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.

Oplan Termites

Oplan Termites

You Might Start Missing Your Termites After Kickin'em Out. After All, They Have Been Your Roommates For Quite A While. Enraged With How The Termites Have Eaten Up Your Antique Furniture? Can't Wait To Have Them Exterminated Completely From The Face Of The Earth? Fret Not. We Will Tell You How To Get Rid Of Them From Your House At Least. If Not From The Face The Earth.

Get My Free Ebook

Post a comment