AH

Biol 3711 - Fisheries

Fisheries Overview

  • Human history with fishing highlights its practices since primitive societies.
  • Discovery of shell and bone middens, artifacts supporting evidence of fishing and overfishing.
  • Development of efficient fishing techniques:
    • Better boats and giant factory ships
    • Improved nets and trawls
    • Integration of remote sensing technologies
  • Fisheries landings have dramatically increased since 1950 but have plateaued over time.

Commercial Fishing Concerns

  • In 2006, predictions indicated a potential collapse of fish populations by 2048, but these figures have been revised.
  • Presently, 37% of fished species are still classified as overexploited.

Global Fishing Impact

  • Fish and shellfish provide 16% of global animal protein consumption.
  • The increase in fish catch has not kept pace with fishing effort due to declining populations.

Use of Fish as Animal Feed

  • A portion of the catch is dedicated to animal feed, with decreasing percentages allocated for aquaculture as plant-based feeds have become more viable.

Fisheries Management Practices

  • Fish and shellfish are renewable resources, but even low fishing pressure can lead to population crashes and near extinction.
  • Effective management must set limits (quotas) and establish closures to recover fish populations.
  • Requires detailed knowledge of species' stock sizes, life histories, and ecological behaviors.

Fish Stocks and Management

  • Fish species have broad geographic ranges, often divided into relatively independent stocks based on spawning and nursery grounds.
  • Stocks can become genetically isolated due to geographical and temporal differences (e.g., salmon).
  • Monitoring of stocks involves:
    • Tagging fish with plastic/metal tags for tracking.
    • Using genetic markers or enzyme polymorphisms for identification.

Life History and Stock Assessment

  • Estimating stock size and age structure is crucial for sustainable management, considering fish sizes that are typically harvested.
  • Assessment processes include:
    • Sampling programs accounting for migration and spatial distribution.
    • Recognizing that sampling gear can influence results (e.g., net sizes).

Data Collection Methods

  • Most fishery data sources stem from landings, yet these data can be biased as fisheries often focus on areas with higher fish density.
  • Important factors affecting data include:
    • Number of fishing vessels.
    • Number of personnel involved.
    • Types of fishing gear used.
    • Duration of fishing activities.

Catch per Unit Effort (CPUE)

  • To factor in variable fishing effort, landings are expressed as CPUE.
  • Metrics may be misleading if fish learn to avoid fishing boats or fishing efforts decline over time.

Determining Fishery Yield

  • Managers need to estimate the potential yield (kg/year) while avoiding overexploitation.
  • Models must consider:
    • Reproduction rates.
    • Recruitment levels.
    • Growth rates across different life stages.

Maximum Sustainable Yield (MSY)

  • Managers establish limits to optimize sustainable yields over multiple years, preventing stock stress.
  • Fishers align their efforts with optimizing production, where intermediate stock sizes can foster greater growth rates.
  • Regulations, such as size limits on caught individuals, help maintain sustainable fisheries:
    • Catching larger fish leaves more resources for younger fish.

MSY Management Challenges

  • Gathering precise measurements of population sizes, growth rates, and reproductive rates poses significant challenges, leading to uncertainties in MSY models.
  • Management plans tend to be species-specific which can inadvertently impact other species (e.g. bottom trawling affects cod populations).
  • Societal demands often push for increased fishing efforts despite sustainability issues.

Overfishing Dynamics

  • Overfishing occurs when fish are harvested faster than they can reproduce, leading to stock reductions.
  • Increased fishing pressures can disrupt trophic structures, exemplified by the decline of cod populations in Newfoundland.

Apex Predator Loss

  • Studies indicate substantial declines in apex predator populations due to overfishing.
  • The biomass of top carnivores is around 10% of what it was in the 1960s.

Fishing at Lower Trophic Levels

  • Planktivorous fish (e.g. anchovies, sardines, menhaden) play a crucial ecological role.
  • Menhaden fished extensively for fertilizer has seen declines in population numbers and sizes, affecting larger fish populations.
  • Restrictions have allowed for some recovery of menhaden populations.

Effects on Food Webs

  • Removing fish across various trophic levels, combined with ocean warming and pollution, has led to the dominance of certain 'junk' species.
  • Notable increases in jellyfish populations affect zooplankton, including fish eggs.

Fishing Techniques

  • Different fishing methods utilize various gear types, affecting catch efficiency:
    • Hooking Methods: Longlines with thousands of hooks used for species like tuna.
    • Shoreline Nets: Nets that trap fishes along coastlines.
    • Gill Nets: Mesh nets catching fish by gills, often resulting in bycatch.
    • Seine Nets: Purse seines that encircle schools of fish can unintentionally capture marine mammals.
    • Trawling: Bottom and pelagic trawls capture fish but can cause significant ecosystem disruption.
    • Baited Traps: Use in specific fishing grounds to catch mobile crustaceans.

Bycatch Concerns

  • Bycatch refers to the incidental capture of non-target species, contributing to declines in their populations.
  • Devices like turtle exclusion devices aim to reduce bycatch from gill nets and longlines.
  • Drift nets have been banned due to excessive bycatch, impacting various marine animals.

Bottom Trawling Impacts

  • Although efficient, bottom trawling is destructive to benthic ecosystems, leading to significant bycatch and long recovery times.
  • This method can deplete species that are prey for targeted species and harm various marine habitats.