Fate of yellowfin bream, Acanthopagrus australis after ingesting offset and/or inline barbed and barbless J and circle hooks

Abstract

Abstract Offset J and circle hooks (nickel-plated carbon steel) were modified by removing the barb and bending the front parallel (‘inline’) with the shaft (circle only) to assess their utility for reducing mortality after ingestion by one of Australia’s most commonly angled species—yellowfin bream, Acanthropagrus australis—and for increasing hook ejection and corrosion. One-hundred-and-fifty-one fish were angled from large holding tanks using six passively fished hook treatments (barbless and barbed offset J hooks, and barbed and barbless offset and inline circle hooks), which were all similar in size. Thirty-five fish were mouth hooked (mostly on circle hooks), while the remaining 116 ingested hooks (n\u2009=\u200917–24 per treatment), had their lines cut and were released in pairs into 110-l tanks and monitored along with 14 control fish (not hooked) for six weeks. One control (7%) and 26 (22%) hook-ingested fish died (16 after a vital organ was perforated), with 23 mortalities occurring within ten days. Mortalities were not affected by hook design, but were significantly greater among fish with retained (19 of 35 individuals) rather than ejected (3/81) hooks. For the fish that ejected their hooks (70%), there were no differences in frequencies among the six treatments, but both ejected and retained barbless hooks corroded significantly faster (9 and 3×, respectively) than barbed designs. Irrespective of the treatment, on average after six weeks, surviving hook-ingested fish had a lower mean weight than controls, but those that ejected hooks had greater mean weights than those that retained hooks. Notwithstanding some loss of weight (as an index of health), the data support a supposition that many hook-ingested fish released with the line cut will eventually eject hooks of varying designs and survive.