Do minke whales employ unique feeding strategies in the Saguenay Fjord?
Certain individual whales show a marked preference for specific feeding sites. Numerous anecdotal observations suggest that these individuals develop feeding strategies that are adapted to their preferred feeding area. The minke whales that frequent the Saguenay Fjord, a limited habitat with specific physical characteristics, are the ideal subjects for the verification of such a hypothesis.
To go through the looking glass
Researchers compared feeding-strategy data collected on minke whales present in the Laurentian Channel between 1997 and 1999 with data collected on minke whales present in the Saguenay Fjord between 2001 and 2003. These data included detailed descriptions of all visible surface behaviour. From 2001 to 2003, they also closely observed five photo-identified minke whales that visited the Saguenay Fjord on a regular basis to feed.
The feeding strategies of the minke whales that visit the Saguenay are different than strategies employed by minke whales that visit the Laurentian Channel. The physical properties of these two areas may explain the variance. In the Saguenay, minke whales spend a considerable amount of time herding prey near the surface. To do so, they regularly perform chin up blows, underwater exhalations on the dive and head slaps (see “I want to know more”). The Laurentian Channel deep-water upwelling—created by tide, currents and underwater topography—naturally musters minke whale prey near the surface. Consequently, minke whales execute fewer herding manoeuvres in this sector. There are also differences in the use of various feeding strikes; Saguenay minke whales use lateral and ventral manoeuvres more often, while those present in the St. Lawrence are more prone to execute oblique manoeuvres.
Observations made in the Saguenay between 2000 and 2003 have led researchers to believe that minke whales in this area may be learning and transferring feeding strategies among themselves. The head slap was noted for the first time in 2000 when a minke whale known as Loca was seen executing this manoeuvre in the Saguenay. The head slap consists of pushing the head and part of the thorax out of the water only to let it fall back energetically against the water’s surface. The number of minke whales executing this particular manoeuvre in the Saguenay increased from one in 2000 to six in 2003.
Ned Lynas, Ursula Tscherter, Jordy Thomson and Katie Kuker of Ocean Research and Education Society (ORES)
I want to know more
Minke whale feeding strategies in the Saguenay Fjord and St.Lawrence Estuary
As defined by ORES
Minke whales in the Saguenay Fjord appear to have developed feeding strategies that are well adapted to their specific environment. The herding manoeuvres described below were originally observed exclusively in the Saguenay. In recent years several minke whales have been observed executing these same manoeuvres outside the Fjord.
During a feeding bout a minke whale will come to the surface from different directions and—as well as surfacing frequently and regularly to breathe—it will execute various herding manoeuvres to herd and cluster prey before ultimately engulfing it in a feeding strike.
« The lateral chin-up blow »
During this manoeuvre the minke whale surfaces slowly, usually on its right side, pushing its head well into the air. It then twists its head to take a breath and rolls back to the right when re-submerging. As it goes through these motions, the whale’s white throat becomes clearly visible and the ventral grooves do not expand.
The head slap
The whale makes a lunge, similar to an oblique lunge (see below), well out of the water at an angle of 30o to 45o. Yet, unlike what is observed during a feeding strike, when a whale executes a head slap the ventral grooves do not expand and no water is expulsed from the mouth. As it reaches the highest point of its lunge, the whale bends its head back, pushes its thorax downward and slaps the surface, creating a huge splash and an audible sound. This manoeuvre is most likely used to frighten prey.
Underwater exhale on the dive
After a series of regular surface breaths, the whale will strongly exhale just below the surface, projecting a fountain of frothing water into the air. This manoeuvre is often accompanied by an audible roaring sound that is possibly used to startle the fish.
Generally performed after herding manoeuvres, feeding strikes are executed to engulf prey. Feeding strikes are performed with the body in different planes: right-side up (regular plane, belly down), upside down (belly up) and laterally (on the side). Feeding strikes are performed faster than herding manoeuvres. During a feeding strike the grooves are expanded and water is squeezed out of the mouth. Occasionally fish can be seen either swimming very near the surface or leaping above it when a whale executes a feeding strike.
Arcs are semicircular feeding strikes executed just below the surface. After executing an arc, the whale most often rolls back to the regular plane to breathe. The whale can execute this strike either on its side (lateral arc) or on its back (ventral arc). In the case of a lateral arc, the whale does not break the surface beyond exposing the belly and/or the tips of a flipper and fluke.
As it captures its prey, the minke whale partly emerges in an energetic manner. It may break the surface on the regular plane, belly down (oblique lunge), on its side (lateral lunge) or upside down (ventral lunge) at an angle of 30o to 45o or even vertically (vertical lunge). If the whale’s blowholes are clear, it may take a breath.