A review of post-whaling abundance, trends, changes in distribution and migration patterns, and supplementary feeding of Southern Hemisphere humpback whales

Abstract

Southern Hemisphere humpback whales (Megaptera novaeangliae) were heavily targeted during modern commercial whaling operations, with some 216,000 individuals killed between 1903 and 1973. That impacted the abundance of all the seven breeding stocks of the species. Most of these stocks have been recovering from whaling pressure although the understanding of the current growth rates of some stocks, and how the rates compare across stocks are lacking. Updated information is fundamental for understanding the species’ current status, and to support the review of management plans promoting its protection and recovery, especially considering current changes in ocean environments due to climate change. This work offers a comprehensive overview of the current knowledge on Southern Hemisphere humpback whales breeding stocks’ status. The aim is to provide information on their post-whaling growth trends and changes in distribution and migration patterns. Within that, records of supplementary feeding records (i.e. feeding beyond their formally described feeding grounds) are described. We have also identified knowledge gaps and note that the establishment of research collaborations, as well as standard methodologies for data collection can be important steps for the acquisition of better comparable data sets for the analysis of the current status of humpback whales and to fill such gaps. The compiled information provided can be used as part of an In-Depth Assessment of the species by the International Whaling Commission.

The Evolutionary History of Baleen Whales in The Genome Era

“…Therefore, our results probably reflect the abundance of humpback whales migrating to the western part (i.e., including mostly the South Atlantic and Pacific breeding populations) of the Southern Ocean. Recent estimates arrived at an abundance estimate of 47,119 humpback whales in the western part of the Southern Ocean (Seyboth et al, 2023), which corresponds to 61% of the pre-whaling abundance estimate obtained here. Using the growth rate estimated by Zerbini and colleagues (2019) for this region at 7% would imply that this population could be at pre-whaling abundance by 2045.…”

“…Estimates of pre-whaling humpback whale abundance in the Southeast Pacific are scarce, but a few assessments were performed based on catch records and recent abundance surveys (Félix et al, 2020;Warwick-Evans et al, 2022), which suggested a pre-whaling abundance at ~22,000, some three times lower than the genome-based estimates. Given recent post-whaling population surveys in the Southeast Pacific (Seyboth et al, 2023;Warwick-Evans et al, 2022) and a population annual growth rate of 5.5% (Félix et al, 2020), our findings suggest that the Southeast Pacific humpback whales would be currently at ~16% of their pre-whaling numbers and will likely reach pre-whaling levels only by 2056.…”

“…On the other hand, since the establishment of the first protection measures in the 20 th Century, some baleen whale populations appear to have recovered substantially with appreciable annual growth rates (IWC, 2018). For instance, humpback whale populations in both hemispheres have increased at high rates, and in some cases, likely back to the presumed pre-whaling levels of abundance (e.g., Barlow & Clapham, 1997;Bortolotto et al, 2016;Ford et al, 2009;Seyboth et al, 2023;Thomas et al, 2016;Zerbini et al, 2019). Some right whale populations (e.g., off South Africa) have also shown substantial growth (e.g., Stamation et al, 2020).…”