A maximum likelihood estimate of natural mortality for brown tiger prawn (Penaeus esculentus) in Moreton Bay (Australia)

TL;DR

This study used a delay difference model with maximum likelihood to estimate natural mortality of brown tiger prawn in Moreton Bay, providing the first direct estimate that is lower than previous assumptions.

Contribution

It introduces a new model-based approach to estimate natural mortality for brown tiger prawn, improving accuracy over prior methods.

Findings

Estimated natural mortality is 0.031 week$^{-1}$

Model successfully estimates multiple stock parameters simultaneously

First direct estimate of natural mortality for this species in the region

Abstract

The delay difference model was implemented to fit 21 years of brown tiger prawn (Penaeus esculentus) catch in Moreton Bay by maximum likelihood to assess the status of this stock. Monte Carlo simulations testing of the stock assessment software coded in C++ showed that the model could estimate simultaneously natural mortality in addition to catchability, recruitment and initial biomasses. Applied to logbooks data collected from 1990 to 2010, this implementation of the delay difference provided for the first time an estimate of natural mortality for brown tiger prawn in Moreton Bay, equal to $0.031 \pm 0.002$ week$^{-1}$. This estimate is approximately 30\% lower than the value of natural mortality (0.045 week$^{-1}$) used in previous stock assessments of this species.