Coarse Fish Scale Reading

Gareth D Davies

National Fisheries Service

Technical Officer 1

March 2015

Why age coarse fish?

WFDAge structure of fish populations

Core Fisheries Monitoring Programme

Pre/ Post-Habitat Rehabilitation

Stock Assessments

Project WorkClimate Change

Invasive Non-Native Species

Structures used in age determination

Pharyngeal

teeth

Operculum

Fin rays

Otolith

Scales Vertebrae

Scale Morphs

Scale Proportion Hypothesis

Advantages of Back-Calculation

0

200

400

600

800

1000

1200

1 2 3 4 5 6 7 8

Nu

mb

er o

f fi

sh u

sed

to

calc

ula

te M

LA

Age

Advantages of Back-Calculation

0

200

400

600

800

1000

1200

1 2 3 4 5 6 7 8

Num

ber

of fi

sh u

sed

to c

alcu

late

ML

A

Age

0

50

100

150

200

250

1 2 3 4 5 6 7 8

Len

gth

(m

m)

Age (years)

Annuli

oMLA

Advantages of Back-Calculation

Growth Performance

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Le

ng

th (m

m)

Age (years)

FastVery fast

AverageSlow

Very slow

R. Waverney

Percentage standard growth = 110%

x

Example 1. Salmonid Scale

Example 2. Coarse Scale

Fishery Management

Fishery Management

3+ ?

Fishery Management

1+ !

Case Study

Chub (Leuciscus cephalus)

Long lived species – 20+ years

Multiple/ protracted spawing

Length @ end of 1st growing season ranges from <25 mm to > 70 mm

Can lead to errors in scale analysis

Case Study

193 mm 196 mm

Thank you

Any questions?

Twitter: @GarethDDaviesEA

E-mail:Gareth.d.davies@environment-agency.gov.uk

Chub

365 mm

13+

Chub

365 mm

13+

Barbel

565 mm

21+