Circle hooks

A circular hook design in which the point of the hook is perpendicular to the hook shank. Circle hooks are used widely in many recreational and commercial fisheries and recently have been shown to reduce both the hooking rate and the mortality of turtles that are hooked on pelagic longline gear. As a result of several successful field trials (Bolten and Bjorndal, 2005; Watson et al., 2005), these hooks are becoming increasingly used in longline fisheries.

Experiment to Evaluate Gear Modification on Rates of Sea Turtle Bycatch in the Swordfish Longline Fishery in the Azores Phase 3

Study Type: 

wild

Location: 

Azores

Target catch: 

Swordfish and blue shark

Effect on bycatch species: 

There was no significant difference in the number of loggerhead sea turtles caught in the Azores longline swordfish and blue shark fishery between straight 16/0, offset 16/0, and offset 18/0 circle hooks.

Effect on target catch: 

Straight 16/0 circle hooks caught the most blue sharks in the Azores longline swordfish and blue shark fishery, followed by offset 18/0 circle hooks. Offset 16/0 circle hooks caught the fewest blue sharks.

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Fishing methods to reduce sea turtle mortality associated with pelagic longlines

Study Type: 

wild

Location: 

NW Atlantic

Target catch: 

swordfish and tuna

Effect on bycatch species: 

Reduced interactions

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Field Study

Study Type: 

wild

Location: 

Eastern Pacific Ocean

Target catch: 

Mahi-mahi and tunas, billfishes, sharks (TBS)

Effect on bycatch species: 

Decreased hookings of sea turtles

Effect on target catch: 

Not consistent

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Field Study 723

Study Type: 

wild

Location: 

Western North Atlantic

Target catch: 

Swordfish and tuna

Effect on bycatch species: 

Circle hooks decreased loggerhead and leatherback catch; even more effective for loggerheads when combined with mackerel bait

Effect on target catch: 

Circle hooks combined with mackerel bait increased swordfish catch by weight. With squid, decreased swordfish catch, increased bluefin and albacore tuna catch. Mackerel bait decreased bigeye and albacore tuna catch.

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Field Study 705

Study Type: 

wild

Location: 

Southwest Atlantic

Target catch: 

Tuna

Effect on bycatch species: 

American style longlines - no significant difference in catch rates for blue or porbeagle sharks, seabirds or sea turtles. Spanish style longline - significant decrease in pelagic stingray catch rates on circle hooks, no significant differences in catch

Effect on target catch: 

Albacore catches increased with circle hooks on both types of longline. Shortfin mako shark catch rates increased with circle hooks on the American style longlines.

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Field Study

Study Type: 

wild

Location: 

Central Mediterranean Sea

Target catch: 

swordfish

Effect on bycatch species: 

Circle hooks captured fewer (2) loggerheads compared to 2J hooks (9)

Effect on target catch: 

16/0 hooks resulted in a non-statistically significant decrease in catchability compared to size 2 J hooks, but statistically significant decrease compared to size 4 and 5 J hooks

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Field Study

Study Type: 

wild

Location: 

Eastern Pacific

Target catch: 

tuna and billfish

Effect on bycatch species: 

Small circle hook (C15) had lowest catch of sharks

Effect on target catch: 

Small circle hook (C15) had lowest catch of billfish

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Field Study

Study Type: 

wild

Location: 

Eastern Pacific Ocean

Target catch: 

Billfish and tuna

Effect on bycatch species: 

Significant differences were found between J4 and C15 and between J4 and C18.

Effect on target catch: 

Significant differences between catch rates were only found between the J-4 and C18 hooks. Large circle hooks (C18) had the lowest catch rates for tunas and small circle hooks (C15) had the lowest catch rates for billfish

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Field Study 657

Study Type: 

wild

Location: 

Pacific Ocean

Target catch: 

Tuna

Effect on bycatch species: 

Blue and oceanic whitetip shark bycatch increased.

Effect on target catch: 

Tuna catches were significantly higher, but lengths for bigeye and skipjack were smaller; shortbill spearfish and striped marlin catch was lower; no difference in swordfish catch rates, but lengths were greater

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