Cod Biology and Fishery Flashcards
What is the scientific name of Atlantic cod?
Gadus morhus
What family do cod belong to?
Gadidae
What class do cod belong to?
actinopterygii
Describe physical characteristics of Atlantic cod
-Protruding upper jaw
-Chin barbel
-Light and curved lateral line
-Three dorsal fins
-Two ventral fins lacking spines
-Truncated caudal fin
What other fish belong in the family Gadidae?
-Haddock
-Whiting
-Saithe
What are some distant relatives of cod?
Grenadiers, toadfishes and anglerfishes
How are cod historically important?
-Fished in Neolithic age
-Important food item for the Vikings
-10th Century fishers sailed to Iceland searching for cod
What is the distribution of cod?
-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
What are the preferences of Atlantic cod?
-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
How have young cod adapted to sub-zero environments?
Have special enzymes that act as anti-freeze
What type of fish are cod?
Demersal (1m to 600 m)
What depths are adult cod found at?
150 - 200 m
What depths are juveniles found at?
30 - 80m
How many distinct cod stocks are there?
24
How many cod stocks are in the North Eastern Atlantic?
14
How many cod stocks are in the North West Atlantic?
10
Where is the largest stocks of cod?
The NE Atlantic Artic Cod stock
Where are the NE Artic cod stock found?
In the Barents Sea area
When and where does the NE Artic cod spawn?
March and April along the Norwegian coast
Do the stocks mix in the NE?
Yes, there is considerable mixing
-Some Icelandic cod migrate to Barents sea or Newfoundland
How does individual stocks affect cod biology?
-Dependent on local conditions of their habitat
-Mature fish of northern populations migrate south to spawning areas
-Young and juveniles are relatively non-migratory
What habitats do cod prefer?
-Can be found in all habitats
-With/without seaweed
-Muddy and sandy areas
What is the favorite habitat of cod?
Sea beds with coarse sediments
What are cod spawning grounds like?
-Spawning grounds range from Fjords and bays to areas of offshore waters
Are cod solitary?
No, they are shoaling species and move in large, size structured aggregations
What is the role of larger cod in a shoal?
Larger fish act as scouts and lead shoal’s direction, particularly during post spawning migrations inshore for feeding
Do cod feed during migrations?
Feed actively during the day
How fast can Atlantic cod swim?
Average speeds of 9 - 17 cm/sec and can cover a mean range of 99 to 226/ m2
What affects age of maturity in Atlantic cod?
Age at maturity varies with temperature
When are 50% of cod are mature in Irish waters?
2 years
What age do cod mature in the North sea and Baltic sea?
3 years
What age do cod mature in Norwegian and Icelandic waters?
6 years
What age do cod mature in Greenland?
8 years old
What size are cod at maturity for most stocks?
2 -4 kg and 60- 75 cm
What size are mature cod in Labrador, Newfoundland and Baltic?
1 - 1.5kg and 45-50 cm
Where are the largest cod found?
In coldest regions
How old can cod get?
20 - 25 years of age
What is the maximum length of cod?
1.5 m
What is the maximum weight of cod?
95 kg
Are cod in Irish waters fast growing?
Yes, can be 35 cm in their 1st year
What is the average size of cod at 4 years?
70 cm
What is the average size of cod at 12 months?
14 -18 cm
What is the average size of cod at 6 months?
8 cm
What is the average size of cod at 2 years?
25 - 35 cm
Where do cod spawn?
Over continentals shelf, inside the 200 m line over a wide range of temperatures
What time of year do cod spawn in Fjords (Nordic Cod)?
January / March
When does Northern Sea cod spawn?
April
When does Baltic sea cod spawn?
All the way to October
Will cod migrate to spawning grounds?
Yes, some travel 100 s of miles
How many eggs can female cod lay?
Up to 2.5 million
How many eggs can cod produce per kilo of body weight?
500,000 eggs per kg
How many eggs was found in 34 kg female?
9 million
How many eggs will a first time spawner lay?
500,000 eggs
What is the average amount eggs laid?
2 -7 million
Describe cod eggs
Transparent, 1.5 mm in diameter
What could be a reason that Baltic cod produce larger eggs?
A possible adaptation to float in low salinity waters (10%)
How do females release gametes?
In a ventral mount
How long does it take for cod eggs to hatch?
12 days to 4mm fry
Describe fertilised eggs
-Planktonic, drift with ocean currents
-Generally dispersed northward to nursery grounds
How long does it take for fry to reach 2 cm?
After 10 days feeding on copepods
What type of feeder are adult cod?
Omnivorous carnivores
-Active hunters and considered apex predators
What has happened due to decreasing cod populations?
Their prey populations have experienced rapid growth
What do adult cod eat?
-Sand eels
-Whiting
-Haddock
-Mackerel
-Herring
-Plaice
-Squid
-Polychaetes
-Crustacean decapods
Are cod cannibalistic?
Yes
What do young cod feed on?
Krill and other benthic crustacea
What can cod’s diet have an effect on?
The colour of the skin
-Those that eat crustaceans will be more reddish
What parasites affect cod?
-Copepods
-Digenetic and monogenetic flukes
-Acanthocephalans
-Cestodes
-Nematodes
-Myxozoans
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What parasites affect cod?
-Copepods
-Digenetic and monogenetic flukes
-Acanthocephalans
-Cestodes
-Nematodes
-Myxozoans
-Protozoans
What are the predominant group of cod parasites in the NE Atlantic
-Trematodes ( 19 species)
-Nematodes ( 13 species)
Describe the cod fishery
-Majority taken as bycatch in Celtic sea
-Difficult to control fishing mortality (f)
-Landed in mixed demersal fisheries
What methods are used to catch cod?
Bottom otter trawls, seines and beam trawls
What countries fish cod?
Ireland, UK, France and Belgium
What are some measures to reduce overfishing cod?
-More sustainable quotas
-Closure of specific areas during spawning season
-Use of selective fishing equipment to reduce cod by-catch
What fishery is cod a major by-catch of?
Nephrops trawls
What has helped reduced cod by-catch in nephrops trawls?
SELTRA sorting box reduced cod by-catch by 81%
How much has the Swedish Grid reduced cod by-catch during Nephrops trawls?
100% reduduction
