What’s the Problem?
Fish spawning aggregations are extremely important to local ecosystems and economies, but they are not resilient to anything greater than light fishing pressure. In some cases, FSAs have been lost even from subsistence fishing1, which is often considered sustainable2.
The reasons for FSA vulnerability vary, but often it is a result of the predictable nature of FSA formation, and the life history characteristics of many FSA-forming species. Moreover, spawning in FSAs is considered to represent 100% of the total reproductive output for most species studied to date3, such that FSA fishing can have profound effects on populations, often over brief time spans4.
Characteristics of FSA-forming species may include:
- Slow growth rates
- Late sexual maturity
- Small home-range size as adults
- Complex life cycle
- Protogynous hermaphroditism
Slow Growth and Late Maturity
Generally, species with shorter life cycles are more resilient to heavy exploitation, and may recover quickly from low stock numbers. Many FSA-forming species have slow growth rates and delayed sexual maturity, making their stocks less resilient to fishing.
Small Home Ranges
Many reef fishes have sedentary life styles as adults and may occupy small home ranges (with the exception of migrations to spawning areas). Site specificity and narrow habitat ranges can make these species easy targets for fishermen5.
Complex Life Cycles
Most reef species exploit a variety of habitats throughout their life cycle. Most often, the larvae of reef species are pelagic, inhabiting the open ocean, whereas the adults are sedentary reef inhabitants.
Many species may also use reef-adjacent habitats, such as mangrove and seagrass beds, during juvenile stages.
Some reef species, such as groupers and wrasses, begin life as functional females, and then transition into functional males later in life. This is termed protogynous hermaphroditism.
Size selection of either smaller or larger individuals within the population, as can occur with fishing, may alter the sexual composition of the population, reducing reproductive output and, therefore, the number of larvae available to maintain local populations.
1 Hamilton and Kama 2004
2 Kuster et al. 2005
3 Shapiro et al. 1993
4 Sadovy and Domeier 2005, Rhodes and Tupper 2008
5 Morris et al. 2000
6 Johannes et al. 1999
7 Sala et al. 2001
8 Aguilar-Perera 2006
9 Sala et al 2003