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GEARNET: Improving gillnet selectivity

As a GEARNET pilot project, this study was proposed by NEFS 11, and in particular Capt. Jason Driscoll (F/V Karen Lyn). The project was coordinated by Ken La Valley (University of New Hampshire / Seagrant) in collaboration with Shelly Tallack (GMRI). GEARNET is funded by NOAA Fisheries Cooperative Research Program. 

Research question 

Under the ‘catch shares’ and sector management system that now regulates the Northeast groundfish fishery, fishermen will benefit more than ever by improving the selectivity and thus, efficiency of their fishing operations. For example, for a number of fishermen in NEFS 11, to fish within the species allocations that they have, their goal is to maximise their catch of high-allocation species (e.g. pollock) while minimizing their catch of low-allocation species (e.g. cod). The specific objectives of this study are: 

  • Evaluate differences in catch composition (i.e. selectivity) between gillnets placed 2, 4 and 6 feet off the sea floor, compared to a control net; and 
  • Use this information to identify potential gillnet designs that may reduce cod and other non-target groundfish landings while targeting pollock.

Study design and approach 

The study took place between August and November of 2011, on board three commercial gillnet vessels based out of New Hampshire. 

  • All experimental strings were set in the same area, and soaked for 12 or 24 hours. 
  • All net panels were 100 feet long and 6 1/2” mesh (Table 1). 
  • A randomized block design was used to place control and experimental panels within a string (Table 2)
  • This design was used to minimize between-panel and positional effects on the data.

 


Table 1: The randomized block design for the placement of experimental panels within a string during field trials.


Table 2: Experimental net configurations.

The control panel was constructed of 6.5” diamond mesh, and was 25 meshes deep with each panel being 100 feet in length (Figure 2A). In contrast, each experimental panel was constructed of 6 1/2” mesh for the upper section of the panel, and 12” diamond mesh for the selectivity panel. The selectivity panel was constructed at 2 ft, 4 ft and 6 ft for the three different experimental designs (Figure 2B, Table 2).


Figure 2: The design of the Control (A) and Experimental (B) nets.