Fin whale (Balaenoptera physalus) COSEWIC assessment and status report: chapter 9
Limiting Factors and Threats
Baleen whale populations are potentially affected by whaling, bycatch in fisheries, ship strikes, disease, and habitat degradation possibly due to altered prey quality or abundance as a result of fishing pressure or pollution (Clapham et al. 1999). Acoustic disturbance from shipping and industrial activities is another potential threat.
Factors that could limit the persistence and recovery of this species are primarily a reflection of the overall state of the oceans, and do not lend themselves well to management. These include primarily habitat degradation through reduced prey availability and reduced fitness from chemical pollution.
Reduced prey availability
Whale habitat is commonly associated with the distribution of prey (Gaskin 1982). For example, Whitehead and Carscadden (1985)showed how local whale abundance was related to capelin concentrations. Consequently any reduction in prey availability can be viewed as a reduction in available habitat. Available prey can be reduced in several ways including the direct and indirect effects of commercial fishing, climate change or inter-specific competition (see Inter-specific interactions, in the Biology section).
O'Shea and Brownell (1994) concluded that there was no evidence of toxic effects from metal or organochlorine contamination in baleen species (see also Sanpera et al. 1996), largely because they feed at relatively low trophic levels. However, other marine mammals are thought to be at risk from immunotoxic chemicals (Ross 2002). Effects that have been shown for marine mammals include depression of the immune system, reproductive impairment, lesions and cancers (Aguilar et al. 2002).
Concentrations of organochlorines sufficient to warrant concern were found in fin whale samples taken in the Gulf of St. Lawrence in 1991–92 (Gauthier et al. 1997). However, a retrospective analysis comparing these samples to earlier ones collected in 1971–72 off Newfoundland and Nova Scotia found that the St. Lawrence concentrations were significantly lower (Hobbs et al. 2001). This is consistent with the decreasing trends found for other marine mammals (principally pinnipeds) in eastern Canada (Hobbs et al. 2001), although Muir et al. (1999) found that organochlorine contaminants in cetaceans show both increasing and decreasing trends, depending on species and geographic location.
In the absence of large-scale commercial whaling, entanglement in fishing gear may be the most serious overall threat to baleen whales (Volgenau et al. 1995, Clapham et al. 1999). One difficulty in assessing the potential threat of entanglements is that many probably go unreported or unnoticed. In Newfoundland, reporting improved with the implementation in 1979 of a program to assist fishermen with entangled cetaceans (Lien 1994).
In Newfoundland, the most commonly entangled whale species are humpback and minke whales (Ledwell and Huntington 2002). Fin whales become entangled but less frequently (Lien 1994). Fatal entanglements have been documented by the Center for Coastal Studies (Bob Bowman, personal communication. Center for Coastal Studies, P.O. Box 1036, Provincetown, MA 02657), and there is also evidence of entanglement (not necessarily fatal) from photo-identification studies (Agler et al. 1990).
The recent development of an anchored gill net fishery in the Bay of Fundy is a potential concern. Three humpback whales were found entangled with this gear in September 2003 (Charles B. Schom, personal communication. Surge Inc. Unit C, 157 Water St., St. Andrews, NB, E5B 1A7). Seven fin whales were found entangled in lobster gear on the edge of the southern Scotian Shelf in 2003. However, cause of death was not determined and it is possible the animals became entangled after death (Jerry Conway, personal communication. Resource Management Branch, Department of Fisheries and Oceans, P.O. Box 1035, Dartmouth, NS, B2Y 4T3).
Many entanglements of other baleen whales involve the flukes, and this may also be true for fin whales (B. Bowman, personal communication). Unlike humpback whales, entanglement scars on the flukes and caudal peduncles of fin whales are difficult to document since fin whales rarely fluke up when diving.
In the Pacific the offshore driftnet fishery is the only fishery in which a fin whale death has been reported in U.S. waters (Carretta et al. 2002). Some gillnet entanglements may go unreported if whales swim away with attached gear. Also, Carretta et al. (2002) suggest the risk of entanglement for large whales is small because they appear to be able to swim through gear without becoming entangled or causing damage. Fin whales apparently are less likely to die from entanglement than most other cetacean species because of the relatively small size of their flippers and flukes, and because they are large enough to extricate themselves from gear when they do become entangled (Lien 1994).
In British Columbia, no fin whales were identified in cetacean stranding reports from 1990–1996 (Baird et al. 1991, Guenther et al. 1995, Willis et al. 1996), but several incidents of entangled unidentified large whales were reported. During a 2004 survey, a fin whale was observed off southeastern Moresby Island entangled in what appeared to be a crab-pot line (J.K.B. Ford, personal communication).
Most stranded or entangled cetaceans in British Columbia, Newfoundland and Labrador would likely go unseen and unreported because of the remoteness of much of these coasts, particularly if the entangled animal travelled away from fishing areas towing gear. Because of the relative sizes of the continental shelves, fin whales overlap less with coastal fisheries in the northeastern Pacific than in the northwestern Atlantic. Consequently, the potential for interactions with net fisheries is currently much lower for the Pacific population.
Most ship strikes occur with ships 80 m or longer travelling at 14 kts or faster, and fin whales are struck more frequently than other balaenopterids (Laist et al. 2001). A fin whale was struck in British Columbia in the summer of 1999 (Anonymous 2002), while in 2002, four arrived dead in Puget Sound on the bows of tankers (J. Calambokidis, personal communication). In June 2004, a dead floating fin whale was found off the west coast of Vancouver Island, apparently struck and killed by a ship (J.K.B. Ford, personal communication).
Fin whales have also been found dead on the bows of vessels entering Halifax Harbour (Paul Brodie, personal communication). In a 13-year period, 26% of stranded fin whales in the Mediterranean could be linked directly to ship strikes (Notarbartolo-Di-Sciara et al. 2003). Not all ship strikes are fatal. Pesante et al. (2000) found that 4% of animals in a photo-identification catalogue bore marks of ship encounters on their dorsal surface or fins.
Ship strikes are likely under-reported because struck and killed animals are apt to sink before they can be observed. There is also speculation that in regions of high ambient ship noise, animals may become habituated with a consequent reduction in avoidance behaviour (R. Sears, personal communication).
In British Columbia, port expansion is being considered near Vancouver to accommodate the largest “super” tankers (VPA 2004). Any increase in commercial vessel traffic and/or vessel size in British Columbia’s exposed shelf waters would be of concern for fin whales. A similar argument could be made for the St. Lawrence seaway, one of the busiest shipping routes on the continent, and for the approaches to Halifax Harbour.
Anthropogenic noise in the marine environment has increased substantially since the 1950s (Croll et al. 2001), and this rapid change in the acoustic environment may have profound implications for marine mammals that evolved in a much quieter environment (Tasker et al. 1998). The potential effects of noise on baleen whales include habituation, acoustic masking, avoidance behaviour, temporary hearing loss, and in extreme cases, permanent loss of hearing or other physiological damage (Croll et al. 2001).
Concern has primarily focused on industrial noise from offshore oil and gas developments. Numerous studies have documented behavioural responses-- primarily avoidance--to seismic surveys(Gordon et al. 1998). Fin whales were part of a study conducted by Stone (2003), who found that baleen whales were sighted less frequently and exhibited avoidance behaviour when air guns were firing. In addition, sei and fin whales tended to dive less during these times, possibly because received levels are lower near the surface than at depth(Richardson et al. 1995).
Canada’s first offshore production project began off Nova Scotia in 1992 (NSPD 2004). Environmental assessments relating to these projects concluded that the associated impact on marine mammals would be negligible to minor and short-term (Davis et al. 1998, Thomson et al. 2000). However many data gaps, particularly with respect to acoustic propagation (Gordon et al. 1998), remain unaddressed.
In British Columbia, concerns regarding oil and gas exploration are relatively new. A recent Royal Society panel (RSC 2004) recommended the lifting of a 30-year moratorium on exploration. However, the panel outlined a rigorous regulatory regime and highlighted the importance of filling numerous data gaps, including the collection of baseline data, and the definition of critical habitat for endangered marine species, prior to commencement of exploratory activities. This is of particular interest for fin whales since areas where they occur in relatively high densities overlap with areas with high hydrocarbon potential.
Threats to populations from whaling persist. Fin whales are still hunted in Greenland under the IWC’s Aboriginal subsistence whaling exemption. Also, Iceland has expressed interest in resuming whaling for fin whales.
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