44 



Abstract — A general model for yield- 

 per -recruit analysis of rotational (per- 

 iodic) fisheries is developed and ap- 

 plied to the sea scallop (Placopecten 

 magellanicus) fishery of the northwest 

 Atlantic. Rotational fishing slightly 

 increases both yield- and biomass-per- 

 recruit for sea scallops at F^y^. These 

 quantities decline less quickly when 

 fishing mortality is in-creased beyond 

 ^MAX than when fishing is at a constant 

 rate. The improvement in biomass- 

 per-recruit appears to be nearly inde- 

 pendent of the selectivity pattern but 

 increased size-at-entry can reduce or 

 eliminate the yield-per-recruit advan- 

 tage of rotation. Area closures and rota- 

 tional fishing can cause difficulties with 

 the use of standard spatially averaged 

 fishing mortality metrics and reference 

 points. The concept of temporally aver- 

 aged fishing mortality is introduced as 

 one that is more appropriate for seden- 

 tary resources when fishing mortality 

 varies in time and space. 



Yield- and biomass-per-recmit analysis for 

 rotational fisheries, with an application to the 

 Atlantic sea scallop (Placopecten magellanicus) 



Deborah R. Hart 



Northeast Fisheries Science Center 



166 Water St 



Woods Hole, MA 02543 



E mail address Deborati HartsSnoaa gov 



There has been growing interest in 

 using rotational fishing to manage ses- 

 sile or sedentary stocks (e.g. Caddy and 

 Seijo, 1998). Under such a strategy, fish- 

 ing mortality in a given area is varied 

 periodically. Typically, the area is 

 closed for a period of time, then fished, 

 and then closed again. The openings of 

 the different areas are timed so that at 

 least one area is open to fishing each 

 year. This approach has been proposed 

 or is being used for abalone, corals, sea 

 cucumbers, geoduck clams, sea urchins, 

 and several species of scallops (Sluc- 

 zanowski, 1984; Garcia, 1984; Botsford 

 et al., 1993; Caddy, 1993; Heizer, 1993; 

 Campbell et al., 1998; Caddy and Seijo, 

 1998; Lai and Bradbury, 1998). 



Recently, area closures have been 

 used to help manage the Atlantic sea 

 scallop (Placopecten magellanicus) fish- 

 ery off the northeastern United States. 

 Three areas on Georges Bank were 

 closed to scallop and groundfish fish- 

 ing in December 1994 to help protect 

 depleted groundfish resources. Subse- 

 quently, there have been substantial in- 

 creases in scallop abundance, biomass, 

 and mean size in these areas; mean 

 scallop biomass in the closed areas, as 

 measured by the Northeast Fisheries 

 Science Center (NEFSC) sea scallop 

 survey, rose from 0.6 kg/tow in 1994 

 to 15.8 kg/tow in 2000.' During limited 



Manuscript accepted 20 September 2002. 

 Fish. Bull. 101:44-.57(2003). 



' NEFSC (Northeast Fisheries Science Cen- 

 ter). 2001. Report of the 32nd north- 

 east regional stock assessment workshop 

 (32nd SAW). Stock Assessment Review 

 Committee (SARC) consensus summary 

 of assessments. NEFSC Ref Doc. 01-05. 

 289 p. (Available from NEFSC, 166 Wa- 

 ter St., Woods Hole MA 02M:\.\ 



openings of these areas to fishing in 

 1999 and 2000, nearly 5000 metric tons 

 (t) of scallop meats (about 20'* of the 

 total landings during this period) were 

 landed, while biomass levels remained 

 high. In April 1998, two areas in the 

 Mid-Atlantic Bight were closed to scal- 

 lop fishing for three years in order to 

 protect high concentrations of juvenile 

 scallops. Scallop biomass has increased 

 markedly since the closures in these 

 areas as well, from 0.8 kg/tow in 1997 

 to 9.7 kg/tow in 2000^ and about 3500 

 t of scallop meats have been landed in 

 these areas in the year since they were 

 reopened in May 2001. These data 

 suggest that temporary or rotational 

 closures can help increase scallop bio- 

 mass and yield. For these reasons, a 

 rotational management system for the 

 U.S. Atlantic sea scallop fishery is cur- 

 rently under consideration. 



Many common fisheries models may 

 not be appropriate for sessile stocks 

 because these models assume spati- 

 ally uniform fishing mortality (Caddy, 

 1975). Such a "dynamic pool" assump- 

 tion is strongly violated when a sessile 

 stock is fished rotationally so that a 

 portion of the stock is not fished in 

 a given year. For this reason, many 

 previous analyses of rotational fisher- 

 ies have used either spatially explicit 

 simulations (e.g. Caddy and Seijo, 

 1998), per- recruit analyses of pulse 

 fishing, where all vulnerable individu- 

 als are removed from an area when the 

 area is fished (e.g. Sluczanowski, 1984), 

 or per-recruit analyses of a single co- 

 hort (e.g. Gribble and Dredge, 1994). 

 Spatially explicit models suffer from 

 then- complexity, making it difficult to 

 extract general principles from model 



