Percorrer por autor "Wachtendonk, Rachel"
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- Blue whale body condition assessed over a 14-year period in the NE Pacific: annual variation and connection to measures of ocean productivityPublication . Wachtendonk, Rachel; Calambokidis, John; Flynn, KiirstenLarge marine mammals can serve as an indicator of the overall state of the environment due to their apex position in marine food webs and their functions as sentinels of change. Reductions in prey, driven by changes in environmental conditions can manifest in reduced fat stores that are visible on whales. We developed a non-invasive technique using photographs of blue whales taken on the US west coast from 2005-2018 (n=3,660) and scored body condition based on visible undulations from the vertebral processes and body shape. We analyzed patterns in the body condition of whales across years and their relation to oceanographic conditions. Females with calves had significantly poorer body conditions and calves had significantly better body conditions compared to other adult whales (Chi-Square, x(2 =) 170.36, df=6, p<2.2e-16). Year was a significant factor in body condition (Chi-Square, x(2 =) 417.73, df=39, p<0.001). The highest proportion of whales in poor body condition was observed for 2015 (one of the only two years along with 2017 where >50% had poor body condition) coincides with the marine heat wave that affected the NE Pacific 2014-2016. A cumulative mixed model examining the relationship between body condition and environmental variables revealed that negative Pacific Decadal Oscillation and longer upwelling seasons correlated with better blue whale body condition, likely to be due to higher primary productivity and prey availability. This study indicates that with an adequate scoring method, photographs collected during boat based surveys can be used to effectively evaluate whale health in response to a changing ocean.
- Blue whale body condition from photographs taken over a 14- year period in the NE Pacific: annual variation and connection to measures of ocean productivityPublication . Wachtendonk, Rachel; Andrade, José PedroLarge marine mammals can serve as an indicator of the overall state of the environment due to their long lifespan and position in marine food webs. Reductions in prey, driven by changes in environmental conditions can have resounding impacts on the trophic system as a whole, which can manifest in reduced fat stores that are visible on whales. Poor health can lead to reduced survivorship and fitness, both of which can be detrimental to recovering populations. A non-invasive technique using digital photographs of blue whales taken in the NE Pacific from 2005-2018 (n=3,660) scored the overall body condition based on visible vertebrae and body shape. The data was analyzed to determine if there were patterns in the health of whales across years and whether overall poor health was related to oceanographic conditions and predictors of prey abundance. Overall, known females with calves had significantly poorer body conditions and calves had significantly better body conditions in comparison to the general population (Chi-Square, p<2.2e-16). Year was a highly significant factor in body condition (Chi-Square, p<0.001). The only two years where >50% of animals had poor body condition were 2015 and 2017 (no other year was above 45%). The 2015 maximum proportion of whales in poor body condition coincide with the marine heat wave that affected the NE Pacific 2014-16 and impacted other whale populations. We modeled the impact of various environmental indices on blue whale body condition and found the yearly average Pacific Decadal Oscillation value and yearly average Bakun Upwelling Index both influence body condition scores due to their role in promoting primary productivity and prey availability for these whales. This study indicates our scoring method effectively evaluated blue whale health and how they respond to a changing ocean.
- Cetacean and sea turtle observations in the remote mid-atlantic (NW) oceanPublication . Wachtendonk, Rachel; Smultea, Mari A.; Pedrie, KolbyDue to its remoteness, little is known about the occurrence and abundance of cetaceans and sea turtles in the pelagic mid-Atlantic Ocean. Data on cetacean and sea turtle occurrence and distribution were collected by dedicated biological observers to address U.S. monitoring and mitigation requirements associated with a vessel based academic geophysical survey in international waters in the northwestern and mid -Atlantic Ocean from 14 June through 16 July 2018. A total of 6,949 km (503 h) of visual observations occurred while surveying north from Bermuda and ending in Woods Hole, Massachusetts. A total of 928 cetaceans representing at least 14 species and 15 sea turtles representing three species were observed. The most frequently observed cetacean species was the Atlantic white-sided dolphin (Lagenorhynchus acutus) (340 individuals; 37%) followed by the short-beaked common dolphin (Delphinus delphis) (286 individuals; 31%) and pilot whales (Globicephala spp.) (95 individuals; 10%). These sighting data also included an extralimital sighting of a sperm whale (Physeter macrocephalus) calf at 43.44 degrees N latitude and 36.85 degrees W longitude, and extralimital sightings of Atlantic white-sided dolphins below 38 degrees N latitude. Loggerhead sea turtles (Caretta caretta) were seen most frequently (6 individuals). This study addresses a data gap in documented occurrence and lack of occurrence of cetaceans and sea turtles over a large pelagic area in the northwestern Atlantic Ocean during summer.