Longterm mortality patterns in San Diego County common dolphins

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Long-term mortality patterns in San Diego County
common dolphins
K. Danil1 and J. St. Leger2
1Southwest Fisheries Science Center 2Sea World
San Diego
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Study Area

• San Diego County
• 125 Km coastline

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Oceanography of the Region

• Temperate, 14 20 C, seasonal upwelling
• El Niño/La Niña
• Regime Shifts
• Warm water sardine regime
• Warmer SST, lower salinity, deeper thermocline
• Decreased primary production
• Cool water anchovy regime
• Lower SST, higher salinity, shallower thermocline
• Increased primary production

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Species of Focus

• Delphinus capensis

• Delphinus delphis

broadly distributed
coastal (w/in 50 nmi)
abundance 487,622
abundance 1,893
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Causes of MortalityDelphinus spp.
N 59
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Trauma

• Fishery Interactions (50)
• Unknown sources (25)
• Gunshot (25)

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Encephalopathy

• Cerebral abcessation

• Cerebral necrosis

• Encephalitis

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Domoic Acid Toxicosis

• Neurotoxin produced by diatom, Pseudonitzchia spp
• Primary vector planktivorous fish (anchovy)
• Ataxia, seizures, decreased responsiveness to
  stimuli
• Atrophy of hippocampus, myocardial fibrosis
• D. delphis and D. capensis

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Delphinus capensis
N 28
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Delphinus capensis

• 2004 Fishery entanglement (4/4)

• 2006 Domoic Acid Toxicosis (2/3),Undetermined
  (1/3)

• 2007 Domoic Acid Toxicosis (6/13),Trauma (6/13,
  Peptostreptococcus prevotii infection (1/13)

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Delphinus delphis
N 27
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Delphinus delphis

• 2003-2005 Encephalopathy, Domoic Acid, Trauma

• La Niña (1989)
• Domoic acid?
• Brucella?
• Morbillivirus?
• Reidarson et al 1998

• 1989/1995

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Delphinus spp.
Cool anchovy
Warm sardine
Cool anchovy
El Niño
La Niña

• Stranding peaks during anchovy regimes
• Distribution shift
• Move closer to shore during Winter (Forney
  barlow 1998)
• Health
• Domoic acid
• Encephalopathy

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Delphinus spp.
sardine
anchovy
anchovy

• Domoic Acid?

• Lesions in 87 of hearts
• Subepicardial scars, focal patchy fibrosis, focal
  myocardial degeneration or necrosis

Domoic acid
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Delphinus spp.
sardine
anchovy
anchovy
Encephalopathy
Encephalopathy

• Lesions in 89 of brains examined
• 100 associated with trematode ova

• Lesions in 48 of brains examined
• 5 associated with trematode ova

Intermediary host less available
change in diet
James McBain
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Summary

• Mortality patterns differ between Delphinus
  species
• D. delphis largely impacted by encephalopathy
• D. capensis largely impacted by trauma and domoic
  acid toxicosis
• Coastal, lower abundance
• Oceanographic oscillations influence Delphinus
  strandings and possibly their health
• Increased Delphinus strandings may be expected
  for the next fifteen years
• Change in occurrence of trematode encephalopathy
  may signal change in diet

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To think about

• Will global warming dampen effect of current cool
  water anchovy regime or shorten the cycle?

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Acknowledgements

• Jason Larese
• Carrie Leduc
• Janet Lowther
• Erika Nilson
• Fionna Matheson
• Bill Perrin
• Prescott Grant
• Kelly Robertson
• Jay Sweeney
• Gaby Serra-Valente
• Marissa Trego

• Jim Carretta
• Susan Chivers
• Jim Gilpatrick
• Brittany Hancock
• Larry Hansen
• Erin Harper
• Nicole Hedrick
• John Henderson
• Mike Henshaw
• Lauren Hess
• Nick Kellar