Incidence of Predation on Chum Salmon Fry in Marine Waters near Juneau

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