Marine Biology and Fisheries Dynamics Study Guide

Marine Biology and Fisheries Dynamics

Overview of Species Dynamics

  • Discussion of the position and movement of marine species in the Mid Atlantic region.
    • Reference to individual species and their population dynamics.
    • Importance of propagation in terms of species survival.
    • Mention of kinship and population behaviors.

Interaction of Geology, Oceanography, and Biology

  • Overview of how geology and oceanographic conditions influence biological outcomes in marine environments.
    • Cod as the dominant species in the ecosystem due to specific geological and oceanographic factors.
    • Productive nature of the ecosystem as not random, but a result of colocated conditions.

Declines in Fish Populations

  • Acknowledgment of a displayed graph showing the decline of ground fish species, particularly cod, from the 1950s to the early 2000s.
  • Identification of three primary reasons for the decline in fish populations:
    1. Biological Interactions
    • Interaction across all life history stages: predator-prey relationships.
      • Not just adult fish eating each other; includes relationships among all life stages.
      • A reduction in one population leads to cascading effects on predators and prey.
      • Omnivores may switch food sources, exerting pressure on different prey species.
    1. Fishing Pressure
    • Historical commercial fishing on Georges Bank started in the 1750s.
      • Shift to offshore fishing due to overfishing of inshore stocks.
      • Removal of larger fish impacts breeding populations available for reproduction.
      • Larger females contribute exponentially more offspring than smaller females due to biomass scaling non-linearly with length.
      • Ongoing removal of large individuals decreases the reproductive potential of the population.
      • Example: If larger fish are removed, less large fish are available to reproduce, leading to lower total reproduction rates.
    1. Environmental Factors
    • Effects of abnormal temperature conditions on all life history stages.
      • Optimal growth conditions and survival thresholds for larvae, juveniles, and adults.
      • Increasing temperatures can lead to metabolic stress and reduced growth rates.
      • Case study of temperature abnormalities in the 1990s that reduced fish maturity and survival rates for cod.
      • Interrelation of water temperatures and lifecycle success in fish populations.

The North Atlantic Oscillation (NAO)

  • NAO as a significant climate cycle affecting fisheries.
    • Interaction with other global climate cycles impacting regional fish populations.
    • Ability to predict climatic trends and their impacts on fisheries biology.
    • Influence of the NAO on Labrador Current strength affects upwelling and productivity in the Gulf of Maine.

Changes Resulting from Environmental Factors

  • Relationship between changes in currents, temperatures, and food availability for fish larvae.
  • Issues with larvae being displaced from their normal habitat due to changes in the wind field and water temperatures, affecting recruitment into populations.

Shift in Food Web Dynamics on Georges Bank

  • Historical dominance of benthic food webs transitioning to pelagic-dominated systems.
  • Importance of cod as a previously dominant player changing due to fish population dynamics.
  • Emphasis on the time frame of around fifty years for this transition to occur.

Current Management and Sanctuary Practices

  • Description of current management practices in Georges Bank, involving:
    • Sanctuary areas protecting ecosystems from harvesting.
    • Managed rotational harvests for fish and shellfish.
  • Evidence that sanctuaries result in larger fish and improved fish populations.
    • Impact of sanctuaries extends to non-sanctuary fishing areas due to larval flow and population mixing.
  • Involvement of trained observers measuring fishing activities and stock assessments throughout the fishing seasons.
  • Annual meetings for stock assessments resulting in evidence-based management practices.

Introduction to Kelp Forests

  • Transition from discussing fish populations to kelp ecosystems.
  • Overview of kelp as a unique primary producer that is not a true plant but a protist.
  • Kelp Forests vs. Kelp Beds:
    • Kelp forests show vertical structure with canopies, providing numerous habitats for marine life.
    • Kelp beds lack the same height and complexity, primarily existing close to the substrate.
  • Description of ideal conditions for healthy kelp growth (depth, light, nutrient availability).

Kelp Anatomy and Growth Dynamics

  • Components of kelp include:
    • Thallus: The entire body, consists of blades, stipes, and holdfasts.
    • Holdfast: Attachment structure, not roots, allows kelp to anchor to substrate strongly.
    • Stipe: Stem-like structure connecting blades to holdfast; can perform photosynthesis and structural support.
    • Blades: Main site of photosynthesis, facilitating light capture across a large surface area.
  • Kelp growth rates can be exceptionally rapid, especially under optimal environmental conditions:
    • Southern California can see up to 50 cm of growth per day due to favorable conditions.

Reproductive Cycle of Kelp

  • Sporophytes: Adult kelp that are diploid, producing spores through sporophylls.
    • Highly fecund, illustrated by annual outputs of zoospores, reaching estimations of 1 x 10^11 spores per kelp.
  • Gametophytes: Result from zoospore settlement and develop into sexual phase producing gametes.
  • Significant importance placed on larval development and survival rates in maintaining healthy populations.