Until recently, zoologists believed that all species of phocids (true seals), a pinniped family, use a different maternal strategy than do otariids (fur seals and sea lions), another pinniped family. Mother otariids use a foraging strategy. They acquire moderate energy stores in the form of blubber before arriving at breeding sites and then fast for 5 to 11 days after birth. Throughout the rest of the lactation (milk production) period, which lasts from 4 months to 3 years depending on the species, mother otariids alternately forage at sea, where they replenish their fat stores, and nurse their young at breeding sites. Zoologists had assumed that females of all phocid species, by contrast, use a fasting strategy in which mother phocids, having accumulated large energy stores before they arrive at breeding sites, fast throughout the entire lactation period, which lasts from 4 to 50 days depending on the species. However, recent studies on harbor seals, a phocid species, found that lactating females commenced foraging approximately 6 days after giving birth and on average made 7 foraging trips during the remainder of their 24-day lactation period.

    The maternal strategy evolved by harbor seals may have to do with their small size and the large proportion of their fat stores depleted in lactation. Harbor seals are small compared with other phocid species such as grey seals, northern ele- phant seals, and hooded seals, all of which are known to fast for the entire lactation period. Studies show that mother seals of these species use respectively 84 percent, 58 percent, and 33 percent of their fat stores during lactation. By comparison, harbor seals use 80 percent of their fat stores in just the first 19 days of lactation, even though they occasionally feed during this period. Since such a large proportion of their fat stores is exhausted despite feeding, mother harbor seals clearly cannot support all of lactation using only energy stored before giving birth. Though smaller than many other phocids, harbor seals are similar in size to most otariids. In addition, there is already some evidence suggesting that the ringed seal, a phocid species that is similar in size to the harbor seal, may also use a maternal foraging strategy.

    Companies that must determine well in advance of the selling season how many unites of a new product to manufacture often underproduce products that sell well and have overstocks of others. The increased incidence in recent years of mismatches between production and demand seems ironic, since point-of-sale scanners have improved data on consumers' buying patterns and since flexible manufacturing has enabled companies to produce, cost-effectively, small quantities of goods. This type of manufacturing has greatly increased the number of new products introduced annually in the United States. However, frequent introductions of new products have two problematic side effects. For one, they reduce the average lifetime of products; more of them are neither at the beginning of their life (when prediction is difficult) or at the end of their life (when keeping inventory is expensive because the products will soon become obsolete). For another, as new products proliferate, demand is divided among a growing number of stock-keeping units (SKU's). Even though manufacturers and retailers can forecast aggregate demand with some certainty, forecasting accurately how that demand will be distributed among the many SKU's they sell is difficult. For example, a company may be able to estimate accurately the aggregate number of shoes it will sell, but it may be uncertain about which specific types of shoes will sell more than other types.