Scientific survey report

Danish International Bottom Trawl Survey

2018

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 6236.6 279570
Herring 1150.2 48294 65 325
Whiting 768.3 7681 70 440
Cod 227.9 156 130 980
Plaice 193.2 1145 110 570
Haddock 137.1 766 150 450

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

Common dab

Norway pout

Mackerel

Grey gurnard

Whiting

Plaice

Haddock

Lemon sole

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)
Alloteuthis subulata European common squid 0.0 5 40 80
Cancer pagurus Edible crab 0.7 4 96 114
Clupea harengus Herring 137.8 2650 75 280
Enchelyopus cimbrius Four-bearded rockling 0.2 2 240 260
Gadus morhua Cod 19.6 29 170 860
Gasterosteus aculeatus Three-spined stickleback 0.0 6 50 60
Glyptocephalus cynoglossus Witch 1.8 7 210 420
Hippoglossoides platessoides American plaice 1.8 82 60 290
Limanda limanda Common dab 5.7 93 70 300
Loligo forbesii Northern squid 0.6 2 160 220
Melanogrammus aeglefinus Haddock 42.6 291 180 430
Merlangius merlangus Whiting 86.2 597 70 410
Microstomus kitt Lemon sole 0.5 4 200 260
Myoxocephalus scorpius Sculpin 0.1 1 190 190
Myxine glutinosa Hagfish 0.0 1 300 300
Platichthys flesus Flounder 0.1 1 240 240
Pleuronectes platessa Plaice 4.4 52 120 330
Pollachius virens Saithe 9.4 6 370 730
Pomatoschistus spp. Sand gobies 0.0 1 40 40
Scomber scombrus Mackerel 26.9 657 170 210
Sprattus sprattus Sprat 3.3 614 55 135
Trisopterus esmarkii Norway pout 16.3 579 100 190
Trisopterus minutus Poor-cod 0.1 3 130 190

Area - 4A

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Alloteuthis subulata European common squid 5.1 213 40 100
Amblyraja radiata Starry ray 2.1 4 220 520
Anarhichas lupus Catfish 2.9 2 490 600
Argentina sphyraena Lesser silver smelt 4.4 132 130 250
Callionymus lyra Common dragonet 0.0 1 90 90
Callionymus maculatus Spotted dragonet 0.0 3 100 130
Capros aper Boarfish 0.0 1 100 100
Clupea harengus Herring 39.4 519 190 320
Eledone cirrhosa Horned octopus 0.3 3
Engraulis encrasicolus Anchovy 0.0 1 180 180
Eutrigla gurnardus Grey gurnard 25.1 131 190 420
Gadiculus argenteus Silvery pout 0.1 14 70 100
Gadus morhua Cod 72.2 69 250 950
Glyptocephalus cynoglossus Witch 2.5 8 260 450
Helicolenus dactylopterus Blue-mouth redfish 0.1 9 90 100
Hippoglossoides platessoides American plaice 2.1 52 100 220
Illex coindetii Southern shortfin squid 1.6 48 60 120
Limanda limanda Common dab 8.2 90 130 290
Lithodes maja Norway king crab 0.7 3 70 77
Loligo forbesii Northern squid 2.7 27 70 270
Loligo vulgaris European squid 0.3 1 240 240
Lophius piscatorius Angler fish 28.6 9 190 790
Melanogrammus aeglefinus Haddock 29.5 212 160 450
Merlangius merlangus Whiting 106.7 443 150 430
Merluccius merluccius Hake 9.1 60 130 330
Microstomus kitt Lemon sole 3.2 11 230 360
Pleuronectes platessa Plaice 6.7 15 300 400
Pollachius virens Saithe 13.8 16 380 590
Rossia macrosoma Stout bobtail squid 0.0 1
Scomber scombrus Mackerel 910.9 10337 170 280
Scyliorhinus canicula Lesser-spotted dogfish 0.8 1 620 620
Todaropsis eblanae Lesser flying squid 0.1 2 60 70
Trachurus trachurus Horse mackerel 0.2 3 130 240
Trisopterus esmarkii Norway pout 105.2 11112 80 210
Trisopterus minutus Poor-cod 1.1 18 140 210

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.2 4
Agonus cataphractus Pogge 0.9 37 60 170
Alloteuthis subulata European common squid 47.6 13667 20 140
Alosa fallax Twaite shad 0.8 1 430 430
Amblyraja radiata Starry ray 8.0 16 130 480
Ammodytes marinus Lesser sandeel 24.9 3106 50 190
Anarhichas lupus Catfish 0.9 1 470 470
Arnoglossus laterna Scaldfish 0.2 15 80 130
Buglossidium luteum Solenette 0.1 16 60 120
Callionymus lyra Common dragonet 0.8 19 80 240
Callionymus maculatus Spotted dragonet 0.0 2 130 140
Cancer pagurus Edible crab 17.8 28 94 206
Chelidonichthys lucerna Tub gurnard 0.2 1 270 270
Ciliata mustela Five-bearded rockling 0.1 2 140 210
Clupea harengus Herring 973.0 45125 65 325
Cyclopterus lumpus Lumpfish 0.5 2 170 200
Echiichthys vipera Lesser weever 1.8 66 90 170
Eledone cirrhosa Horned octopus 0.2 2
Enchelyopus cimbrius Four-bearded rockling 0.5 12 170 230
Engraulis encrasicolus Anchovy 0.4 36 70 150
Entelurus aequoreus Snake pipefish 0.0 1 470 470
Eutrigla gurnardus Grey gurnard 665.1 8277 80 390
Gadus morhua Cod 136.2 58 130 980
Gasterosteus aculeatus Three-spined stickleback 0.0 3 60 70
Glyptocephalus cynoglossus Witch 1.0 3 330 420
Gymnammodytes semisquamatus Smoothed sandeel 0.1 12 120 175
Hippoglossoides platessoides American plaice 34.8 909 90 300
Homarus gammarus European lobster 0.7 1 98 98
Hyperoplus lanceolatus Greater sandeel 0.2 2 250 320
Illex coindetii Southern shortfin squid 0.0 2 60 80
Lampetra fluviatilis River lamprey 0.0 1 310 310
Leucoraja naevus Cuckoo ray 1.2 2 370 510
Limanda limanda Common dab 951.3 15199 60 330
Lithodes maja Norway king crab 8.7 19 61 109
Loligo forbesii Northern squid 7.0 41 110 260
Loligo vulgaris European squid 7.2 33 140 280
Lophius piscatorius Angler fish 5.6 11 160 530
Maurolicus muelleri Pearlside 0.0 1 60 60
Melanogrammus aeglefinus Haddock 65.0 263 150 420
Merlangius merlangus Whiting 575.4 6642 70 440
Microstomus kitt Lemon sole 21.0 148 160 360
Mullus surmuletus Striped red mullet 1.2 34 110 220
Mustelus asterias Starry smooth-hound 5.3 16 380 620
Myoxocephalus scorpius Sculpin 2.7 37 80 240
Nephrops norvegicus Norway lobster 7.4 194 23 60
Pecten maximus Great scallop 0.3 2
Pholis gunnellus Butter fish 0.0 1 190 190
Platichthys flesus Flounder 2.0 11 200 310
Pleuronectes platessa Plaice 182.2 1078 110 570
Pollachius virens Saithe 0.2 1 300 300
Pomatoschistus spp. Sand gobies 0.0 1 60 60
Raja clavata Thornback ray 1.0 1 500 500
Raja montagui Spotted Ray 4.3 9 310 550
Rossia macrosoma Stout bobtail squid 0.0 11
Sardina pilchardus Pilchard 0.2 26 80 130
Scomber scombrus Mackerel 64.0 1482 160 250
Scophthalmus maximus Turbot 2.5 3 320 380
Scyliorhinus canicula Lesser-spotted dogfish 12.8 18 350 630
Sepia officinalis Common cuttlefish 0.1 2 50 60
Sepiola atlantica Atlantic bobtail squid 0.0 6
Solea solea Sole 2.0 7 220 340
Sprattus sprattus Sprat 629.3 152534 50 140
Todaropsis eblanae Lesser flying squid 0.0 1
Trachinus draco Greater weever fish 3.2 15 190 380
Trachurus trachurus Horse mackerel 0.4 8 100 250
Trisopterus esmarkii Norway pout 11.6 1012 90 180
Trisopterus minutus Poor-cod 0.5 14 110 190
Zeus faber John dory 0.3 2 190 200

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 29484.3 1973276
Herring 6387.1 471734 55 280
Whiting 5046.3 49000 30 380
Plaice 429.3 2952 100 490
Haddock 421.5 1693 70 460
Cod 40.3 51 210 740

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

Horse mackerel

Whiting

Common dab

Grey gurnard

Plaice

Mackerel

Haddock

Lemon sole

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)
Amblyraja radiata Starry ray 0.1 1 210 210
Callionymus lyra Common dragonet 0.1 3 170 230
Cancer pagurus Edible crab 6.6 32 76 148
Chelidonichthys lucerna Tub gurnard 0.2 1 300 300
Clupea harengus Herring 129.8 1354 145 275
Eutrigla gurnardus Grey gurnard 15.9 148 140 360
Gadus morhua Cod 1.0 4 210 380
Hippoglossoides platessoides American plaice 6.8 147 110 240
Hyperoplus lanceolatus Greater sandeel 0.0 2 165 170
Limanda limanda Common dab 31.7 424 110 290
Loligo forbesii Northern squid 0.6 9 80 130
Loligo vulgaris European squid 0.3 3 130 170
Melanogrammus aeglefinus Haddock 5.5 43 70 370
Merlangius merlangus Whiting 18.5 169 50 370
Microstomus kitt Lemon sole 0.8 6 150 270
Pecten maximus Great scallop 0.2 3
Pleuronectes platessa Plaice 16.5 149 120 410
Pollachius virens Saithe 15.9 3 400 1090
Scomber scombrus Mackerel 19.0 121 210 360
Trachinus draco Greater weever fish 6.2 35 220 400
Trachurus trachurus Horse mackerel 0.7 4 240 270
Trisopterus esmarkii Norway pout 21.8 779 50 190

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.1 3
Agonus cataphractus Pogge 0.1 9 90 140
Alloteuthis subulata European common squid 0.2 62 20 90
Amblyraja radiata Starry ray 11.7 26 190 470
Ammodytes marinus Lesser sandeel 820.1 29721 125 255
Arnoglossus laterna Scaldfish 0.7 65 70 130
Buglossidium luteum Solenette 0.6 64 40 120
Callionymus lyra Common dragonet 2.8 83 110 240
Cancer pagurus Edible crab 39.1 55 109 209
Chelidonichthys lucerna Tub gurnard 4.7 12 210 440
Clupea harengus Herring 3869.0 158860 55 280
Echiichthys vipera Lesser weever 20.0 767 80 160
Enchelyopus cimbrius Four-bearded rockling 1.4 34 160 240
Eutrigla gurnardus Grey gurnard 1008.0 11972 120 360
Gadus morhua Cod 36.3 39 220 740
Galeorhinus galeus Tope 1.2 1 610 610
Glyptocephalus cynoglossus Witch 0.9 3 310 420
Gymnammodytes semisquamatus Smoothed sandeel 6.3 507 160 210
Hippoglossoides platessoides American plaice 56.7 1135 100 270
Hippoglossus hippoglossus Atlantic halibut 6.5 2 570 720
Homarus gammarus European lobster 1.0 1 120 120
Hyperoplus lanceolatus Greater sandeel 99.6 3253 185 295
Illex coindetii Southern shortfin squid 1.5 18 110 170
Limanda limanda Common dab 2111.5 35803 90 340
Lithodes maja Norway king crab 5.0 7 100 124
Loligo Loligo sp 1.7 115 10 130
Loligo forbesii Northern squid 2.4 263 20 170
Loligo vulgaris European squid 0.2 1 180 180
Lophius piscatorius Angler fish 6.6 4 210 640
Lumpenus lampretaeformis Snake blenny 0.0 1 280 280
Melanogrammus aeglefinus Haddock 416.1 1650 70 460
Merlangius merlangus Whiting 1670.1 17827 30 380
Merluccius merluccius Hake 14.7 7 360 830
Microchirus variegatus Thickback sole 0.1 1 160 160
Microstomus kitt Lemon sole 107.6 904 120 380
Mullus surmuletus Striped red mullet 0.5 5 140 230
Mustelus mustelus Smooth hound 2.6 1 900 900
Myoxocephalus scorpius Sculpin 0.5 8 130 200
Myxine glutinosa Hagfish 0.0 1
Nephrops norvegicus Norway lobster 14.2 506 22 53
Phrynorhombus norvegicus Norwegian topknot 0.0 1 80 80
Platichthys flesus Flounder 1.8 8 230 320
Pleuronectes platessa Plaice 366.0 2410 120 490
Pomatoschistus spp. Sand gobies 0.0 1 50 50
Raja clavata Thornback ray 52.1 15 580 910
Raja montagui Spotted Ray 16.9 20 310 580
Rossia macrosoma Stout bobtail squid 0.0 5
Scomber scombrus Mackerel 319.3 1972 160 370
Scophthalmus maximus Turbot 10.5 13 210 460
Scophthalmus rhombus Brill 3.0 4 330 400
Scyliorhinus canicula Lesser-spotted dogfish 120.1 161 420 690
Scyphozoa Scyphozoans 444.1 0
Solea solea Sole 0.6 4 190 300
Sprattus sprattus Sprat 2496.1 232138 50 145
Squalus acanthias Spurdog 52.9 11 740 1210
Todaropsis eblanae Lesser flying squid 0.1 1 100 100
Trachinus draco Greater weever fish 1.1 11 180 360
Trachurus trachurus Horse mackerel 5.6 96 40 270
Trisopterus esmarkii Norway pout 3.7 119 60 200
Trisopterus luscus Bib 0.2 2 190 200
Trisopterus minutus Poor-cod 0.1 1 210 210
Zeus faber John dory 0.2 1 210 210

Area - 4C

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Agonus cataphractus Pogge 0.3 20 80 150
Alloteuthis subulata European common squid 3.4 494 30 140
Ammodytes marinus Lesser sandeel 0.4 30 50 195
Arnoglossus laterna Scaldfish 0.1 5 110 190
Buglossidium luteum Solenette 0.7 96 50 110
Callionymus lyra Common dragonet 1.7 58 30 220
Cancer pagurus Edible crab 32.1 122 50 181
Chelidonichthys cuculus Red gurnard 1.0 6 230 300
Chelidonichthys lucerna Tub gurnard 1.3 7 210 300
Ciliata mustela Five-bearded rockling 0.1 1 230 230
Clupea harengus Herring 2388.3 311520 75 270
Dicentrarchus labrax Bass 1.4 1 510 510
Echiichthys vipera Lesser weever 33.4 1614 50 180
Enchelyopus cimbrius Four-bearded rockling 0.0 2 110 150
Engraulis encrasicolus Anchovy 0.1 2 160 180
Eutrigla gurnardus Grey gurnard 28.6 320 130 310
Gadus morhua Cod 3.1 8 300 410
Gaidropsarua macrohthalmus Big-eye rockling 0.1 1 240 240
Galeorhinus galeus Tope 234.3 18 950 1610
Homarus gammarus European lobster 18.0 47 47 126
Hyperoplus lanceolatus Greater sandeel 50.7 1609 145 360
Lampetra fluviatilis River lamprey 0.0 1 280 280
Limanda limanda Common dab 156.0 2196 30 290
Liparidae Sea-snail 0.0 3 40 60
Loligo Loligo sp 0.2 48 10 40
Loligo forbesii Northern squid 1.2 10 60 240
Merlangius merlangus Whiting 3357.7 31004 50 340
Microstomus kitt Lemon sole 15.6 316 50 260
Mullus surmuletus Striped red mullet 10.3 80 150 300
Mustelus asterias Starry smooth-hound 45.2 21 520 970
Mustelus mustelus Smooth hound 31.4 12 750 1090
Myoxocephalus scorpius Sculpin 0.9 25 40 150
Pholis gunnellus Butter fish 0.3 17 120 200
Phrynorhombus norvegicus Norwegian topknot 0.0 1 130 130
Platichthys flesus Flounder 1.9 7 220 340
Pleuronectes platessa Plaice 46.9 393 100 390
Pomatoschistus spp. Sand gobies 0.0 2 20 60
Raja brachyura Blonde ray 8.7 4 470 710
Raja clavata Thornback ray 5.5 5 360 720
Raja montagui Spotted Ray 4.4 5 350 540
Sardina pilchardus Pilchard 68.8 760 120 250
Scomber scombrus Mackerel 146.2 747 100 400
Scophthalmus maximus Turbot 1.5 3 280 320
Scyliorhinus canicula Lesser-spotted dogfish 139.7 270 300 650
Sepiola atlantica Atlantic bobtail squid 0.1 24
Solea solea Sole 2.7 27 160 290
Sprattus sprattus Sprat 5620.6 743543 55 145
Trachurus trachurus Horse mackerel 2407.0 372677 40 270
Trisopterus esmarkii Norway pout 0.1 22 60 90
Trisopterus luscus Bib 58.7 443 150 290
Trisopterus minutus Poor-cod 18.6 397 130 190
Zeus faber John dory 0.2 1 230 230