Humpback rise-blue whale blues.
During the first decade of our research (80s) in the Mingan/Anticosti study area we saw humpback whales, but not nearly in the numbers we have seen recently. Highest daily sightings amounted to rarely more than 5-10 individuals. By the early 90s, however, sightings of humpbacks increased noticeably and we can now find 20-40 humpbacks with regularity in our study area on any given day with some 3day periods yielding as many as 70 different humpback whales. The numbers of humpbacks were made up of old stalwarts known since the 80s with new individuals joining the herd through immigration and birth. In fact the last 10yrs in particular have been witness to a regular baby boom for humpbacks. It should be noted that finback whales, commonly sighted since the 80s in our area, have also had a noted increase in births over the last 4 years.
A total of 106 calves have been reported
since 1980. From 1980-year of the first humpback sightings to 1990 we
recorded 10 calves, from 1991-2000 there were 31, and from 2001-2008
64 were reported. Female humpbacks observed in the St Lawrence
generally have their first calf at 10yrs of age. This we know because
females first sighted as calves reached sexual maturity and returned
with calves of their own during our years of study. And, though they
can give birth every two years, mature females from our study area have
a calf every 2to 7yrs.
The recent increase in calving is of course due to an increasing local summer population of adult females added through immigration and of returning individuals reaching sexual maturity.
One female-Pseudo has had 8 calves since 1982, Fleuret has had 7 since first seen in 1982, Ebene has had six since 1983, and four have returned with 5 claves. The highest numbers of calves seen were in 1997=8, 2003=7, 2005=16, 2007=14, and 2008=11, the latter 3 yrs being the most prolific.
Twelve females observed over at least 5 yrs have, however, never been seen with calves. This may be due to not having been sighted in years they had calves, that they had not reached sexual maturity or perhaps an environmental cause impeded reproduction.
Because we have not had a regular presence in the northeastern St. Lawrence, where daily sightings can approach 200 or more humpbacks in July and August, we have certainly missed calves born into the overall St Lawrence population over the years. The St. Lawrence humpback catalog presently stands at nearly almost 750 individuals.
Why this increase in humpbacks? Interestingly humpback numbers began to rise in the late 80s just when the blue whale sightings in the Mingan area began to decline precipitously. We know that humpback whales will consume prey including krill (euphausiids) capelin, sand lance, herring, mackerel and small squid. In the St. Lawrence they appear to be predominantly piscivorous, while of course the blue whale is a krill specialist.
Could the severe decline of cod, haddock and red fish (sebastes) due to over-fishing have disrupted the food chain and caused an imbalance in biomass which favored the humpback, finback and minke whales? If the removal of top fish predators that prey on capelin, sand lance and herring allowed the smaller forage fish to fill the void left by over-fishing, it could have caused greater predatory pressure on krill. This increasing biomass of forage fish, preying heavily on krill, could be too much competition for blue whales. And in turn may be the reason that blue whales have vacated a habitat they once used commonly. It may seem strange to think that capelin can out compete much larger blue whales, however, in massive schools forage fish are formidable competitors.
Increased access to abundant food sources appears to be benefiting humpback whales both in attracting new individuals to the region, but also in reproductive fitness. The same can be said of finback whales, which have also produced a robust number of calves in the last 4 years. Harbor porpoise, Atlantic white-sided dolphins, and minke whales have also probably been benefiting from this increase in forage fish.
This more abundant food leads to well-fed humpback whales, to greater individual and population fitness, and increased reproduction
How long will this last? Will there be a
crash in the quantity of krill? Will humans exploit this new biomass
and source of protein, and cause it to collapse? How will the added
effects caused by global warming affect these interconnected
populations of predator and prey? The latter could be locally
beneficial as well as detrimental. What seems clear, however, is that
over-fishing has not been good for cod and other fish predators, while
it appears to benefit certain marine mammals such as humpback
whales-for the moment.
Is this temporary or will the trend continue? Hopefully we will be able to monitor this over the next years of study. This is why long-term studies are invaluable.