c 

NOAA Technical Memorandum NMFS 

JUNE 1981 

STOCK ASSESSMENT ACTIVITIES 

WITHIN THE 

NATIONAL MARINE FISHERIES SERVICE 

NOAA-TM-NMFS-SWFC-12 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 
NOAA Technical Memorandum NMFS 

The National Oceanic and Atmospheric Administration (NOAA) was organized in 1970. It has 

evolved into an agency which establishes national policies and manages and conserves our oceanic 

coastal, and atmospheric resources. It provides managerial, research, and technical expertise to 

produce practical services and essential information for the programs concerned with such resources. 

The National Marine Fisheries Service (NMFS) provides the United States with an integrated 

program of management, research, and services concerned about the protection and rational use of 

living marine resources for their aesthetic, economic, and recreational value. NMFS determines the 

consequences of the naturally varying environment and human activities on living marine resources. 

NMFS provides knowledge and services to foster the efficient and judicious use of those 

resources. NMFS provides for domestic and for international management and conservation of these 

living resources of the sea. 

To carry out its mission, the organization also provides for communication of NMFS information. 

In addition to its formal publications, NMFS uses the NOAA Technical Memorandum series for 

informal scientific and technical publications. These documents are specialized reports that require 

multiple copies when complete formal review and editorial processing are not appropriate or feasible. 

The management and control of Technical Memorandums has been delegated to the Research Centers, 

Regional Offices, and corresponding staff offices within NMFS. Therefore, requests for copies of 

Technical Memorandums should be sent to the author or to the originating office for the material. 
NOAA Technical Memorandum NMFS 

This TM serles IS usea tor documentation and tmeiy communlcatvon 01 prelmnary resuits. tmtertm repom. (H 

SMcIaI ouroose inlorma!ion. and t-ave not recewea complete lormai rewew. eaciormi control. or detaded editing 

JUNE 1981 

STOCK ASSESSMENT ACTIVITIES 

WITHIN THE 

NATIONAL MARINE FISHERIES SERVICE 

NOAA-TM-NMFS-SWFC-12 

U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige, Secretary 

National Oceanic and Atmospheric Administration 

Dr. John V. Byrne, Administrator 

National Marine Fisheries Service 

William H. Stevenson, Acting Assistant Administrator for Fisheries 
STOCK ASSESSMENT ACTIVITIES WITHIN 

THE NATIONAL MARINE FISHERIES SERVICE 

Page 

Executive Summary 1 

1.0. Introduction 

1.1. 

1.2. 

Stock Assessment as a Concept 

The Criteria of Relevance, Accuracy, and Precision 

2.0. Stock Assessment Methods 

2.1. Information from the Fisheries 

2.1.1. Fisheries Statistics 

2.1.2. Effort Sampling 

2.1.3. Catch Sampling 

2.1.4. Tagging Studies 

2.2.1. Fishing Surveys 

2.2.2. Visual Surveys 

2.2. Information from Fisheries-Independent Surveys 

2.2.1.1. Trawl Surveys 

2.2.1.2. Longline and Trap Surveys 

2.2.2.1. Aerial Surveys 

2.2.2.2. Land-Based Counts 

2.2.2.3. Underwater Surveys 

Fish Egg and Larva Surveys 

2.2.4.1. Acoustical Surveys 

2.2.4.2. Other Remote Sensing Methods 

2.2.3. 

2.2.4. Remote Sensing 

2.2.5. Environmental Indices 

Fisheries Analysis for Stock Assessment 

2.3.1. Surplus Production Model 

2.3.2. Yield per Recruit Model 

2.3.3. Virtual Population AnalysislCohort Analysis 

2.3.4. Spawner-Recrui t Model 

2.3.5. 

2.3.6. Change in Ratio Models 

2.3.7. Ad Hoc Models 

2.3.8. Ecosystem Models 

2.3. 

Models for Use with Marking Experiments 

3.0. Adequacy of Techno1 ogy 

3.1. Fishery and Marine Mammal Statistics 

3.2. Fishery-Independent Resource Surveys 

3.2.1. Fishing Surveys 

3.2.2. Visual Counts 

3.2.1.1. Trawl Surveys 

3.2.1.2. Longline and Trap Surveys 

3.2.2.1. Aerial Surveys 

3.2.2.2. Land-Based Counts 

3.2.2.3. Underwater Counts 

3.2.3. Fish Egg and Larva Surveys 

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3.2.4. Remote Sensing 

3.2.5. Environmental Indices 

Fisheries Analysis for Stock Assessment 

3.2.4.1. Acoustical Surveys 

3.2.4.2. Other Remote Sensing Methods 

3.3. 

3.4. Geographic Coverage 

3.5. Financial, Personnel, and Vessel Resources 

3.6. Technology 

4.0. Communication of Results 

5.0. Scientific Mix 

6.0. Discussion and Recommendations 

7.0. Cited References on Stock Assessment Methods 

8.0. Selected References on Stock Assessment Methods 

Appendix: Evaluation Matrices 

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LIST OF EXAMPLES 

Page 

1 - Guianas Shrimp Logbook Program 

2 - Shrimp Trip Interview Program 

3 - Menhaden Catch Sampling 

4 - Shrimp and Groundfish Tagging Program . 

5 - Bottom Trawl Survey Sampling Program 

6 - Eastern Bering Sea Crab-Groundfish Surveys 

7 - Northern Gulf of Mexico Groundfish Bottom Trawl Survey 

8 - Aerial Surveys of Dolphins by Line Transect 

9 - Aerial Surveys by Strip Transects of Coastal Dolphins 

10 - Aerial Survey by Commercial Fish Spotters 

11 - Cal ifornia Gray Whales 

12 - Northern Sea Lions 

13 - Ichthyoplankton Survey on Abundance of Adult Spawning Fish 

14 - Vertical Acoustic Assessment with Trawling for Target 

Verification 

15 - Sonar Mapping Acoustical Surveys 

16 - Stock Recruitment Studies of Northern Anchovies 

17 - Correl ation Model s 

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LIST OF FIGURES 

Page 

1 - Logbook form used in shrimp fishery in South American waters 

2 - Field work sheet - shrimp trip interview 

3 - Shrimp trip interview form 

4 - Dates, locations, and number of tagged shrimp released 

5 - Movement patterns of tagged shrimp released in 1979 

6 - Strata used in the standard bottom trawl survey from 

Cape Hatteras to the Scotian shelf 

7 - Cruise tracks for the northern portion of the 1979 

autumn bottom trawl survey from Long Island to 

the Scotian shelf 

8 - Stratification scheme and snow crab distribution for 

the 1975 eastern Bering Sea survey 

9 - Groundfish survey areas in the northern Gulf of Mexico 

10 - Example computer plot of finfish biomass (pounds per 

hour with standard trawl for area west of Mississippi 

River del ta 

11 - Flight chart for southern California area showing typical 

flight track and fish and mammal observations 

12 - California Cooperative Oceanic Fisheries Investigations 

basic station plan 

13 - A portion of the region covered during 1977 Pacific whiting 

survey, showing transects spaced at 10-n.mi. intervals 

14 - Trackline covered during 1979 Bering Sea walleye pollock 

survey, showing transects spaced at 30-n.mi. intervals 

15 - Relationship between population biomass and surplus production (sustainable yield) 

16 - Changes in biomass, number, and average weight of animals 

in an unfished cohort during its lifetime 

17 - Yield per recruit model 

18 - Spawner-recruit model 

19 - NMFS allocation of research resources, FY 1979 

1979 

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LIST OF TABLES 

Page 

1 - Counts of southward migrating gray whales from stations 

near Monterey, California 

2 - Estimates of abundance for California gray whales and 

their confidence interval s expressed as a percent of 

the estimate 

3 - Total counts of northern sea lions from the eastern 

A1 euti an I sl ands 

4 -Optimal allocation of sampling effort for minimizing the 

sampling error in estimating the relative abundance 

of selected species 

5 - Application of certain resource assessment techniques by 

NMFS Research Centers to stock identified in Council 

management plans or to meet Marine Mammal Act or treaty 

requi remen ts 

research at NMFS Centers and Regions 

category 

Centers during fiscal year 1979 

6 - Breakdown of approximate funds and positions devoted to 

7 - FY 1979 sea days used for assessment surveys by vessel 

8 - Sea days used for assessment surveys by NMFS Fisheries 

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STOCK ASSESSMENT ACTIVITIES WITHIN THE 

NATIONAL MARINE FISHERIES SERVICE 

EXECUTIVE SUMMARY 

The purpose of this report is to present results of the Stock Assessment 

Task Force investigation into the nature and scope of the existing stock 

assessment studies within National Marine Fisheries Service (NMFS). The Task 

Force focused its review on fishery and marine mammal populations as this work 

provides information to resource managers. The traditional fisheries 

definition of the term "stock assessment'' is the collection and analysis of 

biological and statistical information to determine the changes in abundance 

or relative abundance of living resource populations in response to fishing. 

This report describes current stock assessment methodology used within NMFS, 

with examples and evaluation of adequacy for each method. 

These methods include collecting fishery statistics and conducting 

fishery-independent surveys, such as trawl surveys, aerial surveys, marine 

mammal counts, fish egg and larva surveys, acoustical assessment, and 

environmental indices. The application of fishery analysis models for stock 

assessment then draws on the results of fishery and survey data collection 

projects. From its review, the Task Force concluded that stock assessment 

methodologies are not perfect. Each method has a particular set of biological 

and physical conditions under which it works best. Each method has a specific 

set of assumptions and associated costs. Existing methods are not completely 

interchangeable; each measures a slightly different aspect of stock abundance. 

As a result, no single approach or technique is suitable for all species or 

areas. 

One hundred and fifty different fish and marine mammal stocks are 

currently being assessed by NMFS research centers. These assessments are not 

one-time endeavors but require continued updating because of the dynamic 

nature of the stocks involved. Of the total national funds available for 

fishery research in FY79, 59% supported traditional stock assessment research 

by NMFS centers and regions. 

positions were involved in stock assessments. A total of 3,070 sea days of 

vessel time was required. The assessments for many of the minor fisheries or 

fish stocks that occur as by-catches in targeted fisheries, while based on the 

best scientific information available, are adequate only in the context of the 

pro forma requirements of the legislative acts. Stock assessments for most of 

the important stocks do provide estimates of stock size (absolute or relative) 

and information on trends in population abundance. 

The Task Force concluded that there is a need to accelerate technological 

developments for stock assessment. 

traditional sampling approaches are of particular importance. In addition, 

advances in survey technology are needed for stocks for which adequate and 

cost effective survey techno1 ogi es do not exi st. 

Approximately 54% of the 788 fulltime research 

Methods to evaluate the accuracy of 
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The Task Force also concluded that significant improvement in stock 

assessment will come from investigations of biotic and abiotic aspects of 

recruitment and inter-specific relations, i.e., causal mechanism of 

recruitment, and from ecosystem studies. Furthermore, the Task Force strongly 

emphasized the importance of improving the quality and timeliness of fishery 

statistics. This improvement will directly affect the quality of the 

assessments. 

The advent of conservation and environmental legislation over the past 

decade has created an urgent need to improve the quality and timeliness of 

stock assessment information. Stock assessment studies have been 

significantly extended to provide inforniation on the U.S. resources harvested 

by the domestic fisheries which have increasing need for data on a large 

variety of fish, shellfish, and marine mammals. 

The increased need fortimely, and in many cases urgent, stock assessment 

results requires that the quality of communications on stock assessment 

conclusions as they relate to resource management information be substantially 

improved. Preparation of stock assessment reports for various management 

bodies leaves little time for scientists to write manuscripts for scientific 

publication. As a result, peer review is often lacking. 

Within NMFS, stock assessment research is guided by mandates of federal 

legislation such as the Magnuson Fishery Conservation and Management Act, 

Marine Mammal Protection Act, and Endangered Species Act, and of international 

treaties such as the International Convention for Conservation of Atlantic 

Tuna. For resources where stock assessment is not mandated by legislation, 

research is guided by NMFS scientific missions to understand the population 

dynamics and to monitor important fish stocks. The question of proper mix of 

NMFS research can be addressed at three levels: stock assessment work versus 

other fisheries-related research; balance of stock assessment research among 

fishery resources under the Center's purview; and level of stock assessment 

analysis for a particular resource with respect to frequency, precision, and 

combi nat i on of methodol ogi es. 

These various research studies currently under way throughout NMFS 

ultimately affect the status of the fishery resources and the resulting stock 

assessments. A fundamental knowledge of the impact of natural changes in the 

environment and its resources on the survival and growth of fish populations 

is needed to understand population trends and interactions of the population 

with other biota in the ecosystem. Hence, future stock assessment must be seen 

in a much more holistic manner and current research activities should be 

designed to understand the processes and events in the inanimate and 

biological environment. 

The Task Force, recognizing that research demands and management needs 

vary among regions and fisheries, recommends that NMFS act to: 

1) enhance the timely collection and processing of improved or new 

fisheries data to meet the needs of resource managers and 

researchers ; 
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2) expand the concept of a multidisciplinary (ecosystem) approach to 

stock assessment, integrating information from environmental, ocean 

variability, and fisheries impact studies; 

3) improve knowledge of both biotic and abiotic aspects of the 

recruitment function and inter-specific relations, so that resource 

managers may evaluate the potential of regulatory measures which 

affect resource productivity; 

I 4) advance the theoretical and technical bases for stock assessment; 

5) communicate with and inform user groups in order to increase their 

understanding of the strengths and weaknesses of assessment 

techniques, and the implications of these techniques to management 

deci si ons ; 

6) recognize that new information demands for management have eroded the 

peer review process, and to explore methods to improve such peer 

review. 
-4- 

STOCK ASSESSMENT ACTIVITIES WITHIN THE 

NATIONAL MARINE FISHERIES SERVICE 

1.0. INTRODUCTION 

Considerable concern has been expressed by members of the Regional 

Fisheries Councils created under the Magnuson Fishery Conservation and 

Management Act of 1976, by members of the Marine Mammal Commission, by members 

of state fisheries and game agencies, and by academia, regarding the adequacy 

and emphasis of existing National Marine Fisheries Service (NMFS) stock 

assessment activities. Questions have been raised regarding the most 

effective technology in the conduct of such activities by NMFS and whether 

assessments are adequate in terms of the needs of the councils. 

To respond to these inquiries, the Assistant Administrator for Fisheries 

of the National Oceanic and Atmospheric Administration (NOAA) in April 1979 

established a Stock Assessment Task Force to investigate the nature and scope 

of existing stock assessment studies within NMFS. Dr. Dayt n L. Alverson, 

Director of the Northwest and Alaska Fisheries Center, NMFS', was requested to 

chair the Task orce. Members included Dr. Brian Rothschild, Senior 

Administrator for Fishe ies'; Dr. Lamarr Trott, Acting Director, Office of 

Science and Environment'; Dr. Robert Edwards, Director, Northeast Fi sheries 

Center; Dr. William Fox, Jr., Director, Southeast Fisheries Center; and Dr. 

Izadore Barrett, Director, Southwest Fisheries Center. Upon Dr. A1 verson's 

retirement in January 1980 from NMFS, Dr. Barrett assumed chairmanship of the 

Task Force. 

Scientist, NOAA E ; and, from NMFS, Mr. Jack Gehringer, Deputy Assistant 

The Task Force was requested to investigate and consider the following: 

1) current stock assessment activities within NMFS-including 

methodology, assumptions, form of outputs, and accuracy and precision 

of findings; 

2) relation of stock assessment and monitoring activities to more 

fundamental processes influencing the behavior, abundance, and 

population characteristics of fisheries resources; 

3) potential of new technological and stock assessment activities; and; 

4) questions of the best overall combination of different types of 

research which NMFS must and should consider. 

A general outline was developed by the Task Force Chairman and agreed 

upon by its members. 

on the following major topics: Stock Assessment as a Concept, Stock Assessment 

The material has been organized to provide information 

'Position in April 1979. 
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Methods, Adequacy of Stock Assessment Methods, Allocation of Financial, 

Personnel, and Vessel Resources to Stock Assessment, Geographic Appl ication to 

Stock Units or Marine Mammal Species, Communicating Results to User Groups, 

and Proper Mix of Science. 

A discussion of some of the problems confronting NMFS in the conduct of 

stock assessment studies, and recommendations to the Assistant Administrator, 

are also included. A series of matrices is added as an Appendix, to point 

out, in a condensed form, the large volume of the work conducted by NMFS to 

carry out its management responsibilities. 

This document was prepared by a Working Group of NMFS Scientists, 

including Miles Alton, Dayton L. Alverson, Murray Hayes, and Michael Tillman, 

NWAFC; Andrew Kemmerer, Joseph Powers, and James Zuboy, SEFC; Izadore Barrett, 

Tim Smith, and Gary Stauffer, SWFC; Emory Anderson, NEFC; and James Meehan and 

Lamar Trott, F/SR. Brian Rothschild, University of Maryland, also contributed 

to the document. 

direction was provided by the Guidance Group made up of the NMFS Center 

Directors. 

Murray Hayes was chairman of the Working Group. Overall 

1.1. Stock Assessment as a Concept 

The term ''stock assessment" in fisheries science has been applied to the 

collection and analysis of biological and statistical information to determine 

the changes in sizes or relative sizes of living fishery resource populations 

(or stocks) in response to the effects of fishing and, in some instances, to 

predict future trend patterns. 

leads to conclusions that equate large population sizes with the term 

"healthy" and small population sizes with the term "threatened" or "overfished." 

standpoint; that is, factors such as disease, adequacy of food, and viability 

of the individuals in the populations are frequently ignored. Hence, for the 

most part, stock assessment within NMFS has been traditionally concerned with 

abundance and distribution of stocks and their size, sex, and age composition. 

From such data, information is generated on the numbers surviving, numbers 

dying, growth rates of individuals and populations, and trends in population 

sizes, particularly in the presence of fishing. 

parameters, allowable biological harvests have been estimated in light of the 

goal of maximizing such yields. 

The process of stock assessment frequently 

Stock assessment has seldom been approached from an ecosystem 

Finally, from these 

There are many possible objectives for conducting stock assessments. 

example, the stock assessment activity might be designed to estimate the 

growth rate of a particular species, or to determine the relation between 

catch and effort in the fishery of a single species or a group of species. 

Such a stock assessment might then be used to develop a model which 

interrelates biological and economic factors to determine a level of fishing 

effort that will maximize net revenue to fishermen. U1 timately, most stock 

assessment activities are conducted to develop fishery-management information. 

For 

The many possible objectives and techniques for stock assessment raise 

the following issues: 1) What are appropriate objectives for stock assessment? 

2) Which of several techniques should be employed to satisfy a particular 
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objective? and 3) Is the attainment of particular objectives impeded by a lack 

of techniques, or do certain available techniques require improvement? 

Fisheries management objectives have changed considerably over the last 

decade. 

maximum catches, present fisheries management goals involve social and 

economic objectives within biological constraints. The biological (maximum 

catch) objectives of earlier management were relatively simple to define and 

could be measured directly in the magnitude of the catch. 

economic objectives of later management, however, tend to be more diffuse and 

complex; they are with us, nevertheless, as indicated by recent 

mar i ne- resource 1 egi sl at i on. 

While earlier objectives were primarily oriented toward attainment of 

The social and 

The Marine Mammal Protection Act of 1972 (MMPA), for example, declares 

that stocks of marine mammals should not fall below a level "...which will 

result in the maximum productivity of the population or the species, keeping 

in mind the optimum carrying capacity of the habitat and the health of the 

ecosystem of which they form a constituent element." The Magnuson Fishery 

Conservation and Management Act of 1976 (MFCMA) seeks to attain optimum yield 

for each stock of fish, which, among other things, "...is prescribed on the 

basis of the maximum sustainable yield.. .as modified by any relevant economic, 

social, or ecological factor." The Endangered Species Act of 1973 (ESA) 

imp1 ies that "...overutilization for commercial, sporting, scientific, or 

educational purposes'' is a factor in determining whether a species is 

endangered or threatened. 

are specific sanctions with respect to their capture.) 

(If a species is endangered or threatened, there 

It is clear that these laws provide us with responsibilities which fall 

into two management-related areas. The first area is conceptual and involves 

terms--such as maximum productivity; optimum carrying capacity; health of the 

ecosystem; optimum yield; relevant economic, social, or ecological factor; and 

overutilization--which are not simply nor easily defined. Many years may pass 

before scientifically valid definitions of these terms are agreed upon. These 

terms, each of which contains not only biological, but also social and 

economic implications, are very vague and considerable disagreement exists 

about their interpretation. 

called upon to advise whether stock abundance is above or below maximum 

productivity, or whether stocks are harvested at a level deemed overutilized, 

it is critical to isolate the complex issues raised by terminology and, by so 

doing, provide a basis for better future definitions. 

Because stock assessment specialists are often 

The second area is operational and involves estimating whether a 

population is at a level below the defined ''optimum" level. 

level has been defined, an estimate of population abundance made, and the 

estimate falls below the optimal level, is the estimate below the optimal 

level real or is it due to a chance deviation? On what basis should resource 

harvesting be terminated? 

If an optimum 

Our new laws have created new demands on stock assessment activities. 

The results of stock assessment affect both the livelihood of those who 

harvest or process fishery resources and the sensibilities of those who feel 

that harvesting of some species should be terminated or greatly reduced. 

Developing a strategy for attaining the social and economic resource 
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objectives therefore places considerable emphasis on the completeness, 

accuracy, and precision of stock assessment. 

1.2. The Criteria of Relevance, Accuracy, and Precision 

Stock assessment is a science-based activity oriented to provide 

information for management of fisheries, marine mammals, and their 

environment. Such information provides the biological boundaries and limits 

within which the socioeconomic bounds of man's use are set. Within the 

analytical process, the criteria of relevance, accuracy, and precision bear 

heavily on success; consequently, these criteria provide the benchmarks for 

evaluation of credibility. 

The criterion of relevance is paramount in a mission-oriented agency, 

such as NMFS, which has multiple objectives. Work must be selected which will 

provide both immediate and long range information for various constituencies-- 

fisheries managers, marine mammal managers, environmental managers, commercial 

and marine recreational fishermen, processors, consumers, and concerned 

laymen. 

are properly influenced by the constituents themselves through the various 

institutions for pub1 ic input. 

interpretation of such inputs and for setting priorities for relevant work. 

The major problem is the selection of priorities. These decisions 

Agency "managers" are responsible for 

Once the relevant work is selected, the criteria of accuracy and 

precision provide the measure of success. In most scientific undertakings 

such as stock assessment, the objective is to predict--that is, to attempt to 

develop information that reflects conditions which will be found in the real 

world. The degree to which such information conforms with reality is termed 

accuracy. Particularly in biological systems, variation occurs in appl ication 

of a survey or sampling technique and results vary from one experiment to 

another. 

biological system, and the measure of that variation around the real 

(parameter) value is termed precision. While precision for a given level of 

effort may be improved by careful statistical design, the primary means to 

improve precision is increased sampling, which translates directly to costs. 

Theory suggests that variation is an inherent characteristic of a 
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2.0. STOCK ASSESSMENT METHODS 

After the objectives of fisheries management are clearly understood, it 

is necessary to select the most appropriate stock assessment technique for 

meeting the particular objectives. 

techniques be chosen? 

criteria for choosing among stock assessment techniques with respect to 

understanding the fishery. 

How should one or several of the available 

Answering this question involves development of 

The existence of new requirements affecting the nature and time frame in 

which stock assessment objectives are defined and the ensuing need to develop 

criteria to clarify the adequacy of stock assessment techniques set the stage 

for determining the state-of-the-art in stock assessment and for NOAA-NMFS to 

develop its programs. 

techniques appropriate to their attainment need to be surveyed; the cost 

effectiveness of each technique needs to be developed; and recommendations 

need to be made. 

Particular objectives need to be identified; the 

NMFS currently utilizes a variety of techniques to acquire information on 

stock sizes and trends. Frequently, several of these techniques may be used 

to evaluate or assess the stock condition for a single species or species 

complex. Stock assessment usually begins with an evaluation of catch and 

effort data collected from a fishery or fisheries. Such data are frequently 

augmented by port sampling of landings designed to collect information on the 

biological attributes (size, age, sex, and reproductive condition) of the 

populations (stocks). Fisheries-independent data collected during biological 

surveys are used where fisheries statistics are inadequate or require 

complementing. Such surveys may take the form of aerial reconnaissance, 

direct sampling of populations with fishing gear, sampling of egg and larva 

forms with quantitative plankton nets, and remote sensing techniques. 

data may subsequently be modified or interpreted in light of environmental 

indicators. 

These 

Although a variety of methods exist for stock assessment analyses, some 

may not be applicable to a particular species, species group, or geographic 

area; some cannot be employed because of the manner in which historical data 

have been collected from the fisheries. 

information is 1 imited due to species behavior, technological 1 imitations, 

costs, etc. 

Hence, the variety of applicable 

These methodological constraints must be considered along with such 

factors as available manpower, financial resources, etc. Some fisheries are 

more valuable than others, and certain fisheries show a greater variability in 

abundance with time. The more valuable the fisheries, the more "leverage'' is 

associated with a particular stock assessment. 

underestimate of stock size has a considerably different implication for a 

fishery that exhibits a net benefit of $100,000 than for a fishery with a net 

benefit of $1,000,000. 

examination of assessment methodology might be warranted for the more valuable 

fish. 

Thus valuable, highly variable fisheries may warrant a different set of stock 

assessment strategies than low valued or low variability fisheries. 

For example, a 10% 

Greater sampling intensity or a more detailed 

The more variable a fishery, the more observations need to be taken. 
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Another factor to be evaluated is the margin of return of information for 

the investment of research resources. Low value and low variability fisheries 

might be managed if sufficient research is undertaken. 

variability fisheries, even if highly valued, may not be better managed, even 

with a considerable expenditure of resources. 

However, high 

Each NMFS Center must evaluate methodologies in terms of the above 

factors and select the most feasible approach within its financial and 

equipment resources. Stock assessment from egg and larval studies has, for 

example, been employed consistently in the California Current area and less 

frequently in the Gulf of Mexico; it has been more or less inapplicable in the 

northeast Pacific and northwest Atlantic. 

fishing gear has been, to a greater or lesser extent, a mainstay of the stock 

assessment studies conducted by the Northwest and Alaska Fisheries Center, the 

Southeast Fisheries Center, and the Northeast Fisheries Center. Remote 

sensing and aerial sensing have been used by both the Southwest and Southeast 

Fisheries Centers. All Centers make extensive use of routinely collected 

statistical data from foreign and domestic fisheries. 

Direct sampling with commercial 

In this section on methodology, we will consider the sources of data-- 

from the fishery itself, from fishery-independent surveys, and from the 

environment--and how these are integrated through fisheries analyses to 

produce stock assessments. 

2.1. Information from the Fisheries 

A primary source of information for stock assessment is the fisheries 

themselves. The mechanisms for collection of such information vary among 

fisheries, areas, and agencies. For example, landings data from the 

commercial fisheries are generally collected by federal agents on the east and 

Gulf coasts and by state agents on the west coast. Recreational catch 

statistics, on the other hand, are usually collected by creel census 

techniques applied on a random sampling basis. Fishing effort and location 

data may be collected by mandatory logbooks in some fisheries and by interview 

data in others. These data collected from the fisheries, however, may be 

organized in functional groups as follows: 

1) traditional fisheries statistics on participation, catch, effort, and 

fish products; 

2) catch sampling data for species, sex, size, and age composition, and 

for food habits and reproduction; 

3) logbook, interview, or survey data for detailed area of catch, 

effort, and socioeconomic descriptors; and 

4) tagging studies to identify origin of stocks, migrations, growth, and 

rate of exploitation. 
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2.1.1. Fisheries Statistics 

Fisheries statistics are a primary source of information on the status 

of fish stocks. These statistics include routine scientific data collected 

from samples of the fishery catch but do not include data collected during 

resource surveys carried out by scientific organizations. 

To be of most value, catch data should be reported by species or stock 

and-by area and time; associated effort data should be reported on the most 

refined basis possible, e.g., trawl hours as opposed to number of days absent 

from port. 

one day to several months. Trip data can be reported on individual sales 

transaction records (also called weigh-out slips o r f i s h tickets) which are 

filled out by the purchasing dealer in cooperation with the vessel captain. 

Alternatively, the information on the fishing trip may be collected through 

interviews by a port agent with a vessel captain at the conclusion of a trip. 

Data collected on fish tickets include weight and price of catch by species, 

and date of sale; sometimes area of capture, fishing effort, and gear type is 

also included. The individual vessel is generally identified so that effort 

can be standardized among vessels. 

Landings data are generally collected on a per trip basis, which last 

Summary 1 andi ngs data are reported at periodic interval s ( usual ly 

monthly) by wholesale dealers. These reports give total 1 andi ngs , value, and 

price ranges, but provide little useful data on fishing effort or location. 

Summary landings data may be sufficient for stock assessment when only total 

catch information is required and there is an independent measure of fishing 

effort. Generally, however, more detailed information is needed. 

Landings data are usually collected by census techniques, i.e., 100% 

sampling, but may sometimes be collected for a portion of the fishery only, 

e.g., the commercial fishery in contrast to the recreational fishery, or 

commercial landings sold to leading wholesale dealers. In such cases, 

landings data for these portions of the fishery are used as an index. 

Statistical sample design theory, therefore, needs to be developed to improve 

the accuracy of the estimates of total landings and to increase cost 

effectiveness. Although it would be possible theoretically to estimate total 

landings based on sampling, uncertainties about the fishery universe and its 

sampling variability have precluded most attempts at estimation. 

Special methods are general ly required to estimate recreational catch. 

permit data gathering; therefore, survey problems are often difficult. Creel 

census techniques are applied on a random sampling basis. Two-stage sampling 

may also be used, which combines creel census (intercept survey) to determine 

catch-per-unit effort and telephone or mail surveys to estimate total effort. 

The National Recreational Fishing Survey is designed to provide estimates of 

catch by species on a bimonthly basis. Results from the first survey year are 

now being eval uated. 

Recreational catch does not flow through a number of channels, which would 

Fi shery statistics for stock assessment are col 1 ected by federal and 

state governments. The division of responsibility is by local arrangement. 
-11- 

On the west coast, the states often collect comprehensive fishery statistics 

while the federal government has a limited role. 

the federal government operates regional statistical data collection systems, 

with input from the states. 

have developed through a partnership approach implemented by specific 

state-federal agreements on collection of statistics. 

On the east and Gulf coasts, 

In some cases, integrated data collection systems 

Fishery statistics are the heart of fishery information systems used 

by economists, biologists, and managers. Such systems provide summary 

information to economists on the economic status of fisheries, specific data 

to biologists for stock assessment, and data to managers for management 

analysis. For example, fishery statistics often include price and product 

flow data, which are of little use for stock assessment but are important to 

economists and to analytical models of total fishery systems. Because of a 

need to serve many users, fishery statistical systems have developed somewhat 

independently of, rather than as a result of, the requirements for stock 

assessment. Consequently, biol ogi sts have sometimes devel oped i ndependent 

data files for analysis. Managers are often unable to use these detailed 

statistical data files unless they have adequate data management support to 

redesign existing operational systems. 

2.1.2. Effort Sampl i ng 

While fishery statistics collected by fish tickets or port agents 

provide nominal data on effort per trip, more detailed records of individual 

fishing activities are collected by interviews or logbooks. These techniques 

provide detailed records of individual fishing operations, such as the number 

of sets or hauls by gear type, or a summary of a day's fishing activities. 

Data usually include estimated weight of catch by haul, date, time, and 

location, which, when combined with data on physical characteristics of the 

individual fishing vessel, can be used to standardize fishing effort among 

vessel s to obtai n essent i a1 f i shi ng mortal i ty estimates. 

Logbook or interview data are generally collected by state agencies on 

The recent 

the west coast' and by federal port agents or state-federal programs on the 

east and Gulf coasts. Such arrangements rely on the confidence that exists 

between the fisherman and the data collection agent or biologist. 

decision to separate such data from enforcement use will do much to improve 

acceptance of the data. 

A difference of opinion exists as to the desirability of mandatory 

versus voluntary participation in logbook and interview programs. Advocates 

of mandatory programs point to successful use by the International Pacific 

Halibut Commission (IPHC) and certain states, and to the legal leverage at 

hand. 

that will ing participation provides "better data." 

Advocates of voluntary programs point to other successes and suggest 

The results, however, are 

'Except ions are the international arrangements for col 1 ect i ng 

information on halibut (IPHC) and on yellowfin tuna and skipjack 

( International Convention for Conservation of At 1 antic Tuna ( ICCAT) ) . 
-12- 

the significant factors, and they will ultimately be governed by local custom 

and social confidence in the management institution. 

In addition to effort data, logbook and interview programs provide 

contacts with the fisheries that yield ancillary data on "conditions" of the 

target species, interrelationships among elements of the catch, and estimates 

of such factors as discards at sea. 

programs follow. 

Examples of logbook and interview 

Example 1.--Guianas Shrimp Logbook Program 

In 1972, the Southeast Fisheries Center established a system for 

collecting information on catch and fishing effort for the Guianas-Brazil 

shrimp fishery as part of its responsibility under the U.S.- Brazil Agreement. 

The Agreement requires that vessel skippers keep records of their fishing 

activity. A logbook form was designed after consultation with fleet 

operators, plant processors, and representatives of the Brazilian fisheries 

department (Fig. 1). The form provides a record of information on fishing 

time, area, and catch for each trip. To aid the skipper in describing his 

fishing area, the logbook form includes a chart of the fishing grounds marked 

with grid zone numbers and depths. 

drags made and number of hours fished each day, and separate entries are made 

for day and night fishing. Catch is given as total pounds (heads-off weight) 

caught each day, and the fisherman is asked to indicate the species and the 

predominant size category. 

Fishing time is recorded as number of 

The Agreement requires that logbook records be kept for fishing in the 

Area of Agreement off Brazil. The U.S. industry, however, realizing the 

importance of this information, has taken a far-sighted step by volunteering 

to record and submit these data for the entire area of the fishery. In 

addition to the logbook reports, each processing plant reports the size 

composition of each vessel's landings. 

although NMFS provides the logbook forms and processes and analyzes the 

statistical data, the U.S. industry collects and submits the information. The 

collection of raw data is the most important part of any fishery statistics 

system and represents a significant input of time and effort by industry 

members--the vessel captains and the fleet managers--to provide the basic 

information necessary to understand and manage this fishery. 

It is important to point out that, 

The information from the logbook reports is tabulated and made 

available in summary form. The summary, prepared by computer print-out on a 

monthly or quarterly basis, shows the catch in pounds and the fishing effort 

in number of drags made and number of hours fished for each fishing zone and 

depth range. 

effort which will best describe the fluctuations in the stocks. 

This information is further used to study the unit of fishing 

Example 2.--Shrimp Trip Interview Program 

The shrimp trip interview is conducted by Southeast Fisheries Center 

Fi shery Reporti ng Speci a1 i sts (FRS) . Each FRS randomly sampl es approximately 

30% of the total shrimp vessel trips in his assigned area. Data are collected 

on a field work sheet (Fig. 2) and include the following: vessel name, date 

of landing, dealer, size and number of shrimp trawls, catch by species, 
-13- 

SHRIMP LOG BOOK 

VESSEL NAME 

DEPART FROM 

(OFFICIAL WO I 

NET SIZE____ 

CAPTAIN5 NAVE 

I I I I I I I I I I 1 I I I I 1 

I I 1 1 I 1 I I 

Figure l.--bgbook form used in shrimp Eishery in South Amerlcan waters. 
E 

HOM COeM 88-20 

(>-I Jl 

U.S. DEPAHThCNT OF COMMtRCE 

HATIOHAL OCCAKIC AN0 ATYOSPHKRIC ADUINI~TRATION 

NATIONAL UA~INL riwcmics scnvicL 

VESSEL DATE OF MO. DAY YH. 

NAME LANDING 

FOR',/ #I PPRO VED 

OAlB NO. I1 -R2390 

DEALER 

-~ 

NIGWT ONLY 

DAY OULY 

OAY AH0 NIGHT 

NUFIBER OF 

TRPXLS 

BROWN SMUIUP 

TOTAL 

CATCH 

PINK SHRIMP 

IHITE 5KRlMP 

5EA BOQS 

c HIJ. I c tlrw. 

P Hta. Q Nl#. 

I 

IIEADS-ON POUNDS BOXES 

CONDITION U 

I3 

LANDED 

HEADS-OFF U III RRELS n DASKETS 

RSMAkKS 

1 

I 

UOAA 131- (8-10 

- 

'igurc 2. --Field work sheet - shrimp trip interview. 
-1 5- 

grounds and depths fished, effort in hours by day and night, and condition 

landed. The FRS also interviews the dealer and obtains total catch by species 

and size category for all vessels landing on a given day (Fig. 3). An estimate 

of the total effort can be obtained.by combining all of this information. 

The total catch and total effort data are then utilized in production 

models to estimate sustainable yield for each species, and in summary 

tabulations for other biological and economic studies. studies. 

2.1.3. Catch Sampling 

assessment, including data on species, sex, size, and age composition of 

catches, that are used to obtain growth and mortality information vital for 

fisheries analysis. 

obtained. 

vessels or by observers aboard foreign fishing vessels, but efforts are being 

made to increase onboard sampling of the domestic fleet to improve information 

on discards at sea. Observers also collect data on the incidental capture of 

marine mammals in high seas fisheries for tuna and salmon. 

sampling of catch is combined with log or interview data to further 

characterize individual catches and/or to extrapolate individual catch samples 

to the sampled universe. For these purposes, careful attention to random 

collection of samples and statistical design is essential to permit 

extrapolation of sample data to stock parameters. 

sampling program follows. 

Catch sampling provides critically important biological data for stock 

Feeding habits and reproductive information are a1 so 

Catch samples are normally taken by port samplers for domestic 

Frequently port 

An example of a catch 

Port sampling of domestic catches, as with fisheries statistics and 

effort sampling, is generally conducted by state agencies on the west coast 

and through federal arrangements on the east and Gulf coasts. On both coasts, 

catch sampling data aboard foreign vessels are collected through the federal 

foreign fisheries observer program. Careful statistical design is required to 

combine such data from various sources. 

Example 3.--Menhaden Catch Sampling 

A prime example of catch sampling is that conducted by the Southeast 

Fisheries Center in the Gulf of Mexico and Atlantic menhaden fisheries. The 

program has been in effect for over 20 years and has contributed significantly 

to our biological knowledge of menhaden and to our ability to provide 

management advice on the fisheries. 

The sampling program covers the entire coastline from Rhode Island to 

Louisiana. 

arrives at the processing plant, covering five to six boats per day, five days 

a week, for the entire season. It is possible to take such a seemingly small 

sample because of the slight variability found among individual fish from a 

given school. The length, weight, and a scale sample are taken for each fish. 

The vessel number and area of capture are also noted. The sample data, 

combined with the landing records of the processing plants, are used to 

estimate the number of fish landed weekly at each plant, and this information 

is then summed to estimate the total number harvested for the year. 

The port samplers take a ten-fish sample from each boat as it 

The 
-16- 

41-%3 I 16 I 51-67 1 17 1 

PFORM 88-20B U.S. DEPAHTMENT Or COt-iAERCE NOFA/NMI.'S F0P.M APPROVED 

Om N0.41-R7590 

EXP 1-31-82 IIPORT VCSSEL OFFICIAL NO. DATE MO. DAY Yrt. 

(1-2) NAYE (3-8) (15-20) 

TRIPS TYPE GRADING DEALER NO 

(32-37) (38) (69-71 1 S 

AIcEA (21-24) DucP'rir (25-26) IDEPTH (25Z 

I 

DAYS FISHED AYS FISHED . 

(27-31) 

7 

SPECIES 

BROWN 

PINK 

WHITE 

I 

I 

I 

I 

t 

1 

r.22 

NOAA iotau aa-20 8 

Figure 3. --Shrimp trip interview fonn. 

PIECES 19 - UNDER 15 21 I 

15-20 1 22 I 

21-25 23 

.26-x, 24 I 

31-Y) 25 

(18 

41-9 

51 

6 

-67 

OVER 

17 

:b 

28 

x I 1 I 

PIECES 29 

UNDER IS 31 

1 

IS-= I 32 

21-2s 

26-33 

31-40 I 35 

4t-5~ I 34 1 

51-47 1 37 

PIECES I9 I ALL 40 
-1 7- 

sample data are also used to construct life tables for estimating growth and 

mortal ity parameters. 

Most of the menhaden vessels now carry logbooks for recording effort 

data as well as total catch. The data obtained by catch sampling will 

eventually be correlated with the logbook effort data to provide more viable 

management advice. 

2.1.4. Tagging Studies 

Tagging programs are designed to address stock origin, migration, 

growth, mortality, population size, or rate of exploitation; some have 

multiple purposes. These programs tend to be more closely associated with 

research programs than are other data collected from the fishery itself, 

although tags are commonly recovered in connection with catch sampling and 

interview programs. Example of a tagging program follows. 

Example 4.--Shrimp and Groundfish Tagging Program 

An example of one approach for acquisition of stock assessment 

information from tagging data is provided by the shrimp and groundfish program 

of the Southeast Fisheries Center. 

catch and effort statistics collected from the commercial fisheries, to 

delineate shrimp stocks in the Gulf of Mexico, develop a yield-per-recruit 

model, and ultimately predict biological yield. Conventional fisheryindependent trawling surveys are not relied on extensively to satisfy these 

objectives. 

within seasons, months, and perhaps weeks, the shrimp cannot be aged, and the 

re1 ationshi p between adult spawning populations and recruitment is not 

understood. Past offshore trawling surveys, however, have provided valuable 

information on species and size distribution patterns and some indications of 

the temporal and spatial characteristics of spawning. Additionally, estuarine 

trawling surveys are still used by state resource managers to provide data for 

controlling the opening and closing of shrimp fishing seasons. 

Tagging data are used in conjunction with 

Because shrimp are short-lived and population size varies greatly 

The tagging program involves extensive cooperation among the States of 

Louisiana and Texas, universities, Sea Grant, Mexico, and commercial 

fishermen. In 1979, for example, over 113,000 shrimp were individually tagged 

and released in 16 geographically distinct areas (Fig. 4). Overall, 

approximately 7% of the tags were returned although, for selected areas, up to 

as many as 25% of the tags came back. 

fishermen who were encouraged to participate in the program through various 

contests sponsored by universities in which cash prizes were awarded. 

Most of the tagging is done from NOAA research vessels. A 12.2-meter 

(40 ft.) standard shrimp trawl is used to collect shrimp for tagging. 

time is less than 15 minutes to minimize injury to the animals. 

vessel, the shrimp are quickly sorted from the catch and placed in large sea 

water tanks where they are held 30 to 45 minutes to isolate healthy shrimp 

from those injured by the trawl. 

for species, sex, and tail length data; a narrow plastic ribbon tag is 

inserted through their tails with a needle coated with a broad sprectrum 

Returns were primarily from commercial 

Tow 

On board the 

The shrimp are then individually examined 
-18- 

JULY-OCT 1979 12,800 

MAY 1979 11,600 

SEP 1979 200 GULF OF MEXICO 

MAY 1979 1,400 

APR-AUG 1979 15,700 

JUNE 1979 600 

Y 

*.de 

SHWIIIW TAGb'iRIG 

RELEASE AREAS - 1979 

j 

igure 4. --Dates, locations, and number of tagged shrimp released in 

10 " 

!8" 

26" 

24" 

22" 

I 

120" 

I 1 

92" 90" 

- .18" 

I I 

__- 

18" 

94" 
-19- 

antibiotic; tag numbers are recorded; and the tagged shrimp are placed back 

into large sea water tanks. 

are again examined to remove any which appear unhealthy. 

the healthy tagged shrimp are then placed into disposable canisters for 

release on the bottom of the ocean. The canisters are equipped with springloaded ends held in place with a salt-block trigger. The canisters are 

dropped over the side of the vessel to fall to the bottom, where the ends 

break away after 10 minutes of soaking to release the shrimp. 

After a period of 3 to 4 hours, the tagged shrimp 

Selected numbers of 

Examples of the type of information already gained from the shrimp 

tagging program include verification that all three shallow-water shrimp 

species common from Texas to Mexico, i.e., brown (Penaeus aztecus), white (P. - 

setiferus), and pink (P. duorarum) shrimp, are transbounda'm. 5), and 

that growth rates for Eoth brown and white shrimp vary with season and 

environmental conditions. Information on shrimp movement and migration 

patterns, and on the contribution of specific estuarine systems to the 

offshore stocks, has also been gained, along with preliminary estimates of 

seasonal mortal ity rates. 
-20- 

96OW 92' 90' 

GULF OF MEXICO 

Figure 5. --Movement patterns of tagged shrimp released in 1979. 
-21- 

2.2. Information from Fisheries-Independent Surveys 

Marine f i shery resources di spl ay 1 arge temporal and spatial vari abi 1 i ty 

in abundance and distribution. Harvest statistics are frequently insufficient 

from which to develop unbiased estimates of the magnitude of biomass 

fluctuations in time or space for either a particular stock or a resource 

complex. Commercial or recreational fishing activities are generally directed 

toward maximizing profit or pleasure by adapting fishing strategies and 

harvest efficiency to market conditions, availability of fish, and the like. 

Accordingly, catch-effort data are often inadequate by themselves as a measure 

of abundance for ,individual stocks, despite adjustments to correct for these 

biases. Mixed fisheries exist in which landings and effort data are more a 

reflection of the behavior of fishermen (discarding and culling of selected 

species or sizes of fish, selective fishing, etc.) than of selected species or 

stock size. Even for those infrequent stocks for which fishery statistics are 

complete and largely unbiased, these data provide little or no information on 

pre-recruit abundance and distribution, growth and maturity rates, or species 

interactions (e.g., food habits). 

To provide resource information independent from the fisheries, a number 

of field techniques are used. 

trap) surveys, 2) visual counting and enumeration of marine mammals and 

fishery resources with aerial , 1 and-based, and underwater surveys, 3) fish egg 

and larva surveys, 4) acoustic and other remote sensing techniques, and 5) use 

of environmental indicators. A description of these basic methodologies and 

their analytical techniques is described in the sections which follow. 

These include 1) fishing (trawl, longline, 

2.2.1. Fishing Surveys 

2.2.1.1. Trawl Surveys 

Perhaps the most important stock assessment activities involved with 

field surveys are those concerned with direct trawl surveys of pre-recruits 

and the exploitable portion of fish populations. 

types of surveys follow. 

Three examples of these 

Example 5.--Bottom Trawl Survey Sampl ing Program 

Beginning in 1963, the predecessor of the Northeast Fisheries Center 

(NEFC) initiated a bottom trawl survey sampling program in the continental 

shelf waters of the northwest Atlantic, designed to monitor fluctuations in 

the structure and size of fish populations independent of commercial fishery 

statistics, and to provide a quantitative index for the finfish biomass 

components of the northwest Atlantic ecosystem. The survey program was also 

established to facilitate estimation of fish production within the continental 

shelf region, and to provide basic ecological data (growth rates, maturity 

rates, feeding interrelationships, etc.) on a broad geographic scale so that 

causal relationships between the quantity and distribution of fish production 

and changes in environmental and biotic factors might be determined. 

The first bottom trawl survey was conducted in the autumn of 1963. 

This and subsequent autumn surveys during 1964-66 sampled the continental 
-22- 

shelf from western Nova Scotia to Hudson Canyon. 

extended south to Cape Hatteras, North Carolina. 

survey was initiated covering the same area as the autumn survey. 

In 1967, the survey was 

Beginning in 1968, a spring 

In 1972 the surveys were expanded; previously the 26-meter (15-fathom) 

contour marked the innermost limits of the trawl sampling. To fill this gap in 

coverage, the Sandy Hook Laboratory in New Jersey began an inshore survey in 

waters of 26 meters (15 fathoms) to less than 9 meters (5-fathom contour). 

The first inshore survey in the fall of 1972 extended from Montauk Point, 

New York, to Charleston, South Carolina. At the same time, the Sandy Hook 

Laboratory initiated an offshore survey south of Cape Hatteras to Cape 

Canaveral, Florida. Coverage south of Cape Hatteras was assumed by South 

Carolina in 1973 with NMFS funding. Since then, semiannual or annual surveys 

have been conducted. One small gap remained in the coverage, between Cape 

Fear and Cape Hatteras, which has been sampled by routine autumn and spring 

surveys since the fall of 1978. 

In 1977 a new time series of summer inshore surveys began (less than 

60 fathoms or 110 m) in an effort to increase the comprehensive data base as 

well as to obtain more information on species of recreational interest. 

Coverage was carried out from Cape Hatteras to Maine that year, and in 1978 

the summer survey was continued south to Cape Fear. 

Methods--An objective of these survey efforts is to obtain a statistically valid sample, which will provide valid estimates of sampling error 

(variance). 

throughout all the possible ecological zones of the survey area is also 

required. To satisfy these statistical and biological considerations, a 

stratified random sampling design is chosen for the surveys. 

A method to assure a fairly uniform distribution of stations 

Depth is used as the primary boundary determinant because of its known 

relationship to finfish distribution. Figure 6 depicts offshore and inshore 

strata from Cape Hatteras to the Nova Scotian shelf. The entire survey area 

from Nova Scotia to Cape Canaveral has been stratified, with the major stratum 

boundaries being determined by depth (less than 5, 5-10, 10-15, 15-30, 30-60, 

60-100, and 100-200 fathoms). 

Stations are selected randomly within each sampling stratum. Each of 

the larger strata is divided into areas equivalent to 5 minutes latitude by 

10 minutes longitude. 

sampling unit. (This means only one trawl haul is necessary to characterize 

that unit.) 

which are numbered consecutively. Numbers are drawn from a random table or 

generated by computer and the stations are so selected. Only one station in 

each of the 5 x 10-minute areas is selected, to assure that the stations are 

disperse and that every possible trawling site within a stratum has an equal 

chance of being selected. 

strata cannot be divided into the 5 x 10-minute rectangles; in this case, the 

small er 2-1/2 by 2-mi nute rectangles are used. 

Each of these rectangles is considered a homogenous 

Each of these units is further subdivided into 10 sub-units, 

The smaller narrow inshore and deeper offshore 

The number of stations occupied within a stratum is roughly 

proportional to its area. 

Bank, and some of the inshore areas with great potential pollution impact, are 

Certain strata in priority areas, such as Georges 
-23- 

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-24- 

sampled more heavily. 

sampled more heavily because at least two stations are needed to permit 

variance computation. 

Some of the small inshore and offshore strata are also 

Approximately 400-450 stations are occupied in a complete survey 

between Cape Hatteras and Nova Scotia. 

200 square nautical miles; sampling allocation south of Cape Hatteras is about 

the same. 

This represents one station for every 

The surveys are conducted so as to minimize steaming time and maximize 

vessel time. Southern areas are usually completed first, with the ship 

general ly working northerly to preserve synopticity. 

The order in which the stations are visited depends in large measure 

upon their relation to the shortest cruise track and the overall cruise plan. 

An example of a cruise track for a portion of the bottom trawl survey is 

presented in Figure 7. 

There are two standard survey trawls: a #36 Yankee and a #41 Yankee 

trawl. The #36 was used on spring and fall offshore surveys through 1972 and 

on all fall and summer surveys since then. The #41 has been used on spring 

surveys since 1973. Initially, the #36 trawl was adequate to provide the 

abundance indices needed for most commercially important species. However, in 

the late 1960s and early 1970s, the abundance of fish dropped and a larger 

trawl was needed. The #41 trawl opens to 5 m, about 2 m higher than the #36. 

The sweep on both trawls is rigged with rollers. Ground cables are not used, 

to permit fishing over rough bottom. During the inshore surveys conducted by 

the Sandy Hook Laboratory from the fall of 1972 until and including the spring 

of 1975, a 3/4 size #36 trawl rigged with a chain sweep and ground cables was 

used. All trawls have a 1.25 cm stretched-mesh liner in the cod-end and upper 

belly. 

All trawls and otter doors are tested and measured during special gear 

mensuration cruises before being used on a survey. During these cruises, each 

trawl is towed in several directions relative to the surface current, at 

several different speeds, and at different scope (ratio of wire out to depth). 

During these tows the opening of the trawl is monitored acoustically with 

trawl-mounted transducers. Each trawl and set of doors must operate within 

certain specifications before they are used on a survey. 

a temperature profile is obtained with an expendable bathythermograph (XBT) 

system. A surface bucket temperature is also taken, and a surface water 

sampl e is col 1 ected for subsequent sal i ni ty measurement. In i nshore areas, an 

optional bottom salinity measurement is taken along with oxygen 

determinations, especially during summer months. Observations on weather, sea 

state, and position are also recorded. 

When arriving on a pre-selected station, and before the trawl is set, 

A standard trawl haul begins when the predetermined amount of wire is 

let out and the winch drums are locked. The haulback process begins 

30 minutes later. 

2-1/2:1 offshore in depths greater than 185 meters (100 fathoms). 

is towed at 3.5 knots (over-the-bottom speed). 

The scope varies from 5:l in the shallow nearshore areas to 

The tow direction is generally 

The trawl 
-25- 

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-26- 

toward the next station, although this is not always the case, especially in 

very rough weather or in areas where the bottom is steeply graded. 

latter conditions, a depth contour is followed. 

recorded during each tow. 

Under the 

A fathometer trace is also 

The catch is dumped onto a table and sorted by species. The sorted 

fish and invertebrates are weighed to the nearest kilogram and measured to the 

nearest centimeter (to the end of the center caudal fin ray of the fish). 

When large catches are impractical or impossible to sort, they are subsanipled 

by weight or volume before sorting. After weighing and measuring has been 

compl eted, sampl e col 1 ections are made. 

Routine collections include scales, otoliths, or other hard parts, for 

age and growth studies, as well as stomachs for food habit studies. Tissue 

samples are taken for pathology or contaminant studies. Gonadal conditions 

are noted and ovaries are removed from selected species for fecundity studies. 

Special sampling requests are numerous--occasionally too numerous to 

satisfy during a cruise--but a great deal of effort is devoted to obtaining 

special samples required by colleagues. Specimens have been collected for 

studies in taxonomy, evolution, and contaminants; for medical and 

physiological experiments; and for teaching collections. It is the pol icy to 

try, after the assessment and inhouse collections have been made, to honor all 

outside requests. 

col lections have also been made. 

made before a trawl haul, with bongo nets towed obliquely from surface to 

bottom and back to the surface. Frequently during the trawl hauls, a surface 

plankton net will be towed for neuston collections. 

During many cruises, to better uti1 ize vessel time, ichthyoplankton 

Ichthyopl ankton collections are general ly 

For each station, all pertinent data are recorded on a single, 

two-sided waterproof paper log. 

of all data obtained at a station. It is also used by automatic data 

processing personnel. After a cruise, the field log is coded, and all 

required data are punched onto computer cards directly from the log. Most 

tallies, expansions, and coding were formerly done ashore because conditions 

at sea and their effects on the scientists created situations where errors 

could be introduced. With jurisdiction over an extended fishery conservation 

zone and the more immediate need for these data, the logs, if at all possible, 

are coded at sea and ready for keypunching within one or two days fol lowing a 

cruise. 

This log serves as an original written record 

Analytical techniques--The application of NEFC bottom trawl survey 

data to fish stock assessments has been reviewed by Clark (1979). For stocks 

in which biological sampling of the commercial and recreational catch has been 

limited or nonexistent, survey data have provided the only basis for 

determining basic population parameters such as size and age structure, 

geographic and seasonal distribution patterns, growth and mortality rates, 

maturity and fecundity, food habits, yield per recruit, and trends in 

abundance. 

which a fishery data base exists, thereby providing a supplementary and 

independent source of information and evaluation. 

These population characteristics are also evaluated for stocks for 
-27- 

Trends in stock abundance are evaluated from survey relative abundance 

indices calculated in terms of stratified mean catch per tow in numbers or 

weight; i.e., 

k 

h=l 

where yst = stratified mean catch per tow, 

N = total area of all strata within the set, 

Nh 

yh 

k = number of strata in the set. 

= area of the hth stratum, 

= mean catch per tow in the hth stratum, and 

In 

values is 

are loqar 

cases where the variance of the distribution of catch-per-tow 

much greater than the mean (non-normal), individual tow catch values 

thmical ly transformed, and stratified mean catch-per-tow is computed 

with the transformed values. 

stabilization of variance although the resulting distribution may not 

necessarily be normal. 

The validity of survey mean catch per tow as an index of abundance has 

been demonstrated both on a stock basis and for the total fishable biomass as 

a whole (Clark and Brown 1977). 

commercial data are available (i .e., Georges Bank haddock, Georges Bank silver 

hake, and Atlantic mackerel), trends in the time-series of survey abundance 

indices tend to parallel trends in stock size estimates derived from virtual 

This transformation generally results in 

For individual stocks for which adequate 

population analysis (VPA) based on catch-at-age data (C1 ark 1979). 

length-frequency data also tend to conform closely to those obtained from 

commercial catch samples when allowance is made for gear selectivity 

differences. Correspondence between survey and fishery data implies that 

survey data should be useful on a real-time basis for estimating stock 

parameters not attainable from fishery data. 

Survey 

Clark (1979) reviewed the use of survey data in estimating recruit 

year-cl ass strength, stock abundance and total biomass 1 evel s, catch 1 evel s 

corresponding to specified levels of fishing mortality, and fishing mortality 

in the most recent year of the fishery. 

empirical relationships between VPA results (year-class size, total stock 

size, fishing mortality), and survey values (catch-per-tow at age, total mean 

catch-per-tow values) are derived from a time series of observations and used 

with the most recent survey index for estimating current or future conditions 

of the parameter in question. 

are not available or sufficient for VPA, survey indices have been used in 

evaluating relative stock size and/or future catch through: 1) analyses of 

In most of these applications, 

For stocks in which fishery catch-at-age data 

.,.... 
-28- 

historical trends between fishery catch and concomitant survey values, e.g., 

Gulf of Maine cod; 2) analyses of comniercial catch per effort and total and 

pre-recruit survey indices, e.g., Georges Bank yellowtail flounder, Gulf of 

Maine redfish; and 3) areal expansion of survey indices to obtain a minimum 

population biomass estimate, e.g., Loligo and Illex squid. 

Example 6.--Eastern Bering Sea Crab-Groundfish Surveys 

The Northwest and Alaska Fisheries Center survey of the southeastern 

Bering Sea has been planned to assess the crab stocks, with modifications to 

include assessment of groundfish. For the species of commercial crabs (red 

and blue king crab, Paralithodes camtschatica and P. lat us, respectively, 

and the snow (Tanner) crabs, Chionoecetes bairdi anaC. + opilio , the survey 

provides estimates of population size and distribution by size and sex. 

Additional information is gathered on shell, age, and egg conditions. 

Within-season density distribution information on legal crabs is transmitted 

to U.S. fishermen to aid them in locating productive areas. As an adjunct to 

the survey, tagging studies are conducted periodically to arrive at estimates 

of growth, mortality, exploitation rate, and movements. Survey and tagging 

results, plus information from the fisheries, provide the basic data for 

analysis of stock condition. 

For the principal groundfish species, the survey provides estimates of 

apparent abundance, density distribution, size, sex, and age composition. 

Annual trends in survey abundance indices (total population by size and age 

groups) are compared with foreign fisheries information for evaluating stock 

conditions. 

essenti a1 component of the Bering Sea ecosystem model (DYNUMES) devel oped by 

Laevastu et al. (1979). 

The survey information is added to the data base, which forms an 

Methods--The boundaries of the survey encompass the main distribution 

and fisheries for the principal crab species. 

time of the year (May-August) that follows the spring molting and mating, and 

when population movements of crabs are slowed. 

period also coincides with a favorable time for assessment, when bathymetric 

movements of several of the flatfish species onto the shelf and into the 

survey area have been completed. Although there is a depth shift to shallower 

waters by adult walleye pollock, Pacific cod, and the larger turbots, the 

survey only covers a modest portion of the geographical and bathymetric ranges 

for these species. It does cover the main distribution of crab and sole 

juveniles and a representative portion of the distribution of pollock, 

Greenland Turbot, and arrowtooth flounder juveniles. 

and time of year, the survey appears to be optimal for surveying commercial 

crabs and soles. 

Survey period is scheduled at a 

For groundfish, the survey 

Thus, in terms of area 

Trawl stations are laid out on a systematic grid (Fig. 8), with each 

station located at the center of a 20 x 20-mile square. At each station, a 

standardized method of sampling takes place. A commercial-type bottom trawl 

with a weighted footrope for maintaining contact with the sea bottom is used. 

From scuba diver observations and acoustic mensuration, the trawl has been 

observed to sweep, on the average, a bottom width of 40 feet with a vertical 

opening of 4-6 feet. 

small animals. Trawl accessories (number and size of floats, door type and 

A small mesh cod-end liner is used for retention of 
-29- 
-30- 

size, dandy lines, etc.) are kept the same for each survey, and the same 

research vessel, the NOAA research vessel Oregon, is used. When another or 

other vessels assist the Ore on in the survey, trawling trials are conducted 

between the vessels to esta -dkh relative fishing power. Catches of assisting 

vessels are converted to standard (Oregon) units. 

nearshore navigational aid. The trawl is set so that the intended station 

position is passed midway through the tow. 

30 minutes, with the beginning of the tow timed when the trawl is estimated to 

have reached the sea bottom. 

time of the trawl has been estimated from trawl performance studies. After 

30 minutes, the end of the tow is marked by the starting of the trawl winches. 

The Loran-C readings are recorded at the start and end of each tow, and the 

straight line distance between these points is computed for an estimate of the 

actual distance trawled along the sea bottom. The reference vessel Oregon 

trawls, on the average, a distance of one nautical mile in 30 minutes. 

Station position is located by means of Loran-C, with radar used as a 

Duration of trawling is 

The relation between bottom depth and settling 

During each tow, the echo sounder obtains a continuous record of 

bottom depth and of fish signs that may be present in the water column. 

depth soundings, an average bottom depth is computed for each station. The 

intensity, extent, and depth orientation of fish signs are related to fish 

catches. At each station, environmental data in the form of surface and 

bottom temperature, depth-temperature profile, and extent of cloud cover are 

collected. 

expendable bathythermograph cast. 

From 

Water temperatures are measured by bucket thermometer and 

In the handling of the catch at each station, the total catch is 

weighed by means of a dynamometer. If the total catch is less than 1,200 kg, 

the entire catch is sorted and subsampled for biological information. If the 

catch exceeds 1,200 kg, the crabs are removed and a representative portion of 

the fish catch is removed, by methods presented by Hughes (1976), before 

sort i ng and subsampl i ng. 

Most animals in the trawl samples are identified by species, although 

those that are difficult to identify reliably are grouped by genus or combined 

within a higher taxonomic level. Catch weights for all taxa are determined by 

weighing baskets of sorted animals to the nearest 0.5 kg on a 141-kg capacity 

platform scale. 

expanding the number determined from a weighed subsample. 

Numbers of individuals are determined by direct count or by 

After weighing and counting, the catches of species of principal 

interest are further processed for length-frequency and individual specimen 

data, e.g., length-weight frequency, age structures, fecundity. 

Aboard ship, pertinent station and catch data are placed on magnetic 

tape by means of a data logger which is programmed to format data, make range 

checks, and insure completeness; later at shoreside facilities, the taped 

information is transferred to computer media. 

Analytical techniques--When the survey data have been placed on 

computer disk files, they are edited by a series of computer programs to 

detect errors and inconsistencies. 
-31- 

Age material collected during the survey is read by the Center's Age 

Reading Unit. For those species in which aging methods have been validated, 

age structures are read in a production mode with reliability checks of the 

readers. 

When the survey data, including age determinations, have been checked 

for their accuracy, the data are ready for analysis and for the generation of 

the foll owing standard outputs: 

1) abundance indices for the principal groundfish and crab species and 

for species groups. These indices are expressed in weight and/or 

number caught per unit distance fished. They are computed by 

station and stratum for the total survey area and selected size and 

age groupings. 

2) estimates of age and size composition of the available population 

by stratum and for the total survey area; 

3) estimates of apparent biomass and population size by stratum and 

for the total survey area; 

4) length-weight re1 ationships; 

5) growth rate parameters; 

6) species composition of the catch by station; 

7) relative ranking of the species in terms of weight and numbers 

caught and presented by strata, depth zones, and total survey area; 

8) computer-generated plots showing (a) the locations of the stations, 

(b) the geographical distribution of catch rates of the principal 

species by size and age groupings, (c) distribution of surface and 

bottom temperatures in the survey area, (d) length-weight 

regressions, (e) length and age frequencies, and (f) growth rate 

curves. 

Other estimates, such as mortality and survival rates, population 

composition in terms of stage of maturity, and species assemblages, can be 

generated from the survey data. 

Variances and confidence intervals of abundance indices and population 

estimates for the principal species are computed based on stratified sampling 

theory (Cochran 1962). 

analysis differs from that for snow crab data analysis. 

stratification is based on historical and current information on density 

distribution. There is no stratification of the annual survey area for 

groundfish; periodically, however, when the annual survey area is expanded to 

include areas north of the survey area, and in deeper than usual water for 

sampling, a stratified scheme (Fig. 8) is followed, based upon density and 

commercial catch distribution patterns of the principal groundfish species 

(pol 1 ock, ye1 1 owfin sol e). 

Stratification of the survey area for king crab data 

For both species, 
-32- 

All population estimates are provided in terms of sex and sexes 

combined. At times, information is provided on fecundity, species 

composition, predator-prey relations, and other aspects of the dynamics and 

ecology of the population surveyed. 

distribution for the survey area is also provided on a routine basis. 

Surface and bottom temperature 

Since no reliable estimate of the catchability coefficient is 

available (ratio between the number of fish in the path of the trawl and the 

number actually caught), estimates of biomass and population size are in terms 

of the population available and therefore vulnerable to the sampling gear. 

Thus, for several of the species surveyed, particularly semi-demersal forms 

and species whose distribution extends beyond the survey area, estimates of 

biomass and population size are expressed as apparent, and abundance indices 

of these population are properly qualified. 

For some important commercial stocks, such as king crab, yellowfin 

Both the adults and 

sole, and other sole species, a catchability coefficient of 1.0 is assumed for 

those sizes of animals fully recruited to the trawl. 

juveniles of these species appear to be confined to the survey area and live 

near or on the sea bottom. Thus, for king crab, an estimate of absolute 

abundance of the juveniles and adults is provi ed each year. These estimates 

are further broken down by size and sex groups . abundance of yellowfin sole for animals ages six and older is also provided on 

a annual basi s. 

9 An estimate of absolute 

Although young ages of many of the populations are not fully recruited 

to the gear, abundance indices of these young ages or pre-recruits are given. 

For some populations, indices may be given for the young ages but not the 

older ages because of the latter's poor representation in the survey area. 

Example 7.--Northern Gulf of Mexico Groundfish Bottom Trawl Survey 

The Southeast Fisheries Center initiated a bottom trawl survey in 1972 

in the Gulf of Mexico to monitor trends in groundfish biomass. The survey was 

in direct response to requests from groundfish fishermen and processors for 

better information concerning the status of these stocks. 

independent assessment was the only practical way to provide this information 

as only a relatively small and apparently variable portion of the groundfish 

catch was ever recorded through f ishery-dependent methods. The 1 argest single 

harvester of groundfish is the shrimp fishery, with only about 20% of the 

harvest being taken by directed fisheries. 

taken by the shrimp fleet is discarded and never appears on any of the fishing 

records. 

A fisheryThe majority of the groundfish 

Approximately 170 species of fish occur in the bottom trawl catch of 

the directed groundfish fishery or as discards from the shrimp fishery 

(Roithmayr 1965). Only six species, however, are of significance in the 

'Estimates are made of the number of legal size crabs (males greater 

than a specified size) and the number of males that will be recruiting 

to the fishery the following year. 
-33- 

fisheries, with Atlantic croaker (Micropogon undulatus , spot (Leiostomus 

xanthurus), and seatrouts (Cynoscion arenarius dnothus) an - comprising the 

bulk of the catches. 

Initially, trawl surveys were conducted seasonal ly to establish 

seasonal trends in biomass, species composition, distribution patterns, and to 

collect data for developing biological profiles of dominant species. After 

several years, however, the surveys were reduced in frequency in order to 

concentrate on periods of maximum and minimum abundance to obtain information 

for estimates of stock mortalities. Monitoring activity was maintained. 

A major problem with groundfish surveys is that they do not encompass 

inshore waters where significant proportions of the groundfish stocks occur 

during all seasons. 

of the primary survey vessel, Oregon 11. Several inshore surveys, however, 

were conducted from 1974 to 1976 with? shal low draft vessel, George - M. 

Bowers. 

Methods--Selection of the initial survey area was predicated on 

historicmoratory fishing data, data from the directed groundfish fleet, 

and information from selected commercial fishermen. It was later expanded to 

extend beyond the traditional fishing grounds to ensure that unforeseen shifts 

in population densities would not invalidate the surveys. Currently, the 

survey area is divided into one primary and two secondary areas (Fig. 9). The 

primary area includes most of the principal groundfish fishing areas and is 

characterized by relatively high and homogeneously distributed standing stocks 

of groundfish. Densities of groundfish decrease rapidly in the secondary 

areas, with concurrent increases in distributional variabilities. 

The survey design essentially is completely random with some 

stratification imposed as a result of available vessel days. Coverage of the 

primary area is emphasized, with less attention given to the two secondary 

areas. The western secondary area, however, generally does receive more 

coverage than the eastern area due to higher standing stocks and more 

commercial fishing activity. The three areas are divided into 10-minute 

blocks of latitude and longitude which in turn are divided into sixteen 

2 1/2-minute sampling areas. As a function of available vessel days, a 

selected number of 10-minute blocks is randomly picked, with rep1 acement, from 

each of the three areas, and then one sample area is randomly selected, 

without replacement, from the 10-blocks. A computerized cruise optimization 

routine is used to both select the blocks and sample areas and to define the 

This lack of inshore coverage is due to depth limitations 

shortest possible cruise track to all of the sampling areas (Leming and Holley 

1978). 

Upon arrival at a sampling area, an XBT cast is made, along with a 

surface bucket sample for temperature and sal inity measurements. 

possible, secchi disk and water color measurements are also obtained. Three 

10-minute tows generally are made in each sample area with a standard 12.2-m. 

(40-ft.) semi-balloon shrimp trawl rigged with a loop chain and rollers. 

Trawl mesh is 5.1-cm (2-in.) stretch throughout with 4.4-cm. (1.7-in.) stretch 

mesh in the cod-end. A tickler chain is used between the trawl doors. The 

sampling trawl is fished off the port outrigger with a 30-fm bridle attached 

When 
-34- 
-35- 

to the towing wire. 

prior,to each cruise. Normal towing speed is 3 knots. 

The sampling trawls are mensurated periodically, but not 

The three short tows were selected instead of a single 30-minute tow 

in order to provide data for investigating small scale distributional patterns 

of the benthic organisms. Generally 500 to 700 tows representing 200 to 250 

sampling areas are made per cruise. 

one sample (three tows) for every 40 square nautical miles in the primary 

survey area, with less coverage in the secondary areas. 

This sampling intensity equates to about 

Once a trawl tow is completed, the entire catch is dumped on the deck 

and weighed. Depending on total weight, the catch is either examined in its 

entirety or a representative subsample is taken for processing. All species 

are identified, weighed, and measured for computations of species composition; 

scales and other hard parts are studied for age estimates; sex and maturation 

of individuals are determined, and stomach content are analyzed. Selected 

specimens and measurements are also collected to satisfy requests from other 

investigators. 

All data are logged onto station data sheets. The format of these 

sheets allows recorded data to be key-punched directly onto computer cards for 

processing. Various edit routines are used to edit the data, although manual 

editing is still used extensively. All key-punching and computer processing 

occur after the vessel has returned to port. 

Analytical Techniques--As soon as all data from a particular survey 

have been edited and are available in a computer-compatible format, computergenerated plots showing station locations and catch rates are developed for 

distribution to the groundfish industry (Fig. 10). These plots generally are 

only for total finfish, although species plots are also generated periodically 

to satisfy specific needs. 

Attempts were made initially to increase the precision of the biomass 

estimates derived from the survey data, based on stratified sampling theory 

with the strata selected according to depth (Juhl et al. 1975). Depth, 

however, proved to be an inappropriate parameter for stratification. More 

recent attempts are concentrating on historical abundance indices, coupled 

with bottom type, to stratify the data to achieve a higher level of precision. 

Most available biomass estimates are based on analytical treatments with 

assumed random samples from a normally distributed population. 

levels at 95% confidence thus often range as high as 100% of the estimate. 

Precision 

Improvements are needed in the analytical approaches used to estimate 

numbers and biomass of the groundfish stocks in the northern Gulf of Mexico. 

These improvements have been hindered in the past due to inadequate computer 

capabilities, a problem which is now beginning to disappear. A number of 

problems exist, however, which are not disappearing. These involve those 

assumptions common to most bottom trawl surveys which have their greatest 

impact on the accuracy of the survey samples. 

catchability coefficient of 1.0 for all species under all conditions and an 

assumption that all standard trawls fish the same under all conditions. These 

assumptions are known to be invalid. 

Examples include an assumed 
-36- 

FRS OREGON CRUISE 71, 11/02/76 - 12/dP/76 

TOTAL FINFISH 

. 'J1 

A! 

r c 

C 

A C 

CB 

i) D 

0 0 

:L I 

I e 

L 

f n n n 

D 

C 

0 " D D 

'0 t 

I 

5 Ql .O 9 

- 

! 

D i/ c 

C r 

C c 

D 

B= 500-IOc)C 

C= 300- 503 

Dm 100- JCO 

E= 0- 100 

n 

a 

n 

k3 H 

A 

0 E 5 

Figuse 1C.--Example computer plot of finfish biomass (pounds per hour with 

standard trawl) for area west of Mississippi River delta. 
-37- 

2.2.1.2. Longline and Trap Surveys 

A number of important fish stocks are not available to traditional 

forms of fishery-independent surveys. 

the purview of the United States but are especially prevalent in waters 

surveyed by the Southeast Fisheries Center. 

techniques are used, although none is particularly quantitative and all have 

significant inherent biases. 

fishes which include not only the highly-publicized colorful species of the 

true coral reefs in south Florida and the Caribbean but also large and 

valuable stocks of snappers, groupers, grunts, and porgies. These species 

occupy rocky habitat on the outer South Atlantic shelf as far north as Cape 

Hatteras, and fishing banks and live bottom areas in the Gulf of Mexico. Reef 

fish communities are almost always associated with hard substrate and high 

relief; thus, trawl surveys are generally precluded. In those few areas level 

enough for trawling, trawls are still not a preferred survey technique as the 

heavy gear may damage habitat. Survey schemes based on existing acoustical 

systems also are not appropriate because of the often intimate association of 

reef fishes with their substrate, which makes it difficult if not impossible 

to distinguish the fish from substrate in acoustic records. Ichthyoplankton 

surveys also are not very effective because, even with fairly intensive 

sampling efforts, very few eggs and larvae from reef fish are ever taken. 

Apparently the typically tropical pattern of nonsynchronous and protracted 

spawning precludes the existence of sufficient densities of ichthyoplankton 

for stock assessment. 

These stocks occur in all waters under 

Various forms of survey 

An example of one of these resources is the reef 

Trap and bottom longline surveys are used extensively for fisheryindependent assessment of deep water snapper and grouper stocks in the 

southeast region. 

useful for the more important market species. 

These gears will take a variety of species and are very 

In general, a completely random approach is used to select sampling 

stations within predefined areas. These areas are selected on the basis of 

known bottom conditions, historical sampling records, and commercial fishing 

reports. Station selection is randomized across depth strata and day-night 

periods. Because systematic sampling throughout all seasons has not been 

accomplished for most of the species taken with traps and bottom longlines, 

most of the sampling of a particular area is done during the same season year 

after year to develop an historical data base for trend analyses. 

in.), three-strand braided nylon main1 ine with gangions used for hook 

attachment. 

(300-lb.) test nylon monofilament. 

the mainline, and the hooks are normally of a #6 or #9 Japanese circle style. 

The gangions are spaced about 3.7 m. (12-ft.) apart on the mainline, with the 

latter set in 183-m. (600-ft.) shots. A set generally consists of two or 

three shots of mainline. Anchors are set at the start and f i n i s h o f each set, 

along with sufficient longline to reach surface buoy poles. The poles 

normally are equipped with radar reflectors and blinking lights for ease of 

location under both day and night conditions. 

stern of the vessel with pick-up along the side rail. Biological data 

Bottom longline fishing gear generally consists of a 7.9-mm. (5/16 

The gangions normally are fabricated from 1-m. lengths of 136-kg. 

Snaps are used to attach the gangions to 

The sets are made from the 
-38- 

collected generally include species, size, and weight; samples are taken of 

scales, otoliths, gonads, and stomachs. 

in the commercial fisheries. These currently include rectangular, West 

Indies, Z-, Cuban, and modified lobster traps. 

that collected from the bottom longine surveys are taken here as well. 

in terms of a capture rate, rather than density. 

results may be expressed as the number of a particular species caught per 100 

hooks per 24 hours, and trap results may be expressed similarly as the number 

of organisms taken per trap per 24 hours of fishing. 

Trap surveys are generally conducted with traps similar to those used 

Biological data identical to 

Results from bottom longline and trap surveys generally are expressed 

For example, longline 

Pelagic longline survey techniques are not used extensively for 

surveys of pelagic stocks. 

exploratory, to provide information on seasonal distribution, availability, 

and species composition. 

method available for sampling many of the pelagic fish stocks, such as large 

tunas and billfishes, they are used periodically for collecting specimens for 

tagging and for acquisition of biological samples. 

Their use historically has primarily been 

As they represent the only fishery-independent 

2.2.2. Visual Surveys 

2.2.2.1. Aerial Surveys 

Surveys with commercial fishing gears, as noted earlier, have 

performed an important role in the stock assessment activities of the 

Northwest and Alaska Fisheries Center, the Northeast Fisheries Center, and the 

Southeast Fisheries Center. 

to pelagic and semi-pelagic species, and a variety of other techniques have 

evolved to assess these populations. Aerial surveys have frequently been used 

to assess populations of near-surface schooling pelagic fish species. 

mammal populations in Alaska, eastern tropical Pacific, Gulf of Mexico, and 

South Atlantic, have also been extensively surveyed by scientists at NWAFC, 

SWFC, and SEFC, with aerial survey methods, especially for the ice-associated 

seals, endangered whales such as the bowhead and gray whale, oceanic tropical 

dol phi ns, and coastal bottl enose dol phi ns. Exampl es of aeri a1 surveys are 

given below: 

The method, however, is not nearly as applicable 

Marine 

Exampl e 8.--Aeri a1 Surveys of Dol phi ns by Li ne Transect 

The objective of this survey method i s t o count individual animals or 

groups of animal s (school s, baski ng aggregat i ons, etc. ) from an aircraft a1 ong 

predetermined tracklines or flight paths. The numbers of animals or groups of 

animals seen per unit searching effort, and the amount of area "effectively" 

searched per unit of searching effort, provide information on spatial 

distribution and population densities of stocks of animals in question. 

Depending on the animal being studied and the amount of information which can 

be obtained on each sighting, estimates of absolute abundance of individuals 

may be possible at best, while relative abundance of aggregations can be 

calculated at the minimum. 
-39- 

Methods--The survey is conducted from an aircraft with unobstructed 

downward and lateral visibility on both sides. 

suitable range, dependent upon the location of airport facilities. To 

facilitate making detailed observations of animals sighted, the aircraft must 

have a relatively slow minimum cruising speed and good maneuverabil ity for 

circling. These problems were encountered in aerial dolphin surveys made by 

the SWFC off the Pacific coasts of Mexico, and Central and South America, 

where a sl ower, shorter-range aircraft was f i nal ly sel ected. 

The aircraft must also have 

The basic in-flight procedures involve several observers rotating 

through sighting positions, with one rest position. The observers need to 

in communication via intercom. When sightings are made, it is usually 

necessary to deviate from the flight path at the time of sighting in order 

make more detailed observations on the school; circling at lower altitude 

frequently needed. 

For surveys of pelagic animals, smoke bombs or dye markers thrown f 

the airplane at the time of initial flyover are useful in relocating the 

animals. Large format photography has proved useful in determining the 

numbers of animal s in dol phi n aggregations. 

be 

to 

S 

'om 

A major requirement for utilizing aerial survey techniques for stock 

assessment is that the animals be visible from the air. 

fraction of the population which is being sighted must be estimable. 

pelagic dolphin surveys, for instance, it is assumed that all of the animals 

which were on the trackline (line transect surveys) when the aircraft passed 

over were seen. 

beaches, and of the number of coastal bottlenose dolphins, Tursiops, in a 

strip (strip transect surveys), suffer because the proportion of the 

population which is actually visible at any one time is not known. The direct 

count methods will be discussed in the next section. 

In addition, the 

In 

Surveys of the number of pinnipeds hauled out of the water on 

In the dolphin surveys. it has been noted that species differ in their 

visibility from the air. 

i nordi nately vi si bl e animal , especi a1 ly near the track1 i ne. 

Barham (1979) suggests that Gkampus griseus is an 

Correspondi ngly - -- , larger aggregations of dolphins- are bei ieved to be more visible at greater 

distances from the trackline than are smaller schools. 

Environmental conditions affect the visibility of animals from the 

air: the presence of rain or low clouds, and especially sea state and sun 

position. Frequently, in extensive surveys, environmental conditions will 

change markedly over the course of single flights. Recent developments in 

line transect theory suggest that, if one conducts the survey so as to insure 

that all of the animals on the trackline are seen, such variations in 

visibility, within limits, will not seriously affect the stock assessment. 

During an aerial survey, two separate data streams are obtained: the 

sequence of sightings, with ancillary detailed observations, and the record of 

survey tracks actually searched. Although these two must be analyzed 

together, they are best recorded separately. The actual trackline searched is 

complex in aerial surveys because observers cease searching while detailed 

observations of the sighted animals are made. 

searched may be variously described; in the dolphin surveys, the starting and 

The details of the track 
-40- 

ending positions and times are recorded for several segments of each track 

flown. During each segment of each trackline, the sea state, ground speed, 

sun position, and altitude are recorded, along with times and positions at 

intermediate points for reference following. 

When a sighting is made, observers complete a systematic list of 

specific observations. 

are made for species identification, percent composition of each species 

present, number of animals present, and the position of the sighting relative 

to the trackline. 

In the SWFC dolphin surveys off Mexico, observations 

The measurement of the location of sighted animals relative to the 

trackline is extremely important, both for 'line transect and for strip survey 

analysis. 

trackline to the animals can be used to validate the assumption that a strip 

was, in fact, searched completely. For the former analysis, the rate of 

decline of the frequency distribution of distances from the trackline provides 

the information for determining the area effectively searched per unit of 

searching effort. 

For the latter, the frequency distribution of distances from the 

The location of the sighted schools can be measured by the 

perpendicular distance from the trackline to the object, or by combining the 

bearing to the object and the straightline distance. 

either case is essential. Inertial navigation systems have been successfully 

used to measure such distances (Jackson 1979). 

Maximal precision in 

The survey pattern is very important to the eventual inferences which 

can be made from an aerial survey. 

determined, ideally with the lines selected at random over the whole area 

inhabited by the population during the survey period. 

when the range of the stock is not clearly known or occurs substantially 

offshore. Additional problems are presented when the animals are visible only 

at certain points in their range, and when unknown fractions of the 

populations are at such sites. Aerial surveys of most pinnipeds have suffered 

from the inability to define meaningful "random samples'' of the range of the 

populations to survey. It is important that accurate position information be 

recorded during the surveys, especially at the time of sighting, to determine 

exactly how much area was surveyed. 

A priority trackline placement must be 

This can be a problem 

The two streams of data must be analyzed together in developing stock 

assessments from aerial survey data. For any but extremely small scale 

surveys, the data are best analyzed on a computer. Computer programs to 

integrate these two streams of data need to be written which are sufficiently 

flexible to allow for the extensive selection and reanalysis of the data 

necessary in a detailed analysis for stock assessment. 

dolphin survey data, selections which were made included only those 

observations made while searching, only those of certain species, only those 

of certain minimum school sizes, and only those made within certain distances 

from the trackline (Holt and Powers 1979). 

In the analyses of the 

Analytical techniques--Under ideal conditions where an estimate of 

absolute numbers of individuals can be obtained, the basic equation to be used 
-41- 

is 

N=DxSxA 

where N denotes the number of animals in the population; D, the density of 

schools; S, the average school size; and A, the area inhabited at the time of 

the survey. The techniques used to estimate S and A vary greatly, depending 

on the particulars of the situation. For example, if the school size is large 

and highly variable, sufficient observations may not be available to estimate 

this adequately from the survey data alone (Smith 1975). 

The line transect approach to estimating density has been the subject 

of much recent research, culminating in a recent monograph by Burnham et a1 . (1980). They note several different estimation formulae which have been used 

in the literature and explore the statistical properties of many of these. 

While the proper choice of density estimation formulae is too complex a 

subject to discuss here, it can be noted that those authors favor a flexible 

curve-fitting approach, termed the Fourier series estimator, in most 

situations. This was used in the analysis of the dolphin survey data (Holt 

and 

is, 

Powers 1979). 

The essential characteristic of 

however, 

all of the line transect estimators 

n f(0) 

2L D= 

where n denotes the number of sightings made; L, the length of trackline 

searched; and f(0) a parameter estimated from the frequency distribution of 

perpendicular sighting distances. 

sightings decline exponentially with distance from the trackline, the estimate 

of f(0) is the inverse of the mean sighting distance. In other situations the 

estimation of f(0) is considerably more complex. Laake et al. (1979) describe 

a general computer program TRANSECT which is available for obtaining some of 

the alternate estimators of this parameter. 

corresponding sampling variation formulae are discussed in Burnham et al. 

(1980). 

In one simple case where the numbers of 

These estimators and 

If estimates of the variances of the mean school size S and of the 

area inhabited A are available, it is possible to obtain an estimate of the 

variance of the estimate of total population size with the delta method (Seber 

1973); for an example, see Holt and Powers (1979). 

this method will depend on the complexity of the final formulae used. 

Note that the details of 

If the conditions of the survey do not allow for an estimate of 

absolute population size, it may be possible to obtain absolute density of 

individuals (by omitting A in the first set of formulae), or absolute density 

of schools (by omitting A and S). Finally, if some of the assumptions are 

violated, such as all of the animals on the trackline being seen, it may be 

possible to obtain relative population sizes to compare between surveys. 

would then be necessary to repeat a survey with the same characteristics, 

however, in order to obtain useful information from the study. 

It 
-42- 

Example 9.--Aerial Surveys by Strip Transects of Coastal Dolphins 

Coastal populations of bottlenosed dolphin (Tursio s) in the 

southeastern and Gulf regions of the United States often --- ive portions of 

their lives confined to bays and inlets where they are easily observed from 

aircraft. Aerial surveys, using a special case of line transect methods, 

i.e., strip transects, can be an effective way of estimating numbers. 

Methods--A typical survey of this type was reported by Leatherwood 

(1979).Wrththese methods, the aircraft surveys a strip of the population 

range, and it is assumed that all animals in that strip are seen. 

of herds encountered are recorded, and, since the aggregations of Tursio s in 

size of individual animals. Detailed observations on environmental conditions 

such as sea state and sun angle are also noted. 

The numbers 

coastal waters are small, estimates may be made of the herd size an -7-57 of t e 

The strips are usually chosen so that the bay or inlet is 

systematically represented in the sample. In addition, flights are planned to 

be carried out only when weather, time of day, and other environmental factors 

are within a control range. If weather does not fall within this range, the 

flight is postponed. 

Replicates of the strips are flown to enable estimate variations. 

Leatherwood (1979) gives the specific criteria. 

Analytical techniques--The basic formula for estimating abundance from 

strip surveys is as in the previous section 

N=DxSxA 

where N is the abundance of individuals, D is the density of herds (number per 

unit area), S is the herd size, and A is the area. Density of herds is: 

n 

W2L 

D= - 

where n is the number sighted per strip, W is 1/2 of the strip width and L is 

the strip length. As noted before, this is a special case of the general line 

transect model. Sampling variances are obtained from the replicate strips as 

in Seber (1973). 

The effect of visibility and of environmental conditions has a 

significant impact on strip surveys. 

even for those sightings within the strip, because the distribution provides 

some implications as to the validity of the assumption that all animals within 

the strip can be seen. 

also affect the visibility assumption, and may reduce the usefulness of the 

estimate as a minimum abundance index. 

Sighting distances should be recorded 

Variable sighting conditions during the survey period 

Example 10.--Aerial Survey by Commercial Fish Spotters 

Method--The method provides indices of apparent abundance of 

near-surface schooling fish from observation logs of aerial fish spotters who 

locate fish concentrations from airplanes and guide commercial fishing vessels 

in the catching operation. This multiple species method has been used 
-43- 

primarily off southern California for monitoring coastal pelagic stocks. The 

fishery for these stocks has utilized aerial fish spotters since the latter 

years of the sardine fishery. 

to NMFS since 1962 to provide flight logs of their observations. The spotters 

fly single-engine aircraft throughout the range of the fisheries in search of 

fish concentrations. Flights are made throughout the year during daylight and 

nighttime hours. Pilots do not follow any pre-specified flight track but 

scout those areas where concentrations of target species are likely to be 

found. 

their observations of fish schools on log maps supplied by NMFS (Squire 1972). 

They also trace their flight track on the map (Fig. 11). 

Many of these pilots have been under contract 

In this sense, the survey pattern is opportunistic. Pilots record 

In past years, the flight logs were returned to NMFS for processing. 

Annual summaries of apparent abundance by species were compiled. More 

recently, a computerized data management system has been devel oped. 

Currently, as the flight logs are received, the data are coded on formatted 

forms and key-punched. 

computer programs. 

made and stored in a data base system for retrieval and analysis at a later 

date. 

These data are then verified and edited by a series of 

After all the obvious errors are corrected, a data tape is 

This method of assessment works best for schooled fish species or 

marine mammals that are often observed in the surface waters. Daytime 

observations require good lighting and visibility so that color changes in the 

surface waters or surface disturbances, which indicate presence of a fish 

school, can be readily detected. Nighttime observations rely on the detection 

of the faint glow of bioluminescence emitted by plankton, resulting from the 

disturbance by a moving school of fish. Detection in the dark hours is 

inhibited by moonlight and the glow from city lights. 

by characteristic school shape, speed, or behavior in the pattern of reflected 

glitter from sunlight in daytime hours. In dark hours, species identification 

is enhanced by characteristic school response to a directed flash of light. 

Species are identified 

Analytical techniques--The analysis of the fish spotter log 

information is similar to that for catch and effort data. In this case, 

however, a fish sighting, which is equivalent to a vessel catch, is not a 

removal from the population and the magnitude of the sighting is not 

constrained by vessel capacity. The pilot records the following for each 

flight: date, pilot name, time of day, plane identification, total flight 

hours, and flight path trace; and for each sighting: species, location, number 

of schools, and estimated tonnage of each school, or estimated tonnage of the 

school group. Effort should ideally measure the surface area of the ocean 

surveyed. 

detail that would be required for accurate estimates of effort. In the 

southern California area, for example, the coastal region has been divided 

into a grid of 10' square blocks (8 by 10 n.mi.), and effort is measured in 

units of block flights and total flying time. A block flight is defined as 

the crossing of a grid block by the flight path trace. 

spend from a few minutes to a few hours with one grid block, depending on 

occurrence of fish schools or vessel activity. 

Because of the nature of the system, pilots cannot record the 

The pilot may actually 
-44- 

MARINE RESOURCE MONITORING SYSTEM 

LOS ANGELES 

Figure 11.--Flight chart €or southern California area showing typical flight t 

and fish and mammal observations. Block area grid is overlayed on 

chart for coding observations. (Squire 1-972) 

rack. 
-45- 

Quality control of the recorded observations is promoted through 

frequent contact with the pilots. Species identification and tonnage 

estimates can often be confirmed by associated vessel catches. 

instances, sighted schools are diffuse and scattered, making estimates of 

school numbers and tonnages impractical. Flight path location is subject to 

potential inaccuracies because of the small scale of the flight log map 

relative to the size of the actual airspace surveyed. 

improved with the addition of landmarks and popular fishing banks on the maps. 

In a few 

Accuracy can be 

Survey design for this opportunistic method, as in the catch and 

effort case, cannot be rigorously controlled. 

area can be promoted by contracting with as many pilots as possible. 

southern California, for example, the fishery targets on a variety of species. 

The seasonal distribution of these species is sufficiently variable to 

encourage the pilots to survey frequently over wide areas. Unfortunately, the 

areas surveyed are somewhat less than the full range of the species. 

Questions of sample size are not generally raised because of the relatively 

inexpensive nature of the data collection. 

Survey coverage over time and 

Off 

Analysis of these data for other than simple routine summaries 

requires use of computers and a well-structured data base. 

California example, a computerized data management system was developed by 

Caruso (1979). 

data coding instructions, data verification, and data storage and retrieval. 

This system reduces the time needed to complete sophisticated analysis and 

insures that data accuracy does not deteriorate with processing. 

For the southern 

This system sets up a filing scheme for returned flight logs, 

The primary parameter estimate for stock assessment purposes is either 

a day or night index of apparent abundance. 

measure of the resource magnitude available to the fishery, and should reflect 

population densities in the area of the fishery in much the same way as CPUE. 

There is no obvious method for expanding this relative index directly into a 

population estimate. In the southern California example, the index measure 

has been in units of tons of fish per block flight for a calendar year. This 

index, calculated separately for day and night flights, is the ratio of the 

annual tally of observed school tonnages to the total number of block flights. 

Variance estimates have not been considered. The time series for northern 

anchovy, jack mackerel, Pacific mackerel, and Pacific bonito have shown trends 

that are consistent with results of other stock assessment methods. This 

estimation procedure assumes that pilots are essentially equivalent, i.e., 

their skills are similar and the effective width of their search paths are the 

same. 

This estimate is a relative 

4 

An alternative analytical procedure is currently under investigation 

which applies the fishing power analysis of the catch and effort method as 

described by Robson (1967) and Francis (1974). In this case, a multiplicative 

model of tons of fish T can be expressed as a function of various factors: 

pilots p, season s, region r, day/night t, fish abundance a, and effort as a 

covariate E, i.e., 

T=u'p's'r't'a*bE*e (1 1 

where u is the mean and e is a lognormal error term. The factor a is 
-46- 

interpreted to be the yearly fish abundance effect and can be estimated by 

analysis of variance models of the linearized log transformation of (l), i.e., 

T = u' t p' + s' t r' + t' t a' t b'ln E t e (2 1 

where the factors are now the logarithm of factors in (1). 

model appears to be the best method for estimating the index of abundance a, 

the applicability of the assumption to the southern California aerial spotter 

data has not been completely examined. 

Although this 

Important assumptions are: 

1) e is lognormally distributed, 

2) interaction terms are negligible, and 

3) effort is a significant covariate. 

The advantage of this model is that the estimated index of abundance 

and its variance for the entire time series can be estimated in one analysis 

which takes into account major factors that influence sighting. In this case 

the abundance index will be dimensionless and the sum of the index over the 

years must equal zero (i.e., a' = 0). This means that with each new year, 

the updated analysis of variance will estimate a new time series of the annual 

abundance factor, a', sl ightly different from the previous values. 

2.2.2.2. Land-Based Counts 

Marine mammals, turtles, and salmon have evolved migratory patterns 

which temporarily visually expose the animals in specific areas. Censusing 

techniques developed to estimate population size from visual counts are 

distinctly different from the usual fishery methods. For example, whales 

typically undertake lengthy migrations between summer feeding grounds in high 

latitudes and winter breeding grounds in low latitudes. During these 

movements, some populations pass headlands or are confined to narrow pathways 

where individuals can be counted as they surface to breathe. 

other hand, typically swim ashore (haul out) on specific beach areas 

(rookeries) to give birth and to mate. Turtles crawl ashore on beaches to lay 

their eggs. Salmon, because of their anadromous behavior, are concentrated in 

the rivers of the Pacific northwest and Atlantic northeast during both the 

juvenile and mature adult stages. Research agencies will frequently set up 

stations along the rivers to monitor the seaward migration of the juvenile 

salmon smolts or to count the returning adults during their upstream migration 

to the spawning grounds. 

Seals, on the 

A primary advantage of these counting techniques is that major funding 

levels are not required to obtain an observation platform. Rather than using 

valuable charter time to survey, the observer goes directly to the place where 

the animals are found. 

effort, some segment of the population may not be available for censusing. 

For example, some whales may be submerged when swimming by a station and not 

be seen, female seals may be feeding away from the rookeries when counts are 

taken, and only a portion of female turtles breed. In these cases, accessory 

experiments must be undertaken to derive correction factors which improve the 

accuracy of population estimates. 

The primary disadvantage is that, despite intensive 

Prior knowledge about the behavior of 
-47- 

animals in the census area usually eases the task of designing and 

imp1 ementi ng such experiments. 

The problem of estimating population size from direct counts of a 

proportion of the population is especially exemplified by beach surveys for 

sea turtles in the southeastern and Gulf regions of the United States. 

Surveys of the beach for evidence of turtle nesting activity have been made 

from aircraft and on the ground. However, only the adult females lay eggs and 

only some fraction of them may be breeding. In addition, the data unit being 

counted is the animals's track left as it crawls to the water. Some judgment 

can be made as to the freshness of the track, but this aspect compounds the 

problem by introducing a possibility of overcounting the nesting activity. 

Therefore, it must be reiterated that counting methods rely considerably on 

knowledge of behavior before the counts can be expanded to population 

estimates. 

Since the estimation of the number of smolting or spawning salmon for 

a particular river system is generally the responsibility of state fishery 

agencies, the methodology will not be discussed in this report. 

The following examples typify the counting methods used for whales and 

seals and may be contrasted with the usual fisheries stock assessment methods 

discussed previously. 

which these are a subset, is given by Eberhardt et al. '(1979); many of these 

are derivatives of usual fisheries techniques. 

A full review of marine mammals census methods, of 

Example 11.--Cal ifornia Gray Whales 

Methods--The California stock of gray whales leaves its feeding 

grounds in the Bering and Chukchi Seas in October and migrates down the North 

American coast to winter along the west coast of Mexico. 

migration, the gray whales tend to hug the coast, and at various places the 

migratory corridor is quite narrow. Between Point Lobos and Point Sur on the 

Monterey Peninsul a near Monterey, Cal ifornia, aerial surveys indicate that 93% 

of the population passes within 3.2 km of shore. 

During this 

Since winter of 1967/68, the predecessor of the National Marine Mammal 

Laboratory has exploited the migratory behavior of gray whales along the 

Monterey Peninsula by making a shore count at either Yankee Point or nearby 

Granite Canyon, California. At a height of 21-23 m above sea level at these 

two places, an observer is likely to see most of the whales which pass by in 

day1 ight. 

Each year a watch has been maintained from 0700 to 1700 by two 

observers alternating 5-hour shifts, seven days a week. An observer watches 

to the north for southward migrating whales. For each sighting, the number of 

groups seen, the number of animals in each group, and the time of sighting are 

recorded. 

estimates the distance from shore and records wind direction, Beaufort Sea 

state, and comments on visibility (fog, glare, etc.). 

When the whales pass by directly offshore, the observer also 
-48- 

Analytical techniques--The total counts obtained each year during 

December 18 - February 4 (excluding December 25 and January 1 holidays) are 

shown in Table 1. Reilly et al. (1980) examined these data in detail to 

obtain a statistically valid estimator for total population abundance. Their 

analysis indicated that observers consistently underestimated the number of 

whales in a group, that whales migrated at the same rate at night as during 

the day, and that observers' abilities to sight whales declined significantly 

beyond 2.4 km. 

Table 1.--Counts of southward migrating gray whales from stations 

near Monterey , Cal i forni a. 

Season Count 

1967/68 3,120 

1968/69 3,081 

1969/70 3,064 

1970/71 3,034 

1971/72 2,588 

1972/73 3,304 

Season Count 

1973/74 3,492 

1974/75 3,348 

1976177 4.058 

1975/76 3,797 

3 127 

3,568 

Shore observations were compared with results from concurrent aerial surveys. 

If a constant rate of migration occurred throughout 24 hours, the number 

passing in day j (nj) was defined to be 

n = (cif(ni)/t.)*24 j J 

where ni = the number counted in the ith sighting 

f(ni) = the bias correction function for undercounting 

by observers, as compared to concurrent aerial surveys 

ti = total time watched during the jth day, 

on as ni as 

J 

and Reilly et al. defined the bias correct 

ni + 0,350 if 

f(ni) = ni + 0.0 if 

ni + 0.333 if 

on funct 

ni = 1 

ni = 2,3 

ni - > 4. 

Whales which passed by before or after the census period were 

accounted for by assuming a normal distribution curve for the sightings. 

those which were missed as a function of their distance from shore, Reilly 

For 
-49- 

et al. developed a correction factor by comparing sightings from shore inside 

and outside of 2.4 km with concurrent aerial observations. 

The cumul ative proport ions of the popul ation expected each day were 

calculated from past daily count data and found to fit a normal cumulative 

di st ribut i on. 

The estimates of abundance and 95% confidence intervals obtained from 

the gray whale count data are shown in Table 2. The estimates all have 

confidence intervals under - + 20%. 

Table Z.--Estimates of abundance for California gray whales and 

their confidence intervals expressed as a percent of 

the estimate. Source: Reilly et al. (1980). 

Season 

1967168 

1968169 

1969170 

1970171 

1971172 

1972173 

1973174 

1974175 

1975/76 

1976177 

1977178 

Estimate 

10,767 

11,384 

11,748 

11,356 

9 , 637 

13,167 

13,010 

12,069 

14 , 930 

16,511 

13,644 

Confidence interval (%) 

18.5 

19.0 

18.5 

19.1 

18.5 

18.3 

18.5 

19.2 

17.5 

17.5 

17.9 

The aerial surveys were made during good visibility. No corrections 

in the counts have been made for low visibility counting periods. Reilly 

et al. concluded that, as a result, the reported estimates were below actual 

values since no correction had been made for changes in visibility; poor 

weather, for example, would affect an observer's ability to count passing 

whales accurately. The highest estimate, 16,511 for 1976177, is probably the 

best estimate available since there was an exceptionally clear and stormless 

winter during which better than average visibility 

lowest estimate, 9,637 in 1971172, occurred during 

to be "stormier" than usual. Further research wil 

correction factors for visibility. 

Example 12.--Northern Sea Lions 

would be expected. The 

a year which was reported 

develop appropriate 

Methods--Northern sea lions haul out on the eastern A1 eut i an Is1 ands 

throughout the year but occur in greatest numbers on land between May and 

October during the breeding and molting seasons. 

breeding occurs, and 23 haul-out sites, where no breeding takes place, have 

been identified in this area. 

Seven rookeries, where 

The height of the breeding period occurs during 
-50- 

June-August, and the maximum number of animals is expected to be ashore then 

at both the rookeries and haul-out sites. 

During 1975-77, the National Marine Mammal Laboratory exploited this 

behavioral pattern to census the number of sea lions in the eastern Aleutian 

Islands (Braham et al. 1977). 

of the coastline, at altitudes of 90-240 in and at speeds of 150-190 km/hr. 

For sites having more than 20 animals, observers took photographs with 35 mm 

cameras equipped with telephoto lenses, motor drive units, and high speed 

color film (ASA 160-200). Otherwise, visual counts were recorded. 

Aircraft were flown over each area within 400 m 

Analytical techniques--The total counts obtained during four aerial 

survevs are shown in Table 3. Examinins the data in detail, Braham et al. 

found" no statistical differences when the same sites were compared to 

succeeding survey years using Wilcoxon's Signed Rank Test (Hollander and Wolfe 

1973). Consequently, it was possible to pool the 1975-77 data. However, as 

noted in Table 3, inclement weather affected visibility during the June 1975 

survey, resulting in a rather low total count; therefore, that total count was 

not considered to be a replicate. Omitting it gave a mean value of 21,881 sea 

lions with 95% confidence limits of 511% (19,390 - 24,372). 

Table 3.--Total counts of northern sea lions from the eastern 

Aleutian Islands. Source: Braham et al. (1977). 

- Year Month Total Count si tesa 

1975 Juneb 

August 

11,406 

21,221 

1976 June 22,142 

August 20,239 

29 

40 

35 

41 

1977 June 23,922 40 

aNumber of sites visited where sea lions were seen. 

bIncl ement weather affected vi s i b i 1 i ty . 

2.2.2.3. Underwater Surveys 

The best current survey techniques for reef fish stocks are those 

based on visual methods supplemented with photographic and video imaging 

systems. Reef fishes almost invariably occur in clear water. Consequently, 

various survey techniques based on sightings (as used for numerous land 

animals) are possible. These techniques can be used two ways: visual surveys 

may be used alone to measure stocks on a selected reef, or a set of subsets of 

reefs may be taken as a sample of all reefs. 

stock abundance computed for the subsets is extrapolated to total abundance by 

In the latter case, the mean 
-51- 

relating the mean to the total amount of reef habitat available. 

can be estimated in various ways, but vessel surveys which use over-the-side 

video methods are preferred. 

Reef habitat 

A variety of visual methods is used to measure abundance of reef 

fishes. Generally these methods fall into two categories: 1) those which 

depend upon direct human sightings (Brock 1954, Parker et al. 1979, Stone et 

al. 1979) and those that rely on photographic and video records (Alevizon and 

Brooks 1975, Ebeling et al. 1971, Smith and Tyler 1973). 

si ghti ngs are general ly preferred since avail ab1 e camera systems provide 

limited fields of view which make accurate species identification and 

quantification virtually impossible. Photographic and video systems, however, 

offer the advantage of providing permanent records which can be studied after 

compl et i on of surveys. 

Direct human 

Directed visual surveys generally are accomplished either by scuba 

divers or by manned submersibles. 

they are depth-limited. 

advantages of scuba surveys and are not depth-limited. 

submersibles, however, is high: good submersibles and support vessels cost 

$8,000 to $10,000 per day. 

Scuba surveys are less expensive, although 

Submersibles, on the other hand, offer most of the 

The cost of 

Direct visual surveys require highly skilled biological observers to 

be effective. Species identification under water is difficult, especially 

since fish cannot be handled directly and all identifications have to be 

accomplished spontaneously. Fish collections, however, often are made in 

conjunction with man-in-the-sea techniques to provide specimens for 

verification of species identifications. Total kill of the fish in a selected 

survey area is usually attempted through the use of ichthyocides or 

explosives. Although ichthyocides provide the best method for collecting some 

of the small cryptic species, they are destructive and time-consuming to use. 

Photographic and video surveys offer some advantages. They incur 

minimal risk to human life and, in their simplest form, are relatively 

inexpensive. Their disadvantages relate primarily to limited fields of view, 

which hinder accurate species identification. Surveys of this type include 

over-the-side television and photographic systems, tethered remotely-operated 

cameras, and cameras mounted on remotely-operated vehicles. Camera systems 

mounted on towed sleds [e.g., Remote Underwater Fisheries Assessment System 

(RUFAS)] have not proved to be very useful because reef fish tend to avoid 

rapidly-moving vehicles. 

television system lowered from a vessel to the bottom, could ultimately prove 

useful because it can simultaneously image a 360' sphere. An observer placed 

in a hemispherical viewing chamber thus would have an enhanced view of the 

scene as if it were viewed from a submersible. 

A video scheme, based on a multicamera color 

Analytical methods used for both visual and photographic/video surveys 

are generally based on line transect or quadrate count theory. 

former, measurements of the location of sighted fish relative to a given 

trackline must be accurately estimated. For the latter, counts must be 

reasonably representative of the area surveyed. Water clarity, currents, and 

time of day all affect interpretation of data and must be considered in the 

analysis. 

For the 
-52- 

2.2.3. Fish Egg and Larva Surveys 

The assessment of the abundance of spawning stocks of fish can be 

accomplished by conducting surveys of the abundance of eggs, larvae, and 

juveniles. 

stages in the life history of fish and some shellfish, permitting convenient 

sampling with simple equipment over broad areas. 

surveys are more reliably used for hindcasting (e.g., estimating the size of a 

spawning stock that produced the quantity of eggs ascertained from a survey) 

than for forecasting (e.g., predicting year-class strength from an estimated 

quantity of eggs or 1 arvae) . 

Pelagic fish eggs and larvae are the most numerous and vulnerable 

Results from egg and larvae 

The basis f o r t h i s method is to sample quantitatively a known volume 

of sea water from a known area. 

arithmetically expanded to determine the total population size. This can then 

be arithmetically converted to the size of the spawning stock if fecundity and 

the sex ratio of the adults are known. Details of the procedures are 

adequately expl ained by Smith and Richardson (1977). 

The number of animals caught are then 

In the U.S., the most extensive surveys have been conducted by 

Cal ifornia Cooperative Oceanic Fishery Investigations (CalCOFI) which has 

surveyed the waters from the Oregon-California border to the tip of Baja 

California and Gulf of California since 1950. These studies have focused 

principally on the California sardine and northern anchovy and, to a lesser 

extent, on Pacific mackerel, jack mackerel, and rockfishes. Smith and 

Richardson (1977, 1979) cite many examples of this work. Extensive egg and 

larvae (ichthyopl ankton) surveys, which have been both single- and especially 

multispecies oriented, have been conducted by NMFS in the northwest Atlantic 

and in the Gulf of Mexico. 

provided the bases for stock assessments. 

Results from these surveys have not, however, 

Use of surveys is wide-spread in European waters and is used to 

estimate population sizes of North Sea herring, capelin, cods, and flatfish 

(Smith and Richardson 1979). 

abundance has been shown for many species, especially the North Sea herring, 

where long time series of data are available (Postuma and Zijlstra 1974). 

The relation between stock size and larval 

Example 13.--1chthyoplankton Survey on Abundance of Adult 

Spawning Fish 

This method assesses the abundance of adult spawning fish stocks with 

a shipboard ichthyoplankton survey designed to measure the distribution, 

density, and production rate of the spawning products, fish eggs, and larvae. 

Methods--The survey can be conducted from almost any seaworthy vessel 

equipped with a hydrographic winch that can be operated in coordination with 

the vessel speed in order to maintain strict standards of a quantitative net 

tow. 

towed along an oblique trajectory, although vertical and horizontal tows are 

also possible. 

The most common nets used by CalCOFI and by NMFS researchers are the slowspeed bridle ring net and the paired Bongo net fitted with either 0.333 mm- or 

The basic piece of sampling gear is a fine-mesh plankton net which is 

A variety of net designs has been developed over the years. 
-53- 

0.505 mm-mesh nylon nets. 

various parameters to quantify the net tow, such as a cable meter to measure 

amount of wire out, an inclinometer to measure the wire angle, and a flowmeter 

to measure the volume of water filtered. 

Additional meters are required to measure the 

The survey pattern is generally designed to sample the temporal and 

spatial distribution of the spawning distribution of the species being 

studied. Surveys are usually composed of multiple cruises, frequently with 

more than one research ship, scheduled over the spawning seasons of the target 

species. 

species ' spawni ng di stri but i on. 

Station patterns follow a specified grid that encompasses the 

The basic information for each sample is the number of fish eggs or 

The required data for each sample are station identification, 

larvae beneath a unit sea surface area (10 square meters in the CalCOFI 

example). 

parameter values of the net tow, and number of fish eggs and larvae. The 

CalCOFI program has recently developed a sophisticated data management system 

whereby these data are compiled, verified, and stored for future retrieval and 

analysis. 

The ichthyoplankton survey can be used to assess most marine fishes 

that have pelagic eggs and feebly swimming larvae distributed throughout the 

upper mixed layers of the ocean. The method, however, requires that the 

taxonomy of the eggs and larvae be reliably known, and would be effective for 

species with demersal or highly buoyant eggs only if the larvae are 

epipelagic, although horizontal neuston tows could be used to sample buoyant 

eggs. Species with fast-swimming, rapid-growing larvae could probably not be 

sampled successful ly. 

Analytical techniques--Data from this survey can be divided into field 

and laboratory observations. 

number, position, date, time, etc. and document quantitative characteristi s 

of the net tow. The station standard haul factor (SHF, the number of 10 m 

sea surface units sampled) is calculated from the latter net tow data by the 

equation 

Field data identify the sample with station 

5 

SHF = 10 (a'' b'l d) 

where a is area of the mouth of the plankton net in square meters, 

b is the length of the tow in meters, 

d is the effective depth of the tow in meters. 

b, the length of tow, is measured by the number of revolutions of the 

flowmeter; d is estimated from the maximum length of wire out and average 

tangent of the wire angle taken at 30-second intervals over the retrieval of 

the net. 

In the laboratory, the volume of plankton is measured, and large 

samples are fractioned into smaller subsamples. Trained sorters separate the 

ichthyoplankton from the rest and identify and count the eggs and larvae of 

the high priority species. For some studies, sorters may identify egg 
-54- 

development stages or may measure length of larvae to the nearest 

1/2 millimeter. 

larvae for which the species name is known. 

and larva counts are combined via the station ID to give the standard number 

of eggs or larvae per station. 

Later, identification and counts are made for other eggs and 

The two data sets of SHFs and egg 

Quality control is a major concern. In the CalCOFI case, plankton 

nets must continually be examined for holes and flowmeters are frequently 

recalibrated. Net tows are repeated if the flowmeter fails during the tow or 

if the wire angle exceeds 51' at any time during the tow. 

identifications and counts are later confirmed by ichthyoplankton experts. 

The data management system includes a set of data verification programs which 

screen data errors and inconsistencies. 

Plankton sorters' 

The survey pattern should be designed to cover the temporal and areal 

If there is a 

On the 

range of the spawning distribution of those species of concern. 

multitude of species, as in the CalCOFI example, then cruises must be 

scheduled at approximate monthly intervals for almost a year's period. 

other hand, if the objectives are to assess only one or two dominant species, 

cruises can be scheduled for the primary spawning months. 

cruises then depends on the length of the spawning season. 

The number of 

The recommended station pattern is a centric systematic area sample 

grid. A CalCOFI example is shown in Figure 12. This station pattern meets 

the conditions for random sampling (Milner 1959) and is conducive to efficient 

ship operations. The number of samples per survey needs to be large enough to 

apply the central limit theorem to estimates of densities of the fish eggs and 

larvae. 

desired level of precision. 

target sample size is 2,000 plankton tows. For an abbreviated anchovy survey, 

a sample of 600 tows is adequate. 

The number of stations required per survey is a question of the 

For an annual multispecies CalCOFI survey, the 

The basic results produce an egg and larva survey area distribution 

map of the spawning stock(s), an estimate of the density of eggs or larvae or 

their total abundance (egg or larva census estimate), and/or an estimate of 

the egg or larva production rate. 

information on egg and larva mortality rates. Analyses of egg stage or larva 

size-frequency data, along with know1 edge of devel opmental rates or growth 

rates in order to age staged eggs and sized larvae, are also needed. 

These latter estimates require further 

The density estimates in terms of average number of eggs or larvae per 

10 m2 sea surface area are best compiled by regions if the pattern of stations 

is not uniformly distributed over the survey area. 

estimated C is the average 

In general, the density 

n 

C = ( c 

i=l 

SHF Ci) ni 

where Ci is the count of eggs or larvae per station, and ni is the number of 

samples in survey region or area. The empirical estimate of the variance of 

density is sufficent if the sample size is large enough so that the central 

limit theorem applies. Usually the frequency distribution of counts per 
-55- 

z 

a 

v, 

a 

m 

0.' 

%' ". 

e' ". 

9 
-56- 

sample is highly skewed because of the contagious (or patchy) distribution of 

eggs and larvae in the sea. 

is required before the probability distribution for the mean density estimate 

wi 11 be symmetrical. 

Consequently, a large (ca. 100) number of samples 

The census estimate L is simply 

L = CoA 

2 where A is the size of the survey area in 10 m sea surface units. 

estimation procedures for egg and larvae production rates are considerably 

more complicated. 

The 

For these indices to be consistent among years, a number of 

assumptions must hold. 

sample of the spawning products. 

station pattern or by stratifying stations into geographic regions. 

the time period during which spawning products (eggs and larvae) are 

accessible to the gear must be the same year to year. 

function of their developmental and growth rates, which in turn are functions 

of ambient temperature and food supply. 

parameters occur among years, then correction factors should be derived to 

adjust census index appropriately. If differential size-dependent net 

avoidance or retention occurs, and if the average egg stage or size of larva 

varies among years, then a second adjustment may be necessary. Finally, it is 

important that fecundity or female egg production be consistent among years. 

The results of a recent histological study of anchovy gonads by Hunter and 

Goldberg (1980) suggest that female anchovies spawn as frequently as once per 

week. Fecundity, therefore, is potentially a dynamic process. 

First, the station pattern must provide an unbiased 

This problem can be minimized with a uniform 

Second, 

This period is a 

If large fluctuations in these 

Both the density and census estimates can be used as an index of 

abundance of the spawning stock(s). 

estimates provides useful information on the status of the resource. 

indices, in turn, can be used indirectly and directly to estimate the 

magnitude of the spawning biomass that produced the eggs and larvae surveyed, 

although additional information is required. The indirect method requires a 

second historical time series of spawning biomass estimates derived from other 

independent methods, such as a cohort analysis of fishery catch statistics. 

If the correlation between the two time series is sufficient, biomass 

predictions can be estimated from the latest index value by the regression of 

spawning biomass on egg or larvae index. 

An up-to-date time series of such 

These 

An extension of this method was developed to estimate the spawning 

biomass of northern anchovies for the CalCOFI area. In this case, since a 

historical time series of anchovy abundance was not available, the existing 

relationship between the larva census estimate and spawning biomass for the 

closely related sardine was used to relate anchovy larvae to anchovy biomass. 

The development of this procedure is given in Smith (1972) and the Northern 

Anchovy Fi shery Management P1 an (Appendix I, PFMC 1978). 

The direct method of estimating spawning biomass (B) is based on the 

relationship 

B = E/e 
-57- 

where E is the estimated rate of egg production over the spawning area, and 

e is the stock fecundity rate or the capacity for eggs by a 

unit weight of fish stock. 

This is determined by the fecundity of mature females, expressed as eggs per 

unit time per unit weight, and the proportion by weight of the mature stock 

composed of spawning females within each unit time (Smith.and Richardson 

1977). 

Preliminary application of this direct estimate has been attempted on 

northern anchovies in the CalCOFI area. 

are conducted: 1) to estimate daily egg production with plankton tows 

designed specifically to sample anchovy eggs, and 2) to estimate stock 

fecundity rate with midwater trawl samples to collect female gonads. The 

results to date are encouraging (Parker 1980), and further testing of the 

sampling procedures and parameter estimation algorithms is planned. 

In this case, two separate surveys 

2.2.4. Remote Sensing 

2.2.4.1. Acoustical Surveys 

Two acoustical survey methods have been used by NMFS scientists to 

determine distribution and abundance characteristics of marine fishes. These 

include vertical (echo sounder) surveys, depl oyi ng fishing systems to verify 

targets, and sonar mapping surveys. Examples of each method are given below. 

Example 14.--Vertical Acoustic Assessment With Trawling for 

Target Verification 

At present, echo sounding is the most widely used hydroacoustical 

technique for estimating quantities of marine fish. 

sound wave downward and processing the received echo signals to estimate fish 

abundance. Equipment design is based on hydroacoustical theory and current 

scattering models. The echo signals received from a fish population may be 

either counted individually (echo counting) or integrated (or summed) over a 

selected interval of time (echo integration). To perform their counting 

function, echo counters must be able to resolve a single target with respect 

to its angle and range. 

single-target resolution because the resulting density estimate is a function 

of the received signal from the volume of water surveyed. 

swim in aggregations (in such a manner that individual echo signals cannot be 

easily resolved), echo integration is the common technique currently used. 

It involves sending a 

Echo integrators, however, do not require 

As most target fish 

Methods--The present hydroacoustical system used at the Northwest and 

Alaska Fisheries Center is a portable real time digital echo sounder data 

processing system designed for echo integration and direct in-situ target 

strength measurement using a dual beam transducer (Ehrenberg 1974), which has 

been employed since 1976. Refinements since that time have been concerned 
-58- 

mainly with improving the stability of the echo sounder receivers to meet the 

requirements of the dual beam measurement method. A large (higher resolution) 

dual beam transducer is also now used with the system described in Dark et al. 

(1980), Traynor and Ehrenberg (1979), and Traynor and Nelson (1979). 

its development and application, a major effort has been expended on equipment 

calibration to ensure accurate knowledge of system parameters. 

During 

Using the present system and its predecessors, a survey program 

involving approximately 600 days of research vessel time has been conducted 

since 1974. This program was initiated based on experience obtained during 

more qualitative survey efforts conducted during 1966-73. 

addition to helping meet the needs of several of NWAFC's stock assessment 

programs, has furnished a valuable background for evaluating the present 

system. 

information on the distribution, availability, vulnerability, and echo 

signatures of the important, acoustically-detectable fish stocks of the 

northeast Pacific and eastern Bering Sea. This information has primarily been 

derived from basic, and largely qualitative observations, i.e., the continuous 

real time examination of echogram displays as well as the process and results 

of midwater trawling operations. One of its primary values is that, when used 

in conjunction with a knowledge of stock management requirements and the 

capabilities and limitations of other methods, it has provided most of the 

basis for evaluating the feasibility of employing hydroacoustical surveys, 

Surveys have been conducted in conjunction with assessments of certain semipelagic stocks, such as offshore herring and shelf rockfish, and major semidemersal stocks, such as Pacific whiting and eastern Bering Sea pollock. 

The field work, in 

Of equal importance is the acquisition of a large amount of 

All surveys have been conducted during daylight hours because the fish 

are aggregated and much more clearly segregated by species, making detection 

and identification more feasible. 

systematic transect patterns which are designed to cross depth contours and 

maximize the likelihood of encountering the target species, There are large 

differences among species types with respect to their degree of patchiness. 

Therefore, differences exist both in the spacing of transects and in the 

amount of adaptive survey effort needed. This additional effort is beyond 

that required for the basic transect pattern necessary to delineate the 

distributions of the stocks. 

Surveys are usually carried out with 

Pacific whiting and, especially, eastern Bering Sea pollock are 

typically found in large, readily distinguished, mono-specific midwater 

"school s" (aggregations of schools) oriented para1 1 el to depth contours. 

these species, broadly spaced zig-zag transect patterns (Fig. 13 and Fig. 14) 

designed to provide relatively uniform coverage have been used successfully. 

No additional survey effort is expended to more precisely del ineate school 

boundaries. Because of the size of schools, it is impractical to attempt to 

implement this kind of effort. However, because survey effort has usually 

been partially dictated by practical constraints, rather than by survey 

objectives alone, it would useful to be able to examine how changes in 

transect spacing affect the precision of abundance estimates. 

The highly contagious spatial distributions of Pacific herring found 

off the Washington-British Columbia coast, and of most species of rockfish, 

require a substantially different survey strategy than that used with hake and 

With 
- 59- 

50 * O( 

49'0( 

40% 

4 7-00 

46'09 

4 5-00 

44-15, 

I 

Figure 13. --A portion of the region covered during 1977 Pacific whiting survey, 

showing transects spaced at 10-n.ni. intervals. 
-60- 

d 0 

a 

175" \Iv 170" 165" 160' 155" 150" 775 E 180 

6 O> 

55' 

5 0" 

Figure 14.--Trackline covered during 1979 Bering Sea walleye pollock survey, 

showing transects spaced at 30-n.mi. intervals. Trackline was 

located between 50- and 250-fm isobaths. Locations are midwater 

trawl stations, including those made during special st.udies of 

Aleutian Basin pollock. 
-61- 

pollock. Although there are major differences in the characteristics of 

herring and rockfish stocks, they are alike in that they occur in extremely 

patchily-distributed near-bottom schools. 

the basic transect pattern is a systematic one, it is essential that transects 

be closely spaced, i.e., at about 2- to 4-mile intervals, and that a large 

part of the available survey time be spent delineating the distribution of 

individual aggregations as they are encountered. Because of these 

requirements, surveys of this type are essentially impossible to implement for 

broad geographic areas, e.g., those which must be covered during whiting and 

pol 1 ock surveys. 

If (as has been the case to date) 

A good example of this type of survey is provided by a 1979 survey of 

herring stocks off the northern Washington-southwest Vancouver Island coast. 

During this survey, approximately 25% of the time was used for midwater trawl 

sampling, 20% for coverage of the systematic pattern, and 55% for intensive 

surveying of the few areas where herring were abundant. 

systematic survey design for herring might be more efficient, but it is 

difficult to specify criteria for stratification. 

A stratified 

Survey experience with rockfish has clearly shown that hydroacoustical 

methods cannot yet be usefully amlied as an assessment method (except in the 

case 

fact that 

of the 

they are 

uniiue 

very 

shortbelly”rockfish, 

patchily distributed, 

Sebastes 

the 

e. 

echo signatures of 

In addition to the 

individual species are not easily recognized, and are very.difficult to 

discern in mixed-species schools. 

shown that intensive surveys designed to examine the microdistribution and 

schooling behavior of rockfish are needed to better define the potential of 

hydroacoustical and other survey methods. Recent information also suggests 

that certain species may be more successfully surveyed at night. 

These, and other complicating factors, have 

Analytical Techniques--The b ic data collected during surveys are 

Whenever 

9 echo biomass density estimates (kg/m ) obtained at one-minute intervals 

(0.15 n.mi. at 9 knots) along survey transects for each of up to 

50 transducer-referenced and 10 bottom-referenced depth strata. 

possible, the estimates of target strength used to scale the basic echo 

integrator outputs [which are proportional to density] to estimates of 

density, are obtained in-situ using the dual beam measurement method 

(Ehrenberg 1974, Ehrenberg et al. 1976, Traynor and Ehrenberg 1979). 

rationale for, and practical constraints on, the use of this method are 

described by Traynor and Nelson (1979). 

made, a value for the target strength parameter is obtained from the 

literature on fish target strength measurements. 

The density estimates (kg/m3) for each one minute interval are su med 

over depth intervals to provide estimates of areal biomass density (kg/m ). 

The depth intervals appropriate for this summation and the transect sections 

to which the analysis is confined are determined both from echogram 

examination by experienced personnel, and from the results of midwater 

trawling. Midwater trawl samplng, for species identification and biological 

data collection only, is done in real time, i.e., during the echo integrator 

survey period, with aimed trawling techniques. 

individual areal biomass density estimates are examined to define the 

The 

If dual beam measurements cannot be 

! 

The distributions of the 
-62- 

geographic boundaries appropriate for calculation and extrapolation of mean 

density estimates. 

Because successive density estimates along the survey transects are 

serially correlated and therefore not indepen ent, an estimate of the variance 

of the mean which uses the sample variance, S', will tend to be biased low. 

To correct for this bias, variance estimation methods based on cluster 

sampling theory are used. Each survey transect is usually treated as a 

cluster. 

then calculated from information on the nu ber of transects in the area, the 

amount of within-transect correlation, Simulation studies (Williamson 1979) 

indicate this variance estimate is unbiased. 

The estimated variance of the mean density for a defined area is 

average number of one-minute density (kg/m h ) estimates per transect, and the 

The total biomass estimate and its variance for the region surveyed 

are calculated by combining the estimates for those areas defined during 

analysis of the data. 

specified change in average target strength can be easily calculated, it is 

not yet practical to attempt to determine explicitly the variance of this 

parameter. 

Although the effect on biomass estimates of any 

Its probable range of values, however, can usually be estimated. 

Example 15.--Sonar Mapping Acoustical Surveys 

The sonar mapping method (Smith 1970) of stock assessment is a 

shipboard acoustical survey of the upper mixed layer of the ocean with a 

horizontal sonar beam directed perpendicular to the ship's path. This 

technique provides a count of the number of pelagic fish schools per unit area 

and a measure of their horizontal dimensions; together, these provide an index 

of fish biomass. 

(1976), Hewitt et al. (1976), and Mais (1974). 

equipped with calibrated sonar electronics and midwater trawl gear. The 

sampling gear in this case is an acoustic beam directed horizontally on an 

axis perpendicular to the forward direction of the vessel. 

systems developed by CalCOFI programs with NMFS and California Department of 

Fish and Game (CF&G) use 30 kHz sonars. 

considered to be fish schools. 

species composition of the upper mixed layer. 

The details o f t h i s method have been documented by Hewitt 

Methods--The required survey platform is a seaworthy research vessel 

The sonar mapping 

The echo returns in most cases are 

Midwater trawl gear is used to sample the 

Because of the highly patchy spatial distribution of pelagic fish 

schools, a survey grid scheme of 20' squares is recommended by CF&G. 

vessel travels along transects that are spaced 6 to 20 miles apart and cross 

each grid. 

fish predominantly form into schools and when the deep scattering layer is at 

maximum depth. 

school concentrations at night when fish are most vulnerable to capture. 

The primary measurements of each observed fish school are its location 

in the horizontal plane and its diameter along the axis of the sonar beam. 

Any information from visual observations or from the vertical echo sounder on 

species, school thickness, fish size, behavior, and predators is also 

recorded. Collectively, the measurements yield the number and surface area of 

The 

The vessel operates at 9 to 12 knots during daylight hours when 

Midwater trawl samples are taken in areas of the greatest fish 
-63- 

fish schools per unit area, the geographic distribution of fish schools within 

the survey area, and the frequency distribution of fish school sizes. 

Acoustic echoes of fish schools can be recorded on sonar paper or 

magnetic tape. 

counts and measures school dimension in the laboratory at the end of the 

survey. 

processor that interprets acoustical echoes, and the size and intensity of the 

school is recorded on magnetic tape. 

CF&G (Mais 1977) routinely uses paper records and manually 

NMFS (Hewitt et al. 1976) developed a prototype computerized data 

The side-scanning method of sonar mapping was developed to detect, 

with acoustical sensing, compact fish schools residing in the upper surface 

layer of the ocean. The usual vertical echo sounding method was found to be 

an inefficient acoustical sampler for such fish schools as northern anchovy in 

the CalCOFI area because the schools tend to avoid ships and the volume of the 

insonified water cone, through which the sound is emitted, in the surface 

layers is small. 

Sonar mapping is most effective for a species that is the dominant 

schooling fish in the upper mixed layer. 

non-random distribution, should preferably be small and scattered over a wide 

area. The adult schools must occur in pelagic waters where the bottom depth 

exceeds 50 fathoms; otherwise, the return echo from the bottom will mask any 

echo from an insonified school. Good weather conditions are necessary to 

maintain a steady horizontal acoustical beam unless the vessel is equipped 

with a stabilizing transducer. In addition, a mixed layer is desirable to 

minimize beam distortions that result from refraction of the beam by changes 

in water density at the thermocline. 

schooling behavior can change quite rapidly, these conditions are best met 

during daylight hours in the winter spawning months when schools are the 

smallest and most widely scattered, and when the upper mixed layer has its 

maximum thickness. 

Schools, which will have a patchy 

In the case of northern anchovies, whose 

Analytical techniques--The basic observations of the sonar mapping 

method are counts of fish schools and measure of the horizontal dimension in 

meters of the detected schools. Data on species identification, school 

thickness, and fish density within a detected school must be made by other 

means. In practice, species identification is determined subjectively by 

examination of the acoustical record by experienced personnel. They also 

supplement this decision with visual observation notes and midwater trawl 

catches in the general vicinity. For the moment, a practical survey method 

does not exist for determining fish density within a detected school. An 

underwater photographic procedure has been developed and purse seine captures 

of insonified schools have been done, but school compaction and estimates of 

school compaction are both extremely variable and these data give a wide range 

of values. Graves (1977) estimated densities of 50 to 366 fish/m3 using 

free-fa1 1 cameras to take pictures of fish schools. Hewitt et al. (1976) 

estimated values that ranged from 0.52 to 533 fish/m3 from catches of a purse 

seiner. School thickness can be measured from acoustical records of schools 

detected by an echo sounder. For most surveys, this sample will be small and 

is quite likely inaccurate because fish tend to avoid the ships. 
-64- 

Another basic observation is the measure of the effective range 

interval of the sonar beam in which 100% of all fish schools can be 

acoustically detected. In practice, the effective range interval for each 

transect is assigned upon inspection of the sonar records. 

equipment, this range is normally from 200 to 1,000 meters (Mais 1977). 

detection range frequently changes as a result of refraction of the sonar beam 

by internal waves and changes in the thermal stratification of the water 

column. 

provide quantitative criteria for setting the effective range, but this 

technique has not been implemented. 

school size categories. 

probability of school detection declines as the distance from the ship 

increases and as the school size decreases. 

signal and associated echo decays as it passes through water. 

the problem of estimating effective path width for line transect surveys. The 

estimation procedures for line transect theory should be applied to estimation 

for effective range intervals. 

Depending on the 

This 

Smith (1977) developed a sound velocity profile scheme which would 

The effective range interval varies for 

Beyond some threshold distance from the ship, the 

The strength of the acoustical 

This parallels 

Quality control for sonar mapping surveys has two aspects. First, 

periodic calibration of the sonar electronics and transducer is important to 

maintain signal and echo quality that otherwise may deteriorate over time. 

Second, research cruises should be scheduled to coincide with the most 

favorable fish school behavior and hydrographic conditions to minimize the 

impact of environmental variability on the annual stock assessment. 

Survey design criteria consider three main conditions: patchy 

Because of the highly 

non-random distribution of schools (Smith 1977), school formation in day1 ight 

hours, and season for best environmental conditions. 

contagious distribution of fish schools, the survey area should be divided 

using the grid system. 

that empirical variance estimates can be calculated for the mean number of 

schools per square mile. 

frequency of schools. 

averaged for each grid, and the grid summaries added together to obtain the 

total statistics for the survey region. In the CalCOFI example, sonar mapping 

can easily sample in a single survey as much as 2 or 3% of the sea surface 

area containing a major portion of the central subpopulation of northern 

anchovies. 

At least two transects should transverse each grid, so 

More transects should be run in grids with high 

The data are then computed by transects, the transects 

The primary parameter estimated per transect is the number of fish 

schools per square mile and the average school diameter in meters. Empirical 

estimates of variance can be calculated. From these data, estimates of schoo 

surface area in each grid can be estimated, assuming circular school shapes. 

In practice, where school thickness measures are too few in number and actual 

fish packing density estimates are lacking altogether, expansion of the schoo 

surface area into biomass estimates is unreliable. 

2.2.4.2. Other Remote Sensing Methods 

A number of other remote sensing techniques have been experimented 

with and are occasionally used in exploratory fishing surveys. 

techniques can be divided into two types. 

involving detection and enumeration of individuals or groups of animals (e.g., 

These 

The first is of a direct form 
-65- 

fish schools) and plants. The second type involves remote measurements of 

specific physical or biological parameters other than those directly 

associated with the animal or plant of interest, which may then be used to 

infer the desired information, such as the presence or absence of a certain 

species of fish. 

remote sensing platform used, e.g., satellite, aircraft, or vessel, and into 

passive and active forms depending on how the sensor is coupled to the 

phenomenon being sensed. 

form the basis of important assessment activities but can offer technical 

opportunities to extend assessment methods. 

Of the direct forms of remote sensing, aerial photography is probably 

the most commonly used technique for stock assessment. It has been used 

extensively for surveys of coastal pelagic species in the northern Gulf of 

Mexico and, more recently, to augment surveys of dolphins in the Pacific and 

seals and whales in the northwest (Kemmerer 1979, 1980). To be effective, 

however, aerial photography must be designed for a particular application, 

because high sun angles, optical properties of the water, and the color 

signature of the animal being sensed must be considered to ensure meaningful 

results. Multispectral photography has proved very useful for this 

application since it provides definitive information on best film and filter 

combinations for the specific conditions expected during assessment surveys. 

These two types can be further categorized according to the 

Most of the remote sensing methods do not currently 

A major advantage of aerial photography is that it provides a 

permanent record which can be analyzed in a laboratory. 

useful information from significantly greater water depths under environmental 

conditions not possible with the naked eye. 

normally is done on viewing devices which enlarge the scene from three to 

forty times. 

It can also provide 

Photographic interpretation 

Another form of direct remote sensing is provided through the use of 

low-light-level image intensifiers which amp1 ify the bioluminescence caused by 

fish agitating certain forms of plankton. This bioluminescence encases fish 

schools with a faint light which, when amplified sufficiently with an image 

intensifier, can be displayed on a video monitor and recorded on video tape. 

These systems have been used effectively in the southeast region for surveys 

of menhaden and other coastal pelagics, and are being used commercially for 

tactical direction of fishing operations and assessment of the harvest 

potential of selected pelagic species (Roithmayr 1971). Their principal 

limitations relate to species identification, limited water penetration 

(although substantially greater than that possible with the naked eye), poorly 

defined relationships between fish school surface area and biomass, and 

limited operation at night during dark-of-the-moon periods. 

Another form of direct remote sensing is provided by the unmanned 

submersibles developed by NMFS which are periodically used for assessment of 

benthic animals. These submersibles are considered remote sensing systems 

because they rely on photography, television, or both, for data acquisition. 

They are of two types: those sledded or those flown across the bottom. Both 

types are towed by research vessel s. 

Examples of flown systems include Remote Underwater Fi sheries 

Assessment Systems-I and -11 (RUFAS-I and -11). The RUFAS-I consists of a 
-66- 

towed submerged platform equipped with 1 ights, television and photographic 

cameras, and acoustic transducers (Seidel 1970). It is flown about 1 m above 

the ocean floor by system operators using acoustical signals and television 

images to regulate flight. 

southeast coast off the United States for photographic surveys of calico 

scal 1 op (Argopecten 9i bbus) . 

used for sensors operating in spacecraft. Because of the lack of spatial 

resolution provided by spacecraft sensors, most marine animals cannot be 

detected. Consequently, investigators have concentrated on remote 

measurements of oceanographic parameters assumed to influence the distribution 

and abundance of marine animals. Satellite forms of remote sensing, however, 

are not used significantly for resource assessment although a number of 

experiments which show potential have been completed or are under way. 

The system has been used extensively of the 

RUFAS-I I i s not operational. 

Indirect forms of remote sensing for stock assessment are generally 

The remote measurement of sea surface temperature is sufficiently 

advanced so that it can be considered operational from satellites and 

aircraft. 

and absolute accuracies of about l.O°C, are possible with improved thermal 

scanners such as those aboard TIROS. 

measurements relate to spatial resolution (only about 1 km) and cloud cover. 

With sensors operating in the microwave region of the electromagnetic 

spectrum, however, cloud cover problems disappear. Unfortunately, there are no 

operational microwave temperature sensors aboard any satellites; the ones 

which have been used experimentally indicate that spatial resolutions of 25 km 

are the best to be expected within the next decade. Aircraft thermal sensors 

are not spatially limited in resolution as resolution can be varied by 

changing the sensor or aircraft altitude. 

Temperature gradient measurements approaching 0.1OC in sensitivity 

The principal problems with satellite 

Sea surface temperature measurements with remote sensors are not used 

significantly by NMFS for stock assessment purposes although they are used by 

west coast fisherman as a tactical aid for their fishing operations. An 

experimental program was initiated in 1975 by the National Envi ronmental 

Sate1 1 ite Service (NESS) and Sea Grant for del ivering sate1 1 ite-derived 

temperature information on coho salmon (Oncorh nchus kisutch), chinook (0. 

tshawytscha) , and a1 bacore (Thunnus a1 al'*hermen. The primarysensor used was a very high mion radiometer (VHRR) operated from NOAA-5. 

The experiment reportedly has been successful and is receiving strong support 

from fishermen (Jurick 1977). In a similar experiment, sea surface 

temperatures obtained from aircraft were successful ly used to he1 p fi shermen 

locate coho salmon within a relatively small coastal area (Wright et al. 

1976). On the east coast, temperature charts are mailed to longline fishermen 

by NESS for waters from Georges Bank south into the Gulf of Mexico. 

charts reportedly are used by the fishermen to locate concentrations of 

swordfish (Xiphias w. 

two NASA experimental satellite systems -- LandSat and Nimbus-7 -- and appears 

to be useful for inferred measurements of chlorophyll and turbidity, 

information on current systems and water mass boundaries, environmental and 

pollution studies, and for inferred distribution patterns of some pelagic 

school i ng fish. 

These 

Ocean color remote sensing is currently available, principally from 
-67- 

Several investigations have been recently completed or are under way 

which emphasize ocean color measurements from spacecraft and aircraft. The 

LandSat Menhaden and Thread Herring Investigation was conducted from 1975 to 

1977 in the northern Gulf of Mexico to determine how remotely sensed data 

could be used in assessment and harvest applications. 

primary target species. 

of these fish could be inferred from LandSat multispectral scanner data with 

accuracies approaching 90% (Kemmerer 1979, 1980). 

Menhaden was the 

The investigation demonstrated that the distribution 

Probably the most significant sensor for ocean color remote sensing is 

the Nimbus-7 Coastal Zone Color Scanner (CZCS). 

specifically for inferred measurements of chlorophyll and turbidity. Good 

results already have been achieved although the satellite data have been very 

1 imited due to unrelated data processing problems. 

This sensor is designed 

In 1979, NMFS initiated a remote sensing program to evaluate the 

usefulness of remote color measurements for enhancing understandings of marine 

ecosystem dynamics related to fisheries. This program, referred to as Large 

Area Marine Pollution Experiment (LAMPEX) , initially re1 ied on aircraft 

sensors but, due to the demonstrated success of CZCS, has begun to emphasize 

the satellite sensor for measurements of chlorophyll and possibly turbidity. 

An expansion of LAMPEX into the southeast region currently is being considered 

so that marine ecosystems unique to each area can be compared and improved 

understandings related to fisheries can be developed. 

Remote measurement of surface currents is a very difficult observation 

to make remotely. The most successful technique available is used only 

experimentally and is based on remote measurements from shore stations 

(Barrick et al. 1974). Radar signals are transmitted from the shore station 

and scattered by ocean waves. The waves act as tracers of superimposed 

currents due to slight velocity changes in the waves caused by the currents. 

The technique will provide current data on a 3-km by 3-km grid to a range of 

about 70 km from shore. 

position and 10 cm/sec rms for current speed. 

Error estimates are about 3 degrees in azimuthal 

There appear to be several methods to determine surface circulation 

with satellite-supported sensors. None, however, with the possible exception 

of satellite-linked drifting buoys, is operational. These methods include the 

use of water color differences in near-shore areas to compute circulation, 

monitoring thermal fronts such as the Gulf Stream with infrared measurements, 

the use of radar altimetry as a measure of surface geostrophic set-up, and 

determining surface wind stress and its incorporation in calculations of 

Eckman transport. The accuracy of these various methods is not known, 

although it is likely that only the more energetic and discontinuous flows 

will be measurable from space with useful precision. 

A special form of remote sensing is being used for studies of the 

movement and distribution patterns of marine mammals and sea turtles. This 

form requires attachment of a small transmitter to an animal for transmission 

to a receiver located in a surface vessel, aircraft, or spacecraft. In salt 

water, the transmitter antenna must be above the water surface for effective 

use. The limited range of most radio transmitters for animal tracking has 

prompted investigators to begin development of transmitters which can be 
-68- 

1 ocated by sate1 1 ites (Gandy et a1 . 1977). Devel opmental efforts have focused 

on the Random Access Measurement System (RAMS) on Nimbus-6 and, more recently, 

on the ARGOS system aboard TIROS. 

they enable suitable transmitters to be located several times a day with 

accuracies approaching a few kilometers. 

Both satellite systems are similar in that 

Satellite tracking of marine animals has several limitations. The 

most obvious of these is that the animal must surface during a pass of the 

receiving satellite to be located. The transmitters also are relatively large 

and heavy, which limits their application to the larger marine animals. 

Finally, the transmitters are relatively expensive, costing in excess of 

$3,000 each. 

satellite-supported receivers may help to reduce the size and cost of these 

systems, although it is unlikely that any significant advances will be 

available for general application for at least 5 years. 

Significant advances in transmitter design and in the 

2.2.5. Environmental Indices 

The use of marine environmental information in assessment of the 

abundance and distribution of marine fish populations is, in itself, a 

developing science. Frequently, environmental information is offered as a 

possible explanation, in a qualitative sense, of observed trends in stock 

abundance or fishery success and, in particular, to changes in recruitment, 

stock distribution, growth, or mortality rate. 

broad range of biotic activity including behavior, distribution patterns, 

accessibility, etc. The collection and evaluation of such information vary 

widely, as do analytic evaluations. 

environmental indices into stock assessment models is in the theoretical stage 

and varies for each application. It does, however, have the promise of 

reducing costs and increasing precision in stock assessment. 

Ocean 'IC1 imate" influences a 

As a result, the formulation of 

Large scale variation in atmospheric circulation patterns results in 

changes, such as wind strength direction, air temperature, storms, cloud 

cover, etc., which can drastically affect fishery resources and their 

habitats. 

most important effect of such environmental changes is on the recruitment of 

young fish into harvestable stocks. Pronounced effects may be experienced in 

early life stages due to such factors as changes in wind-driven ocean current 

patterns which alter the normal drift of larvae from spawning to nursery 

grounds; changes in primary production patterns and associated planktonic 

community structures that affect the availability of suitable food for normal 

larval development; and altered mixing processes and/or stabil ity of the water 

column that change the availability of suitable food for normal larval 

devel opment. 

From the viewpoint of fisheries conservation and management, the 

The use of environmental information can range in sophistication from 

scientists' expressed opinion on the 1 ikely relationship between observed 

biological and environmental conditions, to a complex multivariate regression 

analysis. This latter approach generally requires concurrent time series of 

biological and environmental conditions. Often biological events or 

parameters are measured on an annual scale while the actual causal mechanism 

may occur over a relatively short time period. At the same time, the ability 
-69- 

to obtain continuous measures of the environment is limited to such factors as 

surface temperatures, winds, sea surface heights, or atmospheric pressure. 

These may be only secondarily related to the actual causal environmental 

variable which, in turn, is modifying the biological condition of the stock. 

The use of environmental information in the predictive mode is the 

subject of numerous research projects in fisheries science. These studies 

involve finding empirical correlations between one of a number of 

environmental indices and annual yield, abundance, or recruitment, and/or 

investigating the causal environmental mechanisms that contribute to the 

recruitment success. In this way, environmental information contributes to 

the precision of stock assessment by improving the forecasts of stock 

abundance based on better estimates of recruitment, or by the inclusion of 

environmental variables in one of the traditional fishery analysis models 

(surplus production, stock recruitment, etc.) or ecosystem models. These 

studies are not only important to future NMFS stock assessment but also to 

related fishery habitat studies, fishery oceanography, and aquaculture 

programs. An understanding of the causal mechanisms associated with survival 

in the early life stages is the basis for environmental monitoring programs 

which, in turn, could improve forecasting ability. The goal is to use 

environmental data to understand better environmental influences and, 

ultimately, to increase the accuracy of stock assessments. 

For the pelagic fisheries, the more readily obtainable surface and 

near surface oceanographic data have been used for recruitment assessments of 

such species as Atlantic menhaden, Pacific mackerel, and northern anchovy, and 

for locating commercial concentrations of such species as yellowfin tuna, 

skipjack tuna, albacore, and swordfish, based on their association with 

oceanic frontal structures. New satellite technologies, enabling large area 

surveillance of sea surface temperatures, chlorophyll, currents, etc., should 

permit even further applications of environmental information in assessments 

of pelagic biological populations. 

For midwater and demersal populations, as Pacific hake and Dover sole, 

the situation is quite different due, in part, to the greater difficulty in 

monitoring subsurface environmental conditions. Progress is being made, 

however, in understanding pre-recruit survival for such species which have 

pelagic eggs and larvae that, for a period of time, occupy the ocean's upper 

1 ayers. 

Recent NMFS research to define trophodynamics and direct environmental 

effects is demonstrated in the following two examples: 

Example 16.--Stock Recruitment Studies of Northern Anchovies 

Considerable progress has been made in recent years in forecasting 

recruitment of the northern anchovy stock in the California Current region 

from environmental indices. It was hypothesized that the strength of an 

incoming year-class is determined by the mortality rate of early larvae. 

abundance of food particles of the proper size and species in the ocean's 

upper mixed layer has been found to be critical to the survival of 

fi.rst-feeding anchovy larvae. By monitoring the density, distribution, and 

species of food particles during the spawning season, the failures of the 

The 
-70- 

1974, 1975, and first half of the 1978 year classes were predicted (Lasker, in 

press). This work also demonstrated that adequate food patches occur when the 

upper mixed layer is relatively stable. Major storms or upwelling can 

disperse food particles to concentrations below the level of successful 

feeding and larval survival. Continued research and monitoring of these 

environmental variables wi 11 lead to improved recruitment forecasts and stock 

assessments. The methods developed in this research program for the northern 

anchovy should have broad application to other fishery regions around the 

world. 

Example 17.--Correlation Models 

A number of research studies have met with some success in finding 

correlative physical, chemical, and/or biological ocean variables which help 

expl ai n some of the 1 arge annual fl uctuat i ons i n recruitment , popul at i on 

biomass, and fishery yield as measured from fishery information. This 

approach generally incorporates significant environmental covariates into 

traditional equilibrium yield models. These fits often offer reasonable 

hypotheses of the causal mechanisms of early mortality and, therefore, the 

factors that regulate recruitment. 

mackerel (Scomber japonicus) off California, Parrish and MacCall (1978) found 

good correlations between upwelling and surface transport indices, and 

year-class strength. 

covariates to a Ricker spawner-recruit model. 

incorporating both density-dependent terms and environmental terms, accounted 

for as much as 75% of the variation. 

model, they were able to evaluate various management schemes for setting size 

limits and harvest quotas based on criteria of long term stock size and yield. 

Working with fishery statistics on Pacific 

In this case, the environmental indices were added as 

With this model coupled to a cohort 

Their recruitment models, 

On the east coast of the United States, Nelson et al. (1977), using a 

similar model, showed that the deviations from a Ricker spawner-recruit model 

for Atlantic menhaden were highly correlated to zonal Ekman transport. Based 

on this, they hypothesized that onshore transport acted as a mechanism to move 

larval menhaden from offshore spawning areas to inshore nursery grounds. 

Therefore, strong year classes resulted from years with strong onshore 

transport. 

Along the Gulf Coast, researchers have developed yield models of 

penaeid and other Gulf shrimps where annual yield is expressed as a function 

of f i shi ng effort, Mi ssi ssi ppi River discharge, and/or estuarine temperatures. 

Such models are much more appropriate than surplus yield models because of the 

overriding impact of the environment on yield, and the extremely short life 

span of shrimp. At average levels of river discharge and effort, the model 

predicts yield estimates which approximate MSY derived from the production 

model. In general, low freshwater discharge and high estuarine salinity and 

temperature result in lower yields. Using this model, it should be possible 

to forecast annual yields (or quotas) from projected river discharge values 

for a given level of fishing effort. 

or lowering annual harvest, based on the quantity of shrimp available. 

Such models provide criteria for raising 
-71- 

2.3. Fisheries Analysis for Stock Assessment 

Fisheries analysis uses mathematical models to combine statistical, 

survey, and environmental data in assessing trends in stock sizes, and in 

determining yield estimates from harvested resources. 

interpreted from simp1 e total catch trends, catch-per-unit-effort (CPUE) 

trends, or from more complex evaluations involving an integration of catch 

data with biological and environmental parameters for the stocks under study. 

There are many books on this subject (e.g., Beverton and Holt 1957, Gulland 

1969, and Ricker 1975). All fisheries centers within NMFS normally utilize a 

series of standard fishery models to evaluate stock conditions and theoretical 

equilibrium yields available at various stock sizes. 

model s fol 1 ows. 

Stock conditions may be 

A description of these 

2.3.1. Surplus Production Model 

Adequate information frequently is not available to provide an 

understanding of the complexities of the population process--growth, natural 

mortality, and reproduction. Under these circumstances, surplus production 

models can be very useful in determining empirical relationships between 

surplus production (extracted as equilibrium yield) and stock biomass (as 

measured by an index, usually CPUE). 

model the effect of fishing on the population. 

These relationships can then be used to 

Models relating surplus production to biomass usually assume that 

surplus production is greatest at some intermediate level of biomass, not at 

maximum population biomass (Fig. 15). There are several reasons for smaller 

surplus production at higher population biomasses: 

1) Near maximum biomass, efficiency of reproduction is reduced and the 

number of recruits is often less than at lower biomass levels; 

2) If food supply is a limiting factor, then growth is inhibited at 

1 arge biomass 1 eve1 s. 

Under stab1 e environmental conditions, recruitment and growth are 

balanced by natural mortality for an unexploited population, and thus there is 

no surplus production. When fishing begins, biomass is reduced and any of a 

combination of things may happen--the available food may be used more 

efficiently by the remaining population, reproductive efficiency may be 

increased, or natural mortality may be reduced. Surplus production is then 

generated, which would induce the population to recover to the maximum biomass 

level if fishing were stopped. 

The basic data requirements for conducting a production model analysis 

are: 1) total catch in weight (sometimes numbers) from the population by year, 

and 2) total fishing effort in standardized units by year. While these basic 

data requirements appear to be rather simple, this appearance is only 

superficial. Total catch (particularly the by-catch or incidental species 

and recreational catch) is frequently difficult to obtain. Fishing effort 

must be adequately separated when more than one species is being caught, and 

must be standardized to some common units when different gear types are used. 
-72- 

Population biomass 

Figure 15.--Relationship between population biomass and surplus production 

(sustainable yield). 

occurs at some intermediate population biomass (Pmsy). 

Maximum sustainable yield (MSY) usually 
-73- 

This is especially difficult when there are different gear types exploiting 

relatively different age groups, and/or there are strong efficiency 

interactions among population densities, time-area strata, gear types, and 

amount of effort employed. 

through logbook or interview systems. 

The fishing effort data are usually generated 

Surplus production model outputs which are most useful to the fishery 

manager include estimates of maximum sustainable yield, and the corresponding 

levels of fishing effort and population size. 

treated in this very simplistic manner primarily when there is a lack of 

adequate data for a detailed assessment of the effects of exploitation. 

costs accrued in obtaining this benefit are the creation of numerous 

assumptions, many of which are known, a priori, not to be satisfied fully, and 

the inability to analyze the effects of altering the variables which can be 

controlled by fishery managers (e.g., fishing season, size at first capture, 

re1 ative rates of fishing mortal ity among age groups, etc.) . 

The exploited population is 

The 

2.3.2. Yield per Recruit Model 

One of the most useful concepts in fishery science is that of 

e q u i l i b r i u m yield per recruit. 

estimated, growth can be balanced against mortality to obtain optimum yield 

(Fig. 16). The concept has proved useful not only as a stimulating theory 

about the productivity of exploited fish stocks, but also as a basic working 

tool for fishery managers. 

When growth and mortal ity rates can be 

The concept of equil ibrium is intimately tied to the yield per recruit 

approach. Equilibrium implies that, given a constant rate of fishing, a 

popul at ion wi 11 attain some 1 ong-term average biomass 1 eve1 and produce 1 ongterm average yield. 

by a given year-class (a cohort of fish spawned during the same year) is the 

difference between the sum of the weight gained by individuals in the 

population and the sum of the weight of fish lost due to death (natural or 

fishing) in any given year. 

generally difficult to estimate, the yield per recruit, as opposed to total 

yield, is modeled by assuming a constant level of reproduction. 

Under equilibrium conditions, the yield or net production 

Since the size of an incoming year class is 

Fishery managers can use this concept to further their understanding 

of a fishery, and to make predictions as to how the yield per recruit will 

respond to changes in the amount of fishing effort and to which sizes or uses 

of fish it is applied. Generally, yield per recruit models are used in three 

ways: 

effort, changes in the yield per recruit are examined by changing the 

age-at-first-capture by the fishery (Fig. 17a); 2) Given that the fishery 

operates on a certain age-at-first-capture pattern, changes in the yield per 

recruit are examined over a range of fishing effort (Fig. 17a); or 3) A 

simultaneous combination of 1) and 2) are examined for changes in yield per 

recruit due to concomitant changes in fishing effort and age-of-first-capture 

(Fig. 17b). This latter approach has also given rise to the concept of 

eumetric fishing, whereby a nearly constant total population size can be 

maintained, and possible density-dependent effects on growth, mortality, and 

1) Given that the fishery operates at a certain level of fishing 
-74- 

YIELD-PER-RECRUIT THEORY 

Numbers \\\ I \ Growth clreater 

1 

I 

I 

iomass per! 

Time-size 

Figure 16.--Changes in biomass, number, and average weight of animals in an 

unfished cohort-during its lifetime. 

1. 

2. 

3. Yield-per-recruit strategy: set the size limit as close as 

Animals increase in weight and decrease in numbers with time. 

At some point in the life span, biomass peaks. 

possible to the size of peak biomass (critical size). 
-75- 

soplelh 

A cumelrit curve 

forFv r/R 

B : eumelric curve 

for lp v Y / F 

Fiqure 17.--?ie3~! per recruit (Fig. 17a) shown as a function of fishing 

mortality F and of' agc-at-first--ca~ture tp fCJr -3 fixed F. 

I'irjuce 17b is a two-dimensions: isopleth relat.iiicj yield per 

recruit to age (tu' ) and fishing mortality (from Banliister 1977) 
-76- 

reproduction minimized by selecting the age-at-first-capture level which 

maximizes yield per recruit for each level of fishing effort (Fig. 17b). 

Three analytical methods have been developed for implementing the 

yield per recruit model. The first method, developed by Baranov (1918), 

assumes that: the average growth rate in length is constant for all fish which 

are of exploitable size, weight is proportional to the cube of length, and 

recruitment is spread uniformly throughout the recruiting year. Because of 

these assumptions, a very simple mathematical model can be used to examine 

changes in yield per recruit due to changes in fishing effort and length at 

recruitment. Although Baranov's method is sound, its usefulness is 1 imited 

since most fish stocks violate one or more of its assumptions. The second 

method, developed by Beverton and Holt (1957), is similar to Baranov's method 

except that the von Bertalanffy (1938) growth function is used in place of the 

assumption of a constant growth rate in length. 

by Ricker (1975), is the most flexible in that it allows growth and mortality 

rates to change over the exploitable life span of the fish. Although Ricker's 

method is computationally more difficult to use than Beverton and Holt's 

method, it is commonly used when mortality rates are age-specific, or when 

growth is not representable by the smooth asymptotic growth functions. 

The third method, developed 

Some of the difficulties encountered by fishery managers in applying 

the yield per recruit concept are: 

1) Because of the large variability in recruitment, it is often 

convenient to recommend maximizing yield per recruit for each entering year 

class, ignoring the factors that control year class strength. Unfortunately, 

fishing effort levels which maximize yield per recruit can substantially 

reduce spawning stock size and may adversely affect future recruitment. 

fishery where several gear types exploit different size ranges. 

2) It is difficult to achieve maximum yield per recruit level in a 

3) It is difficult to obtain projected increases in yield per recruit 

in a fishery where discarding occurs. 

4) If recruitment is not constant, optimal management strategies based 

on yield per recruit can differ substantially from strategies based on 

assessments of the maximum sustainable yield. 

2.3.3. Virtual Population AnalysislCohort Analysis 

Virtual population analysis, or cohort analysis, is a technique used 

to calculate past fishing mortality rates and abundance of year classes 

(cohorts) at successive ages. When the analysis is applied to all year 

classes of a particular stock of fish, the result is an estimate of fishing 

mortality and stock size at all ages in each calendar year represented in the 

data base. 

total stock size for that year. The fishing mortality estimates by age group 

in each year show the mortality pattern and also enable the calculation of an 

average mortality rate for the stock for each year. 

The stock sizes by age in each year can then be summed to give the 
-77- 

This analysis is a sophisticated method of stock assessment, requiring 

a comprehensive statistical collection program to provide a lengthy time 

series of total catch/landing data and annual samples of length-age 

composition of the stock, as well as an estimated or assumed natural mortality 

rate for each age, and an estimated or assumed fishing mortality rate for at 

least one age for each year class. However, where virtual population analysis 

is applicable, i.e., where good aging is possible, the level and quality of 

scientific advice that can be provided is among the most accurate available. 

Current population sizes can be estimated from the correlation of 

historical time series of abundance at recruitment size. Fishing mortality 

can be estimated by VPA with indices of abundance, recruitment, or fishing 

effort, using projected index values derived from fishery statistics or 

resource surveys. 

2.3.4. Spawner-Recrui t Model 

The spawner-recrui t (stock-recrui tment) model describes the 

relationship between the number of spawners in a stock and the number of 

recruits produced (Fig. 18). The model has rather limited application on a 

year-to-year basis because the relationship of recruitment to parental stock 

is obscured by environmentally-induced fluctuations and the high fecundity of 

most marine species. Successful reproduction, and subsequent recruitment, may 

rest largely on favorable environmental conditions and, in the short term, may 

actually have little relationship to the size of the parental stock. 

The model has been useful, however, in assessing the stocks of Pacific 

salmon which spawn once and die. The model is relatively effective in this 

case because: 1) recruitment depends to a substantial degree on the size of 

the parental stock, 2) recruitment to the fishery occurs mostly just prior to 

spawning, and 3) the factors which tend to limit the size of the stock operate 

principally in the freshwater spawning and nursery areas, and not in the ocean 

feeding grounds. 

The data required by the model, escapement (number of spawners) and 

subsequent catch, are relatively easy to obtain compared to most fishery data. 

Direct counts of spawners are made in many streams, and catch statistics 

provide an estimate of recruitment when added to the escapement. 

is a curve relating the number of recruits which can be expected from a given 

number of spawners when a long time series of data is available. 

The result 

2.3.5. Models for Use with Marking Experiments 

A whole class of models has been derived to take advantage of 

information obtained from tagging experiments. Among the parameters which can 

be estimated from these data are survival rates, population sizes, recruitment 

estimates, and estimates of movement or migration. 

Typically, a large number of fish are randomly selected from the 

population, marked or tagged in some manner, and reintroduced into the 

population. The fish are recovered subsequently by either research fishing 
-78- 

SPAWNERS 

Figure 18. --Examp1 of a generalized stock-recruitment curve of the type -& R=aPe , where R is the number of recruits, P is the size of 

parental. stock or spawners, and a andB are constants. 
-791 

efforts or by a commercial or recreational fishery. In a simple situation, 

individuals are tagged on only one occasion and recaptures made over an 

extended period of time. 

occasions and recaptures made at subsequent sampling periods. 

More generally, tags are placed on a number of 

Problems which can affect estimates of population parameters made from 

tagging data include: mortality due to the tag, different animal behavior 

induced by the tag, and incomplete reporting of recovered tagged fish due 

either to their being nonrecognizable or by deliberate intent. Often if these 

situations are suspected, the tagging procedure itself can be modified to take 

them into consideration. 

Extensive use has been made of tagging studies in the crab populations 

of the Bering Sea and in sablefish populations throughout the northern 

Pacific. 

2.3.6. Change in Ratio Models 

marked-to-unmarked ratios to estimate population abundance and survival. 

models are particularly effective where a differential harvest occurs, such as 

the male-only seal harvest on the Pribilof Islands. 

Fishery managers have made use of changes in observed sex ratios or 

The 

2.3.7. Ad Hoc Models 

Analytical situations often arise which cannot be fitted into a 

''standard" model. These generally occur where the life history of the fish is 

unique or where the sampling procedures clearly violate the assumptions made 

by traditional models. In these cases, traditional models are either modified 

to the specific application or ad hoc models are created to estimate the 

population parameters. For example, a model was created specifically for the 

estimation of growth and natural mortality of king crab in the eastern Bering 

Sea, and that model will probably have little application elsewhere. 

2.3.8. Ecosystem Models 

Newer computer-based models provide multispecific and ecosystem 

approaches to stock assessment. 

fisheries context focus on the mechanisms of species interactions, both among 

themselves and with the marine environment, and their effects on the 

production of commercially harvestable fish biomass. Unlike the rigid single 

species models mentioned above, these models attempt to focus, in a functional 

manner, on the interspecific and intraspecific relationships which have the 

most significant impacts on biomass dynamics. 

Ecosystem models employed in the marine 

The most fundamental difference between single species and ecosystem 

models is that predation, and trophodynamics in general, is included in the 

latter, thus quantitatively connecting the dynamics of all species represented 

in a given ecosystem. 

stock assessment methods when the ecosystem approach is employed. One of the 

Therefore, trophodynamics forms the basis for fish 
-80- 

great shortfalls of the single species approach has been the determination of 

the a1 1-encompassing parameter "natural mortal ity," referring to deaths from 

all causes other than fishing. In its traditional form, this parameter has 

rarely been adequately estimated. However, in the ecosystem approach, 

"natural mortality" is broken down into functional components (losses due to 

predation, internal or external stress, etc.) which can be estimated more 

directly. Ecosystem models a1 so provide a potential method for understanding 

and representing the relationships between marine mammals and fish resources. 

These links can only be represented as they occur in the food chain itself. 

The basic processes which are represented in most ecosystem models 

are : 

1) Trophodynamics - representation of predation as the most important 

quantitative linkage between species in the ecosystem; 

2) Growth - parameters which vary with trophic and environmental 

effects ; 

3) Mortality - component effects such as spawning stress, predation, 

starvation, and environmental stress; 

4) Reproduction and recruitment; 

5) Migration - representation of biomass distribution over time, area, 

and depth, primarily as a function of environmental effects; 

6) Age or size structure - key to the representation of 

trophodynamics; and 

7) Effects of fishing. 

Ecosystem models require more and different data than do conventional 

single species models. If these models are to play an important role in 

fisheries assessment and management in the future, there will have to be a 

major reorientation of fisheries data collection, e.g., more emphasis on the 

estimation of trophodynamic and environmental parameters. 

Two examples of ecosystem models presently being used in fisheries 

assessment and management are a numbers-based Andersen-Ursi n model for the 

North Sea, and the Laevastu-Favorite Dynamic Numerical Marine Ecosystem Model 

(DYNUMES) , a biomass-based model devel oped at the Northwest and A1 aska 

Fisheries Center. 

While direct use of ecosystem models for management purposes lies in 

Examples include first-order estimates of abundances 

the future, output from existing models has already provided significant 

information on stocks. 

of presently unexploited species which may come under exploitation in the 

future (e.g.! squid in the Bering Sea), results which suggest that marine 

mammal and bird predation on certain species (e.g., herring in the Bering Sea) 

may exceed commerci a1 harvests, determi nations of "carryi ng capacities" of 

given regions, representations of the effects of large scale "natural 

fluctuations" on fish resource dynamics, and evidence that certain species may 

be exploited at different trophic levels with significant differences in yield. 
-81 - 

3.0. ADEQUACY OF TECHNOLOGY 

Two major issues are involved in discussing the adequacy of assessments. 

From the perspective of the manager, adequacy is judged by whether or not the 

assessments meet the needs expressed by management objectives. For example, 

information on growth, mortality, and size selectivity may be sufficient to 

assess the effects of using different mesh sizes in trawls on yield per 

recruit, but estimates of recruitment and population magnitude may not be 

sufficient to estimate the effect of setting a quota on catch. Sufficiency is 

judged by the risk that managers are willing to take with respect to achieving 

the goals of the management plan. 

From this perspective, the scientist can advise on the adequacy of 

assessments only in the context of expressed needs of management. 

scientist can, in general, relate the scale of assessment information to the 

scale of stock manipulation required to meet management objectives; thus, his 

report may deal with the adequacy of assessments for meeting a particular goal 

but not the adequacy of that goal. 

The 

This section deals with the adequacy of current assessments in the 

context of technological sufficiency. This can, in turn, be viewed from two 

different aspects. First, how well can the present populations be described 

quantitatively and qualitatively? Secondly, how well can the future state of 

stocks be predicted with and without changes in the fisheries? 

All of the methods employed have certain advantages and disadvantages in 

terms of conducting stock assessment activities. The factors influencing 

choice are largely dependent on the applicability of the method to the species 

or stocks examined, and the resources and manpower available to undertake 

stock assessment; in some instances, however, certain factors are applied in 

the absence of other reliable approaches. In this section, strengths and 

weaknesses of each approach previously described will be discussed, and 

adequacy of the technology for resource assessment will be commented on 

bri ef 1 y . 

3.1. Fishery and Marine Mammal Statistics 

earlier, have been traditionally utilized in stock assessment; statistical 

data can be collected relatively cheaply and made available to the sci'entists 

for assessment. The data, if collected in a reasonably reliable fashion, can 

be applied to a number of standard fisheries models which provide a 

theoretical framework for understanding the functioning of a fish and marine 

mammal stock under exploitation. 

Fisheries statistics (including marine mammal statistics), as noted 

A tally of the season's total catch is the primary statistic required 

for fishery,analysis. The adequacy of this statistic depends on the nature 

and extent of the fishery. 

incomplete reporting, at sea-discard, etc. For many fisheries which operate 

from a number of ports and use various types of gear, catch records should 

Many circumstances can reduce its accuracy, e.g., 
-82- 

preferably be recorded by vessel landings so that catch statistics can be 

subtotal 1 ed and analyzed for any fishery component. 

For fisheries regulated by a quota, the collection of catch statistics to 

monitor the accumulative catch imposes the constraint of real time data 

compilation. In most fishery cases, compilation of catch statistics is too 

slow for real time stock assessment analyses. 

bottleneck in updating stock assessments in a timely manner for resource 

managers or advisory groups. 

This tends to create a 

Stock assessment using fishery statistics also suffers because, in many 

instances, the data are collected for purposes other than analyzing the 

conditions of fish stocks, e.g., tax purposes. In addition, for many stocks, 

the data collected are incomplete, vary among states, and provide little 

information on the origin of catch and the amount of effort deployed for its 

retrieval. 

The quality-of-effort data depends on the specification of the unit of 

measurement. For stock assessment purposes, effort must be proportional to 

fishing mortality. For a newly developing fishery, it is the biologists' 

responsibility to specify the requirement. 

sacrificed for simplicity so that fishermen are willing to provide needed 

data. In the case of developed fisheries for which effort statistics have not 

been rigorously collected, scientist have often had to assemble an effort-time 

series from the available data. 

des i red. 

In this case, idealism must be 

Often the specified unit is less than 

The fishery assessment models, other than the surplus production model, 

use estimates of growth and mortality rates and the age composition of the 

catch. This requires a catch sampling program with sound statistical design 

and sufficient sample size. 

the catch sampling program must be ongoing. 

estimates is dependent on the ability to correctly age the fish sampled. In 

all instances, aging techniques are tedious and not 100% accurate. 

For a dynamic population and/or changing fishery, 

The adequacy of parameter 

Tagging studies in marine fisheries often rely on the commercial/ 

recreational fisheries to catch fish for tagging and to recapture tagged fish. 

These studies on fish or marine mammals require considerable planning and 

experimental design. The primary assumption is that behavior of tagged 

animals is unchanged by the tag and tagging operation. The adequacy of 

tagging studies depends on cooperation of the fishery in returning tags and 

associated information, experimental design of the study and 

representativeness of the tagged individuals in the population. Tagging studies without too many problems can give insight to stock structure and 

migrations. 

abundance are less reliable because of the differential behavior and mortality 

of the tagged segment of the stock. 

designed to provide timely estimates because the analysis of the data cannot 

be completed until tagged individuals are recaptured. 

On the other hand, estimates or rates of exploitation and 

In general, tagging studies are not 
-83- 

3.2. Fishery-Independent Resource Surveys 

3.2.1. Fishing Surveys 

3.2.1.1. Trawl Surveys 

The strength of trawl surveys stems from the long-term standardization 

of data collected, as well as the kinds of data collected. 

used to obtain current estimates of parameters of stock condition (abundance, 

fishing mortality, and age composition) that could not readily be obtained 

from commercial fisheries sources for many species. Estimates of stock 

condition can be available a few months after the completion of a survey, 

allowing timely decisions and early action by management. 

Survey data may be 

The annual abundance indices from survey series can be of utmost 

importance in examining past trends in order to estimate current stock 

abundance. There are many examples in which survey abundance indices reliably 

reflect abundance changes. 

demonstrated for species which have adequate commercial data available for 

comparison. For a few species, such as eastern Bering Sea king crab and 

ye1 1 owf i n sol e, surveys have provided a close approximat ion of expl oi tab1 e 

population or biomass size. For many of the important species in demersal 

animal communities, survey abundance indices provide a current reference of 

stock condition for the management specialist. 

composition for important demersal stocks can also be obtained from surveys. 

For some species, this estimate may be the only one available because data 

collected from the fisheries may not be reliable. 

An important strength of surveys is that biological information 

(growth rate, age, size, 'sex, maturity, fecundity, tissue samples for genetic 

studies, food habits, population density distribution) can be obtained from a 

great number of species within their main geographical distribution. Thus, 

the surveys can give insight into the dynamics of populations, stock 

structure, reproductive potential, trophic interactions, etc., that could not 

be obtained otherwise. 

The validity of these indices has been 

Current estimates of age 

Currently, three types of forecasts are feasible, based on survey and 

There is accumulating evidence that surveys are providing a 

fisheries information: recruitment strength; population abundance from 

estimates of recruitment; and catch levels, given estimates of fishing 

mortality. 

reliable index to recruitment or year-class strength for many species. Where 

there is an adequate time series on abundance by age from both the survey and 

the fisheries, a relationship between survey pre-recruit abundance indices and 

the strength of the corresponding year-classes in the fisheries has often been 

observed. Such examples have been found with eastern Bering Sea pollock and 

king crab, and for certain finfish species off the Atlantic seaboard. 

Surveys also provide reliable and relevant data for use in traditional 

fishery dynamic models and the formulation of new conceptual and analytical 

frameworks of fishery production. 

and synoptic nature of the surveys in identifying and measuring major scales 

of temporal and spatial variability in populations and their environment, and 

in revealing trophic interactions which occur within the intervening 

popul at i ons. 

This is made possible because of the design 
-84- 

Surveys provide a long-term documentation of physical conditions 

(water mass characteristics, temperatures, and sal inity) associated with 

resource di stri but i on , dens! ty , recruitment , and growth, as we1 1 as other 

descriptors of populations and population interactions. Such documentation 

has not been available from the fisheries. 

On the negative side, surveys are very costly and provide somewhat 

imprecise estimates of relative abundance. 

single surveys of northwest Atlantic fish stocks have exhibited a 95% 

confidence interval of plus or minus 50%. Similarly, low levels of precision 

have been found for estimates of abundance of fish stocks from resource 

surveys conducted in the northeast Pacific and eastern Bering Sea. 

Indices of relative abundance from 

A limitation of multispecies trawl surveys is that they have been 

developed for many species and therefore are not as optimal for many 

individual species as a single-species survey would be. This can be readily 

appreciated by examining the differences between species in terms of optimal 

allocation schemes to increase precision (Table 4). 

A serious drawback to the analysis of survey data is the difficulty in 

determining the underlying probability distribution function for trawl survey 

catch data. We have only a general knowledge about the distributional 

features of populations and are almost totally uninformed on how these 

features change relative to environment. We also know very little about an 

animal ' s response to sampl i ng gear, because response depends upon si ze/age, 

physiological state, temperature, 1 ight, etc. 

The performance of the sampling trawl itself may vary in relation to 

depth, topography of the sea bottom, surface and subsurface currents, and the 

interaction of these with the speed of the vessel. 

were kept constant, change in the behavior of the animals would still present 

various probabilities. 

Even if all gear factors 

3.2.1.2. Longline and Trap Surveys 

Longline and trap surveys use passive gears, r e q u i r i n g t h e cooperation 

of the fish for capture. The cooperation, or catchability, varies by species, 

size within species, area, season, time of day, type of gear, and other 

factors. All of these factors introduce biases of varying and unknown degrees 

into the surveys. Overall, the best results obtainable with these gears 

include statements of the presence, but not the absence, of certain species, 

and crude estimates of relative abundance. 

techniques, however, such as mark and recapture, they will provide useful 

assessment information. In general, traps appear to collect a wider variety 

of the animal life of a particular area, while bottom longlines, by virtue of 

hook and bait size, tend to collect the larger fish. 

When combined with other survey 

The primary advantage of bottom longline and trap surveys is that they 

provide a means to sample areas which could not otherwise be surveyed. Their 

primary disadvantage is the unknown selectivity and the resulting inability to 

use results directly for stock assessment. 

the same disadvantage, as well as requiring significantly more gear in a set, 

thereby increasing costs. 

Pelagic long1 ine surveys suffer 
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Longline and trap surveys have many inherent problems but represent 

the only avail able fishery-independent survey technique for acquiring 

information on certain fish stocks. Significant increases in survey coverage 

with these techniques would greatly enhance the value of the results and, in 

turn, would probably provide needed information with which to evaluate their 

effectiveness. A major advantage of these forms of surveys, much like trawl 

surveys, is that biological information (e.g.? growth rate, age, size, sex, 

maturity, fecundity, tissue samples for genetic studies, food habits, and 

population distribution) can be obtained from a great number of species within 

their area of primary geographical distribution. 

insight into dynamics of populations, stock structure, reproductive potential, 

trophic interactions, etc., which could not be obtained otherwise independent 

of the fisheries. 

Thus, the surveys can give 

3.2.2. Visual Counts 

3.2.2.1. Aerial Surveys 

The general approach of aerial surveys for stock assessment appears to 

be useful and, in some cases, is perhaps the only possible approach. In the 

case of the porpoise populations off Mexico and Central America, for example, 

ship-based surveys and mark-recapture studies have not been adequate. 

method has the advantage of being relatively fast to execute in the field and 

can be applied to large areas easily. 

mammals, there is little or no response by the animals to the airplane prior 

to first fly-over; if movement occurs, it is moderate and occasional. The 

success of aerial surveys for population assessment depends heavily on the 

experimental design and on the assumptions that all of the animals are seen on 

the trackline or in a given path. In addition, the line transect methods rely 

on precision in measurements of the distances to the sighted objects. 

The 

As opposed to ship surveys of marine 

The strength of aerial surveys by commercial fish-spotters lies in the 

re1 at i ve i nexpense of col 1 ect i ng abundance i nformat i on on 1 oca1 pel agic f i sh 

stocks because aerial fish-spotters are commonly utilized by the fleet. 

pilot logbook system may generate a superior data base for stock assessment 

compared to the usual vessel catch and effort data. Based on results from the 

southern California example, this index of apparent abundance, calculated from 

simple annual summaries, appears to be responsive to population fluctuations 

when compared to other measures of abundance. 

assessment method is only feasible for epipelagic resources which spend a 

considerable portion of their time near the surface and are commercially 

fished with the aid of spotter aircraft. 

A 

Implementation of this 

One weakness of the-method is that quality of the data is the 

responsibility of the contracted pilots. Differences in the pilots' searching 

abilities and school size estimates must be considered in the final analysis. 

The unit of measurement for effort is not precise and, therefore, adds 

variance to the estimate. For more sophisticated analysis of variance 

procedure, annual values of the time series will change each time a new data 

year is added. 

measure of abundance cannot be directly calculated from the index. 

In this case, since the index is dimensionless, an absolute 
-87- 

As with a1 1 f i shery-dependent surveys, aeri a1 surveys by commerci a1 f i sh 

spotters suffer from the fact that the sample obtained is not random. 

is directed toward those areas where communication and/or intuition have 

indicated that fish will be. 

standardization of the search effort are important but lack generality between 

surveys. Fishery-independent aerial surveys can solve some of these problems 

only through increased cost. 

comparable ship surveys, and the assumptions of analysis are more closely met 

with aircraft. Therefore, fishery-independent aerial surveys should take 

their proper place along with other survey methods for stock assessment 

anal ysi s. 

Search 

Therefore, the assumptions made to effect 

However, the cost per survey area is less than 

The problems with aeri a1 surveys (both f i shery-dependent and 

-independent) are obvious: they are limited to oceanic areas relatively close 

to land or landing areas, and they survey only the surface layer of the ocean. 

In addition, the probability of mechanical or human failures increases with 

extended flight times and flight frequency, and safety becomes a 

consideration. 

Another problem with aerial surveys is the inability to identify 

adequately the species or stock encountered and to obtain high precision, lowbias estimates of aggregation size. These abilities can be improved by 

comparing aerial sightings with shipboard sampling efforts, but the cost of 

doing so is great. Other more technical methods have included photography 

which, under the right conditions, has proved to be useful. 

3.2.2.2. Land-based Counts 

The apparent advantage of counting methods for marine mammals and 

turtles is the high degree of precision which is achieved. The precision is 

mi sl ead i ng , however , because the number of animal s ( sea 1 i ons, whal es , porpoise or turtles) which may be seen at any given time depends not only on 

season but also on the time of day, weather, and other factors which remain 

unknown. The bias of the counts may be reduced by proper stratification of 

the sampling effort, but at an increased cost. For example, there may be a 

period during the day in which the number of animals at a sea lion rookery is 

at a maximum. If an aircraft has to fly one hour each way to view the rookery 

for a short optimal period, then the cost per sample is large. Further study 

is needed to estimate the missing proportion of the population: the sea lions 

not at the rookery, the cetaceans or turtles beneath the visible surface 

layer, and the turtles not crawling up onto nesting beaches. Until that time, 

the counts can be considered only minimum estimates and, thus, indices of 

abundance. 

can be very productive. 

The use of counts in conjunction with other techniques, however, 

Future problem areas in which counting methodology might be useful ly 

applied include assessing the impact of outer continental shelf oil 

development projects and evaluating the interactions of marine mammal 

populations with fisheries. 

in abundance are necessary to assess the status of marine mammal stocks 

relative to contemplated or ongoing management decisions. 

In either case, population estimates and trends 
-88- 

3.2.2.3. Underwater Counts 

Underwater visual forms of assessment can provide reasonably precise 

and accurate estimates of relative abundance. 

however, and have spatial and temporal limitations. Man-in-the-sea approaches 

have the added need for skilled and experienced observers, and the 

disadvantage of risk to human life. 

They are expensive to conduct, 

3.2.3. Fish Egg and Larva Surveys 

Egg and larva surveys for stock assessment have a number of 

advantages. The sampling gear, excluding the platform, is relatively 

inexpensive, and standard frames, nets, and various flow meters are readily 

available. The survey can be conducted from any seaworthy vessel without 

major installations of equipment. 

quantitative tows can be taken within the accepted tow guidelines. The 

technique can be applied to a wide variety of marine fish species because most 

marine species have pelagic eggs and/or larvae. Simultaneous oceanographic 

measures of physical and chemical environment of the epipelagic zone can 

easily be added to the survey. Plankton samples contain not only fish eggs 

and larvae of a variety of species, but also information on phytoplankton and 

other zooplankton. 

information can be gained on spawning seasons, distribution of the adult 

population, and possible stock boundaries. 

With relatively 1 ittle training, standard 

In addition to the indices of abundance, considerable 

The method also has weaknesses. Species identification of eggs and 

larvae is limited, although great strides have been made in recent years for 

species of the California Current and in waters off the mid-Atlantic states. 

The survey technique requires a major commitment of vessel sea time, 

particularly if a time series of the index of abundance is established. It 

requires a large staff of marine technicians, plankton sorters, fish 

identifiers, data managers, and research personnel to collect, process, and 

analyze the samples. The analysis of the data can follow acceptable 

statistical procedures, but a number of statistical problems still exist in 

compi 1 i ng and i n t e r p r e t i n g t h e compl ex distributions of sampl e egg and 1 arva 

data. The potential dynamics of stock fecundity rate could add variation in 

the index values that would otherwise be interpreted as fluctuation in stock 

abundance. This topic needs further study. 

3.2.4. Remote Sensing 

3.2.4.1. Acoustical Surveys 

The principal advantages of quantitative echo sounder surveys include: 

1) the possibility of obtaining information on abundance of many pelagic, 

semi-pelagic, and semi-demersal fish stocks for which there are no practical 

alternative assessment methods, as well as providing information needed for 

evaluation of other methods, e.g., bottom trawl surveys for semi-pelagic and 

semi-demersal stocks; 2) distinctly greater sampl ing volume (most of the 
-89- 

water column) and sampling rate than other methods; 3) 

a large quantity of information on distribution, behavior, and potential 

vulnerabiity of many fish stocks, that is not attainable by other means; 4) 

lower data collection costs than other methods in some cases, due to rapid 

geographic coverage, quantity of data collected per unit time, and potential 

for basic data processing to be done in real- time; 5) a theory of basic 

quantification technique, i .e., echo integration, which is well developed 

(Swingler and Hampton 1979); 6) the estimation of scale factors required to 

estimate absolute density (via target strength measurement and re1 ated 

studies), usually a more tractable problem than that encountered when 

estimating similar factors (catchabil ity and other conversion coefficients) 

required for alternative survey methods; and 7) the ability to monitor 

calibration of sampl ing equipment continuously. 

the ability to provide 

Another advantage is the ability of the physical scientist to analyze 

theoretically the performance of hydroacoustical signal processing techniques. 

This advantage has to be qualified, however, because it has too often focused 

an undue amount of attention on the ''worst case" limitations of the method. A 

realistic evaluation of the method's usefulness can only be done after a fish 

stock has been specified, and the desired types of information (distribution, 

re1 at i ve abundance, absol ute abundance, etc. ) and t hei r qual i ty def i ned . The 

advantages and disadvantages of the total survey process, therefore, must be 

considered. 

The main limitations of quantitative echo sounder surveys are: 1) the inability to detect targets on the seabed and at the surface, and sampling 

volume 1 imi tations in near surface waters (or near transducer) ; 2) 

inability to identify targets directly, because identification is dependent on 

experienced personnel and/or direct capture techniques, the latter being 

essential when collection of biological data is required; 3) the requirement 

for more highly trained equipment operators and technical support personnel 

than most other survey methods; 4) the echo integration technique which is 

not applicable to species which frequently occur in densities high enough to 

cause multiple scattering, shading, etc., e.g., northern anchovy; however, 

echo sounder surveys of such species provide useful information on 

distribution, behavior, and relative abundance; 5) the determination of scale 

factors required to convert echo integrator outputs to estimates of absolute 

density, a difficult and complex task; 6) 

that for most other survey methods; however, as shown by its widespread use by 

other nations, this is infrequently significant compared to the cost of 

research vessel time and the lack ofalternative methods; and 7) poorly 

understood capabililties and limitations of the method, and a theory that is 

questioned. 

In any type of survey, knowledge of the stock's distributionavailability pattern is critical to the reliability of abundance estimates 

derived by averaging and extrapolating the basic survey data. Its importance, 

however, tends to be overlooked when hydroacoustical methods are evaluated. 

Improvements in the precision and accuracy of the abundance estimates can do 

nothing to correct for uncertainties in the distribution-availability pattern. 

This has significant implications with respect to deciding which types of 

investigations should be pursued to improve the survey process. Although 

improvements in the precision and accuracy of estimates of echo integrator 

the 

higher initial equipment cost than 
-90- 

output scale factors are important to increasing the r e l i a b i l i t y o f absolute 

abundance estimates, it often is equally important to better define the 

spatial and temporal distribution of the stocks which are the subject of 

hydroacoustic surveys. 

gear, but either an increase in the intensity of survey efforts, a change in 

survey designs, or the development of experimental surveys designed 

specifically to provide answers to the distribution question are required. 

For stock assessment, sonar mapping provides two indices: estimated 

number of fish schools and estimated surface area of schools. The quality of 

these estimates is determined by the subjectivity of species identification 

and the measurement of effective range interval. Biomass estimates are based 

on the total surface area of schools, depending on school volume estimates and 

fish-packing densities. 

schools have a consistent geometric shape, such as a cylinder. Squire (1978) 

showed that the assumption of a circular school overestimates the surface area 

by 72%. Because of the large variation in the few estimates of fish-packing 

densities, there is no reliable value that can be assumed for any particular 

survey. Although it is interesting to assume various values of fish-packing 

densities, there is no criterion for judging the best biomass estimate from 

the wide range of possible values. On the other hand, if great care has been 

taken each year to schedule the survey each year to coincide with prime 

conditions and the time when the target species is by far the dominant 

schooling fish, the estimate of the total surface area of schooled fish should 

then provide a good index of abundance of the target species in the upper 

mixed layer. 

This can be done with existing survey equipment and 

Volume estimates depend on the assumption that 

Sonar mapping is a relatively quick and comparatively inexpensive 

survey method. 

presented soon after the end of the survey. 

to be an effective survey method for only a short seasonal period. 

Survey results are relatively simple to compile and can be 

Sonar mapping, however, is likely 

3.2.4.2. Other Remote Sensing Methods 

Other remote sensing methods involving photography and TV images (both 

aerial and underwater) for primary means of detection are not used extensively 

in NMFS stock assessment programs. 

oceanographic parameters in stock assessment analysis is becoming the topic of 

a number of research efforts within NMFS, but they are not in general use yet 

in routine stock assessment efforts. For purposes of this report, brief 

comments on adequacy of these methods are included in the respective 

description section 2.2.4.2. 

strip transects given in section 2.2.2.1 also applies to photographic and TV 

image surveys. 

The inclusion of remote measures of 

Much of the adequacy discussion of line and 

3.2.5. Environmental Indices 

The use of environmental indices in stock assessment has proceeded in 

two directions. First, the incorporation of environmental covariates into 

classical fishery management models has, in a number of instances, been 

successful in reducing the variance about fit of the models. 

has been directed toward understanding causal mechanisms by which 

Second, research 
-91- 

environmental conditions affect the survival of fish in marine populations. 

Particular emphasis has been placed on early life stages where recruitment 

levels are determined. These studies have only been possible for those stocks 

having available an accumulated information base on stock structure, 

recruitment, and/or detailed catch statistics. In general, necessary 

environmental data time series are only available for a few of the more common 

parameters. In most cases, these data must be synthesized by the appropriate 

time/area scale, which can be expensive and time-consuming. Furthermore, the 

key environmental variables will probably not be those that are routinely 

monitored, such as surface ocean temperatures, wind, etc. Because the 

interaction between population dynamics and the environment is complex, it is 

quite likely that one or a set of environmental indices will be found only for 

the critical or more understood species for which stock assessment can be 

improved. 

implemented into routine stock assessment analyses to generate timely 

information for fishery managers. If such models prove valid with continued 

monitoring of the stocks and environment, it is only a matter of time before 

fishery managers wi 11 use environmental information to forecast recruitment, 

stock levels, and exploitation rates. 

Few, if any, of these research studies to date have been 

3.3. Fisheries Analysis for Stock Assessment 

Models used for stock assessment attempt to represent, with a series of 

equations, the biology of the fisheries on a particular stock. 

is necessary to make a number of simplifying assumptions. 

stock increases, and as the time series of fisheries data becomes longer, the 

degree of complexity of the model can be increased and the number of 

assumptions reduced. This evolution through a series of increasingly complex 

models is common. 

production model are as follows: 

To do this, it 

As knowledge of the 

For example, the major assumptions associated with the 

1) The fishery can reach an equilibrium; i.e., stock structure will 

adjust to, and stabilize at a given constant level of fishing effort. 

2) Environmental factors are constant or average out over the long term. 

3) The fishery is operating on a "unit stock," i.e., a stock capable of 

independent exploitation or management and containing as much of an 

inter-breeding unit, or as few reproductively isolated units, as 

possible. 

4) One unit of fishing effort produces the same relative effect on the 

stock; that is, it catches the same percentage of the stock, 

regardless of the time or place it is applied, or of the size of the 

stock. 

5) The rate of natural increase of stock responds immediately to changes 

in population density; i.e., the time lag between spawning and 

recruitment of progeny to the catchable stock is ignored. 

6) The rate of natural increase at a given weight of population is 

independent of the age composition of the population. 
-92- 

As more data become available and biological know1 edge accumulates, a 

yield-per-recruit model may be formulated to account specifically for, or 

relax a number of, the above assumptions, including at least numbers 4, 5 and 

6. 

interpreted with caution. When inadequate data are used, the results are 

usual ly 1 ittle more than pro forma and should be clearly recognized as such. 

The major benefit of standard fisheries models is to provide a theoretical 

framework for understanding the functioning of a fish stock under exploitation 

and for estimating stock parameters. In addition, the application of the 

model itself will often point out data deficiencies and, consequently, will 

direct future data acquisition. 

Thus, even when sufficient data are available, the results must be 

The question of adequacy, then, is not just one of adequacy of the models 

but also adequacy of the data base and of the criteria for choosing the proper 

model. It must be decided whether a single-species representation will 

suffice for management or if a multispecies ecosystem model is required, 

before meaningful management advice for a specific fishery can be offered. If 

the latter, a data base is needed upon which estimates of the parameters of 

multispecies holistic ecosystem-type approaches can be based. It is in this 

area that fisheries analysis is lacking. 

3.4. Geographic Coverage 

Information on the stocks of fishes and marine mammals for which NMFS 

Research Centers are currently undertaking stock assessment studies is given 

in Table 5. 

importance of the technique, frequency of assessment, character of the survey, 

and cooperative nature of assessment, if relevant. 

For each assessment activity, information is provided on the 

One hundred and fifty different stocks are currently being assessed by 

the NMFS Research Centers. In general, these are the stocks that have been 

identified in fisheries management plans. 

based on the best scientific information available, is adequate only in the 

context of the pro forma requirements of the act. This is the case for many 

minor fisheries and for many stocks that occur as by-catches in targeted 

fisheries. 

Table 5 does not necessarily imply that it is "adequate." 

In many cases the assessment, while 

Consequently, the fact that a method is listed as ''primary" in 

For most stocks, the primary technique of stock assessment is analysis of 

fisheries statistics. 

production statistics. However, in all assessments, fisheries statistics 

provide basic information and data essential to more sophisticated analysis. 

The latter are possible when statistical data on effort, size, age, and growth 

characteristics are available. 

In many cases, these are limited to catch and 

Stock assessments are frequently augmented by survey data collected by 

Table 5 indicates that trawl surveys of adults are the most 

Trawl surveys have a long history of 

research vessels independent of the biases inherent in data from the fisheries 

themselves. 

frequently employed survey technique. 

use and provide samples from mixed fish populations that can be used to 

extract species, size, and age data needed for further analysis. 

also provide data on enviromental parameters, associations, and feeding that 

are needed for ecological studies. 

Such surveys 
-93- 

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- 100- 

Table 5.--cont. 

SOURCE OF DATA 

CODES 

Data Usage 

0 Used but not adequate method 

1 Primary method 

2 Secondary method 

3 Developmental stages only 

Frequency 

D 

M 

Bi 

N 

Q 

S 

Tr 

A 

B 

T 

Ad hoc - special purpose 

Monthly 

Bi-monthly 

Monthly in season 

Quarterly 

Semi-annual 

Tri-annual 

Annual 

Biennial 

Triennial 

Survey Type 

b biomass index 

i relative abundance 

q qualitative index 

t total counts 

Cooperative Source 

Fo Foreign cooperative research 
-101- 

Acoustical remote sensing techniques have been the subject of 

considerable research in recent years, and their application has become the 

preferred method for surveying schooling pelagic fish (anchovy, capelin, 

herring, etc.) and semi-demersal fish (Pacific whiting, pollock, etc.). Egg 

and larval surveys provide comprehensive assessment data but have most 

frequently been applied to pelagic fish. 

Finally, it should be noted that Table 5 does not list certain important 

stocks. In general, these include the complex array of near-shore or shoal 

water species exploited principally by marine recreational fishermen, and a 

number of species which occur primarily as by-catch in commercial fisheries. 

3.5. Financial, Personnel, and Vessel Resources 

A breakdown of the funds and positions expended for research at NMFS 

Centers and Regions during Fiscal Year 1979 is given in Table 6. Of the 

national total made available for research (approximately $41.5 million), 59% 

was made available for stock assessment activities, and another 9% was 

a1 located to the development of stock assessment theory and/or survey 

technology. Management costs were not included as research. 

the line item title serves as an accurate descriptor of the research activity 

category. Besides "Stock Assessment" and "Stock Assessment Theory 

Development," the 1 ine items "Fisheries Oceanography," "Survey Technology 

Devel opment , 'I "F i s her i es Ha b i tat I nvest i gat i ons , I' 'I I ncreas i ng Use of 

Resources," "Aquaculture," and "Fisheries Products Qual ity and Safety" are 

used as research activities categories in this analysis. 

includes most of the activities in the "Resource Surveys'' and "Data Analysis" 

line items of MARMAP, collection of Commercial and Recreational Fisheries 

Statistics, collection of biological information through the Foreign Vessel 

Observer Program, and studies of Recreational Fish, Marine Mammals, Endangered 

Species, and Anadromous Fish. 

Development" is derived from activities, included in "Data Analysis" line 

items, which devote significant effort to improving our understanding of 

fish/fish-multispecies; ecosystem modeling would be included in the category. 

budgetary line items from which this information is derived (i.e., from 

current year task plans). 

Figure 19 represent general comparisons. For example, some of the habitat 

investigation work (especially in the northwest) could well be assigned to 

"Stock Assessment" or "Stock Assessment Theory Devel opmentll categories. 

large majority of funds available for research has, in recent years, been 

spent on stock assessment activities, although a growing proportion of 

research in some regions is channeled to undertake a variety of fisheries 

habitat investigations. Of the 788 fulltime permanent ceilings available for 

research, 54% were allocated to traditional stock assessment activities and 

another 10% to undertake the development of stock assessment theory and/or 

survey technology. Although the remaining research categories are itemized 

separately, they are not in all instances mutually exclusive from stock 

assessment activities. Areas of research, such as fishery oceanography and 

fishery habitat investigations, contribute significantly to the evolution of 

stock assessment theory and/or the development of life history information 

In many cases, 

"Stock Assessment" 

The category of "Stock Assessment Theory 

There is some artificiality in the assignment of field studies to 

Therefore, the numbers given in Table 6 and 

A 
-102- 

Table 6.--Breakdown of approximate funds and positions devoted to 

research at NMFS Centers and Regions.l/ 

of total spent on research.) 

Percentages are 

Types of research SK # Pos. 

(%I (%I 

Stock 

assessment 

24,308.1 425 

(59%) (54%) 

Stock assessment 2,980.1 54 

theory development (7%) (7%) 

Survey technology 

development 

Fisheries habitat 

investigations 

Increasing use of 

re sources 

Aquaculture 

Fisheries 

oceanography 

921.5 23 

(2%) (3%) 

4,721.9 125 

(11%) (16%) 

1,542.9 45 

(4%) (6%) 

3,678.6 61 

(9%) (8%) 

1,136.1 22 

(3%) (3%) 

Fisheries products 2,067.3 33 

quality and safety (5%) (4%) 

Total research 41,356.5 788 

- 1/ Approximate figures for funding and personnel were derived 

by categorization of FY 1979 CYTPs. 
-103- 

Allocation of funds 

Figure 

Fisheries product quality - 

and safety .......... 

Fisheries oceanography ..... 

......... .......... .......... .......... .......... 

..... 

..... 

.... 

Increasing use 

Aquaculture 

of resources 

F islieries habitat 

investigations 

S u rve y tec li no I og y 

development 

Stock assessment theory - 

deve I op me n t 

Allocation of personnel 

and safety 

Fisheries OceanograPhY -’ 

Aquaclllture - 

Increasing use 

of resources 

Fisheries habitat 

investigations 

Stock assessment theow -- 

Survey technology 

development 

development 

19. --NMFS al.location of research iesvurces, FY 1979 

(Centers and regions combined) 

Traditional stock 

assessment 

Traditional 

assess men t 

stock 
-104- 

which is critical in the execution of stock assessment work. 

no single research category can stand alone, due to the large degree of 

interdependence in the progress of marine science. 

allocation of personnel and funds depends, to a degree, on the urgency of 

information requirements and the adequacy of supporting scientific studies in 

the other disciplines. 

In this sense, 

In all NMFS Centers, the 

Another major input to stock assessment is the use of surveys of various 

kinds (trawl, eggs and larvae, hydroacoustical, and environmental) conducted 

from NOAA, NMFS, and charter vessels. Approximately 95% of the 3,215 sea days 

used by NMFS in Fiscal Year 1979 was identified as contributing to stock 

assessment research. 

assessment surveys by vessel type. 

Table 7 lists the number of sea days used for stock 

Table 7.--FY 1979 sea days used for assessment surveys 

by vessel category. 

Vessel category Number of sea days 

NOAA fl eet 

NMFS program vessel 

Charter 

Foreign vessel s 

Other 

Total 

1,710 

400 

460 

400 

100 

3,070 

Fishery Centers vary greatly in the utilization of surveys as a method of 

assessment (Table 8). 

resources, research interests, and needs in each Region, all of which help 

determi ne where the current research emphasis wi 11 be. 

This is due to the inherent differences in available 

Table 8.--Sea days used for assessment surveys by NMFS 

Fisheries Centers during fiscal year 1979. 

Center Number of sea davs 

NWAFC 

NEFC 

SWFC 

SEFC 

Total 

1,254 

770 

722 

274 

m 
-105- 

3.6. Technol ogy 

The technological adequacy of the different resource assessment methods 

employed by NMFS has not been directly evaluated in this report. 

adequacy relates primarily to the accuracy of survey samples, which, for the 

most part, is largely unknown. 

available with which to computeaccurately sampling efficiencies for one of our 

primary assessment tools -- the survey trawl. 

techno1 ogy , whi 1 e not revol uti oni zi ng resource assessment, coul d aid 

significantly in establishing accuracy levels, which, in turn, would increase 

confidence in survey results. 

This 

For example, almost no information is 

Advances in appropriate 

Throughout this report, the need for fisheries-independent surveys has 

been stressed; yet, for a number of our most important fisheries, the 

technology for independent surveys is lacking. Examples include menhaden and 

other shallow water coastal pelagic species in the southeast, oceanic pelagics 

such as billfish and tunas, most reef fish species, and many crabs. 

lists many more species where fisheries-independent surveys are not, or are 

seldom, used because cost-effective survey technologies are lacking. 

Table 5 

There are many other areas in stock assessment where technological 

advancements, while not revolutionizing assessment strategies, should 

nevertheless significantly improve our understanding of fishery ecosystems. 

The remote sensing technologies, including ocean acoustics and aerospace 

remote sensing, offer many potentials, ranging from improvements in 

applications of traditional sampling techniques, to synoptic monitoring of 

estuarine and oceanic parameters affecting the distribution, movement, 

recruitment, and general well-being of fish stocks. In addition, synoptic 

information on ocean productivity, circulation, source and fate of pollutants, 

water mass patterns, and other parameters should significantly aid in 

monitoring the dynamics of marine ecosystems and, in turn, improve our ability 

to abstract and model fishery ecosystems. 

Technol ogical advancements a1 so are needed speci f ical ly to reduce the 

amount of labor needed to age fish (e.g., automatic scale readers) and to 

sort, count, and identify fish eggs and larvae. Advancements in the 

technology related to materials, hydrodynamic stabil ity, and attachment 

procedures for fish tags are also needed to improve retention characteristics 

for long-term tagging studies. Technological improvements in tracking 

technologies for fish, marine mammals, and sea turtles, such as those offered 

by satellites, would also provide a capability to monitor the movements and 

migration patterns of these animals over their entire distributional range and 

throughout a significant portion of their life cycle. 

Technol ogy a1 so could improve current methods of gathering f i shery 

statistics and, at the same time, reduce labor costs. 

simple devices placed on commercial trawls to monitor actual time fished, to 

more compl icated data logger systems aboard research vessel s to record 

automatically vessel location and activity. Satellite monitoring of fishing 

effort and distribution could also be an important contribution, using 

technology such as transponders on the vessels to provide location information 

and fishery independent methods such as synthetic aperture radar surveillance 

approaches. 

Examples range from 
-105- 

Advances in computer and communication technologies should also have 

significant benefits for stock assessment. These latter technologies should 

provide new capabilities in applications of complex multidiscipline and 

multispecies analytical and simulation approaches to resource assessment and 

management questions. 

to be the subject of additional studies proposed by NOAA and the Office of 

Techno1 ogy Assessment. 

Evaluation of such technologies is beyond the scope of this report but is 
- 107- 

4.0. COMMUNICATION OF RESULTS 

The communication process is a vital link between the scientists 

preparing stock assessments and the user groups (industry, councils, states, 

NMFS management components, other management agencies, etc.). 

not merely the dissemination of assessment results to the users but also 

includes participation by the users in planning scientific studies (e.g., 

trawl surveys) which will provide data to be used in the assessments, and in 

review of the results and implications of the assessments. 

This process is 

Communication begins in the planning phase of the assessment process. 

Currently, council, state, industry, and academic representatives meet with 

NMFS scientists from the Southwest and the Northwest and Alaska Fisheries 

Centers, to assist in the planning of resource surveys. Such user group 

participation also occurs to some extent in the Northeast and Southeast 

Fisheries Centers. This involvement is vital in establishing understanding 

and cooperation, and insuring that the assessment results will have 

credibility with the users. 

interpretation, NMFS scientists can, should, and do confer with industry and 

other user components to obtain supporting quantitative and qualitative 

information. Participation by NMFS scientists on scientific and statistical 

committees of fishery management councils, council oversight committees, 

various planning committees, etc., provides formal means for exchange of 

ideas, proposals, and results, which serve to enhance the communicative 

process. 

federal-state-council assessment workshops has been held for the purpose of 

reviewing NMFS assessments, including data bases and their limitations and 

inadequacies, areas of needed research, etc.; reviewing state research 

activities which relate to assessment data needs; and establishing and 

furthering channels of communication among scientists. 

During the process of data analysis and 

In the Northeast Fisheries Center, a series of regional 

In the Southeast Fisheries Center, which provides scientific support for 

Focusing the exchange 

three Councils, the Office of Fishery Management was established as the 

primary interface between the Councils and the Center. 

of needs and information through a primary channel, rather than having the 

three Councils deal independently with each of the Center's seven 

laboratories, has contributed to enhancing the communication process in the 

southeast. 

Adequate communication is essential for the dissemination of assessment 

results. 

in a variety of ways and in varying degrees of formality and complexity. 

Initial phases include the distribution of trawl survey results in the form of 

industry or fishermen's reports. Informal cruise reports are also issued, 

which describe the general objectives, scope of activity, and results of each 

survey. 

composition of species catches on a per tow basis. 

This should essentially be a continuous process that can go forward 

These reports include the location, magnitude, and approximate size 

Assessment results (i .e., recent harvest levels, catch-per-unit effort, 

survey abundance indices, estimates of stock size, recruitment, and fishing 

mortality and prognosis of future catch levels) for species-stocks of concern 

are presented informally to Councils, industry, etc., at which time there is 
-108- 

opportunity for user group criticism and verification. 

enhanced by the use of visual aids and non-technical vocabulary to ensure 

maximal understanding by the audience. 

Presentations may be 

Fol 1 owi ng compl eti on of a1 1 assessment analyses, a f i nal report, 

generally in the format of a laboratory reference report, technical report, or 

other internal document, is prepared and issued to the councils, states, 

industry, NMFS management components, and others. Where management may * involve an international commission, the report may be issued as a research 

document to International North Pacific Fisheries Commission, International 

Convention for Conservation of Atlantic Tuna, International Commission for 

North Atlantic Fisheries, etc. 

comprise the scientific input to fishery management plans or amendments 

thereto. 

an annual status-of-the-stocks report is issued as an internal document to 

summarize the most recent assessment for each species-stock done at that 

Center. 

managers and others. 

Final written reports at this stage generally 

In some of the Centers, particularly the Northeast Fisheries Center, 

This document has proved to be of particular interest and value to 

The assessment process may result in publication in a professional or 

otherwise refereed scientific journal ; however, this usually occurs only if 

the assessment presents new techniques or approaphes, or a previously 

unreported assessment analysis of a particular species or fishery. 

Communication of assessment results to those who utilize them in 

implementing management decisions, and equally to those (industry, pub1 ic) who 

are affected by management, is a necessity. Constant attempts must be made to 

improve the quality of the communication process. 

receptive to the users to gain their respect and understanding. 

recognizes and understands how assessments are conducted, how and why their 

data are incorporated into and employed in the process, and the sensitivity of 

the results to errors in the data and the implications thereof; and if 

industry feels that it is contributing significantly to the assessment 

process, it may achieve a greater sense of responsibility and concern. If 

industry and others better understand the assessment process, they will be 

less apt to negatively criticize the results. 

mutual comprehension is attained also will tend to improve credibility. 

Scientists must be 

If industry 

Communication at a level where 
-109- 

5.0. SCIENTIFIC MIX 

Within NMFS, stock assessment research is directed by mandates of federal 

legislation (MFCMA, MMPA, and ESA) and of international treaties such as ICCAT 

for Atlantic tunas. For resources where stock assessment is not mandated by 

legislation, research is guided by the NMFS scientific mission to understand 

the population dynamics and to monitor important fish stocks. The question of 

proper mix of NMFS research can be addressed at three levels: stock assessment 

work versus other fisheries-related research; allocation of stock assessment 

research among fishery resources under the centers' purview; and level of 

stock assessment analysis for a particular resource with respect to frequency, 

precision, and combination of methodologies. With respect to the first level, 

the overall NMFS a1 location of budget and personnel for traditional stock 

assessment, as given in an earlier section, is 59% of research dollars and 54% 

of research personnel. Developmental stock assessment activities make up an 

additional 15% of the budget and 10% of the personnel. The remaining 30% of 

the budget and 36% of personnel are distributed among fisheries habitat 

investigations, aquaculture, fishery resource development, fishery product 

quality and safety, and fishery oceanography. 

The mix of science in each Center varies considerably. These differences 

result from 1) the amount of funding, equipment, and type of personnel 

available, and 2) the varying assortment of species within its area of concern 

that come under legis1 ative or congressional mandates. 

result from the size of these resources, their ecological and economic value, 

and the extent of external social-political pressures. Although the primary 

purpose of NMFS stock assessment research is to provide advice to the 

decision-making process of fishery management, the analyses that make up the 

stock assessments are an integral part of other NMFS research, such as habitat 

investigations and fishery resource development. 

Differences a1 so 

Allocation of the Center's resources depends on the evaluation of such 

criteria as: 1 egi sl at i ve mandates, 1 eve1 of resource management, i ntensi ty of 

fishery relative to some maximum, generation time of the stock, political 

urgency of the problem, intensity of user review and expectations, quality of 

available stock assessment technology, available budget and manpower, and 

perceived national need. Resource questions requiring scientific 

investigation are in a constant state of flux. 

fishery resources is continually undergoing change to some unknown extent. 

For anything other than retrospect, any particular stock assessment is good 

for only an instant in time, soon to become outdated. As a result, today's 

proper mix of science and resources to solve today's problems will not 

necessarily be proper tomorrow with tomorrow's probl ems. 

The status of individual 

Evaluation of criteria must be a continuing process to maintain a current 

proper mix of research activities; an ideal systematic process for attaining a 

proper mix is not a reality. 

not necessarily appear advantageous to a user group or to the research staff, 

for example. 

different priorities. 

research on its associated resource (or the lowest priority if it fears 

Even so, the mix of research activities would 

These groups will have a narrower focus of the criteria and 

Any user group will assign the highest priority to 
-110- 

restrictive regulations). 

assignments become first priority, independent of earlier priority. The 

question of "proper mix" then is a matter of one's perspective. 

questioned with respect to proper mix, the Center Directors should be prepared 

to discuss the Centers' responsibilities, allocation criteria, and the 

criteria evaluation in relation to manpower and budgetary limitations. 

To the research staff, the approved research 

When 

With all this said, the remaining underlying question for any particular 

stock assessment research is "When is enough, enough?" This question cannot 

be answered technically without a quantitative analysis of alternative stock 

assessment methods for each resource problem, including such things as the 

most cost-effective method or mixture of methods, required levels of 

precision, frequency of results, and a forecast of the risks associated with 

being wrong. Prior to these types of analyses and evaluations, no one can say 

whether the mixture of science is proper although the mix may be 

"satisfactory" to solve the problems or answer the questions being addressed. 

The arrays of research studies currently under way throughout NMFS 

ultimately affect the status of the fishery resources and the resulting stock 

assessments. 

population with other biota in the ecosystem is contingent on fundamental 

knowledge of the impact on survival and growth of natural events in the 

environment, habitat alterations, disease, predator/prey relationships, 

competition, and the whole area of man's impact on the environment and its 

resources. Hence, stock assessment must be seen in a much more holistic 

manner than it has in the past, and the aggregate of current activities are 

all designed ultimately to understand the processes and events of the 

inanimate and biological environment. 

Understanding population trends and interactions of the 
-111- 

6.0. DISCUSSION AND RECOMMENDATIONS 

The current level of stock assessment activity in NMFS was mandated by 

new legislation aimed at protecting U.S. fisheries, endangered species, and 

marine mammals. 

largely for high-value fisheries or fisheries requiring international 

agreement for management purposes. This was considered reasonable because 

neither the manpower nor the money was available to do assessments for all 

stocks. The advent of conservation and environmental legislation over the 

past decade has resulted in a sense of urgency concerning improvements in the 

quality and timeliness of stock assessment information. 

addition, a significant extension of stock assessment studies to provide 

information on resources harvested by domestic fisheries, thus increasing the 

demand for data on a wide variety of fish, shellfish, and marine mammals. 

Additional monies were provided to support the activity; however, manpower 

restrictions remain. In addition, the required new stock assessments are, in 

many cases, for stocks on which few of the necessary basic data exist; 

research is therefore required to provide estimates of the basic parameters 

before stock assessment can begin. 

Prior to these legislative acts, stock assessments were done 

There has been, in 

Put in this political and scientific context, and considering the 

state-of-the-art in stock assessment theory and technology, the assessment 

coverage accorded to fish and marine mammal stocks as indicated in Table 5 may 

or may not be considered adequate, depending on one's perspective. 

example, the fishery management council i n i t s plan development cycle might 

consider a given level of assessment effort as inadequate, while the 

scientists feel it is the best they can provide under the circumstances and 

that it may be adequate for first-round management decisions. Certainly, the 

scientist would like to provide a better assessment, just as the Council 

member would like to have one; however, reality should produce a compromise as 

to what really is adequate in terms of quantity and quality of assessments in 

the management/legislative context. 

For 

The perfect stock assessment methodology does not exist. Existing 

methods are not completely interchangeable; each measures a slightly different 

aspect of stock abundance, and its use depends on the questions or problems at 

hand. Each method has a particular set of biological and physical conditions 

under which it works best. Each method has a specific set of assumptions and 

associated costs. 

will be inaccurate. 

frequently imprecise and that improving on precision and accuracy may be 

costly. This can be important if crucial management decisions are being 

weighed. 

In all cases, there is a degree of risk that conclusions 

We must further recognize that assessment methods are 

In considering methodology, it is apparent that no single approach or 

technique is suitable for all species or areas. In addition, assessments are 

not one-time endeavors but require continuous updating due to the dynamic 

nature of the stocks involved. Regardless of these shortcomings, stock 

assessment activities do provide estimates of stock size and they do generate 

information on trends in stock sizes. 

technology applied is generally the best available at the present time. 

In this sense, we accept that the 

Stock 
-112- 

assessment scientists are continuously seeking new technologies to improve the 

quality of the stock assessment information techniques. However, the greater 

immediate need lies in timely collection and processing of improved fisheries 

data to meet the near-term needs of resource managers. 

The Stock Assessment Task Force cannot overemphasize the importance of 

improving the quality and timeliness of fishery statistics collected from the 

commercial and recreational fishermen. A1 though substantial progress has been 

made in this area under the MFCMA, effort data are still lacking for a large 

number of species, and total catch for some species is still a best guess. To 

gain more effective access to the information available on commercial fishing 

activities, it is necessary to develop cooperative arrangements with the 

fishing fleet itself to make greater use of logbook information, observations 

at sea, etc. 

The Task Force does recognize the need to improve substantially the 

quality of communications on stock assessment activities to the various user 

groups. Some of the problems which have arisen may reflect a tendency of the 

scientific community to have oversold its ability to provide accurate 

information on stock trends and abundance. Hence, stock assessment scientists 

themselves may be partially responsible for constituent and peer expectations 

which are too high with regard to precision and timely availability of stock 

assessment data. 

The view of the Task Force is that stock assessment activities do not 

constitute a separate scientific discipline pursued only for management 

purposes. 

biological studies, ecological studies, and environmental research contributes 

to the data base for stock assessment. 

studies reflect an interpretation of natural and man-imposed events on living 

marine resources; hence, the aggregate of mortality coefficients generated by 

changes in the natural environment--pollution, fishing, etc.--must be 

integrated to interpret factors influencing changes and consequences of 

management strategy. 

concept of a multidisciplinary approach to stock assessment investigations, 

and managers should avoid fractionalization of research programs along 

disciplinary 1 ines. 

On the contrary, a great portion of the data collected for 

As noted earlier, stock assessment 

There is a growing recognition of the need to expand the 

The foregoing discussion leads us to conclude that the improvement in 

knowledge about the recruitment function and inter-specific re1 ations 

represents two of the most important needs. 

aspects of these two processes need investigation. Managers will not be able 

to adjust resource productivity, nor evaluate the effects of many commonly 

used regulatory methods, without such know1 edge. 

Both the biotic and abiotic 

Technological limitations which confront stock assessment activities have 

not been addressed in this report in any depth. 

however, the importance of technology for providing improvements in these 

areas. 

needs vary among regions and fisheries, recommends that NMFS act to: 

The Task Force recognizes, 

The Task Force, in recognizing that research demands and management 

1) enhance the timely collection and processing of improved or new 

fisheries data, both commercial and recreational, to meet the needs 

of resource managers and researchers; 
-113- 

2) expand the concept of a multidisciplinary (ecosystem) approach to 

stock assessment which integrates information from environmental, 

ocean variability, and fisheries impact studies; 

3) improve knowledge of both biotic and abiotic aspects of the 

recruitment function and inter-specific relations, so that resource 

managers may evaluate the potential of regulatory measures affecting 

resource productivity; 

4) advance the theoretical and technical bases for stock assessment; 

5) communicate more effectively with user groups to improve their 

understanding of the strengths and weaknesses of assessment 

techniques and their implications to management decisions; and 

6) recognize that new information demands for management have eroded the 

peer review process and that NMFS should explore methods to improve 

such review. 
-114- 

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-1 21 - 

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-1 22- 

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1973. Scientific advice on catch levels. Fish. Bull., U.S. 

71(2 325-335. 

Horwood, J. W. 

1976. Interactive fisheries: A two species Schaefer model. Int. 

Comm. Northw. Atlant. Fish., Sel. Pap. 1:151-155. 

Jackson, C. H. N. 

1939. The analysis of an animal population. J. Anirn. Ecol. 

8(2) :238-246. 

Jones, R. 

1961. The assessment of long-term effects of change in gear 

selectivity and fishing effort. Mar. Res. 2:l-19. 
-128- 

Laevastu, R., F. Favorite, and H. A. Larkins. 

1979. Resource assessment and evaluation of the dynamics of the 

fisheries resources on the NE Pacific with numerical ecosystem 

models. U.S. Dep. Commer., Natl. Oceanic Atmos. Admin., Natl. 

Mar. Fish. Serv.; NWAFC, Seattle, MA, NWAFC Processed Rep. 79-17, 

35 p. 

Larkins, P. A., and A. S. Houston. 

1964. A model for simulation of the population biology of Pacific 

salmon. J. Fish. Res. Board Can. 21:1245-1265. 

Lett, P. F. 

1978. A multispecies simulation for the management of the southern 

Gulf of St. Lawrence cod stock. Can. At1 . Fish. Sci. Advis. Comm. , Res. Doc. 78/21. 

Lett, P. F. , A. C. Kohler, and D. N. Fi tzgerald. 

1975. Role of stock biomass and temperature in recruitment of 

southern Gulf of St. Lawrence Atlantic cod, Gadus morhua. J. Fish. 

Res. Board Can. 32:1613-1627. 

Murphy, G. I. 

1965. A solution of the catch equation. Fish. Res. Board Can. 

22:191-202. 

Paloheimo, J. E. 

1961. Studies on estimation of mortalities. I. Comparison of 

method described by Beverton and Holt and a new linear formula. 

J. Fish. Res. Bd. Canada 18(5):645-662. 

Paloheirno, J. E., and L. M. Dickie. 

Int. Explor. Mer. 155:152-163. 

1964. Abundance and fishing success. Rapp. P.-v. Reun. Cons. 

Pella, J. J., and P. K. Tomlinson. 

Comm., Bull. 13:419-496. 

1969. A generalized stock production model. Inter-Am. Trop. Tuna 

Pope, J. A. 

1972. An investigation of the accuracy of the virtual population 

analysi s us! ng cohort analysis. 

Res. Bull. 9:65-74. 

Int. Comm. Northwest At1 . Fi sh. , 

Pope, J. G. 

1976. The effect of biological interaction on the theory of mixed 

fisheries. Int. Comm. Northw. Atlant. Fish., Sel. Pap. 1:157-162. 

1954. Stock and recruitment. J. Fish. Res. Board Can. 11:559-623. 

Ricker, W. E. 
-129- 

1913. Linear regression in fishery research. J. Fish. Res. Bd. 

Canada 30:409-434. 

Riffenburgh, R. H. 

1969. A stochastic model of interpopulation dynamics in marine 

ecology. J. Fish. Res. Board Can. 26:2843-2880. 

Robson, D. S. and D. G. Chapman. 

1961. Catch curves and mortality rates. Trans. her. Fish. SOC. 

90:181-189. 

Schaefer, M. B. 

1954. Some aspects of the dynamics of populations important to the 

management of the commercial marine fisheries. Inter-Am. Trop. 

Tuna Comm., Bull. 1(2):27-56. 

1951. A study of the dynamics of the fishery for yellowfin tuna 

in the eastern tropical Pacific Ocean. Inter-Am. Trop. Tuna Comm., 

Bull. 2 ~247-268. 

Tillman, M. R., and D. Stadelman. 

1975. Development and example application of a simulation model of 

the northern anchovy fishery. Fish. Bull., U.S. 74:118-130. 

Tomlinson, P. K., and N. 3. Abramson. 

1961. Fitting a von Bertalanffy growth curve by least squares. 

Fish. Bull., Calif. Fish. Game 116:l-69. 

Ulltang, 0. 

1977a. Methods of measuring stock abundance other than by the use 

of commercial catch and effort data. FA0 Fish. Tech. Pap., 

171: 23 p. 

19//b. Sources of errors in and limitations of virtual population 

analysis (cohort analysis). J. Cons. Int. Explor. Mer. 37:249-260. 

In press. Factors of pelagic fish stocks which affect their 

reaction to exploitation and require a new approach to their 

assessment and management. Rapp. P.-v. Reun. Cons. Int. Explor. 

Mer. 177. 

Walter, C. J. 

1975. Optimal harvest strategies for salmon in relation to environmental variability and uncertainty about production parameters. 

J. Fish. Res. Board Can. 32:1777-1784. 

Walter, C. J., and R. Hilborne. 

1975. Adaptive control of fishery systems. J. Fish. Res. Board 

Can. 33(1):145-159. 
-130- 

Walter, G. G. 

1973. Delay-differential equation models for fisheries. J. Fish. 

Res. Bd. Canada 30:939-945. 

19/5. Graphical methods for estimating parameters in simple models 

of fisheries. J. Fish. Res. Bd. Canada 32:2163-2168. 

19/6. Nonequil ibrium regulation of fisheries. Int. Comm. Northw. 

ATIant. Fish., Sel. Pap. 1:129-140. 

19i8. A surplus yield model incorporating recruitment and applied 

to a stock of Atlantic mackerel (Scomber scombrus). J. Fish. Res. 

Bd. Canada 35:229-234. 
-A1 - 

APPENDIX 

EVALUATION MATRICES 

The development of the assessment report pointed out the complexity and 

large volume of the work conducted by NMFS to carry out its management 

responsibilities. 

devel oped. 

To put this into a condensed form, a series of matrices was 

MATRIX I: Evaluation of Current NMFS Assessment Efforts Related to 

Management Needs. 

The first matrix identifies the current status of NMFS assessment efforts 

and the additional efforts that are needed to meet management unit 

requi rements. 

preliminary management plan, is identified by ecological group (Matrix 111) 

and importance. Methods currently in use to provide stock assessments for 

each management unit were identified with a general indication of the methods' 

accuracy. The level of assessment (Matrix IV) derived from the method(s) used 

was then identified. The levels ranged from a simple catch trend to a complex 

ecosystem yield estimate. 

Each management unit, within a fishery management pl an or 

To put the existing efforts into a proper 

perspective the ass 

management unit was 

requirements of the 

concludes with the 

ssment level and accuracy level curren 

identified. Additional efforts needed 

management unit were then identified. 

dentification of FY 1980 base budget f 

y rewired by a 

to meet the current 

The matrix 

gures and the 
-A2- 

additional resources needed, if any, to meet the currently required level of 

effort. 

The various elements included within Matrix I are identified below: 

El ement 

no. Name and DescriptionjExampl es 

1. Management Category: Specific FMP, international agreement, 

or mandate, e.g. Gulf of A1 aska Groundfish Management P1 an, 

Marine Mammal Protection Act. 

2. Management Unit (within Management Category) : A species or 

species group, e.g. , northern anchovy, reef fishes, Pacific 

whiting, flounder complex. 

3. Ecological groups: See List 1 below (page A30). 

4. Commercial importance (of a Management Unit): Indicated by 

Value and weight (Volume) of annual landings, using the folmg categories msociated code symbols. 

Val ue 

> $150 million 

$76-150 mil 1 ion 

$10- 75 million 

< $10 million 

No ne 

Volume (m.t.1 

> 100 thousand 

51-100 thousand 

10- 50 thousand 

< 10 thousand 

No ne 

Symbol 

Y 

0 

The current "Fishery Statistics of the United States for 

1979," is the source document. The value of foreign catch 

is calculated from the ex-vessel prices used to compute 

poundage fees charged (see page 87 of the reference). 

Discard estimates, if available, are footnoted or entered in 

Remarks. 

5. Recreational importance (of a Management Unit) : Indicated by 

Participation (No. of fishermen), Costs ($1, and Volume of 

catch, using the following categories and associated code 

symbol s. 

- 
-A3- 

Participation 

(No. of fishermen) costs Volume (m. t.) Symbol 

> 5 million 

2-5 million 

> $150 million 

$76-150 mil 1 ion 

> 50 thousand 

26-50 thousand 

E 0.5-2 million $10- 75 million 5-25 thousand 

< 0.5 million < $10 million < 5 thousand 

No ne No ne No ne 0 

endangered; otherwise 1 

7. Adequacy of NMFS Current Assessment Methods (for methods 

1 i sted bel ow) . 

(a) Fisheries information 

(b) Aerial survey (counts) 

(c) 

(d) 

(e) Ship surveys (acoustical 1 

(f) Other remote sensing surveys 

(g) Environmental surveys 

Ship surveys (adults and/or juveniles) 

Ship surveys (eggs and larvae) 

The adequacy and frequency of use of each method are 

indicated by the fol 1 owing symbol s : 

(1) For methods other than 

primary methods: 

(2) For primary method: Adequacy 

cF r equency 

Adequacy 1 evel s and code symbol s: 

Symbol 

Adequacy 1 evel Symbol (if primary method) 

Adequate 

Marginal 

In adequa te 

Unknown 

Q 

e 
-A4- 

Frequency of use (indicated in circle in center of symbol) is , coded as follows: 

Frequency Circle code 

Occurs more than once a year 0 

Occurs once a year 0 

Bi enni a1 0 

Tri enni a1 6 

Irregular a3 

8. Assessment Level and its degree of accuracy. This pertains 

to each Management Unit. 

(see List 2, page A38). Information on Assessment Level and 

its accuracy is entered for: (a) Current Level by NMFS for 

the Management Unit, and (b) Current Level required for the 

Management Unit. The following code symbol is used for both 

(a) and (b): 

Assessment Levels are defined below 

B Assessment Level 

Degree of accuracyAssessment Level Circle code Degree of accuracy Symbol 

No ne 

Catch trend 

Relative abundance trend 

Equilibrium yield 

Annual yield forecast 

Mu1 ti species total 

biomass yield 

Ecosystem yield 

113 0 Within 30% of 

0 true value 

0 

@ 

0 

0 Conservatively 

biased (31-60%) 

0 less than true 

val ue) 

tsl Grossly accurate 

(+31-60% of true 

vZ1 ue) 

Inaccurate ( > f60%) 

Unknown lol 
-A5- 

9. Additional technological , analytical , and sampling effort 

10. 

11. 

needed to meet current and projected management requirements. 

whatare considered to be the two (note 2 columns under each 

i tem) most critical Information El ements for a Management 

Unit. 

mis case, as indicated below, effort is not defined in 

terms of funds and personnel. 

These items relate to effort required with respect to 

Information Elements are shown in List 3-31). 

For the Techno1 ogical and Analytical efforts the categories 

and symbols are: 

c 

Technical and Analytical 

effort category 

Devel opmental program needed. 

(No techniaue or present techn i que requi res repl acemen t . ) 

Increase effort in current 

devel opmen tal program. ( No 

technique or present technique requires repl acement.) 

Improve present technique. 

Symbol 

(No. of Information 

Elements is entered 

in center circle) 

Q 

No effort. i.e.. no Information 

Element identified for additionalef f or t . 0 

For the Sampling efforts, the categories and symbols are: 

Symbol 

(No. of Information 

Elements is entered 

Sampling effort category in center circle) 

Introduce new sampling program. 

Q Increase present sampling effort 

( ei ther si ze of individual sampl es, 

no. of samples, geographic coverage, freauency of sampling). 
-A6- 

No effort, i.e., no Information 

El ement identified for additional 

rn 

0 

Under each of items 9, 10, and 11, the most important 

Information Element (of the two selected) is indicated 

in the left half of the column. 

12. Funds and Personnel by Management category. Estimates of 

funds and man-years are entered as indicated. 

estimates are for ganagement Categories, not Management 

Units. 

Note that 
1 

I 

=! 

= 

I ilUIIMOM( f 

e 

- 

ml 

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0 "" I 

1 

iii 

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0 

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la 

I I I I I 

I I I I I 

00 OOQO 

e, 

-t0 I 

P 4 

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UIIm - 

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urnmom 

$000. 

Y u)g 

%- os 
h 

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m_ * * ---I--- 

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c 

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-A21 - 

MATRIX 11: Applicability of Assessment Vethods to the Information 

Elements Required. 

The second matrix identifies the many information elements used in 

fisheries management. Most of the elements are data series. The matrix 

indicates the sampling methods used to obtain informational elements and 

identifies which informational elements are needed for specific analytical 

methods. Assessment methods are shown in List 4 (page A31). 

= Method applicable for acquiring data for Information element. 

B1 ank = Method not applicable for acquiring data for Information 

El emen t . 
v) 

0 

c 

-i 

I 

m 

v) 

-I 

s 

1 

A 

UJ 

I 

m 

m 

v) 

0 

m 

z 

--I 

m 

;D 

.- II - 0 cn 3 * 

0 E: m 

v) 3 

0, -. 2 

_. n 

ID v) 

0 

s. m 

0 z 

Mork ond = 

recovery - 

Change in - N 

rotio 

I 

I- - 

production 

Yield per l- recruit 0 

T recruit 

Multispecies 

models 

Ecosystem 

models I/ 

Predictiye o/ 

regressions - 

11 Sampling the ZI 

fisheries - c - - Togging 

0 Bottom trawl j. survey - 

0 I/ Trop survey or pot 

1 Acousticol 

5 

v) 

survey 

n 

Acousticol- - bottom trow1 z survey -2 

T '1 I/ Aerial 

survey -k and lorvae 

-t - -I0 (1 Other remote &I surveys - 
-A23- 

MATRIX 111: Applicability and Adequacy of Sampling Type Assessment 

Methods Relative to Different Ecological Groups. 

In Matrix I11 an attempt was made to condense the various management 

units into 16 ecological groups. 

sampling methods for assessing the ecological group was then identified using 

estimates of precision and accuracy associated with each method/group pairing. 

The applicability or adequacy of various 

Accuracy and precision level s and their corresponding symbol s are: 

Ac curacy 

Within + 30% - 

Conservatively biased 

(31-60% less than 

true value) 

Precision Symbol 

Within + - 30% 

B 

Grossly accurate Grossly precise 

(+ -31-60%) (+ -31-60%) 

Inaccurate 

> + 60% - 

Imprecise 

> - + 60% 17 

Unknown Unknown 61 ank 

Note that estimates of accuracy and precision levels are 

indicated for the Ecological Group as a whole, not the 

example of the group. 
Iv 

ID, 

s 

'5 

b 

9 

7 

YJ 

I 

z 

- 

z 

0 

a 

-I 

I 

rn 

D 

cn 

-I 

n 

cn 

I 

m 

m 

cn 

- 

", I: 

n 

0 .r 

c 

E3 -

4 

IXI 

I 

w 

0 

1- 

c II 

rn 

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a- 
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t a 

n 

” = 

0 

U 0 

m 

I 

7 3 

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E 

I - 

~ 

I 

.- c 

C 

a 

a 

- 

71 

e 

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.- a 

a 

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- 

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e 

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7- 

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C t+- El- - 

Ft- I- I 

+ .+ e qa oi 

a 

-- - IQl a 

- 

I I I 

-tf-l- 
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I 111 

c XI 

5 

[XI 

- c 

c 

X 

x 7 

um 

i E I 

C 

C 
a, 

z 

VI 0 0

E 

e. 

z 

0 

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cn 

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D 

r 

E; x 

D 

cn 

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m 

m 

cn 

0 

rn 

z 

-i 

m 

3D 

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E 

'Om 

0% 

3 

35. 

-a 

VI m 0

VI 

3 

m 

.. 

VI 

E /c 

x - T +- L 

E 

c -f 

t- - r 

z II 3 

I+ 

w 0 

$! ?/c 

5 

-tIt 

w 

0 c - $! 

c - 

- c 

c 

- 

; 

B 

L 

Y 

a 

a 

- 

- l- T 

-I - T 

-1- 
-.428- 

MATRIX IV: Information El ements Required for Different Assessment 

Level s. 

Matrix IV identifies the informational elements required for each level 

of assessment. 

The relative need for Information Element in order to achieve 

Assessment Level is categorized as foll ows: 

Requi remen t 

Information Element essential 

Symbol 

[XI Information Element desirable 

Information Element not required B1 ank 
CODE KEY-MATRIX MATRIX IV. IV. 

Requirement 

Informotion Element esrentiol 

Information Element desiroble 

Information Element not required 

I N FOR MAT I ON EL EM E N T S 

-- Symbol 

blonk 

Information Elements required for 

different Assessment - Levels. 

r ASSESSMENT LEVELS 

. Mortality rote 

-A29- 
-A31 - 

7. Ecosystem yield. - Highest order assessment, requiring extensive 

knowledge of characteristics, dynamics, and interrelationships of 

biotic and abiotic components. 

Note: It is implied in these definitions that each succeeding 

Assessment Level has the benefit of all i nformati on avai 1 ab1 e to 

precedi ng 1 eve1 s . 

List 3 - Information Elements 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

Spec i es descr i pti on 

Species di stri buti on 

Stock identification 

Catch series 

Di scard series 

Effort series 

Length series 

Age series 

Growth rates (assumes sufficient length-weight data) 

Re1 ative abundance 

Mortal i ty rate 

Exploitation rate 

Reproductive rate 

List 4 - Assessment Methods 

A. Analytical 

1. Mark and recovery 

2. Change in ratio 

3. Surplus production 

4. Yield-per-recruit 

5. Virtual popul ation/cohort 

6. Spawner- recrui t 

7. Mu1 tispecies models 

8. Ecosystem models 

9. Predictive regressions 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

10. 

11. 

12. 

13. 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

23. 

Behavior 

Catchabil i ty 

Absol Ute popul ation size 

(biomass or number) 

Annual recruitment 

Envi ronmen tal i ndi ces 

Causal environmental mechani sms 

Species i nteractions- - 

competition, predator-prey 

Physiological 

Mu1 tiple factors (behavior, 

environmental , population 

parameters, etc. 1 

B. Sampling 

Sampling the fisheries 

Tagging 

Bottom trawl survey 

Dredge survey 

Trap or pot survey 

Se tl i ne survey 

Acoustical survey 

Ac ousti cal -bottom trawl survey 

Landbased count 

Aerial survey 

Fish eggs and larvae 

Environmental indices 

Underwater survey 

Other remote surveys 
-A21 - 

YATRIX I1 : Appl icabil i ty of Assessment Methods to the Information 

Elements Required. 

The second matrix identifies the many information elements used in 

fisheries management. The matrix 

indicates the sampling methods used to obtain informational elements and 

identifies which informational elements are needed for specific analytical 

methods. 

Most of the elements are data series. 

Assessment methods are shown in Li st 4 (page A31). 

= Method applicable for acquiring data for Information element. 

B1 ank = Method not applicable for acquiring data for Information 

El emen t .