Phase III – Incorporating reef fish spawning aggregations into optimal designs for no-take fishery reserves

A wide range of reef fishes aggregate in large numbers to spawn, including many species from highly valued food fish families such as the Lutjanidae and Serranidae. Reef fish species forming spawning aggregations are often highly mobile, with migrations to spawning sites ranging from a few to hundreds of kilometres. Targeted fishing on fish migrating to and from aggregations also occur, though is less well documented than fishing on aggregations. The overall goal of this research was to address critical information gaps and develop robust scientific approaches for the management and conservation of commercially important species that aggregate to spawn in the western Indian Ocean. The study was conducted in Kenya, Seychelles and Zanzibar, Tanzania. Projects beneficiaries included the scientific community, management and conservation organizations and local communities.

This research programme demonstrated the feasibility of using basic information from spawning aggregation-based fisheries to systematically evaluate management needs in data-poor contexts. This was achieved through a developed conceptual approach that involved estimation of key aggregation and fishery parameters (Chapters 3 to 10), and the application of those parameters in a vulnerability assessment (Chapter 11) and a no take reserve (NTR) model for spawning aggregations (Chapter 12). The study was implemented through three work programmes. Firstly, site-based surveys and sampling programmes to determine key parameters and information for management, focusing on reproductive biology, spatial and temporal dynamics of aggregations and key fisheries aspects for aggregating species. Secondly, development of novel approaches for assessing the management needs of spawning aggregations, including the development of a predictive vulnerability framework for data-poor contexts and models to examine the effects of no-take reserves for spawning aggregations. The project also aimed to develop policy advice for the management of spawning aggregation fisheries.

In the first programme, the study aimed to quantify the Siganus sutor fishery, to identify potential spawning aggregation sites and how these are fished by fishers from Msambweni on the south coast of Kenya. Results showed that S. sutor is a major contributor to the local artisanal catches in Msambweni and it is also subjected to targeted fishing of reported spawning aggregations. Trends in GSI indicated that reproductive seasonality in S. sutor is characterised by two peak periods of spawning (June to July and November to February) occurring within a protracted spawning season.  Results proved that S. sutor migrates from inshore areas to nearby offshore-submerged coral reef sites to aggregate and spawn between November and February, on the south coast of Kenya. Using a range of methods, three spawning aggregation sites were located, aggregation formation was verified and spatial and temporal patterns investigated. Collectively, these results support the interpretation that S. sutor only move to offshore patch reefs to spawn. This study also provided new knowledge on the spawning aggregation dynamics of S. sutor at offshore spawning aggregation sites in the Seychelles. The findings of this study confirmed that S. sutor visit the Polite and Dividi aggregation sites mostly around the full moon in Seychelles which is further evidence that the use of these offshore sites by S. sutor is related to transient spawning aggregation formation. Secondly this study preliminary evaluation highlighted the potential for indicator-based frameworks to enable rapid assessment of the vulnerability of reef fish populations to aggregation fishing in data-poor contexts. Spawning aggregation behaviour as clearly an important determinant of the intrinsic vulnerability to fishing (Sadovy and Domeier 2005) should be included in vulnerability frameworks for reef fish. Spawning aggregations of E. fuscoguttatus were verified at two sites in the Diani-Tiwi area, based on a combination of abundance increases and observations of spawning-related behaviour. Observations of spawning-related behaviour at aggregations sites, increased densities of fish and fishers’ knowledge combine to provide strong evidence for the occurrence of E. fuscoguttatus spawning aggregations at the two sites on the south coast of Kenya.

This study contributes to management by providing the state of knowledge about the spawning patterns of S. sutor in the Msambweni area, which can guide future management measures for a species that is subjected to spawning aggregation fishing. Combined with the results from previous study, this finding led to the submission of a Policy Brief to the Kenyan government recommending that a species specific management plan for S. sutor be developed and that spawning aggregations be managed through protected areas. The stakeholder process leading to the voluntarily decision by fishers and fishing entities to cease targeting the spawning aggregations has removed this fishing pressure, but the informal management approach is not without risks. Detailed information on spatial and temporal dynamics of spawning aggregations is required by fishers to enable them to avoid catching aggregating fish.

This study has provided far more detailed estimates of key spawning parameters than previously available (Robinson et al. 2008b), which can be used in this informal management approach. However, the lack of formal management makes monitoring, control and surveillance problematic and there is no legal mechanism for dealing with breaches in the agreement should they occur. Management measures that focus specifically on a population’s spawning behaviour should be founded on knowledge that (i) the population aggregates for the purpose of spawning, and that (ii) the spawning aggregations are fished.

Results of this project have been published in a book that can be cited as follows: Robinson J and Samoilys MA (Co-editors) (2013) Reef Fish Spawning Aggregations in the Western Indian Ocean: Research for Management. WIOMSA/SIDA/SFA/CORDIO. WIOMSA Book Series 13. ISBN: 978-9987-9559-2-3