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Gear, sampling design, and catch processing generally followed the procedures
in Dark et al. (1983). Several differences in the collection and care of otoliths
have been described by Boehlert and Yoklavich (1984). Otoliths used in the
present study were initially collected for other work; therefore, fish comprising
the age subsample were systematically chosen until a predetermined number
for each size class was attained. When mortality rates were estimated in the
present study, the original age subsample was applied to a simple random
sample of length-frequency data to remove any potential sampling bias (Dark
1975) which may have been introduced during sample collection.

The length-frequency data were chosen for each species in the following
manner. For 5. pinniger, the limited length-frequency data from the 1980 survey
were combined with length-frequency data collected in 1980 by the Washing-
ton Department of Fisheries and the Oregon Department of Fish and Wildlife.
For 5. diploproa, the length-frequency sample was restricted to fish from lat 40°
26' to 48° 47' N, where 76% of the fish in the age sample were collected. This
was done because Boehlert and Kappenman (1980) detected increases in
growth rate with latitude for 5. diploproa when specimens were compared from
this and two other geographic regions (i.e., lat 34°-37°, 37°-40°, 40°-48° N).
Thus, all 5. diploproa otoliths were analyzed as a single stock, even though 24%
were collected south of 40° N, in order that the effects of using surface versus
section ages could be evaluated with as large an age sample as possible.
Resulting growth curves would most likely represent fish from the northernmost
strata (40°^8° N) described by Boehlert and Kappenman (1980).

Ageing

Ages were determined from the same whole and sectioned left sagittal otolith
of 5. diploproa and 5. pinniger by one of three readers from the same
laboratory. The variability in ageing the otolith data set within and between
readers is presented in Boehlert and Yoklavich (1984). Surface ages for both
species were derived from whole otoliths by the method of Boehlert and
Yoklavich (1984). The otolith was read from the focus to the dorsal edge or, in
the case of older individuals, from the focus to the posterodorsal region (Figure
1A, IB). Otoliths from many older specimens, particularly 5. diploproa, possess
posterior projections. Pairs of translucent and opaque bands in these regions



■|48 CALIFORNIA FISH AND CAME

were included in the counts for 5. diploproa but not for S. pinniger;
methodology for the latter species follows the general technique in Six and
Norton (1977).




FICURE 1. External surface of the whole otolith from (A) a 32 cm fork length (FL) female Sebastes
diploproa with a surface age of 22 years and a section age of 25 years, and (B) a 52 cm FL
male 5. pinniger with a surface age of 18 years and a section age of 19 years. (C) anterior,
(D) dorsal, (F) focus, (P) posterior, (V) ventral, (W) posterior projection.

Dorsoventral otolith sections (0.4 mm thick; Figure 2) were obtained with a
double-bladed diamond saw; each section was mounted on a microscope slide
and polished to remove surface artifacts (Nichy 1977, Boehlert 1985). The
otolith section was read (30X or 100X) from the focus to the dorsal edge. For
older individuals, the reader began counting toward the dorsal tip, then
followed a distinct ring from the dorsal region of the section into the internal
dorsal quadrant and continued counting towards the section edge (Figure 2).

In many species of rockfishes, surface and section ages tend to agree for
younger individuals (Beamish 1979b, Shaw and Archibald 1981, Boehlert and
Yoklavich 1984). For example, C. Boehlert and M. Yoklavich (unpub. data)
systematically subsampled every fourth otolith pair from 5. diploproa and every
third otolith pair from 5. pinniger used in this study and found mean differences
between surface and section ages of < 2 years for 5. diploproa females aged
< 1 2 and males < 1 7 years and 5. pinniger females < 7 and males < 8 years. For
this reason, we assigned a section age equal to the surface age for all remaining
otoliths with surface ages less than or equal to the values listed above. Thus, an
otolith from an 5. pinniger male with a surface age of 6 years was given a section
age of 6 years if the otolith had not been included earlier in the subsample. This
procedure allowed an increased sample size.



ROCKFISH AGEING TECHNIQUES 149




FIGURE 2. Dorsoventral cross section of the left otolith from a 31 cm fork length (PL) Sebastes
diploproa with a surface age of 28 years and a section age of 39 years. (D) dorsal, (F)
focus, (E) external surface, (I) internal surface, (V) ventral. Surface ages were
determined by counting rings on the external side of the otolith from the focus
towards the dorsal edge.



Mortality and Growth Rates

Total instantaneous mortality rates (Z) were estimated by calculating the
slope of the descending right side of the age-frequency distribution (catch
curve) by simple linear regression (Ricker 1975). Total instantaneous mortality
rates were compared by using an f-test (Meter and Wasserman 1974).

Individual length at age data were fit to the von Bertalanffy growth model
(Ricker 1975) by a nonlinear regression routine (Dixon 1981 ). Von Bertalanffy
growth curves were compared by using the chi-square test for homogeneity of
individual parameters (Rao 1973) and by the method developed by Gallucci
and Quinn (1979) in which the von Bertalanffy growth function is reparame-
terized with the introduction of a new parameter (w). Results of all statistical
tests were considered significant at P < 0.05.

RESULTS
Sebastes pinniger

Otoliths were collected from a total of 363 female and 516 male S. pinniger
specimens between latitudes 43° 11' and 49° 16' N. Females had maximum
surface ages to 22 years and section ages to 34 years (Table 1). Differences
between the two methods were greater for males; maximum surface and
section ages were 25 and 60 years, respectively (Table 1 ).

Fitted growth curves for males based on each ageing method are more similar
than growth curves for females. Estimates of Loo for both sexes based on
surface ages significantly exceeded those based on section ages (by nearly 6 cm
fork length (fl) for females and 4 cm fl for males, Figure 3). The difference in
growth estimates between treatments apparently occurs beyond the region of
the curve where statistical tests on cu are most powerful (Gulland 1983).



150 CALIFORNIA FISH AND GAME

TABLE 1. Mean Fork Lengths at Age (FL in Centimeters) and Standard Deviation (SD) for Female

and Male Sebastes pinniger Based on Surface and Section Ages. S Indicates the Number of
Otoliths.

Surface Section

Age

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

33 — — — — —

34 — — — 1 50.00

Males

2 3 16.00 1.73 2

3 5 21.80 1.30 4

4 3 25.00 3.61 4

5 4 35.25 4.92 3

6 3 35.33 1.53 6

7 20 38.70 3.63 13

8 24 40.42 2.47 22

9 18 43.61 3.45 9

10 29 45.24 2.89 18

11 42 47.00 2.85 20

12 70 48.49 1.85 35

13 69 49.59 2.02 28

14 55 50.22 1.90 22

15 47 51.55 1.77 23

16 52 51.79 2.05 13

17 25 52.84 1.65 23

18 24 53.46 1.82 24

19 9 53.33 1.32 27

20 6 53.67 2.25 27

21 3 53.33 0.58 27

22 4 54.25 0.96 22

23 _ _ _ 12

24 — _ — 12

25 1 57.00 — 12



N


FL


SD

Females


N


FL


SD


4


15.50


0.58


3


15.67


0.58











1


15.00





3


30.00


4.36


3


30.00


4.36


4


31.75


0.50


2


32.00





11


37.27


3.55


8


36.38


3.50


6


37.67


1.86


5


36.80


3.70


18


41.28


2.70


9


41.00


7.63


13


44.08


4.52


16


43.50


3.20


18


46.11


3.43


20


46.10


3.65


37


49.27


2.91


28


46.71


4.47


64


49.92


2.69


50


49.50


3.70


57


52.23


2.49


47


50.64


3.59


38


53.97


2.83


34


52.53


2.26


33


54.48


2.58


18


52.22


3.14


23


55.52


2.13


21


53.90


3.06


14


56.00


1.84


16


54.06


2.64


15


57.00


1.60


13


55.46


2.96


2


59.50


2.12


15


54.80


2.51


2


61.50


3.54


11


55.00


1.73











6


53.83


2.64


1


59.00





4


54.75


1.71











8


56.38


2.39











5


57.20


2.49











5


56.60


2.19











5


57.40


6.07











4


57.00


4.83











1


50.00














3


58.33


1.15











1


58.00






15.50


2.12


20.25


2.50


24.25


3.30


33.00


8.72


34.17


3.31


39.31


3.86


40.36


2.61


43.78


3.03


43.06


4.08


45.05


3.75


47.09


2.73


47.79


2.77


47.45


3.69


47.83


2.37


50.46


2.26


49.13


1.89


50.71


1.90


49.89


1.97


50.48


2.59


51.33


2.11


50.32


2.06


51.50


1.83


50.42


1.83


50.58


3.68


(Conti


nued)



ROCKFISH AGEING TECHNIQUES 151



TABLE 1— Continued

26 — — —

27 — — —

28 — — —

29 — — —

30 — — —

31 — — —

32 — — —

33 — — —

34 — — —

35 — — —

36 — — —

37 — — —

38 — — —

39 — — —

40 — — —

41 — — —

42 — — —

43 — — —

44 — — —

45 — — —

46 — — —

47 — — —

48 — — —

49 — — —

50 — — —

51 _ _ _

52 — — —

53 — — —

54 — — — — —

55 — — — — —

56 — — — 1 56.00

57 — — — — —

58 — — — — —

59 — — — 1 55.00

60 — — — 1 56.00



14


52.07


2.23


8


52.50


2.14


7


52.14


2.34


2


51.00


1.41


5


52.60


1.82


10


52.30


2.63


3


51.67


0.58


8


52.50


1.85


3


54.00


1.00


6


52.83


1.17


3


54.33


4.62


2


52.50


2.12


10


52.80


1.99


1


52.00





6


52.67


1.86


2


54.00


1.41


2


53.50


0.71


1


53.00





1


52.00





4


53.25


1.89


1


50.00





1


48.00





1


52.00





2


52.00


1.41


1


53.00





1


53.00






Catch curves constructed from surface and section ages of 5. pinniger dearly
differed (Figure 4). Regardless of the ageing technique used, however, both
sexes were fully recruited to the fishery by age 12. Estimates of Z derived from
surface and section ages significantly differed for both sexes: Z values estimated
from section ages were 61% less for females and 78% less for males than those
calculated from surface ages (Table 2).



152



CALIFORNIA FISH AND GAME

















K


K


to


U)


Surface


63.40


0.13


0.46


8.09


Section


57.70


0.16


0.14


9.37



363




10



20



30 40

Age (years)



50



60



FIGURE 3. Fitted von Bertalanffy growth curves, parameter estimates (see text for explanation),
and mean lengths at age based on surface (closed circles) and section ages (open
circles) of otoliths from (A) female and (B) male Sebastes pinniger. Points
representing single individuals are not shown. N indicates sample size.



ROCKFISH AGEING TECHNIQUES



153



E

3
Z



o



A


A


//, V , ,




/v


B


/\.




A


C


/ , , , , lA , . . ,




/'^'"K. ,


D


/ —


H{\hA



10



20 30



40



SO 60



Age (years)



FIGURE 4. Catch curves based on (A, C) surface and (B, D) section ages of otoliths from (A,
B) female and (C, D) ma\e Seb^stes pinniger.



Sebastes diploproa

Otoliths from 1,131 female and 922 male 5. diploproa were collected
between lat 36° 49' and 48° 47' N. Both sexes of 5. diploproa reached much
greater ages than those attained by 5. pinniger. Female 5. diploproa attained
ages similar to males and had surface ages to 55 years and section ages to 81
years compared with 46 and 84 years, respectively, for males (Table 3). Growth
curves of either sex based on surface and section ages were essentially identical,
and parameter estimates and co were not significantly different (Figure 5).

Catch curves constructed from surface and section ages of 5. diploproa
clearly differed (Figure 6). In all cases, particularly among females, substantial
variation occurred between year classes, with a succession of weak year classes
between ages 10 and 20. Therefore, Z was determined for fish older than 21
years. As with 5. pinniger, significant differences were found between estimates
of Z derived from surface and section ages for both sexes; estimates based on
section ages were 55% less for females and 76% less for males than those based
on surface ages (Table 2).



154



CALIFORNIA FISH AND CAME



TABLE 2. Estimates of Total Instantaneous Mortality (Z) for Sebssles pinniger and 5. diploproa.
Range Indicates Ages Over Which Z Was Determined.

Surface Section

Sex Z Range Z Range

Sebasles pinniger

Female 0.452 12-22 0.178 12-34

Male 0.405 12-25 0.089 12-60

5. diploproa

Female 0.109 25-48 049 22-71

Male 0.130 23-40 0.031 26-75



50
40
30
20

101-


50










A


*^


^^j^^Sotio


f .-p^7QA^03:^rQrft^o„


o


■e^^"'" o




/




I^ K t.


u


f


Surface


34.54 0.10 -4.34


3.39




Section


34.08 0.10 -4.45


3.37


.... 1


... 1 .... 1 . ,


n = 1131

.. 1 .... 1 .... 1 .... 1


... 1 ... .



40



B




r^^^^


^^J*'^


-^






TT-O






K






K


t.


w


Surface


30.00







16


-1.97


4.79


Section


29.87


n





16
922


-2.01


4.75



I



I I .... I .... I



10



20



30



40



50



60



70



80



Age (years)



90



FIGURE 5. Fitted von Bertalanffy growth curves, parameter estimates (see text for explanation),
and mean lengths at age based on surface (closed circles) and section ages (open
circles) of otoliths from (A) female and (B) male Sebastes diploproa. Points
representing single individuals are not shown. N indicates sample size.



ROCKFISH AGEING TECHNIQUES



155






10 20 30 40 50 60 70 80



FIGURE 6.



Age (years)

Catch curves based on (A, C) surface and (B, D) section ages of otoliths fronn (A,
B) female and (C, D) male Sebastes diploproa.



DISCUSSION
Differences in Growth

The effects of changing the methodology of fish age determination can vary
from a minor error to major differences. Estimates of maximum age in the genus
Sebastes have changed markedly in recent years (Beamish 1979b; Bennett et al.
1982; Leaman and Nagtegaal 1987); thus, one would expect similarly remark-
able differences in estimates of growth within a species. For 5. pinniger,
estimates of the Loo were significantly lower when section rather than surface
ages were used although the increase in the growth completion rate (von
Bertalanffy's k) for both sexes (Figure 3) was not significant. Therefore, when
surface ages are used, errors in ageing incorrectly place older, larger individuals
into younger age groups, thus inflating their mean lengths at age (Wilson 1985).
This results in lower mean lengths at age for many of these section age groups
relative to surface age groups, and a corresponding decrease in Loo based on
section ages.

Another explanation to account for the differences between growth curves
constructed from surface and section ages in 5. pinniger is that a curve fitting
problem occurs, particularly for females. Thus, Loo may be overestimated when
data are available for only the ascending limb of the von Bertalanffy growth
function (Knight 1968, Gallucci and Quinn 1979, Vaughan and Kanciruk 1982).
Note that the estimate of Loo is typically greater than the maximum observed
length in our study (Table 1, Figure 3). Because surface ages have a lower range
than section ages and are more concentrated on the ascending limb of the
growth curve, they may fail to adequately estimate the upper portion of the



156 CALIFORNIA FISH AND GAME

curve, which represents Loo. For example, the large differences between
estimates of L oc for female 5. pinniger may occur because their surface ages are
more concentrated on the ascending portion of the curve than are those of
males (Table 1). This situation is analogous to fitting growth curves with
incomplete representation of the range of ages (Hirschhorn 1974).

Unexpected results of our study were the similarities in estimated growth
parameters for 5. diploproa based upon section and surface ages (Figure 5)
despite the much higher maximum section ages (Table 3). This difference from
5. pinniger is likely due to our surface ageing methodology. We suggest that the
surface ageing technique for 5. diploproa has changed over several years to
provide older age estimates. Boehlert (1980), for example, used surface ages
and observed only 0.5% of all specimens in excess of 25 years of age compared
with 18.9% in the present study. Earlier surface ages for 5. diploproa were
assigned without rolling or tilting the otoliths, thus preventing the enumeration
of additional annuli on the posterior "winglike" projections (Figure 1A). More
recently, annuli located on posterior projection (present in older individuals of
many species of Sebastes) have been included in surface age counts in order
that surface ages more closely represent section ages (Chilton and Beamish
1982, Boehlert and Yoklavich 1984). In the present study, surface ages for 5.
pinniger were assigned using standard criteria for this species (Six and Norton
1977) without including these counts (which are typically less well developed
on otoliths of 5. pinniger); the counts were included in assigning surface ages
to 5. diploproa. Thus, while maximum ages increased, counts including the
posterior projection resulted in surface ages closer to section ages and
minimized the higher mean length estimates for ages on the ascending arm of
the growth curve as seen in the surface ages of 5. pinniger (Figures 3, 5). Had
the age estimates from Boehlert (1980) or the "other agency" readers in
Boehlert and Yoklavich (1984) been used, it is likely that differences in growth
parameters similar to those for 5. pinniger would have been observed for 5.
diploproa.

TABLE 3. Mean Fork Lengths at Age (FL in Centimeters) and Standard Deviation (SD) for Female
and Male Sebastes diploproa Based on Surface and Section Ages. N Indicates the Number
of Otoliths.

Surface Section

Age

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18



N


FL


SD

Females


N


FL


SD


8


13.00


1.31


7


12.86


1.35


12


14.83


1.53


14


14.93


1.54


24


16.54


1,38


16


16.50


1.54


36


18.47


2.09


32


17.72


2.04


68


20.40


2.31


76


20.38


2.23


119


22.59


2.02


117


22.60


2.03


125


23.22


2.02


117


23.15


2.04


119


24.97


2.21


130


24.97


2.14


82


25.71


1.92


75


25.73


2.05


61


26.48


2.47


60


26.30


2.68


25


26.56


1.45


30


26.63


1.43


20


27.15


3.28


21


27.00


2.66


13


26.46


2.50


12


25.50


3.53


8


27.50


1.69


4


27.50


1.73


2


28.00


1.41


6


27.17


2.64


11


29.36


2.42


5


28.60


2.07


10


29.30


1.77


7


29.14


1.57


7


29.71


1.60


11


29.45


0.93










(Continued)



ROCKFISH AGEING TECHNIQUES 157



TABLE 3— Continued

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81



13


30.15


15


30.13


10


30.00


21


30.71


18


31.33


17


31.53


25


31.80


18


31.33


14


32.21


23


32.22


20


33.30


21


33.19


14


33.07


9


33.33


17


33.47


7


34.29


17


34.53


15


35.53


12


35.58


15


34.47


10


35.50


6


34.33


8


35.00


5


34.60


4


34.00


7


35.57


2


36.50


4


36.50


5


34.80


2


35.50


2


36.50


2


38.00



1.68 7

1 .06 11

2.45 11

1.55 27
1.88 19
2.37 15
1.91 17
1.97 9

2.46 14
2.19 9
1.81 9
1.57 3
2.40 8
3.16 1
2.15 9

2.56 7
2.53 9
1.60 9
1.73 12

2.50 7
1.90 13
1.86 4
2.14 8

2.51 5
1.41 7
1.13 4
0.71 11
1.00 11
1.64 6
0.71 7
0.71 3
1.41 10

_ _ 4

_ — 4

_ — 5

_ — 8

36.00 1.00 2

_ — 6

_ — 4

_ _ 6

_ — 3

_ — 5

_ — 2

_ — 3

_ _ 4



Males

1 12 11.33 1.61 11

2



8 14.87 0.99 6



29.57


2.15


30.36


1.80


30.36


1.75


30.81


1.49


30.37


1.67


30.80


0.94


30.59


1.37


31.22


1.99


30.79


2.12


31.89


2.15


30.56


2.01


32.67


1.53


32.25


1.75


37.00





33.44


2.30


33.43


1.72


34.22


2.17


33.56


1.51


32.58


1.73


32.57


1.90


33.77


2.86


34.25


2.36


34.38


2.39


33.87


2.00


36.00


1.15


34.50


1.29


33.09


1.97


35.33


3.30


33.29


2.73


33.29


2.43


35.33


0.58


34.50


2.68


34.50


1.91


36.00


1.41


36.00


1.22


35.37


2.45


34.50


2.12


35.83


1.94


34.25


3.10


34.67


2.34


32.00


2.65


35.80


1.92


35.50


0.71


36.33


2.08


35.50


1.29


35.50


1.41


35.00


1.41


35.75


1.71


38.00





34.67


2.08


35.00





30.00


z


39.00





34.00





36.00





34.00





36.00





35.50


3.54


11.09


1.45


15.00


1.10


(Continued)



158


CAI


LIFORNIA Fl


SH AND C/


TABLE 3— Continued




Surface




Age


N


hL


i/J


3


27


16.15


2.16


4


47


17.70


1.92


5


86


19.98


2.02


6


100


21.87


1.86


7


128


23.23


1.82


8


114


24.32


1.91


9


62


24.69


2.05


10


30


24.23


2.16


11


15


25.53


3.20


12


16


25.81


1.83


13


7


26.43


1.72


14


8
9


27.63
28.22


2 07


15


0.83


16


7


27.57


1.27


17


11


27.64


1.43


18


9


28.56


1.51


19


5


28.00


1.22


20


13


28.92


1.12


21


9


28.44


1.67


22


9


29.56


2.13


23


29


28.93


2.20


24


16


29.44


1.71


25


20


29.15


1.31


26


15


29.73


1.10


27


17


30.41


1.84


28


13


30.46


1.39


29


16


29.94


1.18


30


16


30.19


2.48


31


9


30.11


1.90


32


6


31.00


0.89


33


4


29.75


2.22


34


5


30.40


0.55


35


5


30.80


0.84


36


3


30.33


1.15


37


7


30.43


1.27


38


1


30.00





39


2


29.50


3.54


40


4


30.50


1.29


41

42

43


1


31.00





44

45

46


1


31.00





47











48











49

50

51

52

53

54

55

56

57

58

59

60

61




















62

63

64

65












Section



""AT

27

48

79

101

124

119

61

32

21

14

11

6

8

5
10

6

3

9
14
12
14
13
14
15

6

6

5

4

4

6

S

1

2

6

1

1

4

4

2

2

3

4

5

8

5

6

6

2

1

2

1

3

1

6

2

2

2

1

2

2

1

2

1



hi


Si)


16.48


2.08


17.63


2.05


19.77


2.25


21.71


1.96


23.16


1.83


24.12


2.11


24.90


1.79


24.28


2.25


25.52


3.12


25.57


1.70


25.82


2.96


27.67


2.42


27.63


1.30


28.40


1.67


28.50


1.27


27.17


1.17


29.67


1.15


28.67


1.41


28.64


1.08


28.92


1.24


28.32


1.50


29.31


1.18


29.43


1.40


29.13


0.99


27.67


3.88


29.50


0.84


30.20


1.10


28.25


2.50


29.25


0.96


29.33


1.75


30.00


0.71


30.00





30.00


2.83


29.83


0.98


30.00





26.00





30.25


2.63


30.75


1.71


28.50


0.71


29.50


2.12


30.00


2.00


30.25


0.50


29.80


0.84


30.50


1.51


30.20


1.92


29.83


2.86


28.67


1.63


30.50


2.12


31.00





31.50


0.71


30.00





31.33


2.52


30.00





31.50


0.84


30.50


0.71


31.50


0.71


30.00





30.00





29.50


2.12


30.50


1 3 5 6 7

Online LibraryCalifornia. Dept. of Fish and GameCalifornia fish and game (Volume 76, no.3) → online text (page 3 of 7)