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Alternative reproductive tactics and inverse size-assortment in a high-density fish spawning aggregation
- Karkarey, Rucha, Zambre, Amod, Isvaran, Kavita, Arthur, Rohan
- BMC ecology 2017 v.17 no.1 pp. 10
- Plectropomus, body size, courtship, demographic statistics, females, fisheries, grouper, habitats, males, population density, spawning, India
- BACKGROUND: At high densities, terrestrial and marine species often employ alternate reproductive tactics (ARTs) to maximize reproductive benefits. We describe ARTs in a high-density and unfished spawning aggregation of the squaretail grouper (Plectropomus areolatus) in Lakshadweep, India. RESULTS: As previously reported for this species, territorial males engage in pair-courtship, which is associated with a pair-spawning tactic. Here, we document a previously unreported school-courtship tactic; where territorial males court multiple females in mid-water schools, which appears to culminate in a unique ‘school-spawning’ tactic. Courtship tactics were conditional on body size, local mate density and habitat, likely associated with changing trade-offs between potential mating opportunities and intra-sexual competition. Counter-intuitively, the aggregation showed a habitat-specific inverse size-assortment: large males courted small females on the reef slope while small males courted equal-sized or larger females on the shelf. These patterns remained stable across two years of observation at high, unfished densities. CONCLUSIONS: These unique density-dependent behaviours may disappear from this aggregation as overall densities decline due to increasing commercial fishing pressure, with potentially large consequences for demographics and fitness.