Search The Database

This study tested the use of different types of fishing gears to compare their effectiveness in catching the invasive blue crab (Callinectes sapidus) in the Northern Adriatic Sea. The tested gears included traditional fyke nets and four types of crab pots with either single or double chambers. Results indicated that both the double chamber pot and fyke nets were most effective gears overall in terms of catch efficiency and yield (catch per unit effort). However, the double chamber pot had significantly higher species selectivity, with lower bycatch of the native green crab (Carcinus aestuarii), as well as greater size selectivity (targeting larger adults). 

Understanding the behavior of snow crab in response to escape gaps is important as it may impact escape success, including the number of attempts, as well as time taken to escape successfully. The study filmed movements of snow crabs through different sized and shaped escape gaps in a laboratory setting and compared movement patterns with those of pot netting mesh. The results showed that escape success strongly depends on crab orientation, the time required to escape a trap can be reduced when using escape gaps, and escape gap design strongly influences size selectivity. In addition, escape probability decreases with crab size. Specifically, circular gaps can retain target-sized crabs while releasing undersized crabs, while elongated or wide gaps increase the risk that target-sized crabs escape. Additionally, side-by-side gaps or mesh can cause limb entanglement and delayed escape.

Tests were conducted in the Hawaii-based tuna longline fishery to determine if removing the shallowest hooks from pelagic longline sets would maximize the catches of target species while minimizing the incidental catch of non-target species.  Catch rates of bigeye tuna (Thunnus obesus) were not significantly different between the two set types but catch rates of sickle pomfret (Taractichthys steindachneri) were significantly higher in experimental compared to control sets.  Statistically fewer wahoo, dolphinfish, blue marlin, striped marlin and shortbill spearfish (Acanthocybium solandri, Coryphaena hippurus, Makaira nigricans, Kajikia audax, and Tetrapturus angustirostris) were caught on the experimental sets. 

Pelagic longlines targeting bigeye tuna (Thunnus obesus) and lustrous pomfret (Eumegistus ilustris) in Hawaii were weighted with lead weights, enabling fishing deeper in the water column than traditional pelagic longlines.  Weighted longlines caught 31 target species with a slightly higher catch per unit effort (CPUE) of 1.3 fish/100 hooks (49 kg/100 hooks) compared to traditional gear (38 target species and a CPUE of 1.08 fish/100 hooks or 41 kg/100 hooks).  Bigeye tuna CPUE for the weighted gear was higher, 0.95 fish/100 hooks (36 kg/100 hooks), compared to traditional gear, 0.56/100 hooks (21 kg/100 hooks).In a second trial in a fishery targeting tuna and billfish, swordfish (Xiphias gladius) CPUE was very similar for weighted (0.3 fish/100 hooks or 17 kg/100 hooks) and traditional (0.25 fish/100 hooks or 14 kg/100 hooks) gear.  This technique could be used to reduce sea turtle and other bycatch species interactions, however this was not tested during this initial trial study.

Fishing experiments were designed to test various gear modifications for the pelagic longline fishery in Hawaii, United States, to reduce sea turtle interactions. The experiments tested (1) daytime "stealth gear" (2) deep daytime setting, and (3) circle hooks combined with hook timers. Stealth gear and deep setting both caught significantly fewer swordfish compared to the control, although overall catch was reduced by 39% using stealth gear and was approximately similar to the control using deep setting. Neither gear configuration resulted in the take of any sea turtles (compared to one turtle in the control). Initial testing of hook timers with circle hooks resulted in the catch of two sea turtles. Circle hooks were also 40% as effective as J hooks at catching swordfish, and 94% as effective at catching tuna (by weight and value). 

Fishing experiments were designed to test various gear modifications for the pelagic longline fishery in Hawaii, United States, to reduce sea turtle interactions. The experiments tested (1) daytime "stealth gear" (2) deep daytime setting, and (3) circle hooks combined with hook timers. Stealth gear and deep setting both caught significantly fewer swordfish compared to the control, although overall catch was reduced by 39% using stealth gear and was approximately similar to the control using deep setting. Neither gear configuration resulted in the take of any sea turtles (compared to one turtle in the control). Initial testing of hook timers with circle hooks resulted in the catch of two sea turtles. Circle hooks were also 40% as effective as J hooks at catching swordfish, and 94% as effective at catching tuna (by weight and value). 

Experimental trials were carried out in Argentina comparing franciscana (Pontoporia blainvillei) bycatch rates in standard gillnets with gillnets with increased acoustic reglectivity by infusion with barium sulphate (BaSO4) and increased flexural stiffness of the nylon twine. There was no significant difference in franciscana bycatch rates or target catch rates among the three net types.  

Experimental trials were carried out in Argentina comparing franciscana (Pontoporia blainvillei) bycatch rates in standard gillnets with gillnets with increased acoustic reglectivity by infusion with barium sulphate (BaSO4) and increased flexural stiffness of the nylon twine. There was no significant difference in franciscana bycatch rates or target catch rates among the three net types.  

Tests with captive, as well as wild, juvenile sandbar sharks (Carcharhinus plumbeus) were undertaken to determine the effectiveness of electropositive metals in reducing the interactions with longline gear.  Electropositive metals deterred feeding in groups of captive juvenile sharks for a short period of time and altered the swimming patterns of individuals when food motivation was not present.  In the field, electropositive metals placed within 10 cm of the bottom longline hooks reduced the catch of sandbar sharks by around two thirds, compared to the catch on hooks with a placebo.

Tests with captive, as well as wild, juvenile sandbar sharks (Carcharhinus plumbeus) were undertaken to determine the effectiveness of electropositive metals in reducing the interactions with longline gear.  Electropositive metals deterred feeding in groups of captive juvenile sharks for a short period of time and altered the swimming patterns of individuals when food motivation was not present.  In the field, electropositive metals placed within 10 cm of the bottom longline hooks reduced the catch of sandbar sharks by around two thirds, compared to the catch on hooks with a placebo.