Fish Migration 1 Flashcards
What is migration
mass movement from one area or habitat to another, with characteristic regularity in time or according to life history stage (Bond, 1996)
Scales of movement
Small scale (km’s) Seasonal inshore onshore movement eg.blennies.
Medium scale (100’s km) Migrations between spawning and feeding areas (herring, cod, plaice)
Large scale (1000’s km)
e.g. transoceanic (bluefin tuna) or diadromous migrations (salmon)
Why migration fish are targeted by commercial fisheries
Although only ~1% of all fish species are migratory, migration is an important feature in the life cycle of most commercial fish species
Migrating fish are easier to catch:
Migrations are predictable in time and space
When migrating, fish often aggregate and occupy concentrated distributions
Oceanodromy:
migrations occurring entirely in the sea
Potamodromy:
migrations occurring entirely in freshwater
Diadromy:
migrations between fresh and saltwater
(three types of diadromy)
What are the three types of diadromy
Anadromy (e.g. salmon)
Catadromy (e.g. European eel)
Amphidromy (e.g. ayu Plecoglossus altivelisi), Japan
Why do fish migrate?
To exploit biotic conditions (food availability, predator abundance) and abiotic (temperature, salinity, depth) that are optimal for a particular stage of development or at a certain time of year
To regulate population density and widen distribution
Selective advantage: migrations improve survival and reproductive success
Anadromy:
more common in cool temperate and subpolar waters. Biological productivity of sea > freshwater; growth, survival size at maturity and fecundity maximised by spending the major growth period at sea
Catadromy:
more common in warm-temperate to tropical waters. Biological productivity of freshwater > seawater; growth, survival size at maturity and fecundity maximised by spending the major growth period in freshwater
Amphidromy:
most common on oceanic islands in tropical to cool-temperate waters. Thought to provide a mechanism for fish to recolonise rivers after perturbations (e.g. volcanoes/droughts)
In eels during transition from freshwater to saltwater what changes take place
Skin thickening, mucus production (protection)
Colour change from brown/green to silver with counter shading (reduces risk of predation)
Eyes increase in size by up to 50% and ability to see at low light levels is enhanced
Fat stores are increased (eels do not feed on seaward migration).
Swim bladder thickens and becomes more vascularised
General life cycle of eels
Spawn at sea and die afterwrd.
Leptocephalus larvae spend 1-2 years at sea, moving back towards parental origin, primarily with the aid of ocean currents.
Metamorphosis to glass eel stage takes place in coastal waters
What was the swim tunnel experiment on eels
Five silver A. anguilla covered 2850 km in 95 days
(van den Thillart et al., 2004). Shown to be efficient swimmers.
Can complete the migration from Europe to the Sargasso sea on their stored energy reserves and within 3.5-6 months
What role do ocean currents have in eels migration spawning travels
Eels gain speed and increase travel efficiency by entering south- and west-flowing ocean currents that begin west of Africa and continue as part of the subtropical gyre system to the Caribbean.
