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Summary:

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. Sighting frequency was significantly lower with active pingers than in dummy or control trials, but there wre no significant differences between the dummy and control trials. Preliminary results suggest that acoustic pingers attached to gillnets may be used to successfully prevent tucuxi bycatch.

Summary:

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.

Summary: 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.

Summary:

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%.

Summary:

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.

Summary: 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.

Summary: 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.

Summary: 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.

Summary: Bycatch—the incidental catch of nontarget species—is a principal concern in marine conservation and fisheries management. In the eastern Pacific Ocean tuna fishery, a large fraction of nonmammal bycatch is captured by purse-seine gear when nets are deployed around floating objects. We examined the spatial distribution of a dominant species in this fishery’s bycatch, the apex predator silky shark (Carcharhinus falciformis), from 1994 to 2005 to determine whether spatial closures, areas where fishing is prohibited, might effectively reduce the bycatch of this species. We then identified candidate locations for fishery closures that specifically considered the trade-off between bycatch reduction and the loss of tuna catch and evaluated ancillary conservation benefits to less commonly captured taxa. Smoothed spatial distributions of silky shark bycatch did not indicate persistent small areas of especially high bycatch for any size class of shark over the 12-year period. Nevertheless, bycatch of small silky sharks (<90 cm total length) was consistently higher north of the equator during all years. On the basis of this distribution, we evaluated nearly 100 candidate closure areas between 5◦N and 15◦ N that could have reduced, by as much as 33%, the total silky shark bycatch while compromising only 12% of the tuna catch. Although silky sharks are the predominant species of elasmobranchs caught as bycatch in this fishery, closures also suggested reductions in the bycatch of other vulnerable taxa, including other shark species and turtles. Our technique provides an effective method with which to balance the costs and benefits of conservation in fisheries management. Spatial closures are a viable management tool, but implementation should be preceded by careful consideration of the consequences of fishing reallocation.

Summary: 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.