Noteworthy (formerly Hot Topics)(pdf)
Here we present items that are new or noteworthy and of potential interest to fisheries managers.
Unusual Mortality Event: Gray Whales
Since January of 2019, elevated numbers of eastern North Pacific gray whale (Eschrichtius robustus) mortalities have occurred along the west coast of North America, stretching from Mexico to Alaska. In May of 2019, the increased strandings were declared an Unusual Mortality Event (UME) (Table 2, Figure 2).
Table 2: Total number of gray whale strandings by location from 1 January-30 October, 2019.
Gray whale life history includes an annual round-trip migration of up to 20,000 km. The mortalities started off the western coast of southern Baja California Peninsula where gray whales over-winter to mate and calve. Mortalities followed the late winter/spring migration up to Alaskan waters where foraging occurs before the fasting return journey south. The first Alaskan gray whale stranding occurred on 9 May in Turnagain Arm of Cook Inlet. Mortalities have continued throughout the summer with hotspots around Kodiak Island, Bristol Bay, and coastal waters of the Bering Strait and Chukchi Sea (Figure 3).
Figure 2: Number of gray whale strandings in Alaska by year, 2001-2019 (2019 numbers through 30 October).
As part of the UME investigation process, NOAA has assembled an independent team of scientists to coordinate with the Working Group on Marine Mammal Unusual Mortality Events to review the data collected, sample stranded whales, and determine the next steps for the investigation. Full or partial necropsy examinations were conducted on a subset of the whales. Preliminary findings in several of the whales have shown evidence of emaciation; however, these findings are not consistent across all of the whales examined. Furthermore, while benthic prey (primarily ampelecid amphipods) in the Bering, Chukchi, and Beaufort Seas are considered the mainstay of gray whale foraging, there is also significant variability in foraging behavior depending on the location, season, year, and subset of whales (Moore et al., 2007; Calambokidis, 2013).
The eastern North Pacific gray whale is considered something of an "ecosystem sentinel" for the North Pacific and western arctic ecosystems. Correlations between changes in the distribution and behavior of gray whales and environmental change in these regions indicates the species may be effective sentinels (Moore, 2008).
A gray whale UME also occurred along the West Coast from Mexico to Alaska in 1999/2000. Although no de.nite conclusion was reached, the most likely precipitating factor was considered malnutrition, possibly associated with a decrease in the quantity and quality of prey items or the numbers of gray whales overwhelming the prey base as the population reached carrying capacity.
Figure 3: Locations of gray whale strandings in Alaska (NOAA/NMFS Alaska Region Marine Mammal Stranding Network unpublished data).
Contributed by Kate Savage, DVM NOAA Fisheries Protected Resources Division
Unusual Mortality Event: Ice Seals
In April, the ice-covered areas of the Bering Sea are crucial reproductive grounds for populations of bearded, ringed, spotted, and ribbon seals that collectively number more than 1 million individuals. But in 2018 and 2019, the April sea ice in the Bering Sea was a small fraction of its typical extent. A NOAA cruise in 2018 found no ribbon or spotted seals in their preferred breeding areas. The nearest sea ice was hundreds of miles to the north, and areas of ice visited by the vessel did not seem to have seal densities high enough to indicate that the breeders had simply relocated to the north. The possibility of major reproductive failures in at least those two species in U.S. waters cannot be ruled out.
Two measures of body condition in spotted seal pups suggested that condition had declined over the period 2014-2018, though the sample sizes are small (Figure 4).
Figure 4: Condition of spotted seal pups (April-early May).
In spring and summer of 2018 and 2019, 282 bearded, ringed, spotted, and unidentified seal carcasses (primarily young) were reported from beaches of the Bering and Chukchi seas (Figure 5). Many of the seals appeared to have been emaciated at the time of death.
The numbers of stranded seals were roughly 5-7 times the annual average from 2000-2017, prompting NOAA to declare an unusual mortality event (UME) (Figure 6). Samples were collected from some of the carcasses and analyses are underway to investigate plausible causes of the mortality.
The increased mortality of seals indicated by the strandings in 2018-2019 and the apparent decline in condition of spotted seal pups are, at face value, consistent with the dramatic losses of sea ice habitat for pupping and nursing in both years. However, they could also involve follow-on ecosystem effects such as competition for prey from northward shifts in distribution of large .sh predators.
Contributed by Peter Boveng NOAA Fisheries Marine Mammal Laboratory
Figure 5: Map of locations of reported ice seal carcasses in 2018 and 2019.
Figure 6: Ice seal strandings by month.
Contrasting Trends in Northern Fur Seal Foraging effort Between St. Paul and Bogoslof Islands: 2019 Preliminary Results
The Eastern Stock of northern fur seals (Callorhinus ursinus), which is comprised of three breeding islands (St. Paul [SP], St. George [SG], and Bogoslof [BG] islands), is listed as depleted under the Marine Mammal Protection Act. Since 1998, pup production on the Pribilof Islands (SP and SG) has declined by 51% or at an annual rate of 3.4% (Towell et al., 2019). In contrast, pup production on BG has increased at an annual rate of 10% since 1997 (Towell et al., 2019). While the ultimate cause(s) of the Pribilof Islands fur seal decline have yet to be identified, low pup growth rates on SP appear to be a key distinction compared to the healthy population and high pup growth rates on BG. The large differences in growth rates between SP and BG are primarily attributed to disparity between the islands in the provisioning cycle of females.
On BG, nursing females make short duration foraging trips and spend a higher proportion of their time on shore provisioning their pup, which results in greater growth rates. Females from SP make extended foraging trips and compensate by spending longer periods on shore but are unable to make up for pup mass loss during these longer trips (Springer et al. (2010), Figure 7).
Figure 7: Mean foraging trip durations of lactating northern fur seals tracked from Bogoslof (green) and St. Paul (black) islands during the summer lactation period (2005 and 2006) in relation to daily growth rate for male (solid line) and female (dashed line) pups (data from Springer et al. (2010)).
Researchers at the Alaska Fisheries Science Center Marine Mammal Laboratory (MML) are currently conducting research examining foraging effort for northern fur seals from SP and BG. In August 2019, adult females from each island were equipped with satellite-linked dive recorders to measure foraging trip durations, foraging locations, and dive depth distributions. Preliminary data show that the contrasting trend in foraging effort between SP and BG continues. Average foraging trip duration of fur seals from SP is 7.8±10.4 (SE) days (individual range: 6.5-10.1 days, N=9), whereas trips are significantly shorter (average: 3.9±10.4 days) for fur seals on BG (individual range: 2.9-5.5 days, N=6). The trip durations measured on BG have increased compared to previous years (2011: 3.1±10.2 days), consistent with the hypothesis that fur seals from this population are experiencing localized resource depletion as this population continues to expand (Kuhn et al., 2014). Final data on foraging trip durations will be available after the tracking instruments are recovered (SP, late September) or when instruments stop transmitting (BG).
Figure 8: Change in fat mass (±SE) over the lactation period for northern fur seals from Bogoslof (green) and St. Paul (black) islands in 2005 and 2006. Red line denotes no change (data from Springer et al. (2010)).
In conjunction with these ongoing field efforts, a collaborative effort between researchers at the Joint Institute for the Study of the Atmosphere and Ocean (University of Washington), Lenfest Ocean Program, and MML was initiated in 2018 to examine the energetic expenditure of lactating females and the consequences of variation in maternal foraging behavior. This effort involved a retrospective analysis of an existing dataset from 1995 and 1996 on the field metabolic rates of lactating females from the Pribilof Islands, as well as the development of a bioenergetic model to estimate the current energy intake and prey consumption of the fur seal population from the Pribilof Islands. The results of this work have revealed several key findings that provide insights into the apparent links between trip durations and pup growth rates. First, lactating females from the Pribilof Islands appear to have reached a metabolic ceiling, meaning that they are working hard to find food and have very limited flexibility to adjust to changes in prey resources without extending trip durations. Second, the output from the bioenergetic model indicates that lactating females currently consume roughly 26-27% of their body mass per foraging day at sea, a number that is surprisingly similar to a study conducted in the 1970s (Perez and Bigg, 1986). Walleye pollock comprised an average of 42-80% of the total prey biomass consumed in years encompassing 1995-2010, with considerable interannual variation in size-specific consumption. Specifically, consumption of adult pollock generally increased in years when young pollock (age-0 and age-1) were less abundant.
The continued disparities in trip duration between SP and BG in 2019, similar to observations from the mid-2000s (Figure 7), suggest that inter-island differences in pup growth rates are also likely to be present. These findings are relevant given that lower pup growth rates result in a lower mass at weaning, which is likely to lead to a lower probability of survival. The results from the bioenergetics studies suggest that high maternal overhead, as a result of high metabolic rates and long trip durations, is likely reducing the amount of energy available for lactation. This provides an explanation not only for the reduced pup growth rates observed for the Pribilof Islands but also for the inability of females at these islands to gain fat mass across the lactation period (Springer et al. (2010), Figure 8).
Collectively, the results of the foraging effort and bioenergetics studies suggest that lactating females on SP are having dificulty finding food in close proximity to the rookery, which could adversely affct pup growth rates and contribute to the ongoing population decline on St. Paul Island.
Contributed by Carey Kuhn, Jeremy Sterling (NOAA/AFSC/MML), and Elizabeth McHuron (JISAO, University of Washington)
Local Environmental Observer (LEO) Network
The NMFS AFSC is interested in documenting and learning from citizen science observations that may be incorporated into Ecosystem Status Reports (ESRs). The 2017 ESR identified the LEO Network as a potential platform for tracking these observations and were encouraged by the Council and SSC to continue exploring the utilization of this framework in future reports. Other citizen science efforts exist in Alaska, but to our knowledge these efforts are mostly project specific (e.g., bird spotting and identification) or community specific and do not provide suficient breadth to cover the myriad of anomalous environmental observations relevant to the Council. While the LEO Network also su.ers from this issue, it still appears to be the citizen science database with the most coverage across species and regions of the state.
The LEO Network was launched in 2012 by the Alaska Native Tribal Health Consortium (ANTHC) as a tool for local observers in the Arctic to share information about climate and other drivers of environmental change. Anyone may join the network and provide observations, and the network now spans the globe. Consultants with relevant expertise often, but not always, review the observations and provide feedback. The observations are of unusual environmental events or notable environmental changes, reported by geographic location and date, and classi.ed by relevant category (or multiple relevant categories) such as Weather, Land, Fish, Sea Mammals, Ocean/Sea, etc. (Figure 9).
Figure 10 shows LEO Network observations from 2 August, 2018 to 14 August, 2019 in the northern Bering Sea (NBS) LME with the frequency by category (dates were speci.ed to occlude observations that were part of the ESR in 2018). These categories are based on analysis of the 76 total observations in 2018 and 2019 (for the dates speci.ed above) in the NBS and are not limited to the marine environment. The observations in Figure 10 were made in 29 total communities. Of particular note for northern Bering Sea communities over the last year was the impact of extreme weather events, inclusive of thunderstorms, smoke, and high seasonal temperatures. The latter was noted as delaying ice formation along rivers and coasts, inhibiting normal travel and subsistence hunting and .shing patterns, and leading to deaths in multiple cases when snow machines and four wheelers fell through thin ice.
Similarly to Figure 10, Figure 11 shows LEO Network observations from 2 August, 2018 to 14 August, 2019 in the eastern Bering Sea (EBS) LME with the frequency counts by category. There were 14 total observations in 12 communities over this time period in the EBS.
Contributed by Marysia Szymkowiak NOAA Fisheries Alaska Fisheries Science Center
Figure 9: LEO Network observations in Alaska for 2018 and 2019 (August to August). Colors distinguish the source of the observation: gray are from public media (e.g., radio, newspaper) and blue are citizen observations.
Figure 10: Number of LEO Network observations (counts) in 2018 and 2019 (August through August) by category in northern Bering Sea communities.
Figure 11: Number of LEO Network observations (counts) in 2018 and 2019 (August through August) by category in eastern Bering Sea communities.