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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Food quality matters for southern resident killer whales    
    For southern resident killer whales, the fattier the prey the better.   
      
      
     Date:   
         February 17, 2023   
     Source:   
         University of British Columbia   
     Summary:   
         Not all Chinook salmon are created equal, and this has a major   
         impact on the energetics for southern resident killer whales. A   
         recent study quantified the lipid content in Fraser River Chinook   
         salmon -- the southern resident's preferred meal -- and found that   
         spring-run Chinook salmon, the earliest to arrive to the Salish   
         Sea are lipid-rich and energy dense; a critical factor for the   
         killer whales who prey on them.   
      
         Fraser River Chinook salmon that come later in the season have   
         lower energy density.   
      
      
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   FULL STORY   
   ==========================================================================   
   Not all Chinook salmon are created equal, and this has a major impact   
   on the energetics for southern resident killer whales. A recent   
   study quantified the lipid content in Fraser River Chinook salmon --   
   the southern resident's preferred meal -- and found that spring-run   
   Chinook salmon, the earliest to arrive to the Salish Sea are lipid-rich   
   and energy dense; a critical factor for the killer whales who prey on   
   them. Fraser River Chinook salmon that come later in the season have   
   lower energy density.   
      
      
   ==========================================================================   
   "This research helps us quantify the energetic requirements of the   
   southern residents," said Jacob Lerner, lead author of the study and a   
   doctoral student in the Pelagic Ecosystems Lab at the Institute for the   
   Oceans and Fisheries.   
      
   "For example, if the southern residents ate just low-lipid salmon, they   
   would have to eat around 80,000 more Chinook salmon every year than if   
   they just ate high-lipid salmon."  Southern resident killer whales are an   
   iconic species in British Columbia's Salish Sea and down the northeastern   
   Pacific coast. With black and white markings, these marine mammals can   
   weigh up to 12,000 pounds and be up to 26 feet long. They are fierce,   
   social creatures that live and hunt in family group pods. And, sadly,   
   there are only 73 left in the world.   
      
   Critically endangered by a number of anthropogenic factors, including   
   noise pollution and high levels of water contaminants, their decline   
   is mostly based on the limited availability of their preferred prey --   
   Chinook salmon. However, there are many distinct populations of Chinook   
   salmon available throughout the year, some with stock-specific differences   
   in energy density, and not all in decline.   
      
   "We began with an initial hypothesis that these salmon were all created   
   equal, that they all have the same value to resident killer whales. And   
   we quickly realized that this is not true at all," said Lerner. "They   
   all have different levels of lipid content."  Quantifying that lipid   
   content is important as it directly relates to the caloric value of a   
   salmon, assigning its value as prey. Specific estimates of lipid content   
   for Chinook populations with different distributions, or run- timings,   
   could be used to inform trends in killer whale populations, properly time   
   fisheries closures, or even decide which hatcheries to augment to increase   
   high quality food availability for southern residents, Lerner said.   
      
   This is particularly important as southern resident killer whales are a   
   migratory species and often spend their winter months elsewhere. When they   
   return to the Salish Sea for the spring and summer, their arrival often   
   coincides with the arrival of the spring-run Fraser River Chinook salmon.   
      
   "Southern resident killer whales used to come here earlier in the   
   spring season when they could eat early migrating Chinook salmon," said   
   Brian Hunt, associate professor in the Institute for the Oceans and   
   Fisheries. "Those early Chinook were very energy dense as they need to   
   fuel their long freshwater migration back to their spawning grounds,   
   but those stocks have been declining. With the whales coming later,   
   they mainly have access to Chinook from the lower Fraser.   
      
   These fish don't migrate very far, and have lower energy density."   
   As a major source of prey for southern residents, estimates of lipid   
   content from Fraser bound Chinook salmon may be one of the keys to   
   helping both threatened species. "We identified a spectrum of high,   
   medium and low-lipid Chinook populations from the Fraser that can be   
   used to better inform energetics models and manage both species," Lerner   
   stated, "We also identified life history parameters for the salmon to   
   predict where on this spectrum they may fall."  Though the study has   
   quantified lipid content in Fraser River Chinook, and shown new light   
   on its life history drivers, there is still little information on how   
   ocean conditions influence this energy accumulation.   
      
   "We plan to keep monitoring Fraser Chinook salmon fat content," said   
   Hunt. "And one of questions we want to answer is how changing ocean   
   conditions might be affecting their energy accumulation. Our concern is   
   that ocean warming and food web shifts in the North Pacific Ocean are   
   leading to lower energy accumulation in Chinook salmon. This will have   
   implications for both the Chinook themselves -- will they have enough   
   energy for return migration and spawning? -- and the killers whales that   
   depend on them."   
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Fish # Marine_Biology # Dolphins_and_Whales # Fisheries   
             o Earth_&_Climate   
                   # Water # Environmental_Science #   
                   Energy_and_the_Environment # Renewable_Energy   
       * RELATED_TERMS   
             o Salmon o Coho_salmon o Atlantic_salmon o Fish_migration o   
             Right_whale o Trout o River o Baleen_whale   
      
   ==========================================================================   
   Story Source: Materials provided by University_of_British_Columbia. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Lerner, J.E., Hunt, B.P.V. Seasonal variation in the lipid   
      content of   
         Fraser River Chinook Salmon (Oncorhynchus tshawytscha) and its   
         implications for Southern Resident Killer Whale (Orcinus orca) prey   
         quality. Scientific Reports, 2023 DOI: 10.1038/s41598-023-28321-9   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230217152315.htm   
      
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