MANUAL OF FISHERIES SCIENCE Part 2 - Methods of Resource Investigation and their Application

MANUAL OF FISHERIES SCIENCE

Part 2 - Methods of Resource Investigation and their Application

Edited by

M.J. Holden
Fisheries Laboratory
Lowestoft
Suffolk
England

and

D.F.S. Raitt
Fishery Resources and Environment Division
FAO
00100 Rome, Italy

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, June 1974

PREPARATION OF THIS DOCUMENT

This document was produced in a provisional version solely for use as background documentation at the FAO/DANIDA Training Centre in the Methodology of Fisheries Science held in Frederikshavn, Denmark from 28 August to 22 September 1972. On the basis of the experience gained in using it as training material it has been revised and edited with a view to circulating it for comment by international workers in this field.

This revised version will be used at the second FAO/DANIDA Training Centre in the Methodology of Fisheries Science (Biology) to be held in Kelibia, Tunisia, from 29 July to 23 August 1974. Comments and criticisms are welcomed and should be addressed to the Aquatic Resources Survey and Evaluation Service, Fishery Resources and Environment Division, FAO, Rome.

Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics.

1.	INTRODUCTION TO FISHERIES SCIENCE
	1.1	History of fisheries science
	1.2	History of a fishery
	1.3	Why investigate a fishery?
	1.4	The rôle of the fisheries’ scientist
	1.5	How to investigate a fishery
		1.5.1	Catch and fishing effort data
		1.5.2	Length and age composition data
		1.5.3	Biological investigations
		1.5.4	Population dynamics
	1.6	The scope of this manual
	1.7	References
2.	POPULATION AND SAMPLING
	2.1	Random sampling error
	2.2	Bias
	2.3	Some statistical terms
		2.3.1	Mean
		2.3.2	Variance and standard deviation
		2.3.3	Normal distribution and confidence limits
	2.4	Stratified sampling
	2.5	Practical aspects of market sampling
	2.6	Sampling on a vessel
		2.6.1	Sampling on a research vessel
		2.6.2	Sampling on a commercial vessel
	2.7	The collection of fisheries statistics
	2.8	Basic attitudes to the collection of fisheries statistics
	2.9	Fish identification
	2.10	Collecting catch and fishing effort data
		2.10.1	The collection of catch data
		2.10.2	The collection of fishing effort data
		2.10.3	The area of fishing
		2.10.4	Date of capture
		2.10.5	The importance of recording data in a standard manner
	2.11	References
	APPENDIX 2.1: Examples of Collection of Catch and Effort Data
1.	A DEMERSAL FISHERY LANDING AT A MAJOR PORT
	1.1	Wet fish landings
	1.2	Frozen fish landings
	1.3	Recording forms
2.	AN AFRICAN LAKE FISHERY
	2.1	Collection of basic data
	2.2	Landings
	2.3	Weight recorded away from the landing site
	2.4	Total effort
	2.5	Catch per unit effort
3.	A PURSE SEINE FISHERY
	3.1	Collection of basic data
	3.2	Catch data
	3.3	Effort data
	3.4	Catch-per-unit effort
	APPENDIX 2.2: Notes on Fishing Effort Statistics
1.	FISHING TIME
2.	FISHING POWER
3.	GENERAL REMARKS PROVIDING DATA ON FISHING EFFORT
3.	THE MEASUREMENT OF FISH AND SHELLFISH
	3.1	The measurement of fish
		3.1.1	Choice of length dimension to measure
		3.1.2	Methods of measuring
		3.1.3	Measuring damaged and processed fish
	3.2	The measurement of shellfish
		3.2.1	Molluscs
		3.2.2	Crustacea
	3.3	Form for recording measurements
	3.4	Units of measurement and grouping data
	3.5	Reporting of length-composition data
	3.6	Weighing
	3.7	References
	APPENDIX 3.1: Definition of linear measurements
	APPENDIX 3.2: ‘One-man’ measuring board
	APPENDIX 3.3: A method of measuring headless fish
	APPENDIX 3.4: Specimen recording forms
	APPENDIX 3.5: Specimen reporting form
4.	AGE DETERMINATION AND AGE COMPOSITIONS
	4.1	Age determination from skeletal structures
	4.2	Collection of otoliths and scales
		4.2.1	Otoliths
		4.2.2	Scales
	4.3	Storing and mounting
		4.3.1	Otoliths
		4.3.2	Scales
	4.4	Methods of preparation and viewing
		4.4.1	Otoliths
			4.4.1.1	The structure of the otolith
			4.4.1.2	Viewing the fresh otolith
			4.4.1.3	Viewing the whole otolith
			4.4.1.4	Preparing a cross section of an otolith
			4.4.1.5	Viewing the cross section with transmitted light
			4.4.1.6	The burning technique
			4.4.1.7	Unusual growth zones
		4.4.2	Scales
			4.4.2.1	The structure of the scale
			4.4.2.2	Preparing and viewing scales
	4.5	Other techniques
	4.6	Validation
		4.6.1	Timing of ring formation
		4.6.2	Following a large year-class through a fishery
		4.6.3	The Petersen method
		4.6.4	Injection techniques
	4.7	Allocation of a birthday
	4.8	Special uses for otoliths and scales
		4.8.1	Spawning zones
		4.8.2	Stock patterns
	4.9	Difficulties and possible sources of error
		4.9.1	Differences between otoliths from the same fish
		4.9.2	Variation of age at length
		4.9.3	False rings and check zones
	4.10	Causes of zone and ring formation
	4.11	The indirect age determination of fish
		4.11.1	The Petersen method
		4.11.2	Tagging
	4.12	Determination of growth rates from scales and otoliths
	4.13	Age compositions
		4.13.1	Use of age-length keys
		4.13.2	The number of fish to age
		4.13.3	Age-length keys for different years
		4.13.4	Age-length keys for each sex
		4.13.5	Frequency of construction of age-length keys
	4.14	Publishing stock record data
	4.15	References
5.	SEX, MATURITY AND FECUNDITY
	5.1	Introduction
	5.2	Teleosts
		5.2.1	Sex determination
		5.2.2	Maturity stages
			5.2.2.1	Total (isochronal) spawners
			5.2.2.2	Partial (hetereochronal) spawners
		5.2.3	Gonad indices
		5.2.4	Length - maturity keys
			5.2.4.1	Bias in the maturity length-key
		5.2.5	Fecundity
			5.2.5.1	Total spawners
			5.2.5.2	Partial spawners
	5.3	Elasmobranchs
		5.3.1	Sex determination
		5.3.2	Maturity stages
		5.3.3	Fecundity
	5.4	Fecundity - length relationships
	5.5	References
6.	FOOD AND FEEDING
	6.1	Introduction
	6.2	Some principle lines of general ecology
		6.2.1	What is ecology?
		6.2.2	The ecosystem
		6.2.3	Steps and components of the ecosystem
		6.2.4	Food chains and trophic levels
		6.2.5	Gross production and net production
		6.2.6	Production and ecological efficiencies
	6.3	Estimation of the food intake of fish
		6.3.1	Qualitative assessments of food intake from stomach content analyses
			6.3.1.1	Frequency of occurrence
			6.3.1.2	Numerical occurrence
			6.3.1.3	Dominance
			6.3.1.4	Total volumes
			6.3.1.5	Percentage volume
			6.3.1.6	Gravimetric
			6.3.1.7	Points method
			6.3.1.8	Discussion
		6.3.2	Quantitative assessments of food intake
	6.4	References
7.	THE AQUATIC ENVIRONMENT
	7.1	Introduction
	7.2	Planning the sampling programme
		7.2.1	Temperature observations
		7.2.2	Application of temperature data
		7.2.3	Chemical sampling
		7.2.4	Light intensity
		7.2.5	Pollution
	7.3	The biotic environment
		7.3.1	Phytoplankton standing crop and primary production
		7.3.2	Zooplankton biomass
		7.3.3	Fish egg and larval surveys
	7.4	References
	APPENDIX 7.1: Worked example of correction of temperature readings
8.	UNIT STOCKS, MIGRATIONS AND STOCK DIFFERENTIATION
	8.1	The unit stock
	8.2	Migration
		8.2.1	Migration and currents
		8.2.2	Terminology of fish migration
	8.3	Methods of studying fish migrations
		8.3.1	Marking
		8.3.2	Tagging
			8.3.2.1	General characteristics of a tag
			8.3.2.2	Internal tags
			8.3.2.3	External tags
		8.3.3	Tagging experiments
			8.3.3.1	Planning the experiment
			8.3.3.2	Running the experiment
			8.3.3.3	Rate of returns from a tagging experiment
		8.4	Other methods of differentiation between stocks and following migrations
			8.4.1	The distribution of fishing effort
			8.4.2	Echo surveys
			8.4.3	Parasite studies
			8.4.4	Immunogenetic techniques
			8.4.5	Scale studies
			8.4.6	Meristic characters
	8.5	References
9.	THE EFFECT OF FISHING ON FISH
	9.1	Introduction
	9.2	How much fish
		9.2.1	Absolute methods
			9.2.1.1	Release and recapture
			9.2.1.2	Swept area and swept volume
			9.2.1.3	Egg and larval surveys
			9.2.1.4	Acoustic techniques
			9.2.1.5	Virtual population analysis
		9.2.2	Relative methods
			9.2.2.1	Commercial indices of catch per unit effort
			9.2.2.2	Research vessel indices of catch per unit effort
		9.2.3	Effects of gear upon sampling
			9.2.3.1	Mesh selection
			9.2.3.2	Gear selection
		9.2.4	Summary
	9.3	Population dynamics
		9.3.1	Construction of a model
		9.3.2	Use of the models and the results
		9.3.3	The future development of models
		9.3.4	Monitoring the stocks
	9.4	International coordination and cooperation
	9.5	References

LIST OF CONTRIBUTORS

P. Agger, Danmarks Fiskeri-og-Havundersøgelser, Charlottenlund, Denmark

O. Bagge, Danmarks Fiskeri-og Havundersøgelser, Charlottenlund, Denmark

O. Hansen, Danmarks Fiskeri-og Havundersøgelser, Charlottenlund, Denmark

E. Hoffman, Danmarks Fiskeri-og Havundersøgelser, Charlottenlund, Denmark

M.J. Holden, Fisheries Laboratory, Lowestoft, Suffolk, England

G.L. Kesteven, Fishery Research and Development Project, Mexico

H. Knudsen, Danmarks Fiskeri-og Havundersøgelser, Charlottenlund, Denmark

D.F.S. Raitt, Food and Agriculture Organization of the United Nations, Rome, Italy

A. Saville, Marine Laboratory, Aberdeen, Scotland

T. Williams, Fisheries Laboratory, Lowestoft, Suffolk, England

PREPARATION OF THIS DOCUMENT

CONTENTS