Incidence of Predation on Chum Salmon Fry in Marine Waters near Juneau
Craig Farrington
Alaska Dept of Fish & Game
The Southeast Sustainable Salmon Funds made this project possible
Gastric lavage apparatus, a.k.a.
the Vomit-O-Matic
DIPAC fry monitoring
Relative abundance of chum fry from mid-May to mid-June in marine waters
near Juneau
010002000300040005000600070008000
Mid-week date
To
tal
of
chu
m f
ry c
aptu
red
Seine sample Trawl sample
Potential predators of salmon fry in marine waters near Juneau
0
2 0
4 0
6 0
8 0
1 0 0
1 2 0
1 4 0
1 6 0
1 8 0
Sa
mp
le s
ize
Salmon fry predation by species
0
20
40
60
80
100
120
140
160
180Pink fry in stomachs
Chum fry in stomachs
NO fry in stomachs
28%
8%
1%
CPUE of Dolly Varden using variable mesh gillnet
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
Fis
h p
er g
illn
et h
ou
r
Cumulative percent cpue for Dolly Varden
0%
20%
40%
60%
80%
100%
120%
5/15
/2003
5/21
/2003
5/27
/2003
6/2/
2003
6/8/
2003
6/14
/2003
2nd quartile - May 29, 2003
Size of Dolly Varden captured by variable mesh
gillnet
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
E a rly (p rio r t o M a y 2 0 ) M id d le (M a y 2 0 - 3 1 ) L a te (Ju n e )
Me
an
le
ng
th (
cm
)
(P = 0 .0 1 ),n = 1 9
(P = 0 .0 5 ),n = 8 1
n = 6 9
Condition of chum fry in stomachs
Incidence of prey items in stomach contents
Chum fry % chum Pink fry
Other finfish remains Cumacean Amphipod Isopod Euphasid Shrimp Crab Annelids
% non-chum Total
Incidence 43 31% 2 50 20 11 2 3 5 2 2 69% 140Weight (g) 208.5 69% 31% 300.5
Crustacea
EARLY vs. LATE DOLLY VARDEN STOMACH CONTENTS
Prior to May 20 May 20 on
% chum fry by weight 86% 62%
AVERAGE WEIGHT OF DV STOMACH CONTENTS
All prey items 2.8gIncident with chum fry 5.2gIncident without chum fry 1.0g
Percent incidence of predation on wild chum
fry, early vs late
0
10
20
30
40
50
60
70
Early (prior to May 20) Late (May 20 onward)
Sam
ple
nu
mb
er
-3%
2%
7%
12%
17%
22%
Chum fry Otoliths % Wild
Conclusions (preliminaryPeak of the relative abundance of chum salmon fry (predominantly hatchery origin) in local waters is May 21 - June 1Wild chum fry likely appear earlier in local waters with unknown abundance and run timingDolly Varden char are the main early marine predators on chum salmon fry (28% incidence of chum fry in stomachs) in local Juneau watersDolly Varden peak abundance – May 27- and midpoint of ‘run’ – May 29 - are both concurrent with the peak residence of hatchery chum fryLarger sized Dolly Varden in early Spring targeted chum fry; smaller sized Dolly Varden arrive later and target other smaller prey items (invertebrates) in their dietsAs a prey item in the diet of Dolly Varden, the potential energetic value of chum fry is roughly 4 times that for non-chum prey items