Research Methods for Cephalopods

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Research Methods for Cephalopods
Google Images
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Phylum MolluscaClass Cephalopoda
Sepiodea (cuttlefish)
Octopoda (Octopus)
Teuthoidea (squid)
Nautiloidea (Nautilus)
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Vampire Squid
Vampyromorpha (Vampyroteuthis infernalis)
Vampire squid from hell
Mix of squid and octopus
Google Images
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Range expansions in response to warming sea
surface temperatures?
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Why are squid important?
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Striped Bass
Dogfish
Goosefish
Weakfish
Tilefish
Scup
Mackerel
Clupeids
Forage Fishes
BenthicInvertebrates
Figure T.E. Essington
Crustaceans
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Striped Bass
Dogfish
Goosefish
Weakfish
Tilefish
Scup
Mackerel
Clupeids
Forage Fishes
BenthicInvertebrates
Figure T.E. Essington
Crustaceans
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Eat a lot!
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How may changes in squid abundance due to fishing
(or changing environmental conditions) impact
their prey populations?
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Need to understand trophic ecology Prey
composition of squid? How does their diet change
with body size and season? Species of prey
consumed by squid? Sizes of prey?
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• Methods to determine prey composition
• I. Gut content analysis
• Collect squid via bottom- or mid-water trawl
  - Different body sizes, seasons, times of day
• Record length, mass, sex, maturity stage
• Identify prey to coarse taxonomic groupings
• Otoliths, scales, bones, beaks, hooks,
  exoskeletons

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Methods to determine prey composition

• I. Gut content analysis
• Squid masticate their food take bites of prey
• High digestion rates some prey not detected
• Thus, mass and number not good methods for
  quantifying prey composition.
• frequency of occurrence is best option -
• although still underestimates
• prey composition.

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Percent frequency of occurrence
Season

• Indicates the proportion of squid stomachs that
  contained a given prey type
• Describes presence or absence of a prey type
• High frequency of occurrence may not mean prey
  type is of nutritional importance (or
  energetic impt.), but only that it is consumed
  with some regularity

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How does squid diet change with ontogeny?
Presence / Absence Data
Squid
Fish
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How does predation by squid change with body size
and season?
Presence / Absence Data
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Methods to determine prey composition

• II. Stable Isotope Analysis
• Diet analysis can be problematic due to
  well-digested prey and empty stomachs
• Diets only provide information on last feeding
  event (snapshot)
• Stable isotopes provide a time-integrated
  measure of feeding -
• - Reflect materials actually assimilated by
  squid over time - Allow better use of
  sampled squid - no loss of information
• Squid muscle tissue and beaks reflect food
  composition

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d15N
15N14N
A 3 - 4 enrichment of the heavy nitrogen
isotope represents a typical trophic level
increment Indication of feeding relationships
and energy pathways
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Methods to determine prey composition
II. Stable Isotope Analysis Muscle
tissue Mixing models generate more precise
estimates of the percent contribution of prey
items to squid diets
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How does trophic position change body size and
season?
Delta 15N ()
Squid mantle length (mm)
A 3 - 4 enrichment of 15N a typical trophic
level increment
Squid muscle tissue (mantle)
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II. Stable Isotope Analysis Eye lenses

• Squid muscle tissue reflect materials
  assimilated weeks / month
• Eye lenses may contain record of food
  consumption over life span
• Chronological deposition of eye lens (Matt
  Parry, PhD Thesis)
• Measure 15N and 13C in each lens layer and
  relate layer to body size
• Understand ontogenetic changes in trophic level
  of squid (sampling limitations)

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How does trophic position of individual squid
over lifespan?
Squid A
Squid B
Squid C
d15N ()
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• How may squid impact prey populations?
• Prey composition of squid?
• How does their diet change with body size and
  season?
• Gut Content Analysis
• Stable Isotope Analysis (Muscle tissue Eye
  Lenses)
• Species of prey consumed by squid?
• Sizes of prey?

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What are the species of prey consumed by squid?
Compare morphological features of digested fish
otoliths and squid beaks with guide books and
reference collection
Northern smooth-tongue (Leuroglossus schmidti)
Brokenline lanternfish (Lampanyctus jordani)
Squid Lower beak
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What are the sizes of fish and squid prey?
Otolith length (width) to fish body length
Lower rostral beak length to squid mantle length
Regression equations provided by Bill Walker
(unpublished)
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Prey size spectrum
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How may changes in squid abundance due to fishing
(or changing environmental conditions) impact
their prey?

• Trophic Ecology / Feeding Relationships
• Next steps
• Estimate consumption rate (bioenergetics models)
• Estimate population biomass (surveys trawl
  acoustic)
• Construct size-structured food web models
• - Quantify the predatory / competitive impact of
  squid
• - Evaluate effects of squid predation /
  competition under alternative fisheries
  management scenarios.

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Cool Video!