Welcome to the second issue of Fish Briefs! Articles in Issue Two: Robert S. Gregory, John T. Anderson. "Substrate selection and use of protective cover by juvenile Atlantic cod Gadus morhua in inshore waters off Newfoundland" in Marine Ecology Progress Series, 146:9-20, 1997 S.F. Thrush et al. "Disturbance of the Marine Benthic Habitat by Commercial Fishing: Impacts at the Scale of the Fishery" in Ecological Applications. 8 (3): 866-879, 1998. Prena et al. "Experimental otter trawling on a sandy bottom ecosystem of the Grand Banks of Newfoundland: analysis of trawl bycatch and effects on epifauna" Marine Ecology Progress Series, 1999. 181:107-124. Callum M. Roberts. "Ecological advice for the global fisheries crisis" in TREE, 12 (1): 35-38, 1997. ************ As you will remember, Fish Briefs is a "plain language" summary of the latest scientific papers about fish with a focus on their interactions with habitat. It is distributed every two months by American Oceans Campaign and is peer reviewed by a volunteer scientific panel to ensure that the scientific results are not lost in the translation. Fish Briefs is an experiment in translation of technical research papers for those who are trying to apply the information. Our audience includes fishermen, fishery managers, scientists, conservationists, government officials and others. If you know someone who wants to see Fish Briefs, please forward their email. If they don't have email, we can fax or mail it to them. If you have comments, questions or suggestions, please email me at aoccb@wizard.net. Also email me if you do not want to receive Fish Briefs. We hope you find this bulletin helpful. Please forward at will. American Oceans Campaign is a national environmental organization dedicated to safeguarding the vitality of the oceans and our coastal waters. AOC is committed to scientific information in advocating for sound public policy. We are equally committed to developing partnerships with all entitites interested in protecting the environment. Carla Brown aoccb@wizard.net www.americanoceans.org 202-544-3526
Peter Auster, Editor National Undersea Research Center, University of Connecticut www.nurc.uconn.edu *********** Robert S. Gregory, John T. Anderson. "Substrate selection and use of protective cover by juvenile Atlantic cod Gadus morhua in inshore waters off Newfoundland" in Marine Ecology Progress Series, 146:9-20, 1997 ****** Young Cod Hide from Predators in Seafloor Habitats Young cod start out shallow in coastal bays and offshore banks of Newfoundland. By the time they are four years old, they move to deeper waters. Since adult cod like to eat young cod, this separation between adults and young probably keeps many young cod alive. In this study, scientists used submersibles to determine habitat requirements of young cod. The scientists did 10 dives, marking changes in cod and habitat in one minute increments. They saw 196 cod from 1-4 years old, and three cod that were older. The scientists made two key observations. First, they noticed that most young cod occur in waters that are 60-120 meters deep. Second, almost all the cod occurred near three-dimensional habitat. They also saw some differences between one-year-old cod and cod 2-4 years old. While all cod congregated near shelter, the older cod swam closer to the choice spots right beside the structures. The one-year-old cod occurred more often near gravel. This proximity to habitat structure was also reflected in the swimming styles of the fish. The one-year-old cod were actively swimming, whereas the sheltered older cod were inactive. When young cod hide behind rocks and cliffs, they save energy which they would otherwise use swimming or being vigilant. Conserving energy is even more important in winter, when cold water reduces activity and fewer prey are available. The study concluded that cod use habitat structure to hide from predators. No cod were feeding during this study. Cod feed little in winter and this work took place in April. Contact: Robert Gregory - bgregory@athena.nwafc.nf.ca ********** S.F. Thrush et al. "Disturbance of the Marine Benthic Habitat by Commercial Fishing: Impacts at the Scale of the Fishery" in Ecological Applications. 8 (3): 866-879, 1998. ***********
Fish Gear and Species Diversity In this study, scientists sampled 18 sites in the Hauraki Gulf in New Zealand. They collected cores, grab samples and video along a gradient of fishing effort. In other words, samples came from areas with no fishing, a little fishing, and a lot of fishing. They sampled from areas that had been fished by a variety of gears, including trawls, dredges and seines. Estimating fishing effort is difficult, and the scientists acknowledge their subjectivity in this area. They calculated fishing effort in different locations based on local legislation and information from local fishery managers. The study validated many of the predictions that have been made concerning how seafloor animal communities will change as a result of broad-scale habitat disturbance. Importantly, the study concluded that more fishing effort results in lower species diversity and reduced numbers of large and long-lived animals. Many species find refuge in the structures built by immobile animals that live on the surface of the seafloor and create three-dimensional structure. This study showed that the greatest ecological impacts were the removal of species such as molluscs and sponges, which provide this crucial three-dimensional habitat for other species. This study directly linked less complex habitat with increased fishing pressure. Some species are not reduced in areas with high fishing effort. These are often the smaller species with shorter lives. In other cases, adults buried deep in sediment are sometimes not affected, whereas the young living closer to the surface are either killed, damaged or transported away from the habitat. The scientists calculated that 15-20% of the change in the species composition of the animal community on the seafloor can be attributed to trawl and dredge fisheries. Over such a large area of the seafloor, this is clearly a broad-scale human impact. This finding applies to an 80 kilometre area with a range of habitat types and accounts for natural variability of location and sediments. Contact: Simon Thrush - s.thrush@niwa.cri.nz ************ Prena et al. "Experimental otter trawling on a sandy bottom ecosystem of the Grand Banks of Newfoundland: analysis of trawl bycatch and effects on epifauna" Marine Ecology Progress Series, 1999. 181:107-124. ************ Effects of an Otter Trawl
Of all mobile fishing gear, the otter trawl is generally considered to have the least effect on seafloor habitats. Scientists in eastern Canada have been studying this gear to get a clearer picture of how it affects the composition of bycatch, seafloor habitat and seafloor communities. The area studied was a sandy bottom 20 km by 20 km at depths of 120-146 meters. The area was closed to trawling, which allowed the scientists to study only the effects of their trawling effort. In 1992, they sampled the site and found it had more than 139 species - an area rich in life. From 1993 to 1996, the scientists annually did 12 tows in each of three areas. They sampled both the trawled areas and the untrawled areas nearby. They used two kinds of gear to determine the effects of trawling. A rockhopper otter trawl (for both producing the impacts and sampling large animals), and a sled to sample smaller animals living on and in the sediment. Species that showed significant decreases due to trawling were snow crabs, basket stars, sea urchins, sand dollars, brittle stars and soft corals. The more trawling effort, the less bycatch they caught. This may be because the species were removed from the area by trawling, killed or damaged by the trawl, eaten by local predators after damage, or for those that are mobile, moved away from the area. The weight of all species decreased by 24% when compared to unfished sites. No significant effects from trawling were observed for the 4 common mollusc species captured by the sled. Sand dollars, brittle stars, and sea urchins were significantly damaged by being fished with this gear. This study shows that trawling on sand habitats can produce detectable changes in seafloor communities. Contact: Donald Gordon - GordonD@mar.dfo-mpo.gc.ca *************** Callum M. Roberts. "Ecological advice for the global fisheries crisis" in TREE, 12 (1): 35-38, 1997. *************** Reserves Replenish the Ocean In August 1995, fisheries scientists met at a symposium organized by the South Atlantic Fishery Management Council. This paper summarizes their findings about marine reserves. In the past, a central goal of fisheries management was to catch the maximum number of fish without fishing to extinction. This goal was called MSY or maximum sustainable yield. MSY was calculated using: 1. the size of a fish population, and 2. the minimum number of fish
necessary to keep reproducing for a healthy population. Calculating MSY proved to be extremely difficult. Instead of being a fixed quantity, MSY varies in relation to environmental conditions and the interaction of species. Even when MSY was calculated, the management tools used to reach MSY proved inadequate, resulting in risky management. In this article, Roberts argues that "current fisheries management practices leave little room for error." He notes how it is difficult to model species interactions. Normally, when people are faced with risk and uncertainty, they get "insurance." Roberts says that one important form of "insurance" is no-take marine reserves, where fishing is restricted in parts of the ocean. Studies of these reserves show that they function as fish nurseries, and have "spillover", where fish disperse into fishing grounds and replenish stocks. Reserves serve as a hedge against the limitations of management. For example, one standard management policy which promotes conservation is gear modification, such as increasing the size of mesh on nets. This decision may be quite helpful, but it cannot solve all the problems. The nets still catch slow-reproducing and exploited species such as sharks. Reserves ensure there are some places where no sharks are caught. Reserves conserve more than fish, but also habitat which is needed especially by young fish. Reserves also serve as reference areas to identify how an unexploited ecosystem functions. How much area should be closed? It depends on levels of enforcement and how exploited the fish are already. Roberts says we don't need perfect data to start reserves because they can be adjusted as more data comes in. He also says marine reserves are not an excuse for a free-for-all elsewhere. They should be accompanied by other appropriate management techniques in the rest of the ocean. Contact: Callum Roberts - cr10@york.ac.uk ************ Fish Briefs - Issue Two - November 1999 ***** Fish Briefs is reviewed by a volunteer scientific advisory committee. ***** The members of the committee include: ***** Steve Ganey, Alaska Marine Conservation Council ***** Rich Langton, Maine Department of Natural Resources ***** Ron Hill, National Marine Fisheries Service ***** Barbara Jeanne Polo, American Oceans Campaign ***** Francis Juanes, University of Massachusetts ***** Les Watling, University of Maine ***** Les Kaufman, Boston University S#1 S#2 >*********************************************************************** ***** >Richard F. Ambrose, Ph.D >Director
>Environmental Science & Engineering Program >Department of Environmental Health Sciences >Rm 46-081 CHS (310)825-6144 >Box 951772 (310)206-1984 >University of California (310)206-3358 FAX >Los Angeles, CA 90095-1772 rambrose@ucla.edu >*********************************************************************** *****