David @ Tokyo

Following on from the previous post in relation to the IUCN extinction risk downgrade for the Humpback (and minke) whale species, here's some more positive information from another paper submitted to the IWC Scientific Committee by Trevor Branch:

ABSTRACT
Austral summer estimates of abundance are obtained for humpback whales (Megaptera novaeangliae) in the Southern Ocean from the IWC's IDCR and SOWER circumpolar programmes. These surveys have encircled the Antarctic three times: 1978/79­1983/84 (CPI), 1985/86­1990/91 (CPII) and 1991/92­2003/04 (CPIII), criss-crossing strata totalling respectively 64.3%, 79.5% and 99.7% of the open-ocean area south of 60°S. Humpback whales were absent from the Ross Sea, but were sighted in all other regions, and in particularly high densities around the Antarctic Peninsula, in Management Area IV and north of the Ross Sea. Abundance estimates are presented for each CP, for Management Areas, and for assumed summer feeding regions of each breeding stock. Abundance estimates are negatively biased because some whales on the trackline are missed and because some humpback whales are outside the survey region. Circumpolar estimates with approximate midpoints of 1980/81, 1987/88 and 1997/98 are 7,100 (CV=0.36), 10,200 (CV=0.30) and 41,500 (CV=0.11). When these are adjusted simply for unsurveyed northern areas, the estimated annual rate of increase is 9.6% (95% CI 5.8­13.4%), near the maximum possible for humpback whales. All breeding stocks are estimated to be increasing but increase rates are significantly greater than zero only for breeding stocks D and E. If the rate of increase is >5%, total abundance in the Southern Hemisphere is greater than 50,000 and is similar to the summed northern breeding ground estimates (~53,000 from 1999­-2005). Some breeding ground abundance estimates are far greater, and others far lower, than the corresponding IDCR/SOWER estimates, in a pattern apparently related to the latitudinal position of the Antarctic Polar Front.

And again in the "Total Southern Hemisphere abundance" of the "Discussion" section of the paper on page 9, Branch concludes that "...it is fairly safe to conclude that there are more than 50,000 humpback whales in the Southern Hemisphere."

Here's a reproduction of "Figure 1" from this document, which indicates humpback sightings around Antarctica:
It should make for interesting comparison with the corresponding figure from Branch's other paper on increasing Blue whale abundance.

Labels: humpbacks, Trevor Branch

A paper submitted to the IWC Scientific Committee provides further confirmation of the recovery of the Antarctic blue whale:

ABSTRACT
Sightings from the IDCR and SOWER austral summer surveys were analysed to provide abundance estimates for Antarctic (true) blue whales (Balaenoptera musculus intermedia) south of 60°S. The IDCR/SOWER ship-borne surveys have completely circled the Antarctic three times: 1978/79–1983/84 (CPI), 1985/86–1990/91 (CPII) and 1991/92–2003/04 (CPIII), covering strata totalling 64.3%, 79.5% and 99.7% of the ocean surface between the pack ice and 60°S. During the surveys, blue whales were only rarely sighted but were present around the Antarctic. Average sighting rates (schools per 1,000 km of primary search effort) were 0.24 (CPI), 0.36 (CPII) and 0.78 (CPIII). Respective circumpolar abundance estimates were 453 (CV=0.40), 559 (CV=0.47) and 2,280 (CV=0.36), with mid-years of 1980/81, 1987/88 and 1997/98. When adjusted simply for unsurveyed regions, the circumpolar rate of increase was 8.2% (95% CI 3.8–12.5%) per year, although they are still under 1% of their pre-exploitation abundance. These abundance estimates are negatively biased because they exclude some Antarctic blue whales that are north of 60°S, and because a low number of blue whales on the trackline may be missed. Additionally, estimates may include a small proportion of pygmy blue whales, probably less than 1%. Abundance estimates were also provided for each IWC Management Area and for each individual survey, but these have high associated uncertainty.

Here's a reproduction of "Figure 1" from the document, showing blue whale sightings around Antarctica:
From the paper:

Antarctic blue whales were sighted around the Antarctic, thus it is not surprising that the abundance estimates are spread among all of the IWC Management Areas. Highest historical catches were taken from Areas I–III, which have lower current abundances of Antarctic blue whales than Areas IV–VI. However, estimates are highly variable from year-to-year because of the low numbers of sightings, a feature also apparent in JARPA estimates for Areas IV and V...

Assuming this pace of recovery is maintained, Antarctic blue whale abundance will still only recover to a level of 10,000 in 20 years time. Under such a scenario, ongoing (and indeed consensus) protection seems inevitable for the next 2 decades, at least.

The paper also notes that the rate of increase (albeit with the 95% confidence interval of 3.8–12.5%) is close to the theoretical biological maximum. It's fascinating given how scarce blue whales are that they are still able to find breeding opportunities to be able to exhibit such a recovery.

It will be interesting to follow developments as hopefully a clearer picture about the Antarctic blue whale recovery emerges, and any differences in rate of increase in different parts of the Antarctic become apparent.


The paper was authored by Trevor Branch, who is a leading player in the IWC SC's Antarctic baleen whale abundance estimate work.

Labels: blue whales, Trevor Branch