Question

Catch curve is used to estimate

• A. Natural mortality
• B. Total mortality
• C. Optimum catch
• D. Optimum recruits

Hint:

Mortality Estimation in Fisheries: Length-Converted CATCH CURVE $\rightarrow$ Estimates TOTAL MORTALITY ($Z$). ($Z = F + M$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Fisheries stock assessment demography: length-converted catch curves plot the natural logarithm of cohort abundance against relative age to estimate the instantaneous total mortality coefficient ($Z = F + M$).
Key Formula or Approach:
\[ \ln \left( \frac{C(t_1, t_2)}{\Delta t} \right) = a - Z \cdot t \quad \implies \quad \text{Slope of Descending Limb } = -Z \text{ (Total Mortality)} \]

Step 2: Detailed Explanation:
In fish stock assessment methodologies (Beverton and Holt, Pauly 1983):
- A Catch Curve (Length-Converted Catch Curve) is a fundamental demographic graphical tool where the natural log of catch per unit age interval [$\ln(N/\Delta t)$] is plotted against relative age ($t$).
- The linear descending right limb of the catch curve represents fully exploited cohorts undergoing exponential mortality ($N_t = N_0 e^{-Z t}$).
- The negative slope of the linear regression fitted to this descending limb gives a direct, precise mathematical estimate of the Instantaneous Total Mortality Rate ($Z$), where $Z = F + M$ (Fishing mortality $+$ Natural mortality).

Step 3: Final Answer:
Therefore, catch curve is used to estimate Total mortality, corresponding to option (B).