Advancement of

Sunray Venus Culture

Macrocallista nimbosa

through Evaluation of Alternative

Growout and Harvesting Methods

Leslie N. Sturmer, Todd Osborne, William WhiteUniversity of Florida IFAS

Rex EllisSt. Johns River Water Management District

Sunray Venus Clam

Culture in Florida

Eight Years of Research

and Development

Bottom bags (4’ x 4’, 16 ft2) made of 9 mm polyester mesh material

Evaluation of Growout Methods: Bottom Bag• Standard hard clam culture

methods used as a starting point − In Florida, the typical culture

method is the bottom bag• Results were not consistent,

2007-9 − Survivals ranging from 24-76%− Site and substrate-dependent

• Shell deformities or irregularities observed of sunray venus in bags− Observations ranging from

8-48% per bag in early trials Limited to ventral margin with one valve having excessive curvature resulting in a depression

Broadcasted seed covered with 9 mm mesh polyester netting edged with lead line and additional layer of plastic netting

staked with PVC pipe

Evaluation of Growout Methods: Bottom Plant• Preliminary evaluation of bottom plants

as a culture method, 2009-10 − Good survival− Faster growth than bottom bags− Shell deformities <2%

• Special lease provisions limit use of mechanical harvesting on shellfish aquaculture leases

• Growers restricted to use of hand tools (e.g., rake) to harvest bottom-planted sunray venus clams

Project Objectives1) Eliminate barriers to commercial production

of a promising new aquaculture species by utilizing alternative culture and harvest methods− Document production and product quality

characteristics of two culture methods 2) Compare effects of harvesting bottom-planted

sunray venus clams with a mechanical harvesting device versus those associated with harvesting bottom bags− Document water quality and soil properties

associated with two harvest methods

Funded by Florida Department of Agriculture and Consumer Services, Florida Aquaculture Grant Program, 2013-14

• Treatments − Bottom plants, 9 mm polyester mesh netting,

½” mesh HDPE cover netting, 8’ x 10’, 80 ft2

− Bottom bags (16 ft2), belt of 5, 80 ft2 per row• Replication, n=4• Stocking density, 55/ft2

• Seed size, 15-20 mm SL• Site, UF lease, Cedar Key, FL• Plant, November 2012• Harvest, ~12 months later, 2013

Growout Methods

• Mechanical harvesting device, “box” harvester used in Virginia− SS box-shaped− 5 hp pump delivers pressurized

water via nozzles along spray bar− No tines, angle of box digs into

substrate− Wire basket collects clams

Harvest Methods

Sampling Design

• Before-After, Control-Impact, Paired (BACIP)

– Establish baseline prior to planting or harvesting

• Control sites– Direct comparison of culture

and harvest methods • Experimental sites

– Differentiate natural changes from those caused by harvesting

• Reference sites

• Survival the same for both culture methods• Bottom-planted sunray venus were

− 29% larger in shell length (p<0.0001)− 76% heavier in total weight p<0.0001)− 60% more meat weight (wet) (p=0.0023)− 80% increase in yield (lb/16ft2) (p=0.0126)

Production Characteristics

48.4 48.1

17.3

4.7

16.7

47.4

61.9

29.9

8.3

28.2

0

10

20

30

40

50

60

70

Survival (%) Length (mm) Weight (g) Meat Wt (g) Yield (lb/16 ft2)

Bottom Bags Bottom Plant

• Grit evaluation, 5-point scale where 0=no grit and 4=extremely gritty− At harvest, sunray venus were rated as

“slightly to moderately” gritty − After 24 hours of purging, 70% reduction in

grit for clams harvested by both methods− After 48 hours, values same for both methods

• Shell deformities (p=0.01)

− 3.1 + 0.9%, bottom bags− 0.5 + 1.0%, bottom plant

• Shell breakage (p=0.12)

− 0.5 + 0.4%, bottom bags− 2.9 + 2.2%, bottom plant

• Shelf life, 10 days− 100%, both culture

methods

Product Quality Characteristics

1.3

0.4 0.3

1.7

0.50.3

0

0.5

1

1.5

2

2.5

0-Hours 24-Hours 48-HoursPurge Time

Grittiness (0-4 Scale)

Bottom Bags Bottom Plant

• Nine sondes (YSI 6600) deployed − 5’ in cardinal directions from

both bag and bottom plants − One sonde placed mid-way between

culture unit replicates− Additional sondes placed 25’

down current of both culture units

Effects of Harvest Methods on Water Quality

MID

5 ftBot.

Plant

20 ft

5 ft

5 ft

5 ft

5 ft

N-BP-5

W-BP-5 E-BB-5

S-BP-5

BP-25

Bags

5 ft

5 ft

20 ft

N-BB-5

BB-25

S-BB-5

5 ft

N• Multiple parameters measured

continuously (every minute) for 48 hours pre- and post-harvest− Water temperature− Salinity− Dissolved oxygen− Turbidity

• Turbidity (resuspension of small soil particles into water column) was greatest concern and showed noticeable differences− Intensity: Maximum values and

max mean values of sondeswith highest detected turbidity

− Duration: Time required to return to corrected background conditions (30 min pre-harvest)

• Each harvest replicate treated as an independent evaluation as ambient conditions (tide, current, wind, back-ground turbidity) differed

Effects of Harvest Methods on Turbidity

Rep 1 - 23 Oct 2013

Rep 2 - 18 Nov 2013

Rep 3 - 3 Dec 2013

Rep 4 - 16 Dec 2013

-48 hrs

+24 hrs

+48 hrs

-24 hrs

0 hrs

Turb

idity

(NTU

)Tu

rbid

ity (N

TU)

Turb

idity

(NTU

)Tu

rbid

ity (N

TU)

Intensity

Duration

Comparison of highest mean turbidity values for harvest methods with 30 min pre- and post-harvest values

Effects of Harvest Methods on Turbidity (NTU)

60.5 b74.5 ab

99.8 a

81.8 ab

0

20

40

60

80

100

120

30 min Pre Bottom Bag Bottom Plant 30 min Post

Replicate 1

Data were analyzed using General Linear Model analysis with Tukey’s post-hoc test in SAS Software

30.3 b

60.7 a

37.2 b30.9 b

0

20

40

60

80

100

120

30 min Pre Bottom Bag Bottom Plant 30 min Post

Replicate 2

31.9 b41.0 a

49.0 a 49.0 a

0

20

40

60

80

100

120

30 min Pre Bottom Bag Bottom Plant 30 min Post

Replicate 3

16.5 b

65.6 a

52.7 a

23.0 b

0

20

40

60

80

100

120

30 min Pre Bottom Bag Bottom Plant 30 min Post

Replicate 4

• Replicate 1 – Outgoing tide, winds light (6-10 knots) out of north, following falling tide• Turbidity associated with harvesting bags returned to background levels in 2 minutes,

and in 5 minutes with pump harvester

Effects of Harvest Methods on Turbidity

Rep 1 Sonde S-BP-5

Rep 1 Sonde S-BB-5Bags Harvested

(upstream)

Bags Harvested

Pump Driven Harvester

Time on 23-Oct-13

Comparison of bag harvest duration (top graph) and pump-driven harvester (bottom graph)

• Replicate 2 – Incoming tide from S to N, winds (3-5 knots) out of sout• Return interval for bag harvest not determined as it was greater than time between

harvest activities, return to background for pump-driven harvester was 9 minutes

Effects of Harvest Methods on Turbidity

Rep 2 Sonde N-BP-5

Bags Harvested

Pump Driven Harvester

Bags Harvested (upstream)

Rep 2 Sonde N-BB-5

Time on 18-Nov-13

Comparison of bag harvest duration (top graph) and pump-driven harvester (bottom graph)

• Commercial-scale trial, 17 June 2014− Unfarmed area of 300 ft2 (25’ by 12’ plot)

• Eleven sondes deployed − 5’ and 25’ in cardinal directions from

mid-points of test plot − 45’ to south of plot with one sonde located

at mid-point of plot and two located 20’ to east and west

• Turbidity measured every minute for 24 hours pre- and post-harvest

Effects of Pump-driven Harvest on Turbidity

N-25

Mock Harvest

Area

20 ft

20 ft

20 ft20 ft

20 ft20 ft

5 ft

5 ft5 ft

5 ft

20 ft

N-5

W-25 W-5 E-25E-5

S-5

S-25

SW-45 S-45 SE-45

Effects of Pump-Harvester on TurbidityComparison of sondes located 5’ from harvest area over 30 min pre- and post-harvest

• Maximum turbidity values per harvest set ranged from 62 to 98 NTU• Return to baseline levels (19.1+2.6 NTU) was within 3 min after first harvest set,

immediately after second set, took longer after third set (7 min) due to tidal change

Effects of Pump-Harvester on TurbidityComparison of sondes located 25’ from harvest area 30 min pre- and post-harvest

• Maximum turbidity values per harvest set ranged from 24 to 60 NTU• Return to baseline levels (13.1+1.4 NTU) was within 2-10 minutes

Effects of Pump-Harvester on TurbidityComparison of sondes located 45’ from harvest area 30 min pre- and post-harvest

• Maximum turbidity values in first and second harvest set were 25 and 52 NTU• Return to baseline levels (17.8+0.9 NTU) was within 6 min after first harvest set,

with little to no change during or after second and third sets as values returned to baseline during harvest

0

40

80

120

160

11:1016-Jun

17:1016-Jun

23:1016-Jun

5:1017-Jun

11:1017-Jun

17:1017-Jun

23:1017-Jun

5:1018-Jun

11:1018-Jun

Turb

idit

y (N

TU

)

North South East WestSonde Locations (5’ from Harvest Area):

Harvest

Effects of Pump-Harvester on Turbidity

• A weather event was captured 14 hours post-harvest (1:10 am) with wind speeds gusting to 26 knots out of ESE (wind direction which most influences test area)

• Maximum turbidity recorded at all sondes ranged from 123 to 155 NTU• Duration (4.5 hrs) and wind effect had greater influence on turbidity than harvester

Comparison of sondes located 5’ from harvest area 24 hours pre- and post-harvest

Effects of Harvest Methods on Soil Properties

• Soil cores collected (n=3)− Prior to planting to establish

baselines − At harvest (week 0) per culture

replicate to compare effects of harvest methods

− At reference (unfarmed) sites to compare with baseline and harvest methods

− At 4 and 8 weeks to evaluate changes over time

• Soil samples analyzed for particle size distribution− Sand− Fines (clay + silt)− Organic matter

Effects of Harvest Methods on Soil Properties• Sand and fines content

differed significantly between plant and harvest− Variation minimal over year− Sands increased 97-98% − Fines decreased 3 to 2.3%

• At harvest and 4 weeks post-harvest, sand and fines were similar at all sites

• At 8 weeks, sand was higher and fines lower at bottom bag sites in comparison to bottom plant and reference sites

• Over time, sand content significantly decreased and fines content significantly increased at bottom plant and reference sites

85

88

91

94

97

100

Plant Harvest - Wk0 Harvest - Wk4 Harvest - Wk8

Sand

(%)

Reference Bottom Bag Bottom Plant

0

2

4

6

8

10

Plant Harvest - Wk0 Harvest - Wk4 Harvest - Wk8

Fine

s (%

)

Recovery of Harvest Tracks

• Cross-sectional soil elevation profiles were monitored to capture harvest tracks and recovery– PVC pipe arrays pushed

into the substrate perpendicular to harvest sites

• 3-6 pipes located in harvest area

• Reference pipes on each end of the array placed outside harvest area

– Distances from bottom substrate to top of the frame at each pipe measured at weeks 0, 4, and 8

– Differences in elevation at week 0 to reference values reflected effects of culture/harvest methods

– Differences in subsequent weeks reflected soil infill or loss over time

• Soil elevations of harvest tracks standardized to reference conditions (“ground 0”) • At harvest, sediments were mounded at bag sites while a track depth of -3.7 cm was created

by the harvester. By week 4, adjacent bottom bag sites appeared to have supplied sediments to fill in harvester tracks. By week 8, both recovered to levels similar to reference conditions.

• Soil elevations significantly differed between harvest sites at each sampling period; differences were only ~7.5 cm at week 0 and <1 cm by week 8.

3.8

0.3

-0.9

-3.7

-1.8 -1.6

-5

-2.5

0

2.5

5

Harvest - Wk0 Harvest - Wk4 Harvest - Wk8

Soil

Elev

atio

n (c

m)

Bottom Bag Bottom Plant

Recovery of Harvest Tracks

0

Summary

Sunray venus production was increased by 80% using the bottom plant method versus bottom bags

Culture period to reach market size (~50 mm SL) could be reduced by 15-20% (1.8-2.5 months) using bottom plant method, which lessens risks associated with mortality

Product quality of sunray venusharvested from bottom plants was not compromised

Summary

Turbidity values either did not differ between harvest methods or were higher during the bag harvest and natural events compared to the pump-driven harvester

Impacts to water column were short term as turbidity values returned to background levels within 5-9 minutes

Consistent changes in the soils suggested that natural processes were more active in sorting particle size than were harvest methods

Summary • Physical effects of mechanical shell-

fish harvesters are reported in the literature to be short-lived with rate of recovery varying among study sites

• To determine extent and duration of potential impacts of mechanical harvesting in Florida, a pump-driven harvester was tested under actual lease conditions

• Science-based information was provided to FDACS to address statutory or regulatory barriers to allow for this harvesting activity

Questions?

For more infomaton, contact Leslie Sturmer, LNST@ufl.edu, or visit http://shellfish.ifas.ufl.edu