Fish need protecting during spectacular breeding frenzies, study shows.

March 29, 2016 by Lewis Smith


The spawning frenzies which create “massive and spectacular” gatherings of fish need to be protected, a scientist has warned.

Bass, bluefin tuna and several other species in European waters spawn in large gatherings – aggregations – that have been targeted by fishermen.

Stiff new regulations have been introduced in recent months to protect bass, including measures to prevent them being caught while breeding, but management of spawning aggregations remains the “elephant in the room”, said Professor Yvonne Sadovy, of the University of Hong Kong.

She issued the warning after publication in the journal BioScience of a study she carried out to assess data on fish species that aggregate to spawn, which she concluded can be safely fished if “done right” but that need careful controls.

Unless fish like bass are given adequate protection while breeding, she said, they could suffer disproportionate damage to stocks that will push them into perhaps irreversible decline.

Professor Sadovy cited the example of the passenger pigeon which went extinct in 1914. One of the prime reasons for its rapid decline and demise was that hunters targeted the communal nesting sites.

Examples of species cited in the paper that are targeted as they aggregate to spawn and to migrate to their spawning grounds include Alaska (walleye) pollock, Atlantic cod, capelin, Atlantic mackerel, herring and European pilchard, which are all among the world’s top 20 catches by weight.

Professor Sadovy said bass is another: “The sea bass is a really excellent example of a well-known and highly considered commercial species that really should be protected while spawning.

“Little is really understood about the spawning migrations and behaviours because these have not been a target for serious fisheries research.

“Management of spawning aggregations is an ‘elephant in the room’ as far as fishery management is concerned for many species and, as fishing pressures increase and more fishing focuses on them, they are going to be challenging to protect.

“As for most species that are exploited at different life history phases and by different fisheries in different places (as is the European sea bass) it is really hard to pinpoint one or main causes. However, literature clearly shows that aggregating species taken on their aggregations are particularly susceptible and that attention to management of aggregations is needed.”

Examples of species targeted as they aggregate to spawn and to migrate to their spawning grounds include Alaska (walleye) pollock, Atlantic cod, capelin, Atlantic mackerel, herring and European pilchard, which are all among the world’s top 20 catches by weight.

In her paper, an overview of data on fish species that aggregate to spawn, Professor Sadovy said that the evidence showed a “truly precautionary approach is essential” to reduce the risk of population declines.

Among the aggregating fish to have suffered a serious decline already is the yellow croaker. In the 1970s it was a major coastal fishery for China, peaking at about 200,000 tonnes a year, yet by the mid 1990s it had slumped by more than 90 per cent.

“The species has never recovered despite massive restocking programs and management measures. Wild fish are now uncommon,” she said in the paper.

“Fishing on spawning aggregations is heavily implicated in the declines of many species. Of all 163 groupers and 134 seabreams globally, many of those that aggregate to spawn are the most threatened species.”

She cited the example of the Atlantic Nassau grouper which formed large aggregations targeted by fishers who faced little in the way of fisheries regulations. “The species is now endangered, and most of its aggregations have disappeared or became severely reduced,” she said. By contrast, the red grouper, which does not form spawning aggregations, remains viable for commercial fishers.

Atlantic cod and halibut also aggregate and they suffer stress or disruption from the presence of fishing gear which could “ultimately affect reproductive success and population growth”.

What is needed, she said, are rule changes that ensure all fish aggregations are protected by the precautionary approach.

“There is nothing inherently wrong with fishing on spawning aggregations—if it is done right. At subsistence levels, this was done for centuries, and if properly managed, commercial targeting of spawning fish can be sustained.

“The bottom line is that evidence strongly suggests that we should fish spawning aggregations at commercial levels cautiously—and only with adequate management and monitoring.

“Where there is insufficient management and enforcement, it is proposed that no fishing of spawning aggregations should occur until appropriate measures are implemented to ensure their sustainable use.

“The sustainable exploitation of fish spawning aggregations needs to be mainstreamed into fishery management.

“Managing fisheries that target spawning aggregations, as we must do while they are still abundant, will seriously test our ability to apply truly precautionary management.”


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