A surfacing finback will show markings that help identify them in photographs

   

DOLPHIN FLEET FINBACK WHALE SIGHTINGS SUMMARY FOR 2010

John C. Conlon

Our 2010 whale watch season has come to end. It is late autumn and the leaves are falling. Whale watching is on hold until next spring though autumn is the time for data analysis. So, here follows a summary on fin whales for the 2010 whale watch season. It was, as always, an overall different kind of year from last year for balaenopterid sightings. Fin whale sightings were down from last year: though last year was certainly a great year for fin whales locally as was 2008. As the fin whale sightings dropped this year so did the number of minke whale sightings though to an even greater degree. The number of sea bird sightings also dropped dramatically. Both fin and minke whale sighting rates decreasing as the season progressed.

Looking at fin whales for the year there are four issues discussed through this summary: feeding strategy, analysis of 2010 data from spatial distribution and individual identification perspectives; photographic data collection; and, a noteworthy anecdote (photo) from the season.

The majority of fin whale movement in local waters we tend to view in reference to feeding opportunities. This year’s observations of surface feeding were rare to say the least. Often what we observe at the surface as seemingly random movements is indicative of subsurface feeding. On those occasions that we see surface feeding it is an activity that is shrouded by white water and often difficult to comprehend.

Field observations and more detailed scientific studies indicate that high speed while opening the mouth is integral to fin whale feeding. In particular it helps in pursuit of mobile prey. Any field worker also knows fin whales will move quickly between scattered prey patches. In their paper, Recent Fluctuations in Abundance of Baleen Whales in the Southern Gulf of Maine in Relation to Changes in Selected Prey, Payne et al. (1990) suggested that this tendency to regularly move between loosely scattered prey patches could explain the low inter-annual rate of change in southern Gulf of Maine fin whale abundance during inter-annual high rates of change in prey abundance.

In order to deal with prey fin whales depend on high energy lunges through prey patches for at least two reasons. First, they need to open their mouth appropriately for prey capture. Second, it produces a loud snapping noise potentially acting as a corralling mechanism.

As fin whales lunge through prey they typically roll some 90 degrees to their right side down. Lunging opens the mouth wide. The jaw base and synovial jaw-tip joints allow the lower mandibles to open to over 80 degrees as well as allow the two lower jaw bones to splay outward. The jaw-opening action creates the aforementioned “snap”. Brodie, P. F. in, Noise Generated by the Jaw Actions of Feeding Fin Whales. (Can. J. Zool. 1993) suggested this snapping noise, reverberating down the length of the oil-infused mandibles, and surrounding the prey ball, acoustically drives the fish toward the throat which is the only area not surrounded by the sound transmitting bone.

Two fin whales rolled right side down showing rorquals (left) and lower jaw (right).

Gulf of California, Mexico. John C. Conlon.

Water and food fill the gaping mouth. The tongue becomes inverted as an oral sac and drops through the floor of the mouth into a ventral pouch of expanded rorquals. Recently, Jeremy Goldbogen (2010) in, The Ultimate Mouthful: lunge feeding in rorqual whales, published in American Scientist, suggests that this volume of food and water coming into the buccal cavity more than doubles the fin whale’s own volume as the lunging whale body almost completely stops. When fin whales feed at the surface it is at this stopping point that we see the ricochet of the fin whale’s body as it lurches at the water’s surface.

The ventral pouch, which extends from the jaw tip almost to the navel, expands as the 100 or more muscle and blubber lined rorquals, or throat grooves, balloon out. This roughly doubles the diameter of this portion of the body, as the tongue and ventral grooves are capable of large scale expansion. It also allows holding of this oral sac full of water and food. As a fin whale closes its mouth the musculature of the ventral pouch contracts. Excess water is expelled through the baleen plates. This action forces most of the engulfed seawater out between the 600 plus baleen plates that hang perpendicularly from the entire upper jaw length.

With rorquals pulled inward and the whale’s acceleration stopped, a fin whale pushes its tongue toward its palate while contracting the rorquals. This forces more seawater out through the baleen. The fringed inner edges of the baleen form a dense mat against which food is trapped. The tongue may help scrape food from inside the baleen plates while much of the food would be suspended in water remaining in the animal’s mouth. The food is then swallowed.

Early this year Kate Longley graciously circulated the Goldbogen paper to Dolphin Fleet field guides. While not a “scientific” paper per se it was quite detailed. Indeed it did an effective job of summarizing Goldbogen et al. (2009, 2007 and 2006) research in recent years as the author described fin whale subsurface feeding in detail. This feeding is no passive engulfment process. Goldbogen et al. reveal that fin whales actively move forward as the lunge occurs. These authors acknowledge multilayered muscle working with the ventral grooved blubber. The authors also acknowledge De Bakker et al. (1987) Histology of the Grooved Ventral Pouch of the minke whale, Balaenoptera acutrostrata, with special reference to the occurrence of laminated corpuscles (Can. J. Zool.). The authors describe nerves in the rorqual muscle and blubber capable of sensing mechanical stress. Goldbogen suggests that this awareness of active engulfment helps create a cross flow filtering process that eliminates the clogging of baleen by passively filtered prey while prolonging the period of peak drag.

Goldbogen’s description of subsurface feeding involves three to five lunges per feeding dive, yet, we see surface feeding as single lunges. In the midst of these surface feeding bouts it is regularly noted that fin whales swim in circles generally observed as semi circles. It is regularly said that this is an attempt to corral food as the white right side of a fin whale’s head is toward the center of the circle. This idea, though often repeated, is questionable at best and likely not the case. While comparing clockwise versus counter-clockwise circles from both the northwest Atlantic and the Gulf of California of western Mexico, Treshy and Wiley in, Asymmetrical Pigmentation in the Fin Whale: a test of two feeding related hypotheses (1992. Mar. Mamm. Sci.) reported that 52% of circles were clockwise circles or that “fin whales turned equally in both directions”. Watkins and Schevill in, Aerial Observation of Feeding Behavior in Four Baleen Whales, (1979, J. Mamm.) noted that these circles may or may not occur as fin whales feed beneath the surface. Perhaps this circling is a function of prey-patch size. It is likely that the circles are simply an attempt to get the animal’s body oriented back toward the prey patch.

Tershy and Wiley showed, by comparison, that 97.4% of Gulf of California and 81.1% of Atlantic rolls were right side down. In that same paper comparing right side down lateral lunges the authors also state that fin whales do not roll right side down at significantly higher rates than their cogeners blue, sei, Bryde’s or minke whales. Right side down, they suggest, seems likely to be the right-side preference seen in many mammals. These two comparisons are but two ways in which fin whale feeding behavior varies considerably depending on water column location, geographic location, as well as prey species just to name a few of the variables.

Spike showing both propeller scars and a caudal entanglement scar.

With the help of Dolphin Fleet captains and field guides we collected some 218 total data lines on fin whales this year. Two hundred and six usable photo ID shots came from 62 data lines with accompanying photographs. From April 10 th to the 30 th most photographed fin whale sightings were from the northeastern portion of Cape Cod Bay with several more from just outside Race Point. Between the 1 st and 31 st of May the number of sightings dropped markedly and were scattered from Race Point Channel to the east and north of the Triangle and toward the old BD buoy. There were no photo records of fin whales in the first two weeks of June and only two photo records in the second two weeks of the month: the channel and the Triangle. The first two weeks of July again had only two photo records in the Triangle area. The second two weeks of July had three photo sightings in Race Point Channel and one more toward the Triangle. The first half of August gave us 2 photo data sets from the south and central Stellwagen area. The second half of August gave us four photo-data lines from the area off the southeast corner of Stellwagen. For the entire remainder of the season we had only one photo-data line on the 19 th of September from Pace Point Channel. Twenty-six of the 62 photo ID lines came from northeastern Cape Cod Bay while 11 other photo data lines came from Race Point Channel. The southeastern Stellwagen region accounted for eight while the triangle and old BD areas accounted for eleven and four photo-data lines respectively. One additional photo line came from the mid-Stellwagen area.

Comparing this year’s fin whale sightings to 2009 distribution the 62 photo ID lines of 2010 is just over 3/4s of the 80 photo ID data lines from 2009. The second consecutive year of decreases in data lines from the previous year. Ironically the fewer data lines this year gave us 53 individuals for 2010 compared to 44 for 2009. One explanation for this decrease in data is that both 2008 and 2009 offered many more sightings of fin whales in the Race Point Channel and our trips regularly passed through there en route to the Triangle. There simply were fewer sightings of fin whales in the Race Point Channel this year. Having said this it is worth noting that the photos themselves were generally very good. This is a combination of two things. First, field guides were getting good photos of not only dorsal fins but also series shots of the right sides of the animals. Second, neither of these would be possible without the captains getting better positioned along the sides of the animals.

The total of known individuals for 2010 was 33. Named individuals IDed this year are: Alacran, Amp, Belt, Bond, Braid, Comb (with her first Dolphin Fleet recorded calf), Cusp, Cyrano, Darth (with her second Dolphin Fleet recorded calf), Fluker, Hook, Johnny Depp, Lenin, Lightning, Loon, Nightcap, Rila, Scorpion, Sagitta, Skeg, Spike, Sunspot and Teton. Unnamed previously known individuals are: 06 143, 07 164m, 07 227, 08 019c, 08 020, 08 039c, 08 122, 08 143, 08 174, 09 020. We had two sighting each of Comb and Darth with their respective calf of this year. This is our first record of a calf for Comb whose Dolphin Fleet sighting record goes back to 2006. In these four cases the photos were of good quality. These double sightings, generally of good focus and at good angles, means that we have considerably more confidence in the sightings of mother / calf records for the year. When photographing calves it is helpful if the photo series begins at the forward end of the head. This helps in calf identification given the smaller proportion of a calf’s heads. Comb, while not photographed, was seen in late summer without her calf while Darth’s calf was seen late in the summer without Darth. These sightings are indicative of fin whales weaning their calves at about seven months.

We had 18 new individual fin whales that were not tied to previous sighting records. Comb’s and Darth’s two calves bring our total to 20 new individuals. Combined this brings our 2010 total to 53 individuals including the two calves. Twenty of this year’s identified individuals had multiple records. Scorpion topped the list with 5 photo records. Other individuals had few or even only one record for the season. Sixty-three percent of the year’s fin whales had previous sighting records while 38% were new this year. Obviously the two calves have no previous record. The remaining 18 may indeed have been new individuals or they may have been calves from previous years though not able to have been matched due to photo quality issues. Clearly speculation! With the addition of these new animals to our Dolphin Fleet catalog these twenty individuals allowed us to cross the milestone number of 100 bringing the total number of individuals in our catalog to 112. All of the early named individuals and unnamed 07 XXX individuals are in the Fin Whale catalogs on the boats. The accompanying life history sheets are up to date to 2010.

Darth (above) and her 2010 calf (below).

Given my ongoing concerns regarding mother / calf pair documentation I'm particularly pleased with several other of this year’s sightings. First; this year’s photos of Scorpion's second known calf, Alacran (07 039c). This is the second consecutive year that Alacran has been photographed. Scorpion’s previous known calf was born in 1985. We also had sightings of 08 039c born to 07 164m. This is the third consecutive year that both these juveniles have been photographed. I'm also pleased with this year’s documentation of Darth with her second known calf. This is our second record of a female fin whale with calves from two consecutive breeding cycles. That is accepting that they produce a calf every second or third year. After five years of work our Dolphin Fleet Fin Whale Catalog now has twelve recorded fin whale calves including those of Comb and Darth this year.

An acknowledgement of the year’s most rewarding photo(s) goes to Mark Gilmore. On a somewhat grey April 25 th at 3:06 PM. Mark shot a series of photos spanning Rila’s entire left side. In the first photo (first at head of summary) Rila’s blowholes are just closing. On the frame’s right side is the spout’s condensing water droplets hitting the surface and the spout’s fading mist. The in-between frames show the sheen of water sliding off the animal’s back as water droplets continue hitting the water’s surface. Mark’s next to last frame in the set (second at head of summary) is of Rila’s lower left flank showing sloughing skin and sloughing yellow diatom film, along with a beautifully clear image of Rila’s dorsal fin. In fact when one looks at enlargements of Mark’s original digital images on a computer an amazing array of tiny depressions and small scrapes and scars becomes apparent. Rila is one of the few fin whales for who we have several sets, now one more, of left side shots. Left side shots are important to fin whale identification but, because of our fin whale right side preference, are lacking in our Dolphin Fleet catalog. This is the fifth consecutive year we have photo sightings of Rila along with one additional photo sighting from 2002. Nice work, Mark!

Lastly, I'd like to say THANK YOU to our field guides and captains for their work! Good photos of fin whales came in this year and many of those animals are known to us. My sincerest appreciation goes to those who contributed to this year’s research. First, thank you to Dr. Carole Carlson and her entire team of field guides (Irene, Nancy, Kate, Sarah, Beth, Therese, Gwen, Liz, Mark, Mike, Dennis and Peter), and volunteers from the Cape Cod Museum of Natural History. This team collected the written and photographic data. None of the data collection was possible without the Dolphin Fleet captains: Dennis, Mark, Todd, John, Pete, Scott, and Chad whose skill and patience are very much appreciated by both our research staff and our passengers. Thank you to Kate Longley and to Mick Rudd for editing notes into our website sections. Thank you to Anna Jankowicz-Conlon for data entry assistance and photographic editing of our fin whale catalog. Thank you again to Dr. Carole Carlson, our Director of Education and Research, for overseeing all the written, photographic, and GPS data collection processing to usable form. Thank you especially to Steve Milliken and the Dolphin Fleet for steady encouragement and support to make this research on fin whales, and our entire research and education program, a reality. It is wonderful to work as a guide and researcher with and for people who are concerned for the wellbeing of both the fin whales and the ocean world in which they live. Finally, THANK YOU, MERCI, GRACIAS to you, our Dolphin Fleet passengers. Your time, enthusiasm, encouragement, and support by joining us on our trips, is invaluable to the work that we at the Dolphin Fleet accomplish. Looking forward to seeing you all in 2011!

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