Decreasing body lengths in North Atlantic right whales

Joshua D Stewart; John W Durban; Amy R Knowlton; Morgan S Lynn; Holly Fearnbach; Jacob Barbaro; Wayne L Perryman; Carolyn A Miller; Michael J Moore

doi:10.1016/j.cub.2021.04.067

Decreasing body lengths in North Atlantic right whales

Curr Biol. 2021 Jul 26;31(14):3174-3179.e3. doi: 10.1016/j.cub.2021.04.067. Epub 2021 Jun 3.

Authors

Joshua D Stewart¹, John W Durban², Amy R Knowlton³, Morgan S Lynn⁴, Holly Fearnbach⁵, Jacob Barbaro⁴, Wayne L Perryman⁴, Carolyn A Miller⁶, Michael J Moore⁶

Affiliations

¹ National Research Council Postdoctoral Fellow for Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla Shores Drive, La Jolla, CA, 92037, USA. Electronic address: joshua.stewart@noaa.gov.
² Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla Shores Drive, La Jolla, CA, 92037, USA; Southall Environmental Associates, Inc., Soquel Dr., Aptos, CA, 95003, USA.
³ Anderson Cabot Center for Ocean Life, New England Aquarium, Boston, MA, 02110, USA.
⁴ Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla Shores Drive, La Jolla, CA, 92037, USA.
⁵ Marine Mammal Research Program, SR3, SeaLife Response, Rehabilitation and Research, S 216th St., Des Moines, WA, 98198, USA.
⁶ Department of Biology, Woods Hole Oceanographic Institution, Woods Hole Rd., Woods Hole, MA, 02543, USA.

PMID: 34087102
DOI: 10.1016/j.cub.2021.04.067

Abstract

Whales are now largely protected from direct harvest, leading to partial recoveries in many previously depleted species.¹ However, most populations remain far below their historical abundances and incidental human impacts, especially vessel strikes and entanglement in fishing gear, are increasingly recognized as key threats.² In addition, climate-driven changes to prey dynamics are impacting the seasonal foraging grounds of many baleen whales.² In many cases these impacts result directly in mortality. But it is less clear how widespread and increasing sub-lethal impacts are affecting life history, individual fitness, and population viability. We evaluated changes in body lengths of North Atlantic right whales (NARW) using aerial photogrammetry measurements collected from crewed aircraft and remotely operated drones over a 20-year period (Figure 1). NARW have been monitored consistently since the 1980s and have been declining in abundance since 2011 due primarily to deaths associated with entanglements in active fishing gear and vessel strikes.³ High rates of sub-lethal injuries and individual-level information on age, size and observed entanglements make this an ideal population to evaluate the effects that these widespread stressors may have on individual fitness. We find that entanglements in fishing gear are associated with shorter whales, and that body lengths have been decreasing since 1981. Arrested growth may lead to reduced reproductive success⁴^,⁵ and increased probability of lethal gear entanglements.⁶ These results show that sub-lethal stressors threaten the recoveries of vulnerable whale populations even in the absence of direct harvest.

Keywords: cetaceans; drones; entanglements; photogrammetry; sub-lethal impacts.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Anthropogenic Effects*
Body Size*
Climate
Hunting
Unmanned Aerial Devices
Whales*