Fish Stock Assessment

Definition of Maximum Sustainable Yield (MSY): Fish populations are renewable resources that must be maintained at levels needed to produce sustainable a catch.

Fishery Managers are responsible for establishing the targets or reference quantities for how much of a specific fish species can be caught while maintaining fishes natural environment and a population that will produce a Maximum Sustainable Yield indefinitely.  

Chronic Fishing - Catching and killing too many fish over time results in:

• Reduced standing fish population and that species’ natural ability to replenish itself
• Reduction in capacity and potential to produce MSY over time
• Extreme situations will lead to “overfished” status and sometimes depletion of a species

Populations can only rebuild themselves to sustainable levels if Overfishing is first eliminated.

There is always the other side of the coin too, if a fleet of fishing boats does not catch the Maximum Sustainable Yield, then so much harvesting potential goes under-consumed and natural selection will occur.    

The main-focus for a sustainable fishery management is its most comprehensive understanding and estimated calculations regarding the accurate amount of a fish population (fish stock) over time.  That is why we need Fishery managers to regulate how much of any specific species is harvested to keep balance.  There are always natural fluctuations of sustainable fish stocks over time, so it’s not always a perfect science.  That is why if anything, fishery manger’s will play it a little on the “safe” side in their estimates. 

Fluctuations in Fish Populations:

• Any impacts on a species growth, natural selection/ mortality, movement, reproductive rate and environmental changes can cause a population fluctuation. Fishing (Sport or Commercial) can cause excessive mortality and therefore have an possible adverse effect on a species population.

Dynamics of a Fish Population

This is the study of how fish populations vary in size and age structure, as well overall capacity and abundance under the influence of any number of biological and environmental factors, including the impact of fishing mortality.

Fish Population Models

Comprehensive computer models and data algorithms that apply all the gathered information about a fishery to form the basis for the educated estimates of a fishery’s fish population status and the overall effects, if any from fishing (mortality).

Fish Population Models are designed to allow fishery managers (and scientists) to determine:

• Harvesting Sustainability of a Fishery (not subject to chronic overfishing)
• Whether, or not the current fish stock is sufficient enough to produce a Maximum Sustainable Yield over time, which means it is not being overfished.   

• The “Stock Assessment” determines the current-status of the fish stock (population) in relationship to management targets and models. Any changes or fluctuations, one year over the next, or over time are monitored and researched.
• Stock Assessments will ultimately prevent overfishing as they directly influence how much a specific fish or species can be caught, while still maintaining a sustainable target population and fish stock size. Stock assessments allow fishery managers to Adjust (up or down) the fishing mortality limits in order to adapt to changing stock status and any fluctuations in environmental conditions.
• Stock Assessments can stop a species depletion event from happening. These assessments ultimately are the deciding factor in determining fish stock depletion (it is being overfished) status, and what can be done/ must be done in order to rebuild the species population to a sustainable stock level.  
• Stock Assessment also can help monitor the positive sustainable impacts to a species population from any implemented regulatory measures. 

Fish Population Model Inputs?

The only way to detect population trending is for these Fish Population models to require a tremendous amount of uniquely defined fishery data, and analyze it over a set period-of-time.

 Sources of Information?

It is known fact that Professional fisherman (those who pay the bills by fishing) are experts in finding and catching fish.  That is why it is paramount that the industry monitors their total catch, the species variations in catch, size frequency and how much overall effort was committed to harvesting their catch, is all vital information and very important data needed to estimate any population trends over time. 

• Fishery-Dependent Data is generated by monitoring commercial fisherman and reporting/ analyzing against those results.
• Fishery-Independent Data is collected and analyzed by Independent fishery scientists.

Fishery Management has two primary determinations and drivers:

Is the Fishery in an overfished condition?

The question:  What are the Current Estimates of the fish population status

Is overfishing occurring?

The question:  Is the fish catch of the local fleet exceeding the established target level that math and science says will maintain the fish population?

Inputs

Abundance      Resource Survey, age/ size data $ Fishery CPUE

Biology            Age, growth, maturity, reproduction

Catch              Age, size data, other logbook data and observation

Environment    Climate, Ecosystem and Species Habitat

Population Model

Population Increases

Population Decreases

Movement

Outputs

Stock Status

Management Evaluation & Fishery Strategy

Optimum Sustainable Yield – Informed by scientific socioeconomics

Fisheries managers:

• Must have very clear estimates of the current status fish stocks under his/her management,
• The Size of the population that is sustainable over time, is only known with established targets and reference points,
• Basically, fishery managers must have a scientific assessment and analysis representing how much fish can be caught without causing a substantial reduction in the fish population below that specific species or environmental communities population amount over time.

 Fish populations can be both “saved” and “sustained” overtime by:

• It is important that they industry is always seeking to improve its scientific understanding of the fisheries complete ecosystem and any of the environmental factors that have already, are currently or possibly will in the future impact a fish population.
• Using the new scientific information and adapting the fisheries practices around it.
• Keep the fishery operating within sustainable limits over the long term, while implementing new monitoring and information gathering techniques.
• To be a science based adaptive and precautionary practice, sustainable fisheries management must be continuous and able to adapt to new measures, methods and techniques.