Non‐lethal entanglement of humpback whales (Megaptera novaeangliae) in fishing gear in northern Southeast Alaska

Abstract

Aim Entanglement in fishing gear is recognized as a potentially significant source of serious injury and mortality for humpback whales (Megaptera novaeangliae) in some parts of their range. In recent years, the number of humpback whales reported to have been entangled in Alaska has increased. In 2003-04 we quantified the prevalence of non-lethal entanglements of humpback whales in northern Southeast Alaska (SEAK) with the ultimate goal of informing management discussions of the entanglement issue for the Central North Pacific stock of humpback whales.Location The near-shore waters of northern Southeast Alaska.Methods We photographed individual humpback whales' caudal peduncles as they dived and then examined the photographs for scars indicative of a previous entanglement. ResultsThe percentage of whales assessed to have been non-lethally entangled at some time in their lives ranged from 52% (minimal estimate) to 71% (conditional estimate) to 78% (maximal estimate). Of these, the conditional estimate is recommended because it is based solely on unambiguous scars. Eight per cent of the whales in one portion of the study area (Glacier Bay/Icy Strait) acquired new entanglement scars between 2003 and 2004, although the sample size was small. Calves were less likely than older whales to have entanglement scars, and males may be at higher risk than females. Whales with more photographs and/or photographic coverage may be more likely to be assessed as having been entangled than whales with fewer photographs and/or coverage.Main conclusions Caudal peduncle scars reveal that the majority of humpback whales in northern SEAK have been entangled. Comparison with statistics on reported entanglements suggests that most whales apparently shed the gear on their own, unless humans are disentangling whales much more often than is reported. While cumulative estimates of the percentage of whales with entanglement scars (e.g. the conditional estimate) provide useful baseline information, future efforts should focus on monitoring the annual rate of entanglement scar acquisition as a more powerful measure of contemporary entanglement rates. Our findings indicate that entanglement of humpback whales in fishing gear in SEAK is a management issue warranting increased attention. A proactive approach is needed to address the problem and to identify and implement preventive measures.

Monitoring North Atlantic right whale Eubalaena glacialis entanglement rates: a 30 yr retrospective

“…A study of humpback whales in the North Atlantic found 64.9% of the population to have entanglement scarring when first assessed in 2003 and acquiring new scarring at an average annual rate of 12.1% (Robbins 2009). A study of humpback whales off southeast Alaska found 71% of that population to have entanglement scarring, with an annual acquisition rate of 8% between 2002 and 2003 (Neilson et al 2009). Other species of large whales also experience entanglement (Read et al 2006; see NOAA Stock Assessment Reports at www.nmfs.noaa.gov/pr/sars/), but there are relatively few studies with sufficiently detailed photo-identification data to assess population-wide and annual rates of entanglement.…”

Behavioral responses to fishing line entanglement of a juvenile bottlenose dolphin in Shark Bay, Australia

“…In addition to ingestion, entanglement in fishing gear can also result in death [16]. Studies of entanglement are usually based on necropsies or scarring [10] [16], but there are a few that have examined the impact of entanglement on cetacean behavior [17] [15] [18]. Virtually no studies have detailed behavioral changes based on observations of individuals before, during, and after entanglement.…”

“…Drift nets are estimated to kill thousands of dolphins (Delphinus delphis, Stenella coeruleoalba) in the Mediterranean each year [9]. The majority of humpback whales (Megaptera novaeangliae) in near-shore waters of northern Southeast Alaska bear scars of non-lethal entanglement [10]. Fishing gear entanglement is the leading cause of death for large whales in the Northwest Atlantic [11], and is one of the greatest threats to the critically endangered Mediterranean monk seal [12].…”

Fisheries as a source of marine debris on beaches in the United Kingdom

“…Debris collected from other North Sea coastlines such as Germany, the Netherlands, Belgium, France, Norway and Denmark, has been largely attributed to shipping and fishing activity (Galgani et al, 2000;van Franecker et al, 2005;Vauck and Schrey, 1987). Furthermore, fishing gear, operational as well as floating fragments, has been shown to cause entangling and mortality of marine animals (Derraik, 2002) including seabirds (Bugoni et al, 2008;Simeone et al, 1999;Stempniewicz, 1994;Votier et al, 2011;Zador et al, 2008), cetaceans (Johnson et al, 2005;Neilson et al, 2009;Ramos et al, 2011;Robbins and Matilla, 2004), turtles (Carr, 1987), sharks (Sazima et al, 2002) and seals (Hanni and Pyle, 2000;Hofmeyr et al, 2006;Page et al, 2004).…”