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Fisheries Monitoring and Assessment > Cod Biology and Fishery > Flashcards

Cod Biology and Fishery Flashcards

1
Q

What is the scientific name of Atlantic cod?

A

Gadus morhus

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2
Q

What family do cod belong to?

A

Gadidae

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3
Q

What class do cod belong to?

A

actinopterygii

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4
Q

Describe physical characteristics of Atlantic cod

A

-Protruding upper jaw
-Chin barbel
-Light and curved lateral line
-Three dorsal fins
-Two ventral fins lacking spines
-Truncated caudal fin

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5
Q

What other fish belong in the family Gadidae?

A

-Haddock
-Whiting
-Saithe

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6
Q

What are some distant relatives of cod?

A

Grenadiers, toadfishes and anglerfishes

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7
Q

How are cod historically important?

A

-Fished in Neolithic age
-Important food item for the Vikings
-10th Century fishers sailed to Iceland searching for cod

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8
Q

What is the distribution of cod?

A

-Found on both sides of Atlantic
-NW North Carolina, both coasts of Greenland, Iceland and Labrador Sea
-NE range from Bay of Biscay to areas around Iceland and the Barents sea

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9
Q

What are the preferences of Atlantic cod?

A

-Cold water species
-Variety of habitats from shoreline to continental shelf
-Adults prefer 2 to 8 degree, but can be found in temps of 20

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10
Q

How have young cod adapted to sub-zero environments?

A

Have special enzymes that act as anti-freeze

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11
Q

What type of fish are cod?

A

Demersal (1m to 600 m)

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12
Q

What depths are adult cod found at?

A

150 - 200 m

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13
Q

What depths are juveniles found at?

A

30 - 80m

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14
Q

How many distinct cod stocks are there?

A

24

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15
Q

How many cod stocks are in the North Eastern Atlantic?

A

14

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16
Q

How many cod stocks are in the North West Atlantic?

A

10

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17
Q

Where is the largest stocks of cod?

A

The NE Atlantic Artic Cod stock

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18
Q

Where are the NE Artic cod stock found?

A

In the Barents Sea area

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19
Q

When and where does the NE Artic cod spawn?

A

March and April along the Norwegian coast

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20
Q

Do the stocks mix in the NE?

A

Yes, there is considerable mixing
-Some Icelandic cod migrate to Barents sea or Newfoundland

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21
Q

How does individual stocks affect cod biology?

A

-Dependent on local conditions of their habitat
-Mature fish of northern populations migrate south to spawning areas
-Young and juveniles are relatively non-migratory

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22
Q

What habitats do cod prefer?

A

-Can be found in all habitats
-With/without seaweed
-Muddy and sandy areas

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23
Q

What is the favorite habitat of cod?

A

Sea beds with coarse sediments

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24
Q

What are cod spawning grounds like?

A

-Spawning grounds range from Fjords and bays to areas of offshore waters

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25
Q

Are cod solitary?

A

No, they are shoaling species and move in large, size structured aggregations

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26
Q

What is the role of larger cod in a shoal?

A

Larger fish act as scouts and lead shoal’s direction, particularly during post spawning migrations inshore for feeding

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27
Q

Do cod feed during migrations?

A

Feed actively during the day

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28
Q

How fast can Atlantic cod swim?

A

Average speeds of 9 - 17 cm/sec and can cover a mean range of 99 to 226/ m2

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29
Q

What affects age of maturity in Atlantic cod?

A

Age at maturity varies with temperature

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30
Q

When are 50% of cod are mature in Irish waters?

A

2 years

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31
Q

What age do cod mature in the North sea and Baltic sea?

A

3 years

32
Q

What age do cod mature in Norwegian and Icelandic waters?

A

6 years

33
Q

What age do cod mature in Greenland?

A

8 years old

34
Q

What size are cod at maturity for most stocks?

A

2 -4 kg and 60- 75 cm

35
Q

What size are mature cod in Labrador, Newfoundland and Baltic?

A

1 - 1.5kg and 45-50 cm

36
Q

Where are the largest cod found?

A

In coldest regions

37
Q

How old can cod get?

A

20 - 25 years of age

38
Q

What is the maximum length of cod?

A

1.5 m

39
Q

What is the maximum weight of cod?

A

95 kg

40
Q

Are cod in Irish waters fast growing?

A

Yes, can be 35 cm in their 1st year

41
Q

What is the average size of cod at 4 years?

A

70 cm

42
Q

What is the average size of cod at 12 months?

A

14 -18 cm

43
Q

What is the average size of cod at 6 months?

A

8 cm

44
Q

What is the average size of cod at 2 years?

A

25 - 35 cm

45
Q

Where do cod spawn?

A

Over continentals shelf, inside the 200 m line over a wide range of temperatures

46
Q

What time of year do cod spawn in Fjords (Nordic Cod)?

A

January / March

47
Q

When does Northern Sea cod spawn?

A

April

48
Q

When does Baltic sea cod spawn?

A

All the way to October

49
Q

Will cod migrate to spawning grounds?

A

Yes, some travel 100 s of miles

50
Q

How many eggs can female cod lay?

A

Up to 2.5 million

51
Q

How many eggs can cod produce per kilo of body weight?

A

500,000 eggs per kg

52
Q

How many eggs was found in 34 kg female?

A

9 million

53
Q

How many eggs will a first time spawner lay?

A

500,000 eggs

54
Q

What is the average amount eggs laid?

A

2 -7 million

55
Q

Describe cod eggs

A

Transparent, 1.5 mm in diameter

56
Q

What could be a reason that Baltic cod produce larger eggs?

A

A possible adaptation to float in low salinity waters (10%)

57
Q

How do females release gametes?

A

In a ventral mount

58
Q

How long does it take for cod eggs to hatch?

A

12 days to 4mm fry

59
Q

Describe fertilised eggs

A

-Planktonic, drift with ocean currents
-Generally dispersed northward to nursery grounds

60
Q

How long does it take for fry to reach 2 cm?

A

After 10 days feeding on copepods

61
Q

What type of feeder are adult cod?

A

Omnivorous carnivores
-Active hunters and considered apex predators

62
Q

What has happened due to decreasing cod populations?

A

Their prey populations have experienced rapid growth

63
Q

What do adult cod eat?

A

-Sand eels
-Whiting
-Haddock
-Mackerel
-Herring
-Plaice
-Squid
-Polychaetes
-Crustacean decapods

64
Q

Are cod cannibalistic?

A

Yes

65
Q

What do young cod feed on?

A

Krill and other benthic crustacea

66
Q

What can cod’s diet have an effect on?

A

The colour of the skin
-Those that eat crustaceans will be more reddish

67
Q

What parasites affect cod?

A

-Copepods
-Digenetic and monogenetic flukes
-Acanthocephalans
-Cestodes
-Nematodes
-Myxozoans
-

67
Q

What parasites affect cod?

A

-Copepods
-Digenetic and monogenetic flukes
-Acanthocephalans
-Cestodes
-Nematodes
-Myxozoans
-Protozoans

68
Q

What are the predominant group of cod parasites in the NE Atlantic

A

-Trematodes ( 19 species)
-Nematodes ( 13 species)

69
Q

Describe the cod fishery

A

-Majority taken as bycatch in Celtic sea
-Difficult to control fishing mortality (f)
-Landed in mixed demersal fisheries

70
Q

What methods are used to catch cod?

A

Bottom otter trawls, seines and beam trawls

71
Q

What countries fish cod?

A

Ireland, UK, France and Belgium

72
Q

What are some measures to reduce overfishing cod?

A

-More sustainable quotas
-Closure of specific areas during spawning season
-Use of selective fishing equipment to reduce cod by-catch

73
Q

What fishery is cod a major by-catch of?

A

Nephrops trawls

74
Q

What has helped reduced cod by-catch in nephrops trawls?

A

SELTRA sorting box reduced cod by-catch by 81%

75
Q

How much has the Swedish Grid reduced cod by-catch during Nephrops trawls?

A

100% reduduction

Fisheries Monitoring and Assessment (10 decks)

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