Scientific survey report
Danish International Bottom Trawl Survey
2025
The Danish research vessels Dana and Havfisken are used for the
Danish participation in the Baltic International Trawl Survey (BITS),
which, since 1982, has had the purpose of annually monitoring cod and
other species.
Internationally, each nation surveys part of the area, with some
overlap in coverage and depth stratification, in a coordinated sampling
design. After agreement between countries a common standard trawl gear
and standard sampling procedures were implemented in 2000, resulting in
the consistent coverage of the western and central Baltic Sea.
The BITS is conducted twice a year in the first and fourth quarters
as a depth-stratified survey. The strata are based on sub-divisions and
depth layers. Each year the necessary stations are randomly selected
before the beginning of the international trawl surveys, from a list of
clear haul data. These stations are a stratified randomly selected
sub-sample of the possible trawl tracks.
The standard haul is a 30-minutes haul with a towing speed of 3
knots. Trawling only takes place during daylight, defined as the time
between 15 minutes past sunrise and 15 minutes before sunset.
All data can be found in the ICES DATRAS database (https://datras.ices.dk/Data_products/Download/Download_Data_public.aspx)
and details about the survey design and survey standardization before
2000 can be found in the ICES BITS manual (Anon. 2000).
Funding
The data collection is co-funded by the European Union through the European Maritime, Fisheries and Aquaculture Fund.
Period
Quarter 1
Activity
Here is shown a map with the survey activity for both vessls. The map shows both valid and invalid stations, a station can be deemed invalid if the haoul could not be conducted within the guilines of the survey manual
Trawl Stations
Each trawl stations consists a haul of 30 minutes where all the catch
documented, including litter. Biological samples to determine
e.g. stock, age matuity are taken from individual fish.
Bongo Stations
Each bongo stationsions in conducted with a set of three bongonets,
with net sizes 150, 300 and 500 micrometers. These are used for the
registartion of fishlarvey, plankton abundance and jelly fish.
CTD Stations
CTD (Conductivity - Temperature - Depth), are measured trough the
water column, and used to calculate e.g. the oxygen and salinity
content, key environmental variables for life in the ocean.
CTD Results
Here is shown a map the results of the CTD measurments at the bottom. The heatmap is made with linear interpolation between measurments, and can be seen as the general trend in the monment of the survey. If any CTD stations are not plotted data has not yet been precessed
Bottom oxygen
Bottom temperature
Bottom salinity
Catch Overview
Below is a table with the total catche and catches for selected species, in wiegth and numbers. The numbers are in some instances calculated based on representative subsampling of some abundant species. The maps illustrates for biodiveity the number of different species cougt on each station, and for CPUE (catch per unit effort) the catch in numbers standadized to a unit effort of one hour of hauling.| Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) | |
|---|---|---|---|---|
| Total Catch | 52980.3 | 1778644 | ||
| Herring | 12106.3 | 416791 | 75 | 295 |
| Sprat | 11227.0 | 990984 | 55 | 165 |
| Cod | 8888.8 | 48665 | 50 | 820 |
| Plaice | 4942.9 | 91203 | 50 | 420 |
| Sole | 6.9 | 46 | 120 | 360 |
CPUE
CPUE (catch per unit effort) shown as the catch in Numbers rasied to
to pr hour of hauling
CPUE for Selected Species
CPUE (catch per unit effort) shown as the catch in Numbers rasied to to pr hour of hauling. The dots indicates the stations, and red dots indicates that a species where not found at all in that station. The scale is different between plots
Cod
Plaice
Sole
Sprat
Herring
Biodiversity
Shown is the Number of species cought by station
Length Distributions
Here is shown the length distribution For the 10 most abundant comercieal species cought during the survey, allocated to each ship. The black line represents the average length distribution of the 5 years previus surveys.
Sprat
Herring
Dab
Plaice
Whiting
Cod
Flounder
Haddock
Grey gurnard
Mackerel
All Species Caught
The table below is an overview of all the different species cought in the survey, devided into the different ices areas covered by the surve.
Area 20
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Arnoglossus laterna | Scaldfish | 0.1 | 7 | 70 | 140 |
| Callionymidae | Dragonets | 8.7 | 281 | 100 | 230 |
| Clupea harengus | Herring | 77.0 | 8859 | 95 | 155 |
| Eutrigla gurnardus | Grey gurnard | 0.1 | 12 | 80 | 170 |
| Gadus morhua | Cod | 4.6 | 39 | 120 | 510 |
| Hippoglossoides platessoides | Long rough dab | 7.5 | 333 | 60 | 200 |
| Limanda limanda | Dab | 14.4 | 305 | 110 | 260 |
| Loligo | Loligo sp | 0.6 | 5 | ||
| Melanogrammus aeglefinus | Haddock | 0.2 | 4 | 160 | 200 |
| Merlangius merlangus | Whiting | 148.4 | 5387 | 100 | 220 |
| Microstomus kitt | Lemon sole | 1.1 | 18 | 140 | 200 |
| Nephrops norvegicus | Norway lobster | 0.1 | 4 | 32 | 40 |
| Platichthys flesus | Flounder | 0.7 | 2 | 130 | 390 |
| Pleuronectes platessa | Plaice | 3.9 | 86 | 100 | 300 |
| Scomber scombrus | Mackerel | 0.1 | 1 | 200 | 200 |
| Sprattus sprattus | Sprat | 5.9 | 1193 | 70 | 130 |
| Syngnathus acus | Great pipefish | 0.0 | 1 | 410 | 410 |
| Trachinus draco | Greater weever fish | 0.1 | 1 | 230 | 230 |
| Trisopterus esmarkii | Norway pout | 0.0 | 1 | 120 | 120 |
Area 21
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Agonus cataphractus | Pogge | 0.0 | 2 | 140 | 150 |
| Arctica islandica | Ocean quahaug | 6.0 | 0 | ||
| Argentina sphyraena | Lesser silver smelt | 0.1 | 6 | 120 | 140 |
| Arnoglossus laterna | Scaldfish | 0.8 | 75 | 70 | 160 |
| Buglossidium luteum | Solenette | 0.0 | 2 | 100 | 100 |
| Callionymidae | Dragonets | 8.5 | 633 | 80 | 210 |
| Callionymus lyra | Common dragonet | 5.1 | 178 | 90 | 230 |
| Callionymus maculatus | Spotted dragonet | 4.6 | 494 | 80 | 150 |
| Cancer pagurus | Edible crab | 6.9 | 14 | 90 | 178 |
| Clupea harengus | Herring | 2013.8 | 124132 | 75 | 280 |
| Cyclopterus lumpus | Lumpfish | 1.1 | 1 | 300 | 300 |
| Dicentrarchus labrax | Bass | 0.9 | 1 | 450 | 450 |
| Eledone cirrhosa | Horned octopus | 0.3 | 1 | ||
| Enchelyopus cimbrius | Four-bearded rockling | 0.2 | 7 | 170 | 210 |
| Engraulis encrasicolus | Anchovy | 0.2 | 19 | 110 | 150 |
| Eutrigla gurnardus | Grey gurnard | 52.6 | 1172 | 70 | 340 |
| Gadus morhua | Cod | 128.4 | 738 | 100 | 790 |
| Gasterosteus aculeatus | Three-spined stickleback | 0.1 | 28 | 40 | 70 |
| Glyptocephalus cynoglossus | Witch | 0.4 | 3 | 230 | 330 |
| Hippoglossoides platessoides | Long rough dab | 124.9 | 5615 | 60 | 290 |
| Hyperoplus lanceolatus | Greater sandeel | 0.0 | 1 | 230 | 230 |
| Limanda limanda | Dab | 1114.4 | 27167 | 70 | 340 |
| Loligo | Loligo sp | 1.5 | 169 | ||
| Lumpenus lampretaeformis | Snake blenny | 4.9 | 388 | 130 | 290 |
| Melanogrammus aeglefinus | Haddock | 515.6 | 2364 | 120 | 420 |
| Merlangius merlangus | Whiting | 2030.0 | 55460 | 80 | 340 |
| Merluccius merluccius | Hake | 9.5 | 146 | 90 | 350 |
| Microstomus kitt | Lemon sole | 3.7 | 53 | 140 | 250 |
| Mullus surmuletus | Striped red mullet | 3.7 | 93 | 100 | 240 |
| Myoxocephalus scorpius | Sculpin | 21.0 | 216 | 80 | 280 |
| Myxine glutinosa | Hagfish | 0.0 | 1 | 310 | 310 |
| Nephrops norvegicus | Norway lobster | 60.7 | 2427 | 41 | 42 |
| Ommastrephidae | 1.0 | 9 | |||
| Pandalus borealis | Northern pink shrimp | 7.6 | 1677 | ||
| Petromyzon marinus | Sea lamprey | 0.0 | 2 | 180 | 230 |
| Pholis gunnellus | Butter fish | 0.1 | 3 | 180 | 190 |
| Platichthys flesus | Flounder | 447.9 | 2617 | 90 | 410 |
| Pleuronectes platessa | Plaice | 950.7 | 18999 | 90 | 420 |
| Pollachius pollachius | Pollack | 0.1 | 1 | 220 | 220 |
| Pomatoschistus spp. | Sand gobies | 0.0 | 6 | 70 | 100 |
| Sardina pilchardus | Pilchard | 1.0 | 83 | 90 | 130 |
| Scomber scombrus | Mackerel | 1.4 | 23 | 170 | 220 |
| Scophthalmus maximus | Turbot | 5.4 | 7 | 230 | 440 |
| Scophthalmus rhombus | Brill | 15.6 | 40 | 160 | 490 |
| Scyliorhinus canicula | Lesser-spotted dogfish | 0.3 | 1 | 410 | 410 |
| Solea solea | Sole | 1.8 | 13 | 210 | 290 |
| Sprattus sprattus | Sprat | 517.6 | 45784 | 55 | 150 |
| Squalus acanthias | Spurdog | 0.2 | 1 | 380 | 380 |
| Syngnathidae | Pipefishes and seahorses | 0.0 | 1 | 410 | 410 |
| Trachinus draco | Greater weever fish | 91.3 | 1422 | 130 | 360 |
| Trachurus trachurus | Horse mackerel | 4.4 | 192 | 100 | 340 |
| Trigla lucerna | Tub gurnard | 1.4 | 7 | 190 | 390 |
| Trisopterus esmarkii | Norway pout | 0.1 | 6 | 90 | 130 |
| Trisopterus minutus | Poor-cod | 0.5 | 13 | 90 | 180 |
| Zoarces viviparus | Eelpout | 0.1 | 2 | 150 | 210 |
Area 22
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Agonus cataphractus | Pogge | 0.2 | 13 | 110 | 150 |
| Amblyraja radiata | Starry ray | 0.6 | 1 | 440 | 440 |
| Ammodytes tobianus | Sandeel | 0.0 | 1 | 180 | 180 |
| Arctica islandica | Ocean quahaug | 247.2 | 0 | ||
| Arnoglossus laterna | Scaldfish | 0.4 | 37 | 50 | 160 |
| Buglossidium luteum | Solenette | 0.0 | 3 | 80 | 110 |
| Callionymus lyra | Common dragonet | 1.5 | 57 | 110 | 190 |
| Callionymus maculatus | Spotted dragonet | 0.1 | 6 | 80 | 140 |
| Cancer pagurus | Edible crab | 0.6 | 1 | 150 | 150 |
| Caridea | Shrimps | 0.0 | 3 | ||
| Clupea harengus | Herring | 1268.0 | 89340 | 75 | 295 |
| Ctenolabrus rupestris | Goldsinny | 0.0 | 2 | 70 | 90 |
| Cyclopterus lumpus | Lumpfish | 0.8 | 3 | 120 | 220 |
| Enchelyopus cimbrius | Four-bearded rockling | 0.1 | 3 | 80 | 210 |
| Eutrigla gurnardus | Grey gurnard | 23.5 | 280 | 90 | 370 |
| Gadus morhua | Cod | 44.6 | 1168 | 90 | 820 |
| Gasterosteus aculeatus | Three-spined stickleback | 5.7 | 2516 | 40 | 80 |
| Glyptocephalus cynoglossus | Witch | 0.1 | 1 | 210 | 210 |
| Gobius niger | Black goby | 0.3 | 24 | 70 | 130 |
| Hippoglossoides platessoides | Long rough dab | 16.3 | 430 | 80 | 300 |
| Hyperoplus lanceolatus | Greater sandeel | 0.1 | 6 | 180 | 235 |
| Limanda limanda | Dab | 2225.1 | 52113 | 60 | 300 |
| Loligo | Loligo sp | 0.0 | 5 | 50 | 90 |
| Lumpenus lampretaeformis | Snake blenny | 0.8 | 69 | 100 | 290 |
| Melanogrammus aeglefinus | Haddock | 6.4 | 55 | 160 | 320 |
| Merlangius merlangus | Whiting | 398.9 | 11728 | 10 | 300 |
| Merluccius merluccius | Hake | 0.2 | 2 | 160 | 320 |
| Microstomus kitt | Lemon sole | 0.9 | 7 | 160 | 330 |
| Mullus surmuletus | Striped red mullet | 0.1 | 4 | 120 | 170 |
| Myoxocephalus scorpius | Sculpin | 40.5 | 629 | 70 | 260 |
| Neogobius melanostomus | Round goby | 0.3 | 12 | 60 | 160 |
| Pholis gunnellus | Butter fish | 0.2 | 14 | 130 | 180 |
| Platichthys flesus | Flounder | 436.3 | 2647 | 90 | 400 |
| Pleuronectes platessa | Plaice | 2699.1 | 55807 | 50 | 330 |
| Pomatoschistus spp. | Sand gobies | 0.1 | 32 | 50 | 130 |
| Scomber scombrus | Mackerel | 2.0 | 30 | 190 | 240 |
| Scophthalmus maximus | Turbot | 9.5 | 13 | 170 | 480 |
| Scophthalmus rhombus | Brill | 0.5 | 5 | 170 | 210 |
| Solea solea | Sole | 4.1 | 28 | 120 | 350 |
| Sprattus sprattus | Sprat | 2035.6 | 268630 | 55 | 160 |
| Symphodus melops | Corkwing | 0.1 | 5 | 30 | 100 |
| Syngnathidae | Pipefishes and seahorses | 0.0 | 1 | 140 | 140 |
| Syngnathus acus | Great pipefish | 0.0 | 1 | 410 | 410 |
| Trachinus draco | Greater weever fish | 0.1 | 1 | 210 | 210 |
| Trachurus trachurus | Horse mackerel | 0.1 | 3 | 130 | 140 |
| Trisopterus minutus | Poor-cod | 0.0 | 2 | 90 | 140 |
| Zoarces viviparus | Eelpout | 3.8 | 120 | 120 | 260 |
Area 23
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Agonus cataphractus | Pogge | 0.1 | 4 | 130 | 180 |
| Arnoglossus laterna | Scaldfish | 0.2 | 8 | 110 | 140 |
| Callionymus lyra | Common dragonet | 0.1 | 1 | 190 | 190 |
| Callionymus maculatus | Spotted dragonet | 0.1 | 9 | 80 | 130 |
| Ciliata mustela | Five-bearded rockling | 0.0 | 1 | 140 | 140 |
| Clupea harengus | Herring | 601.6 | 23760 | 85 | 295 |
| Cyclopterus lumpus | Lumpfish | 0.3 | 1 | 170 | 170 |
| Eutrigla gurnardus | Grey gurnard | 0.9 | 11 | 90 | 350 |
| Gadus morhua | Cod | 469.9 | 7384 | 100 | 530 |
| Gobius niger | Black goby | 0.1 | 3 | 110 | 120 |
| Hippoglossoides platessoides | Long rough dab | 0.2 | 5 | 140 | 180 |
| Limanda limanda | Dab | 700.0 | 11354 | 80 | 310 |
| Lumpenus lampretaeformis | Snake blenny | 0.0 | 1 | 210 | 210 |
| Melanogrammus aeglefinus | Haddock | 0.3 | 1 | 310 | 310 |
| Merlangius merlangus | Whiting | 212.8 | 4392 | 90 | 270 |
| Microstomus kitt | Lemon sole | 0.2 | 1 | 260 | 260 |
| Myoxocephalus scorpius | Sculpin | 8.7 | 48 | 150 | 290 |
| Mytilus edulis | Blue mussel | 497.3 | 0 | ||
| Platichthys flesus | Flounder | 116.1 | 585 | 140 | 390 |
| Pleuronectes platessa | Plaice | 482.1 | 5778 | 100 | 390 |
| Pomatoschistus spp. | Sand gobies | 0.1 | 1 | 170 | 170 |
| Sardina pilchardus | Pilchard | 0.4 | 28 | 110 | 120 |
| Scophthalmus maximus | Turbot | 2.1 | 4 | 220 | 340 |
| Scophthalmus rhombus | Brill | 2.9 | 10 | 180 | 440 |
| Solea solea | Sole | 0.8 | 4 | 170 | 360 |
| Sprattus sprattus | Sprat | 89.6 | 6922 | 70 | 155 |
| Symphodus melops | Corkwing | 0.0 | 1 | 100 | 100 |
| Trachurus trachurus | Horse mackerel | 0.1 | 3 | 130 | 140 |
| Zoarces viviparus | Eelpout | 0.1 | 2 | 160 | 230 |
Area 24
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Agonus cataphractus | Pogge | 0.2 | 7 | 130 | 180 |
| Alosa fallax | Twaite shad | 1.1 | 3 | 300 | 390 |
| Arctica islandica | Ocean quahaug | 34.4 | 0 | ||
| Asterias rubens | Common starfish | 11.0 | 0 | ||
| Clupea harengus | Herring | 2336.6 | 46621 | 80 | 270 |
| Cyclopterus lumpus | Lumpfish | 1.1 | 3 | 180 | 200 |
| Enchelyopus cimbrius | Four-bearded rockling | 0.2 | 2 | 250 | 320 |
| Engraulis encrasicolus | Anchovy | 3.8 | 184 | 130 | 170 |
| Gadus morhua | Cod | 744.5 | 3824 | 80 | 640 |
| Gasterosteus aculeatus | Three-spined stickleback | 0.0 | 10 | 50 | 60 |
| Hyperoplus lanceolatus | Greater sandeel | 0.0 | 3 | 180 | 190 |
| Limanda limanda | Dab | 117.8 | 1583 | 100 | 300 |
| Lumpenus lampretaeformis | Snake blenny | 0.1 | 9 | 140 | 240 |
| Melanogrammus aeglefinus | Haddock | 3.6 | 31 | 180 | 250 |
| Merlangius merlangus | Whiting | 104.3 | 1056 | 90 | 380 |
| Myoxocephalus scorpius | Sculpin | 3.8 | 33 | 130 | 240 |
| Mytilus edulis | Blue mussel | 7.6 | 0 | ||
| Platichthys flesus | Flounder | 178.9 | 1024 | 90 | 390 |
| Pleuronectes platessa | Plaice | 581.6 | 8104 | 70 | 350 |
| Scomber scombrus | Mackerel | 9.9 | 126 | 200 | 240 |
| Scophthalmus maximus | Turbot | 3.9 | 14 | 180 | 310 |
| Solea solea | Sole | 0.2 | 1 | 280 | 280 |
| Sprattus sprattus | Sprat | 775.8 | 67001 | 70 | 160 |
| Zoarces viviparus | Eelpout | 0.6 | 11 | 140 | 290 |
Area 25
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Agonus cataphractus | Pogge | 0.0 | 2 | 110 | 120 |
| Alosa fallax | Twaite shad | 24.9 | 81 | 160 | 400 |
| Clupea harengus | Herring | 5809.4 | 124078 | 105 | 295 |
| Cyclopterus lumpus | Lumpfish | 0.6 | 2 | 150 | 190 |
| Enchelyopus cimbrius | Four-bearded rockling | 26.2 | 389 | 30 | 330 |
| Engraulis encrasicolus | Anchovy | 0.1 | 6 | 120 | 220 |
| Gadus morhua | Cod | 7496.8 | 35512 | 50 | 570 |
| Gasterosteus aculeatus | Three-spined stickleback | 4.4 | 2024 | 30 | 80 |
| Limanda limanda | Dab | 1.6 | 12 | 170 | 290 |
| Melanogrammus aeglefinus | Haddock | 0.5 | 2 | 300 | 320 |
| Merlangius merlangus | Whiting | 13.6 | 123 | 140 | 360 |
| Myoxocephalus scorpius | Sculpin | 8.9 | 74 | 130 | 270 |
| Platichthys flesus | Flounder | 5529.7 | 27520 | 140 | 410 |
| Pleuronectes platessa | Plaice | 225.5 | 2430 | 120 | 360 |
| Saduria entomon | Saduria | 0.0 | 3 | ||
| Scomber scombrus | Mackerel | 8.8 | 40 | 200 | 420 |
| Scophthalmus maximus | Turbot | 2.1 | 7 | 210 | 310 |
| Sprattus sprattus | Sprat | 7802.5 | 601455 | 75 | 165 |
| Trachurus trachurus | Horse mackerel | 0.0 | 1 | 130 | 130 |