FISH 312: Fisheries Ecology

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Fisheries Ecology
Biological factors
Physical factors
Temperature, pH, oxygen, light, salinity, etc.
Predation, competition, disease
Diversity and Abundance
Human factors
Fishing, land use, dams, pollution, introduced
species, etc.
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Sub-disciplines of Ecology
Nutrient cycling Physiological Behavioral Evolutio
nary Population Community Landscape
Primary focus of the class
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Physiological and Morphological Aspects of Ecology

1. Limitation
2. Tolerance
3. Temperature Units
4. Biological rhythms
5. Behavioral regulation
6. Morphological constraints

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Limitation and Tolerance
Law of the Minimum Under steady-state
conditions the essential material available in
amounts most closely approaching the critical
minimum needed will tend to be the limiting one.
For example In a lake, primary production may
be limited by Phosphorous rather than by
Nitrogen, and addition of Nitrogen may have no
effect on production. At other times of the year
light may be limiting.
From Odums Ecology text
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Limitation and Tolerance
Law of Tolerance The presence and success of
an organism depend upon the completeness of a
complex of conditions. Absence or failure of an
organism can be controlled by the qualitative or
quantitative deficiency or excess with respect to
any one of several factors which may approach the
limits of tolerance for that organism. For
example The ability to exist and thrive may
depend on such physical factors as dissolved
oxygen, temperature, salinity, pH, etc. Steno
refers to species with narrow tolerances (e.g.,
stenothermal narrow temperature tolerance)
eury refers to those with wide tolerances
(e.g., euryhaline wide salinity tolerance).
From Odums Ecology text
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Time and Temperature
For poikilotherms, physiological processes,
including development of embryos, progress at a
rate determined by temperatures. In many cases,
the stage of development reflects a rough
correspondence between time (number of days) and
temperature (number of ºC gt 0). Thus, for
example, coho salmon embryos develop from
fertilization to hatching in about 500
temperature units (TUs). This might occur after
50 days at 10º or 100 days at 5º.
10º X 50 days 500 TUs 5º X 100 days
500 TUs
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Effect of temperature on the development rates of
European sea bass
(Jennings and Pawson 1991)
hatch to 50 mouth opening
Time (days)
Time (hours)
60 80 100 120 140 160 180 200
4 6 8 10 12 14 16
fertilization to hatch
9 10 11 12 13 14 15 16 17
Mean temperature (oC)
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What is the relationship between feeding,
temperature, and growth?
?
Growth rate
low
high
Temperature
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Growth (gain or loss in weight) depends on the
interaction between food and temperature.
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Morphological Constraints
Just as some organisms are specialists or
generalists in terms of physiological tolerance,
some are specialists and others are generalists
in terms of morphology (shape). Careful
examination of the mouth parts, fins, and shape
indicates the extent to which the species is
adapted for particular kinds of prey and
movement, or is adapted to prey on a wider range
of organisms and show a wider range of locomotion
patterns. These attributes, along with
patterns of physiology, may determine the range
or a species and its responses to changing
conditions.
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Biological Rhythms
We are strongly controlled by internal
(endogenous) circadian rhythms affecting
temperature, physiology, behavior, etc. External
zeitgebers set the clock each day. Physiology
and behavior are strongly controlled by such
rhythms, with periods of a year, a lunar month, a
day, or a tidal cycle. The reproductive biology
and feeding patterns are intimately linked to
such rhythms. Examples include vertical feeding
migrations from deep water towards the surface to
feed on plankton, annual migrations from feeding
to breeding grounds, synchrony of breeding on
spring high tides, and movement from the bottom
to the middle of the water column on high and low
tides.
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Behavioral Regulation
In addition to the physiological capacity to
tolerate a range of conditions (e.g.,
temperature, salinity, oxygen, etc.), mobile
organisms often move to adjust their environment,
searching for physiologically optimal conditions.
For example, manatees leave salt water in winter
for warm springs, and are attracted to the heated
effluent from power plants. However, areas that
are optimal for some environmental features may
not be optimal for others, and behavioral
regulation may conflict with other needs such as
feeding and reproduction.
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Approaches to studying physiological
ecology Example salinity and the distribution
of starry flounder
1. Correlate larval catch rate of flounders with
average salinity among years to study recruitment
success
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Approaches to studying physiological
ecology Example salinity and the distribution
of starry flounder
2. Conduct surveys and correlate the catch rate
of adult flounder with the salinity of the water
to study behavior
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Approaches to studying physiological
ecology Example salinity and the distribution
of starry flounder
3. Conduct an experiment to determine the
ability of flounder to survive at different
salinities
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Approaches to studying physiological
ecology Example salinity and the distribution
of starry flounder
4. Conduct a behavioral experiment on the
salinity preferences of individual flounder
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Behavioral Ecology

• Perspectives on behavior (why animals do what
  they do)
• Mechanism how does it work (e.g., vision,
  reflex, etc.)?
• Ontogeny how does it develop in an individual
  (learning)?
• Ecological significance how does it help an
  animal survive?
• Phylogeny how did it evolve?

• Analogy Why do we stop at red lights?
• Light of a particular wavelength is perceived by
  pigments in the retina, sending a message via the
  optic nerve, etc.
• We are taught by our parents that red indicates
  danger.
• Stopping at lights increases our odds of
  surviving to reproduce.
• Red is the color of fire and of blood, hence we
  have evolved instinctive wariness upon seeing the
  color.

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Behavioral Ecology

• Natural and sexual selection
• Individuals vary in heritable phenotypic traits
• More individuals are produced than the habitat
  can support
• Individuals possessing appropriate traits tend to
  survive
• Individuals surviving to maturity vary in
  reproductive success, related to competition and
  mate choice

• Natural selection can be balancing, directional
  or disruptive

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Behavioral Ecology

• Spatial distribution
• Territory resources (food, nesting site)
  actively defended, within or among species
• Home range area routinely used but not actively
  defended
• Migration movements of individuals between
  habitats, coordinated in time and space
• Schooling synchronous, polarized movements of
  individuals (sometimes distinguished from
  shoaling)

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Behavioral Ecology

• Foraging (we need to eat, but it is not our only
  need)
• Organisms differ greatly in activity, metabolic
  demand, and food consumption.
• Energy maximizers high intake rate, active,
  often short lifespan, high risk
• Time (or risk) minimizers low intake rate,
  inactive, long lifespan, low risk

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Tuna an energy maximizer
Rockfish a time minimizer
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Behavioral Ecology

• Reproduction and Parental Investment
• Sex determination (genetic vs. environmental
  determinate vs. hermaphroditic, protandrous,
  protogynous, or simultaneous all-female species)
• Mating system (monogamy, polyandry, polygyny,
  etc.)
• Mode of reproduction (broadcast spawning, single
  pair, internal or external fertilization)
• Parental investment anisogamy (females produce a
  smaller number of larger gametes than males, and
  so are generally more choosy regarding mates).
  Females also typically have a larger total
  investment in gametes than males.
• However, in most animals, everyone has a mother
  and a father. Thus the average reproductive
  success of males and females is the same but
  there is usually more variation in males than in
  females (e.g., elephant seals and other species
  with harems).

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Behavioral Ecology

• Life history traits link behavioral and
  population ecology
• Age and size at first reproduction
• Longevity and maximum size
• Number of eggs (fecundity, clutch or brood size)
  and size of eggs or offspring
• Frequency of reproduction (iteroparous or
  semelparous, annual or otherwise)
• Parental care

These traits are all related to patterns of
mortality on adults and juveniles
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Behavioral Ecology
Fitness probability of surviving to a given
age, multiplied by the reproductive success
(e.g., egg production) at that age, summed over
the individuals whole life.
W S (lx bx)
Where l age-specific survival and b is
age-specific reproductive success, and x is age.
This simple equation allows us to compare the
fitness of different life history patterns.
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Life history comparison of anadromous and
non-anadromous sockeye
Age form length survival number fecundity fitness
1st spring kokanee 28 0.1 50    
sockeye 28 0.1 300    
1st fall kokanee 60 0.4 20 3 0.12
sockeye 60 0.4 120 3 0.12
2nd spring kokanee 80 0.5 10    
sockeye 80 0.5 60    
2nd fall kokanee 120 0.8 8 24 0.38
sockeye 180 0.3 18 85 0.51
3rd fall kokanee 180 0.6 4.8 85 0.82
sockeye 360 0.4 7.2 700 1.68
4th fall kokanee 300 0.8 3.84 500 3.84
sockeye 560 0.8 5.76 3000 5.76
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Population Ecology

• Abundance (number of organisms)
• Biomass (weight)
• Density (number or biomass per unit of distance,
  area or volume)
• Production (number or biomass per area or volume
  per time)

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Population Ecology
Survivorship patterns Species with high rates of
juvenile mortality and low rates of adult
mortality will tend to be long-lived,
iteroparous, fecund and slow-growing (e.g.,
rockfish) Species with high rates of adult
mortality and low rates of juvenile mortality
will tend to be short-lived, semelparous and fast
growing (e.g., salmon) Species with low rates of
adult and juvenile mortality and large offspring
will tend to reproduce late in life, and
reproduce at a low rate (e.g., sharks, whales)
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Population Ecology
Density-dependent mortality Compensatory
mortality increases as the density of organisms
increases. This means that at low densities,
populations tend to increase but at high
densities, fewer offspring are produced per
capita, and the population levels off or even
declines. Competition for food, limited breeding
sites, and disease are common causes of
compensatory mortality.
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Spawner-recruit relationships
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Spawner-recruit relationships Iliamna Lake
sockeye salmon
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Population Ecology
Density-dependent mortality Depensatory
mortality increases as the density of organisms
decreases. This means that at low densities
there are higher per capita mortality rates, and
the population can fluctuate widely. This kind
of mortality can result from predators that take
a fixed number rather than a fixed percentage of
the population.
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The number of salmon killed by bears each year on
Hansen Creek rises to an asymptote and then
levels off the proportion killed decreases with
density.
60
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Population Ecology
Density-independent mortality Some forms of
mortality do not vary with density but result
from physical factors that operate without regard
to density. However, even some of these factors
(freezing, flooding, high temperatures) may
interact with density. For example, at high
densities, some organisms may be forced to breed
in marginal habitats, where they are more
vulnerable to adverse physical conditions.
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Population Ecology
Strong year class Phenomenon In long-lived
organisms that breed many times over their lives,
most seasons of reproduction produce no offspring
at all. However, when environmental conditions
are good, high survival results. In such cases,
the year class spawned in that year dominates
the population for (and often sustains the
fisheries) for years to come.
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Age composition of herring caught in the North
Sea. Data from Hjort (1914), diagram from
Jennings et al. Marine Fisheries Ecology
Percentage of sample
Age of herring (years)
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Community Ecology

• Characterization of communities
• Abundance (number or density of organisms)
• Diversity (number of species)
• Evenness or dominance (extent to which the
  species are equally abundant)
• Resistance (the ability or tendency of a
  community to remain the same in the face of
  environmental change)
• Resilience (the speed with which a community
  returns to its former state after it has been
  perturbed)

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Community Ecology

• Perspectives on the controls over communities
• Non-equilibrium perspective
• Equilibrium perspective
• Biotic factors
• a) predation
• b) competition
• c) disease
• 4. Abiotic factors
• a) habitat age
• b) opportunities for colonization
• c) stability

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Community Ecology
Why do the Hawaiian islands have fewer species of
fishes and corals than are found in the
Philippines? Why are many species in Hawaii
endemic? What factors controls the extent and
diversity of fish and coral species among the
different Hawaiian islands?
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Community Ecology
Mature vs. Pioneer communities of
species large small Dominance? no yes Life
span long short Diet specialized generalized
Growth slow fast