Table 2.
Optimal size and number of marine reserves as a function of larval dispersal in an overcapitalized TAC-regulated fishery in which the fishing effort is three times that required for MSY in a single-owner fishery. Here, a MR layout (i.e. the combination of number and size of MRs) is considered optimal when it provides the highest catch for a specific level of larval dispersal. The annual TAC is computed by setting fishing mortality at MSY (f = fMSY = qEMSY) under conventional quota management (i.e. without MRs) and the fishable stock is either assumed to be the total biomass in size classes 2 and 3 along the coastline (i.e. both outside and inside MRs) or, alternatively, only the biomass in the fishable ground (i.e. outside MRs). Effects of reserves on catch and stock biomass are reported as per cent increment (or decrement, if negative) with respect to those obtained at MSY under conventional quota management, i.e. in the absence of reserves. Statistical significance is computed as the fraction of times in which the mean catch (biomass) over a 10-year span under reserve implementation is greater than that under conventional management. Dispersal range and reserve size are measured in the same units as the coastline, which comprises 100 contiguous 1-km patches (i.e. 100 km). In (a), juveniles and adults are assumed to be sedentary (retention rate = 96% in stages 1–3), whereas, in (b), juveniles and adults are mobile (retention rate = 13% in stages 1–3). All other parameters are as reported in table 1.
| range of dispersal of 90% of larvae | larval retention rate (%) | optimal size of protected area (total, %) | optimal no. reserves | mean size of each reserve | TAC computed on fish stock inside and outside reserves |
TAC computed only on fish stock outside reserves |
||
|---|---|---|---|---|---|---|---|---|
| Δbiomass (%) | Δcatch (%) | Δbiomass (%) | Δcatch (%) | |||||
| (a) sedentary adults (adult retention rate = 96%) | ||||||||
| 5 | 26 | 40 | 40 | 1 | 16 ± 7.8** | 8.9 ± 7.2† (n.s.) | 53 ± 12** | −12 ± 7.2† (n.s.) |
| 10 | 13 | 38 | 20 | 1.9 | 22 ± 10** | 13 ± 9* | 57 ± 14** | −11 ± 7.8† (n.s.) |
| 20 | 7 | 36 | 10 | 3.6 | 28 ± 12** | 17 ± 11** | 62 ± 15** | −9.2 ± 8.5† (n.s.) |
| 50 | 3 | 36 | 4 | 9 | 34 ± 11** | 20 ± 11** | 66 ± 15** | −10 ± 8.4* |
| 100 | 1 | 36 | 2 | 18 | 29 ± 11** | 21 ± 11** | 59 ± 14** | −13 ± 7.3* |
| (b) mobile adults (adult retention rate = 13%) | ||||||||
| 5 | 26 | 40 | 24 | 4 | 0 ± 1.5 (n.s.) | 0 ± 1.4 (n.s.) | 42 ± 9.2** | −8 ± 6.22 (n.s.) |
| 10 | 13 | 40 | 12 | 5 | 1.4 ± 3.1 (n.s.) | 0 ± 2.9 (n.s.) | 48 ± 11* | −10 ± 6.5† (n.s.) |
| 20 | 7 | 41 | 6 | 6.6 | 3.9 ± 2.2* | 3.4 ± 2.0* | 44 ± 9** | −13 ± 5.5† (n.s.) |
| 50 | 3 | 41 | 2 | 20 | 24 ± 10** | 13 ± 9* | 63 ± 15** | −15 ± 7.5* |
| 100 | 1 | 40 | 1 | 40 | 39 ± 14** | 23 ± 13** | 74 ± 19** | −14 ± 8.9* |
*0.01 ≤ p < 0.05; **p < 0.01; †(n.s.) 0.05 ≤ p < 0.10; (n.s.) p > 0.