SLIDE 1 E va lua tion of the L a rg e Me sh Be lly Pa ne l in Sma ll Me sh F ishe rie s a s a Me thod to Re duc e Ye llowta il a nd Windowpa ne F lounde r Byc a tc h on Ge org e s Ba nk
Cornell University Cooperative Extension Marine Program - Riverhead, NY Emerson Hasbrouck John Scotti, Tara Froehlich Kristin Gerbino, Joseph Costanzo Cornell University
- Dept. of Natural Resources – Ithaca, NY
Patrick Sullivan Superior Trawl – Narragansett, RI Jonathan Knight F/V Karen Elizabeth – Point Judith, RI Captain Christopher Roebuck
F unde d by the Nor the ast Coope r ative Re se ar c h Pr
am
SLIDE 2 Project Purpose
The project addressed yellowtail and windowpane flounder bycatch concerns on Georges Bank by evaluating the effectiveness of a standard net modified with a large mesh belly panel to reduce bycatch of these species in deep water while targeting squid and whiting
- The project was proposed by GB small mesh fishermen as
means to pursue gear certification to be used for yellowtail and windowpane bycatch avoidance in GB small mesh fisheries when Accountability Measures are triggered.
- Based on similar inshore work conducted by CCE and funded
through CFRF
SLIDE 3 Project Summary
The vessel towed the control trawl (3-bridle 4-seam standard box trawl) and experimental trawl (box trawl modified with the large mesh belly panel) simultaneously. Comparisons were based on paired differences in catch by species.
Four species were analyzed including yellowtail flounder, windowpane flounder, squid and whiting
(Point Judith, RI), a twin- trawl vessel, was chartered to conduct all at-sea research.
SLIDE 4 Sketch of Large Mesh Belly Panel
The large mesh panel was made of 80cm (32”) mesh 6mm poly webbing, 2 meshes deep X 16 meshes wide sewn into the standard 16cm (6”) mesh of the belly. With the ‘saw-toothing’ of the 16cm mesh, this yields an effective opening of 3 full meshes deep, a total of about 8’ of large mesh. The panel attaches five 16cm meshes (approx. 2.5’) behind the footrope and goes from gore to gore (22 meshes wide or approx. 30’).
356 x 16cm 80cm large mesh 1st bottom belly 126 – 16cm meshes 16cm sawtooth 80 cm webbing 115 – 16cm meshes 16cm sawtooth GORE
SLIDE 5 Large Mesh Belly Panel
A net diagram is included in the report as is a description
construction of the belly panel for different size nets.
SLIDE 6 Project Locations
Phase 2 Phase 1
SLIDE 7 Phase 1 Summary
- Phase 1 of the project was conducted in January 2014 at the
Southern Flank of Georges Bank, near Munson Canyon
- 40 paired tows were completed in one 6-day trip
- Squid was the target species
- All tows were 30 minutes in length
- Tows occurred during both the day & night
SLIDE 8 Phase 1 Results – Yellowtail Flounder
Paired Tow Difference (lbs) (Control-Experimental)
Distribution of Paired Tow Differences for Yellowtail Flounder
Frequency
The large mesh belly panel significantly reduced the quantity of yellowtail bycatch. Paired t-test results showed a significant difference in catch weight between the control and experimental net (p=<0.0001).
SLIDE 9 Phase 1 Results – Yellowtail Flounder
2000 4000 6000 8000 10000 12000 14000
LARGE MESH BELLY PANEL CONTROL Catch Weight (lbs)
Total Catch Weight of Yellowtail Flounder (lbs) in the Experimental and Control Net for All Tows Combined
The large mesh belly panel reduced yellowtail flounder bycatch by 72.3%.
SLIDE 10 Phase 1 Results – Windowpane Flounder
The large mesh belly panel significantly reduced the quantity of windowpane bycatch. Paired t-test results showed a significant difference in catch weight between the control and experimental net (p=<0.0001).
Distribution of Paired Tow Differences for Windowpane Flounder
Paired Tow Difference (lbs) (Control – Experimental) Frequency
SLIDE 11 Phase 1 Results - Windowpane Flounder
The large mesh belly panel reduced windowpane flounder bycatch by 50.9%.
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
LARGE MESH BELLY PANEL CONTROL Catch Weight (lbs)
Total Catch Weight of Windowpane Flounder (lbs) in the Experimental and Control Nets for All Tows Combined
SLIDE 12 Phase 1 Results - Whiting
Paired t-test results showed no significant difference in whiting catch between the control net and the net modified with the large mesh belly panel (p=0.8817).
Paired Tow Difference (lbs) (Control – Experimental)
Distribution of Paired Tow Differences of Whiting
Frequency
SLIDE 13 Phase 1 Results - Whiting
50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
LARGE MESH BELLY PANEL CONTROL Catch Weight (lbs)
Total Catch Weight of Whiting (lbs) in the Experimental and Control Nets for All Tows Combined
Retention of whiting was maintained using the large mesh belly panel net.
SLIDE 14 Phase 1 Results - Squid
Paired t-test results showed a significant difference in the catch weight between the control and experimental net (p = 0.0022). The experimental net retained more squid than the control net. Although this may be a statistically significant result for this project, it is probably not biologically or commercially significant. The mean of the paired differences was only 5 lbs. Distribution of Paired Tow Differences for Squid
Paired Tow Difference (lbs) (Control-Experimental) Frequency
SLIDE 15 Phase 1 Results - Squid
200 400 600 800 1000 1200 1400
LARGE MESH BELLY PANEL CONTROL
Catch Weight (lbs)
Total Catch Weight of Squid (lbs) in the Experimental and Control Nets for All Tows Combined
SLIDE 16 Phase 1 Other Effects Day Vs. Night - Yellowtail
Frequency 500 1000 5 10 15 Frequency 500 1000 1 2 3 4
DAY
Paired Differences (lbs) (Control – Experimental)
Experimental fishing occurred both day and night. Data was analyzed for differences between day/night catches.
Paired Tow Differences for Yellowtail Flounder Catch
Paired Differences (lbs) (Control – Experimental)
NIGHT
SLIDE 17 Phase 1 Day Vs. Night Results Yellowtail
T-test results showed a significant difference in the catch
weights between the control and experimental nets during day tows (p-value <0.0001). Non-parametric bootstrap analysis provided similar results.
The t-test results showed a non-significant result for catch
differences at night (p-value = 0.08757). However, the non- parametric bootstrap analysis returned a significant result (p-value = 0.026). The data are Gaussian, so the t-test is the more appropriate statistic to use.
Only 5 night tows caught yellowtail. Night-time results on
their own are therefore lacking statistical strength.
SLIDE 18 Phase 1 Day Vs. Night Windowpane Flounder
DAY
Paired Differences (lbs) (Control – Experimental)
Paired Tow Differences for Windowpane Flounder Catch
Paired Differences (lbs) (Control – Experimental)
NIGHT
Frequency
50 100 150 200 250 300 2 4 6 8 12 Frequency
50 100 150 200 250 300 0.0 0.5 1.0 1.5 2.0
SLIDE 19 Phase 1 Day Vs. Night Results Windowpane Flounder
T-test results showed a significant difference in the catch
weight between the control and experimental net during day tows (p-value <0.0001). Non-parametric bootstrap analysis provided similar results.
T-test results showed a non-significant result for catch
differences at night (p-value = 0.07701). However, the non- parametric bootstrap analysis returned a significant result (p=0.008). The data are Gaussian, so the t-test is the more appropriate statistic to use.
7 night tows caught windowpane, 2 of which caught less than
- ne pound. Night-time results on their own are therefore
lacking statistical strength.
SLIDE 20
Phase 1 Other Effects - Side (Port vs. Starboard)
We looked at yellowtail and windowpane flounder
catches on each side of the vessel separately to see if the results were different based on which side of the vessel the control or experimental net was fished on.
The experimental and control nets were switched once
during the experiment in order to randomize for side.
We performed t-tests and non-parametric bootstrap
analysis on the paired tow differences in catch for side.
SLIDE 21 Phase 1 Side Results Yellowtail
Paired Tow Differences for Yellowtail Flounder Catch
Frequency 500 10 1 2 3 4 5
Frequency 500 1000 1 2 3 4
Control Net on the Port Side Control Net on the Starboard Side T-test results showed a significant difference in the catch weight between the control and experimental nets when the control net was on the port side (p-value =0.0002087) and a significant difference when the control net was on the starboard side (p-value <0.0001). Non- parametric bootstrap analysis provided similar results.
Paired Differences (lbs) (Control – Experimental) Paired Differences (lbs) (Control – Experimental)
SLIDE 22 Phase 1 Side Results Windowpane
Paired Tow Differences for Windowpane Flounder Catch
Control Net on the Port Side Control Net on the Starboard Side T-test results showed a significant difference in the catch weight between the control and experimental nets when the control net was on the port side (p-value<0.0001) and a significant difference when the control net was on the starboard side (p-value <0.0001). Non-parametric bootstrap analysis provided similar results.
Frequency
50 100 150 200 250 300 1 2 3 4 5 6 Frequency
50 100 150 200 250 300 2 4 6 8 10
Paired Differences (lbs) (Control – Experimental) Paired Differences (lbs) (Control – Experimental)
SLIDE 23
Phase 1 Door Spread Summary
We tested to see if there was a statistically significant
difference in door spread between the control and experimental nets at the start of the tow and the end of the tow.
T-test results showed no significant difference in door
spread at the start of the tow (p-value = 0.5554) or at the end of the tow (p-value = 0.2809).
Since there is no statistically significant difference in
door spread, there is no reason to analyze actual catch as a function of door spread. Door spread has no effect.
SLIDE 24 Phase 2 Summary
- Phase 2 of the project was conducted in August 2014 on the Northern
Area of Georges Back designated as Cultivator Shoals
- 42 paired tows were completed in one 5-day trip
- Whiting was the target species
- Tows were 15 minutes in length and occurred during both the day &
night
SLIDE 25 Phase 2 Results – Yellowtail Flounder
Distribution of Paired Tow Differences for Yellowtail Flounder
The large mesh belly panel significantly reduced the quantity of yellowtail bycatch. Paired t-test results showed a significant difference in catch weight between the control and experimental net (p=<0.0001).
Frequency 20 40 60 80 2 4 6 8 10 12
Paired Tow Difference (lbs) (Control-Experimental)
SLIDE 26 Phase 2 Results – Yellowtail Flounder
Total Catch Weight of Yellowtail Flounder (lbs) in the Experimental and Control Net for All Tows Combined
The large mesh belly panel reduced yellowtail flounder bycatch by 80.7%.
200 400 600 800 1000 1200 LARGE MESH BELLY PANEL CONTROL Catch Weight (lbs)
SLIDE 27 The large mesh belly panel significantly reduced the quantity of windowpane bycatch. Paired t-test results showed a significant difference in catch weight between the control and experimental net (p=0.0023).
Distribution of Paired Tow Differences for Windowpane Flounder
Frequency 5 10 5 10 15
Phase 2 Results - Windowpane Flounder
Paired Tow Difference (lbs) (Control-Experimental)
SLIDE 28 Phase 2 Results - Windowpane Flounder
The large mesh belly panel reduced windowpane flounder bycatch by 59.3%.
Total Catch Weight of Windowpane Flounder (lbs) in the Experimental and Control Nets for All Tows Combined
20 40 60 80 100 120 LARGE MESH BELLY PANEL CONTROL Catch Weight (lbs)
SLIDE 29 Phase 2 Results - Whiting
Distribution of Paired Tow Differences of Whiting
Frequency
1000 2000 3000 400 5 10 15 20 25 30
Paired Tow Difference (lbs) (Control-Experimental)
Paired t-test results showed no significant difference in the catch weight between the control and experimental net (p = 0.1787).
SLIDE 30 Phase 2 Results - Whiting
Total Catch Weight of Whiting (lbs) in the Experimental and Control Nets for All Tows Combined
Retention of whiting was maintained using the large mesh belly panel net.
5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 LARGE MESH BELLY PANEL CONTROL Catch Weight (lbs)
SLIDE 31 Phase 2 Results - Squid
Paired t-test results showed no significant difference in the catch weight between the control and experimental net (p = 0.1339).
Distribution of Paired Tow Differences for Squid
Frequency
0.0 0.5 5 10 15 20 25
Paired Tow Difference (lbs) (Control-Experimental)
SLIDE 32 Phase 2 Results - Squid
Retention of squid was maintained using the large mesh belly panel net.
Total Catch Weight of Squid (lbs) in the Experimental and Control Nets for All Tows Combined
2 4 6 8 10 12 LARGE MESH BELLY PANEL CONTROL Catch Weight (lbs)
SLIDE 33 Phase 2 Other Effects Day Vs. Night - Yellowtail
DAY
Paired Differences (lbs) (Control – Experimental)
Experimental fishing occurred both day and night. Data was analyzed for differences between day/night catches.
Paired Tow Differences for Yellowtail Flounder Catch
Paired Differences (lbs) (Control – Experimental)
NIGHT
Frequency 20 40 60 80 2 4 6 8 12 Frequency 20 40 60 80 0.0 0.5 1.0 1.5 2.0
SLIDE 34
Phase 2 Day Vs. Night Results Yellowtail
T-test results showed a significant difference in the
catch weight between the control and experimental net during day tows (p-value <0.0001) and a significant difference during night tows (p-value = 0.02717). Non- parametric bootstrap analysis provided similar results.
Only 5 tows occurred at night. Night-time results on
their own are therefore lacking statistical strength.
SLIDE 35 Phase 2 Day Vs. Night Windowpane Flounder
DAY
Paired Differences (lbs) (Control – Experimental)
Paired Tow Differences for Windowpane Flounder Catch
Paired Differences (lbs) (Control – Experimental)
NIGHT
Frequency 5 10 4 8 12 Frequency 5 10 0.0 1.0 2.0 3.0
SLIDE 36
Phase 2 Day Vs. Night Results Windowpane Flounder
T-test results showed a significant difference in the
catch weight between the control and experimental net during day tows (p-value = 0.0033).
There was no significant difference in the catch weight
between the control and experimental net during the night tows (p-value = 0.2122). Non-parametric bootstrap analysis provided similar results.
Only 2 night tows caught windowpane flounder. Night-
time results on their own are therefore lacking statistical strength.
SLIDE 37
Phase 2 Other Effects - Side (Port vs. Starboard)
We looked at yellowtail and windowpane flounder
catches on each side of the vessel separately to see if the results were different based on which side of the vessel the control or experimental net was fished on.
The experimental and control nets were switched twice
during the experiment in order to randomize for side.
We performed t-tests and non-parametric bootstrap
analysis on the paired tow differences in catch for side.
SLIDE 38 Phase 2 Side Results Yellowtail
Paired Tow Differences for Yellowtail Flounder Catch
Control Net on the Port Side Control Net on the Starboard Side T-test results showed a significant difference in the catch weight between the control and experimental nets when the control net was on the port side (p-value =0.00036) and a significant difference when the control net was on the starboard side (p-value <0.0001). Non-parametric bootstrap analysis provided similar results.
Paired Differences (lbs) (Control – Experimental) Paired Differences (lbs) (Control – Experimental)
Frequency
20 40 60 80 100 2 4 6 8 12
Frequency
20 40 60 80 100 2 4 6 8 1
SLIDE 39 Phase 2 Side Results Windowpane
Paired Tow Differences for Windowpane Flounder Catch
Control Net on the Port Side Control Net on the Starboard Side
Paired Differences (lbs) (Control – Experimental) Paired Differences (lbs) (Control – Experimental)
Frequency 5 10 2 4 6 8 Frequency 5 10 2 4 6
SLIDE 40 Phase 2 Side Results Windowpane
T-test results showed a nearly significant difference in the
catch weights between the control and experimental nets when the control net was on the port side (p-value =0.061). However, bootstrap analysis of the same data yielded a significant result (p-value = 0.012). The Shapiro-Wilk test for normality indicated that the data is not Gaussian. Therefore, the bootstrap is the more appropriate test and the catch difference is significant.
There was a significant difference in the catch weights
between the control and experimental nets when the control net was on the starboard side (p-value =0.01616). Non- parametric bootstrap analysis provided similar results.
SLIDE 41
Phase 2 Door Spread Summary
We tested to see if there was a statistically significant
difference in door spread between the control and experimental nets at the start of the tow and the end of the tow.
T-test results showed no significant difference in door
spread at the start of the tow (p-value = 0.07014) or at the end of the tow (p-value = 0.0897).
Since there is no statistically significant difference in
door spread, there is no reason to analyze actual catch as a function of door spread. Door spread has no effect.
SLIDE 42 Summary of Results
Species Phase 1 Phase 2 Yellowtail Flounder Significant reduction (72.3%) Significant reduction (80.7%) Windowpane Flounder Significant reduction (50.9%) Significant reduction (59.3%) Whiting No Statistical Difference in catch between control and experimental nets No Statistical Difference in catch between control and experimental nets Squid Statistical difference. Mean of the differences is 5 lbs. No Statistical Difference in catch between control and experimental nets
Possible additional effects of day/night, side and door spread do not have an effect
SLIDE 43
Ba se d o n the se re sults, sho uld the la rg e me sh b e lly pa ne l g e a r te c hno lo g y b e a ppro ve d a s a n Ac c o unta b ility Me a sure in the sma ll me sh Ge o rg e s Ba nk fishe rie s?
SLIDE 44 Acknowledgements
NMF
S No rthe a st Co o pe ra tive Re se a rc h Pro g ra m
F
/ V K a re n E liza b e th – Ca pta in Chris Ro e b uc k a nd Cre w, Po int Judith, RI
Supe rio r T
ra wl I nc . – Jo na tha n K nig ht, Pt. Judith, RI
Sq uid T
ra wl Ne two rk Pro je c t Adviso ry Co mmitte e , Wo rking Gro up, Pla nning Gro up a nd me mb e rs
