Fisheries Biology: An Introduction

L1: Introduction to Fisheries Biology

• Fisheries science combines fish biology and population studies
• Fisheries biology utilizes basic biology for conservation

Current Issues in Fisheries

• Overharvesting impacts commercial fisheries
• Harvesting lower trophic levels affects predators
• Bycatch, habitat degradation (dams, seabed damage), and pollution (microplastics) are significant concerns
• Climate change, invasive species, and aquaculture practices (escapees, parasite/disease transfer) pose challenges

Key Areas in Fisheries Science

• Genetics studies how genes make the fish what they are
• Ecology studies how fish interact with their environment
• Physiology studies how the fish organ systems work
• Behaviour discusses fish action
• Parasitology involves the parasites which affect the fish

L2: Reproduction and Life Histories

• Reproductive effort is measured by the number of eggs per female and egg biomass
• Gonadosomatic Index (GSI) is the weight of gonads as a percentage of body weight
• Energy budget is C=Pg + Pr + R + U + F (Consumption = Production of growth + Production of reproduction + Respiration + Waste + Excretion)

Reproductive Strategies

• Key traits include fecundity, reproductive age, gamete size
• Also includes reproductive behaviour (mating systems, courtship, parental care), seasonal timing, sex change, and spawning frequency

Diversity in Fish Reproductive Strategies

• High egg production can equal low survival rate
• Low egg production can equal high survival rate

Factors Influencing Reproductive Success

• Egg survival strategies include sheer numbers, concealment, nest protection
• Live-bearing species increase the egg survival rate by Retaining eggs in the body
• Early life stages require ample food and species have a restricted reproduction time frames

Semelparity vs Iteroparity

• Semelparity is one-time reproduction
• Semelparous species will migrate long distances and will be most successful in Stable environments
• Salmon use overlapping generations or Straying as a compensatory mechanism
• Iteroparity is multiple reproductive events and is most successful in unpredictable environments

Finding Mate

• Mate selection is influenced by Visual cues like colour, pattern, size, light placement
• Mate selection is influenced by Sonic cues like vibrations
• Mate selection is influenced by Chemical signals like pheromones
• Deep-sea fish rely on pheromones due to lack of light
• Male lampreys release bile acid pheromone as a strong sex hormone
• Invasive sea lampreys in the Great Lakes are controlled by pheromones and chemical treatments in spawning streams

Control of Reproduction

• Regulation is triggered by external cues
• Gametogenesis and reproductive behaviour starts at a specific point
• Endocrine systems translate environmental cues into changes
• Most temperate fish is able to spawn once per year
• There is an annual cycle of endocrine activity in the hypothalamic-pituitary-gonad (HPG) axis
• Reproductive timing in captive fish is manipulated based on water temperature and light
• Endocrine disruptors like pollutants mimic fish hormones and can lead to Reduced fertility and Abnormal development

Eggs in Oviparous Fish Species

• Oviparous species lay eggs which develop externally
• Intraspecific variability is egg size, which differs by fish
• BOFFFFs (Big Old Fat Fecund Female Fish) have reduced reproductive abilities and disrupt the general age structure
• Sharks and rays lay eggs encased in protective cases which optimize water flow and facilitates gas exchange
• Most fishes lay heavy, sinking eggs (demersal eggs)

Egg Buoyancy

• Buoyant eggs float at the surface of intermediate depths
• Eggs use Tendrils or hooks for secure anchoring or Temporary adhesives
• Elasmobranchs like Sharks and rays produce 2-20 eggs
• Viviparous species produce very few eggs
• Teleost or bony fish produce a lot of eggs

Spawning Behaviour

• Includes mass spawning, beach spawning
• Includes polyandrous spawning, pair spawning

Parental Care in Bony Fish

• Parental care taking the form of egg guarding or nest building
• Parental care includes cleaning the spawning site or fanning eggs to oxygenate them
• Parental care includes using Internal gestation, Oral brooding, or Burying eggs

Egg Retention

• Process involves Internal Incubation and Viviparity, retaining fertilized eggs internally
• There can be an Early deposition of internally fertilized eggs during the cleavage stage
• There can be a Releasing well-nourished juveniles or even young adults (viviparity)
• All these provide Protection from predators and harsh environmental conditions

Viviparity

• This is where hatched young are released from the female
• Simple internal incubation involves internal development but no additional nutrients
• Nutrients, gas exchange, and waste removal occur via a placental structure

Hermaphroditic Fish

• Hermaphroditic fish have both male and female reproductive organs
• Synchronous hermaphrodites have ovaries and testes present at the same time but spawn with other individuals.
• Sequential hermaphrodites start as one sex and transition later, regulated by an endocrine system in response to external stimuli

Alternative Reproductive Strategies

• These strategies allow for greater versatility in reproduction
• Atlantic salmon males mature early
• Sunfish exhibit small sneaker males that rush in

Fisheries Implications of Reproduction

• Fish requires protection during spawning
• Fishing mortality should target fish during spawning
• Species that produce many eggs can quickly recover from overfishing
• Species that produce few offspring struggle to rebound

L3: Early Life History Stages and Recruitment

• Early feeding is a critical transition from yolk dependence to active feeding
• The fish is more vulnerable and high mortality may occur from starvation
• Sensory system and feeding apparatus development limits feeding
• Prey density and survival affect fish
• High prey density gives higher survival chances
• Low prey density results in likely mortality
• Rapid growth and development decreases a fish's vulnerability to predators

Abiotic Factors Affecting Early Life Stages in Fish

• Temperature and pH fluctuations, acid runoff, wave action, and water currents

Recruitment

• Recruitment is when eggs develop into fish that then reproduce
• Recruitment is affected by the rate of survival of fish during their early life stages
• Recruitment is measured by how many fish are added to a population in a year
• Year class strength is the relative success of recruitment in any given year
• Density-dependent factors include competition and predation
• Density-independent factors include weather and environmental conditions

Recruitment Models

• These models show the relationship between the number of spawning adults and recruits
• They are used in the management of fisheries in order to predict harvesting and determine sustainability
• Exponential growth, starts with low Spawners and ends with the Max reproductive rate
• Beaverton-Holt model, starts with exponential growth then has a Max reproductivity
• Ricker model-increase initially with increasing spawners, but decline after reaching max # of recruits

L4: Feeding

• Detritivores feed on freshly dead or decomposing organic matter
• Herbivores includes fish larvae feed on zooplankton/small benthic and pelagic animals; they can be Filter feeders and have Specialized mouths to scrape films and other vegetation
• Omnivores eat both foods of plant and animal origin
• Carnivores eat live animals or parts including Microcarnivores like zooplankton and Macrocarnivores like larger animals

Feeding Habits

• Euryphagous species eat mixed diets
• Stenophagous species eat limited assortments
• Monophagous species eat one food type

Mouth Structure and Feeding

• The type of mouth and it's orientation provides insight into feeding habits
• There is a Digestive apparatus that correlates between feeding and the structure of the digestive system
• Fish consuming algae have longer guts with larger SA
• Carnivorous fish have shorter gut lengths

Food Demand and Metabolic Rate

• As temperature and metabolic rate increase, food demand increases
• Food demand(per g of body tissue) decreases with size, as does metabolic rate

Piscivorous Fish

• These fish consume fish prey which includes broadly distributed and large fish
• Piscivorous fish predation causes large effects
• Piscivorous fish are valuable harvestable fish
• Piscivorous fish are flexible and opportunistic
• Primary Piscivores shift to piscivory within the first few months of life
• Secondary Piscivores shift later in life, maintaining energy efficiency and increase the size of prey

Feeding Behaviour in Piscivores

• Luring involves sit-and-wait behaviour
• Stalking involves unobtrusive pursuit of prey before attack
• Chasing involves high cruising and accelerating speeds
• Hunting includes lungers and pursuers, and body shapes which can minimize drag
• Ambush involves Camouflage and high-speed attacks
• Prey is usually Ingested whole making it More species can eat one fish item
• Other feeding behaviours exist including blood-sucking, scale eating and fin and eye biting

Life History of Piscivores

• Some species use ram suspension (filter) feeding which includes small dense food items
• Most piscivorous fish begin feeding on zooplankton and then shift to prey fish
• Some forgo zooplankton stage or shift very early
• A shift gives more Energy
• Natural selection favours life history strategies that minimize zooplanktivorous stage
• Freshwater primary piscivores spawn earlier than most fish and prey fish are abundant

Population and Community Effects

• Trophic cascades extend down several trophic levels impacting prey and primary producers
• A large piscivore population will
  • Decrease abundance of zooplanktivorous fish
  • Increase zooplankton
  • Decrease phytoplankton
• A small piscivore population will
  • Increase abundance of zooplanktivorous fish
  • Decrease zooplankton
  • Increase phytoplankton

Implications for Conservation and Management

• Removal of top predators have ecological consequences
• Predator removals or additions can helps manage fisheries

Selective vs Random Predation

• Selective predation means consuming prey in different proportions than prey are in habitat through vulnerability, size and nutrition metrics
• Random feeding is feeding indiscriminately in accordance with food availability

Foraging Behaviour Theories

• Optimal foraging theory (OFT) says that prey will be prefered if they provide more energy for the time they require to secure the food, and diet selection is based on amount of prey available
• Ideal free distribution(IFD) theory says that habitat selection will only occur if it increases fitness and the relationship will be linear
• Rate Rule is when minimize rate of mortality to maximize fitness

5: Trophic Ecology

• Ecosystem management aims for sustainable resource management
• management is shifting away from simple and becoming more determined and use techniques to stay sustainable

Trophodynamics

• It is measured via nutrient and energy fluxes(how E moves through food webs and chains) and food webs/chains describe these relationships and uncertainties exist
• Food chains combine species into groups within trophic levels
• Food chains are a Linear chain describing fluxes and transfer efficiencies between trophic levels
• Food chains are also Quantitative comparisons

Weaknesses of the Food Chain Approach

• Many fish species feed at more than one trophic level so it does not account for this
• food chains Imply bottom up control and have no set efficiency value for E transfer b/ween trophic levels
• Does not account for organisms that differ w/in species and Material unused by organisms is returned to food web

Food Webs

• Food webs illustrate complex feeding relationships
• Food webs are Typically built based on dietary analyses
• has complex limitations for things eaten

Limitations of Food Web Content Analysis

• It Only snapshots diet and time to digest
• hard to compare as is not stable
• Immunological analyses aid and help find species

Limitations of Food Webs

• There must be Stable dietary relationships.
• Food webs will assume they identify diet
• and seasonal shifts that do not occur much
• isotopes that must be stable and isotopes shift

Stable Isotopes

• Heavier isotopes form stronger bonds
• Lower trophic levels deposit levels or heavier isotope loads.
• C and nitrogen indicate locations

Food Web Fingerprinting

• Food has “unique fingerprint” due to its differences
• indicate where energy stores are from
• Nitrogen is also location indicator

Tracking applications

• shift food depending location and species

Analyzing profiles

• can store profile as profile analysis

Benefits of Isotopes

• diet stays stable
• asses important pathways
• compare the diet species
• assimilate

Restrictions

• even distribution

6: Migration

• migration is movement from habitat area
• and must be efficient over time
• and stages

Terminology

• Ocean
• Fresh

fish will migrate to feed where ever is needed for development

Fish use what resources they have

• Ocean fish use a long path of fresh

Ocean tuna are often studied

• and they use to cross wide to be tracked

To get from salmon migration

• they must end up

navigation of migration

• uses mental mapping

navigation data collection

• and has to be more precise

Tagging is now used

• with radio data and is less tracked
• can store all device

Tagging has dettach method

• is expencive