Why Do Fish Grow Forever or Understanding Longevity in Fishes

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Why Do Fish Grow Forever?orUnderstanding
Longevity in Fishes

• Rainer Froese
• 13.11.07

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Longevity in Fish

• Maximum age on record for a species
• Used for
• r versus K strategists
• proxy for natural mortality M 4.5/tmax
• 1 of 5 criteria to estimate resilience

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Taylor 1958

• Longevity as age at 95 of L8
• t95 3 / K

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Longevity vs Taylors 3/K
1 1
353 species, FishBase 11/2006
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Longevity vs Temperature
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Longevity vs Maximum Length
Maximum age and length known for 1036 species of
fishes, FishBase 11/2006
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Maximum Length vs Longevity
Maximum length and age known for 1036 species of
fishes, FishBase 11/2006 (Slope 0.80, 95 CL
0.76-0.84, r2 0.6124)
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L8 vs tmax within Species
6410 growth studies FishBase 11/2006
Median slope for populations within 141 species
0.42 (95 CL 0.39-0.46)
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Longevity vs Age at Maturity
tmax 4 tm
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Empirical Equations for Longevity
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Longevity vs Environment
Diadromous
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Longevity vs Habitat
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Longevity vs Trophic Level
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Why Do Fish Grow Forever?

• Textbooks
• Lagler et al. (1977)
• "...birds and mammals have to expand part of
  their caloric intake for the maintenance of body
  temperature and in supporting themselves fish in
  contrast are poikilotherms and get such support
  from the surrounding water."
• Fishes living in a fluid medium that supports
  them mechanically can continue growth throughout
  their lives...
• Fish are far superior in protein-building than
  domestic live-stock

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Alternative Hypothesis Assumptions

• Access to food is not different among fish and
  other animal groups
• Adult size has evolved to best fit the respective
  niche
• Animals strive to reach adult size as fast as
  possible

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Alternative Hypothesis

• Fish growth is limited by the need to extract
  oxygen from water
• Fish grow as fast as they can, but it takes them
  forever to reach maximum size
• Size at maturity is less then maximum size
  because they can not afford to wait forever
• Fish need longer than air-breathers to reach size
  at maturity

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Facts

• Relative size at maturity (Lm / Lmax)
• Fish 0.44 (n530, 95 LCL 0.421, UCL0.451)
• Marine mammals 0.76 (n9, LCL0.716, UCL0.803)
• birds? reptiles?
• Relative age at maturity (tm / tmax)
• Fish 0.24 (n229, LCL0.224, UCL0.253)
• Marine mammals 0.13 (LCL 0.0913, UCL 0.198)
• Birds 0.05 (LCL0.0364, UCL0.0695)

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Whale shark vs Fin whale

• The largest fish, the Whale shark (Rhincodon
  typus) needs about 9 years to reach maturity at
  about 5.5 m and 750 kg, and about 60 years to
  reach a maximum length of 14 m and 12 tons.
• The fin whale (Balaenoptera physalus) needs about
  7 years to reach maturity at a size of about 20 m
  and about 36 tons, with a maximum size of about
  25 m and 70 tons.

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Whale shark vs Fin whale
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White shark vs Killer whale

• The Great white shark females take about 12 years
  to reach maturity at 4.5-5 m and about 0.8 tons
  they need 36 years to reach a maximum size of 7.2
  m and 3.4 tons
• Killer whales (Orcinus orca) reach maturity in
  6-10 years at 5-6 m length and about 1.8 tons,
  with the typical size of about 7 m and 3.8 tons
  reached a few years later.

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Great white shark vs Killer whale
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Conclusion

• Fish clearly lack behind the growth performance
  shown by marine mammals and birds
• Their relative size at first maturity is
  significantly lower than in birds and mammals,
  yet they take relatively longer to reach that
  size
• Gills suck

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Exercises

• Select one of these species
• Orange roughy (Hoplostethus atlanticus)
• Beluga (Huso huso)
• Anchoveta (Engraulis ringens)
• Discuss age (tmax, tm), habitat, food, growth,
  reproduction, suitability to fishing