High tech “spot burning” courtesy of NOAA’s Bathymetric Data Viewer.
A fossilized head of a prehistoric fish embedded in bottom sediment? The top right insert on Chart 1 at the top of this page is actually the weathered surface of the spoils mound in the disposal area west of Cape May Point near Buoy R “10”. This manmade feature, as sculptured by Mother Nature, interacts with currents like a natural shoal.
The screenshot is a Bathymetric Attributed Grid (BAG) Color Shaded Relief image displayed by the online Bathymetric Data Viewer (BDV). This is a National Oceanic and Atmospheric Administration (NOAA) application. A 17-foot obstruction, File Number 15208 in the Coast Survey’s Automated Wreck and Obstruction Information System (AWOIS), was recorded as the least depth within the disposal area during a hydrographic survey. The date of the most recent hydrographic survey where there is “BAG” coverage is the date of the displayed bathymetry, which in this case is 2013.
Obstructions were marked on government raster nautical charts (RNC) as “Obstn”, usually inside of a dashed circle, or as in this case, a free form shape. Sometimes there wasn’t a charted circle, for example, for wrecks that aren’t considered a danger to navigation. The nomenclature “Wk” was all that’s charted. In such cases, the feature is under a sounding number.
Some wrecks and prominent bottom features and formations were not specifically charted or removed from charts because they weren’t considered dangers to navigation. Now, with Electronic Navigation Charts (ENC), sometimes there is a circle without nomenclature except for a sounding number. Thus, there are less charted cues than before. Fortunately, raster charts can still be viewed as a basemap using the NOAA ENC Viewer where ENC charts can be made transparent to enable viewing both charts integrated together.
Past & Present
The BDV NOAA chart layer was converted from RNC to ENC format in late 2021, but still gives us the opportunity to look through and under the chart at available sonar-like images. Using this capability where “BAG” imaging is available enables detection of bottom features otherwise missed. BAG imaging is like side-scan sonar without the sonar shadow. For the spoils mound, zooming in shows the mound’s rugged character. For BAG imaging, images in water deeper than 35 to 40 feet become grainy. Note that the brightness and contrast in the illustration were adjusted to highlight the feature for illustration purposes.
Nautical charts are prepared to support navigation. Bathymetric contour lines are widely spaced which helps keep the chart uncluttered. The reduction in displayed nomenclature on ENC Charts further reduces the clutter, but also takes away many of the raster charting cues that were so helpful for finding wrecks and obstructions. Bathymetric charts display contour lines in more graduations. This provides a more representative depiction of the bathymetry. However, the true character of the bottom still isn’t fully revealed. Features such as rock outcroppings and natural reefs aren’t apparent due to the smoothing effect of the contour lines.
By looking under the chart using the BDV and BAG images, we’re able to see uncharted features, such as the sediment waves shown by the lower right insert on Chart 1. They aren’t a danger to navigation and aren’t charted. BAG images, and to a lesser extent BDV Digital Elevation Models (DEM) Color Shaded Relief images of sounding data, enable us to find them.
Studying and setting waypoints for sub-features can help anglers target the spots that attract sportfish. Chart 2 for example provides another example of an uncharted natural features, and the configuration and character of fish haven deposits which are not charted if in conformance with reef minimum depth permit requirements. The middle left image in Chart 2 shows what presents as a deep bowl in a ragged edge with a rapid drop-off into deep water.
A feature like this is of interest because of the subsurface turbulence caused by interaction with currents. Baitfish swept in and upset by the turbulence become easier targets for predators like striped bass or summer flounder. The extended edge in this area is quite rugged, none of which is conveyed by the nautical chart. There are drop-offs, trenches, and possible outcroppings that create an interesting trolling lane.
Both “DEM” and “BAG” imaging provide resources for scouting conditions in fish havens. In the case of Fish Haven #7, there is full DEM coverage and partial BAG coverage. The right middle and bottom images on Chart 2 are BAG screenshots that provides a more detailed representation of some of the reef deposits and how currents have shaped the bottom around them.
Fish Havens
Where BAG imaging isn’t available, DEM “dimples” (little mounds) show masses on the bottom. The more pronounced the dimple, the larger the mass. For fish havens, the dimples can often be correlated with recorded positions of reef deployments. With some electronic trickery, reef program drawings can be made see through and laid over top of see-through raster nautical charts on top of DEM images. Where BAG coverage is available, it automatically displays on top of the DEM data layer (and under the see-through chart if clicked on) when using the BDV.
Fish haven charting practice blots out features therein and only show the minimum authorized depth except where there is a charted feature. Sometimes features are obscured by or under a sounding number or charted place name. When using the BDV, zoom in until the number or placename disappears, or click off the chart layer, as shown by Chart 3. There is an anomaly alongside the letter “A”. Although it’s very small, it demonstrates how chart nomenclature can obscure or hide features, and why looking under the chart helps find structure. This illustration shows a raster chart. However, the same principle applies for ENC Charts.
By zooming in on BAG images, uncharted features sometimes become visible that are not discernable when zoomed out. For example, the middle right insert on Chart 3 shows an uncharted feature with a shipwreck-like shape. It could simply be natural formation. However, the shape is intriguing.
A 104-foot wreck northeast of the Outer Wall provides an even more cogent example. This is the 90-foot fishing vessel Star Dust, AWOIS File Number 9935 at coordinates 38° 50.640N, 75° 04.512W, and shown on Chart 4. The wreck is in the middle of the zero on the raster chart and between a 3 and a 1 on the ENC Chart! This feature was found using the AWOIS Map Viewer, and then by looking at the BDV displays and National Ocean Service (NOS) Descriptive Reports (DR) which included the side-scan sonar image shown in the illustration (NOS DR H12065, 2013).
Much more impressive is the massive natural formation northwest of the wreck. There is a quick drop off to deep water, but the character of the feature and its fishing potential aren’t revealed by nautical chart sounding data. It has the appearance of a submerged headland with a ravine on the south side. This underwater point juts out into the current stream where channeling the flow could produce natural “bait chutes”. When conditions are right, predators can stage at the downstream end of the chow line. It took just minutes of armchair scouting the Bay Entrance to find this formation; but for the modern technology one could fish for years and never know what’s really there!
Log In For A Look
Where there is BAG image coverage, there will usually be a corresponding DR because the BAGs are derived from multibeam sonar data collected during hydrographic surveys. Checking DRs provides the date of the sonar data that the “BAG” image is displaying. Obviously, the older the image, the greater potential for changes to have occurred since the data were collected.
All of the DEM and BAG images used as illustrations here were screenshots from the BDV Color Shaded Relief data layers. Various commercial products also use the same data layer, often with different color palettes. Some include enhancements such as bathymetric contours with 1-foot intervals. My practice is to crosscheck BDV images with the Navionics boating app and its color shaded relief data layer (derived from NOAA BAG and DEM data) and sonar bathymetry contours. The coordinates I record are, insofar as practicable, taken from the Navionics display for consistency and because I use Navionics electronic charts with my boat’s electronics. My experience is that comparable products from other brands provide similar results.
Sometimes the bottom contours are displayed better by the commercial products than by NOAA data. One such location is Bombay Hook Point Shoal where using the described techniques can be practiced. Contours were much more evident when using the Navionics display of 1-foot contours and color shaded relief. The shoal ridgeline appears to be of geologic origin rather than depositional. The submerged point is only a foot or two below the surface. At its outer end, the bottom slopes downward and then drops quickly to about 25 feet of depth. There’s a small bowl or shallow ravine on either side of the outer end.
The configuration and location relatively close to the ship channel puts the submerged point in position to interact with tidal currents. What caught my eye was the potential for baitfish to be pulled into the bowl and then funneled around the end of the submerged point. This looks like a setup for striped bass to ambush bait on either side of the point when current is running. I didn’t find any site-specific fishing reports tagging this spot. But, it’s not too far from Ship John Shoal Light. So, if chunking bait or casting bucktails to the rocks there isn’t producing, consider running over to Buoy GC “1” to try jigging or trolling along the entire edge.
There’s a lot of useful information about structural features that can be discovered by manipulating BDV data layers and zoom levels. Drilling down into the data is a good off-season project for anglers wanting to improve their local knowledge about fishing conditions and to refine their fishing tactics.
