Scientific survey report

Danish International Bottom Trawl Survey

2026

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 8786.1 158694
Haddock 4220.9 15308 140 530
Whiting 1617.2 15230 90 400
Plaice 464.6 3875 90 410
Herring 383.1 18712 80 280
Cod 47.1 59 130 880

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

Dab

Haddock

Whiting

Grey gurnard

Plaice

Lemon sole

Norway pout

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)
Agonus cataphractus Pogge 0.0 7 70 120
Alloteuthis subulata European common squid 0.1 15 30 70
Arnoglossus laterna Scaldfish 0.1 8 50 150
Buglossidium luteum Solenette 0.0 1 80 80
Callionymus lyra Common dragonet 0.7 21 110 210
Cancer pagurus Edible crab 5.2 15 90 170
Ciliata mustela Five-bearded rockling 0.1 1 210 210
Clupea harengus Herring 82.8 1938 110 280
Engraulis encrasicolus Anchovy 0.0 3 80 100
Eutrigla gurnardus Grey gurnard 5.0 91 110 390
Gadus morhua Cod 6.4 9 130 790
Glyptocephalus cynoglossus Witch 0.3 1 340 340
Hippoglossoides platessoides Long rough dab 4.4 132 100 240
Limanda limanda Dab 107.2 1993 50 300
Loligo forbesii Northern squid 0.2 2 100 160
Maurolicus muelleri Pearlside 0.1 55 30 70
Melanogrammus aeglefinus Haddock 44.6 131 170 470
Merlangius merlangus Whiting 128.2 1054 150 400
Merluccius merluccius Hake 0.4 8 100 270
Microstomus kitt Lemon sole 6.1 30 140 370
Mullus surmuletus Striped red mullet 0.0 1 140 140
Myoxocephalus scorpius Sculpin 0.9 3 190 300
Pecten maximus Great scallop 0.1 1
Pleuronectes platessa Plaice 21.2 191 150 370
Pollachius virens Saithe 0.5 2 210 400
Pomatoschistus spp. Sand gobies 0.0 16 30 40
Rossia macrosoma Stout bobtail squid 0.0 1
Sardina pilchardus Pilchard 0.0 5 90 120
Scomber scombrus Mackerel 0.5 3 260 300
Scophthalmus rhombus Brill 2.0 1 460 460
Scyliorhinus canicula Lesser-spotted dogfish 1.7 2 430 780
Solea solea Sole 2.1 3 320 420
Sprattus sprattus Sprat 50.9 10399 65 125
Todaropsis eblanae Lesser flying squid 0.0 1 60 60
Trachurus trachurus Horse mackerel 0.3 14 120 150
Trisopterus esmarkii Norway pout 1.2 193 80 130
Trisopterus minutus Poor-cod 0.5 16 110 210
Zeus faber John dory 0.0 1 120 120

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 1.0 18
Agonus cataphractus Pogge 0.4 21 80 150
Alloteuthis subulata European common squid 30.1 8817 20 110
Amblyraja radiata Starry ray 6.8 29 180 430
Ammodytes marinus Lesser sandeel 0.0 9 70 180
Aphia minuta Transparent goby 0.0 79 30 50
Arnoglossus laterna Scaldfish 0.5 44 90 130
Atherina presbyter Sand-smelt 0.0 1 100 100
Buglossidium luteum Solenette 0.7 57 70 130
Callionymus lyra Common dragonet 0.3 9 70 210
Callionymus reticulatus Reticulated dragonet 0.0 17 40 80
Cancer pagurus Edible crab 29.1 72 92 183
Ciliata mustela Five-bearded rockling 0.2 3 150 200
Clupea harengus Herring 299.9 16769 80 260
Cyclopterus lumpus Lumpfish 0.4 1 180 180
Diplecogaster bimaculata Two-spotted clingfish 0.0 1 30 30
Echiichthys vipera Lesser weever 0.1 5 110 150
Eledone cirrhosa Horned octopus 0.2 1
Enchelyopus cimbrius Four-bearded rockling 0.6 13 140 260
Engraulis encrasicolus Anchovy 2.4 387 70 150
Entelurus aequoreus Snake pipefish 0.0 1 260 260
Eutrigla gurnardus Grey gurnard 406.7 6834 110 300
Gadus morhua Cod 32.8 39 180 880
Gasterosteus aculeatus Three-spined stickleback 0.0 3 50 60
Glyptocephalus cynoglossus Witch 0.3 1 330 330
Hippoglossoides platessoides Long rough dab 12.1 319 120 230
Illex coindetii Southern shortfin squid 0.0 5 30 40
Limanda limanda Dab 778.5 13456 50 320
Lithodes maja Norway king crab 1.6 2 99 102
Loligo forbesii Northern squid 26.2 107 30 500
Loligo vulgaris European squid 8.5 19 160 330
Maurolicus muelleri Pearlside 0.0 2 50 70
Melanogrammus aeglefinus Haddock 4176.3 15177 140 530
Merlangius merlangus Whiting 1427.2 13862 90 370
Microchirus variegatus Thickback sole 0.0 1 120 120
Microstomus kitt Lemon sole 20.9 220 90 350
Mullus surmuletus Striped red mullet 0.9 23 120 200
Mustelus asterias Starry smooth-hound 15.5 28 340 840
Myoxocephalus scorpius Sculpin 0.8 7 140 260
Nephrops norvegicus Norway lobster 0.4 7 25 50
Pecten maximus Great scallop 0.1 0
Pholis gunnellus Butter fish 0.0 1 160 160
Phrynorhombus norvegicus Norwegian topknot 0.0 1 80 80
Platichthys flesus Flounder 1.0 4 280 320
Pleuronectes platessa Plaice 441.7 3654 90 410
Pomatoschistus spp. Sand gobies 0.1 74 20 60
Raja brachyura Blonde ray 1.3 1 570 570
Raja clavata Thornback ray 4.0 3 480 620
Raja montagui Spotted Ray 2.9 4 380 550
Rossia macrosoma Stout bobtail squid 0.0 7
Sardina pilchardus Pilchard 3.9 849 60 230
Scomber scombrus Mackerel 0.3 6 180 260
Scophthalmus maximus Turbot 12.7 9 240 550
Scophthalmus rhombus Brill 3.0 5 320 390
Scyliorhinus canicula Lesser-spotted dogfish 84.8 142 240 640
Sepia officinalis Common cuttlefish 0.2 4 50 80
Sepiola atlantica Atlantic bobtail squid 0.0 1
Solea solea Sole 1.0 3 250 350
Sprattus sprattus Sprat 305.0 59685 60 150
Squalus acanthias Spurdog 0.2 1 360 360
Syngnathus acus Great pipefish 0.1 3 390 430
Syngnathus rostellatus Lesser pipefish 0.0 3 90 120
Syngnathus typhle Broad-nosed pipefish 0.0 1 110 110
Taurulus bubalis Sea scorpion 0.1 4 120 130
Todaropsis eblanae Lesser flying squid 0.0 1 60 60
Trachinus draco Greater weever fish 8.3 40 270 380
Trachurus trachurus Horse mackerel 3.4 201 70 340
Trisopterus esmarkii Norway pout 0.7 60 90 180
Trisopterus luscus Bib 2.1 11 150 280
Trisopterus minutus Poor-cod 0.8 15 120 220

Area - 4C

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Agonus cataphractus Pogge 1.3 72 50 140
Aphia minuta Transparent goby 0.0 1 40 40
Callionymus lyra Common dragonet 0.6 20 60 210
Callionymus maculatus Spotted dragonet 0.0 1 50 50
Cancer pagurus Edible crab 13.4 39 86 175
Ciliata mustela Five-bearded rockling 0.2 3 140 260
Clupea harengus Herring 0.4 5 220 255
Dicentrarchus labrax Bass 21.8 66 200 400
Eutrigla gurnardus Grey gurnard 0.7 6 190 270
Gadus morhua Cod 7.9 11 190 480
Helicolenus dactylopterus Blue-mouth redfish 0.2 1 210 210
Hippoglossoides platessoides Long rough dab 0.0 1 170 170
Homarus gammarus European lobster 2.7 4 41 140
Limanda limanda Dab 12.8 213 100 280
Liparis liparis Sea snail 1.9 51 100 150
Merlangius merlangus Whiting 61.8 313 180 360
Microstomus kitt Lemon sole 0.1 5 90 170
Mullus surmuletus Striped red mullet 0.0 1 130 130
Mustelus asterias Starry smooth-hound 2.0 12 310 400
Myoxocephalus scorpius Sculpin 0.2 6 80 170
Pecten maximus Great scallop 3.3 12
Pholis gunnellus Butter fish 0.1 8 100 180
Platichthys flesus Flounder 0.1 1 230 230
Pleuronectes platessa Plaice 1.7 30 100 280
Sardina pilchardus Pilchard 0.0 1 80 80
Scyliorhinus canicula Lesser-spotted dogfish 2.4 6 210 640
Solea solea Sole 5.6 67 70 310
Sprattus sprattus Sprat 0.1 24 55 120
Syngnathus acus Great pipefish 0.0 1 270 270
Taurulus bubalis Sea scorpion 0.3 5 80 180
Trisopterus luscus Bib 10.8 81 130 340