Sei whale

Sei whales usually travel alone[40] or in pods of up to six individuals.[38] Larger groups may assemble at particularly abundant feeding grounds. Very little is known about their social structure. During the southern Gulf of Maine influx in mid-1986, groups of at least three sei whales were observed "milling" on four occasions – i.e. moving in random directions, rolling, and remaining at the surface for over 10 minutes. One whale would always leave the group during or immediately after such socializing bouts.[38] The sei whale is among the fastest cetaceans. It can reach speeds of up to 50 km/h (27 kn) over short distances.[8] However, it is not a remarkable diver, reaching relatively shallow depths for 5 to 15 minutes. Between dives, the whale surfaces for a few minutes, remaining visible in clear, calm waters, with blows occurring at intervals of about 60 seconds (range: 45–90 sec.). Unlike the fin whale, the sei whale tends not to rise high out of the water as it dives, usually just sinking below the surface. The blowholes and dorsal fin are often exposed above the water surface almost simultaneously. The whale almost never lifts its flukes above the surface, and are generally less active on water surfaces than closely related Bryde's whales; it rarely breaches.[7]

Feeding at the surface

Krill, shrimp-like marine invertebrate animals, are one of the sei whale's primary foods.

This rorqual is a filter feeder, using its baleen plates to obtain its food by opening its mouth, engulfing or skimming large amounts of the water containing the food, then straining the water out through the baleen, trapping any food items inside its mouth.

The sei whale feeds near the surface of the ocean, swimming on its side through swarms of prey to obtain its average of about 900 kg (2,000 lb) of food each day.[8] For an animal of its size, for the most part, its preferred foods lie unusually relatively low in the food chain, including zooplankton and small fish. The whale's diet preferences has been determined from stomach analyses, direct observation of feeding behavior,[41][42] and analyzing fecal matter collected near them, which appears as a dilute brown cloud. The feces are collected in nets and DNA is separated, individually identified, and matched with known species.[43] The whale competes for food against clupeid fish (herring and its relatives), basking sharks, and right whales.

In the North Atlantic, it feeds primarily on calanoid copepods, specifically Calanus finmarchicus, with a secondary preference for euphausiids, in particular Meganyctiphanes norvegica and Thysanoessa inermis.[44][45] In the North Pacific, it feeds on similar zooplankton, including the copepod species Neocalanus cristatus, N. plumchrus, and Calanus pacificus, and euphausiid species Euphausia pacifica, E. similis, Thysanoessa inermis, T. longipes, T. gregaria and T. spinifera. In addition, it eats larger organisms, such as the Japanese flying squid, Todarodes pacificus pacificus,[46] and small fish, including anchovies (Engraulis japonicus and E. mordax), sardines (Sardinops sagax), Pacific saury (Cololabis saira), mackerel (Scomber japonicus and S. australasicus), jack mackerel (Trachurus symmetricus) and juvenile rockfish (Sebastes jordani).[44][47] Some of these fish are commercially important. Off central California, they mainly feed on anchovies between June and August, and on krill (Euphausia pacifica) during September and October.[48] In the Southern Hemisphere, prey species include the copepods Neocalanus tonsus, Calanus simillimus, and Drepanopus pectinatus, as well as the euphausiids Euphausia superba and Euphausia vallentini[44] and the pelagic amphipod Themisto gaudichaudii.

Ectoparasites and epibiotics are rare on sei whales. Species of the parasitic copepod Pennella were only found on 8% of sei whales caught off California and 4% of those taken off South Georgia and South Africa. The pseudo-stalked barnacle Xenobalanus globicipitis was found on 9% of individuals caught off California; it was also found on a sei whale taken off South Africa. The acorn barnacle Coronula reginae and the stalked barnacle Conchoderma virgatum were each only found on 0.4% of whales caught off California. Remora australis were rarely found on sei whales off California (only 0.8%). They often bear scars from the bites of cookiecutter sharks, with 100% of individuals sampled off California, South Africa, and South Georgia having them; these scars have also been found on sei whales captured off Finnmark. Diatom (Cocconeis ceticola) films on sei whales are rare, having been found on sei whales taken off California and South Georgia.[37][48][49]

Due to their diverse diet, endoparasites are frequent and abundant in sei whales. The harpacticoid copepod Balaenophilus unisetus infests the baleen of sei whales caught off California, South Georgia, South Africa, and Finnmark. The ciliate protozoan Haematophagus was commonly found in the baleen of sei whales taken off South Georgia (nearly 85%). They often carry heavy infestations of acanthocephalans (e.g. Bolbosoma turbinella, which was found in 40% of sei whales sampled off California; it was also found in individuals off South Georgia and Finnmark) and cestodes (e.g. Tetrabothrius affinis, found in sei whales off California and South Georgia) in the intestine, nematodes in the kidneys (Crassicauda sp., California) and stomach (Anisakis simplex, nearly 60% of whales taken off California), and flukes (Lecithodesmus spinosus, found in 38% of individuals caught off California) in the liver.[37][48][49]

Mating occurs in temperate, subtropical seas during the winter. Gestation is estimated to vary around 103⁄4 months,[50] 111⁄4 months,[51] or one year,[52] depending which model of foetal growth is used. The different estimates result from scientists' inability to observe an entire pregnancy; most reproductive data for baleen whales were obtained from animals caught by commercial whalers, which offer only single snapshots of fetal growth. Researchers attempt to extrapolate conception dates by comparing fetus size and characteristics with newborns.

A newborn is weaned from its mother at 6–9 months of age, when it is 8–9 m (26–30 ft) long,[27] so weaning takes place at the summer or autumn feeding grounds. Females reproduce every 2–3 years,[50] usually to a single calf.[8] In the Northern Hemisphere, males are usually 12.8–12.9 m (42–42 ft) and females 13.3–13.5 m (44–44 ft) at sexual maturity, while in the Southern Hemisphere, males average 13.6 m (45 ft) and females 14 m (46 ft).[26] The average age of sexual maturity of both sexes is 8–10 years.[50] The whales can reach ages up to 65 years.[53]

The sei whale makes long, loud, low-frequency sounds. Relatively little is known about specific calls, but in 2003, observers noted sei whale calls in addition to sounds that could be described as "growls" or "whooshes" off the coast of the Antarctic Peninsula.[54] Many calls consisted of multiple parts at different frequencies. This combination distinguishes their calls from those of other whales. Most calls lasted about a half second, and occurred in the 240–625 hertz range, well within the range of human hearing. The maximum volume of the vocal sequences is reported as 156 decibels relative to 1 micropascal (μPa) at a reference distance of one metre.[54] An observer situated one metre from a vocalizing whale would perceive a volume roughly equivalent to the volume of a jackhammer operating two metres away.[55]

In November 2002, scientists recorded calls in the presence of sei whales off Maui. All the calls were downswept tonal calls, all but two ranging from a mean high frequency of 39.1 Hz down to 21 Hz of 1.3 second duration – the two higher frequency downswept calls ranged from an average of 100.3 Hz to 44.6 Hz over 1 second of duration. These calls closely resembled and coincided with a peak in "20- to 35-Hz irregular repetition interval" downswept pulses described from seafloor recordings off Oahu, which had previously been attributed to fin whales.[56] Between 2005 and 2007, low frequency downswept vocalizations were recorded in the Great South Channel, east of Cape Cod, Massachusetts, which were only significantly associated with the presence of sei whales. These calls averaged 82.3 Hz down to 34 Hz over about 1.4 seconds in duration. This call has also been reported from recordings in the Gulf of Maine, New England shelf waters, the mid-Atlantic Bight, and in Davis Strait. It likely functions as a contact call.[57]

BBC News quoted Roddy Morrison, a former whaler active in South Georgia, as saying, "When we killed the sei whales, they used to make a noise, like a crying noise. They seemed so friendly, and they'd come round and they'd make a noise, and when you hit them, they cried really. I didn't think it was really nice to do that. Everybody talked about it at the time I suppose, but it was money. At the end of the day that's what counted at the time. That's what we were there for."[58]

In general, the sei whale migrates annually from cool and subpolar waters in summer to temperate and subtropical waters for winter, where food is more abundant.[7] In the northwest Atlantic, sightings and catch records suggest the whales move north along the shelf edge to arrive in the areas of Georges Bank, Northeast Channel, and Browns Bank by mid- to late June. They are present off the south coast of Newfoundland in August and September, and a southbound migration begins moving west and south along the Nova Scotian shelf from mid-September to mid-November. Whales in the Labrador Sea as early as the first week of June may move farther northward to waters southwest of Greenland later in the summer.[72] In the northeast Atlantic, the sei whale winters as far south as West Africa such as off Bay of Arguin, off coastal Western Sahara and follows the continental slope northward in spring. Large females lead the northward migration and reach the Denmark Strait earlier and more reliably than other sexes and classes, arriving in mid-July and remaining through mid-September. In some years, males and younger females remain at lower latitudes during the summer.[30]

Despite knowing some general migration patterns, exact routes are incompletely known[30] and scientists cannot readily predict exactly where groups will appear from one year to the next.[73] F.O. Kapel noted a correlation between appearances west of Greenland and the incursion of relatively warm waters from the Irminger Current into that area.[74] Some evidence from tagging data indicates individuals return off the coast of Iceland on an annual basis.[75] An individual satellite-tagged off Faial, in the Azores, traveled more than 4,000 km (2,500 mi) to the Labrador Sea via the Charlie-Gibbs Fracture Zone (CGFZ) between April and June 2005. It appeared to "hitch a ride" on prevailing currents, with erratic movements indicative of feeding behavior in five areas, in particular the CGFZ, an area of known high sei whale abundance as well as high copepod concentrations.[76] Seven whales tagged off Faial and Pico from May to June in 2008 and 2009 made their way to the Labrador Sea, while an eighth individual tagged in September 2009 headed southeast – its signal was lost between Madeira and the Canary Islands.[77]

A sei whale (foreground) caught off Finnmark.

In the North Atlantic between 1885 and 1984, 14,295 sei whales were taken.[10] They were hunted in large numbers off the coasts of Norway and Scotland beginning in the late 19th and early 20th centuries,[73] and in 1885 alone, more than 700 were caught off Finnmark.[79] Their meat was a popular Norwegian food. The meat's value made the hunting of this difficult-to-catch species profitable in the early twentieth century.[80]

In Iceland, a total of 2,574 whales were taken from the Hvalfjörður whaling station between 1948 and 1985. Since the late 1960s to early 1970s, the sei whale has been second only to the fin whale as the preferred target of Icelandic whalers, with meat in greater demand than whale oil, the prior target.[78]

Small numbers were taken off the Iberian Peninsula, beginning in the 1920s by Spanish whalers,[81] off the Nova Scotian shelf in the late 1960s and early 1970s by Canadian whalers,[72] and off the coast of West Greenland from the 1920s to the 1950s by Norwegian and Danish whalers.[74]

A sei whale being harpooned off Japan.

In the North Pacific, the total reported catch by commercial whalers was 72,215 between 1910 and 1975;[10] the majority were taken after 1947.[82] Shore stations in Japan and Korea processed 300–600 each year between 1911 and 1955. In 1959, the Japanese catch peaked at 1,340. Heavy exploitation in the North Pacific began in the early 1960s, with catches averaging 3,643 per year from 1963 to 1974 (total 43,719; annual range 1,280–6,053).[83] In 1971, after a decade of high catches, it became scarce in Japanese waters, ending commercial whaling in 1975.[44][84]

Off the coast of North America, sei whales were hunted off British Columbia from the late 1950s to the mid-1960s, when the number of whales captured dropped to around 14 per year.[5] More than 2,000 were caught in British Columbian waters between 1962 and 1967.[85] Between 1957 and 1971, California shore stations processed 386 whales.[48] Commercial Sei whaling ended in the eastern North Pacific in 1971.

A total of 152,233 were taken in the Southern Hemisphere between 1910 and 1979.[10] Whaling in southern oceans originally targeted humpback whales. By 1913, this species became rare, and the catch of fin and blue whales began to increase. As these species likewise became scarce, sei whale catches increased rapidly in the late 1950s and early 1960s.[44] The catch peaked in 1964–65 at over 20,000 sei whales, but by 1976, this number had dropped to below 2,000 and commercial whaling for the species ended in 1977.[5]

Since the moratorium on commercial whaling, some sei whales have been taken by Icelandic and Japanese whalers under the IWC's scientific research programme. Iceland carried out four years of scientific whaling between 1986 and 1989, killing up to 40 sei whales a year.[86][87] The research is conducted by the Institute of Cetacean Research (ICR) in Tokyo, a privately funded, nonprofit institution. The main focus of the research is to examine what they eat and to assess the competition between whales and fisheries. Dr. Seiji Ohsumi, Director General of the ICR, said,

"It is estimated that whales consume 3 to 5 times the amount of marine resources as are caught for human consumption, so our whale research is providing valuable information required for improving the management of all our marine resources."[88]

He later added,

"Sei whales are the second-most abundant species of whale in the western North Pacific, with an estimated population of over 28,000 animals. [It is] clearly not endangered."[89]

Conservation groups, such as the World Wildlife Fund, dispute the value of this research, claiming that sei whales feed primarily on squid and plankton which are not hunted by humans, and only rarely on fish. They say that the program is

"nothing more than a plan designed to keep the whaling fleet in business, and the need to use whales as the scapegoat for overfishing by humans."[90]

At the 2001 meeting of the IWC Scientific Committee, 32 scientists submitted a document expressing their belief that the Japanese program lacked scientific rigor and would not meet minimum standards of academic review.[91]

In 2010, a Los Angeles exclusive Sushi restaurant confirmed to be serving sei whale meat was closed by its owners after a covert investigation and protests lead to prosecution by authorities for handling an endangered/protected species. [92]

Mass death events for sei whales have been recorded for many years and evidence suggests endemic poisoning (red tide) causes may have caused mass deaths in prehistoric times. In June 2015, scientists flying over southern Chile counted 337 dead sei whales, in what is regarded as the largest mass beaching ever documented.[107] The cause is not yet known; however, toxic algae blooms caused by unprecedented warming in the Pacific Ocean, known as the Blob, may be implicated.[108]