Between 20 and 24 marine extinctions, ranging from algal to mammal species, have occurred over th... more Between 20 and 24 marine extinctions, ranging from algal to mammal species, have occurred over the past 500 years. These relatively low numbers question whether the sixth mass extinction that is underway on land is also occurring in the ocean. There is, however, increasing evidence of worldwide losses of marine populations that may foretell a wave of oncoming marine extinctions. A review of current methods being used to determine the loss of biodiversity from the world’s oceans reveals the need to develop and apply new assessment methodologies that incorporate standardized metrics that allow comparisons to be made among different regions and taxonomic groups, and between current extinctions and past mass extinction events. Such efforts will contribute to a better understanding of extinction risk facing marine flora and fauna, as well as the ways in which it can be mitigated.
The Puzzling Disappearance of Sea Lions in Alaska : Is the North Pacific Ecosystem on the Verge of Collapse?
Science, Faculty ofOceans and Fisheries, Institute for theUnreviewedFacult
New insights into the Quileute whalers of Washington State from ecology and archaeology
Archaeological data from Washington State indicate that northern fur seals will likely once again be a dominant predator in the California Current System
Additional file 1: of Fine-scale foraging movements by fish-eating killer whales (Orcinus orca) relate to the vertical distributions and escape responses of salmonid prey (Oncorhynchus spp.)
Impacts of harbour seals on Chinook and coho salmon in the Strait of Georgia
Historically, Chinook and coho were two of the most valuable commercial and recreational salmon s... more Historically, Chinook and coho were two of the most valuable commercial and recreational salmon species in western North America, particularly in the Salish Sea. However, marine survival rates of these species have declined dramatically since the 1970s as numbers of harbour seals increased. This correlation has led some scientists to hypothesize that seal predation may be impeding the recovery of Chinook and coho salmon, primarily because reduced exploitation rates over past decades have not returned them to historic abundances. While seal consumption of adult salmon has been quantified in past studies, few attempts have been made to estimate predation on out-migrating smolts. Most existing estimates of predation on juveniles are based on the presence/absence of hard structures in seal fecal material, which cannot determine salmon species and are susceptible to biases associated with survival of diagnostic hard structures during the digestion process. Here, DNA-based diet data is combined with several modeling approaches to estimate annual seal consumption of juvenile salmon in the Strait of Georgia. Results suggest that seal predation on juvenile Chinook and coho may be responsible for up to half of the total natural mortality experienced by these species during the early marine stage. Estimates of mortality from this analysis will inform predator-prey models that could be used to test alternative management strategies that may facilitate recovery of key populations of salmon
1 Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Colu... more 1 Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, BC V6T 1Z4, Canada Corresponding author: [email protected] 2 Transient Killer Whale Research Project, Victoria, BC V8V 3A1 3 Marine Life Studies, Moss Landing, California 95039 4 Southwest Fisheries Science Center, National Oceanic and Atmospheric Administration, La Jolla, California, USA
Canadian Journal of Fisheries and Aquatic Sciences, 2021
The decline of southern resident killer whales (Orcinus orca) may be due to a shortage of prey, b... more The decline of southern resident killer whales (Orcinus orca) may be due to a shortage of prey, but there is little data to test this hypothesis. We compared the availability of prey (Chinook salmon, Oncorhynchus tshawytscha) sought by southern residents in Juan de Fuca Strait during summer with the abundance and distribution of Chinook available to the much larger and growing population of northern resident killer whales feeding in Johnstone Strait. We used ship-based multifrequency echosounders to identify differences in prey fields that may explain the dynamics of these two killer whale populations. Contrary to expectations, we found that both killer whale habitats had patchy distributions of prey that did not differ in their frequencies of occurrence, nor in the size compositions of individual fish. However, the density of fish within each patch was 4–6 times higher in the southern resident killer whale habitat. These findings do not support the hypothesis that southern resident...
An array of predators that consume juvenile salmon (genus Oncorhynchus Suckley, 1861) may account... more An array of predators that consume juvenile salmon (genus Oncorhynchus Suckley, 1861) may account for the poor returns of adult salmon to the Salish Sea. However, the Pacific Great Blue Heron (Ardea herodias fannini Chapman, 1901) is rarely listed among the known salmon predators, despite being regularly seen near salmon streams. Investigating heron predation by scanning nesting sites within 35 km of three British Columbia (Canada) rivers for fecal remains containing passive integrated transponder (PIT) tags implanted in >100 000 juvenile salmon from 2008 to 2018 yielded 1205 tags, representing a minimum annual predation rate of 0.3%–1.3% of all juvenile salmon. Most of this predation (99%) was caused by ∼420 adult Pacific Great Blue Herons from three heronries. Correcting for tags defecated outside of the heronry raised the predation rates to 0.7%–3.2%, and was as high as 6% during a year of low river flow. Predation occurs during chick-rearing in late spring and accounts for 4....
Journal of zoo and wildlife medicine : official publication of the American Association of Zoo Veterinarians, 2018
Decreased health may have lowered the birth and survival rates of Steller sea lions ( Eumetopias ... more Decreased health may have lowered the birth and survival rates of Steller sea lions ( Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands over the past 30 yr. Reference ranges for clinical hematology and serum chemistry parameters needed to assess the health of wild sea lion populations are limited. Here, blood parameters were serially measured in 12 captive female Steller sea lions ranging in age from 3 wk to 16 yr to establish baseline values and investigate age-related changes. Whether diving activity affects hematology parameters in animals swimming in the ocean compared with animals in a traditional aquarium setting was also examined. Almost all blood parameters measured exhibited significant changes with age. Many of the age-related changes reflected developmental life history changes, including a change in diet during weaning, an improvement of diving capacity, and the maturity of the immune system. Mean corpuscular hemoglobin and mean corpuscular volume were also ...
Aerial surveys are sometimes used to assess the densities of wide-ranging whales, as well as chan... more Aerial surveys are sometimes used to assess the densities of wide-ranging whales, as well as changes in their distributions in response to human activity. Such surveys also provide data used to estimate numbers of animals exposed to different received levels of seismic sound, as required by regulators. However, estimates of abundance are often biased because they fail to account for the effects of seismic operations on the surfacing and diving behavior of whales. Our objective was to determine the extent to which analyses of the distribution of bowhead whales Balaena mysticetus are affected by changes in visual 'availability' caused by seismic operations. We used aerial survey data collected during seismic operations in the Alaskan Beaufort Sea from late August to early October 2008 and fit spatial density surface models to bowhead sighting data to predict whale density in an ensonified area. We also incorporated availability correction factors to determine the sensitivity of density estimates to changes in surfacing and diving behavior caused by seismic operations. The influence of altered whale behavior was then evaluated by comparing a series of realistic simulated scenarios in which models incorporated undisturbed or seismic disturbance-related correction factors. Results suggest that the numbers of bowhead whales present in the vicinity of seismic operations during the bowhead autumn migration are underestimated if the behavioral effects of seismic operations on whales are ignored. Our study highlights the importance of accounting for changes in whale behavior that can affect sightability when estimating numbers and distribution of whales in the vicinity of industrial activity.
Three rays opportunistically obtained near Margarita Island, Venezuela, were identified as lesser... more Three rays opportunistically obtained near Margarita Island, Venezuela, were identified as lesser devil rays Mobula cf. hypostoma, but their disc widths were between 207 and 230 cm, which is almost double the reported maximum disc width of 120 cm for this species. These morphometric data suggest that lesser devil rays are either larger than previously recognized or that these specimens belong to an unknown sub‐species of Mobula in the Caribbean Sea. Better data are needed to describe the distribution, phenotypic variation and population structure of this poorly known species.
Summary Most marine mammals are predators, but some are also preyed upon by other species. Intera... more Summary Most marine mammals are predators, but some are also preyed upon by other species. Interaction between marine mammals and their prey influences the structure and dynamics of marine ecosystems. Similarly, predators and prey have shaped each other’s behaviors, physiologies, morphologies, and life-history strategies. However, there is little empirical evidence of these influences due to the relative scale and complexity of marine ecosystems and the inherent difficulties of observing and documenting marine mammal predator–prey interactions.
Sea lions of the world. Proceedings of the Symposium Sea Lions of the World: conservation and research in the 21st century, September 30-October 3, 2004, Anchorage, Alaska, USA
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Papers by Andrew Trites