Population Reconstruction Using a State-Space Model Based on an In Situ Mark-Resighting Method to Assess the Abundance of Spawners at Fish-Spawning Aggregation

• Activity Number: 418
• Type: Topic Contributed
• Date/Time: Tuesday, August 11, 2015 : 2:00 PM to 3:50 PM
• Sponsor: Scientific and Public Affairs Advisory Committee
• Author(s): Lynn Waterhouse* and Brice X. Semmens and Christy Pattengill-Semmens and Croy McCoy and Bradley Johnson and Phillipe Bush and Scott Heppell
• Companies: and Scripps Institution of Oceanography and REEF and Department of Environment, Cayman Islands Government and Department of Environment, Cayman Islands Government and Department of Environment, Cayman Islands Government and Department of Environment, Cayman Islands Government
• Keywords: mark resight ; mark recapture ; population estimation ; bayesian ; hierarchical modeling ; state space model

Abstract

This study presents a reconstruction of the abundance of an endangered species, the Nassau grouper, at a spawning aggregation in Little Cayman Island, Cayman Islands. We describe an in situ visual mark-resighting design which can be used to estimate total abundance of spawners at the aggregation site. Mark-resight data is used to estimate the population size during each spawning aggregation, which in turn can be fit using a state space model to obtain an estimate the population growth rate. Simulation methods are used to identify trade-offs between number of individuals tagged and number of subsequent surveys required in order to meet an acceptable level of uncertainty in population estimates. We evaluate the inclusion of covariates such as observer, date, and time. An estimate of the growth rate is found by fitting a state space model to the posterior distributions of Bayesian estimates for population abundance over time. Additional pieces of information in the form of length-frequency data and video pans can be used to increase the precision of the estimate of abundance and provide more information on the health of the population.