Marine Top Predator Ecology & Conservation Notes

Occupy a high trophic level (e.g., predatory sharks).
Have few predators (e.g., turtles).
Exert top-down control on food webs due to high energetic demands (e.g., whales).
Often wide-ranging.
Humans are also considered marine top predators.

Keystone species: Disproportionately affect species occurrence, distribution, and density (e.g., sea otters maintaining kelp forests by controlling sea urchins).
Ecological indicators: Sensitive species providing early warning systems for environmental changes (e.g., Kittiwakes indicate sandeel abundance, sea surface temperature (SST), and fishery impacts).
Combat climate change: Great whales sequester an average of ~ $33$ tons of $CO_2$ (natural carbon capture) through nutrient flux (whale pump, great whale conveyor belt) and biomass/deadfall carbon storage.
Ecosystem engineers: Connect multiple ecosystems, deposit nutrients (seabirds), balance food webs, keep prey populations healthy, and maintain vital habitats (sharks).

Particularly susceptible to population impacts due to: long lifespan, low reproductive output, and iteroparous reproductive strategy.
Low fecundity necessitates high sub-adult and adult survival.

Incidental take of non-target species or undesirable size/age classes of target species.
Considered the single greatest threat to many marine mammal populations globally.
Examples: Critically endangered Vaquita porpoise primarily threatened by gillnet fisheries.
Impacts multiple taxa (turtles, seabirds, marine mammals, sharks) across various fishing gears (longlines, gillnets, trawls).
International agreements exist to reduce bycatch (e.g., for sea turtles, seabirds, sharks).

Marine animals, including invertebrates, fish, seabirds, and marine mammals, rely heavily on sound for communication, feeding, and social behavior.
Human noise sources include shipping, naval sonar, seismic surveys, and construction (e.g., pile driving).
Impacts: displacement from critical habitats, stranding or death (military sonar linked to whale deaths), and avoidance behavior (e.g., penguins from seismic activity, porpoises from pile driving).
Legislation is in place to address noise pollution (e.g., EU Marine Strategy Framework Directive, IMO guidelines, protected species acts).

Threats rarely act in isolation; multiple stressors (e.g., fisheries depletion, pollution, climate change, habitat loss, noise, direct takes) cumulatively impact top predators.

Legislation: Implement fishing bans in key areas, mandate bycatch reduction devices, enforce vessel speed limits, ban harmful pollutants (e.g., PCBs), and prohibit whaling.
Reduce bycatch: Utilize bycatch mitigation methods.
Marine Protected Areas (MPAs): Establish MPAs to protect key areas like nurseries, foraging grounds, and biodiversity hotspots.
Land-based protection: Safeguard critical bird colonies and turtle nesting beaches.
Reduce pollution and habitat degradation: Implement measures to decrease overall environmental contamination and habitat destruction.