Acoustic Recordings of Sei Whales

Simultaneous sightings and acoustic detections of sei whales (Balaenoptera borealis) are scarce, and there are few published data describing their vocalizations. Analysis of recordings from directional frequency analysis and recording sonobuoys in the presence of sei whales in the Southern Ocean in March 2013 identified both downsweep and upsweep calls.

Sound frequencies within all calls were between 34 and 87 Hz with an average call duration of 1.1 s. These very low-frequency sounds share characteristics with sei whale calls recorded near the Hawaiian Islands and off Cape Cod in winter and summer, respectively, but are the first documented sei whale calls in the Southern Ocean that are clearly less than 100 Hz.

1. INTRODUCTION

Sei whales occur throughout the Southern Hemisphere, predominantly offshore, migrating between low-latitude tropical and subtropical regions in the winter and temperate and subpolar latitudes in summer (Leaper et al., 2008; Reilly et al., 2008). Miyashita et al. (1995) report summer distribution of sei whales in the Southern Hemisphere to be mainly between 40°S and 50°S in the South Atlantic and southern Indian oceans and between 45°S and 60°S in the South Pacific.

There were relatively few sightings of sei whales from the International Decade of Cetacean Research – Southern Ocean Whale and Ecosystem Research (IDCR-SOWER) circumpolar cruises south of 60°S (Branch and Butterworth, 2001) where the search effort for these cruises was concentrated.

In International Whaling Commission (IWC) Management Area V, the region where the sei whales in this study were detected, sei whale catch data show that nearly 17 000 animals were taken between 1914 and 1977 (Leaper et al., 2008).

Few recordings of vocalizations attributed to sei whales have been corroborated with visual sightings, and their repertoire is therefore poorly understood. Knowlton et al. (1991) recorded vocalizations in the presence of sei whales off Nova Scotia in August and September that comprised two phrases of frequency modulated sweeps between 1.5 and 3.5 kHz.

These shared similar frequency characteristics with the long bursts of pulses with a peak energy of 3 kHz recorded by Thompson et al. (1979) between Nova Scotia and Newfoundland. McDonald et al. (2005) recorded vocalizations in the presence of sei whales off the Antarctic Peninsula in February that comprised broadband, tonal, and frequency modulated sounds between 100 and 600 Hz with durations of 1–3 s. McDonald et al. noted distinctive frequency “stepping” in many of the tonal and frequency swept calls. Calls recorded by Gedamke and Robinson (2010) off East Antarctica in the summer also had frequency stepping within a similar frequency range, and they attributed those calls to sei whales on the basis of the results of McDonald et al., although there were no corroborating sightings of sei whales.

Rankin and Barlow (2007) described vocalizations from sei whales near the Hawaiian Islands in November that comprised two types of calls: Downsweeps from 100 to 44 Hz with a duration of 1.0 s and downsweeps from 39 to 21 Hz with a duration of 1.3 s. Baumgartner et al. (2008) recorded vocalizations using autonomous ocean gliders off Cape Cod in May that were significantly associated with visual observations of sei whales. These sounds were similar to those recorded by Rankin and Barlow (2007): Downsweeps ranging from 82 to 34 Hz over 1.4 s.

These occurred most often as single calls, but pairs and triplets were also detected. Newhall et al. (2012) were able to successfully localize calls with similar properties to those recorded by Baumgartner et al. (2008) that they attributed to sei whales. They found less variability among calls from the same location than among calls from different locations, suggesting some acoustic differentiation between individuals might be possible, at least in the short term.

During the 2013 Southern Ocean Research Partnership (SORP) Antarctic Blue Whale Project (ABWP) cruise, two sei whale sightings were made south of the subantarctic Auckland Islands, in the New Zealand Exclusive Economic Zone. Vocalizations associated with these sightings were recorded using directional frequency analysis and recording (DIFAR) sonobuoys. This enabled a description of the characteristics of sei whale calls in this area of the Southern Ocean.

2. METHODS

The ABWP cruise in 2013 used DIFAR sonobuoys to detect, localize, and track Antarctic blue whales. Sonobuoys were deployed from research vessel FV Amaltal Explorer throughout the cruise, including during the passage to and from New Zealand and the main study area near the pack ice north of the Ross Sea and opportunistically close to sightings of species other than blue whales (Miller et al., 2013). A dedicated visual survey was also conducted by a team of experienced observers from the open-air flying bridge and the enclosed bridge, using naked eye and binoculars. On 11 March on the return leg of the survey, two apparently solitary sei whales were seen by the visual observers in sea states of Beaufort 3–4. The sightings were separated by a distance of 11 km and occurred approximately 160 km south of the Auckland Islands. There were no other cetaceans seen in the 2 days before the first sei whale sighting or for nearly 20 h after the second. After the first sighting, the course of the vessel was altered to confirm species identification.

The vessel approached to within 150 m of the whale, and it was clearly observed through several surfacing bouts.

Two DIFAR 53 F sonobuoys with an omnidirectional pressure sensor were deployed during this time. One had been deployed opportunistically before the first sighting occurred; the second was deployed in response to the first sighting but before the second sighting. Sonobuoy signals were received by VHF radio onboard the research vessel, digitized, recorded, processed, and the DIFAR bearings to calls resolved as described by Miller et al. (2013). Where the same signal was received on both sonobuoys, the time of arrival difference was also measured to determine the hyperbolic surface describing possible locations of the vocalizing whale. Recordings were analyzed using Adobe audition 3.0 and pamguard (www.pamguard.org; Gillespie et al., 2008).

For analysis and measurement, recordings were resampled from an original recording sample rate of 48 000 samples per second to a sample rate of 6000 samples per second to facilitate processing. Spectrograms were generated by fast Fourier transform (4096 FFT size, 97% overlap, Hamming window, 1.46 Hz frequency resolution, 682.67 ms time resolution, 21.33 ms time step size).

The high frequency, low frequency, frequency change, peak frequency duration, and inter-call interval of each call were measured. Only a small number of calls was recorded, and measurements were made from all calls. However, ship and ambient noise were present during the recordings, and the resulting low signal to noise ratio of many of the calls precluded further analysis beyond the measurement of these parameters.

An Indepth Perspective on Sei Whales

The sei whale is a baleen whale, the third-largest rorqual after the blue whale and the fin whale  It inhabits most oceans and adjoining seas, and prefers deep offshore waters.It avoids polar and tropical waters and semienclosed bodies of water. The sei whale migrates annually from cool and subpolar waters in summer to winter in temperate and subtropical waters, with a lifespan of 70 years.

Reaching 19.5 m (64 ft) long and weighing as much as (28 long tons; 31 short tons) the sei whale consumes an average of 900 kg (2,000 lb) of food every day; its diet consists primarily of copepods, krill, and other zooplankton.[6] It is among the fastest of all cetaceans, and can reach speeds of up to 50 km/h (31 mph) (27 knots) over short distances.The whale's name comes from the Norwegian word for pollock, a fish that appears off the coast of Norway at the same time of the year as the sei whale.

Following large-scale commercial whaling during the late 19th and 20th centuries, when over 255,000 whales were taken,the sei whale is now internationally protected,although limited hunting occurs under a controversial research program conducted by Japan.

As of 2008, its worldwide population was about 80,000, nearly a third of its prewhaling population.

Etymology:

Sei is the Norwegian word for pollock, also referred to as coalfish, a close relative of codfish. Sei whales appeared off the coast of Norway at the same time as the pollock, both coming to feed on the abundant plankton.

The specific name is the Latin word borealis, meaning northern. In the Pacific, the whale has been called the Japan finner; "finner" was a common term used to refer to rorquals. In Japanese, the whale was called iwashi kujira, or sardine whale, a name originally applied to Bryde's whales by early Japanese whalers. Later, as modern whaling shifted to Sanriku — where both species occur — it was confused for the sei whale. Now the term only applies to the latter species.

It has also been referred to as the lesser fin whale because it somewhat resembles the fin whale

The American naturalist Roy Chapman Andrews compared the sei whale to the cheetah, because it can swim at great speeds "for a few hundred yards", but it "soon tires if the chase is long" and "does not have the strength and staying power of its larger relatives".

Taxonomy:

On 21 February 1819, a 32-ft whale stranded near Grömitz, in Schleswig-Holstein. The Swedish-born German naturalist Karl Rudolphi initially identified it as Balaena rostrata (=Balaenoptera acutorostrata). In 1823, the French naturalist Georges Cuvier described and figured Rudolphi's specimen under the name "rorqual du Nord". In 1828, Rene Lesson translated this term into Balaenoptera borealis, basing his designation partly on Cuvier's description of Rudolphi's specimen and partly on a 54-ft female that had stranded on the coast of France the previous year (this was later identified as a juvenile fin whale, Balaenoptera physalus).

In 1846, the English zoologist John Edward Gray, ignoring Lesson's designation, named Rudolphi's specimen Balaenoptera laticeps, which others followed.

 In 1865, the British zoologist William Henry Flower named a 45-ft specimen that had been obtained from Pekalongan, on the north coast of Java, Sibbaldius (=Balaenoptera) schlegelii — in 1946 the Russian scientist A.G. Tomilin synonymized S. schlegelii and B. borealis, creating the subspecies B. b. schlegelii and B. b. borealis.

In 1884–85, the Norwegian scientist G. A. Guldberg first identified the "sejhval" of Finnmark with B. borealis.

Sei whales are rorquals (family Balaenopteridae), baleen whales that include the humpback whale, the blue whale, Bryde's whale, the fin whale, and the minke whale. Rorquals take their name from the Norwegian word røyrkval, meaning "furrow whale",because family members have a series of longitudinal pleats or grooves on the anterior half of their ventral surface. Balaenopterids diverged from the other families of suborder Mysticeti, also called the whalebone whales or great whales, as long ago as the middle Miocene.

Little is known about when members of the various families in the Mysticeti, including the Balaenopteridae, diverged from each other.

Two subspecies have been identified—the northern sei whale (B. b. borealis) and southern sei whale (B. b. schlegelii).

Their ranges do not overlap.

Description:

The sei whale is the fourth-largest balaenopterid, after the blue whale (up to 180 tonnes, 200 tons) and the fin whale (up to 70 tonnes, 77 tons) and the humpback whale (up to 40 tonnes, 44.5 tons)

In the North Pacific, adult males average 13.7 m (45 ft) and adult females 15 m (49 ft), weighing 15 and 18.5 tonnes (16.5 and 20.5 tons), while in the North Atlantic adult males average 14 m (46 ft) and adult females 14.5 m (48 ft), weighing 15.5 and 17 tonnes (17 and 18.5 tons)

In the Southern Hemisphere, they average 14.5 (47.5 ft) and 15 m (49 ft), respectively, weighing 17 and 18.5 tonnes (18.5 and 20.5 tons).

In the Northern Hemisphere, males reach up to 17.1 m (56 ft) and females up to 18.6 m (61 ft),while in the Southern Hemisphere males reach 18.6 m (61 ft) and females 19.5 m (64 ft) — the authenticity of an alleged 22 m (72 ft) female caught 50 miles northwest of St. Kilda in July 1911 is doubted.

The largest specimens taken off Iceland were a 16.15 m (53.0 ft) female and a 14.6 m (48 ft) male, while the longest off Nova Scotia were two 15.8 m (52 ft) females and a 15.2 m (50 ft) male.

 The longest measured during JARPN II cruises in the North Pacific were a 16.32 m (53.5 ft) female and a 15 m (49 ft) male.[31][32] The longest measured by Discovery Committee staff were an adult male of 16.15 m (53.0 ft) and an adult female of 17.1 m (56 ft), both caught off South Georgia.

Adults usually weigh between 15 and 20 metric tons — a 16.4 m (54 ft) pregnant female caught off Natal in 1966 weighed 37.75 tonnes (41.6 tons), not including 6% for loss of fluids during flensing.[24] Females are considerably larger than males.

At birth, a calf typically measures 4.4–4.5 m (14–15 ft) in length.

Anatomy:

The whale's body is typically a dark steel grey with irregular light grey to white markings on the ventral surface, or towards the front of the lower body. The whale has a relatively short series of 32–60 pleats or grooves along its ventral surface that extend halfway between the pectoral fins and umbilicus (in other species it usually extends to or past the umbilicus), restricting the expansion of the buccal cavity during feeding compared to other species.

The rostrum is pointed and the pectoral fins are relatively short, only 9%–10% of body length, and pointed at the tips.

It has a single ridge extending from the tip of the rostrum to the paired blowholes that are a distinctive characteristic of baleen whales.

The whale's skin is often marked by pits or wounds, which after healing become white scars. These are now known to be caused by "cookie-cutter" sharks (Isistius brasiliensis).

It has a tall, sickle-shaped dorsal fin that ranges in height from 38–90 cm (15–35 in) and averages 53–56 cm (21–22 in), about two-thirds of the way back from the tip of the rostrum.

Dorsal fin shape, pigmentation pattern, and scarring have been used to a limited extent in photo-identification studies.

The tail is thick and the fluke, or lobe, is relatively small in relation to the size of the whale's body.

Adults have 300–380 ashy-black baleen plates on each side of the mouth, up to 80 cm (31 in) long. Each plate is made of fingernail-like keratin, which is bordered by a fringe of very fine, short, curly, wool-like white bristles.

The sei's very fine baleen bristles, about 0.1 mm (0.004 in) are the most reliable characteristic that distinguishes it from other rorquals.

The sei whale looks similar to other large baleen whales. The best way to distinguish between it and Bryde's whale, apart from differences in baleen plates, is by the presence of lateral ridges on the dorsal surface of the Bryde's whale's rostrum. Large individuals can be confused with fin whales, unless the fin whale's asymmetrical head coloration is clearly seen. The fin whale's lower jaw's right side is white, and the left side is grey. When viewed from the side, the rostrum appears slightly arched (accentuated at the tip), while fin and Bryde's whales have relatively flat rostrums.

Surface Behaviors:

Sei whales usually travel alone or in pods of up to six individuals. 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.

The sei whale is among the fastest cetaceans. It can reach speeds of up to 50 km/h (27 kn) over short distances.

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.

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.

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,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.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.

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,[45] 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).

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.

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 and the pelagic amphipod Themisto gaudichaudii.

Reproduction:

Mating occurs in temperate, subtropical seas during the winter. Gestation is estimated to vary around 103⁄4 months,[48] 111⁄4 months,[49] or one year,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,so weaning takes place at the summer or autumn feeding grounds. Females reproduce every 2–3 years,usually to a single calf

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).[25] The average age of sexual maturity of both sexes is 8–10 years. The whales can reach ages up to 65 years.

Vocalizations:

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.

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.

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.

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.

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.

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."

Range and Migration:

Sei whales live in all oceans, although rarely in polar or tropical waters.

The difficulty of distinguishing them at sea from their close relatives, Bryde's whales and in some cases from fin whales, creates confusion about their range and population, especially in warmer waters where Bryde's whales are most common.

In the North Atlantic, its range extends from southern Europe or northwestern Africa to Norway, and from the southern United States to Greenland.

The southernmost confirmed records are strandings along the northern Gulf of Mexico and in the Greater Antilles.

Throughout its range, the whale tends not to frequent semienclosed bodies of water, such as the Gulf of Mexico, the Gulf of Saint Lawrence, Hudson Bay, the North Sea, and the Mediterranean Sea. It occurs predominantly in deep water, occurring most commonly over the continental slope,in basins situated between banks,or submarine canyon areas.

In the North Pacific, it ranges from 20°N to 23°N latitude in the winter, and from 35°N to 50°N latitude in the summer.

Approximately 75% of the North Pacific population lives east of the International Date Line,but there is little information regarding the North Pacific distribution. Two whales tagged in deep waters off California were later recaptured off Washington and British Columbia, revealing a possible link between these areas,but the lack of other tag recovery data makes these two cases inconclusive. Occurrences within the Gulf of California have been fewer. In Sea of Japan and Sea of Okhotsk, whales are not common, although whales were more commonly seen than today in southern part of Sea of Japan from Korean Peninsula to the southern Primorsky Krai in the past, and there had been a sighting in Golden Horn Bay,and whales were much more abundant in the triangle area around Kunashir Island in whaling days, making the area well known as sei – ground,and there had been a sighting of a cow calf pair off the Sea of Japan coast of mid-Honshu during cetacean survey.

Sei whales have been recorded from northern Indian Ocean as well such as around Sri Lanka and Indian coasts.

In the Southern Hemisphere, summer distribution based upon historic catch data is between 40°S and 50°S latitude in the South Atlantic and southern Indian Oceans and 45°S and 60°S in the South Pacific, while winter distribution is poorly known, with former winter whaling grounds being located off northeastern Brazil (7°S) and Peru (6°S).

The majority of the "sei" whales caught off Angola and Congo, as well as other nearby areas in equatorial West Africa, are thought to have been predominantly misidentified Bryde's whales. For example, Ruud (1952) found that 42 of the "sei whale" catch off Gabon in 1952 were actually Bryde's whales, based on examination of their baleen plates. The only confirmed historical record is the capture of a 14 m (46 ft) female, which was brought to the Cap Lopez whaling station in Gabon in September 1950. During cetacean sighting surveys off Angola between 2003 and 2006, only a single confirmed sighting of two individuals was made in August 2004, compared to 19 sightings of Bryde's whales.

 Sei whales are commonly distributed along west to southern Latin America including along entire Chilean coasts, within Beagle Channel to Isla Grande de Tierra del Fuego,and possibly feed in the Aysen region.

Migration:

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.

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.

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.

Despite knowing some general migration patterns, exact routes are incompletely known and scientists cannot readily predict exactly where groups will appear from one year to the next.

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.

Some evidence from tagging data indicates individuals return off the coast of Iceland on an annual basis.

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.

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.

Population Estimates:

The current population is estimated at 80,000, nearly a third of the prewhaling population.

A 1991 study in the North Atlantic estimated only 4,000.

Sei whales were said to have been scarce in the 1960s and early 1970s off northern Norway. One possible explanation for this disappearance is that the whales were overexploited. The drastic reduction in northeastern Atlantic copepod stocks during the late 1960s may be another culprit.

 Surveys in the Denmark Strait found 1,290 whales in 1987, and 1,590 whales in 1989.Nova Scotia's population estimates are between 1,393 and 2,248, with a minimum of 870.

A 1977 study estimated Pacific Ocean totals of 9,110, based upon catch and CPUE data.Japanese interests claim this figure is outdated, and in 2002 claimed the western North Pacific population was over 28,000,a figure not accepted by the scientific community.

In California waters, there was only one confirmed and five possible sightings by 1991 to 1993 aerial and ship surveys,and there were no confirmed sightings off Oregon coasts such as Maumee Bay and Washington. Prior to commercial whaling, the North Pacific hosted an estimated 42,000.

 By the end of whaling, the population was down to between 7,260 and 12,620.

In the Southern Hemisphere, population estimates range between 9,800 and 12,000, based upon catch history and CPUE.

The IWC estimated 9,718 whales based upon survey data between 1978 and 1988. Prior to commercial whaling, there were an estimated 65,000.

Credits: Society of Marine Mammalogy 

All About Sei Whales

The Sei Whale is a large baleen whale. Reaching lengths of up to 62 feet, the sei whale's dark steel gray body frequently looks galvanized. As with other baleen whales, the female is larger than the male. The body is frequently covered with small pit-like circular scars, originating in the bites of cookie-cutter sharks. Underneath, the belly is grayish white around the ventral grooves, which stretch only midway between the base of the flippers and the navel. The right lower lip is gray and baleen plates are primarily grayish black. The whale's snout is barely arched, while its slightly pointed rostrum (the forward extension of the upper jaw) sports a single median dorsal ridge. Two-thirds of the body length behind the head, a tall dorsal fin is very falcate, or curved like a sickle. The leading edges of the flukes are occasionally white.

Instead of teeth, it has great plates of horny baleen which extend from the upper jaw. These are used to strain food from large mouthfuls of water. It has two blowholes and the blow is either bushy or columnar and is usually quite tall (up to 10 feet high). Unlike the blue and fin whales, when the sei whale surfaces, the blowholes often appear at the same time as the dorsal fin, rather than before. They also do not usually arch their back or raise their flukes when diving.


DISTRIBUTION AND HABITAT:

Sei whales live within the Atlantic, Indian, and Pacific Oceans, primarily in subtropical, temperate and subpolar waters. Their distribution and migratory patterns are not well known. They are usually observed in deeper waters, far from most coastlines. They are not usually encountered within New Jersey’s coastal waters. According to the New Jersey Endangered and Nongame Species Program, there are no sightings currently documented within New Jersey waters for this species.

DIET:

Sei whales feed on tiny crustaceans known as krill as well as small schooling fish such as herring, capelin, and sand lance. They also feed on squid. They feed by filter feeding with their mouthful of baleen. They do so by taking a large mouthful of both prey and water, closing their mouth, and then pushing the water out of their mouth using their enormous tongue. The prey items are then left within the mouth, trapped by the strips of baleen, and ready to be swallowed. The sei whale eats an average of 2,000 pounds of food per day. They may often be seen feeding within groups of 2-5 individuals. In the North Atlantic Ocean, they will also be seen feeding near other species of whale, such as the humpback, and dolphins.

LIFE CYCLE:

Little is known about the sei whale life cycle and behavior. Like other baleen whales, it is likely that long-term bonds are rare. Females will give birth once every 2-3 years beginning when they are 10 years old. Most calves are born in the winter and grow quickly feeding on the milk of their mother. They will nurse on their mother’s milk for 6-9 months. Males play no role in raising their young.

Sei whales are one of the fastest swimming species of whale. They can reach speeds of 34.5 miles/hour. Their only predator, aside from humans, is the killer whale (Orchinus orca). Sei whales may live to at least the age of 50 years if not longer.

CURRENT THREATS, STATUS, AND CONSERVATION:

All of the large whale species have been at risk of extinction due to a long history of whaling. The principal attraction of whaling was the whale's blubber, which yielded oil ideal for lamp oil and, much later, in the production of margarine. Baleen was also of value. Whalebones were also used in the manufacture of glue, gelatin and manure. Besides being eaten by humans, the meat has also been used in dog food and, when dried and crushed, cattle feed.

Commercial whaling of sei whales ended in 1987 due to the decline of the species. It was listed by the federal government as endangered in 1970 and, as a result of that federal status, was automatically added to the New Jersey endangered species list following enactment of the New Jersey Endangered and Nongame Species Conservation Act in 1973. Sei whales are provided with additional protection with the Marine Mammal Protection Act of 1972. It is unknown whether sei whales are recovering throughout much of their range. Ship strikes and entanglements may be slowing their recovery. The global population is currently thought to be approximately 80,000.

Sei whales face a number of threats, all of which are caused by humans. These threats include entanglement in fishing gear, collisions with ships, and habitat impacts including noise pollution.

One of the greatest threats to sei whales is entanglement in fishing gear. Sei whales may become wrapped-up in nets and/or fishing line around their tail, mouth, or other body part. Discarded nets and lines may float at sea for decades or become snagged on rocks or debris at the ocean bottom. Once entangled in fishing gear, the whale may face an agonizing death, pulling the gear along while it swims for many days, months, or even years, as the gear slowly cuts through their body and causes swimming to become more difficult. Scars on whale bodies are often an indication of a previous entanglement from which they escaped.

Collisions with ships are an increasing threat to sei whales. The increasing number of large and fast ships results in whales and ships being in close proximity more often. Unfortunately, whales do not always know or have time to react to the approach of large ships and they get hit, usually resulting in their death.

Negative impacts to whale habitat may take the form of development, pollution, noise, overfishing, and climate change. Shipping channels, aquaculture, offshore energy development, and recreational use of marine areas may destroy whale habitat or displace whales which would normally use the area. Oil spills and other chemical pollutants are also a threat to whales and the prey which they feed on.

Another form of pollution is noise pollution. Whales’ primary means of communication, navigation, locating food, locating mates, and avoiding predators and other threats is through their sense of hearing, which is much more highly developed than that of humans. Noise pollution created by ship traffic or offshore construction may negatively impact whales by disrupting otherwise normal behaviors associated with migration, feeding, alluding predators, rest, breeding, etc. Any changes to these behaviors may decrease survival, simply by increasing efforts directed at avoidance of the noise and the perceived threat. Active sonar, such as that used by the Navy, also threatens marine mammals by disrupting navigation, foraging and communication abilities. There have been instances of whale stranding and death caused by acoustic trauma. This may be due to a fatal injury within the structure of the ear, or may result from the distressed animal surfacing too rapidly and developing nitrogen bubbles within their blood (decompression sickness). In addition to the direct threat posed by active sonar, it may indirectly harm marine species by causing changes in behavior.

Overfishing of the small fish and squid which sei whales feed upon is another potential cause for concern as well as the potential impacts of global climate change. This issue may be the greatest long-term threat to the marine habitat and its species. Climate change may significantly alter the chemical balance of the seas, off-shore currents, and plankton distribution and abundance, thereby affecting migration routes of marine species and impacting the entire food web.

Although sei whales are large animals, we don’t currently know a great deal about their habitat use off the coast of New Jersey. It is likely, in fact, that they may not occur within New Jersey’s waters which only extend 3 nautical miles off the coastline. It is likely, however, that they do occur within the ocean waters beyond 3-nautical miles. It is unknown whether they may be using those offshore waters as a migratory pathway between their summer feeding grounds in the north and their winter breeding grounds in the south. Surveys are currently being conducted off the New Jersey coastline in order to determine where whales are located, how many individuals are there, and during what time of year. Based on these findings, further knowledge regarding their habitat use in New Jersey waters may be gained and attention may then focus on protecting important habitats.

Credits : Conserve Wildlife New Jersey 

Introduction

This is an Exclusive Blog on Sei Whales who are relatively Unknown even among Whale Lovers and Researchers.

Sei Whales are the Third Largest Baleen Whale.

They are constantly threatened by Japanese Whalers in the Pacific.

It is My Hope that this Blog will create some awareness about Sei Whales.