sharks are in troublegood news for sharks
On the West coast of North America, the commercial shark fishery started around 1915 and hit its first peak in 1939, when over 9.3 million pounds of shark were landed. The primary target was the soupfin shark, which earned its name from its fins being used to make shark fin soup. The sharks’ liver oil was used to make vitamin A until scientists found a way to produce it synthetically. Between 1936 and 1944, over 24 million pounds of soupfin shark were landed in America. The fishery collapsed in 1945 because soupfins had basically been wiped out. To this day, the population has not recovered. This pattern is commonly referred to as the boom and bust cycle, which is typically when a few fishermen begin to exploit one species of shark, and as soon as it becomes lucrative, a boom follows. Because of the slow reproductive rate of sharks and the lack of regulations for new fisheries, the fishery quickly goes into a bust cycle of precipitous decline. You can see this cycle repeat itself on Figure 1.
From 1950 to 1976, commercial shark landings averaged below 1 million pounds each year until the commercial shark fishery hit its second peak in 1979, when 11.6 million pounds of shark were landed on the west coast of America. This time, the primary target was the spiny dogfish (actually a shark). The spiny dogfish was used to make fish and chips. In 1979, 9.4 million pounds of spiny dogfish were landed on the west coast. Spiny dogfish are now on the IUCN Red List as having a high risk of extinction. The commercial thresher shark fishery peaked in 1982, when over 2.3 million pounds were landed on the west coast (see Figure 2). Since the early 1970s, scientists (Holden 1973; Hanan 1984) have warned that it is not possible to sustainably fish threshers or any other elasmobranch species without further research. Despite these warnings, over 40 years later thresher sharks continue to be targeted. The research considered imperative for a sustainable fishery has not been conducted. In 2008, 73,400 pounds of thresher shark were landed in the Santa Barbara area (see figure 3). All three species of thresher sharks have recently been added to the International Union for the Conservation of Nature (IUCN) Red List as vulnerable to extinction. Like many other sharks, threshers are very slow to reproduce. They take eight to ten years to become sexually mature and after a nine to ten-month gestation period only yield one or two pups. They do not spawn hundreds of eggs as some other fish do.
Drift gillnets are the method of choice when it comes to commercially fishing threshers, a method that has been responsible for a high number of marine mammal injuries and casualties as result of bycatch. (Bycatch is a term used to refer to any species caught accidentally while fishing for another species.) Fortunately, electronic pingers have greatly reduced marine mammal interactions.
Bycatch is a huge threat to sharks. According to the Food and Agriculture Organization (FAO), there are few fisheries that don’t catch sharks as bycatch, and some fisheries actually catch more sharks than the targeted species. Estimates suggest tens of millions of sharks are caught as bycatch each year. Longlining, trawling and gillnetting are responsible for most shark bycatch. Mexico and Japan have a joint commercial swordfish effort that is unregulated. The landing reports from these fisheries are inaccurate, so the extent of the bycatch is unknown. Longlines and gillnets are used to target swordfish off Baja, California but a lot of threshers and other sharks end up as bycatch. Many threshers caught in local gillnets have had hooks in their mouths from longlines.
Commercial fishing and bycatch are by no means the only threat to threshers. Sport anglers find great thrills in catching threshers. Thresher and mako shark tournaments are held three times a year right here in Southern California. One big problem with fishing sharks for sport is that there is no way to accurately keep track of how many are being killed. Some shark tournaments require you to bring the whole shark back to the dock, but others give you the option to catch-and-release for conservation purposes. However, in 2007, a collaborative study was initiated by the Pfleger Institute of Environmental Research, the Southwest Fisheries Science Center and the NMFS Southwest Region for Sustainable Fisheries Division to examine the post-release survival of common thresher sharks. In response to the growing recreational fishery for highly migratory sharks, this pilot project used pop-up satelite archival transmitters (PSAT) to study the movement patterns and post-release survivability of rod-and-reel caught common thresher sharks. The recovery of a PSAT provided high-resolution temperature and depth data, and determined that one mature female, estimated at 335 pounds, died within 48 hours of release. Preliminary results suggest that capture stress, especially in large individuals, may lead to increased mortality in this fishery. This type of research is long overdue.
Why do we still continue to kill sharks locally, considering:
• The slow reproductive rate of sharks;
• The warnings from scientists about sustainability;
• Inadequate management by the California Department of Fish & Game, as evidenced by steadily declining landings;
• Historically high commercial landings, followed by severe population declines;
• Inaccurate sport fishing landing reports, which make impact assessments impossible;
• The unknown amount of post catch-and-release deaths;
• The inaccurate bycatch estimates;
• The inaccurate Mexican and Japanese landing reports?
In a few words, we still kill sharks because of consumer demand.
We the consumers need to educate ourselves about this problem and stop this demand.
References:
Hanan, Doyle A. 1984. Analysis of the Common Thresher Shark (Alopias vulpinus) in the California Bight.
U.S. Department of Commerce, National Oceanic and Atmosheric Orginization (NOAA), National Marine Fisheries Service (NMFS), Southwest Fisheries Science Center (SWFSC) Administrative Report LJ-84-10C, 34 pages.
Cited in: Review of the U.S. West Coast Commercial Shark Fisheries.
David B. Holts. Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, CA 92038.
Holden, M. J. 1973. Are Long-Term Sustainable Fisheries for Elasmobranchs Possible?
Verbal Reports from the Reunion of the International Council for the Exploration of the Sea 164:360-367
Cited in: Review of the U.S. West Coast Commercial Shark Fisheries.
David B. Holts. Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, CA 92038.