By ‘deep water’ here I don’t mean ocean trenches, I mean continental slopes, ~400 metres down and deeper.

I’m currently reading a book about whale identification – including deep water species.

In the past 50 years:
The number of new deep water shark species known has exploded.
The number of new deep water beaked whale species known has exploded.

This leaves as many questions unanswered as answered. What’s the range? Same species or different? For almost all beaked whales, for instance, it’s not known whether the species is endangered or not.

That makes me wonder – is there a way to systematically study deep water shark and whale species?

Some ridiculous ideas I’ve had are:

• a worldwide network of underwater hydrophones
• cameras attached to deep-ocean dredging nets already being used
• organic sample collection attached to cookie-cutter sharks
• a network of underwater feeding stations
• a better way to “see” underwater, eg. imaging passive sonar, low light upward-looking camera.
• trackers and cameras attached to commensal fish such as remoras and pilot fish
• a submarine built to look like a whale or shark
• thermal (hot water) attractor
• camera attached to whale or shark that photographs other members of the same species

Which would be most cost effective?
Which would be most thorough?
Which would be least destructive?

Some Ideas I’ve already rejected

• Equipment attached to predatory crustaceans eg. barnacles, isopods. Too small.
• Equipment within whale feeding grounds: squid, sardines, zooplankton. Too easily eaten, too easily avoided.
• Active and passive thermal IR imaging. To much absorption by water.

mollwollfumble said:

By ‘deep water’ here I don’t mean ocean trenches, I mean continental slopes, ~400 metres down and deeper.

I’m currently reading a book about whale identification – including deep water species.

In the past 50 years:
The number of new deep water shark species known has exploded.
The number of new deep water beaked whale species known has exploded.

This leaves as many questions unanswered as answered. What’s the range? Same species or different? For almost all beaked whales, for instance, it’s not known whether the species is endangered or not.

That makes me wonder – is there a way to systematically study deep water shark and whale species?

Some ridiculous ideas I’ve had are:

• a worldwide network of underwater hydrophones
• cameras attached to deep-ocean dredging nets already being used
• organic sample collection attached to cookie-cutter sharks
• a network of underwater feeding stations
• a better way to “see” underwater, eg. imaging passive sonar, low light upward-looking camera.
• trackers and cameras attached to commensal fish such as remoras and pilot fish
• a submarine built to look like a whale or shark
• thermal (hot water) attractor
• camera attached to whale or shark that photographs other members of the same species

Which would be most cost effective?
Which would be most thorough?
Which would be least destructive?

Some Ideas I’ve already rejected

• Equipment attached to predatory crustaceans eg. barnacles, isopods. Too small.
• Equipment within whale feeding grounds: squid, sardines, zooplankton. Too easily eaten, too easily avoided.
• Active and passive thermal IR imaging. To much absorption by water.
  

bump

This thread is meant to tie closely into the “salmon” thread, connected through our ignorance of the eels graveyard, where they all go to spawn (and presumably die).

Where is it and what is so special about it?

There have been attempts to track eels to their spawning ground, in 2009, 2014 and 2015. All three have been unsuccessful so far.

This one from 2009, tracks Irish eels into the North Atlantic. https://sci-hub.tw/https://science.sciencemag.org/content/325/5948/1660.full
The tracks are heading in the right direction, but none gets further south than the North of Spain.

The one from 2015, by CSIRO, tracks eels released in the North Atlantic for up to 96 days, but the eels were almost a likely to head in the complete wrong direction, arguing against navigation by magnetism.

More generally, we have:

Aquatic animal telemetry: A panoramic window into the underwater world

Partial migration in fishes: definitions, methodologies and taxonomic distribution

“Until relatively recently, freshwater anguillid eels were synonymous with obligate migration. whereby mature adults migrate from freshwater habitats to spawning the sea. A landmark study, however, showed that A. anguillaare actually composed of two distinct migratory contingents: the first with individuals that make the journey from marine to fresh water (migrants) and the second with individuals that never migrate into fresh water but spend their whole lives in the sea.

“There are a number of examples of breeding partial migration in the sturgeon order. The orange roughy, a bathypelagic marine fish which makes spawning migrations. molecular analysis of the black herring revealed that there were genetic differences between fish from three regions that share common feeding grounds but migrate to spawn in distinct areas.

https://www.nature.com/articles/ncomms1174
“Information has been obtained about their migration behaviour using high-technology satellite tags, which have shown that migrating eels usually swim at deeper depths of about 500–900 m during the day and at shallower depths of 100–300 m at night. None of these tagging studies have documented the behaviour of eels that clearly reached their spawning areas. Until recently, various published and unpublished attempts in the last 30 years to capture or observe adult eels within their spawning areas have failed in both the Sargasso Sea and western North Pacific.”

Trawling for eels in the western North Pacific. Red and yellow circles in the following figure (ignore the white circles, marking failures).