I watched cormorants catch and release fish as they surfaced from repeated dives, letting large fish slip back into the water without any attempt to eat them. This was not a one-time event. I saw it happen again and again, often with different birds and in calm conditions.
The behavior stood out because it went against what I normally expect to see. These fish were not small. Some were large enough that keeping them would seem worth the effort. Yet the birds showed no sign of struggle, competition, or urgency. They simply let the fish go.
Why cormorants catch and release fish
Cormorants are visual hunters that respond quickly to movement underwater, using fast dives and pursuit techniques similar to those described in my post on cormorant fishing techniques and outlined in the Cornell Lab of Ornithology’s Double-crested Cormorant species profile. When a large fish moves within range, the bird reacts instinctively and grabs it. That initial strike does not always mean the fish will be eaten.
In many cases, the fish may be too large, too bony, or awkward to swallow efficiently. Cormorants do not tear prey apart. If a fish cannot be repositioned head-first and swallowed cleanly, releasing it may be the better choice.
Size, energy, and feeding efficiency
During colder months, energy balance matters. Chasing and handling a large fish takes effort, especially in cold water. If the payoff does not justify the cost, letting the fish go and targeting smaller prey can be more efficient.
I noticed that the fish being released were often larger than what I usually see cormorants consume. Smaller fish are easier to swallow and digest and allow the bird to resume hunting quickly.
Environmental factors that may influence release behavior
Cold water can also affect muscle control and swallowing. A fish that might be manageable in warmer conditions can become more difficult to handle when temperatures drop.
There is also the risk of interference. Holding a large fish at the surface makes a cormorant more visible and vulnerable. Nearby predators or aggressive birds can turn a successful catch into a liability. Releasing the fish removes that risk.
Observing behavior without forcing conclusions
I cannot say that one single factor explains every release I observed. Behavior in the wild is rarely driven by only one variable. What I can say is that this pattern was consistent, deliberate, and repeated across multiple birds.
Watching cormorants catch and release fish was a reminder that not every hunting attempt ends in a meal. Sometimes the smartest decision an animal makes is knowing when to let go.
These moments are easy to miss, but they are often the most instructive. Careful observation, without assumptions, is how patterns begin to make sense.
Fascinating.