Report for April-May-June 2001)
Continues Effort to Estimate Steller Sea Lion
Survival and Study Food Habits
Personnel from the National Marine Mammal Laboratory (NMML) conducted a Steller sea lion (Eumetopias jubatus) research cruise in the Gulf of Alaska from 19 to 29 May 2001. The primary cruise objective was to search for sea lions marked and tagged as pups to improve estimates of survival, with a secondary objective to collect scats for food habits studies. Each of the 29 known rookery and haul-out sites in the Kodiak Archipelago, Shelikof Strait, and Kenai Peninsula areas were visited (Figure 1 above). Nine of the sites were occupied by 100 or more sea lions, 13 were occupied by 10-100 sea lions, and 7 were unoccupied. We resighted 39 of the 258 pups branded at Sugarloaf Island and Marmot Island rookeries in July 2000, and 6 of 12 young-of-the-year and juvenile sea lions that had been captured at Long and Sea Otter Islands near Kodiak in March 2001. We also observed three animals with plastic flipper tags. One observed at the Ushagat (southwest) haulout in the Barren Islands had been tagged as a pup on Atkins Island, 325 nautical miles (nmi) (600 km) to the southwest, on 28 June 2000. Another at Shakun Rocks in northern Shelikof Strait had been tagged as a pup on Chirikof Island, approximately 185 nmi (340 km) to the southwest, on 29 June 2000. A total of 71 scats were also collected for food habits analysis. Other marine mammal sightings during the cruise included about six fin whales at Uyak Bay on the west side of Kodiak Island; three fin whales off the southwest side of Takli Island in Shelikof Strait, hundreds of humpback whales on the morning of 24 May off the Barren Islands; and hundreds of unidentified large whales off the east side of Kodiak Island, especially between Cape Chiniak and Cape Barnabas. Also, four killer whales were observed at the Cape Sitkinak sea lion haul-out site. The whales cruised past the haulout several times, but with no apparent interest or interaction between sea lions and whales.
By John Sease and Brian Fadely.
Aleutians Passes Cruise: Killer Whale Component
The decline of Steller sea lions in the central and western areas of the North Pacific Ocean and the Bering Sea has precipitated a number of research projects seeking to investigate possible causal factors. One of these, the Aleutians Passes Project, has two fundamental goals: 1) examination of productivity near sea lion rookeries and haulouts and 2) documentation of the number and ecotype of killer whales (Orcinus orca) in waters between Unimak and Seguam Passes in the central Aleutian Islands chain. This project combines a suite of oceanographic and biologic measures to examine productivity. Standard hydrographic measurements (conductivity-temperature- depth (CTD) and sea surface temperature (SST)), nutrient availability and primary production, zooplankton prey field assessment (acoustic and prey capture), and spatial pattern and relative abundance of seabirds and marine mammals are all used to determine specific and relative productivity within the study area. The number and ecotype of killer whales are investigated using standard photoidentification methods and the collection of biopsy tissue samples for isotopic analysis. Preliminary results of the first field season of killer whale observations are presented here.
Marine mammal surveys were conducted from 4 to 24 June 2001, beginning and ending in Seward, Alaska. The study focuses on the relative productivity and occurrence of killer whales at four Aleutian Islands passes: Seguam, Amukta, Akutan and Unimak. The passes border Steller sea lion rookeries and haulouts where populations are either in decline or holding steady. The surveys focused on transect lines along and across the passes (Figure 1 below). The four passes are distinctly different in physiography: Seguam—narrow and deep; Amukta— broad and deep; Akutan—narrow and shallow; Unimak—broad and shallow. Thus, the four passes provide a baseline for a suite of comparisons of hydrography and productivity at dynamic centers of seawater exchange between the North Pacific Ocean and the Bering Sea.
Two primary marine mammal observers maintained a watch from port and starboard sides of the bridge of the University of Alaska research vessel Alpha Helix for 12 to 16 hours each day when conditions were suitable for survey (i.e., Beaufort <05; visibility > 1 km). Observers at port and starboard stations searched with naked eye and binoculars (7X or higher) with reticles. Observers scanned for 1 hour at each station, followed by a 1-hour break. The two primary observers were assisted in sighting marine mammals by University of California at Irvine seabird researchers conducting surveys from either the port or starboard side (depending on glare) and by the ship’s crew. Data were recorded by the starboard observer using WinCruz software on a laptop computer interfaced to the ship’s Global Positioning System (GPS). Positions along the cruise track were updated at 2-minute intervals. When marine mammals were seen, bearing and reticle to the sighting, species, group size (best/high/low estimates) and the animals’course and speed were recorded. During transit to the study area, only killer whales were approached for photographs. All other sightings were recorded in passing mode. After reaching the study area, other cetaceans were sometimes approached for positive identification.
When killer whales were seen within the study area, the marine mammal team moved to the bow of the Alpha Helix to photograph whales as the ship maneuvered as close to the whales as possible. During calm sea conditions, a rigid hull inflatable boat (RHIB) was deployed to provide close access to whales for high-quality photographs and biopsy attempts. Whales were approached from behind on their left sides to obtain standard identification photographs of their dorsal fins and saddle patches. On two occasions, close approaches were made from the RHIB to obtain biopsy tissue samples using a crossbow to deliver a hollow-tipped dart. A tissue sample was obtained on the first occasion; on the second occasion the whales proved elusive. Attempts were made to biopsy individuals that were distinctive, but this was not accomplished due to the tight spacing of the whales. The tissue biopsy was split into two samples: a skin sample, stored in DMSO for DNA and isotopic analysis; and a blubber sample, frozen for analysis of contaminants. Attempts to biopsy whales were limited by several factors. At times when oceanographic work was not under way, sea conditions limited work from the RHIB to two occasions. Also, emphasis was placed on obtaining identification-quality photographs prior to biopsy attempts, which were made at the end of encounters when whales were more difficult to approach closely.
A total of 265 hours of survey for marine mammals was completed, including transit to (81.5 h) and survey in (183.5 h) the study area. Viewing conditions were usually good to excellent, with little disruption to surveys by rain or fog. Ten marine mammal species were seen, with Steller sea lions the most common pinniped seen when animals hauled out on land were included. Dalls porpoise (Phocoenoides dalli) were the cetaceans most often seen. Fin whales (Balaenoptera physalus) were seen during transits to and from the study area, but not in the study area. Regions of high fin whale sighting rates included waters near the Semidi Islands on the outbound leg and at the Shumagin Islands on the return passage. Fin whales usually were seen in groups of 2-10 whales and were often near humpback whales (Megaptera novangliae), although the two species did not appear to interact. Although seen with fin whales, humpbacks were also seen as singletons and pairs, often along the coast or near islands. Minke whales were seen as singletons throughout the cruise, with two to three animals that seemed resident in Akutan Pass. Although ubiquitous, Dalls porpoise were particularly common near Samalga Pass, where counts were an order of magnitude higher than in any other region. Surprisingly, sperm whales (Physeter macrocephalus) were common north of Seguam Island and in Seguam Pass, but were not seen elsewhere.
Killer Whale Encounters and Sightings
Twenty sightings were made of a total of 295 killer whales over the course of the cruise (Figure 1 above). Fifty killer whales were seen as the ship was departing Seward with the remaining 245 whales seen in the study area. Overall, when best and high estimates of group size were tallied, the number of killer whales seen ranged from 295 to 332 for the cruise and from 245 to 276 whales for the study area. These provisional counts likely under-represent the total number of animals because the counts made in transit are probably low. There was a hiatus of sightings between the Kenai Peninsula and Unimak Pass, both going to and returning from the study area.
There were 10 encounters with killer whales when the cruise schedule permitted approach and focused efforts to obtain identification photographs, and 10 sightings where counts-only were obtained while the ship was in transit (Table 1 below). Fifty-five rolls of black and white film and three 90-minute digital video tapes were shot during the 10 encounters. Each encounter usually began with the sighting of a comparatively small group of animals (two to five whales, often including one adult male), but after approach of the first identified animals additional whales were usually seen. The first two encounters occurred as the ship was leaving Seward and likely were whales in the area known and photographed by Alaskan researchers during the past 10-15 years. The remaining eight encounters occurred in the study area at locations ranging from Seguam to Unimak Passes.
Killer whales were often seen in regions where they were photographed during surveys conducted in 1992 and 1993, including Makushin Bay along the north coast of Unalaska Island, where the largest group was encountered. Waters southwest of Unimak Pass and north of Seguam Island also appeared to be areas of concentration for killer whales. While there was no concerted attempt to cross-match killer whales seen to those photographed in the study area in 1992 and 1993, at least four whales (AK 160-163) appeared to be individuals photographed during the earlier surveys. In addition, several males had very distinctive dorsal fins that should aid in group identification on surveys scheduled later this summer.
|Table 1. Aleutians Passes Cruise: Killer Whale Encounters and Sightings. (DES = digital echosounder, * = encounter truncated)|
|4 June||1||Resurrection Bay||12-14||1 roll +|
|4 June||2||Gore Pt/S. Kenai Penin.||38-42||6 rolls|
|7 June||Sighting||Kres #1 - Kres #2 DES tow||1 B male||None|
|7 June||3||Krenitzin Island||42-46||15 rolls|
|9 June||4||NW Seguam Island||34-38||8 rolls|
|10 June||Sighting||Seguam Pass/CTD line||8||None|
|11 June||5||NW Seguam Island||4||2 rolls|
|11 June||6||Seguam Pass||7||1 roll|
|11 June||Sighting||Seguam Pass/DES tow||2||None|
|13 June||*7||Seguam Pass||22-25||4 rolls|
|13 June||*8||NW Umnak Island||5-6||2 rolls|
|13 June||Sighting||N. Umnak Island/DES tow||10-12 (min)||None|
|14 June||Sighting||N. Akutan Pass/CTD line||4||None|
|14 June||Sighting||Akutan Pass/CTD line||1 male||None|
|15 June||Sighting||N. Akutan Pass/CTD line||5||None|
|15 June||9||Unalaska Bay B Dutch||18-22||4 rolls|
|17 June||10||Unalaska/Makushin Bay||50-55||12 rolls|
|17 June||Sighting||N. Akutan Island||15-18||None|
|18 June||Sighting||Unimak Pass/CTD line||12-15||None|
|18 June||Sighting||Unimak Pass/CTD line||5-7||6 frames|
|10 Encounters||295-322||55 rolls+|
|10 Sightings||245-276||6 frames|
We witnessed no attacks by killer whales on marine mammals, nor did we see killer whales near Steller sea lion haulouts. We did see killer whales swimming near Dalls porpoise on two occasions, and on one instance a large male made a lunging leap that seemed directed at the porpoise. On both occasions we were in passing mode and did not watch the encounter in detail. Thus, no conclusions should be drawn from these observations other than killer whales may have been pursuing Dalls porpoise. In Unimak Pass, three humpback whales near Akun Island were seen repetitively flipper-slapping as a killer whale group passed them and one male turned back for a closer approach. Again, no attack was witnessed. While fish eating by killer whales could not be determined with certainty, whales encountered north of Seguam Island (Encounter 3 or 4) (Table 1 above) appeared to be feeding on fish, as determined by the ship’s echosounder.
By Sue Moore.
Cook Inlet Beluga Whales, June 2001
Beluga whales in Cook Inlet, Alaska, have been the center of scientific, management, and media attention for several years (see AFSC Quarterly Report, Oct-Dec 2000 issue). The NMFS has conducted systematic aerial surveys of all coastal areas within the inlet and tracklines across the inlet each June or July since 1993. Data from these surveys have shown a gradual decline in distribution, with fewer sightings in the southern part of Cook Inlet and a drop in abundance (from 653 animals in 1994 to 347 in 1998) until 1999, when Native Alaskan groups stopped hunting belugas, based on concerns for the population. Since then, abundance has been estimated to be 367 animals in 1999 and 435 in 2000, suggesting that the decline has halted or reversed.
The number of whales taken by Native hunters was well correlated to the evident decline in abundance. NMFS considered this sufficient evidence such that, in May 2000, the small, isolated stock was designated as Depleted under the Marine Mammal Protection Act, providing a legal mechanism for NMFS to regulate the harvest. Habitat degradation in Cook Inlet was also considered, because Anchorage (the biggest city in Alaska), several military bases, petroleum extraction, and sewage outfall occur in northern areas of the inlet. However, NMFS found little evidence to support loss of habitat as a mechanism of decline in this case, thus habitat protection through the Endangered Species Act was not considered necessary to the recovery of the Cook Inlet stock at the time.
Continuing the annual surveys of Cook Inlet is a major priority of the NMML beluga project. NMFS conducted aerial surveys from 5 to 12 June 2001 (55 flight hours) including six passes covering coastal areas of the northern part of Cook Inlet, where almost all belugas have been found in recent years, as well as the southern part of the inlet and 1,186 km of offshore transects (Figure 1 above). The project used the same aircraft (an Aero Commander), research protocol, and observers as used in most of the past 9 years. Viewing conditions were generally good to excellent. Except for two beluga whales observed near Homer (the first for this project since 1994), all whales were found in a few primary areas in bays or near river mouths around the northernmost parts of the inlet (especially the Susitna Delta, Knik Arm, and Chickaloon Bay/Turnagain Arm). This distribution is consistent with distributions documented across the past three decades. The index count, based on medians of multiple counts of the groups encountered, was 211 in June 2001. This is below index counts for years prior to 1998 (305 in 1993, 281 in 1994, 324 in 1995, 307 in 1996, and 264 in 1997), but the 2001 count is essentially the same as counts made during the past 3 years (193 in 1998, 217 in 1999, and 184 in 2000) (Figure 2 below). Abundance estimates—corrected for missed groups, whales below the surface, and surfacings not seen—are typically 1½ to 2½ times the index counts: 653 (CV = 0.43), 491 (CV = 0.44), 594 (CV = 0.28), 440 (CV = 0.14), 347 (CV = 0.29), 367 (CV = 0.14), 435 (CV = 0.23) in 1994-2000, respectively.
By Dave Rugh and Rod Hobbs.
Calculating the Haul-out Proportion of Alaska Harbor Seals
The proportion of harbor seals that are hauled out and, thus, available to be counted during aerial surveys varies as a function of environmental covariates, such as date, time of day, tidal state, and weather. In recent studies we estimated the number of harbor seals that would have been counted during an aerial survey of the Gulf of Alaska in 1996, if all sites had been surveyed under ideal conditions. We conducted a separate analysis of harbor seal haul-out behavior to estimate the proportion of seals that would have been at sea under ideal conditions (and, therefore, not available to be counted). We monitored the haul-out behavior of 112 radio-tagged harbor seals from radio signals recorded remotely at four Alaskan haul-out sites (Grand Island in 1994, Cordova in 1995, Pedersen Glacier in 1998, and Cape Peirce in 2000). For each site, we created a statistical model of the proportion of seals hauled out as a function of environmental covariates. Using these models, we identified the environmental conditions that would result in the greatest proportion of seals hauled out. Although those ideal conditions differed between sites, the proportion of seals predicted to be hauled out under those conditions was consistent (84%) at the two sites we believed to have representative data, Grand Island and Cape Peirce. We are drafting a manuscript which describes the haul-out behavior models, combines the results from adjusting survey counts and haul-out proportions to ideal environmental conditions, and estimates the population size of harbor seals in the Gulf of Alaska in 1996.
By Mike Simpkins.
Harbor Seal Haul-out Behavior and Movements in Tidewater Glacial Fjords
Biologists from NMML and the Alaska Department of Fish and Game (ADF&G) continued a study on the haul-out behavior and movement of harbor seals using tidewater glacial fjords in Southeast Alaska. Because tidewater glaciers attract some of the highest concentrations of harbor seals recorded in Alaska, an initiative is under way to more fully understand the ecology and site fidelity of seals that use the floating ice during their annual cycle. Data collected on daily haul-out patterns and habitat use will provide biologists greater confidence in estimating seal abundance and will also provide insight into why seals aggregate in such large numbers on glacial ice. As in 1999, the study focused on two fjords–Tracy and Endicott Arms–located approximately 80 km south of Juneau. Seal captures and instrument deployments were completed in two phases: 19-30 April from the NOAA ship John N. Cobb and 26-31 May from the U.S. Fish and Wildlife Service vessel Curlew and the John N. Cobb. Of the 20 animals captured, 15 were fitted with both VHF head tags and time-depth recorders (TDRs) and 5 with VHF flipper tags. The head tags and TDRs will fall off during the seals’ annual molt, which begins in early August. The TDRs were equipped with radio beacons and will be recovered using aerial and boat reconnaissance. In contrast to 1999, when all instruments were deployed in Tracy Arm, 16 of 20 instruments this year were deployed in Endicott Arm. Radio monitoring stations were deployed near the glaciers at both Tracy and Endicott Arms and near the fjords’ shared mouth to record when seals were hauled out on the floating ice and to track movements in and out of the fjords. These stations are being serviced regularly and will continue collecting data until the end of the molting season. The NMML and ADF&G also collaborated with the University of Alaska in Juneau (UAS) to conduct direct observations of seals from a land-based camp in Tracy Arm. The camp was occupied for about 6 weeks from late May to early July. The primary goal of the study was to test several methodologies for quantifying potential interactions between seals and tour vessels, which make daily excursions through the ice field at Tracy Arm to view the glacier.
By John Jansen, Dave Withrow, and Jack Cesarone.
Harbor Seal and Cruise Ship Interactions
Plans are being made to study the potential disturbance of harbor seals using glacial ice habitats in Disenchantment Bay, Alaska (40 km north of Yakutat), in a collaborative effort by NMML, the ADF&G, and the Yakutat Tlingit Tribal Council. The 2-3 year study will be supported by the Northwest Cruise Association (NWCA) through an agreement with the Yakutat Tlingit Tribal Council. There is concern about possible impacts of vessel traffic on harbor seals, particularly during the pupping period, which coincides with the onset of the tour vessel season. An average 1-2 NWCA vessels enter the bay daily between mid-May and mid- September; the frequency of smaller boat traffic, such as charters, appears to be negligible, with two or fewer visits per week. To aid in the study design, a NMML biologist visited Yakutat in mid-June to learn about the area and concerns from the tribal elders, to evaluate ideas for potential study designs, and to develop the logistical considerations for implementing field work next year such as seal and ice distributions, ship- or land-based observation points, and vessel traffic corridors. A study proposal will be completed by December 2001, with the study anticipated to begin early spring 2002.
By John Jansen, Dave Withrow, and John Bengtson.