Making these customary items are one of my areas of expertise, the researching and replication of material culture is the basis for my quality of contemporary practice.
I will try to outline the various components.
Type of hook, technique and purpose
these 2 hooks are different in their use and the species that they target, so the one on the left which is a Pa kahawai, has a relatively short barb with plenty of lashing because it is used to catch kahawai, a schooling fish which congregates even to this day is patches of over 3- hectares at times. It is a free fighting fish that chases around baitfish, and so the lure is dragged behind the waka, and the fish are pulled in and flicked on board, much in the same way i have seen tuna fishermen flick their catch on board. The Paua/haliotis iris shell is used much in the same way a spinner flashes and reflects light, giving the impression of a living swimming baitfish. This hook is used to catch by either hooking in the mouth by more commonly by hooking in the corner bone plates on the side of the kahawai or the inner gills.
Shank and barb angles/faces
In a Pa kahawai matau, the shell is cut first and then a wooden shank is crafted to fit it. One of my ancestors Te Rangi Hiiroa gives a step-by-step diagrammatic version of how they are made in his book, The Coming of the Maori, I am away from home at the moment but i an post this later when i get a chance. The angles are varied but are crucial to having enough material on each piece (shank-barb) to enable a decent purchase by the lashing material. A common but hard to master triangular lashing is used for the strongest effect. Our people were adept at using this lashing technique as everything, housing architecture, canoes etc all used the same technique.
The second hook is a gorge hook, only used to honk the gills of fish like groper, john dory etc, any fish that had a large protruding mouth and swallowed or gobbled their prey whole, designed to hook into the gills and then draw the weight to a point low down on the shank to relieve pressure on the extended or most distant areas of the barb from the shank.
gum as glue,
has been recorded that gum was used but from experience is of little or no value for this application, once you have figured out the angles needed for the joined faces and have mastered the lashing technique, it is more a nuisance than anything.
lashing and lashing materials
lashing media is usually toi cordyline, or flax, which can be stripped down very quickly to produce a quick and strong line, we call this process mire, but its very similar to the 3 twine twist and then untwist technique that sailors learnt and used for their rope. Once again our people were used to doing this on large scales and our flax ropes were one of the reasons why Europe found it advantageous to trade and settle here through the industrial revolution of the 17-1800s.
This rope was for everyday use almost indestructable for these applications. This type of lashing vs knotting is self tightening, every new lashing layer tightens on the those below it and eventually the last ones are pulled up under the others to produce a never ending lash (one that does not come undone).
In general, we did not wear our working hooks around our necks, they were reserved for ritual versions of the matau, sometimes referencing the narrative of Maui fishing up the North island or of the significant role that matau and the food they caught played in Maori society.
Sometimes there is a hidden throng of line that is lashed over, this line can run from part way up both the shank and barb, so that there are 2 points of stress to take the strain of the fighting fish, so one throng inside the curved inner apex between shank and barb and the other stress loaded lash at the bottom end of the matau., other times a rebate cut is made so that a tongue or protruding centre slice of the barb can be sandwiched between two outer flanges of the shank and then it give an added opportunity for a much stronger stress loaded join. These 2 previous options are not common though, hook making was a common and communal activity for those that lived adjacent to the sea, they weren't meant to last forever, they were working tools to catch everyday fish that were plentiful in those times.
I hope this helped