incidence of predation on chum salmon fry in marine waters near juneau
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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