Remodelling the Scallop Lantern Net

Final Report

Island Scallops Ltd

AIMAP 2011-P18

Executive Summary

Further expansion of the BC scallop aquaculture industry is currently constrained by difficulties in acquiring new farm area. Growth of the industry relies on innovations in farming technology and increases in production efficiency. This AIMAP project addressed the need for technology that improves the production system for scallops during the ocean grow-out stage.

The standard material employed in the grow-out of scallops in BC is the cylindrical “lantern” net. The objective of the project was to remodel the lantern net to increase efficiency and productivity without increasing farm footprint. The technical approach was to develop a new, larger-diameter lantern net design in order to increase the capacity of the existing farm infrastructure. With the support of AIMAP funding, two new nets were successfully designed, modified, and tested. They comprised a 90-cm diameter, 12-tier net and an 80-cm diameter, 15-tier net.

Although the new net design did not prove to be suitable for the intended purpose of growing scallops to harvest size, it did show potential for culturing smaller scallops during the intermediate growth stage. Further trials are required to assess growth rate and survival of scallops in the new lantern nets, but based on area alone the new design significantly increases the capacity of a farm by at least 50%. Consequently, the innovative nets potentially have a significant economic impact on scallop aquaculture through increased productivity and decreased production cost.

Introduction

Scallop aquaculture has been under development in British Columbia for over two decades. Currently, the opportunity for expansion of scallop farm area is very limited, so growth of the industry is dependent on innovations in farming methods and more efficient use of existing farm space. The project addressed this problem by remodelling the nets used in scallop farming to allow increased production without increased farm size.

In BC, scallops are typically cultured in cylindrical mesh “lantern” nets suspended from horizontal “longlines” submerged in deep water. This technology has been successfully employed in Japan and, with modifications, has proved to be a dependable method of producing a high quality scallop in BC waters. Traditionally, lantern nets are 50 cm in diameter and comprise 10 compartments (tiers). Island Scallops Ltd (ISL) has already made significant improvements to the standard lantern net by designing a 60-cm diameter net with 12 compartments, constructed of larger mesh and stronger steel. More recent refinements have included larger net entry openings, overlapping stitching design, and changes in mesh sizes. This custom net is now in widespread use at BC scallop farms. 

The objective of the current project was to further customize the lantern net design to allow scallop farming to become more efficient and cost effective. This involved the design, manufacture, and testing of a new net with a larger diameter and additional tiers. Successful employment of the innovative net was anticipated to significantly increase productivity at the existing farms without increasing the footprint.

The project was consistent with the following AIMAP goals:

• increased sustainable production through increased productivity and reduced production costs
• increased diversification through the development of alternate species (scallops).

Methods and Solutions

Two new lantern nets were designed for the project: an 80-cm diameter net with 15 tiers and a 90-cm diameter net with 12 tiers. The approach was to compare performance in these nets with that in the 60-cm diameter, 12-tier model currently used by the industry.

All tiers in the new nets were stocked at the same scallop density based on the standard farm practice of loading each tier in the 60-cm diameter nets with 25-30 scallops about 10 cm in size. Table 1 shows current and projected production and costs using the three net designs. The increased capacity per net provided by the 90-cm diameter, 12-tier net design (124%) was slightly greater than the 80-cm diameter, 15-tier net design (120%). However, the increased capacity per longline was significantly higher with the 80-cm diameter nets (61%) than the 90-cm nets (49%) due to the overall number of nets per longline.

The new lantern nets were ordered from a Chinese manufacturer with a successful history of supplying custom scallop farming materials to ISL. Specific details of construction included net denier (strand thickness), wire frame diameter, and top and side rope size and configuration. Unfortunately, when the samples arrived, it was apparent that the framework of the larger diameter nets was not strong enough to maintain the shape of the net when fully loaded with scallops. Also, the number of ropes along the sides of the nets was insufficient. 

Subsequently, the nets were re-designed with a central support rope and four additional side ropes. The original manufacturer, however, was unable to provide the modified net order. In the fall of 2011, a trip was made to China to visit various factories that could produce the custom nets. The improved nets were eventually supplied by Atlantic Capes Fisheries Inc.^{Footnote 1}

Adding a central support rope was a significant improvement to the design of the larger diameter nets, but ultimately did not completely solve the problem. To further strengthen the framework, the central support rope was looped around the wire frame at the base of each tier and secured with a metal hog-ring.
While effective, these modifications essentially doubled the cost of the nets due to the added labour and small size of the custom order. As a result, the number of nets ordered was reduced by about one-third, from 425 to 285 of each design, as a cost savings. The modifications also resulted in a significant delay in receiving the lantern nets and consequently testing them in the ocean. Nevertheless, the nets were eventually loaded with scallops and placed at the ocean farms for evaluation. 

Due to the abbreviated ocean testing period, a significant difference in scallop growth and mortality was not recorded in the new nets in comparison with in the existing nets by the end of the project. However, an assessment of the functionality of the new net design under commercial conditions was completed. The primary problem with both designs was that, fully loaded with
large scallops and fouled by epiphytes, the nets approached the maximum swing load rate for the booms on the work boats and were not very manageable.

Summary and Conclusions

The original design of the larger-diameter lantern nets required modifications to provide adequate support. Alterations were successfully incorporated into the design, but ultimately the new model was not suitable for the intended purpose; the new nets could not be used to grow scallops to harvest size since the weight of a fully-loaded, fouled net was unmanageable.

However, the remodelled nets may have potential for culturing smaller scallops during the intermediate growth phase and in this way significantly increase the capacity of a farm. Further work will be conducted to assess the growth and survival of smaller scallops in the larger-diameter nets. Based on the total surface area of net per longline, the increased capacity provided by the new nets is 50% for the 90-cm diameter, 12-tier nets and 63% for the 80-cm diameter, 15-tier nets.

Overall, the increased capacity provided by the new net design supports further development of lantern nets for the company and the BC scallop farming industry. This will allow increased production without a significant increase in farm infrastructure or footprint, which will allow increased efficiency at all scallop farms using lantern nets.

Deliverables

Following is a summary of project deliverables:

• Development of a novel net design
  
  A new larger-diameter lantern net design was successfully designed and tested. This net effectively and significantly increased the capacity of each scallop longline. However, it did not prove to be acceptable for growing scallops to harvest size due to the weight when fully loaded with harvest size scallops. The new nets will be re-used for growing smaller, pre-harvest size scallops.

• Increased utilization of farm infrastructure
  
  Even though the new nets will not be employed as intended, their use for growing intermediate-size scallops will optimize utilization of farm infrastructure by increasing the capacity per longline.

• Comparison with existing lantern net
  
  No difference was observed in growth and mortality of scallops cultured using the existing nets and the two new models during the project due to the shortened testing period. Since these nets were not considered suitable for final grow-out of scallops, comparison of scallop meat size at harvest will not be made.