Search The Database

Summary:

Several versions of a terrapin excluder design were tested on crab traps to determine how effective they were in reducing terrapin bycatch and what the effect on catch rates of targeted crabs was. All tests consisted of modified and unmodified traps being set in an alternate fashion. A wire bar placed across the opening of the traps was unsuccessful in reducing terrapin bycatch. A second design, which was a rectangular frame (5x10 cm) was successful. Standard traps caught 13 out of 15 terrapins during 1992 and 46 out of 51 during 1995, with the remainder of terrapins being caught by traps modified with the frame. Additional testing of the rectangular frame size, determined the 4.5x10 cm frame reduced terrapin bycatch the most (22 terrapins caught in unmodified vs. none in modified traps). Additionally, crab catch rates were 9% higher in the modified traps (4.5x10 cm) compared to the unmodified traps and crabs were of similar sizes in the two traps. In comparison, crab catch rates were 11% higher than in the unmodified traps when the 5x10 cm excluder design was used in 1994 (multiple sites) and 49% higher in 1995 (single site).

Summary:

In northern hemisphere trawl fisheries, little is known about the extent of cable strike seabird mortality or techniques to mitigate it. We compared the rate of heavy seabird strikes by third-wire cables and warps, using three mitigation measures compared to a control of no mitigation. Experiments were conducted aboard two catcher-processor vessels targeting walleye pollock (Theragra chalcogramma) in the eastern Bering Sea: one that rendered offal into fish meal and fish oil (Vessel R) and one that minced offal prior to discharge (Vessel M). More birds attended Vessel M, but the rate of seabird cable strikes was higher on Vessel R due to the greater aerial extent of its cables. Streamer lines significantly reduced heavy seabird strikes by both cable types regardless of discharge characteristics. Reducing the aerial extent of third wires also reduced third-wire strike rates, but this method was less effective than streamer lines. Warp booms designed to divert seabirds from warps failed to reduce seabird warp strikes, but this technique could be improved. These results show for the first time that seabird strikes with modern third-wire trawl sonar cable systems can be reduced through mitigation or gear modification and that warp strikes can be mitigated with techniques similar to those found successful in southern hemisphere fisheries. 

Summary: Leaders in offshore, deep water pound nets in the Virginia portion of Chesapeake Bay incidentally take protected sea turtles. To reduce this take, federal resource managers restricted the use of traditional leaders during periods of peak sea turtle strandings. In response to these restrictions, a modified leader was developed. Testing of the new design in 2004 and 2005 indicated that the modified leader significantly reduced sea turtle interactions. Finfish were also sampled from the nets in the study, with results showing no difference in catch weights of four finfish species and the experimental leader harvesting significantly more of a fifth species than the control.

Summary:

Circle hooks and J-style hooks were tested on pelagic longline vessels (US Atlantic) to determine if the use of circle hooks reduced bycatch mortality while maintaining target species catch rates.  0⁰ offset circle hooks were determined to increase the survival of bycatch species at haulback while having little impact on target species catches.  Specifically, J-style hooks had a significantly higher total overall catch rate.  Catch rates of yellowfin tuna in the fall were higher (significantly) for circle hooks and pelagic stingrays (spring caught) were the only species that had a significantly higher catch rate on J-style hooks. Circle hooks caught four times as many yellowfin tuna in the mouth compared to J-style hooks.  Yellowfin tuna and dolphinfish caught on circle hooks in the fall and spring respectively, were significantly larger than those caught on J-style hooks.  Survival rates of dolphinfish and escolar were statistically higher at haulback when circle hooks were used in the fall and spring respectively. 

Summary:

Groundfish trawl nets were fitted with a rigid grate in an effort to exclude Pacific halibut while retaining the target species.  The grate was placed in front of the trawl codend, which allowed the target species to pass through while Pacific halibut escape.  Escape rates of Pacific halibut were 94% when the grate was used while 72%, 67% and 79% of Dover sole, rex sole and flathead sole were retained respectively.  These values were significantly different except for flathead sole.  The only size class of halibut that passed through the gate in large proportions were less than 3 kg.

Summary:

Two experiments (1. stow net set from small dory (4 m) and 2. a trawler was set in front of the mouth of the net to accelerate the flow of water) were conducted comparing three lengths of square-mesh codends (3, 2 and 1-m) made from 27-mm mesh with a conventional 34-mm diamond mesh design.  Overall, the square-mesh codend incrementally (from 1 to 3-m) selected the target school prawns across narrower selection ranges and for the most part selected prawns that had a larger size at 50% retention.  Fewer bycatch fish were also retained when the square-mesh codend was used.  In addition, there were differences between the two experiments and the impact of catch weight on the selectivity of school prawns.   The 2 and 3-m square-mesh codends retained proportionately more school prawns by both weight and number during the first experiment but less than the diamond and 1-m square-mesh designs during experiment 2, reflecting that more small school prawns were caught during the second experiment.

Summary:

Two experiments (1. stow net set from small dory (4 m) and 2. a trawler was set in front of the mouth of the net to accelerate the flow of water) were conducted comparing three lengths of square-mesh codends (3, 2 and 1-m) made from 27-mm mesh with a conventional 34-mm diamond mesh design.  Overall, the square-mesh codend incrementally (from 1 to 3-m) selected the target school prawns across narrower selection ranges and for the most part selected prawns that had a larger size at 50% retention.  Fewer bycatch fish were also retained when the square-mesh codend was used.  In addition, there were differences between the two experiments and the impact of catch weight on the selectivity of school prawns.   The 2 and 3-m square-mesh codends retained proportionately more school prawns by both weight and number during the first experiment but less than the diamond and 1-m square-mesh designs during experiment 2, reflecting that more small school prawns were caught during the second experiment.

Summary:

Fishery observer data was used to estimate interactions between hard shelled sea turtles and dredge gear in the US Mid Atlantic before and after the implementation of chain mats.  A total of 288 annual interactions between hard shelled sea turtles and dredge gear were estimated to have occurred between 2001 and 2006, while 20 annual interactions occurred between 2006 and 2008, after chain mats were introduced into the fishery.  If chain mats had not been used during this second time period (2006-2008), it was estimated that 125 interactions would have occurred. Therefore, the introduction of chain mats reduced the rate of interactions between hard shelled sea turtles and dredge gear.

Summary:

A double codend was compared to the standard codend in the Clarence River penaeid trawl fishery in southeastern Australia, to determine its effects on total catch, retained and discarded school prawns, sizes of discarded prawns, discarded fish and immediate and short-term mortalities of discarded juvenile school prawns.  The only significant difference between gear types was the immediate and short-term discard mortalities, which were reduced by 13.8% and 17.1% respectively when the double codend was used.  Additional analysis also showed that mortalities of school prawns increased with the quantity of jellyfish. 

Summary:

Two new types of turtle excluder devices were tested in the Northern Australia prawn fishery, to determine their ability to exclude sea turtles from capture.  The first design, JT 1, had a large escape opening across the width of the top panel ahead of the codend, with the forward edge of the escape weighted down and the aft edge buoyed.  This design did not prevent the capture of sea turtles or other large sharks and rays but caught 6.6% more tiger prawns and 10.5% more endeavour prawns than the standard net.  The second design, JT 2, had two large holes (200 cm long x 30 meshes deep) cut into the side panels of the net ahead of the codend with the aft edge weighted and two standard (40 mesh wide) bigeye escape panels were added between the two side openings.  The second design also did not prevent the capture of sea turtles or other large sharks and rays but did reduce finfish bycatch by 5% and caught 5.2% more tiger prawns and 6.9% more endeavour prawns compared to standard nets.