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A long-term study assessed the efficiency of acoustic pingers (AQUAmark 100, 20-160kHz) in reducing the encounter rates of finless porpoises (Neophocaena spp.) with fishing nets. The study used a passive recorder to obtain acoustic encounter rates of echolocating finless porpoises over two eight-month periods. Encounter rates were significantly lower in periods when pingers were in use, but this effect decreased over time. By the end of each study period, the number of encounters was greater than those during periods without pingers, suggesting that habituation had occurred. However, when pingers were reactivated after four months of no use, encounters returned to lower levels, such as those observed during the beginning of the experiment. The results suggest that habituation to pingers may be mitigated by alternating periods of silence with periods of active pinger use. 

The study combined fisher questionnaires, acoustic monitoring, and participatory experiments to investigate the occurrence of bottlenose dolphins (Tursiops truncates) in the gillnet fisheries of Northern Cyprus. Dolphins were present in fishing grounds throughout the year, and were detected at 28% of net sets. Net damage was six times greater when dolphins were present during sets. Use of an acoustic pinger (AQUAmark 200, 5-160kHz) was tested, but had no significant effect on dolphin presence. 

The experiment evaluated the effectiveness of two types of pingers (Aquamark 100 and Aquamark 200) to reduce the bycatch rate of harbor porpoise (Phocoena phocoena) in a set gillnet fishery in the Black Sea. The study also evaluated the effects of the pingers on catch of target and non-target fish species. There was no significant difference in catch of target and non-target fish species in trials with pingers versus control sets. There was also no significant difference between number of harbor porpoises caught in nets using pingers and when no pingers were used, although a low overall number of porpoises were caught (eight harbor porpoises were caught during the experiment – three in control nets, three in nets using the Aquamark 100, and one in nets using the Aquamark 200). 

 Preliminary field studies were carried out on a potentially cetacean-friendly acoustic deterrent system for seals (played using underwater loudspeakers). The “smart seal deterrent signal” produces a startle response in seals rather than an aversion to a very loud noise, and is transmitted at a sound level which is not harmful to seals, even at very close distances. There was some evidence that the acoustic deterrent was effective at deterring gray seals (Halichoerus grypus) from fishing operations, although there was a low seal interaction rate regardless of whether the device was on or not. 

The study investigated the effects of bait size and hook size on catching efficiency and size selectivity in Icelandic longline fisheries targeting cod (Gadus morhua), haddock (Melanogrammus aeglefinus), tusk (Brosme brosme), ling (Molva molva) and wolffish (Anarhichas lupus). Five sizes of hooks and two sizes of bait were tested. Larger bait (30 grams vs. 10 grams) caught more large fish and fewer small fish of all species, with the exception of ling. Additionally, haddock catches were reduced by 57% when the large bait was used. Increasing hook size lowered capture efficiency for all species, but only had a minor effect on size selectivity. 

The study tested the use of a horizontally divided codend with small square mesh (40mm) and a simple frame to stimulate fish to swim into the upper compartment of a separator trawl. The majority of fish were separated successfully from Nephrops norvegicus, but fish preference for both trawl compartments was uniform. Additionally, separation efficiency was lower for small roundfish and flatfish. 

This study investigated the efficiency of a sieve‐panel to separate bycatch species from Norway lobster (Nephrops norvegicus) in trawl gear via mechanical and behavioral means. Four different designs of varying panel mesh size or inclination were tested. The sieving efficiency for Nephrops increased from ~17% to ~71% as mesh size increased, and decreased with increasing carapace length, but did so less as panel inclination and mesh size increased. The sieving efficiency for roundfish was low, while the efficiency for flatfish decreased with fish size. Although results are promising, the sieving efficiency for the largest, most valuable Nephrops remained too low for commercial implementation of the gear modifications. 

The experiment aimed to determine what size of cull ring would reduce the catch of pre-recruit stone crab (Menippe mercenaria) and other bycatch while maintaining legal-sized catch. Catch compositions of crabs from unmodified plastic commercial stone crab traps and traps fitted with three sizes of cull rings were compared in the stone crab fishery across Florida’s west coast. Traps outfitted with cull rings retained bigger crabs, had less bycatch, and fewer pre-recruit crabs, while yielding the same number of legal-sized crabs as traps without cull rings. A 55.6 mm cull ring was then distributed to commercial fishermen, who reported anecdotally that they liked the performance of the rings and felt that it would improve the efficiency of their operations.   

 Data was collected on the relative performance of single and multiple round, rectangular, and square escape gaps across three fishing operations. Compared to control traps, those with escape gaps maintained catches of legal-sized P. pelagicus, but caught 51–100% fewer undersized individuals. Generally, rectangular escape gaps and especially multiple configurations were the most effective. Escape gaps represent a low-cost option for minimizing interactions with unwanted catches throughout the fishery.

The individual and cumulative effects of increasing mesh size and installing three escape gaps (36 × 120 mm) in collapsible‐netted round traps were assessed to address concerns associated with excessive discarding in an Australian portunid fishery. Compared to conventional traps of 56‐mm mesh throughout, those with the same mesh size and escape gaps caught significantly fewer (by 54%) undersized blue swimmer crabs, Portunus armatus, and yellowfin bream, Acanthopagrus australis (by 64%). Irrespective of escape gaps, simply increasing the mesh size to 75 mm did not significantly affect catches of undersized P. armatus, although 87% fewer A. australis were retained. Traps with both 75‐mm mesh and escape gaps maintained reductions of A. australis, but had a clear cumulative effect on P. armatus selection, retaining 84% fewer undersized individuals across a larger size at retention. The results support using escape gaps in existing conventional traps, but illustrate the need to configure the minimum legal mesh size to approach the desired target size of P. armatus as a precursor to maximizing trap selectivity.