To Remove the Hook or Not: Experimental Degradation of Fishhooks and Implications to Catch-and-Release Angling and Commercial Fishing Applications

Defense Date

7-27-2016

Document Type

Capstone

Degree Name

M.S. Marine Biology

First Advisor

David W. Kerstetter

Second Advisor

Robin Sherman

Abstract

How to best release a caught fish is an enduring question in fisheries science. The "conventional wisdom" has always been to cut the line, thereby leaving the hook in the animal whereby the animal benefits from reduced handling allowing it to fully recover and survive until the hook degrades to a point at which it can be shed. Baseline data was determined on the degradability of commonly used hooks in both recreational and commercial fisheries in waters of the Florida Straits and the Gulf of Mexico, which may be of critical importance if high mortality rates associated with retained hooks are not adequately described within stock assessments. Seawater and various pH values (1.5 pH, representative of the conditions for elasmobranch and marine mammal gastric digestion; 2.5 pH, corresponding to pH for teleost gastric digestion; 7.8 pH, corresponding to the pH of teleost blood plasma) were selected from the literature as representative of varying taxa and conditions as treatments for ten separate hook types, four generally intended for commercial fisheries and six for recreational fisheries. Degradation of the hooks was quantified both weight (to the nearest mg) and tensile strength loss (to the nearest kg) and analyzed quantitatively by regression analyses and a Tukey-Kramer HSD. Statistical significance supporting modeled degradation was assessed at the =0.05 level by R2 adjusted (Denoted “Adj. R2”) values (>0.70) and p values (ANOVA< 0.05). Most of the hooks submerged in physiological-strength acid solutions and seawater remained largely unchanged throughout the study. Mass percent and tensile strength decreases between sample days (including no change at all) suggest that the materials used for commercial and recreational fish hooks can resist corrosion from stomach acids at a pH as low as 1.5 and ambient seawater. The results of this study and a comprehensive literature review suggest that regardless of treatment, the assumption that deeply embedded hooks will degrade completely or to a point where they can be shed in a relatively short amount of time (i.e., days) is unlikely and indicates the need to better understand the consequent effects of long-term presence of fishing hooks.

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