western australianfisheries

department of agriculture, fisheries, and forestry

fisheries department jurasdiction

• fish stock within jurasdiction management

• involves

  • restrictions of the type of fishing gear allowed

  • spatial boundaries of the fishery itself

  • sometimes spatial extent of 2 fisheries in the same jurasdiction overlap

    • e.g. Commonwealth Eastern Tuna and Billfish Fishery and Commonwealth Small Pelagic Fishery off eastern Australia

  • State and territory fisheries agencies typically manage fisheries out to 3 nautical miles

    • majority of economic activity occurs in this area due to higher biological productivity/location of high value species/geographic location of aquaculture production

  • australia government generally manages fisheries in waters from 3 nautical miles out to 200nautical miles out from the australian coast

australian zone

the area 3 nautical miles to 200 nautical miles from the australian coast that

managed by the australian government

fisheries

• an area where fish are caught

• defined by species of fish is caught and way they are caught

  • e.g. may be raised through aquaculture or caught wildly

commercial fisheries

industry of catching a particular fish species or other marine species for profit

fisheries management

• State departments manage most inshore coastal fisheries

• Commonwealth Government manages offshore fisheries

• Regional management agencies can help manage species that migrate between international borders

  • e.g. tuna

fisheries science

• Fisheries scientists estimate no. of fish that can be sustainably taken for each target species

• Needs detailed biological information to determine sustainable yields

  • Population distribution and size

  • Rates of growth

  • Reproduction

  • Recruitment rates (rate young join the population)

  • Mortality rates

determining the age of fish

• bands on fish scales or ear bones = otoliths

• Age of fish can be estimated using this

population size

• can be estimated with tagging and estimating proportions that are captured

population dynamics

• the ways a given population grows and shrinks over time

• Controlled by birth, death and migration

assessing population dynamics

• fisheries study a population known as a ‘fish stock’ and conduct a stock assessment

• Include fishery catches which affect stock over time

fish life history

• Births increase the ‘stock’

• Many species change sexes during their lifetime

  • Protecting small fish protect future breeding female populations

• Older females produce more eggs

  • Used when deciding maximum size limits

• Some species become sexually mature when they reach a certain size

  • Used to estimate minimum legal size limits

mortality

• Reduces the ‘stock’

• includes natural mortality (predators, starvation, diseases) and fishing mortality

• Needed with birth rates when determining sustainable yields

maximum sustainable yield

• highest average catch that can be continuously taken from a population (stock) in average environmental conditions

• Used to manage commercial fisheries

• ¡Important to keeping the level of fishing (mortality) just below the level which causes a decline in a population

  • ¡Catches can’t be higher than recruitment

maximum economic yield

• ¡Used to manage commercial fisheries

• ¡Limits set at a level to maximise fisheries profits

• ¡Often set at catch levels below MSY

monitoring catch

• stock assessment = ¡Continuously monitoring numbers help determine if populations are biologically sustainable

• ¡Can look at trends over long periods of time

• ¡Used to help set the total allowable catches for the following year

• ¡Measurements and age estimates also monitored

issues

• Without accurate information on how many fish there are in the ocean for the fisheries, it can be difficult to estimate how many fish can be caught in a commercial fishery

• Resulting in a significant increase in Aquaculture

counting fish

• Commercial fisheries catches have been documented since 1950 by the Food and Agricultural Organisation (FAO)

  • Does not count for recreational catches

• ¡Some countries do not have the management and restrictions to prevent overfishing

• ¡Fish move around

• ¡Many places unexplored in the ocean

• ¡Survey techniques outdated which makes reference points invalid

stocks

• Fishery stocks within biologically sustainable levels decreased to 64.6% in 2019

• 1.2% lower than in 2017

• It was 90% in 1974

tagging fish

• used to find information

  • growth

  • life span

  • movement

mark-release-recapture

• process of tagging a fish, releasing it and recollecting (recatching)

• when captured (or not) data collected can provide population estimates, fish growth over the elapsed time period and mortality rate estimate

anchor tag

• small piece of nylon tubing ‘anchored’ to the back of a fish with a T-like end

• can be seen on fish

Passive Integrated Transponder (PIT) tags

• transmit a unique ID number and must be read by a separate magnetic reader