Download Ron Heintz, NOAA Alaska Fisheries Science Center

Effect of Predators on
Pacific Herring in the Gulf
of Alaska
Ron Heintz
Alaska Fisheries Science Center
Auke Bay Laboratories
June 17, 2015
Why Is It Important to Understand
Predation Effects on Herring
• Predation rates often exceed levels of natural mortality used in
stock assessments
• Predation can be a force in structuring population dynamics
• Incorporation of predation rates in assessments alters the
biological reference points used for management
• Accounting for predation is key to developing ecosystem based
approaches to fishery management
2
How To Tell If Predators are
Important to Herring
Identify predators
Predator abundance
Diet composition
Daily consumption
Abundance of prey, mortality rates,
production
Do predators select herring?
3
Who Eats Herring in the GOA
39 bird species
5 cartilaginous fish
33 bony fish
32 inverts
14 mammals
123 predators
4
Herring Stocks in Alaska and Northern BC
Based on 2009 Assessments
Prince William
Sound
Lynn Canal
Closed to fishing
> decade
Sitka
Gulf of Alaska
Sporadically
open/closed
Open to fishing
5
Consumers of Spawn
and Larvae
Photo by Frans Lanting
Spawn loss rates up to 95%
Most of predation due to birds, invertebrates
Larvae vulnerable to invertebrates –
Larval vulnerability to fish increases with size
Photo by Sandy McRuer
6
Who Eats Juveniles?





27 birds species
35 fish species
1 baleen whale
3 pinnipeds
dogfish
7
Do Pink Salmon Eat Herring in PWS?
Pink salmon consumption of
herring in PWS
Adults 0% volume 20091
70% volume 20101
3% volume 20111
Freq. of Occurrence in 22001
stomachs (2010-2011)
0 % larvae
0.7 % 25-150 mm
<0.1 % > 150 mm
Juveniles
DeRiso et al. 2008
1. Sturdevant et al. 2013, 2. Willette et al. 1997,
3. Boldt and Haldorson 2002,
4. Cross et al. 2005, 5. Sturdevant et al. 1996
unclear record
30% mass = larvae2
1.1% mass = fish3
0.6-40% vol = fish4
0% mass = fish5
8
Birds Eat Substantial Numbers of
Juveniles in PWS During Winter
Recruitment 2 years after consumption
Winter Consumption of Juvenile Herring by Birds
Juvenile herring consumed (millions)
6000
All birds
5000
recruits
4000
3000
2000
1000
0
1990
1991
1993
1994
1996
1998
2000
2004
2005
2007
Bishop et al. 2015
9
Groundfish Consume Juvenile
Herring in Winter
Longline surveys conducted over 3 winters in age-0 habitats
16% of 1930 stomachs contained herring
50% of Pac. Cod
27% of Pollock
5% Great sculpin
16
18
Herring in pollock
stomachs
(November 2010, 2011)
Frequency
14
12
10
8
6
12
10
Herring in cod
stomachs
(March 2011, 2012)
8
6
4
4
2
2
0
14
Frequency
16
40
80
1 20
1 60
Herring length (mm)
200
0
Bishop et al. 2013
90
1 20
1 50
1 80
Herring length (mm)
21 0
10
Who Eats Adults?
11
Estimated Consumption of
West Coast Vancouver Island
(WCVI) Herring Adults
Do consumption rates track abundance?
Humpback
Whales
Estimates are for WCVI
including
La Perouse Bank
N. Fur Seal
P. Cod
Dogfish
Cumulative consumption is
~54% of WCVI and SOG
spawning biomass.
Similar to earlier estimates for
Hake, sablefish, cod ~41%
Lingcod
Hake
Schweigert et al. 2010
Ware and McFarlane 1995
12
Ecopath Estimates of Consumption
in GOA 1990-1994
% of Adult Herring Biomass Consumed in GOA
• Cumulative =
68.5%
% of Adult Biomass
40
35
30
25
20
• Summer only
• 50+ m
15
10
5
• Bottom trawl
survey
0
• SEAK not
included
Aydin et al. 2007
13
Arrowtooth Removals Depend
on Herring Abundance
160000
PWS Pre-fishery Biomass from ASA
Tonnes
120000
80000
40000
0
1970
1980
1990
2000
2010
2020
14
Are Whales Important Predators?
25000
Whale Abundance – N. Pacific
20000
15000
10000
5000
Number of Whales
20,000 whales ~7.5 million
people
0
1970
1980
1990
2000
2010
( Darling, Nicklin, Barnes 2009)
Similar rate of increased obs’d
• BC
• PWS
• SEAK
15
Zooplankton
(may include euphausiids)
unknown
Whales Can Eat
Lots of Herring
Euphausiids
Pollock
Herring
Forage fish
(may include herring)
16
Whale Diets Viewed Through
Isotopes and Fatty Acids
15
N enrichment
PWS whale fatty acids more similar
to herring than krill
Whale, Herring , Krill Fatty Acids
Euphausiid
1 .0
SEAK
PWS
Krill
0.5
PWS
SEAK
0.0
Pacific herring
PWS
SEAK
Thysanoessa raschii
-0.5
Herring
PWS whale trophic position
is highest among sampled whales
Herring
-1 .0
-2
Eupausiid
-1
0
1
2
Whale
17
Whale Consumption Rates
Depend on Location
Tonnes consumed
18
PWS
Ly nn Canal
Sitka Sound
Winter
07-08
Location &
Winter
∑ Tonnes
Consumed
PWS 07-08
2639
PWS 08-09
4388
1-Mar-08
Sitka 07-08
1018
PWS
Sitka Sound
Ly nn Canal
Sitka 08-09
788
Lynn Canal
07-08
732
Lynn Canal
08-09
501
12
6
0
1-Sep-07
Tonnes consumed
30
1-Nov -07
1-Jan-08
Winter
08-09
20
10
0
1-Sep-08
1-Nov -08
1-Jan-09
1-Mar-09
18
Whales in PWS Consume
a Significant Biomass
24000
20000
2008 Stock biomass
16000
12000
2007 Stock biomass
8000
Range of winter mortality
4000
‘98 Harvest level
0
Low
Best
High
2007-2008
Low
Best
High
2008-2009
19
Proportion Consumed
Number Consumed
Paradoxically…. Schooling
May Attract Predators
Number of Prey
20
Summary
The importance of predators depends
Life stage
Population abundance
Ecosystem conditions
Habitat herring occupy
Location in the GOA
Herring schooling behavior increases their susceptibility
to predation at low stock sizes
Effects of predators on post-metamorphic juveniles
is a significant data gap
21