### Age and Growth of Klamath River Green Sturgeo n (Acipenser medirostris)

Prepared by: Rodney J. Nakamoto U. S. Forest Service Redwood Sciences Laboratory 1700 Bayview Drive Arcata, Californi a 95521 and Tom T. Kisanuki Greg H. Goldsmith U. S. Fish and Wildlife Service Coastal California Fish and Wildlife Office 1125 16th Street Arcata, California 95521

Funded by:
U.S. Fish and Wildlife Service Klamath River Fishery Resource Office 12 15 South Main Street, Suite 212 Yreka, California 96097

Project # 93-FP-13 January 31, 1995

### Age and Growth 

### of Klamath River Green Sturgeo n 

### (Acipenser medirostris)

Rodney J. Nakamoto U. S. Forest Service Redwood 

### Sciences Laboratory 1700 Bayview Drive Arcata, California 95521

Tom T. Kisanuki Greg H. Goldsmith U. S

. Fish and Wildlife Service Coastal California Fish and Wildlife Office 1125 16th Street Arcata , California 95521

Funded by: U.S. Fish and Wildlife Service Klamath River Fishery Resource Office 

### 1215 South Main Street, Suite 212 Yreka, California 96097 Project # 93-FP-13

January 

### 31, 1995The mention of trade names of commercial products i n this repor t does not constitute endorsement by the U.S

. Forest Service or the U.S. Fish and Wildlife Service.LIST OF TABLE S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*................. ii
LIST OF FIGURE S . . . . . . . . . . . . . . . . . . . . . ..*................................... . iii ABSTRACT .. . . . .. . . . . . . . . . . . . . . . . . .. . . . ..*......... iV INTRODUCTION . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .1 STUDY ARE A . . . . . . . . . . . . . ..*...........................*....................... 2 METHOD S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*........................ 2 Field Procedure s . . . . . . . . . . . . . . . . . . . . . . . . . ..*...........................* 2 Beach Seinin g . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Net Harvest Monitorin g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*........... 4 Laboratory Procedure s . . . . . . . . . . ...*..................................*.. 5 RESULT S . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 5 DISCUSSIO N . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . 11 RECOMMENDATION S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*........*.......... 15 LITERATURE CITE D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18LIST OF TABLES

1. Regression equations developed for the relationship between fork length (fl, cm) an d total length (tl, cm) of green sturgeon (Acipenser medirostris, Ayers) measured from the Klamath River, California, 1990-199 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*............................ 6LIST OF FIGURES

Figure 1. Map of the Klamath River and Yurok Indian Reservation depicting sample reache r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Mean an d range o f lengt h at age for sturgeon age d using the Optical Patter n Resoulution System (OPRS) and microfiche reader. Estimates using the microfiche reader are the average of two independen t reading s a . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.

4.

5.

6.

7. Length-frequency distribution (5 cm groupings) for male, female, and unknown sex green sturgeo n measured fro m the Klamath River, California, 1990-99 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Length-age relationship for male, female, juvenile, and unknown sex green sturgeon measured from the Klamath River, California, 1990-199 3 . . . . . . . . . . . . . . . . ..*..................

. 10

Length-frequency distributions of green sturgeon measured as part of the beach seining and Native American gill net harvest monitoring activities conducted by the U.S

. Fish and Wildlife Service, Arcata, California, in the Klamath River for periods 1979-1982 an d 1990-1993............................12

Mean, range, and sample size fo r total lengths of male and female green sturgeon measured from the Klamath River, California , 1980-1982 and 1990-199 3 . . . . . . . ..*..................... 13

Mean length at age for green sturgeon measured from the Klamath River, California, between 1980-1982 and 1990-1993........16

iiiDuring 1990 through 1993, green sturgeo n (Acipenser medirostris) pectoral fin rays and biologica l 

### data wer e collected as par t of the Native American gill net harvest monitoring program 

### and beac h seining program conducted by the U.S. Fish and Wildlife Service (USFWS) , Coastal California Fish and Wildlife Office (CCFWO) , in the Klamath River, California. These data 

### were utilized jointly by the U.S. Forest Service,Redwo od Sciences Laborator y (RSL) and CCFWO to assess the age and growth of Klamath River green sturgeon. This project was funded by the Klamath Rive r Basin Fisheries Task Force, a program funded through th e USFWS ' Klamath River Fisheries Resourc e Office, in Yreka, California. Pectoral fin rays fro m 

### 154 green sturgeon were sectioned and aged by two independent readers. Thirty-four percent of the age estimates differed by lees than two years. Sixty-six percent differed b y less than five years. The irregular shape of the fin ray combined wit h close spacing and discontinuity of the circuli and incorporation of secondary fi n rays contributed significantly to the variability in age estimates between 

### readers

. Upstream migrant female green sturgeon were less numerous, older, and longer than male sturgeon. Green sturgeon harvest and life history data suggest that male sturgeon become sexually mature sometime after reachin g 

### 120 centimeter (cm ) total length ; while female sturgeon mature after attaining approximatel y 

### 145 cm total length. The results suggest that green sturgeo n 

### life histor y can be divided into three general phases : 1) freshwater juveniles (~3 ye ars old); coastal migrants 

### (3-13 years old for females an d 3-9 years old for males; and adults 

### (213 years old for females and 2;9 years old for males).

i vDuring 1992 , the U.S. Fish and Wildlife Service, 

### Coastal California Fish and Wildlife Office (CCFWO), and the U.S. Forest Service, Redwood Science Laboratory (RSL) were jointly funded through the Klamath River Basi n Fisheries Task Force to conduct an ag e and growth investigation on green sturgeon (Acipenser medirostris) from the Klamath River. This Task Force wan created under the provision of the passage of the 1986 Klamath River basin Conservation Area Fish ery Restoration Program (P.L. 99-552). This public law was initiated to restore the anadromous fish stocks of the Klamath River basin, and t o offset the effects of dams, floods, timbe r harvest, mining, and other detrimental impacts (Klamath River Basin Fisheries Task Force 1991). Within California, green sturgeon have been reported i n the Sacrmento, Eel, Klamath and Trinity river systems. Presently, green sturgeon have disappeared from the Eel River. Green sturgeon tend to spend much of their life i n the ocean (Chadwick 1959, Mille r 1972), returning to freshwater streams to spawn. Tagging information suggests that there is significant interchange among green sturgeon populations along the Pacifi c Coast (Chadwick 1959). Klamath and Trinity river green sturgeon are unique i n that they represent the only California population which migrat e significant distances upstream (Fry 1973). Currently, information pertaining to green sturgeon biology is scarce (Housto n 1988). The USFWS has identified green sturgeon as one of five stocks of special concern due to their depressed stock status (USFWS 1988). Further , Moyle (1989) identified green sturgeon in California as a species of uncertain status needing additional investigation. Basic information pertaining to the ecolog y of any fisher y population is essential for effective management. The scarcity o f information pertainin g to green sturgeon ecology is a significant barrier to developing an effective management plan for this species. The objectives of this study were to:

1. Define the age composition of sturgeon harvested in th e 1990-1993 Klamath River gill net fishery.

2. Define the age compositio n of gree n sturgeon captured incidentally in CCFWO's 1989-1990 beach seining project in the Klamath River estuary.

3. Provide descriptive growth data on Klamath River green sturgeon.

4. Determine the utilit y of pectoral fin ray sections in estimating age of green sturgeon. the5. Examine the utility of using Optical Pattern Recognition System (OPRS) for age and growth interpretation work of green sturgeon.

6. Expand the current biological database on gree n sturgeon.

The Klamath River originates in Oregon and flows in a southwesterly direction into California. The Klamath River drains approximately 14,400 square kilometers (kd) and 26,000 km2 in Oregon and California, respectively. Iron Gate Dam on the Klamath River at river kilomete r (rkm) 306, an d Lewiston Dam on the Trinity Rive r (rkm 179) represent the upper limits of anadromous Salmonid migration in thes e basins. The Klamath Rive r has historically supported larg e runs of anadromous fish such as chinook salmon (Oncorhvnchus tshawvtscha) , steelhead trout (p. mykiss) , eulachon (Thaleichthys pacificus) , Pacific lampre y (Entosphenus tridentata) , and smaller runs of coho salmon (O. kisutch) and green sturgeon Acipenser medirostris)

. These fisheries have significantly contributed to subsistence, sport , and commercia l fisheries in California. Generations of Native Americans have utilized fishing grounds in the Klamath River basin. Salmon , steelhead, and sturgeon have historically provided the mainstay of the Native American economy and culture in the are a (Bearss, 1981).

Field Procedures
Sturgeon data and biological samples were collected from the mouth of the Klamath River , upstream 70 rkm to th e river's confluence with the Trinity River , at Weitchpec, CA. The Klamath River flows through the Yurok Indian Reservation throughout this distance (Figure 1). The data and samples were collected in conjunction with the Native American gill net harvest monitoring and beac h seining activities conducted by the CCFWO, Arcata, California, during the 1990-1993 seasons. Beach Seininq. The beach seining program in the Klamath River estuary was conducted to target the adult run of fall chinook salmon. This program

was terminated after the 1990 season. During the 1990 season the sampling period extended from Jul y 23 t o October 2. Seining times for the 1990 season varied daily to target the tidal period from before slack low tide to immediately after the slack low tide. Seining schedules were conducte d during daylight hours. Sturgeon catch during the beach seining operatio n was

2\Tenver Creek

Monitoring boundries Yurok Indian Reservation boundary

Middle Klama th Area



# . . . *

‘. ‘.

. -e-

_ I --. 

# A

% ‘.

. . -. 

# 9 ‘.

. . 

# 4

. . . 0; ‘. : i __ Johnson 1

-..
-. ‘. Pecwan Creek

., : ‘. \ -. ‘.

. . . Upper Klamath Area

Trinity River-\ 

### Figure 1. Map of the Klamath River and Yurok Indian Reservation depicting sampling reaches.

3largely dependent on the physical characteristics of the seinin g site. Those sites which were characterize d as off-channel, slow-water habitats favored sturgeon capture. A 150 meter (m ) x 6 m beach seine net with a 5.4 cm bar mesh bag section was deployed wit h a jet boat , and retrieved to shore using gas-powered winches. Eight net sets were made each sampling day. Captured sturgeon were identified to species , measured for fork and total length, weighed , tagged with a Peterson disc tag , and a pectoral fin was excised prior to release. Fins were stored in plastic bags and frozen prior to conducting laboratory processing and analyses. Net Harvest Moitoring. Coastal California Fish and Wildlife Office staff monitored the spring and fall Native American gill net fishery which target anadromou s salmonids an d sturgeon in the Klamath River. Detailed descriptions of the monitoring methodology are available in USFWS (1992)

. The spring monitoring period generally begins in early April, and concludes in mid-July. The number of sturgeon captured was generally dependent on spring flows. High spring flows hamper the operation of the Native American gill nets resulting in lower harvest rates and therefore fewer sturgeon available to measure. The fall fishery monitoring begins in mid-July, and usually ends in latter September , although in some years , dependent upon fishing quotas, has extended into October and November. Gill net harvest information was collected b y CCFWO crews from three contiguous areas (estuary, middle Klamath, and upper Klamath) of the Klamath River on the Yurok Indian Reservation (Figure 1). The estuary area was defined as the lower 6 rkm, from the mouth to the U.S. Highway 101 bridge. The middle Klamath area is from the 101 bridge to Surpur Creek, a distance of 2 7 rkm

. The upper Klamath area constitutes the final 3 3 rkm, beginning at Surpur Creek and ending at the confluence with the Trinity River, at Weitchpec, CA. During periods of allowed fishing , CCFWO crews surveyed gill net fishermen in th e estuary at two hour intervals. Native American fishers were interviewed during each time stratum to obtain information on the number of each fish species caught , the type and number of nets fished, and the number of hours fished. Those fishes made available by the fishers for examination were identified to species, measured, weighed, examined for identification characteristics (fin-clips, tags, etc) , and sampled for scales (salmonids) or pectoral fin rays (sturgeon). The fins were transported to the laboratory and frozen until processing. Sex determinations were made based on examination of gonads. In those cases when the gonads were not available for examination the sex was listed as unknown. The fishery was monitored fou r to fiv e days per week i n the middle and upper Klamath areas during the allowed fishing period. CCFWO crews interviewed Native American fishers for netting effort and biological information , in the manner previous described.

4Laboratory Procedures
Frozen pectoral fin rays were thawed in boiling water, an d defleshed with

a stiff brush. The leading fin ray was isolated, and allowed to air dry. The fin rays were mounted on plywood strips and thin-se ctioned using a lapidary saw (Raytec , Jem Saw Model 45) , in accordance to methods described by Brennan and Cailliet (1989). The fin ray sections were then adhered t o a glass microscope slide using clear nail polish. The fin ray sections were examined with a microfiche reade r equipped with

a 30x lens. Banding patterns on the fin ray sections were interpreted in accordance to criteria outlined by Brennan and Cailliet (1989). It was assumed that the combination of one translucent (formed during th e summer) and one opaque (formed during the winter) band represented a single years growth. The authors examined the fin sections independently and assigned numerical values to indicate the numbe r of summer growth (annular) bands for each individual fish. A Optical Pattern Resolutio n System/t m - (OPRS, BioSonics 1985) was employed to determine the feasibility and utility of this system in interpretin g green sturgeon fin ray sections. This system utilizes 

### a Ikegami (model ICD-4422) video camera linked to a Olympi c BH2 microscope via a Olympi c MTV-3 coupler. The camera interfaces with Biosonics OPRS software based o n a 386 microcomputer. Prepared fin ray sections were placed in the microscope and the image was projected onto a video monitor. A reference line wa s 

### drawn fro m the center to the posterio-lateral margi n of the fin ray section and the software was allowed to select annular locations based on differential light transmission between winter and summer growth bands. The lo cations of each of the selected annuli were evaluated by the operator. All measurements for a part icular fin ray were store d as recor ds in a computer file.

Between 1990 and 1993, 243 sturgeon were measured as part of the Native American gill net harvest monitoring program and 30 sturgeon were measured as part of the beach seining program on the Klamath River. Regression equations were developed for the relationship between fork length and total length for males, females, and males and females combined (Table 1). Examination of P statistics and correlation coefficients for the equations suggested that the combined male and female equation best explained this relationship. The leading pectoral fin ray fro m 154 of the 243 sturgeon collected between 1990 and 1993 was prepared for age and growth assessment. Ages were assigned to 148 sturgeon by two independent readers. Thirty-four percent of the two age estimates differed by less than two years. Sixty-six percent of

STable 1. Regression equations developed for the relationship between fork length (fl, cm) and total lengt h (tl, cm) of green sturgeo n (Acip enser medirostris, Ay ers) measured from t he Klamath River, 1990-193.

Sex n Model r2 p Mal e 58 tl = -2.087 8 + 1.1202(fl) 0.99 0.0001 Female 33 tl = -8.306 0 + 1.1597(fl) 0.95 0.0001 Combined / 1 91 tl = -4.6131 + 1.1374(fl) 0.98 0.0001

6the ago estimates differed by less than 5 years. The average difference between ago assignment s war 4 year8 (range O-19 years). The mean of readings assigned by reader 1 (2 1 years , range 1-45 years) was 1 year greater than the mean of readings assigned b y reader 2 (2 2 years, range 2-54 years). Age assignments fo r 115 o f the 148 sturgeon wer e also mad e using the OPRS system

. The average age assigned by the OPRS syste m 

### was 29 years (range 1-72 years). Age assignments by the OPRS age assignments using the microfiche system were consistently older than the reader. OPRS age assignment s averaged 8 years greater than the average ag e assignment using the microfiche reader. Total length variation withi n 

### a given age war greater for those sturgeon aged using the OPRS system compared to those aged using the microfiche (Figure 2). In addition, the OPRS results suggested that betwee n ages 1-9 total length (tl) remains nearly static. Greater magnification, image clarity, and the computer enhanced ability of the OPRS system to differentiate between light and dark banding patterns may have resulted in the counting o f false or incomplete annuli which resulted in th e greater variabilit y in the length-age relationship. Due to the greater variability in the data noted for th e OPRS readings and the poor relationship at young ages, the average of the two microfiche readings will be used for furthe r discussions of age. Weight information was collected in conjunction wit h fork length (fl) data fo r 56 males, 31 female s and 23 individuals of undetermined sex

. Male sturgeon averaged 58 kilogram8 (kg) (range 20-112 kg) while female sturgeon averaged 94 kg (rang e 29-148 kg). The relationship between fork length and weight, and total length and weight wer e described by: weight = -27.9903 + 0.0039(fork length')

n = 90 r& .85 p < 0.0001 weight = -20.0434 + 0.0027(total length

n = 110 r& .58 p < 0.0001 Sex was determined for 165 individuals between 1990-1993. Female sturgeon were less abundant, older , and significantly longer than male sturgeon (Figures 3, 4). Female sturgeon averaged 32 years old (range 22-46 years) while males averaged 23 years old (range 9-45 years). Sturgeon <60 mm tl were collected primarily during the beach seining operations within the Klamat h River estuary. The beach seining operation was discontinued after the 1990 season. During 1990 , 27 smal l green sturgeon were captured. These fish averaged 52 mm tl (range 32-66 mm tl). Age estimates for these individuals indicated that these individuals averaged 3 years old (range l-4 year s old). Previous years' data indicate that withi n the

7

## Age 

## (years)

Figure 2

. Mean and range of length at age for sturgeon aged using the Optical Pattern Resolution System (OPRS) and microfiche reader. Estimates using the microfiche reader are th e average of two independent readings.“a3,171-17sswqI176-180*‘”181-165*w;l186-1903196-20020102t%206-2102ll-21s216220221-225226-230231-235236240241-245246-250251-255-260!

### 300- I 275-

. 250-

. 0 

### 225-

. 0



### z 200-

. s 175, 5

. g) 150- a o, 8 

### 5 125-

. g loo-

. 75'

. 50-A A ' ri A 25-

.

0 I

- I

- " ' I

- n

- a
- n

- ' 1

0 5 10 15 20 25 30 35 40 45 50 Age 

### (years)
Figure 4. Length-age relationship for male, female, juvenile, 

### and unknown sex green sturgeon measured from the Klamath River, California, 1990
- 1993.

10Klamath River estuary the abundance of these smal l sturgeon peaks between July and September. Juveniles generally spend up to 3 years i n freshwater prio r 

### to migrating to sea , primarily durin g the summer-fall perio d (Em m ett et al. 1991, USFWS). A conspicuous lack of individuals measuring between 71-115 mm was observed in the length-frequency distribution for sturgeon collected between 1990 and 1993 (Figure 5). Similar length-frequency distributions were obtained by the USFWS (1982, Figure 5)

. Previously published information suggests that individuals within thi s size range are migratory marine residents and seldom venture into freshwater. We further ex amined data collected on 610 green sturgeon measured i n the Klam ath River between 1980 and 1993. Previously published information indicates that green sturgeon can reach 230 cm fl (256 cm tl) and 159 kg (Hoyle 1976). However , they seldom exceed 130 cm fl (144 cm tl) a n d 45 kg (Skinner 1962). Within this study , 431 of the 610 individuals exceeded 130 cm fl (mean 160 cm , range 132 -233 cm). We compared the lengths of male and female sturgeon measured between 1980-1982 to those measured between 1990-1993 (Figure 6). The results demonstrate that the patterns noted between 1990-1993 wer e l similar to those noted between 1980-1982. Female sturgeon were generally larger and less numerous than male sturgeon.

DISCUSSION
Significant difficulties were encountered in aging the pectoral fin ray sections. The annular patterns consisted of alternating dark and translucent bands. The wide dark bands result from the abundant formatio n of connective tissue during the summer , converted later to bone tissue; the narrow translucent bands correspond to the perio d of metabolic inactivity during the winter (Brennan and Cailliet 1991). Examination of the prepared fi n ray sections using a microfiche reader revealed that annular patterns within the sections 

### were extremely difficult to differentiate. The irregular shape of the fin ray combined with close spacing and discontinuity of th e circuli and incorporation of secondary fin ray s made confident age assessment difficult. These difficulties have been encountered by other researchers (Roussow 1957, USFWS 1983, Brennan and Cailliet 1989). The observed variability in sturgeon size at each age appears to be characteristic of sturgeo n studies (Semakula and Larkin 1968, Kolhorst et al. 1980, USFWS 1983). Kolhorst et al. (1980) suggested that size variation at each age may be real. The reduced growth rates of older fish and prespawning age fish , formation of spawning checks, long migrations or adverse environmental conditions may contribute to decreased ability to accurately assess age from pectoral fin ray sections

11

### 10 

### 9 8 7
6 5 4 3 2 1 0 -

-

-

I

-

I

-

I

-

-

-

-

-

-

-

I

-

m

-



### 10

9
8 7
6 5 4 1979-1982 n=187



### 19904993 n=154

Figure 5. Length-frequency distributions of green sturgeon measured as par t of the beach seining and Native American net harvest monitoring monitoring activities conducted by the U.S

. Fish and Wildlife Service, Arcata , California, in the Klamath River for periods 1979-l982 and 1990-l993.

1229

47

fj 30 

# I “‘]] 34 

## 24 

# 1 23 

# I 36

I,

0

L 11



### 100 ' 

## 1980 1981 1982 1990 1991 1992 1993 

## Year
Figure 6. Mean, range , and sample size for total lengths of male and female green sturgeon measured in the Klamath River, California, 1980-l982 and 1990-1993.

13(Roussow 1957 , Sokolov 

### and Malyutin 1978, Kolhorst et al. 1980, Keenlyne and Jenkins 1993, Rein and 

### Beamesderfer 1994). The relative rarity of males between ages 3-9 years an d 

### females between the 

### ages of 3-13 years suggest s that these individuals spend 

### relatively little time in freshwater. Within the Klamath River these individuals are usually observed between July and October (USFWS 1982, 1983, 1992). Previous reports have documented the marine migratory behavior o f subadult and adult green sturgeon. Green sturgeon tagged in San Pablo Bay were recovered as far north
as Gray’s Harbor and as far south as Santa Cruz (Chadwick 1959; Miller 1972). Roedel (1941) reported the capture o f a green sturgeon weighing 3.3 kg offshore between the towns of Huntington Beach and Newport, CA. Chadwick (1959) concluded that there i s considerable interchange between green sturgeon populations along the 

### Pacific Coast. Females unde r 145 cm t l 

### did not appea r in the record. The smallest female sturgeon sampled between 1990 and 1993 was 148 cm tl. Size selectivity of the gill net would not preclude capture of females smaller tha n 145 cm tl as individuals under this size are commonly caught. The absence of small females in the harvest suggests that either prior to reachin g 145 cm tl gonadal development was insufficient to determine sex or that female s 

### return to freshwater sometime 

### afte r reaching 145 cm tl. This length would correspond to an age of abou t 13 years old. Males generally appeared in the harvest record after reaching 120 cm tl (8 years old). The size at which males mature is 

### questionable as the gill net sampling efficiency i s 

### biased toward individuals greater than 120 cm tl. In addition, sex determination was based
on gonadal observations. In many cases individual sturgeon less than 120 cm tl may have been caught but due to their small size they were released. In these cases, the observers would not have been able to determine sex. Although the length frequency distribution suggests that male sturgeon may begin spawning sometime after reaching 120 cm tl, this conclusion is tentative ; male sturgeon may become reproductively active prior to reaching 120 cm tl. The data suggests that male green sturgeon may become reproductively mature 

### at a younger 

### age than female green sturgeon. Differences in age at first spawning between sexes have bee n noted for other sturgeon species. Semakula and Larkin (1968) noted that the age at first spawning for white sturgeon (Acioenser transmontanus) from th e Frasier River is 11-22 years (81-137 cm tl) for males an d 11-34 years (81-231 cm tl) for females

. Roussow (1957) reported age at first spawning for lake sturgeon (Acioenser fulvescens) in Canada varied between 12-19 years and 14-23 years for males and females, respectively. Keenlyn an d Jenkins (1993) reported tha t male pallid sturgeon mature at ages 5-7 years while females ma y begin spawnin g sometime after 17 years old.

14The use o f pe ctoral fin rays for estimatin g the age of sturgeon was not a precise method

. However , these results do not totally discount the utility of this method. Comparison of the length-age relationship reported b y the USFWS (1983) to the relationship obtained in the herein reveals 

### that the relationehips are ver y similar (Figure 7). The similarity in the relationships adds more strength to the utility o f pectoral fin ray analysis. The pectoral fin ray analysis offers a simple and practical tool for fisheries managers. The pectoral fin rays can be obtained without sacrificing the sturgeon. Green sturgeon are a long-lived species, with a life span of several decades. Age estimates fo r nearly 70% o f the individuals differed by less than 5 years . The results o f this study an d previously published information suggest that green sturgeo n life history can be divided into three general phases : 1) freshwater juveniles years old), 2) coastal marine migrants (3-9 years fo r males , 3-13 years fo r females) and 3) adults. Further research aimed a t investigating spawnin g periodicity, fecundity, survival, and the degree to whic h adults may use rivers other than their nata l rivers for reproduction is neede d in order to effectively manage this long-lived species
.

The OPRS system may be a valuable tool for gree n sturgeon age assessment. The computer assisted technology offer s a fast and precis e means of fin ray i nterpretations. In contrast to the microfiche, th e OPRS may over-estimate the age of sturgeon. This was attributed to the acute discriminato ry abilities of the OPRS system. Additional experimentation and calibration may be necessary to fully utiliz e this technology for age analyses of sturgeon fin
rays . The utility of this system should be further explored. The use of pectoral fin rays in this study for estimating the age of sturgeon was no t a precise method. However, the observed variability between age estimates does not totally discount the utility of this method . The us e of fi n rays offers a simple and practical tool for fishery managers. The fin rays can be obtained without sacrificing the sturgeon. The fin rays are readily sectioned , and most managers possess the skills necessary to perform the age interpretation work. Green sturgeon are long-lived, with a life span of several decades. Age determination increased in difficulty with increased ag e of the sturgeon. At present, fin ray analysis is the most readily available method of estimating sturgeon age. This method in

c onjunction with biological data is extremely useful for estimating the age at which these fish become reproductively mature. The use of a high quality lapidary saw with is imperative for producing precise, thin cross this study was marginal, and had to be modified

15 a micro-adjustable feed ramp sections. The saw utilized in with a " home-made" feed

### 250

200 - 

### 1980-1982
-+- 1990-1993 l



### 1 0 2 0 3 0 

## Age (years)

Figure 7

. Mean length at age for green sturgeon sampled from the Klamath River, California, between 1980-l982 and 1990-1993.

16mechanism

. We found it difficult to produce consistant cross sec tions, thus necessitating repeated l efforts. The inabilit y of the operator t o smoothly feed the fi n rays stemmed from the inferio r mechanism. Initiation of sturgeon tagging programs in orde r to provide validation for aging techniques , and information pertaining t o the recurrence of 

### l spawning and dispersion along the Pacific coast would be helpful. Application of external tags in conjunction with biological markers (much a s tetracycline) would allow age validation , and provide empirical information on growth rates, and migration characteristics. The external tags would help identify whether sturgeon tagged in the Klamath River basin areutilizing other Pacific Coa st re utilizing other Pacific coast rivers and bays , and whether green sturgeon utilize multiple nata l waters. Continuation of data collection in conjunction with the Native American gill net fishery i s recommended

. On-going data needs include collectio n of length-weight data , s e x r atios , and gonadal development and fecundity. This long-term information is necessary to monitor any potential changes in the sturgeon age and siz e composition, and sex ratio. Consideration of the timing of collection of fin ra y samples may increase the accuracy of age estimation. Rein and Beameederfer (1994) noted that within the Columbi a River system, fin rays should be collected either before May or after July in order to better ensure that annular formation was complete. In conjunction with age and growt h assessment work, conducting genetic stock identification work on green sturgeon would be very helpful towards the defining potentially distinct Pacific coast populations. Green sturgeon are assumed to be highly migratory , are they utilizing multiple natal streams? Are there distinct populations of green sturgeon, or o ne common gene pool? Answers to these questions would have profound implications for the future of sturgeon management. There is considerable need to understand the biolog y of green sturgeon, yet most government agencies are constrained by budgetary and personnel limitations. We recommend that fishery managers coordinate, and utilize an integrated approach to share research needs and costs. This coordination would prevent work duplication and promote comparable data.

17

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20