Entanglement is a costly life‐history stage in large whales

Abstract

Individuals store energy to balance deficits in natural cycles; however, unnatural events can also lead to unbalanced energy budgets. Entanglement in fishing gear is one example of an unnatural but relatively common circumstance that imposes energetic demands of a similar order of magnitude and duration of life‐history events such as migration and pregnancy in large whales. We present two complementary bioenergetic approaches to estimate the energy associated with entanglement in North Atlantic right whales, and compare these estimates to the natural energetic life history of individual whales. Differences in measured blubber thicknesses and estimated blubber volumes between normal and entangled, emaciated whales indicate between 7.4 × 1010 J and 1.2 × 1011 J of energy are consumed during the course to death of a lethal entanglement. Increased thrust power requirements to overcome drag forces suggest that when entangled, whales require 3.95 × 109 to 4.08 × 1010 J more energy to swim. Individuals who died from their entanglements performed significantly more work (energy expenditure × time) than those that survived; entanglement duration is therefore critical in determining whales’ survival. Significant sublethal energetic impacts also occur, especially in reproductive females. Drag from fishing gear contributes up to 8% of the 4‐year female reproductive energy budget, delaying time of energetic equilibrium (to restore energy lost by a particular entanglement) for reproduction by months to years. In certain populations, chronic entanglement in fishing gear can be viewed as a costly unnatural life‐history stage, rather than a rare or short‐term incident.

Multi-year longitudinal profiles of cortisol and corticosterone recovered from baleen of North Atlantic right whales (Eubalaena glacialis)

“…Elevated baleen corticosterone concentration could be related to the energetic burden of lactation or of recovery during the following year; lactation is known to be an energetically expensive state for large whales (Fortune et al, 2013;van der Hoop et al, 2017). Cortisol showed a similar pattern in (Carballeira et al, 1987).…”

“…(2) Does either hormone show any indication of degradation in older baleen at the tip of the plate (i.e., poorer assay parallelism)? (3) Does either glucocorticoid show elevations that coincide with known energetically-expensive states, such as pregnancy and lactation (Fortune et al, 2013, van der Hoop et al, 2017? (4) What are the relative concentrations of cortisol and corticosterone in baleen?…”

Assessing cetacean body condition: Is total lipid content in blubber biopsies a useful monitoring tool?

“…Many baleen whale populations are still listed as Endangered under the International Union for Conservation of Nature's Red List, and most of the 22 beaked whale species are currently listed as Data Deficient. For baleen whales specifically, which undertake long migrations between high-latitude feeding grounds and low-latitude breeding grounds (Lockyer, 2007), entanglement in fishing gear is now almost ubiquitous in some populations (Neilson, Straley, Gabriele, & Hills, 2009;Robbins, Knowlton, & Landry, 2015;van der Hoop, Corkeron, & Moore, 2016). For baleen whales specifically, which undertake long migrations between high-latitude feeding grounds and low-latitude breeding grounds (Lockyer, 2007), entanglement in fishing gear is now almost ubiquitous in some populations (Neilson, Straley, Gabriele, & Hills, 2009;Robbins, Knowlton, & Landry, 2015;van der Hoop, Corkeron, & Moore, 2016).…”

Automated detection and tracking of marine mammals: A novel sonar tool for monitoring effects of marine industry

“…Many of the activities associated with these industries pose acute risks to marine wildlife; for example, marine mammals can be injured or killed as a result of vessel collisions (Vanderlaan & Taggart, 2007), fisheries gear entanglement (van der Hoop, Corkeron, & Moore, 2017), and fisheries bycatch (Read, Drinker, & Northridge, 2006). In many cases, the nature and extent of these interactions can have important consequences for the demographics of affected populations and endanger the existence of some species (Read et al, 2006).…”