The importance of targeted spawning aggregation fishing to the management of Seychelles’ trap fishery

The formation of spawning aggregations at predictable sites and times is known to confer vulnerability to overexploitation among reef fishes exhibiting this trait. The aim of this study was to determine the importance of targeted fishing on spawning aggregations for the status and management of the trap fishery for Siganus sutor (Rabbitfish: Siganidae) in Seychelles. S. sutor was verified as an aggregative spawner and, at two of the main spawning sites, aggregations were subject to a highly targeted trap fishery. Trends in catch-per-unit-effort and yield over time (1991–2006) were not indicative of an overfished siganid resource, and a yield curve signalled that fishing has been within sustainable limits. While a demographic assessment indicated that overfishing had occurred in 1998 and 2007, the reference points may have been overly conservative and the results reflect the size structure of only the exploited component of the population. Aggregation fishing was estimated to contribute 8% of annual effort and 15% of annual catch in the fishery, indicating that this practice does not exert a major influence on stock and fishery status. Given the conflicting results of yield and demographic assessments, precautionary management measures are warranted and should be informed by the distribution of effort among life history stages. Spatial or temporal measures to protect spawning aggregations will have limited effectiveness as the majority of effort is directed at non-spawning fish. We conclude that fisheries with aggregation components can be sustainable at commercial levels of use if based on relatively resilient transient spawners.

► We verify a highly targeted spawning aggregation fishery for Siganus sutor.
► The overall fishery for the siganid resource has been fished within sustainable limits.
► Aggregation targeting was not the primary driver of stock and fishery status.
► The partitioning of fishing pressure among life history stages is important for management.
► Commercial aggregation fisheries for resilient transient spawners can be sustainable.