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

Spatial and temporal patterns in fishing and catch rates from the 12 months of creel survey datashowed that the bulk of catches and hence fishing effort on S. sutor were from the inshore areas inthe seagrass beds fringing the shore or within the lagoon inside the fringing reef, or within Gazi Bay.The shift in fishing effort during the spawning season to offshore, including the possible spawningaggregation sites, provides support for the existence of these temporal spawning aggregationsand the interpretation that fishers target them. However, GSI values also showed a peak in June-July (Chapter 4). We were unable to verify this through fishers’ knowledge and rough weatherconfounds the fishing pattern: the fact that fishers do not fish offshore during the presumed nonspawningseason may simply be a result of the strong seas during that south-easterly monsoonseason. Nevertheless we maintain that fishing the three spawning aggregation sites during the fullmoon periods of Nov-Mar represents a targeted spawning aggregation fishery for S. sutor in theMsambweni area.The results leave us with several questions: how common are offshore spawning aggregation sitesfor S. sutor along the Kenyan coast? Are the sites off Msambweni a feature of this broken up stretchof reef with no distinct fringing reef, or do S. sutor find offshore patch reefs outside the fringing reeffurther north? Do S. sutor spawn simply in pairs in their home ranges during June-July? Possibly,they do migrate to the offshore aggregation sites in June-July but fishers do not fish them at thattime because the weather is very rough and the sites inaccessible to fishers in dug-out canoes.This was corroborated by very few landings from the three spawning sites during the south-eastmonsoon months of June-July.Fishers reported a 3.5 fold increase in their catch rates when fishing spawning aggregations whichgave them substantially higher catch rates. However, they also reported substantial declines (>70%)in catch rates of S. sutor over the last 20 years. This trend may reflect a rate of decline in the sizeof spawning aggregations or overall declines in the stock, or both. The maximum numbers of S.sutor observed underwater on the three aggregation sites was only 184 (Chapter 5), compared withseveral hundred observed in Seychelles (Robinson et al. 2004). Several fishers said that the sizes ofS. sutor spawning aggregations today are far below the levels observed before the 1980s, and also lastfor a shorter period, and that knowledge of S. sutor spawning aggregations has become increasinglywidely known, though, perhaps surprisingly, they did not attribute declines in catches to targetedfishing of aggregations. Negative impacts from targeted fishing of spawning aggregations are nowwell documented (e.g. Sadovy 1994, Claro and Lindeman, 2003, Sadovy and Domeier, 2005). Thedeclines reported here by fishers, the possible changes in spawning behaviour of S. sutor and the lownumbers in aggregations are all cause for concern over the sustainability of current fishing practiceson S. sutor populations. However, the “r” strategy life history pattern seen in S. sutor of short lifespan of around 2 years (Jehangeer 1988; Grandcourt 2002), protracted spawning season and dualmodes of spawning may make the species resilient to heavy fishing pressure.Value of spawning aggregation fishing of S. sutor to fishersThis study established that fishers exploit three S. sutor likely spawning aggregation sites for homeconsumption and sale locally, a practise that they say has existed for generations. We calculated thatcatches of S. sutor landed from basket traps and hook and lines within the estimated total periodof aggregation spawning (16 days), was valued at $6,685 and this represents 25.8% of the annualS. sutor catch (23,551 kg.yr -1 ). However, this estimate is likely to be an over-estimate because itassumes that all active fishers would fish aggregations during the reproductive period. Therefore weproposed a more realistic, albeit approximate, estimate of the total annual catch from these threeaggregations as 2,701kg.yr -1 , valued at $2,971, representing 11.5% of the total annual S.sutor catch,based on a projected number of fishers potentially fishing these sites. A concurrent study measuredthe combined area of the three spawning aggregation sites at 0.064km 2 (Chapter 5) which indicatesthe spawning aggregation harvest of 2,701kg.yr -1 is equivalent to a yield of 42.2 t.km -2 .yr -1 of S.sutor; a yield that is 7 times more than the average productivity of Kenyan reefs (Samoilys et al.25