Oiled Sea Otter Capture Course

Capture Equipment and Techniques

Logistical Support

A capture program for sea otters requires specialized equipment (Appendix 6 Download PDF) and personnel knowledgeable about its operation. Key equipment for the logistical support of the program include state-of-the-art communications equipment, capture boats and support vessels, and aircraft.

(a)Communications. Communication between capture teams, transport vessels, and rehabilitation facilities is essential for a successful sea otter rescue program. During a capture operation, the communications equipment aboard each support vessel should provide reliable contact with emergency assistance, the rehabilitation center, other capture vessels, and aircraft. Marine band radios, single side band radios, hand-held radios, and cellular telephones vary in effectiveness, depending on the location of the capture operation, coastal geography, and shore-based relay equipment. Prior knowledge of the available frequencies for radio communications within the home range of sea otters will facilitate communications during a spill.

(b) Capture Boats and Support Vessels. The location of the oil spill will determine the most efficient way to capture sea otters. If the spill is close to a harbor or area with easy boat access, daily excursions with small capture boats are best. For spills not quickly accessible by small boats, the safest and most efficient way to capture sea otters is to deploy larger support vessels (i.e. 40 to 60-foot fishing boats) with one or two skiffs each. The total number of support boats will depend on the size of the spill, the number of otters at risk, and the coastal geography. During the Exxon Valdez oil spill (EVOS), twenty large support vessels were used. Support boats should have 240 square feet of deck space to store 20 large kennel cages, communications equipment compatible with those employed on other capture vessels, and U.S. Coast Guard approved marine safety equipment. If the support boats remain at sea for several days or longer, they should have sleeping accommodations, adequate fresh water and provisions for the crew and capture team, seawater pumping capacity to clean equipment and rinse down otters, and adequate fuel storage. Each boat also should have a freezer that can store 200 lbs of seafood for feeding the otters.

Sea otters should be captured using 18 to 20-foot skiffs. Unless hazardous sea conditions warrant the use of inflatable boats, rigidhull skiffs are recommended because they provide a more stable working platform. When operating without a support vessel, the capture boat should be equipped with a marine radio and directional finder, plus a hand-held radio. In some areas cellular phone service may be available. When the capture boat operates in association with a larger support vessel, a hand-held radio is adequate for communication. For safety, each skiff should have reserve outboard motors and standard marine safety equipment. Outboard motors are less reliable in oil contaminated water because oily debris may be sucked into the water intake/ cooling system. Consequently, we recommend frequent maintenance checks for motors to ensure uninterrupted capture operations.

(c) Aircraft. If the capture operation is more than fifty miles from the rehabilitation center, helicopters and airplanes should be used to transport the sea otters. This will reduce the transport time for the otter, thereby improving the animal’s chances of survival. The support vessels should deliver kennel cages containing the otters to a suitable shore location where they can be transferred to a helicopter or airplane. Ideally, the aircraft should be large enough to carry five or more large kennel cages and an animal care specialist, although smaller aircraft have proven useful.

Capturing Sea Otters

The techniques and equipment for capturing sea otters have been refined in recent relocation programs. Three methods are currently used for the nonlethal capture of adult sea otters: dip net, tangle net, and Wilson trap. The method of choice will depend on location and activity level of the otter, level of expertise of the capture personnel, and ocean conditions. Alternative methods such as deterrents and herding to move sea otters away from a spill site have been attempted with only limited success (Davis et al., 1988a).

(a) Dip Net Technique. This method requires the least amount of specialized equipment. It is best suited for capturing sea otters that have hauled out and young sea otters that are resting or grooming in open water. Adult sea otters that are feeding or otherwise attentive are least likely to be captured with a dip net. The method requires: 1) a maneuverable skiff (generally 18 to 20 feet in length), 2) a stout, long-handled salmon dip net (Figure 2.1), 3) an experienced boat driver, and 4) a strong person to handle the dip net. The person holding the dip net should crouch in the bow of the boat and hold onto a bow rope. The skiff operator approaches the sea otter at high speed and then throttlesback as the person scoops the animal into the net. The netted otter should be held against the side of the boat at the surface of the water until the skiff operator or an assistant can help bring the animal into the boat.

During the capture operation, the sea otter may become aware of the boat’s approach and attempt to escape. Otters that assume a defensive, pawing posture or swim away by backing up on the water’s surface are the easiest to capture. A sea otter that evades the first capture attempt will become wary and more difficult to capture on subsequent attempts. Although oiled sea otters may be lethargic and easier to capture than healthy otters, no more than five attempts should be made to capture an otter. If the animal is vigorous enough to evade easy capture with a dip net, then it probably does not require rehabilitation. The physiological stress experienced by the otter during a prolonged chase may be as harmful as the oil. Thus, the duration of pursuit must be weighed against the following factors: 1) the likelihood of the animal surviving present oiling, 2) the potential for future oiling, 3) the possibility for future capture, and 4) the threat to the animal of continued pursuit. If capture is warranted but the dip net technique is unsuccessful, then other capture methods should be considered.

(b) Tangle Net Technique. This passive method of capture should be used around kelp beds or in areas of predictable or regular sea otter movements. Tangle nets may also be used in open water, especially in areas of predictable otter movements, but are generally less successful. A large number may be captured with time and patience, but this method is the least selective capture technique and requires constant monitoring. The tangle net should be a modified gill net made of 10 inch (23 cm) stretchmesh netting, a foam core float line, a one inch (3 cm) nylon rope serving as a lead line, and a single anchor line (Figure 2.2). Foam core (corkless) float line is preferred over surface cork (peanut) floats, which are often chewed by entangled otters. The nets should be 18 feet (6 m) deep and 100 to 300 feet (33-100 m) long. Equipment and facilities for repairing and cleaning nets will also be needed.

Tangle nets should be deployed with the anchor upcurrent so that the net will be stretched out by the flow of water. Nets are set in open channels or swaths cut within the kelp canopy, around the kelp boundary, or within otters’ routine travel areas. In areas with kelp, the down-current end of the net can be wrapped loosely around kelp fronds and marked with a small buoy to aid in net recovery. Certain oceanographic circumstances may require the placement of anchors on both ends of the net. The nets should have enough scope on the anchor line and a large enough buoy to prevent the anchored end of the net from being pulled underwater by currents or tides.

If a small skiff with a hydraulic net spool is available, the net can be deployed more quickly and efficiently using the Klinkhart/Hecht Method (Figure 2.3). For this method, a site is selected along the shore or near a small island. The anchor line of the tangle net is secured to the shore, and the boat is backed away allowing the net to reel off the spool. The free end of the net is marked with a buoy and dropped into the water. Otters tend to follow the shoreline and become entangled in the net. If the natural movement of otters does not result in a capture, the boat can be used to slowly herd the otters in the direction of the net. This technique is also effective in offshore kelp beds. To recover the net, the process is reversed. The free end of the net is secured to the spool and slowly wound in, drawing the boat toward the shore until the anchor is recovered.

Sea otters can drown once they become entangled. Therefore, tangle nets should be continuously monitored and the entangled otters quickly removed. To avoid disturbing sea otters in the capture area, the nets should be monitored from shore using a spotting scope or binoculars. If it is not possible to quickly retrieve the otters, then tangle nets should not be used. Tangle nets should not be deployed under the following conditions: 1) in shallow water where nets can snag on rocks, 2) in stormy weather and rough sea conditions, 3) in nursery areas with many females and pups, or 4) overnight in areas with abundant sea otters or pinnipeds.

An exception to the last precaution occurs in areas of low sea otter abundance, where the nets may be left overnight. The nets should be checked every two hours during the day, beginning at first light and ending at dusk. Because most sea otters are entangled at night, a capture boat should be used to check the nets early in the morning. If two otters are entangled within reach of each other, they should be removed first to prevent fighting and injuries.

To remove an otter, the net should be pulled across the bow of the boat. The entangled animal is lifted onto the boat and placed into a restraint box (see Figure 3.1). A stuff bag (a nylon duffle bag filled with foam rubber or rags) should be pressed firmly against the otter’s chest while it is untangled or the net is cut away. Care should be taken to avoid injuring the otter or personnel when cutting the net. This physically demanding process requires two experienced people.

Tangle nets need constant maintenance by someone skilled in net repair. Holes should be repaired after each capture. During an oil spill, nets often become contaminated and should be washed with Dawn TM (Proctor & Gamble) dish washing detergent. Nets can be cleaned on board the support vessel by scrubbing portions of the net in a container partially filled with the detergent solution.

(c) Wilson Trap Technique. The diver-operated Wilson trap was developed in California for capturing sea otters (Figure 2.4). It is very effective for capturing a specific animal. The trap consists of a coneshaped, aluminum frame (30-35 inches long, 32 inches in diameter) which supports a net bag. The metal frame is attached to a diver operated underwater propulsion vehicle (UPV). The trap and UPV may be operated by divers using open-circuit, Self Contained Underwater Breathing Apparatus (SCUBA) or closed-circuit SCUBA (rebreathers). The latter is more effective with the Wilson trap, because no air bubbles are produced to alert the otter of a diver’s approach. Personnel with extensive diving experience are mandatory. The divers should have underwater navigation skills, underwater propulsion vehicle experience, and be physically capable of long-distance underwater swims with bulky equipment. Once proficient in these skills, the diver can consider additional training in the use of rebreather equipment. Training in the use of the Wilson trap with rebreathers is available through the USFWS and the CDFG.

The Wilson trap is designed to capture sea otters resting on the water’s surface. Experienced capture teams can often catch more than one otter at a time. The capture team requires a minimum of four people; at least two divers, a dive tender, and a boat operator. Whenever possible, capture teams should be in communication with an on shore observer who monitors the location of the otters. The dive boat should be anchored at least 150 feet downwind of the target animals. In general, the two divers maneuver their UPV and Wilson trap to a position below the target. The UPV is then driven straight up at full speed to trap the otter(s) at the surface. A draw-string is used to close the net bag once an otter is in the trap. Two carbon-dioxide-filled cartridge floats can be attached to the trap to float the captured animal at the surface while the divers await the boat’s arrival.

(d) Deterrents and Herding. Several attempts have been made to control sea otter movements in order to decrease the number of otters contaminated during a spill (Davis et al., 1988a). Unfortunately, no current method consistently deters sea otters from entering an oil spill area. Sea otters will avoid boats and respond to cracker shells, horn blasts and killer whale vocalizations, but the animals rapidly habituate to these stimuli. Despite slight modifications in behavior, the duration of response to deterrents and attractants is inadequate for protecting sea otters from potential contamination during an oil spill.


Sea otters are highly susceptible to capture-related stress; therefore, handling should be minimized. Health problems may result from capture, handling, transport, and holding of the animals (see Chapter 5). At least one member of the capture team should be experienced in recognizing stress and capture myopathy syndrome, and be able to initiate treatments.

Despite their sensitivity to stress, sea otters have sharp claws and powerful jaws that can inflict serious wounds. Only experienced wildlife biologists should handle sea otters. The following equipment is required for handling these animals: 1) net bags, 2) restraint boxes (see Chapter 3, Figure 3.1), 3) leather gloves, 4) kennel cages, and 5) capture forms.

Also, food and ice should be available for otters awaiting transport. Scales for weighing the animals, equipment for tagging them, and capture forms (Appendix 2, Forms C, D, E Download PDF) should be accessible on the support boat. Daily record keeping is essential; daily journals should include date and time of activities with detailed descriptions of capture locations and methods. A copy of each otter’s capture form should be attached to the kennel cage.

Once an otter has been captured, it should be transferred to a kennel cage as soon as possible. This can take place either aboard the support vessel or on shore. Otters captured with a dip net or a Wilson trap can be placed directly into a kennel cage. An otter captured in a tangle net should be brought aboard the skiff and placed in a restraint box. Restraint boxes come in a variety of sizes and designs, including simple boxes with and without lids, and wedge-shaped boxes. Preferably, restraint boxes should have a sliding lid and a sliding vertical door at one end. (See Chapter 3, Figure 3.1.) Otters placed in restraint boxes are transferred to kennels by placing the sliding door of the box next to the open door of a kennel cage. The sliding vertical door is opened, and the otter walks into the kennel cage.

If the restraint box does not have a sliding door, a small net bag with a drawstring closure is useful for transferring the otter from the box to a kennel cage (Figure 2.5). The net bag is draped over the opening of the box before the otter is released from the capture device. The captured otter is placed directly onto the net which drops into the box. By quickly pulling the draw string the net bag is closed around the otter. The box restricts the movements of the netted otter and facilitates handling for examination or transfer to a kennel cage.

Small, lethargic otters may be moved by picking the animal up by its hind legs. The animal is held upside down, twelve inches or more in front of the handler, with its head facing away from the handler. Because the suspended otter tends to roll forward, its teeth and front paws should remain out of reach of the handler. From this position, the otter can be placed directly into a restraint box or kennel cage.

Each animal is weighed and visually examined before transfer from the net bag or restraint box to the kennel cage. Weight, sex, estimate of age class, state of vitality, and estimated degree of oiling are recorded on the capture data forms. Identification tags should be attached to the hind flippers. This is accomplished by pulling the hind flippers through the sliding, vertical door at the end of the restraint box. (See Chapter 3.)

If a veterinarian or animal care specialist is aboard the support vessel, the otter should be examined for signs of hypothermia, hyperthermia, or other medical problems. If veterinary support is unavailable, biologists should monitor captured otters for significant changes in behavior or health. In particular, body temperature, seizures, and respiratory distress should be recorded on the capture form (Appendix 2, Form C Download PDF). This should accompany information on the capture time, date, location, and the specific information for each animal. One copy of the capture form should remain with the otter, one should be sent to the USFWS, and one should remain on the capture boat.

Sea otters that are heavily or moderately oiled are susceptible to hypothermia and should be placed in sheltered areas on the support vesse1. Seafood should be offered to all of the otters every three hours as they await transport to the rehabilitation center. The time, type of food, and amount eaten should be recorded on the capture form which is sent with the otter to the rehabilitation center.


Transportation of the sea otters from the support vessel to the rehabilitation center may occur by boat, aircraft, or truck (Cramer, 1990). The goal is to move the sea otter to the rehabilitation facility as quickly and safely as possible, minimizing the time between capture and treatment. Newly captured sea otters should be taken to a convenient beach or harbor for transfer. If there is a delay in transport, the otters should be placed in a quiet area and monitored regularly for signs of hyperthermia (panting, warm hind flippers) or hypothermia (shivering, cold hind flippers). Access to water and food should be provided. A veterinarian or veterinary technician should advise the capture crews on the triage, standard care, and emergency care needed for otters during the holding period (see Chapter 4). The air temperature of the holding area and in the transport aircraft or vehicle should not exceed 60°F (15°C). Unless an otter shows signs of hypothermia, approximately five pounds of crushed ice should be added to the cage. A water sprayer or hose may also be used to cool healthy otters and prevent further fouling of the fur.

Transport kennels containing otters should be secured to the decks of vessels or the floor of the aircraft. At least one person accompanying the otters should be an animal care specialist.