Methods of Capture

Ever wonder how researchers are able to safely capture a sea otter without it swimming away?  After many years, researchers have developed several methods for capturing sea otters.  The method used depends upon the circumstances. 

For example, in the event of an oil spill, dip netting may be the best choice as it is unsafe for divers to get in the water.  On the other hand, if a specific otter needs to be brought in for medical evaluation or to retrieve an instrument a diver operated Wilson trap paired with shore spotters is the most effective method for capture.  You can find more information about each of these techniques below and you can also go along on a dive and see how divers use the Wilson trap method in the video below.


Dip Netting

Dip netting requires the least amount of specialized equipment: fast, maneuverable boat; stout, long-handled dip net; an experienced boat driver and a strong person to handle the dip net. This method is best suited for capture of otters hauled out or young otters in open (no kelp) water. For water captures, the boat approaches the otter at high speed and then the driver throttles-back as a person on the bow scoops the otter into the net. Often, if the otter evades the first capture attempt, it will be very difficult to capture on subsequent attempts.

Tangle Net

Tangle nets are modified gill nets approximately 3-9m deep and 33-100m long that are set at the water surface in areas of open water or in channel within the kelp. The nets are set to entangle otters as they travel/swim into the net. A large number of otters may be captured, but this method is the least selective capture technique. To avoid injury to the captured otters, the nets must be continuously monitored and entangled otters removed quickly. Caution must also be taken to avoid incidental capture of other marine mammals in the area.

Wilson Trap

Diver operated Wilson trap is a method that is very effective for the capture of specifically selected otters. Experienced teams can often capture more than one otter at a time. Over the years there have been numerous equipment alterations or “upgrades” however the general technique has remained the same. The trap consists of a cone-shaped, aluminum frame which supports a net bag. The trap is attached to a diver propulsion vehicle (DPV). Divers using rebreathers (closed-circuit SCUBA that produces no bubbles) can operate the DPVs with traps to approach targeted otters from underwater without producing bubbles that would alert and spook the otters. Once divers maneuver their DPVs and traps into position under the targeted otter(s), the DPV is driven straight up at full speed to trap the otter(s) at the surface. A purse-string is used to close the net bag when the otter is in the trap.


Go diving with a diver as he captures a sea otter as part of a heath survey in California.