Abundance estimates and trends for humpback whales (Megaptera novaeangliae) in Antarctic Areas IV and V based on JARPA sightings data

Abstract

Sighting survey data from the Japanese Whale Research Program under Special Permit in the Antarctic (JARPA) are analysed to obtain abundanceestimates for humpback whales (Megaptera novaeangliae) south of 60°S. The surveys were conducted during the 1989/90–2004/05 austral summerseasons (mainly in January and February); the survey areas alternated between Area IV (70°E–130°E) and Area V (130°E to 170°W) each year.Primary sighting effort totalled 293,811 n.miles over 6,188 days. Abundance estimates are obtained using standard line transect analysis methodsand the program DISTANCE. Estimated densities of humpback whales were highest east of the Kerguelen Plateau (80°E–120°E). Abundanceestimates for Area IV range from 2,747 (CV = 0.153) in 1993/94 to 31,134 (CV = 0.123) in 2001/02, while those for Area V range from 602 (CV= 0.343) in 1990/91 to 9,342 (CV = 0.337) in 2004/05. The estimates are similar to those obtained from the International Whaling Commission’sIDCR-SOWER surveys, which were conducted in Area IV (in 1978/79, 1988/89 and 1998/99) and in Area V (in 1980/81, 1991/92 and 2001/02–2003/04). Estimated annual rates of increase for Area IV (16.4%; 95% CI = 9.5–23.3%) and Area V (12.1%; 95% CI = 1.7–22.6%) are also similarto those obtained from the IDCR-SOWER surveys. The total abundance in Areas IV and V based on the most recent JARPA surveys (2003/04 and2004/05 combined) is 37,125 (95% CI = 21,349–64,558); the confidence interval incorporates estimated additional variance. Results of severalsensitivity tests are presented that suggest that estimates of abundance and trends are not appreciably affected by factors such as different approachesto deal with survey coverage (which in some cases was poor or included gaps). Changes in the order in which survey strata were covered andpotential effects are investigated using a nested GLM approach; a QAIC model selection criterion suggests a preference for not attempting to adjustfor such changes. Under various sensitivity approaches, the point estimates of increase rates are not greatly affected for Area IV. Although theydrop by typically a half for most approaches for Area V, they nevertheless remain within the confidence limits of the base case estimate of 12.1%per year (95% CI = 1.7–22.6%). The presented results thus suggest that the estimated abundance of humpback whales in Area IV has increasedrapidly. Although there is also an increase indicated for Area V, it is neither as rapid nor as precisely estimated. Taking these results together withthe similar rates of increase estimated from coastal surveys off western and eastern Australia for Breeding Stocks D and E respectively, and givendemographic limitations on the increase rates possible for closed populations of humpback whales, the hypothesis is advanced that whales fromBreeding Stock E may have shifted their feeding distribution westward as their numbers have increased, perhaps to take advantage of the higherdensities of krill to be found to the west.

Substantial decline in energy storage and stomach fullness in Antarctic minke whales (Balaenoptera bonaerensis) during the 1990s

“…Regarding other krill feeders, sighting surveys have shown that the abundance of large baleen whales increased substantially during the JARPA period e.g. blue (B. musculus) and southern right (Eubalaena australis) whales and especially humpback whales (Megaptera novaeangliae) (Branch et al, 2004;Branch and Rademeyer, 2003;Matsuoka et al, 2011). Thus it is possible that our results reflect the reverse of Laws' 'krill surplus hypothesis' (Laws, 1977).…”

Abundance estimates and trends for Antarctic minke whales (Balaenoptera bonaerensis) in Antarctic Areas IV and V for the period 1989/90–2004/05

“…Because stratum areas vary from year to year as a result of different ice edge locations, it is not immediately obvious whether such modeling approaches should be based on the density or on the abundance in a stratum, and arguments can be offered to support either approach. Matsuoka et al (2011) found little difference in results for the two approaches for humpback whales. This is also the case for the Antarctic minke whale abundances and their trends as indicated in Table 13 of this paper.…”

“…This weakens the power of these data to detect such effects. For humpback whales, similarly no significant effect of survey mode and survey timing was detected (Matsuoka et al, 2011). Table 5 shows abundance trend estimates for equation ( 7)-( 10) in base case.…”

“…To be able to correct for biases in distance and angle estimation, a distance and angle estimation experiment was conducted on each vessel each year (Nishiwaki et al, 2006). The correction factors estimated for observed angles and distances for each vessel which are listed in Matsuoka et al (2011) have been used for these analyses. More details of the methodology for estimation of these correction factors may be found in Branch and Butterworth (2001).…”

Vocalizing humpback whales (Megaptera novaeangliae) migrating from Antarctic feeding grounds arrive earlier and earlier in the Perth Canyon, Western Australia

“…These animals spend November to May in Antarctica feeding on Antarctic krill (Euphausia superba) and taking advantage of the highly productive upwellings (Jenner et al, 2001;Bestley et al, 2019). Historic whaling records and satellite tags show that this population resides in the Antarctic International Whaling Commission (IWC) Management Area IV during this time (Jenner et al, 2001;Matsuoka et al, 2011;Bestley et al, 2019). Amongst others, the Southern Kerguelen Plateau is a hotspot for phytoplankton blooms, which consequently attracts high densities of humpback whales during the feeding season (Schallenberg et al, 2018;Bestley et al, 2019).…”