Hidden Predator: What a Dungeness Crab Taught Me About Bias

Most of us go about our lives without ever knowing that a chunk of reality is left on the cutting room floor of our mind. For the most part it is not a problem, until it becomes a pattern of engrained unconscious bias. And it is surprisingly easy to get caught in this trap.

Sea lions, with their booming presence and fluid grace, are impossible to miss. But most intertidal creatures, like the Dungeness crab, go largely unnoticed. Not because they're unimportant, but because they're not wolf eels, giant pacific octopus, or nudibranchs. Put simply, Dungeness crabs are not what most divers are looking for when they're in the water.

The divers I know plan trips around specific creatures or environments. This is understandable, diving is time consuming and can be expensive; and a goal-oriented approach makes sense when time at a location is limited. I was the same when I started diving, it seemed logical. But, slowly, I learned that the more I focussed on searching for a specific thing, the less I actually saw.

As humans, cognitive shortcuts like inattentional blindness help us bring order to a chaotic world. Its pitfall is that it can also lead us to think we have seen or experienced everything of value that there is about a situation, individual, or place. 

Learning this lead to some questions: was my bias about Dungeness crabs justified? Are they really a boring homogenous group of crustaceans? Or, while my attention has been focussed elsewhere, have I missed how interesting they really are?

I begin each dive suspended between two worlds: a known and life-giving atmosphere above, a mostly unknown and non-breathable fluid below. Face down at the surface with my back to the sun (or rain) I slow my breath and heartbeat, using the natural rhythm of the tide as my guide. In this suspended state, my presence in the water softens and my physical and mental experience of being immersed melts to a comfortable and welcoming embrace. The intention, for the most part, is to become driftwood. Fish, seals, crabs—they don’t like surprises, especially from the surface. Stillness buys their trust. Or at the very least, it renders me a benign observer.

On this particular dive in Shute Passage, BC, my softening ritual was disturbed by a flicker of movement in the sand. Shifting my vision to the corner of my eye while remaining perfectly still, I noticed a Dungeness crab crouched low, claws pulled tight to its body, its gaze locked on something above. I’m used to Dungeness crabs sitting passively, tucked into seaweed, or scuttling (seemingly) aimlessly along the seafloor. But this one was different. Its posture was one of action and intention. 

Not prepared for what was about to happen, I tried to slowly inch my camera toward my face, careful not to lose the trust I had gained.

Like most, I had always thought of the Dungeness crab as a basic scavenger—industrious, yet passive, relatively dull and unglamorous. But nature rarely conforms to our expectations. It exists beyond the tidy boundaries of what appeals to audiences in our books, glossy magazines, and TV shows. Entirely unaware of the limits I had placed on it (and the existential rabbit hole opening up in my mind) this Dungeness crab's eyes appeared to be tracing the movements of three pile perch, their silver bodies flashing in the dappled sunlight.

Dungeness crabs are opportunistic feeders known to eat bivalves, clams, small fish, shrimp, isopods, amphipods, and algae. They have poor eyesight and rely on their antennules—delicate, sensitive antennae—to detect the scent of potential prey. These antennules help the crab hunt by detecting changes in odour chemicals in the surrounding water. Unfortunately, Dungeness crabs are losing their ability to smell, and possibly survive. As levels of atmospheric carbon dioxide go up the pH of the ocean goes down leaving an acidity level that damages the Dungeness crab's olfactory system and impairs their ability detect important odours in the water.

Now, less than an arm’s length away, my Dungeness crab sat motionless; except for its antennules quietly combing for the scent of the perch. Time felt like it slowed. Getting my camera in position took an eternity.

Then, as if unleashed by a tightly wound spring, the Dungeness crab burst forward, claws tucked under its chin like a boxer’s fists. Six spiny legs worked in unison, churning up clouds of sediment as it charged toward the potential meal. The perch scattered in a flash, their survival instincts likely honed by countless similar escapes. And the hunt was over. But behind the lens I was riveted, my assumptions shattered by the crab’s skill and athleticism. Then came a wave of sadness, and a twinge of shame—why had I never paid more attention to Dungeness crabs? Clearly, this was no mere scavenger but a deliberate and very capable predator.

Growing up, I felt confined by expectations—both from society at large and from the well-meaning people around me. I loved science and the outdoors, I played soccer and loved fashion. I painted murals on my bedroom wall and dug for insects in the back garden. Alongside this ran a constant stream of comments about what a girl “should” be and how she “should” act. I didn't know it at the time, but those words created invisible boundaries that shaped how I saw myself and limited what I believed was possible. 

Over time, those assumptions became walls—ones I only began to dismantle in my 30s. Watching this Dungeness crab, it occurred to me how easily and subconsciously I had done to it as others had done to me. I had boxed it into a role that fit my narrow understanding of its nature. I assumed I knew what it was capable of despite it never having been the focus of my attention. 

This Dungeness crab’s surprising skill as a predator highlights the ease with which hidden cognitive processes like, inattentional blindness, can shape what we see and value in the world.

My experience in Shute Passage serves as a reminder that there is usually far more to someone—or something—than meets the eye, if you soften your gaze and take the time to really look. These moments of revelation are why I now dive without expectations, letting intuition and happenstance be my guide.