The effects of barotrauma on five species of South African line-caught fish
DOI: 10.2989/1814232X.2013.805594
Title: The effects of barotrauma on five species of South African line-caught fish
Journal Title: African Journal of Marine Science
Volume: Volume 35
Issue: Issue 2
Publication Date: August 2013
Start Page: 243
End Page: 252
Published online: 12 Aug 2013
ISSN: 1814-232X
Author: SE Kerwathabc*, CG Wilkea & A G?tzde
Affiliations:
a Fisheries Research, Department of Agriculture , Forestry and Fisheries , Private Bag X2, Rogge Bay , 8012 , South Africa
b Zoology Department , University of Cape Town , Private Bag X3, Rondebosch , 7701 , South Africa
c Department of Animal Sciences , Stellenbosch University , Private Bag X1, Matieland , 7602 , South Africa
d Elwandle Node, South African Environmental Observation Network (SAEON) , Private Bag 1015, Grahamstown , 6140 , South Africa
e Department of Zoology , Nelson Mandela Metropolitan University , PO Box 77000, Port Elizabeth , 6031 , South Africa
Abstract: Management measures for South African line-caught fish include output controls such as closed seasons, bag and size limits and no-take moratoria. The main condition for these measures to be effective is that undesirable catches can be successfully released. However, most of the line-caught fish species are susceptible to barotrauma, a condition caused in physoclists by the rapid reduction of hydrostatic pressure during the ascent to the surface during capture. We investigated the effects of barotrauma on five commercially important species: roman Chrysoblephus laticeps, silver kob Argyrosomus inodorus, hottentot Pachymetopon blochii, santer Cheimerius nufar and carpenter Argyrozona argyrozona. A classification of the external signs of barotrauma was developed and internal and external signs of barotrauma were examined in relation to fishing depth and fish size, and compared between species. Immediate post-release mortality was investigated during a catch-and-release experiment. Medium-term survival of C. laticeps (~1 d) was examined by returning fish to depth in cages and subsequent monitoring on SCUBA. Our results indicate that most of the fish experience barotrauma even when caught at relatively shallow depths. External signs include extension of the inflated, everted stomach through the mouth, distended eyes, protrusion of the hind-gut and other organs through the cloaca, and gas bubbles in the dermal tissue between the fin rays. The absence of any obvious external signs of barotrauma can be misleading as dissections of such fish revealed ruptures of the swimbladder and other internal injuries consistent with barotrauma. Our results indicate that there might be significant post-release mortality, a factor that needs to be taken into account during stock assessment predictions and during the implementation of catch restrictions.
Accepted: 27 Mar 2013

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