This paper was written as part of the 2011 Alaska Oceans Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.
The affects of sea otter (Enhydra lutris) reintroduction in Southeast Alaska on the dive fisheries of southern Southeast Alaska
Team Ostentatious Otters
The reintroduction of sea otters (Enhydra lutris) into Southeast Alaska by the Alaska Department of Fish and Game (ADF&G) between 1965 and 1969 has lead to an observed increase in the otter population of approximately 15,000 individuals in the past 40 years. ADF&G reintroduced 412 sea otters from Amchitka Island and Prince William Sound to six sites in Southeast Alaska. In the same areas there has also been an observed decrease in number of the otters prey species, some of which are of economic importance to Southeast Alaska and support lucrative dive fisheries. The ecosystems of this region are ideal for sea otters and their prey. Southeast Alaska's sea otter population may experience a significant increase and that increase is in a prime location to observe the resulting impacts. We believe that if the increasing sea otter population sufficiently reduces the biomass of its prey species, it could negatively affect the dive fisheries of the area, many of which depend on the same organisms. The 2007-2008 Southeast Alaskan dive fisheries ex-vessel value was estimated at nearly $6 million and the dive fisheries themselves provide hundreds of jobs for Alaskans. These fisheries generate a substantial amount of money for local communities, and are valuable assets to the Alaskan economy. Recent observations have shown that the increases in sea otter populations that are occurring throughout Southeast Alaska are already having an impact on some of the dive fisheries. We have proposed several mitigation plans that we believe would regulate the increasing sea otter populations in a way that would support a stable otter population and sustainable dive fisheries. Regardless of which plans are implemented, if a mitigation process is not put into effect soon, the over predation by sea otters could potentially damage the population of its prey species to unsustainable levels, and could cause the Southeast Alaskan dive fisheries to become inoperable.
Southeast Alaska's marine ecosystem is undergoing changes due to an increase in sea otter population. The sea otters were originally introduced to Southeast Alaska by the Alaska Department of Fish and Game during the sea otter reintroductions that started in 1965. Of the 412 sea otters reintroduced in 1965, 89% were relocated from Amchitka Island while the remaining 11% came from Prince William Sound (Jameson et al., 1982 ). These sea otters were relocated to the following five sites in Southeast Alaska: Yakobi Island, Chichagof Island, Baranof Island, Prince of Wales Island, and Cape Spencer (Jameson et al., 1982). The relocation was considered a success, with the otter population stabilizing and increasing in the years immediately following the repopulation effort. According to a U.S. Geological Survey, the population of sea otters in 2002-2003 had reached approximately 8,949 individuals (Esslinger et al., 2009). Current estimates put the population around 15,000 otters. This is almost double the population of just seven years ago. However, because the pre-fur-trade sea otter population in Southeast Alaska is unknown, it is difficult to tell whether the current sea otter population and/or population growth rate is typical.
Before the exploration of Alaska by Vitus Bering in 1741, otters were abundant along Southeast Alaska's coast (Figure 1). However, in the next 170 years Southeast Alaskan sea otters were virtually eliminated by Russian and American fur traders as seen in Figure 2 (Heubert, 2010). It is estimated that Russian fur traders harvested between 150,000 and 300,000 sea otters (Pritchett et al, 2008). Each fur was estimated at a price equal to a year wages in Russia. Regardless, with the population in Southeast Alaska increasing as seen in Figure 3, from the 412 otters originally relocated to approximately 15,000 individuals in less than 50 years, and with the growth rate in Southeast Alaska ranging from an increase of 15.7% to 23.3% per year between 1966 and 1988, changes in the ecosystem should be expected (Pritchett et al, 2008). The Southeast Alaskan sea otter population is increasing and if no mitigation plan is introduced and their population is left alone, their esculating presence will threaten the organisms that they prey upon.
The sea otter population growth has caused an impact on Southeast Alaska's marine ecosystems. The rapid increase of sea otters is occurring in areas where sea otters haven't existed for several decades, and where the ecosystem has changed in their absence. Because they are the primary consumers of an almost untouched food supply, the sea otters have been able to spread rapidly across Southeast Alaska. This is having an impact on their prey species, which is a cause for concern to Southeast Alaska's dive fisheries which rely on the same prey species. Southeast Alaska is home to several very important sea urchin, sea cucumber, crab and geoduck fisheries all of which now have to compete with the growing population of sea otters as seen in Figure 3. In fact, in 1996 the only commercial abalone fishery in Southeast Alaska was closed due to its inability to compete with sea otters as well as the poor management of the fishery (Imamura, 1994; Heubert, 2010).
Our paper will present an examination of the impact the rising otter population is having on the prey species and the affects this will have on Southeast Alaskan fisheries specifically in Southern Southeast Alaska. We will discuss the role that otters have in Southeast Alaska's marine ecosystem, and emphasize the economic effects of the increasing sea otter population. Finally, solutions will be discussed and future management plans will be considered.
Sea Otter Biology
The sea otter, Enhydra lutris, was originally found in waters around the Japan, Sakhalin, Kamchatka Island, the Commander Islands, Aleutian Islands, Southern Alaska, British Colombia, Washington, Oregon, and California. Sea otters typically vary in color from dark brown to red-brown. The chest, throat and head are whitish or gray. In weight, the males range from 20-45 kg, and 15-30kg for females (Nowak, 1991). Adults usually reach a length of around 1.4 m (Schneider, 2008).
The sea otter, unlike other marine mammals, has no layer of fat insulating its body. Instead, the otter relies on trapped air in its thick fur. The otter's thick fur has made it a target of fur traders for centuries. If the otter does not properly maintain its fur, the insulating layer will be less effective at maintaining the otter's body temperature. For example, if the otter's fur is exposed to oil and not properly cleaned, then it will stop insulating the otter, causing hypothermia (Nowak, 1991). Due to these possible consequences, grooming is imperative to their survival (Schneider, 2008). The fur of sea otters contains one million hairs per square inch, the most of any mammal (Nowak, 1991).
Mating occurs year-round, with high points depending on the area. Males become sexually mature between four and six years of age, while females mature sooner at the age of four. The gestation period can range anywhere from six months to nine months. Births take place in the water. There is usually only one pup born, since only one can be raised at a time. While maturing, otter pups are carried by their mothers for about one month, at which time the otter pups learn to dive. However, the pup is still dependent upon its mother for about six months (Nowak, 1991). In the wild sea otters have been found to live for approximately 15 to 20 years (Schneider, 2008). Sea otters are usually segregated by gender, with males in higher densities than females. Males move into female areas to breed (Nowak, 1991). Otters do not migrate, so the occasional seasonal movements are the largest extent of an otter's travel (Schneider, 2008).
Because of its poor insulation method, a sea otter may eat roughly 23% of its body weight in one day in order to sustain its body temperature (Bodkin et al., 2004). An otter's diet consists mainly of marine invertebrates, such as sea urchins, abalone, crabs and mollusks (clams are the largest portion of the diet in Southeast Alaska). In order for an otter to reach its prey, which live primarily on the seafloor, it must dive to depths ranging between 30 and 100 meters (Bodkin et al., 2004). Usually these dives last from around a minute to a minute and a half, however, longer dives have been recorded (Nowak, 1991). To obtain food from these invertebrates sea otters have been observed to employ crude tools such as rocks to break open the shells of their prey organisms (Nowak, 1991).
The fact that sea otters must have access to large amounts of food has not seemed to have a detrimental effect on the Southeastern population. Before the sea otters were reintroduced, there was a growing abundance of prey species. This combined with few natural predators has provided the otters with an environment in which they are not only free to acquire an adequate amount of food but are also able to reproduce rapidly and provide for their offspring. This is a major factor that has influenced the increase in Sea otter populations.
Sea Otter Predators and Prey
The trophic pyramid of Southeast Alaska includes the top predator, the killer whale (Orcinus orca). Killer whales are capable hunters, and it has been hypothesized that the sea otters in the Aleutian Islands have been undergoing a decline due to predation by killer whales (Schneider et al., 2008). However, the sea otters in Southeast Alaska are rarely preyed upon by killer whales. Killer whales have even been observed in close proximity to sea otters that they could have attacked, but the two species usually appear to ignore one another. During the rare times when the sea otters do appear to feel threatened they will usually seek cover, such as in a kelp beds or reefs (Matkin et al, 2007). With the absence of killer whale predation, Southeast Alaska's adult sea otters lack a major natural predator. There are, of course, still threats to the species survival; it is not uncommon for new born sea otter pups to be victims to predation by bald eagles.
The most prominent cause of death for sea otters in Southeast Alaska is due to human activity. It is generally illegal to hunt sea otters; however, they can still be harvested by Alaska Natives for subsistence harvest and as a source of material for use in handicrafts. Currently Alaska Natives are not allowed to sell whole pelts to non-natives, and the regulation is worded to prevent non-Natives from possessing whole pelts. The harvest of sea otters by Alaska Natives is not regulated by Federal Law, providing the harvest is not wasteful. The number of otters harvested is limited to what can be reasonably utilized. In addition, mortalities can also be caused by the accidental drowning of sea otters that get caught and tangled in fishing nets. One of the most significant causes for a decline in sea otter population in Alaska since the Russian fur trade was the 1989 Exxon Valdez oil spill that killed over 1,000 sea otters (Schneider et al., 2008).
There was little to no population of sea otters recorded in Southeast Alaska for over 50 years after the end of the Russian fur trade. During this time, when the sea otters were absent, their prey species, many of which are benthic organisms that graze on kelp and seaweed, began to flourish (Estes et al., 1995). Several new fisheries took advantage of this sudden abundance of marketable organisms such as: abalone, sea cucumber, geoduck clams and red sea urchin. Dive fisheries for these species were established throughout Southeast Alaska (Pritchett et al., 2008). These fisheries were obligated to acquire permits which helped insure that each harvest did not exceed the maximum sustainable yield, and allowed the populations of otter prey species to stay well above pre-fur trade levels. Then in 1965 the Alaska Department of Fish and Game reintroduced sea otters into Southeast Alaska. The abundant food supply allowed the sea otters population to expand. To the frustration of the Alaskans, whose livelihood depended on the dive fisheries, sea otters also prey upon the same organisms as the dive fisheries. Since sea otters consumption is not controlled by permits or size requirements, like the fisheries are, they are able to out compete the fisheries.
Southeast Alaska is composed of a complex system of islands, glaciers and estuaries. Most of the region's seafloor is dominated by shallow rocky bottoms, and its waters are cold and nutrient rich due to both upwelling from the Pacific Ocean and its temperate latitude. This makes it a good habitat for a diverse ecosystem. Southeast Alaska is host to many soft and rocky bottom benthic organisms including crabs, mollusks, and echinoderms, as well as anadromous and oceanodromous fish species and large kelp forests. It is also home to several species of marine mammals in addition to sea otters.
Kelp forests, which occur worldwide in temperate latitudes, are a critical part of Southeast Alaska's marine ecosystem. The kelp canopy dampens waves and reduces light penetration; creating the understory conditions favored by some species and reducing coastal erosion. Kelp forests themselves form multilevel environments similar to tropical rainforests, with different species of fishes and other pelagic organisms ranging throughout the water column, benthic organisms on the substrate, among these are several organisms living and feeding on the kelp itself. Kelp forests also provide concealment to many prey species, and can also function as nursery grounds for juvenile organisms and breeding grounds for others (Steneck et al., 2002).
However, unlike their terrestrial counterparts, kelp, while being more diverse and productive, tends to have a shorter lifespan, much faster growth rate, and is more susceptible to both predation by herbivorous organisms such as sea urchins and destruction due to storms. This makes kelp forests seem rather ephemeral. Entire kelp forests can be completely wiped out in a certain area, then return nearly as quickly.
Regardless of its diverse population the Southeast Alaskan marine ecosystem is still very susceptible to change, especially in regards to fluctuations in kelp forest size. Over the past few centuries the Southeast Alaskan ecosystem has fluctuated wildly due to either the extermination or proliferation of kelp forests. Long before Europeans reached Southeast Alaska in the 18th century the Stellar's sea cow was one of the primary consumers of kelp (the degree to which is unknown) before being wiped out by native subsistence hunters. There followed several periods of kelp forest fluctuation, which was now mostly regulated by the abundance of sea urchins and their predator, the sea otter. With each peak or depression in the kelp forest population the ecosystem of Southeast Alaska changed drastically between a region populated by kelp forest communities and a state of sea urchin domination (Dayton et al., 2000).
Southeast Alaska's marine ecosystem is ideal for sea otters. The estuaries and rocky, shallow and sheltered waters of the region provides optimal habitat for the otters. The abundance of both shelter and prey along with the fact that their primary predator seems to have little or no impact on their population, has allowed for a large increase in sea otter population to occur. The ecosystem of Southeast Alaska has been greatly affected by the reintroduction of sea otters and may provide valuable information to future reintroduction plans.
Sea otters are now a fundamental part of Southeast Alaska's marine ecosystem, and they are keystone predators in many North American west coast rocky marine communities (Kvitek et al., 1992). Before the Russian fur trade of the 1700's Southeast Alaska's ecosystem and sea otter populations were relatively stable. However, by the 1900's the otter population had been nearly wiped out. Because of this, the populations of herbivorous invertebrates (such as sea urchins, sea cucumbers and other prey species of sea otters) were able to flourish. This flourishing of the herbivorous invertebrates subsequently caused a decrease in the flora of Southeast Alaska, specifically kelp. The then abundant food supplies allowed the reintroduced sea otter populations to rise dramatically. The rise in sea otters caused a decrease in herbivorous invertebrates and that in turn caused an increase in kelp density. (This correlation between herbivorous invertebrates and kelp depending on the presences of sea otters is what makes sea otters a keystone species.) Sea otters have also been shown to have a significant impact on soft-bottom communities—a 1992 survey showed that an increase in sea otter concentration in an area directly impacted both the number and size of butter clams and other soft-bottom organisms (Kvitek et al., 1992). In less than 50 years after the reintroductions, the population of sea otters as of 2002 had increased to approximately 8,949 individuals (U.S. Geological Survey, 2009). With very few limiting factors, the otter population could continue to grow having a severe impact on its prey species and the Southeast Alaskan ecosystems as a whole.
The large sea otter population limits the size and abundance of large herbivorous invertebrates which then leads to a proliferation of kelp and associated fauna (Kvitek et al., 1992). This process is allowing sea otters to spread rapidly across Southeast Alaska. Sea otters will continue to spread across the region until they reach their carrying capacity. Carrying capacity is determined by the size at which a particular population will stabilize in a particular environment where its supply of resources—food and shelter—remains constant (Garrison, 2007). As the sea otters eat they are reducing the amount of herbivorous invertebrates which in turn leads to the growth of kelp beds which are the primary shelter of sea otters. As the sea otter population expands the amount of shelter provided to the otters increases but the amount of food decreases. Southeast Alaska's sea otter population will continue to rise and they will continue to spread across Southeast Alaska until their population is stable with their food supply. Southeast Alaska is home to some of Alaska's largest sea cucumber, sea urchin and geoduck fisheries, and the rapid rate of sea otters expansion has caused a drop in these species population which has caused concern for the dive fisheries. The affects of the Southeast Alaskan sea otter population growth on species that aren't preyed upon by the otters should also be taken into account. The benefits and/or disadvantages of competition with sea otters for food, and the proliferation of kelp forests for other ecologically important species, may be just as significant as the dive fisheries' dilemma.
Southeast Alaskan dive fisheries harvest primarily three species of invertebrates: geoduck clams, sea cucumbers, and red sea urchin. All of which are primarily located in southern Southeast Alaskan waters. The 2007/08 ex-vessel values of Southeast Alaskan dive fisheries were conservatively estimated at $5,966,544. Up until 1995 Southeast Alaska also had prominent abalone fisheries, which was closed in an effort to stabilize the population that was under pressure from the newly reintroduced sea otters and an efficient fishery.
The first commercial geoduck clam permit was issued in 1985. The current harvest of geoduck clams is valued at $1,954,582. Geoduck clams tend to accumulate detrimental microorganisms or compounds such as paralytic shellfish poisoning. Because of this, harvests are allowed by permit only and are generally approved only from October through May to minimize PSP toxin levels, and all harvests must pass a PSP sample before a fishery may ship live product. Harvests are also generally limited to beds that have available biomass estimates, the maximum harvest rate is about 2% per year. The strict management rules are imposed because geoducks are long-lived and reproduction is both sporadic and low (Pritchett et al., 2008).
The first sea cucumber harvests began in 1983, which is now valued at $3,774,428 annually. Because of their rapid decomposition once eviscerated, sea cucumber catch is limited for individual fishermen. The largest sea cucumber fishery is located in Southeast Alaska. The maximum harvest rate for sea cucumbers is 6% of the biomass estimate. Alaskan sea cucumber harvests peaked in 1989 with 2.3 million lbs (Pritchett et al., 2008; Woodby et al., 2005).
Harvest of red sea urchin began in Southeast Alaska in 1981. The current harvest of red sea urchins is valued at $237,534. Red sea urchins are primarily harvested for their gonads, commonly known as uni, or roe. The maximum annual harvest levels for red sea urchin are at 6% of the biomass estimate. Fisheries can only be open if a biomass survey has been conducted in the previous three years. Sea urchin harvests in Alaska peaked in 1997 with 6.5 million lbs harvested (Pritchett et al., 2008; Woodby et al., 2005).
The reintroduction of sea otters into Southeast Alaska has had a negative effect on the dive fisheries located in southern Southeast Alaska. Fisheries managers believe that the current abalone population is too low to allow a commercial fishery and the species is not likely to produce the adequate amount of offspring to return the population to a sustainable level. The fisheries managers also believe that the overfishing and predation by sea otters is to blame for this decrease in population of abalone. Sea otters have had a major role in the closing of several commercial harvest areas for sea cucumber, geoduck clam, and red sea urchin. In one year sea otters accounted for the removal of 16,000,000 sea urchins in southern Sitka Sound (Pritchett et al., 2008).
Given the effects the sea otter reintroduction has had on the biology and economics of southern Southeast Alaska, as well as the rest of Southeast Alaska, mitigation plans must be instigated. The most effective way to halt the decline of otter prey species would be to considerably reduce the otter population. One possible solution is through the sterilization of individual otters. These methods are feasible because they directly reduce the amount of otters born in the future. Using these methods could be viewed as inhumane and would take vast amounts of man hours to round up a significant amount of sea otters. Furthermore, this method of mitigation is very expensive. The average price to perform one of these procedures is approximately $200 per otter. To perform such a large scale population control seems very challenging and time consuming in the long run; however the primary fall back of this mitigation method is the conflict of its inhumanity to the sea otters.
Sea otters are considered a keystone species in their ecosystem and if the reduction of sea otters were to take place quickly it could be detrimental to the organisms that rely on them, such as kelp. Careful mitigation procedures would have to occur to allow a gradual decline in sea otters that could be controlled.
Alaskan state congressman Don Young has introduced legislation aimed at increasing sea otter harvest and pelt sales. He is targeting Southcentral and Southeast Alaskan sea otters due to their growing populations and increasing consumption of herbivorous invertebrates. The Marine Mammal Protection Act allows Alaskan Natives to take sea otters for subsistence use. However, it limits sales of pelts that have been made into handicrafts or clothing. Don Young would like to allow Alaska Natives to increase subsistence harvest and sale of whole pelts. He believes this increase in harvest will not only control the sea otters ever growing population but it will also give value to the sea otters through the village or individual native person, who harvest the otter. This mitigation plan would not only control the sea otters growth but it would bring income into Alaska both by the sale of sea otter pelts and by the increase in dive fisheries due to the decline in sea otters. However, environmental and animal rights groups oppose the bill. They argue that marine mammals play an important role in the natural balance of costal waterways. They also claim that by allowing full pelts to be sold poachers will take advantage of subsistence otter harvests minimal oversight (Schoenfeld, 2010). An increase in the management of sea otter harvest could alleviate illegal hunting.
For example, in 1975, the Alaska Department of Fish and Game prepared a predator control plan to combat the rising predation of moose by wolves in the Southeast Yukon. To control the wolf population ADF&G began to use aerial hunting. These methods are considered very controversial even to this day due to the brutality of the measures taken. Even with the use of these harsh control strategies, the wolf population by autumn of 1991, nine winters after control measures ended, wolf numbers exceeded the pre-control population size and wolf density had increased (Boerje, 1996).
It is important to note that wolves and otters, along with their respective prey species, may not react the same way to this kind of management program. Also, this plan would probably have a negative effect due to the relationship between sea otters and human beings. Generally in the public's view, sea otters, unlike wolves, are viewed as endearing and harmless. To the public, control of these creatures would seem inhumane and lacking rationale.
Central California also went through sea otter relocations in the 1980s. The otter population numbered fewer than 2,000 and the U.S. Fish and Wildlife Service was afraid that an oil spill or another similar catastrophe could wipe out the entire sea otter population of California, which had been nearly hunted to extinction in the mid 19th century. To prevent such a serious event an ambitious repopulation plan was undertaken in the early 1980s to revive the population. They relocated 100 otters from California's central coast to San Nicolas Island, 100 km west of Los Angeles. While the sea otter relocation effort was very popular with the general public, the otters also proved to be voracious consumers of many species because of their appetites. Those involved with the fisheries in the region were furious. In 1986 Congress struck a compromise and set up "no-otter zones" around key fishing areas. The zones were intended to eliminate the growing competition between fisheries and sea otters. The U.S. Fish and Wildlife Service were required to collect any otters that entered this zone and return them to San Nicolas Island. After several years this task proved exceedingly difficult because translocated otters began to compete with the fisheries for food. In 1993 it was decided that enforcing these "no-otter-zones" was unrealistic, the entire project was abandoned and the agency quietly stopped enforcing the "no-otter zones". Because the growing population of sea otters didn't have to receive permits or follow regulations, fishermen began to complain that the otter population was damaging their business. Some fishermen have reported that the otters contributed to reducing harvest resources by up to 80% in the two years following the collapse of the "no-otter zones" (Vogel, 2000).
If we decided to introduce "no-otter zones" around key dive fishing areas in southern Southeast Alaska we could maintain both dive fisheries and a stable sea otter population. To do so we could relocate the sea otters captured in the "no-otter zones" to northern Southeast Alaska which still has locations with abundant prey and habitat yet has few dive fisheries. The main problem with this mitigation technique is the amount of time and money it would take to constantly relocate otters out of the "no-otter zones". It is the same reason this technique didn't work in Southern California.
Another possible course of action would be to let the otter population continue to grow naturally with no intervention U.S. Fish and Wildlife Service. The population of sea otters would eventually reach its carrying capacity where its population would stabilize with the available biomass. The sea otters marine ecosystem would return to a natural equilibrium similar to before the Russian fur trade of 1741 (Jameson et al., 1982). This course of action is beneficial to the southern Southeast Alaskan marine ecosystem but would have a detrimental effect to the local dive fisheries in the area. With otters approaching their full carrying capacity there would be a finite amount of biomass available to the dive fisheries for future harvest. This decrease in biomass would effectively cease all dive fishery operations in southern Southeast Alaska. This could, however, give rise to new industries, such as kelp harvesting, and/or benefit existing marine resources.
It is now apparent, due to the anticipated effects of sea otter reintroduction on the marine ecosystems of southern Southeast Alaska, that some combination of mitigation plans must be put into use as soon as possible in order to avoid the decline of the currently sustainable dive fishery industry in southern Southeast Alaska. The most functional and realistic of these plans would be to combine the "no-otter zone" mitigation plan with Alaska State Representative Don Young's proposed mitigation process aimed at increasing sea otter harvest and pelt sales by Alaskan natives. These management strategies would be combined in such a way that would allow an increase in harvest from the proposed "no-otter zones". This would both protect the dive fisheries as well as sustain a stable sea otter population, in addition to bringing revenue into the state through the sale of sea otter pelts and the continuation of dive fisheries.
Regardless of whether an effective mitigation plan is put into place, the fate of the Southeast Alaskan sea otter population should be subject to intense observation. This is an opportunity to test new mitigation plans that can be employed elsewhere in similar dilemmas and/or observe the Southeast Alaskan ecosystems as the proliferation of kelp continues and the marine environment returns to an ecological state that hasn't existed in Southeast Alaska since the fur trade in the 18th century. It is not out of the question that the benefits of a large sea otter population could outweigh the loss of the dive fisheries. Nevertheless, if a mitigation plan is put into place it should be efficient, simple, and well enforced (both in regards to the sea otter population and the hunting of the otters). This is too good of an opportunity to waste.
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