Benefits of closed area protection for a population of scallops

Abstract

Despite the current interest in using closed areas for fisheries management, few studies have actually examined the benefits for invertebrate fisheries such as scallops. This study details the dynamics of a population of great scallops Pecten maximus (L.), within a closed area and an adjacent fished area off the Isle of Man, over a 14 yr period (1989 to 2003). Scallop densities were very low in both areas when the closed area was set up, but increased at an accelerated rate over time within the closed area. Scallop densities also increased on the adjacent fishing ground, but not to the same extent. Consequently, the density of scallops above the minimum legal landing size (110 mm SL) was more than 7 times higher in the closed area than in the fished area by 2003. There was also a shift towards much older and larger scallops in the closed area and, correspondingly, lower estimates of total mortality. Experimental dredging of 2 plots within the closed area confirmed that fishing drove these differences in population dynamics and structure. These patterns of scallop density, age and size structure resulted in the exploitable biomass (adductor muscle and gonad) of scallops being nearly 11 times higher in the closed area than in the fished area by 2003, and the reproductive biomass was 12.5 times higher. This is significant for fisheries management because the build up of high densities of large P. maximus individuals enhanced local reproductive potential and therefore the likelihood of export of larvae to the surrounding fishing grounds. Along with these direct benefits of closed area protection, juvenile scallops had higher survival and individual growth rates in the closed area, apparently in response to reduced fishing disturbance. Although juvenile scallops are not subject to direct removal by fishing, protection during this critical phase therefore appeared to assist the recovery of the closed area population. In summary, this study joins a growing number indicating that the use of closed areas offers a range of benefits over more traditional methods of managing fisheries. Fisheries for relatively sedentary and long-lived species such as P. maximus appear to be particularly suitable for this type of management.

Assessing the Impacts of Establishing MPAs on Fishermen and Fish Merchants: The Case of Lyme Bay, UK

“…Greater stakeholder involvement is required for the successful establishment and management of MPAs (Jones 1999;Jones and Burgess 2005;Beukers-Stewart et al 2005). In the case of Lyme Bay, the multiplicity of direct and indirect interests means that there is a need to include more people in the decision making process, such as recreational users and local businesses.…”

Detecting larval export from marine reserves

“…However, modeling results suggest that spillover effects may be greatest, but most difficult to detect, in cases where dispersal distances are long relative to reserve size. A review of existing empirical evidence is consistent with the implications of these theoretical findings: that detecting larval export in field studies is likely to be very challenging except when the increase in production within reserves is exceptionally large (9-12, 15-18, 37), the mean dispersal scale is not too long relative to reserve size (9-11, 13, 14), or sampling designs take advantage of directional dispersal and employ a suite of sampling sites at the appropriate spatial scale (9,12,13,(15)(16)(17)(18)37).…”

“…At the center of this debate is the suggestion that larvae from highly productive populations in marine reserves may move outside reserves and enhance populations in harvested areas (7,8). A few studies have demonstrated spatial and/or temporal patterns of recruitment or abundance that suggest larvae exported from reserves can enhance nearby fished populations (9)(10)(11)(12)(13)(14)(15)(16)(17)(18). However, the larval export effect remains controversial (3), in part because empirical evidence remains limited (6).…”

Linking bio-oceanography and population genetics to assess larval connectivity

“…Mar Ecol Prog Ser 463: [159][160][161][162][163][164][165][166][167][168][169][170][171][172][173][174][175] 2012 grounds (Gell & Roberts 2003, Beukers-Stewart et al 2005, Pelc et al 2009). …”

“…The positive effects of spatial management tools, such as marine reserves, on recovery of exploited stocks have been documented world-wide (Gell & Roberts 2003, Lester et al 2009, Aburto-Oropeza et al 2011), particularly in sessile or sedentary stocks (Lester et al 2009). For mobile species, adjacent fished areas might benefit from density-dependent spillover (Gell & Roberts 2003, Hilborn et al 2004, whereas both mobile and sedentary species may benefit from enhanced recruitment through larval dispersal from protected spawning grounds (Gell & Roberts 2003, Beukers-Stewart et al 2005, Pelc et al 2009). …”