FIN WHALE (Balaenoptera physalus)

It is the second baleen whale in size (sub-orden of mysticetes) after the blue whale. The females can reach 19 to 22 metres in length (75 tons) although individuals of up to 24 m have been described in the Northern Hemisphere and up to 27 in the Southern (120 tons).

The reason why the coloration of the lower jaw is asymmetric (it is dark on the left side and white on the right), a unique feature in cetaceans, is still unknown.

Distribution
The fin whale is cosmopolite. It can be found, solitary or in groups, in almost all oceans, normally from temperate regions to polar waters, less often around the tropics. It is common to sight this species in coastal areas as well as in open seas. In the Mediterranean Sea, there is a population that genetically differs from the North Atlantic.

The fin whales feed on krill, small fishes and cephalopods that can be captured down to 200m deep. Through their baleens (260-480) that are suspended from the upper jaw and are around 1m long, they filter food. The ventral side of their body presents 50 to 100 grows in between the pectoral fins. These allow the mouth and thoracic cage to expand when the water filled with food enters, recovering its normal aspect when throwing it out again through the baleens, as well as its hydrodynamic shape.

Biological cycle
There is little information on this species reproduction as well as on the existence of breeding or calving areas. Males reach sexual maturity at around 17m in length while the females reach it at around 6-7 years old (18m). The breeding cycle is 2-3 years long. After a 11-12 month gestation period, a calf is born (6-6.5m and 1800-2700kg). The calfs lactate and stay with their mother during the first 6-8 months of their life.

The fin whales are thought to live for around 80 years.

Acoustic signals
The fin whales, as all the other balleen whales, do not produce clicks but vocalizations called songs or calls which production mechanism is still a matter of study. The larynx (this would be different from odontocetes that lack vocal cords) would be involved here.

These vocalizations of the fin whales are produced at very low frequencies and can be heard along hundreds of kilometers, using underwater acoustic tunnels formed by the difference in salinity and temperature of the different water layers.

These songs are defined as sequences of a variety of acoustic signals that are regularly produced. In general, the signals are produced in intervals of 7 to 26 seconds. The acoustic signals included in these songs are:

  • Individual pulses of around 20 Hz.
  • Irregular series of 20 Hz pulses.
  • Stereotyped 20 Hz signals called bouts. These can be produced during hours (up to 32.5). The intervals between pulses are very regular.
  • Repetitive sequences of 20 Hz pulses.
The following table describes the different types of fin whale calls, with their characteristic frequencies and levels.

Signal type Frequency range (Hz) Peak frequency (Hz) Source level (dB re 1 uPa)

Moans 16-750 20 160-190
Pulse 40-75 -- --
Pulse 18-25 20 --
Ragged pulse < 30 -- --
Rumble -- < 30 --
Moans, down-sweeps 14-118 20 160-190
Constant call 20-40 -- --
Moans, tones, upsweeps 30-75 -- --
Rumble 10-30 -- --

While the exact mechanisms of the fin whale's acoustic emissions are not known, one of their roles is, without doubt, long distance communication. It is also thought that they can use their signals for orientation while at depths, through the echo that is returned by the under water relief.

Nevertheless, these vocalisations are also produced in courting situations, where they can be used by the males to sexually attract the females.

Listening to fin whales

Flash
Recording made in the Gulf of California in March 1999. The play-back speed has been accelerated 10 times with respect to its normal speed to allow it to be perceived by the human ear. The double pulses that can be heard may seem to be caused by reflections, but the pulses actually are produced in this double rhythm.

Flash
The two first pulses of the previous recording are repeated here at the real speed. In order to hear these low frequency sounds (in this case, most of the energy is concentrated below 65 Hz) you will need good quality speakers or headphones.
Main threats

Since the beginning of the 20th century until 1986, the main threat to this species was the large scale hunt.

Today, its hunt is forbidden in all countries, except Iceland (since 2003). Here it was reported that 9 fin whales were caught until August 2007. Nevertheless, there are still a few threats left, as for example collisions with ships, chemical and/or inorganic pollution and acoustic pollution.

In spite of being a fast swimming animal (it can reach speeds over 30 km/h), collisions with shipping traffic are a common cause of death, especially in the Mediterranean.

Image of a 13 m long fin whale in Vilanova i la Geltrú (Barcelona), February 23, 2007. Two more cadavers of the same species were found at other places along the Spanish coast in the same week. All three animals appeared to have died due to a collision.

The fundamental role of this species in the food chain is being threatened: the banishment from a specific location, or the extinction of a population, leads to a general and irreversible imbalance of the entire ecosystem, as it would allow the uncontrolled multiplication of their preys.

Assessing the real impact of the anthropogenic disturbances on cetaceans in general, as well as the traumas that they cause, is not a trivial task. It requires a continuous investigative effort, the combination of many scientific disciplines and the active participation of the society in order to make, with its collaboration, the conservation of cetaceans an obligatory step and to return the sea to its natural balance.

Images