Bruce R. Mate

Tracking apex marine predator movements in a dynamic ocean

Pelagic marine predators face unprecedented challenges and uncertain futures. Overexploitation and climate variability impact the abundance and distribution of top predators in ocean ecosystems. Improved understanding of ecological patterns, evolutionary constraints and ecosystem function is critical for preventing extinctions, loss of biodiversity and disruption of ecosystem services. Recent advances in electronic tagging techniques have provided the capacity to observe the movements and long-distance migrations of animals in relation to ocean processes across a range of ecological scales. Tagging of Pacific Predators, a field programme of the Census of Marine Life, deployed 4,306 tags on 23 species in the North Pacific Ocean, resulting in a tracking data set of unprecedented scale and species diversity that covers 265,386 tracking days from 2000 to 2009. Here we report migration pathways, link ocean features to multispecies hotspots and illustrate niche partitioning within and among congener guilds. Our results indicate that the California Current large marine ecosystem and the North Pacific transition zone attract and retain a diverse assemblage of marine vertebrates. Within the California Current large marine ecosystem, several predator guilds seasonally undertake north–south migrations that may be driven by oceanic processes, species-specific thermal tolerances and shifts in prey distributions. We identify critical habitats across multinational boundaries and show that top predators exploit their environment in predictable ways, providing the foundation for spatial management of large marine ecosystems.

Blue whale habitat and prey in the California Channel Islands

Abstract Whale Habitat and Prey Studies were conducted off southern California during August 1995 (WHAPS95) and July 1996 (WHAPS96) to (1) study the distribution and activities of blue whales and other large whales, (2) survey the distribution of prey organisms (krill), and (3) measure physical and biological habitat variables that influence the distribution of whales and prey. A total of 1307 cetacean sightings included 460 blue whale, 78 fin whale and 101 humpback whale sightings. Most blue whales were found in cold, well-mixed and productive water that had upwelled along the coast north of Point Conception and then advected south. They were aggregated in this water near San Miguel and Santa Rosa Islands, where they fed on dense, subsurface layers of euphausiids both on the shelf and extending off the shelf edge. Two species of euphausiids were consumed by blue whales, Thysanoessa spinifera and Euphausia pacifica , with evidence of preference for the former, a larger and more coastal species. These krill patches on the Channel Island feeding grounds are a resource exploited during summer–fall by the world’s largest stock of blue whales.

Cumulative human impacts on marine predators

Stressors associated with human activities interact in complex ways to affect marine ecosystems, yet we lack spatially explicit assessments of cumulative impacts on ecologically and economically key components such as marine predators. Here we develop a metric of cumulative utilization and impact (CUI) on marine predators by combining electronic tracking data of eight protected predator species (n=685 individuals) in the California Current Ecosystem with data on 24 anthropogenic stressors. We show significant variation in CUI with some of the highest impacts within US National Marine Sanctuaries. High variation in underlying species and cumulative impact distributions means that neither alone is sufficient for effective spatial management. Instead, comprehensive management approaches accounting for both cumulative human impacts and trade-offs among multiple stressors must be applied in planning the use of marine resources.

Satellite-monitored movements of the northern right whale

The northern right whale, Eubalaena glacialis, remains the most critically endangered of the large cetaceans despite international protection since 1936. We used satellite-monitored radiotags to identify the late-summer and fall habitat use patterns of right whales in the western North Atlantic. We tagged 9 whales in the Bay of Fundy (BOF) and successfully tracked them for a total of 13,910 km (x = 1,546 km) in 195 whale-tracking days (range 7-42 days each, x = 21.7 days). Individuals tracked for more than 12 consecutive days (N = 6 whales) left the BOF at least once and had higher average speeds (x = 3.5 km/hr) than those that stayed within the bay (x = 1.1 km/hr). Three of the tagged whales not only left the BOF, but traveled more than 2,000 km each before returning to the general tagging area. One adult female with a calf went to New Jersey and back to the BOF (3,761 km) in 42 days. Most locations were along bank edges, in basins or along the continental shelf. Eighty percent of locations were in water <182 m (100 fathoms [F]) deep. All of the tagged whales were located in or near shipping lanes. Right whale distribution coincided with areas intensively used by humans for fishing, shipping, and recreation. Individuals moved rapidly among areas previously identified as right whale habitat. Whale locations plotted on sea surface temperature (satellite infrared) images suggest that one whale spent time at the edge of a warm core ring and others spent extended periods in upwellings. Observations of whales surfacing with mud on their heads suggest that these whales fed near the BOF seafloor. Satellite telemetry is a useful means of tracking cetacean species that are difficult to view, move long distances, and might be too expensive to monitor by other means.

North Atlantic right whales, Eubalaena glacialis, exposed to paralytic shellfish poisoning (PSP) toxins via a zooplankton vector, Calanus finmarchicus

Abstract The seriously endangered north Atlantic right whale ( Eubalaena glacialis ) is regularly exposed to the neurotoxins responsible for paralytic shellfish poisoning (PSP) through feeding on contaminated zooplankton acting as a vector of these dinoflagellate toxins. This chronic exposure occurs during several months each summer while the whales are present on their late summer feeding ground in Grand Manan Basin in the lower Bay of Fundy. Based on estimated ingestion rates, we suggest that these toxins could affect respiratory capabilities, feeding behavior, and ultimately the reproductive condition of the whale population.

Association Between Blue Whale (Balaenoptera musculus) Mortality and Ship Strikes Along the California Coast

Blue whales (Balaenoptera musculus) are distributed worldwide, and although severely depleted by commercial whaling, their abundance off the California coast now appears to be increasing. Little is known about natural causes of mortality of blue whales, but human-related mortality continues despite legal protection. Ship strikes are a significant mortality factor for other species of baleen whale, and changes in shipping traffic have been advocated to minimize further deaths. Between 1988 and 2007, 21 blue whale deaths were reported along the California coast, typically one or two cases annually. Three pulses in strandings were observed, with three carcasses observed in fall 1988, three in 2002, and four in fall 2007. Two of the four animals in 2007 were first observed dead in the Santa Barbara Channel and had wounds typical of a ship strike. Blue whale strandings were spatially associated with locations of shipping lanes, especially those associated with the Ports of Los Angeles and Long Beach, and were most common in the fall months.

Spatial and Temporal Occurrence of Blue Whales off the U.S. West Coast, with Implications for Management

Mortality and injuries caused by ship strikes in U.S. waters are a cause of concern for the endangered population of blue whales (Balaenoptera musculus) occupying the eastern North Pacific. We sought to determine which areas along the U.S. West Coast are most important to blue whales and whether those areas change inter-annually. Argos-monitored satellite tags were attached to 171 blue whales off California during summer/early fall from 1993 to 2008. We analyzed portions of the tracks that occurred within U.S. Exclusive Economic Zone waters and defined the ‘home range’ (HR) and ‘core areas’ (CAU) as the 90% and 50% fixed kernel density distributions, respectively, for each whale. We used the number of overlapping individual HRs and CAUs to identify areas of highest use. Individual HR and CAU sizes varied dramatically, but without significant inter-annual variation despite covering years with El Niño and La Niña conditions. Observed within-year differences in HR size may represent different foraging strategies for individuals. The main areas of HR and CAU overlap among whales were near highly productive, strong upwelling centers that were crossed by commercial shipping lanes. Tagged whales generally departed U.S. Exclusive Economic Zone waters from mid-October to mid-November, with high variability among individuals. One 504-d track allowed HR and CAU comparisons for the same individual across two years, showing similar seasonal timing, and strong site fidelity. Our analysis showed how satellite-tagged blue whales seasonally used waters off the U.S. West Coast, including high-risk areas. We suggest possible modifications to existing shipping lanes to reduce the likelihood of collisions with vessels.

Long-range movement of humpback whales and their overlap with anthropogenic activity in the South Atlantic Ocean.

Humpback whales (Megaptera novaeangliae) are managed by the International Whaling Commission as 7 primary populations that breed in the tropics and migrate to 6 feeding areas around the Antarctic. There is little information on individual movements within breeding areas or migratory connections to feeding grounds. We sought to better understand humpback whale habitat use and movements at breeding areas off West Africa, and during the annual migration to Antarctic feeding areas. We also assessed potential overlap between whale habitat and anthropogenic activities. We used Argos satellite-monitored radio tags to collect data on 13 animals off Gabon, a primary humpback whale breeding area. We quantified habitat use for 3 cohorts of whales and used a state-space model to determine transitions in the movement behavior of individuals. We developed a spatial metric of overlap between whale habitat and models of cumulative human activities, including oil platforms, toxicants, and shipping. We detected strong heterogeneity in movement behavior over time that is consistent with previous genetic evidence of multiple populations in the region. Breeding areas for humpback whales in the eastern Atlantic were extensive and extended north of Gabon late in the breeding season. We also observed, for the first time, direct migration between West Africa and sub-Antarctic feeding areas. Potential overlap of whale habitat with human activities was the highest in exclusive economic zones close to shore, particularly in areas used by both individual whales and the hydrocarbon industry. Whales potentially overlapped with different activities during each stage of their migration, which makes it difficult to implement mitigation measures over their entire range. Our results and existing population-level data may inform delimitation of populations and actions to mitigate potential threats to whales as part of local, regional, and international management of highly migratory marine species.

Controlled and in situ target strengths of the jumbo squid Dosidicus gigas and identification of potential acoustic scattering sources

This study presents the first target strength measurements of Dosidicus gigas, a large squid that is a key predator, a significant prey, and the target of an important fishery. Target strength of live, tethered squid was related to mantle length with values standardized to the length squared of -62.0, -67.4, -67.9, and -67.6 dB at 38, 70, 120, and 200 kHz, respectively. There were relatively small differences in target strength between dorsal and anterior aspects and none between live and freshly dead squid. Potential scattering mechanisms in squid have been long debated. Here, the reproductive organs had little effect on squid target strength. These data support the hypothesis that the pen may be an important source of squid acoustic scattering. The beak, eyes, and arms, probably via the sucker rings, also play a role in acoustic scattering though their effects were small and frequency specific. An unexpected source of scattering was the cranium of the squid which provided a target strength nearly as high as that of the entire squid though the mechanism remains unclear. Our in situ measurements of the target strength of free-swimming squid support the use of the values presented here in D. gigas assessment studies.

Striking the right balance in right whale conservation

Despite many years of study and protection, the North Atlantic right whale (Eubalaena glacialis) remains on the brink of extinction. There is a crucial gap in our understanding of their habitat use in the migratory corridor along the eastern seaboard of the United States. Here, we characterize habitat suitability in migrating right whales in relation to depth, distance to shore, and the recently enacted ship speed regulations near major ports. We find that the range of suitable habitat exceeds previous estimates and that, as compared with the enacted 20 nautical mile buffer, the originally proposed 30 nautical mile buffer would protect more habitat for this critically endangered species.