Lec 10: Fish

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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 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
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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 Supercl
ass 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 Fish Distributions
Amphibians 2500 spp 58 are marine
Reptiles 6000 41 are FW
Birds 8600 1 occupy both
Mammals 4500 Fish 25000
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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 gt 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
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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 gt 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 gt 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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V. Growth
A. Size of fish (state, world records) lt1 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) -sma
ll increase in size gt 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 NEWShttp//news.bbc.c
o.uk/go/pr/fr/-/2/hi/science/nature/4645708.stm
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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 WaLb eqn.) 3. Condition factor (ratio
of weightlength)
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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. ProductionBiomass 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. 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 gt
M C A G Works in theory problems with
application
K
N
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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