An example of harvest rule control for recovery the jack mackerel population

Cristian Canales- IFOP- Chile

Main questions

1. What we want to do with jack mackerel (JM) population?

2. What is the status of JM population?

3. Why and how rebuild the JM population?

What we want to do with JM population?

• We suppose there’s an implicit desire, that is the conservation. What does conservation mean?

• The sustainable exploitation: all countries want to be at the bussiness for long time.

• Ideally, we want to get the maximum yield and maintain it over time (MSY). How the reach it?

“Believe or not believe in MSY”

• Why in fishery management is considered a biomass escapement level?.

• When we accept the existence of S-R relationship (no parents -> no recruits), we are accepting the existence of MSY implicitly.

What is the status of JM population?

• A general target of many fishery resources is to maintain the population and its fishery around MSY (Bmsy and Fmsy).

• In this sense, the pair (Bmsy; Fmsy) defines the Biological Reference Points - BRP (or any quantity close to these). When we cannot estimate the MSY variables properly, we can adopt a proxy (~40%Bo)

• We have talked about about this. See Canales C.(SWG-11-JM-01, 2012), Canales & Hintzen (SWG-11-JM-09, 2012)

MSY

What is the status of JM population?

SSB<SSBmsy

SSB>SSBmsy

F>Fmsy

(1) Stock is overfished

& Overfishing is occurring

(2) Stock is not overfished

but Overfishing is occurring

F<Fmsy

(3) Stock is overfished

but Overfishing is not

occurring

(4) Stock is not overfished

& Overfishing is not

occurring

(Cooper, 2006)

Estimating the MSY in JM

Recruitments

What is the status of JM population?

Two ways to recovery the population

1) Constant fishing mortality (F=Fmsy),Here Fmsy is applied independently of population status

2) Ramp strategy (F = Fmsy * SSB/SSBo),Here the Fmsy is reduced as a proportion of population depletion when the overfished have been declared

The target is reached after 8 years

It is necessary more than 10 yrs to reach the target

Ramp strategy: The cost are lower catches at the beginning , but in the future, landings will be larger.

If the recruitment doesn’t back to historical level, the MSY won’t be reached never.

If a regime shift is going on, the BRP should be re-evaluated

Remarks1. To recovery the population, it is necessary to declare the condition as overfished

2. To declare the overfished condition, it is necessary define BRP (target and/or limit)

3. The population recovery may be reached, considering the variables related to MSY (or proxy) as biological reference points (BRP)

4. Considering the uncertainty of the future recruitments, a harvest rule control should be defined in order to sure the population’s rebuild.