Things to know before buying a plankton net

So it has come to my attention that even though many people are aware that we specialize in plankton net manufacturing, not everyone knows exactly what specifications they need for their nets. So I decided to write an article on the subject in the hopes of clarifying a few things.

First of all, it is very important to know if you are conducting a brand new study or if your research is based on a previous study with set parameters. 

If you are doing a study based on a previous study, then it is extremely important that the net you order has the same specifications as the one used in the previous study. 

On the other hand, if you are starting a new study, then the actual specs of your net will be based on the rate of water going through your net during the research, the size of the organisms that you want to capture, the speed of your tow and the type of tow you will be doing.

Now that this is out of the way, here is the list of specifications that we will need to be able to quote you the proper net for your needs;

• Measuring Units

Since the nets are used for scientific research, it is standard practice to use the metric system. Most measurements are given in centimetres, metres and microns.

• Mouth Opening

Most standard plankton nets have a circular mouth, thus we require the diameter that you need. The diameter will determine the surface area of the mouth, thus the water flow rate going through the net at your given tow speed.

• Net Length

Most plankton nets follow a standard rule ratio based on the diameter of the mouth of 1:3, 1:4 and 1:5. This being said, we can assemble any ratio that suits your needs. The length of the net will have an impact on the volume of water inside the net at any given time. Combined with the mesh size, and opening percentage and your tow speed, you should be able to know if the flow of water is adequate to properly go through the net and through the cod end.Mesh Size

• Mesh Size

The mesh size is directly correlated to the size of the organism that you are trying to catch. A rule of thumb is that your mesh size should be 10% smaller than the average size of the organism you are trying to capture. 

• Tow Speed

The tow speed will usually be related to the net dimensions, mesh size and mesh opening percentage. The speed usually varies between 1 and 3 knots. Any faster and the net might explode, any slower and the net the water flow will not be sufficient to go through the cod end

• Type of Tow

There are 3 types of tows; horizontal, vertical and oblique. When towing from a moving ship, most times you will be doing horizontal and oblique tows. No extra equipment is required for horizontal tows. 

For oblique tows, most often you will require an extra weight, this must be mentioned so that we can adapt the net to hold this weight.

For vertical tows, it is recommended to add a small weight in the cod end to add ballast and help it sink lower than the net. 

Here are a few bonus questions to ask yourself before moving forward with the purchase:

• How many units do you need?

Most people tend to order the minimum amount of nets that they require, but this can cause issues. It is not rare that clients contact us during their field study indicating that they have damaged or lost a net and need a new one assembled ASAP. 

For this reason we recommend always ordering a minimum of one extra net and ideally 2 extras. This way you can conduct your study no matter what happens.

• Is there a strong risk of damage between uses?

Depending on where you are conducting your study, there can be many ways of damaging your nets. On sea vessels, many items on the deck can be very sharp which can easily damage your research gear. This is why we recommend purchasing a protection transport bag to reduce the risks of damage between studies. 

• You already have some parts

Most researchers tend to study the same organisms year after year which is why they repeatedly buy the same gear. All our nets, cod ends and rings are standard designs. So if your net and cod end are lost/damaged, but you still have your ring with bridle, then you don’t need a new ring and bridle and can order only the net and cod end

• Can you easily do repairs during your study?

Damages often happen during field research. This is unfortunate, but a reality of the situation. Now the question left to answer is: Can you do repairs during your field study or not? Most of our metal parts are made of Stainless Steel, but for some nets and certain situations where total weight is an issue, we sometimes use aluminum.

Stainless Steel is fairly easy to repair on a vessel, most of them are equipped with the proper gear to do repairs at sea.

Aluminum, on the other hand, is slightly more complicated and most ships are not equipped to complete these repairs at sea. 

This is very important to know before you order your gear.

I know that this article is not an extensive guide on plankton net usage, but it’s a quick help guide on the most common questions that I received at the moment of purchase.

I hope this helps some of you and feel free to contact me directly at info@filmarnets.com for any questions you might have or if you want to move forward with an order!

Have a great day 

Francis Brisebois