Many traditions of coastal peoples may be viewed as traditional forms of marine conservation because, like modern fisheries management, they restrict fishing gear, fishing times, and places, but their effects are little studied in practice. A study was undertaken of human culture and fisheries resources in an area of southern Kenya, designated as a national marine reserve, to determine the effect of the existing 'traditional management' on fisheries yields and on the ecological condition of the fished reefs. This area has one of the oldest and most elaborate cultural traditions concerning sacred sites and rituals of sacrifice along the Kenyan coast. The purpose of the customs is, however, to appease spirits rather than to regulate fish stocks which are traditionally seen to fluctuate independently of fishing effort. Many of these traditions have decayed in recent times as Islamization of the culture has occurred, and authority has shifted towards national organizations, weakening the effectiveness of the traditional leaders. Coincidentally, fishers have adopted new or foreign gear, colleagues, and traditions. Two adjacent landing sites (Mvuleni and Mwanyaza) have, however, successfully stopped pull seiners from landing their catch at their sites for over 20 years through passive means. Other landing sites have adopted pull seining. Both landing areas use arguments based on tradition to justify their use of gear. The two landings that restrict pull seining have higher per capita fish catches than those that do not. Nonetheless, there were no obvious differences in the ecological condition of the reefs at these two management areas; both areas were amongst the most degraded reefs reported in East Africa. Biological diversity and coral cover were reduced greatly in all these areas compared to other fished or fully-protected marine park or reserve sites established by the national government. Presently, traditional management is not effective in protecting species diversity or ecological functions, which was probably never the intention of the customs. The conflict between national organizations and local fishers arises because some resource users are concerned that the management proposed by the national organizations will eventually lead to the total loss of access to, and control of the resource by local fishers. There is, therefore, a need to resolve conflicts concerning gear use and regulation, and a need to increase awareness of the expectations and management programmes among the national and local organizations. Many of the traditional forms of management are compatible with the policies of national organizations, but confusion and conflict occur concerning enforcement and its benefits. To solve these conflicts discussions are required between traditional and national fisheries leaders to develop mutually-acceptable policies that augment and share the power of management.
Highly mobile marine megafauna species, while widely distributed and frequently threatened, often aggregate in distinct localized habitats. Implementation of local management initiatives within these hotspots is more achievable than developing effective conservation strategies that encompass their entire distributions. Such measures have the potential for disproportionate population-level benefits but rely on a detailed understanding of spatiotemporal habitat use. To that end, we examined the residency and small-scale habitat use of 51 whale sharks (Rhincodon typus) over 5 years at an aggregation site in Tanzania using passive acoustic telemetry. Whale sharks were highly resident within and across years, with a combined maximum residency index of 0.39. Although fewer sharks were detected from March to September, residency was high throughout the year. Ancillary photographic-identification data showed that individual residency persisted before and after tag attachment. Kernel utilization distributions (KUD) and movement networks both revealed the same spatiotemporal pattern of habitat use, with a small core habitat (50% KUD area for all sharks combined = 12.99 km 2 ) that predictably changed on a seasonal basis. Activity spaces did not differ with time of day, sex, or size of the sharks, indicating a population-level pattern driven by prey availability. The small and predictable core habitat area at this site means that site-based management options to reduce shark injuries and mortality from boat strike and fishing gear entanglement can be spatially targeted for maximum effectiveness and compliance by human users.
Background. The Western Indian Ocean is a globally important region for the whale shark Rhincodon typus, with well-studied coastal aggregation sites in southern Mozambique, Seychelles and Djibouti. Here we present an overview of a new study at Mafia Island, Tanzania. Methods. We monitored whale shark abundances on 103 boat trips from October 2012–March 2013. We also used passive acoustic telemetry (VEMCO® V16 tags) and photographic identification to monitor the residency times and local movements of 29 tagged individuals. Shark sizes were estimated using laser photogrammetry. Results. In total we observed 87 individual sharks with a mean of 5.1 ± 5.2 (± SD) per trip and a peak in December of 8.2 ± 6.3. Total length ranged from 4.1 to 9.7 m and almost all sharks were immature. After boat-based visual observations dropped to zero in March 2013 (with the same ongoing sampling effort), the acoustic array still detected 75% of tagged sharks. Tagged individuals were detected by the acoustic array for 73 ± 40 days on average. They showed a strong site fidelity to a 15 km2 area in the inner part of the bay and then progressively moved offshore at the end of the season, matching a decrease in plankton abundance. Sharks were mostly observed feeding on dense patches of the pelagic shrimp Lucifer hanseni, often in association with planktivorous fishes. Photo IDs from 2007-09 and 2012-13 indicate that a large proportion of the juvenile individuals return to Mafia Island each spring-summer. Conclusion. The size range and gender distribution of whale sharks at Mafia Island is similar to other coastal aggregations in the Indian Ocean, but the relatively high site fidelity and residency time stands in contrast.
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