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REPRINT FROM Calif. Fish and Game 59(3) : 191-195.


MAKOTO KIMURA National Marine Fisheries Service La Jolla, California 92037

A special scale r e a d i n g session d e s i g n e d to b r i n g t o g e t h e r o l d a n d n e w scale readers t o compare t h e c r i t e r i a f o r estimating t h e f i r s t annulus i n sardine scales &,), e x a m i n e d scales collected f r o m t h e 1941 t h r o u g h 1962 sardine landings. Estimates of 1 1 b y t h e o r i g i n a l readers w e r e consistently l o w e r t h a n those o f t h e n e w e r readers. The r e p o r t e d increase i n Pacific sardine l e n g t h a t t h e f o r m a t i o n of first annulus a p pears to b e due t o a change i n t h e o l d e r reader's c r i t e r i a f o r t h e posit i o n o f t h e f i r s t annulus. I n addition, t h e r e w a s a g r a d u a l r e p l a c e m e n t o f t h e o l d e r readers b y n e w e r ones w h o consistently r e a d h i g h e r a n d thus o v e r e s t i m a t e d 11. Hence, it a p p e a r s t h a t t h e r e was n o r e a l change i n sardine g r o w t h r a t e s d u r i n g these years.

W a l f o r d a n d Mosher (1943a, 1943b) validated t h e use of scales f o r estimating the age of t h e Pacific sardine a n d set criteria f o r t h e scale annulus. I n 1960, I suspected the sardine scale readers were not strictly following the criteria in locating the first or innermost annulus. The radius of this a n n u l u s is used to estimate the L, (defined as ( i ) ) the calculated length of t h e fish a t the end of the first year of life ( M a r r 1 9 6 0 ) , or ( i i ) the calculated length of the fish a t the time of formation of t h e r i n g in the first year of life ( P h i l l i p s 1948a). F r o m information obtained on the time of a n n u l u s formation on known-age sardine ( K i m u r a a n d Sakagawa 1972) the second definition is recommended. The L1 is one of the basic measurements f o r estimating growth ( P h i l l i p s 1948b). It has also been used as a p a r a m e t e r t o separate subpopulations ( F e l i n 1954) , a n d to support certain hypothesis a b o u t the population ( M a r r 1 9 6 0 ) . The importance of the p a r a m e t e r warr a n t e d t h a t a s t u d y be made to determine if scale readers were changing L1 estimates by mislocation of the first annulus. P r e l i m i n a r y analysis of the scale-age d a t a a n d rereads of a random number of scales f o r the 1941-42 through 1961-62 seasons indicated t h a t the only conclusive way to settle the matter was by direct comparison of scale reading between the original scale readers a n d t h e readers then in tenure. This report describes the results of the comparative scale reading.


On March 25-29, 1963, the three original scale readers a n d t h e circa
1963 scale readers met a t Hopkins Marine Station, Monterey, California, to determine whether the l a t t e r readers were following the original
Accepted for publication March 1973.


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readers’ criteria i n reading Pacific sardine scales. Since the three original readers h a d been away f r o m such work f o r so long, certain steps were taken to ensure their ability to read scales i n the same way as they d i d d u r i n g their tenure. F o r practice they were sent, 4 months before the formal meeting, 100 scale slides which each h a d read a n d recorded d u r i n g his tenure. They also practiced as a g r o u p prior to t h e formal meeting, a n d a test was carried out f o r consistency in aging with 60 slides selected f r o m t h e 1 9 4 1 4 2 t h r o u g h 1 9 4 3 4 4 season. They agreed a b o u t 88% of t h e time, which compared favorably to t h e 80-90% agreement when they were i n tenure. T h e 1963 readers d i d not practice b u t were told to read in t h e same m a n n e r as they were doing. A t the formal meeting each reader read independently t h e same preselected scales f r o m 105 scale samples of fish taken i n t h e S a n Pedro, California, fishery. The pre-selected scales were those selected originally by the historical scale readers ( a s recorded on scale cards) a n d were distinguished f r o m t h e others f o r the present test b y encircling with a glass-marking pen. The remaining scales on t h e slide were l e f t i n view to aid each reader i n his evaluation of t h e annulus. Other test scale readings included individual readings on t h e same slides b u t each individual selec+g a scale of his choosing, two-separate g r o u p readings on the same slides, a n d a final reading whereby all seven readers together read a series of slides. All showed the same t r e n d a s is described f o r the test i n the present report. A f t e r viewing the scale on a scale projector, the reader recorded the r a d i i of all annuli, a n d also the margin of the scale on a scale card. The reader went through the same procedure f o r each of the 105 slides; five slides f o r each of t h e 21 seasons f r o m 1 9 4 1 4 2 t h r o u g h 1961-62, the same method used a n d described b y F e l i n a n d Phillips (1948). T h e back-calculated lengths of the fish a t various annuli were obtained w i t h a nomograph by the method of Phillips (1948a). The average L1values were calculated f o r t h e original a n d t h e 1963 readers, respectively, a n d the results compared. T h e average Ll’s f r o m the historical data used to prepare the age a n d length reports f o r t h e Pacific sardine reported by Wolf (1961) were also calculated f o r comparison. RESULTS

A graphic comparison of L1 estimations by seasons f o r both g r o u p s of readers a n d the historical readers shows t h a t the L1estimates of t h e original readers were consistently lower t h a n those of the 1963 readers 1 ( F i g u r e 1).The historical average L h a d a positive t r e n d w i t h time b u t t h e other two d i d not.

A comparison of the scale readings shows t h a t t h e 1963 scale readers were not following the criteria of the original readers. Therefore, the average L1 values which were used as a basic measurement f o r estim a t i n g growth, to separate subpopulations, a n d t o s u p p o r t certain hypothesis about the population needed to be reexamined. F o r example, M a r r (1960) f o u n d a positive t r e n d with time i n the L1values f o r t h e year-classes 1934 t h r o u g h 1955 f o r the fishery a t S a n Pedro. H e assumed t h a t the increase in length of L was caused by biological o r 1



2 0




environmental factors which affected the Pacific sardine ; but, this s t u d y indicates t h e change in L1 was the result of scale reader bias. The consensus of opinions among scale workers is t h a t consistency among a g r o u p of readers, or t h e presence of experienced readers guarantee results comparable to past results, However, there were two experienced readers present a t the time the historical L1 estimation began its a b r u p t increase in t h e mid-1940’s. The present s t u d y indicates t h a t while t h e 1963 readers were consistent among themselves, their criteria were inconsistent with those of the original readers. K i m u r a a n d Sakagawa (1972) concluded on t h e basis of a comparison of L1 of known age sardine with the average L1 of fish aged by t h e early a n d recent scale readers t h a t the early readers’ L1 estimations were closer to t h a t obtained f r o m the known age fish. T h e results obtained here indicate a need f o r some k i n d of s t a n d a r d or length-by-age values to serve as a reference to the readers i n obtaini n g back-calculated length measurements. A suggested s t a n d a r d is a series of random, stratified-by-age scales, i.e., 0-, I-, II-, III-, . . . n-year-old fish scales, preferably selected f r o m the time period when t h e validators of t h e scale (otolith a n d a n y other bony structures used i n a g i n g ) method were i n tenure, or were used by the validators as t h e basis of their study. F o r the sake of simplifying comparative readings a n d as assurance t h a t the same scale will be read a t all times, the initial readers of the s t a n d a r d series of slides should circle t h e selected scale w i t h a marking pen. Similarly, the slides read routinely d u r i n g a season should also be circled by the initial reader so t h a t both a reader a n d the checker can be certain to have examined t h e same scales. The presence of such a set of s t a n d a r d slides probably would ( i ) assure continuity i n the m a n n e r of the scale interpretation by t h e original validators of the scale or a n y other method used i n estimating fish age, ( i i ) counteract a n d monitor the effect of dominance of a n y individual scale reader, a n d ( i i i ) deter the occurrence of similarly costly mistakes a s illustrated i n this study.

CONCLUSIONS T h e circa 1963 scale readers have not been reading like the original readers and, apparently, have not been following the same criteria i n estimating t h e L1.The L1 value change i n time resulted f r o m scalereader subjectivity a n d was not caused by biological or environmental factors. ACKNOWLEDGMENTS My thanks to the original scale readers, Dr. L. A. W a l f o r d , Mr. K. H. Mosher, a n d M r . J. B. Phillips, a n d to t h e 1963 scale readers, Miss A. E. D a u g h e r t y , Mr. H. H y a t t , a n d Mr. R. S. Wolf, f o r participating i n the scale-reading workshop. The editorial assistance of staff members of the National Marine Fisheries Services, a n d t o a number of other staff members of the same organization who gave their time as ‘‘sounding b o a r d s ” a r e acknowledged. RFRNE EE E CS
Felin, Frances E. 1954. Population heterogeneity in the Pacific pilchard. Fish Wildl. Sew., Fish. Bull. 8 6 ( 5 4 ) : 201-225.




Felin, Frances E. and Julius B. Phillips. 1948. Age and length composition of the sardine catch off the Pacific coast of the United States and Canada 1941-42 through 1 9 4 6 4 7 . Calif. Div. Fish and Game, Fish Bull. (69) : 122 p. Kimura, Makoto and Gary T. Sakagawa. 1972. Observations on scale patterns and growth of the Pacific sardine reared in the. labpratory. Fish. Bull., U.S. 70( 3 ) : 1,043-1,052. Rlarr, J o h n C. 1960. The causes of major variations in t h e catch of the Pacific sardine, Sardinops caertclea ( G i r a r d ) . Proceedings F A 0 World Sci. Meet. Biology of Sardines and Related Species, Rome, 14-21 September 1 9 5 9 ; 667-791. Phillips, Julius B. 1948a. Comparison of calculated fish lengths based on scales from different body areas of the sardine, Sardinops caerulea. Copeia, 1948, 2 : 94-106. 1948b. Growth of the sardine, Sardinops caerulea, 1941-42 through 1 9 4 8 4 7 . Calif. Div. Fish and Game, Fish Bull. (71) : 33 p. Walford, Lionel A. and Kenneth M. Mosher. 1943a. Studies on the Pacific pilchard or sardine (Sardinops caerulea) 2. Determination of t h e age of juveniles by scales and otoliths. U.S. Fish Wildl. Serv. Spec. Sci. Rep. 21, 2 9 p. (Reissued in Spec. Sci. Rep. Fish. 15 : 31-95,1950.) 1943b. Studies on the Pacific pilchard or sardine (Sardinops caerulea). 3. Determination of age of adults by scales and effect of environment on first year’s growth a s i t bears on age determination. U.8. F i s h Wildl. Serv. Spec. Sci. Rep. 21, 29 p. (Reissued in Spec. Sci. Rep. Fish. 15 : 96-131, 1950.) Wolf, Robert S. 1961. Age composition of the Pacific sardine 1932-1960. U.S. Fish Wildl. Serv. Res. Rep. 53, 36 p.



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