Spatio-temporal changes in Beluga Whale, Delphinapterus leucas, distribution: results from aerial surveys (1977-2014), opportunistic sightings (1975-2014), and satellite tagging (1999-2003) in Cook Inlet, Alaska.
The waters of Cook Inlet, Alaska, are occupied year-round by a small, distinct population of beluga whales, Delphinapterus leucas (Fig. 1). One of the earliest descriptions of this population's distribution within Cook Inlet is found in Cornelius Osgood's 1933 account from an ethnological expedition undertaken in 1931:
"Of the sea-mammals used for food, fur, or both (hair-seal, ground-seal, sea-otter, sea-lion, porpoise, beluga and whale) which were found in the Lower inlet, only two (hair-seal and beluga) were found elsewhere, that is, in the Middle inlet and seasonally in the Upper inlet" (p. 697).
Aerial surveys using fixed-wing aircraft were introduced in Alaska in the 1930's to assess wildlife populations (Eicher, 1953; Jones et al., 2007). The first aerial surveys to estimate beluga whale numbers were conducted in 1954 in Bristol Bay, Alaska (Brooks (1)). Investigations by the Alaska Department of Fisheries were primarily in response to concerns expressed by commercial fishermen about beluga predation on Pacific salmon, Oncorhynchus spp. (Brooks (1)). The Alaska Department of Fish and Game (ADFG) flew the first aerial surveys to enumerate the Cook Inlet be
"Aerial surveys of Cook Inlet which I made in 1963 and 1964 indicated a summer population of 300 to 400 animals" (p. 3).
The information was limited, however, as Klinkhart (2) did not include a map or any descriptions of where or exactly when surveys took place during those summers.
In the 1970's, increasing interest in petroleum development throughout Alaska waters led to the National Oceanic and Atmospheric Administration (NOAA) funding large-scale, systematic surveys to determine seasonal distribution of seabirds and marine mammals. The Outer Continental Shelf Environmental Assessment Program (OCSEAP (3)) large-scale surveys of the Gulf of Alaska included aerial surveys of mid-inlet waters in lower and central Cook Inlet (primarily south of East and West Foreland) during the mid- to late 1970's (Harrison and Hall, 1978) and early 1980's (Leatherwood et al. (4)). Only a few belugas were observed during these surveys (Fig. 2). The paucity of sightings was likely due to the survey design, which did not include coastal waters within the inlet. Leatherwood et al. (4) noted:
"Belugas were also observed repeatedly in the Cook Inlet complex during our transit flights into and out of Anchorage, particularly near the estuary of the Kenai River" (p. 312).
An OCSEAP study that originally focused on Steller sea lion, Eumetopias jubatus, investigations in the Gulf of Alaska (Calkins and Pitcher (5)) was "expanded to include an examination of the distribution and abundance of belukha whales (Delphinapterus leucas) in Cook Inlet" (p. 146). This first attempt to thoroughly document CIBW seasonal distribution using aircraft occurred in the late 1970's (Murray (6); Murray and Fay (7)). Under the direction of ADFG, aerial surveys were conducted in Cook Inlet from November 1977 through August 1979.
ADFG resumed aerial surveys in the early 1980's as part of the Susitna Hydroelectric Project funded by the Alaska Power Authority (Calkins (8)). This study documented CIBW distribution in the upper inlet (north of East and West Foreland) during the ice-free season to assess potential impacts from proposed dam development on the Susitna River. Summary maps, and sometimes tables, showing seasonal sighting data from these ADFG studies were presented in contract reports (Murray (6), Calkins (8, 9, 10)) but never published in a peer- reviewed journal.
The Alaska Fisheries Science Center's National Marine Mammal Laboratory (NMML) received photocopies of some of the original field logs and maps from these ADFG studies in 1999. (11) Initially, beluga whale sightings from the June and July flight summaries were digitized and mapped, and subsequently compared to whale distributions from National Marine Fisheries Service (NMFS) aerial surveys conducted during the period 1993-2008 (Rugh et al., 2010). Rugh et al. (2010) documented a significant northward contraction in the early summer range of CIBWs since the 1970's. In 2012, all available tracklines and sightings from the 1977-79 and 1982-83 surveys were scanned and digitized to update the CIBW Opportunistic Database maintained by NMML (Vate Brattstrom et al. (12)). We present the ADFG survey methods and effort in Appendix 1 (1977-79) and Appendix 2 (1982-83) (13) transcribed from the original field notes and maps.
After the ADFG surveys, distribution studies did not resume until the 1990's. NMFS began dedicated CIBW distribution and abundance surveys in June 1991 (NMFS (14); Shelden and Mahoney (15)). Subsequent aerial surveys during the period 1993-2014 focused on distribution and abundance primarily in June (Rugh et al., 2000, 2005; Shelden et al., 2013, Hobbs et al., 2015a; Shelden et al. (16)). NMFS also conducted aerial surveys in August from 2005 to 2012 specifically to look at the proportion of beluga calves in the northernmost waters of Cook Inlet (Hobbs et al., 2015b). Additional months were sampled from July 2001 to April 2002 to document CIBW numbers and distribution in other seasons (Rugh et al., 2004). The U.S. Department of Interior, Minerals Management Service (MMS, now the Bureau of Ocean Energy Management (BOEM)) also flew beluga whale distribution surveys during February and March of 1997 (Hansen and Hubbard (17)). Using these datasets, we compared CIBW distribution across months and years from the late 1970's to 2014.
In 1999, NMFS began capturing CIBWs during the summer months and attaching satellite-linked time-depth recorders to their dorsal ridges (Ferrero et al., 2000; Hobbs et al., 2005; Goetz et al. (18)). In all, 18 belugas were captured and tagged during this project which continued until 2002. Some of these tagged whales transmitted locations during the fall, winter, and spring; therefore, we included these data to supplement the sighting data, particularly for months when aerial survey effort was limited. We also included sightings from the CIBW Opportunistic Database to provide additional, though anecdotal, insights into beluga distribution.
Attempts to estimate abundance for the Cook Inlet population in the past have often been based on observations of a single, large concentration of animals and applying a correction for surface intervals when animals are not visible beneath the turbid waters in the inlet (Hazard, 1988). The listing of CIBWs on the List of Candidate Vertebrate and Invertebrate Marine Species under the U.S. Endangered Species Act in 1988 (NOAA, 1988) was, in part, based on abundance estimates from these studies which suggested at minimum about 500 whales (Hazard, 1988). Calkins (10), reporting on Murray's aerial survey findings (Appendix 1), noted:
"In subsequent aerial survey/ sighting combinations, the highest minimum direct count I have obtained for a single day was 479 animals [sic. 473 in Appendix 1] on 21 August 1979. Some investigators have speculated that three times as many whales are present as are counted in this type of survey. Using a correction factor of 2.7 to account for submerged whales (which was developed for estimating belukha whales in similar conditions in Bristol Bay) yields a minimum estimate of 1,293 whales in Cook Inlet in August 1979" (p. 110).
Applying this correction (2.75 per Frost et al. (1985)) to surveys undertaken by NMFS in June 1991 (Shelden and Mahoney (15), correcting the estimate presented in NMFS (14)), where the highest count was 370 whales on a single day, resulted in an estimate of 1,018 belugas. Subsequent estimates produced from NMFS surveys (1994-2014) were based on correction factors developed for Cook Inlet (Hobbs et al., 2015a). These estimates show a steep decline in abundance prior to the moratorium on Alaska Native subsistence hunting (1994-98: -13.7% (SE = 4.5%) per year), and a 1.3% (SE = 0.8%) per year decline since harvest management regulations were put in place in 1999 (Shelden et al. (16)). The Cook Inlet stock was listed as depleted under the U.S. Marine Mammal Protection Act in 2000 (NOAA, 2000). In 2008, the Cook Inlet population was listed as endangered under the U.S. Endangered Species Act (NOAA, 2008).
This paper provides a review of CIBW spatio-temporal distribution based on results from aerial surveys, satellite-telemetry, and opportunistic sightings. With the continued decline in abundance of CIBWs (Hobbs et al., 2015a) and concomitant contraction in range observed during early summer (Rugh et al., 2010), identifying areas used by these whales during ice-covered and ice-free periods is critical to the recovery of this endangered population.
Cook Inlet, Alaska, (lat. 59[degrees]61.5[degrees]N, long. 149[degrees]-154[degrees]W) is a semi-enclosed tidal estuary covering an area of roughly 20,000 [km.sup.2] with 1,350 km of shoreline (Fig. 1). The inlet extends about 370 km (200 n.mi.) southwest from Knik Arm to Cape Douglas and has marine connections with Shelikof Strait and the Gulf of Alaska, and freshwater input from many large rivers.
Osgood (1933) described the inlet as four regions: Lower, Middle, Upper, and Inland, based on the villages occupied by the Athapaskan-speaking Tanaina, a sea-hunting Alaska Native culture. The lower inlet region (which included the village of Seldovia) was described as having a mild climate and salt water. The middle inlet was less mild and salt-fresh water mixed and included the villages of Kenai and Tyonek. The upper inlet included Knik Arm (the village of Eklutna) and was described as a cold climate with waters that were a mixture of dirty, fresh, and salt. Inland villages were on the Susitna River and Iliamna River, regions described as fresh water only with cold climates. Osgood (1933) noted that belugas were found in lower, middle, and seasonally, in the upper inlet. For the purposes of this paper, we simplified the division of the inlet into upper and lower regions, separated at East Foreland and West Foreland (Fig. 1).
Tides in Cook Inlet are semi-diurnal, with two unequal high and low tides per tidal day (tidal day = 24 h 50 min). The mean diurnal tidal range varies from roughly 6 m (19 ft) at Homer to 9.5 m (30 ft) at Anchorage. These extremes in tide expose vast expanses of mudflats in the upper inlet, between the Beluga River and Little Susitna River (we refer to this region as the Susitna Delta), and in Knik Arm, Chickaloon Bay, and Turnagain Arm (Fig. 1). Beluga whales navigate these regions on the flooding and ebbing tides, following the deeper channels as the mud flats flood, allowing the whales to move closer to the shoreline and into the rivers. Whales move to the edges of the mudflats, to what appears to be mid-inlet waters, as the tide ebbs. We considered the mudflat edge to be an extension of the shoreline when describing whale distribution, and mid-inlet waters are defined as deeper than 10 m (Fig. 1).
Sea ice generally forms in October-November, reaches its maximum extent in February, then recedes and melts in March-April. By December, much of the upper inlet north of North Foreland and Point Possession is covered with ice ranging in thickness from 10 cm (new/pancake) to 30-70 cm (all as first year because there is no multi-year ice present in the inlet); and in concentrations ranging from 10% to 70-80% coverage (i.e., open (1/10) to close pack (7/10 to 8/10) (Mulherin et al. (19)). Hereafter, percent coverage is used in lieu of tenths when describing ice concentrations.
Thawing and refreezing create a dynamic ice environment. Tidal action and tidal currents often shatter sea ice in Cook Inlet to the extent that there is seldom uniform coverage. Waters are typically ice-free south of East and West Foreland until January, when ice extent and thickness increase, reaching maximums between mid-February and early March (Mulherin et al. (19)). In colder winters, ice extends south as far as Anchor Point and Augustine Island, filling Kamishak Bay to Cape Douglas on the lower west side of Cook Inlet. Despite the possibility of ice entrapment, beluga whales continued to inhabit upper inlet waters (Goetz et al. (18)). In general, beluga whales are pagophilic (i.e., "ice-loving") and uniquely adapted to survive in Arctic and subarctic waters.
The endangered CIBW population lives in close proximity to Anchorage, the largest city in Alaska, and waterways frequented by fishing fleets, container ships, air traffic, oil and gas development, and military operations. The magnitude and the accumulated anthropogenic pressures within Cook Inlet beluga habitat are of particular concern for this small, isolated population (Norman et al., 2015).
Aerial Survey Datasets
Alaska Department of Fish and Game
From November 1977 through August 1979, aerial survey observers documented the seasonal distribution of CIBWs and also recorded the presence of other marine mammals including harbor seals, Phoca vitulina; minke whales, Balaenoptera acutorostrata; sea otters, Enhydra lutris; and harbor porpoises, Phocoenaphocoena. Survey altitude ranged from 91 to 152 m (300-500 ft). This extensive effort included year-round surveys of coastal and mid-inlet waters in the upper and lower inlet. Survey platforms included floatplanes and helicopters with one pilot and one observer. Sightings (including group sizes) and tracklines were hand-drawn on a simple outline of the inlet or a NOAA chart of the particular area of Cook Inlet surveyed. Sometimes these data were later transcribed to another map template showing the outline of the entire inlet. Field notes were often, but not always, included with the maps that were received by NMML.
ADFG also conducted aerial surveys from May through August 1982 and April through July 1983 in upper Cook Inlet. Similar to the beluga whale surveys conducted in the 1970's, survey altitude ranged from 91 to 152 m (300-500 ft). Survey aircraft were primarily single engine floatplanes with one pilot and one or two observers onboard. Field notes or annotated maps displayed flight paths and sightings. Unlike the MMS and NMFS surveys described in the following sections, the ADFG efforts were not documented in annual field reports or publications; therefore, Appendices 1 (1977-79) and 2 (1982-83) include transcriptions of all available field notes, survey tracklines, and sighting locations.
Maps were created using ArcView (20) geographical information system software (ver. 10.1). Plots showing sighting locations were projected using the Alaska Albers Equal Area Conic coordinate system which provided a more accurate depiction for area-use measurements. Each map was scanned and saved into a PDF, then the digital image was exported as a JPEG file. This file was imported into ArcMap as a raster dataset layer and saved as a georeferenced map. Beluga sighting locations and survey tracklines were redrawn as graphics then converted to shapefiles. The sighting shapefiles were edited to include group sizes for the maps in Appendices 1 and 2.
Minerals Management Service
In 1997, aerial surveys for beluga whales in ice-free areas of Cook Inlet occurred from 12 Feb. through 14 Mar. (Hansen and Hubbard (17)). Surveys were flown in a Twin Otter equipped with side bubble windows for the two observers. These windows allowed observers to view ahead of and beneath the aircraft. Similar to the NMFS surveys described in the following section, a computer operator collected survey data using an acquisition program designed for marine mammal surveys. The surveys covered 9,406 km of trackline and were flown at an altitude of 305 m (1,000 ft). Daily summaries and maps that included trackline effort and marine mammal species observations are provided in Appendix B in Hansen and Hubbard (17). Beluga whale sighting locations (lat., long. from Table 4 in Hansen and Hubbard (17)) were imported and plotted in ArcMap. Group sizes and general locations of these sightings are provided in Table 1.
National Marine Fisheries Service
During the period 18-21 June 1991, aerial surveys (21) were flown to document the distribution and group sizes of beluga whales in Cook Inlet (Shelden and Mahoney (15)). The survey aircraft was a NOAA Twin Otter that was equipped with side bubble windows for the two observers. The survey altitude range was 152 to 305 m (500-1,000 ft). A computer operator collected survey data using an acquisition program designed for marine mammal surveys. Effort included coastal and mid-inlet waters north of Chinitna Bay and Anchor Point. Daily summaries and maps are provided in Shelden and Mahoney (15).
From 1993 to 2012, NMFS conducted annual surveys to determine abundance and distribution of belugas in Cook Inlet (hereafter referred to as "NMFS abundance surveys") (Rugh et al., 2000; 2005; Shelden et al., 2013) after which NMFS began a series of biennial surveys in 2014 (Hobbs, 2013; Shelden et al. (16)). Flights primarily took place in June, though in some years surveys began in late May (2005, 2011, and 2012), or were conducted in July (1993 and 1995). Surveys were flown in twin engine, high wing aircraft (Aero Commander or Twin Otter) equipped with side bubble windows. Surveys were flown at an altitude of 245 m (800 ft). Because most sightings occur near shore, two observers were positioned on the shoreward side of the aircraft, independently recording observations to help assess how often groups were missed. A third observer scanned mid-inlet waters and a computer operator recorded survey data. All marine mammals observed within the study area were included in the sighting database (Shelden et al., 2013:87-122).
Survey effort during the NMFS abundance surveys was fairly consistent across years with at least two survey flights covering lower inlet waters (south of East and West Foreland and north of Cape Douglas and Elizabeth Island) and multiple flights over the upper inlet. Daily summaries and maps showing sightings and trackline effort were published in Rugh et al. (2000, 2005) and Shelden et al. (2013). Surveys on a smaller scale were conducted in May (Rugh et al. (22)), August (Hobbs 'et al., 2015b; Rugh et al. (23, 24), Shelden et al. (25,26,27,28,29), Sims et al. (30)), September (Withrow et al. (31); Shelden et al. (32)), and October (Shelden et al. (32)).
To document year-round beluga whale distribution, surveys were flown 1-2 days each month (with the exception of December and March) from July 2001 to April 2002 (Rugh et al., 2004). Aircraft and methods were the same as those used during the NMFS abundance surveys. Effort included coastal and mid-inlet waters in the upper inlet, and mid-inlet tracklines between East and West Foreland and the southern tip of Kalgin Island in the lower inlet. Daily summaries and maps showing sightings and effort were published in Rugh et al. (2004).
Beluga whale sighting locations from all of the NMFS surveys were imported and plotted in ArcMap. Group size estimates from the NMFS abundance surveys have been corrected for availability and perception biases (see Hobbs et al., 2015a) but counts from all other studies (ADFG, NMFS, and MMS) are uncorrected.
Overview of Aerial Methods
It is important to note the differences and similarities among these aerial surveys. Surveys conducted by ADFG in the 1970's and 1980's were at lower altitudes (300-500 ft), in single engine airplanes or helicopters, and usually with only one observer on board. Although the pilot also searched for whales, detectability would be biased downward. MMS and NMFS surveys followed similar protocols with paired observers, side bubble windows, and survey altitudes at or above 800 ft. This improves detections though whale groups may still be missed (Hobbs et al., 2015a). Coverage of the inlet varied from project to project and season to season (e.g., Appendices 1 and 2, Rugh et al., 2004), largely driven by weather and day length, such that the summer period had the greatest amount of survey effort (Fig. 3). Therefore, we present the seasonal results by year (representing each project) and month, to account for any similarities or differences in subsequent analyses and discussions.
Satellite Tagging Dataset
Beluga whales in Cook Inlet were captured and tagged in late May 1999 (n = 1), September 2000 (n = 2), late July-August 2001 (n = 7), and late July-August 2002 (n = 8) (Table 2). The tagged whales included eight males and ten females ranging in size from 257 to 442 cm. Tags were placed on the dorsal ridge and held in place via plastic pins inserted through the blubber layer below the ridge (Fig. 4). Belugas were instrumented with either a satellite-linked time-depth recorder (Wildlife Computers Ltd., Redmond, WA) containing a Telonics ST-16 ARGOS transmitter (Telonics, Mesa, AZ) (ST-16), a smart position or temperature transmitting tag (SPOT2) (Wildlife Computers Ltd., Redmond, WA), or both (Table 2). Tags were programmed to transmit 24 hours a day (ST-16) or every 10 days for 24 hours (SPOT2). Tags transmitted locations from capture date to last uplink from 1 to 295 days (average = 116.4, SD = 84.5) (Table 2). Goetz et al. (18) reanalyzed tag data presented in Ferrero et al. (2000) and Hobbs et al. (2005), applying a land avoidance algorithm and removing gaps in data of longer than 1 day from the interpolated track. We used this revised dataset for the seasonal distribution analysis. Maps displaying individual whale locations each month for the four study years are provided in Appendix 3, with the exception of the four whales whose tags transmitted for fewer than 2 analysis days (Table 2).
Opportunistic Sightings Dataset
NMFS maintains a Microsoft Access database of beluga whale sightings provided by the public opportunistically (i.e., no associated effort data), from aircraft patrols (e.g., Civil Air Patrol, NMFS Enforcement, and military recon), dedicated beluga whale surveys (vessel, shore-based, and aerial), other wildlife surveys, and industry monitoring studies. The CIBW Opportunistic Database was queried for all sightings from 1975 (the earliest reported sighting in the database) through 2014. Sightings from beluga whale aerial surveys that had associated effort (ADFG, NMFS-NMML, and MMS) were excluded as these are presented in the aerial survey datasets section. Although a number of monitoring studies have occurred in Cook Inlet, particularly in the last decade (e.g., Polasek et al., 2015; Carlson et al., 2015; Kendall and Cornick, 2015), we included these data here only if sightings were provided to NMFS for inclusion in the database.
We note that after the moratorium on the subsistence hunt in 1999, and subsequent listing of the CIBW population as endangered, the number of sightings in the database increased substantially due to public outreach, NMFS enforcement patrols, and monitoring studies (Table 3). Most sightings in the lower inlet were opportunistic (78%), while monitoring and patrols provided almost half of the sightings reported in the upper inlet.
Beluga whale sightings were identified by year (representing each aerial survey project) as well as month when plotting the seasonal distributions for summer (June-Aug.), fall (Sept.-Nov.), winter (Dec.-Feb.), and spring (Mar.-May). Each sighting record on these plots represents a sighting location, not total number of belugas seen. For the summer, when much of the aerial survey effort took place (Fig. 3), each month includes separate maps for the 1970's, 1980's, 1990's, and 2000's, to alleviate the occurrence of overlapping sightings. Tagging data were also plotted by month within each season, and identified by year. Additional data summaries include specific dates when tag transmissions coincided with aerial survey effort or opportunistic sightings (Table 4). This provided a means to "ground truth" (33) tagged whale locations as well as document when whales were missed during aerial survey efforts.
Results and Discussion
The greatest amount of survey effort was expended during the period of June-July-August (Fig. 3). In particular, aerial surveys designed to estimate abundance of CIBWs have occurred annually, primarily in June, from 1994 to 2012 (Rugh et al., 2000; 2005; Shelden et al., 2013; Hobbs et al., 2015a) and biennially beginning in 2014 (Shelden et al. (16)). Most whales were tagged in late July and early August, only one whale was tagged in late May and transmitted locations throughout the summer season (Table 2). The CIBW Opportunistic Database yielded 865 summer sightings from the period 1975-2014, with 65% reported in August (Table 3).
In the 1970's and 1980's, belugas were often observed near East and West Foreland or in Trading Bay (near the mouth of McArthur River) in June (Appendices 1 and 2, respectively), but from the early 1990's until 2012, whales were not seen in these regions (Fig. 5). Beluga distribution within the inlet during June contracted into the northernmost regions of the upper inlet temporally and spatially (Rugh et al., 2010). Though the range occupied by this population had contracted northward by the late 1990's, the percentage of whales in the population occupying the Susitna Delta remained fairly constant over time, at roughly half of the population during the periods 1978-79, 1993-97, and 1998-2008 (Rugh et al., 2010).
Knik Arm was another area occupied by large numbers of beluga whales in the 1990's (Fig. 5c) and up until 2007 (Fig. 5d), after which whales were not found in this area during the NMFS abundance surveys (Fig. 5e) (Shelden et al., 2013; Hobbs et al., 2015a; Shelden et al. (16)). Since the analyses in Rugh et al. (2010) ended with the 2008 survey, we revisited the dataset and compared the proportion of whales found in the upper inlet during the period 2009-14. The contraction in range, represented by directional distribution ellipses that captured 95% of CIBW sightings, continued northward while still centering within the Susitna Delta (Fig. 6). On average, 83% (SE = 5%; n = 320) of the population was observed in the Susitna Delta during 2009-14, compared to half of the population during the earlier time periods (Rugh et al., 2010).
The satellite-tagged whale remained near the Little Susitna River, among the largest number of whales (average group size = 248, range 178-314) seen in the Susitna Delta during the NMFS abundance survey in June 1999 (Table 4). Only on 17 June did this whale venture across the inlet to Point Possession before looping back to Fire Island and returning to the Susitna Delta that same day (Fig. 7a).
Opportunistic sightings in the lower inlet were rarely reported in June and group sizes were typically 1-2 animals (Table 3). Almost all sightings reported in the upper inlet were north of Trading Bay (North Foreland) and Moose Point (Fig. 1). Similar to the NMFS abundance surveys, the last reports of belugas in upper Knik Arm (i.e., Eagle Bay/Goose Bay area and north) during early June were in 2007, with more recent reports occurring only near the entrance of Knik Arm at the Port of Anchorage.
Mid-inlet waters and much of the lower inlet coastline were not surveyed by ADFG in 1978 and 1979, respectively (Appendix 1), and upper inlet surveys in the 1980's did not include Turnagain Arm (Appendix 2) (Fig. 8a, b). NMFS surveys (Rugh et al. 2000, 2004; Withrow et al. (31)) included all coastal and some mid-inlet waters in the upper inlet and south to Kalgin Island (Fig. 8c). The only year NMFS calculated an abundance estimate in July was in 1995, which also included all coastal waters north of Elizabeth Island and Cape Douglas (Rugh et al. 2000). Rugh et al. (2000) noted:
"In the past, belugas were more concentrated in the upper inlet in June than in July: in the 1970's, the percent of sighting in the upper inlet relative to the lower inlet dropped from 86% in June to 52% in July ...; and in the 1980's, percentages dropped from 100% in June to 32% in July.; but in the 1990's, this annual shift in distribution was no longer evident (from 99% to 98% for both June and July)" (p. 13).
We speculate that this change in behavior (i.e., whales remaining in the upper inlet in July) continued into the 2000's. Whales were not found south of East and West Foreland in July 2001 during NMFS surveys (Fig. 8c) but effort was hampered by low clouds and fog in Redoubt Bay (Rugh et al., 2004). The number of whales counted in July 2001 fell within the range of counts obtained that June (Rugh et al., 2004:6).
Whales tagged with satellite transmitters in 1999 and 2002 spent most of their time in the Susitna Delta in July (Fig. 7b). CIBW opportunistic sightings during these years did not overlap temporally or spatially with tag locations. Overall, survey efforts and sightings, both systematic and opportunistic, were less frequent in July (Fig. 3, Table 3) compared to the other summer months. Opportunistic sightings in the lower inlet included a few large groups during the 1980's. Since then, most sightings in the lower inlet have been of single whales (Table 3).
Aerial survey effort increased again in August with almost half of the 25 survey years sampled (Fig. 3). In the 1970's, ADFG observed large numbers of beluga whales in the inlet south of East and West Foreland in August (Appendix 1). In 1978, all beluga sightings were in the lower inlet compared to over 70% in 1979 (Fig. 9a). A similar pattern of large numbers of whales moving from upper inlet waters to the lower inlet seems evident in the 1980's. Though survey effort did not include lower inlet waters (Fig. 8b, Appendix 2), the number of whales found in the upper inlet in August 1982 (176 whales) was similar to the August 1979 count (130 whales); and when compared to early June counts in 1982 (over 300 whales, Appendix 2), there were half as many whales in the upper inlet in August.
NMFS did not conduct surveys in August in the 1990's, though by early September 1993 the whales ranged from the Drift River and Kenai River in the lower inlet (the southern extent of the survey area) to Knik Arm (see Fall section). The August 2001 nMfS survey included coastal and mid-inlet tracklines in the upper and lower in let, south to Kalgin Island (Rugh et al., 2004). As mentioned previously, although this was not a NMFS abundance survey, the same methods were used. Whale numbers compared well with those observed in June (June, 211 belugas; August, 205 belugas) suggesting that most if not all of the population remained in the upper inlet (Fig. 9c), unlike the shifts in distribution to the lower inlet observed during the earlier time periods.
In 2005, NMFS began a series of surveys in the upper inlet to document beluga calving rates (Hobbs et al., 2015b). These surveys occurred annually until August 2012. Similar to ADFG surveys in the 1980's, all survey effort and sightings were north of East and West Foreland (Fig. 9c). Counts were similar to those obtained during the June abundance surveys for the period 2005-12 (Hobbs et al., 2015b), suggesting the contraction in range observed since the late 1970's and early 1980's occurred not only in June (as per Rugh et al., 2010) and July (Rugh et al., 2000) but also in August. Unlike the June surveys during the period 2008-12, whales were found in Knik Arm each August, often in large groups (average group size = 82, SD = 54) (Hobbs et al., 2015b).
Of the ten whales transmitting tag locations during August, only two ventured briefly south of East and West Foreland (Fig. 6c, Appendix 3). The whale tagged in 1999 remained in the upper inlet in August, primarily in Knik Arm and the Susitna Delta (Appendix 3). In 2001, most of the whales remained in the upper inlet, with the exception of one adult female who explored the waters south of West Foreland on 31 Aug. before returning to the upper inlet (Appendix 3).
In 2002, all whales transmitted locations during the month of August (Appendix 3). Similar to whales tagged in 2001, most remained in the upper inlet moving between the Susitna Delta, Knik Arm, and Turnagain Arm (Fig. 7c). One whale, the only adult female transmitting locations throughout the month, entered the lower inlet on 11 Aug. where she remained north of Kalgin Island for a day before returning to the upper inlet (Appendix 3). Tag transmissions overlapped with a number of opportunistic sightings in 1999, 2001, and 2002, and aerial survey effort in 2001 (Table 4).
Similar to July, opportunistic sightings in the lower inlet during August in the late 1970's included large groups of whales (Table 3). Since then reports of a single whale or small groups (3-13 whales) have been the norm.
Early summer had the greatest concentrations of whales in the upper inlet during all time periods. Shifts in distribution were evident in the 1970's and 1980's with large numbers of whales dispersing into lower inlet waters by mid- to late summer. This was not the case during the later survey periods when most of the Cook Inlet population continued to occupy the upper inlet well into late summer. The reduction of this population by half in the 1990's (Hobbs et al., 2015a) and the northward contraction of range during this period (Rugh et al., 2010) suggest a consolidation of the population into a few preferred habitats.
Nearly half of the population occupied the Susitna Delta in early summer during all time periods (Rugh et al., 2010), and over 83% after 2007 when whales were no longer observed in Knik Arm. Whales returned to the Susitna Delta each year, and often remained in spite of extensive Native subsistence hunting in this region during the early 1990's (Mahoney and Shelden, 2000). Goetz et al. (2012) modeled habitat preferences using the NMFS 1994-2008 abundance survey data. They found that in large areas, such as the Susitna Delta and Knik Arm, there was a high probability of beluga presence, and when present, group sizes were likely to be larger. Presence also increased closer to rivers with Chinook salmon, Oncorhynchus tshawytscha, runs (such as the Susitna River), and the Susitna Delta also supports two major spawning migrations of eulachon, Thaleichthys pacificus, a small, schooling smelt, in May and July. Stomachs from stranded belugas collected at the same time as the NMFS abundance surveys contained only Pacific salmon (Quakenbush et al., 2015).
It is not clear why belugas have not been seen in Knik Arm in June from 2008 to 2014. This change in distribution is not evident in the analyses presented by Rugh et al. (2010) or Goetz et al. (2012) because analyses ended with the June 2008 survey. Knik Arm was not abandoned for the entire summer, however, as large groups were observed here every August during the period 2008-12 (Hobbs et al., 2015b). Goetz et al. (2012) noted that anthropogenic disturbance, characterized as distance relative to coastal cities and oil development, was a significant predictor of beluga presence. Though presence increased with distance from these areas, the authors cautioned that many of the anthropogenic sources were south of the Susitna Delta, and that prey preferences rather than avoidance of development may be a stronger driver for this predicted distribution.
Belugas appear to have stronger site fidelity during the early summer period, as evidenced by a single tagged whale and aerial survey records. The one whale tagged during the beginning of this season transmitted locations throughout the entire summer period, remaining in the Susitna Delta from late May to late July, before exploring Turnagain Arm in late July, and Knik Arm in August. While some of the whales tagged in late July and August moved throughout the upper inlet in August, others remained for long periods in a few locations such as Knik Arm, the Susitna Delta, and Turnagain Arm (Appendix 3).
Preliminary analyses of the dive data collected by the tags indicate whales made shorter, shallower dives during the period from June to November compared to the longer, deeper dives recorded during December to May (Goetz et al. (18)). Closer examination of the whale tagged in late May 1999 showed time at surface increased daily over a 2-week period from 31 May to 11 June (Hobbs et al., 2015a). This would be expected as belugas follow anadromous fish runs into shallow channels within the tidal flats of the Susitna Delta. Spending more time at the surface also increases the likelihood of aerial observers detecting these whales.
Near the end of August, two of the tagged whales spent brief periods in the lower inlet. In all three years, a few whales spent time in mid-inlet waters of the upper inlet in August (Fig. 7c). These behaviors may be representative of much larger groups of whales. Unfortunately, lower inlet and most mid-inlet tag locations did not coincide with aerial survey effort or opportunistic sightings. Nevertheless, by late summer some beluga whales begin to traverse into the lower inlet and mid-inlet waters of the upper inlet.
In the fall, day length shortens and anadromous fish runs come to an end. Survey effort was also much reduced during the September-October-November period (Fig. 3, Fig. 10). The CIBW Opportunistic Database included 595 fall sightings during the period 1975-2014 (Table 3). Most opportunistic sightings were reported in September (63%) and decreased throughout the season. Thirteen tags transmitted locations of whales during the month of September, and eleven continued to transmit into November (Fig. 11).
ADFG did not survey Cook Inlet in September during the 1970's and 1980's (Fig. 3). NMFS surveys in 1993 (Withrow et al. (31)) included the coastline and mid-inlet waters of Cook Inlet north of the Drift and Kenai rivers. Belugas were encountered at the northern and southern limits of this survey--ranging from Turnagain Arm and Knik Arm to Kenai River and Drift River (Fig. 10a). The highest count, 197 whales on 3 Sept., included groups ranging in size from 5 to 59 whales (Withrow et al. (31)). Whale numbers dropped substantially during the 18-19 Sept. surveys (12 and 57 whales, respectively) when whales were found only in Knik Arm, Chickaloon Bay, and Turnagain Arm.
In 2001, NMFS conducted an aerial survey that included coastal and mid-inlet waters north of Harriet Point and Kasilof River (Rugh et al., 2004). On 15 Sept., a few belugas were seen near Beluga River (3 whales) and large groups were found in Knik Arm (113 whales) and Turnagain Arm (70 whales) (Fig. 10a). This count (186 whales) was in the middle of the range of daily counts (165-210 whales, average = 186) made in June that same year (Rugh et al., 2005).
A two day survey was conducted by NMFS in September 2008 with the objective of searching for beluga whales in lower Cook Inlet. Effort included 1) a coastal trackline down the western side of the inlet from the Little Susitna River to Cape Douglas, midinlet tracklines, and a coastal trackline along Kachemak Bay on 19 Sept.; and 2) a coastal trackline of the upper inlet north of Point Possession and the Beluga River tidal flats on 20 Sept. (Shelden et al. (32)). All whales observed (~66 total) were in the upper inlet in Knik Arm, Turnagain Arm, and Chickaloon Bay (Fig. 10a). This count also fell within the range of counts (58-126 whales) obtained in June 2008 (Shelden et al., 2013).
With the exception of one whale that spent time in the lower inlet in Chinitna Bay, tagged whales (n = 12) remained in the upper inlet during September (Fig. 11a, Appendix 3). Whales transmitting locations in 1999 and 2000 remained in the upper inlet north of North Foreland and Point Possession (Fig. 11a). One of the whales tagged in 2000 remained in Knik Arm during September. The other left Knik Arm on 15 Sept. and travelled to Turnagain Arm and Chickaloon Bay, similar to the whale tagged in 1999 (Appendix 3).
All of the whales tagged in 2001 transmitted locations in September (Appendix 3). Most (5 of 6) remained in the upper inlet while one female whale spent at least part of the month (34) in the lower inlet in Chinitna Bay (Fig. 11a). By September 2002, four of the six tagged whales, all males, were still transmitting locations (Fig. 11a). All remained in the upper inlet, but each would at times travel independent of the other tagged whales (to Turnagain Arm or Trading Bay) then rejoin one or more in the Susitna Delta or Knik Arm (Appendix 3). Tag transmissions overlapped with a number of opportunistic sightings in 1999, 2001, and 2002, and aerial survey effort in 2001 (Table 4).
CIBW opportunistic sightings began to increase in the lower inlet during September, though most reports were still occurring in the upper inlet (Table 3). With the exception of one sighting (6 whales) in 1975 in Kachemak Bay, all reports were from 1999 to 2011 and occurred in and near the Kasilof and Kenai rivers (32%), and Chinitna (23%), Illiamna/ Iniskin/ Cottonwood (19%), Kamishak (7%), and Kachemak bays (16%).
In 1978, all beluga groups (75 whales total, Appendix 1) observed during aerial surveys were in the lower inlet (Fig. 10b). In 2001, NMFS flew mid-inlet transects on 12 Oct. in the upper inlet and in the lower inlet as far south as Harriet Point and Kasilof River; and on 15 Oct., a coastal survey of the upper inlet (Rugh et al., 2004). A small group of three whales was seen near the Little Susitna River during mid-inlet transects but most whales (162 total) were observed in Knik Arm during the coastline survey. Rugh et al. (2004) noted that similar to the September 2001 count, the October count of 162 whales was "well within the range of the daily counts in June ... which meant that in October most of the whales were still in upper Cook Inlet" (p. 8).
On 22 Oct. 2008, NMFS flew an exploratory effort to look for belugas in Kamishak Bay similar to surveys in September of that same year (Shelden et al. (32)). The shoreline survey from Cape Douglas to the Little Susitna River included effort in some parts of Kamishak Bay and from Chinitna Bay to Point MacKenzie. Unlike the ADfG surveys in the 1970's, no whales were found.
Only 2 of the 12 tagged whales travelled into the lower inlet during October (Fig. 11b). Both followed the western shoreline south to Redoubt Bay (in 2000 and 2002) but only the whale tagged in 2002 continued south to Chinitna Bay (Appendix 3). This whale travelled 6 days from West Foreland to Chinitna Bay, exploring Tuxedni Bay and Redoubt Bay twice before returning to the upper inlet 19 days later, and remained in Trading Bay until the end of the month (Appendix 3). Tag transmissions overlapped with opportunistic sightings in 2000 and 2001, and aerial survey effort in 2001 (Table 4). No CIBW opportunistic sightings were reported during October 2002.
Overall, the number of CIBW opportunistic sightings began to decline from September to October in both upper and lower Cook Inlet (Table 3). With the exception of a single sighting in Kachemak Bay in 1976, all lower inlet sightings were during the period 1998 to 2010. Most were reported along the west side of the inlet (59%) in Redoubt, Tuxedni, Chinitna, Illiamna/Iniskin, and Kamishak bays. East side sightings were in or near Kenai River (36%). Upper inlet sightings were in areas occupied by whales during the summer months (Trading Bay (3%), Turnagain Arm (19%), Knik Arm (71%), Chickaloon Bay (4%), and the Susitna Delta (3%)) with almost all reported between 1999 and 2014 (two sightings occurred in Knik Arm in 1991).
Typically, ice begins to form in the upper inlet by November, and though there was no mention of ice during the one-day ADFG survey in 1977, and a note stated no whales were observed in upper Cook Inlet, all documented effort occurred in the lower inlet (Appendix 1). ADFG counted 41 whales (35) on 22 Nov. (Appendix 1) with 6 of the 10 sightings occurring south of East and West Foreland (Fig. 10c). By early November 2001, ice was present in Knik Arm, Turnagain Arm, Chickaloon Bay, and along the shore from Fire Island to Drift River during the NMFS survey (Rugh et al., 2004). Small numbers of whales were found in Turnagain Arm (3 and 6 whales), Knik Arm (14 whales), and Trading Bay (1 whale) on 9 Nov. (Fig. 10c).
All of the tagged whales transmitting locations in November (n = 11) remained in the upper inlet (Fig. 11c) and continued to travel within both Knik Arm and Turnagain Arm. One whale also explored deeper waters of the upper inlet, and another spent the first week of November in Trading Bay before returning to the Little Susitna River (Appendix 3). Tag transmissions overlapped with opportunistic sightings in 2000 and 2001, and aerial survey effort in 2001 (Table 4).
Similar to the systematic surveys, opportunistic sightings continued to decline from October to November (Table 3). Sightings occurred between 1999 and 2014, with the exception of one sighting at Kenai River in 1982 and one in Knik Arm in 1991. All CIBW opportunistic sightings in the lower inlet were in the Kenai River (63%), Kachemak Bay (25%), or Redoubt Bay (12%). Upper inlet sightings were in Knik Arm (93%), Turnagain Arm-Chickaloon Bay (3%), the Susitna Delta (2%), and Trading Bay (2%).
Some belugas move between the upper and lower inlet during the fall, as evidenced by one tagged whale during each year of the tagging study (Fig. 11a, b). NMFS surveys in 2001 continued to detect large numbers of whales in the upper inlet until November, when ice extent and concentration may have affected the ability of aerial observers to detect belugas. Dispersal of large numbers of whales into lower inlet waters in the fall was not evident in the later years of the NMFS surveys. Tagged whales still transmitting locations by the end of the fall had remained in or returned to the upper inlet (Fig. 11).
This differs markedly from surveys in the 1970's, when whales began to disperse into the lower inlet by midsummer. Although sightings occurred in the lower inlet during fall surveys in the 1970's, counts were low (41-75 whales) compared to the summer. It is possible that smaller, dispersed groups were harder to detect. In the early 1990's, whale groups appeared to disperse by late September (Withrow et al. (31)), though we have only one survey in the fall during this time period and no opportunistic sightings. By 2001, the contraction of this population's range into the upper reaches of Cook Inlet appeared to continue not only through the summer months but into the fall (Rugh et al., 2004; Shelden et al. (32)).
The winter period covers the months from December through February. Winter survey efforts and sightings, both systematic (Fig. 3, Fig. 12) and opportunistic (Table 3), were few compared to other seasons, in part because of weather and short day length. Nine of the satellite tags continued to transmit location data at the beginning of the season (Table 2), though only four were still functioning in February (Fig. 13; Appendix 3).
December was the only month with no aerial survey effort (Fig. 3). Data from nine satellite tags showed whales in the upper inlet and areas just south of East and West Foreland (Fig. 13a, Appendix 3). Belugas inhabited shallow, nearshore areas as well as deeper, mid-inlet waters, primarily in the region north of East and West Foreland and south of Point Possession. Only whales transmitting locations in 2000 and 2002 entered Knik Arm and Turnagain Arm during December (Appendix 3).
The CIBW Opportunistic Database included 16 sightings for the month of December (Table 3), all during the period 1999-2014. With the exception of one sighting of two whales at Kenai River in 2002, all sightings were in the upper inlet. Group sizes, when provided, ranged from 1 to 30 whales. Only one opportunistic sighting, on 17 Dec. 2001, coincided with locations transmitted from tagged whales (Table 4).
In 1978, during a survey flight that followed the ice edge (Appendix 1), belugas were found in three groups (12, 50, and 30 whales) in ice-free water south of Kasilof River (Fig. 12). On a series of mid-inlet tracklines on 22 Jan. 2002, belugas were in five small groups (15 whales total, Fig. 12) in sea ice ranging from 10% to 30% cover age (Rugh et al., 2004). None were found during the shoreline survey on 25 Jan. when "much of the area was ice-covered, making it difficult to find whales" (Rugh et al., 2004:9).
In January 2001, tagged whales remained south of the Susitna Delta (Fig. 13b, Appendix 3), never entering Knik Arm or Turnagain Arm where all CIBW opportunistic observations occurred. Tagged whales behaved similarly in January 2003. The three tagged whales travelled extensively between the Susitna Delta and East and West Foreland, often but not always together, crossing mid-inlet waters, and entering the lower inlet and returning to the upper inlet multiple times (Appendix 3). Only during January 2002 did a tagged whale spend any time in Knik Arm and Turnagain Arm (Appendix 3). Tag transmissions from this whale overlapped spatially and temporally with aerial survey effort and opportunistic sightings during the period 18-25 Jan. (Table 4).
The CIBW Opportunistic Database included 17 sightings for the month of January, of which 13 occurred in the upper inlet (Table 3). Just over half of the upper inlet sightings were reported in Turnagain Arm, an area easily accessible by car. Average group size was 100-200 whales in the lower inlet during the 1980's and 2000's, and 3 to 15 whales, respectively, in the upper inlet during those same time periods (Table 3).
February surveys were flown by ADFG, MMS, and NMFS (Fig. 3). Belugas were not seen during ADFG surveys in 1979 (Appendix 1). Ice was present throughout much of the inlet and snow storms prevented exploration south of Kachemak Bay on 25 Feb. In 1997, MMS observers saw belugas on 12 and 28 Feb. (Fig. 12, Table 1), but not on 15 Feb. despite thorough coastal coverage south to Chinitna Bay and Ninilchik (Hansen and Hubbard (17)). Hansen and Hubbard (17) reported that ice conditions near Kalgin Island ranged from 40% to 60% coverage in mid-February to open water by late February. The authors noted "the presence of extensive shorefast ice at the mouth of the Susitna River and other major streams made it difficult to see if whales were in these areas" (p. 13). Belugas were not seen during NMFS aerial surveys on 25-26 Feb. 2002 (Rugh et al., 2004). Ice covered much of the survey area, in the range of 70% to 100% coverage mid-inlet and in Knik Arm and Turnagain Arm, with areas of open water (50% coverage) just south of the Susitna River.
During February 2002, the last whale transmitting locations moved from Knik Arm into mid-inlet waters before entering the lower inlet (Fig. 13 c, Appendix 3). Transmissions overlapped with areas surveyed by the aerial team (Table 4). Three whales tagged in 2002, all males, continued to transmit positions in February 2003 (Fig. 13 c). One young male beluga frequented Turnagain Arm and joined another young male in Knik Arm (Appendix 3). The three whales moved throughout upper inlet waters before travelling south of East and West Foreland in mid-February (Appendix 3). Tag transmissions from two of these three whales were in the vicinity of an opportunistic sighting (Table 4).
No CIBW opportunistic sightings were reported in February during the 1970's, 1980's, or 1990's (Table 3). Nine of the eleven CIBW opportunistic sightings reported in February between 2001 and 2014 were in the upper inlet in Trading Bay (56%), Turnagain Arm (22%), and Knik Arm near the Port of Anchorage (22%). Lower inlet sighting included 50 whales near Drift River in Redoubt Bay and a lone whale in the Kenai River (Table 3).
Winters in Cook Inlet are characterized by short day lengths and ice-covered waters. Despite the possibility of ice entrapment, CIBWs remained in upper inlet waters particularly during the later time period (Rugh et al., 2004; Hobbs et al., 2005; Goetz et al. (18)). Large tidal fluctuations create a dynamic ice environment such that whales were able to access the upper reaches of Knik Arm and Turnagain Arm during the winter period. Although whales transmitting locations in 2001 never entered these areas, opportunistic sightings confirmed whales were present.
Goetz et al. (18) found that movements of tagged belugas were influenced by the presence of ice in Cook Inlet during the winter. After examining the biweekly proportion of ice type (ranging from very open pack to compact ice) throughout the inlet, from Dec. 2001-Mar. 2002 and Dec. 2002-Apr. 2003, total ice cover was always less than 50% for every 2-week period. When ice was present, belugas were most commonly found in open pack ice (winter of 2001-02) and very open pack ice (winter of 2002-03). During the winter of 2001-02, belugas (n = 2) preferred open water only 2% of the time when ice was present compared to 30% during the winter of 2002-03 (n = 3). On most occasions when belugas preferred open water, ice covered less than 10% of Cook Inlet.
In addition to this close association with ice, diving was another behavior that may have confounded detection during winter aerial surveys. Preliminary analyses of the tag data indicate whales were diving deeper and longer during the period December-May compared to the period June-November (Goetz et al. (18)). Average depth (m) and duration (minutes) increased almost three times, from 3.0 m (SD = 4.7) to 8.2 m (SD = 12.3) and 1.6 minutes (SD = 1.9) to 5.2 minutes (SD = 5.5) for the 11 whales equipped with ST-16 tags (Goetz et al. (18):19).
The combination of poor sighting conditions (low light levels in winter and white whales among ice floes) and whale behavior (close association with ice, longer, deeper diving patterns, and smaller groups) made it difficult to ground truth or even detect groups during this season. This was most evident during the NMFS survey that overlapped with tagged whale locations and detected whales in January but not in February. Combining satellite-tagging with real-time acoustic monitoring and aerial ground truthing may be the best option for quantifying habitat use patterns and visual detectability during winter.
During spring (Mar.-Apr.-May), ice is still present in Cook Inlet. By March, ice cover has reached its maximum extent and begins to recede and melt through March and April. Spring survey efforts and sighting reports, both systematic (Fig. 3, Fig. 14) and opportunistic (Table 3), increased throughout the season. Four tags continued to transmit whale locations at the beginning of the season (Fig. 15), though by May, as aerial survey effort increased, only one tag continued to function (in 2003). Tagging of an adult male beluga in 1999 occurred on the last day of May (Table 2, Appendix 3).
Belugas were found on both aerial survey days in 1978 and one of the two survey days in 1979 (Appendix 1). The number of whales counted in 1978 ranged from 43 (5 sightings) on 1 Mar. to 146 (17 sightings) on 2 Mar., compared to the lone group of 11 whales seen mid-inlet in 1979 (Fig. 14a). Ice appeared to be more prevalent in the inlet in 1979; maps showed ice along the shore in the lower inlet and near Kalgin Island in mid-March, vs. 1978 when the northernmost areas of the upper inlet had large expanses of open water by early March.
The survey area was ice free during the 1997 aerial surveys (Hansen and Hubbard (17)). Sighting locations, number of sightings, and group sizes were similar to those observed during the MMS February surveys (Fig. 14a, Table 1). NMFS did not fly surveys in March 2002, however, it was noted during the April survey that ice still covered much of the upper inlet (Rugh et al., 2004).
The last tag transmitting in 2002 stopped on 9 Mar.; at the time, the male beluga was in the lower inlet in waters north and west of Kalgin Island (Fig. 15a, Appendix 3). Similar to behaviors observed during the winter months, the three male whales transmitting locations in 2003 continued to travel extensively in mid-inlet waters north of East and West Foreland (Fig. 15a, Appendix 3).
All CIBW opportunistic sightings in the lower inlet (Table 3) were between Ninilchik and the Kenai River. None of the opportunistic sightings in the upper or lower inlet overlapped with tagged whale locations. Most upper inlet sightings were reported in Turnagain Arm (29%) and Knik Arm (62%), with lone sightings in Trading Bay (1 whale) and near Tyonek (22 whales).
The 1978 aerial surveys occurred in the lower inlet (Appendix 1), while the 1983 surveys were restricted to the upper inlet north of North Foreland and Moose Point (Appendix 2). In 1978, beluga whales were found in roughly five groups (about 56 whales total (35)) in bays along the west side of the lower inlet (Fig. 14b). Four groups were observed on each survey day in 1983 (6 Apr.: n = 10 whales; 28 Apr.: n = 38 whales (35)) (Fig. 14b). In contrast to the ADFG surveys, ice covered much of the upper inlet during NMFS surveys conducted 2-3 Apr. 2002 (Rugh et al., 2004). Two groups (8 and 10 whales) were found on mid-inlet transects on 2 Apr., while none were found during the coastal surveys on 3 Apr., despite fair to excellent viewing conditions.
By April 2003, only two whales were transmitting locations. One tag stopped transmitting near the Susitna River on 1 Apr. (Appendix 3). Hobbs et al. (2005) did not analyze tag data collected after March, as only one whale continued to transmit locations through April and most of May. That whale remained in the upper inlet for the entire month, travelling between Knik Arm, Turnagain Arm, and the Susitna Delta (Fig. 15b, Appendix 3).
CIBW opportunistic sightings increased substantially from March to April (Table 3), though none coincided with aerial survey effort or tag transmissions. Lower inlet sightings prior to 2000 (Table 3, n = 14), with the exception of one sighting in the Kenai River, were on the west side of the inlet in or near Illiamna/Iniskin (57%) or Kamishak (36%) bays. Since then, all opportunistic sightings have been reported in or just north of the Kasilof (n = 4) and Kenai rivers (n = 32), or in Redoubt Bay (n = 1). In the upper inlet, sightings were reported during all time periods with groups ranging from 1 to 25 whales. Most sightings occurred in the Susitna Delta (27%), Turnagain Arm/Chickaloon Bay (37%), and Knik Arm (30%), with a few in Trading Bay (5%) and near East Foreland (1%).
Aerial surveys occurred in May during 7 of the 25 aerial survey years (Fig. 3, Fig. 14c), in part, because NMFS abundance surveys began near the end of May before continuing into June (which is also reflected in the low number of effort hours during May: Fig. 3). In 1978, ADFG found only two groups (20 and 7 whales) in the upper inlet on 22 May (Appendix 1), while upper inlet surveys in the early 1980's documented large numbers of belugas north of Threemile Creek and Moose Point (Appendix 2). Three groups were seen each year with counts ranging from 45 (17 May 1982) to 262 whales (27 May 1983).
In 2005, the NMFS abundance survey began on the last day of May (Shelden et al., 2013). Belugas were found in Chickaloon Bay (37 whales) and in the Susitna Delta near the Ivan River (229 whales) and the Little Susitna River (7 whales) during a survey that included coastal waters north of the Kenai River and West Foreland (Shelden et al., 2013). In contrast, a NMFS survey of the upper inlet conducted in early May 2006 (Rugh et al. (22)) found only small numbers of whales: four sightings (18 whales total) on 2 May and six sightings (25 whales total) on 3 May (Fig. 14c). Broken ice was present in the Susitna River in early May 2006 (Rugh et al. (22)), but had melted away by the time the NMFS abundance survey began on 6 June (Shelden et al., 2013), and 296 whales (11 groups) were found in the upper inlet that day.
Similar to 2005, the abundance surveys in 2011 and 2012 included days at the end of May (Shelden et al., 2013). Two groups of belugas were found during the upper inlet survey on 31 May 2011: in Chickaloon Bay (57 whales) and the mouth of the Little Susitna River (200 whales) (Fig. 14c). Three days of lower inlet surveys occurred in May during the 2012 survey (Shelden et al., 2013). About seven belugas were found near West Foreland headed toward Trading Bay on 31 May (Fig. 14c). Whales were seen in Trading Bay on subsequent survey days (see Summer section and Fig. 5e).
On the last day of May in 1999, NMFS tagged a beluga whale near the Little Susitna River (Fig. 15c). This whale remained in the Susitna Delta until the end of July (see Summer section). In 2003, locations from the last remaining tag show the whale travelled back and forth between the Beluga River and Knik Arm before transmissions ended on 25 May (Fig. 15c, Appendix 3). Tag transmissions coincided with one CIBW opportunistic sighting on 31 May 1999 (Table 4).
CIBW opportunistic sightings increased in the upper inlet and declined in the lower inlet from April to May (Table 3). Lower inlet sightings prior to 2000 (n = 2) were in Kachemak or Iniskin bays, while the remaining opportunistic reports occurred in the Kenai River almost annually since 2007.
Similar to winter, the year-to-year variability in ice extent and concentration appeared to affect the ability of aerial observers to detect beluga whales during the spring. In spring, when the ice breakup begins, whales gather together as they regain access to river mouths. In early spring, whales continued to move throughout mid-inlet waters. Not until late spring and early summer, when anadromous fish return to natal streams, did whale behaviors shift to longer surfacing periods and shallower diving patterns (Hobbs et al., 2015a; Goetz et al. (18)). Group sizes tended to be smaller in spring, until the end of May when whales began to coalesce into larger groups at the river mouths. Most aerial survey and opportunistic sightings, and all tag locations, were in the upper inlet by May.
Cook Inlet is a complex and dynamic environment, covered in ice part of the year and opaque waters year-round that confound detection of beluga whales. This review of the tremendous amount of survey effort undertaken thus far shows how little we still know outside of the open water season and early summer period. Based on available information from aerial surveys, tagged whales, and opportunistic sightings, these whales show a preference for waters in the upper portion of Cook Inlet, and when the population declined (Hobbs et al., 2015a), the distribution of animals became more concentrated in the northern region (Rugh et al., 2010). Although belugas do inhabit mid-inlet waters and bays in the lower inlet, sightings south of East and West Foreland have been relatively rare in the past two decades. This contraction in range was observed not only during the summer months (Rugh et al., 2000; 2010) but also into the fall during the later period of this seasonal study (Rugh et al., 2004; Shelden et al. (32)). There has also been a shift away from Knik Arm in early June, observed since 2008, but this area was not abandoned entirely as whales were observed there in August. It is unknown if this contracted distribution is a result of changing habitat (Moore et al., 2000; Norman et al., 2015), prey concentration, or predator avoidance (Shelden et al., 2003), or if it could be explained as the contraction of a reduced population into a small number of preferred habitat areas (Rugh et al., 2010; Goetz et al., 2007, 2012).
Remaining in the upper inlet exposes beluga whales to potential natural and anthropogenic threats such as ice entrapment, stranding, vessel traffic, coastal development projects, dredging, and increased proximity to urban runoff and waste from the largest city in Alaska, Anchorage (Norman et al., 2015). Contraction of the population into the upper inlet, not only during early summer (Rugh et al. 2010) but also throughout the year, may increase vulnerability to catastrophic events and localized group mortality events (Hobbs et al., 2015c). Live strandings are not uncommon for this population, when they become trapped on the upper inlet mudflats on the ebbing tide. And although the whales refloat and swim off on the incoming tide, prolonged stranding could compromise survival (Vos and Shelden, 2005; Burek-Huntington et al., 2015).
Habitat associations during the early summer period have been studied, and note "beluga presence was negatively associated with sources of anthropogenic disturbance and positively associated with fish availability and access to tidal flats and sandy substrate" (Goetz et al., 2012). These predicted habitats varied depending on whale group size, where larger groups were more closely tied to tidal flats and high flow rivers (a proxy for suitable habitat for anadromous fish). Distributions predicted in Goetz et al. (2012) were similar to those observed during the late 1970's, possibly indicating that as this population recovers it may reoccupy these areas.
Based on our review, additional studies are needed to better quantify habitat use patterns during seasons other than early summer. Acoustic monitoring studies are underway in Cook Inlet, attempting to detect whales year-round (Castellote et al., 2011). However, these studies depend on animals vocalizing to determine presence. Combining satellite-tagging with real-time acoustic monitoring and aerial ground truthing may be the best option for quantifying habitat use patterns and visual detectability particularly during ice-covered seasons.
This paper would not have been possible without the dedicated observers who spent many hours of many days and months searching for Cook Inlet belugas. ADFG observers included D. Calkins, N. Murray, S. Starr, C. Hamilton, W. Keefer, M. Cunningham, M. Chihuly, D. McAllister, S. Albert, R. Sleeper, T. Cunning, and D. Lewis (and a few whose names were illegible on the hand written notes). NMFS observers included R. Angliss, D. DeMaster, K. Goetz, R. Hobbs, J. Laake, L. Litzky, B. Mahoney, J. Mocklin, W. Perryman, D. Rugh, K. Shelden, C. Sims, B. Smith, L. Vate Brattstrom, J. Waite, and D. Withrow. MMS (BOEM) observers included D. Hansen, J. Hubbard, M. Baffrey, P Johnson. B. Mahoney, B. Smith, and P. Johnson.
Aircraft and pilots were provided by Kenai Air, Rust's Flight Service, Era Aviation, NOAA, Commander Northwest, Northern Commanders, and Clearwater Air. NMFS aerial surveys were conducted under NMFS permit 791 (P771#63), 782-1360, and 7821438, and 14245. Beluga whale tagging teams included B. Mahoney, D. Seagars, D. Vos, M. Eagleton, K. Laidre, R. Hobbs, L. (Litzky) Hoberecht, R. Ferrero, J. Cesarone, D. Baird, K. Dimmick, R. Dimmick, C. Goode, W. Gossweiler, B. Hanson, N. Lord, P. Merryman, G. O'Corry-Crowe, R. Olson, C. Saccheus, W. Walker, L. Quakenbush, PS. Hill, B. Smith, R. Standifer, R. Stephan Jr., G. Tallekpalek, S. Moore, D. Bogan, C. Dovichin, C. Garner, K. Peirce, A. Vrem, M. Wahl, and J. Metz. Tagging was conducted under NMFS Permit 957 and 782-1438 (Amendment No. 3). Considerable thanks are owed to the many people who provided sighting information, particularly through the Cook Inlet beluga sighting network. This manuscript benefited greatly from the comments provided by J. Waite, H. Ziel, and three anonymous reviewers.
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Please note: Some tables or figures were omitted from this article.
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|Title Annotation:||p. 1-31|
|Author:||Shelden, Kim E.W.; Goetz, Kimberly T.; Rugh, David J.; Calkins, Donald G.; Mahoney, Barbara A.; Hobb|
|Publication:||Marine Fisheries Review|
|Date:||Mar 22, 2015|
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