Marine Fish Habitat and Ecology in sequential (Top to Bottom) Include:
Pelagic (Epipelagic, Mesopelagic)
Benthic or Demersal
Open ocean and no association with substrate.
Within the water column and not the ocean seafloor
This zone is generally from the surface water to a depth of 1000m
The pelagic zone is divided into different zones at depths defined by the temperature of the water, sunlight penetration, and a few other characteristics.
Pelagic Zone (Epipelagic)
From the surface water to approximately 200m in depth where sunlight still penetrates.
Water temperatures remain higher compared with the deeper ocean depths.
Fish in this epipelagic zone are usually caught using Trolling gear, handling gear and pelagic longline gear with hooks.
Shallow-set longline gear places hooks within the upper 100m. (common for swordfish)
Deep-set longline gear places hooks between 70 and 350m with deeper hooks in the mesopelagic zone and common when fishing for bigeye tuna.
Pelagic Zone (Mesopelagic)
This Pelagic zone ranges from the 200m depth to approximately 1,000m depth
The thermocline of the ocean may occur in this zone, which is characterized by a severe drop in the waters temperature as you continue to increase depth. Temperature range and variations in temperature differs in depths across the ocean.
The thermocline will usually stay close and hug the epipelagic and mesopelagic zones. It acts as the barrier between the upper mixed ocean waters and the mostly calm waters below.
Fisherman in Hawaii that are utilizing the Deep-set longline fishing method, will set their shallowest hooks in the epipelagic zone at around the 70m mark, and then set their deepest hooks in the mesopelagic zone at a depth of about 350m.
Pelagic Zone (Bathypelagic)
This Pelagic Zone ranges from 1,000 to 4,000m in depth
Commercial Fisherman’s Pelagic Longline Gear cannot access these depths
Below this zone is what is referred to as the Abyssopelagic Zone, which is characterized by extremely cold water temperatures and zero sunlight penetration.
Benthic or Demersal – Ocean Bottom
The ocean seafloor or bottom substrate.
Therefore, Benthic or demersal fish will live in close relation with the ocean seafloor.
Amaebi (Deepwater Shrimp) are a Benthic species and will always be found in depths between 350 and 850m.
The Oceans “Deep Slope”
All the Vertical habitat living along the oceans substrate at a depth range of 40m to 500m.
The deep slope of the Hawaiian Islands is characterized by an extremely steep (often vertical) slope, which can make it difficult to maintain the vessel within the narrow band of habitat that lives only at specific depth around each of the islands.
These highly sought after bottom fish species include: Hapu’upuu (Grouper/ Sea Bass), Opakapaka (Pink Snapper), Onaga (Longtailed Red Snapper), Ehu (Shortail Red Snapper).
The Hawaiian Coral Reefs are made up of limestone (Calcium Carbonate) structures that are created by massive colonies of coral polyps (cnidarians) that have conglomerated and created a symbiotic relationship with the local algae species (zooxanthellae).
What happens in this relationship is that the coral polyps form colonies that provide the required habitat and substrate for the algae.
On the flip side, the algae in turn provides the coral reefs polyps with the nutrients it needs, which are only derived from the process of photosynthesis.
Species of reef fish include Uhu (Parrotfish), Palani (Surgeonfish) and Kumu (Goatfish)
When fresh and seawater mix to create a brackish (intermediate salinity) habitat, this is what is referred to as an Estuary.
In nature, the most common location for an estuary occurs at a river’s mouth where the sea water comes in and out, but ultimately becomes diluted by freshwater.
Mullet and milkfish are some species of Hawaiian estuarine fish.