Age, growth and per-recruit assessment of the Saldanha and Langebaan stock of Chelon richardsonii
type: CreativeWork
description: Chelon richardsonii are omnivorous, particle feeders found specifically within inshore and estuarine habitats on the west and south coast of South Africa. They are the primary target of the gillnet and beach-seine fishery in this region. Despite being managed through a multifaceted approach of gear restrictions and total allowable e↵ort, the fishery is thought to be oversubscribed and the stock is regarded as being overfished. The social and economic importance of this fishery necessitates an update of the life history parameters of C. richardsonii to enable an accurate assessment the current status of the stock. The fishery in Saldanha and Langebaan was described via investigating changes in sexratio, mean length (mm) and standardised catch-per-unit-e↵ort (CPUE). Firstly, exploration of sex ratio indicated a significant switch between the two periods (1998-2002 and 2017), resulting in a predominantly male biased population (1.7 males: 1 female). Secondly, through investigation of three length-frequency distributions of commercial catch of C. richardsonii (1998-2002, 2009-2011 and 2017) a reduction in mean total length (TL) of 36.5 mm was observed. Lastly, the standardisation of the Netfishery CPUE for the time series of 2008-2016 through the application of a Generalised Additive Mixed Model (GAMM) showed a reduction of approximately 30% in relative abundance of C. richardsonii. Chelon richardsonii exhibited a fast growth, a maximum age of six and matured relatively early at two years old. Growth was best described using a three parameter von-Bertalan↵y growth model; where L1 is the asymptotic length, K is the rate at which L1 is reached and t0 is the age when the average length is zero. The data collected in 2017 expressed two problems. Firstly, as a result of high gillnet selectivity, smaller individuals within younger age classes were missing. Secondly, due to growth overfishing and/or a small sample size (n = 353) older and larger adults were missing. Consequent…
abstract: Chelon richardsonii are omnivorous, particle feeders found specifically within inshore and estuarine habitats on the west and south coast of South Africa. They are the primary target of the gillnet and beach-seine fishery in this region. Despite being managed through a multifaceted approach of gear restrictions and total allowable e↵ort, the fishery is thought to be oversubscribed and the stock is regarded as being overfished. The social and economic importance of this fishery necessitates an update of the life history parameters of C. richardsonii to enable an accurate assessment the current status of the stock. The fishery in Saldanha and Langebaan was described via investigating changes in sexratio, mean length (mm) and standardised catch-per-unit-e↵ort (CPUE). Firstly, exploration of sex ratio indicated a significant switch between the two periods (1998-2002 and 2017), resulting in a predominantly male biased population (1.7 males: 1 female). Secondly, through investigation of three length-frequency distributions of commercial catch of C. richardsonii (1998-2002, 2009-2011 and 2017) a reduction in mean total length (TL) of 36.5 mm was observed. Lastly, the standardisation of the Netfishery CPUE for the time series of 2008-2016 through the application of a Generalised Additive Mixed Model (GAMM) showed a reduction of approximately 30% in relative abundance of C. richardsonii. Chelon richardsonii exhibited a fast growth, a maximum age of six and matured relatively early at two years old. Growth was best described using a three parameter von-Bertalan↵y growth model; where L1 is the asymptotic length, K is the rate at which L1 is reached and t0 is the age when the average length is zero. The data collected in 2017 expressed two problems. Firstly, as a result of high gillnet selectivity, smaller individuals within younger age classes were missing. Secondly, due to growth overfishing and/or a small sample size (n = 353) older and larger adults were missing. Consequent…
author: Horton, Matt
language: eng
date published: 2018
date modified: 2026-07-22T22:23:13Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Department of Biological Sciences

PropertyValue
property ID: Handle
value: http://hdl.handle.net/11427/29745