Safe Hooks, Safe Sharks?

Russ Vetter, Leg II SHARK CRUISE. Today we are headed for the dock. Yesterday was mostly routine except for high winds. High winds and sea state make retrieving the line and handling the sharks both unsafe and very wet. We set in winds around 20 knots (one knot=one nautical mile per hour) and by retrieval time at 5:30 p.m., we had quite a swell running. The crew was adept at keeping the bow upswell and things went well, although a bit wet. Fortunately, no large animals were caught or things would have gotten more complicated.

Wednesday marked the end of the second repeat of our standard catch survey, all stations covered, which left this morning for the beginning of our new objective for leg III, a comparison of the catch rates and incidental mortality associated with “J” hooks and “circle hooks”. We have been hoping for years to have the sea time to compare catch rates and mortality between these two gear types (here's a photo of Wes Vetter holding traditional J and circle hooks) This year we have 13 days on Leg III of the Shark Cruise to make this comparison.

Long-term fisheries trend data requires that every variable associated with fishing is done exactly the same, year after year, or that a conversion factor is generated that allows conversion from the original gear to the new gear. NOAA Fisheries has mandated that some fisheries that accidentally catch a lot of sea turtles in addition to the fish they really want (the turtles are called "bycatch") change from J to circle hooks, with the hope that this approach will reduce the number of sea turtle deaths.

As you might be able to visualize from the picture, the circle hook has a rounded shank and the barb points back towards the shank. While a J hook is good for catching fish destined to be eaten, if a shark or turtle swallows the bait and the hook goes down to the stomach, the J hook has a tendency to lodge in the gut causing bleeding and the hook must be left in the animal. However, the circle hook will slide back up to the jaw. Reduced mortality has been documented for sea turtles, but not for sharks. Our preliminary observations from our studies in the tropics suggest that circle hooks limit mortality in sharks, too.

Our goal on Leg III is to show that catch rates remain unchanged on the newer hooks or to develop a conversion factor to allow the previous 15 years to be accurately compared to the new data. You can imagine that every type of fishing or sampling gear has some sampling characteristics. For example the large hooks that we use will catch large fish while small fish can take bites of bait and never get hooked. If the circle hooks are less attractive to sharks or more sharks get the bait without getting hooked, then our catch rate might drop by 10%. We would not want to tell everyone that the shark population dropped 10% in one year when it was really our gear working less well. If we know this is happening we can adjust our catch rates up by 10% so the data matches that from previous years.

As we head to the docks, the volunteers are busy talking about what they will do and eat when they get off. Meanwhile chief scientist Suzy Kohin makes lists of all the things that need to be purchased, repaired, and replaced between Friday and Sunday, when we sail again. ABOARD THE R/V DAVID STARR JORDAN, off San Diego, California