NA_Yaragina-KH_Nedreaas-V_Koloskova-H_Mjanger-H_Senneset-N_Zuykova-P_Aagotnes.pdf (1.493Mb)

Fifteen years of annual Norwegian-Russian

cod comparative age readings

Natalia A.Yaragina ¹ , Kjell H.Nedreaas ²

Valentina P. Koloskova ¹ , Hildegunn Mjanger ² ,

Harald Senneset ² , Natalia V. Zuykova ¹ , and Per Ågotnes ²

1Polar Research Institute of Marine Fisheries and Oceanography (PINRO), Murmansk, Russia

2 Institute of Marine Research (IMR), Bergen, Norway

The 12

Norwegian - Russian Symposium

Norway, 21-22 August 2007

The basic purpose

•Clear up possible reasons of age discrepancies

•Standardize methods

•Draw up recommendations in ageing

•Avoid serious errors in routine work

( discover and correct errors immediately)

Numbers of cod otoliths exchanged in 1992-2006

No. of otoliths

Ownership Time of year ICES areas Year

IMR PINRO 1 half year

2 half

year I IIa IIb Total

1992 357 398 555 200 441 314 0 755

1993 200 200 200 200 205 82 113 400

1994 200 200 200 200 200 86 114 400

1995 283 209 292 200 241 74 177 492

1996 198 150 148 200 199 69 80 348

1997 193 199 238 154 243 125 24 392

1998 199 200 200 199 224 125 50 399

1999 200 200 200 200 224 125 51 400

2000 200 200 200 200 199 151 50 400

2001 200 200 200 200 193 158 49 400

2002 200 200 200 200 197 103 100 400

2003 200 200 200 200 200 113 87 400

2004 200 200 200 200 200 175 25 400

2005 200 200 200 200 250 125 25 400

2006 200 200 200 200 148 177 75 400

Total 3230 3156 3433 2953 3364 2002 1020 6386

Portions of cod otoliths sampled in different areas (1992-2006)

1

2a

2b

Cod otolith

Techniques of cod ageing:

Norwegian (IMR)(N) and Russian (PINRO) (R)

N:The opaque zone is continuous along the edge. The summer growth has ended. The zone should not be counted as an annual ring until the beginning of the next year.

Four opaque zones correspond to only three calendar years.

R:A wide opaque zone is continuous along the edge. The summer

growth has ended.

Three translucent zones correspond to three calendar years.

August-September

3 years

Initial discrepancy in cod age

readings (dark curve) and after re- reading (pink curve)

R² = 0.4834 R² = 0.1901

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

1st half1992

2nd half1993

1st half1995

2nd half1996

1st half1998

2nd half1999

1st half2001

2nd half2002

1st half2004

2nd half2005

%

Comparison of age reading (N-R) for each year (using t-criterion for dependent

samples)

t

-10 -8 -6 -4 -2 0 2 4 6

1992 1994 1996 1998 2000 2002 2004

Results by months

Percentage of agreement in age

reading for different areas

Percentage of agreement in age reading by cod ages

% agreement

R² = 0.43

0 20 40 60 80 100

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

Age, year

Between reader bias by cod ages

Conclusions

• Equipment has been standardized

• The Labs have received important

lessons ( methods, reasons of discrepancies, training procedure, need of regular

meetings )

• Differences in cod age reading between

two labs have decreased

Further work

• Further analysis of data (concerning growth rate, information on fish size, ownership of otoliths, risk analysis etc)

• Formation of Reference collection

• Age-validation studies

Congratulations with

15 years

anniversary !