Surface Trawl | U.S. Fish & Wildlife Service

Surface Trawl

Description

Surface trawl example

Surface trawls typically are either Otter trawls or Frame trawls. Frame trawls, particularly Push trawls, are described in detail in the Push Trawl module. Thus, this module will concentrate on Otter trawls. Otter trawls used for surface and near-surface sampling have additional floats that keeps the net near the surface. This surface trawl can be stern trawled by one boat or bow trawled in tandem by two boats.

For background information on trawls, including surface trawls, see Introduction to Trawls module.

Habitat deployed	Lakes, Mid- to large rivers, flooded tributaries. Deep or shallow water.
Target species	small to medium bodied fishes and size classes- gar (Lepiosteidae), white bass (Morone chrysops), silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon idella), shad (Clupeidae), buffalo (Ictiobus spp.), carpsucker (Carpiodes spp.), minnows and shiners (Cyprinidae), Suckers (Catostomidae)

Overview and Concepts of Surface Trawls

Surface trawl intro and concepts

Surface Trawl Intro and Concepts

VIDEO LINK: https://youtu.be/fgV6HHuhULA

Surface Otter Trawl Anatomy

A surface otter trawl dorsal view.

A surface otter trawl dorsal view.

Fyke/ATF installed in a trawl.

A surface trawl on deck being readied for deployment. The major parts are labeled.

A surface trawl closeup

A surface trawl closeup. Netting material is Dyneema. Note the increased number of floats on the Headrope.

A surface trawl Otter board being deployed.

The surface trawl is being deployed. Note that the trawl is floating and the attachment of the Warp (or towing rope) and the Sweeps to the Otter board.

Introduction to Surface trawls

Two Surface Trawl Designs

Two Surface Trawl Designs

VIDEO LINK: https://youtu.be/Qq2EWZc6CoU

Netting materials include Dyneema (which floats and is highly tear resistant)
Otter boards float
The headrope has more floats than does a benthic Otter trawl headrope
The footrope has less weight than a benthic Otter trawl
One of the trawls illustrated has Wings

For additional information on net design, Otter boards, cod end function, fykes, and tying, lines, rigging, maintenance, storage, and some technical aspects, see Introduction to Trawls module.

Field Methods

Preparation and Rigging

Readying surface trawl for sampling

Readying surface trawl for sampling. The two Warps (tow lines) are large diameter nylon line. Warps are stored on reels.

One of the Otter boards positioned to be tied to the Warps and trawl Sweeps

One of the Otter boards positioned to be tied to the Warps and trawl Sweeps.

The sweeps on each end of the trawl are being readied to attach to the Otter boards.

The sweeps on each end of the trawl are being readied to attach to the Otter boards. Note the large diameter Warp in the foreground.

Trawl Sweeps are being attached to the Otter Boards

Trawl Sweeps are being attached to the Otter Boards.

Closeup of image immediately above showing Sweep attachment to the Otter Board.

Closeup of image immediately above showing Sweep attachment to the Otter Board.

A shackle used to tie the Warp or towing line to an Otter board.

A shackle used to tie the Warp or towing line to an Otter board.

A Warp is tied to an Otter board with a shackle.

A Warp is tied to an Otter board with a shackle.

Surface Trawl Stern Trawling 1 Boat

Surface Trawl Stern Trawling 1 Boat

VIDEO LINK: https://youtu.be/W8VPzoG22EA

The buoy is deployed initially off the stern

The buoy is deployed initially off the stern

The cod end follows overboard.

The cod end follows overboard.

The cod end and rear half of the trawl body is tossed overboard.

The cod end and rear half of the trawl body is tossed overboard.

The trawl is being played out as the boat maneuvers in a crescent path.

The trawl is being played out as the boat maneuvers in a crescent path.

The trawl mouth is out, and the Otter boards follow.

The trawl mouth is out, and the Otter boards follow.

The trawl is deployed, and sampling begins

The trawl is deployed, and sampling begins. Warps are attached about ¾ of waterline up from the stern. Stern trawling.

The trawl is sampling a transect

The trawl is sampling a transect. The floats are visible on the water surface and a warp is attached to each side.

The boat is moving in crescent patterns to minimize prop wash into the trawl.

The boat is moving in crescent patterns to minimize prop wash into the trawl.

The sampling run has been completed and the crew is pulling in the Warps to retrieve the net.

The sampling run has been completed and the crew is pulling in the Warps to retrieve the net.

The trawl is coming near the boat

The trawl is coming near the boat. An Otter board is nearly to the hull for retrieval.

The Otter boards are retrieved and the trawl body and cod end is being pulled onto the deck.

The Otter boards are retrieved and the trawl body and cod end is being pulled onto the deck.

The trawl and boards have been fully retrieved and the cod is being untied to process the catch.

The trawl and boards have been fully retrieved and the cod is being untied to process the catch.

Surface Trawl Bow Trawling 2 Boats

Surface Trawl Bow Trawling 2 Boats

VIDEO LINK: https://youtu.be/2YvKX_AALgM

The bow surface trawl is being deployed

The bow surface trawl is being deployed. The Warp to the Otter board on the left is secured to the second vessel. The Otter board warp attached to the right side boat in view is out of sight further on the right. The trawl and buoy are visible ahead of the bow.

The left-hand Otter board is being deployed from the second vessel.

The left-hand Otter board is being deployed from the second vessel.

The bow trawl is fully deployed

The bow trawl is fully deployed. A warp is visible on the right. The boats run in reverse with the current.

Left side vessel is bow trawling

Left side vessel is bow trawling. The Warp can be seen extending off to the right (upstream).

Left side crew is retrieving their Otter board at the end of the sampling run.

Left side crew is retrieving their Otter board at the end of the sampling run.

7. The trawl has been retrieved

The trawl has been retrieved. The cod end has the catch and is being emptied on the bow.

The catch is composed of numerous smaller-bodied individuals of several species

The catch is composed of numerous smaller-bodied individuals of several species