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TUNA FISHING SEA TRIALS NEW ZEALAND

INTRODUCTION

The objective of trial number three was to set a minimum of 4,000 hooks through the modified USD under the normal fishing conditions on a commercial fishing vessel, and evaluate its seaworthiness, and ease of use.

The trial was undertaken on the domestic longline fishing vessel F.V. Atu S., owned by Moana Pacific Ltd.

 

Sea Trial Stages
Description
of the fishery
Trial 1
F.V. Daniel Solander
Trial 2
F.V. Brenda Kay
Trial 3
F.V. Atu S
TRIAL NO. 3 : F.V. Atu S
VESSEL SPECIFICATIONS

The F.V. Atu S specifications are provided in Table 20.

Table 20. Vessel specifications for fishing vessel F.V. ATU S

Length
Beam
Draft
Gross Weight
32 metres
6.4 metres
4 metres
181 tonnes
Table 21. Summary of fishing gear used on F.V. ATU S
Mainline
3.5mm nylon with 450kg breaking strain - Brand Tolilon 74km of line on board and about 65 - 70km used per shot.
Branch lines
2.02mm nylon with 215kg breaking strain - Brand Shogun (Japanese type) Each 14.4m long
Hooks
Three types 17/0 Eagle claw, Japanese 3.6, and Mustad 16/0 DR Tuna Circle hooks An armour spring and crimp used to attach each hook to it's branch line
Clips
2.6mm x 100mm with a 6/0 barrel swivel
Floats
25kg buoyancy, 360mm in diameter Float line = 14.4m of 5mm rope
Line shooter
LS4 monofilament line setter (Lindgren Pittman) Usually sets at 10.5 knots or 325 rpm (main wheel 1m circumference)
Light sticks
100mm Big light
Setting details
speed of vessel -normally 8.5 knots Normally 1320 hooks per shot one clip every eight seconds, 12 per basket with 1.5 empty baskets by beacons 3 beacons per set

TRIAL NO. 3 : F.V. Atu S - Vessel set up

Figure 13

A number of new design features were incorporated into the USD constructed for the F.V.Atu S. to overcome problems experienced on earlier trials. The changes are described below. The USD was attached to the stern at the centreline.

Chute

The chute section of the USD was 9.5m long, and tapered along its length. The slot width was milled to two different widths along the length of the chute; 11 mm above the water line and 20 mm below the water line. The decreased width above water level was to help constrain the water flow and trace within the device above sea level. A 3.5 metre length of RHS, a 12mm x 50mm M/S flat bar and two 12mm rounds were welded on the lower side of the chute (Fig 14 ) to aid deployment and retrieval of the device through the new roller carriage section (see description below) and to increase the strength of the chute.

Figure 14
Figure 15
Figure 16
A roller carriage system which significantly improved the ease with which the USD could be retrieved and deployed was developed. The nylon rollers constrained the USD during recovery and deployment without the jamming that occurred with the previous slide system or any need of a locking arm

F.V. Atu S.
Figure 17

Strop Attachment

Because of problems with the paravanes, an alternative system for maintaining the chute at the required angle in the water was devised. This involves a chain and shock absorber system joining the tube to the transom of the fishing vessel. The length of chain dictates the angle of the chute and consequently the setting depth.

F.V. Atu S.
Figure 18
 
Figure 19

RESULTS

On 17th February 1989, while steaming to the fishing grounds the USD was deployed. Deployment was simple and took less than five minutes.

The USD was set at an angle of forty degrees from vertical, the angle was measured using a suspended vertical spirit level and adjustable protractor.

The USD performed well during the two hours of steaming at approximately ten knots. The USD was then deployed and used during a normal setting procedure.

After 13 minutes of setting, the mainline carried across the transom to the USD and become tangled around the shackles connecting the chute to the transom. The skipper removed the USD and continued shooting in the normal manner. Details of the trial conditions are provided in Table 21.

Table 21. Details of trial

DISCUSSION

During setting, the mainline is ejected from the stern, via a shooter at a faster rate than the vessel is steaming.

This allows a greater sag in each basket. As a result of this there is an excess of mainline floating in the water just behind the stern during setting. When combined with the prop wash, wind and swell, it is an easy matter for the line to become tangled around the strop connector.

DESIGN MODIFICATIONS

The skipper on the F.V. Atu S suggested the following modification to the chute.

1. Attachments at and below the waterline.

Nothing should be in the water at all except the chute, especially if the chute is operating along the vessel's centre line. Any attachments at the base of the transom or on the chute beneath or near the waterline increase the chances of foul ups.

2. Streamlining

With the current design force on the chute is created by drag through the water. This is exacerbated by its proximity to the prop wash. A potential way to minimise this would be to increase the streamlining of the leading edge of the chute.

3. Chute Backbone

The square metal support which makes up the leading edge may need to be strengthened.

4. Position

The chute would have much less chance of foul ups if placed on the port side of the vessel. This also minimises the chances of bait loss through the force of the prop wash. In normal setting circumstances baits are thrown off the port side. This is to minimise foul ups and minimise bait loss. The F.V. Atu S has a three person setting team (minimum) which allows for setting the chute up on the port side.

CONCLUSION

During the short period the chute operated the device successfully deployed bait under the water. The device achieves its purpose and the current design performs that function well. What remains to be done is implementation of a deployment method based around the port side and stronger simpler points of attachment. These points should not be construed as a major problem. The chute is very close to achieving it's initial objective of a successful 4,000 hook trial.

 

TRIAL NO. 4 -F.V. ATU S.
INTRODUCTION
On the previous trial shackles and chain that coupled the device to the boat tangled with the mainline.To overcome these problems, the connection point was moved 1.5 up the chute, so that it was well clear of the waterline. A rubber shock absorber system was incorporated into the connection to minimise direct and sudden impact on the device while maintaining it at an angle which enabled the bait delivery depth of 3m to be met.
 
Figure 20
Figure 21
METHODS  

The chute was labelled along it's length at .5 meter intervals, from 3m above the end of the chute, where the bait exits, to 6m along it's length.

From observing which of these labels was at the water line at any given moment, it was possible to determine how deep the chute was delivering the bait. For example, if the first label , at 3m, was at the water line, it meant that a bait leaving the chute at that moment would be 1.4m under the water. These depths and related labels on the chute are shown in Table 22.

Table 22. Bait delivery depths of device related to labels on the device

Distance (m) from bottom of device Label on chute Depth of bait delivery (m)
3
1
1.4
3.5
2
1.75
4
3
2.1
4.5
4
2.6
5
5
3.2
5.5
6
3.8
6
7
4.7
The chute's setting depth was monitored three times in each setting operation. This was done by noting the label which was the closest to the water at five second intervals for a period of five minutes. This gave fifteen minutes of monitoring during each set to determine where the most common setting depth was.

RESULTS

The new system was tested five times. Four times in an actual line setting operation and once while steaming. The trials were conducted off the north east coast of New Zealand, the location of the trials is given in Table 23.

Table 23 Location of trials - third trip F.V.ATU S

Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
34 25S
34 14S
34 26S
35 08S
Not recorded
174 09E
174 54E
175 15E
175 69E
Not recorded

H00K TRIALS

The USD delivered 5,270 baited hooks without entanglements during the four sets.

SETTING DEPTH

The elasticity of the Forsheda mooring compensator deteriorated over the four sets and this reduced the setting angle and depth of the USD. On the first set the bait exit point was consistently deeper than 3 metres, but by the fourth set the depth of the bait exit point had reduced to around 2 metres.

WEATHER CONDITIONS

The conditions were mild for all four fishing sets, and the fifth trial during normal steaming. For all the shots the swell was never above 1m and the wind always from 10 to 15 knots. The vessel speed was always between 8 and 9 knots.

DISCUSSION

The chute delivered 5,270 hooks without the entanglement problems of previous trials. One or two light sticks caused minor entanglements. This was soon rectified by placing the light stick further up the branch line so they did not come into contact with the chute. The operators of the chute found it simple to use.

However, the chute did not meet it's requirement for setting hooks at a depth of 3m. Graphs 1 to 5 demonstrate that initially the setting depth was mainly in excess of 3m. But by the fifth set this had dropped to a point where more than half of the hooks were being set at a depth less than 3m.

This is most likely due to a stretching of the rubber strop used to govern the setting depth. It was noticed by the third day that the chute was riding higher in the water. The rubber strop was found to have stretched. Given the mild conditions in which testing was performed, the crew of the vessel and the observer believed that under strong conditions the rubber would have snapped.

CONCLUSION

A stronger and more reliable measure for governing the setting depth is required. The skipper suggested that a strong steel spring in place of the rubber would be more effective.

ADDENDUM

Since this trial a new method for controlling the setting depth on the chute has been developed and trialled. This system involves a caged spring which is strong enough to withstand the considerable pressures placed upon it by the chute, while still maintaining the required setting depth (Fig 22). Only one set of data has been collected on the setting depths.

This confirmed a setting depth of greater than 3m. Observations over a ten day period during setting confirmed a constant setting depth in excess of three metres.

Figure 22
Figure 23

Bait Setting Times

An important operating standard for the USD is speed with which baits can be fed into the USD. New Zealand vessels set one baited hook between every 7 and 9 seconds. A number of timing experiments were carried out on the various models, and the results are summarised in Table 1.

Table 1: Run times for various types of bait and various tube lengths.

Length
of tube
Vessel speed (knots)
Device setting
Bait
Number of trials
Mean (sd) of run times(seconds)
6
6.5-7.5
Venturi without snood arm
sanmar (50 gm)
23
4.49 (0.57)
6
6.5-7.5
Venturi without snood arm
squid(20 - 30 count)
54
3.93 (0.53)
6
6.5-7.5
Venturi without snood arm
squid(40 - 60 count)
56
4.08 (0.44)
6
6.5-7.5
Snood arm and venturi
sanmar (50 gm)
49
3.40 (0.27)
6
6.5-7.5
Snood arm and venturi
squid (20 - 30 count)
46
3.16 (0.39)
7
6.5-7.5
Snood arm and no venturi
sanmar (50 gm)
50
3.52 (0.97)
7
6.5-7.5
Snood arm and no venturi
squid (20 - 30 count)
50
3.35 (0.42)
9
6.5-7.5
Snood arm and venturi
sanmar (50 gm)
7
4.01 (0.28)

9

6.5-7.5
Snood arm and venturi
squid (20 - 30 count)
29
4.05 (0.67)

CONCLUSIONS FROM ALL COMMERCIAL TRIALS OF THE USD

USD CONFIGURATIONS

The configurations on three commercial vessels reflect both the incremental design changes from the experience gained during the trial process and requirements of individual vessel layout, fishing practices and skipper/crew requirements. Although the basic design concept remained unchanged each vessel had unique requirements. If the USD is used widely in the fishery it is likely that a range of options, will be necessary to tailor the USD to each vessel's requirements.

Setting tube

The setting tube operated in a range of setting depths from three to seven metres. As the length of the tube increase so does the weight and strengthening required.

Figures 24 and 25 outlines some of the modifications in tube design and material under consideration for the development of a 12 metre USD for a 50 metre tuna vessel. As the weight increases other aspects of the USD (such as the carriage and deployment and retrieval system) will require strengthening as well.

Figure 24

On several trials problems occurred where the snood was pulled out of the setting tube before the baited hook had left the base of the tube. The use of brushes at the top of the tube has overcome this problem.

Bait trough

The major design requirement for the trough was to ensure adequate and even flushing of the water over the trough surface and the smooth passage of water to the mouth of the setting tube. The devices with multiple water outlets at the top of the trough provided adequate flushing.

Hinge assembly

The basic hinge assembly with the use of shock absorbers performed effectively on all trials.

Carriage system

Although problems occurred in moving the tube into and out of the setting position during the F. V. Daniel Solander and F. V. Brenda Kay trials, improved roller carriage design used on the F. V. Atu S second trial has over come this problem. For the larger 50 metre vessels a hydraulic lift may be necessary because of the increased length and weight of the USD.

Setting Angle devices

Paravanes

When paravanes were trialled in the open sea by tuna fishing vessels significant problems occurred. The commercial trials identified three drawbacks in using the paravanes.

1. The paravanes made setting the USD difficult in rough seas. Once the paravane was in the water it created a strong downward force making retrieval of the device from the water a slow and arduous process.. Setting tubes fitted with paravanes were also difficult to deploy and retrieve, particularly in adverse conditions.

2. Larger vessels with vastly greater prop wash turbulence experienced problems with two of the paravane types being unable to hold the minimum setting angle required. Although the Arrowhead paravane had the smallest surface area of any of the paravanes trialled it was by far the most powerful and the only one that achieved a correct setting angle when trialled from the F.V. Daniel Solander in the Southern ocean.

3. During the setting process, hooks and snoods were occasionally caught in the paravane, causing delays in the longline setting operation while the USD was retrieved and hooks/snoods removed. Potential causes of the problem were considered ranging from operator error to a back wash phenomenon behind the vessel.

Shock absorbers

The shock absorber method of angle setting has successfully operated in rough seas over several trips on a 30 metre tuna vessel. The use of a Forsheda mooring compensator may be appropriate for smaller (10 - 15 metre) vessels. Larger vessels will require a spring shock absorber.(see figs 20 and 23).

Weighted tube

An alternative to the shock absorber method may be to add weight the tube to set the angle of the setting tube. Weights could be added or subtracted from the tube to adjust for varying setting speeds and propeller wash conditions (see Figure 24 E)

Recovery and deployment devices

The optimal angle for deploying and retrieving the USD is the angle of set when the device is fishing (40 to 50 degrees). Because of vessel configurations, none of the trials were able to deploy and retrieve at this angle. The vertical deployment and recovery device (as used on the first ATU S trial) was the least effective method, and potentially the most hazardous if the USD (when vertical) had broken loose from the mounting in a rough sea.

The need for up to five crew to deploy and retrieve the device (as occurred on the F. V. Daniel Solander) trial can be overcome by the use of a modified carriage system (see Figure 24), and a hydraulic retrieval and deployment device. For vessels up to 30 metres length a simple block and tackle pulley system would be sufficient to deploy and retrieve the setting tube.

Safety Issues

The early commercial trials identified a number of safety issues related to the operation of the USD device. Modifications made for the F.V. Atu S second trial ensured adequate safety of the crew during the deployment, retrieval and fishing stages. These modifications included removing the paravanes, reducing the friction of the setting tube on the carriage system, changes in the securing system for the device when not in use, and changing the deployment and recovery system so that crew did not have to lean out over the stern of the vessel.

ACKNOWLEDGEMENTS

This work was commissioned by the Department of Conservation through the Conservation Services Levy funded by the New Zealand fishing industry.

We would like to acknowledge the assistance of Department of Conservation staff (in particular Janice Molloy and Ian West).

Valuable assistance was also provided by Harry Verney (skipper of the M. V. Frae), Mike and Soo Wells (owners of the F.V . Kariqa), Jeff Moffat (Skipper of the F.V. Atu S), Tony Irvine (Managing Director , Moana Pacific Engineering for providing engineering assistance and the design of the spring shock absorber), Brent Marshall, (Northern Fleet Manager, Moana Pacific Fisheries), Professor Manly (advice on chi squared statistic). Carl Fry, (Skipper of the F. V. Daniel Solander), Scott Roger, First Mate, and crew. Paul Brewer, (Skipper of the F.V.Brenda Kay), Kent Peters, (General Manager,Tobe International )

REFERENCES

Barnes, P. and Walshe, K. 1997. Underwater setting methods to minimise the accidental and incidental capture of sea birds by surface longliners. Report on a prototype device developed by Akroyd Walshe Ltd. / Paul`s Fishing Kites Ltd. Science for Conservation: 66 Department of Conservation Wellington, New Zealand.

Brothers, N. 1991; Albatross mortality and Associated Bait Loss in the Japanese Longline Fishery in the Southern Ocean. Biological Conservation, 55 : 255 - 268

Croxall, J.P. and Prince, P.A. 1990; Recoveries of Wandering Albatrosses Diomeda exulans ringed at South Georgia 1958 - 1986. Ringing and Migration, 11 : 43 - 51

Duckworth, K. 1995; Analyses of factors which influence accidental capture of sea birds in the Japanese southern bluefin tuna longline fishery in New Zealand waters, 1989 -93. New Zealand Fisheries Assessment Research Document 95/26

Weimerskirch, H., Brothers, N., and Jouventin, P. 1997; Population dynamics of Wandering Albatross Diomeda exulans and Amsterdam Albatross D. amsterdamensis in the Indian Ocean and their relationships with long-line fisheries: Conservation Implications. Biological Conservation, 79 : 257 - 270

Description
of the fishery
Trial 1
F.V. Daniel Solander
Trial 2
F.V. Brenda Kay
Trial 3
F.V. Atu S
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