Unanswered Forum Topics

A mechanical separating bycatch reduction device was tested in the Spencer Gulf king prawn trawl fishery to reduce the incidental capture of giant cuttlefish (Sepia apama) and blue swimmer crabs (Portunus armatus). Different sizes of Nordmore grids were tested. Two Nordmore grids were inserted into the posterior extension sections and triangular escape exits were cut out. One grid was located in the extension with an angle of -45 degrees (small grid) and the second large grid was set at a 30 degree angle in the extension.

A review of recently published articles dealing with the effects of magnetic fields on elasmobranchs and potential use in bycatch avoidance was conducted. The authors suggest these papers ignore that teleosts may also demonstrate magnetite based magnetoreception and that electroreception is present in many teleosts. Based on this, the possibility of induction based indirect magenetoreception in telosts should also be considered. The authors suggest that experiments showing teleosts are insensitive to magnetic deterrents is likely a result of flawed design and sample sizes.

A laboratory study was conducted to determine the impact of an electrical field on mortality rates and histological changes on model marine organisms. The tests were carried out to provide more information on the impact of electrotrawling om marine species. Two species of invertebrates, brown shrimp (Crangon crangon L.0) and king ragworm (Alita virens S.) were used as model species for crustaceans and polycheates, respectively.

Alternative trap designs were tested to determine their ability to reduce bycatch of ecologically important herbivore species such as parrotfish and surgeonfish. Catches from traditional Antillean chevron traps were compared to catches from traps with 1) short escape gaps (20X2.5 cm), 2) traps with tall escape gaps (40X2.5 cm) and 3) traps with a panel of large aperture mesh. The mean number of fish caught in the various traps were: 11.84 (control), 4.88 (short gap trap), 4.43 (tall gap traps) and 0.34 (large mesh traps).

Experiments were conducted aboard longline vessels operating in the Seychelles targeting swordfish and tuna. Experimental longlines fitted with hook timers and temperature depth recorders were used to identify differences in species composition, quantity and depth of catch between night sets using a shallow basket (swordfish target) and day sets using both shallow and deep baskets (tuna target). The majority of species were caught during day sets (75%). Lancetfish was the main bycatch species during daytime sets.