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Design and Implementation of a Fishery-Independent Shallow Water
Trawl Survey for Maryland’s Portion of Chesapeake Bay
Brandon Muffley and Alexei Sharov
MD Dept. of Natural Resources, Fisheries ServiceAnnapolis, MD
Background
• Why needed ?Why needed ?– Chesapeake 2000 commitment to multispecies approaches– Past/current studies lack spatial and temporal coverage needed– Few studies incorporate shoal (shallow) areas– Wide range of information gained on a variety of economically & ecologically important species
• ChesFIMS surveyChesFIMS survey Broad scale survey – mid-water trawls in mainstem of C. B. Shoal survey – bottom trawl in shallow waters of MD C. B.
Solomons
Shoal Survey Design
• Stratified random design• Proportional station allocation• Trawl design from MD DNR crab survey
Surveys conducted in four mid-Bay strata, chosen for compatibility with broad scale efforts, and with existing surveys
20014 Strata108 Stations3 Sampling Periods6 minute trawls
S1
S2
S3
S4
Solomons
Shoal Survey Design (con.t)
• Stratified random design• Proportional station allocation based on variance estimates
Surveys conducted in nine mid & upper Bay strata, chosen for compatibility with broad scale efforts, and with existing surveys
20029 Strata120 Stations3 Sampling Periods6 minute trawls
S5
S6
S7
S8
S9
Annapolis
Data Collection
Biological Information• Species ID• Length (TL)• Weight• Sex (blue crab)• Gut content
Water Quality• Temperature• DO• Salinity• Depth• Secchi
Misc. Information• Tide State• Bottom Substrate• Boat Speed/RPM• Position Coordinates• Air Temp.
Summary Statistics2001 May July September Total
# of Trawls 103 108 107 318318
# of Fish 2358 8754 4630 1574215742
Total Weight (kg)
34.8 40.2 82.1 157.1157.1
# of Species 22 22 22 3636
2002 May July September Total
# of Trawls 118 113 120 351351
# of Fish 1837 2477 3061 73757375
Total Weight (kg)
29.2 66.5 117.7 213.3213.3
# of Species 23 27 25 3434
Species Caught
American Eel Northern Searobin Atlantic Silverside Oyster Toadfish Bay Anchovy PigfishBlackcheek Tonguefish Silver Perch Blue Crab SkilletfishCroaker SpotHarvestfish Spotted Seatrout Hogchoker Striped Bass Horseshoe Crab Summer FlounderLizardfish Weakfish Naked Goby White PerchNorthern Kingfish Windowpane FlounderNorthern Pipefish Winter FlounderNorthern Puffer
July 2002
Yearly Distribution of Abundance
0 - 1011 - 2526 - 5051 - 100101 - 1200
3 0 3 6 Miles
N
2001 Total N
SolomonsSolomons
0 - 1011 - 2526 - 5051 - 100101 - 1200
3 0 3 6 Miles
N
Total N2002
SolomonsSolomons
Yearly Distribution of Biomass
N
5 0 5 Miles
0 - 100101 - 500501 - 10001001 - 30003001 - 60006001 - 1000010001 - 17000
2001 Total g
SolomonsSolomons
6 0 6 Miles
N
10001 - 170006001 - 100003001 - 60001001 - 3000501 - 1000101 - 5000 - 100
2002
SolomonsSolomons
Total g
Overall Catch Tow -1 by Species
July 2001 September 2001
Bay Anchovy Blue Crab White Perch
Croaker Spot Striped Bass
Hogchoker Summer Flounder Weakfish
Lizardfish N. Kingfish Other
Overall Biomass Tow –1 by Species
July 2001 September 2001
Bay Anchovy Blue Crab White Perch
Croaker Spot Striped Bass
Hogchoker Summer Flounder Weakfish
Lizardfish N. Kingfish Other
Abundance Trends
0
20
40
60
80
1990 1992 1994 1996 1998 2000 2002 2004
mea
n C
atch
to
w-1 May July September
Tangier Sound – Blue Crab
MD DNR crab trawl surveyMD DNR crab trawl survey ChesFIMS shoal surveyChesFIMS shoal survey• Fixed stations * Stratified random stations• Few stations * Numerous stations• 16’ semiballoon otter trawl * 16’ semiballoon otter trawl• 6 minute tows * 6 minute tows
5 different strata sampled by both surveys
0
50
100
150
200
250
300
350
400
450
15-20
20-25
26-30
31-35
36-40
41-45
46-50
51-55
56-60
61-65
66-70
71-75
76-80
81-85
86-90
91-95
Length (mm)
Fre
qu
ency
May
Biological CharacteristicsMean Length (mm)
May 67.2
• Size and size-at-age • Growth rates
• Habitat Preferences/Associations (adults & juveniles)• Recruitment
Bay AnchovyBay Anchovy
* For a number of species
0
50
100
150
200
250
300
350
400
450
15-20
20-25
26-30
31-35
36-40
41-45
46-50
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56-60
61-65
66-70
71-75
76-80
81-85
86-90
91-95
Length (mm)
Fre
qu
ency
May July
Biological CharacteristicsMean Length (mm)
May 67.2
July 43.9
• Size and size-at-age • Growth rates
• Habitat Preferences/Associations (adults & juveniles)• Recruitment
Bay AnchovyBay Anchovy
* For a number of species
0
50
100
150
200
250
300
350
400
450
15-20
20-25
26-30
31-35
36-40
41-45
46-50
51-55
56-60
61-65
66-70
71-75
76-80
81-85
86-90
91-95
Length (mm)
Fre
qu
ency
May July September
Biological CharacteristicsMean Length (mm)
May 67.2
July 43.9
Sept 48.1
• Size and size-at-age • Growth rates
• Habitat Preferences/Associations (adults & juveniles)• Recruitment
Bay AnchovyBay Anchovy
* For a number of species
Species Diversity
By StrataBy Strata
Species Diversity vs. Species Richness
0
1
2
3
4
5
6
7
Sp
ecie
s t
raw
l-1
September 2002
6 68
13
22
189
11 11
25
Species Diversity
By SeasonBy Season
Species Diversity vs. Species Richness
0
1
2
3
4
5
6
LittleChoptank
Tangier Pocomoke CalvertCliffs
Overall
Sp
ec
ies
tra
wl-1
May July September All 2001
2222
22
Species Diversity
By YearBy Year
Species Diversity vs. Species Richness
0
1
2
3
4
5
6
Little Choptank Tangier Pocomoke Calvert Cliffs Overall
Sp
ecie
s tr
awl-
1
2001 2002 July 01 & 02
7
19 15
11
27228
16
15
2
Gear Comparison Study
0
10
20
30
40
50
60
70
80
90
100
Deep Stations(8m)
ShallowStations (4m)
Day Trawls Night Trawls Overall
me
an
Ca
tch
to
w-1
Why needed:Why needed:* Allow both surveys to be combined* Estimate small scale spatial and temporal covariation* Different sampling scheme* Different gear – fishing efficiencies
Diet AnalysisSeason
Strata Spring Summer Fall Total
Chester 7 14 0 2121
Eastern Bay 0 2 0 22
Choptank 0 10 0 1010
Little Choptank
0 2 0 22
Tangier 28 94 48 170170
Pocomoke 24 74 4 102102
Patapsco 52 55 30 137137
Severn/South 42 39 2 8383
Calvert Cliffs 0 11 0 1111
Season Total 153153 301301 8484 538538
Species Collected Croaker Spot Weakfish Hogchoker Striped bass White perch Northern Kingfish A. Silverside
Trophic LinkagesPredator – preyMultispecies modelsBioenergetic models
Sample Diets Gut contents flushed, sample split, taxa identified, weighed and counted
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Prey Item
(from Miller et. al. 2001)
Striped Bass - Upper Bay (n = 24)
SummaryInformation Gained:Information Gained:
• Survey design and implementation• CPUE and Biomass estimates• Species abundance and distribution• Life history characteristics (i.e. growth and habitat use)• Species diversity and richness• Recruitment• Trophic linkages – gut analysis• Time series of abundance
Management Implications
Spatially&
Temporallyextensive
Species rich
Other Areas of Interest:Other Areas of Interest:• Water quality• Trawl time• Volumetric analysis / gear comparison
Acknowledgements•Project funded by CBSAC through NOAA CB Office
• Nate Herman• Tom Miller • Jon Volstad• Phil Jones• Dale Weinrich• Paul Genovese• Harry Rickabaugh• Keith Witeford• Mark Matsche• Tony Jarzynski• Jim Mower• Bob Sadzinski
• Marek Topolski• Harley Speir• Harry Hornick• Butch Webb• Bruce Pyle• Jim Thompson• Kinte Thompson• Kevin Donaldson• Bennie Williams• Jen Ball• Matapeake interns