Scientific survey report
Danish International Bottom Trawl Survey
2025
The Danish research vessel Dana is used for the Danish participation
in the International Bottom Trawl Survey (IBTS), which has the purpose
of annually monitoring fish species. Internationally, each nation
surveys part of the area, with some overlap in coverage and depth
stratification, in a coordinated sampling design.
The IBTS 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 can be found in the ICES IBTS manual.
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. 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.
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
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 | 21911.3 | 443819 | ||
| Haddock | 11449.3 | 43436 | 140 | 480 |
| Whiting | 4120.6 | 45774 | 80 | 430 |
| Herring | 1249.6 | 47065 | 85 | 320 |
| Plaice | 394.2 | 3387 | 120 | 470 |
| Cod | 151.1 | 157 | 120 | 1000 |
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
Whiting
Haddock
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 (and Cod) cought during the survey, allocated to each ship. The black line represents the average length distribution of the 5 years previus surveys.
Cod
Sprat
Herring
Whiting
Haddock
Dab
Norway pout
Grey gurnard
Mackerel
Plaice
Horse 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) |
|---|---|---|---|---|---|
| Aequipecten opercularis | Queen scallop | 0.4 | 9 | ||
| Agonus cataphractus | Pogge | 0.0 | 2 | 120 | 140 |
| Alloteuthis subulata | European common squid | 0.1 | 13 | 40 | 70 |
| Amblyraja radiata | Starry ray | 1.9 | 5 | 280 | 420 |
| Arnoglossus laterna | Scaldfish | 0.0 | 2 | 110 | 140 |
| Callionymus lyra | Common dragonet | 0.1 | 2 | 180 | 220 |
| Callionymus maculatus | Spotted dragonet | 0.0 | 1 | 150 | 150 |
| Cancer pagurus | Edible crab | 2.1 | 5 | 100 | 168 |
| Clupea harengus | Herring | 421.9 | 10556 | 85 | 265 |
| Cyclopterus lumpus | Lumpfish | 2.5 | 1 | 390 | 390 |
| Echiichthys vipera | Lesser weever | 0.0 | 1 | 140 | 140 |
| Engraulis encrasicolus | Anchovy | 0.2 | 19 | 80 | 180 |
| Eutrigla gurnardus | Grey gurnard | 8.7 | 186 | 70 | 330 |
| Gadus morhua | Cod | 12.2 | 42 | 130 | 830 |
| Hippoglossoides platessoides | Long rough dab | 29.5 | 539 | 80 | 240 |
| Illex coindetii | Southern shortfin squid | 0.0 | 1 | 100 | 100 |
| Limanda limanda | Dab | 56.9 | 678 | 90 | 310 |
| Loligo forbesii | Northern squid | 4.7 | 27 | 110 | 270 |
| Loligo vulgaris | European squid | 3.3 | 13 | 120 | 290 |
| Lophius piscatorius | Angler fish | 6.2 | 1 | 730 | 730 |
| Melanogrammus aeglefinus | Haddock | 281.3 | 705 | 140 | 460 |
| Merlangius merlangus | Whiting | 92.5 | 2280 | 100 | 330 |
| Microstomus kitt | Lemon sole | 8.2 | 39 | 180 | 350 |
| Mustelus asterias | Starry smooth-hound | 1.7 | 1 | 750 | 750 |
| Pleuronectes platessa | Plaice | 20.3 | 163 | 150 | 360 |
| Pomatoschistus spp. | Sand gobies | 0.0 | 4 | 40 | 50 |
| Raja clavata | Thornback ray | 1.7 | 1 | 610 | 610 |
| Rossia macrosoma | Stout bobtail squid | 0.0 | 1 | ||
| Sardina pilchardus | Pilchard | 0.5 | 39 | 80 | 260 |
| Scomber scombrus | Mackerel | 12.6 | 292 | 160 | 230 |
| Scophthalmus maximus | Turbot | 1.5 | 1 | 420 | 420 |
| Scophthalmus rhombus | Brill | 0.3 | 1 | 280 | 280 |
| Scyliorhinus canicula | Lesser-spotted dogfish | 0.4 | 1 | 470 | 470 |
| Solea solea | Sole | 0.3 | 1 | 300 | 300 |
| Sprattus sprattus | Sprat | 54.3 | 16241 | 60 | 150 |
| Trachinus draco | Greater weever fish | 0.1 | 2 | 220 | 230 |
| Trachurus trachurus | Horse mackerel | 1.5 | 72 | 90 | 240 |
| Trisopterus esmarkii | Norway pout | 1.0 | 56 | 100 | 190 |
| Trisopterus minutus | Poor-cod | 1.5 | 58 | 90 | 210 |
Area - 4A
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Alloteuthis subulata | European common squid | 3.2 | 854 | 20 | 80 |
| Amblyraja radiata | Starry ray | 1.1 | 4 | 220 | 390 |
| Argentina sphyraena | Lesser silver smelt | 1.2 | 34 | 60 | 240 |
| Callionymus lyra | Common dragonet | 0.0 | 2 | 70 | 90 |
| Callionymus maculatus | Spotted dragonet | 0.0 | 3 | 120 | 130 |
| Clupea harengus | Herring | 1.4 | 11 | 225 | 320 |
| Enchelyopus cimbrius | Four-bearded rockling | 0.8 | 13 | 150 | 280 |
| Eutrigla gurnardus | Grey gurnard | 26.1 | 217 | 170 | 320 |
| Gadiculus argenteus | Silvery pout | 0.9 | 222 | 50 | 90 |
| Gadus morhua | Cod | 52.5 | 29 | 140 | 1000 |
| Glyptocephalus cynoglossus | Witch | 1.9 | 6 | 300 | 420 |
| Helicolenus dactylopterus | Blue-mouth redfish | 0.2 | 2 | 160 | 190 |
| Hippoglossoides platessoides | Long rough dab | 7.0 | 196 | 60 | 240 |
| Illex coindetii | Southern shortfin squid | 1.5 | 29 | 60 | 150 |
| Limanda limanda | Dab | 8.3 | 159 | 120 | 260 |
| Lithodes maja | Norway king crab | 1.5 | 2 | 96 | 108 |
| Loligo forbesii | Northern squid | 2.0 | 20 | 30 | 270 |
| Lophius piscatorius | Angler fish | 42.8 | 14 | 250 | 730 |
| Melanogrammus aeglefinus | Haddock | 529.2 | 1923 | 160 | 480 |
| Merlangius merlangus | Whiting | 327.6 | 1351 | 110 | 410 |
| Merluccius merluccius | Hake | 3.4 | 48 | 70 | 470 |
| Micromesistius poutassou | Blue whiting | 5.0 | 34 | 220 | 360 |
| Microstomus kitt | Lemon sole | 4.4 | 19 | 180 | 340 |
| Molva molva | Ling | 38.8 | 9 | 530 | 1300 |
| Myxine glutinosa | Hagfish | 0.0 | 1 | 150 | 150 |
| Nephrops norvegicus | Norway lobster | 37.4 | 585 | 32 | 65 |
| Pleuronectes platessa | Plaice | 3.3 | 14 | 250 | 320 |
| Pollachius virens | Saithe | 174.7 | 250 | 390 | 520 |
| Rossia macrosoma | Stout bobtail squid | 0.3 | 11 | ||
| Scomber scombrus | Mackerel | 1.9 | 26 | 160 | 280 |
| Scophthalmus maximus | Turbot | 0.8 | 1 | 360 | 360 |
| Todaropsis eblanae | Lesser flying squid | 13.5 | 159 | 80 | 130 |
| Trachurus trachurus | Horse mackerel | 1.1 | 15 | 130 | 370 |
| Trisopterus esmarkii | Norway pout | 49.6 | 2799 | 90 | 210 |
| Trisopterus minutus | Poor-cod | 4.4 | 76 | 150 | 220 |
Area - 4B
| Latin name | English name | Weight (kg) | Number | Min. Length (mm) | Max. Length (mm) |
|---|---|---|---|---|---|
| Aequipecten opercularis | Queen scallop | 1.7 | 42 | ||
| Agonus cataphractus | Pogge | 0.1 | 8 | 70 | 130 |
| Alloteuthis subulata | European common squid | 85.3 | 16359 | 20 | 110 |
| Amblyraja radiata | Starry ray | 11.8 | 27 | 150 | 470 |
| Ammodytes marinus | Lesser sandeel | 20.0 | 5671 | 80 | 175 |
| Anguilla anguilla | Eel | 1.3 | 1 | 750 | 750 |
| Aphia minuta | Transparent goby | 0.0 | 15 | 30 | 40 |
| Arnoglossus laterna | Scaldfish | 0.6 | 58 | 50 | 130 |
| Aspitriglia cuculus | Red gurnard | 1.4 | 8 | 230 | 270 |
| Buglossidium luteum | Solenette | 2.8 | 309 | 50 | 120 |
| Callionymus lyra | Common dragonet | 3.8 | 96 | 130 | 230 |
| Callionymus maculatus | Spotted dragonet | 0.0 | 1 | 140 | 140 |
| Callionymus reticulatus | Reticulated dragonet | 0.0 | 6 | 50 | 100 |
| Cancer pagurus | Edible crab | 32.8 | 67 | 80 | 209 |
| Clupea harengus | Herring | 826.4 | 36498 | 85 | 290 |
| Cyclopterus lumpus | Lumpfish | 0.3 | 1 | 190 | 190 |
| Dicentrarchus labrax | Bass | 1.6 | 2 | 420 | 440 |
| Echiichthys vipera | Lesser weever | 1.3 | 46 | 80 | 160 |
| Eledone cirrhosa | Horned octopus | 0.3 | 1 | ||
| Enchelyopus cimbrius | Four-bearded rockling | 1.2 | 31 | 110 | 280 |
| Engraulis encrasicolus | Anchovy | 0.4 | 67 | 80 | 140 |
| Eutrigla gurnardus | Grey gurnard | 620.9 | 10525 | 80 | 330 |
| Gadus morhua | Cod | 86.4 | 86 | 120 | 850 |
| Gaidropsarus vulgaris | Three-bearded rockling | 0.1 | 3 | 150 | 180 |
| Gasterosteus aculeatus | Three-spined stickleback | 0.0 | 1 | 40 | 40 |
| Glyptocephalus cynoglossus | Witch | 0.3 | 2 | 240 | 290 |
| Gymnammodytes semisquamatus | Smoothed sandeel | 0.0 | 1 | 210 | 210 |
| Helicolenus dactylopterus | Blue-mouth redfish | 0.6 | 5 | 170 | 220 |
| Hippoglossoides platessoides | Long rough dab | 61.9 | 1500 | 100 | 240 |
| Homarus gammarus | European lobster | 0.9 | 2 | 72 | 97 |
| Hyperoplus lanceolatus | Greater sandeel | 0.1 | 3 | 235 | 285 |
| Illex coindetii | Southern shortfin squid | 1.5 | 200 | 40 | 100 |
| Leucoraja naevus | Cuckoo ray | 0.4 | 1 | 380 | 380 |
| Limanda limanda | Dab | 1122.6 | 20787 | 70 | 330 |
| Lithodes maja | Norway king crab | 3.7 | 9 | 22 | 109 |
| Loligo forbesii | Northern squid | 46.6 | 225 | 40 | 360 |
| Loligo vulgaris | European squid | 25.5 | 66 | 130 | 340 |
| Lophius piscatorius | Angler fish | 5.7 | 4 | 100 | 600 |
| Lumpenus lampretaeformis | Snake blenny | 0.0 | 1 | 290 | 290 |
| Melanogrammus aeglefinus | Haddock | 10638.7 | 40808 | 150 | 460 |
| Merlangius merlangus | Whiting | 3700.4 | 42143 | 80 | 430 |
| Microstomus kitt | Lemon sole | 44.9 | 447 | 130 | 370 |
| Mullus surmuletus | Striped red mullet | 7.7 | 97 | 90 | 270 |
| Mustelus asterias | Starry smooth-hound | 40.9 | 59 | 340 | 910 |
| Myoxocephalus scorpius | Sculpin | 0.4 | 3 | 160 | 230 |
| Myxine glutinosa | Hagfish | 0.0 | 1 | 310 | 310 |
| Nephrops norvegicus | Norway lobster | 30.2 | 934 | 20 | 64 |
| Pecten maximus | Great scallop | 0.9 | 3 | ||
| Phrynorhombus norvegicus | Norwegian topknot | 0.0 | 7 | 50 | 80 |
| Platichthys flesus | Flounder | 7.8 | 31 | 230 | 360 |
| Pleuronectes platessa | Plaice | 370.6 | 3210 | 120 | 470 |
| Pollachius pollachius | Pollack | 0.7 | 1 | 440 | 440 |
| Pomatoschistus spp. | Sand gobies | 0.0 | 52 | 30 | 50 |
| Raja brachyura | Blonde ray | 10.9 | 6 | 400 | 790 |
| Raja clavata | Thornback ray | 33.4 | 15 | 420 | 810 |
| Raja montagui | Spotted Ray | 17.2 | 18 | 280 | 810 |
| Rossia macrosoma | Stout bobtail squid | 0.1 | 60 | ||
| Sardina pilchardus | Pilchard | 1.3 | 132 | 70 | 240 |
| Scomber scombrus | Mackerel | 152.9 | 3445 | 160 | 310 |
| Scophthalmus maximus | Turbot | 7.5 | 11 | 240 | 440 |
| Scophthalmus rhombus | Brill | 7.9 | 12 | 300 | 430 |
| Scyliorhinus canicula | Lesser-spotted dogfish | 80.9 | 173 | 230 | 680 |
| Sepia officinalis | Common cuttlefish | 3.9 | 21 | 50 | 200 |
| Sepiola atlantica | Atlantic bobtail squid | 0.1 | 26 | ||
| Solea solea | Sole | 0.3 | 2 | 190 | 290 |
| Sprattus sprattus | Sprat | 1037.6 | 199025 | 55 | 140 |
| Squalus acanthias | Spurdog | 14.4 | 38 | 280 | 920 |
| Syngnathidae | Pipefishes and seahorses | 0.0 | 4 | 60 | 240 |
| Syngnathus acus | Great pipefish | 0.0 | 2 | 350 | 360 |
| Todaropsis eblanae | Lesser flying squid | 0.3 | 8 | 40 | 90 |
| Trachinus draco | Greater weever fish | 11.8 | 55 | 250 | 400 |
| Trachurus trachurus | Horse mackerel | 14.4 | 593 | 90 | 260 |
| Trigla lucerna | Tub gurnard | 1.8 | 10 | 230 | 290 |
| Trigloporus lastoviza | Streaked gurnard | 0.7 | 4 | 240 | 270 |
| Trisopterus esmarkii | Norway pout | 294.7 | 17903 | 80 | 240 |
| Trisopterus luscus | Bib | 10.8 | 158 | 110 | 250 |
| Trisopterus minutus | Poor-cod | 15.0 | 363 | 80 | 240 |
| Zeus faber | John dory | 1.3 | 3 | 140 | 330 |