Vol. 96: 175–185, 2011 DISEASES OF AQUATIC ORGANISMS Published October 6 doi: 10.3354/dao02385 Dis Aquat Org OPENPEN ACCESSCCESS FEATURE ARTICLE Lethal entanglement in baleen whales Rachel M. Cassoff1,7, Kathleen M. Moore2, William A. McLellan3, Susan G. Barco4, David S. Rotstein5, Michael J. Moore6,* 1University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania 19104, USA 2International Fund for Animal Welfare, Yarmouthport, Massachusetts 02675, USA 3Biology and Marine Biology, University of North Carolina, Wilmington, North Carolina 28403, USA 4Virginia Aquarium & Marine Science Center Stranding Response Program, Virginia Beach, Virginia 23451, USA 5Smithsonian Museum Support Center, Osteoprep Laboratory, 4210 Silver Hill Road, Suitland, Maryland 20746, USA 6Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA 7Present address: Duke University Marine Laboratory, Beaufort, North Carolina 28516, USA ABSTRACT: Understanding the scenarios whereby fishing gear entanglement of large whales induces mortality is important for the development of mitiga- tion strategies. Here we present a series of 21 cases involving 4 species of baleen whales in the NW Atlantic, describing the available sighting history, necropsy observations, and subsequent data analyses that enabled the compilation of the manners in which entanglement can be lethal. The single acute cause of entanglement mortality identified was drowning from entanglement involving multiple body parts, with the animal’s inability to surface. More protracted causes of death included impaired foraging during entangle- ment, resulting in starvation after many months; sys- Location, recovery, beaching, necropsy and disposal of large temic infection arising from open, unresolved entan- dead whales pose unique challenges. However, examination glement wounds; and hemorrhage or debilitation due of chronically entangled whale mortalities enables mitigation by modification of fishing gear and practices. to severe gear-related damage to tissues. Serious gear-induced injury can include laceration of large Photo: Cynthia Browning vessels, occlusion of the nares, embedding of line in growing bone, and massive periosteal proliferation of new bone in an attempt to wall off constricting, encir- INTRODUCTION cling lines. These data show that baleen whale entan- glement is not only a major issue for the conservation The rapid expansion of global fisheries since the of some baleen whale populations, but is also a major turn of the last century has led to an increasingly concern for the welfare of each affected individual. large presence of fishing gear in baleen whale (mys- ticete) habitat (Myers & Worm 2003, Pauly 2009). KEY WORDS: Baleen whales · Entanglement · Since many baleen whale populations inhabit and Mortality · Cetacean · Strandings · Fishing gear · migrate across continental shelf waters, where >95% Necropsy · Northwestern Atlantic of fishing effort occurs, they are at serious risk of encountering and becoming entangled in gear (Pauly Resale or republication not permitted without written consent of the publisher 2009). While many baleen whales are able to release *Corresponding author. Email: [email protected] © Inter-Research 2011 · www.int-res.com 176 Dis Aquat Org 96: 175–185, 2011 themselves from fishing line or net, as evidenced by tent with entanglement (Wiley et al. 1995). In addi- scarring patterns on many individuals (Knowlton et tion, 57% of humpback whales observed in the Gulf al. 2005), the outcome of entanglement can include of Maine had entanglement scars on their caudal long-term severe injury and mortality. peduncle (Robbins & Mattila 2004). For stocks in Worldwide, fatal entanglements are a source of some areas, such as the Gulf of Maine, entanglement non-natural mortality in baleen whale populations, mortality is slowing rates of recovery (Volgenau et al. many of which are at low levels of abundance due to 1995). intensive commercial whaling efforts during the past Baleen whales are unique compared to other, 2 centuries (Perrin et al. 1994, Clapham et al. 1999). smaller cetaceans, in that entanglement mortality of- Exacerbating this problem is the fact that entangle- ten results from chronic pathological processes, rather ment mortality and its effects on population trends than drowning. During an encounter with fishing are likely greatly underestimated, due to underre- gear, baleen whales often have enough strength to porting by fishermen and a low probability of discov- break away from the lines and initially evade death. ery and recovery at sea (Cole et al. 2006). Most bal- However, a portion of the gear may remain affixed to aenopterid carcasses (e.g. blue, Bryde’s, fin, minke, one or more body parts, commonly the mouth, flippers and sei whales), regardless of body condition, ini- and caudal peduncle (Lien 1994, Johnson et al. 2007). tially sink upon death and then only refloat later if The whale can become further entangled in this re- they bloat. In contrast, balaenid whales (e.g. right maining gear, constricting body parts as the animal whales) and some humpback whales (family Balaen- struggles to free itself or flexes and extends its body opteridae) that are in good body condition typically during swimming (Weinrich 1999). float. Some entangled right whale carcasses can be Not only can entanglement directly impair loco - negatively buoyant due to emaciation at the time of motion and foraging ability, leading to starvation, death, after which point they may either bloat from but it can also cause debilitating injury to tissues decomposition and then resurface, or remain sub- through physical trauma, constriction, or immobiliza- merged (Moore et al. 2007). tion (Knowl ton et al. 2005, Moore et al. 2006). Serious In the western North Atlantic, entanglement mor- and debilitating tissue damage caused by attached tality has slowed the recovery of some populations of gear likely plays a major role in the pathogenesis of baleen whales. The most severely affected species is fatal chronic entanglement in baleen whales. Many the Critically Endangered North Atlantic right whale of the chronic traumatic entanglement injuries are Eubalaena glacialis (NARW). Despite over 75 yr of deep and extensive, penetrating through multiple legal protection, the NARW has an estimated popula- tissue layers and involving several areas of the body. tion of between 400 and 450, making it one of the In a study of all existing necropsy reports for lethally rarest baleen whale species in the world (Kraus et al. entangled western NARWs for a 30 yr period (Moore 2005, Josephson et al. 2009). A recent analysis of et al. 2004), it was found that every whale had sus- photo-identified NARWs found that >75% of the tained gear-induced wounds that penetrated at least population had scars from a previous entanglement to the level of the dermis. In one case, fishing line had in fishing gear and that some of these animals had wrapped so tightly around the flippers that it had cut experienced as many as 6 separate entanglement through all of the soft tissues, eventually embedding events. Annual rates of entanglement are also on the several centimeters into the bone. In another case, rise (Knowlton et al. 2005). A minority of gear entan- line had become anchored to both flippers and grad- glements of NARWs resulted in mortality. Of the ually excised a 1.5-m-wide section of blubber across 50 reported deaths of this species between 1986 the dorsum. Additionally, there have been 2 reported and 2002, there were 18 (6 confirmed and 12 pre- cases of entangled NARWs with severe constriction sumed) cases of fatal gear entanglement (Moore et of the flippers, resulting in immobilization and disuse al. 2004, Kraus et al. 2005). Human-caused mortality osteoporosis (Moore et al. 2006). of NARWs continues to be a serious problem (Cas - Gear-induced wounds can lead to death by impair- well et al. 1999, Fujiwara & Caswell 2001). ing critical biological functions, becoming a source In the Northwest Atlantic, entanglement in fishing of hemorrhage, or providing a portal of entry for gear is also a significant source of mortality for pathogens. Thirty years of longitudinal observations endangered humpback whales Megaptera novaean- of NARWs (Knowlton & Kraus 2001) showed that gliae. Five out of the 38 (16%) humpback whales that serious (deeply penetrating or infected/necrotic) tis- stranded in the mid-Atlantic to southeastern states of sue damage associated with entanglement injuries the USA between 1985 and 1992 had injuries consis- was likely to be a predictor of mortality. Cassoff et al.: Lethal entanglement of whales 177 The progression to death due to entanglement, straight distance from the tip of the snout to the fluke particularly when it involves severe gear-induced tis- notch), total body weight, and a description of car- sue damage, is likely to be slow and painful. There- cass quality. Age or age class was reported as either fore, from a welfare perspective, lethal entangle- the minimum known age based on sighting histories ments of baleen whales are, arguably, one of the archived in the NARWC sightings database main- worst forms of human-caused mortality in any wild tained at the New England Aquarium, or estimated animal. Moore et al. (2006) examined 6 cases of age based on published growth curves (Stevick 1999, lethally entangled NARWs and found that the aver- Olsen & Sunde 2002, Moore et al. 2004). Total body age time to death was 5.6 mo. However, some whales weight