Productivity and Sustainability Analysis Conducted for Coral Reef Fishes in Guam

Researchers in the PIFSC Fisheries Research and Monitoring Division recently conducted a Productivity and Susceptibility Analysis (PSA) for coral reef fishes in Guam. The results will help the Western Pacific Regional Fishery Management Council prioritize species needing stock assessment, identify species within a family that may be highly susceptible to impacts from fisheries, and group species with similar vulnerabilities to overfishing. As a first step in the project, both boat- and shore-based creel survey data (for years 1982-2011) from Guam were obtained from the Western Pacific Fisheries Information Network (WPacFIN) and summarized. The most frequently landed coral reef species and families were identified, and spatial and temporal patterns in landings and fishing methods were examined.

Thirty-three of the most frequently landed coral reef species were identified and included in a PSA. The PSA assigned to each species in the analysis a relative score of vulnerability to overfishing as well as a score for the quality of the data used in the analysis. The vulnerability score was based on attributes describing the productivity of the species and the susceptibility of the species to overfishing. The 6 productivity attributes included in the analysis were: longevity, maximum size, von Bertalanffy growth coefficient (k), natural mortality rate, age at 50% maturity, and trophic level. The four susceptibility attributes included in the analysis were: fishery value, vertical distribution, geographic concentration, and behavior affecting catchability. A Ward's hierarchical cluster analysis was applied to the vulnerability scores to identify significant groups of species with similar vulnerability scores.

Figure 1. Results of a productivity and susceptibility analysis of reef fishes in Guam. Each number represents a species (see Table 
        1). Each color represents a family.  Five clusters of species (based on vulnerability scores) were identified by using Ward's 
        hierarchical cluster analysis.
Figure 1. Results of a productivity and susceptibility analysis of reef fishes in Guam. Each number represents a species (see Table 1). Each color represents a family. Five clusters of species (based on vulnerability scores) were identified by using Ward's hierarchical cluster analysis.
Table 1 — Productivity and Susceptibility Analysis (PSA) results. Scores were based on 6 productivity attributes each given a score of 1 (low) to 3 (high) and 4 susceptibility attributes also scored 1 (low) to 3 (high). Final vulnerability scores indicate the species vulnerability to overfishing. Species with low productivity and high susceptibility had higher vulnerability scores and were more vulnerable to overfishing.
Number Species Vulnerability Productivity Susceptibility
3 Aprion virescens 2.22 1.17 2.25
32 Varioloa louti 2.22 1.17 2.25
28 Scarus schlegeli 2.16 1.33 2.38
17 Lethrinus obsoletus 2.12 1.5 2.5
7 Cheilinus trilobatus 2.1 1.67 2.62
10 Ellochelon vaigiensis 2.08 1.33 2.25
14 Hipposcarus longiceps 2.01 1.67 2.5
18 Lethrinus rubrioperculatus 1.95 1.5 2.25
8 Chlorurus microrhinos 1.94 1.33 2
12 Epinephelus merra 1.89 1.67 2.33
9 Scarus schlegeli 1.88 1.5 2.12
21 Monotaxis grandoculis 1.88 1.33 1.88
26 Sargocentron spiniferum 1.85 1.17 1.25
6 Caranx sexfasciatus 1.8 1.5 2
5 Caranx melampygus 1.78 1.73 2.25
24 Naso unicornis 1.74 1.33 1.5
1 Acanthurus lineatus 1.71 1.83 2.25
19 Lutjanus fulvus 1.6 2 2.25
4 Caranx ignobilis 1.58 1.5 1.5
27 Scarus psittacus 1.58 2.5 2.5
15 Kyphosus cinerascens 1.54 1.83 2
16 Lethrinus harak 1.54 1.83 2
2 Acanthurus triostegus 1.42 2.33 2.25
13 Gerres longirostris 1.42 2.33 2.25
23 Naso lituratus 1.42 1.67 1.5
29 Selar crumenophthalmus 1.35 2.5 2.25
22 Mulloidichthys flavolineatus 1.31 2.33 2.12
20 Lutjanus kasmira 1.3 2.17 2
25 Parupeneus barberinus 1.27 1.83 1.5
11 Epinephelus fasciatus 1.25 2 1.75
33 Chlorurus sordidus 1.12 2.5 2
30 Siganus argenteus 1.01 2.83 2
31 Siganus spinus 1.01 2.83 2

Summarization of the creel survey data revealed that the top landed coral reef species in Guam were S. crumenophthalmus, N. unicornis, and S. spinus. The Acanthuridae family has accounted for the largest portion of landings from 1982-2011. Results of the PSA indicated that the three species most vulnerable to overfishing based on the productivity and susceptibility attributes included in the analysis were: 1. Aprion virescens, 2. Variola louti, and 3. Scarus schelegeli (Table 1). Four species were identified as having low data quality: C. trilobatus, S. schellegeli, and S. spiniferum, and E. vaigiensis). The lack of data for these species may have inflated their vulnerability scores. Five significant clusters were identified. Species within a family were rarely grouped in the same cluster (Figure 1).

The project was a first step in developing a framework for coral reef stock assessments in the Western Pacific. The results of this project may be used to identify highly vulnerable species that may serve as an indicator species for a family or may assist managers in identifying appropriate species to group for management. There are a number of uncertainties and assumptions associated with the creel survey data and PSA; these are discussed in the report of the study. The methods used in the study may be applied in the future to a larger number of species and to other regions to help prioritize species for management.