Developing a Salmon Excluder for the Pollock Fishery -A cooperative research project- NMFS Race Division and the North Pacific Fisheries Research Foundation John Gruver United Catcher Boats Association North Pacific Fishery Research Foundation
Original Objectives Develop a bycatch reduction device (BRD) that relied on behavior for escapement Minimal pollock loss Utilize soft materials that could be repeatedly rolled onto a net reel with no change in performance A design easily embraced by fishermen and would not significantly alter normal fishing activities
The Concept - Selectivity of salmon excluders is based entirely on behavioral differences between pollock and salmon Fish Behavior: Salmon can make forward progress in a pollock net and will react to both changes in water flow (rock in a stream) and oncoming pollock. Pollock cannot swim forward (much) and do not react as much to eddies and lees. We know this from 2002 Didson sonar work inside nets (NPRB project)
Diagrams of some of the excluder designs developed and tested 2003-2013
Our Development Process 3367 Funnel in Swan Intermeadiate 2004 B Season EFP Trials Aboard the F/V Destination 38.00" Trawl Intermediate is 168 clean meshes across per panel by 4 panels at the forward installation point. 25 md 4" diamond mesh buffer strip Top Escapement Holes extend 30 inches past aft end of tunnel. 83.35" 18' (144 bars) of 1.5" per bar 240 ply polyester square mesh knotless netting Side Escapement Holes extend 6 inches past aft end of tunnel. Brainstorming sessions with fishermen, gear designers, NMFS scientists Aft view, looking forward Circumference of Funnel = 92% of Trawl Circumference Side View Develop detailed drawings of a design(s) for testing Use a flume tank to test designs. Memorial University, St. Johns, Newfoundland
Our Development Process And bring along some help because it takes a lot more trials, model reconstruction, and more work one would expect!
Our Development Process Build a full size excluder for field testing
OKAY! Quit Wishin, Go Fishin Field work conducted under an EFP Permit provides pollock and salmon amounts outside the AFA and CDQ TACs and bycatch caps
Wait! There s one more little thing. How do you reliably test for escapement; both salmon and pollock? Answer: Design a recapture net that: 1. Will not have a significant impact on the trawl 2. Will not impede escaping salmon and pollock 3. Is easily handled by the deck crew 4. Durable enough to survive the field work and deck crew And, by the way, there is no existing design to reference..
After a developing an initial design, additional tank work, and a few re-designs, we had a recapture net!
One more detail. How will you know if the full sized excluder and re-capture net will take the shapes developed at the flume tank? Answer: Cameras, sonar, and sea trials
Original Concept - Funnel Style Excluder 3367 Funnel in Swan Intermeadiate 2004 B Season EFP Trials Aboard the F/V Destination 38.00" Trawl Intermediate is 168 clean meshes across per panel by 4 panels at the forward installation point. 25 md 4" diamond mesh buffer strip Top Escapement Holes extend 30 inches past aft end of tunnel. 83.35" 18' (144 bars) of 1.5" per bar 240 ply polyester square mesh knotless netting Side Escapement Holes extend 6 inches past aft end of tunnel. Aft view, looking forward Circumference of Funnel = 92% of Trawl Circumference Side View
Funnel Style Salmon Excluder Flume tank model; Memorial University; St. Johns, Newfoundland
Original Concept Variation - Tunnel Style Excluder 3367 (modified) Tunel in Swan Intermeadiate 25 md diamond mesh buffer strip 18' (144 bars) of 1.5" per bar 240 ply polyester square mesh knotless netting 90.28" 98.78" Aft view, looking forward 6 mesh wide diamond mesh joiner strip Side View
Tunnel Style Salmon Excluder Flume tank model; Memorial University; St. Johns, Newfoundland
Tunnel salmon excluder results from EFP tests and follow up testing by fleet Results Salmon escapement ~ 13% (right out of the blocks!) Average Pollock escapement ~3%, a lot more on some tows (why?) Trials by fishermen discovered problems with clogging, jellyfish and high catch rates pollock fishing
BUT.. Funnel and Tunnel excluder s reliance on square mesh to achieve the desired shape had a big downside. EFP Trials and later trials by fishermen showed problems with pollock becoming pinned at entrance to excluder In the extreme, loss of trawl door spread and damage to net Imagine a 3000 hp vessel using a tunnel design excluder losing door spread Square mesh doesn t have the dynamic qualities of diamond netting.
Post Funnel and Tunnel Concept - The Flapper Excluder Version 1 a.k.a. Don t mess with the flow era. Flapper Concept Originated from video observations of salmon swimming forward during turnarounds and haulback (slowdowns). Panel blocking access to escapement hole does nothing to restrict flow of fish and functions by allowing escapement during slowdowns (panel drops down) Vessel slows down to ½ towing speed to open the access to escapement hole Flapper valve panel 168 Clean Flapper valve panel 168 Clean 4" Section 100 md 3 pt. / 2 bar 4" Section 100 md 3 pt. / 2 bar 4" Section 100 md 3 pts. / 2 bar Escapement Holes 66 Clean 4" Section 100 md 7 pts. / 2 bars Flapper Style Excluder Position While Towing - note that Flapper Panel held against the inside walls of the trawl intermeadiate by water flow. 116 Clean 4" Section 100 md 3 pts. / 2 bar Escapement Holes 66 Clean 4" Section 100 md 7 pts. / 2 bars Packer Tube Packer Tube Flapper Style Excluder Position During Haulback Slowdown - note that Flapper Panel has dropped due to the reduced water flow and has collapsed forming a "ramp" that guides salmon swimming forward up and out the escapement holes.
Results from V1 Flapper excluder testing and information from subsequent usage in fishery Chinook escapement averaged 12%-20% depending on fishing styles of boats (periodic turns versus only one slowdown); pollock loss ~1% Practical effects on pollock fishing (at first) thought to be limited to having to do periodic slowdowns Gear must be hauled during periodic slowdowns, bringing it up higher into the water column Real downside of this approach was actually that net spends more time in part of water column with higher salmon catch rates. Tradeoff of escapement rate versus canceled out by higher salmon catch rates not obvious at first
Back to the Drawing Board - and the Tank Flapper Version 2 Combination of Tunnel and Flapper without the Square Mesh Netting! Recapture Net Recapture Codend Excluder Escape Port Last Tapered Section of Trawl Excluder Tube Flapper Panel Packing Tube / Codend
The V2 Flapper Concept V2 Flapper was originally designed to fit into the last tapered section of the trawl but due to water flow issues it was moved directly aft into a straight tube section V2 Flapper panel weighted so that it is half way down at towing speed, also floated hood creates room for escapement A hood was added to increase escape area V2 flapper panel pushes up if large mass of pollock is coming down the net Hood Excluder Escape Port Last Tapered Section of Trawl Weighted Area Flapper Panel Packing Tube or Codend
V2 Flapper Excluder Flume tank model; Memorial University: St. Johns, Newfoundland
Results from Flapper excluder testing 2012 and information from subsequent usage in fishery V2 Flapper reduces Chinook rates by 25%-34%; pollock loss <1% Chum salmon escapement minimal (chum behavior different?) Workable Chinook excluder which became widely adopted into pollock fishery in 2012 and 2013 Tuning of weight on flapper to vessel HP necessary for correct function
V2 Flapper Excluder is an effective excluder but.. Hard to tune weighting to get panel to stay in desired (half way down) position during towing Tuning requires lots of vessel-specific video work and adjustments due to differences in vessel horsepower and net type Chinook escapement rates good (25-34%) but steps taken to increase that rate did not show any improvement (e.g. artificial adding light) Flapper V2 not effective for chum salmon bycatch reduction (because top escapement for chums not workable?) Two different excluders needed?
Back to the Drawing Board, and the Tank, AGAIN! The Over/Under Excluder a new design based on an old concept. Float Rope Weight Upper Hood Lower Hood Weight Float Rope
Over/Under Excluder Flume tank model; Memorial University: St. Johns, Newfoundland
Performance Results in 2012 and 2013 Trials Chinook escapement rates (GOA) 40% Chum salmon escapement rates Bering Sea 20% Pollock loss Bering Sea <0.1% GOA pollock escape rate ~3% but not problematic No signs of negative effects on nets (so far) Potentially easier to tune to specifics of vessels and nets
Thanks to: NMFS Race Division Craig Rose & Carwyn Hammond North Pacific Fisheries Research Foundation John Gauvin Flume tank crew at Memorial University Our EFP captains and crews Field coordinators Katy McGauley, Joe Collins, Ken Hansen And: Swan Net USA, Dantrawl, NET Systems, Hampidjan USA, LFS Trawl