To protect aggregations or not: questions that challenge

Many larger, exploited, reef fishes conduct part or all of their reproduction in aggregations. However, it is not always clear whether their management should involve controls on fishing of aggregating fish instead of, or in addition to, more conventional management controls. Examples of conventional approaches include annual catch quotas, size and bag limits, etc. Assuming (a) that management is needed, and (b) that aggregations are targeted, what factors need to be considered when devising suitable management and monitoring plans for aggregating species?

In this, new, ‘Perspectives' column I identify, aided and abetted by the SCRFA Board, biological and practical questions that could, perhaps should always be considered. Obviously, each case depends on the local social and economic contexts, as well as on the species and fishery involved. However, in many different cases, several or more of the following questions might have to be considered. In subsequent newsletters, and, hopefully with the help of feedback from readers' own perspectives and experiences, SCRFA will try to supply answers to each question, as well as illustrative examples. In the first instance, I would welcome feedback on the Biological considerations.

Biological considerations
1.Is a high proportion of annual catch taken during the aggregation period, as opposed to the non-aggregation period? For some species, like the Nassau grouper, for example, most annual landings are, or were, taken from spawning aggregations in several countries.
2. Does the species form relatively few, large, aggregations within its geographic range, or many smaller ones? In the former case, aggregation protection may be particularly important.
3. For fish species that change sex (such as groupers or emperors), is it possible that important social information is exchanged when fishes gather to spawn? In some species, for example, aggregations are the only times that large numbers of fish come together.
4. How do young fish learn where their conspecifics aggregate to spawn? Is it possible that sexually immature fish need to follow reproductive adults to find spawning aggregation sites?
5. For species that depend on critical habitat for spawning, or where the habitat itself is threatened, are special protective measures advisable for the habitat?
6. Is catchability of spawning fish different from that when they are not spawning? Catchability of aggregating fish can be higher or lower compared to catchability of non-aggregating fish, depending on the species and fishing method(s) used.
7. Could removal of fish from aggregations affect their spawning behaviour, or negatively impact reproductive output? Is reproductive potential influenced by fishing activity during the reproductive season either by the presence of fishers, or because of high removals of spawning fishes?
8. Does fishing on aggregations truncate size/age structure or reduce genetic diversity? For some species, the largest individuals may live in deep water for much of the year, becoming accessible to a shallow-water fishery only at spawning, while maximum size or age may be partly determined by genetics.

Practical considerations
1. Is aggregation management and enforcement of regulations easier than for nonaggregating fishes? Ease and expense of enforcement and implementation must be important management considerations.
2. Do the public understand aggregation management? Public perception of the taking of spawning fish, which are visibly full of eggs (=future babies), should not be undervalued.
3. Do fish prices vary between spawning and non-spawning seasons? In some areas, the glut of fish produced by fishing aggregations can lower unit market prices such that more fish have to be taken for a given level of income than during the non-aggregation season.
4. Does aggregation protection lead to higher fishing effort before and/or after the protected period as part of ‘derby' fisheries.
5. Is there wasteful mortality associated with aggregation-caught fish? This could occur when fish are taken live (as for the live reef food fish trade of Southeast Asia and the western Pacific), or because of high predation rates on fishing lines during aggregation periods.
6. What is the best way to monitor exploited fishes that aggregate to spawn? Because of the possibility of hyperdepletion, whereby catch rates of fish that continue to aggregate remain high even as the overall populations declines, data on catches should be collected both during the aggregation as well as the nonaggregation season.
7. Are broodstock difficult to obtain for mariculture research? Spawning aggregations could be valuable occasional sources of spawners in good condition.

In summary, the successful management of reef fish species that aggregate to spawn is achievable using a range of tools in the managers' legislative toolbox. Each species, region and socio-economic circumstance is different, so often there is no one tool that will be most effective. Many issues need to be considered in deciding on appropriate management approaches in each case. The bottom line, of course, is that aggregating fish often need protection if there is a high vulnerability to overfishing at their spawning aggregations.

And lest we forget, the management of spawning aggregations or spawning habitats is precautionary and variously called-for by a Statement of Concern agreed at ITMEMS2 (Second Inter-Tropical Marine Ecosystem Management Symposium), and a Recommendation by delegates to IUCN's Fourth World Conservation Congress (see: www:http://www.scrfa.org/server/spawning/concern.htm). Time/area closures for protection of spawning areas and periods are called for under the Convention on Biological Diversity, and protection of spawning habitat is included in Article 6.8 of the United Nations Food and Agriculture Organization's Code of Conduct for Responsible Fisheries.

Yvonne Sadovy

Dec 2005