Escapement of Cape hakes under the fishing line of the Namibian demersal sampling trawl

T. Jørgensen, A. Engås, E. Johnsen, T. Iilende, Paulus Inekela Kainge, P. Schneider

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Swept area surveys in Namibian waters provide input data to the stock assessment model. To evaluate the model's predictions, it is important to understand the catch efficiency of sampling trawls. The objective of this study was to establish whether Cape hakes Merluccius capensis and M. paradoxus escape under the fishing line and to identify any species or length dependence of escape rates. Experiments were carried out in Namibian waters during two cruises in October 2002 and October 2003. A collection bag was mounted under the trawl to catch fish escaping below the fishing line. Environmental data and photographs of fish in front of the trawl were also taken. Escapement of hake varied by species, length, depth and year. It was generally below 5% for M. capensis but escapement in 2002 averaged 10-20% for M. paradoxus, and in 2003 it was over 50% in the shallow area (300m), decreasing to 10% in the deep area (570m). Oxygen level variation seemed to explain the marked between-year difference in escapement. Escapement of M. capensis decreased marginally with increasing fish length, whereas escapement of M. paradoxus showed a marked increase with increasing fish length in shallow waters and no length dependence in deep waters. Species differences in behaviour and vision may partly explain the observations.
Original languageEnglish
JournalAfrican Journal of Marine Science
Volume29
Issue number2
Pages (from-to)209-221
ISSN1814-232X
DOIs
Publication statusPublished - 2007
Externally publishedYes

Keywords

  • Aquatic Science
  • Benguela
  • Cape hakes
  • Catchability
  • Escapement
  • Ground gear
  • South-East Atlantic
  • Survey trawl
  • Fish
  • Oxygen
  • Sampling
  • Water analysis
  • deep water
  • escapement
  • fish
  • fishing
  • modeling
  • sampling
  • shallow water
  • size effect
  • stock assessment
  • trawling
  • Africa
  • Angola
  • Atlantic Ocean
  • Atlantic Ocean (Southeast)
  • Namibia
  • Southern Africa
  • Sub-Saharan Africa
  • Merluccius capensis
  • Rexea solandri
  • MARINE
  • BOTTOM-TRAWL
  • SELECTIVITY
  • CATCHABILITY
  • MERLUCCIUS
  • MANAGEMENT
  • BEHAVIOR
  • benguela
  • catchability
  • ground gear
  • survey trawl
  • Namibia Africa Ethiopian region
  • sampling trawl
  • Pisces Vertebrata Chordata Animalia (Animals, Chordates, Fish, Nonhuman Vertebrates, Vertebrates) - Osteichthyes [85206] Merluccius capensis species Merluccius paradoxus species cape hake common
  • 00512, General biology - Conservation and resource management
  • 07502, Ecology: environmental biology - General and methods
  • 07508, Ecology: environmental biology - Animal
  • 07516, Ecology: environmental biology - Wildlife management: aquatic
  • 62800, Animal distribution
  • Conservation
  • Population Studies
  • swept area survey applied and field techniques
  • Biogeography
  • Wildlife Management

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