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 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). 

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. 

In south-eastern Australia, baited, round traps (comprising 50–57-mm mesh netting) are used to target giant mud crabs (Scylla serrata) and blue swimmer crabs (Portunus armatus) in spatially separated fisheries.  Two experiments assessed the utility of (1) traps partially or completely covered in larger mesh (91 mm to match the minimum legal size of the smaller P. armatus), and (2) any cumulative benefits of fitting species-specific escape gaps. In experiment 1, there were no differences among catches of legal-sized portunids associated with either partial, or complete trap coverage with larger mesh. Irrespective of mesh coverage, both designs of 91-mm traps also retained significantly fewer (by up to 42%) undersized P. armatus and A. australis. In experiment 2, replicate traps completely covered in 91-mm mesh were tested against conventional traps comprising 56-mm mesh, and traps with the same mesh sizes, but also three escape gaps configured for either S. serrata (46 × 120 mm) or P. armatus (36 × 120 mm). All modified traps maintained catches of legal-sized S. serrata, and only the 91-mm traps with escape gaps caught fewer legal-sized P. armatus. Fewer undersized S. serrata, P. armatus and Acanthopargus australis (yellowfin bream, mean catches reduced by up to 49%) were retained in all larger-meshed than small-meshed traps, and in all of those traps with escape gaps (by up to 95%) than without. While there were no significant cumulative benefits of escape gaps in larger-meshed traps (measured by a statistical interaction), there was a trend of fewer unwanted catches overall. These data support configuring portunid traps with mesh sizes matching the morphology of the smallest legal-sized target species.