Biodiversity of Fishes Summary Rainer Froese GEOMAR (08.02.18) http://www.fishbase.de/rfroese/BiodivSummary.ppt

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

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 = 0.296 Winf, max age tmax at 0.95 Linf = 4.5/M are constant

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

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), 0.001 (eel-like)

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

Growth in Weight

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

M = 0.2

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

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

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

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

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. 2015. Revisiting the limits of exploitation)

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

Population Growth BioDivPopGrowthMSY.xls

Logistic Curve Properties BioDivPopGrowthMSY.xls

The Schaefer Production Model BioDivPopGrowthMSY.xls

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

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

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

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

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

Questions?