While sharks play important roles in the world’s marine ecosystems, there are times when we’d like them to just go away. In the case of the longline fishery, sharks can annihilate or scare away a fisherman’s catch, damage fishing gear, and lead to waste, especially when sharks themselves get hooked. The Hawai`i longline fleet alone catches about 19 sharks for every thousand hooks thrown into the water.
To avoid shark depredation and bycatch, the fishing industry and scientists have investigated possible chemical, magnetic, and electrical deterrents. Recently they discovered that certain types of metals can repel sharks, even when food is involved.
At the Western Pacific Fishery Management Council’s Scientific and Statistical Committee meeting last month, John Wang, a scientist with the National Oceanic and Atmospheric Administration, presented the results of his study of electropositive metal effects on shark feeding behavior conducted last year in waters off O`ahu’s North Shore.
In cooperation with the shark-viewing tour company Hawaiian Shark Adventures, Wang and NOAA’s Yonat Swimmer sunk wooden `opelu-baited poles, two at a time, into waters where Galapagos, sandbar, and tiger sharks were swimming. From the safety of a shark viewing cage, they watched how the sharks reacted. In each trial, one of the poles was held adjacent to a control metal (lead), while the other was held near a metal from the Lanthanide series of elements, also known as rare earth metals.
What they found surprised them, Wang said, noting that the sharks exhibited very distinct aversion behaviors around the electropositive Lanthanide metal. At the meeting, Wang showed video footage taken from inside a viewing cage of sharks swimming up to and eating the bait from the control poles, while sharks that approached the poles near the Lanthanide metal jerked their heads away from the bait at the last second or avoided the pole altogether. These aversion responses, which included sudden and abrupt changes in a shark’s head or body motion, increased when the sharks approached the electropositive poles, he said.
Even so, the metals did not always keep the sharks from taking a bite from the `opelu. In 77 trials, sharks took their first bites of bait from the control poles 75 percent of the time, Wang said.
Wang’s and Swimmer’s results are consistent with discoveries made by SharkDefense, LLC, in the Bahamas. According to a December 2006 report by SharkDefense’s Michael Herrmann and Eric Stroud and consulting marine biologist Patrick Rice, when approached with acrylic poles tipped with certain Lanthanide metals, “sleeping” lemon and nurse sharks would wake and react violently.
“The strength of avoidance behavior appeared to roughly correlate to the position of the metal in the Lanthanide series, with elements 57-64 showing more reactivity than elements 75-71,” the report states.
The report continues that calcium and strontium, which are highly electropositive metals, are potent, but last only one to two hours in seawater.
“An alternative to high priced pure Lanthanide metals are alloys of early-Lanthanide metals, particularly Neodymium-Praseodymium alloy, which offer benefits of high electropositivity, machinability, and somewhat stronger corrosion resistance than the pure Lanthanide metal component in seawater,” the report states.
In response to questions from the committee, Wang stated that Stroud’s preliminary work on pelagic target species suggests that these metals won’t affect them. As for his own future studies, Wang said he hopes to investigate the reaction of sharks in different behavioral states to the metals, the effectiveness of combinations of metals, and habituation tests, among other things. He adds that he has not been able to find any information on the toxicity of the metals.
SSC member Dan Pohlemus pointed out that the issue of corrosion also needs to be dealt with, since Wang stated that the corrosion rate for the Lanthanide metals tested is two grams per hour.
Council Staff Opposes Petition
To List Loggerheads Turtles
As Endangered Species
For the past several years, the conservation community and the Hawai`i longline fishing industry have battled over regulations intended to protect threatened and endangered sea turtles from being caught or killed by longline fishing gear. In 2000, the fishery was shut down, but reopened in 2004 under new regulations that have reduced turtle bycatch significantly.
Even so, the battles continue. Last year, the Hawai`i Longline Association proposed raising some of the caps imposed by the National Marine Fisheries Service on fishing effort and turtle catches. Also, the law firm Earthjustice, on behalf of the Turtle Island Restoration Network and the Center for Biological Diversity, filed a petition with NMFS and the U.S. Fish and Wildlife Service to reclassify the North Pacific population of the loggerhead sea turtle (Caretta caretta) from the status of threatened to endangered and designate as critical habitat all state and federal waters and Exclusive Economic Zones used by the turtles for foraging off Hawai`i and the U.S. West Coast.
Not surprisingly, the Western Pacific Fishery Management Council opposes the reclassification.
“Whilst loggerhead populations are depressed … the status of endangered is unwarranted,” Paul Dalzell, the council’s chief scientist, said at the Scientific and Statistical Committee meeting.
The petitioners argue that current trends suggest the North Pacific loggerheads will probably be “quasi-extinct” (defined as 50 adult females) within about 50 years. Dalzell noted, however, that according to the National Oceanic and Atmospheric Administration’s most recent five-year review of the loggerhead population, it is not in a “steady monotone decline.”
The Hawai`i swordfishing fleet is allowed to catch 17 loggerheads before it is shut down for the rest of the year. Given that, Dalzell said, “I’m really now beginning to have serious doubts on the impacts of longlining on loggerheads,” and noted that a recent turtle workshop on longlining in the North Pacific revealed that loggerheads are being caught there at a rate that is 100 times what it is in Hawai`i.
Trying to save loggerheads by focusing only on the fishery here is “like trying to wage a war on drugs and focusing on El Salvador,” he said.
By all accounts, Baja California and Japan are the critical loggerhead habitats, Baja being where they forage and Japan where they nest.
“The coastal fishery bycatch issue [as opposed to pelagic fishery bycatch] is the number one hot button issue,” Dalzell said. According to research by Japan’s Takashi Ishihara, which was presented at the workshop, many thousands of loggerheads are being caught in pound nets – cages with an opening at one end that leads to several chambers.
Ishihara estimates that there are 750 large and 11,400 smaller pound nets around Japan. At a single pound net in Miyama, Ishihara found that 96 percent of the loggerheads caught died and 16 were killed in just one day. Dalzell multiplied the estimated monthly loggerhead catches from a Japanese pound net by the number of large pound nets around Japan and suggested that the nets could capture roughly 70,000 and kill 20,000 loggerheads a year.
While he admitted that those numbers aren’t accurate, since not all large pound nets are located near nesting areas, Dalzell pointed out that these nets are also used in Taiwan and China.
“This and those coastal fisheries in Baja are what’s hammering the loggerhead,” Dalzell said.
An October 2007 article on small-scale fisheries bycatch in Baja California, published in PLoS ONE, estimates that a minimum of 299 loggerhead turtles were killed by the local gillnet fishery in 2005 and the bottom-set longline fishery killed at least 680. The study, by Hoyt Peckham, David Maldonado Diaz, Andreas Walli, Georgita Ruiz, Larry Crowder, and Wallace Nichols, states that total loggerhead mortality in the area is probably much higher than 1,000 because they used minimum factors (hooks, fishing days, etc.) in their calculations, and because they estimated bycatch for only two of 12 or more fleets that fish in or near loggerhead high-use areas.
Despite the obvious impacts of fishing on loggerheads, Dalzell said concentrating on nesting areas will do more for the turtles than fishing restrictions or regulations.
An article by Rebecca Lewison of San Diego State University and Crowder of Duke University published last year in Conservation Biology, however, suggests that fishing regulations are indeed necessary, but should not be limited to longlining.
Their article, titled “Putting Longline Bycatch of Sea Turtles into Perspective,” states that while bycatch rates from individual vessels are low, “the amount of gear deployed by longline vessels suggests that cumulative bycatch of turtles from older age classes is substantial. Current estimates suggest that even if pelagic longlines are not the largest single source of fisheries-related mortality, longline bycatch is high enough to warrant management actions in all fleets that encounter sea turtles. Nevertheless, preliminary data also suggest that bycatch from gillnets and trawl fisheries is equally high or higher than longline bycatch with far higher mortality rates. Until gillnet and trawl fisheries are subject to the same level of scrutiny given to pelagic longlines, our understanding of the overall impact of fisheries bycatch on vulnerable sea turtle populations will be incomplete.”
Crowder and his co-authors of the October 2007 article on Baja bycatch also seem to side with the petitioners in regard to the status of the North Pacific loggerhead population. The article states that censuses of North Pacific loggerheads nesting in Japan “indicate as much as a 90 percent decrease in nesting females within the past three generations to fewer than 1,000 per year, qualifying the population for critically endangered status.”
Groups Seek Federal Listing
For Black-Footed Albatross
On October 1, 2004, Earthjustice, again on behalf of the Turtle Island Restoration Network and the Center for Biological Diversity, submitted a petition to the U.S. Fish and Wildlife Service requesting that the black-footed albatross (Phoebastria nigripes) be listed as a threatened or endangered species and that critical habitat for the bird be designated. The petition stated that commercial fisheries in the North Pacific were inadvertently killing from one to five percent of the global population of the albatross and that the restrictions that had been imposed on the Hawai`i-based longline fleet were inadequate because they allowed fishing in albatross foraging areas.
At the time the petition was submitted, the FWS was busy trying to comply by 2005 with a court-approved settlement regarding listing rules and informed the groups that it had insufficient resources to initiate the process of reviewing the petition.
Three years later, on October 9, 2007, the FWS announced it was finally initiating the 90-day period during which the public can submit data, comments, and information to be considered by the FWS in its review of the petition. In its Federal Register announcement, the FWS stated that the petition provided “credible scientific information that incidental mortality in commercial longline fisheries may threaten the existence of the black-footed albatross.”
At the SSC meeting, however, Dalzell argued that the population information kept by the FWS is so poor, “there isn’t the data available to make a decision.”
Information is kept in cardboard boxes and the banding system for black-footed and Laysan albatrosses is not well designed, he said, adding, “Data collected for population assessments and demographic measurements has been basically, if you forgive the expression, pissed against the wall.”
Dalzell said that the information presented in the petition is years out of date and claimed that the population is stable and has been so for a decade, with about 60,000 nesting pairs a year.
As far as bycatch by the Hawai`i longline industry, that has been reduced ten-fold – from an estimate of between 1,000 and 2,000 birds a year in the 1990s and 2000, to the present estimate of “ones and tens” a year, Dalzell said. Since 2002, between 16 and 89 black-footed albatrosses interacted with the Hawai`i longline fleet each year.
“There seems to be no correlation between black-footed albatross populations and longline growth,” Dalzell said, adding that most of the population is in the Northwest Hawaiian Islands, which “are as protected as you can get.”
Despite similar comments submitted to the FWS by the council in 2005, the agency concluded in its October announcement, “Although mitigation measures have reduced mortality of black-footed albatrosses in some (U.S.-based) fisheries, the information in the petition indicates that fishery-related threats to the species throughout its range are ongoing.”
— Teresa Dawson
Volume 18, Number 10 April 2008