persistence of prey hot spots in southeast alaska scott m. gende national park service, glacier bay...
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Persistence of prey ‘hot Persistence of prey ‘hot spots’ in southeast Alaskaspots’ in southeast Alaska
Scott M. GendeScott M. Gende
National Park Service, Glacier Bay Field Station, National Park Service, Glacier Bay Field Station, 3100 National Park, Juneau, Alaska, USA; 3100 National Park, Juneau, Alaska, USA;
[email protected][email protected]
Michael SiglerMichael Sigler
National Marine Fisheries Service, Alaska National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratory, Fisheries Science Center, Auke Bay Laboratory,
Juneau, Alaska, USA; [email protected], Alaska, USA; [email protected]
1. Are there high aggregations of pelagic fish prey in space and time?
2.Do these ‘hot spots’ persist through time?
3.What is the response of predators to these aggregations?
Questions:Questions:
~40 km study ~40 km study areaarea
Methods:Methods:
1. Hydroacoustic surveys for 1. Hydroacoustic surveys for pelagic prey conducted June 2001-pelagic prey conducted June 2001-May 2004May 2004
2. Periodic midwater trawls to 2. Periodic midwater trawls to sample prey energy and confirm sample prey energy and confirm echo soundecho sound3. Concurrent observations of top 3. Concurrent observations of top predators including Steller sea lions predators including Steller sea lions and humpback whalesand humpback whales
4. Transformed data from 4. Transformed data from estimates of biomass to energy estimates of biomass to energy densities integrated across the densities integrated across the water columnwater column5. Blocked data into tenths of a 5. Blocked data into tenths of a latitudinal minute such that each latitudinal minute such that each ‘block’ constituted approximately ‘block’ constituted approximately 1.83 km)1.83 km)
Methods:Methods:
1. Hydroacoustic surveys for 1. Hydroacoustic surveys for pelagic prey conducted June 2001-pelagic prey conducted June 2001-May 2004May 2004
2. Periodic midwater trawls to 2. Periodic midwater trawls to sample prey energy and confirm sample prey energy and confirm echo soundecho sound3. Concurrent observations of top 3. Concurrent observations of top predators including Steller sea lions predators including Steller sea lions and humpback whalesand humpback whales
4. Transformed data from 4. Transformed data from estimates of biomass to energy estimates of biomass to energy densities integrated across the densities integrated across the water columnwater column5. Blocked data into tenths of a 5. Blocked data into tenths of a latitudinal minute such that each latitudinal minute such that each ‘block’ constituted approximately ‘block’ constituted approximately 1.83 km)1.83 km)
Methods:Methods:
1. Hydroacoustic surveys for 1. Hydroacoustic surveys for pelagic prey conducted June 2001-pelagic prey conducted June 2001-May 2004May 2004
2. Periodic midwater trawls to 2. Periodic midwater trawls to sample prey energy and confirm sample prey energy and confirm echo soundecho sound3. Concurrent observations of top 3. Concurrent observations of top predators including Steller sea lions predators including Steller sea lions and humpback whalesand humpback whales
4. Transformed data from 4. Transformed data from estimates of biomass to energy estimates of biomass to energy densities integrated across the densities integrated across the water columnwater column5. Blocked data into tenths of a 5. Blocked data into tenths of a latitudinal minute such that each latitudinal minute such that each ‘block’ constituted approximately ‘block’ constituted approximately 1.83 km)1.83 km)
Methods:Methods:
1. Hydroacoustic surveys for 1. Hydroacoustic surveys for pelagic prey conducted June 2001-pelagic prey conducted June 2001-May 2004May 2004
2. Periodic midwater trawls to 2. Periodic midwater trawls to sample prey energy and confirm sample prey energy and confirm echo soundecho sound3. Concurrent observations of top 3. Concurrent observations of top predators including Steller sea lions predators including Steller sea lions and humpback whalesand humpback whales
4.4. Blocked data into tenths of a Blocked data into tenths of a latitudinal minute such that each latitudinal minute such that each ‘block’ constituted approximately ‘block’ constituted approximately 1.83 km)1.83 km)5. Transformed data from 5. Transformed data from estimates of biomass to energy estimates of biomass to energy densities integrated across the densities integrated across the water columnwater column
Methods:Methods:
1. Hydroacoustic surveys for 1. Hydroacoustic surveys for pelagic prey conducted June 2001-pelagic prey conducted June 2001-May 2004May 2004
2. Periodic midwater trawls to 2. Periodic midwater trawls to sample prey energy and confirm sample prey energy and confirm echo soundecho sound3. Concurrent observations of top 3. Concurrent observations of top predators including Steller sea lions predators including Steller sea lions and humpback whalesand humpback whales
5. Transformed data from 5. Transformed data from estimates of biomass to energy estimates of biomass to energy densities integrated across the densities integrated across the water columnwater column
kJ x 10kJ x 1066/km/km22
4. Blocked data into tenths of a 4. Blocked data into tenths of a latitudinal minute such that each latitudinal minute such that each ‘block’ constituted approximately ‘block’ constituted approximately 1.83 km)1.83 km)
Results:Results:
On average prey energy density is not On average prey energy density is not equal across monthsequal across months
0
5,000
10,000
15,000
20,000
25,000
30,000
JUN
AUGO
CTDEC
FEBAPR
JUN
AUGO
CTDEC
FEBAPR
JUN
AUGO
CTDEC
FEBAPR
Mill
ion
s k
J/k
g2
2001 2004
0
5,000
10,000
15,000
20,000
25,000
30,000
JUN
AUGO
CTDEC
FEBAPR
JUN
AUGO
CTDEC
FEBAPR
JUN
AUGO
CTDEC
FEBAPR
Cold winter months (Nov-Feb) are Cold winter months (Nov-Feb) are hothot
Mill
ion
s k
J/k
g2
2001 2004
SeasonSeasonal haul-al haul-outout
> 20000
10000-20000
5000-10000
1000-5000
Distribution of pelagic prey energy November Distribution of pelagic prey energy November 20032003
1-1000
SeasonSeasonal haul-al haul-outout
> 20000
10000-20000
5000-10000
1000-5000
Distribution of pelagic prey energy December Distribution of pelagic prey energy December 20032003
1-1000
SeasonSeasonal haul-al haul-outout
> 20000
10000-20000
5000-10000
1000-5000
Distribution of pelagic prey energy January Distribution of pelagic prey energy January 20042004
1-1000
SeasonSeasonal haul-al haul-outout
> 20000
10000-20000
5000-10000
1000-5000
Distribution of pelagic prey energy February Distribution of pelagic prey energy February 20042004
1-1000
SeasonSeasonal haul-al haul-outout
> 20000
10000-20000
5000-10000
1000-5000
Distribution of pelagic prey energy March 2004Distribution of pelagic prey energy March 2004
1-1000
SeasonSeasonal haul-al haul-outout
> 20000
10000-20000
5000-10000
1000-5000
Distribution of pelagic prey energy April 2004Distribution of pelagic prey energy April 2004
1-1000
SeasonSeasonal haul-al haul-outout
> 20000
10000-20000
5000-10000
1000-5000
Distribution of pelagic prey energy May 2004Distribution of pelagic prey energy May 2004
1-1000
SeasonSeasonal haul-al haul-outout
Distribution of pelagic prey energy November Distribution of pelagic prey energy November 20032003
SeasonSeasonal haul-al haul-outout
80-100%
60-80%
40-60%
20-40%
Proportion of observed Steller sea lions Proportion of observed Steller sea lions November 2003 November 2003
0-20%
SeasonSeasonal haul-al haul-outout
80-100%
60-80%
40-60%
20-40%
0-20%
Proportion of observed Steller sea lions Proportion of observed Steller sea lions December 2003 December 2003
SeasonSeasonal haul-al haul-outout
80-100%
60-80%
40-60%
20-40%
0-20%
Proportion of observed Steller sea lions January Proportion of observed Steller sea lions January 2004 2004
SeasonSeasonal haul-al haul-outout
80-100%
60-80%
40-60%
20-40%
0-20%
Proportion of observed Steller sea lions Proportion of observed Steller sea lions February 2004 February 2004
R2 = 0.4084
0%
10%
20%
30%
40%
50%
- 5,000 10,000 15,000 20,000 25,000
R2 = 0.38
Avg. energy density of each block
% o
f m
on
ths s
ea lio
ns
fou
nd
fora
gin
g w
ith
in t
hat
blo
ck
Strong relationship between the average Strong relationship between the average energy density of each block energy density of each block (winter)(winter) and the and the
distribution of Steller sea lionsdistribution of Steller sea lions
SeasonSeasonal haul-al haul-outout
>70%
60-70%
Hot spot persistence: the probability of Hot spot persistence: the probability of encountering a hot spot across all winter monthsencountering a hot spot across all winter months
50-60%
SeasonSeasonal haul-al haul-outout
>70%
60-70%
Hot spots do not persist during the non-winter Hot spots do not persist during the non-winter monthsmonths
50-60% 20-30%
SeasonSeasonal haul-al haul-outout
Proportion of winter surveys when sea lions seen Proportion of winter surveys when sea lions seen foraging foraging
>40% 30-40% 20-30%
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
0% 10% 20% 30% 40% 50% 60% 70%
% of months when spot is hot
R2 = 0.02
No relationship between hot spot No relationship between hot spot location and foraging sea lions during location and foraging sea lions during
the non-winter monthsthe non-winter months
Non-Non-winterwinter%
of
mon
ths s
ea lio
ns
fou
nd
fora
gin
g w
ith
in t
hat
blo
ck
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
0% 10% 20% 30% 40% 50% 60% 70%
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
0% 10% 20% 30% 40% 50% 60% 70%
% of months when block is hot
% o
f m
on
ths s
ea lio
ns
fou
nd
fora
gin
g a
t th
e s
pot
R2 = 0.02
R2 = 0.41
Sea lions consistently utilized the prey Sea lions consistently utilized the prey hot spots during the winter (Nov-Feb)hot spots during the winter (Nov-Feb)
Non-Non-winterwinter
WinterWinter
1.1. Are prey aggregated in time and Are prey aggregated in time and space?space?• Overwintering herring schools result in high Overwintering herring schools result in high
prey aggregations Nov-Feb and occur in prey aggregations Nov-Feb and occur in consistent locations.consistent locations.
2.2. Do these prey ‘hot spots’ persist?Do these prey ‘hot spots’ persist?• Some hot spot areas persisted through time; Some hot spot areas persisted through time;
the probability of encountering a high the probability of encountering a high concentration of prey exceeded 70% for some concentration of prey exceeded 70% for some areasareas
3.3.Do predators respond to this Do predators respond to this persistence?persistence?• Strong relationship (during the winter) between Strong relationship (during the winter) between
sea lion distribution and distribution of prey. sea lion distribution and distribution of prey. However, it appears that sea lions response is However, it appears that sea lions response is greatest in areas with highest prey persistence greatest in areas with highest prey persistence rather than highest prey densityrather than highest prey density
So what?So what?
Abundance of prey j
in the environmentEncounter rate
with prey j
Attack rates on
prey j
Capture rates on
prey j
Consumption rates on prey j
Nj
λj
aj
cj
Kj
λj /Nj
aj / λj
cj /aj
Kj /cj
Relative Encounter
rate
Attack
probability
Capture
success
Consumptionprobability
Foraging Efficiency
(Intake/Effort)
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
xxxx
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
xxxx
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
xxxx = mid efficiencyII
EE
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
xxxx = mid efficiency
Low density, low persistence of prey Low density, low persistence of prey patchespatches
xxxx
II
EE
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
Low density, low persistence of prey Low density, low persistence of prey patchespatches
xxxx
xxxx = mid efficiencyII
EE
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
Low density, low persistence of prey Low density, low persistence of prey patchespatches
xxxx
xxxx = mid efficiency
= low efficiency
II
EE
II
EE
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
Low density, low persistence of prey Low density, low persistence of prey patchespatches
xxxx
xxxx = mid efficiency
= low efficiency
II
EE
II
EE
xxxx
Low density, high persistence of prey Low density, high persistence of prey patchespatches
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
Low density, low persistence of prey Low density, low persistence of prey patchespatches
xxxx
xxxx = mid efficiency
= low efficiency
II
EE
II
EE
xxxx
Low density, high persistence of prey Low density, high persistence of prey patchespatches
TT11 TT22 TT33 TT44
High density, low persistence of prey High density, low persistence of prey patchespatches
Low density, low persistence of prey Low density, low persistence of prey patchespatches
xxxx
xxxx = mid efficiency
= low efficiency
II
EE
II
EE
xxxx
Low density, high persistence of prey Low density, high persistence of prey patchespatches
= high efficiency
IIEE
Density may not be Density may not be the only the only characteristic of prey characteristic of prey aggregations that are aggregations that are important to important to predators; predators; persistence may be persistence may be just as important, just as important, particularly for those particularly for those that do not have the that do not have the ability to search large ability to search large areas efficiently.areas efficiently.