New approach needed for global fisheries management

— NOAA photo

From ecoRI News (ecori.org)
The tiniest plants and creatures in the ocean fuel entire food webs, including the fish that much of the world’s population depends on for food and work.

In a paper recently published in Science Advances, National Oceanic and Atmospheric Administration (NOAA) Fisheries researcher Jason Link and colleague Reg Watson from the University of Tasmania’s Institute for Marine and Antarctic Studies suggest that scientists and resource managers need to focus on whole ecosystems rather than solely on individual populations.

Population-by-population fishery management is more common, but a new worldwide approach could help avoid overfishing and the insecurity that it brings to fishing economies, according to the paper.

“In simple terms, to successfully manage fisheries in an ecosystem, the rate of removal for all fishes combined must be equal to or less than the rate of renewal for all those fish,” said Link, the senior scientist for ecosystem management at NOAA Fisheries and a former fisheries scientist at the Northeast Fisheries Science Center, in Woods Hole, Mass.

The authors suggest using large-scale ecosystem indices as a way to determine when ecosystem overfishing is occurring. They proposed three indices, each based on widely available catch and satellite data, to link fisheries landings to primary production and energy transfer up the marine food chain.

Specific thresholds developed for each index make it possible, they said, to determine if ecosystem overfishing is occurring. By their definition, ecosystem overfishing occurs when the total catch of all fish is declining, the total catch rate or fishing effort required to get that catch is also declining, and the total landings relative to the production in that ecosystem exceed suitable limits.

“Detecting overfishing at an ecosystem level will help to avoid many of the impacts we have seen when managing fished species on a population-by-population basis, and holds promise for detecting major shifts in ecosystem and fisheries productivity much more quickly,” Link said.

In the North Sea, for example, declines in these indices suggested that total declines in fish catch indicative of ecosystem overfishing was occurring about 5-10 years earlier than what was pieced together by looking at sequential collapses in individual populations of cod, herring, and other species. Undue loss of value and shifting the catches in that ecosystem to one dominated by smaller fishes and invertebrates could have been avoided, according to the authors.

The first index used in the study is the total catch in an area, or how much fish a given patch of ocean can produce. The second is the ratio of total catches to total primary productivity, or how much fish can come from the plants at the base of the food web. The third index is the ratio of total catch to chlorophyll, another measure for marine plant life, in an ecosystem.

Proposed thresholds for each index are based on the known limits of the productivity of any given part of the ocean. Using these limits, the authors said local or regional context should be considered when deciding what management actions to take to address ecosystem overfishing. Having international standards would make those decisions much easier and emphasize sustainable fisheries.

“We know that climate change is shifting many fish populations toward the poles, yet the fishing fleets and associated industries are not shifting with them,” Link said. “That already has had serious economic and cultural impacts.”

The authors note that they are able to follow these shifts over time and see how they can exacerbate or even contribute to ecosystem overfishing.

Fisheries are an important part of the global economy. In addition to trade and jobs, fish provide the primary source of protein to more than 35 percent of the world’s population, and 50 percent of the people in the least developed countries, according to the authors. Regions where the greatest amount of ecosystem overfishing occurs are also where impacts can be the greatest.

The researchers looked at 64 large marine ecosystems around the world and found those in the tropics, especially in Southeast Asia, have the highest proportion of ecosystem overfishing. Temperate regions also have a high level of ecosystem overfishing, with limited capability to absorb shifting fishing pressure from the tropics as species move toward the poles.

Vessel traffic screwing up cod communication

Atlantic cod.

Via ecoRI News (ecori.org)

National Oceanic and Atmospheric Administration (NOAA) scientists studying sounds made by Atlantic cod and haddock at spawning sites in the Gulf of Maine have found that vessel traffic noise is reducing the distance over which these animals can communicate with each other. As a result, daily behavior, feeding, mating and socializing during critical biological periods for these commercially and ecologically important fish may be altered, according to a study recently published in Nature Scientific Reports.

Three sites in Massachusetts Bay, two inside the Stellwagen Bank National Marine Sanctuary (SBNMS) and one inshore south of Cape Ann, were monitored for three months by researchers at the Northeast Fisheries Science Center (NEFSC) laboratory in Woods Hole, Mass., and at the sanctuary offices in Scituate, Mass. Vocalizations, such as Atlantic cod grunts and haddock knocks, were recorded by bottom-mounted instruments at each site during spawning in winter and spring.

“We looked at the hourly variation in ambient sound pressure levels and then estimated effective vocalization ranges at all three sites known to support spawning activity for Gulf of Maine cod and haddock stocks,” said Jenni Stanley, a marine research scientist in the passive acoustics group at the NEFSC and SBNMS and lead author of the study. “Both fluctuated dramatically during the study. The sound levels appear to be largely driven by large-vessel activity, and we found a signification positive correlation with the number of automatic identification system (AIS) tracked vessels at two of the three sites.”

AIS is an automatic tracking system, used on ships and by vessel-traffic services. It provides information on a vessel, such as its unique identification number, position, course, and speed, which can be displayed on a shipboard radar or electronic chart display.

Ambient sounds — those in the surrounding environment — include animals vocalizing, physical sounds such as wind and water movement or geological activity, and human-produced sound from ships and marine construction. Many marine animals use ambient sound to navigate, to choose where to settle, or to modify their daily behaviors including breeding, feeding, and socializing.

Cod grunts were present for 100 percent of the spring days and 83 percent of the winter days. Haddock knocks were present for 62 percent of the winter days within the three-month sampling period. However, ambient sound levels differed widely at the three sites, both on an hourly and daily time scale. The Atlantic cod winter spawning site, nearest the Boston shipping lanes, had the highest sound levels, while the Atlantic cod spring spawning site inshore south of Gloucester, Mass., had the lowest. Sound levels in the haddock winter spawning site, further offshore in the sanctuary, were in the middle of the range detected in the study.

Study data were also used to calculate the estimated distance a fish vocalization would be heard at each of the spawning sites. The effective radius ranged widely, from roughly 4 to 70 feet, and was largely dependent on the number of tracked vessels within a 10-nautical-mile radius of the recording sites.

Lower-level, chronic exposure to increased ambient sound from human activities is one of the most widespread, yet poorly understood, factors that could be changing fish behavior, according to researchers. If they can’t hear as well as they need to, then sound signals from other fish can be lost, compromised, or misinterpreted in ways that can cause a change in behavior. Since Atlantic cod, for example, vocalize to attract mates and listen for predators, not hearing those signals could potentially reduce reproductive success and survival.

“Anthropogenic sound in certain ocean regions has increased considerably in recent decades due to various human activities such as global shipping, construction, sonar, and recreational boating,” Stanley said. “As ocean sound increases, so does the concern for its effects on populations of acoustic signalers, which range from invertebrates to marine mammals. We don’t know if or to what extent specific species can adapt or adjust their acoustic signals to compete in this environment.”

Peter Baker: Restore the prey of cod to restore cod

 

(See this excerpt from a Portuguese documentary  about cod fishing.)

A recent study illustrates what has happened to New England’s once plentiful Atlantic cod population, and the findings highlight the big role that little fish play in our marine ecosystems and economy. It’s no secret that New England’s cod are in trouble. Overfishing has so severely depleted the population that federal officials declared a fishery disaster and Congress appropriated more than $30 million in aid. But even as the bottom fell out of cod stocks, many fishermen insisted the fish were still plentiful in their nets and disputed the science supporting tighter catch limits. Why did fishermen see a bounty while scientists in fact called it a bust? Researchers at the National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center say a change in the forage fish, or small prey species, the cod were eating offers an explanation. In an article published in May in the Canadian Journal of Fisheries and Aquatic Science, the authors say that around 2006 the dominant prey for cod switched from Atlantic herring to sand lance — small, eel-like fish that burrow in the sediment of the seafloor. Sand lance were abundant in an area known as Stellwagen Bank, and so cod, too, congregated there. Soon, cod fishermen focused so much effort on the bank that some 45 percent of the cod caught in a year came from just a 100-square-mile area in the region. But scientific surveys assessing the cod population over more than 20,000 square miles in the Gulf of Maine continued to show that the larger population was seriously depleted. Clearly, the abundance in one small region didn’t accurately reflect the overall status of cod. The authors say they hope that the findings can “help fishery managers, scientists and the industry understand and resolve apparent conflicts between assessment results and the experiences of the fishing industry.” While this study helps to explain the recent past, it also holds important lessons for the future of fishing. The switch in cod diet from herring to sand lance held major implications for one of the region’s most important fish. Over the years, through intensive fishing for prey species such as Atlantic herring and menhaden, plus the depletion of other historically important prey such as river herring and shad, the “menu” of forage fish available to cod and other predators has changed. We need a management system that better monitors and responds to the ways prey and predators interact. Such a system is available, and it’s called ecosystem-based fisheries management. Scientists have long known that simply measuring and managing one fish species at a time is insufficient. So they’ve put decades of work into developing the ecosystem-based approach to provide a much more accurate and useful picture of what’s occurring in the water. A good ecosystem-based fisheries management program would take the needs of predator species into account and let managers restore the abundance of prey, causing a resurgence of fish stocks and, ultimately, providing greater opportunity for the fishermen who depend on them.

Peter Baker directs the Pew Charitable Trusts’ U.S. ocean conservation efforts in the Northeast and Mid-Atlantic. This piece originally appeared on ecori.org.