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Overview of State-Managed Marine Fisheries in Southwestern Alaska with reference to the southwest stock of sea otters. Regional Information Report 5J03-02, Alaska Department of Fish and Game, Juneau, Alaska.
Abstract
EXECUTIVE SUMMARY
The Southwest stock of sea otters Enhydra lutris has been declining over the last two decades. The U.S. Fish and Wildlife Service (FWS) is currently reviewing the status of sea otters and contemplating listing the species under the Endangered Species Act. This purpose of this report is to provide background information to the FWS about the potential for interactions of commercial fisheries and sea otters, both during the period of sea otter decline and for future projections. This report addresses potential interactions in commercial fisheries managed by the State of Alaska, including those for which federal agencies delegate management authority to the State. Potential interactions between fisheries and sea otters include direct entanglement in fishing gear leading to direct mortality and/or serious injury, and competition for prey species. Fisheries with potential for entanglement are considered separately from fisheries with potential for competition in this report. With a few exceptions, fisheries that have potential for competition with sea otters do not use gear that has potential for entanglement.
The National Marine Fisheries Service has determined that the set gillnet fishery for salmon, trawl fisheries for groundfish, and pot fisheries for Pacific cod Gadus macrocephalus, king crab Paralithodes camtshaticus, and Tanner crab Chionecetes bairdi have the potential to entangle sea otters. To evaluate the potential for entanglement in state-managed fisheries, an analysis of trends in fishing effort in state-managed fisheries that use set gillnets, trawls, and pots, and occur in the range of the Southwest stock of sea otters, was conducted over the period 1970 to present.
The FWS has determined that sea otters feed primarily on benthic invertebrates in shallow water (<100 m). Fisheries for benthic invertebrates in the range of the Southwest stock of sea otters include those for Dungeness crab, shrimps, razor and other clams, sea urchins, sea cucumbers, sea urchins, scallops, and octopus. To evaluate the potential for competitive interactions of fisheries and sea otters, narrative descriptions of the fisheries for these benthic invertebrates which occur within the range of the Southwest stock of sea otters are included in this report, along with summaries of catch and effort data.
The range of the Southwest stock of sea otters is defined by FWS as including the coastal areas of the Aleutian Islands, the north side of the Alaska Peninsula from False Pass to the Kvichak River, the south side of the Alaska Peninsula from False Pass to Cape Douglas, the Kodiak Archipelago, the Barren Islands and Kamishak Bay in Cook Inlet, and the Pribilof Islands.
The State of Alaska generally manages those waters which occur within 3 miles of shore. In some instances, usually where there was a management history that predated the Fishery Conservation and Management Act of 1976, the federal government has delegated management authority to the State. For some other “parallel” fisheries, management regulations are coordinated between state and federal waters so that the same seasons, gear restrictions, quotas nd other regulations apply.
There are very few recorded instances of sea otter take in Alaskan fisheries, and entanglement risk is thought to be very low. Some gears, such as salmon gillnets, theoretically have the potential to entangle sea otters, but are usually fished outside of sea otter habitat or in other ways such that the reported instances of sea otter entanglement is very low. No fishery records or observations suggest that fishing gear encounters contributed to the decline of sea otters.
Most commercial fisheries in the area of the Southwest stock of sea otters that take benthic invertebrates occur offshore, well outside the foraging range of sea otters. Exceptions to this include fisheries for Dungeness crabs, sea cucumbers, and sea urchins. There is a long history of competitive interactions between Dungeness crab fishermen and sea otters in other locations. Sea otters are usually able to forage far more efficiently and persist at lower crab densities than is feasible for commercial fishermen or allowed under fishing regulations. Alaskan crab fisheries are restricted by seasons, sex, and size limits, leaving the females and undersized males unharvested.
A very small fishery for green sea urchins exists along the west side of Kodiak Island, with a few landings recorded from Unalaska Island as well. While there is potential for overlap with sea otter diets, fishery quotas are thought to be low enough so as to not cause local depletion, and removals have occurred only in limited areas.
Red sea cucumber fisheries occur around Kodiak Island, and to a lesser extent in several areas off of the Alaska Peninsula. The fisheries are regulated by area-specific guideline harvest levels which are thought to be conservative and not result in localized depletion. Sea cucumber fishers are present in the nearshore areas for a very limited number of days each year, so disturbance is not thought to be a problem. In addition, a significant proportion of the sea cucumber resource occurs below practical diving limits and is not harvested, although it is well withing sea otter diving ranges.
In many instances, state fishing regulations are in addition to, and more conservative than, associated federal fishing regulations. For instance, most state waters in the central and western Gulf of Alaska are closed permanently to trawling. The state waters Pacific cod fishery is restricted to fixed gear only. In addition, restrictions are placed on numbers of pots or jigs in an effort to provide for slow-paced fisheries that minimize effects on habitat and other species. State regulations prohibit directed fisheries for sharks and, with a few minor exceptions, no fisheries are permitted for forage fishes owing to their ecological role in the marine environment. Very strong resource conservation principles are embedded in a number of policies that guide the Alaska Board of Fisheries in their development of state fishing regulations, including the Sustainable Salmon Fishery Policy, Policy on King and Tanner Crab Resource Management, and the Guiding Principles for Groundfish Fishery Management.
... Northern sea otters are not likely to interact with groundfish fisheries in the Alaska EEZ because the areas of fishing and the types of prey preferred by otters do not overlap with the groundfish fisheries. Otters feed primarily in the rocky near shore areas on invertebrates, while groundfish fisheries are conducted further offshore on groundfish species (Funk 2003). Otters may also feed on clams in Federal waters in the soft sediment substrate of Bristol Bay and Kodiak areas (70 FR 46365, August 9, 2005). ...
... No mortality or serious injuries to sea otters were observed in the EEZ. One sea otter mortality in the trawl fishery of the BSAI was reported in 1997, but no other sea otter mortality in the groundfish fisheries in the EEZ off Alaska has been reported (Funk 2003). Because this action is limited to the non-pelagic trawl fisheries and would make no changes to the fisheries that may impact sea otters, this action is not likely to affect northern sea otters in any manner not already considered under previous ESA consultations. ...
this document. Chapter 3 contains information on the affected environment, Chapter 4 discusses the biological and environmental impacts of the alternatives as required by NEPA. Impacts on endangered species and marine mammals are also addressed in this section. Chapter 5 contains a Regulatory Impact Review (RIR) which addresses the economic impacts of the alternatives and Chapter 6 discusses the IRFA as required under the RFA. The proposed action would modify the existing license limitation program (LLP) for the Alaska scallop fishery. Beginning in 2001, a Federal Scallop License Limitation Program (LLP) license is required on board any vessel deployed in scallop fisheries in Federal waters off Alaska. Under the LLP, 7 vessel owners are licensed to fish statewide (outside Cook Inlet Registration Area) utilizing two 15 foot dredges, and two vessels owners are licensed to fish statewide with a single 6-foot dredge. All 9 licenses permit vessel owners to fish inside Cook Inlet with a single 6-foot dredge
... The Alaska Board of Fisheries develops management plans in open, public meetings after considering public testimony and advice from various scientists, advisors, fishermen, and user interest groups. Alaska by Species, 1960-2003 1960 1965 1970 1975 1980 1985 1990 1995 2000 Year Millions of Sockeye, Coho, Pink, and Chum Alaska, by species, from 1960Alaska, by species, from -2003. Sockeye, coho, pink, and chum catches are scaled by the left axis; Chinook catches are scaled by the right axis. ...
Risk measures can summarize the complex variability inherent in fisheries management into simple metrics. We use quantitative risk measures from investment theory to analyze catch and revenue risks for 90 commercial fisheries in Alaska, USA, nearly a complete census. We estimate the relationship between fishery characteristics and catch risk using nonparametric random forest regression to identify attributes associated with high or low risks. Catch and revenue risks for individual Alaskan fisheries are substantial and are higher than risks for farmed food alternatives. Revenue risks are greater than catch risks for most fisheries, indicating that price variability is an additional source of risk to fishermen. Regression results indicate that higher productivity species tend to be higher risk, and there is an increasing gradient of risk moving north and west across Alaskan waters, with the remote western Bering Sea fisheries tending to have the highest risks. Low risk fisheries generally have large catches and support larger fleets. Finally, fisheries with greater catch history under some form of dedicated access privileges tend to have lower catch risks.
We used restriction-enzyme analysis of polymerase-chain reaction-amplified, mitochondrial DNA (mtDNA) to assess genetic differentiation of subspecies and populations of sea otters, Enhydra lutris, throughout the range of the species. There were several haplotypes of mtDNA in each subspecies and geographically separate populations. MtDNA sequence divergence of haplotypes of sea otters was 0.0004-0.0041 base substitutions per nucleotide. E. L nereis appears to have monophyletic mitochondrial DNA, while E. I. lutris and E. I. kenyoni do not. Different frequencies of haplotypes of mtDNA among populations reflect current restriction of gene flow and the unique histories of different populations. There are two or three haplotypes of mtDNA and diversity of haplotypes is 0.1376-0.5854 in each population of otters. This is consistent with theoretical work, which suggests that population bottlenecks of sea otters probably did not result in major losses of genetic variation for individual populations, or the species as a whole.
Bycatch management measures instituted for groundfish fisheries of the eastern Bering Sea have focused on reducing the incidental capture and injury of species traditionally harvested by other fisheries. These species include king crab, Paralithodes and Lithodes spp.; Tanner crab Chionoectes spp.; Pacific herring, Clupea harengus pallasi; Pacific halibut, Hippoglossus stenolepis; and Pacific salmon and steelhead trout, Oncorhynchus cpp. Collectively, these species are called 'prohibited species', as they cannot be retained as bycatch in groundfish fisheries and must be discarded with a minimum of injury. Regulations promulgated in the 1940s and 1950s prohibited taking and retaining these species except by specific gear types. The concept of prohibited species was incorporated into regulations implemented following passage of the Magnuson Stevens Fishery Conservation and Management Act (MSFCMA) in 1976, first for controlling foeign fisheries within the U.S. Exclusive Economic Zone, and then for the development of domestic fisheries thereafter. The North Pacific Fishery Management COuncil (NPFMC) and the National Marine Fisheries Service (NMFS) have enacted many management mesures to allocate, control, and reduce the incidental take of prohibited speice sin groundfish fisheries. This paper provides a historical review of thse measures and analysis of their effectiveness.
Sea otter (Enhydra lutris) populations were exploited to near extinction and began to re-cover after the cessation of commercial hunting in 1911. Remnant colonies of sea otters in the Aleutian archipelago were among the first to recover; they continued to increase through the 1980s but declined abruptly during the 1990s. We conducted an aerial survey of the Aleutian archipelago in 2000 and compared results with similar surveys conducted in 1965 and 1992. The number of sea otters counted decreased by 75% between 1965 and 2000; 88% for islands at equilibrial density in 1965. The population decline likely began in the mid-1980s and declined at a rate of 17.5%/year in the 1990s. The minimal population estimate was 8,742 sea otters in 2000. The population declined to a uniformly low density in the archipelago, suggesting a common and geographically widespread cause. These data are in general agreement with the hypothesis of increased predation on sea otters. These data chronicle one of the most widespread and precipitous population declines for a mam-malian carnivore in recorded history.
After nearly a century of recovery from overhunting, sea otter populations are in abrupt decline over large areas of western Alaska. Increased killer whale predation is the likely cause of these declines. Elevated sea urchin density and the consequent deforestation of kelp beds in the nearshore community demonstrate that the otter's keystone role has been reduced or eliminated. This chain of interactions was probably initiated by anthropogenic changes in the offshore oceanic ecosystem.
The abundance of Bristol Bay red king crab Paralithodes camtschaticus has fallen to historically low levels in recent years. Concerns about depressed spawning stock levels and economic hardships associated with fishery closures in 1994 and 1995 prompted reevaluation of the status quo harvest strategy and investigation of alternative strategies to rebuild the stock. Using a length-based model initialized with the 1994 population abundance, we simulated future effects of seven alternative rebuilding strategies on this stock. Strategies ranged from the status quo strategy through increasingly restrictive harvest strategies culminating in complete fishery closure until the stock is rebuilt. Statistics on catch, variation in catch, effective spawning biomass, probability of rebuilding, probability of fishery closure, and present exvessel value were collected for comparisons. Sensitivities of the harvest strategies to natural mortality, handling mortality, stock-recruitment relationship, and measurement error were examined. Reducing the status quo harvest rate greatly shortened rebuilding time and enhanced long-term catch. The most conservative strategy achieved a 50% probability of rebuilding the stock to a target 25,000 t of effective spawning biomass in 12 y. In terms of catch and present exvessel value, the status quo strategy performed best among the seven strategies over a short-term (≤20 y) planning horizon, whereas strategies with a mature male harvest rate of 50-75% of the status quo level performed best over longer planning horizons. Scenarios with lower natural mortality, higher handling mortality, or a more density-dependent stock-recruitment relationship favor the implementation of more conservative strategies. Our analysis of population and fishery dynamics leads us to recommend a 25-50% reduction in harvest rate to rebuild this depressed stock.
(1) Counts through time were compiled for five sea otter (Enhydra lutris) populations in the north-east Pacific Ocean that were below equilibrium density: Attu Island, south-east Alaska, British Columbia, Washington State, and central California. Similar data were obtained from the equilibrium density population at Amchitka Island in 1971 and 1986. (2) Shorelines of Attu and Amchitka islands each were divided into forty-five segments, within which lineal (length of shore at mean higher high water) and areal (mean higher high water to the 10-fathom (18.3-m) depth contour) measures were made of the amount of habitat. (3) Rate of increase for the four northern populations was 17-20% year-1. Density- or size-dependent changes in rate of increase could not be demonstrated for any of these populations. The California population, in contrast, has undergone three apparent growth phases: the early 1900s to the mid-1970s when it increased about 5% year-1; the mid-1970s to the mid-1980s when it declined about 5% year-1; and the mid-1980s to 1988 when it increased about 7% year-1. An exponential growth model accounted for 92-98% of the variation in counts through time in all cases. (4) Population increase at Attu Island was achieved largely by range expansion as opposed to increased density. Range expansion in lineal and areal habitat occurred at 11% and 13% year-1, respectively; neither rate was lower (P > 0.25) than the observed rate of increase in numbers of animals counted. (5) Despite similarities in island size and physical environment, the most conservative estimates of population density at Amchitka Island were > 3 X greater than maximum density estimates for Attu Island. (6) Surveys of Amchitka Island from the mid-1930s through the mid-1980s indicate that the population increased to a peak in the 1940s; declined abruptly thereafter; and subsequently increased to a new and higher equilibrium in the 1960s, where it has since remained. (7) These population data, together with information on sea otter foraging and benthic community structure at Attu and Amchitka islands, suggest that multiple population equilibria exist in this system, emanating from complex trophic interactions low in the food web. I hypothesize that the lower population equilibrium is achieved largely or exclusively on an invertebrate diet consisting principally of herbivorous sea urchins. When unregulated by sea otter predation, the rocky benthos is deforested by sea urchin grazing. As growing otter populations compete increasingly for food, grazing intensity declines and the system shifts to one dominated by kelp beds, in turn leading to increased production, a shift in habitat structure, and population increases of kelp bed fishes. Apparently this new food resource elevates the sea otter population to a higher and more stable equilibrium.
Enhydra lutris at Amchitka Island spent 55% of daylight hours foraging; there were distinct early morning and late afternoon peaks in foraging activity; and fish made up over 60% of their overall diet by volume. The more recently established populations at Attu Island and off the coast of Oregon are far below equilibrium density. At both Attu and in Oregon, sea otters spent 17% of daylight hours foraging; there was no peak in foraging activity; and herbivorous macroinvertebrates made up their entire diet. Subsequent to overexploitation of sea otters, uncontrolled populations of herbivorous sea urchins greatly reduced or eliminated sublittoral kelp assemblages. In areas only recently reoccupied by otters, sea urchins are abundant and easily accessible as prey. Otters in these areas invest relatively little effort in foraging, and distribute that effort uniformly throughout the day. Where otters are abundant sea urchins are scarce, in turn promoting the growth of kelp beds and an associated fish fauna. Consequently otters at Amchitka invest more time in pursuit of more elusive prey (fish), and distribute that effort disproportionally toward morning and evening to correspond with availability of kelp bed fishes. -from AuthorsEnhydra lutris Amchitka Island Attu Island Oregon
The effects of small population size on genetic diversity and subsequent population recovery are theoretically predicted, but few empirical data are available to describe those relations. We use data from four remnant and three translocated sea otter ( Enhydra lutris) populations to examine relations among magnitude and duration of minimum population size, population growth rates, and genetic variation. Mitochondrial (mt)DNA haplotype diversity was correlated with the number of years at minimum population size (rs = −0.741, p = 0.038) and minimum population size (rs = 0.709, p = 0.054). We found no relation between population growth and haplotype diversity, although growth was significantly greater in translocated than in remnant populations. Haplotype diversity in populations established from two sources was higher than in a population established from a single source and was higher than in the respective source populations. Haplotype frequencies in translocated populations of founding sizes of 4 and 28 differed from expected, indicating genetic drift and differential reproduction between source populations, whereas haplotype frequencies in a translocated population with a founding size of 150 did not. Relations between population demographics and genetic characteristics suggest that genetic sampling of source and translocated populations can provide valuable inferences about translocations.
A comparison of western Aleutian Islands with and without sea otter populations shows that this species is important in determining littoral and sublittoral community structure. Sea otters control herbivorous invertebrate populations. Removal of sea otters causes increased herbivory and ultimately results in the destruction of macrophyte associations. The observations suggest that sea otter reestablishment indirectly affects island fauna associated with macrophyte primary productivity.