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. Sub-disciplines of Ecology. Nutrient cycling

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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.


Sub-disciplines of Ecology

Nutrient cycling

Physiological

Behavioral

Evolutionary

Population

Community

Landscape

Primary focus of the class


Physiological and Morphological Aspects of Ecology

  • Limitation

  • Tolerance

  • Temperature Units

  • Biological rhythms

  • Behavioral regulation

  • Morphological constraints


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: Odum’s Ecology text


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: Odum’s Ecology text


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 > 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


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)


What is the relationship between feeding, temperature, and growth?

?

Growth rate

low

high

Temperature



Morphological Constraints between food and temperature.

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.


Biological Rhythms between food and temperature.

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.


Behavioral Regulation between food and temperature.

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.


Approaches to studying physiological ecology: between food and temperature.

Example: salinity and the distribution of starry flounder

1. Correlate larval catch rate of flounderswith average salinity among years to study recruitment success


Approaches to studying physiological ecology: between food and temperature.

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


Approaches to studying physiological ecology: between food and temperature.

Example: salinity and the distribution of starry flounder

3. Conduct an experiment to determine the ability of flounder to survive at different salinities


Approaches to studying physiological ecology: between food and temperature.

Example: salinity and the distribution of starry flounder

4. Conduct a behavioral experiment on the salinity preferences of individual flounder


Behavioral Ecology between food and temperature.

  • 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.


Behavioral Ecology between food and temperature.

  • 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


Behavioral Ecology between food and temperature.

  • 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)


Behavioral Ecology between food and temperature.

  • 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


Tuna: an energy maximizer between food and temperature.

Rockfish: a time minimizer


Behavioral Ecology between food and temperature.

  • 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 amother 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”).


Behavioral Ecology between food and temperature.

  • 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


Behavioral Ecology between food and temperature.

Fitness: probability of surviving to a given age, multiplied by the reproductive success (e.g., egg production) at that age, summed over the individual’s whole life.

W = Σ (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.



Population Ecology sockeye

  • 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)


Population Ecology sockeye

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)


Population Ecology sockeye

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.



Spawner-recruit relationships: sockeye

Iliamna Lake sockeye salmon


Population Ecology sockeye

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.


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%

~ 25%


Population Ecology Creek rises to an asymptote and then levels off; the proportion killed decreases with density.

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.


Population Ecology Creek rises to an asymptote and then levels off; the proportion killed decreases with density.

“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.


Age composition of herring caught in the North Sea. Creek rises to an asymptote and then levels off; the proportion killed decreases with density.

Data from Hjort (1914), diagram from Jennings et al. Marine Fisheries Ecology

Percentage of sample

Age of herring (years)


Community Ecology Creek rises to an asymptote and then levels off; the proportion killed decreases with density.

  • 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)


Community Ecology Creek rises to an asymptote and then levels off; the proportion killed decreases with density.

  • 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


Community Ecology Creek rises to an asymptote and then levels off; the proportion killed decreases with density.

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?


Community Ecology Creek rises to an asymptote and then levels off; the proportion killed decreases with density.

Mature vs. Pioneer communities:

# of species large small

Dominance? no yes

Life span long short

Diet specialized generalized

Growth slow fast


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