Information Needs and Recommendations
Two paradoxes permeated the committee’s discussion. First, the available behavioral and physiological evidence for the 1990s suggests that individuals in the declining western stock of Steller sea lions are at least as healthy as individuals in the eastern stock, which has been increasing by about 2% per year. Second, the western stock has not shown signs of recovery despite substantial restrictions imposed on commercial groundfish fisheries since 1999. This has raised questions about the presumed interaction between sea lions and commercial fishing activity. The available data are inadequate either for fully justifying or for overturning fishery management measures to protect Steller sea lions. Therefore, the National Marine Fisheries Service (NMFS) and the North Pacific Fishery Management Council still will be obligated to make regulations based on inconclusive information. Because many of the disputes over management actions (the reasonable and prudent alternatives) arise from the divergent interests of stakeholders, resolution may not occur until there is considerable evidence confirming one (or more) of the hypotheses or there is a clear and sustained recovery of the Steller sea lion population.
CURRENT AND FUTURE INFORMATION NEEDS
The ability to determine the effects of restrictions on fisheries on recovery of the Steller sea lion population will depend not only on the biophysical data that are collected but also on the management regime
that is in place when the data are collected. If present closures are maintained or expanded in response to demands for a more precautionary approach to Steller sea lion protection, it will likely be difficult or impossible to attribute future population changes to the new management regime. This difficulty arises because these management changes will take place in a continuously varying physical and biological environment. To complicate matters further, Steller sea lion management measures themselves have not been static. Statistically, changes that might be attributed to future management measures will be deeply “confounded” by changes in other components of the ecosystem.
To obtain targeted information requires definition of fisheries management options and specification of monitoring data that would allow determination of the efficacy of each option. By “efficacy” we mean a reversal of declining Steller sea lion abundance trends. This approach is referred to as an adaptive management experiment (Walters, 1986).
It remains unclear whether existing fisheries restrictions and closed areas should be treated as “precautionary” policies with respect to Steller sea lions. Some of the most credible hypotheses about the recent decline— including killer whale predation, continued illegal shooting and subsistence harvest, productivity declines due to regime shifts, and persistent changes in fish community structure due to predator-prey interactions— are not addressed by reducing the biomass of fish caught in sea lion critical habitat.
There are a few obvious data and monitoring requirements to include in future adaptive management options for Steller sea lions:
Steller sea lion abundance, sex ratio, and survival/productivity rate from recapture patterns of marked (branded) animals at geographically diverse rookeries. Also, there should be continued monitoring of the response variables described in Chapter 6 at a variety of locations in the western and eastern stocks.
Spatial and temporal patterns of fishing activity (efforts, fishing areas) for all fisheries working in proximity to Steller sea lions.
Spatial abundance and seasonal distribution patterns of key fishes that are important prey for Steller sea lions in particular areas, including pollock, Atka mackerel, herring, and sand lance. In this regard, broader systematic use should be made of the localized depletion and tagging estimation procedures that have been tested recently in relation to Atka mackerel and the combined acoustic and trawl survey methods that have provided much insight into the details of interaction patterns in places like Prince William Sound.
Recommendation: The NMFS should make a commitment to long-term sampling and monitoring of population and ecosystem variables such as sea lion and fish population structure and variation, harmful algal blooms, and oceanographic conditions indicative of climate regime shifts. Such intense monitoring should be continued until sea lions are delisted under the Endangered Species Act (ESA).
The fine geographic scale surveys of Steller sea lions on rookeries or haulout sites should be continued. Spatial analyses help distinguish causes that are global (or regional) in scale from causes that operate at local spatial scales. The documentation of site-specific trends, especially when evaluated in the context of related environmental variation, could greatly enhance understanding of the causes.
In addition, it is essential that the pup branding program be continued and expanded geographically. These data are essential for estimating pup and adult survival and would allow for the modernization of Steller sea lion demographics required for population models.
The observer program should be extended to smaller boats whenever feasible. Small boat fisheries (e.g., salmon, crab, herring) in the immediate vicinity of rookeries and haulouts should be monitored for interactions with sea lions, such as entanglement in or injury by fishing gear, disturbance of mothers and pups on rookeries, and illegal shooting or harassment. These activities may directly threaten sea lion survival relative to more gradual impacts associated with reduced availability of prey.
Fishermen in Alaskan native and other communities constitute a largely untapped resource. Their involvement in sea lion research is essential from both an educational and a scientific perspective. Such endeavors could be modeled after the biosampling protocol used in the harbor seal program or the ongoing count of killer whales off Kodiak Island.
Recommendation: More complete information should be obtained from the subsistence harvest of Steller sea lions. For example, tissues should be sampled, teeth extracted, sex determined, etc. Greater attention must be devoted to a socioeconomic study of all fishers and subsistence hunters, including efforts to enlist their knowledge of historic and contemporary Steller sea lion population trends.
The possibility that killer whale predation is a major factor in the decline of the Steller sea lion population is not easily dismissed. Killer
whales are abundant, intelligent, behaviorally flexible, and known to be rapacious consumers of large marine mammals. The predation of killer whales on Steller sea lions was previously thought to be minor, but recent reevaluations of their abundance suggest that killer whales could be a major source of sea lion mortality.
Recommendation: An integrated set of investigations should be conducted to address the contribution of predation to sea lion mortality. Killer whale abundance is a critical component of all modeling approaches. Surveys should extend throughout the western and eastern ranges of Steller sea lions. In addition to abundance surveys, observational studies of killer whale feeding behavior will be important for estimating the size of the transient killer whale population. Transient animals are known to feed primarily on marine mammals such as sea lions, in contrast to resident killer whale pods that are believed to feed primarily on fish. Efforts should be made to determine if killer whales follow fishing vessels or are disproportionately aggregated around Steller sea lion breeding or haulout sites. Individual killer whales should be tagged so that their seasonal movements can be tracked by satellite. The resultant data may indicate whether individual whales (or their pods) are disproportionately associated with fishing operations or Steller sea lion rookeries and haulouts. A major advantage of satellite tags is that they reveal patterns of movement at locations inaccessible to observers, a particular problem during the harsh winter months.
Slaughter of Steller sea lions for a wide variety of purposes—predator control, fox food, scientific inquiry—was sanctioned for decades before it was finally outlawed in 1990. What remains unknown is the extent to which the current law is obeyed. Loss of fish catches to sea lions was the leading motivation for historical predator control and eradication efforts. Although technology has improved the fish-finding and navigational abilities of fishing fleets, fishing gear (e.g., salmon gillnets, halibut longlines, groundfish trawls) remains largely unchanged, with continuing potential for interference by sea lions. Hence, the estimated unreported and illegal takes may be substantially in excess of the conservation modeling estimates.
Recommendation: Confidential interviews and novel approaches should be used to document current levels of lost catch to Steller sea lions and contemporary responses of fishers, including moving to other fishing areas, use of seal bombs, and shooting of animals. The exercise will not be easy because protection of identity and confidentiality will be of paramount importance. Nonetheless, the
committee encourages efforts to document the extent of unauthorized killing of sea lions to help understand the unexplained Steller sea lion mortality.
Because ecological systems are always in a state of flux, any “history” assumes a profound and confounding role in the reconstruction and understanding of specific population trajectories. In fact, the absence of adequate time series data has compromised both the population and ecosystem modeling efforts (see Chapter 6). Although a better understanding of the sea lion decline may not reveal why the western stock has failed to recover, two factors are particularly pertinent.
First, the role of infectious disease should be assessed through retrospective analyses of archival serum and tissue samples from 1980 to 1990 to cover the period of rapid population decline. At the same time, these samples should be tested for the presence of toxins and pollutants.
Second, fishery observer records should be consulted for accounts of killer whale attacks on sea lions. These records may constitute a valuable resource on plausible top-down influences on the sea lion population. Fishery observers should be tasked to document Steller sea lion sightings (killer whales and entanglements in fishing gear).
Recommendation: A protocol should be implemented to test archival blood and tissue samples and collate observer records by year and geographic location.
MONITORING TO EVALUATE MANAGEMENT EFFICACY
The committee identified five possible fishery management options that should be paired with appropriate monitoring programs to provide information valuable for assessing prospects for reversing the population decline. These options are evaluated with regard to their scientific potential for discerning the role of the groundfish fishery in the Steller sea lion decline. Each option would require continuation of the existing monitoring program (i.e., continued census of trend sites and collection of demographic data based on pup branding and resighting). The committee made the assumption that it is possible to craft each of these options so as to satisfy the requirements of the ESA, but did not attempt to evaluate the legality of each option. The five options are presented below.
Wait and see (maintain current closures indefinitely. Current
closures offer one strategy to evaluate current trends in the Steller sea lion decline and the potential for recovery. Under this option, the most valuable monitoring information would be from tags that reveal immediate causes of mortality. A lack of recovery with the current closures would shift suspicion to one of the direct mortality hypotheses (continued culling, predators). A tagging program would provide some insight into the likelihood of these hypotheses so that management actions could be adjusted appropriately.
Eliminate thedirectfishery impacts, with greatly expanded closures. This would mean closing most of the Atka mackerel fishery in the Aleutians, the main pollock fishing areas in the southern half of the eastern Bering Sea, the roe herring fisheries near rookeries in the Gulf of Alaska, and perhaps others. Under this option, the most important information needs would concern population dynamics of the fishes, particularly responses that may underlie the recent dominance of the fish community by gadoids. This community shift could become further entrenched if the groundfish catches are reduced through increasing restrictions on the fishery.
Use replicated closed and open rookeries to experimentally evaluate localized fishery impacts. Spatial management units consisting of two sets of closed and open areas would be established with each treatment area centered on a rookery. The western population would be divided into management regions with at least two closed and two open rookeries per region. Because most monitoring activities are conducted at rookeries (pup counts, measurement of vital rates, juvenile tagging, etc.) it makes the most sense to use rookeries (rather than rookeries and haulouts) as the experimental units. Also, sea lions are thought to be more vulnerable near rookeries because of the presence of pups and juveniles and because females must forage near the rookeries so they can return to nurse their pups. The closed treatment units would be subject to fishery closures and the open units would have sea lion-related fishery restrictions removed. The lifting of fishery restrictions in the open areas is important to achieve adequate contrast among treatments in the experiment.
The logic in this design is to recognize that there is no best “baseline” or precautionary policy for the population in view of uncertainty about the causes of the decline so every part of the population should be treated as having a highly uncertain future no matter what restrictions are placed on the fisheries. Multiple (replicate) treatment/control sites are necessary for comparison because of the strong possibility that different portions of the sea lion population have and will continue to be affected by different
stressors. If there are multiple problems due to multiple food/ predation/fishing issues, replicated comparisons will be necessary to guard against incorrectly applying the results from any one treatment/control comparison to other areas that may not be comparable. Under this option, the most critical monitoring needs would be detailed local Steller sea lion censuses and spatial analysis of fish population changes for each experimental unit in the overall design.
Implement a “titration experiment” that progressively increases restrictions on fisheries (such as area closures) until it is clear whether or not a positive response can be achieved via fishery management. In essence, this option is a continuation of the historical policy on Steller sea lion protection since the ESA listing in 1992. While this “incrementalist” approach may be intuitively appealing from socioeconomic and practical management perspectives, it has at least two drawbacks. First, it would be taking place in a background of continuing ecosystem change due to factors such as oceanographic regime changes, so the “treatment effects” of management would be badly confounded with such changes on decadal timescales (for at least the next few decades). This would increase the chances of both “false positive” and “false negative” measured outcomes over the next 10 to 20 years at least. Second, this approach would have very high economic costs in the event of false positive signals that trigger the progression toward more fishery restrictions to continue for longer than they should. This economic cost would be in the form of lost fishery revenues and increased fishing costs for more distant operational deployment of fleets.
Micromonitor and manage localized interactions between sea lions and fisheries to reduce mortality where and when it occurs in the future. In this case, all basic monitoring activities (abundance, prey fields, mortality agent distribution) around at least some key rookeries would be increased to pinpoint the time and place of mortality events and take immediate management measures as necessary. This approach would require very considerable investment in invention and testing of new monitoring methods, particularly tagging systems for determining proximate causes of mortality. The expense would be greatly increased by a requirement for year-round, continuous monitoring to allow detection of concentrated impact in particular places or seasons. This approach is less able to detect and respond to evidence of delayed or cumulative interaction effects, such as increased predation in response to chronic food shortages. There is a disadvantage to commercial
fisheries because regulations might change frequently during the course of a fishing season.
Recommendation: Of these management options, the committee concluded that option 3 offers the greatest benefits with regard to increasing the scientific understanding of the effect of fisheries on Steller sea lions. This is the only option that does not risk ineffective, long-term regulation of the fishing industry because it should reveal relatively quickly whether restrictions on fisheries will help prevent further decline. This option does not involve any pretense that the impacts of future changes in various “natural” factors like predator populations can eventually be unraveled through modeling and correlative studies. This option would provide a powerful comparative setting within which to carry out various detailed research studies on Steller sea lion behavior and performance in alternative ecological (prey field) environments while controlling for common effects of large-scale oceanographic regimes.
The experimental policy option 3 is designed to improve management while at the same time facilitating research on the causes of decline and failure to recover. Open areas restore opportunities for fisheries by removing restrictions; closed areas remove potentially negative local impacts of fisheries on sea lions. A careful evaluation of past fishing effort in the proposed experimental areas will be required to assess the amount of displaced fishing effort. Placement of open areas where fishing effort has historically been high would decrease the potential for negative impacts arising from shifting effort from the closed to open areas. Some of the many considerations for the design of such an experiment include
Fished area (under normal management plans)—The groundfish fisheries have been the focus of restrictions to protect sea lions based in part on the large amount of biomass removed by this fishery, but the potential effects of other fisheries have not been as thoroughly examined. Hence, there are two basic “experimental treatment” options for area closures: (1) closure to groundfish fisheries only, or (2) closure to all fishing. A positive response to treatment (1) would measure the impact of the groundfish fisheries separately from the effects of other fisheries. A positive response to treatment (2) would implicate fishing activities, but there would be uncertainty as to whether the response was due to exclusion of the groundfish fisheries or exclusion of another fishery, for example herring or salmon. Closure of these areas to all fishing activity would provide the greatest contrast with the open areas for assess-
ment of fishery-related effects on Steller sea lions. If only the groundfish fisheries are excluded from the closed areas, logbook data and as much observer coverage as possible should be obtained for other fisheries. Closures should be designed to minimize displacement of fisheries to more distant, and less safe areas. Strict enforcement would be essential for the correct interpretation of effects of the closures.
Size and number of treatment areas—The size of the closed areas depends on both fish movements and sea lion movements. The radius of the closure might range between 20 and 50 nautical miles (centered on a rookery). Replicates of each open/closed area comparison site will be required to assess the effects of environmental variability.
Timescale—Some short-term results are possible (disease, possibly fish depletion, increase in direct mortality), but there must be recognition of and commitment to the need to maintain monitoring until longer-term recruitment and mortality responses are fully evident in the sea lion population (5 to 10 years). There should be a contingency plan to modify or curtail fishing in open areas if these areas show dramatic sea lion mortality as might occur under some scenarios, for example substantial fishery bycatch of Steller sea lions.
Although option #3 provides the best chance of providing new information about the role of the fisheries in the Steller sea lion decline, there is no guarantee that the outcome of this adaptive management experiment will provide an unequivocal result. A small, positive response to the fishery closures may be masked by fluctuations in other factors that also contribute to the decline, especially when the results are examined at shorter time scales. Nonetheless, this approach will at least indicate whether or not fishing activities near rookeries are a major factor threatening the recovery of the sea lion population and therefore will provide an improved baseline of knowledge for policymakers in the future.