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

ut the potential for recovery at the same site following ‘complete’ eradication remains unknown(Sadovy and Domeier 2005) and may operate on time-scales not suited for study. By contrast, themechanisms underlying the persistence of established spawning aggregations are more amenableto study. Here, we report on the impacts of a natural disturbance on the persistence of grouperspawning aggregation site at Farquhar atoll in Seychelles.In December 2006, a cyclone passed directly over Farquhar atoll in the southwest corner of theSeychelles archipelago at which spawning aggregations are known to form in the months ofDecember to February. Research conducted at a key spawning site at the atoll between 2003 and2006 verified spawning aggregation by Epinephelus polyphekadion and Epinephelus fuscoguttatus(Robinson et al. 2008). The objectives of this study were to (1) assess the impacts of the 2006 cycloneon spawning aggregation habitat at the site and (2) determine whether spawning aggregations ofEpinephelus polyphekadion and Epinephelus fuscoguttatus continue to form at the site following thedisturbance.MethodsFamiliarisation dives conducted at the study site in January 2010 on lunar days (LD) 18 and 19revealed that aggregation habitat had changed dramatically since the most recent site survey ofNovember 2006 (Robinson et al. 2008). Using a November 2006 geo-referenced Google Earthimage imported into ArcGIS, changes in spawning habitat and area usage between the 2003-2006 period and 2010 were examined. GPS positions that marked the perimeter of spawningaggregation areas during previous assessments (i.e. between 2003 and 2006; Robinson et al.2008b) were reconciled with the outline of reefs in the 2006 imagery. Extrapolations were madewhere cloud cover obscured reefs. Over 2 days (LDs 28 and 29) in January 2010, a period close tothe known spawning time for both species (Robinson et al. 2008b), the core spawning areas werereassessed by divers. As with earlier surveys (Robinson et al. 2008b), we considered the core of theaggregations to be areas where obvious signs of spawning behaviour were observed, as opposed toareas (‘boundary areas’; Robinson et al. 2008b) that had high densities of aggregating fish but nosigns of spawning behaviour. Signs of spawning behaviour were primarily the presence of gravidfemales being guarded and courted by territorial males. The extent of boundary reef areas was notdetermined in 2010.Fixed transects were used to survey aggregations between 2003 and 2006 (Robinson et al. 2008b).Following the disturbance, one of three fixed transects in the core was completely lost, while asecond was partially lost. As a result, random point counts (7-m radius) were introduced in 2010 inorder to confirm that aggregations of E. fuscoguttatus and E. polyphekadion still formed following thedisturbance. Ten counts were conducted per census across reefs where signs of spawning behaviourwere observed. In order to use this method for E. fuscoguttatus, censuses were only performed afew days (LD 27-29) before spawning, when gravid females were present and territorial maleswere generally tolerant of divers. Censuses of E. polyphekadion, which allow divers to approachclosely, began earlier on LD 20. In 2010, bad weather prevented diving between LD 23 and 26,inclusive. Density estimates of E. fuscoguttatus and E. polyphekadion aggregations made in 2010were compared qualitatively with density estimates from aggregations observed in January 2004,since formal statistical comparisons were invalidated by the change in sampling methodology (i.e.from fixed to random sampling units).To determine if reproductive behaviour was affected by the habitat disturbance, the relativefrequency of occurrence (RFOO) of spawning-related signs and behaviours, i.e. aggression,courtship, gravid females and gamete release, was assessed during the census. RFOO of behaviour(e.g. courtship) is the ratio of the number of fish showing that behaviour to the total number offish observed in the point count (Pet et al. 2005).87