Glacier Changes Drive New Challenges for Balancing Visitor Access and Natural Resource Protection

• Scott Gende, Natural Resources Team Lead, Alaska Region
• Jamie Womble, Program Manager, Southeast Alaska Network
• Andy Bliss, Physical Scientist, Southeast Alaska Network

About this issue of Alaska Park Science

The articles in this issue explore dynamic challenges and emerging opportunities for management to ensure that the National Park Service mission is met and visitors have high-quality experiences in Alaska’s national parks. Management decisions are often a result of finding compromises or the best possible outcome based on values as much as science. Because of that, articles in this issue may be presented from a particular perspective or express opinions. Those opinions are the authors’ own and do not necessarily reflect the views or opinions of the National Park Service.

Cruise ship passengers get an up-close experience of a tidewater glacier.

The National Park Service (NPS) was founded on the mandate of preserving some of the nation’s most cherished resources, and for the enjoyment and use by current and future generations. Recognizing the inevitable conflict produced by this dual mandate, NPS Management Policies (NPS 2006) acknowledge that virtually every type of use by park visitors impacts some resources in some way. What’s more, the severity of resource impacts typically occurs across a continuum with no clearly defined, action-triggering threshold. Park managers are thus tasked with deciding which activities are appropriate, and then balancing the volume of visitors that should be allowed to partake in those activities relative to their expected impacts to the park’s natural and cultural resources. An outcome of trying to resolve the conflict is that decisions on visitor access tend not to focus on preventing an impact from occurring but rather defining the degree to which the impact is deemed acceptable (Gende et al. 2019).

When faced with these decisions, a prudent starting point for park managers is to ask whether limiting access or managing natural resources in a certain manner runs counter to the park’s founding purpose. Park purposes are derived from the act of Congress that set aside the unit for protection and provides the appropriate context for these decisions. For example, the founding mandate of some historical parks is to preserve landscapes for “authentic interpretation” of significant historical events, such as an important battle. Doing so allows visitors to experience the area as it was at the time of the historical event, thereby helping the park to meet its fundamental purpose. However, this may result in active manipulation of the park’s natural resources, such as maintaining a grassland that would normally be transforming into a forest due to successional dynamics (e.g., Young and Mahan 2023). In such a scenario, the impacts to the natural resources that result from intensive vegetation management is deemed acceptable in order to meet the site’s founding mandate.

While the tension between visitor use/access and natural resource protection has long been at the forefront of park decision making, rapid, landscape-scale changes are now forcing many park managers to reconsider what were historically deemed acceptable tradeoffs. These decisions are becoming more pressing owing to altered trajectories of plant and animal populations and fundamental shifts in ecosystem processes.

Here we describe an emerging issue in Glacier Bay National Park and Preserve that exemplifies the inherent difficulty when balancing resource protection with visitor access. Initially protected, in part, to provide access to tidewater glaciers, Glacier Bay will soon only have one accessible tidewater glacier. This glacier provides habitat for a large aggregation of harbor seals and is protected by limiting access. Thus, some difficult questions arise: Can the park still meet its founding mandate if existing tidewater glacier access restrictions persist? If not, are there access alternatives that produce acceptable levels of disturbance risk to seals? Our goal is to contextualize these questions by summarizing (1) the park’s founding purposes, (2) contemporary visitor access, (3) the dynamics of the tidewater glaciers and harbor seals in the park, and (4) the attributes of existing access regulations to help understand what’s currently deemed acceptable.

A cruise ship near the terminus of Margerie Glacier in Tarr Inlet.

NPS

Founding Mandates and Visitor Access at Glacier Bay

Glacier Bay was set aside for protection to achieve two fundamental purposes: to preserve an area that provides scientific opportunities to study landscape evolution in a dynamic glacial environment, and to protect an area where visitors can access and enjoy tidewater glaciers “of the first rank” by “ordinary travel.” In 1925, when Calvin Coolidge signed Presidential Proclamation #1733 that first protected Glacier Bay as a national monument, “ordinary travel” was by large steamship. Steamships started making transits into Glacier Bay as early as the late 1880s with the specific purpose of providing passengers access to the tidewater glaciers. Over time, steamships gave way to ocean liners and ocean liners evolved into large cruise ships. Today’s cruise ships, the largest of which (of those that currently visit Alaska) can carry nearly 5,000 passengers, bring more than 95% of the more than 700,000 visitors that annually visit the park. In addition to bringing a large volume of visitors, cruise ships also provide access to the tidewater glaciers to a wide diversity of visitors spanning socioeconomic backgrounds and physical capabilities, thereby making the park more “…accessible to every segment of American society” (NPS 2006). Given that there are no roads and few trails in the backcountry of the park, and owing to their historical access and reference in the original proclamation, cruise ships represent an important means by which the park meets its founding mandate.

How does this access and enjoyment occur? When cruise ships visit Glacier Bay, they do not tie up to a dock or drop anchor to deploy tenders; all passengers remain onboard during the 8-12 hours the ship transits the fjord. Upon entry into the park, all cruise ships follow a similar course from the park’s entrance in Icy Strait up the western arm of Glacier Bay’s Y-shaped fjord and into Tarr Inlet to access and enjoy the Margerie Glacier. Depending on the density of icebergs calved from the glacier, the ships can often safely approach the glacier’s terminus, providing an extraordinary experience for visitors. Ships typically spend one to several hours near the tidewater glacier, which also allows on-board interpretation to occur.

Icebergs are particularly important to seals when they are pupping or molting. If they are disturbed and flush into the water, it could interrupt their nursing and expose them to cold water and predators when they are most vulnerable.

NPS/Jamie Womble

During most of the summer, however, cruise ships are prohibited (per CFR 36 13.1178, 2025) from a similar approach of the Johns Hopkins Glacier, located just around the corner in Johns Hopkins Inlet. This prohibition occurs despite the glacier being accessible, tidewater, and, by all accounts, of “first rank.” The reason for this restriction, which spans from 1 May until 1 September, is based on resource protection: vessels can disturb seals and Johns Hopkins Inlet is the location of the largest seasonal aggregation of harbor seals in Glacier Bay, typically numbering over 2,000 individuals (Womble et al. 2020). Seals haul out on icebergs in the inlet for pupping, molting, and avoiding predators. Disturbance can send them back into the water thereby disrupting those vital activities. Observational studies conducted in Johns Hopkins and other glacial fjords demonstrate that the closer marine vessels approach seals, the greater chance the seal will abandon the ice and flush into the water (Jansen et al. 2010, Young et al. 2014). While the impacts of a disturbance event can vary in magnitude, seal pups are particularly vulnerable. If disturbed, pups can become separated from their mothers, and statistical models have demonstrated that even small increases in time spent in the cold glacial waters can result in newborn pups entering negative energy balance with potential deleterious impacts on survival (Harding et al. 2005, Jansen et al. 2010).

The unrestricted access to Margerie Glacier, and the extraordinary experience it provides, helps the park meet the mandate for access and enjoyment of a tidewater glacier “of first rank.” With this mandate met, the access restrictions for cruise ships to the Johns Hopkins Glacier are deemed acceptable, which allows the park to maximize protections from disturbance for the aggregation of seals in Johns Hopkins Inlet.

Passengers view the Johns Hopkins Glacier from the deck of a cruise ship that is stopped at Jaw Point--a much different experience than the close-up view at Margerie Glacier. Taken in July 2023, it shows the recent trend of ice density being increasingly sparse for much of the inlet.

The Last Accessible Tidewater Glacier?

When Glacier Bay was first set aside for protection in 1925, a ship entering the fjord would be able to access a number of tidewater glaciers including but not limited to the Muir, Grand Pacific, Margerie, Lamplugh, McBride, and Johns Hopkins/Gilman (Figure 1; McNabb and Hock 2014). Today only Margerie and Johns Hopkins/Gilman glaciers are both tidewater and accessible, although their dynamics differ markedly.

Figure 1. The distribution of tidewater glaciers in Glacier Bay in 1925 (left panel) compared to today (right panel). The colored polygons reflect only the lower reaches of the tidewater glaciers to highlight the contrast between the two time periods.

The right panel includes the route typically taken by cruise ships for most of the summer. Ships go to the face of Margerie Glacier in Tarr Inlet but turn around at Jaw Point at the mouth of Johns Hopkins Inlet so passengers see the glacier 7 miles away.

Johns Hopkins Glacier is one of the few tidewater glaciers in Alaska that is advancing: its terminus advanced over 1 mile (1.6 km) since 1948 (McNabb and Hock 2014) and the lower reaches have thickened by over 328 feet (100 m; Larsen et al. 2007). Recent satellite-derived velocity measurements and digital elevation models demonstrate that the terminus area of the glacier has slowed down and has continued to thicken and gradually advance in recent years (Kaluzienski et al. 2023). In sharp contrast, Margerie Glacier is both rapidly thinning and receding (Figure 2). While efforts are underway to better estimate the speed of recession, observations from NPS interpretative rangers traveling on cruise ships noted at least several years ago that the northern part of Margerie’s terminus now ends on land (no longer reaches saltwater).

Figure 2. Margerie Glacier (a) in Tarr Inlet has started to retreat in recent years after decades of stability. Johns Hopkins Glacier in Johns Hopkins Inlet (b) has been advancing since the 1920s, making it unusual among glaciers in Alaska.

Outlines shown here were traced from Landsat and Sentinel satellite images (McNabb and Hock 2014, with updates by Bliss). Note: the color scale is decadal from 1980-2020, and then annual 2020-2023. Background images © ESRI.

If the recent past is a gauge for the near future and projections of increasing temperatures continue, the grounding of Margerie Glacier, and its recession back into the valley, is imminent. Should this occur, the Johns Hopkins would become the last accessible tidewater glacier to cruise ships in the park.

Seasonal Dynamics of Seals and Ice
Managers at Glacier Bay National Park and Preserve have a long history of supporting research and monitoring efforts to help inform decisions when resources and values may be impacted by vessel operations and visitor activities (e.g., Gende et al. 2005, Piatt and Gende 2007). Given more than 30 years of managing visitor access in areas used by harbor seals, it’s not surprising that the park has supported long-term monitoring of the harbor seal aggregations in Glacier Bay since the 1990s (Mathews and Pendleton 2006, Womble et al. 2010, Womble et al. 2020). In sum, up to 4 replicate aerial photographic surveys are flown each year in mid-June, coinciding with the peak in pupping, and in mid-August to coincide with the peak in molting. In Johns Hopkins Inlet, the surveys follow a systematic route, whereas a more opportunistic route is flown to cover the myriad beaches, reefs, islands, and islets (collectively, “terrestrial sites”) that are also used by seals throughout the summer. All photos are analyzed to estimate the total number of seals present. These data have generated important insights into the dynamics of seals and ice, with possible implications regarding access restrictions in Johns Hopkins Inlet.

Foremost, analysis of the data during the first several decades of monitoring revealed that, in June, icebergs and harbor seals were typically spread throughout the inlet including areas just up to, and at times beyond, Jaw Point. By August, the density and distribution of ice had diminished significantly (up to 7 times reduction) resulting in seals and ice becoming highly clustered near the terminus of the glacier (Womble et al. 2020, Womble et al. 2021). More recently, however, the phenomena of largely clustered ice and seals near the glacier’s terminus has been documented during the June surveys as well (Figure 3), possibly due to the growth of the glacier’s end moraine (Kaluzienski et al. 2023).

The largest seasonal aggregation of harbor seals in Glacier Bay is associated with Johns Hopkins Glacier, typically including more than 2,000 seals.

UNESCO/Mark Kelly

Figure 3. Harbor seal distribution in Johns Hopkins Inlet during June and August 2007 (left) and in 2019 (right). Notice that seal and ice distribution diminish during the summer and, over time, there is less ice overall and seals are aggregated closer to the glacier terminus.

The second relevant finding is that ice density appears to influence seal reactions to an approaching vessel. In an observational study where seal flushing distances were quantified in response to private, tour, and charter vessels, in addition to cruise ships, Young and others (2014) found that seals tended to remain on the ice at closer approach distances during periods of low iceberg density compared to periods when icebergs are abundant. For that research, disturbance was defined as seals flushing from the ice into the water as a result of an approaching vessel, although it’s worth noting that a seal can still be disturbed without flushing from the ice.

Together, the research and monitoring results demonstrate that the risk of seal disturbance, particularly near the mouth of Johns Hopkins Inlet, is comparatively much lower in recent years compared to several decades ago owing to larger expanses of open water free of both ice and seals. While these results are timely and scientifically derived, they do not resolve whether the lower level of risk represents an acceptable level of risk. We thus review the attributes and implications of the existing access restrictions to help contextualize what’s currently acceptable.

Acceptability in Disturbance Risk

Access restrictions to Johns Hopkins Inlet for cruise ships (and other vessels) have been in place since the 1990s by designating a line that demarcates when and where cruise ships can go. Prior to the tourism season, park staff communicate to the cruise ship companies the suite of restrictions and operating requirements for the upcoming summer, including a reminder of the “line” in place from 1 May through 31 August, that extends due west from Jaw Point separating the go/no-go area. This access regulation is easily understood, can be designated on an electronic chart, and is communicated in sufficient time prior to the season to allow ships to integrate into navigational planning. As a result, violations of the regulation are exceedingly rare.

However, the designation of a static line at Jaw Point, and the decision to allow access to Margerie Glacier throughout the summer, represents a management approach for reducing, rather than eliminating, the risk of disturbance to seals. For example, there are a number of days, particularly in the early part of the summer, when large volumes of icebergs and, at times, many hauled-out seals, have drifted past Jaw Point and into the area where cruise ships are allowed. While ships are expected to maneuver to avoid disturbing seals (“except when safe navigation requires”), icebergs drifting into the cruise ship route constitutes an infrequent yet unavoidable scenario throughout the summer. What’s more, private, tour, and charter vessels are afforded access to Johns Hopkins Inlet beginning 1 July (CFR 36 13.1178 2025) and these vessels have also been documented disturbing seals, albeit at lower rates than cruise ships (Young et al. 2014). Finally, monitoring data have demonstrated that a small number of harbor seals still use icebergs in Tarr Inlet during the summer, occasionally including mothers with newborn pups. Indeed, NPS interpretative rangers traveling on the ships regularly point out seals on ice to passengers as part of the outreach efforts when ships are near the Margerie Glacier.

Passengers view harbor seals hauled out on an iceberg in Tarr Inlet, near the Margerie Glacier. The opportunity to see harbor seals contributes to the extraordinary experience of visitors to these inlets.

Ship operators are expected to minimize risk of disturbance by making prudent navigational decisions based on ice distributions they encounter. Identifying a course that avoids aggregations of seals and minimizes a chance encounter is one of the primary goals for deck officers when they enter Tarr Inlet. In fact, it’s not uncommon to see up to 4 deck officers, and the marine pilot, standing on the ship’s bridge scanning the water ahead with binoculars to identify any seals hauled out on ice. Yet, as any vessel operator that has visited these areas can attest, the jagged nature of icebergs can often hide a resting seal until the vessel is too close to avoid it. What’s more, the tide-driven currents and unpredictable winds can quickly close an open water lead creating the possibility that, even if a ship had no ice or seals around it during approach, ice and resting seals can quickly surround the ship upon exit. Not surprisingly, ship captains tend to be extraordinarily risk averse when it comes to proceeding into areas with even moderate iceberg density, in part to avoid the possibility of damaging the hull. This creates a somewhat self-regulating scenario: when icebergs (and seals) are likely to overlap with the route the ships take, ship personnel are less likely to proceed. This is one of the reasons (in addition to time constraints) why, even after Johns Hopkins Inlet opens on 1 September to cruise ships, only a small number of them choose to travel all the way to the face of the glacier.

The current approach to managing acceptable levels of seal disturbance is based, in part, on static decisions: when and where vessels are allowed is designated independent of the actual conditions vessels would encounter in those areas during those periods. An alternative would be a more dynamic (adaptive) approach, although it is worth noting the hurdles that the park would face if it pivoted to a framework where access restrictions are based on ice and seal distributions encountered in real time. For example, recent studies have demonstrated that ice in the inlet can be highly variable depending on ice calving dynamics and local environmental variables including winds, currents, and tides (Kaluzienski et al. in press). Thus, it is unclear how long after a survey is conducted that the data would reflect the conditions in the inlet given that they can change daily or even hourly. Alternatively, the park could use satellite imagery to help inform the dynamic decision, although persistent cloud cover can preclude accurate information for weeks at a time. Finally, images from land-based cameras can be collected (and possibly transmitted) on an hourly basis (Keinholz et al. 2019, Kaluzienski et al. in press), but would need to be summarized and conveyed to ships in a useable format in near real-time—a labor-intensive and time-consuming process.

In 2023, a partnership was initiated between the NPS, the University of Texas, and Texas A&M University (with support from the National Science Foundation) with the goal of using existing data from research and long-term monitoring to better understand disturbance risk under possible alternatives to the existing access restrictions in Johns Hopkins Inlet. While the project will focus on developing state-of-the-art quantitative tools to explore different scenarios, ultimately it will be up to park managers to define acceptable risk levels relative to the benefits of enhanced visitor access. Through careful assessment of the science of seal behavior and a commitment to continued long-term monitoring of the seal population, the park is in excellent position to identify alternatives that fulfill the enabling legislation of the park and helping to resolve the inherent conflict of the dual mandate.

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