Amanda L. Bradford

Leaner leviathans: body condition variation in a critically endangered whale population

Abstract The role of environmental limitation and density-dependent regulation in shaping populations is debated in ecology. Populations at low densities may offer an unobstructed view of basic environmental and physiological interactions that impact individual fitness and thus population productivity. The energy reserves of an organism are reflected in its body condition, a measure linking individual fitness and the environment. From 1997 to 2007, we monitored the critically endangered western gray whale (Eschrichtius robustus) population on its primary summer feeding ground off the northeastern coast of Sakhalin Island, Russia. This effort resulted in a large data set of photo-identification images from 5,007 sightings of 168 individual whales that we used to visually assess western gray whale body condition. We quantified temporal variation in the resulting 1,539 monthly body condition determinations with respect to observations of reproductive status and sex. Western gray whale body condition varied annually, and we identified years of significantly better (2004) and worse (1999, 2006, and 2007) body condition. This study is the 1st to track the within-season body condition of individual whales. Body condition improved significantly as the summer progressed, although results suggest that not all whales replenish their energy stores by the end of the season. The body condition of lactating females was significantly worse than that of other whales at all times and was most often determined to be compromised. The body condition of their weaning calves exhibited no temporal variation and was consistently good. It is possible lactating females provide an energetic buffer to their offspring at the expense of their own body condition and future reproductive success. Findings from the analysis establish a foundation for quantifying links between western gray whale body condition, demographic parameters, and environmental conditions; and provide a baseline for monitoring individual and population condition of an ecosystem sentinel species in a changing environment. Overall, this study highlights the presence of density-independent environmental and physiological mechanisms that affect the abundance and growth of populations.

Critically endangered western gray whales migrate to the eastern North Pacific

Western North Pacific gray whales (WGWs), once considered extinct, are critically endangered with unknown migratory routes and reproductive areas. We attached satellite-monitored tags to seven WGWs on their primary feeding ground off Sakhalin Island, Russia, three of which subsequently migrated to regions occupied by non-endangered eastern gray whales (EGWs). A female with the longest-lasting tag visited all three major EGW reproductive areas off Baja California, Mexico, before returning to Sakhalin Island the following spring. Her 22 511 km round-trip is the longest documented mammal migration and strongly suggests that some presumed WGWs are actually EGWs foraging in areas historically attributed to WGWs. The observed migration routes provide evidence of navigational skills across open water that break the near-shore north–south migratory paradigm of EGWs. Despite evidence of genetic differentiation, these tagging data indicate that the population identity of whales off Sakhalin Island needs further evaluation.

Revised stock boundaries for false killer whales (Pseudorca crassidens) in Hawaiian waters

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Spotted seal haul-out patterns in a coastal lagoon on Sakhalin Island, Russia

Spotted seals (Phoca largha) are pagophilic seals distributed mainly in the Okhotsk, Bering, and Chukchi Seas (Shaughnessy and Fay 1977), but use coastal haul-outs during ice-free months (Burns 1970). These hauling areas are common in bays, estuaries, and river mouths, where spotted seals congregate near seasonally available and abundant prey, primarily spawning fishes (e.g., Tikhomirov 1961; Gol’tsev 1971; Makhnyr and Perlov 1988). Although the presence of spotted seals at coastal haul-outs can be continuous throughout the open water season (Frost et al. 1993), individual seals tend to spend relatively little time in these areas between extended near-shore foraging trips (Lowry et al. 1998). While annual habitat use patterns of spotted seals at sea have been documented (Lowry et al. 2000), haul-out patterns of seals summering in coastal regions are not well described. Spotted seals occur along the coast of Sakhalin Island, Russia, in the western Okhotsk Sea, during ice-free periods (Tikhomirov 1961; Kosygin et al. 1986; Lagarev 1988). Previous summer counts of spotted seals have suggested that nearly 10,000 seals use hauling areas on Sakhalin Island, which are found predominantly on the island’s eastern coast (Kosygin et al. 1986). Results presented here provide information on habitat use, numbers, and haul-out patterns of spotted seals in a coastal lagoon located on northeastern Sakhalin Island.

Injury determinations for marine mammals observed interacting with Hawaii and American Samoa longline fisheries during 2010--2014

Cetacean interactions (i.e., hookings and entanglements) with the Hawaii and American Samoa longline fisheries observed during 2007-2011 were compiled, and the number of cetacean deaths, serious injuries, and non-serious injuries by fishery, species, and management area assessed. These values form the basis of the mortality and serious injury estimates included in the Stock Assessment Reports of stocks impacted by these fisheries. Injury determinations were made using a revised process for distinguishing serious from non-serious injuries (NMFS, 2012). In the Hawaii deep-set fishery, 50 cetacean interactions were observed from 2007 to 2011; most involved false killer whales (48.0%), resulted in death or serious injury (73.5%), and occurred outside the U.S. EEZ (54.0%). In the Hawaii shallow-set fishery, 46 cetacean interactions were observed from 2007 to 2011; most involved Risso’s dolphins (45.7%), resulted in death or serious injury (77.2%), and occurred outside the U.S. EEZ (91.3%). In the American Samoa deep-set fishery, 14 cetacean interactions were observed from 2007 to 2011; most involved rough-toothed dolphins (42.9%), resulted in death or serious injury (92.9%), and occurred within the U.S. EEZ (85.7%).