1. Methods: Collection of Blue Catfish Otoliths
Bob Greenlee
Department of Game and Inland Fisheries
To gain information related to the populations supporting these fisheries VDGIF has relied on LF EF in fresh-olighaline sections of tidal rivers.
Exploratory work in these systems began in the early 1990’s and
During the period 2001/2002, standardized fixed station survey work began in four river systems – the James, Mattaponi, Pamunkey, and Rappahannock

2. Four Tidal River Systems
Stations in
Four Tidal River Systems
To gain information related to the populations supporting these fisheries VDGIF has relied on LF EF in fresh-olighaline sections of tidal rivers.
Exploratory work in these systems began in the early 1990’s and
During the period 2001/2002, standardized fixed station survey work began in four river systems – the James, Mattaponi, Pamunkey, and Rappahannock

3. Sampling Strategy Summer Low Frequency (15 pps) Boat Electrofishing
Fixed station design
EF boat and Pick-up boat
Standard run length
Two netters on each boat
Extra netters to assist in landing of unusually large fish (~> 20 Kg)
Otoliths Collected for Age & Growth beginning in 2002
2002 – 2004 otolith subsampling based on N per cm-group
High variability in individual growth => age-length key of limited value
After 2004, stratified random subsampling
This work was conducted in the mid-july – August timeframe with a single EF run per station per survey – after 2002 EF runs were standardized to 600 s per run.
2 netters in EF boat and 2 netters in P/U boat w/ additional netters on hand to assist in the landing of unusually large fish
In 2002 we began collecting otoliths for age and growth analyses
Through 04 these were collected using a N / cm-group subsampling strategy
Given high var in individual growth, use of age-length keys to assign ages to un-aged fish was problematic, so after 2004 we switched to a random sub sampling strategy to collect otoliths

7. Modeling Growth – James River
Mean Total Length-at-Age w/ 95% C.I.
2002 – 2008
L(Age) = ( * Age)
r2 = 0.98
Using Fishery Analyses and Simulation Tools software (FAST 2.0) –plugging and chugging – solutions to the von Bert equation were found for both the James and Mattaponi, but FAST 2.0 indicated no solution derived for Pamunkey or Rapp. And, the solution for the James looks spurious , with L 3.9 meters.
Modeling growth – Age 1 – 17 in James and Rappahannock, and age 1 – 15 in the Mattaponi and Pamunkey. Growth in all four populations fit linear models.
von Bertalanffy (Linf = 3,874 mm; K = 0.081; t0 = yrs, r2 = 0.98)

8. Modeling Growth – Mattaponi River
Mean Total Length-at-Age w/ 95% C.I.
2006 & 2008
L(Age) = ( * Age)
r2 = 0.98
von Bertalanffy (Linf = 1,438 mm; K = 0.048; t0 = yrs, r2 = 0.99)

9. Growth Rates – Differences Among Rivers
(mean total length-at-age w/ 95% Confidence Intervals)
Comparing growth in the four rivers in graphical form, the differences are fairly dramatic,
By way of age-11 blue cats in the Rapp average just 465 mm, while the same age fish in the James avg. 771 mm and in the Pamunkey 814 mm

10. Growth – Declines in Three of Four Rivers
(mean total length-at-age and 95% Confidence Intervals)
A discussion of length-at-age
Significant declines in growth occurred in three of the four rivers
While growth remained stable in the James – we see tight 95% CI for data pooled
For the Mattaponi the data were pooled & compared to to increase sample size – sig declines age 9 – 12
In the Rappahannock declines in occurred between 2002 and 2005 for ages 8 – 12 & 14 & a few younger age-classes
in the Pamunkey, when comparing 2002 and 2005, declines occurred for all ages adequately sampled in 2002.
Mann-Whitney rank sum test for each age sampled

11. Declines in Growth Associated With Increases in Density
(Mean Total Length Age-10 and CPUE)
In the Pamunkey and Rappahannock declines in growth were associated with increasing density – that is – age-10 was inversely related to CPUE
Pamunkey; r2 = 0.77; p< 0.01
Rappahannock; r2 = 0.99; p< 0.01
In contrast, no shift in growth occurred in the James, even in the face of dramatic increases in catch rates

12. Catch Curve-Based Total Annual Mortality Estimates
River A
Age(Max)
Age Range in Analysis
r 2
James
0.265
28.9
3–20
0.96
Mattaponi
0.208
28.5
3–13
0.78
Pamunkey
0.323
22.4
0.83
Rappahannock
0.256
29.5
2–17
0.81
Using data pooled among years
Catch Curve-based estimates of total annual mortality – A – ranged from
21% in the Mattaponi to 32% in the Pamunkey
With the exception of the Pamunkey, theoretical maximum age was consistent among rivers
Ranging from 28.5 to 29.5

13. Variable Recruitment
Recruitment is variable in all four populations

14. In three of the four populations, catch-curve residuals from year-classes common in surveys separated by two year intervals (2006 and 2008) were correlated----
Patterns of year-class strength persisted and were reflected in Catch-curve residuals
in the James, Mattaponi….

15. Sample From Tributary of James
Play “Shocking The James” video now

16. Unbelievably abundant– One of two tanks collected during 10 minutes of electrofishing on the Rappahannock River
One of two 150 gal. tanks 2’ X 4’ - this tank was less than ¼ full of water once all fish removed

17. Sample From Tributary of James
Shifting to a sample from a trib of the tidal James river, we see an indication of the dramatic river-to-river differences in composition of catch

18. Trophy oriented anglers fishing the tidal James have seen their river record go from 37.6 kg in 2004

19. Sample From Tributary of James

20. Sample From Tributary of James

21. Sample From Tributary of James

22. Sample From Tributary of James