Introduction to Fisheries Biology

• Historically, low human populations and high natural fish populations had little impact on fish.
• By the 1800s, concerns about overfishing began to surface.
• Early fisheries relied on catch statistics from commercial fishers to assess fish populations, and compared areas that were and weren't fished for trends.
• Fisheries science studies fish biology and populations.
• Fisheries biology is key to backing basic biology with conservation strategies.

Current Issues in Fisheries

• Overharvesting in commercial fisheries threatens populations.
• Harvesting in lower trophic levels poses problems for predators dependent on those food sources.
• Bycatch results in the unintentional capture of non-target species.
• Habitat degradation, like dams and seabed damage, harms fish environments.
• Pollution, including microplastics, contaminates aquatic ecosystems.
• Climate change alters fish habitats and impacts the resources available.
• Invasive species disrupt native ecosystems and can outcompete food sources.
• Aquaculture escapees can transfer parasites and diseases to wild fish populations.

Key Areas in Fisheries Science

• Genetics identifies genetic relationships and protects fish stocks.
• Ecology studies ecosystem interactions and species effects.
• Physiology examines environmental effects on fish.
• Behaviour includes stress, feeding, and aquaculture techniques.
• Parasitology studies fish diseases.

Reproduction and Life Histories

• Reproductive effort refers to the investment of energy in reproduction.
• Reproductive effort is measured by the number of eggs per female or egg biomass per female.
• Gonadosomatic Index (GSI) is the weight of the gonads as a percentage of body weight.
• The energy budget is described by the equation C=Pg + Pr + R + U + F
• C is the total energy consumed.
• Pg represents growth.
• Pr represents reproduction.
• R represents metabolism which is increased by stress.
• U represents urine and excretion.
• F represents feces.
• Fish allocate less energy to growth and more towards reproduction as they age.

Reproductive Strategies

• Key traits of reproductive strategies include:
  • Fecundity
  • Reproductive age
  • Gamete size
  • Reproductive behaviour
  • Seasonal timing
  • Spawning frequency

Fish Reproductive Strategies

• High egg production with low survival rate increases the likelihood of some offspring surviving.
• Low egg production with high survival rate relies on protection or retention investment which increases the odds of survival.

Factors Influencing Reproductive Success

• Egg survival strategies involve:
  • Sheer numbers that are common among high fecundity species
  • Concealment of eggs to hide them from predators
  • Protection of nests increases the odds for survival
  • Retention of eggs in the body like live-bearing species to guard the young through birth
• Timing and location of reproduction are also key.
  • Early life stages require access to ample food.
  • Some species have a narrow reproductive window
  • Others have a long reproductive period that may continue year-round.
    • This is especially common near the equator and in tropical climates

Semelparity vs. Iteroparity

• Semelparity means one-time reproduction where all energy is invested into a single reproductive event before dying
  • Semelparity is common in species that migrate long distances.
  • It is an adaptive strategy for stable, predictable environments with compensatory mechanisms in place
  • Example of compensatory mechanisms in salmon:
    • Overlapping generations remain for varying times preventing whole cohorts from failing
    • Straying causes some salmon to spawn in different rivers, increasing the chance of survival
• Iteroparity means multiple reproductive events throughout a lifetime
  • Iteroparity favours unpredictable environments where if one spawning season fails, they can continue to try in later seasons

Mate Selection in Fish

• Finding mates relies on:
  • Visual cues like colour, pattern, size, and placement of photophores that are organs that produce light
  • Sonic cues using vibrations for communication
  • Chemical signals using pheromones
• Deep-sea fish rely on pheromones for mate detection due to the lack of light
  • For example, anglerfish have enlarged olfactory organs
• Male lampreys release a bile acid pheromone that acts as a strong sex hormone and pheromones to attract females
  • Pheromones can trigger searching and preference behaviour in females
  • Pheromones are used as tools for controlling of invasive sea lampreys in the Great Lakes
• Invasive sea lampreys severely affect native fish populations like Lake Trout
  • Currently, chemical treatments are used in lamprey spawning streams.
  • Pheromones are being tested as possible alternatives to chemical treatments

Control of Reproduction

• Regulation of reproduction is largely controlled by external cues that trigger gametogenesis and the onset of reproductive behaviour.
• Endocrine systems act as mediators that translate environmental cues into morphological, physiological, or behavioural changes.
• Most temperate fish spawn once per year
• Annual cycles of endocrine activity in hypothalamic-pituitary-gonad (HPG) regulate preparation for spawning and the spawn itself
• Environmental variables affecting reproduction include:
  • light that depends on the photoperiod
  • Temperature of the water
  • Water flow from flooding patterns
  • Changes in Salinity
  • Lunar and Tidal cycles that can dictate migration
  • Availability of food
• Human influence on breeding can include the manipulation of reproductive timing in captive fish by adjusting temperature and photoperiod.
• Pollution can be a concern
  • Certain pollutants, like pulp mill effluents, can mimic fish hormones involved in reproduction
  • Endocrine disrupting chemicals can interfere with normal reproduction
  • Pollution can therefore lead to reduced fertility and abnormal development

Oviparous Fish Reproduction

• Oviparous organisms lay eggs that develop externally.
• Egg size varies significantly across species and also within the same species.
• Big Old Fat Fecund Female Fish (BOFFFFs) are crucial for sustaining fish populations
• Commercial fisheries often target BOFFFF which can reduce population reproductive potential and disrupt age structure in fish stocks.
• Egg case adaptations in sharks and rays involve protective egg cases where the shape optimizes water flow and facilitates gas exchange for developing embryos.
• Egg weight and buoyancy causes most fish species to create heavy, sinking eggs that are also called demersal eggs whereas other species create buoyant eggs that float on the surface.
• Egg attachment strategies include eggs that drift freely and those which attach to other surfaces
  • Adhesion is secured using tendrils and hooks
  • Salmon use temporary adhesives to stick eggs to surfaces before covering

Spawning Behaviour and Parental Care

• Various spawning behaviors can include:
  • Mass spawning
  • Beach spawning to avoid predators
  • Polyandrous spawning with single females and multiple males
  • Pair spawning
• Parental care in bony fish can be displayed via egg gaurding and nest building
  • Eggs can be fanned to oxygenate them
  • Eggs can be brooded internally or orally
  • Eggs can be buried

Egg Retention, Internal Incubation, and Viviparity

• Egg retention involves retaining fertilized eggs internally for early deposition inside the body
• Retention allows for releasing well-nourished juveniles via viviparity.
• Egg retention advantages:
  • Protection from predators and harsh environmental conditions
  • Increased offspring survival rates
• Viviparity is when hatched are released from the inside of a female where there are two types of incubation:
  • Simple internal incubation where eggs develop internally but receive no additional nutrients
  • Placental viviparity where nutrients, gas exchange and waste removal occur via a placenta. An example of an animal exhibiting this trait are sharks

Sex Differences in Fish

• Sex determination in fish leads to distinct males and females throughout their lives
• Size differences between sexes often occur where females are larger than males
• Fish have hermaphroditic breeding where the have both male and female reproductive organs
  • Synchronous hermaphrodites have ripe ovaries and testes at the same time but spawn with other individuals
  • Sequential hermaphrodites start transitioning from one sex to the other
• Sex transition is regulated by the endocrine system in response to external stimuli

Alternative Reproductive Strategies

• The evolution of alternative reproductive strategies allows for greater versatility in reproduction among animals
• Early-maturing male Atlantic salmon will try to fertilize eggs while larger males and females spawn
• Small sneaker sunfish will rush in to fertilize eggs while dominant males and females spawn

Fisheries and Reproduction

• Fishing regulations vary based on fish species and spawning locations
  • Regulations may protect fish during spawning season
  • Regulations also may target fish for catching during the spawn
• Fish adapt to heavy fishing pressures in different ways
  • Species that produce large numbers of eggs can often recover more quickly from overfishing
  • Species that produce fewer offspring, like live-bearing species, struggle to rebound population numbers

Early Life History Stages

• Early life stages and recruitment involves a number of developmental stages, starting at egg and ending at juvenile
• During a basic life history phase:
  • Some newly hatched fish are extremely small and undeveloped
  • Other newly hatched fish are very similar to miniature adults
  • Gradual transitions occur through the freshwater teleost
  • Pronounced metamorphosis can occur through marine species
• The first larval stage is dependent on the yolk for nutrition
  • Fry is a general term for larvae
  • Alevins are yolk sac larvae in salmon and trout if the species has the trait

Early Feeding in Fish

• Transition to active feeding can a critical period, as are most vulnerable times in a fish’s life
• The move can be associated with high mortality, especially starvation
• Development of the mouth is key, such as size and mobility and limit feeding
• Survival is more likely to occur when prey density rates are high
• Low prey density can result in high mortality
• Food sources largely depend on the animal
  • Phytoplankton, Ciliates, Molluscs

Predation on Fish Larvae

• Larger fish and invertabrates are primary predators
• Rapid growth and development is crucial for reducing vulnerability to predators
• Environmental sensitivities depend on:
  • Temperature fluctuations
  • Acid runoff
  • Wave action
  • Currents

Larvae Survival in Bass

• Stable and consistent warming produces higher survival rates
• Fluctuating temperatures produce low offspring survival rates

Recruitment

• Recruitment is defined as the rate of conversion of eggs into fish that reproduce in the next generation
• It depends on the relative survival rate of fish during early life stages
• It is important to ensure that fisheries are sustainable if the fish can be added to the population
• Marine fisheries is regulated by biologists where the age of fish and their breeding pattern dictates when the fishery can start harvesting them out
• Different species can display various patterns with regards to their age such as salmon
• To manage recruitment, there are a number of elements to consider:
  • weather
  • competition
• Fisheries and Biologists are crucial due to their ability to create and understand relationships

Recruitment Models

• The relationship is dependant on the amount of spawning adults and #recruitments
• Diff factors and conditions should align for what the model depicts and aims to add
• Factors depend on the specific issues
  • Abiotic
  • Biotic

Manage Fisheries

• Models can predict the amount of each harvest
• Evaluate recruitment success is directly related to health and popoubtion

Growth Model

• This is dependant on population sixes, growth and reproductive output

Beaverton – Holt Model

Assumptions to consider: - Juvenile density dependence and limiting factors

Ricker Model

• recruitment increases with number of spawners Factors to consider; cannibalism

Feeding

• Adaptations for more food
• Chemical adaptations
• Sensations
• Elecrtomagnetism

Feeding Strategies

Detritivores: eat dead animal matter and organic material that comes from those areas Herbivores: start feeding on zoonplankton and adapt to eat algae

More Feeds

• mixed diet and consumes large variety of food types Stenophagous -eat limited assortment of food types Monophagous-consume only one type of food

Mouth types

• Different types of food and sizes can be used as indicators, as well as digestive adaptations
  • Herbivaours are a great example of what can impact the ecosystem Food impacts demand and is directly related to metabolism

Food

• Food sources that consume fish
• Flexible and opportunistic
• feeding behaviours for more niche eating patterns: Primary and Secondary

Feeding Behaviou and Diets

• There can be ontogenetic shift- shift in feeding
• natural selection
• match with availability

Populations

• high abundances reduces food

Diets

• There to maintain high survival
• Prey-driven diets exist

Selective vs random: feed in different portions or the proportion Consuming prey

• Specialists are selective regardless of abundance
• opportunistic

Ecology

• Key parts of the community are to maximize energy

Food Webs as a whole function

Limitations

• what are the relationships
• can also look at isotope C and N exist in stable forms
• Can have different levels Tracking by what previous diets influences the most

Migration

Allows an advantage Ocean, freshwater

• Migration to allow survival and production

Examples

Ocean migration: blue fin for example; and migration

Types are eels and salmon Olocation or ability is key

Migration

Preciseness is important for certain species Homonog has magnetic

Tools for the migration

External or detection Acoustic, to show real time

Limitations

• expensive tool The most valuable ones in action

Aquaculture Inland

Challenges with wild species include; wild fish Cage breaking

Solutions

• limits of coast is necessary
• food chains
• fish - fish problems

Hatcheries

• artificial rearing Mainly for supporting community

Has good features on community

However it does create questions on how successful and sustainable

• what are the factors to consider
• behavioural differences

Genetic

Domestication potential are genetic

Wild vs nature. How to avoid problems Success on how we want to make use of what we have.

Declining and running well We need to re - evaluate to take into account And manage accordingly We need to access as a collective whole

What to look for

Cautions to take

What to use for fish

• manage the resources
• look at what factors

Growth Rate in fish Continuous and shows the well being

There’s and energy equation

Factors impacting growth

• high quality is important
• age for maturity is important

Exercise is important

Growth

There’s a weight- based factor

It is dependant on hormones

• how we can use tag devices with a lot to determine.

Length and Frequency

• back calculation and ring and hard surfaces
• look at structures and what to use Can live free or die
• there’s and ethothermal nature in the animals

Optimum Temperature requirements of living

Aquatica Important factors influencing growth

Osmoregulation: salt and water levels influencing water movement.

Challenges: saltwater composition

More specific, or less precise based what

• levels or components to the environment are used

Pollution and other metals

• need to remove

Fish history

• to conserve

Difficulties creating an understanding of what is good

• look at what is at stake
• what is best To get a better understanding on the fisheries population and how to support and protect it.