fish. characteristics of fish skeleton made of bone air (swim) bladder for buoyancy mucus to reduce...
TRANSCRIPT
Fish
Characteristics of Fish
• Skeleton made of bone
• Air (swim) bladder for buoyancy
• Mucus to reduce friction, antibacterial agent
• Gill cover (operculum) to protect gills and pump water through them (oxygen)
• Small, thin scales for rapid swimming
• Flexible fins (not stiff as in sharks)
• Lateral line and other senses, but no ampullae
• Ectothermic (cold blooded)
Major Groups of North Atlantic Fish
• Demersal Fish: Benthic, groundfish (lives on/near the ocean floor)
–Cods: cod, haddock, pollock, cusk, hake
–Flatfish: flounder (sole), halibut, plaice, turbot
• Pelagic Fish: open water
– Herrings: herring, sardines, shad, smelt, menhaden, gaspereau, capelin
– Tuna
– Mackerel, Salmon, Eel
Deep Sea Fish
• Deep sea fish tend to live below 400 m
• They have anatomical adaptations to live at these depths such as: large mouths and teeth, modified appendages to serve as lures, and large stomachs
• Many are smaller than 6 inches
Grenadier: 450-800 m Gulper: 500-3000 m
Hatchet: 200-6000 m Swallower: 500-1500 m
Lantern: 200-1000 m Scaly dragon: 200-1500 m
Viper: 500-2500 m Tripod: 900-3500 m
Angler Fish
• There are several different species
• They usually live between 1500-5000m
• Some have a luminous barbel
• They use a lure to attract prey
• There is one species where the female is 12x the size of the male; he lives as a parasite on her body
Fisheries and Fishing Techniques
Fisheries Facts
• Unlike other natural resources such as oil and gas, fish are a renewable resource
• People in coastal regions have been using fish as a major food source for thousands of years
• In 1997, the global fishery took 100.8 million tons of fish, crustaceans and molluscs
• Fishing employs ~15 million people worldwide, but is the most dangerous job in the US (155 deaths:100 000 fishers)
• Of the thousands of species of marine organisms in the ocean, only about 500 species are regularly caught as part of a commercial fishery
• The largest commercial harvest is herring and relatives (sardines, anchovies) which comprise 20% of the worldwide catch each year
• The top five fish harvesters in order from greatest to least are: China, Japan, US, Peru, Russia
Commercial Fisheries
• Major types of commercial fisheries include:– Groundfish: cod, haddock, hake– Pelagic Fish: sardine, anchovy, herring,
mackerel, tuna– Crustaceans: crab, lobster, shrimp, krill– Molluscs: oyster, mussel, clam, squid, scallop
Technology Improves Catches
• 75% of fishers are cast commercial fleets who find fish using:– Satellite sensors– Aerial photography– Scouting vessels– Sonar– GPS
• Huge factory ships follow along to can and freeze the fish as soon as they are caught
Fishing Techniques: Trawling (dragging)
• The most common method of fishing
• A funnel shaped net is towed behind the fishing vessel
• Can be towed on the bottom to catch groundfish or at midwater to catch pelagic fish
• Bottom dragging is very destructive to the benthic ecosystems
Trawling
Purse Seine
• A net circles a school of fish, the bottom of the net is pulled tight and the fish are hauled aboard
Purse Seine
Scallop Dragger
• Scallops are caught by dredging – a metal frame with a net attached rakes the sandy bottom
• This method is also destructive to the benthic environment
Scallop Dragger
Gillnetting/Driftnetting
• A passive fishing method (40-50km long)
• A gillnet is a wall of netting set in a straight line equipped with weights at the bottom and floats at the top
• Fish swim through the net and are caught when their gills become entangled in the net
• If the nets are allowed to drift freely, the method is called driftnetting
• Must be checked daily
Gill Net
Long-lining
• Long lines of baited hooks 40-50 km long
• There are thousands of baited hooks placed in the open ocean, or along the bottom
Long-lining
Lobster Pots
• Lobsters are caught in baited traps with funned shaped openings allowing only one direction of travel – in
• They can be single traps, or in groups on a line
Lobster Trap
Weirs
• A passive fishing method
• A weir is an enclosure made of nets and poles permanently attached to the bottom
• Leader fences direct fish into the circular weir where they will swim in circles until they are removed by the fisher
• Herring and sardines are often caught in weirs
Weirs
Jigging
• Squid and cod are often caught by jigging – a line of hooks are continually jerked to lure the fish to bite
Fishery Problems: By-catch
• Animals that are unintentionally killed when desirable organisms are fished
• In many cases, by-catch exceeds the target catch
• Thousands of dolphins were caught in tuna nets until regulations changed the net design and ship maneuvers
• Every method of fishing has this problem
• About 20 million tons of unwanted fish may be discarded annually either because regulations prevent capture of these fish or because it is not economical to process them
Ghost Fishing
• Nets will keep fishing after they have been lost due to storms or negligence
• Fish and other organisms will rot in the nets because there is no-one to collect them
• Gill nets and long-lining cause the most problems
Habitat Destruction
• Destroying the ocean floor in the process of dragging nets
• The bottom becomes ‘naked’ and it takes a long time to recover – if it does
• Trawlers and scallop draggers cause the most damage
Declining Fish Populations
• Fish stocks worldwide have been declining; many have collapsed due to overfishing
• Other reasons for declining numbers are mismanagement, habitat destruction, interference with breeding, and increased ocean pollution
Fisheries Management
• Scientists study fish stocks to determine estimates of the population count and the reproductive biology of the species
• This information allows scientists to estimate the growth rate of the stock and determine the Maximum Sustainable Yield (MSY)
• Scientists can determine the minimum size of fish to be caught to ensure juveniles are not being harvested
• They can also determine times of the year when no fishing should be allowed to protect breeding seasons
• Scientists make recommendations to the fisheries managers
• Fisheries managers set the Total Allowable Catch (TAC) (total tonnage of fish that a fleet can catch)
• They also set quotas (total tonnage of fish that a fisher can catch)
Fisheries Mismanagement
• Poor science leads to poor estimates
• Managers disregard scientists recommendations
• Fishers do not obey quotas
• Other factors (not taken into consideration) may deplete the population: foreign fishers, weather, pollution etc…