Trends in Age Structure and Productivity of Pacific Walruses Harvested in the Bering Strait Region of Alaska, 1952–2002

Abstract

Pacific walruses (Odobenus rosmarus divergens) are harvested by subsistence hunters in Alaska as they migrate north through the Bering Strait in the spring. Harvest records and biological specimens have been collected from the Bering Strait communities of Little Diomede, Gambell, and Savoonga since the 1950s. Harvest levels in the Bering Strait region peaked in the late 1980s and declined thereafter; however, there was considerable variation in the size and composition of the harvests among communities and over time. The relationships among characteristics of the community harvests and the presence of temporal trends were investigated using generalized linear models. The proportion of females in the catch increased over time in all three communities, while the proportion pregnant among harvested females declined over the range of sample years. The ages of harvested walruses increased over time in all three communities through the 1980s, after which trends in age stabilized or began to decline. The age of first reproduction was significantly older for females sampled in 1975-1985 than for females sampled between 1952 and 1962 or 1992 and 1998. Factors thought to have influenced the size and composition of the catch over the past 50 yr include hunter preferences, harvest management regimes, environmental conditions, and changes in the population itself.

Impacts of changing sea-ice conditions on Arctic marine mammals

“…Some walrus harvest data show that the proportion of females in the catch has increased while the relative proportions of pregnant females have declined and the age of first reproduction has shifted. These changes are suggested to be related to harvest management regimes and changing environmental conditions resulting in a distributional shift for females and slower rates of growth, perhaps due to food limitations caused by a shift from a benthic to a pelagic-dominated system (Garlich-Miller et al 2006;Grebmeier et al 2010). Atlantic walruses might be somewhat more resilient to changes in sea ice because they utilize more near-shore areas for feeding (Born 2005), but all walruses are dependent on benthic-pelagic coupling permitting rich benthic communities of bivalves, which are fed in part by vertical flux from ice-algae and MIZ algal blooms (Hobson et al 1995;Grebmeier et al 2006a, b;Tamelander et al 2006).…”

The Pacific Arctic Region

“…An analysis of fi ve decades (1950s-2000s) of walrus harvest records in the Bering Strait region, showed that the age at harvest for males and females increased and the pregnancy rate decreased over time (Garlich-Miller et al 2006 ). The age at fi rst , 1971-1978(Smith 1987 reproduction increased from 8 years in the 1950s and 1960s to 10 years in the late 1970s to early 1980s, suggesting that females were energetically stressed during the later period and the population overall was less productive.…”

Limitations of an optimum sustainable population or potential biological removal approach for conserving marine mammals: Pacific walrus case study

“…Past estimates of natural mortality were 1.5% annually (Fay et al, 1997), which based on a historical population estimate of approximately 250,000 walrus, represents about 3750 walrus, about half the range-wide harvests of 6000-9000 walrus in the mid 1980s (Fay et al, 1997). Current range-wide reported harvests have halved to 2400-4700 walrus since the 1990s (Garlich-Miller et al, 2006). In contrast, large-scale environmental changes are expected to increase natural mortality.…”

“…Fish and Wildlife Service, provides the most recent indications of change in age structure, productivity, and status of Pacific walrus. However, lack of data on walrus (e.g., recruitment rates or age/gender-specific survival), environmental health and conditions, biases in hunter preferences, and different harvest management regimes were acknowledged to limit conclusions about the relationship between life history parameters, population size, and the dynamic carrying capacity of the Beringian region (Garlich-Miller et al, 2006).…”