DMR Rope Study Reveals Options for Weak Rope

The Atlantic Large Whale Take Reduction Team (TRT) met in April 2019 and recommended new regulatory measures for the lobster fishery in the Northeast. The National Marine Fisheries Service (NMFS) set a target to reduce the risk of entanglement to North Atlantic right whales by 60 percent. While the State of Maine has recently challenged the 60% goal and is currently assessing its own risk reduction target, each state or lobster management area is working to define regional strategies to reduce the risk of entanglement to right whales in their area. The Maine Department of Marine Resources (DMR) staff is currently gathering information on what can be accomplished through meetings with the lobster industry. Potential measures could include a combination of trawl minimums by distance from shore, trap reductions, and the use of weaker rope on all or a portion of vertical lines.

Rope tests
Tests of more than 200 ropes document the reduction in breaking strength from knots and splices. DMR photo.

DMR recognized that data on the diversity of gear and vertical line configurations in the fleet were missing in the TRT management discussions, and applied for funding through the Section 6 Species Recovery Grants to States program. The project aimed to develop a baseline of information by region and relative to gear’s use by distance from shore. Awarded in the summer of 2018, the project includes three parts: a gear survey, testing the functional breaking strength of vertical lines in use in the fishery, and understanding the strain vertical lines are under when hauling under various conditions. The survey was conducted in August 2018 through January 2019 in collaboration with Maine Lobstermen’s Association, Massachusetts Lobstermen’s Association, the Atlantic Offshore Lobstermen’s Association, the University of Maine, New Hampshire Fish and Game, and the Rhode Island Department of Environmental Management.

In total, the survey had 647 responses from Maine, 139 responses from Massachusetts, 57 responses from New Hampshire, 13 responses from Rhode Island, and 11 responses from offshore fishermen. The survey was available through an online portal on the DMR website. In Maine, Massachusetts and Area 3, the survey was also administered by phone. Within Maine, the responses were distributed across Zones A through G, Zone A, the largest zone, had the lowest response rate, and Zone D, the third largest zone, had the highest response rate.The survey collected data on the area fished, traps per trawl, and vertical line configuration. Preliminary findings support what was generally understood about the Maine lobster fishery — gear configurations and rope diameter used in vertical lines increase as gear is fished further from shore.

In addition to the gear survey, project partners collected used vertical line samples in order to test the breaking strength of rope. Understanding the breaking strength of vertical lines already in use helps inform regulations that outline weak rope requirements. As of June 2019, 215 breaking strength tests have been completed. The manufacturers and types of rope varied, and the average age of the rope ranged from 3 to 6 seasons. Preliminary findings show the smaller the rope diameter, the lower the breaking strength regardless of rope type, and that the presence of knots and splices significantly lower the breaking strength of the rope. Survey results show that 96% of ropes currently fished are modified with a knot, splice, or both. Forty-eight percent have both knots and splices. Given the lower breaking strengths of ropes with knots and splices, most of the rope being fished has a functional breaking strength that is less than the manufacturers’ breaking strength. This suggests that using certain types of knots and splices that are already being fished will help meet weak rope requirements. Preliminary results demonstrate that rope weakens as it it fished. Data show a significant, negative relationship between the breaking strength of rope and number of seasons fished.

DMR tested the relationship between rope breaking strength, diameter, rope modifications, and number of seasons fished. Results show that both diameter, rope modifications, and number of seasons fished significantly impact breaking strength. Rope diameter and modifications have the strongest influence on breaking strength followed by the number of seasons fished. A major concern with proposed weak rope requirements is the potential impact to the safety of fishing operations. The project team documented the strain vertical lines are under while being hauled in varying fishing conditions and gear configurations. Eleven fishermen have participated to date. Based on the initial research findings, vertical line strain is most impacted by the combination of traps per trawl and the depth in which the gear is set.

DMR, FB Environmental Associates (FBE), and the University of Maine are continuing to collect load cell data to understand where and how weaker ropes can be fished safely. Additionally, testing is being conducted to modify existing gear to achieve a weak rope equivalent for consideration as regulations are developed. Lastly, project partners will talk with fishermen to improve understanding of how any trawling up requirements will affect the strain that vertical lines are under. These data will provide insight as the lobster industry determines best fishing practices, and alternative fishing set ups to meet the new regulations.