Fisherfriend of the Isles

Based on my experience so far, each Fisherfriend is basically like Margoss, only they take about 2-3 hours in a raid to reach Best Friend and purchase all unique items from. Each turnin item gives 75 rep instead of 50, there are bosses to summon just like the elemental that will make every catch give you the turnin, while the buff is active you fish up 3-4 of the turnin instead of only 1-2, and each fisherfriend has fewer and cheaper items. You need to be close enough to the fisherfriend to have the [spell=239673] buff to catch the turnin or boss summoner. The boss's health goes up the more people hit it, but it does still seem to be more efficient to have as many people fighting as possible.

Sha'leth works differently than the others, however. In the lake next to her is a moving pool of fish, where you can fish up [item=146962] and [item=146968]. Stand by Sha'leth and throw the scale to summon [npc=120454], which drops 20-50 minnows for everyone who tags it. Make sure to fish with your bobber starting in front of the pool, and try not to stand in it, because that can make it so you can't click your bobber. Note that Sha'leth sells the [item=133719], one of the best ways to gather Runescale Koi and to raise artifact power for your [item=133755]. (When you use the murloc, try to stand somewhere clear, like a bridge, so you can see the fish, or very small, like the top of a pillar, so the murloc has nowhere to run. Other people CAN pick up the fish it drops, so if everyone is dropping them in the same spot, please try to contribute your fair share. If you pick up more fish than you can carry, the extras will be sent to your mailbox.)

Warning! When you turn in items for rep, the fisherfriend will take ALL of them, even if you are at max reputation already! Be very careful when near/at Best Friend.

There are six fisherfriends, and they rotate daily. So far there doesn't seem to be a way to tell which one is up besides looking for yourself or checking custom groups. Each fisherfriend is associated with one fishing area (the five zones and the ocean) and sells the fish for their area (10 for 10), each special bait for their area (25 each), a fishing bobber toy (100, Best Friend), and one other item (generally 50, Good Friend). Reaching Best Friend with all six grants Fisherfriend of the Isles, which gives [item=152583], unlocking new tints for [item=133755].

[npc=120456] in Val'sharah (53.41, 72.86) at Lorlathil sells [item=152565] and [item=147309].
[npc=120457] in Highmountain (32.62, 40.80) by Thunder Totem sells [item=152556] and [item=147310].
[npc=120458] in Stormheim (90.69, 10.87) at Shield's Rest sells [item=152574] and [item=147307].
[npc=120459] in Suramar (50.71, 49.34) sells [item=143748] (cost = 5 each) and [item=147311].
[npc=120460] in Broken Shore (33.70, 49.80) sells ocean fish related things, [item=152554] and [item=147312]
[npc=120266] in Azsuna (43.21, 40.55) sells [item=152555] and [item=147308]

I will update this as new information comes out.

The six fishermen have a daily rotation.
Each fisherman has his own coin.
Each coin awards 75 reputation points with said fisherman
The daily rotation of fisherman is:

[faction=2101] - [faction=2102] - [faction=2097] - [faction=2098] - [faction=2099] - [faction=2100]

[faction=2101] Suramar 50.71 , 49.34
[faction=2102] Broken Shore 33.70 , 49.80
[faction=2100] Stormheim 90.69 , 10.87 (Shield's rest)
[faction=2097] Azsuna 43.21 , 40.55
[faction=2098] Val'sharah 53.41 , 72.86 (Lorlathil)
[faction=2099] Highmountain 32.62 , 40.80 (Thunder totem)

For those looking for TomTom way points
/way Thunder Totem 32.4 41.8 Akule Riverhorn
/way Suramar 50.71, 49.34 Sha'leth
/way #646 33.70, 49.80 Impus (Broken Shore)
/way Azsuna 43.21, 40.55 Ilyssia of the Waters
/way Val'sharah 53.41, 72.86 Keeper Raynae
/way Stormheim 90.69, 10.87 Corbyn


Flight Points:

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• Akule - Thunder Totem (Western bridge leading out)
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• Sha'leth - Meredil or Crimson Thicket (just outside Suramar on the Northern bridge close to Su'esh)
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• Impus - Deliverance Point (northern islelet of island to west, just past the shipwrecks)
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• Ilyssia - Illidari Stand (follow path to north-west, right side of road where the Sea Lion Ravyn-Drath sits on the beach to left)
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• Keeper - Lorlathil (pond to west)
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• Corbyn - Shield's Rest (raven on rock, half way between FP and sea)
• 
  

Edit: updated with DF version of the co-ordinates (credit to @YodasEvilTwin below)