Day 12: Fishing Scars Across The Sea
ROLL on, thou deep and dark blue Ocean, roll!
Ten thousand fleets sweep over thee in vain;
Man marks the earth with ruin; his control
Stops with the shore; upon the watery plain
The wrecks are all thy deed, nor doth remain.
~ Lord Byron
Dear Sam,
For his own time (early 1800s), the claim that “[man’s] control stops with the shore” might not have been far off. Lord Byron, or “The Limping Devil” as family (and the more hurtful of his friends) called him, wrote his poems in the early days of the industrial revolution — when fishing boats could move only as fast as the prevailing winds, and fishermen brought in only what they could catch on their double-hooked hand-lines. Scallop fishing in the Northeast Atlantic was mostly inshore and not particularly developed [1].
I’ll gently gloss over the entire history of fishing in the Northeast to say that present-day fishing is a different scene. There are now ships with large working decks (1910), drum winches to mechanically haul gear (1920s), steel hulls (1940s), sonar and modern dredges (1950’s), and GPS (1970s) [2]. These developments allow fishermen to precisely and efficiently fish areas where they know scallops will likely be. Today, that means precision dredging — dragging steel frames with chain-linked mesh — along the sea floor.
What’s kind of incredible about HabCam is that we can see the marks left behind by dredging. HabCam has a side-scan sonar that acoustically images 50 meters of sea floor on either side of the vehicle. The images usually reveal nothing more than sandwaves and boulders and other natural forms, but occasionally you will see long, unnatural streaks that cut across the image –thin ribbons along the sea bottom that are unmistakably human-made.
It’s clear that these marks exist and are left behind from dredging, but what we don’t really know is how long these marks persist. Are these freshly laid tracks, or have they been there for years?
That’s one of the questions we’ve been trying to answer with HabCam. There’s a lot of debate over the persistence of these marks. In the past, some studies have concluded that dredge tracks disappear after a few hours, while others find evidence of dredge tracks months after the gear initially had passed through the area. What we see with HabCam suggests that dredges could be leaving impressions in the sea floor even longer than that.
What are the impacts of these marks? When we see man-made scars on land that cut across the landscape, whether they are in the form of roads or clear-cut strips of forest for electric poles and wires, we wonder about habitat fragmentation. Do these ribbons form barriers that plants and animals have a tough time crossing? Do they cut off important sources of food or shelter? Do they split up populations and communities, or impact animal behaviour?
Are those the same kinds of questions we should be asking about sea-floor dredge tracks?
The nature of marine life means habitat fragmentation is going to be different underwater than on land. Most water-dwellers at some stage in their life-cycle are free-swimming and mobile in the water column, and currents can distribute these little tiny plankton and larvae hundred and thousands of miles away from where they’re born. Even so, there are epifauna and infaunal creatures that are living on top of, or embedded in, the sea floor, some of which are totally immobile. How do dredge tracks impact their survivorship? How do the tracks affect the resiliency of the communities that rely heavily on epifauna as habitat?
Plenty of questions, few answers. That`s what makes this job so cool.
I sometimes harp on research — It can feel far away from the discipline of dreamy exploration and discovery that it might seem to be from the outside, but every now and again it does feel like you’re probing the natural world, learning new things, and when you’re lucky, discovering something new.
Love,
Mike
