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.