The recovery of North Atlantic right whales,Eubalaena glacialis, has been constrained by human-caused mortality

Abstract

North Atlantic right whales (NARW), Eubalaena glacialis, were nearly exterminated by historical whaling. Their abundance slowly increased up until 2010, to a maximum of fewer than 500 whales, and since then they have been in decline. We assessed the extent to which the relatively slow increase demonstrated by NARW was intrinsic, and how much could be due to anthropogenic impacts. In order to do so, we first compared calf counts of three populations of Southern right whales (SRW), E. australis, with that of NARW, over the period 1992–2016. By this index, the annual rate of increase of NARW was approximately one-third of that of SRW. Next we constructed a population projection model for female NARW, using the highest annual survival estimates available from recent mark–resight analysis, and assuming a four-year calving interval. The model results indicated an intrinsic rate of increase of 4% per year, approximately twice that observed, and that adult female mortality is the main factor influencing this rate. Necropsy records demonstrate that anthropogenic mortality is the primary cause of known mortality of NARW. Anthropogenic mortality and morbidity has limited the recovery of NARW, and baseline conditions prior to their recent decline were already jeopardizing NARW recovery.

Gross and histopathologic diagnoses from North Atlantic right whale Eubalaena glacialis mortalities between 2003 and 2018

“…NARWs have been legally protected under the US Endangered Species Act and Marine Mammal Protection Act for nearly 50 yr and the Canadian Species at Risk Act for 15 yr (DFO 2014). Despite this long-term protection, NARWs have experienced no ap preciable recovery, in contrast to their southern hemisphere counterpart, southern right whales E. australis (Cooke et al 2015, Bannister et al 2016, Findlay et al 2017, Corkeron et al 2018.…”

“…While a period of population growth for NARWs was documented around the turn of this century, in 2010 NARWs started to decrease in number once again , Pettis et al 2018. This decline has been attributed to a variety of factors, primarily low reproductive rates , Pettis et al 2018) and high mortality rates caused by entanglement in fishing gear and vessel strikes (Kraus 1990, Caswell et al 1999, van der Hoop et al 2013, Corkeron et al 2018, Kenney 2018. At the end of 2017, between 392 and 433 (95% confidence range; best estimate = 411) NARWs remained in the population (Pettis et al 2018, based on the methodology of Pace et al 2017).…”

“…NARW reproductive trends demonstrate increasing calving intervals, declining numbers of first-time dams (calving females), and declining percentage of available dams that calve , Pettis et al 2017a. In fact, the annual rate of increase of the NARW population between 1990 and 2016 was 2% (including the decline in abundance observed since 2010), which is only one-third that of their southernhemisphere counterparts (Corkeron et al 2018). While the etiology of poor population recovery in the NARW population, including factors such as repro-ductive failure, is uncertain, anthropogenic stressors such as sub-lethal chronic entanglement and ocean noise are suspected to be contributing factors (Tyack 2008, Rolland et al 2012, van der Hoop et al 2016).…”

Phenological changes in North Atlantic right whale habitat use in Massachusetts Bay

“…Beginning in 2011, the population trajectory shifted to a decline, with the estimated population in 2015 being 458 individuals (Pace et al, 2017). This decline is driven both by increased anthropogenic mortality and by decreased calving rates (Corkeron et al, 2018;Kraus et al, 2016;Pace et al, 2017). The current leading causes of mortality for right whales are entanglement in fishing gear and ship strikes (Johnson, Kraus, Kenney, & Mayo, 2007;Knowlton & Brown, 2007;Kraus et al, 2016).…”

“…The current leading causes of mortality for right whales are entanglement in fishing gear and ship strikes (Johnson, Kraus, Kenney, & Mayo, 2007;Knowlton & Brown, 2007;Kraus et al, 2016). The long-term survival of the species is now considered uncertain, both because of these direct impacts of human activity (Corkeron et al, 2018;Kraus et al, 2016;Pennisi, 2017) and longer term threats from changing distribution of food resources as a result of climate change (Meyer-Gutbrod & Greene, 2018).…”