Fishing gear entanglement threatens recovery of critically endangered North Atlantic right whales

Abstract

North Atlantic right whales frequently become entangled in fishing gear, which can negatively affect their reproductive output and probability of survival. We estimated individual whale health from a hierarchical Bayesian model fit to photographic indices of health. We reviewed 696 whales sighted from 1980 to 2011 and assigned 1196 entanglement events to 573 individuals in six categories of increasing injury severity and estimated monthly median health scores (0-100 scale) for the duration of their life within the study period. We then quantified the relationship between entanglement injury events and their severity with survival, reproduction, and population health. Severe entanglements resulted in worse health for all whales-males and females with severe injuries were eight times more likely to die than males with minor injuries. Females with severe injuries that survived had the lowest birth rates. Though the relationship between entanglement and fecundity was complex, we found that as the health of reproductively active females declined, their calving intervals increased.Unimpacted whale health scores declined significantly over three decades, 1980s, 1990s, and 2000s, suggesting food limitations may be contributing to population-wide health declines. Decadal health scores of entangled whales showed a more notable reduction in health suggesting a clear and perhaps synergistic effect.

Estimating the effects of stressors on the health, survival and reproduction of a critically endangered, long‐lived species

“…Our analysis found an association between the prey abundance index and health, suggesting that the protracted effects of limited prey could affect the ability of a female to reproduce in a given year and, if prolonged, even have consequences for survival. Vessel strikes and entanglements had the greatest immediate effect on the health of exposed individuals, causing a decline that could be rapidly lethal, with the ultimate outcome dependent on the severity of the event, consistent with Knowlton et al (2022). The only strike-related blunt wounds detected were associated with mortality (Sharp et al 2019), and the estimated drop in survival probability was strong enough to capture this lethal outcome.…”

“…Researchers at the New England Aquarium also collate and process information on anthropogenic traumas. Specifically, for all entanglements in fishing gear, data include when the injury was first detected, the last sighting pre-injury, whether fishing gear was still attached to the animal, the first subsequent sighting without gear (if gear was attached) and the severity of the injuries (minor, moderate or severe) (details in Knowlton et al 2012Knowlton et al , 2022. Similarly, for vessel strikes, data include the date of detection of an injury, the last sighting pre-injury and the type of injury (superficial, shallow or deep cuts, or blunt injury, which was scored if a necropsy found evidence of internal trauma).…”

“…Individuals are struck by vessels, which can lead to death or serious injury (Sharp et al 2019). They frequently get entangled in fishing gear, which can cause mortality (Knowlton et al 2012) or have sublethal effects depending on injury severity (Knowlton et al 2022). When fishing gear remains attached to the whale for prolonged periods of time, increased drag imposes additional locomotion and energetic costs that may compromise the ability to survive or reproduce successfully (van der Hoop et al 2017).…”

“…While several studies have detected changes in right whale vital rates associated with some of these stressors (Rolland et al 2016, Meyer‐Gutbrod et al 2021, Knowlton et al 2022), their effects have never been evaluated and compared within the same integrated model. In this study, we build upon the methods to estimate right whale health and anthropogenic effects in Schick et al (2013), Rolland et al (2016) and Knowlton et al (2022), using a 50‐year dataset of right whale sightings, calving events and exposure to stressors to inform a Bayesian state–space model for individual health, survival and reproduction. The model includes the effects of multiple key stressors on underlying health, allowing a direct comparison of their effects in the context of other life‐history events that may challenge an individual.…”

Decline in on-demand fishing gear costs with learning

“…Approaches including seasonal closures, weak links (in and between lines and buoys), sinking groundlines (lines between traps), and more traps per trawl may have helped -but have not solved -the problem of lethal entanglements (Pace et al, 2014;Baumgartner et al, 2019). Because of the increasing rate of serious entanglements (Knowlton et al, 2012;Henry et al, 2020;Knowlton et al, 2022) which often occur in endlines (Johnson et al, 2005; see entanglement reports at NOAA, 2022a), removal of these fixed lines by using on-demand fishing gear has been discussed as a potential solution (Baumgartner et al, 2019;Myers et al, 2019). The use of on-demand gear would provide an option to continue commercial lobster and crab fisheries while eliminating the threat of whale entanglement.…”