Your e-mail string on circle hooks was passed on to us.
Rudy Lukacovic has done a lot of work on circle hook mortality of striped bass in Chesapeake Bay. This work was conducted with anglers and not long-lines or trot-lines. In short, circle hooks reduce hooking mortality because deep-hooking that penetrates major organs is greatly reduced. They also are less efficient, hooking a significantly lower percentage of striped bass per strike. I suppose this combination reduces bycatch as long as anglers don't get frustrated with missed strikes and switch back to j-hooks.
This work has been summarized in
Lukacovic, R. and J. H. Uphoff. 2007. What influences catch-and-release mortality of striped bass caught on natural bait in upper Chesapeake Bay? In Ø. Aas, editor. Global Challenges in Recreational Fisheries Management. Blackwell Press, UK, pp 208-213.
We never received a PDF of the paper, but the Word version of the final draft is available if you would like a copy.
We used logistic regression to determine factors influencing mortality and deep-hooking rates of nearly 1,300 striped bass, Morone saxatilis (Walbaum) caught with natural bait using J-shaped or non-offset circle hooks and released into Chesapeake Bay. Mortality was greater for deeply hooked fish, higher air temperatures, and larger fish; water temperature, salinity and hook style were not significant influences. Hook type and fish length had the greatest positive influence on deep-hooking rate. Odds of dying were 17-times higher if a striped bass was deeply hooked and J-hooks had 3.7-times greater odds of deep-hooking than circle hooks. Anglers using circle hooks landed 27% of fish that struck while those using J-hooks landed 41%. The largest fish (930 mm TL) was nearly five-times more likely to be deep-hooked than the smallest (220 mm TL). Predicted mortality was often high (> 12%) during June-July, while moderate (3-12%) to low (<3%) predictions of mortality mostly occurred during August-October.
Hope this is helpful.
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