Abstract
Vessel strike is recognized as a major modern threat to the recovery of large whale populations globally, but the issue is notoriously difficult to assess. Vessel strikes by large ships frequently go unnoticed, and those involving smaller vessels are rarely reported. Interpreting global patterns of vessel strikes is further hindered by underlying reporting biases caused by differences in countries’ research efforts, legislation, reporting structures and enforcement. This leaves global strike data “patchy” and typically scarce outside of developed countries, where resources are more limited. To explore this we investigated vessel strikes with large whales in the Eastern Tropical Pacific (ETP), a coastal region of ten developing countries where heavy shipping and high cetacean densities overlap. Although this is characteristic of vessel strike “hotspots” worldwide, only 11 ETP strike reports from just four countries (∼2% of total reports) existed in the International Whaling Commission’s Global Ship Strike Database (2010). This contrasts greatly with abundant reports from the neighboring state of California (United States), and the greater United States/Canadian west coast, making it a compelling case study for investigating underreporting. By reviewing online media databases and articles, peer review publications and requesting information from government agencies, scientists, and tourism companies, we compiled a regional ETP vessel strike database. We found over three times as many strike reports (n= 40), from twice as many countries (n= 8), identifying the geographic extent and severity of the threat, although likely still underestimating the true number of strikes. Reports were found from 1905 until 2017, showing that strikes are a regional, historic, and present threat to large whales. The humpback whale (Megaptera novaeangliae) was the most commonly hit species, and whale-watch industries involving small vessels in areas of high whale densities were recognized as a conservation and management concern. Industrial fishing fleets and shipping were suggested to be underrepresented sectors in the database, and are likely high-risk vessels for strikes with whales. We demonstrate the implications of known vessel strike reporting biases and conclude a more rapid assessment of global vessel strikes would substantially benefit from prioritized research efforts in developing regions, with known vessel strike “hotspot” characteristics, but few strike reports.
Highlights
Intensive commercial harvesting of large whales in the nineteenth and twentieth century reduced most populations to a fraction of their original size, and left many species on the brink of extinction (Clapham et al, 1999)
While vessel strike can threaten the recovery of large whale populations, it is small and endangered whale populations that are most vulnerable to anthropogenic threats (Clapham et al, 1999; Cates et al, 2017)
We found evidence for 13 new vessel strike reports with large whales prior to 2010 that were not reported in the International Whaling Commission (IWC) (2010) database (32.5%), and evidence of 16 vessel strikes (40%) that have occurred since
Summary
Intensive commercial harvesting of large whales in the nineteenth and twentieth century reduced most populations to a fraction of their original size, and left many species on the brink of extinction (Clapham et al, 1999). Vessel strike and entanglement are considered to be the two major modern threats to large whales at the population level (Thomas et al, 2016). While vessel strike can threaten the recovery of large whale populations (e.g., the North Pacific blue whale, Balaenoptera musculus, Carretta et al, 2015; Rockwood et al, 2017), it is small and endangered whale populations (or population segments) that are most vulnerable to anthropogenic threats (Clapham et al, 1999; Cates et al, 2017). For the critically endangered North Atlantic right whale, 45% (n = 39) of diagnosed mortalities between 1970 and 2010 were attributed to vessel strike, and it was recognized as the major threat to the survival of the species (Van der Hoop et al, 2013). An additional concern is the welfare of the whales that (initially) survive a strike, with numerous reports globally of large whales exhibiting severe injuries believed to have been caused by vessels (Kraus, 1990; Osmond and Kaufman, 1998; Laist et al, 2001; Van Waerebeek et al, 2007; Neilson et al, 2012), which likely caused suffering for extended periods
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