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Fishing Terms Glossary Fishing, Sonar & GPS terms
By Barry Featheringill


Arch or Fish hook   The way a liquid crystal display sonar unit shows fish. If a fish is directly beneath you at some point while it was being displayed, it will show up as an arch-shaped signal on the screen

Acquisition Time. This is the time that a GPS receiver takes to determine a position from at least three satellites.

Backwater  A body of water (as an inlet or tributary) that is out of the main current of a larger body generally shallow.

Bar  A submerged or partly submerged bank (as of sand or mud) along a shore or in a river often obstructing navigation. Often found at the mouths of rivers.

Beam (Sonar Beam)  A sonar beam is the wide, cone-shaped projection of sound waves formed as sound travels underwater . See also Cone angle

Bottom Hardness.   Bottom hardness refers to the density (or composition) of the bottom. This is determined by interpretation of the sonar return. Hard bottom appears thin and black, softer bottom returns appear thicker and less black. Needs to be kept in mind that a sloping bottom may appear to be a softer bottom than it actually is 

Break   Drop off with structure on it. Mistakenly used to mean any sudden change in the bottom

Breakline   A distinct line that leads to an abrupt change in the bottom depth, composition or cover transition. This term can have several meanings. Sometimes is used as term for a drop-off/ledge or it may refer to part of a weed-line the fish are hanging on. Can also refer to where rock meets mud or gravel.

Carolina Rig   A Carolina rig separates the hook and worm from the lead with a leader. To tie one, you slip a lead on your line, follow it with a bead and then tie on a barrel swivel. A leader of varying length is tied to the swivel and a hook tied to the leader. Hook size varies with the size of the bait you plan to use.

Cavitation  This is the effect of air bubbles created as boat motor propeller rotates and move moves through the water.

Channel (Creek or River) In a reservoir the creek or river used before the lake was created. If you looked at a cross-section these would be the deepest areas. Topographical maps generally show creeks or rivers as hash-marked line. Frequently on large rivers there are channels and there is a drop-off that is associated with the edge of the channel created by flow of the river.

Chart Speed  This is a usually controllable feature on sonar units that sets the speed at which sonar information moves across the display screen. Faster setting shows sonar information for more pings and shows more detail, but information moves quickly across the screen. A slower setting permits viewing more sonar history but not as much detail.

Chartplotter. Navigation device that show Present Position on a Map, along with track, waypoints and routes.

Chunk Rock   Above average size natural rock or boulder.

Community Hole  Place where everybody and his brother/sister fishes.

Cone, Cone Angle   The theoretical shape taken by sonar signals as they disperse while traveling through water. Although thought of as being cone-shaped, the signals actually take more of  a suspended balloon shape.

Cover  This term is use in relation to weeds, trees, branches, buck brush, tules, rock, stickups and/or man-made objects like docks. Cover is often confused with structure the difference being cover is not geological in nature.  You can have cover on structure.

Current Seam  Where the current with high velocity meet up with a current with low velocity. Normally found in the same area as eddy’s. (Note: fish will hang around the area of low velocity and dart into area of high velocity when food source drifts past.)

Cut  Term for a small deep cove. In respect to a river it is where the water flow has undercut the bank on the outside of a bend in the river.

Definition   The ability of sonar unit to gather detail. How close sonar targets can be to each other and still be recognized as separate by the unit.

Dragging   Term referring to a retrieve, or actually, a lack of retrieve akin to drifting with a splitshot rig.

Drop- off   A sudden or fast change in depth frequently associated with a creek channel, point, flat or any combination of these. Contour lines on a topographical map will be close together.

Drop shot, Down shot   Two names used in connection with a finesse rig which places the sinker at the end of the line and the hook or hooks above it without loops.

Echo   A key to sonar operation. Sound emitted by the transducer which reflects off the bottom structure or fish is the first echo, which the sonar unit receives, interprets and displays on a screen

Eddy  Where the current in a river or tidal water rotates back in an upstream direction. Cause by something a point of land or large rock. The eddy’s can vary in size.

Edge  An abrupt change in the cover or structure .

Flat  Area of the bottom of a body of water that does not change more than a couple of feet in depth. A flat  will be represented by contour lines that are very far apart.

Funnel  Where water is funneled down to pass through a section of land such as between two islands or a manmade feature such as a culvert.

GPS  Global Positioning System is a satellite-based navigation system made up of a network of satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use.

Grayline   Is a technical feature in the sonar involved in screening interference which is designed to help display the relative density of objects on the screen. This is an innovation of Lowrance  electronics which shows as a shaded area below a black target line which can more clearly identify the difference between hard bottom and grass or fish not part of the bottom. It can also show a school of shad which are   tightly bunched  and possibly in a defensive mode due to predators on the feed.

Hump  An underwater island that normally rises gradually. Will be shown on topographical map as contour lines that create a circle or oval type shape.

Interference   Anything that causes sonar unit to display unwanted signals, or prevents desired signals from being displayed. This is sometimes called noise, is usually displayed as random dots. Most interference comes from electrical (sparks or radio waves) or cavitational (air bubbles washing across the face of transducer) sources.

Lay-down  Wood cover that lies horizontally and is almost parallel to the water surface.

Ledge  A severe drop-off. Commonly will be 70 to 90 degrees in angle and drops for more than 20 feet vertically. Topographical map will represent this with contour lines that are very close together.

Map Datum. A map datum refers to particular survey of the earth’s surface that is referenced when creating a chart (i.e. WGS84). This translates the coordinates from the sphere to a flat surface.

Mudline Line where stained or clear water meets dirty water. This is a condition that is normally caused by winds blowing waves into a muddy shoreline. Can also be the result of heavy boat traffic.

North, Magnetic. This is the reference point of a compass. Magnetic North uses the magnetic field of the earth to align pointer of compass.

North, True.  True North uses the earth’s axis as reference point for North. GPS units usually default to True North settings. (Note: GPS heading may vary from compass heading)

Oxbow.  Something (as a bend in a river) resembling an oxbow. Place where river has created a shallow low current body of water that will reconnect with river downstream.

Pea Gravel  Small rock that is no larger than ˝ inch in diameter. (Good area to check during the spawn for bass)

Pinnacle A very abrupt hump that generally rises from deep water is small in area on the top. On a topographical map will appear as a bunch of small circle on top of each other.

Pixels. The picture elements or small blocks that make up the image of  liquid crystal display (LCD). This is measure in vertical and horizontal numbers that indicates the quality of the resolution.

Point  A shoreline feature where the shoreline makes a turn out into the lake and cuts back on itself forming a peninsula. These can be large main lake features at the opening of a creek arm or as small as a boat. In natural lakes, a point may not be that obvious. It may only be discernable by weed growth outlining the point underwater. In this case, look at the weeds as if they were the shoreline. On a topographical map, the contour lines make a two-sided triangle (for lack of a better term).

Point Primary  Point that is on the main lake or the entrance to a large cove

Point Secondary Point that is inside a cove. These are smaller than a ‘primary point’ and are further away from the main lake.

Power Output. The amount of sound energy emitted into the water by sonar transmitter. It is measure either as RMS (Root mean Square) or P-T-P (Peak To Peak). Greater the power output the more signal penetration through weedlines and thermoclines and reach greater depths.

Pulse Width.  Is the length of time that sonar sound burst is transmitted into water. Shorter pulse widths provide better target separation, but do not travel to great depths.

Resolution  The ability of a sonar display to show the fine details.

Rip-Rap    Normally a man-made bank of rock. Found on the front of dams, points and front of shore line properties.

Route. A series of waypoints linked together is a specific order to show a path between two points and saved in GPS memory. Route can be used when travel between two or more locations as it is a more accurate and faster method than repeatedly selecting separate waypoints each time  you travel the same area.

Saddle  A narrow piece of land that extends out from the shoreline  (sometimes visible) and connects to an underwater island or hump. This will drop down before it meets the underwater island then it will again come up in depth . On a topographical map the contour lines will appear as underwater point extending from the shoreline. As lines extend from the shoreline lines on each side will get closer together and then start getting further apart as they come closer to the island or hump.

Second Return.  The ‘second return’ is a term that describes the appearance of a second sonar return below the major return at exactly twice the true depth. This second return is caused by the sonar signal bouncing off the bottom once and rebounding to the water surface and then traveling  back down to the bottom to be reflected again. These second returns are very common in shallow water or hard bottoms. The secondary return can be a guide to set the sensitivity when in shallow water.

Sensitivity/Gain   Control on sonar unit that determines how powerful a signal will be sent through the transducer. Hard bottom requires a little less sensitivity than do softer bottom.

Splitshotting  Basic plastic worm technique which began with a splitshot pinched on the line 18 to 30 inches above the hook. When drifted, reeled or “pulled” with a low rod angle, in order to move the bait along in a swimming mode. Has expanded to include any method using light line fishing that separates the sinker and hook, with or without a leader.

Sonar  An abbreviation derived from SOund, NAvigation , and Ranging.

Staging  Term relating to what bass are doing in the late winter/early spring in relation to Structure. Fish move up from their deep water winter living area and will “Stage” on primary points, channel bends, breaks, drop-offs and secondary points before the move to the shallows. These staging area can often be very concentrated on structure.

Standing Timber  This refers to the trees that are still standing in the water. Some trees may still be alive or trees that were left standing when the lake was created and have died.

Stick-ups  Small dead bushes which are sticking out of the water. Normally found near the shoreline or on shallow flats. These ‘stick-ups’ usually are no more than 4 feet tall.

Strolling    A drift-fishing method which actually relies on propulsion of the electric trolling motor. Its use is actually banned my most tournaments

Structure   The difference and especially the slight or subtle difference, in apportion of the bottom. ‘Structure’ can be ledge, river channel, break, hump, etc.

S-Turn   Place in river run where it creates a S form.

Sweep set   Hook setting technique used by splitshotters. Since small hooks and baits are taken easily by feeding bass, only a mild, sweeping motion of the rod is required when line is tight to the fish. This accomplished by bringing the rod across the body left or right.

Target   Anything denser than water that reflects enough sonar signals to be received and displayed by the sonar unit. Can bee weeds, boulders, trees and stumps, dense concentration of algae in the thermocline, baitfish, and fish.

Target Separation. This measurement of the minimum distance that fish-finder needs to be able to recognize very close objects as distinct targets.

Thermocline. Water layers of different temperatures that create sonar reflections due to the density of the differing water temperatures. Thermocline will appear as a continuous band across the sonar display above the bottom contour

Tide High  The time in which the tide is the highest.

Tide Low  The time when the tide is the lowest.

Tide Outgoing  The time in which the tide is going out.

Tide Slack The time in which tidal movement is at it’s lowest. This happens four times a day at each high and low tide

Topo map  Abbreviated term for topographical map that is the best tool available to catalog and view the arrangement of things on the Earth's surface. In referring to a lake it shows various depths.

Track. The series of points that defines where you have traveled in the past on GPS are called ‘Tracks.. Tracks are saved at regular time intervals. Tracks are helpful to see hwere you have been and to be able to get back to where you started.

Transducer   Sonar component that converts electrical impulses from transmitter into sound waves, sends them into the water, receives sound waves and converts them back into electrical impulses, and feeds them back to the sonar unit.

Transition zone  Change from one type of structure to another.

WAAS. This stands for Wide Area Augmentation System. WAAS is a complimentary technology to GPS that provides enhanced accuracy through correction signals broadcast from Federal Aviation Administration satellites. With this signal the accuracy of GPS is improved.

Water Brackish  Where tow different types of water mix. Where ocean or sea water meets freshwater.

Water Dirty  Water that has visibility of less than 6 inches. Frequently, green or muddy.

Water Clear  Water where the visibility is greater than 10 feet.

Water Stained  Water that has a brownish or greenish color with limited visibility

Water Swill  The heaviest, nastiest, weedy area in a body of water

Weed-break  Area of a weedbed where the weeds meet open water or one type of weed meets with another type of weed.

Weed Mat  Vegetation growing in the water that creates an almost solid formation on the top of water. This frequently will hold fish.

Vegetation- emergent  Aquatic vegetation that comes to the top of the water’s surface and is clearly visible.

Vegetation- Pre-emergent  Aquatic vegetation that does not come up to the water surface

Y  A creek channel intersection.