Fishing Mortality Rate Fishing Effort Rate and Catch

The instantaneous rate of fishing mortality F denotes the force of the fishery on the stock. The F and abundance N determine the rate of catch:

dC dt

The fishing mortality rate generally must be estimated from data, often including data on the fishing-effort rate E, a measure of the amount of fishing gear used per unit time. The theoretical relationship between the two is F — qE, where q, the 'catchability coefficient', is constant and specific to the gear, vessel, location, and possibly other factors. Much effort in fishery modeling is devoted to estimating q and standardizing E for a particular fishery.

Catch Ct over period t can be found by integrating catch rate (eqn [24]) with respect to time. Because Nt depends on M as well as F, the solution requires knowing the natural mortality rate. A formulation that does not require M explicitly (though it does implicitly) is

where F, is the (constant) fishing mortality rate during period t, and Nt the average population size in the same period.

For an age-structured population, eqn [24] is applied to each age class:

dCa dt

Given Ma, eqn [26] can be solved by integration to obtain catch at age over the year (or any time interval). The result is the Baranov catch equation, a cornerstone of fishery models:


Given annual catch at age Cat, annual total catch is simply the sum across ages, Ct = XaCa,t. The annual yield (catch in weight) is

where the Wa are the average weights at age during the period.

Was this article helpful?

0 0
Worm Farming

Worm Farming

Do You Want To Learn More About Green Living That Can Save You Money? Discover How To Create A Worm Farm From Scratch! Recycling has caught on with a more people as the years go by. Well, now theres another way to recycle that may seem unconventional at first, but it can save you money down the road.

Get My Free Ebook

Post a comment