Migration

Fish Migration Lecture Notes

Introduction to Fish Migration

  • "The directed movement of individuals from one place to another" - defining migration as purposeful movement rather than random dispersal.

  • "The movement of fish between widely separated and well-defined areas, usually as a population".

  • Specific objective of migration: to exploit optimal feeding and breeding habitats.

  • Only 1% of fish species show extensive migrational behavior; however, their contributions to ecosystem dynamics and economic value are significant.

Benefits of Fish Migration

  • Fish migration enables individuals to exploit diverse habitat conditions that may offer better feeding opportunities and breeding environments.

    • Different Requirements by Life Stages:

      • Fry, juveniles, and adults have varying habitat needs.

  • Increased Feeding Potential:

    • Different areas provide unique food resources for larval and adult stages.

    • Reduces competition between adult fish and their offspring.

    • Facilitates the utilization of planktonic food availability, especially in marine contexts.

  • Avoidance of Adverse Environmental Conditions:

    • Adult fish often possess physiologically or physically adapted means to survive harsher environmental conditions compared to larvae.

  • Improved Reproductive Success:

    • Migration allows fish to move to habitats with suitable conditions for reproduction (e.g. optimal temperature for development, examples include bass and plaice).

  • Constraints Affecting Migration:

    • Phylogenetic and historical factors tend to influence migratory routes and behavior (e.g., observed in salmonids and eels).

Costs of Migration

  • Energetic Costs:

    • The physical effort involved in swimming across vast distances.

  • Increased Risk of Predation:

    • Migrating fish, such as salmon smolts, face predation risks, including from species like Merganser ducks.

  • Developmental Costs:

    • Associated with physiological processes like osmoregulation during migration.

  • Risk of Reproductive Failure:

    • Poor synchronization of timing with environmental or prey availability can adversely affect reproductive success; evolution might differ between species.

  • Conclusion on Benefits vs. Costs:

    • The balance is favorable for the evolutionary adaptation of migration since overall benefits, particularly for the survival of early life stages, outweigh the costs involved.

    • Example: Species like capelin and grunion demonstrate successful survival strategies by migrating.

Adaptive Nature of Migration

  • Migration and spawning patterns are often historical adaptations to predation pressures (e.g., capelin spawning in response to environmental variables).

    • Capelin (Mallotus villosus): Highly synchronous inshore spawning influenced by onshore winds that provide favorable conditions for egg development.

  • Benefits: Warm currents carry food and provide safe spawning environments during critical periods.

Types of Migration

  • Oceanadromous Migration: Occurs entirely within marine environments (e.g., seabass, plaice).

  • Potadromous Migration: Involves movements entirely within freshwater (e.g., roach).

  • Diadromous Migration: Involves migration between marine and freshwater environments, prominent in some fish species (e.g., salmonids, eels).

Types of Diadromy

  1. Anadromy:

    • Example Species: Salmonids, Acipenser, shad, lampreys.

    • Lifecycle: Spawning occurs in freshwater; early growth stages happen in freshwater, while larval migration occurs to sea; adults return to freshwater for spawning.

    • Terminology: "Ana" translates to 'up' indicating upstream movement back to natal rivers.

  2. Catadromy:

    • Example Species: Anguillid eels (e.g., European eel, American eel).

    • Lifecycle: Individuals primarily feed and grow in freshwater, migrating to the sea for spawning.

    • Notable Adaptations: Variations in morphology and DNA adaptations determined the differences among species, and juvenile eels adaptively utilize both fat and energy reserves in their life cycle.

  3. Amphidromy:

    • Example Species: Galaxiids.

    • Lifecycle: Involves a pattern where larvae migrate to the sea for early growth and development, later returning to freshwater for further development and reproduction.

Genetic and Biological Implications

  • Genetic studies indicate that fish populations within individual river systems display distinct genetic markers, necessitating their return to natal rivers for reproduction.

  • Physiology defines migration concept, as with Pacific Anadromous species that exhibit semelparity (reproduce once and die) versus Atlantic species capable of iteroparity (multiple spawning events).

  • Sockeye salmon (Oncorhynchus nerka) serves as an example for illustrating these patterns.

Rationale Behind Long-Distance Migration

  • Early life stage survival is influenced by factors such as predation and food availability.

  • Cushing’s Match-Mismatch Hypothesis (1975): Larval mortality risk is highest when the timing of larval hatching coincides negatively with food availability (often plankton). Fish must adapt their spawning strategies temporally and spatially to maximize survival potential of their progeny.

  • Spatial Consideration: Newborn larvae are placed intentionally in areas where food is available, which enhances their growth and survival rates.

Influence of Latitude on Diadromy

  • Geographic influences chart patterns of diadromous species.

    • Tropical Rivers: Exhibit high productivity; thus, catadromous species manifest more often at low latitudes.

    • Temperate Regions: Higher latitudes show more anadromous species where they tend to migrate back to fresh water for feeding and spawning.

    • Notable observations indicate that providing additional food can decrease migration behaviors (e.g., Arctic Charr).

Ecological and Conservation Implications

  • Understanding migration routes leads to species conservation efforts, enabling proactive strategies for habitat preservation and minimal impact on life cycles.

  • Additionally crucial for optimizing the capture and management of commercial species like diadromous fish (e.g., salmon, NZ whitebait).

Case Studies and Practical Examples

  • Galaxiid Fish in New Zealand: Represent amphidromous life stages; common practices risk over-exploitation of genetically unique stocks due to their vulnerability.

  • Sea Bass Migration (Dicentrarchus labrax): Ranges shown from the Mediterranean to northern Europe. They do not spawn in waters below 8.5 to 9°C, necessitating southward migration for reproduction.

  • Temperature and Gonadal Development: Significant correlation where higher temperatures (>10°C) enhance female gonadal development for successful reproduction (Pawson et al. 2000).

  • European Plaice (Pleuronectes platessa): Key commercial species; migratory patterns are well-mapped allowing for robust fishery management practices. Utilizes ocean currents to assist in migration, showcasing energy conservation behaviors during movement, which can save between 20-40% of energy use compared to continuous swimming (Metcalfe 1992).

Mechanisms for Navigation and Homing

  • Natal Homing Hypothesis: Individuals display innate abilities to locate and recognize their birthplace via natural cues.

    • Innate navigational senses may include utilizing Earth's magnetic fields or following various environmental cues (observed in salmonids).

  • Social Facilitation Hypothesis: Young individuals may learn migrational routes by following experienced adults, forming a knowledge transfer over generations.

  • Evidence of Chemical Imprinting: Species such as salmon exhibit behaviors indicating that they can chemically ‘imprint’ on the scent of their natal river, navigating back from the sea (Dittman & Quinn 1996, Ueda 2011).

Additional Notes on Species and Genetics

  • Populations in the North Atlantic (e.g., “North Sea stock”) demonstrate migratory behaviors connected to specific spawning sites influenced by genetic markers. Studies indicate that while there are identifiable migration routes, specific populations may interbreed across overlapping feeding areas but still adhere to general natal homing principles.