Estuaries rank among the most anthropogenically impacted aquatic ecosystems on earth. There is a growing consensus on anthropogenic impacts to estuarine and coastal environments, and consequently the ecological, social, and cultural values. The protection of these values is legislated for within the U.S. and Aotearoa New Zealand (NZ). The respective environmental catchment philosophy ‘Mauka Makai’ and ‘Ki Uta Ki Tai’ (lit. inland to sea) of Indigenous Hawaiian and Ngāi Tahu forms the overarching principle of this study. The scientific component of this study measured shellfish population indices, condition index, tissue and sediment contamination which was compared across the landscape development index, physico-chemical gradient and management regimes. Within the socio-cultural component of this study, Indigenous and non-Indigenous local residents, ‘beach-goers’, managers, and scientists were interviewed towards their perception and experience of site and catchment environmental condition, resource abundance and changes, and management effectiveness of these systems.

Both the ecological and cultural findings recognised the land as a source of anthropogenic stressors. In Kāneohe Bay, Hawaii, the benthic infaunal shellfish density appears to be more impacted by anthropogenic conditions compared with the surface dwelling Pacific oyster, Crassostrea gigas. The latter was indicative of environmental condition. Although the shellfish fishery has remained closed since the 1970s, clam densities have continued to decline. This is the first C. gigas population survey, showing variabile distiribution, the highest abundance located at urban residential piers. The clam-bed sediment contamination concentrations exceeded the Sediment Quality Guidelines and were comparable to findings in the U.S. This requires further investigation by local authorities. Lower C. gigas condition index was associated with elevated tissue arsenic concentration.

Native fish and plant life (limu) rather than shellfish were important species to harvest/gather in Kāneohe Bay. However, active shellfish culturing was currently being trialled or commercially operated, while the recreationally fishery has been closed for > 30 years. Introduced fishery pressures and landscape development were highlighted as key issues in the Bay. Kānaka Maoli fishery practices and traditional management systems were responses to perceived decline in native fisheries. Extensive restoration efforts were occurring in Hawaii that may aid to reduce anthropogenic input. Interview analysis was limited by low sample size. ‘Mauka makai’ and local fishery-ecology management systems were recommended by more experienced (>20 yrs) Indigenous and non-Indigenous participants.

In Canterbury, New Zealand, the New Zealand littleneck clam, Austrovenus stutchburyi, was indicative of environmental condition, while the pipi, Paphies australis, was only abundant at one site, and the dredge oyster Tiostrea chilensis were sparse and without individuals of harvestable sizes. The A. stutchburyi condition index was positively influenced by salinity and negatively with tissue Metal Pollution Index (MPI), tissue E. coli, and sediment MPI. The A. stutchburyi density negatively correlated with both tissue and sediment metal concentrations. Additionally, tissue inorganic arsenic and tissue E. coli concentrations exceeded the guidance for human consumption. The latter exceeded multiple times, and included low salinity sites at the urban and high-intensity rural estuary. Sites of elevated contaminants shared similarities that can further guide monitoring and restoration efforts.

The top environmental indicators provided by interview participants aligned with the known global stressors within estuaries. The values of Ngāi Tahu were compromised more often than other cultural affiliations in New Zealand. Ngāi Tahu fishery practices and restoration efforts have responded to perceived decline in native fisheries. ‘Inland-to-sea’ management systems were recommended by Indigenous and non-Indigenous environmental specialists. The anthropogenic impacts of stressors on estuarine systems requires ongoing assessments of environmental condition, and effects on ecological and cultural values.