Testing assumptions about sex change and spatial management in the protogynous gag grouper, Mycteroperca microlepis

Gag grouper Mycteroperca microlepis are protogynous hermaphrodites, for which the assumption of female-driven reproductive potential may be inaccurate. In protogynous species, male abundance, fertilization success, and stock productivity are affected by where and when sex change occurs and how fishing pressure affects male recruitment and survivorship. In this study, we integrated large spatial-scale data with high-resolution data from a 3 yr study sampling gag at deep-water sites with varying spatial management (a marine protected area [MPA], a seasonally closed area, and an 'Open area'). Gag exhibited complex spatial ecology; females formed pre-spawning aggregations before migrating to deep-water spawning sites, which overlapped with locations where males were sampled year-round. The observed male sex ratio in the MPA was 5% compared to the expected 15%. It was 0% in less protected areas. Sex change occurred occasionally in small fish and before, during, and after the spawning season. In addition, sex change was observed in pre-spawning female-only aggregations as well on the spawning grounds, indicating that male social cues are not requisite. We propose that shallow-water, pre-spawning aggregations are a key spatio-temporal bottleneck to gag productivity. They appear to be an important source of transitionals and are heavily fished, which may negatively impact male recruitment to the spawning grounds. Our results indicate that overall gag abundance is low, MPAs do not protect all recruiting males (as previously assumed), and current regulations are not sufficient for the male population to recover to historic levels (~17% male).

Modelling age-dependent movement: an application to red and gag groupers in the Gulf of Mexico

We develop and test spatial population dynamics models that estimate age-dependent offshore movement of fish populations from spatial fishery data. Spatially aggregated population dynamics models produced biased estimates of maximum sustainable yield (MSY) reference points when spatial dynamics were simulated. Spatial population dynamics models provided relatively unbiased estimates of MSY reference points regardless of whether spatial dynamics were simulated. We demonstrate that by using conventional fishery data that are disaggregated spatially, it is possible to estimate movement with age and obtain more accurate estimates of management reference points. The new spatial models were fitted to data for Gulf of Mexico red grouper (Epinephelus morio) and gag grouper (Mycteroperca microlepis) to estimate spatial distribution and offshore movement with age. Offshore ontogeny was estimated to be stronger for gag grouper than red grouper and predicted a larger fraction of older gag grouper in deeper waters.

First record of Caligus mutabilis (Copepoda: Caligidae), in sea-farmed Mycteroperca microlepis (Perciformes: Serranidae) in Brazil

Sea lice (copepods) are widespread pathogens in marine teleost cultivation around the world. The sea louse Caligus mutabilis Wilson, 1905, is recorded here for the first time in sea-farmed gag grouper, Mycteroperca microlepis, in Brazil.

When can we reliably estimate the productivity of fish stocks?

In modern fishery stock assessments, the productivity of exploited stocks is frequently summarized by a scale-invariant “steepness” parameter. This parameter, which describes the slope of the spawner–recruit curve, determines resilience of a stock to exploitation and is highly influential when estimating maximum sustainable yield. In this study, we examined conditions under which steepness can be estimated reliably. We applied a statistical catch-age model to data that were simulated over a broad range of stock characteristics and exploitation patterns and found that steepness is often estimated at its upper bound regardless of underlying productivity. The ability to estimate steepness reliably was most dependent on the true value of steepness, the exploitation history of the stock, natural mortality, duration of the time series, and quality of an index of abundance; this ability was relatively unaffected by levels of stochasticity in recruitment and sampling intensity of age compositions. We further explored the method of inverse prediction to improve estimates of steepness and conclude that this approach holds promise. We illustrate the utility of simulation and inverse prediction methods with two fish stocks located off the southeastern United States, greater amberjack ( Seriola dumerili ) and gag grouper ( Mycteroperca microlepsis ).