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Blue whale Listed: 6/2/1970 Status since listing: increased The blue whale (Balaenoptera musculus) is the largest animal ever known to have lived on Earth [1]. Blue whales are found in all oceans worldwide and are separated into populations from the North Atlantic, North Pacific and Southern Hemisphere [1]. Each population is composed of several stocks that typically migrate between higher- latitude summer feeding grounds and lower-latitude wintering areas. The largest numbers of blue whales in U.S. waters are within the eastern North Pacific stock. Other U.S. stocks occur in waters off the coast of Alaska, Hawaii, and the Northeast [1]. Pre-whaling blue whale populations had about 350,000 individuals [3]. In 1868, the invention of the exploding harpoon gun made the hunting of blue whales possible and in 1900, whalers began to focus on blue whales and continued until the mid 1960s [1, 3]. During this time, it is estimated that whalers killed up to 99% of blue whale populations [3]. Currently, there are about 5-10,000 blue whales in the Southern Hemisphere and about 3-4,000 in the Northern Hemisphere [3]. Current threats include collisions with vessels, entanglement in fishing gear, reduced zooplankton production due to habitat degradation, and disturbance from low-frequency noise [1]. The offshore driftnet gillnet fishery is the only fishery likely to take blue whales, but few mortalities or serious injuries have been observed [2]. The Eastern North Pacific Stock feeds in waters off the coast of California (sometimes ranging into Oregon) from June to November and then migrates south to Mexico (sometimes going as far south as Costa Rica) in winter/spring [2]. The number of whales reported off the coast of California increased from 704 in 1979/80 to 2,584 whales in 1996, and then dropped to 788 whales in 2001. Following this drop, numbers began to increase and in 2003, 1,744 whales were reported [2]. It is not certain if the increasing trend indicates a growth in the size of the stock, or just increased use of California waters [2], but the stock is generally thought to have increased [1], and because of its size dominates the trend of the species in U.S. waters. Blue whales feeding along the Aleutian Islands are probably part of a central western North Pacific stock that is thought to migrate to offshore waters north of Hawaii in winter [4]. Sightings of blue whales in Hawaiian waters are infrequent, although acoustic recordings indicate that blue whales occur there. There are no estimates of population size for this stock [4]. No blue whales were sighted during aerial surveys of Hawaiian waters conducted from 1993 to 1998 or during shipboard surveys conducted in the summer/fall of 2002 [4]. The blue whale is an occasional visitor along the Atlantic coast of the Northeast [5]. Sightings of blue whales off Cape Cod, Massachusetts, in summer and fall may represent the southern limit of the feeding range of the western North Atlantic stock that feeds primarily off the Canadian coast [5]. Blue whales have been sighted as far south as Florida, however, and the actual southern limit of this stock’s range is unknown [5]. Because blue whales are not frequently seen in U.S. Atlantic waters, there are insufficient data to determine the stock's population trend [5]. In 1997, the total number of photo-identified individuals for eastern Canada and New England was 352 [1]. [1] National Marine Fisheries Service. 1998. Recovery plan for the blue whale (Balaenoptera musculus). Prepared by Reeves R.R., P.J. Clapham, R.L. Brownell, Jr., and G.K. Silber for the Silver Spring, MD. 42 pp. |
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