Photo-identification of fin whales (Balaenoptera physalus) along the US west coast, Baja California, and Canada
Falcone, E., B. Biehl, A. Douglas, and J. Calambokidis. 2011. Photo-identification of fin whales (Balaenoptera physalus) along the US west coast, Baja California, and Canada. Final report for order number JFI3F09SE516 from the Southwest Fisheries Science Center, La Jolla, CA.
The fin whale (Balaeanoptera physalus) is a large baleen whale with a broad geographic distribution. Fin whales were subjected to commercial whaling until the mid-twentieth century and were severely depleted throughout their range by the time they received protection in the late 1970’s (Mizroch et al. 1984). While there is evidence that many populations are recovering, the extent of recovery has varied regionally and proven difficult to quantify; based on capture records they likely remain far below pre-exploitation levels in all or most areas where they occur (Perry et al. 1999). Subsequently they remain listed under the United States Endangered Species Act and subject to regulation to encourage continued population growth (Reilly et al. 2008).
In general fin whales have proven more difficult to study than related species such as blue and humpback whales, and subsequently they are less well described throughout most of their range. Population assessments in many regions where they occur lack precision, related to several challenging aspects of their biology and life history. Not all fin whale populations appear to undergo predictable latitudinal seasonal migrations like most other large whales, a factor which complicates stock assessments in several regions, but particularly so in the North Pacific (Watkins et al. 2000). They tend to favor offshore habitat that is less accessible to routine surveys making data collection challenging and costly throughout much of their range (Reilly et al. 2008). Additionally, they are not as distinctively and consistently marked as some other large baleen whale species, for which photo-identification studies have proven invaluable in documenting population structure, size, and growth as well as migratory patterns. Despite these challenges, there are several populations in the world that are being studied with a variety of emerging methods, including photo-identification (Agler et al. 1993, Tershy et al. 1993, Zanardelli et al. 1992) and genetics (Bérubé et al. 1998). These better-known populations are mostly regionally isolated and/or in closer proximity to the coast (the Northeastern United States, the Mediterranean Sea, and the Sea of Cortez), and thus may not be representative of the species in other areas. Nevertheless, many of the methods being used are broadly applicable and can inform research in less studied regions.
The eastern North Pacific is a region where fin whales appear to be recovering in some areas, but for which data to document the extent of recovery are sparse (Mizroch et al. 2009). NOAA/NMFS currently recognizes three fin whale stocks in US waters based primarily on whaling data and the results of discovery tagging: the Northeast Pacific stock (including the Gulf of Alaska and Bering Sea), the California/Oregon/Washington stock (extending west 300 nmi), and the Hawaii stock (central North Pacific at lower latitudes, documented primarily acoustically) (Caretta et al. 2005). A comprehensive review of available North Pacific fin whale data by Mizroch et al. (2009) called into question the accuracy of these designations, and underscored the importance of incorporating additional data to better characterize the complex distribution of fin whales in the ocean basin. While genetic studies are currently underway as one means of addressing this, photo-identification is another low-impact method potentially available to document stock boundaries and trends.
Opportunistic photographs of fin whales have been collected by a number of research organizations during the course of other studies since the 1980’s (please see the acknowledgements section for contributor details). Cascadia Research Collective (Olympia, WA) is one such organization, and throughout this time had amassed an archive of fin whale photographs from the US West Coast, as well as smaller numbers of photos from peripheral regions including the pacific coast of Baja California, Mexico and the Queen Charlotte Islands, British Columbia. This collection grew considerably with the inception of an ongoing marine mammal study at the SCORE range beginning in 2006, an active naval training range centered around San Clemente Island approximately 100 nmi off the coast of southern California. Fin whales occur regularly in this offshore area, occasionally in dense aggregations, and this study has provided increased opportunities to collect photos of fin whales in recent years.
Historical photographs from this region had not been thoroughly cataloged previously in part because sample sizes were insufficient, but also because North Pacific fin whales appear to be even less distinctively marked than other studied populations making cataloging that much more difficult. In many other populations the blaze and chevron pigmentation patterns are reliably bright and well-defined, with enough individual variation to serve as a primary identifying feature along with the shape of the dorsal fin, which can vary considerably in fin whales (Agler et al. 1990). For many whales sighted along the US West Coast these pigmentations patterns are often muted and do not photograph well, and thus are not consistently available to match by. Part of any photo-ID study of these whales should ultimately involve a close look at mark rates, mark change, and the reliability of available features relied upon for matching, since other studies have shown many marks on fin whales to be transitory over sometimes relatively short periods (Agler et al. 1991).
The purpose of this contract has been to compile all available photographic data for fin whales from the US West Coast and adjacent areas through 2008, develop a reliable method for cataloging these whales which incorporates measures of both photo quality and individual distinctiveness, and internally reconcile these photographs into a catalog of unique individuals with an associated database of their sightings. Results presented here include resighting rates of individual whales both within and between designated regions and across years, and a preliminary assessment of regional variation in several physical characteristics.