As I wrote before, for my 2nd thesis (2000) I developed a bait for the longline fishery of snapper in NZ (that later became this paper), and had to get deep into the science of longlining and got to interact with the guru of this gear Dr Svein Løkkeborg, that still is, in my opinion, the person that understand at best the complicated events that have to happen from the moment that you set to the moment that you haul your fish on deck.
that was me once upon a time…
I based my thesis on the development of a bait for the longlining fishery of snapper (Pagrus auratus), using different proportions of industry surplus Greenshell™ Mussel (Perna canaliculus) and gurnard (Chelodinichthys kumu), which are known to be part of the snapper diet.
Both these species contain large amounts of glycine and alanine, which are known to stimulate feeding behaviour in snapper, and are substantial part of processing residues in the NZ industry, so I did the whole research diving into environmental chemoreception by fish, baiting technology and sausage-making process (best way to store bait), then tested the baits in a Snapper farm and working on small demersal longliners of the east coast of NZ.
I compared the results for 1000 hooks of my bait against the same quantity of hooks baited with control squid bait. And squid was 83.93% more effective compared to my bait… so that wasn't very good… although the catches with my bait were low, the selectivity for snapper over the standard mix of species with squid) was 29.25 % higher, which was very encouraging.
Since them… among my way too many interests are the chemistry, effectiveness, handling and price of bait (see here) but in particular against squid as bait… that it seems is mostly caught to then be used to catch more expensive fish.
So when this paper “Effect of pelagic longline bait type on species selectivity: a global synthesis of evidence” by Eric Gillman and other researchers came trough my screen, interest was immediate. And while the article does not dwell on the topics I did, it touches close to the aim of my thesis, even if I aimed at a demersal species:
No studies were identified that found an artificial bait to be economically viable for use in pelagic longline fisheries. Developing an artificial pelagic longline bait that retains acceptable catch rates of market species but reduces catch risk of species of conservation concern warrants investment in research and development.
Furthermore, it does raise a key issue… catching more of all, or catching less but more specific?
They say:
A related research priority is to investigate potential socioeconomic effects on pelagic longline fisheries from changing bait type. For instance, would it be economically viable for an artisanal fishery that currently catches squid to use as longline bait to replace this quasi-free bait source with purchased fish bait, and would the change in catch rates of market species caused by this change in bait type be viable? Understanding the ecological effects on the stock status of forage fish species, and socioeconomic effects on food security, from increased demand for these species for use as bait by longline fisheries, and estimating the conservation gains to species of conservation concern from reduced longline fishing mortality that could be achieved from changes in bait type, are additional research priorities.
Here is the abstract … yet read the original!
Fisheries can profoundly affect bycatch species with ‘slow’ life history traits. Managing bait type offers one tool to control species selectivity. Different species and sizes of marine predators have different prey, and hence bait, preferences. This preference is a function of a bait’s chemical, visual, acoustic and textural characteristics and size, and for seabirds the effect on hook sink rate is also important. We conducted a global meta-analysis of existing estimates of the relative risk of capture on different pelagic longline baits. We applied a Bayesian random effects meta-analytic regression modelling approach to estimate overall expected bait-specific catch rates. For blue shark and marine turtles, there were 34% (95% HDI: 4–59%) and 60% (95% HDI: 44–76%) significantly lower relative risks of capture on forage fish bait than squid bait, respectively. Overall estimates of bait-specific relative risk were not significantly different for seven other assessed taxa. The lack of a significant overall estimate of relative capture risk for pelagic shark species combined but significant effect for blue sharks suggests there is species-specific variability in bait-specific catch risk within this group. A qualitative literature review suggests that tunas and istiophorid billfishes may have higher catch rates on squid than fish bait, which conflicts with reducing marine turtle and blue shark catch rates. The findings from this synthesis of quantitative and qualitative evidence support identifying economically viable bycatch management measures with acceptable tradeoffs when multispecies conflicts are unavoidable, and highlight research priorities for global pelagic longline fisheries.