Why Do Fish Grow Forever Rainer Froese Institute

Overview • A look at longevity • A look at growth • Discussion

Longevity in Fish • Maximum age on record for a species • Used for

Taylor 1958 • Longevity as age at 95% of Linf • A 95 =

Nice Paper • Submitted to CJFAS • REJECTED • Too narrow

Why Do Fish Grow Forever? Textbooks: Lagler et al. (1977): ". . . birds

Alternative Hypothesis: Assumptions • Access to food is not different among the considered groups

Alternative Hypothesis • Fish growth is limited by the need to extract oxygen from

Facts • Relative size at maturity (Lm / Lmax) – Fish 0. 44 (n=530,

Whale shark vs Fin whale • The largest fish, the Whale shark (Rhincodon typus)

White shark vs Killer whale • The Great white shark needs 36 years to

Conclusion • Fish clearly lack behind the growth performance shown by marine mammals and

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Why Do Fish Grow Forever? Rainer Froese Institute of Marine Science Kiel, Germany rfroese@ifm. uni-kiel. de

Overview • A look at longevity • A look at growth • Discussion

Longevity in Fish • Maximum age on record for a species • Used for – r versus K strategists – proxy for natural mortality – 1 of 5 criteria to estimate resilience

Taylor 1958 • Longevity as age at 95% of Linf • A 95 = 3 / K • 353 species with longevity and VBGF from Fish. Base

Longevity vs Taylor’s 3/K

Longevity vs Temperature

Longevity vs Maximum Length

Longevity vs Age at Maturity

Empirical Equations

Longevity vs Environment

Longevity vs Habitat

Nice Paper • Submitted to CJFAS • REJECTED • Too narrow

Longevity vs Trophic Level

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 livestock

Alternative Hypothesis: Assumptions • Access to food is not different among the considered groups • Adult size has evolved to best fit the respective niche • Animals strive to reach adult size as fast as possible

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

Facts • Relative size at maturity (Lm / Lmax) – Fish 0. 44 (n=530, 95% LCL =0. 421, UCL=0. 451) – Marine mammals 0. 76 (n=9, LCL=0. 716, UCL=0. 803) – birds? reptiles? • Relative age at maturity (tm / tmax) – Fish 0. 24 (n=229, LCL=0. 224, UCL=0. 253) – Marine mammals 0. 13 (LCL= 0. 0913, UCL = 0. 198) – Birds need 0. 05 (LCL=0. 0364, UCL=0. 0695)

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.

Whale shark vs Fin whale

White shark vs Killer whale • The Great white shark needs 36 years to reach a maximum size of 7. 2 m and 3. 4 tons; females take about 12 years to reach maturity at 4. 5 -5 m and about 0. 8 tons weight. • Killer whales (Orcinus orca) reach maturity in 610 years at 5 -6 m length and about 1. 8 tons weight, with the typical size of about 7 m and 3. 8 tons reached a few years later.

Great white shark vs Killer whale

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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