Scientific survey report

Danish International Bottom Trawl Survey

2016

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 10392.7 320645
Herring 4615.4 114850 75 280
Whiting 1768.0 29936 60 370
Plaice 504.2 2700 100 520
Cod 148.5 64 130 1020
Haddock 87.8 416 140 550

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

Whiting

Common dab

Grey gurnard

Norway pout

Plaice

Haddock

Lemon sole

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)
Alloteuthis subulata European common squid 0.1 37 20 80
Ammodytes marinus Lesser sandeel 0.0 6 90 160
Callionymus lyra Common dragonet 0.0 2 40 160
Callionymus maculatus Spotted dragonet 0.0 1 100 100
Cancer pagurus Edible crab 1.7 4 121 150
Clupea harengus Herring 22.5 1241 85 220
Engraulis encrasicolus Anchovy 0.0 6 70 110
Eutrigla gurnardus Grey gurnard 2.9 30 120 310
Gadus morhua Cod 36.0 15 150 930
Gasterosteus aculeatus Three-spined stickleback 0.0 1 50 50
Gobiidae True gobies 0.0 2 60 60
Hippoglossoides platessoides American plaice 1.9 54 30 230
Hyperoplus lanceolatus Greater sandeel 0.1 5 200 280
Limanda limanda Common dab 10.5 91 20 310
Maurolicus muelleri Pearlside 0.0 1 60 60
Melanogrammus aeglefinus Haddock 1.1 1 470 470
Merlangius merlangus Whiting 9.5 283 80 330
Microstomus kitt Lemon sole 1.8 9 180 330
Pleuronectes platessa Plaice 36.5 162 100 350
Scophthalmus maximus Turbot 0.7 1 340 340
Scophthalmus rhombus Brill 2.0 3 300 490
Scyliorhinus canicula Lesser-spotted dogfish 1.2 1 640 640
Solea solea Sole 2.5 10 200 320
Sprattus sprattus Sprat 19.6 2515 50 140
Syngnathidae Pipefishes and seahorses 0.0 1 70 70
Trachinus draco Greater weever fish 1.1 5 270 380

Area - 4A

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Alloteuthis subulata European common squid 0.9 233 30 80
Amblyraja radiata Starry ray 4.6 8 190 440
Callionymus maculatus Spotted dragonet 0.0 1 110 110
Clupea harengus Herring 1174.1 19780 175 265
Eledone cirrhosa Horned octopus 0.1 1 60 60
Engraulis encrasicolus Anchovy 0.1 4 170 180
Eutrigla gurnardus Grey gurnard 8.7 37 220 370
Gadus morhua Cod 26.2 6 290 920
Glyptocephalus cynoglossus Witch 0.9 3 330 360
Hippoglossoides platessoides American plaice 1.3 33 110 260
Limanda limanda Common dab 1.4 17 140 220
Lithodes maja Norway king crab 0.7 2 68 92
Loligo forbesii Northern squid 1.9 4 90 480
Melanogrammus aeglefinus Haddock 17.4 41 240 470
Merlangius merlangus Whiting 37.0 206 140 330
Microstomus kitt Lemon sole 0.8 2 290 360
Pleuronectes platessa Plaice 0.9 2 350 370
Pollachius virens Saithe 6.0 2 480 800
Scomber scombrus Mackerel 0.0 1 180 180
Sprattus sprattus Sprat 0.0 1 150 150
Todaropsis eblanae Lesser flying squid 0.2 3 90 100
Trisopterus esmarkii Norway pout 48.4 5622 80 210
Trisopterus luscus Bib 0.1 1 210 210

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.1 4 30 50
Agonus cataphractus Pogge 0.3 13 100 210
Alloteuthis subulata European common squid 8.2 2422 20 120
Alosa fallax Twaite shad 1.8 6 300 340
Amblyraja radiata Starry ray 26.6 57 120 500
Ammodytes marinus Lesser sandeel 0.0 10 70 130
Arnoglossus laterna Scaldfish 0.2 11 100 150
Buglossidium luteum Solenette 0.5 48 40 110
Callionymus lyra Common dragonet 1.0 33 90 210
Callionymus maculatus Spotted dragonet 0.1 7 110 150
Cancer pagurus Edible crab 13.4 20 139 192
Chelidonichthys lucerna Tub gurnard 0.2 1 290 290
Clupea harengus Herring 3418.8 93828 75 280
Echiichthys vipera Lesser weever 1.1 51 80 150
Enchelyopus cimbrius Four-bearded rockling 0.5 14 120 220
Engraulis encrasicolus Anchovy 1.9 371 60 170
Eutrigla gurnardus Grey gurnard 732.3 7904 70 360
Gadus morhua Cod 86.3 43 130 1020
Glyptocephalus cynoglossus Witch 2.4 15 200 360
Gobiidae True gobies 0.0 11 30 50
Hippoglossoides platessoides American plaice 37.3 1041 70 320
Homarus gammarus European lobster 1.7 1 146 146
Hyperoplus lanceolatus Greater sandeel 0.2 5 230 320
Illex coindetii Southern shortfin squid 0.5 3 50 280
Leucoraja naevus Cuckoo ray 0.7 1 500 500
Limanda limanda Common dab 1364.4 22081 60 350
Lithodes maja Norway king crab 6.0 13 50 116
Loliginidae 12.8 4123 10 70
Loligo forbesii Northern squid 4.5 20 130 320
Loligo vulgaris European squid 4.2 16 120 380
Lophius piscatorius Angler fish 1.2 2 190 400
Lumpenus lampretaeformis Snake blenny 0.0 1 340 340
Maurolicus muelleri Pearlside 0.0 3 40 40
Melanogrammus aeglefinus Haddock 69.3 374 140 550
Merlangius merlangus Whiting 1721.4 29447 60 370
Microchirus variegatus Thickback sole 0.0 1 120 120
Microstomus kitt Lemon sole 51.1 372 130 370
Mullus surmuletus Striped red mullet 1.5 18 170 210
Mustelus asterias Starry smooth-hound 4.3 10 390 620
Myoxocephalus scorpius Sculpin 1.9 11 190 260
Nephrops norvegicus Norway lobster 20.6 638 20 56
Platichthys flesus Flounder 6.6 21 220 390
Pleuronectes platessa Plaice 466.7 2536 100 520
Raja clavata Thornback ray 1.5 1 610 610
Raja montagui Spotted Ray 1.1 3 280 460
Rossia macrosoma Stout bobtail squid 0.0 5
Sardina pilchardus Pilchard 0.0 1 190 190
Scomber scombrus Mackerel 1.5 6 200 360
Scophthalmus maximus Turbot 9.0 12 210 420
Scophthalmus rhombus Brill 1.6 2 350 390
Scyliorhinus canicula Lesser-spotted dogfish 4.9 11 190 570
Sepiolidae Bobtail squids 0.3 157
Solea solea Sole 3.3 9 240 390
Sprattus sprattus Sprat 767.8 123729 45 145
Squalus acanthias Spurdog 18.9 14 380 1020
Syngnathidae Pipefishes and seahorses 0.0 2 110 120
Trachinus draco Greater weever fish 10.6 48 130 400
Trachurus trachurus Horse mackerel 2.9 73 90 360
Trisopterus esmarkii Norway pout 11.8 453 70 210
Trisopterus luscus Bib 0.2 2 190 200
Trisopterus minutus Poor-cod 0.6 10 100 210
Zeus faber John dory 0.3 1 280 280

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 21836.2 590867
Herring 10889.8 226721 60 320
Whiting 2939.6 41158 30 450
Haddock 457.0 4160 70 520
Plaice 444.3 2158 120 540
Cod 161.4 253 50 860

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.

Herring

Horse mackerel

Sprat

Whiting

Common dab

Grey gurnard

Mackerel

Norway pout

Haddock

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)
Amblyraja radiata Starry ray 1.1 1 490 490
Ammodytes marinus Lesser sandeel 0.2 89 70 170
Argentina sphyraena Lesser silver smelt 0.0 1 120 120
Callionymus lyra Common dragonet 0.1 2 150 160
Cancer pagurus Edible crab 7.4 19 89 185
Clupea harengus Herring 633.7 8786 95 320
Echiichthys vipera Lesser weever 0.1 2 140 170
Enchelyopus cimbrius Four-bearded rockling 0.1 1 240 240
Eutrigla gurnardus Grey gurnard 58.7 462 150 380
Gadus morhua Cod 131.8 198 50 840
Glyptocephalus cynoglossus Witch 3.4 10 310 400
Gymnammodytes semisquamatus Smoothed sandeel 0.5 34 150 200
Hippoglossoides platessoides American plaice 107.9 2139 120 260
Hyperoplus lanceolatus Greater sandeel 10.4 306 170 310
Illex coindetii Southern shortfin squid 0.1 1 130 130
Limanda limanda Common dab 59.9 419 120 340
Loligo forbesii Northern squid 0.6 22 40 200
Lophius piscatorius Angler fish 0.9 1 370 370
Melanogrammus aeglefinus Haddock 81.0 483 80 450
Merlangius merlangus Whiting 145.6 3014 50 440
Merluccius merluccius Hake 169.3 102 180 1120
Microstomus kitt Lemon sole 7.0 35 190 310
Myxine glutinosa Hagfish 0.0 1
Pleuronectes platessa Plaice 87.2 300 180 500
Pollachius virens Saithe 5.5 10 250 520
Scomber scombrus Mackerel 265.1 1095 260 430
Scophthalmus maximus Turbot 3.1 3 310 390
Scophthalmus rhombus Brill 3.5 2 350 600
Solea solea Sole 0.7 3 230 340
Todaropsis eblanae Lesser flying squid 0.7 6 100 160
Trachinus draco Greater weever fish 28.6 124 220 410
Trachurus trachurus Horse mackerel 347.5 1097 60 390
Trisopterus esmarkii Norway pout 31.0 4219 50 190

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.1 2
Agonus cataphractus Pogge 0.0 2 120 130
Alloteuthis subulata European common squid 0.5 86 30 100
Alosa fallax Twaite shad 0.5 1 400 400
Amblyraja radiata Starry ray 5.7 12 280 460
Ammodytes marinus Lesser sandeel 93.6 13726 70 180
Argentina sphyraena Lesser silver smelt 0.0 1 170 170
Arnoglossus laterna Scaldfish 0.1 5 110 130
Buglossidium luteum Solenette 0.3 28 70 110
Callionymus lyra Common dragonet 0.6 17 50 240
Callionymus maculatus Spotted dragonet 0.0 2 80 100
Cancer pagurus Edible crab 35.6 52 74 210
Chelidonichthys lucerna Tub gurnard 5.6 15 200 430
Clupea harengus Herring 9853.5 191799 60 320
Echiichthys vipera Lesser weever 1.9 71 100 150
Enchelyopus cimbrius Four-bearded rockling 0.9 28 150 220
Engraulis encrasicolus Anchovy 0.5 11 140 200
Eutrigla gurnardus Grey gurnard 566.1 5680 130 340
Gadus morhua Cod 28.4 52 80 860
Glyptocephalus cynoglossus Witch 1.2 6 250 350
Gymnammodytes semisquamatus Smoothed sandeel 6.3 458 110 220
Hippoglossoides platessoides American plaice 48.5 958 90 290
Homarus gammarus European lobster 2.0 2 72 137
Hyperoplus lanceolatus Greater sandeel 54.5 2059 160 290
Illex coindetii Southern shortfin squid 1.7 15 110 280
Leucoraja naevus Cuckoo ray 0.6 2 350 380
Limanda limanda Common dab 1219.8 19818 80 340
Lithodes maja Norway king crab 11.4 38 51 122
Loliginidae 14.6 2625 30 90
Loligo forbesii Northern squid 11.9 910 20 200
Lophius piscatorius Angler fish 11.7 6 320 590
Melanogrammus aeglefinus Haddock 376.0 3677 70 520
Merlangius merlangus Whiting 1856.9 29495 30 450
Merluccius merluccius Hake 29.9 15 390 1030
Microstomus kitt Lemon sole 72.0 554 140 370
Molva molva Ling 3.4 1 740 740
Mullus surmuletus Striped red mullet 0.7 6 200 230
Mustelus mustelus Smooth hound 2.0 1 800 800
Myoxocephalus scorpius Sculpin 0.5 4 140 230
Nephrops norvegicus Norway lobster 9.0 199 26 51
Pecten maximus Great scallop 0.1 2
Pholis gunnellus Butter fish 0.0 1 180 180
Pleuronectes platessa Plaice 301.0 1362 150 540
Pollachius virens Saithe 0.1 1 170 170
Raja brachyura Blonde ray 0.4 1 410 410
Raja montagui Spotted Ray 7.6 8 300 630
Rossia macrosoma Stout bobtail squid 0.0 7
Sardina pilchardus Pilchard 0.1 1 190 190
Scomber scombrus Mackerel 674.9 2744 80 420
Scophthalmus maximus Turbot 7.8 7 240 530
Scophthalmus rhombus Brill 0.4 1 310 310
Scyliorhinus canicula Lesser-spotted dogfish 31.7 39 430 700
Solea solea Sole 2.6 9 210 380
Sprattus sprattus Sprat 782.5 64527 50 145
Squalus acanthias Spurdog 20.4 14 280 1140
Todaropsis eblanae Lesser flying squid 0.5 4 80 140
Trachinus draco Greater weever fish 0.9 4 300 350
Trachurus trachurus Horse mackerel 17.0 347 30 370
Trisopterus esmarkii Norway pout 2.4 410 60 200

Area - 4C

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Agonus cataphractus Pogge 0.1 8 30 130
Alloteuthis subulata European common squid 4.2 608 20 130
Ammodytes marinus Lesser sandeel 6.2 505 120 170
Buglossidium luteum Solenette 0.1 9 80 110
Callionymus lyra Common dragonet 0.5 15 90 210
Cancer pagurus Edible crab 14.4 46 63 175
Chelidonichthys cuculus Red gurnard 0.4 3 230 240
Chelidonichthys lucerna Tub gurnard 9.3 33 200 450
Chelon labrosus Thick lipped mullet 3.9 3 450 640
Clupea harengus Herring 402.6 26137 70 270
Echiichthys vipera Lesser weever 23.5 1157 60 170
Engraulis encrasicolus Anchovy 3.7 101 130 190
Entelurus aequoreus Snake pipefish 0.0 1 390 390
Eutrigla gurnardus Grey gurnard 15.7 193 140 370
Gadus morhua Cod 1.2 3 330 340
Galeorhinus galeus Tope 50.7 4 1210 1630
Gymnammodytes semisquamatus Smoothed sandeel 0.0 1 170 170
Homarus gammarus European lobster 5.4 12 61 108
Hyperoplus lanceolatus Greater sandeel 196.7 9966 150 310
Limanda limanda Common dab 393.7 5493 40 320
Loliginidae 0.3 51 20 80
Loligo forbesii Northern squid 4.0 109 20 140
Merlangius merlangus Whiting 937.1 8650 50 410
Microstomus kitt Lemon sole 7.6 43 150 320
Mullus surmuletus Striped red mullet 6.4 66 140 250
Mustelus asterias Starry smooth-hound 13.5 23 260 870
Mustelus mustelus Smooth hound 36.8 19 320 1090
Myoxocephalus scorpius Sculpin 0.9 13 90 230
Pecten maximus Great scallop 0.4 1
Pholis gunnellus Butter fish 0.0 1 180 180
Phrynorhombus norvegicus Norwegian topknot 0.0 1 150 150
Pleuronectes platessa Plaice 56.1 496 120 440
Raja brachyura Blonde ray 4.1 5 240 580
Raja clavata Thornback ray 91.2 137 180 760
Raja montagui Spotted Ray 2.8 3 220 820
Rossia macrosoma Stout bobtail squid 0.0 14
Sardina pilchardus Pilchard 18.3 149 180 270
Scomber scombrus Mackerel 292.7 1362 190 400
Scophthalmus maximus Turbot 9.2 7 250 560
Scyliorhinus canicula Lesser-spotted dogfish 129.2 271 130 660
Solea solea Sole 5.3 51 150 300
Sprattus sprattus Sprat 97.0 10501 30 140
Trachurus trachurus Horse mackerel 618.2 159642 20 260
Trisopterus luscus Bib 0.1 2 190 200
Trisopterus minutus Poor-cod 1.1 39 80 180
Zeus faber John dory 0.2 1 220 220