1. Biodiversity of Fishes Summary
Rainer Froese
GEOMAR
( )

3. Fish Diversity of the Oceans
Arctic 140
Atlantic
5,000
Pacific
10,000
Pacific
10,000
Indian
6,000
Antarctic 380
Total: ~18,000 marine or diadromous fishes, several thousand in more than one Ocean

4. Size Matters Largest fish: Whale shark, 18 m, 34 t
Smallest fish: attached male anglerfish, several tiny cyprinids & gobies, 1 cm, 0.01g
Max growth rate, fecundity, speed, trophic level, life span increase with size
Metabolic rate, relative brain size, relative gill area and K, rmax and M decrease with size
topt = 1.65/M, max growth = Winf, max age tmax at 0.95 Linf = 4.5/M are constant

5. Size Distribution
Frequency distribution of maximum lengths in 23,685 species of fishes, Median = 15.9 cm

6. Relationship Between Weight and Length
W = a * Lb
with weight in grams and length in cm
For parameter estimation use linear regression of data transformed to base 10 logarithms
log W = log a + b * log L
Typical value for b ~ 3 -> isometric growth
For a = 0.01 (fusiform), 0.1 (roundish), (eel-like)

7. Von Bertalanffy Growth Function
Lt = Linf (1 – exp(-K * (t – t0)))
Where
Lt = length (cm) at age t (years)
Linf = asymptotic length if t = infinite
K = parameter indicating how fast Linf is approached (1/year)
t0 = hypothetical age at L = 0 (years)
Wt = Winf (1 – exp(-K * (t – t0)))b
b = 3 or exponent of length-weight relationship

8. Growth in Weight

9. The M Equation Nt = N0 e –M t Where
M is the instantaneous rate of natural mortality
N0 is the number of specimens at a t = 0
Nt is the number of specimens at time t

10. M = 0.2

11. Average Adult Life Expectancy
where Ex is the average life expectancy after reaching age x and l are
the probabilities of reaching x and subsequent ages. If mortality M is more or
less constant such as in adult fish, then the equation simplifies to
Charnov 1993, Life history invariants, Oxford University Press

12. Reproductive Strategies
A: One-time spawners; B: live bearers or parental care; C: high fecundity, no care
Froese & Pauly 2013, Fish Stocks, Encyclopedia of Biodiversity, Academic Press

13. The Mechanics of Sex under Water
Eggs have to be fertilized (or activated) by the right sperms
Eggs are few and large (>1mm - 10 cm) or numerous and small (< 1 mm), internal, attached or drifting
Sperms are very small, very numerous, mobile, outside
Survival of gametes in water is short (few minutes)
Courtship and mating aims to increase fertilization rate

14. Stock-Recruitment Relationships
Recruits
(N)
Spawning stock biomass
(tonnes)

15. Use of Hockey-Stick in Management
Conceptual drawing of the hockey stick relationship between spawning stock size and recruitment.
SSBlim marks the border below which recruitment declines with > 50% probability, SSBpa marks a
precautionary distance to SSBlim, and 2 * SSBpa can be used as a proxy for SSBmsy, the stock size that
can produce the maximum sustainable catch [ContHS.xlsx]. (Froese et al Revisiting the limits of exploitation)

16. What Determines Recruitment?
Eggs need to encounter right salinity, temperature, current, wind, and absence of predators
After absorption of the yolk sac, larvae need to find food within days or reach a “point of no return”
Juveniles grow up in small nursery areas with limited carrying-capacity (shelter & food)
As a result of mostly starvation and predation, the number of recruits that a population can produce in a given ecosystem is limited
Because of this limited recruitment, populations can not grow much larger than 4 times the population size (SSBpa) needed to produce the minimum number of eggs needed for the average number of recruits

17. Population Growth
BioDivPopGrowthMSY.xls

18. Logistic Curve Properties
BioDivPopGrowthMSY.xls

19. The Schaefer Production Model
BioDivPopGrowthMSY.xls

20. Surplus Production Implications
Surplus production (Y) is the production of biomass beyond what is needed to maintain current population size
If a fishery only catches the surplus production, then the population size remains as is
If a fishery catches more, then the population shrinks
If it catches less, then the population grows
At carrying capacity there is no surplus production; production equals loss by mortality

21. Fisheries Management Basics
MSY
MEY
Cost of fishing €
Growth
overfishing €
Economic
overfishing
Fpa
Recruitment
overfishing
Flim ? †

22. EU Fisheries Management
MSY
MEY
Cost of fishing € €
Subsidies
Flim ? †

23. Three trawling
revolutions
1376 – the beam trawl is invented
1880s – trawlers gain steam power
Late 20th century – the deep sea comes within reach of the trawl

24. More Food from the Ocean?
Sustainable fishing
stop subsidies, take less than nature, let fish grow before capture, enforce laws, no discards
Redirect “reduction fisheries” to human consumption
“No feeding, low impact” aquaculture of algae and mollusks
Use offal, waste and expired food as feed in carnivore mariculture

25. Questions?