From data compilation to model validation: comparing three ecosystem models of the Tasman and Golden Bays, New Zealand.

The Tasman and Golden Bays (TBGB) are a semi-enclosed embayment system in New Zealand that supports numerous commercial and recreational activities. We present three ecosystem models of the TBGB ecosystem with varying levels of complexity, aimed at contributing as tools to aid in understanding this ecosystem and its responses to anthropogenic and natural pressures. We describe the process of data compilation through to model validation and analyse the importance of knowledge gaps with respect to model dynamics and results. We compare responses in all three models to historical fishing, and analyse similarities and differences in the dynamics of the three models. We assessed the most complex of the models against initialisation uncertainty and sensitivity to oceanographic variability and found it most sensitive to the latter. We recommend that scenarios relating to ecosystem dynamics of the TBGB ecosystem include sensitivities, especially oceanographic uncertainty, and compare responses across all three models where it is possible to do so.

The impact of fishing on a highly vulnerable ecosystem, the case of Juan Fernández Ridge ecosystem.

The Juan Fernández Ridge (JFRE) is a vulnerable marine ecosystem (VME) located off the coast of central Chile formed by the Juan Fernández Archipelago and a group of seamounts. This ecosystem has unique biological and oceanographic features, characterized by: small geographical units, high degree of endemism with a high degree of connectivity within the system. Two fleets have historically operated in this system: a long term coastal artisanal fishery associated with the Islands, focused mainly on lobster, and a mainland based industrial demersal finfish fishery operating on the seamounts which is currently considered overexploited. The management of these fisheries has been based on a classical single-species approach to determine output controls (industrial fleet) and a mixed management system with formal and informal components (artisanal fleet). There has been growing interest in increasing the exploitation of fisheries, and modernization of the fishing fleet already operating in the JFRE. Under this scenario of increased levels of fishing exploitation and the high level of interrelation of species it might be necessary to understand the impact of these fisheries from a holistic perspective based on a ecosystem-based modeling approach. To address these challenges we developed an Atlantis end-to-end model was configured for this ecosystem. The implemented model has a high degree of skill in representing the observed trends and fluctuations of the JFRE. The model shows that the industrial fishing has a localized impact and the artisanal fisheries have a relatively low impact on the ecosystem, mainly via the lobster fishery. The model indicates that the depletion of large sized lobster has leads to an increase in the population of sea urchins. Although this increase is not sufficient, as yet, to cause substantial flow-on effects to other groups, caution is advised in case extra pressure leads the ecosystem towards a regime shift.

Biogeography and historical demography of the Juan Fernandez Rock Lobster, Jasus frontalis (Milne Edwards, 1837).

The genetic structure of present-day populations has been highly affected by glacial periods and physical oceanographic forcing, particularly with respect to species distributions and population gene-flow patterns. We assessed the current genetic composition of the Jasus frontalis population in the southeastern Pacific Islands off the coast of Chile to evaluate their connectivity modulated by contemporary and historic oceanographic processes. Population structure and demographical history for this species were assessed based on classic and Bayesian approaches using 84 sequences of cytochrome oxidase subunit I. In addition, we estimated the time of origin of J. frontalis in the different geographic zones. The analyses show a panmictic population with high gene flow between subcomponents and a lack of genetic structure (F (ST) < 0.008). This high gene flow is mainly modulated by mesoscale oceanographic factors such as eddies and meanders. In a historical spatial context, the most probable common ancestor of J. frontalis could have colonized the region around 0.258 million years before present (MYBP), first becoming established in the Juan Fernández Archipelago and then expanding toward the Desventuradas Islands. The demographic history shows a consistent increase in the effective population size (N ( e )) starting approximately 0.130 MYBP, which is highly correlated with sea-level changes during the last glacial maximum.