Data collection of salmon in the Baltic Sea

Today, commercial salmon fishing in the Baltic Sea consists of coastal fishing with fixed gear. There has been no commercial salmon fishing on the Swedish west coast since 2015.

We collect the following data from commercial fishing:

• Catch data for both landed fish and fish discarded,
• Number of fishing efforts and catch per fishing effort,
• Catch statistics in the form of number and size of fish.

We collect the following biological data during a sample collection

• Length
• Weight
• Age
• Sex
• Scale samples

We conduct fishery sampling four times a year at three different fishermen. We measure length and weight for all species we catch and for salmon we also record sex and age.

Using our genetic analyses of mountain samples, we can determine:

• the presence of different salmon strains in the catches,
• the proportion of wild and farmed salmon in the catch (also obtained from analysing the age on the scales).

By recreational fishing for salmon we mean all fishing that is not commercial fishing, and that is carried out along the coast and in rivers, mainly with rods. However, fishing with fixed gear can also occur.

We collect the following data from the recreational fishing

• Catch per effort
• Catch statistics, number, size and species
• Gear inventory
• Catch from trolling fishing

We also collect data from breeding fishing in the Dalälven River in Älvkarleby, as well as from the Umeälven River in Norrfors.

We also collect data for all life stages of salmon in some selected rivers.

Selected rivers

• Umeälven River/Vindelälven River
• Testeboån River
• Mörrumån River
• Ätran River/Högvadsån River

The following data are collected from the selected rivers:

• Number of migrating spawners
• Density of juvenile salmon and trout (parr: the stage where the fry have left the breeding grounds until the migration to the sea begins) in nursery areas 
• Number of migrating salmon and trout (smolt: young salmon migrating to the sea)

We also collect data for all life stages of salmon in two additional rivers where we monitor the salmon for a few years at a time before moving to another river. We also monitor one river with a focus on trout.

The purpose of the selected rivers is to:

• collect information on the relationship between the number of spawning fish and reproduction that can then be used in other rivers,
• increase knowledge of wild salmon stocks,
• improve the data set that forms the basis for ICES stock estimates.

How we estimate salmon stocks in rivers

The methodology for estimating the number of migrating spawning fish, parr and smolt differs between the different rivers. When the salmon are on their way from the sea to the rivers to spawn, we count the number of spawning fish in several ways, for example by filming with a camera or by following the fish with an echo sounder in fish ladders or across rivers. We also identify individual fish using, for example, PIT tags (passive integration transponders; a pill-shaped cylinder of glass that houses a radio transponder containing a unique code), which are injected into the salmon at the smolt stage. Using this data, we can estimate the survival of the salmon in the sea.

We calculate the production of smolts by fishing according to the Swedish standard for sampling of fish with electricity at locations where the salmon grow up. When the young salmon have grown into smolts and migrate to the sea, we capture them in various types of traps. By tagging, releasing and then capturing the smolts again, we can evaluate the trap's capture efficiency and thus calculate the total migration in the river.