WIOMSA-CORDIO spawning book Full Doc 10 oct 13.pdf

during full moon periods. Siganus sutor showed high site fidelity to spawning aggregation sites inKenya, though the more detailed telemetry data in Seychelles demonstrated that fidelity was notabsolute. Moreover, results from Seychelles also revealed turnover of S. sutor aggregations, inferredfrom aggregation site residency times being much shorter than aggregation duration (Chapter 6).Since this finding has implications for the estimation of aggregation size and therefore the impactsof fishing, further telemetry studies could be conducted on the Kenyan S. sutor aggregations todetermine if it is an aggregating dynamic common to this species.Rabbitfish (Siganidae) are schooling species with large home ranges (Fox and Bellwood 2011) bothof which pose challenges to research of their aggregation fisheries. The UVC results from Kenyaillustrated difficulties in distinguishing whether S. sutor were aggregating for spawning or wereforaging at aggregation sites. However, telemetry results from Seychelles indicated that S. sutor wereonly present at spawning aggregation sites during known spawning periods (Robinson et al. 2007;2011). Thus, a cautious interpretation of the Kenyan aggregations and study sites as being only forspawning is warranted.Regional similarities were found in the aggregation dynamics of the grouper E. fuscoguttatus(Serranidae), further confirming that this species typically forms transient spawning aggregationson outer reef slopes in relation to the new moon for 2-4 months each year (Chapter 6, 7, 8,9). However, acoustic telemetry studies and the existence of prior aggregation data in Seychellesyielded additional insights on aggregation dynamics in this species that should inform futureresearch and management in Kenya. Notably, sex-specific differences in male and female arrival andresidency times at aggregation sites in Seychelles highlight sex-specific variation in vulnerability toaggregation fishing, providing vital information for the design of fine-scale temporal managementmeasures (e.g. temporary fishery reserves or sales/catch restrictions). In addition, variability inthe spatial distribution of E. fuscoguttatus aggregations in Seychelles, due to habitat disturbance,provides a strong argument for larger protected areas that incorporate buffer zones.Similarities also exist between study locations in the socio-economic importance of S. sutoraggregation fisheries. Although catch rates of S. sutor on spawning aggregations increased 4-fold inKenya, aggregations were relatively short-lived and consequently yielded catches representing onlyaround 12% of the total annual catch. Therefore management of this species in Kenya needs toconsider the non-aggregation aspects of the fishery to control fishing mortality, a similar conclusionmade in Seychelles (Robinson et al. 2011) and further demonstrated in the modeling results (Chapter12). The importance of aggregation catch relative to the annual catch made on a population ispartly dependent on density-dependent catchability, i.e. the increase in population density andvulnerability to fishing that occurs with aggregation formation, as well as on aggregation durationand seasonality. Density change is less extreme in rabbitfish than groupers, while aggregations arealso much shorter in duration. Consequently, aggregation fishing is unlikely to be the primarysource of annual fishing mortality rates in rabbitfish (Robinson et al. 2011).Regional differences were seen in aggregation fisheries, such as in gear diversity. For example, whilePraslin Island fishers only use traps to target S. sutor aggregations, fishers in southern Kenya also usehook-and-line and anecdotal reports indicate that ring-nets are used (Chapter 3). Kenyan fishersalso use gillnets and illegal beach seines on S. sutor populations inshore. Gear diversity is known toincrease vulnerability in aggregation-based fisheries: the introduction of nets can result in a rapiddepletion of aggregation abundance (Chapter 11; Claro et al. 2009). These regional differencesfurther reinforce the need for a case-by-case approach to management.A fundamental constraint in addressing the management needs of spawning aggregation-basedfisheries is the difficulty in establishing aggregation status and its relationship to the populationas a whole. Both parameters require years of continued monitoring. In Kenya, E. fuscoguttatusaggregations were at least an order of magnitude smaller than some of those observed in Seychelles124