

4th Quarter of Fall Fishery

Z 16,000 r= -.44· w

0 log R/L r =-.48· <

:I: 14,000 z

w

()

i= 12,000 Z

<....

< 10,000 IL

0

'"0 8,000 -

x

Z

w 6,000

5

a:

() 4,000 wa:

2,000.

0100 110 120 130 140 150 160 170

MEAN LENGTH AGE ZERO (mm)

Figure 10

Estimates of year-elass recruitment at analytical age 0.5 against mean

length of young-of-the-year Atlantic menhaden landed DecemberJanuary off North Carolina (* significant at 95% level).

Even stronger evidence (but not conclusive) would be provided if the relationship was subsequently persistent in future

years of sampling. The converse is not necessarily true,

however. The surveys were designed to take advantage of

this relationship, not to test for it.

A relationship between numbers of Atlantic menhaden

juveniles and subsequent numbers of recruits was observed

indirectly by examining density-dependent growth. There

was a significant inverse relationship between year-class size

and the mean size (fork length) in purse-seine landings

(Ahrenholz et al. 1979, Reish et al. 1985). This relationship

is reviewed here with additional data. The average sizes of

age-O fish in purse-seine landings were inversely correlated

with VPA estimates of year-class strength at age 0.5 (Figs.

10, 11). Since fork length is inversely correlated to estimates

of year-class size, the numbers ofjuveniles alive during the

estuarine growth period should also be correlated (positively) to estimates of year-class size. No similar relationship

was found for gulf menhaden sampled from the commercial

fishery (Nelson and Ahrenholz 1986). However, Guillory

and Bejarano (1980) found a significant inverse relationship

between mean length of juvenile gulf menhaden and commercial catch-per-unit-effort (CPUE) for age-1 fish. It should

be noted, however, that their CPUE values (surrogate for

year-class strength estimates) were not significantly correlated to Vaughan's (1987) VPA estimates of year-class size.

9

20,000

Atlantic Menhaden -Mean Length

18,000 at Age Zero of Fish Landed During

3rd Quarter of Chesapeake Bay

Fishery r=-.63·· Z

W 16,000 log R/L r=-.78·· 0

<

:I:

Z

w 14,000

()

i=

z 12,000 <....

<

IL 10,000 0

"0

x 8,000

. Z

W

6,000

5

a:

()

w 4,000 a:

2,000

120 130 140 150 160 170 180 190

MEAN LENGTH AGE ZERO (mm)

Figure 11

Estimates of year-class recruitment at analytical age 0.5 against mean

length of young-of-the-year Atlantic menhaden landed SeptemberNovember in Chesapeake Bay (** significant at 99% level).

Representative nature of trawl catches

The accuracy and precision of trawl catch rates for estimating

abundance are dependent upon local (site-specific) vulnerability ofjuvenile menhaden to the surface trawl. The width

and depth of the stream where a haul is made influence

vulnerability. Frequently, higher catches in any general area

are made where the stream is narrow and/or shallow. This

may be due to a decrease in potential avenues of escape for

fish avoiding the trawl, but could be a real difference between habitat types. While the trawl is an effective means

of capturing juvenile menhaden in coastal streams, it is less

effective for capturing larger individuals in larger rivers and

in bays and sounds.

Water clarity affects vulnerability. Quite simply, the

clearer the water, the sooner fish can see the trawl and avoid

it. A comparison of day- and night-tow trawl catches was

made for some Gulf estuarine streams surveyed in 1971. The

natural logarithms of the ratio of paired night and day tows

were plotted against the mean secchi disc values measured

during the day portion of the sampling (Fig. 12). These data

pairs display a birectilinear relationship. When the mean secchi value is less than about 45 cm, the relative magnitude

(and rate of change) ofthe difference between night and day

catches is less than when the secchi exceeds 45 cm.
Figure 13

Weighted length-frequency distribution of trawl catches of juvenile

Atlantic menhaden in Hancock Creek, North Carolina, 1972-78.

In some years, many estuarine streams whose data displayed orderly length progressions have a skewed lengthfrequency distribution, in which the left tail (smaller fish)

has not yet formed, and the mode is in the late larvalprejuvenile size range. This indicates that larval or prejuvenile Atlantic menhaden may still be immigrating into the

estuarine stream at the time of the survey. These small fish

are not completely vulnerable to the trawl, as many will pass

through the 6 mm bar-mesh tailbag. An example is given

for Hancock Creek, North Carolina (Fig. 13). Similar conditions frequently occurred in Virginia and Maryland estuaries. During 1972 and 1978, the sampling season was

apparently too early to adequately sample juveniles. During

1973-77 the small fish seemed to have been adequately

sampled. Also, there appeared to be an incomplete representation of larger juveniles (>50 mm) in middle Atlantic and

Chesapeake Bay estuarine waters. Thus, the survey may have

been too late for early-spawned individuals, as these fish may

have already emigrated from the sampling area. Similar but

less-pronounced problems were also detected with some of

the gulf menhaden length-frequencies.

1972

June 15

1977

June 19

Hancock Cr., N.C.

1978

June 22

FORK LENGTH (mm)

wllu

1976

June 15

...1...,....__.....' .........._------

~~ 1. 11 -. 1975 June 18 ~E . LllUul I~ _

I, ...I_ J_~_:e_74_18 __

"Juulu.~ J_~_:e_7_~_2_

50U

40

30

20

1~25 2. 33 }lll,'15 4••351., eo 59 13 11 8' 85 59 IS 91

20

10

0

30

2

10

0

1• I

>-

o

z

w

o

w

a:

\L

-2L-----,1~O;---::'20:.------:3:\::O,...---t.40...------:5!-::O--6-d:O,.-----:;7I,,-O -"""'aboa

Timing of the survey

Survey timing was adopted in the late 1960s from results

of earlier mark-recovery tests and catch-effort sampling. Size

of fish was a principal criterion, but early workers also felt

that the important fall-winter spawned juveniles were vulnerable during the June-july period. The survey was also conducted in September from waters surrounding Long Island,

New York, northward to accommodate spring-summer

spawned individuals (Kroger et al. 1974).

The suitability of the timing of the survey was evaluated

by examining length-frequency distributions ofjuveniles in

the catches. The distributions by stream were examined to

determine if some orderly pattern or shape occurred. If an

orderly distribution occurred, it was examined to determine

if its modal group(s) was (were) within the range of effective vulnerability.

o __-~"--/-:-

SECCHI (em)

Figure 12

Log. of night/day catch-per-tow of juvenile gulf menhaden in relation

to secchi depth (data fitted by eye).

The size offish affects its vulnerability tL 1 surface trawl.

Small fish can pass through the mesh, and larger fish can

more readily avoid the trawl. Kroger et al. (1974) hypothesized that the trawl is best suited for juvenile menhaden 35-60

mm in fork length. Because it is believed that the survey was

conducted at a time when most juveniles fall within this size

range, size-induced sampling bias was not evaluated. A

theoretical treatment of this potential problem is given by

Kjelson and Colby (1976).

Any factors which affect the surface schooling behavior

of young menhaden also affect the vulnerability of these fish

to the trawl, because only the upper portion of the water column is sampled. Effects of temperature, tide, time of day,

and wind on surface schooling of menhaden are unknown.

Despite these difficulties, comparisons of trawl catches with

haul-seine and mark-recapture studies reveal that the trawl

is reasonably effective within the bounds described (Turner

1973, Kroger et al. 1974).

10
FORK LENGTH (mm)

30 Dog River, Alabama

20 8/30/66 Tow 8 4.5%.

10

, I 0

::~ JJ, Tow 7 3.2%.

l~F IlL Tow 6 1.6%.

(/) . ...J

<

:~~ .1 L1 0 Tow 5 0.9%. :>

15 . u.

:1 0

. I LLI a:

w Tow 4 0.3%0 m

:::l:

~:~ luJ I z

Tow 3 0.2%. . l~E .,Llu. Tow 2 0.2%•

lof IIWI. Tow 1 0.1%.

0 20 24 2. 32 38 40 44 "8 62 as 80 84

FORK LENGTH (mm)

20 Hancock Cr., N.C. Tow 6 10%.

10 6/19/77

0

40

30

20 9%.

10

0

>-

~:~ Tow 4 10%. 0

z

w ., 0

:J w

c::

u.. Tow 3 10%.

~:~ Tow 2 7%0

. ,

20 Tow 1 5%.

10

0 20 o 14 Ie 72

Figure 14

Length-frequency distribution by tow with salinity values for juvenile

Atlantic menhaden from the 1977 trawl survey in Hancock Creek, North

Carolina. (The 1977 weighted distribution of Figure 10 resulted from

these distributions.)

Figure 15

Length-frequency distribution by tow with salinity values for juvenile

gulf menhaden from the 1966 trawl sampling activities in Dog River,

Alabama.

Proportional representation of

regional stream densities

Proportional representation of fish densities in regional

streams in the survey was evaluated using length-frequency

distributions. It was assumed that a near-constant proportional cross-section of the juvenile population was not sampled each year if patterns of length-frequency distributions

were not similar within streams among years, when patterns

were differentially mixed among streams within years.

Some survey design problems can be attributed to early

assumptions on life history and the concept of "primary

nursery area." The hypothesis, developed early in the

studies, was that young (late-larval and prejuvenile)

menhaden migrate upstream into small estuarine streams,

where near 00/00 salinity occurs, and then progressively

move downstream as they grow. This hypothesis was supported by observed length-frequencies in a large portion of

the streams sampled, as juveniles appeared to be stratified

by size along the salinity gradient (Figs. 14 and 15). Not

infrequently, however, similar size distributions were observed when no apparent salinity gradient existed (Fig. 16).

11

Implicit to a survey design based on streams selected for the

occurrence of a salinity gradient is the assumption that a

population offish once immigrated into a stream will remain

in that stream until emigration in late summer or fall. Often,

however, length-frequency distributions have missing portions, i.e., the right, left, or middle of an expected sizefrequency distribution was not represented in the catches in

one stream but was present in another stream during the same

year. Thus, it appears that there are varying degrees of interchange between survey streams and the larger estuarine

system to which they are tributary. The interchange appears

to be especially common in the Chesapeake Bay system.

Uniform format of survey

Considerable care was exercised during the 1971-78 Gulf

of Mexico and 1972-78 Atlantic surveys to keep all aspects

of the survey as constant as possible. Some minor problems

were created when a stream could not be adequately sampled due to periodic plant growth such as water hyacinths

(Eichornia crassipes) or duck weed (Lemna sp.) as well as

by irregular boat or barge traffic (note differences in sampling effort between Tables 1 and 2, and 5-8).
Figure 16

Length-frequency distribution by tow for juvenile gulf menhaden from

the 1975 trawl survey in Dog River, Alabama (all salinity measurements

were 0'/00).

Dog River, Alabama All Samples 0 'lb.

~f 6/19/75

.. Ww Tow 7

I, , ,,,,

~1 ,' L11..l.lJ , I , , , , ,~Ow 6

>

:f .."iliuJ, Tow 5

1 .!,Will,,, lI! Tow 4 u..

::f ,,,Iltu.u,.! ... Tow 3

20

10

t.. 28.I,t.llL" 32 38 40 44 48...82 8'&

FORK LENGTH (mm)

Tow 2

Tow 1

84 88 72

CPUE estimates in some fisheries may be useful as a

measure of abundance, if the interacting effects of other age

groups can be separated. CPUE is usually inappropriate for

use with the commercial menhaden purse-seine fishery. For

CPUE to reflect true abundance, the catchability coefficient

must be (nearly) constant. It is, however, inversely related

to population size for both the Atlantic menhaden (Schaaf

1975) and gulf menhaden (Nelson and Ahrenholz 1986)

fisheries.

VPA estimates are the closest to being true estimates of

year-class strength. This analysis provides an estimate of

number of recruits for a fixed time-period before significant

fishing has taken place on the year-class. VPA for Atlantic

menhaden should include age-0.5 fish, as large catches of

estuarine-emigrating juveniles are frequently made. This is

not the case for gulf menhaden, where age-l is an appropriate

recruitment age. A preliminary VPA estimate can be obtained

only for the Atlantic fishery after landing and port-sampling

data are processed for the complete fishing season on 3-yearold fish of a given year-class. The VPA estimates appear

to be stable after the fifth year for the Atlantic and the third

year for the Gulf fishery. Because of these constraints, a

preliminary correlation analysis of the first 3 years of a

survey would not have been possible for either fishery until

about 7 years after the survey was initiated.

General discussion

and conclusions _

Suitability of independent estimates

of year-class strength

Several potentially comparative estimates of year-class

strength can be obtained from commercial purse-seine landing statistics and port samples: Landings in biomass in a fixed

number of subsequent years, landings in numbers at a fixed

age for a given year-class, catch-per-unit-effort for a given

age, or VPA or cohort (backward sequential) analysis which

estimates number of recruits at a fixed age for a given yearclass. Each has advantages and disadvantages.

Estimates of landings in biomass, which during the time

of the survey were dominated by age-2 fish on the Atlantic

and age-l fish in the Gulf of Mexico, are readily obtainable

and are the most accurate. Strong correlations with survey

means would depend on constant growth rates among ageclasses, as well as each age group comprising a near-constant

percentage of the landings among years. Also, the rate of

fishing would have to be nearly constant. These conditi.ons

are not well met, so more adjustments would be needed.

To use age-specific landings in numbers as a measure of

year-class strength, the rate of fishing on the age group would

have to be (nearly) constant from year to year. This condition is only marginally met over short spans of years, so again

adjustments need to be made. Sampling errors about estimates for the numbers-at-age landed appear to be at acceptable levels (see Chester 1984, Chester and Waters 1985).

12

Although substantial biogeographical and life-history information for these two species of menhaden resulted from

juvenile surveys, the original objective of the sampling was

not achieved, i.e., the ability to forecast year-class strength.

It appears that the survey suffered from assumptions that were

not met.

Following the preliminary life-history studies and technique developments of the 1950s and 1960s, the survey was

initiated and the format was "locked in." Since success

would depend on the survey being conducted in a constant

fashion, any new information pertinent to the survey design

could not be implemented. Quite simply, a substantial investment had already been made in research funds and time.

Initial assumptions could not be adequately evaluated as to

whether or not the survey was effective until a sufficient

number of years had passed. Continued adjustments would

require additional years of data for testing, since the historic

database would be incomplete or noncomparable.

Once sufficient data were in hand, the straightforward comparison of weighted mean CPT, using weighting factors

derived independently from survey and catch data, with what

are believed to be analytically the best available estimates

of year-class strength, is fundamental. The lack of a reasonably strong (and significant) relationship is a logical and

prudent stopping point for a survey of this type. A risk is

present, however, as some analytical fault may lie with estimates of ages, numbers landed, and other factors associated
with purse-seine, fishery-dependent measures of year-class

strength.

The results of an extensive number of analyses were not

reported here. These included multiple regressions, various

weighting schemes, a number of derived measures of abundance, and stream or regional combinations in correlation

analyses with a variety of types offishery-derived measures

of year-class strength. Without a preconceived hypothesis

of cause and effect for variables selected in these analyses,

approaches of this type are simply trial-and-error searches,

and will no doubt result in one or more apparent significant

relationships due simply to chance. The risk here, of course,

is that one of the potential trial-and-error solutions is correct.

Development of a new survey format should be undertaken

to incorporate new information from other studies and types

of analyses that were not available or apparent during the

inception of the discontinued survey. Emphasis should be

placed on the geographic timing of the survey relative to

parental spawning in the region, and on obtaining more useful

sampling-stratification criteria.

The stratification criteria used here were geographic. These

criteria apparently did not relate that strongly to actual differences in juvenile fish density. Significant reductions in

the variance about the stratified mean CPT were not gained

over a single-stage model (tow being the primary sampling

unit), or a purely random sampling model.

Some promise with respect to an alternate approach is

offered by the density-dependent growth relationship. While

the observed correlations are not extremely strong, at least

for forecasting purposes, they are encouraging considering

the degrees of bias associated with length parameters derived

from samples of purse-seine landings. The purse-seine

catches are not systematic relative to time of year, and tend

to be selective towards larger individuals. This tends to distort

the apparent relationship on the left-hand portion of Figures

10 and 11, particularly for fishery data from North Carolina

(Fig. 10).

Because of the selective size bias and attempts to reduce

commercial catches of younger-age Atlantic menhaden

(ASMFC 1981), no attempt was made to refine this relationship. Estimates of mean length from field sampling, which

would parallel relative abundance sampling, may be a plausible approach. The discussions presented earlier on lengthfrequencies indicate that this aspect of sampling will also

require substantial refinement. Ifthis approach proves useful,

a verification of the technique may be possible using data

from historic surveys, once more in-depth analytical explanations of the observed length-frequency distributions are

obtained.

13

Citations _

Ahrenholz, D.W., J.F. Guthrie, and C.W. Krouse

1979 Evaluation of Atlantic and gulf menhaden juvenile abundance

surveys. Unpubl. manuscr., Southeast Fish. Cent. Beaufort Lab.,

Natl. Mar. Fish. Serv., NOAA, Beaufort, NC 28516, 41 p.

Ahrenholz, D.W., W.R. Nelson, and S.P. Epperly

1987 Population and fishery characteristics of Atlantic menhaden,

Brevoorria tyrannlls. Fish Bull., U.S. 85:569-600.

ASMFC

1981 Fishery management plan for Atlantic menhaden. Fish. Manage.

Rep. 2, Atlantic States Marine Fisheries Commission, 1400-1 6th St.

N.W., Wash., D.C. 20036. 134 p.

Chester, A.J.

1984 Sampling statistics in the Atlantic menhaden fishery. NOAA

Tech. Rep. NMFS 9, Natl. Oceanic Almos. Admin., Natl. Mar. Fish.

Serv., Seattle, WA 98115-0070, 16 p.

Chester, A.J., and J.R. Waters

1985 Two-stage sampling for age distribution in the Atlantic menhaden

fishery, with comments of optimal survey design. N. Am. J. Fish.

Manage. 5:449-456.

Cochran, W.G.

1963 Sampling techniques. Wiley, NY, 413 p.

Eberhardt, L.L.

1978 Appraising variability in population studies. J. Wildl. Manage.

42:207-238.

Guillory, V., and R. Bejarano

1980 Evaluation ofjuvenile menhaden abundance data for prediction

of commercial harvest. Proc. Annu. Conf. Southeast Assoc. Fish

Wildl. Agencies 34: 193-203.

Henry, K.A.

1971 Atlantic menhaden (Brevoonia tyrannlls) resource and fisheryanalysis of decline. NOAA Tech. Rep. NMFS SSRF 642, Natl.

Oceanic Atmos. Admin., Natl. Mar. Fish. Serv., Seattle, WA 98115-

0070, 32 p.

June, F.C., and J.W. Reintjes

1959 Age and size composition of the menhaden catch along the Atlantic Coast of the United States, 1952-55; with a brief review of the

commercial fishery. U.S. Fish. Wildl. Serv., Spec. Sci. Rep. Fish.

317,65 p.

Kjelson, M.A., and D.R. Colby

1976 The evaluation and use of gear efficiencies in the estimation of

estuarine fish abundance. In Wiley, M. (ed.), Estuarine processes,

vol. 2, p. 416-424. Acad. Press, NY.

Kroger, R.L., A.L. Pacheco, J.F. Guthrie, and L.R. Whitfield

1974 Development and present status ofsurvey methods for estimating

relative abundance ofjuvenile menhaden. Unpubl. manuscr., Southeast Fish. Cent. Beaufort Lab., Natl. Mar. Fish. Serv., NOAA,

Beaufort, NC 28516, 36 p.

Massmann, W.H.

1953 Relative abundance of young fishes in Virgirtia estuaries. Trans.

N. Am. Wildl. Nat. Resour. Conf. 18:439-446.

Massmann, W.H., E.C. Ladd, and H.N. McCutcheon

1952 A surface trawl for sampling young fishes in tidal rivers. Trans.

N. Am. Wildl. Nat. Resour. Conf. 17:386-392.

1954 Postlarvae and young of the menhaden (Brevoorria tyrannus)

in brackish and fresh waters of Virginia. Copeia 1954: 19-23.

Nelson, W.R., and D.W. Ahrenholz

1986 Population and fishery characteristics of gulf menhaden, Brevoortia patronus. Fish Bull., U.S. 84:311-325.

Pacheco, A.L. and G.C. Grant

1966 Part II - Occurrence, abundance, and growth of young

menhaden in a tributary creek of Indian River, Delaware, 1957.

Unpubl. manuscr., Southeast Fish. Cent. Beaufort Lab., Natl. Mar.

Fish. Serv., NOAA, Beaufort, NC 28516, 30 p.
Reish, R.L., R.B. Deriso, D. Ruppert, and R.J. Carroll

1985 An investigation of the population dynamics of Atlantic menhaden

(Brevoortia tyrannus). Can. J. Fish. Aquat. Sci. 42: 147-157.

Savoy, T.F., and V.A. Crecco

1988 The timing and significance of density-dependent and densityindependent mortality of American shad, Alosa sapidissima. Fish

Bull., U.S. 86:467-482.

Schaaf, W.E.

1975 Fish population models: potential and actual links to ecological

models. In Russell, C.S. (ed.), Ecological modeling in a resource

management framework, p. 211-239. Resources for the Future,

Wash., D.C.

Turner, W.R.

1973 Estimating year-elass strength ofjuvenile menhaden. In Pacheco,

A.L. (00.), Proceedings of a workshop on egg, larval, and juvenile

stages of fish in Atlantic coast estuaries, p. 37-47. Tech. Publ. I,

Mid Atl. Coastal Fish. Cent., Natl. Mar. Fish. Serv., NOAA,

Highlands, NJ 07732.

Turner, W.R., G.N. Johnson, and H.R. Gordy

1974 Compendium ofjuvenile menhaden surveys in coastal streams

of the northern Gulf of Mexico. Data Rep. 89, Natl. Mar. Fish.

Serv., NOAA, Seattle, WA 98115-0070, 189 p. (microfiche).

USFWS

1970 National estuary study, vol. 5, p. 82-83. U.S. Fish Wildl.

Serv., Wash., D.C. 20242.

Vaughan, D.S.

1987 A stock assessment of the gulf menhaden, Brevoortia patronus,

fishery. NOAA Tech. Rep. NMFS 58, Natl. Oceanic Atmos.

Admin., Natl. Mar. Fish. Serv., Seattle, WA 98115-0070, 18 p.

Appendix _

(4)

(3)

(2)

(1)

+

mhi

(Yhij - Yhif j=1

mhi

Yhij j=1

Yhi ---

mhi

nh

Yhi Mhi i=l

YR,h nh

Mh i=1 I

L

Yst WhYR,h h=1

Estimates of means and variances were obtained from:

number of regions (geographical strata),_

number of potential streams in region h,

number of streams sampled in region h,

mean stream size (of those sampled) in region

h (equivalent to mean number of potential tows),

size of stream i, region h,

number of tows in stream i, region h,

finite population correction for streams by

region (nhINh),

finite population correction for tows by stream

(mhiIMhi),

catch-per-tow j, in stream i, region h,

mean catch-per-tow in stream i, region h,

weighted mean catch-per-tow for region h,

stratified mean catch-per-tow for entire coast,

L

Wh = regional weight (NhMhl NhMh), h=1

v ( ) = estimate of the variance of an estimate ( ), and

S2h? = estimate of variance of catch-per-tow for stream

i, region h.

Yst

Yhij

Yhi

YR,h

Estimates of weighted mean catch-per-tow were obtained

from the following stratified two-stage cluster sampling

design. Equations are from Cochran (1963).

Given:

L

Nh

nh

Mh

(5)

(6)

Confidence intervals (CI) were estimated as follows using

the appropriate value of Students t:

95% CI = Yst ± t [v(Yst)]1/2. (7)

14