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8:45 AM – 9:35 AM Research Update
Distribution and Habitat AssociationsPhilip Stevens, Research Scientist, FWRI
Spawning Dynamics Joy Young, Biological Scientist, FWRI
Research - Population/Behavioral traits
What is it that Snook do and why do they do it?
Diet Movement
SpawningHabitat Use
Phil Stevens Joy Young
Common Snook habitat use and diet
Philip Stevens, Erick Ault, Dave Blewett, Ross, Boucek, Jenn Rehage,
Alexis Trotter, Beau Yeiser, Joy Young, and Jim Whittington
EstuaryResidence
MovementDiet
RiverResidence
Offshore Residence
Data for Stock Assessment are largely centered on the estuary
What is going on in other habitats, namely offshore reefs and rivers?
To what extent do fish move between habitats and why do they move?
Habitat use and diet
Offshore Reefs
SE Florida
Ft. Pierce Inlet
St. Lucie Inlet
Jupiter Inlet
65 Km (40 Miles) CoastlineAbout 5-12 km (3-8 miles) offshore
Study Sampling Area
Offshore Life History
Average TL = 949 mm (37 inches) for females and 885 mm (35 inches) for males Maximum TL = 1093 mm (43 inches)Age range = 4 -19 years; average ~10 yearsDiet and genetics
0
10
20
30
40
50
60
70
80
500 600 700 800 900 1000 1100
Tota
l Nu
mb
er
of
Spe
cim
en
s
Total Length (mm)
2011-2014 Offshore Specimen Length Frequencies
Males (n=149) Females (n=202)
70% of Observed
Underwater Observations
Roving Count (Opportunistic)Group Size (Number of Fish)Length Distribution (TL) Regional BiasCondition Limited
2009 - 2014 Observation Data
Region Group (Average) Group (Maximum) TL (mm) Avg TL (mm) Max
Ft. Pierce 24 140 835 1150
St. Lucie 29 250 827 1150
Jupiter 18 50 759 1080
Offshore Life History Cont.
Acoustic Telemetry
Of snook originally tagged inshore (n=186), eleven moved offshore
Snook that were tagged offshore (n=61), mostly remained offshore (high residency to reef tract)
Once offshore, very little movement back to inlets and inshore waters (only 4 fish bounced back and forth)
Offshore Movement Patterns
Sampling occurred in evening hours when active spawning is known to occur
99% of females were spawning capable or regressing
11% of females had hydrated eggs (Imminent spawning)
Sampling and hydrated female locations
Offshore Reproduction
None12
3
# hydrated females caught
Ft. Pierce Inlet
St. Lucie Inlet
Jupiter Inlet
Use of offshore habitat has been documented throughout the state. Are these areas important at the population scale?
Rivers
Mexico CostaRica
Panama
Mexico
Mexico
SE Florida
Spring-fed rivers
Tampa Bay
CharlotteHarbor
Everglades
Acknowledgements Luiz Barbieri, Jim Estes, Tom Champeau, Bill Johnson, Bill Pouder, and Ron Taylor
FWC St Pete, Charlotte Harbor, Lakeland, Gainesville, Melbourne, Everglades (FIU)
State Wildlife Grant; Sport Fish Restoration
Southwest Florida Water Management District;
How do we sample rivers? -electrofishing
Stuns the fish – Allows researchers to take measurements and release
CharlotteHarbor
Peace River
Myakka River
Caloosahatchee River
Electrofishing 2004-05
Freshwater Fisheries
Fall04 Win05 Spr05 Sum05 Fall05 Win06 Spr06 Sum06
-0.5
0.0
0.5
1.0
1.5
2.0
2.5 Peace RiverMyakka RiverCaloosahatchee River
SeasonFall04 Win05 Spr05 Sum05 Fall05 Win06 Spr06 Sum06
CP
UE
(fis
h m
inut
e-1)
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
A
B
All rivers combined
Charlotte Harbor Rivers - Seasonality
Blewett et al. 2009
What drives seasonal movements of snook into the rivers?
Date
1/7/2008 1/14/2008 1/21/2008 1/28/2008 6
8
10
12
14
16
18
20
22
24
26EstuaryRiverCanal
Date
1/5/2009 1/12/2009 1/19/2009 1/26/2009
Tem
pera
ture
(°C
)
6
8
10
12
14
16
18
20
22
24
26
Date
1/4/2010 1/11/2010 1/18/2010 1/25/2010 6
8
10
12
14
16
18
20
22
24
26
Water temperatures of the habitats do not differ leading into winter
EstuaryRiverCanal
Water temperatures of the habitats “spread” for three days post-cold front
2 °C
Temperature cue? Not the whole story.
Blewett et al. 2014
Season
F04W
05SP05 S05 F05
W06SP06 S06 F06
W07SP07 S07 F07
W08SP08 S08 F08
W09SP09 S09 F09
W10SP10 S10 F10
W11SP11 S11 F11
W12SP12 S12 F12
W13SP13 S13 F13
Fish
/100
m s
hore
line
0
2
4
6
8
10
12
Flow
(m3 /s
)
0
20
40
60
80
100Fish abundanceActual river flow
Appear to cue on river flow
Summer/fall abundance of snook
Estuary = 3 fish per haul in 183-m seine * gear efficiency of 30% = 10 snook/100m shorelineRivers (summer) = ~1.5 fish per 100m in electrofishing * gear efficiency of 15% = 10 snook/100m shoreline
Annual snook abundance vs. flow
River flow (ln)
1.5 2.0 2.5 3.0 3.5 4.0 4.5
Com
mon
sno
ok a
bund
ance
(ln)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
R2 = 0.90
More Flow = More Snook
Peace River – summer
Peace River – mid fall
Estuary Prey River Prey
Stevens et al. 2010Blewett et al. 2006
By late summer/early fall
Post-spawning fish from the bay
Summer resident snook
Everglades
Study system: ecotonal sites in Everglades National Park
Boucek and Rehage 2013
Study system: ecotonal sites in Everglades National Park
0
Dec Jun Dec Jun Dec Jun Dec Jun
Mar
sh D
epth
(CM
)
-20
0
20
40
60
2011 2012 20142013
Mars
h w
ate
r d
ep
th (
CM
)
20102009
Sampling windowMarsh drying
Marsh stage
ilSunfishes are the dominant prey items
Dec Jun Dec Jun Dec Jun Dec Jun
# of
sun
fish
per 1
00m
0
5
10
15
20
25
30
35# of
sno
ok p
er 1
00 m
eter
s
02468
10121416
Snook and sunfish abundance increases in the dry season, but varies across years
Snook
Sunfishes
Push into river occurs in April/May
Tampa Bay
Southwest Florida Rivers
WetSummer
TransitionFall
DryWinter/Spring
Tampa Bay’s rivers
0.00
1.00
2.00
3.00
4.00
5.00
6.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Cat
ch p
er 1
00
m s
amp
led
Month
2014
2015
Tampa Bay Rivers
0
0.5
1
1.5
2
2.5
3
3.5
Dec-Feb Mar-May Jun-Aug Sep-Nov
Sno
ok
per
10
0 m
of
sho
relin
e
Tampa Bay Rivers
There are about 15 snook per 100m of shoreline (the length of a football field) in both estuary and river habitats
Estuary = 5 fish per haul in 183-m seine * gear efficiency of 30%Rivers = 2.6 fish per 100m shoreline in electrofishing * gear efficiency of 15%
The rivers in TB appear to be an extension of the estuary habitat
Year-round occurrence; no seasonal changes apparent.
SE Florida
Indian River Lagoon Rivers
There are about 15 snook per 100m of shoreline (the length of a football field) in the estuary and 9 snook per 100m in the rivers.
However, other snook species (e.g., fat snook) boost numbers of “snook” per 100m of shoreline to that comparable to the estuary.
Estuary = 5 fish per haul in 183-m seine * gear efficiency of 30%Rivers = 1.3 fish per 100m shoreline in electrofishing * gear efficiency of 15%
The rivers in IRL appear to be an extension of the estuary habitat
Year-round occurrence; no seasonal changes apparent.
Fat Snook
Common Snook
Spring-fed rivers
Overwintering is apparent at this latitude
<50 deg F Gulf temp vs. 72 deg F spring temp
(Picture from observation bubble at Homosassa Springs)
Abundance in rivers less than half that of lower latitudes
0.2-0.6 snook/100m * gear efficiency of 15% =<4 snook/100m
20152013
EstuaryResidence
MovementDiet
RiverResidence
Offshore Residence
Conclusions
Population traits will vary based on the size and shape of the estuary, habitat types, and prey
presented to the species
Thank you!