Scientific survey report

Danish International Bottom Trawl Survey

2015

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 14801.7 939800
Herring 6008.4 303866 75 325
Whiting 1577.1 22499 90 440
Plaice 699.8 4444 100 450
Haddock 388.2 6236 130 520
Cod 253.7 158 100 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

Norway pout

Common dab

Whiting

Grey gurnard

Haddock

Plaice

Lemon sole

Cod

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 4 50 80
Ammodytes marinus Lesser sandeel 0.0 2 80 130
Cancer pagurus Edible crab 2.5 5 109 187
Clupea harengus Herring 3.6 432 90 165
Engraulis encrasicolus Anchovy 0.0 5 90 120
Eutrigla gurnardus Grey gurnard 0.0 1 90 90
Hippoglossoides platessoides American plaice 0.2 6 140 190
Limanda limanda Common dab 8.1 109 70 330
Merlangius merlangus Whiting 0.0 1 130 130
Microstomus kitt Lemon sole 1.4 6 190 330
Pleuronectes platessa Plaice 29.3 140 180 380
Pomatoschistus spp. Sand gobies 0.0 3 40 50
Scophthalmus rhombus Brill 2.7 2 330 520
Solea solea Sole 0.2 1 270 270
Sprattus sprattus Sprat 2.5 652 60 115
Syngnathidae Pipefishes and seahorses 0.0 1 80 80

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 0.2 50 40 80
Argentina sphyraena Lesser silver smelt 0.2 4 150 250
Callionymus lyra Common dragonet 0.0 4 70 120
Callionymus maculatus Spotted dragonet 0.0 3 110 120
Clupea harengus Herring 0.2 1 305 305
Eledone cirrhosa Horned octopus 0.2 3 40 60
Gadus morhua Cod 26.1 27 100 810
Glyptocephalus cynoglossus Witch 0.3 1 350 350
Hippoglossoides platessoides American plaice 2.2 81 80 310
Illex coindetii Southern shortfin squid 0.1 1 120 120
Limanda limanda Common dab 1.3 15 60 320
Loligo forbesii Northern squid 0.0 2 70 70
Loligo vulgaris European squid 0.4 5 80 110
Lophius piscatorius Angler fish 0.1 1 200 200
Lumpenus lampretaeformis Snake blenny 0.0 3 130 160
Maurolicus muelleri Pearlside 0.0 7 50 70
Melanogrammus aeglefinus Haddock 2.3 10 150 420
Merlangius merlangus Whiting 48.9 142 220 440
Merluccius merluccius Hake 17.1 59 230 570
Micromesistius poutassou Blue whiting 0.0 1 170 170
Microstomus kitt Lemon sole 0.4 3 200 250
Nephrops norvegicus Norway lobster 5.8 120 27 58
Ommastrephidae 0.0 1 60 60
Pleuronectes platessa Plaice 3.2 14 240 350
Pollachius virens Saithe 31.5 41 400 620
Rossia macrosoma Stout bobtail squid 0.0 2 30 30
Trachurus trachurus Horse mackerel 0.1 2 180 240
Trisopterus esmarkii Norway pout 26.6 3700 80 200
Trisopterus minutus Poor-cod 0.3 5 160 180

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.6 5
Agonus cataphractus Pogge 0.7 35 60 160
Alloteuthis subulata European common squid 4.8 832 30 180
Alosa fallax Twaite shad 0.2 1 280 280
Amblyraja radiata Starry ray 17.8 45 90 490
Ammodytes marinus Lesser sandeel 5.0 1662 60 210
Argentina sphyraena Lesser silver smelt 0.1 1 210 210
Arnoglossus laterna Scaldfish 0.6 37 100 150
Buglossidium luteum Solenette 0.3 35 30 110
Callionymus lyra Common dragonet 0.7 28 60 240
Callionymus maculatus Spotted dragonet 0.0 6 60 140
Callionymus reticulatus Reticulated dragonet 0.0 2 150 150
Cancer pagurus Edible crab 13.1 16 128 207
Clupea harengus Herring 6004.6 303433 75 325
Cyclopterus lumpus Lumpfish 3.2 2 230 370
Echiichthys vipera Lesser weever 0.1 5 130 140
Enchelyopus cimbrius Four-bearded rockling 0.5 20 100 220
Engraulis encrasicolus Anchovy 33.2 2641 70 160
Eutrigla gurnardus Grey gurnard 674.6 8706 60 360
Gadus morhua Cod 227.7 131 120 1040
Gasterosteus aculeatus Three-spined stickleback 0.0 7 30 60
Glyptocephalus cynoglossus Witch 0.3 2 180 310
Hippoglossoides platessoides American plaice 60.4 1363 70 280
Homarus gammarus European lobster 0.5 1 83 83
Hyperoplus lanceolatus Greater sandeel 0.6 18 180 280
Limanda limanda Common dab 1713.2 30713 50 320
Lithodes maja Norway king crab 10.2 25 60 104
Loliginidae 2.2 623 30 80
Loligo forbesii Northern squid 3.5 19 130 300
Loligo vulgaris European squid 8.2 25 170 380
Lumpenus lampretaeformis Snake blenny 0.1 4 170 340
Lycodes gracilis Vahls eelpout 0.1 1 190 190
Maurolicus muelleri Pearlside 0.0 2 60 60
Melanogrammus aeglefinus Haddock 385.9 6226 130 520
Merlangius merlangus Whiting 1528.2 22356 90 420
Merluccius merluccius Hake 2.1 5 280 480
Microstomus kitt Lemon sole 36.1 299 130 360
Molva molva Ling 1.9 1 750 750
Mullus surmuletus Striped red mullet 16.1 461 110 210
Mustelus asterias Starry smooth-hound 0.8 2 400 510
Mustelus mustelus Smooth hound 1.1 3 460 530
Myoxocephalus scorpius Sculpin 2.9 23 120 250
Myxine glutinosa Hagfish 0.1 3 300 350
Nephrops norvegicus Norway lobster 3.6 71 28 53
Osmerus eperlanus European smelt 0.0 1 90 90
Pholis gunnellus Butter fish 0.0 1 170 170
Platichthys flesus Flounder 11.0 45 190 360
Pleuronectes platessa Plaice 667.3 4290 100 450
Pomatoschistus spp. Sand gobies 0.0 14 30 90
Raja clavata Thornback ray 5.0 2 530 820
Raja montagui Spotted Ray 5.5 4 490 600
Rossia macrosoma Stout bobtail squid 0.0 9
Sardina pilchardus Pilchard 0.9 52 110 260
Scomber scombrus Mackerel 2.1 27 180 320
Scophthalmus maximus Turbot 10.1 5 270 590
Scophthalmus rhombus Brill 4.1 5 310 460
Scyliorhinus canicula Lesser-spotted dogfish 3.6 6 250 660
Sepiola atlantica Atlantic bobtail squid 0.0 9
Solea solea Sole 3.0 13 210 450
Sprattus sprattus Sprat 2705.6 519066 45 145
Squalus acanthias Spurdog 1.7 2 540 580
Syngnathidae Pipefishes and seahorses 0.0 15 70 130
Trachinus draco Greater weever fish 6.5 28 280 390
Trachurus trachurus Horse mackerel 2.0 62 90 290
Trisopterus esmarkii Norway pout 388.0 30556 80 220
Trisopterus minutus Poor-cod 0.4 12 90 220
Zeus faber John dory 0.4 1 300 300

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 36057.5 1319691
Herring 10380.6 127946 55 350
Whiting 3393.7 62049 30 430
Plaice 856.2 4223 120 490
Haddock 705.8 4324 70 550
Cod 259.1 172 70 910

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

Horse mackerel

Norway pout

Grey gurnard

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)
Alloteuthis subulata European common squid 0.0 2 40 50
Ammodytes marinus Lesser sandeel 5.1 808 80 150
Buglossidium luteum Solenette 0.0 1 110 110
Callionymus lyra Common dragonet 0.2 6 120 190
Cancer pagurus Edible crab 1.4 5 113 142
Chelidonichthys lucerna Tub gurnard 0.4 2 250 300
Clupea harengus Herring 1.0 7 200 305
Echiichthys vipera Lesser weever 0.0 1 130 130
Enchelyopus cimbrius Four-bearded rockling 1.4 23 140 300
Eutrigla gurnardus Grey gurnard 85.7 885 140 330
Gadiculus argenteus Silvery pout 0.0 3 90 100
Gadus morhua Cod 187.8 104 240 910
Glyptocephalus cynoglossus Witch 3.9 10 300 420
Gymnammodytes semisquamatus Smoothed sandeel 1.2 97 130 200
Hippoglossoides platessoides American plaice 44.6 974 110 270
Hyperoplus lanceolatus Greater sandeel 54.7 2130 160 320
Limanda limanda Common dab 195.1 1876 110 320
Loligo forbesii Northern squid 16.3 93 40 220
Loligo vulgaris European squid 7.9 21 210 300
Lycodes gracilis Vahls eelpout 0.4 17 150 230
Melanogrammus aeglefinus Haddock 20.5 35 270 510
Merlangius merlangus Whiting 0.6 38 40 320
Merluccius merluccius Hake 20.8 24 350 790
Micromesistius poutassou Blue whiting 60.8 519 200 330
Microstomus kitt Lemon sole 11.0 40 200 370
Molva molva Ling 6.7 1 1100 1100
Myxine glutinosa Hagfish 0.1 2
Nephrops norvegicus Norway lobster 0.4 6 36 52
Pandalus borealis Northern pink shrimp 0.2 0
Pleuronectes platessa Plaice 319.0 1351 190 490
Pollachius virens Saithe 11.4 6 390 650
Scomber scombrus Mackerel 1228.8 9347 220 360
Scophthalmus maximus Turbot 0.7 1 330 330
Scophthalmus rhombus Brill 3.0 3 300 540
Solea solea Sole 1.5 5 270 350
Trachinus draco Greater weever fish 46.3 195 250 410
Trachurus trachurus Horse mackerel 3.6 12 240 380
Trisopterus esmarkii Norway pout 126.8 5912 130 190

Area - 4B

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.9 14 50 90
Agonus cataphractus Pogge 0.0 3 100 150
Alloteuthis subulata European common squid 3.2 441 20 110
Alosa fallax Twaite shad 0.3 1 340 340
Amblyraja radiata Starry ray 14.9 29 140 500
Ammodytes marinus Lesser sandeel 9.7 881 110 210
Argentina sphyraena Lesser silver smelt 0.1 2 160 190
Arnoglossus laterna Scaldfish 0.1 15 60 130
Buglossidium luteum Solenette 0.8 91 60 110
Callionymus lyra Common dragonet 2.9 88 100 250
Callionymus maculatus Spotted dragonet 0.0 5 70 140
Cancer pagurus Edible crab 30.7 51 100 205
Chelidonichthys lucerna Tub gurnard 4.6 10 270 450
Clupea harengus Herring 10262.2 123714 80 350
Echiichthys vipera Lesser weever 22.7 968 70 180
Enchelyopus cimbrius Four-bearded rockling 0.7 16 160 250
Engraulis encrasicolus Anchovy 2.4 83 140 170
Eutrigla gurnardus Grey gurnard 640.7 8355 110 360
Gadus morhua Cod 53.9 56 70 840
Glyptocephalus cynoglossus Witch 2.5 10 250 390
Gymnammodytes semisquamatus Smoothed sandeel 2.0 263 130 160
Hippoglossoides platessoides American plaice 58.8 1296 100 290
Hippoglossus hippoglossus Atlantic halibut 2.5 1 620 620
Homarus gammarus European lobster 0.8 1 107 107
Hyperoplus lanceolatus Greater sandeel 188.5 6205 150 320
Illex coindetii Southern shortfin squid 0.4 4 100 150
Limanda limanda Common dab 2018.1 33668 40 360
Lithodes maja Norway king crab 2.5 7 65 113
Loliginidae 0.1 30 20 70
Loligo forbesii Northern squid 12.6 297 30 190
Loligo vulgaris European squid 6.2 30 110 260
Lophius piscatorius Angler fish 8.9 6 140 590
Lumpenus lampretaeformis Snake blenny 0.3 7 280 380
Melanogrammus aeglefinus Haddock 685.3 4289 70 550
Merlangius merlangus Whiting 1620.0 46904 30 430
Merluccius merluccius Hake 10.1 7 130 760
Microstomus kitt Lemon sole 150.5 1352 120 370
Molva molva Ling 0.1 1 310 310
Mullus surmuletus Striped red mullet 1.3 19 140 270
Mustelus asterias Starry smooth-hound 1.6 1 810 810
Mustelus mustelus Smooth hound 3.0 1 850 850
Myoxocephalus scorpius Sculpin 0.9 6 190 240
Nephrops norvegicus Norway lobster 6.4 182 12 63
Pecten maximus Great scallop 0.1 1 80 80
Platichthys flesus Flounder 0.3 1 300 300
Pleuronectes platessa Plaice 473.8 2403 150 470
Raja clavata Thornback ray 1.1 2 370 480
Rossia macrosoma Stout bobtail squid 0.0 1
Sarda sarda Atlantic bonito 1.4 1 520 520
Sardina pilchardus Pilchard 13.3 341 160 180
Scomber scombrus Mackerel 1378.0 10545 210 420
Scophthalmus maximus Turbot 13.9 9 250 560
Scyliorhinus canicula Lesser-spotted dogfish 14.0 19 310 650
Scyphozoa Scyphozoans 135.9 0
Sepiola atlantica Atlantic bobtail squid 0.0 1 30 30
Solea solea Sole 1.0 5 230 310
Sprattus sprattus Sprat 4394.6 454095 55 150
Squalus acanthias Spurdog 14.7 13 270 1100
Todaropsis eblanae Lesser flying squid 0.2 2 140 150
Trachinus draco Greater weever fish 0.2 1 300 300
Trachurus trachurus Horse mackerel 5.6 72 20 360
Trisopterus esmarkii Norway pout 99.4 4532 30 190
Trisopterus luscus Bib 0.1 1 190 190
Trisopterus minutus Poor-cod 0.4 11 130 180

Area - 4C

Latin name English name Weight (kg) Number Min. Length (mm) Max. Length (mm)
Aequipecten opercularis Queen scallop 0.0 1
Agonus cataphractus Pogge 0.1 17 40 140
Alloteuthis subulata European common squid 3.6 829 20 110
Alosa alosa Allis shad 0.4 3 230 260
Alosa fallax Twaite shad 4.5 54 170 360
Ammodytes marinus Lesser sandeel 0.8 65 120 170
Arnoglossus laterna Scaldfish 0.1 4 110 150
Buglossidium luteum Solenette 0.4 45 70 110
Callionymus lyra Common dragonet 0.8 24 130 220
Cancer pagurus Edible crab 4.9 8 98 188
Chelidonichthys cuculus Red gurnard 0.6 4 210 280
Chelidonichthys lucerna Tub gurnard 16.0 46 190 490
Clupea harengus Herring 117.4 4226 55 265
Echiichthys vipera Lesser weever 18.3 792 60 170
Engraulis encrasicolus Anchovy 8.1 250 120 190
Eutrigla gurnardus Grey gurnard 26.5 363 80 340
Gadus morhua Cod 17.4 12 250 720
Galeorhinus galeus Tope 0.6 1 560 560
Homarus gammarus European lobster 2.7 1 166 166
Hyperoplus lanceolatus Greater sandeel 59.5 2089 140 290
Lampetra fluviatilis River lamprey 0.0 2 190 260
Limanda limanda Common dab 429.3 6731 50 300
Loliginidae 0.0 1 40 40
Loligo forbesii Northern squid 0.7 8 40 170
Loligo vulgaris European squid 1.5 5 110 240
Lophius piscatorius Angler fish 2.7 2 420 450
Merlangius merlangus Whiting 1773.1 15107 30 410
Microstomus kitt Lemon sole 7.7 50 160 300
Mullus surmuletus Striped red mullet 10.0 118 140 270
Mustelus asterias Starry smooth-hound 25.8 17 270 980
Mustelus mustelus Smooth hound 28.2 9 600 1170
Myoxocephalus scorpius Sculpin 1.7 16 130 250
Pegusa lascaris Sand sole 0.3 1 300 300
Pholis gunnellus Butter fish 0.0 2 180 190
Platichthys flesus Flounder 2.1 6 280 360
Pleuronectes platessa Plaice 63.3 469 120 450
Pomatoschistus spp. Sand gobies 0.4 348 30 60
Raja clavata Thornback ray 65.5 80 240 850
Raja montagui Spotted Ray 2.3 2 540 550
Rossia macrosoma Stout bobtail squid 0.0 2
Salmo salar Salmon 2.2 1 540 540
Sardina pilchardus Pilchard 35.0 500 130 240
Scomber scombrus Mackerel 691.1 4166 230 420
Scophthalmus maximus Turbot 1.6 4 210 340
Scophthalmus rhombus Brill 0.3 1 290 290
Scyliorhinus canicula Lesser-spotted dogfish 116.9 289 210 680
Sepia officinalis Common cuttlefish 0.4 2 100 120
Solea solea Sole 6.3 46 130 360
Sprattus sprattus Sprat 6419.0 534518 50 140
Trachurus trachurus Horse mackerel 1224.5 22134 30 390
Trisopterus luscus Bib 4.7 69 60 250
Trisopterus minutus Poor-cod 5.9 123 70 230
Zeus faber John dory 0.5 2 220 250