Hello. Welcome to the laboratories at Institut Maurice-Lamontagne. I’m Tom Bermingham, I’m a biologist at Fisheries and Oceans Canada.
Today, we are interested in the two species of redfish that inhabit the Gulf of St. Lawrence, namely the Sebastes fasciatus, the Acadian redfish, and Sebastes mentella, the Atlantic redfish.
These two fish are really two different species. They reproduce separately, use different depths and have different management issues just like every other species of fish in the Gulf.
However, these two species are morphologically almost identical, which makes them very hard to differentiate. For the Department scientists, this poses a problem since these two species must be studied separately.
But how can we identify both species? In the lab, we often use genetic techniques, which are very hard to export on a deck of a fishing vessel or on a landing dock, even more when we talk about thousands of individuals.
Fortunately, without having to identify all of them, we can assess the proportion of both species in a catch by using a subsample and by observing a small physical characteristic: the number of anal fin rays.
Fisheries and Oceans technicians, just like at-sea observers, must count the anal fin rays on a random sample of a catch.
It may seem simple, but it can get a bit tricky. The anal fin ray of a redfish is always preceded by three spines or hard rays.
Since this never changes between species, we will not count them, and they will be excluded from our count. These spines are very useful to be able to deploy the fin and to be able to count the rays that follow.
A good trick is to use the blade of a knife. You just set it on the third spine so you can pull on the anal fin to be able to deploy it, and use the blade to hide the spines so you can count the rays that follow without having to count one spine by mistake.
It is very important to count the rays at the base of the fin, near the belly of the fish. Several rays will branch off, having one insertion and multiple tips. This is what we call bifid rays.
What is important for us is the number of insertion, and this is what we need to count.
Here, the light is your greatest ally. Whether it’s the sun even when it’s cloudy or a good lamp at night, having a good source of lighting behind the fin helps a lot.
Some counting errors are caused by the misidentification of the first ray. Be careful you only isolate the first three spines and you start your count right after.
Other errors are caused on the last ray, when it’s a bifid ray and it’s counted as two different rays when it actually has only one insertion.
Some tricks to help you with your count (it’s a lot easier to see on fresh fish than on frozen fish) but at the base of every ray, you have a little muscle that is attached to each ray and it creates a little bump when you move the fin like this.
If you are not sure if a ray is bifid, you can look at the base there. If it only has one bump, one muscle, it’s one ray.
Another thing to look at is the last ray here, sometimes it is detached from the other rays. The membrane is cut and the ray is stuck on the belly of the fish right here. If you open the fin like I showed you how to by using the spines here, the last ray can remain stuck and thus you will not be able to count it and the count will be false.
The last little trick to help you. If you’re not sure of your count, the first thing to do is to just flip the fish over and look on the other side. Sometimes, it is a lot easier to see on one side than the other, probably caused by the way the fish was in the trawl, if it was compressed on one side or the other. It can help you a lot with your count.
The at-sea-observer program includes a specific form for redfish directed fishing trips in Units 1 and 2.
This form allows for the recording of the length frequency as well as the anal fin ray count on a sample.
Here is the form for the Newfoundland and Labrador Region. Please note that a different form is used for the Quebec Region. The body of the form is the same as well as the way to complete it, the only difference is in the headers. These forms should be printed on a waterproof paper and completed by using a pencil.
First, you take a random sample of 50 fish. These fish will be used for the counting of rays and will be noted on the left columns according to their number of rays.
Here is what I mean. First, make sure that the mouth is closed and touching the board. We will record the fork length, in this case we have 24 cm.
We will then count the number of anal fin rays: 1, 2, 3, 4, 5, 6, 7. Then, we will sex internally, in this case we have a male.
Second fish. Still make sure that the mouth is closed and touching the board. Fork length for this one is 29 cm.
We will then count the number of anal fin rays: 1, 2, 3, 4, 5, 6, 7, 8. Then we will sex internally, in this case we have a female.
So the female will be on the left side, the male on the right side. You can start your length at 10.
Our first fish was a male, 24 cm, 7 anal fin rays (AFR) count, so I will put a check here. 30
Our second fish is a female, 29 cm and it has 8 anal fin rays, so I will put a check here. You keep going for your first 50 fish taken at random on your sample for the anal fin ray count.
The first 50 fish on which the anal fin ray (AFR) count was done are appearing in those columns. The rest of the sample, on which the fork length and only the sex will be recorded, will appear in these two columns.
After you completed your sample, all you need to do is add up all of the columns for each sex. You may be asked to keep some samples for validation purposes here in the lab at Institut Maurice-Lamontagne.
If this is the case, always make sure that you use the fish on which you counted the anal fin ray. You can keep the fish in waxed box from the Department, onion bags or sand bags.
Always make sure that you put only one sample per bag or per box and that you always include an identification tag like this one so we can link your sample to the data collected.
This is the end of our training, good sampling!