Scientific survey report

Danish International Bottom Trawl Survey

2017

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 8558.3 353723
Whiting 2603.6 39232 60 450
Herring 1326.9 90015 70 290
Plaice 348.9 1769 100 500
Cod 171.9 119 70 1120
Haddock 94.3 535 140 460

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

Mackerel

Grey gurnard

Norway pout

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 2 40 50
Ammodytes marinus Lesser sandeel 0.0 13 70 90
Clupea harengus Herring 1.2 113 95 225
Echiichthys vipera Lesser weever 0.1 1 160 160
Gadus morhua Cod 21.5 8 120 860
Hippoglossoides platessoides American plaice 0.0 1 130 130
Limanda limanda Common dab 1.7 15 130 280
Merlangius merlangus Whiting 1.7 66 90 290
Microstomus kitt Lemon sole 0.2 1 270 270
Pleuronectes platessa Plaice 10.8 50 180 340
Pomatoschistus spp. Sand gobies 0.0 1 40 40
Scophthalmus rhombus Brill 2.9 2 380 480
Solea solea Sole 0.6 1 380 380
Sprattus sprattus Sprat 2.8 307 75 140

Area - 4A

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.0 1
Alloteuthis subulata European common squid 0.0 8 30 70
Anarhichas lupus Catfish 0.9 1 460 460
Argentina sphyraena Lesser silver smelt 4.2 74 60 270
Callionymus lyra Common dragonet 0.0 6 70 110
Callionymus maculatus Spotted dragonet 0.1 6 90 120
Capros aper Boarfish 0.0 4 80 90
Clupea harengus Herring 0.7 7 205 290
Eledone cirrhosa Horned octopus 0.6 7
Eutrigla gurnardus Grey gurnard 0.1 1 260 260
Gadiculus argenteus Silvery pout 0.0 13 60 90
Gadus morhua Cod 33.3 13 330 950
Glyptocephalus cynoglossus Witch 2.5 8 260 440
Hippoglossoides platessoides American plaice 1.5 65 50 220
Illex coindetii Southern shortfin squid 0.4 9 90 150
Limanda limanda Common dab 0.5 2 240 320
Lithodes maja Norway king crab 0.4 1 95 95
Loligo forbesii Northern squid 0.4 2 100 110
Loligo vulgaris European squid 1.5 30 70 180
Lophius piscatorius Angler fish 12.5 5 190 680
Lycodes gracilis Vahls eelpout 0.1 7 100 160
Melanogrammus aeglefinus Haddock 1.3 4 230 380
Merlangius merlangus Whiting 135.1 393 250 450
Merluccius merluccius Hake 14.1 91 210 390
Micromesistius poutassou Blue whiting 25.3 263 180 330
Microstomus kitt Lemon sole 0.2 1 290 290
Molva molva Ling 7.7 4 620 770
Myxine glutinosa Hagfish 0.2 9
Nephrops norvegicus Norway lobster 0.8 5 52 67
Pollachius virens Saithe 65.5 54 390 1080
Rossia macrosoma Stout bobtail squid 0.3 12
Scomber scombrus Mackerel 0.4 2 180 360
Sebastes viviparus Redfish 0.0 1 60 60
Todaropsis eblanae Lesser flying squid 0.2 2 100 100
Trachurus trachurus Horse mackerel 0.3 2 130 350
Trisopterus esmarkii Norway pout 51.4 4886 80 180
Trisopterus minutus Poor-cod 3.4 55 140 220

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 0.3 20 40 150
Alloteuthis subulata European common squid 0.5 114 30 110
Alosa fallax Twaite shad 0.8 1 420 420
Amblyraja radiata Starry ray 12.6 20 90 520
Ammodytes marinus Lesser sandeel 2.9 974 50 200
Argentina sphyraena Lesser silver smelt 0.0 1 170 170
Arnoglossus laterna Scaldfish 0.5 54 40 130
Buglossidium luteum Solenette 0.4 40 60 120
Callionymus lyra Common dragonet 1.1 27 80 230
Callionymus maculatus Spotted dragonet 0.1 6 60 160
Cancer pagurus Edible crab 5.9 8 122 251
Caridea Shrimps 1.9 0
Chelidonichthys cuculus Red gurnard 0.5 2 260 330
Chelidonichthys lucerna Tub gurnard 1.0 2 350 370
Clupea harengus Herring 1325.0 89895 70 275
Cyclopterus lumpus Lumpfish 12.1 7 260 400
Echiichthys vipera Lesser weever 1.0 42 80 160
Eledone cirrhosa Horned octopus 0.3 2
Enchelyopus cimbrius Four-bearded rockling 1.2 41 100 280
Engraulis encrasicolus Anchovy 2.0 140 100 150
Eutrigla gurnardus Grey gurnard 894.2 10193 60 370
Gadus morhua Cod 117.1 98 70 1120
Gasterosteus aculeatus Three-spined stickleback 0.1 24 40 70
Gobiidae True gobies 0.0 5 40 50
Hippoglossoides platessoides American plaice 44.3 1144 60 290
Hyperoplus lanceolatus Greater sandeel 0.2 7 190 280
Leucoraja naevus Cuckoo ray 0.9 2 400 420
Limanda limanda Common dab 1334.3 23455 60 330
Lithodes maja Norway king crab 6.0 10 71 122
Loliginidae 45.8 13279 20 130
Loligo forbesii Northern squid 4.5 22 80 270
Loligo vulgaris European squid 10.0 35 140 300
Lophius piscatorius Angler fish 5.0 4 180 650
Lumpenus lampretaeformis Snake blenny 0.0 2 280 300
Maurolicus muelleri Pearlside 0.0 7 30 60
Melanogrammus aeglefinus Haddock 93.0 531 140 460
Merlangius merlangus Whiting 2466.8 38773 60 390
Microchirus variegatus Thickback sole 0.0 1 110 110
Microstomus kitt Lemon sole 54.5 423 140 370
Mullus surmuletus Striped red mullet 2.1 68 100 250
Mustelus asterias Starry smooth-hound 1.2 3 310 570
Myoxocephalus scorpius Sculpin 1.6 10 150 270
Myxine glutinosa Hagfish 0.0 1
Nephrops norvegicus Norway lobster 10.1 226 22 58
Platichthys flesus Flounder 9.1 39 210 350
Pleuronectes platessa Plaice 338.1 1719 100 500
Pomatoschistus spp. Sand gobies 0.0 6 40 70
Raja brachyura Blonde ray 0.7 1 470 470
Raja clavata Thornback ray 4.7 2 670 700
Raja montagui Spotted Ray 1.8 5 290 420
Rossia macrosoma Stout bobtail squid 0.0 12
Sardina pilchardus Pilchard 0.2 7 90 210
Scomber scombrus Mackerel 416.7 10626 150 210
Scophthalmus maximus Turbot 5.1 5 290 450
Scophthalmus rhombus Brill 1.7 3 290 400
Scyliorhinus canicula Lesser-spotted dogfish 4.0 11 140 600
Sepiola atlantica Atlantic bobtail squid 0.0 1
Sepiolidae Bobtail squids 0.1 49
Solea solea Sole 1.6 8 160 330
Sprattus sprattus Sprat 847.8 151991 55 150
Squalus acanthias Spurdog 8.4 3 410 1040
Syngnathidae Pipefishes and seahorses 0.0 2 120 130
Trachinus draco Greater weever fish 4.6 19 240 420
Trachurus trachurus Horse mackerel 2.1 39 90 320
Trisopterus esmarkii Norway pout 39.5 2809 80 190
Trisopterus luscus Bib 0.3 3 190 210
Trisopterus minutus Poor-cod 0.3 5 130 200
Zeus faber John dory 0.0 1 50 50

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 24543.6 764714
Whiting 9160.4 114804 30 440
Herring 1803.2 69584 70 290
Haddock 1177.0 3648 70 500
Plaice 569.3 3213 120 550
Cod 65.6 233 170 600

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

Whiting

Herring

Common dab

Horse mackerel

Grey gurnard

Mackerel

Haddock

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)
Ammodytes marinus Lesser sandeel 0.0 1 130 130
Callionymus lyra Common dragonet 0.3 10 60 180
Clupea harengus Herring 0.0 1 155 155
Echiichthys vipera Lesser weever 0.3 9 90 170
Eutrigla gurnardus Grey gurnard 46.1 431 160 330
Gadus morhua Cod 0.8 4 250 310
Hyperoplus lanceolatus Greater sandeel 1.6 40 180 320
Illex coindetii Southern shortfin squid 0.1 2 130 130
Limanda limanda Common dab 82.2 772 90 320
Loligo forbesii Northern squid 31.3 345 20 360
Lophius piscatorius Angler fish 0.2 1 220 220
Merlangius merlangus Whiting 0.4 7 40 260
Merluccius merluccius Hake 32.5 20 380 840
Microstomus kitt Lemon sole 0.7 3 130 320
Pleuronectes platessa Plaice 53.6 218 170 440
Scomber scombrus Mackerel 31.0 202 210 360
Scophthalmus rhombus Brill 0.9 1 400 400
Solea solea Sole 1.9 6 270 360
Trachinus draco Greater weever fish 17.3 100 200 410
Trachurus trachurus Horse mackerel 0.5 1 370 370

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.3 8
Agonus cataphractus Pogge 0.1 7 90 150
Alloteuthis subulata European common squid 8.8 2042 20 160
Alosa fallax Twaite shad 0.6 1 410 410
Amblyraja radiata Starry ray 14.4 24 80 490
Ammodytes marinus Lesser sandeel 175.2 17597 100 180
Anarhichas lupus Catfish 13.4 4 640 790
Arnoglossus laterna Scaldfish 1.8 191 60 150
Buglossidium luteum Solenette 4.1 444 50 130
Callionymus lyra Common dragonet 3.8 112 80 250
Cancer pagurus Edible crab 32.6 49 86 203
Chelidonichthys lucerna Tub gurnard 8.5 18 260 490
Clupea harengus Herring 1740.1 65104 70 290
Echiichthys vipera Lesser weever 5.2 210 80 150
Enchelyopus cimbrius Four-bearded rockling 7.2 259 110 230
Engraulis encrasicolus Anchovy 0.1 3 150 170
Eutrigla gurnardus Grey gurnard 748.2 7252 100 380
Gadus morhua Cod 22.0 112 170 600
Gaidropsarus vulgaris Three-bearded rockling 0.0 1 190 190
Glyptocephalus cynoglossus Witch 1.6 6 240 380
Gymnammodytes semisquamatus Smoothed sandeel 4.2 376 135 195
Hippoglossoides platessoides American plaice 84.0 2059 100 260
Homarus gammarus European lobster 4.6 3 117 152
Hyperoplus lanceolatus Greater sandeel 44.2 1187 160 310
Illex coindetii Southern shortfin squid 8.5 76 80 240
Lampetra fluviatilis River lamprey 0.0 1 290 290
Limanda limanda Common dab 2759.5 50215 90 330
Lithodes maja Norway king crab 1.8 5 65 110
Loligo forbesii Northern squid 26.8 1477 20 270
Loligo vulgaris European squid 1.9 5 180 280
Lophius piscatorius Angler fish 25.2 10 200 770
Melanogrammus aeglefinus Haddock 1177.0 3648 70 500
Merlangius merlangus Whiting 6029.3 76448 30 440
Merluccius merluccius Hake 15.5 9 340 840
Microstomus kitt Lemon sole 109.2 831 130 390
Mullus surmuletus Striped red mullet 2.7 25 140 280
Mustelus asterias Starry smooth-hound 4.5 2 800 860
Mustelus mustelus Smooth hound 4.2 2 770 880
Myoxocephalus scorpius Sculpin 0.8 12 100 230
Myxine glutinosa Hagfish 0.1 1 350 350
Nephrops norvegicus Norway lobster 20.8 717 18 61
Platichthys flesus Flounder 0.5 3 200 300
Pleuronectes platessa Plaice 428.3 2270 130 550
Pollachius virens Saithe 2.2 12 240 310
Raja brachyura Blonde ray 2.7 3 470 510
Raja clavata Thornback ray 4.4 3 320 720
Raja montagui Spotted Ray 2.4 4 390 490
Rossia macrosoma Stout bobtail squid 0.1 3
Scomber scombrus Mackerel 753.9 5548 190 390
Scophthalmus maximus Turbot 16.1 14 250 480
Scophthalmus rhombus Brill 3.5 4 340 480
Scyliorhinus canicula Lesser-spotted dogfish 53.5 75 260 670
Solea solea Sole 3.5 17 220 390
Sprattus sprattus Sprat 3652.6 377135 60 150
Squalus acanthias Spurdog 2.3 13 250 580
Todaropsis eblanae Lesser flying squid 1.4 8 100 170
Trachinus draco Greater weever fish 1.9 9 260 360
Trachurus trachurus Horse mackerel 3.8 23 20 350
Trisopterus esmarkii Norway pout 2.7 69 140 190
Trisopterus luscus Bib 0.1 1 190 190
Trisopterus minutus Poor-cod 0.1 4 140 170

Area - 4C

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.0 2
Agonus cataphractus Pogge 0.5 37 80 140
Alloteuthis subulata European common squid 2.8 394 30 110
Alosa fallax Twaite shad 1.6 3 380 450
Ammodytes marinus Lesser sandeel 29.3 3925 90 200
Arnoglossus laterna Scaldfish 0.4 25 90 150
Buglossidium luteum Solenette 1.6 202 50 110
Callionymus lyra Common dragonet 2.0 52 90 230
Cancer pagurus Edible crab 5.8 18 69 170
Chelidonichthys cuculus Red gurnard 0.8 6 170 290
Chelidonichthys lucerna Tub gurnard 8.6 23 210 560
Clupea harengus Herring 63.1 4480 90 250
Dicentrarchus labrax Bass 4.9 6 330 580
Echiichthys vipera Lesser weever 25.2 1397 50 170
Eledone cirrhosa Horned octopus 0.1 1
Engraulis encrasicolus Anchovy 0.0 1 170 170
Entelurus aequoreus Snake pipefish 0.0 1 440 440
Eutrigla gurnardus Grey gurnard 38.9 539 130 350
Gadus morhua Cod 42.8 117 220 390
Gaidropsarus vulgaris Three-bearded rockling 0.2 3 170 190
Galeorhinus galeus Tope 36.6 3 940 1520
Gymnammodytes semisquamatus Smoothed sandeel 0.5 56 140 180
Homarus gammarus European lobster 19.4 33 51 152
Hyperoplus lanceolatus Greater sandeel 203.5 10790 120 340
Illex coindetii Southern shortfin squid 0.1 1 130 130
Limanda limanda Common dab 388.9 5837 80 300
Loligo forbesii Northern squid 2.0 28 80 250
Loligo vulgaris European squid 0.4 2 150 200
Merlangius merlangus Whiting 3130.8 38349 40 340
Microstomus kitt Lemon sole 17.5 107 120 310
Mullus surmuletus Striped red mullet 12.8 121 140 280
Mustelus asterias Starry smooth-hound 196.1 123 440 1070
Mustelus mustelus Smooth hound 81.0 53 440 1090
Myoxocephalus scorpius Sculpin 1.6 26 110 200
Pholis gunnellus Butter fish 0.2 9 90 190
Platichthys flesus Flounder 1.1 5 220 300
Pleuronectes platessa Plaice 87.4 725 120 420
Raja brachyura Blonde ray 9.9 3 540 900
Raja clavata Thornback ray 51.0 21 250 920
Raja montagui Spotted Ray 11.1 14 340 560
Rossia macrosoma Stout bobtail squid 0.0 2
Sardina pilchardus Pilchard 89.6 1019 190 250
Scomber scombrus Mackerel 328.0 2425 200 390
Scophthalmus maximus Turbot 5.1 5 200 490
Scyliorhinus canicula Lesser-spotted dogfish 176.9 346 210 660
Sepiola atlantica Atlantic bobtail squid 0.0 1
Solea solea Sole 2.0 19 180 310
Sprattus sprattus Sprat 616.6 64266 65 135
Trachinus draco Greater weever fish 0.1 1 230 230
Trachurus trachurus Horse mackerel 466.8 10861 20 300
Trisopterus esmarkii Norway pout 0.1 5 70 160
Trisopterus luscus Bib 20.4 158 160 250
Trisopterus minutus Poor-cod 6.4 122 130 190
Zeus faber John dory 0.4 2 220 230