Scientific survey report

Danish International Bottom Trawl Survey

2023

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.

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 16272.4 706493
Haddock 5052.7 60170 120 580
Herring 4521.9 278068 70 325
Whiting 2025.2 20120 60 400
Plaice 274.7 2744 80 420
Cod 164.5 189 110 1040

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 cought during the survey, allocated to each ship. The black line represents the average length distribution of the 5 years previus surveys.

Sprat

Herring

Haddock

Norway pout

Common dab

Whiting

Grey gurnard

Mackerel

Plaice

Blue whiting

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 0.2 2
Agonus cataphractus Pogge 0.0 1 120 120
Alloteuthis subulata European common squid 0.2 34 30 100
Buglossidium luteum Solenette 0.0 4 90 110
Callionymus lyra Common dragonet 0.1 4 140 200
Callionymus maculatus Spotted dragonet 0.0 3 100 150
Callionymus reticulatus Reticulated dragonet 0.0 1 70 70
Cancer pagurus Edible crab 6.6 24 95 148
Clupea harengus Herring 50.6 1216 75 265
Engraulis encrasicolus Anchovy 0.0 13 60 150
Eutrigla gurnardus Grey gurnard 0.2 3 180 250
Gadus morhua Cod 14.0 45 110 670
Hippoglossoides platessoides American plaice 7.6 192 70 240
Illex coindetii Southern shortfin squid 0.7 16 50 140
Limanda limanda Common dab 32.2 558 50 280
Loligo forbesii Northern squid 1.0 5 70 300
Melanogrammus aeglefinus Haddock 96.8 748 150 400
Merlangius merlangus Whiting 26.0 362 80 370
Microstomus kitt Lemon sole 3.8 30 150 280
Myoxocephalus scorpius Sculpin 2.9 12 170 290
Pleuronectes platessa Plaice 27.3 400 90 320
Pomatoschistus spp. Sand gobies 0.0 19 30 70
Rossia macrosoma Stout bobtail squid 0.0 1
Scomber scombrus Mackerel 0.5 17 150 200
Scophthalmus maximus Turbot 1.6 1 420 420
Solea solea Sole 0.9 3 250 340
Sprattus sprattus Sprat 10.7 2327 60 105
Trachurus trachurus Horse mackerel 0.3 14 120 160
Trisopterus esmarkii Norway pout 4.7 384 80 200
Trisopterus minutus Poor-cod 0.2 4 150 190

Area - 4A

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Alloteuthis subulata European common squid 0.2 33 30 90
Amblyraja radiata Starry ray 0.5 2 310 350
Anarhichas lupus Catfish 6.0 2 650 670
Argentina sphyraena Lesser silver smelt 1.1 31 130 240
Cancer pagurus Edible crab 0.9 3 118 120
Clupea harengus Herring 75.4 644 175 325
Eledone cirrhosa Horned octopus 0.1 1
Eutrigla gurnardus Grey gurnard 85.5 606 180 330
Gadiculus argenteus Silvery pout 0.1 13 60 110
Gadus morhua Cod 80.5 88 120 870
Galeus melastomus Blackmouth catshark 1.3 2 580 660
Glyptocephalus cynoglossus Witch 0.3 1 350 350
Hippoglossoides platessoides American plaice 2.8 47 100 250
Hippoglossus hippoglossus Atlantic halibut 5.7 2 600 630
Illex coindetii Southern shortfin squid 2.9 59 40 170
Limanda limanda Common dab 3.1 52 140 240
Lithodes maja Norway king crab 1.1 4 42 101
Loligo forbesii Northern squid 12.1 83 40 270
Lophius piscatorius Angler fish 7.7 5 150 620
Maurolicus muelleri Pearlside 0.0 5 40 60
Melanogrammus aeglefinus Haddock 977.4 3018 130 580
Merlangius merlangus Whiting 225.3 867 160 400
Merluccius merluccius Hake 3.0 9 300 410
Micromesistius poutassou Blue whiting 48.2 434 160 330
Microstomus kitt Lemon sole 2.6 10 200 350
Molva molva Ling 6.7 4 590 790
Nephrops norvegicus Norway lobster 0.0 1 44 44
Pleuronectes platessa Plaice 2.6 9 110 420
Pollachius pollachius Pollack 14.2 5 360 720
Pollachius virens Saithe 89.0 86 370 910
Scomber scombrus Mackerel 2.8 33 160 280
Todaropsis eblanae Lesser flying squid 1.7 20 60 130
Trachurus trachurus Horse mackerel 0.3 8 120 240
Trisopterus esmarkii Norway pout 146.1 17384 70 190
Trisopterus minutus Poor-cod 1.6 30 110 230

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.5 11
Agonus cataphractus Pogge 0.1 10 40 130
Alloteuthis subulata European common squid 17.6 5280 20 120
Amblyraja radiata Starry ray 13.0 42 160 440
Ammodytes marinus Lesser sandeel 0.1 60 65 100
Aphia minuta Transparent goby 0.0 2 30 50
Arnoglossus laterna Scaldfish 0.4 33 80 150
Buglossidium luteum Solenette 2.1 237 70 130
Callionymus lyra Common dragonet 1.6 40 130 250
Callionymus maculatus Spotted dragonet 0.0 5 70 100
Cancer pagurus Edible crab 13.3 32 90 182
Chelidonichthys lucerna Tub gurnard 1.0 4 210 340
Clupea harengus Herring 4395.9 276208 70 300
Cyclopterus lumpus Lumpfish 2.0 1 320 320
Echiichthys vipera Lesser weever 0.2 3 150 170
Enchelyopus cimbrius Four-bearded rockling 1.2 22 100 280
Engraulis encrasicolus Anchovy 7.6 833 60 150
Eutrigla gurnardus Grey gurnard 409.3 5818 80 390
Gadus morhua Cod 70.0 56 200 1040
Glyptocephalus cynoglossus Witch 2.2 11 150 390
Gymnammodytes semisquamatus Smoothed sandeel 0.0 1 165 165
Helicolenus dactylopterus Blue-mouth redfish 0.0 1 150 150
Hippoglossoides platessoides American plaice 25.6 615 60 280
Hyperoplus lanceolatus Greater sandeel 0.2 7 155 290
Illex coindetii Southern shortfin squid 0.4 10 50 120
Limanda limanda Common dab 1184.5 20938 50 320
Lithodes maja Norway king crab 4.6 9 59 103
Loligo forbesii Northern squid 10.5 44 80 310
Loligo vulgaris European squid 12.9 40 150 300
Lophius piscatorius Angler fish 2.6 4 130 430
Lumpenus lampretaeformis Snake blenny 0.0 2 100 280
Maurolicus muelleri Pearlside 0.0 2 40 60
Melanogrammus aeglefinus Haddock 3978.5 56404 120 410
Merlangius merlangus Whiting 1773.8 18891 60 380
Microstomus kitt Lemon sole 22.5 248 100 330
Molva molva Ling 2.3 1 730 730
Mullus surmuletus Striped red mullet 2.6 54 80 270
Mustelus asterias Starry smooth-hound 7.2 22 370 560
Myoxocephalus scorpius Sculpin 1.7 19 100 220
Nephrops norvegicus Norway lobster 11.2 390 21 60
Pecten maximus Great scallop 2.3 8
Pholis gunnellus Butter fish 0.0 2 150 160
Phrynorhombus norvegicus Norwegian topknot 0.0 3 60 90
Platichthys flesus Flounder 0.2 2 210 230
Pleuronectes platessa Plaice 244.8 2335 80 400
Pollachius virens Saithe 0.1 1 260 260
Pomatoschistus spp. Sand gobies 0.0 17 30 70
Raja brachyura Blonde ray 0.5 1 480 480
Raja clavata Thornback ray 13.1 7 530 720
Raja montagui Spotted Ray 0.8 2 380 410
Rossia macrosoma Stout bobtail squid 0.1 33
Sardina pilchardus Pilchard 1.1 92 80 210
Scomber scombrus Mackerel 95.6 2698 150 210
Scophthalmus maximus Turbot 1.2 2 230 350
Scophthalmus rhombus Brill 2.7 2 390 500
Scyliorhinus canicula Lesser-spotted dogfish 13.9 22 320 690
Scyliorhinus stellaris Greater-spotted dogfish 0.7 1 540 540
Sepia officinalis Common cuttlefish 0.4 3 70 110
Sepiola atlantica Atlantic bobtail squid 0.0 1
Solea solea Sole 0.3 1 310 310
Sprattus sprattus Sprat 1738.7 279573 55 180
Syngnathidae Pipefishes and seahorses 0.0 1 90 90
Todarodes sagittatus European flying squid 0.0 2 50 50
Todaropsis eblanae Lesser flying squid 0.3 7 30 110
Trachinus draco Greater weever fish 10.9 55 220 430
Trachurus trachurus Horse mackerel 8.5 410 80 330
Trisopterus esmarkii Norway pout 57.6 4702 40 200
Trisopterus luscus Bib 0.1 1 210 210
Trisopterus minutus Poor-cod 1.3 54 60 220
Zeus faber John dory 0.1 1 190 190

Quarter 3

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 46112.0 987266
Haddock 13035.0 56752 110 550
Whiting 11832.5 155752 50 450
Herring 2738.0 73972 75 340
Plaice 437.9 3593 100 410
Cod 132.6 521 70 670

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 cought during the survey, allocated to each ship. The black line represents the average length distribution of the 5 years previus surveys.

Sprat

Whiting

Herring

Horse mackerel

Haddock

Common dab

Mackerel

Norway pout

Grey gurnard

Plaice

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)
Ammodytes marinus Lesser sandeel 0.0 2 165 190
Callionymus lyra Common dragonet 0.1 1 220 220
Callionymus maculatus Spotted dragonet 0.0 2 80 120
Cancer pagurus Edible crab 0.5 3 93 105
Clupea harengus Herring 11.0 138 185 285
Echiichthys vipera Lesser weever 0.4 13 100 160
Engraulis encrasicolus Anchovy 0.0 1 160 160
Eutrigla gurnardus Grey gurnard 41.2 455 130 320
Gadus morhua Cod 85.8 400 70 670
Glyptocephalus cynoglossus Witch 5.7 20 270 420
Gymnammodytes semisquamatus Smoothed sandeel 0.3 20 140 205
Hippoglossoides platessoides American plaice 25.6 647 110 250
Hyperoplus lanceolatus Greater sandeel 1.7 45 175 315
Illex coindetii Southern shortfin squid 0.4 3 130 170
Limanda limanda Common dab 185.0 1761 110 310
Loligo forbesii Northern squid 16.1 199 50 300
Loligo vulgaris European squid 5.1 10 200 300
Lophius piscatorius Angler fish 2.8 1 550 550
Melanogrammus aeglefinus Haddock 2845.6 5881 110 550
Merlangius merlangus Whiting 126.6 558 200 450
Merluccius merluccius Hake 20.1 6 590 970
Micromesistius poutassou Blue whiting 0.1 2 190 250
Microstomus kitt Lemon sole 36.7 259 150 290
Molva molva Ling 2.8 5 430 500
Myxine glutinosa Hagfish 0.0 1
Nephrops norvegicus Norway lobster 0.2 2 48 62
Pecten maximus Great scallop 0.2 0
Pleuronectes platessa Plaice 46.1 467 130 410
Pollachius pollachius Pollack 13.4 6 500 680
Pollachius virens Saithe 8.2 13 330 520
Raja clavata Thornback ray 5.8 2 620 730
Sardina pilchardus Pilchard 0.1 2 180 180
Scomber scombrus Mackerel 1744.5 14357 220 390
Scophthalmus maximus Turbot 1.6 2 310 360
Trachinus draco Greater weever fish 19.5 117 210 390
Trachurus trachurus Horse mackerel 2.4 7 330 360
Trisopterus esmarkii Norway pout 188.8 9103 50 160

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Alloteuthis subulata European common squid 5.2 1039 20 120
Alosa fallax Twaite shad 0.9 1 440 440
Amblyraja radiata Starry ray 4.0 10 250 460
Ammodytes marinus Lesser sandeel 0.1 8 75 210
Arnoglossus laterna Scaldfish 0.6 57 80 130
Buglossidium luteum Solenette 1.0 106 70 110
Callionymus lyra Common dragonet 1.9 55 110 240
Callionymus maculatus Spotted dragonet 0.0 1 140 140
Cancer pagurus Edible crab 9.0 14 115 197
Chelidonichthys lucerna Tub gurnard 3.2 7 230 440
Clupea harengus Herring 2711.7 72050 75 340
Echiichthys vipera Lesser weever 0.7 30 100 160
Eledone cirrhosa Horned octopus 0.0 1
Enchelyopus cimbrius Four-bearded rockling 2.8 82 150 260
Engraulis encrasicolus Anchovy 0.0 1 130 130
Entelurus aequoreus Snake pipefish 0.0 1 480 480
Eutrigla gurnardus Grey gurnard 310.0 5177 100 350
Gadus morhua Cod 41.5 102 170 660
Galeorhinus galeus Tope 17.9 1 1460 1460
Glyptocephalus cynoglossus Witch 0.2 2 120 310
Gymnammodytes semisquamatus Smoothed sandeel 1.9 110 165 230
Helicolenus dactylopterus Blue-mouth redfish 0.6 5 160 230
Hippoglossoides platessoides American plaice 75.0 1768 100 250
Homarus gammarus European lobster 4.9 9 63 127
Hyperoplus lanceolatus Greater sandeel 45.7 1654 165 310
Illex coindetii Southern shortfin squid 2.3 30 100 180
Leucoraja naevus Cuckoo ray 0.2 1 330 330
Limanda limanda Common dab 2096.6 38143 100 280
Lithodes maja Norway king crab 3.5 7 68 127
Loligo Loligo sp 3.7 3428 10 60
Loligo forbesii Northern squid 49.5 1348 30 300
Lophius piscatorius Angler fish 8.9 10 200 550
Lumpenus lampretaeformis Snake blenny 0.0 1 310 310
Melanogrammus aeglefinus Haddock 10150.6 50693 110 430
Merlangius merlangus Whiting 8678.8 108436 60 370
Merluccius merluccius Hake 17.0 12 370 720
Microstomus kitt Lemon sole 70.5 749 130 320
Mullus surmuletus Striped red mullet 2.2 25 150 260
Mustelus asterias Starry smooth-hound 81.4 32 520 1000
Myoxocephalus scorpius Sculpin 0.3 4 130 200
Nephrops norvegicus Norway lobster 7.1 242 17 48
Pecten maximus Great scallop 0.5 7
Platichthys flesus Flounder 0.7 4 210 280
Pleuronectes platessa Plaice 327.9 2513 100 410
Pollachius virens Saithe 0.2 1 290 290
Raja brachyura Blonde ray 9.7 8 360 800
Raja clavata Thornback ray 23.6 15 370 790
Raja montagui Spotted Ray 4.2 6 380 530
Scomber scombrus Mackerel 2047.7 14279 210 390
Scophthalmus maximus Turbot 21.1 14 240 630
Scophthalmus rhombus Brill 4.5 6 290 530
Scyliorhinus canicula Lesser-spotted dogfish 337.9 485 210 650
Solea solea Sole 0.3 2 250 260
Sprattus sprattus Sprat 4518.0 394690 60 150
Squalus acanthias Spurdog 16.1 24 260 810
Trachinus draco Greater weever fish 1.8 12 180 380
Trachurus trachurus Horse mackerel 156.8 21351 40 380
Trisopterus esmarkii Norway pout 2.6 84 60 180
Trisopterus minutus Poor-cod 0.4 12 140 190

Area - 4C

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.2 11
Agonus cataphractus Pogge 0.1 9 60 130
Alloteuthis subulata European common squid 31.8 3643 20 150
Alosa fallax Twaite shad 0.5 1 370 370
Ammodytes marinus Lesser sandeel 0.1 11 100 190
Arnoglossus laterna Scaldfish 0.1 6 90 140
Bryozoa Bryozoans 257.0 0
Buglossidium luteum Solenette 0.2 16 80 100
Callionymus lyra Common dragonet 5.3 99 60 240
Callionymus maculatus Spotted dragonet 0.0 1 100 100
Cancer pagurus Edible crab 13.3 38 72 187
Chelidonichthys lucerna Tub gurnard 7.5 24 220 430
Ciliata mustela Five-bearded rockling 0.0 1 150 150
Clupea harengus Herring 15.2 1784 80 270
Dicentrarchus labrax Bass 40.6 32 360 630
Echiichthys vipera Lesser weever 31.9 1357 60 190
Engraulis encrasicolus Anchovy 0.1 3 150 170
Entelurus aequoreus Snake pipefish 0.1 5 410 500
Eutrigla gurnardus Grey gurnard 18.6 158 100 340
Gadus morhua Cod 5.3 19 130 610
Galeorhinus galeus Tope 998.7 73 1050 1590
Homarus gammarus European lobster 11.6 21 58 131
Hyperoplus lanceolatus Greater sandeel 11.2 327 170 285
Limanda limanda Common dab 426.3 9080 40 270
Liza ramada Thin lipped mullet 1.6 1 570 570
Loligo Loligo sp 1.5 789 10 60
Loligo forbesii Northern squid 74.4 2338 20 310
Loligo vulgaris European squid 0.5 6 100 120
Maja squinado Common spider crab 0.4 2 84 89
Melanogrammus aeglefinus Haddock 38.8 178 220 310
Merlangius merlangus Whiting 3027.1 46757 50 340
Micromesistius poutassou Blue whiting 0.1 1 260 260
Microstomus kitt Lemon sole 7.2 70 130 320
Mullus surmuletus Striped red mullet 21.4 217 50 290
Mustelus asterias Starry smooth-hound 266.1 134 530 1040
Myoxocephalus scorpius Sculpin 0.5 5 120 200
Pecten maximus Great scallop 0.4 1
Pholis gunnellus Butter fish 0.0 1 170 170
Platichthys flesus Flounder 2.6 8 240 370
Pleuronectes platessa Plaice 63.9 612 100 330
Pomatoschistus spp. Sand gobies 0.0 1 40 40
Raja brachyura Blonde ray 8.8 5 510 690
Raja clavata Thornback ray 40.9 40 280 690
Raja montagui Spotted Ray 14.0 17 400 560
Rossia macrosoma Stout bobtail squid 0.1 35
Sardina pilchardus Pilchard 304.4 3012 90 270
Scomber scombrus Mackerel 563.3 3559 200 410
Scophthalmus maximus Turbot 4.0 5 250 380
Scophthalmus rhombus Brill 1.0 1 420 420
Scyliorhinus canicula Lesser-spotted dogfish 160.3 363 240 640
Sepia officinalis Common cuttlefish 3.4 9 100 230
Solea solea Sole 1.9 16 180 320
Sprattus sprattus Sprat 490.0 121581 65 130
Todaropsis eblanae Lesser flying squid 0.1 1 110 110
Trachinus draco Greater weever fish 1.9 12 160 350
Trachurus trachurus Horse mackerel 1712.5 35563 40 320
Trisopterus esmarkii Norway pout 2.2 175 90 120
Trisopterus luscus Bib 57.2 551 130 270
Trisopterus minutus Poor-cod 33.1 1001 90 190
Zeus faber John dory 0.6 2 250 260