Appendix C: 

Draft Evaluation of the Southern Sea Otter Translocation Program 1987-

2004 
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DRAFT 

Evaluation of the 

Southern Sea Otter 

Translocation Program 

1987-2004 
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i 

Table of Contents 

EXECUTIVE SUMMARY .........................................................................................................................................1

BACKGROUND..........................................................................................................................................................2

TRANSLOCATION PROGRAM PURPOSE, OBJECTIVES, AND EXPECTATIONS ....................................3

RECOVERY OBJECTIVES ............................................................................................................................................4

CONTAINMENT STRATEGY.........................................................................................................................................5

SUMMARY OF THE SEA OTTER TRANSLOCATION PROGRAM (1987-2004)............................................6

TRANSLOCATION RESULTS ........................................................................................................................................7

CONTAINMENT RESULTS ...........................................................................................................................................9

CURRENT STATUS OF THE TRANSLOCATED SEA OTTER COLONY.....................................................13

PREVIOUS EVALUATIONS OF THE SOUTHERN SEA OTTER TRANSLOCATION PROGRAM..........13

1992 Draft White Paper—Zonal Management and Southern Sea Otter Recovery ............................................14

1993 Draft Evaluation .......................................................................................................................................14

2000 Biological Opinion....................................................................................................................................15

CURRENT EVALUATION OF THE TRANSLOCATION PROGRAM............................................................16

Comparison to Other Sea Otter Translocations and Future of the San Nicolas Island Population ..................16

Goals and Objectives of the Southern Sea Otter Translocation Program .........................................................17

Relation of the Translocation Program to Southern Sea Otter Recovery ..........................................................19

Sea Otter Containment.......................................................................................................................................21

Assessment of Failure Criteria Identified in Translocation Plan.......................................................................22

CONCLUSION ..........................................................................................................................................................26

GLOSSARY ...............................................................................................................................................................27

LITERATURE CITED .............................................................................................................................................28
ii 

List of Tables and Figures 

TABLE 1. POPULATION STATUS OF SEA OTTERS AT SAN NICOLAS ISLAND (SNI), 1987-2003.....................................13

FIGURE 1. EXPECTED POPULATION GROWTH OF THE SAN NICOLAS ISLAND COLONY. ...................................................4

FIGURE 2. TRANSLOCATION AND MANAGEMENT ZONES. ..............................................................................................5

FIGURE 3. SEA OTTER HOTLINE POSTER. ........................................................................................................................6

FIGURE 4. SEA OTTER EMIGRATION FROM SAN NICOLAS ISLAND. ................................................................................9

FIGURE 5. SEA OTTERS CAPTURED IN MANAGEMENT ZONE..........................................................................................11

FIGURE 6. FATE OF TRANSLOCATED POPULATIONS IN WASHINGTON, OREGON, AND CALIFORNIA..............................17

FIGURE 7. EXPECTED VS. ACTUAL POPULATION GROWTH AT SAN NICOLAS ISLAND. .................................................20
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 1

Executive Summary 

In 1982, we, the U.S. Fish and Wildlife 

Service (Service) identified the translocation 

of southern sea otters (Enhydra lutris nereis) 

as a critical recovery action for the species. 

At the time, the southern sea otter’s range 

was limited to the central California coast, 

and the prospect of a large-scale oil spill was 

considered to be the sea otter’s greatest 

threat (USFWS 1982). The intent of 

translocation was to establish one or more 

southern sea otter colonies in habitat 

occupied by southern sea otters prior to their 

decimation by the Pacific maritime fur trade 

(1784-1911). The creation of additional 

colonies was expected to reduce the risk that 

all southern sea otters would be lost in a 

single catastrophic event. 

The southern sea otter is protected by the 

Endangered Species Act of 1973 (ESA) and 

the Marine Mammal Protection Act of 1972 

(MMPA). Prior to amendment of the 

MMPA in 1988, these Acts differed with 

respect to the establishment of experimental 

(or translocated) populations. In the case of 

southern sea otters, special legislation was 

passed specifically to authorize 

translocation. Public Law (P.L.) 99-625 

allowed the Service to implement a southern 

sea otter translocation program, while also 

requiring the Service to implement a 

southern sea otter management strategy 

intended to minimize conflict between the 

experimental sea otter population and 

shellfish fisheries. The Service was 

instructed to capture and remove all sea 

otters within a management zone 

surrounding the translocation zone. The 

capture and removal of sea otters was 

intended to contain the new sea otter colony 

and to prevent sea otters from establishing 

colonies in the newly designated “no otter” 

management zone. 

Subsequent to the passage of P.L. 99-625, 

we completed an environmental impact 

statement that evaluated several 

translocation sites and included a southern 

sea otter translocation plan (USFWS 1987). 

San Nicolas Island, an island approximately 

60 miles offshore of southern California, 

was selected as the preferred translocation 

site. From 1987 to 1990, 140 southern sea 

otters were moved to the island from the 

central coast of California. By the end of 

2004, the sea otter colony at San Nicolas 

Island numbered about 32 animals. 

This document evaluates the southern sea 

otter translocation program by comparing 

results to date with the program’s objectives 

and specific failure criteria established at the 

program’s inception. Based on this 

evaluation, we conclude that the southern 

sea otter translocation program has failed to 

fulfill its primary purpose as a recovery 

action and that our recovery and 

management goals for the species cannot be 

met by continuing the program. This 

determination is based on the following 

grounds: 

1) the colony of southern sea otters at 

San Nicolas Island is small, and its 

ability to become established and 

persist is uncertain; 

2) establishment and maintenance of an 

isolated southern sea otter colony at 

San Nicolas Island will not provide 

an adequate safeguard should the 

mainland southern sea otter 

population be adversely affected by a 

catastrophic event; 

3) the recovery strategy for the southern 

sea otter has changed since the 

original recovery plan for the species 

was released in1982; in the revised 

Southern Sea Otter Recovery Plan 

(USFWS 2003), the recovery team 

recommended that we declare the 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 2

translocation program a failure and 

discontinue maintenance of a “nootter” management zone; 

4) attempts to limit natural range 

expansion of southern sea otters will 

disrupt seasonal patterns of 

movement and hinder recovery of 

the southern sea otter; 

5) capturing and moving sea otters out 

of a “no-otter” management zone has 

proven to be ineffective as a longterm management action, largely 

because of the difficulties inherent in 

sea otter capture, the ability of sea 

otters to return rapidly to the 

management zone, and the elevated 

mortality associated with the 

holding, transport, and release of sea 

otters. 

Background 

On January 14, 1977, we, the U.S. Fish and 

Wildlife Service, listed the southern sea 

otter as a threatened species under the ESA 

[16 U.S.C 1531 et seq.] on the basis of its 

small population size, its greatly reduced 

range, and the potential risk of oil spills [42 

FR 2968]. We established a recovery team 

for the species in 1980, and we approved a 

recovery plan for the species on February 3, 

1982 (USFWS 1982). In the recovery plan, 

we identified the translocation of southern 

sea otters as an effective and reasonable 

recovery action, acknowledging that a 

translocated southern sea otter population 

could impact shellfish fisheries that had 

developed in areas formerly occupied by 

southern sea otters. The objectives of 

southern sea otter translocation, as given in 

the 1982 recovery plan, included: (1) 

establishing a second colony (or colonies) 

sufficiently distant from the parent 

population such that a smaller portion of the 

southern sea otter population would be 

jeopardized in the event of a large-scale oil 

spill; and (2) establishing a database for 

identifying the optimal sustainable 

population level for the southern sea otter. 

We anticipated that translocation would 

ultimately result in a larger population size 

and a more continuous distribution of 

animals throughout the southern sea otter=s 

historic range. 

Section 10(j) of the ESA specifically 

authorizes translocation of a listed species to 

establish experimental populations. 

However, the southern sea otter is protected 

under both the ESA and the MMPA, and at 

the time, the MMPA did not contain similar 

translocation provisions. This inconsistency 

was resolved in the case of the southern sea 

otter by the passage of P.L. 99-625 (Fish and 

Wildlife Programs: Improvement; Section 1. 

Translocation of California Sea Otters) on 

November 7, 1986, which specifically 

authorized development of a translocation 

plan for southern sea otters administered in 

cooperation with the affected State. 

The Congressional Record for P.L. 99-625 

provides insight into the purpose of this 

legislation [H.R.4531]. Authorization for 

the translocation of southern sea otters was 

clearly prompted by a desire to protect the 

species and to promote its recovery. 

However, Congress also recognized the 

potential for conflict between a translocated 

sea otter population and fisheries and other 

resource uses. To address this concern, 

Congress included in P.L. 99-625 a 

requirement that any southern sea otter 

translocation plan authorized under this 

legislation must include the designation of a 

management zone that would surround the 

translocation zone. Sea otters entering the 

management zone were to be captured using 

non-lethal means and moved outside the 

management zone. 

If the Secretary of the Interior chose to 

develop a translocation plan under P.L. 99-
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 3

625, the plan was to include: (1) the number, 

age, and sex of southern sea otters proposed 

to be relocated; (2) the manner in which 

southern sea otters were to be captured, 

translocated, released, monitored, and 

protected; (3) specification of a zone into 

which the experimental population would be 

introduced (translocation zone); (4) 

specification of a zone surrounding the 

translocation zone that did not include range 

of the parent population or adjacent range 

necessary for the recovery of the species 

(management zone); (5) measures, including 

an adequate funding mechanism, to isolate 

and contain the experimental population; 

and (6) a description of the relationship of 

the implementation of the plan to the status 

of the species under the ESA and 

determinations under section 7 of the ESA. 

The purposes of the management zone were 

to: (1) facilitate the management of southern 

sea otters and containment of the 

experimental population within the 

translocation zone; and (2) prevent, to the 

maximum extent feasible, conflicts between 

the experimental population and shellfish 

fisheries within the management zone. Any 

sea otter found within the management zone 

was to be treated as a member of the 

experimental population. We were required 

to use all feasible non-lethal means to 

capture sea otters in the management zone 

and to return them to the translocation zone 

or to the range of the parent population. 

In May 1987, we published a final 

environmental impact statement that 

analyzed the impacts of establishing a 

program to translocate southern sea otters 

from their then-current range along the 

central coast of California to the northern 

coast of California, the southern coast of 

Oregon, or San Nicolas Island off the coast 

of southern California. We identified 

translocation to San Nicolas Island as our 

preferred alternative. A detailed 

translocation plan meeting the requirements 

of P.L. 99-625 was included as an appendix 

to our 1987 environmental impact statement. 

Also in August of 1987, we published 

implementing regulations for the 

translocation program [52 FR 29754; 50 

CFR 17.84(d)]. These regulations define the 

translocation and management zones, 

provide the framework for the program, and 

include a set of criteria for determining if the 

translocation should be considered a failure. 

On August 24, 1987, we began to implement 

the translocation plan by moving groups of 

southern sea otters from the coast of central 

California to San Nicolas Island. In 

December 1987, in coordination with the 

California Department of Fish and Game, 

we began capturing and moving sea otters 

that entered the designated management 

zone. 

Translocation Program Purpose, 

Objectives, and Expectations 

The U.S. Fish and Wildlife Service issues a 

final rule governing a reintroduction of 

southern sea otters (Enhydra lutris nereis) 

at, and containment of them in the 

immediate vicinity of, San Nicolas Island, 

Ventura County, California for two 

purposes: 

(1) To implement a primary recovery 

action for a federally listed “threatened” 

species; and, 

(2) to obtain data for assessing 

translocation and containment techniques, 

population dynamics, the ecological 

relationships of sea otters and the near 

shore community, and the effects on the 

donor population of removal of individual 

otters for translocation. 

 

52 FR 29754; August 11, 1987 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

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As is evident in the final rule on the 

translocation of southern sea otters, the 

primary purpose of the translocation 

program was to bring southern sea otters 

closer to recovery and eventually to delisting 

as a threatened species. Through 

translocation, we hoped to establish a selfsustaining southern sea otter population 

(experimental population) that would 

provide a safeguard in the event that the 

parent southern sea otter population were to 

be adversely affected by a catastrophic 

event, such as an oil spill. 

 

Recovery Objectives 

The translocation plan allowed for a 

maximum of 70 sea otters to be moved to 

San Nicolas Island during the first year of 

the program (USFWS 1987). This number 

could be supplemented with up to 70 

animals annually in subsequent years, if 

necessary (up to 250 total), to ensure the 

success of the translocation and to prevent 

the founding population from declining into 

an irreversible downward trend. The intent 

was to ensure that a minimum of 70 sea 

otters would form the nucleus of a breeding 

colony that would eventually grow toward 

the carrying capacity of the environment. 

The population growth of the San Nicolas 

Island colony as anticipated in the 

translocation plan is shown in Figure 1. The 

growth rate of the new colony was expected 

to be between 5 and 15 percent per year. 

According to the translocation plan, the 

experimental population at San Nicolas 

Island would be considered established 

when at least 150 sea otters resided within 

the translocation zone and the population 

had a minimum annual recruitment of 20 

animals. A population of this size was 

expected to be sufficient to supply up to 25 

immature southern sea otters per year for 

several years should it become necessary to 

replenish the parent population after a 

catastrophic event such as an oil spill. 

Assuming that a core population of 70 

southern sea otters could be maintained 

through translocation, we anticipated that 

FIGURE 1. EXPECTED POPULATION GROWTH OF THE SAN NICOLAS ISLAND COLONY. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 5

the experimental population could be 

established within as few as 5 or 6 years. 

Once established, the experimental 

population was expected to continue to 

grow, eventually reaching the lower bound 

of the estimated carrying capacity of the 

habitat (believed to be approximately 280 

animals; USFWS 1987) after 10-15 years. 

Containment Strategy 

P.L. 99-625 allowed for the translocation of 

southern sea otters with the provision that a 

sea otter management zone be established 

around the translocation zone. The 

management zone was intended to isolate 

the experimental population and to limit 

potential impacts of the experimental 

population on existing commercial fisheries. 

Southern sea otters found within the 

management zone were to be captured using 

non-lethal techniques and relocated to the 

parent or experimental population. Both the 

California Department of Fish and Game 

and the Marine Mammal Commission 

advocated this approach, also known as 

zonal management. Public Law 99-625 

states that any sea otter found in the 

designated management zone is to be 

considered a member of the experimental 

population, regardless of whether the animal 

entered the management zone from the 

translocation zone or from the parent 

population. However, it is clear, based on 

Congressional testimony and the final rule 

[52 FR 29754; August 11, 1987], that 

southern sea otter removal activities were 

expected to focus on animals dispersing 

from the translocation zone. 

After consultation with the California 

Department of Fish and Game, we defined 

the sea otter management zone to include 

the coastline from Point Conception to the 

Mexican border and all of the offshore 

islands except San Nicolas Island (Figure 2). 

This management zone created an artificial 

FIGURE 2. TRANSLOCATION AND MANAGEMENT ZONES. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 6

southern barrier for the parent population 

that was to be maintained as long as the 

translocation program was in effect. 

The translocation plan called for the 

Service and the California Department of 

Fish and Game to enforce the management 

zone jointly. We relied on sightings and 

location reports from other federal and state 

agency personnel, fishermen, boat skippers, 

and the general public. To this end, we 

publicized a sea otter hotline (Figure 3), 

which we hoped would allow us to receive 

reports of sea otters in the management 

zone in a timely manner. Upon verification 

of a sea otter sighting, field crews were 

mobilized to capture sea otters and 

transport them to areas outside the 

management zone. 

Ultimately, it was recognized that the longterm feasibility of non-lethal sea otter 

containment would be dependent on the 

availability of adequate release sites outside 

of the management zone. Participants in a 

workshop convened by the Marine 

Mammal Commission in October 1984 

noted that sea otters ultimately could reach 

carrying capacity within designated sea 

otter zones and that the continuation of 

zonal management under such 

circumstances would require some form of 

culling or birth control (Marine Mammal 

Commission 1985). Artificial control of 

fecundity (birth control) and selective or 

random non-lethal removal of sea otters 

residing in the translocation zone were 

included as reserve clauses in the regulations 

implementing P.L. 99-625 as possible 

containment measures, although the area to 

which sea otters might be removed was not 

specified [50 CFR 17.84(d)]. In the final 

rule for the southern sea otter translocation 

program, we clearly stated that we had no 

intention of using these population limiting 

techniques until the southern sea otter 

population was fully recovered, and then 

only after consultation with the California 

Department of Fish and Game, the Marine 

Mammal Commission, and the interested 

public [52 FR 29754]. 

Summary of the Sea Otter 

Translocation Program (1987-

2004) 

Southern sea otters were translocated to San 

Nicolas Island from August 1987 to July 

1990. During this period, 252 sea otters 

were captured along the central California 

FIGURE 3. SEA OTTER HOTLINE POSTER. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 7

coast, but only 139 were actually 

translocated to San Nicolas Island (USFWS 

1995, Rathbun et al. 2000). More than 100 

southern sea otters were deemed unsuitable 

for translocation based on their age, sex, or 

general health; these animals were released 

near their capture sites. At least 6 of the 252 

sea otters captured died of stress-related 

conditions while being held prior to their 

transport to San Nicolas Island. One 

rehabilitated southern sea otter pup (found 

orphaned on the central coast of California 

and cared for by the Monterey Bay 

Aquarium) was also released at San Nicolas 

Island, bringing the total number of sea 

otters released at the island to 140. 

All sea otters translocated to San Nicolas 

Island were flipper-tagged using color-coded 

tags. In addition, a passive integrated 

transponder (PIT) tag unique to each animal 

was inserted under the skin of each 

translocated sea otter. Many of the sea 

otters taken to San Nicolas Island were also 

fitted with radio transmitters to track their 

movements. The primary purpose of the 

tagging and radio telemetry efforts was to 

assist in collecting data called for in the 

translocation plan, including information on 

population dynamics and ecological 

relationships between sea otters and the 

nearshore marine community. A secondary 

purpose was to locate and track sea otters 

that left the translocation zone. 

Translocation Results 

During the first year of translocation efforts 

(August 1987–July 1988), 69 sea otters were 

translocated to San Nicolas Island, but only 

20 were observed at the island by the end of 

the period. Three of the 69 animals died at 

San Nicolas Island, 2 were found dead on 

the mainland (1 had been shot), 3 were 

suspected to have been killed in fishing gear, 

and 1 was recaptured and removed from the 

management zone (Rathbun et al. 1990). 

Forty animals were missing and were 

presumed to have dispersed from the 

translocation zone because there was no 

evidence of additional mortality at the 

island. Emigration from San Nicolas Island 

was higher than anticipated given the 

abundant food resources available to sea 

otters there, the island’s overall habitat 

quality, its isolated location, and the 

presumed barrier afforded by the deep 

waters surrounding it. 

During the first year of the project, captures 

of sea otters for translocation to San Nicolas 

Island were less efficient than expected. Sea 

otters became wary after exposure to intense 

capture activities (dip netting) in their home 

territories. Their wariness affected the 

ability of capture teams to select specific 

individuals and increased the time needed to 

obtain the proper number and composition 

of sea otters for translocation. Capture 

delays imposed additional stress on animals 

awaiting translocation in holding tanks and 

contributed to the deaths of four sea otters 

before they could be translocated (USFWS 

1988). 

Because of the unexpected mortalities and 

high emigration encountered during the first 

year, we amended our regulations for the 

translocation program in 1988 [53 FR 

37577; September 27, 1988]. The 

amendments were intended to minimize 

stress on sea otters, to improve the survival 

of translocated animals, and to minimize 

dispersal of sea otters from the translocation 

zone. Specifically, we provided more 

flexibility in selecting the ages of sea otters 

for translocation, eliminated the restriction 

to capture sea otters only within an August 

to mid-October time frame, eliminated the 

requirement to move a specified number of 

southern sea otters previously implanted 

with transmitters, provided the flexibility 

either to transport sea otters immediately or 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

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to hold them on the mainland before 

releasing them at San Nicolas Island, and 

eliminated the requirement to translocate a 

minimum of 20 sea otters at a time. Based 

on data collected during the first year of 

translocation, we believed that younger sea 

otters were more likely to remain at San 

Nicolas Island (Rathbun et al. 1990). 

 

The second year of the translocation effort 

focused on the translocation of younger sea 

otters. These animals were transported in 

smaller groups (1 to 4 animals) to minimize 

the time they were held in captivity. Once at 

the island, they were immediately released 

from shore in the vicinity of other sea otters. 

By the end of the second year, a total of 126 

sea otters had been moved to San Nicolas 

Island, but only 17 were observed at the 

island (USFWS 1989, USFWS 1990). Even 

with modifications to the program in place, 

emigration from the island by newly 

translocated animals continued to be high. 

During the third year of the program, 14 

additional sea otters were translocated to 

San Nicolas Island, with the last 

translocation occurring on July 19, 1990 

(USFWS 1991). By December of that year, 

the colony at the island was estimated to 

total 15 adult or sub-adult animals and three 

dependent pups. 

No translocations occurred during the fourth 

year of the program because of difficulties 

encountered with implantation of radios in 

sea otters to be translocated to San Nicolas 

Island, an increased need for coordination 

amongst interested parties, and logistical 

constraints. 

Following the fourth year of the 

translocation program, the sea otter 

population at the island was small, about 15 

animals, but appeared to be stable. The sea 

otters that were present were consistently 

observed at specific areas of the island, and 

it was hoped that these animals would 

become the founding nucleus of a larger 

colony. There were concerns that the 

introduction of additional translocated 

animals would disrupt the resident sea 

otters, possibly resulting in additional deaths 

or emigration from the island. Due to the 

perceived precariousness of the colony and 

concerns that translocation itself might 

affect the success of the colony, we 

discontinued the translocation of sea otters 

to San Nicolas Island. Since July 1990, no 

sea otters have been translocated to the 

island. However, we continued monitoring 

the sea otters remaining in the translocation 

zone. Sea otter surveys at San Nicolas 

Island are now conducted by the Biological 

Resources Discipline of the U.S. Geological 

Survey on a bimonthly basis. 

Of the 140 sea otters released at San Nicolas 

Island between August 1987 and July 1990, 

the fate of 70 is known. Three were found 

dead at San Nicolas Island within a few days 

of being translocated. Thirty-six are known 

to have returned to the parent population 

range, and 18 were either captured (11) or 

found dead (7) in the management zone, 

months to years after they were translocated 

(Figure 4). At least 13 sea otters are thought 

to have remained at San Nicolas Island after 

their release. The fate of the other 70 

animals is unknown. Although an intense 

effort was made to locate translocated sea 

otters at San Nicolas Island and in the 

management zone, observations of sea otters 

that returned to the parent population range 

were gathered only opportunistically. 

Despite the absence of a focused effort to 

identify translocated sea otters that returned 

to the parent range, many were resighted 

there, suggesting that additional sea otters 

may have returned to the parent range 

without being detected. We believe that 

most of the missing sea otters emigrated 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 9

from the island and that many of them 

probably returned to the parent population. 

Some of the missing animals may also have 

died as a consequence of translocation, but 

no additional deaths have been verified. 

Containment Results 

Southern sea otter containment was a 

cooperative effort between the Service and 

the California Department of Fish and 

Game. Containment efforts were intended 

to keep the management zone free of sea 

otters in accordance with P.L. 99-625 and 

our implementing regulations. Containment 

operations consisted of three interdependent 

activities: (1) surveillance of the 

management zone; (2) capture of sea otters 

in the management zone; and (3) relocation 

of captured sea otters to the parent range or 

San Nicolas Island. 

Containment activities were triggered by 

sightings of southern sea otters in the 

management zone. In most instances, these 

sightings were made by fishermen or local 

residents. Federal or State biologists 

investigated each reported sighting to 

confirm the presence of sea otters prior to 

launching capture efforts. The number of 

sea otter reports we received from people 

working, recreating, or living near the 

waters of the management zone varied from 

year to year, with the majority of the reports 

(37) received during the first year of the 

translocation program (USFWS 1988). In 

nearly all cases, the number of sea otters 

confirmed in the management zone was 

small, generally one to three animals. It is 

likely that some animals were reported 

multiple times while others transited the 

management zone without being detected. 

Sea otter sightings at San Miguel Island 

proved to be the exception. At San Miguel 

Island, groups of as many as nine sea otters 

were consistently observed in the vicinity of 

Point Bennett from 1991 to 1993. 

FIGURE 4. SEA OTTER EMIGRATION FROM SAN NICOLAS ISLAND. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 10

Capturing southern sea otters in the 

management zone using non-lethal means 

proved to be relatively difficult, and our 

capture efforts were only minimally 

successful. Three capture techniques were 

available for southern sea otter containment: 

(1) dip netting; (2) the deployment of 

passive entangling nets; (3) and the use of 

diver-operated traps (Wilson traps). The use 

of Wilson traps operated by divers equipped 

with closed-circuit SCUBA proved to be the 

most effective technique. Sea otters in the 

management zone were most often found in 

kelp beds, a circumstance that effectively 

eliminated the dip-netting option and 

favored the Wilson-trapping option. Sea 

otters in the management zone were also 

typically found in low densities or were 

found in areas with large numbers of 

pinnipeds, making the use of entangling nets 

impractical. Upon responding to reports of 

sea otters in the management zone, we were 

often unable to locate the animals that had 

been sighted. Even when sea otters were 

found, capture efforts were successful only 

about half the time. 

Once captured, sea otters were transported 

back to the parent range for release. Public 

Law 99-625 allowed sea otters captured in 

the management zone to be released in 

either the translocation zone or the mainland 

range, but when we considered our previous 

efforts to move sea otters to the island, we 

concluded that animals removed from the 

management zone would not likely stay at 

San Nicolas Island. We believed that sea 

otters originating from the island that had 

already left it once were likely to do so 

again. Additionally, sea otters had proven 

that they were capable of negotiating deep 

ocean channels and could travel much 

longer distances than previously anticipated. 

Thus, during our initial containment efforts, 

we returned individual animals to their 

original capture sites on the central coast of 

California instead of releasing them back 

into the translocation zone. 

However, the strategy of releasing sea otters 

at their original capture sites resulted, in 

most cases, in lengthy travel times and 

additional handling of the animals. To 

reduce this source of stress on captured sea 

otters, we revised our strategy in the belief 

that it was more prudent to release 

recaptured animals at more easily accessible 

sites in the northern portion of the parent 

range. This change reduced transport times 

and, we believed, reduced stress and 

improved the well-being of moved sea 

otters. We also hoped that releasing animals 

at the northern end of the range would 

reduce the likelihood that animals would 

return to the management zone because of 

the greater distances they would have to 

travel. 

From December 1987 to February 1993, 24 

sea otters were captured and removed from 

the management zone and returned to the 

parent range (Figure 5). Eleven of these 

animals had been translocated to San 

Nicolas Island, four were offspring of sea 

otters translocated to San Nicolas Island, 

and at least three swam into the management 

zone from the parent range. The origins of 

the remaining six animals were unclear; they 

had either moved down from the parent 

range or were offspring of sea otters 

translocated to San Nicolas Island. Two of 

the sea otters removed from the management 

zone returned to it after traveling hundreds 

of kilometers, only to be recaptured and 

moved again. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 11

In February 1993, two sea otters that had 

been recently captured in the management 

zone were found dead shortly after their 

release in the range of the parent population. 

In total, four sea otters were known or 

suspected to have died within two weeks of 

being moved from the management zone. 

We were concerned that sea otters were 

dying as a result of our containment efforts; 

therefore, in 1993 we suspended all sea otter 

capture activities in the management zone to 

evaluate sea otter capture and transport 

methods. We also recognized that available 

capture techniques, which proved to be less 

effective and more labor-intensive than 

originally predicted, were not an efficient 

means of containing southern sea otters. 

From 1993 to 1997, few sea otters were 

reported in the management zone, and there 

appeared to be no immediate need to address 

sea otter containment. In 1997, the 

California Department of Fish and Game 

notified us that it intended to end its 

southern sea otter research project and 

would no longer 

be able to assist us 

if we resumed 

capturing sea 

otters in the 

management zone. 

In 1998, a group 

of approximately 

100 southern sea 

otters moved from 

the parent range 

into the northern 

end of the 

management zone. 

At the same time, 

range-wide counts 

of the species 

indicated a decline 

of approximately 

10 percent 

between 1995 and 

1998. In light of the decline in southern sea 

otter numbers, we were concerned about the 

potential effects on the parent population of 

moving the large number of southern sea 

otters that had moved into the management 

zone. We asked the southern sea otter 

recovery team, a team of biologists with 

expertise pertinent to southern sea otter 

recovery, for their recommendation 

regarding the capture and removal of sea 

otters in the management zone. The 

recovery team recommended that we not 

move sea otters from the management zone 

to the parent population because moving 

large groups of sea otters and releasing them 

within the parent range would be disruptive 

to the social structure of the parent 

population (DeMaster 1998). We agreed 

with their recommendation. 

In order to notify stakeholders of our 

intended course of action, we held two 

public meetings in August 1998. At these 

meetings, we provided information on the 

FIGURE 5. SEA OTTERS CAPTURED IN MANAGEMENT ZONE. 

0

2

4

6

8

10

12

14

Number of 

Sea Otters 

San Miguel

Island

Cojo Anchorage Anacapa Island Vent ura/ LA

Count y

San Diego Area

Location Captured

Offspring of a

Translocated Sea

Otter or Sea Otter

from Parent

Population

Sea Otter from

Parent Population

Offspring of a

Translocated Sea

Otter

Translocated Sea

Otter 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 12

status of the translocation program, solicited 

general comments and recommendations, 

announced that we intended to reinitiate 

consultation under section 7 of the ESA for 

the southern sea otter containment program, 

and stated that we intended to begin the 

process of evaluating the translocation 

program against the failure criteria 

established for it. 

We distributed a draft section 7 consultation 

on the southern sea otter containment 

program to interested parties for comment 

on March 19, 1999, and issued a final 

biological opinion on July 19, 2000. Our 

reinitiation of consultation was prompted by 

the receipt of substantial new information on 

the population status, behavior, and ecology 

of the southern sea otter that revealed 

adverse effects of containment that were not 

previously considered. In the biological 

opinion, we cited the following information 

and circumstances as prompting reinitiation: 

(1) in 1998 and 1999, southern sea otters 

moved into the management zone in much 

larger numbers than in previous years; (2) 

analysis of carcasses indicated that southern 

sea otters were being exposed to 

environmental contaminants and diseases 

that could be affecting the health of the 

population throughout California; (3) rangewide counts of southern sea otters indicated 

that numbers were declining; (4) recent 

information, in particular the observed 

effects of the Exxon Valdez oil spill, 

indicated that southern sea otters at San 

Nicolas Island would not be isolated from 

the potential effects of a single large oil 

spill; and (5) the capture and release of large 

groups of southern sea otters could result in 

substantial adverse effects on the parent 

population. The biological opinion 

concluded with an assessment that 

continuation of the containment program 

would likely jeopardize the continued 

existence of the species on the grounds that 

(1) reversal of the southern sea otter=s 

population decline was essential to the 

survival and recovery of the species, 

whereas continuation of containment could 

cause the direct deaths of individuals and 

disrupt social behavior in the parent range, 

thereby exacerbating population declines; 

and (2) expansion of the southern sea otter=s 

distribution was essential to the survival and 

recovery of the species, whereas 

continuation of the containment program 

would artificially restrict the range to the 

area north of Point Conception, thereby 

increasing the vulnerability of the species to 

oil spills, disease, and stochastic events. 

On January 22, 2001, we issued a policy 

statement regarding the capture and removal 

of southern sea otters in the designated 

management zone [66 FR 6649]. Based on 

our July 2000 biological opinion, we 

determined that the containment of southern 

sea otters was not consistent with the 

requirement of the ESA to avoid jeopardy to 

the species. The notice advised the public 

that we would not capture and remove 

southern sea otters from the management 

zone pending completion of our reevaluation 

of the southern sea otter translocation 

program, which would include the 

preparation of a supplement to our 1987 

environmental impact statement and release 

of a final evaluation of the translocation 

program that contained an analysis of failure 

criteria. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 13

Current Status of the 

Translocated Sea Otter Colony 

In December 2004, 32 independent southern 

sea otters were counted at San Nicolas 

Island. Data from quarterly counts indicate 

that the population has fluctuated between 

13 and 33 independent animals since July 

1990. Dependent pups are frequently 

observed with these individuals. Within the 

past several years there have been 

indications of slow growth in the population 

that is almost certainly due to the birth and 

recruitment of pups (Table 1) rather than 

immigration of sea otters to the island. One 

southern sea otter pup was born at San 

Nicolas Island during the first year of the 

translocation program (1987-88), and new 

pups have been observed in each subsequent 

year. At least 90 pups are known to have 

been born at the island since the program=s 

inception. 

In 2004, we confirmed the presence of at 

least one sea otter at San Nicolas Island that 

had been translocated there. However, 

virtually all of the sea otters now residing at 

San Nicolas Island are the offspring of those 

originally translocated to the island. This is 

because the founding animals were 

translocated between 15 and 18 years ago, 

and the average life expectancy of southern 

sea otters in the wild is approximately 10 to 

15 years (Riedman and Estes 1990). 

Previous Evaluations of the 

Southern Sea Otter Translocation 

Program 

From the beginning of the translocation 

program, the annual translocation reports 

included a discussion of failure criteria. As 

early as 1990 (USFWS 1990), these reports 

noted that the program appeared to meet 

failure criterion 2, under which the program 

would be considered a failure if fewer than 

25 sea otters remained at San Nicolas Island. 

However, a provision of failure criterion 3 

allowed for continuation of the program if 

reproduction was occurring and dispersal 

into the management zone was small. We 

chose to continue monitoring the 

translocated colony. In subsequent years, 

three additional and more comprehensive 

internal reviews of the program were 

completed. Although each of the 

evaluations concluded that the translocation 

program was failing to meet its objectives, 

none resulted in a formal administrative 

finding that the translocation program had 

failed. 

TABLE 1. POPULATION STATUS OF SEA 

OTTERS AT SAN NICOLAS ISLAND (SNI), 

1987-2003 

Year # Released at 

SNI 

# Born at 

SNI 

Maximum # 

independent 

sea otters* 

87 60 1 27 

88 41** 1 28 

89 35 3 28 

90 4 5 14 

91 0 8 14 

92 0 4 13 

93 0 6 12 

94 0 5 16 

95 0 3 14 

96 0 6 17 

97 0 5 16 

98 0 3 15 

99 0 4 21 

00 0 6 21 

01 0 7 27 

02 0 8 29 

03 0 8 33 

04 0 7 32 

Total 140 90 

*Totals given here exclude dependent pups and 

reflect the highest count made in each calendar year. 

Totals for 1987-1990 are adjusted upwards to include 

the number of sea otters released at the island in each 

of those years, even if a released sea otter was not 

subsequently seen. 

**Includes one rehabilitated sea otter from Monterey 

Bay Aquarium. 

Data source: Hatfield 2005, U.S. Geological Survey 

unpublished data. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 14

1992 DRAFT WHITE PAPER—ZONAL MANAGEMENT AND 

SOUTHERN SEA OTTER RECOVERY

In March 1992, we prepared a draft “white” 

paper for a meeting with the California 

Department of Fish and Game (USFWS 

1992). The paper included background 

material on the rationale for listing the 

southern sea otter as a threatened species, 

the recovery objective of the 1982 southern 

sea otter recovery plan, a summary of the 

translocation program, identification of 

major issues affecting sea otter recovery, 

and several options for the future of the 

southern sea otter translocation program. 

The draft white paper explored two major 

questions: (1) does the existing sea otter 

management zone interfere with recovery? 

and (2) is it feasible to maintain a 

management zone using non-lethal 

techniques? We noted that establishing a 

translocated sea otter population at San 

Nicolas Island had proven to be difficult and 

concluded, based on our experience with the 

Exxon Valdez oil spill in 1989, that even if 

the San Nicolas Island sea otter colony were 

to become established and result in a viable 

population, it might not provide significant 

protection to the species if a large oil spill 

were to come in contact with the parent 

population. 

We considered three options for the future 

of the translocation program in the draft 

white paper: A) eliminate the management 

zone, allow sea otters to remain at San 

Nicolas Island, and allow sea otters to 

expand their range naturally; B) determine 

the translocation program to be a failure and 

attempt to remove sea otters from the 

translocation and management zones; or C) 

leave sea otters at San Nicolas Island and 

continue efforts to maintain the management 

zone. The paper also noted that elimination 

of the management zone would allow sea 

otters to expand their range naturally, 

thereby benefiting sea otter recovery. In 

discussions between the Service and the 

State, the California Department of Fish and 

Game expressed its desire to maintain 

management options for sea otters. As a 

result, the white paper was never finalized, 

and no formal action was taken to declare 

the translocation program a failure. 

 

1993 DRAFT EVALUATION

In 1993, three years after the last sea otter 

was released at San Nicolas Island, 

population surveys indicated that the 

number of sea otters at the island was not 

increasing. Prompted by this lack of 

growth, we prepared a draft evaluation of 

the translocation program (USFWS 1993). 

The 1992 Draft White Paper concluded: 

Continuing containment activities (i.e. at 

San Miguel Island) may result in the 

removal of at least some, and possibly the 

remaining, sea otters. However, 

maintaining the management zone free of 

sea otters using non-lethal techniques 

ultimately will not work using current 

techniques. And as long as the southern 

sea otter is listed as threatened or 

endangered and population growth is 

essential to recovery, using culling 

techniques or techniques that reduce 

reproduction is unacceptable. Restoring 

the southern sea otter to a non-threatened, 

non-endangered status would be enhanced 

by the establishment of the San Nicolas 

Island colony and populations of otters 

south of Point Conception (currently the 

management zone) if recolonization 

occurs. 

USFWS 1992
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 15

The draft evaluation assessed the entire 

translocation program, including the status 

of the San Nicolas Island colony, 

translocation efforts and methods, 

containment efforts and methods, and failure 

criteria. We noted that the degree of 

dispersal of sea otters from San Nicolas 

Island and the mortalities associated with the 

program were both much higher than 

anticipated. Stress to sea otters associated 

with handling and release was thought to be 

a significant factor in these results. 

Despite the fact that most of the translocated 

sea otters had apparently left the island, few 

animals settled in the management zone (11 

of 140 translocated). Sea otter containment 

success up to that point was due to the 

presence of only small numbers of sea otters 

within the zone and the successful 

identification of key areas where sea otters 

tended to congregate, such as Cojo 

Anchorage and San Miguel Island. 

Although the effectiveness of capture 

operations was improved by the addition of 

divers equipped with closed-circuit SCUBA, 

the 1993 draft evaluation again questioned 

whether a non-lethal, zonal management 

program for sea otters was ultimately 

feasible. 

The overall intent of the 1993 draft 

evaluation was to assess the translocation 

program and to determine whether the 

program met regulatory criteria to be 

declared a failure; however, the document 

had a limited distribution and was never 

finalized. When we discussed declaring the 

translocation program a failure with the 

California Department of Fish and Game, 

they requested that we continue the program 

to preserve the option of zonal management 

of sea otters in southern California to reduce 

conflicts with local shellfish fisheries. As a 

result, we deferred our decision on the 

translocation program.

2000 BIOLOGICAL OPINION

In 1998, large groups of male sea otters 

began to enter the management zone from 

the parent population. In subsequent years, 

this movement was determined to be 

seasonal in nature, with most sea otters 

entering the management zone in the winter 

months and returning to the parent range in 

spring (Tinker 2002, unpubl. data). The 

movements coincided with declining 

population counts throughout the range of 

the parent population, and the receipt of 

substantial new information led us to 

reinitiate consultation under the ESA. This 

consultation focused on the containment 

portion of the southern sea otter 

translocation program and sought to 

determine whether containment activities 

would impose additional adverse effects on 

the mainland population that were not 

considered when we developed the 

translocation plan. The resulting biological 

opinion was finalized in July 2000 (USFWS 

2000). 

After reviewing the status of the southern 

sea otter, the environmental baseline for the 

action area, the effects of sea otter 

containment, and cumulative effects, we 

concluded that continuation of sea otter 

containment would likely jeopardize the 

continued existence of the species. Our 

conclusion was based on two 

determinations: 1) reversal of the southern 

sea otter’s population decline was essential 

to its survival and recovery, and 

continuation of sea otter containment could 

lead to deaths of sea otters and disruption of 

the social structure of the population, thus 

exacerbating the population decline; and 2) 

expansion of the southern sea otter’s 

distribution was essential to its survival and 

recovery. Continuing sea otter containment 

would restrict the range of the species, 

resulting in its increased vulnerability to oil 

spills, disease, and stochastic events. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 16

Upon completion of the biological opinion, 

we published a notice of policy regarding 

the capture and removal of sea otters from 

the designated management zone [66 FR 

6649]. We determined that we would not 

capture and remove sea otters from the 

management zone pending our reevaluation 

of the translocation program, including the 

preparation of a supplemental environmental 

impact statement and release of a final 

evaluation of the translocation program. 

Current Evaluation of the 

Translocation Program 

Since the inception of the southern sea otter 

translocation program, we have been 

evaluating data, consulting with our primary 

partners (the California Department of Fish 

and Game and the Marine Mammal 

Commission), and making adjustments to 

the program. This latest draft evaluation 

compares our expectations for the program 

with results attained to date and provides 

analysis of the specific failure criteria 

identified in the translocation plan. 

COMPARISON TO OTHER SEA OTTER TRANSLOCATIONS 

AND FUTURE OF THE SAN NICOLAS ISLAND POPULATION

Experimental translocation of sea otters 

began in 1951. Initially, there were several 

attempts to move relatively small numbers 

of northern sea otters in Alaska. All early 

attempts failed, largely due to high mortality 

associated with a general lack of knowledge 

about how best to transport sea otters. A 

series of northern sea otter translocations 

occurred from 1965 to 1972. During this 

period, 708 northern sea otters were 

translocated from the Aleutian Islands and 

Prince William Sound, Alaska, to the 

Pribilof Islands, southeast Alaska, British 

Columbia, Washington, and Oregon 

(Jameson et al.1982). 

 

Translocations to southeast Alaska, British 

Columbia, and Washington were eventually 

successful, while those to the Pribilof 

Islands and Oregon failed (Riedman and 

Estes 1990). In all cases, post-release 

dispersal of sea otters was evident (Estes et 

al.1989). Considering previous 

translocation efforts, Jameson et al. (1982) 

concluded the following: 1) the number of 

sea otters at a transplant site decreases 

dramatically soon after release; 2) 

emigration appears to be an important factor 

in the initial decline of translocated 

populations; 3) small populations (<25-30 

animals) are probably destined for extinction 

because they are incapable of reproducing at 

a rate that is greater than the combined rates 

of mortality and emigration; 4) it is possible 

to select a general area to reestablish sea 

otters, but the exact locations are difficult to 

predict; and 5) it is possible to reestablish 

sea otters in unoccupied habitat, but it 

appears to require a relatively large nucleus 

population. 

The southern sea otter translocation program 

is the most recent and the most extensively 

planned of all sea otter translocations. 

Capture and transport techniques were 

thought to be sufficiently developed to 

minimize mortalities; the number of sea 

otters to be translocated was considered 

sufficient to establish a colony rapidly in 

unoccupied habitat; and the selected 

translocation site, San Nicolas Island, was 

surrounded by deep ocean channels and 

thought to be situated sufficiently far from 

shore to minimize emigration and dispersal 

(USFWS 1987). In retrospect, our 

expectations for success were overly 

optimistic. Our results to date indicate that 

the southern sea otter translocation program 

has followed the same general pattern of all 

previous sea otter translocations. Initial 

emigration from San Nicolas Island was 

high, leaving a small colony that may or 

may not persist. 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 17

The future of the sea otter colony at San 

Nicolas Island is uncertain. The colony has 

exhibited a pattern of early emigration and 

subsequent growth that appears to be 

roughly intermediate between the patterns 

seen after translocations of northern sea 

otters to Washington and Oregon. Although 

these translocations had similar beginnings, 

they had very different outcomes (Figure 6). 

While the Washington population has grown 

to a relatively large size (about 740 animals 

in 2004), the Oregon population has gone 

extinct. 

The size of the San Nicolas Island 

population has remained far below that 

projected under the translocation plan. Like 

other small populations, the colony at San 

Nicolas Island is vulnerable to the effects of 

demographic and environmental variability. 

These sources of unpredictability make it 

difficult to forecast the future of the colony 

based on existing trends or the example of 

other translocated populations. One 

important distinction must also be made 

between this and all earlier translocations: 

the designation of a management zone is 

unique to the San Nicolas Island 

translocation. Should the colony at San 

Nicolas Island survive, efforts to maintain a 

management zone will impede population 

growth if animals straying from the island 

are consistently removed from the 

population. 

GOALS AND OBJECTIVES OF THE SOUTHERN SEA OTTER 

TRANSLOCATION PROGRAM

The goals identified in the 1987 Southern 

Sea Otter Translocation Plan are: (1) to 

recover the southern sea otter from its 

present 'threatened' status under the ESA; 

and (2) to gain a better understanding of 

characteristics of a sea otter population and 

the marine ecosystem when the sea otter 

FIGURE 6. FATE OF TRANSLOCATED POPULATIONS IN WASHINGTON, OREGON, AND 

CALIFORNIA. 

0

50

100

150

200

250

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Years after Initial Release

Number of 

Sea Otters

Total Released OR

Total Released SNI

Total Released WA

OR Independents

SNI Independents

WA Independents
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 18

population is within range of its optimum 

sustainable population, as defined by the 

MMPA. Research associated with the 

translocation was designed to achieve the 

following objectives: (1) to understand 

southern sea otter population dynamics, in 

particular growth-limiting factors; (2) to 

understand the ecology of southern sea otter 

foraging and the role of southern sea otter 

predation in biological communities in 

central and southern California waters; (3) to 

develop methods for translocating southern 

sea otters; and (4) to evaluate and develop 

methods for containing southern sea otters. 

This research was undertaken in the context 

of competing management demands: to 

protect and conserve southern sea otters, on 

one hand, and to understand and manage 

conflicts between sea otters and shellfish 

fisheries on the other. These were the 

principal forces behind the joint 

management/research translocation program 

put in place in 1987 under the auspices of 

the ESA, the National Environmental Policy 

Act (NEPA) process, and P.L. 99-625. To 

date, we have gathered a significant amount 

of data to assess capture, transport, 

reintroduction, and containment techniques. 

However, our primary recovery objective for 

the southern sea otter translocation program 

remains unfulfilled.

In the context of the goals stated in the 

southern sea otter translocation plan, the 

creation of an established southern sea otter 

population at San Nicolas Island does not 

appear to be achievable. The plan defines 

an “established” population as one that is 

not only reproductively self-sustaining but 

allows for the repeated removal of 

individuals for the reestablishment of 

another southern sea otter population in the 

parent range should a catastrophic event 

occur in the parent range. The logic 

underlying this definition is explained in our 

final rule for the establishment of an 

experimental population of southern sea 

otters: 

The Service does not consider the 

mere presence of sea otters in the 

translocation zone an indication that 

a new population is established. If a 

catastrophic event were to decimate 

a portion of the parent population, it 

is possible that the relocated otters 

could be used to restore the damaged 

portion of the parent population; 

however, it would also likely 

eliminate the value of the new 

population to serve as a reserve 

colony for providing stock to restore 

subsequently damaged areas and it 

could eliminate the reproductive 

viability of the colony such that the 

remaining animals could not be selfsustaining. Therefore, to be 

considered established it must be a 

reproductively viable unit, capable of 

maintaining itself even if 25 animals 

are removed each year for 1 to 3 

years or replacement yield is 

sufficient to maintain the 

experimental population at or near 

carrying capacity during the postestablishment and growth phase or 

carrying capacity phase for the 

purposes of repairing damage to the 

parent population [52 FR 29754; 

August 11, 1987]. 

Two circumstances make achievement of 

this objective unlikely. First, the future of 

the San Nicolas Island colony is uncertain. 

Its consistently small population size makes 

it difficult to predict when or if the 

population will become established. 

Second, if the San Nicolas Island colony 

does become established (with a population 

size of 150 southern sea otters and an annual 

recruitment of 20 animals), our experience 

with the translocation of southern sea otters 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 19

to San Nicolas Island indicates that if a 

catastrophic event were to affect the parent 

population, it is unlikely that we would be 

able to reestablish a viable southern sea otter 

population by moving 25 animals from San 

Nicolas Island annually over a 3-year 

period. The high emigration apparently 

inherent in sea otter translocations and the 

small number of animals available to be 

moved would make it unlikely that a core 

population could become established in the 

damaged area. 

 

RELATION OF THE TRANSLOCATION PROGRAM TO 

SOUTHERN SEA OTTER RECOVERY

The original Southern Sea Otter Recovery 

Plan (USFWS 1982) identified the need to 

establish one or more southern sea otter 

colonies through translocation in order to 

minimize the possibility that a major oil spill 

or series of smaller spills could jeopardize 

the species. The intent behind translocation 

was to enhance the southern sea otter’s 

range and population size. A slow rate of 

population growth, evident in the mid- to 

late 1980s, was viewed as inadequate to 

expand the southern sea otter range rapidly 

enough to ensure the survival of the species 

should a spill occur. These factors led to the 

development of the plan to establish a 

second colony of southern sea otters through 

translocation from the central coast of 

California to San Nicolas Island. 

The Revised Southern Sea Otter Recovery 

Plan (USFWS 2003) identifies several 

factors that have altered the need and 

rationale for the translocation program. The 

change in recovery strategy is the result of 

direct and indirect experience gained since 

publication of the original recovery plan. 

First, the Exxon Valdez oil spill in 1989 

confirmed some of the most pessimistic 

projections of the consequences of such 

events. The spill was uncontrollable and in 

30 days spread over 670 kilometers (400 

linear miles), an area greatly exceeding the 

present range of the southern sea otter in 

central coastal California plus that of the 

translocated colony at San Nicolas Island. 

The distance over which oil rapidly spread 

during the Exxon Valdez disaster indicates 

that the translocated colony at San Nicolas 

Island could not provide a reasonable 

safeguard against an oil spill of this 

magnitude. Moreover, it is estimated that 

several thousand sea otters died in the Exxon 

Valdez oil spill (Garrott et al. 1993, 

DeGange et al. 1994), a number at least 

equaling and probably exceeding the present 

size of the southern sea otter population. 

Efforts to save and rehabilitate oiled sea 

otters were of little or no value to the 

population (USFWS 2003). 

Second, the translocation of southern sea 

otters to San Nicolas Island has not achieved 

its goal of establishing a second, selfsustaining population of southern sea otters. 

To date, our expectations for the 

translocation program are far from being 

met (Figure 7). 

Finally, maintenance of a management or 

“no-otter” zone would hinder southern sea 

otter recovery. Large numbers of southern 

sea otters (50 to 150 animals) have been 

observed frequenting the northern end of the 

management zone since 1998. These 

animals appear to move into and out of the 

zone seasonally from areas along the 

mainland to the north. Recent research 

indicates that these southern sea otters are 

moving great distances throughout the 

southern sea otter range and are an 

important component of the population 

(Tinker 2002, unpublished data). Capture 

and relocation of these animals exposes 

them to increased mortality and may result 

in widespread disruption of the southern sea 

otter population as a whole (USFWS 2000). 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 20

The revised recovery plan of 2003 

acknowledges that the intent and purpose of 

the translocation program have not been 

met. The current strategy for recovering the 

southern sea otter, as reflected in the revised 

recovery plan, is to determine causes of 

increased mortality in the parent population, 

to mitigate these causes, and to allow the 

number and range of southern sea otters to 

increase naturally to such a size that: (1) 

there will be enough survivors to recolonize 

the range without genetic bottleneck effects 

in the event of a major oil spill in central 

coastal California; and (2) a declining trend 

in abundance can be detected with adequate 

statistical assurance prior to the population 

reaching the threshold for endangered status. 

The revised recovery plan also states that a 

primary action for promoting the recovery of 

the southern sea otter at this time should be 

the cessation of zonal management, and that 

without such a change in management, the 

likelihood of recovery is significantly 

lessened (USFWS 2003). Continuation of 

zonal management may result in the direct 

deaths of individual animals removed from 

the management zone and disrupt social 

behavior in the parent population to a degree 

that animals residing in the range of the 

parent population will have a reduced 

potential for survival and recovery. Zonal 

management will also artificially restrict the 

range of the southern sea otter and 

perpetuate the species= vulnerability to the 

adverse effects of oil spills, disease, and 

stochastic events (USFWS 2000). 

FIGURE 7. EXPECTED VS. ACTUAL POPULATION GROWTH AT SAN NICOLAS ISLAND. 

Expected vs. Actual Population Growth

at San Nicolas Island

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Year of Program

Sea Otter Population Size

Highest

Annual

Count,

San

Nicolas

Island
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 21

SEA OTTER CONTAINMENT

Our experience implementing the 

translocation program revealed that 

detecting and confirming the presence of sea 

otters in the management zone was more 

difficult in practice than in theory. Because 

of the large area involved [more than 750 

linear miles (1,200 km) of coastline] we 

were dependent on fishermen, local 

residents, and others to provide reports of 

sea otter sightings. The quality of such 

reports varied considerably, and at times the 

presence of animals could not be verified 

despite multiple reported sightings. At other 

times, a sea otter sighting was confirmed, 

but the animal left the area before a capture 

attempt could be organized. 

Capture operations were also more 

complicated than anticipated. Sea otter 

captures in the management zone most often 

involved divers using Wilson traps and 

closed-circuit rebreathers in place of 

conventional SCUBA equipment. This 

capture technique proved to be effective but 

labor intensive, and success was largely 

dependent on the skills of individual divers 

(Sanders and Wendell 1991). Initially, we 

expected that this technique would be 

sufficient to maintain the management zone 

free of sea otters, but we did not account for 

the decrease in efficiency that occurred 

when the targets of capture operations were 

small numbers of sea otters spread over 

hundreds of miles of coastline. The 

logistical arrangements necessary to mount a 

capture operation were considerable 

regardless of how many sea otters were 

being targeted. Often the target of an 

operation was a small group of sea otters or 

even a single individual. If the capture 

attempt failed, there was little recourse but 

to wait for another opportunity once the 

animal(s) settled down. In contrast, when 

we captured sea otters for translocation to 

San Nicolas Island, we had access to large 

numbers of sea otters that offered multiple 

capture opportunities. If one group of sea 

otters dispersed, capture efforts could be 

easily shifted to another group nearby. 

In addition to underestimating the 

difficulties involved in capturing sea otters, 

we underappreciated their physical 

capabilities and drive to return to their home 

range. It is clear that the deep ocean 

channels surrounding San Nicolas Island did 

not pose a barrier to sea otter movements as 

we initially believed they would. We now 

know, based on the resightings of 

translocated sea otters in the mainland range 

of the parent population and the return of 

southern sea otters removed from the 

management zone, that southern sea otters 

are eminently capable of traversing long 

distances and navigating to the areas where 

they were originally captured. 

Despite the fact that capture operations in 

the management zone were arduous and 

relatively ineffective, the potential for harm 

to the animals themselves was ever-present. 

At least four southern sea otters died within 

two weeks of being removed from the 

management zone and released in the 

mainland range of the parent population. 

Although one animal was a very old male, 

as evidenced by his tooth wear, body size, 

and general condition, and one animal was a 

dependent pup transported with its mother, 

the other two were young, prime-aged 

animals in good health at the time of 

capture. We were unable to determine the 

precise cause of death in these animals, but 

we are concerned that their capture and 

relocation was a significant factor. We 

surmise that these animals, captured in areas 

with low southern sea otter densities and 

rich food resources, were unable to survive 

when released in unfamiliar areas with 

moderate southern sea otter densities and 

relatively sparse food resources. In light of 
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 22

the stress-related deaths of southern sea 

otters captured for translocation to San 

Nicolas Island, we cannot discount the 

possibility that the individual susceptibilities 

of sea otters to stress may have also played a 

role in these mortalities. 

ASSESSMENT OF FAILURE CRITERIA IDENTIFIED IN 

TRANSLOCATION PLAN

Public Law 99-625 authorized southern sea 

otter translocation and provided 

requirements for a southern sea otter 

translocation plan should we pursue the 

creation of a translocation program. The 

legislation did not address the possibility of 

the program’s failure. As a consequence, it 

did not specify criteria that would be used to 

determine whether the program had failed, 

nor did it recommend actions that should be 

taken in the case of failure. When we 

developed the translocation plan and 

implementing regulations for the program, 

we received public comment asking us to 

define what constituted failure of the 

program and what actions we would take if 

the program failed. We responded by 

delineating specific failure criteria in the 

1987 Translocation Plan [52 FR 29754; 

August 11, 1987]. 

The purpose of the failure criteria was to 

identify circumstances under which we 

would generally consider the translocation 

program to have failed. The five failure 

criteria were defined before any 

translocations of southern sea otters were 

undertaken and without the benefit of what 

we know today about the translocation, 

containment, and recovery needs of southern 

sea otters. The criteria focus on the status of 

the translocated population and, in 

hindsight, clearly do not address all the 

circumstances that are relevant to a complete 

evaluation of the program. For example, the 

failure criteria do not address the possibility 

that containment might not be successfully 

accomplished because of southern sea otters 

entering the management zone from the 

mainland range of the parent population 

rather than from the experimental population 

at San Nicolas Island. The failure criteria 

also do not address the possibility that the 

founding population of the San Nicolas 

Island colony might be fewer than 70 

animals, or even the possibility that an 

“established” population at San Nicolas 

Island, defined in our regulations, may be 

insufficient to attain the recovery goals 

established for the program. We believe 

that, ultimately, failure is determined by our 

ability or inability to attain the objectives of 

the translocation program, which are clearly 

set out in our final rule for the establishment 

of an experimental population of southern 

sea otters [52 FR 29754; August 11, 1987]. 

In this draft evaluation of the southern sea 

otter translocation program, we find that the 

translocation program meets failure criterion 

2 as defined in the original 1987 

translocation plan. We also find that the 

translocation program meets, in spirit, 

failure criteria 3 and 4. A summary of our 

analysis of each failure criterion is given 

below. 

 

Criterion 1 has not been met. Sea otters 

have been observed in the translocation zone 

at San Nicolas Island every year since the 

beginning of the program. 

Criterion 1: If, after the first year 

following initiation of translocation or 

any subsequent year, no translocated 

otters remain within the translocation 

zone, and the reasons for emigration or 

mortality cannot be identified and/or 

remedied;
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 23

Criterion 2 has been met. Within 3 years of 

the initial transplant (August 1990), a 

maximum of 15 adult (or sub-adult) sea 

otters resided in the translocation zone. We 

chose not to declare the translocation 

program a failure at that time because 

southern sea otters were reproducing, 

dispersal into the management zone had 

abated, and the California Department of 

Fish and Game expressed a desire to 

continue zonal management of southern sea 

otters. During the subsequent years, the 

colony has fluctuated and is showing signs 

of slow growth. For 11 of the 15 years 

(including 1990), the number of sea otters at 

the island remained below 25. The high 

count for 2004 was 32 adult (or sub-adult) 

sea otters. The future of the colony remains 

uncertain, despite the fact that 18 years have 

passed since the initial translocation. 

The emigration of southern sea otters from 

San Nicolas Island is the primary cause of 

failure under this criterion. Although high 

rates of dispersal were seen in all earlier sea 

otter translocations (Estes et al. 1989), we 

believed that the translocation to San 

Nicolas Island would not result in the 

significant dispersal of animals because of 

the abundance of prey items, the apparent 

suitability of the habitat, and the perceived 

barrier imposed by the surrounding deep 

water. After the first year of translocation, 

we made substantial changes to the program 

with the intent of minimizing or eliminating 

emigration [53 FR 37577; September 27, 

1988]. These changes were implemented 

during the second year of the program, when 

we selected younger sea otters for 

translocation, transported sea otters more 

quickly and in smaller groups, abandoned 

the use of holding pens at the island, and 

released newly translocated sea otters in the 

vicinity of sea otters already residing at the 

island. Despite our efforts, none of these 

changes appeared to result in a decrease in 

emigration. In the final year of the 

translocation effort, we attempted to gain 

more information on sea otter movements by 

implanting radio transmitters in sea otters 

immediately prior to their transport to San 

Nicolas Island. Two of the initial three 

southern sea otters that received implants 

died before they could be transported to the 

island, causing us to abandon this effort. 

While emigration appears to be the obvious 

cause of the initial declines of sea otters at 

San Nicolas Island, we have considered 

whether high rates of mortality could be an 

additional factor in the failure of the colony 

to become established. At least 90 southern 

sea otter pups have been born at the island, 

but only about 32 sea otters resided there in 

2004. At first glance, these numbers appear 

to support the contention that pups are dying 

at an elevated rate. When the numbers are 

viewed in context, however, they suggest a 

different conclusion. Because southern sea 

otters normally live about 10 to 15 years in 

the wild, we assume that the majority of the 

32 southern sea otters now at the island are 

offspring of the original translocated sea 

otters. If we assume a founding population 

of 13 adults at San Nicolas Island (the 

maximum number of sea otters counted in 

1992 and 1993 and the lowest numbers 

recorded at the island following completion 

of the translocation effort) and apply a 

mortality rate for first-year pups consistent 

with what we have observed in the parent 

population (about 40 to 50 percent), account 

for some level of natural pre-reproductive 

mortality, and consider the possibility that 

Criterion 2: If, within three years from 

the initial transplant, fewer than 25 

otters remain in the translocation zone 

and the reason for emigration or 

mortality cannot be identified and/or 

remedied;
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 24

some pups could have been weaned at the 

island but then emigrated elsewhere, we 

would not expect to have many more sea 

otters at the island than we currently have. 

Because of high emigration, we failed to 

create a founding population of 70 animals. 

Instead, our founding population appears to 

have numbered as few as 13 animals, and 

not all of these animals may have 

reproduced. Subsequent growth and 

recruitment into the population has naturally 

been slow. Subtle shifts in mortality rates 

and/or emigration rates disproportionately 

affect small populations, a fact that may 

ultimately result in the loss of the sea otter 

colony at San Nicolas Island. 

There has been considerable speculation 

about whether the fishing gear set at San 

Nicolas Island, most notably lobster traps, 

represents a significant source of mortality 

for the southern sea otter colony. No sea 

otters have been observed in lobster traps at 

San Nicolas Island, and our ability to detect 

mortalities is severely limited by our ability 

to track individual animals and monitor 

fishery interactions. We recognize the 

potential that southern sea otters could 

become trapped and drown in lobster traps. 

However, the recent, albeit slow, growth of 

the sea otter colony suggests that, if trap 

mortality is occurring, it has not prevented 

recruitment into the colony. 

The fact that the translocation program has 

failed under criterion 2 does not necessarily 

mean that the sea otter colony at San Nicolas 

Island is destined to disappear. The future 

of the San Nicolas colony is uncertain. It 

appears unlikely, however, that the colony 

will ever be large enough to supply the 

numbers of sea otters that would be needed 

to perform a successful translocation to the 

mainland range if the parent population were 

reduced or eliminated by a catastrophic 

event. 

 

We are unable to evaluate whether the 

program has failed under criterion 3, taken 

literally, because we never reached the 

minimum number of sea otters at San 

Nicolas Island required to complete the 

transplant phase of the program. The 

translocation plan defines the transplant 

phase as ending when there are at least 70 

healthy southern sea otters of mixed ages 

and sexes within the translocation zone and 

we determine that the population is 

increasing due to natural reproduction. 

Although we translocated twice this number, 

we never achieved the requisite core 

population of 70 animals. From a practical 

perspective, however, the transplant phase 

ended when the last sea otter was 

translocated to the island in 1990. The 

population declined at a significant rate from 

the program’s inception in 1987 to 1992, at 

which time the number of independent sea 

otters at the island was 13. Although pups 

were observed from 1987 to 1992, there 

appeared to be little or no recruitment into 

the population. There were far fewer sea 

otters at the island in 1992 than the 

minimum number (25) required to avoid a 

declaration of failure under failure criterion 

2; however, under provisions of failure 

Criterion 3: If, after two years following 

the completion of the transplant phase, 

the experimental population is declining 

at a significant rate, and the translocated 

otters are not showing signs of successful 

reproduction (i.e. no pupping is 

observed); however, termination of the 

project under this and the previous 

criterion may be delayed, if reproduction 

is occurring, and the degree of dispersal 

into the management zone is small 

enough that the effort to remove otters 

from the management or no-otter zone 

would be acceptable to the Service and 

the affected State;
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 25

criterion 3 we could delay termination of the 

program because pupping was occurring. 

The experimental population has fluctuated 

in number since 1992 and now appears to be 

increasing slowly; reproduction continues to 

occur. The rate of dispersal from the island 

is unknown, but we now know that the deep 

ocean channels surrounding the island do 

not present a barrier to dispersal. Although 

pupping is occurring, it is not clear that the 

San Nicolas colony will survive. If the 

colony does survive, it will have been 

founded on a small subset of the core 

number of 70 healthy sea otters of mixed 

ages and sexes that were intended to found 

the population, a fact that has implications 

for the genetic makeup of the resulting 

population. 

Technically, criterion 4 has not been met. 

This criterion clearly specifies that the 

program would be declared a failure if sea 

otters moved from the translocation zone

and became established in the management 

zone. The criterion does not strictly apply if 

animals immigrate into the management 

zone from the parent range. Nevertheless, 

we believe that from a practical perspective 

the spirit of criterion 4 has been met. 

Beginning in 1998, large groups (50 to 150 

individuals) of sea otters have seasonally 

moved into the management zone from the 

parent range. Although there is no evidence 

of a permanent breeding colony in the 

management zone, commercial fishing 

interests contend that local shellfish 

populations available to the fishery have 

been reduced by the presence of these sea 

otters. 

The difficulties associated with sea otter 

capture and transport, our concern for the 

welfare of animals removed from the 

management zone, the adverse effects of sea 

otter containment on the parent population, 

and the adverse effects on fisheries are 

concerns regardless of whether sea otters 

enter the management zone from the parent 

range or from San Nicolas Island. Although 

criterion 4 is specific and applies only to sea 

otters originating from San Nicolas Island, 

our experience with sea otters entering the 

management zone from either the parent 

range or the translocation zone indicates that 

successful containment of sea otters, or 

maintenance of an “otter-free” management 

zone, cannot be accomplished by simply 

capturing animals in the management zone 

and moving them to another location. 

Criterion 4: If the Service determines, in 

consultation with the affected State and the 

Marine Mammal Commission that sea otters 

are dispersing from the translocation zone 

and becoming established within the 

management zone in sufficient numbers to 

demonstrate that containment cannot be 

successfully accomplished. This standard is 

not intended to apply to situations in which 

individuals or small numbers of otters are 

sighted within the management zone or 

temporarily manage to elude capture. 

Instead it is meant to be applied when it 

becomes apparent that, over time (one year 

or more), otters are relocating from the 

translocation zone to the management zone 

in such numbers that: 1) an independent 

breeding colony is likely to become 

established within the management zone or 

2) they could cause economic damage to 

fishery resources within the management 

zone. It is expected that the Service could 

make this determination within a year, 

provided that sufficient information is 

available;
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 26

Criterion 5 has not been met. The 

experimental population at San Nicolas 

Island, although small and vulnerable, has 

persisted. There are no proposed Federal, 

State, or local actions that threaten to 

devastate the colony. The Department of 

Defense is responsible for the majority of 

human activity at San Nicolas Island. They 

have conferred with us and given 

consideration to southern sea otters when 

developing projects at San Nicolas Island. 

To date, no projects have posed a threat to 

the colony. 

Conclusion 

The primary purpose of the southern sea 

otter translocation program was to bring 

southern sea otters closer to recovery and 

eventual delisting as a threatened species. 

Based on our evaluation of the translocation 

program against the goals for which it was 

undertaken and the failure criteria 

established for its assessment, we conclude 

that the translocation program has failed to 

fulfill its purpose and that our recovery and 

management goals for the species cannot be 

met by continuing the program. 

The San Nicolas Island sea otter colony is 

small, and its future is uncertain. Even if the 

colony were to become established, the 

resulting population would not likely be 

sufficient to ensure survival of the species 

should the parent population be adversely 

affected by a widespread catastrophic event. 

Recovery of the southern sea otter will 

ultimately depend on the growth and 

expansion of the southern sea otter’s range. 

Although we recognize that there are 

conflicts between an expanding sea otter 

population and fisheries that have developed 

in the absence of sea otters, zonal 

management of sea otters has proven to be 

ineffective and compromises the ability of 

the species to recover. 

 

Criterion 5: If the health and well-being 

of the experimental population should 

become threatened to the point that the 

colony’s continued survival is unlikely, 

despite the protection given to it by the 

Service, State and applicable laws and 

regulations. An example would be if an 

overriding military action for national 

security was proposed that would 

threaten to devastate the colony and the 

removal of otters was determined to be 

the only viable way of preventing loss of 

the colony.
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 27

Glossary

carrying capacity: the point at which the 

population reaches a state in which the 

numbers of animals remain relatively 

constant and in balance with the available 

food supply (estimated as a minimum of 280 

animals for San Nicolas Island, but believed 

to be as high as 400-500 animals) 

established population: a translocated 

population at San Nicolas Island that meets 

the following criteria: (1) an estimated 

combined minimum of 150 healthy male and 

female sea otters residing within the 

translocation zone; (2) little or no emigration 

into the management zone occurring; and (3) 

minimum annual recruitment of 20 sea otters 

experimental population: any southern sea 

otter found within the translocation zone or 

the management zone 

failure determination: a determination that 

the translocation program has failed to 

produce a viable, contained experimental 

population at San Nicolas Island based on an 

evaluation of specific failure criteria given 

in 50 CFR § 17.84 (d)(8)

management zone: an area from Point 

Conception to the Mexican border that 

surrounds the translocation zone and from 

which sea otters are required to be nonlethally removed (as long as a translocation 

zone exists) according to the provisions of 

PL 99-625 

 

parent population: the population of 

southern sea otters existing along the central 

California coast north of the management 

zone 

Public Law 99-625: a law enacted on 

November 7, 1986 authorizing the 

translocation of southern sea otters and 

requiring the specification of a translocation 

zone and a management zone as part of any 

proposed translocation plan 

translocation zone: the area surrounding 

San Nicolas Island within which the 

experimental population of southern sea 

otters was released and is required to be 

contained
Draft Evaluation of the Southern Sea Otter Translocation Program 1987-2004 

 

 28

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