Scientific survey report

Danish International Bottom Trawl Survey

2020

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 10504.1 421308
Haddock 5733.8 105800 120 430
Whiting 1379.4 23484 80 380
Herring 604.0 18194 85 340
Plaice 226.7 2295 70 520
Cod 15.4 84 110 600

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

Haddock

Whiting

Herring

Norway pout

Common dab

Grey gurnard

Plaice

Lemon sole

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 1 130 130
Alloteuthis subulata European common squid 0.0 5 40 80
Ammodytes marinus Lesser sandeel 0.0 1 75 75
Arnoglossus laterna Scaldfish 0.0 1 160 160
Buglossidium luteum Solenette 0.0 5 70 100
Callionymus reticulatus Reticulated dragonet 0.0 4 50 80
Cancer pagurus Edible crab 9.8 36 87 183
Clupea harengus Herring 6.5 323 85 225
Engraulis encrasicolus Anchovy 0.0 1 110 110
Eutrigla gurnardus Grey gurnard 0.9 12 160 260
Gadus morhua Cod 1.9 2 180 580
Gasterosteus aculeatus Three-spined stickleback 0.0 3 60 60
Limanda limanda Common dab 6.9 168 80 260
Merlangius merlangus Whiting 9.8 272 100 320
Microstomus kitt Lemon sole 0.6 2 290 290
Myoxocephalus scorpius Sculpin 1.1 8 150 250
Pleuronectes platessa Plaice 136.1 1443 70 280
Pomatoschistus spp. Sand gobies 0.0 4 50 70
Solea solea Sole 0.5 1 350 350
Sprattus sprattus Sprat 1.6 212 60 140

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.3 9
Agonus cataphractus Pogge 0.1 3 140 150
Alloteuthis subulata European common squid 17.9 5267 20 120
Amblyraja radiata Starry ray 5.9 13 200 470
Ammodytes marinus Lesser sandeel 9.9 2502 70 175
Arnoglossus laterna Scaldfish 0.1 7 60 130
Buglossidium luteum Solenette 0.3 28 60 120
Callionymidae Dragonets 0.0 1 80 80
Callionymus lyra Common dragonet 0.5 13 50 220
Callionymus maculatus Spotted dragonet 0.1 13 40 150
Callionymus reticulatus Reticulated dragonet 0.0 2 90 90
Cancer pagurus Edible crab 16.1 34 100 185
Chelidonichthys cuculus Red gurnard 0.4 4 170 280
Clupea harengus Herring 597.5 17871 85 340
Cyclopterus lumpus Lumpfish 6.6 2 290 450
Eledone cirrhosa Horned octopus 0.5 3
Enchelyopus cimbrius Four-bearded rockling 0.2 4 110 250
Engraulis encrasicolus Anchovy 0.3 39 70 150
Eutrigla gurnardus Grey gurnard 392.6 4948 70 340
Gadus morhua Cod 13.5 82 110 600
Gaidropsarus vulgaris Three-bearded rockling 0.0 2 80 90
Gasterosteus aculeatus Three-spined stickleback 0.0 6 60 60
Glyptocephalus cynoglossus Witch 0.9 6 70 350
Gobiidae True gobies 0.0 1 50 50
Gymnammodytes semisquamatus Smoothed sandeel 0.0 2 155 170
Helicolenus dactylopterus Blue-mouth redfish 0.5 9 130 170
Hippoglossoides platessoides American plaice 32.2 787 70 270
Homarus gammarus European lobster 1.3 1 136 136
Hyperoplus lanceolatus Greater sandeel 0.3 11 200 240
Illex coindetii Southern shortfin squid 9.9 380 20 190
Leucoraja naevus Cuckoo ray 2.8 6 330 470
Limanda limanda Common dab 394.7 6372 50 300
Lithodes maja Norway king crab 9.3 22 20 123
Loligo forbesii Northern squid 19.2 89 110 330
Loligo vulgaris European squid 9.8 36 150 350
Lophius budegassa Black-bellied Angler fish 0.2 1 220 220
Lophius piscatorius Angler fish 5.6 8 280 380
Lumpenus lampretaeformis Snake blenny 0.0 1 300 300
Maurolicus muelleri Pearlside 0.0 1 50 50
Melanogrammus aeglefinus Haddock 5733.8 105800 120 430
Merlangius merlangus Whiting 1369.6 23212 80 380
Merluccius merluccius Hake 0.9 2 260 480
Microstomus kitt Lemon sole 13.3 127 150 290
Mullus surmuletus Striped red mullet 1.9 27 130 230
Mustelus asterias Starry smooth-hound 4.0 10 420 570
Mustelus mustelus Smooth hound 0.3 1 420 420
Myoxocephalus scorpius Sculpin 1.8 9 170 290
Nephrops norvegicus Norway lobster 12.4 384 21 55
Pleuronectes platessa Plaice 90.6 852 90 520
Pollachius virens Saithe 0.1 1 230 230
Pomatoschistus spp. Sand gobies 0.0 5 50 50
Raja brachyura Blonde ray 3.5 3 490 640
Raja clavata Thornback ray 3.7 2 620 640
Rossia macrosoma Stout bobtail squid 0.1 21
Sardina pilchardus Pilchard 0.0 3 110 120
Scomber scombrus Mackerel 7.2 102 170 350
Scophthalmus maximus Turbot 13.7 3 280 710
Scophthalmus rhombus Brill 0.6 1 340 340
Scyliorhinus canicula Lesser-spotted dogfish 5.2 9 380 680
Sepiola atlantica Atlantic bobtail squid 0.1 14
Solea solea Sole 1.0 6 210 320
Sprattus sprattus Sprat 1393.6 241373 55 140
Todaropsis eblanae Lesser flying squid 0.1 4 50 70
Trachinus draco Greater weever fish 3.6 14 270 400
Trachurus trachurus Horse mackerel 1.9 25 100 280
Trisopterus esmarkii Norway pout 115.4 8201 90 200
Trisopterus luscus Bib 0.1 1 180 180
Trisopterus minutus Poor-cod 0.1 3 120 160

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 32828.6 791518
Whiting 11895.8 177535 40 400
Haddock 3861.6 52716 80 420
Herring 1597.1 51484 65 320
Plaice 410.1 2974 110 550
Cod 275.2 800 110 900

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

Common dab

Haddock

Herring

Horse mackerel

Grey gurnard

Mackerel

Plaice

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)
Aequipecten opercularis Queen scallop 0.1 5
Anarhichas lupus Catfish 3.8 1 740 740
Callionymus lyra Common dragonet 0.3 6 170 240
Cancer pagurus Edible crab 1.4 7 84 147
Chelidonichthys lucerna Tub gurnard 0.3 2 230 270
Clupea harengus Herring 2.8 22 160 305
Echiichthys vipera Lesser weever 0.1 6 80 130
Eutrigla gurnardus Grey gurnard 42.9 416 140 350
Gadus morhua Cod 249.1 741 190 900
Gymnammodytes semisquamatus Smoothed sandeel 0.1 8 145 155
Hippoglossoides platessoides American plaice 26.5 640 100 250
Hyperoplus lanceolatus Greater sandeel 0.2 6 190 240
Illex coindetii Southern shortfin squid 1.2 15 80 170
Limanda limanda Common dab 80.9 837 90 320
Loliginidae 100.4 1813 20 260
Loligo forbesii Northern squid 5.8 30 80 230
Lophius piscatorius Angler fish 1.3 3 160 320
Melanogrammus aeglefinus Haddock 751.8 3178 100 350
Merlangius merlangus Whiting 438.6 5173 70 310
Merluccius merluccius Hake 71.7 50 170 1030
Microstomus kitt Lemon sole 49.9 292 160 310
Molva molva Ling 4.5 6 450 620
Myxine glutinosa Hagfish 0.0 1
Pleuronectes platessa Plaice 21.3 100 170 390
Pollachius virens Saithe 4.6 3 260 770
Raja montagui Spotted Ray 1.0 1 460 460
Scomber scombrus Mackerel 65.3 463 220 400
Scophthalmus maximus Turbot 1.0 2 250 310
Squalus acanthias Spurdog 0.4 1 460 460
Todaropsis eblanae Lesser flying squid 0.0 1 90 90
Trachinus draco Greater weever fish 42.6 219 160 400
Trachurus trachurus Horse mackerel 0.8 6 200 260
Trisopterus esmarkii Norway pout 0.8 175 40 170
Trisopterus minutus Poor-cod 0.0 1 180 180

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.2 0
Agonus cataphractus Pogge 0.1 5 90 150
Alloteuthis subulata European common squid 21.6 4990 20 120
Amblyraja radiata Starry ray 4.9 11 110 450
Ammodytes marinus Lesser sandeel 1.6 125 45 190
Arnoglossus laterna Scaldfish 0.8 66 70 140
Buglossidium luteum Solenette 1.1 119 60 140
Callionymus lyra Common dragonet 3.9 98 100 250
Callionymus reticulatus Reticulated dragonet 0.0 2 100 150
Cancer pagurus Edible crab 44.1 84 85 200
Chelidonichthys lucerna Tub gurnard 11.8 39 190 500
Clupea harengus Herring 1378.2 48437 65 320
Echiichthys vipera Lesser weever 3.3 120 70 160
Eledone cirrhosa Horned octopus 0.9 1
Enchelyopus cimbrius Four-bearded rockling 5.2 148 130 250
Eutrigla gurnardus Grey gurnard 864.7 14687 120 350
Gadus morhua Cod 20.9 49 110 650
Galeorhinus galeus Tope 39.4 6 380 1550
Glyptocephalus cynoglossus Witch 0.4 2 280 310
Gymnammodytes semisquamatus Smoothed sandeel 17.6 1108 150 205
Helicolenus dactylopterus Blue-mouth redfish 0.3 4 150 180
Hippoglossoides platessoides American plaice 74.9 1589 100 270
Homarus gammarus European lobster 5.0 8 72 116
Hyperoplus lanceolatus Greater sandeel 14.5 411 165 330
Illex coindetii Southern shortfin squid 3.5 45 90 240
Limanda limanda Common dab 2931.5 51148 50 320
Lithodes maja Norway king crab 0.5 2 75 95
Loliginidae 2.6 150 30 110
Loligo Loligo sp 1.5 537 20 50
Loligo forbesii Northern squid 20.6 380 30 300
Lophius piscatorius Angler fish 0.2 1 230 230
Lycodes gracilis Vahls eelpout 0.0 2 150 160
Melanogrammus aeglefinus Haddock 3107.5 49530 80 420
Merlangius merlangus Whiting 4313.9 77674 40 360
Merluccius merluccius Hake 46.5 32 280 970
Microstomus kitt Lemon sole 151.1 1422 120 330
Molva molva Ling 1.6 1 680 680
Mullus surmuletus Striped red mullet 2.8 28 150 290
Mustelus asterias Starry smooth-hound 4.4 2 740 900
Mustelus mustelus Smooth hound 2.3 1 870 870
Myoxocephalus scorpius Sculpin 0.4 8 120 160
Nephrops norvegicus Norway lobster 16.4 438 21 55
Pecten maximus Great scallop 0.1 1
Platichthys flesus Flounder 0.2 1 280 280
Pleuronectes platessa Plaice 323.2 2243 110 550
Raja clavata Thornback ray 25.5 10 390 860
Raja montagui Spotted Ray 6.3 11 360 490
Sardina pilchardus Pilchard 0.6 5 210 240
Scomber scombrus Mackerel 935.6 6824 80 400
Scophthalmus maximus Turbot 20.0 20 170 580
Scophthalmus rhombus Brill 10.3 13 210 460
Scyliorhinus canicula Lesser-spotted dogfish 61.5 90 160 640
Scyphozoa Scyphozoans 791.1 0
Solea solea Sole 1.6 10 180 340
Sprattus sprattus Sprat 3860.3 291361 30 145
Squalus acanthias Spurdog 17.1 5 780 1090
Todaropsis eblanae Lesser flying squid 0.4 3 140 170
Trachinus draco Greater weever fish 5.8 41 220 370
Trachurus trachurus Horse mackerel 41.1 436 20 390
Trisopterus esmarkii Norway pout 0.8 51 30 180
Trisopterus luscus Bib 0.2 2 140 220
Trisopterus minutus Poor-cod 0.9 21 150 190
Zeus faber John dory 0.2 1 240 240

Area - 4C

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Agonus cataphractus Pogge 0.0 2 110 130
Alloteuthis subulata European common squid 10.2 1654 20 140
Amblyraja radiata Starry ray 0.1 1 260 260
Ammodytes marinus Lesser sandeel 0.9 49 110 210
Arnoglossus laterna Scaldfish 0.0 2 130 130
Buglossidium luteum Solenette 0.2 18 80 110
Callionymus lyra Common dragonet 2.7 52 90 230
Cancer pagurus Edible crab 32.6 90 51 181
Chelidonichthys cuculus Red gurnard 1.5 13 190 260
Chelidonichthys lucerna Tub gurnard 8.4 22 210 510
Clupea harengus Herring 216.1 3025 75 275
Dicentrarchus labrax Bass 7.1 7 350 580
Echiichthys vipera Lesser weever 32.5 1751 50 170
Engraulis encrasicolus Anchovy 0.5 16 130 190
Entelurus aequoreus Snake pipefish 0.1 6 300 460
Eutrigla gurnardus Grey gurnard 32.4 356 120 330
Gadus morhua Cod 5.2 10 270 540
Galeorhinus galeus Tope 259.2 21 710 1570
Helicolenus dactylopterus Blue-mouth redfish 0.9 13 140 180
Homarus gammarus European lobster 17.5 35 45 146
Hyperoplus lanceolatus Greater sandeel 122.2 4061 135 310
Limanda limanda Common dab 380.9 5401 100 290
Loligo Loligo sp 0.0 21 20 40
Loligo forbesii Northern squid 5.9 157 40 240
Loligo vulgaris European squid 0.3 1 180 180
Lophius piscatorius Angler fish 2.2 2 310 460
Maja squinado Common spider crab 1.4 2 120 129
Melanogrammus aeglefinus Haddock 2.2 8 260 330
Merlangius merlangus Whiting 7143.3 94688 40 400
Microstomus kitt Lemon sole 21.9 189 110 250
Mullus surmuletus Striped red mullet 41.9 473 130 300
Mustelus asterias Starry smooth-hound 101.0 56 520 1050
Mustelus mustelus Smooth hound 60.3 29 590 1250
Myoxocephalus scorpius Sculpin 0.7 7 130 230
Platichthys flesus Flounder 4.6 16 240 360
Pleuronectes platessa Plaice 65.6 631 110 360
Pomatoschistus spp. Sand gobies 0.0 3 40 60
Raja brachyura Blonde ray 9.5 6 460 820
Raja clavata Thornback ray 23.7 21 220 830
Raja montagui Spotted Ray 0.4 2 200 360
Rossia macrosoma Stout bobtail squid 0.0 4
Sardina pilchardus Pilchard 50.5 546 140 250
Scomber scombrus Mackerel 536.7 4145 180 430
Scophthalmus maximus Turbot 3.0 5 210 360
Scophthalmus rhombus Brill 0.3 1 280 280
Scyliorhinus canicula Lesser-spotted dogfish 200.3 441 310 670
Sepia officinalis Common cuttlefish 1.2 5 90 140
Solea solea Sole 4.4 58 150 260
Spondyliosoma cantharus Black sea bream 0.2 1 240 240
Sprattus sprattus Sprat 865.8 81892 70 140
Taurulus bubalis Sea scorpion 0.4 6 140 200
Trachinus draco Greater weever fish 0.8 5 230 370
Trachurus trachurus Horse mackerel 1336.0 22063 40 280
Trisopterus luscus Bib 3.4 57 100 230
Trisopterus minutus Poor-cod 10.7 479 60 220
Zeus faber John dory 1.2 5 210 260