Georges Bank scallops and fishery closures
Dear MPA News:
I am writing in response to Russ Babcock’s query regarding the effects of long-term closures on Georges Bank sea scallops, Placopecten magellanicus (MPA News 6:10). As discussed below, while scallop abundance and biomass have increased substantially within the closed areas, there is no clear evidence indicating that the closures have enhanced recruitment or landings in the areas remaining open to fishing.
Three large areas on Georges Bank and Nantucket Shoals were closed to groundfish and scallop gear for most of the time since December 1994. The closed areas historically accounted for roughly half of the total sea scallop landings and recruitment in the US portion of Georges Bank before the closures. While these areas can be considered MPAs, they do not qualify as no-take marine reserves: a number of fishing activities have occurred there since they were closed. Most relevant to sea scallops is the substantial ongoing fishery in the closed areas for American lobster (Homarus americanus), a known scallop predator, and limited re-openings of portions of these areas to scallop fishing (first from June 1999 to January 2001, and again since November 2004).
Fishery-independent scallop surveys indicate rapid increases in sea scallop biomass and abundance in the closed areas through 2000, with roughly steady abundance and modest increases in biomass since then. Closed area biomass in 2004 was about 31 times greater than in 1994, while abundance increased about nine times during that period. Closed area biomass and abundance in 2004 were about 18 and five times greater than their long-term 1982-1994 pre-closure means.
Biomass of sea scallops in the open portions of the US Georges Bank population in 2004 was about six times its value in 1994 and three times its 1982-1994 mean. Open area abundance in 2004 was about five times its 1994 value and 1.3 times its 1982-1994 mean. Effort reduction measures (days-at-sea reductions and crew size limitations) and gear restrictions have been implemented gradually in the US sea scallop fishery since 1994. These measures, by reducing fishing mortality and shifting the selectivity of the fishery toward larger animals, would be expected to increase scallop biomass and abundance, so that increases in these numbers in the open areas cannot necessarily be attributed to the closures. Because the exchange of adult scallops between open and closed areas is negligible, any putative contribution of the closed areas to the improved conditions in the open areas would be from increased recruitment. Comparison of open area log-transformed recruitment (“recruits” are defined as two-year old scallops, that are at least a year away from being vulnerable to the fishery) for year classes spawned prior to the closure (1980-1994) to those spawned afterwards (1995-2002) shows an 8% non-significant increase (p=0.61; t=0.51) in recruitment in the post-closure period. Recruitment observed during the most recent three surveys, when biomass in the closed areas has been the highest, has been below average.
Total US Georges Bank landings in the pre-closure period (1982-1994) were about 23% higher than those in the post-closure period (1998-2004; 1998 is the first year that a positive “spillover” effect from the closures could have affected the fishery). By contrast, recent sea scallop landings in the Mid-Atlantic area (from Virginia to Long Island) have been well above average, and this region has attracted most of the scallop fishing effort during the last few years. There have been no long-term closures in the Mid-Atlantic region. Instead, there have been rotational closures as well as the effort reduction and gear restrictions discussed above.
It is clear that the Georges Bank closures were effective in rapidly increasing sea scallop abundance and biomass within these areas. However, current evidence is inconclusive as to whether the closures have increased sea scallop recruitment in the areas open to fishing. Moreover, even assuming that the observed slight increase in open area recruitment is due to the closures, it appears to be insufficient to compensate for the direct loss in yield caused by long-term closures. Rotational closures, by increasing yield per recruit in addition to possible benefits from increased fertilized egg production, are much more likely to improve scallop yield than permanent closed areas.
Deborah Hart
Northeast Fisheries Science Center, Woods Hole, MA 02543, USA. E-mail: Deborah.Hart@noaa.gov
Note: Deborah Hart is in charge of sea scallop research at the Northeast Fisheries Science Center, operated by the US National Oceanic and Atmospheric Administration.
Galapagos and sportfishing
Dear MPA News:
Last month’s issue of MPA News described the pressure being placed on the Galapagos Marine Reserve to permit the business of sportfishing in its waters (MPA News 6:10). Compared to the shark finning that occurs illegally in the reserve and the growing calls among local artisanal fishermen to allow longlining, the prospect of developing a catch-and-release sportfishery might seem relatively benign to some. But it is not an “either/or” scenario. Allowing sportfishing would add yet another layer of pressure to an already-stressed marine environment in Galapagos. Furthermore, the management infrastructure necessary to control this new fishery is not in place. The International Game Fishing Association, which sanctioned the illegal billfishing tournament in Galapagos this past February, is in a powerful position to take a stand in the battle to protect the marine resources there. I would like to see IGFA state that it would not be in the interest of Galapagos resources to open up the sportfishery at this time.
Jack Grove
166 Peace Ave., Tavernier, FL 33070, USA. E-mail: jsgimages@aol.com
Note: Jack Grove is a marine biologist, professional naturalist, photographer, and author of The Fishes of the Galapagos, published by Stanford University Press.