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Selectivity Devices

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Selectivity Section Developments

Horizontal Separator Trawl

Main use: To separate round fish such as cod from flatfish and crab. This panel can be inserted in many designs to the trawl, but preferably a model two seam. It starts at the front of the trawl and executes all the path to the last belly or the division ends in a high and a lowering of the codend. To prevent the migration of fish from the top to the bottom, it is usually made of small mesh size. The trawls of horizontal split were used in experiments of selectivity for the Scotia Fundy and Quebec to separate from the cod of plaice. The height of the panel is modified using strops attached to the shoes, in the Quebec experience the group of experts has been adjusted from 1 to 5 feet from the bottom.

The results differed, Scotia Fundy The greater part of the cod is gone in the bottom section. In the experiments conducted in Quebec 75 per cent of the cod were separated in the upper section of the trawl.

Topless trawl:

main use:

to release round fish species such as cod from species of fish dishes.
When the trawling was introduced for the first time the vessels were targeting the fish dishes and the top and bottom of the screen was equal. When the fish became round was a "square" or the top cover has been added which restricts discharges of round fish on the top of the net.
Since the objective is now to eliminate the catches of cod, and the behavior of the fish. Studies have shown that the flat fish maintained at a low level in the trawl fisheries, the designers removed the "square", now the first and the second summit of flanks have been deleted. These experiences have not led to a significant reduction of catches of fish dishes.
Tests are continuing to edge of a seiner scottish in the Gulf of St. Lawrence. The first results are encouraging.
It is also hoped that this technique will allow the release of the fish without having contact with the gear and reduce the incidence of mortality.

Shortened Lastrige cordes:

main use: to

keep diamond meshes in the codend and the extension piece open under duress.
Ropes are measures the equality with the codend and the net is then securely attached to ropes with approximately 15% of slack. The result is the strings, in taking the towed load leaving the meshes free to open. The slack meshes have a more easy escape for the young fish. Good results from cod discharges have been obtained during the experiments in the Gulf of St. Lawrence.

There have been attempts to develop a device to measure the percentage of slack on the rope of compensation.

Square mesh:

main Use: to

release all juvenile species round fish and size select particular cod. Not recommended for flat fish release.

Tests in the Trawling and purse seine fishing scottish have proved conclusively that the square mesh works extremely well in the liberation of round fish. However, these same tests have proved that it is harmful for the flat-fish escapes.

In some cases the complement the codend is manufactured from square mesh, but it is possible to insert sections of square meshes at strategic points in the net and get good results. These sections are known as "windows".
We must be careful when joining the square mesh with diamond mesh to obtain the correct configuration.
Most square mesh is just running on the Diamond Mesh square, when this happens to knotted can become weak to the nodes. Slip knot is also frequent during the use of knotted netting. The best material for this purpose is knotless netting but this is not commonly used mainly because of the cost factor.
Square mesh asses are now optional in the industry of the groundfish fishery in Nova Scotia, vessels may use one or the other or with a square mesh of 140 mm 155 mm diamond mesh. ?
Square mesh of tests have been carried out in all of the Maritime provinces, the Great Lakes basin and in British Columbia.

Panel with 150 Feet of Doorspread

Chalutiers pêchant au large de la Nouvelle-Écosse, du Canada dans des domaines tels que Georges Bank ont eu d'excellents résultats à l'aide de panneaux de séparation horizontale conçu et fabriqué par Crimond pour libérer la morue tout en ciblant l'églefin.

Le comportement des poissons. Des études ont montré que l'aiglefin nager haute lors de la saisie le chalut alors que les morues ont tendance à garder faible.

Les résultats de certains navires ont montré que, même dans les zones à forte concentration de morue, le ratio de capture de la morue a été aussi faible que 500 livres de morue à 20 000 lbs de l'aiglefin.

Trawlers fishing the coast of Nova Scotia, Canada in areas such as Georges Bank have had excellent results with the aid of signs of horizontal separation designed and manufactured by Crimond to release the cod while targeting haddock.

The behavior of the fish. Studies have shown that the haddock swim high when entering the trawl while the cod tend to keep low.

The results of some vessels have shown that, even in areas with a high concentration of cod, the ratio of capture of cod has been as low as 500 pounds of cod to 20,000 lbs of haddock.

The horizontal panels have now been accepted on the market and are mounted and dismounted by fishermen when necessary.

Our company and the DFO has conducted some of the first commercial test panels with horizontal separation in Quebec, Canada in 1980.

Here are the other results of flume tank tests carried out with the National Sea Products.

One of the objectives was to observe how the committee proceeded to trawl of distortions. The two taken of camera view above show the trawl in #1 with 150 feet of spread and thenbelow door in #2 with 180 feet of spread of door. In these two scenarios, the group was functional.

The final result was another success for the exercise by the trawling industry to establish a sustainable fishery.

Panel with 180 Feet of Doorspread

Concept and History of the Horizontal Separator Panel
Most of the selective devices and gears have been designed and developed from fishermens ideas. This gives rise to the idea that not all fishermen try to circumvent the system, but in any regulation or legislative rules there are law breakers. To enforce these rules and regulations we have to monitor the users, as in your own case Fisheries Enforcement.

Crimond has been at the forefront of many of the developments in species selective gears and devices in the Canadian fishery. In fact we are the first gear company to market Horizontal Panels commercially.

Knowledge of fish behaviour is essential to the design of selective fishing gear and devices.

This information is usually gathered by using underwater cameras in the vicinity of fishing gear used in a real time environment.

Fishermen, and gear technologists, can then design fishing gear to target the desired species and release unwanted bycatch, or species on restricted quotas.

These include selectivity grids which are now used in a variety of fisheries but mainly in the Shrimp and Silver Hake fisheries.

The device we will see today is the Horizontal Separator Panel as opposed to the Vertical Separator Panel. The first experiments with the Horizontal Separator Panels, as far as we know, were conducted in Scotland, where experiments with as much as three panels at different heights in the same trawl have been tried.

This Horizontal Separator Panel is designed to separate species and the use of this panel in Canadian Fisheries is based on the behaviour of two species, Cod and Haddock.

Using underwater cameras it has been observed that when haddock are entering a trawl they rise high and in many cases pass right over the headline of the trawl. Cod on the other hand have a tendency to keep low near the sea bottom. The horizontal separator panel takes advantage of this and the majority of Cod pass under the panel while Haddock rise over it.

The panel is designed so that the top codend retains all haddock, while the cod escape out of the lower codend which is left open. 

The panel is normally attached to the fishing line by two or three strops which can be adjusted easily. The average strop length is set between two and three feet, but can differ according to the area and abundance of cod.

If the mesh size of the panel is large enough some migration of round fish from the lower area to the upper area may occur. However it is highly unlikely that species such as skate, monkfish, halibut, or any of the flatfish species are likely to do this. Any amounts of these species in the catch logs would indicate either of two scenarios.

Trawlers operating off Nova Scotia, Canada in areas such as Georges Bank have had excellent results using horizontal separator panels designed and manufactured by Crimond Enterprises to release cod while targeting haddock.

Fish behavior studies showed that haddock swim high when entering the trawl while cod have a tendency to keep low.  Results from some vessels have shown, that even in areas with high concentrations of cod, the catch ratio of cod has been as low as 500 lbs of cod to 20,000 lbs of haddock. The horizontal panels have now been accepted commercially and are fitted and removed by fishermen when necessary. David Tait and DFO conducted some of the first commercial trials with horizontal separator panels in Quebec, Canada in the 1980s.

 

Below is further results of Flume Tank testing conducted by the company and National Sea Products.
One of the objectives was to observe how the panel performed with trawl distortions. The two camera shots show the trawl in #1 with 180 feet of door spread and then in #2 with 150 feet of door spread. In both scenarios the panel remained functional.  The end result was another successful exercise by the trawling industry to establish a sustainable fishery.

Panel with 180 Feet Doorspread

Trawlers operating off Nova Scotia, Canada in areas such as Georges Bank have had excellent results using horizontal separator panels designed and manufactured by Crimond Enterprises to release cod while targeting haddock.

Fish behavior studies showed that haddock swim high when entering the trawl while cod have a tendency to keep low.  Results from some vessels have shown, that even in areas with high concentrations of cod, the catch ratio of cod has been as low as 500 lbs of cod to 20,000 lbs of haddock.   The horizontal panels have now been accepted commercially and are fitted and removed by fishermen when necessary. David Tait and DFO conducted some of the first commercial trials with horizontal separator panels in Quebec, Canada in the 1980s.
 

Concept and History of the Vertical Separator Panel
An evaluation project was designed as result of a separate Canadian Government/Industry initiative, to determine if a larger mesh size would be beneficial or otherwise to the Canadian offshore shrimp industry.

An experiment was conducted and was designed to reduce the ratio of industrial shrimp in the catch without incurring a loss of larger shrimp. Codends constructed of mesh larger than Canadian regulation size (40 mm) have been tried elsewhere, and there was much interest in the new 55 mm codend mesh regulation introduced in April 1993 in Greenland.

The objective of this experiment was to investigate, under commercial conditions, the selectivity characteristics and catch implications of codends constructed with mesh sizes of 45, 50, and 55 mm.

Unlike similar vertical split panels, which begin several meters behind the footrope, the panel design commenced at the Headrope and Footrope then ran back to the last belly where the separation of the extensions and codends took place. (see drawings) The main objective was to totally eliminate migration of shrimps from one side of the trawl to the other.

Results:

Little or no difference was found in the experimental codend mesh sizes during the survey.(see report)

The MV Northern Osprey@, a 66 meter vessel owned by M.V. Osprey Limited, was used for this experiment during April and May, 1993.  Fishing was conducted in NAFO Subdivisions 2J and 3K, sub-areas 69, 6A, 6B, 6C, and 6E.

 

 

 

 

 

 

 

        
 

 

About Us

Canadian owned, Crimond Enterprises Ltd.
is a unique kind of fishing gear company offering a comprehensive range of products, equipment and ideas to the mobile, and fixed gear sectors of the Fishing Industry. We specialize in the design and construction of species selective fishing gear and selectivity devices.

Head Office in Dartmouth, Nova Scotia
133 Ilsley Avenue, Unit N
Dartmouth NS
Canada B3B 1S9
Tel: +1 902 468-1355
Fax: +1 902 468-3004
email: crimond@crimond.com

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