fish. characteristics of fish skeleton made of bone air (swim) bladder for buoyancy mucus to reduce...

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…