Search The Database

Gillnets with three difference mesh sizes (2 7/8", 3" and 4") were modified to use 200 lbs/200 yard lead line and 11 oz buoyancy floats (versus 50lbs/200 yard lead line and 3 oz floats) to increase the tension in the net. Catch rates of Atlantic sharpnose and bonnethead sharks were significantly lower in the 4" modified net. The proportion of hammer-wrapped bonnethead sharks was significantly higher in the 4" unmodified net and significantly less blacktip sharks were wrapped in the 3" modified net. Selectivity of blacknose sharks varied between the modified and unmodified nets. Catch rates of targeted Spanish mackerel and spot were not significantly different between modified and unmodified nets.

Gillnets with three difference mesh sizes (2 7/8", 3" and 4") were modified to use 200 lbs/200 yard lead line and 11 oz buoyancy floats (versus 50lbs/200 yard lead line and 3 oz floats) to increase the tension in the net. Catch rates of Atlantic sharpnose and bonnethead sharks were significantly lower in the 4" modified net. The proportion of hammer-wrapped bonnethead sharks was significantly higher in the 4" unmodified net and significantly less blacktip sharks were wrapped in the 3" modified net. Selectivity of blacknose sharks varied between the modified and unmodified nets. Catch rates of targeted Spanish mackerel and spot were not significantly different between modified and unmodified nets.

Gillnets with three difference mesh sizes (2 7/8", 3" and 4") were modified to use 200 lbs/200 yard lead line and 11 oz buoyancy floats (versus 50lbs/200 yard lead line and 3 oz floats) to increase the tension in the net. Catch rates of Atlantic sharpnose and bonnethead sharks were significantly lower in the 4" modified net. The proportion of hammer-wrapped bonnethead sharks was significantly higher in the 4" unmodified net and significantly less blacktip sharks were wrapped in the 3" modified net. Selectivity of blacknose sharks varied between the modified and unmodified nets. Catch rates of targeted Spanish mackerel and spot were not significantly different between modified and unmodified nets.

The catches from five experimental trawls (TED + fisheye BRD, upward facing TED, downward facing TED, bigeye BRD and square-mesh panel BRD) were compared to those of the standard twin Florida Flyer prawn trawl. Nets with a combination of a TED and BRD reduced sea turtle catches by 100%, large sponges by 85.3%, sharks by 36.3% and rays by 17.7% and reduced the proportion of soft and damaged prawns by 41.6% and catches of tiger prawns by 6.5%. Upward and downward facing TEDs reduced sea turtle bycatch by 99% and 100% respectively and large sponges by 81.6% and 95.9% respectively. Catches of tiger prawns (P. semisulcatus and P. esculentus) were reduced by 6.3% with the use of TEDs. The BRDs had little impact on the catch of either target or bycatch species.

The type (circle 18/0 0 degree offset and J-style 9/0 10 degree offset) and position of hooks in the water column were tested to determine the effects on catch rates and mortality of elasmobranchs in pelagic and bottom longline fisheries in Brazil. Tests were conducted aboard pelagic and bottom longline vessels. Catch per unit effort (CPUE)  for blue shark (Prionace glauca), silky shark (Carcharhinus falciformis) and oceanic whitetip sharks (Carcharhinus longimanus) were significantly higher with circle hooks than with J-style hooks. Silky, blue and oceanic whitetip sharks had a significantly higher mortality at haulback with J-style hooks. Significant differences in hooking location between the two hook types was found for night, blue, silky and oceanic whitetip sharks. These sharks were more commonly hooked externally vs internally.  No significant differences between hook types was found for the CPUE of the sharks on bottom longlines.  Significantly more blacknose sharks (Carcharhinus acronotus) were alive at haulback when circle hooks were used on bottom longlines. Bottom longlines were also used to test for differences in CPUE by fishing depth.  Demersal hooks had significantly higher CPUEs than those suspended in the water column for blacknose sharks, nurse sharks (Ginglymostoma cirratum), and southern stingrays (Hypanus americanus).

Gillnets with three difference mesh sizes (2 7/8", 3" and 4") were modified to use 200 lbs/200 yard lead line and 11 oz buoyancy floats (versus 50lbs/200 yard lead line and 3 oz floats) to increase the tension in the net. Catch rates of Atlantic sharpnose and bonnethead sharks were significantly lower in the 4" modified net. The proportion of hammer-wrapped bonnethead sharks was significantly higher in the 4" unmodified net and significantly less blacktip sharks were wrapped in the 3" modified net. Selectivity of blacknose sharks varied between the modified and unmodified nets. Catch rates of targeted Spanish mackerel and spot were not significantly different between modified and unmodified nets.

The addition of a filter grid (inclined at ca. 20 degrees) that leads to an escape tunnel in trawl nets allowed 100% of rays and turtles to escape, 75% of manta rays, 40% of billfish and between 20-75% of sharks to escape.

An excluder grate (grid) was tested in the silver hake (Merluccius bilinearis) trawl fishery in Massachusetts Bay, United States to determine its effectiveness in reducing spiny dogfish (Squalus acanthias) bycatch.  The effects of color (white or black), angle and direction of the 50 mm spaced grids were investigated through video observations and data collection.  The number of spiny dogfish caught in trawls with the excluder grate were greatly reduced for all gear configurations, while the number of target species caught remained within typical commercial quantities.  Over 88% of spiny dogfish were excluded by the grate regardless of color or gear configuration. There were no observed differences in the behavior of spiny dogfish between gear configurations or grate colors.

Analyses of the Hawaiian pelagic longline fishery were conducted to determine what factors, including hook type (J or circle) and location (sea mount v open ocean), have impacted the catch of both target and bycatch species.   Standardized catch rates for all tuna species as well as for blue and oceanic whitetip sharks were significantly higher when the wider circle hooks were used.  However, shortbill spearfish and striped marlin catch were significantly lower when circle hooks were used.  No differences in catch rates between the two hook types were seen for bigeye thresher sharks or swordfish.  The average swordfish lengths were significantly larger when circle hooks were used, while average lengths for bigeye and skipjack tunas were significantly smaller.  There was no difference in the average length between the two hooks types for yellowfin or albacore tunas, spearfish or marlins. In addition, the change from J hooks to circle was likely a factor in decling sea turtle bycatch rates. 

Experiments were conducted aboard Korean pelagic longline vessels to determine if there were differences in the catch rates of target (tuna and billfish) and bycatch (sharks and other bony fish) species between 3 types of hooks; 4.0 traditional tuna hook (J-4), size 15 circle hook (C15) and size 18 circle hook (C18).  Within the target group significant differences between catch rates were only found between the J-4 and C18 hooks.  In the bycatch species group, significant differences were found between J4 and C15 and between J4 and C18.  Overall, the large circle hook (C18) had the lowest catch rates for tunas and other fish, while small circle hooks (C15) had the lowest catch rates for billfish and sharks.  Any differences in the length of fish caught by the individual hooks were minimal.