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Lec 10: Fish
I.
Fish Research and Limnology
II. Taxonomy and Systematics
III. Species Richness
IV. Life History
V. Growth
VI. Fisheries and Yield
VII. Local Fisheries
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I.
Fish Research and Limnology
A. Traditionally: A species focus & in isolation
1. Economic importance as fisheries species;
population biology rather than ecology
2. Relatively large, long lived,
3. Unique sampling approaches
4. Very different scales (space, time) than other areas of
aquatic science
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B. Fish research rooted in Ichthyology
1. Natural history
2. Fisheries science; management of fish stocks
3. Government management
4. Not often tought with natural sciences
C. More recent research on fish ecology
1. Community and Ecosystem approaches
2. Recently, links between basic ecology & management
II. Taxonomy and Systematics
A. What is a fish?
'Any of numerous cold-blooded aquatic vertebrates of
the superclass Pisces, characteristic of having fins,
gills, and a streamlined body…' Amer. Heritage Dictionary
B. Phylogenetic lineage of common modern fishes
Phylum Chordata
Subphylum Vertebrata
Superclass Agnatha (hagfish, lampreys)
Superclass Gnathostamata (jawed) (includes the tetrapods)
Class Chondrichthyes (cartilaginous fishes)
Class Osteichthyes (bony fish)
Subclass Actinopterygii (ray-finned)
Division Teleosti (42 orders)
-Symetrical tail, advanced
~94% of inland fishes
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{
Fishes are the most numerous of all vertebrates
Amphibians 2500 spp
Reptiles
6000
Birds
8600
Mammals
4500
Fish
25000
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Fish Distributions
58% are marine
41% are FW
1% occupy both
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III. Species Richness
A. Negative relationship with latitude and altitude
B. Increases with drainage basin area
-Greater habitat diversity
-More potential colonizers
C. Increases with habitat diversity within-lake
D. Recent glaciation => low diversity
-Versus African Rift valley:
e.g. Lake Malawi has 1,000 spp.
E. Invasions
1. Competition, predation on adults, eggs
2. Example: Nile Perch in African Rift lakes
Benefits: productive fishery
Costs: Loss of endemic species (cichlids)
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Haplochromis in Lake Malawi – Feeding Specialization
IV. Life History
A. Reproductive diversity in fishes is enormous
1. Varies by: size at maturity, # eggs, egg size,
reproductive season and timing, longevity,
# clutches / female (year, life)
2. Although closely related species usually use similar
spawning strategies, there is little general evolutionary
trend from primitive to advanced groups.
(large variation w/in diverse FW groups like cyprinids, percids)
B. Hypothesis: Selection for reproductive strategies that
minimize the ratios of:
1. energy expended for reproduction
2. fitness of the genes passed to offspring (F1 => F2)
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IV. Life History
C. Reproductive Effort - energy or time invested in reproduction
1. Assumed to be greater in females – choosy
a. number of eggs (fecundity)
b. fecundity scales geometrically with length
c. size of eggs (reproductive investment per individual)
d. trade-off between number and size of eggs
2. Male gametes assumed to be relatively inexpensive,
reproductive effort is expended in :
a. courtship
b. territoriality
c. parental care
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IV. Life History
D. Frequency of Reproduction over lifetime
1. Semelparous a. spawn once in lifetime, putting eggs in one basket
b. catadromous species do this a lot
2. Iteroparous
a. spawn more than once over lifetime
b. even out variance in reproductive success…..
but contribute a lot of energy to reproduction over lifetime
c. single, extended spawning season (fractional spawning)
d. multiple spawning seasons - long lived fishes
E. Spawning Migrations
1. Hydrodynamic, trophic, reproductive needs met in
a given environment?
2. May have to migrate if not: (sardines => whales)
3. Diadromy: Catadromous & Anadromous
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IV. Life History
F. Population Biology
1. Life history traits are extremely plastic in fishes
2. Survival of young more important than fecundity
3. Extremely high juvenile mortality (starvation,
predation) limits recruitment to the population
4. Recruitment is variable among age-classes & is
reflected in Cohort (or year-class) strength; the
number of fish of a given age in a population
5. Small changes in larval and juvenile mortality can
affect cohort strength
6. Rare to have several strong, consecutive year-classes
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Fishes
>20k spp
Birds
8.5k spp
Herps
8.5k spp
Mammals
5k spp
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V. Growth
A. Size of fish (state, world records)
<1 cm ‘Stout Infantfish’
18m whale shark (eats plankton)
B. Why grow?
1. Predation risk: Prob(predation) vs. size (-linear)
2. Fecudity: eggs/female vs. size (exponential)
-small increase in size => large increase in fecundity
3. Natural mortality: Prob(death by nat. causes) vs. size (-linear)
-less susceptible to lack of food in winter
-small animals are more likely to die by starvation
4. Social rank
-access to and defense of mates and nest sites
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News Update
Scientists find 'smallest fish' By Roland Pease
BBC science correspondent
Researchers have found the smallest known fish on record
in the peat swamps of the Indonesian island of Sumatra.
Individuals of the Paedocypris genus can be just 7.9mm long at
maturity, scientists write in a journal published by the UK's Royal
Society. But they warn long-term prospects for the fish are poor,
because of rapid destruction of Indonesian peat swamps. The fish have to survive in
extreme habitats - pools of acid water in a tropical forest swamp. Food is scarce but the
Paedocypris - smaller than other fish by a few tenths of a millimetre - can sustain their small
bodies grazing on plankton near the bottom of the water.
Human threat
To keep their size down, the fish have abandoned many of the attributes of adulthood - a
characteristic hinted at in their name. Their brain, for example, lacks bony protection and
the females have room to carry just a few eggs. The males have a little clasp underneath
that might help them fertilize eggs individually. Being so small, the fish can live through
even extreme drought, by seeking refuge in the last puddles of the swamp; but they are
now threatened by humans. Widespread forest destruction, drainage of the peat swamps
for palm oil plantations and persistent fires are destroying their habitat. Science may have
discovered Paedocypris just in time - but many of their miniature relatives may already have
been wiped out.
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/4645708.stm
V. Growth
C. Growth and ration
1. Ration most important determinate of growth
2. Three critical levels in a ration-growth curve
a. Maintenance
b. Maximum
c. Optimum
-highest GGE
3. Change in diet critical for growth (Trophic Ontogeny)
-Potential strong effects on zooplankton
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V. Growth
D. Determinate vs. Indeterminate Growth
1. Indeterminate growth in many fishes Why?
Think about the forces affecting vertebrate
morphology and anatomy in general
2. Birds & mammals vs. fish
a. Determinate:
-grow rapidly to a relatively uniform,
unchanging adult size
b. Indeterminate (most fishes)
-age, size, maturity not fixed
-mature at relatively small, but variable size,
then keep growing (or grow larger and die)
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V. Growth
F. Why is determining fish growth rate so difficult?
1. Can you rely on size or maturity?
2. Habitat effect (food, temperature)
3. Sampling biases and artifacts
4. Growth of individuals or the population?
G. Growth in length
1. Easiest measure besides counting
2. Dependent on vertebral length, related to hard
structures used for aging
H. Growth in mass
1. Wet weight
2. Relate to length (produce a useful W=aLb eqn.)
3. Condition factor (ratio of weight:length)
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V. Growth
I. Determining the age of fish
1. General
-Need 'markers' of time
-Seasonal growth rates in temperate lats.
-Seasonal deposition of bone, scales
-Hard structures reflect growth rates as annuli (influence of reprod?)
2. Structures
a. Scales
i. non lethal
ii. circuli: like tree rings
iii. problems: false annuli, regenerated scales,
older fish, difficult to observe
iv. cross-validation
b. Bones (Otolith, Operculum)
i. lethal except for fin rays
ii. annuli clearer than circuli
iii. no regeneration, good for older individuals
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V. Growth
3. Size-Frequency changes
-Discrete cohorts
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VI. Fisheries and yield
A. Production:Biomass
1. Production (Biomass / area / time)
2. Will be higher for small-bodied populations
3. Will be higher for small fish within populations
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VI. Fisheries and yield
B. Management
1. Management of Maximum Sustainable Yield (MSY)
Assume population model - gives peak
yield at intermediate levels of fishing
effort.
K
N
Stock2 = Stock1 + (A + G) - (M + C)
A = weight of new recruits
G = Weight due to growth
M = natural mortality
C = catch
At Equilibrium:
S1 = S2 => M + C = A + G
Works in theory;
problems with application
dN/dt
K/2
K
N
Fishing Effort
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VI. Fisheries and yield
B. Management
2. Fishery catch; CPUE
3. Relationship of lake trophic state and fish production
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VI. Fisheries and yield
B. Management
4. Eutrophication:
-Reduced trophic efficiency
-Shift to fewer piscivorous fish
5. Morpho-Edaphic Index (MEI)
-Fishery production or yield = TDS / mean depth
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