Unanswered Forum Topics

Evaluation of a modified scallop dredge's ability to reduce the likelihood of damage to loggerhead sea turtle carcasses

In 2003 and 2004 the scallop industry, Coonamessett Farm, and the Virginia Institute of Marine Fisheries, with funding from the NOAA Fisheries Service, successfully tested a series of chains that excluded turtles from entering the dredge bag. In twelve trials, divers videoed the results of placing turtle carcasses in the path of a modified scallop dredge. Turtle carcasses went over the dredge in all but three trials. Damage was assessed as “slight or none” in all valid assessments of damage to a carcass following an encounter.

Spatial and temporal impact of pingers on porpoises

Authors investigated the spatial and temporal responses of porpoises to simulated bottom-set nets equipped with periodically operating Dukane NetMark 1000 pingers.

Behavioral responses of Sotalia fluviatilis (Cetacea, Delphinidae) to acoustic pingers, Fortaleza, Brazil

Underwater acoustic pingers were tested in Brazil to evaluate the behavioral responses of tucuxi (Sotalia fluviatilis). Five pingers were evenly placed on a floating 100 m line set along the dolphins' swimming parth in and out of sheltered waters. Dolphin sighting frequencies were recorded for functional and dummy pingers and control trials. Dolphin sightings were significantly lower in areas where the pinger line was set.

Acoustic harassment devices reduce seal interaction in the Baltic salmon-trap, net fishery

AHDs with a source level of 179 dB re 1 µPa rms at 1 m were deployed during three consecutive fishing seasons. Fish catches in traps with AHDs were significantly higher than in the controls, while catch damage in the traps with AHDs was lower. However, towards the end of the fishing season catch damage increased in traps with AHDs.

Effects of pingers on the behaviour of bottlenose dolphins

Trials to assess the behavioural response of free-ranging bottlenose dolphins to continuous and responsive pingers were conducted. In boat based trials both types of pinger affected dolphin behaviour, while in static trials the detection of dolphin vocalisations was significantly lower in the presence of active continuous pingers.

Do pingers reduce interactions between bottlenose dolphins and nets around the Balearic Islands?

A large scale pinger trial was conducted and results showed a 49% decrease dolphin depredation rates when pingers were active. However the different pinger brands tried were not equally effective in reducing depredation. The AQUAmark 210 pingers had significant results, while Dukane Netmark 1000 and SaveWave Dolphinsaver High-impact did not have significant results. Profit per unit increased 9%.

Pingers as deterrents of bottlenose dolphins interacting with trammel nets

The experiment tested the effects of Aquamark 100 pingers on the depredation rate of bottlenose dolphins on trammel nets. Results showed nets equipped with pingers had 87% fewer holes (attributed to damage by dolphins) than nets without pingers.

Behavioral responses of bottlenose dolphins, Tursiops truncatus, to gillnets and acoustic alarms

The authors tested the behavioural response of bottlenose dolphins (Tursiops truncatus) to gill nets equipped with active and control Dukane NetMark 1000 pingers. Although dolphins were observed significantly fewer times within a 100m circular buffer zone from the alarms, overall results showed no significant differences in the number of groups observed, or closest approaches by animals to the net, between active and control periods.

Reduction of harbour porpoise (Phocoena phocoena) bycatch by iron-oxide gillnets

Harbour porpoise bycatch was significantly lower (p<0.01) in high-denisty Iron Oxide (IO) gill nets compared to control nets. There was no significant difference in the acoustic target strength of the IO and control nets, and both nets behaved similarly in flume tank tests. The authors conclude the reduction of harbour porpoise bycatch in the IO nets was a result of the mechanical properties of the nets.

Bycatch mitigation assessment for sharks caught in coastal anchored gillnets

The potential of modifying gillnets to reduce shark bycatch was investigated in the US Spanish mackerel and spot gillnet fisheries. The modified net had larger floats on the head-rope and inreased weight on the lead-line to increase the tension of the net. Results showed that the catch rate of some shark species was significantly reduced in the modified gillnets. Target catch rates of Spanish mackerel did not differ significantly between control and modified nets of the same mesh size.

Trade-offs in the Design of Fishery Closures: Management of Silky Shark Bycatch in the Eastern Pacific Ocean Tuna Fishery

Bycatch—the incidental catch of nontarget species—is a principal concern in marine conservation

The effect of pingers on harbour porpoise, Phocoena phocoena bycatch and fishing effort in the turbot gill net fishery in the Turkish Black Sea coast

Gill nets fitted with Dukane NetMark 1000 pingers had significantly less bycatch of harbor porpoises than control nets and the fish size and catch rates of the target species were not affected.

Are circle hooks effective in reducing incidental captures of loggerhead sea turtles in a Mediterranean longline fishery?

The use of circle hooks (16/0) instead of J hooks (size 2) on pelagic longline gear, reduced the incidental capture of immature loggerhead sea turtles and did not affect the catch rates or fish size of the target species. There was also a significant difference in hook location between the two hooks, with more J hooks being swallowed.

Large-scale experiment shows that nylon leaders reduce shark bycatch and benefit pelagic longline fisheries

Catch rates of blue marlin, snake mackerel and sharks were lower when nylon monofilament leaders, instead of wire leaders, were used on pelagic longline gear but bigeye tuna and black marlin catch rates increased. (No effect on yellowfin). Nylon leaders also had higher bite-off rates than the wire leaders.

Tropical prawn trawl bycatch of fish and seasnakes reduced by yarrow fisheye bycatch reduction device

The yarrow fisheye bycatch reduction device reduced the weight of small bycatch by an average of 22.7% and the number of seasnakes caught by an average of 43.3%, with no loss of tiger prawn.

The effectiveness of bycatch reduction devices on crab pots at reducing capture and mortality of diamondback terrapins (Malaclemys terrapin) in Florida

This study determined that 73.2% of diamondback terrapins could have been prevented from entering crab pots if bycatch reduction devices (BRDs) had been used. Additionally, there was no significant difference in the sex, size or number of crabs in pots fitted with BRDs.

Evaluation of exclusion grids to reduce the bycatch of dolphins, turtles, sharks and rays in the Pilbara trawl fishery

A semi-flexible exclusion grid with a bar spacing of 15.5 cm reduced dolphin bycatch in the Pilbara trawl fishery by close to 50% and reduced the bycatch of sea turtles, large sharks and rays. However, the fate of the dolphins that encountered the grid and escaped is unknown.

Review and evaluation of three mitigation measures-bird-scaring line, underwater setting and line shooter-to reduce seabird bycatch in the north Atlantic longline fishery

Bird-scaring lines, underwater setting and line shooters all reduced the incidental capture of seabirds, with bird-scaring lines being the most effective. These mitigation measures also reduced bait loss and increased the catch rates of target species.

Low-profile gillnet testing in the deep water region of Pamlico Sound, NC.

Low profile gillnets with a panel height of six feet and no tie downs or additional floats had significantly fewer interactions with sea turtles and caught significantly less bycatch than standard gillnets. Catches of the target species (flounder) were also reduced in the low profile gillnets.

Shark catch in pelagic longline fishery: Comparison of circle and tuna hooks

The use of circle hooks (4.3 sun and 5.2 sun) instead of standard Japanese tuna hooks (3.8 sun) on pelagic longlines, had little impact on catch rates, mortality or size composition of blue sharks.

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